Node.js v0.12.5 Manual & Documentation

PDF created by Mirco Zeiss

Content by node.js and its creators

About this Documentation

The goal of this documentation is to comprehensively explain the Node.js API, both from a reference as well as a conceptual point of view. Each section describes a built-in module or high-level concept.

Where appropriate, property types, method arguments, and the arguments provided to event handlers are detailed in a list underneath the topic heading.

Every .html document has a corresponding .json document presenting the same information in a structured manner. This feature is experimental, and added for the benefit of IDEs and other utilities that wish to do programmatic things with the documentation.

Every .html and .json file is generated based on the corresponding .markdown file in the doc/api/ folder in node’s source tree. The documentation is generated using the tools/doc/generate.js program. The HTML template is located at doc/template.html.

Stability Index

Throughout the documentation, you will see indications of a section’s stability. The Node.js API is still somewhat changing, and as it matures, certain parts are more reliable than others. Some are so proven, and so relied upon, that they are unlikely to ever change at all. Others are brand new and experimental, or known to be hazardous and in the process of being redesigned.

The stability indices are as follows:

Stability: 0 - Deprecated
This feature is known to be problematic, and changes are
planned.  Do not rely on it.  Use of the feature may cause warnings.  Backwards
compatibility should not be expected.

Stability: 1 - Experimental
This feature was introduced recently, and may change
or be removed in future versions.  Please try it out and provide feedback.
If it addresses a use-case that is important to you, tell the node core team.

Stability: 2 - Unstable
The API is in the process of settling, but has not yet had
sufficient real-world testing to be considered stable. Backwards-compatibility
will be maintained if reasonable.

Stability: 3 - Stable
The API has proven satisfactory, but cleanup in the underlying
code may cause minor changes.  Backwards-compatibility is guaranteed.

Stability: 4 - API Frozen
This API has been tested extensively in production and is
unlikely to ever have to change.

Stability: 5 - Locked
Unless serious bugs are found, this code will not ever
change.  Please do not suggest changes in this area; they will be refused.

JSON Output

Stability: 1 - Experimental

Every HTML file in the markdown has a corresponding JSON file with the same data.

This feature is new as of node v0.6.12. It is experimental.

Synopsis

An example of a web server written with Node which responds with ‘Hello World’:

var http = require('http');

http.createServer(function (request, response) {
  response.writeHead(200, {'Content-Type': 'text/plain'});
  response.end('Hello World\n');
}).listen(8124);

console.log('Server running at http://127.0.0.1:8124/');

To run the server, put the code into a file called example.js and execute it with the node program

> node example.js
Server running at http://127.0.0.1:8124/

All of the examples in the documentation can be run similarly.

Assert

Stability: 5 - Locked

This module is used for writing unit tests for your applications, you can access it with require('assert').

assert.fail(actual, expected, message, operator)

Throws an exception that displays the values for actual and expected separated by the provided operator.

assert(value[, message]), assert.ok(value[, message])

Tests if value is truthy, it is equivalent to assert.equal(true, !!value, message);

assert.equal(actual, expected[, message])

Tests shallow, coercive equality with the equal comparison operator ( == ).

assert.notEqual(actual, expected[, message])

Tests shallow, coercive non-equality with the not equal comparison operator ( != ).

assert.deepEqual(actual, expected[, message])

Tests for deep equality.

assert.notDeepEqual(actual, expected[, message])

Tests for any deep inequality.

assert.strictEqual(actual, expected[, message])

Tests strict equality, as determined by the strict equality operator ( === )

assert.notStrictEqual(actual, expected[, message])

Tests strict non-equality, as determined by the strict not equal operator ( !== )

assert.throws(block[, error][, message])

Expects block to throw an error. error can be constructor, RegExp or validation function.

Validate instanceof using constructor:

assert.throws(
  function() {
    throw new Error("Wrong value");
  },
  Error
);

Validate error message using RegExp:

assert.throws(
  function() {
    throw new Error("Wrong value");
  },
  /value/
);

Custom error validation:

assert.throws(
  function() {
    throw new Error("Wrong value");
  },
  function(err) {
    if ( (err instanceof Error) && /value/.test(err) ) {
      return true;
    }
  },
  "unexpected error"
);

assert.doesNotThrow(block[, message])

Expects block not to throw an error, see assert.throws for details.

assert.ifError(value)

Tests if value is not a false value, throws if it is a true value. Useful when testing the first argument, error in callbacks.

Buffer

Stability: 3 - Stable

Pure JavaScript is Unicode friendly but not nice to binary data. When dealing with TCP streams or the file system, it’s necessary to handle octet streams. Node has several strategies for manipulating, creating, and consuming octet streams.

Raw data is stored in instances of the Buffer class. A Buffer is similar to an array of integers but corresponds to a raw memory allocation outside the V8 heap. A Buffer cannot be resized.

The Buffer class is a global, making it very rare that one would need to ever require('buffer').

Converting between Buffers and JavaScript string objects requires an explicit encoding method. Here are the different string encodings.

'ascii' - for 7 bit ASCII data only. This encoding method is very fast, and will strip the high bit if set.

'utf8' - Multibyte encoded Unicode characters. Many web pages and other document formats use UTF-8.

'utf16le' - 2 or 4 bytes, little endian encoded Unicode characters. Surrogate pairs (U+10000 to U+10FFFF) are supported.

'ucs2' - Alias of 'utf16le'.

'base64' - Base64 string encoding.

'binary' - A way of encoding raw binary data into strings by using only the first 8 bits of each character. This encoding method is deprecated and should be avoided in favor of Buffer objects where possible. This encoding will be removed in future versions of Node.

'hex' - Encode each byte as two hexadecimal characters.

Creating a typed array from a Buffer works with the following caveats:

The buffer’s memory is copied, not shared.

The buffer’s memory is interpreted as an array, not a byte array. That is, new Uint32Array(new Buffer([1,2,3,4])) creates a 4-element Uint32Array with elements [1,2,3,4], not an Uint32Array with a single element [0x1020304] or [0x4030201].

NOTE: Node.js v0.8 simply retained a reference to the buffer in array.buffer instead of cloning it.

While more efficient, it introduces subtle incompatibilities with the typed arrays specification. ArrayBuffer#slice() makes a copy of the slice while Buffer#slice() creates a view.

Class: Buffer

The Buffer class is a global type for dealing with binary data directly. It can be constructed in a variety of ways.

new Buffer(size)

size Number

Allocates a new buffer of size octets. Note, size must be no more than kMaxLength. Otherwise, a RangeError will be thrown here. Unlike ArrayBuffers, the underlying memory for buffers is not initialized. So the contents of a newly created Buffer is unknown. Use buf.fill(0)to initialize a buffer to zeroes.

new Buffer(array)

array Array

Allocates a new buffer using an array of octets.

new Buffer(buffer)

buffer {Buffer}

Copies the passed buffer data onto a new Buffer instance.

new Buffer(str[, encoding])

str String - string to encode.

encoding String - encoding to use, Optional.

Allocates a new buffer containing the given str. encoding defaults to 'utf8'.

Class Method: Buffer.isEncoding(encoding)

encoding {String} The encoding string to test

Returns true if the encoding is a valid encoding argument, or false otherwise.

Class Method: Buffer.isBuffer(obj)

obj Object

Return: Boolean

Tests if obj is a Buffer.

Class Method: Buffer.byteLength(string[, encoding])

string String

encoding String, Optional, Default: ‘utf8’

Return: Number

Gives the actual byte length of a string. encoding defaults to 'utf8'. This is not the same as String.prototype.length since that returns the number of characters in a string.

Example:

str = '\u00bd + \u00bc = \u00be';

console.log(str + ": " + str.length + " characters, " +
  Buffer.byteLength(str, 'utf8') + " bytes");

// ½ + ¼ = ¾: 9 characters, 12 bytes

Class Method: Buffer.concat(list[, totalLength])

list {Array} List of Buffer objects to concat

totalLength {Number} Total length of the buffers when concatenated

Returns a buffer which is the result of concatenating all the buffers in the list together.

If the list has no items, or if the totalLength is 0, then it returns a zero-length buffer.

If the list has exactly one item, then the first item of the list is returned.

If the list has more than one item, then a new Buffer is created.

If totalLength is not provided, it is read from the buffers in the list. However, this adds an additional loop to the function, so it is faster to provide the length explicitly.

Class Method: Buffer.compare(buf1, buf2)

buf1 {Buffer}

buf2 {Buffer}

The same as buf1.compare(buf2). Useful for sorting an Array of Buffers:

var arr = [Buffer('1234'), Buffer('0123')];
arr.sort(Buffer.compare);

buf.length

Number

The size of the buffer in bytes. Note that this is not necessarily the size of the contents. length refers to the amount of memory allocated for the buffer object. It does not change when the contents of the buffer are changed.

buf = new Buffer(1234);

console.log(buf.length);
buf.write("some string", 0, "ascii");
console.log(buf.length);

// 1234
// 1234

While the length property is not immutable, changing the value of length can result in undefined and inconsistent behavior. Applications that wish to modify the length of a buffer should therefore treat length as read-only and use buf.slice to create a new buffer.

buf = new Buffer(10);
buf.write("abcdefghj", 0, "ascii");
console.log(buf.length); // 10
buf = buf.slice(0,5);
console.log(buf.length); // 5

buf.write(string[, offset][, length][, encoding])

string String - data to be written to buffer

offset Number, Optional, Default: 0

length Number, Optional, Default: buffer.length - offset

encoding String, Optional, Default: ‘utf8’

Writes string to the buffer at offset using the given encoding. offset defaults to 0, encoding defaults to 'utf8'. length is the number of bytes to write. Returns number of octets written. If buffer did not contain enough space to fit the entire string, it will write a partial amount of the string. length defaults to buffer.length - offset. The method will not write partial characters.

buf = new Buffer(256);
len = buf.write('\u00bd + \u00bc = \u00be', 0);
console.log(len + " bytes: " + buf.toString('utf8', 0, len));

buf.writeUIntLE(value, offset, byteLength[, noAssert])

buf.writeUIntBE(value, offset, byteLength[, noAssert])

buf.writeIntLE(value, offset, byteLength[, noAssert])

buf.writeIntBE(value, offset, byteLength[, noAssert])

value {Number} Bytes to be written to buffer

offset {Number} 0 <= offset <= buf.length

byteLength {Number} 0 < byteLength <= 6

noAssert {Boolean} Default: false

Return: {Number}

Writes value to the buffer at the specified offset and byteLength. Supports up to 48 bits of accuracy. For example:

var b = new Buffer(6);
b.writeUIntBE(0x1234567890ab, 0, 6);
// <Buffer 12 34 56 78 90 ab>

Set noAssert to true to skip validation of value and offset. Defaults to false.

buf.readUIntLE(offset, byteLength[, noAssert])

buf.readUIntBE(offset, byteLength[, noAssert])

buf.readIntLE(offset, byteLength[, noAssert])

buf.readIntBE(offset, byteLength[, noAssert])

offset {Number} 0 <= offset <= buf.length

byteLength {Number} 0 < byteLength <= 6

noAssert {Boolean} Default: false

Return: {Number}

A generalized version of all numeric read methods. Supports up to 48 bits of accuracy. For example:

var b = new Buffer(6);
b.writeUint16LE(0x90ab, 0);
b.writeUInt32LE(0x12345678, 2);
b.readUIntLE(0, 6).toString(16);  // Specify 6 bytes (48 bits)
// output: '1234567890ab'

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

buf.toString([encoding][, start][, end])

encoding String, Optional, Default: ‘utf8’

start Number, Optional, Default: 0

end Number, Optional, Default: buffer.length

Decodes and returns a string from buffer data encoded using the specified character set encoding. If encoding is undefined or null, then encoding defaults to 'utf8'. Thestartandendparameters default to0andbuffer.lengthwhenundefined`.

buf = new Buffer(26);
for (var i = 0 ; i < 26 ; i++) {
  buf[i] = i + 97; // 97 is ASCII a
}
buf.toString('ascii'); // outputs: abcdefghijklmnopqrstuvwxyz
buf.toString('ascii',0,5); // outputs: abcde
buf.toString('utf8',0,5); // outputs: abcde
buf.toString(undefined,0,5); // encoding defaults to 'utf8', outputs abcde

See buffer.write() example, above.

buf.toJSON()

Returns a JSON-representation of the Buffer instance. JSON.stringify implicitly calls this function when stringifying a Buffer instance.

Example:

var buf = new Buffer('test');
var json = JSON.stringify(buf);

console.log(json);
// '{"type":"Buffer","data":[116,101,115,116]}'

var copy = JSON.parse(json, function(key, value) {
    return value && value.type === 'Buffer'
      ? new Buffer(value.data)
      : value;
  });

console.log(copy);
// <Buffer 74 65 73 74>

buf[index]

Get and set the octet at index. The values refer to individual bytes, so the legal range is between 0x00 and 0xFF hex or 0 and 255.

Example: copy an ASCII string into a buffer, one byte at a time:

str = "node.js";
buf = new Buffer(str.length);

for (var i = 0; i < str.length ; i++) {
  buf[i] = str.charCodeAt(i);
}

console.log(buf);

// node.js

buf.equals(otherBuffer)

otherBuffer {Buffer}

Returns a boolean of whether this and otherBuffer have the same bytes.

buf.compare(otherBuffer)

otherBuffer {Buffer}

Returns a number indicating whether this comes before or after or is the same as the otherBuffer in sort order.

buf.copy(targetBuffer[, targetStart][, sourceStart][, sourceEnd])

targetBuffer Buffer object - Buffer to copy into

targetStart Number, Optional, Default: 0

sourceStart Number, Optional, Default: 0

sourceEnd Number, Optional, Default: buffer.length

Copies data from a region of this buffer to a region in the target buffer even if the target memory region overlaps with the source. If undefined the targetStart and sourceStart parameters default to 0 while sourceEnd defaults to buffer.length.

Example: build two Buffers, then copy buf1 from byte 16 through byte 19 into buf2, starting at the 8th byte in buf2.

buf1 = new Buffer(26);
buf2 = new Buffer(26);

for (var i = 0 ; i < 26 ; i++) {
  buf1[i] = i + 97; // 97 is ASCII a
  buf2[i] = 33; // ASCII !
}

buf1.copy(buf2, 8, 16, 20);
console.log(buf2.toString('ascii', 0, 25));

// !!!!!!!!qrst!!!!!!!!!!!!!

Example: Build a single buffer, then copy data from one region to an overlapping region in the same buffer

buf = new Buffer(26);

for (var i = 0 ; i < 26 ; i++) {
  buf[i] = i + 97; // 97 is ASCII a
}

buf.copy(buf, 0, 4, 10);
console.log(buf.toString());

// efghijghijklmnopqrstuvwxyz

buf.slice([start][, end])

start Number, Optional, Default: 0

end Number, Optional, Default: buffer.length

Returns a new buffer which references the same memory as the old, but offset and cropped by the start (defaults to 0) and end (defaults to buffer.length) indexes. Negative indexes start from the end of the buffer.

Modifying the new buffer slice will modify memory in the original buffer!

Example: build a Buffer with the ASCII alphabet, take a slice, then modify one byte from the original Buffer.

var buf1 = new Buffer(26);

for (var i = 0 ; i < 26 ; i++) {
  buf1[i] = i + 97; // 97 is ASCII a
}

var buf2 = buf1.slice(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));

// abc
// !bc

buf.readUInt8(offset[, noAssert])

offset Number

noAssert Boolean, Optional, Default: false

Return: Number

Reads an unsigned 8 bit integer from the buffer at the specified offset.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example:

var buf = new Buffer(4);

buf[0] = 0x3;
buf[1] = 0x4;
buf[2] = 0x23;
buf[3] = 0x42;

for (ii = 0; ii < buf.length; ii++) {
  console.log(buf.readUInt8(ii));
}

// 0x3
// 0x4
// 0x23
// 0x42

buf.readUInt16LE(offset[, noAssert])

buf.readUInt16BE(offset[, noAssert])

offset Number

noAssert Boolean, Optional, Default: false

Return: Number

Reads an unsigned 16 bit integer from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example:

var buf = new Buffer(4);

buf[0] = 0x3;
buf[1] = 0x4;
buf[2] = 0x23;
buf[3] = 0x42;

console.log(buf.readUInt16BE(0));
console.log(buf.readUInt16LE(0));
console.log(buf.readUInt16BE(1));
console.log(buf.readUInt16LE(1));
console.log(buf.readUInt16BE(2));
console.log(buf.readUInt16LE(2));

// 0x0304
// 0x0403
// 0x0423
// 0x2304
// 0x2342
// 0x4223

buf.readUInt32LE(offset[, noAssert])

buf.readUInt32BE(offset[, noAssert])

offset Number

noAssert Boolean, Optional, Default: false

Return: Number

Reads an unsigned 32 bit integer from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example:

var buf = new Buffer(4);

buf[0] = 0x3;
buf[1] = 0x4;
buf[2] = 0x23;
buf[3] = 0x42;

console.log(buf.readUInt32BE(0));
console.log(buf.readUInt32LE(0));

// 0x03042342
// 0x42230403

buf.readInt8(offset[, noAssert])

offset Number

noAssert Boolean, Optional, Default: false

Return: Number

Reads a signed 8 bit integer from the buffer at the specified offset.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Works as buffer.readUInt8, except buffer contents are treated as two’s complement signed values.

buf.readInt16LE(offset[, noAssert])

buf.readInt16BE(offset[, noAssert])

offset Number

noAssert Boolean, Optional, Default: false

Return: Number

Reads a signed 16 bit integer from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Works as buffer.readUInt16*, except buffer contents are treated as two’s complement signed values.

buf.readInt32LE(offset[, noAssert])

buf.readInt32BE(offset[, noAssert])

offset Number

noAssert Boolean, Optional, Default: false

Return: Number

Reads a signed 32 bit integer from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Works as buffer.readUInt32*, except buffer contents are treated as two’s complement signed values.

buf.readFloatLE(offset[, noAssert])

buf.readFloatBE(offset[, noAssert])

offset Number

noAssert Boolean, Optional, Default: false

Return: Number

Reads a 32 bit float from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example:

var buf = new Buffer(4);

buf[0] = 0x00;
buf[1] = 0x00;
buf[2] = 0x80;
buf[3] = 0x3f;

console.log(buf.readFloatLE(0));

// 0x01

buf.readDoubleLE(offset[, noAssert])

buf.readDoubleBE(offset[, noAssert])

offset Number

noAssert Boolean, Optional, Default: false

Return: Number

Reads a 64 bit double from the buffer at the specified offset with specified endian format.

Set noAssert to true to skip validation of offset. This means that offset may be beyond the end of the buffer. Defaults to false.

Example:

var buf = new Buffer(8);

buf[0] = 0x55;
buf[1] = 0x55;
buf[2] = 0x55;
buf[3] = 0x55;
buf[4] = 0x55;
buf[5] = 0x55;
buf[6] = 0xd5;
buf[7] = 0x3f;

console.log(buf.readDoubleLE(0));

// 0.3333333333333333

buf.writeUInt8(value, offset[, noAssert])

value Number

offset Number

noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset. Note, value must be a valid unsigned 8 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example:

var buf = new Buffer(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);

console.log(buf);

// <Buffer 03 04 23 42>

buf.writeUInt16LE(value, offset[, noAssert])

buf.writeUInt16BE(value, offset[, noAssert])

value Number

offset Number

noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid unsigned 16 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example:

var buf = new Buffer(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);

console.log(buf);

buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);

console.log(buf);

// <Buffer de ad be ef>
// <Buffer ad de ef be>

buf.writeUInt32LE(value, offset[, noAssert])

buf.writeUInt32BE(value, offset[, noAssert])

value Number

offset Number

noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid unsigned 32 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example:

var buf = new Buffer(4);
buf.writeUInt32BE(0xfeedface, 0);

console.log(buf);

buf.writeUInt32LE(0xfeedface, 0);

console.log(buf);

// <Buffer fe ed fa ce>
// <Buffer ce fa ed fe>

buf.writeInt8(value, offset[, noAssert])

value Number

offset Number

noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset. Note, value must be a valid signed 8 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Works as buffer.writeUInt8, except value is written out as a two’s complement signed integer into buffer.

buf.writeInt16LE(value, offset[, noAssert])

buf.writeInt16BE(value, offset[, noAssert])

value Number

offset Number

noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid signed 16 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Works as buffer.writeUInt16*, except value is written out as a two’s complement signed integer into buffer.

buf.writeInt32LE(value, offset[, noAssert])

buf.writeInt32BE(value, offset[, noAssert])

value Number

offset Number

noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid signed 32 bit integer.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Works as buffer.writeUInt32*, except value is written out as a two’s complement signed integer into buffer.

buf.writeFloatLE(value, offset[, noAssert])

buf.writeFloatBE(value, offset[, noAssert])

value Number

offset Number

noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, behavior is unspecified if value is not a 32 bit float.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example:

var buf = new Buffer(4);
buf.writeFloatBE(0xcafebabe, 0);

console.log(buf);

buf.writeFloatLE(0xcafebabe, 0);

console.log(buf);

// <Buffer 4f 4a fe bb>
// <Buffer bb fe 4a 4f>

buf.writeDoubleLE(value, offset[, noAssert])

buf.writeDoubleBE(value, offset[, noAssert])

value Number

offset Number

noAssert Boolean, Optional, Default: false

Writes value to the buffer at the specified offset with specified endian format. Note, value must be a valid 64 bit double.

Set noAssert to true to skip validation of value and offset. This means that value may be too large for the specific function and offset may be beyond the end of the buffer leading to the values being silently dropped. This should not be used unless you are certain of correctness. Defaults to false.

Example:

var buf = new Buffer(8);
buf.writeDoubleBE(0xdeadbeefcafebabe, 0);

console.log(buf);

buf.writeDoubleLE(0xdeadbeefcafebabe, 0);

console.log(buf);

// <Buffer 43 eb d5 b7 dd f9 5f d7>
// <Buffer d7 5f f9 dd b7 d5 eb 43>

buf.fill(value[, offset][, end])

value

offset Number, Optional

end Number, Optional

Fills the buffer with the specified value. If the offset (defaults to 0) and end (defaults to buffer.length) are not given it will fill the entire buffer.

var b = new Buffer(50);
b.fill("h");

buffer.INSPECT_MAX_BYTES

Number, Default: 50

How many bytes will be returned when buffer.inspect() is called. This can be overridden by user modules.

Note that this is a property on the buffer module returned by require('buffer'), not on the Buffer global, or a buffer instance.

Class: SlowBuffer

Returns an un-pooled Buffer.

In order to avoid the garbage collection overhead of creating many individually allocated Buffers, by default allocations under 4KB are sliced from a single larger allocated object. This approach improves both performance and memory usage since v8 does not need to track and cleanup as many Persistent objects.

In the case where a developer may need to retain a small chunk of memory from a pool for an indeterminate amount of time it may be appropriate to create an un-pooled Buffer instance using SlowBuffer and copy out the relevant bits.

// need to keep around a few small chunks of memory
var store = [];

socket.on('readable', function() {
  var data = socket.read();
  // allocate for retained data
  var sb = new SlowBuffer(10);
  // copy the data into the new allocation
  data.copy(sb, 0, 0, 10);
  store.push(sb);
});

Though this should used sparingly and only be a last resort after a developer has actively observed undue memory retention in their applications.

Addons

Addons are dynamically linked shared objects. They can provide glue to C and C++ libraries. The API (at the moment) is rather complex, involving knowledge of several libraries:

V8 JavaScript, a C++ library. Used for interfacing with JavaScript: creating objects, calling functions, etc. Documented mostly in the v8.h header file (deps/v8/include/v8.h in the Node source tree), which is also available online.

libuv, C event loop library. Anytime one needs to wait for a file descriptor to become readable, wait for a timer, or wait for a signal to be received one will need to interface with libuv. That is, if you perform any I/O, libuv will need to be used.

Internal Node libraries. Most importantly is the node::ObjectWrap class which you will likely want to derive from.

Others. Look in deps/ for what else is available.

Node statically compiles all its dependencies into the executable. When compiling your module, you don’t need to worry about linking to any of these libraries.

All of the following examples are available for download and may be used as a starting-point for your own Addon.

Hello world

To get started let’s make a small Addon which is the C++ equivalent of the following JavaScript code:

module.exports.hello = function() { return 'world'; };

First we create a file hello.cc:

// hello.cc
#include <node.h>

using namespace v8;

void Method(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);
  args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
}

void init(Handle<Object> exports) {
  NODE_SET_METHOD(exports, "hello", Method);
}

NODE_MODULE(addon, init)

Note that all Node addons must export an initialization function:

void Initialize (Handle<Object> exports);
NODE_MODULE(module_name, Initialize)

There is no semi-colon after NODE_MODULE as it’s not a function (see node.h).

The module_name needs to match the filename of the final binary (minus the .node suffix).

The source code needs to be built into addon.node, the binary Addon. To do this we create a file called binding.gyp which describes the configuration to build your module in a JSON-like format. This file gets compiled by node-gyp.

{
  "targets": [
    {
      "target_name": "addon",
      "sources": [ "hello.cc" ]
    }
  ]
}

The next step is to generate the appropriate project build files for the current platform. Use node-gyp configure for that.

Now you will have either a Makefile (on Unix platforms) or a vcxproj file (on Windows) in the build/ directory. Next invoke the node-gyp build command.

Now you have your compiled .node bindings file! The compiled bindings end up in build/Release/.

You can now use the binary addon in a Node project hello.js by pointing require to the recently built hello.node module:

// hello.js
var addon = require('./build/Release/addon');

console.log(addon.hello()); // 'world'

Please see patterns below for further information or https://github.com/arturadib/node-qt for an example in production.

Addon patterns

Below are some addon patterns to help you get started. Consult the online v8 reference for help with the various v8 calls, and v8’s Embedder’s Guide for an explanation of several concepts used such as handles, scopes, function templates, etc.

In order to use these examples you need to compile them using node-gyp. Create the following binding.gyp file:

{
  "targets": [
    {
      "target_name": "addon",
      "sources": [ "addon.cc" ]
    }
  ]
}

In cases where there is more than one .cc file, simply add the file name to the sources array, e.g.:

"sources": ["addon.cc", "myexample.cc"]

Now that you have your binding.gyp ready, you can configure and build the addon:

$ node-gyp configure build

Function arguments

The following pattern illustrates how to read arguments from JavaScript function calls and return a result. This is the main and only needed source addon.cc:

// addon.cc
#include <node.h>

using namespace v8;

void Add(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  if (args.Length() < 2) {
    isolate->ThrowException(Exception::TypeError(
        String::NewFromUtf8(isolate, "Wrong number of arguments")));
    return;
  }

  if (!args[0]->IsNumber() || !args[1]->IsNumber()) {
    isolate->ThrowException(Exception::TypeError(
        String::NewFromUtf8(isolate, "Wrong arguments")));
    return;
  }

  double value = args[0]->NumberValue() + args[1]->NumberValue();
  Local<Number> num = Number::New(isolate, value);

  args.GetReturnValue().Set(num);
}

void Init(Handle<Object> exports) {
  NODE_SET_METHOD(exports, "add", Add);
}

NODE_MODULE(addon, Init)

You can test it with the following JavaScript snippet:

// test.js
var addon = require('./build/Release/addon');

console.log( 'This should be eight:', addon.add(3,5) );

Callbacks

You can pass JavaScript functions to a C++ function and execute them from there. Here’s addon.cc:

// addon.cc
#include <node.h>

using namespace v8;

void RunCallback(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  Local<Function> cb = Local<Function>::Cast(args[0]);
  const unsigned argc = 1;
  Local<Value> argv[argc] = { String::NewFromUtf8(isolate, "hello world") };
  cb->Call(isolate->GetCurrentContext()->Global(), argc, argv);
}

void Init(Handle<Object> exports, Handle<Object> module) {
  NODE_SET_METHOD(module, "exports", RunCallback);
}

NODE_MODULE(addon, Init)

Note that this example uses a two-argument form of Init() that receives the full module object as the second argument. This allows the addon to completely overwrite exports with a single function instead of adding the function as a property of exports.

To test it run the following JavaScript snippet:

// test.js
var addon = require('./build/Release/addon');

addon(function(msg){
  console.log(msg); // 'hello world'
});

Object factory

You can create and return new objects from within a C++ function with this addon.cc pattern, which returns an object with property msg that echoes the string passed to createObject():

// addon.cc
#include <node.h>

using namespace v8;

void CreateObject(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  Local<Object> obj = Object::New(isolate);
  obj->Set(String::NewFromUtf8(isolate, "msg"), args[0]->ToString());

  args.GetReturnValue().Set(obj);
}

void Init(Handle<Object> exports, Handle<Object> module) {
  NODE_SET_METHOD(module, "exports", CreateObject);
}

NODE_MODULE(addon, Init)

To test it in JavaScript:

// test.js
var addon = require('./build/Release/addon');

var obj1 = addon('hello');
var obj2 = addon('world');
console.log(obj1.msg+' '+obj2.msg); // 'hello world'

Function factory

This pattern illustrates how to create and return a JavaScript function that wraps a C++ function:

// addon.cc
#include <node.h>

using namespace v8;

void MyFunction(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);
  args.GetReturnValue().Set(String::NewFromUtf8(isolate, "hello world"));
}

void CreateFunction(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, MyFunction);
  Local<Function> fn = tpl->GetFunction();

  // omit this to make it anonymous
  fn->SetName(String::NewFromUtf8(isolate, "theFunction"));

  args.GetReturnValue().Set(fn);
}

void Init(Handle<Object> exports, Handle<Object> module) {
  NODE_SET_METHOD(module, "exports", CreateFunction);
}

NODE_MODULE(addon, Init)

To test:

// test.js
var addon = require('./build/Release/addon');

var fn = addon();
console.log(fn()); // 'hello world'

Wrapping C++ objects

Here we will create a wrapper for a C++ object/class MyObject that can be instantiated in JavaScript through the new operator. First prepare the main module addon.cc:

// addon.cc
#include <node.h>
#include "myobject.h"

using namespace v8;

void InitAll(Handle<Object> exports) {
  MyObject::Init(exports);
}

NODE_MODULE(addon, InitAll)

Then in myobject.h make your wrapper inherit from node::ObjectWrap:

// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H

#include <node.h>
#include <node_object_wrap.h>

class MyObject : public node::ObjectWrap {
 public:
  static void Init(v8::Handle<v8::Object> exports);

 private:
  explicit MyObject(double value = 0);
  ~MyObject();

  static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
  static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
  static v8::Persistent<v8::Function> constructor;
  double value_;
};

#endif

And in myobject.cc implement the various methods that you want to expose. Here we expose the method plusOne by adding it to the constructor’s prototype:

// myobject.cc
#include "myobject.h"

using namespace v8;

Persistent<Function> MyObject::constructor;

MyObject::MyObject(double value) : value_(value) {
}

MyObject::~MyObject() {
}

void MyObject::Init(Handle<Object> exports) {
  Isolate* isolate = Isolate::GetCurrent();

  // Prepare constructor template
  Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
  tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
  tpl->InstanceTemplate()->SetInternalFieldCount(1);

  // Prototype
  NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);

  constructor.Reset(isolate, tpl->GetFunction());
  exports->Set(String::NewFromUtf8(isolate, "MyObject"),
               tpl->GetFunction());
}

void MyObject::New(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  if (args.IsConstructCall()) {
    // Invoked as constructor: `new MyObject(...)`
    double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
    MyObject* obj = new MyObject(value);
    obj->Wrap(args.This());
    args.GetReturnValue().Set(args.This());
  } else {
    // Invoked as plain function `MyObject(...)`, turn into construct call.
    const int argc = 1;
    Local<Value> argv[argc] = { args[0] };
    Local<Function> cons = Local<Function>::New(isolate, constructor);
    args.GetReturnValue().Set(cons->NewInstance(argc, argv));
  }
}

void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
  obj->value_ += 1;

  args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}

Test it with:

// test.js
var addon = require('./build/Release/addon');

var obj = new addon.MyObject(10);
console.log( obj.plusOne() ); // 11
console.log( obj.plusOne() ); // 12
console.log( obj.plusOne() ); // 13

Factory of wrapped objects

This is useful when you want to be able to create native objects without explicitly instantiating them with the new operator in JavaScript, e.g.

var obj = addon.createObject();
// instead of:
// var obj = new addon.Object();

Let’s register our createObject method in addon.cc:

// addon.cc
#include <node.h>
#include "myobject.h"

using namespace v8;

void CreateObject(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);
  MyObject::NewInstance(args);
}

void InitAll(Handle<Object> exports, Handle<Object> module) {
  MyObject::Init();

  NODE_SET_METHOD(module, "exports", CreateObject);
}

NODE_MODULE(addon, InitAll)

In myobject.h we now introduce the static method NewInstance that takes care of instantiating the object (i.e. it does the job of new in JavaScript):

// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H

#include <node.h>
#include <node_object_wrap.h>

class MyObject : public node::ObjectWrap {
 public:
  static void Init();
  static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);

 private:
  explicit MyObject(double value = 0);
  ~MyObject();

  static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
  static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
  static v8::Persistent<v8::Function> constructor;
  double value_;
};

#endif

The implementation is similar to the above in myobject.cc:

// myobject.cc
#include <node.h>
#include "myobject.h"

using namespace v8;

Persistent<Function> MyObject::constructor;

MyObject::MyObject(double value) : value_(value) {
}

MyObject::~MyObject() {
}

void MyObject::Init() {
  Isolate* isolate = Isolate::GetCurrent();
  // Prepare constructor template
  Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
  tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
  tpl->InstanceTemplate()->SetInternalFieldCount(1);

  // Prototype
  NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);

  constructor.Reset(isolate, tpl->GetFunction());
}

void MyObject::New(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  if (args.IsConstructCall()) {
    // Invoked as constructor: `new MyObject(...)`
    double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
    MyObject* obj = new MyObject(value);
    obj->Wrap(args.This());
    args.GetReturnValue().Set(args.This());
  } else {
    // Invoked as plain function `MyObject(...)`, turn into construct call.
    const int argc = 1;
    Local<Value> argv[argc] = { args[0] };
    Local<Function> cons = Local<Function>::New(isolate, constructor);
    args.GetReturnValue().Set(cons->NewInstance(argc, argv));
  }
}

void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  const unsigned argc = 1;
  Handle<Value> argv[argc] = { args[0] };
  Local<Function> cons = Local<Function>::New(isolate, constructor);
  Local<Object> instance = cons->NewInstance(argc, argv);

  args.GetReturnValue().Set(instance);
}

void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
  obj->value_ += 1;

  args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}

Test it with:

// test.js
var createObject = require('./build/Release/addon');

var obj = createObject(10);
console.log( obj.plusOne() ); // 11
console.log( obj.plusOne() ); // 12
console.log( obj.plusOne() ); // 13

var obj2 = createObject(20);
console.log( obj2.plusOne() ); // 21
console.log( obj2.plusOne() ); // 22
console.log( obj2.plusOne() ); // 23

Passing wrapped objects around

In addition to wrapping and returning C++ objects, you can pass them around by unwrapping them with Node’s node::ObjectWrap::Unwrap helper function. In the following addon.cc we introduce a function add() that can take on two MyObject objects:

// addon.cc
#include <node.h>
#include <node_object_wrap.h>
#include "myobject.h"

using namespace v8;

void CreateObject(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);
  MyObject::NewInstance(args);
}

void Add(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  MyObject* obj1 = node::ObjectWrap::Unwrap<MyObject>(
      args[0]->ToObject());
  MyObject* obj2 = node::ObjectWrap::Unwrap<MyObject>(
      args[1]->ToObject());

  double sum = obj1->value() + obj2->value();
  args.GetReturnValue().Set(Number::New(isolate, sum));
}

void InitAll(Handle<Object> exports) {
  MyObject::Init();

  NODE_SET_METHOD(exports, "createObject", CreateObject);
  NODE_SET_METHOD(exports, "add", Add);
}

NODE_MODULE(addon, InitAll)

To make things interesting we introduce a public method in myobject.h so we can probe private values after unwrapping the object:

// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H

#include <node.h>
#include <node_object_wrap.h>

class MyObject : public node::ObjectWrap {
 public:
  static void Init();
  static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
  inline double value() const { return value_; }

 private:
  explicit MyObject(double value = 0);
  ~MyObject();

  static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
  static v8::Persistent<v8::Function> constructor;
  double value_;
};

#endif

The implementation of myobject.cc is similar as before:

// myobject.cc
#include <node.h>
#include "myobject.h"

using namespace v8;

Persistent<Function> MyObject::constructor;

MyObject::MyObject(double value) : value_(value) {
}

MyObject::~MyObject() {
}

void MyObject::Init() {
  Isolate* isolate = Isolate::GetCurrent();

  // Prepare constructor template
  Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
  tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
  tpl->InstanceTemplate()->SetInternalFieldCount(1);

  constructor.Reset(isolate, tpl->GetFunction());
}

void MyObject::New(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  if (args.IsConstructCall()) {
    // Invoked as constructor: `new MyObject(...)`
    double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
    MyObject* obj = new MyObject(value);
    obj->Wrap(args.This());
    args.GetReturnValue().Set(args.This());
  } else {
    // Invoked as plain function `MyObject(...)`, turn into construct call.
    const int argc = 1;
    Local<Value> argv[argc] = { args[0] };
    Local<Function> cons = Local<Function>::New(isolate, constructor);
    args.GetReturnValue().Set(cons->NewInstance(argc, argv));
  }
}

void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
  Isolate* isolate = Isolate::GetCurrent();
  HandleScope scope(isolate);

  const unsigned argc = 1;
  Handle<Value> argv[argc] = { args[0] };
  Local<Function> cons = Local<Function>::New(isolate, constructor);
  Local<Object> instance = cons->NewInstance(argc, argv);

  args.GetReturnValue().Set(instance);
}

Test it with:

// test.js
var addon = require('./build/Release/addon');

var obj1 = addon.createObject(10);
var obj2 = addon.createObject(20);
var result = addon.add(obj1, obj2);

console.log(result); // 30

Child Process

Stability: 3 - Stable

Node provides a tri-directional popen(3) facility through the child_process module.

It is possible to stream data through a child’s stdin, stdout, and stderr in a fully non-blocking way. (Note that some programs use line-buffered I/O internally. That doesn’t affect node.js but it means data you send to the child process may not be immediately consumed.)

To create a child process use require('child_process').spawn() or require('child_process').fork(). The semantics of each are slightly different, and explained below.

For scripting purposes you may find the synchronous counterparts more convenient.

Class: ChildProcess

ChildProcess is an EventEmitter.

Child processes always have three streams associated with them. child.stdin, child.stdout, and child.stderr. These may be shared with the stdio streams of the parent process, or they may be separate stream objects which can be piped to and from.

The ChildProcess class is not intended to be used directly. Use the spawn(), exec(), execFile(), or fork() methods to create a Child Process instance.

Event: ‘error’

err {Error Object} the error.

Emitted when:

The process could not be spawned, or

The process could not be killed, or

Sending a message to the child process failed for whatever reason.

Note that the exit-event may or may not fire after an error has occurred. If you are listening on both events to fire a function, remember to guard against calling your function twice.

See also ChildProcess#kill() and ChildProcess#send().

Event: ‘exit’

code {Number} the exit code, if it exited normally.

signal {String} the signal passed to kill the child process, if it was killed by the parent.

This event is emitted after the child process ends. If the process terminated normally, code is the final exit code of the process, otherwise null. If the process terminated due to receipt of a signal, signal is the string name of the signal, otherwise null.

Note that the child process stdio streams might still be open.

Also, note that node establishes signal handlers for 'SIGINT' and 'SIGTERM’, so it will not terminate due to receipt of those signals, it will exit.

See waitpid(2).

Event: ‘close’

code {Number} the exit code, if it exited normally.

signal {String} the signal passed to kill the child process, if it was killed by the parent.

This event is emitted when the stdio streams of a child process have all terminated. This is distinct from ‘exit’, since multiple processes might share the same stdio streams.

Event: ‘disconnect’

This event is emitted after calling the .disconnect() method in the parent or in the child. After disconnecting it is no longer possible to send messages, and the .connected property is false.

Event: ‘message’

message {Object} a parsed JSON object or primitive value

sendHandle {Handle object} a Socket or Server object

Messages send by .send(message, [sendHandle]) are obtained using the message event.

child.stdin

{Stream object}

A Writable Stream that represents the child process’s stdin. If the child is waiting to read all its input, it will not continue until this stream has been closed via end().

If the child was not spawned with stdio[0] set to 'pipe', then this will not be set.

child.stdin is shorthand for child.stdio[0]. Both properties will refer to the same object, or null.

child.stdout

{Stream object}

A Readable Stream that represents the child process’s stdout.

If the child was not spawned with stdio[1] set to 'pipe', then this will not be set.

child.stdout is shorthand for child.stdio[1]. Both properties will refer to the same object, or null.

child.stderr

{Stream object}

A Readable Stream that represents the child process’s stderr.

If the child was not spawned with stdio[2] set to 'pipe', then this will not be set.

child.stderr is shorthand for child.stdio[2]. Both properties will refer to the same object, or null.

child.stdio

{Array}

A sparse array of pipes to the child process, corresponding with positions in the stdio option to spawn that have been set to 'pipe'. Note that streams 0-2 are also available as ChildProcess.stdin, ChildProcess.stdout, and ChildProcess.stderr, respectively.

In the following example, only the child’s fd 1 is setup as a pipe, so only the parent’s child.stdio[1] is a stream, all other values in the array are null.

child = child_process.spawn("ls", {
    stdio: [
      0, // use parents stdin for child
      'pipe', // pipe child's stdout to parent
      fs.openSync("err.out", "w") // direct child's stderr to a file
    ]
});

assert.equal(child.stdio[0], null);
assert.equal(child.stdio[0], child.stdin);

assert(child.stdout);
assert.equal(child.stdio[1], child.stdout);

assert.equal(child.stdio[2], null);
assert.equal(child.stdio[2], child.stderr);

child.pid

{Integer}

The PID of the child process.

Example:

var spawn = require('child_process').spawn,
    grep  = spawn('grep', ['ssh']);

console.log('Spawned child pid: ' + grep.pid);
grep.stdin.end();

child.connected

{Boolean} Set to false after `.disconnect’ is called

If .connected is false, it is no longer possible to send messages.

child.kill([signal])

signal {String}

Send a signal to the child process. If no argument is given, the process will be sent 'SIGTERM'. See signal(7) for a list of available signals.

var spawn = require('child_process').spawn,
    grep  = spawn('grep', ['ssh']);

grep.on('close', function (code, signal) {
  console.log('child process terminated due to receipt of signal '+signal);
});

// send SIGHUP to process
grep.kill('SIGHUP');

May emit an 'error' event when the signal cannot be delivered. Sending a signal to a child process that has already exited is not an error but may have unforeseen consequences: if the PID (the process ID) has been reassigned to another process, the signal will be delivered to that process instead. What happens next is anyone’s guess.

Note that while the function is called kill, the signal delivered to the child process may not actually kill it. kill really just sends a signal to a process.

See kill(2)

child.send(message[, sendHandle])

message {Object}

sendHandle {Handle object}

When using child_process.fork() you can write to the child using child.send(message, [sendHandle]) and messages are received by a 'message' event on the child.

For example:

var cp = require('child_process');

var n = cp.fork(__dirname + '/sub.js');

n.on('message', function(m) {
  console.log('PARENT got message:', m);
});

n.send({ hello: 'world' });

And then the child script, 'sub.js' might look like this:

process.on('message', function(m) {
  console.log('CHILD got message:', m);
});

process.send({ foo: 'bar' });

In the child the process object will have a send() method, and process will emit objects each time it receives a message on its channel.

Please note that the send() method on both the parent and child are synchronous - sending large chunks of data is not advised (pipes can be used instead, see child_process.spawn).

There is a special case when sending a {cmd: 'NODE_foo'} message. All messages containing a NODE_ prefix in its cmd property will not be emitted in the message event, since they are internal messages used by node core. Messages containing the prefix are emitted in the internalMessage event, you should by all means avoid using this feature, it is subject to change without notice.

The sendHandle option to child.send() is for sending a TCP server or socket object to another process. The child will receive the object as its second argument to the message event.

Emits an 'error' event if the message cannot be sent, for example because the child process has already exited.

Example: sending server object

Here is an example of sending a server:

var child = require('child_process').fork('child.js');

// Open up the server object and send the handle.
var server = require('net').createServer();
server.on('connection', function (socket) {
  socket.end('handled by parent');
});
server.listen(1337, function() {
  child.send('server', server);
});

And the child would the receive the server object as:

process.on('message', function(m, server) {
  if (m === 'server') {
    server.on('connection', function (socket) {
      socket.end('handled by child');
    });
  }
});

Note that the server is now shared between the parent and child, this means that some connections will be handled by the parent and some by the child.

For dgram servers the workflow is exactly the same. Here you listen on a message event instead of connection and use server.bind instead of server.listen. (Currently only supported on UNIX platforms.)

Example: sending socket object

Here is an example of sending a socket. It will spawn two children and handle connections with the remote address 74.125.127.100 as VIP by sending the socket to a “special” child process. Other sockets will go to a “normal” process.

var normal = require('child_process').fork('child.js', ['normal']);
var special = require('child_process').fork('child.js', ['special']);

// Open up the server and send sockets to child
var server = require('net').createServer();
server.on('connection', function (socket) {

  // if this is a VIP
  if (socket.remoteAddress === '74.125.127.100') {
    special.send('socket', socket);
    return;
  }
  // just the usual dudes
  normal.send('socket', socket);
});
server.listen(1337);

The child.js could look like this:

process.on('message', function(m, socket) {
  if (m === 'socket') {
    socket.end('You were handled as a ' + process.argv[2] + ' person');
  }
});

Note that once a single socket has been sent to a child the parent can no longer keep track of when the socket is destroyed. To indicate this condition the .connections property becomes null. It is also recommended not to use .maxConnections in this condition.

child.disconnect()

Close the IPC channel between parent and child, allowing the child to exit gracefully once there are no other connections keeping it alive. After calling this method the .connected flag will be set to false in both the parent and child, and it is no longer possible to send messages.

The ‘disconnect’ event will be emitted when there are no messages in the process of being received, most likely immediately.

Note that you can also call process.disconnect() in the child process when the child process has any open IPC channels with the parent (i.e fork()).

Asynchronous Process Creation

These methods follow the common async programming patterns (accepting a callback or returning an EventEmitter).

child_process.spawn(command[, args][, options])

command {String} The command to run

args {Array} List of string arguments

options {Object}

cwd {String} Current working directory of the child process

env {Object} Environment key-value pairs

stdio {Array|String} Child’s stdio configuration. (See below)

customFds {Array} Deprecated File descriptors for the child to use for stdio. (See below)

detached {Boolean} The child will be a process group leader. (See below)

uid {Number} Sets the user identity of the process. (See setuid(2).)

gid {Number} Sets the group identity of the process. (See setgid(2).)

return: {ChildProcess object}

Launches a new process with the given command, with command line arguments in args. If omitted, args defaults to an empty Array.

The third argument is used to specify additional options, with these defaults:

{ cwd: undefined,
  env: process.env
}

Use cwd to specify the working directory from which the process is spawned. If not given, the default is to inherit the current working directory.

Use env to specify environment variables that will be visible to the new process, the default is process.env.

Example of running ls -lh /usr, capturing stdout, stderr, and the exit code:

var spawn = require('child_process').spawn,
    ls    = spawn('ls', ['-lh', '/usr']);

ls.stdout.on('data', function (data) {
  console.log('stdout: ' + data);
});

ls.stderr.on('data', function (data) {
  console.log('stderr: ' + data);
});

ls.on('close', function (code) {
  console.log('child process exited with code ' + code);
});

Example: A very elaborate way to run ‘ps ax | grep ssh’

var spawn = require('child_process').spawn,
    ps    = spawn('ps', ['ax']),
    grep  = spawn('grep', ['ssh']);

ps.stdout.on('data', function (data) {
  grep.stdin.write(data);
});

ps.stderr.on('data', function (data) {
  console.log('ps stderr: ' + data);
});

ps.on('close', function (code) {
  if (code !== 0) {
    console.log('ps process exited with code ' + code);
  }
  grep.stdin.end();
});

grep.stdout.on('data', function (data) {
  console.log('' + data);
});

grep.stderr.on('data', function (data) {
  console.log('grep stderr: ' + data);
});

grep.on('close', function (code) {
  if (code !== 0) {
    console.log('grep process exited with code ' + code);
  }
});

options.stdio

As a shorthand, the stdio argument may also be one of the following strings:

'pipe' - ['pipe', 'pipe', 'pipe'], this is the default value

'ignore' - ['ignore', 'ignore', 'ignore']

'inherit' - [process.stdin, process.stdout, process.stderr] or [0,1,2]

Otherwise, the ‘stdio’ option to child_process.spawn() is an array where each index corresponds to a fd in the child. The value is one of the following:

'pipe' - Create a pipe between the child process and the parent process. The parent end of the pipe is exposed to the parent as a property on the child_process object as ChildProcess.stdio[fd]. Pipes created for fds 0 - 2 are also available as ChildProcess.stdin, ChildProcess.stdout and ChildProcess.stderr, respectively.

'ipc' - Create an IPC channel for passing messages/file descriptors between parent and child. A ChildProcess may have at most one IPC stdio file descriptor. Setting this option enables the ChildProcess.send() method. If the child writes JSON messages to this file descriptor, then this will trigger ChildProcess.on(‘message’). If the child is a Node.js program, then the presence of an IPC channel will enable process.send() and process.on(‘message’).

'ignore' - Do not set this file descriptor in the child. Note that Node will always open fd 0 - 2 for the processes it spawns. When any of these is ignored node will open /dev/null and attach it to the child’s fd.

Stream object - Share a readable or writable stream that refers to a tty, file, socket, or a pipe with the child process. The stream’s underlying file descriptor is duplicated in the child process to the fd that corresponds to the index in the stdio array. Note that the stream must have an underlying descriptor (file streams do not until the 'open' event has occurred).

Positive integer - The integer value is interpreted as a file descriptor that is is currently open in the parent process. It is shared with the child process, similar to how Stream objects can be shared.

null, undefined - Use default value. For stdio fds 0, 1 and 2 (in other words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the default is 'ignore'.

Example:

var spawn = require('child_process').spawn;

// Child will use parent's stdios
spawn('prg', [], { stdio: 'inherit' });

// Spawn child sharing only stderr
spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] });

// Open an extra fd=4, to interact with programs present a
// startd-style interface.
spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });

options.detached

If the detached option is set, the child process will be made the leader of a new process group. This makes it possible for the child to continue running after the parent exits.

By default, the parent will wait for the detached child to exit. To prevent the parent from waiting for a given child, use the child.unref() method, and the parent’s event loop will not include the child in its reference count.

Example of detaching a long-running process and redirecting its output to a file:

 var fs = require('fs'),
     spawn = require('child_process').spawn,
     out = fs.openSync('./out.log', 'a'),
     err = fs.openSync('./out.log', 'a');

 var child = spawn('prg', [], {
   detached: true,
   stdio: [ 'ignore', out, err ]
 });

 child.unref();

When using the detached option to start a long-running process, the process will not stay running in the background unless it is provided with a stdio configuration that is not connected to the parent. If the parent’s stdio is inherited, the child will remain attached to the controlling terminal.

options.customFds

There is a deprecated option called customFds which allows one to specify specific file descriptors for the stdio of the child process. This API was not portable to all platforms and therefore removed. With customFds it was possible to hook up the new process’ [stdin, stdout, stderr] to existing streams; -1 meant that a new stream should be created. Use at your own risk.

See also: child_process.exec() and child_process.fork()

child_process.exec(command[, options], callback)

command {String} The command to run, with space-separated arguments

options {Object}

cwd {String} Current working directory of the child process

env {Object} Environment key-value pairs

encoding {String} (Default: ‘utf8’)

shell {String} Shell to execute the command with (Default: ‘/bin/sh’ on UNIX, ‘cmd.exe’ on Windows, The shell should understand the -c switch on UNIX or /s /c on Windows. On Windows, command line parsing should be compatible with cmd.exe.)

timeout {Number} (Default: 0)

maxBuffer {Number} (Default: 200*1024)

killSignal {String} (Default: ‘SIGTERM’)

uid {Number} Sets the user identity of the process. (See setuid(2).)

gid {Number} Sets the group identity of the process. (See setgid(2).)

callback {Function} called with the output when process terminates

error {Error}

stdout {Buffer}

stderr {Buffer}

Return: ChildProcess object

Runs a command in a shell and buffers the output.

var exec = require('child_process').exec,
    child;

child = exec('cat *.js bad_file | wc -l',
  function (error, stdout, stderr) {
    console.log('stdout: ' + stdout);
    console.log('stderr: ' + stderr);
    if (error !== null) {
      console.log('exec error: ' + error);
    }
});

The callback gets the arguments (error, stdout, stderr). On success, error will be null. On error, error will be an instance of Error and error.code will be the exit code of the child process, and error.signal will be set to the signal that terminated the process.

There is a second optional argument to specify several options. The default options are

{ encoding: 'utf8',
  timeout: 0,
  maxBuffer: 200*1024,
  killSignal: 'SIGTERM',
  cwd: null,
  env: null }

If timeout is greater than 0, then it will kill the child process if it runs longer than timeout milliseconds. The child process is killed with killSignal (default: 'SIGTERM'). maxBuffer specifies the largest amount of data allowed on stdout or stderr - if this value is exceeded then the child process is killed.

child_process.execFile(file[, args][, options][, callback])

file {String} The filename of the program to run

args {Array} List of string arguments

options {Object}

cwd {String} Current working directory of the child process

env {Object} Environment key-value pairs

encoding {String} (Default: ‘utf8’)

timeout {Number} (Default: 0)

maxBuffer {Number} (Default: 200*1024)

killSignal {String} (Default: ‘SIGTERM’)

uid {Number} Sets the user identity of the process. (See setuid(2).)

gid {Number} Sets the group identity of the process. (See setgid(2).)

callback {Function} called with the output when process terminates

error {Error}

stdout {Buffer}

stderr {Buffer}

Return: ChildProcess object

This is similar to child_process.exec() except it does not execute a subshell but rather the specified file directly. This makes it slightly leaner than child_process.exec. It has the same options.

child_process.fork(modulePath[, args][, options])

modulePath {String} The module to run in the child

args {Array} List of string arguments

options {Object}

cwd {String} Current working directory of the child process

env {Object} Environment key-value pairs

execPath {String} Executable used to create the child process

execArgv {Array} List of string arguments passed to the executable (Default: process.execArgv)

silent {Boolean} If true, stdin, stdout, and stderr of the child will be piped to the parent, otherwise they will be inherited from the parent, see the “pipe” and “inherit” options for spawn()’s stdio for more details (default is false)

uid {Number} Sets the user identity of the process. (See setuid(2).)

gid {Number} Sets the group identity of the process. (See setgid(2).)

Return: ChildProcess object

This is a special case of the spawn() functionality for spawning Node processes. In addition to having all the methods in a normal ChildProcess instance, the returned object has a communication channel built-in. See child.send(message, [sendHandle]) for details.

These child Nodes are still whole new instances of V8. Assume at least 30ms startup and 10mb memory for each new Node. That is, you cannot create many thousands of them.

The execPath property in the options object allows for a process to be created for the child rather than the current node executable. This should be done with care and by default will talk over the fd represented an environmental variable NODE_CHANNEL_FD on the child process. The input and output on this fd is expected to be line delimited JSON objects.

Synchronous Process Creation

These methods are synchronous, meaning they WILL block the event loop, pausing execution of your code until the spawned process exits.

Blocking calls like these are mostly useful for simplifying general purpose scripting tasks and for simplifying the loading/processing of application configuration at startup.

child_process.spawnSync(command[, args][, options])

command {String} The command to run

args {Array} List of string arguments

options {Object}

cwd {String} Current working directory of the child process

input {String|Buffer} The value which will be passed as stdin to the spawned process

supplying this value will override stdio[0]

stdio {Array} Child’s stdio configuration.

env {Object} Environment key-value pairs

uid {Number} Sets the user identity of the process. (See setuid(2).)

gid {Number} Sets the group identity of the process. (See setgid(2).)

timeout {Number} In milliseconds the maximum amount of time the process is allowed to run. (Default: undefined)

killSignal {String} The signal value to be used when the spawned process will be killed. (Default: ‘SIGTERM’)

maxBuffer {Number}

encoding {String} The encoding used for all stdio inputs and outputs. (Default: ‘buffer’)

return: {Object}

pid {Number} Pid of the child process

output {Array} Array of results from stdio output

stdout {Buffer|String} The contents of output[1]

stderr {Buffer|String} The contents of output[2]

status {Number} The exit code of the child process

signal {String} The signal used to kill the child process

error {Error} The error object if the child process failed or timed out

spawnSync will not return until the child process has fully closed. When a timeout has been encountered and killSignal is sent, the method won’t return until the process has completely exited. That is to say, if the process handles the SIGTERM signal and doesn’t exit, your process will wait until the child process has exited.

child_process.execFileSync(command[, args][, options])

command {String} The command to run

args {Array} List of string arguments

options {Object}

cwd {String} Current working directory of the child process

input {String|Buffer} The value which will be passed as stdin to the spawned process

supplying this value will override stdio[0]

stdio {Array} Child’s stdio configuration. (Default: ‘pipe’)

stderr by default will be output to the parent process’ stderr unless stdio is specified

env {Object} Environment key-value pairs

uid {Number} Sets the user identity of the process. (See setuid(2).)

gid {Number} Sets the group identity of the process. (See setgid(2).)

timeout {Number} In milliseconds the maximum amount of time the process is allowed to run. (Default: undefined)

killSignal {String} The signal value to be used when the spawned process will be killed. (Default: ‘SIGTERM’)

maxBuffer {Number}

encoding {String} The encoding used for all stdio inputs and outputs. (Default: ‘buffer’)

return: {Buffer|String} The stdout from the command

execFileSync will not return until the child process has fully closed. When a timeout has been encountered and killSignal is sent, the method won’t return until the process has completely exited. That is to say, if the process handles the SIGTERM signal and doesn’t exit, your process will wait until the child process has exited.

If the process times out, or has a non-zero exit code, this method will throw. The Error object will contain the entire result from child_process.spawnSync

child_process.execSync(command[, options])

command {String} The command to run

options {Object}

cwd {String} Current working directory of the child process

input {String|Buffer} The value which will be passed as stdin to the spawned process

supplying this value will override stdio[0]

stdio {Array} Child’s stdio configuration. (Default: ‘pipe’)

stderr by default will be output to the parent process’ stderr unless stdio is specified

env {Object} Environment key-value pairs

uid {Number} Sets the user identity of the process. (See setuid(2).)

gid {Number} Sets the group identity of the process. (See setgid(2).)

timeout {Number} In milliseconds the maximum amount of time the process is allowed to run. (Default: undefined)

killSignal {String} The signal value to be used when the spawned process will be killed. (Default: ‘SIGTERM’)

maxBuffer {Number}

encoding {String} The encoding used for all stdio inputs and outputs. (Default: ‘buffer’)

return: {Buffer|String} The stdout from the command

execSync will not return until the child process has fully closed. When a timeout has been encountered and killSignal is sent, the method won’t return until the process has completely exited. That is to say, if the process handles the SIGTERM signal and doesn’t exit, your process will wait until the child process has exited.

If the process times out, or has a non-zero exit code, this method will throw. The Error object will contain the entire result from child_process.spawnSync

Cluster

Stability: 2 - Unstable

A single instance of Node runs in a single thread. To take advantage of multi-core systems the user will sometimes want to launch a cluster of Node processes to handle the load.

The cluster module allows you to easily create child processes that all share server ports.

var cluster = require('cluster');
var http = require('http');
var numCPUs = require('os').cpus().length;

if (cluster.isMaster) {
  // Fork workers.
  for (var i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  cluster.on('exit', function(worker, code, signal) {
    console.log('worker ' + worker.process.pid + ' died');
  });
} else {
  // Workers can share any TCP connection
  // In this case its a HTTP server
  http.createServer(function(req, res) {
    res.writeHead(200);
    res.end("hello world\n");
  }).listen(8000);
}

Running node will now share port 8000 between the workers:

% NODE_DEBUG=cluster node server.js
23521,Master Worker 23524 online
23521,Master Worker 23526 online
23521,Master Worker 23523 online
23521,Master Worker 23528 online

This feature was introduced recently, and may change in future versions. Please try it out and provide feedback.

Also note that, on Windows, it is not yet possible to set up a named pipe server in a worker.

How It Works

The worker processes are spawned using the child_process.fork method, so that they can communicate with the parent via IPC and pass server handles back and forth.

The cluster module supports two methods of distributing incoming connections.

The first one (and the default one on all platforms except Windows), is the round-robin approach, where the master process listens on a port, accepts new connections and distributes them across the workers in a round-robin fashion, with some built-in smarts to avoid overloading a worker process.

The second approach is where the master process creates the listen socket and sends it to interested workers. The workers then accept incoming connections directly.

The second approach should, in theory, give the best performance. In practice however, distribution tends to be very unbalanced due to operating system scheduler vagaries. Loads have been observed where over 70% of all connections ended up in just two processes, out of a total of eight.

Because server.listen() hands off most of the work to the master process, there are three cases where the behavior between a normal node.js process and a cluster worker differs:

server.listen({fd: 7}) Because the message is passed to the master, file descriptor 7 in the parent will be listened on, and the handle passed to the worker, rather than listening to the worker’s idea of what the number 7 file descriptor references.

server.listen(handle) Listening on handles explicitly will cause the worker to use the supplied handle, rather than talk to the master process. If the worker already has the handle, then it’s presumed that you know what you are doing.

server.listen(0) Normally, this will cause servers to listen on a random port. However, in a cluster, each worker will receive the same “random” port each time they do listen(0). In essence, the port is random the first time, but predictable thereafter. If you want to listen on a unique port, generate a port number based on the cluster worker ID.

There is no routing logic in Node.js, or in your program, and no shared state between the workers. Therefore, it is important to design your program such that it does not rely too heavily on in-memory data objects for things like sessions and login.

Because workers are all separate processes, they can be killed or re-spawned depending on your program’s needs, without affecting other workers. As long as there are some workers still alive, the server will continue to accept connections. Node does not automatically manage the number of workers for you, however. It is your responsibility to manage the worker pool for your application’s needs.

cluster.schedulingPolicy

The scheduling policy, either cluster.SCHED_RR for round-robin or cluster.SCHED_NONE to leave it to the operating system. This is a global setting and effectively frozen once you spawn the first worker or call cluster.setupMaster(), whatever comes first.

SCHED_RR is the default on all operating systems except Windows. Windows will change to SCHED_RR once libuv is able to effectively distribute IOCP handles without incurring a large performance hit.

cluster.schedulingPolicy can also be set through the NODE_CLUSTER_SCHED_POLICY environment variable. Valid values are "rr" and "none".

cluster.settings

{Object}

execArgv {Array} list of string arguments passed to the node executable. (Default=process.execArgv)

exec {String} file path to worker file. (Default=process.argv[1])

args {Array} string arguments passed to worker. (Default=process.argv.slice(2))

silent {Boolean} whether or not to send output to parent’s stdio. (Default=false)

uid {Number} Sets the user identity of the process. (See setuid(2).)

gid {Number} Sets the group identity of the process. (See setgid(2).)

After calling .setupMaster() (or .fork()) this settings object will contain the settings, including the default values.

It is effectively frozen after being set, because .setupMaster() can only be called once.

This object is not supposed to be changed or set manually, by you.

cluster.isMaster

{Boolean}

True if the process is a master. This is determined by the process.env.NODE_UNIQUE_ID. If process.env.NODE_UNIQUE_ID is undefined, then isMaster is true.

cluster.isWorker

{Boolean}

True if the process is not a master (it is the negation of cluster.isMaster).

Event: ‘fork’

worker {Worker object}

When a new worker is forked the cluster module will emit a ‘fork’ event. This can be used to log worker activity, and create your own timeout.

var timeouts = [];
function errorMsg() {
  console.error("Something must be wrong with the connection ...");
}

cluster.on('fork', function(worker) {
  timeouts[worker.id] = setTimeout(errorMsg, 2000);
});
cluster.on('listening', function(worker, address) {
  clearTimeout(timeouts[worker.id]);
});
cluster.on('exit', function(worker, code, signal) {
  clearTimeout(timeouts[worker.id]);
  errorMsg();
});

Event: ‘online’

worker {Worker object}

After forking a new worker, the worker should respond with an online message. When the master receives an online message it will emit this event. The difference between ‘fork’ and ‘online’ is that fork is emitted when the master forks a worker, and ‘online’ is emitted when the worker is running.

cluster.on('online', function(worker) {
  console.log("Yay, the worker responded after it was forked");
});

Event: ‘listening’

worker {Worker object}

address {Object}

After calling listen() from a worker, when the ‘listening’ event is emitted on the server, a listening event will also be emitted on cluster in the master.

The event handler is executed with two arguments, the worker contains the worker object and the address object contains the following connection properties: address, port and addressType. This is very useful if the worker is listening on more than one address.

cluster.on('listening', function(worker, address) {
  console.log("A worker is now connected to " + address.address + ":" + address.port);
});

The addressType is one of:

4 (TCPv4)

6 (TCPv6)

-1 (unix domain socket)

"udp4" or "udp6" (UDP v4 or v6)

Event: ‘disconnect’

worker {Worker object}

Emitted after the worker IPC channel has disconnected. This can occur when a worker exits gracefully, is killed, or is disconnected manually (such as with worker.disconnect()).

There may be a delay between the disconnect and exit events. These events can be used to detect if the process is stuck in a cleanup or if there are long-living connections.

cluster.on('disconnect', function(worker) {
  console.log('The worker #' + worker.id + ' has disconnected');
});

Event: ‘exit’

worker {Worker object}

code {Number} the exit code, if it exited normally.

signal {String} the name of the signal (eg. 'SIGHUP') that caused the process to be killed.

When any of the workers die the cluster module will emit the ‘exit’ event.

This can be used to restart the worker by calling .fork() again.

cluster.on('exit', function(worker, code, signal) {
  console.log('worker %d died (%s). restarting...',
    worker.process.pid, signal || code);
  cluster.fork();
});

See child_process event: ‘exit’.

Event: ‘setup’

settings {Object}

Emitted every time .setupMaster() is called.

The settings object is the cluster.settings object at the time .setupMaster() was called and is advisory only, since multiple calls to .setupMaster() can be made in a single tick.

If accuracy is important, use cluster.settings.

cluster.setupMaster([settings])

settings {Object}

exec {String} file path to worker file. (Default=process.argv[1])

args {Array} string arguments passed to worker. (Default=process.argv.slice(2))

silent {Boolean} whether or not to send output to parent’s stdio. (Default=false)

setupMaster is used to change the default ‘fork’ behavior. Once called, the settings will be present in cluster.settings.

Note that:

any settings changes only affect future calls to .fork() and have no effect on workers that are already running

The only attribute of a worker that cannot be set via .setupMaster() is the env passed to .fork()

the defaults above apply to the first call only, the defaults for later calls is the current value at the time of cluster.setupMaster() is called

Example:

var cluster = require('cluster');
cluster.setupMaster({
  exec: 'worker.js',
  args: ['--use', 'https'],
  silent: true
});
cluster.fork(); // https worker
cluster.setupMaster({
  args: ['--use', 'http']
});
cluster.fork(); // http worker

This can only be called from the master process.

cluster.fork([env])

env {Object} Key/value pairs to add to worker process environment.

return {Worker object}

Spawn a new worker process.

This can only be called from the master process.

cluster.disconnect([callback])

callback {Function} called when all workers are disconnected and handles are closed

Calls .disconnect() on each worker in cluster.workers.

When they are disconnected all internal handles will be closed, allowing the master process to die gracefully if no other event is waiting.

The method takes an optional callback argument which will be called when finished.

This can only be called from the master process.

cluster.worker

{Object}

A reference to the current worker object. Not available in the master process.

var cluster = require('cluster');

if (cluster.isMaster) {
  console.log('I am master');
  cluster.fork();
  cluster.fork();
} else if (cluster.isWorker) {
  console.log('I am worker #' + cluster.worker.id);
}

cluster.workers

{Object}

A hash that stores the active worker objects, keyed by id field. Makes it easy to loop through all the workers. It is only available in the master process.

A worker is removed from cluster.workers after the worker has disconnected and exited. The order between these two events cannot be determined in advance. However, it is guaranteed that the removal from the cluster.workers list happens before last 'disconnect' or 'exit' event is emitted.

// Go through all workers
function eachWorker(callback) {
  for (var id in cluster.workers) {
    callback(cluster.workers[id]);
  }
}
eachWorker(function(worker) {
  worker.send('big announcement to all workers');
});

Should you wish to reference a worker over a communication channel, using the worker’s unique id is the easiest way to find the worker.

socket.on('data', function(id) {
  var worker = cluster.workers[id];
});

Class: Worker

A Worker object contains all public information and method about a worker. In the master it can be obtained using cluster.workers. In a worker it can be obtained using cluster.worker.

worker.id

{String}

Each new worker is given its own unique id, this id is stored in the id.

While a worker is alive, this is the key that indexes it in cluster.workers

worker.process

{ChildProcess object}

All workers are created using child_process.fork(), the returned object from this function is stored as .process. In a worker, the global process is stored.

See: Child Process module

Note that workers will call process.exit(0) if the 'disconnect' event occurs on process and .suicide is not true. This protects against accidental disconnection.

worker.suicide

{Boolean}

Set by calling .kill() or .disconnect(), until then it is undefined.

The boolean worker.suicide lets you distinguish between voluntary and accidental exit, the master may choose not to respawn a worker based on this value.

cluster.on('exit', function(worker, code, signal) {
  if (worker.suicide === true) {
    console.log('Oh, it was just suicide\' – no need to worry').
  }
});

// kill worker
worker.kill();

worker.send(message[, sendHandle])

message {Object}

sendHandle {Handle object}

This function is equal to the send methods provided by child_process.fork(). In the master you should use this function to send a message to a specific worker.

In a worker you can also use process.send(message), it is the same function.

This example will echo back all messages from the master:

if (cluster.isMaster) {
  var worker = cluster.fork();
  worker.send('hi there');

} else if (cluster.isWorker) {
  process.on('message', function(msg) {
    process.send(msg);
  });
}

worker.kill([signal=‘SIGTERM’])

signal {String} Name of the kill signal to send to the worker process.

This function will kill the worker. In the master, it does this by disconnecting the worker.process, and once disconnected, killing with signal. In the worker, it does it by disconnecting the channel, and then exiting with code 0.

Causes .suicide to be set.

This method is aliased as worker.destroy() for backwards compatibility.

Note that in a worker, process.kill() exists, but it is not this function, it is kill.

worker.disconnect()

In a worker, this function will close all servers, wait for the ‘close’ event on those servers, and then disconnect the IPC channel.

In the master, an internal message is sent to the worker causing it to call .disconnect() on itself.

Causes .suicide to be set.

Note that after a server is closed, it will no longer accept new connections, but connections may be accepted by any other listening worker. Existing connections will be allowed to close as usual. When no more connections exist, see server.close(), the IPC channel to the worker will close allowing it to die gracefully.

The above applies only to server connections, client connections are not automatically closed by workers, and disconnect does not wait for them to close before exiting.

Note that in a worker, process.disconnect exists, but it is not this function, it is disconnect.

Because long living server connections may block workers from disconnecting, it may be useful to send a message, so application specific actions may be taken to close them. It also may be useful to implement a timeout, killing a worker if the disconnect event has not been emitted after some time.

if (cluster.isMaster) {
  var worker = cluster.fork();
  var timeout;

  worker.on('listening', function(address) {
    worker.send('shutdown');
    worker.disconnect();
    timeout = setTimeout(function() {
      worker.kill();
    }, 2000);
  });

  worker.on('disconnect', function() {
    clearTimeout(timeout);
  });

} else if (cluster.isWorker) {
  var net = require('net');
  var server = net.createServer(function(socket) {
    // connections never end
  });

  server.listen(8000);

  process.on('message', function(msg) {
    if(msg === 'shutdown') {
      // initiate graceful close of any connections to server
    }
  });
}

worker.isDead()

This function returns true if the worker’s process has terminated (either because of exiting or being signaled). Otherwise, it returns false.

worker.isConnected()

This function returns true if the worker is connected to its master via its IPC channel, false otherwise. A worker is connected to its master after it’s been created. It is disconnected after the disconnect event is emitted.

Event: ‘message’

message {Object}

This event is the same as the one provided by child_process.fork().

In a worker you can also use process.on('message').

As an example, here is a cluster that keeps count of the number of requests in the master process using the message system:

var cluster = require('cluster');
var http = require('http');

if (cluster.isMaster) {

  // Keep track of http requests
  var numReqs = 0;
  setInterval(function() {
    console.log("numReqs =", numReqs);
  }, 1000);

  // Count requestes
  function messageHandler(msg) {
    if (msg.cmd && msg.cmd == 'notifyRequest') {
      numReqs += 1;
    }
  }

  // Start workers and listen for messages containing notifyRequest
  var numCPUs = require('os').cpus().length;
  for (var i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  Object.keys(cluster.workers).forEach(function(id) {
    cluster.workers[id].on('message', messageHandler);
  });

} else {

  // Worker processes have a http server.
  http.Server(function(req, res) {
    res.writeHead(200);
    res.end("hello world\n");

    // notify master about the request
    process.send({ cmd: 'notifyRequest' });
  }).listen(8000);
}

Event: ‘online’

Similar to the cluster.on('online') event, but specific to this worker.

cluster.fork().on('online', function() {
  // Worker is online
});

It is not emitted in the worker.

Event: ‘listening’

address {Object}

Similar to the cluster.on('listening') event, but specific to this worker.

cluster.fork().on('listening', function(address) {
  // Worker is listening
});

It is not emitted in the worker.

Event: ‘disconnect’

Similar to the cluster.on('disconnect') event, but specfic to this worker.

cluster.fork().on('disconnect', function() {
  // Worker has disconnected
});

Event: ‘exit’

code {Number} the exit code, if it exited normally.

signal {String} the name of the signal (eg. 'SIGHUP') that caused the process to be killed.

Similar to the cluster.on('exit') event, but specific to this worker.

var worker = cluster.fork();
worker.on('exit', function(code, signal) {
  if( signal ) {
    console.log("worker was killed by signal: "+signal);
  } else if( code !== 0 ) {
    console.log("worker exited with error code: "+code);
  } else {
    console.log("worker success!");
  }
});

Event: ‘error’

This event is the same as the one provided by child_process.fork().

In a worker you can also use process.on('error').

console

Stability: 4 - API Frozen

{Object}

For printing to stdout and stderr. Similar to the console object functions provided by most web browsers, here the output is sent to stdout or stderr.

The console functions are synchronous when the destination is a terminal or a file (to avoid lost messages in case of premature exit) and asynchronous when it’s a pipe (to avoid blocking for long periods of time).

That is, in the following example, stdout is non-blocking while stderr is blocking:

$ node script.js 2> error.log | tee info.log

In daily use, the blocking/non-blocking dichotomy is not something you should worry about unless you log huge amounts of data.

console.log([data][, …])

Prints to stdout with newline. This function can take multiple arguments in a printf()-like way. Example:

var count = 5;
console.log('count: %d', count);
// prints 'count: 5'

If formatting elements are not found in the first string then util.inspect is used on each argument. See util.format() for more information.

console.info([data][, …])

Same as console.log.

console.error([data][, …])

Same as console.log but prints to stderr.

console.warn([data][, …])

Same as console.error.

console.dir(obj[, options])

Uses util.inspect on obj and prints resulting string to stdout. This function bypasses any custom inspect() function on obj. An optional options object may be passed that alters certain aspects of the formatted string:

showHidden - if true then the object’s non-enumerable properties will be shown too. Defaults to false.

depth - tells inspect how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. Defaults to 2. To make it recurse indefinitely pass null.

colors - if true, then the output will be styled with ANSI color codes. Defaults to false. Colors are customizable, see below.

console.time(label)

Mark a time.

console.timeEnd(label)

Finish timer, record output. Example:

console.time('100-elements');
for (var i = 0; i < 100; i++) {
  ;
}
console.timeEnd('100-elements');
// prints 100-elements: 262ms

console.trace(message[, …])

Print to stderr 'Trace :', followed by the formatted message and stack trace to the current position.

console.assert(value[, message][, …])

Similar to assert.ok(), but the error message is formatted as util.format(message...).

Crypto

Stability: 2 - Unstable; API changes are being discussed for
future versions.  Breaking changes will be minimized.  See below.

Use require('crypto') to access this module.

The crypto module offers a way of encapsulating secure credentials to be used as part of a secure HTTPS net or http connection.

It also offers a set of wrappers for OpenSSL’s hash, hmac, cipher, decipher, sign and verify methods.

crypto.setEngine(engine[, flags])

Load and set engine for some/all OpenSSL functions (selected by flags).

engine could be either an id or a path to the to the engine’s shared library.

flags is optional and has ENGINE_METHOD_ALL value by default. It could take one of or mix of following flags (defined in constants module):

ENGINE_METHOD_RSA

ENGINE_METHOD_DSA

ENGINE_METHOD_DH

ENGINE_METHOD_RAND

ENGINE_METHOD_ECDH

ENGINE_METHOD_ECDSA

ENGINE_METHOD_CIPHERS

ENGINE_METHOD_DIGESTS

ENGINE_METHOD_STORE

ENGINE_METHOD_PKEY_METH

ENGINE_METHOD_PKEY_ASN1_METH

ENGINE_METHOD_ALL

ENGINE_METHOD_NONE

crypto.getCiphers()

Returns an array with the names of the supported ciphers.

Example:

var ciphers = crypto.getCiphers();
console.log(ciphers); // ['AES-128-CBC', 'AES-128-CBC-HMAC-SHA1', ...]

crypto.getHashes()

Returns an array with the names of the supported hash algorithms.

Example:

var hashes = crypto.getHashes();
console.log(hashes); // ['sha', 'sha1', 'sha1WithRSAEncryption', ...]

crypto.createCredentials(details)

Stability: 0 - Deprecated. Use [tls.createSecureContext][] instead.

Creates a credentials object, with the optional details being a dictionary with keys:

pfx : A string or buffer holding the PFX or PKCS12 encoded private key, certificate and CA certificates

key : A string holding the PEM encoded private key

passphrase : A string of passphrase for the private key or pfx

cert : A string holding the PEM encoded certificate

ca : Either a string or list of strings of PEM encoded CA certificates to trust.

crl : Either a string or list of strings of PEM encoded CRLs (Certificate Revocation List)

ciphers: A string describing the ciphers to use or exclude. Consult http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT for details on the format.

If no ‘ca’ details are given, then node.js will use the default publicly trusted list of CAs as given in http://mxr.mozilla.org/mozilla/source/security/nss/lib/ckfw/builtins/certdata.txt.

crypto.createHash(algorithm)

Creates and returns a hash object, a cryptographic hash with the given algorithm which can be used to generate hash digests.

algorithm is dependent on the available algorithms supported by the version of OpenSSL on the platform. Examples are 'sha1', 'md5', 'sha256', 'sha512', etc. On recent releases, openssl list-message-digest-algorithms will display the available digest algorithms.

Example: this program that takes the sha1 sum of a file

var filename = process.argv[2];
var crypto = require('crypto');
var fs = require('fs');

var shasum = crypto.createHash('sha1');

var s = fs.createReadStream(filename);
s.on('data', function(d) {
  shasum.update(d);
});

s.on('end', function() {
  var d = shasum.digest('hex');
  console.log(d + '  ' + filename);
});

Class: Hash

The class for creating hash digests of data.

It is a stream that is both readable and writable. The written data is used to compute the hash. Once the writable side of the stream is ended, use the read() method to get the computed hash digest. The legacy update and digest methods are also supported.

Returned by crypto.createHash.

hash.update(data[, input_encoding])

Updates the hash content with the given data, the encoding of which is given in input_encoding and can be 'utf8', 'ascii' or 'binary'. If no encoding is provided and the input is a string an encoding of 'binary' is enforced. If data is a Buffer then input_encoding is ignored.

This can be called many times with new data as it is streamed.

hash.digest([encoding])

Calculates the digest of all of the passed data to be hashed. The encoding can be 'hex', 'binary' or 'base64'. If no encoding is provided, then a buffer is returned.

Note: hash object can not be used after digest() method has been called.

crypto.createHmac(algorithm, key)

Creates and returns a hmac object, a cryptographic hmac with the given algorithm and key.

It is a stream that is both readable and writable. The written data is used to compute the hmac. Once the writable side of the stream is ended, use the read() method to get the computed digest. The legacy update and digest methods are also supported.

algorithm is dependent on the available algorithms supported by OpenSSL - see createHash above. key is the hmac key to be used.

Class: Hmac

Class for creating cryptographic hmac content.

Returned by crypto.createHmac.

hmac.update(data)

Update the hmac content with the given data. This can be called many times with new data as it is streamed.

hmac.digest([encoding])

Calculates the digest of all of the passed data to the hmac. The encoding can be 'hex', 'binary' or 'base64'. If no encoding is provided, then a buffer is returned.

Note: hmac object can not be used after digest() method has been called.

crypto.createCipher(algorithm, password)

Creates and returns a cipher object, with the given algorithm and password.

algorithm is dependent on OpenSSL, examples are 'aes192', etc. On recent releases, openssl list-cipher-algorithms will display the available cipher algorithms. password is used to derive key and IV, which must be a 'binary' encoded string or a buffer.

It is a stream that is both readable and writable. The written data is used to compute the hash. Once the writable side of the stream is ended, use the read() method to get the enciphered contents. The legacy update and final methods are also supported.

Note: createCipher derives keys with the OpenSSL function EVP_BytesToKey with the digest algorithm set to MD5, one iteration, and no salt. The lack of salt allows dictionary attacks as the same password always creates the same key. The low iteration count and non-cryptographically secure hash algorithm allow passwords to be tested very rapidly.

In line with OpenSSL’s recommendation to use pbkdf2 instead of EVP_BytesToKey it is recommended you derive a key and iv yourself with crypto.pbkdf2 and to then use createCipheriv() to create the cipher stream.

crypto.createCipheriv(algorithm, key, iv)

Creates and returns a cipher object, with the given algorithm, key and iv.

algorithm is the same as the argument to createCipher(). key is the raw key used by the algorithm. iv is an initialization vector.

key and iv must be 'binary' encoded strings or buffers.

Class: Cipher

Class for encrypting data.

Returned by crypto.createCipher and crypto.createCipheriv.

Cipher objects are streams that are both readable and writable. The written plain text data is used to produce the encrypted data on the readable side. The legacy update and final methods are also supported.

cipher.update(data[, input_encoding][, output_encoding])

Updates the cipher with data, the encoding of which is given in input_encoding and can be 'utf8', 'ascii' or 'binary'. If no encoding is provided, then a buffer is expected. If data is a Buffer then input_encoding is ignored.

The output_encoding specifies the output format of the enciphered data, and can be 'binary', 'base64' or 'hex'. If no encoding is provided, then a buffer is returned.

Returns the enciphered contents, and can be called many times with new data as it is streamed.

cipher.final([output_encoding])

Returns any remaining enciphered contents, with output_encoding being one of: 'binary', 'base64' or 'hex'. If no encoding is provided, then a buffer is returned.

Note: cipher object can not be used after final() method has been called.

cipher.setAutoPadding(auto_padding=true)

You can disable automatic padding of the input data to block size. If auto_padding is false, the length of the entire input data must be a multiple of the cipher’s block size or final will fail. Useful for non-standard padding, e.g. using 0x0 instead of PKCS padding. You must call this before cipher.final.

cipher.getAuthTag()

For authenticated encryption modes (currently supported: GCM), this method returns a Buffer that represents the authentication tag that has been computed from the given data. Should be called after encryption has been completed using the final method!

cipher.setAAD(buffer)

For authenticated encryption modes (currently supported: GCM), this method sets the value used for the additional authenticated data (AAD) input parameter.

crypto.createDecipher(algorithm, password)

Creates and returns a decipher object, with the given algorithm and key. This is the mirror of the createCipher() above.

crypto.createDecipheriv(algorithm, key, iv)

Creates and returns a decipher object, with the given algorithm, key and iv. This is the mirror of the createCipheriv() above.

Class: Decipher

Class for decrypting data.

Returned by crypto.createDecipher and crypto.createDecipheriv.

Decipher objects are streams that are both readable and writable. The written enciphered data is used to produce the plain-text data on the the readable side. The legacy update and final methods are also supported.

decipher.update(data[, input_encoding][, output_encoding])

Updates the decipher with data, which is encoded in 'binary', 'base64' or 'hex'. If no encoding is provided, then a buffer is expected. If data is a Buffer then input_encoding is ignored.

The output_decoding specifies in what format to return the deciphered plaintext: 'binary', 'ascii' or 'utf8'. If no encoding is provided, then a buffer is returned.

decipher.final([output_encoding])

Returns any remaining plaintext which is deciphered, with output_encoding being one of: 'binary', 'ascii' or 'utf8'. If no encoding is provided, then a buffer is returned.

Note: decipher object can not be used after final() method has been called.

decipher.setAutoPadding(auto_padding=true)

You can disable auto padding if the data has been encrypted without standard block padding to prevent decipher.final from checking and removing it. Can only work if the input data’s length is a multiple of the ciphers block size. You must call this before streaming data to decipher.update.

decipher.setAuthTag(buffer)

For authenticated encryption modes (currently supported: GCM), this method must be used to pass in the received authentication tag. If no tag is provided or if the ciphertext has been tampered with, final will throw, thus indicating that the ciphertext should be discarded due to failed authentication.

decipher.setAAD(buffer)

For authenticated encryption modes (currently supported: GCM), this method sets the value used for the additional authenticated data (AAD) input parameter.

crypto.createSign(algorithm)

Creates and returns a signing object, with the given algorithm. On recent OpenSSL releases, openssl list-public-key-algorithms will display the available signing algorithms. Examples are 'RSA-SHA256'.

Class: Sign

Class for generating signatures.

Returned by crypto.createSign.

Sign objects are writable streams. The written data is used to generate the signature. Once all of the data has been written, the sign method will return the signature. The legacy update method is also supported.

sign.update(data)

Updates the sign object with data. This can be called many times with new data as it is streamed.

sign.sign(private_key[, output_format])

Calculates the signature on all the updated data passed through the sign.

private_key can be an object or a string. If private_key is a string, it is treated as the key with no passphrase.

private_key:

key : A string holding the PEM encoded private key

passphrase : A string of passphrase for the private key

Returns the signature in output_format which can be 'binary', 'hex' or 'base64'. If no encoding is provided, then a buffer is returned.

Note: sign object can not be used after sign() method has been called.

crypto.createVerify(algorithm)

Creates and returns a verification object, with the given algorithm. This is the mirror of the signing object above.

Class: Verify

Class for verifying signatures.

Returned by crypto.createVerify.

Verify objects are writable streams. The written data is used to validate against the supplied signature. Once all of the data has been written, the verify method will return true if the supplied signature is valid. The legacy update method is also supported.

verifier.update(data)

Updates the verifier object with data. This can be called many times with new data as it is streamed.

verifier.verify(object, signature[, signature_format])

Verifies the signed data by using the object and signature. object is a string containing a PEM encoded object, which can be one of RSA public key, DSA public key, or X.509 certificate. signature is the previously calculated signature for the data, in the signature_format which can be 'binary', 'hex' or 'base64'. If no encoding is specified, then a buffer is expected.

Returns true or false depending on the validity of the signature for the data and public key.

Note: verifier object can not be used after verify() method has been called.

crypto.createDiffieHellman(prime_length[, generator])

Creates a Diffie-Hellman key exchange object and generates a prime of prime_length bits and using an optional specific numeric generator. If no generator is specified, then 2 is used.

crypto.createDiffieHellman(prime[, prime_encoding][, generator][, generator_encoding])

Creates a Diffie-Hellman key exchange object using the supplied prime and an optional specific generator. generator can be a number, string, or Buffer. If no generator is specified, then 2 is used. prime_encoding and generator_encoding can be 'binary', 'hex', or 'base64'. If no prime_encoding is specified, then a Buffer is expected for prime. If no generator_encoding is specified, then a Buffer is expected for generator.

Class: DiffieHellman

The class for creating Diffie-Hellman key exchanges.

Returned by crypto.createDiffieHellman.

diffieHellman.verifyError

A bit field containing any warnings and/or errors as a result of a check performed during initialization. The following values are valid for this property (defined in constants module):

DH_CHECK_P_NOT_SAFE_PRIME

DH_CHECK_P_NOT_PRIME

DH_UNABLE_TO_CHECK_GENERATOR

DH_NOT_SUITABLE_GENERATOR

diffieHellman.generateKeys([encoding])

Generates private and public Diffie-Hellman key values, and returns the public key in the specified encoding. This key should be transferred to the other party. Encoding can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

diffieHellman.computeSecret(other_public_key[, input_encoding][, output_encoding])

Computes the shared secret using other_public_key as the other party’s public key and returns the computed shared secret. Supplied key is interpreted using specified input_encoding, and secret is encoded using specified output_encoding. Encodings can be 'binary', 'hex', or 'base64'. If the input encoding is not provided, then a buffer is expected.

If no output encoding is given, then a buffer is returned.

diffieHellman.getPrime([encoding])

Returns the Diffie-Hellman prime in the specified encoding, which can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

diffieHellman.getGenerator([encoding])

Returns the Diffie-Hellman generator in the specified encoding, which can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

diffieHellman.getPublicKey([encoding])

Returns the Diffie-Hellman public key in the specified encoding, which can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

diffieHellman.getPrivateKey([encoding])

Returns the Diffie-Hellman private key in the specified encoding, which can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

diffieHellman.setPublicKey(public_key[, encoding])

Sets the Diffie-Hellman public key. Key encoding can be 'binary', 'hex' or 'base64'. If no encoding is provided, then a buffer is expected.

diffieHellman.setPrivateKey(private_key[, encoding])

Sets the Diffie-Hellman private key. Key encoding can be 'binary', 'hex' or 'base64'. If no encoding is provided, then a buffer is expected.

crypto.getDiffieHellman(group_name)

Creates a predefined Diffie-Hellman key exchange object. The supported groups are: 'modp1', 'modp2', 'modp5' (defined in RFC 2412) and 'modp14', 'modp15', 'modp16', 'modp17', 'modp18' (defined in RFC 3526). The returned object mimics the interface of objects created by crypto.createDiffieHellman() above, but will not allow to change the keys (with diffieHellman.setPublicKey() for example). The advantage of using this routine is that the parties don’t have to generate nor exchange group modulus beforehand, saving both processor and communication time.

Example (obtaining a shared secret):

var crypto = require('crypto');
var alice = crypto.getDiffieHellman('modp5');
var bob = crypto.getDiffieHellman('modp5');

alice.generateKeys();
bob.generateKeys();

var alice_secret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
var bob_secret = bob.computeSecret(alice.getPublicKey(), null, 'hex');

/* alice_secret and bob_secret should be the same */
console.log(alice_secret == bob_secret);

crypto.createECDH(curve_name)

Creates a Elliptic Curve (EC) Diffie-Hellman key exchange object using a predefined curve specified by curve_name string.

Class: ECDH

The class for creating EC Diffie-Hellman key exchanges.

Returned by crypto.createECDH.

ECDH.generateKeys([encoding[, format]])

Generates private and public EC Diffie-Hellman key values, and returns the public key in the specified format and encoding. This key should be transferred to the other party.

Format specifies point encoding and can be 'compressed', 'uncompressed', or 'hybrid'. If no format is provided - the point will be returned in 'uncompressed' format.

Encoding can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

ECDH.computeSecret(other_public_key[, input_encoding][, output_encoding])

Computes the shared secret using other_public_key as the other party’s public key and returns the computed shared secret. Supplied key is interpreted using specified input_encoding, and secret is encoded using specified output_encoding. Encodings can be 'binary', 'hex', or 'base64'. If the input encoding is not provided, then a buffer is expected.

If no output encoding is given, then a buffer is returned.

ECDH.getPublicKey([encoding[, format]])

Returns the EC Diffie-Hellman public key in the specified encoding and format.

Format specifies point encoding and can be 'compressed', 'uncompressed', or 'hybrid'. If no format is provided - the point will be returned in 'uncompressed' format.

Encoding can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

ECDH.getPrivateKey([encoding])

Returns the EC Diffie-Hellman private key in the specified encoding, which can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

ECDH.setPublicKey(public_key[, encoding])

Sets the EC Diffie-Hellman public key. Key encoding can be 'binary', 'hex' or 'base64'. If no encoding is provided, then a buffer is expected.

ECDH.setPrivateKey(private_key[, encoding])

Sets the EC Diffie-Hellman private key. Key encoding can be 'binary', 'hex' or 'base64'. If no encoding is provided, then a buffer is expected.

Example (obtaining a shared secret):

var crypto = require('crypto');
var alice = crypto.createECDH('secp256k1');
var bob = crypto.createECDH('secp256k1');

alice.generateKeys();
bob.generateKeys();

var alice_secret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
var bob_secret = bob.computeSecret(alice.getPublicKey(), null, 'hex');

/* alice_secret and bob_secret should be the same */
console.log(alice_secret == bob_secret);

crypto.pbkdf2(password, salt, iterations, keylen[, digest], callback)

Asynchronous PBKDF2 function. Applies the selected HMAC digest function (default: SHA1) to derive a key of the requested length from the password, salt and number of iterations. The callback gets two arguments: (err, derivedKey).

Example:

crypto.pbkdf2('secret', 'salt', 4096, 512, 'sha256', function(err, key) {
  if (err)
    throw err;
  console.log(key.toString('hex'));  // 'c5e478d...1469e50'
});

You can get a list of supported digest functions with crypto.getHashes().

crypto.pbkdf2Sync(password, salt, iterations, keylen[, digest])

Synchronous PBKDF2 function. Returns derivedKey or throws error.

crypto.randomBytes(size[, callback])

Generates cryptographically strong pseudo-random data. Usage:

// async
crypto.randomBytes(256, function(ex, buf) {
  if (ex) throw ex;
  console.log('Have %d bytes of random data: %s', buf.length, buf);
});

// sync
try {
  var buf = crypto.randomBytes(256);
  console.log('Have %d bytes of random data: %s', buf.length, buf);
} catch (ex) {
  // handle error
  // most likely, entropy sources are drained
}

NOTE: Will throw error or invoke callback with error, if there is not enough accumulated entropy to generate cryptographically strong data. In other words, crypto.randomBytes without callback will not block even if all entropy sources are drained.

crypto.pseudoRandomBytes(size[, callback])

Generates non-cryptographically strong pseudo-random data. The data returned will be unique if it is sufficiently long, but is not necessarily unpredictable. For this reason, the output of this function should never be used where unpredictability is important, such as in the generation of encryption keys.

Usage is otherwise identical to crypto.randomBytes.

Class: Certificate

The class used for working with signed public key & challenges. The most common usage for this series of functions is when dealing with the <keygen> element. http://www.openssl.org/docs/apps/spkac.html

Returned by crypto.Certificate.

Certificate.verifySpkac(spkac)

Returns true of false based on the validity of the SPKAC.

Certificate.exportChallenge(spkac)

Exports the encoded public key from the supplied SPKAC.

Certificate.exportPublicKey(spkac)

Exports the encoded challenge associated with the SPKAC.

crypto.publicEncrypt(public_key, buffer)

Encrypts buffer with public_key. Only RSA is currently supported.

public_key can be an object or a string. If public_key is a string, it is treated as the key with no passphrase and will use RSA_PKCS1_OAEP_PADDING.

public_key:

key : A string holding the PEM encoded private key

padding : An optional padding value, one of the following:

constants.RSA_NO_PADDING

constants.RSA_PKCS1_PADDING

constants.RSA_PKCS1_OAEP_PADDING

NOTE: All paddings are defined in constants module.

crypto.privateDecrypt(private_key, buffer)

Decrypts buffer with private_key.

private_key can be an object or a string. If private_key is a string, it is treated as the key with no passphrase and will use RSA_PKCS1_OAEP_PADDING.

private_key:

key : A string holding the PEM encoded private key

passphrase : An optional string of passphrase for the private key

padding : An optional padding value, one of the following:

constants.RSA_NO_PADDING

constants.RSA_PKCS1_PADDING

constants.RSA_PKCS1_OAEP_PADDING

NOTE: All paddings are defined in constants module.

crypto.DEFAULT_ENCODING

The default encoding to use for functions that can take either strings or buffers. The default value is 'buffer', which makes it default to using Buffer objects. This is here to make the crypto module more easily compatible with legacy programs that expected 'binary' to be the default encoding.

Note that new programs will probably expect buffers, so only use this as a temporary measure.

Recent API Changes

The Crypto module was added to Node before there was the concept of a unified Stream API, and before there were Buffer objects for handling binary data.

As such, the streaming classes don’t have the typical methods found on other Node classes, and many methods accepted and returned Binary-encoded strings by default rather than Buffers. This was changed to use Buffers by default instead.

This is a breaking change for some use cases, but not all.

For example, if you currently use the default arguments to the Sign class, and then pass the results to the Verify class, without ever inspecting the data, then it will continue to work as before. Where you once got a binary string and then presented the binary string to the Verify object, you’ll now get a Buffer, and present the Buffer to the Verify object.

However, if you were doing things with the string data that will not work properly on Buffers (such as, concatenating them, storing in databases, etc.), or you are passing binary strings to the crypto functions without an encoding argument, then you will need to start providing encoding arguments to specify which encoding you’d like to use. To switch to the previous style of using binary strings by default, set the crypto.DEFAULT_ENCODING field to ‘binary’. Note that new programs will probably expect buffers, so only use this as a temporary measure.

Debugger

Stability: 3 - Stable

V8 comes with an extensive debugger which is accessible out-of-process via a simple TCP protocol. Node has a built-in client for this debugger. To use this, start Node with the debug argument; a prompt will appear:

% node debug myscript.js
< debugger listening on port 5858
connecting... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
  1 x = 5;
  2 setTimeout(function () {
  3   debugger;
debug>

Node’s debugger client doesn’t support the full range of commands, but simple step and inspection is possible. By putting the statement debugger; into the source code of your script, you will enable a breakpoint.

For example, suppose myscript.js looked like this:

// myscript.js
x = 5;
setTimeout(function () {
  debugger;
  console.log("world");
}, 1000);
console.log("hello");

Then once the debugger is run, it will break on line 4.

% node debug myscript.js
< debugger listening on port 5858
connecting... ok
break in /home/indutny/Code/git/indutny/myscript.js:1
  1 x = 5;
  2 setTimeout(function () {
  3   debugger;
debug> cont
< hello
break in /home/indutny/Code/git/indutny/myscript.js:3
  1 x = 5;
  2 setTimeout(function () {
  3   debugger;
  4   console.log("world");
  5 }, 1000);
debug> next
break in /home/indutny/Code/git/indutny/myscript.js:4
  2 setTimeout(function () {
  3   debugger;
  4   console.log("world");
  5 }, 1000);
  6 console.log("hello");
debug> repl
Press Ctrl + C to leave debug repl
> x
5
> 2+2
4
debug> next
< world
break in /home/indutny/Code/git/indutny/myscript.js:5
  3   debugger;
  4   console.log("world");
  5 }, 1000);
  6 console.log("hello");
  7
debug> quit
%

The repl command allows you to evaluate code remotely. The next command steps over to the next line. There are a few other commands available and more to come. Type help to see others.

Watchers

You can watch expression and variable values while debugging your code. On every breakpoint each expression from the watchers list will be evaluated in the current context and displayed just before the breakpoint’s source code listing.

To start watching an expression, type watch("my_expression"). watchers prints the active watchers. To remove a watcher, type unwatch("my_expression").

Commands reference

Stepping

cont, c - Continue execution

next, n - Step next

step, s - Step in

out, o - Step out

pause - Pause running code (like pause button in Developer Tools)

Breakpoints

setBreakpoint(), sb() - Set breakpoint on current line

setBreakpoint(line), sb(line) - Set breakpoint on specific line

setBreakpoint('fn()'), sb(...) - Set breakpoint on a first statement in functions body

setBreakpoint('script.js', 1), sb(...) - Set breakpoint on first line of script.js

clearBreakpoint, cb(...) - Clear breakpoint

It is also possible to set a breakpoint in a file (module) that isn’t loaded yet:

% ./node debug test/fixtures/break-in-module/main.js
< debugger listening on port 5858
connecting to port 5858... ok
break in test/fixtures/break-in-module/main.js:1
  1 var mod = require('./mod.js');
  2 mod.hello();
  3 mod.hello();
debug> setBreakpoint('mod.js', 23)
Warning: script 'mod.js' was not loaded yet.
  1 var mod = require('./mod.js');
  2 mod.hello();
  3 mod.hello();
debug> c
break in test/fixtures/break-in-module/mod.js:23
 21
 22 exports.hello = function() {
 23   return 'hello from module';
 24 };
 25
debug>

Info

backtrace, bt - Print backtrace of current execution frame

list(5) - List scripts source code with 5 line context (5 lines before and after)

watch(expr) - Add expression to watch list

unwatch(expr) - Remove expression from watch list

watchers - List all watchers and their values (automatically listed on each breakpoint)

repl - Open debugger’s repl for evaluation in debugging script’s context

Execution control

run - Run script (automatically runs on debugger’s start)

restart - Restart script

kill - Kill script

Various

scripts - List all loaded scripts

version - Display v8’s version

Advanced Usage

The V8 debugger can be enabled and accessed either by starting Node with the --debug command-line flag or by signaling an existing Node process with SIGUSR1.

Once a process has been set in debug mode with this it can be connected to with the node debugger. Either connect to the pid or the URI to the debugger. The syntax is:

node debug -p <pid> - Connects to the process via the pid

node debug <URI> - Connects to the process via the URI such as localhost:5858

DNS

Stability: 3 - Stable

Use require('dns') to access this module.

This module contains functions that belong to two different categories:

Functions that use the underlying operating system facilities to perform name resolution, and that do not necessarily do any network communication. This category contains only one function: dns.lookup. Developers looking to perform name resolution in the same way that other applications on the same operating system behave should use dns.lookup.

Here is an example that does a lookup of www.google.com.

var dns = require('dns');

dns.lookup('www.google.com', function onLookup(err, addresses, family) {
  console.log('addresses:', addresses);
});

Functions that connect to an actual DNS server to perform name resolution, and that always use the network to perform DNS queries. This category contains all functions in the dns module but dns.lookup. These functions do not use the same set of configuration files than what dns.lookup uses. For instance, they do not use the configuration from /etc/hosts. These functions should be used by developers who do not want to use the underlying operating system’s facilities for name resolution, and instead want to always perform DNS queries.

Here is an example which resolves 'www.google.com' then reverse resolves the IP addresses which are returned.

var dns = require('dns');

dns.resolve4('www.google.com', function (err, addresses) {
  if (err) throw err;

  console.log('addresses: ' + JSON.stringify(addresses));

  addresses.forEach(function (a) {
    dns.reverse(a, function (err, hostnames) {
      if (err) {
        throw err;
      }

      console.log('reverse for ' + a + ': ' + JSON.stringify(hostnames));
    });
  });
});

There are subtle consequences in choosing one or another, please consult the Implementation considerations section for more information.

dns.lookup(hostname[, options], callback)

Resolves a hostname (e.g. 'google.com') into the first found A (IPv4) or AAAA (IPv6) record. options can be an object or integer. If options is not provided, then IP v4 and v6 addresses are both valid. If options is an integer, then it must be 4 or 6.

Alternatively, options can be an object containing two properties, family and hints. Both properties are optional. If family is provided, it must be the integer 4 or 6. If family is not provided then IP v4 and v6 addresses are accepted. The hints field, if present, should be one or more of the supported getaddrinfo flags. If hints is not provided, then no flags are passed to getaddrinfo. Multiple flags can be passed through hints by logically ORing their values. An example usage of options is shown below.

{
  family: 4,
  hints: dns.ADDRCONFIG | dns.V4MAPPED
}

See supported getaddrinfo flags below for more information on supported flags.

The callback has arguments (err, address, family). The address argument is a string representation of a IP v4 or v6 address. The family argument is either the integer 4 or 6 and denotes the family of address (not necessarily the value initially passed to lookup).

On error, err is an Error object, where err.code is the error code. Keep in mind that err.code will be set to 'ENOENT' not only when the hostname does not exist but also when the lookup fails in other ways such as no available file descriptors.

dns.lookup doesn’t necessarily have anything to do with the DNS protocol. It’s only an operating system facility that can associate name with addresses, and vice versa.

Its implementation can have subtle but important consequences on the behavior of any Node.js program. Please take some time to consult the Implementation considerations section before using it.

dns.lookupService(address, port, callback)

Resolves the given address and port into a hostname and service using getnameinfo.

The callback has arguments (err, hostname, service). The hostname and service arguments are strings (e.g. 'localhost' and 'http' respectively).

On error, err is an Error object, where err.code is the error code.

dns.resolve(hostname[, rrtype], callback)

Resolves a hostname (e.g. 'google.com') into an array of the record types specified by rrtype.

Valid rrtypes are:

'A' (IPV4 addresses, default)

'AAAA' (IPV6 addresses)

'MX' (mail exchange records)

'TXT' (text records)

'SRV' (SRV records)

'PTR' (used for reverse IP lookups)

'NS' (name server records)

'CNAME' (canonical name records)

'SOA' (start of authority record)

The callback has arguments (err, addresses). The type of each item in addresses is determined by the record type, and described in the documentation for the corresponding lookup methods below.

On error, err is an Error object, where err.code is one of the error codes listed below.

dns.resolve4(hostname, callback)

The same as dns.resolve(), but only for IPv4 queries (A records). addresses is an array of IPv4 addresses (e.g. ['74.125.79.104', '74.125.79.105', '74.125.79.106']).

dns.resolve6(hostname, callback)

The same as dns.resolve4() except for IPv6 queries (an AAAA query).

dns.resolveMx(hostname, callback)

The same as dns.resolve(), but only for mail exchange queries (MX records).

addresses is an array of MX records, each with a priority and an exchange attribute (e.g. [{'priority': 10, 'exchange': 'mx.example.com'},...]).

dns.resolveTxt(hostname, callback)

The same as dns.resolve(), but only for text queries (TXT records). addresses is an 2-d array of the text records available for hostname (e.g., [ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]). Each sub-array contains TXT chunks of one record. Depending on the use case, the could be either joined together or treated separately.

dns.resolveSrv(hostname, callback)

The same as dns.resolve(), but only for service records (SRV records). addresses is an array of the SRV records available for hostname. Properties of SRV records are priority, weight, port, and name (e.g., [{'priority': 10, 'weight': 5, 'port': 21223, 'name': 'service.example.com'}, ...]).

dns.resolveSoa(hostname, callback)

The same as dns.resolve(), but only for start of authority record queries (SOA record).

addresses is an object with the following structure:

{
  nsname: 'ns.example.com',
  hostmaster: 'root.example.com',
  serial: 2013101809,
  refresh: 10000,
  retry: 2400,
  expire: 604800,
  minttl: 3600
}

dns.resolveNs(hostname, callback)

The same as dns.resolve(), but only for name server records (NS records). addresses is an array of the name server records available for hostname (e.g., ['ns1.example.com', 'ns2.example.com']).

dns.resolveCname(hostname, callback)

The same as dns.resolve(), but only for canonical name records (CNAME records). addresses is an array of the canonical name records available for hostname (e.g., ['bar.example.com']).

dns.reverse(ip, callback)

Reverse resolves an ip address to an array of hostnames.

The callback has arguments (err, hostnames).

On error, err is an Error object, where err.code is one of the error codes listed below.

dns.getServers()

Returns an array of IP addresses as strings that are currently being used for resolution

dns.setServers(servers)

Given an array of IP addresses as strings, set them as the servers to use for resolving

If you specify a port with the address it will be stripped, as the underlying library doesn’t support that.

This will throw if you pass invalid input.

Error codes

Each DNS query can return one of the following error codes:

dns.NODATA: DNS server returned answer with no data.

dns.FORMERR: DNS server claims query was misformatted.

dns.SERVFAIL: DNS server returned general failure.

dns.NOTFOUND: Domain name not found.

dns.NOTIMP: DNS server does not implement requested operation.

dns.REFUSED: DNS server refused query.

dns.BADQUERY: Misformatted DNS query.

dns.BADNAME: Misformatted hostname.

dns.BADFAMILY: Unsupported address family.

dns.BADRESP: Misformatted DNS reply.

dns.CONNREFUSED: Could not contact DNS servers.

dns.TIMEOUT: Timeout while contacting DNS servers.

dns.EOF: End of file.

dns.FILE: Error reading file.

dns.NOMEM: Out of memory.

dns.DESTRUCTION: Channel is being destroyed.

dns.BADSTR: Misformatted string.

dns.BADFLAGS: Illegal flags specified.

dns.NONAME: Given hostname is not numeric.

dns.BADHINTS: Illegal hints flags specified.

dns.NOTINITIALIZED: c-ares library initialization not yet performed.

dns.LOADIPHLPAPI: Error loading iphlpapi.dll.

dns.ADDRGETNETWORKPARAMS: Could not find GetNetworkParams function.

dns.CANCELLED: DNS query cancelled.

Supported getaddrinfo flags

The following flags can be passed as hints to dns.lookup.

dns.ADDRCONFIG: Returned address types are determined by the types of addresses supported by the current system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured. Loopback addresses are not considered.

dns.V4MAPPED: If the IPv6 family was specified, but no IPv6 addresses were found, then return IPv4 mapped IPv6 addresses. Note that it is not supported on some operating systems (e.g FreeBSD 10.1).

Implementation considerations

Although dns.lookup and dns.resolve*/dns.reverse functions have the same goal of associating a network name with a network address (or vice versa), their behavior is quite different. These differences can have subtle but significant consequences on the behavior of Node.js programs.

dns.lookup

Under the hood, dns.lookup uses the same operating system facilities as most other programs. For instance, dns.lookup will almost always resolve a given name the same way as the ping command. On most POSIX-like operating systems, the behavior of the dns.lookup function can be tweaked by changing settings in nsswitch.conf(5) and/or resolv.conf(5), but be careful that changing these files will change the behavior of all other programs running on the same operating system.

Though the call will be asynchronous from JavaScript’s perspective, it is implemented as a synchronous call to getaddrinfo(3) that runs on libuv’s threadpool. Because libuv’s threadpool has a fixed size, it means that if for whatever reason the call to getaddrinfo(3) takes a long time, other operations that could run on libuv’s threadpool (such as filesystem operations) will experience degraded performance. In order to mitigate this issue, one potential solution is to increase the size of libuv’s threadpool by setting the ‘UV_THREADPOOL_SIZE’ environment variable to a value greater than 4 (its current default value). For more information on libuv’s threadpool, see the official libuv documentation.

dns.resolve, functions starting with dns.resolve and dns.reverse

These functions are implemented quite differently than dns.lookup. They do not use getaddrinfo(3) and they always perform a DNS query on the network. This network communication is always done asynchronously, and does not use libuv’s threadpool.

As a result, these functions cannot have the same negative impact on other processing that happens on libuv’s threadpool that dns.lookup can have.

They do not use the same set of configuration files than what dns.lookup uses. For instance, they do not use the configuration from /etc/hosts.

Domain

Stability: 2 - Unstable

Domains provide a way to handle multiple different IO operations as a single group. If any of the event emitters or callbacks registered to a domain emit an error event, or throw an error, then the domain object will be notified, rather than losing the context of the error in the process.on('uncaughtException') handler, or causing the program to exit immediately with an error code.

Warning: Don’t Ignore Errors!

Domain error handlers are not a substitute for closing down your process when an error occurs.

By the very nature of how throw works in JavaScript, there is almost never any way to safely “pick up where you left off”, without leaking references, or creating some other sort of undefined brittle state.

The safest way to respond to a thrown error is to shut down the process. Of course, in a normal web server, you might have many connections open, and it is not reasonable to abruptly shut those down because an error was triggered by someone else.

The better approach is send an error response to the request that triggered the error, while letting the others finish in their normal time, and stop listening for new requests in that worker.

In this way, domain usage goes hand-in-hand with the cluster module, since the master process can fork a new worker when a worker encounters an error. For node programs that scale to multiple machines, the terminating proxy or service registry can take note of the failure, and react accordingly.

For example, this is not a good idea:

// XXX WARNING!  BAD IDEA!

var d = require('domain').create();
d.on('error', function(er) {
  // The error won't crash the process, but what it does is worse!
  // Though we've prevented abrupt process restarting, we are leaking
  // resources like crazy if this ever happens.
  // This is no better than process.on('uncaughtException')!
  console.log('error, but oh well', er.message);
});
d.run(function() {
  require('http').createServer(function(req, res) {
    handleRequest(req, res);
  }).listen(PORT);
});

By using the context of a domain, and the resilience of separating our program into multiple worker processes, we can react more appropriately, and handle errors with much greater safety.

// Much better!

var cluster = require('cluster');
var PORT = +process.env.PORT || 1337;

if (cluster.isMaster) {
  // In real life, you'd probably use more than just 2 workers,
  // and perhaps not put the master and worker in the same file.
  //
  // You can also of course get a bit fancier about logging, and
  // implement whatever custom logic you need to prevent DoS
  // attacks and other bad behavior.
  //
  // See the options in the cluster documentation.
  //
  // The important thing is that the master does very little,
  // increasing our resilience to unexpected errors.

  cluster.fork();
  cluster.fork();

  cluster.on('disconnect', function(worker) {
    console.error('disconnect!');
    cluster.fork();
  });

} else {
  // the worker
  //
  // This is where we put our bugs!

  var domain = require('domain');

  // See the cluster documentation for more details about using
  // worker processes to serve requests.  How it works, caveats, etc.

  var server = require('http').createServer(function(req, res) {
    var d = domain.create();
    d.on('error', function(er) {
      console.error('error', er.stack);

      // Note: we're in dangerous territory!
      // By definition, something unexpected occurred,
      // which we probably didn't want.
      // Anything can happen now!  Be very careful!

      try {
        // make sure we close down within 30 seconds
        var killtimer = setTimeout(function() {
          process.exit(1);
        }, 30000);
        // But don't keep the process open just for that!
        killtimer.unref();

        // stop taking new requests.
        server.close();

        // Let the master know we're dead.  This will trigger a
        // 'disconnect' in the cluster master, and then it will fork
        // a new worker.
        cluster.worker.disconnect();

        // try to send an error to the request that triggered the problem
        res.statusCode = 500;
        res.setHeader('content-type', 'text/plain');
        res.end('Oops, there was a problem!\n');
      } catch (er2) {
        // oh well, not much we can do at this point.
        console.error('Error sending 500!', er2.stack);
      }
    });

    // Because req and res were created before this domain existed,
    // we need to explicitly add them.
    // See the explanation of implicit vs explicit binding below.
    d.add(req);
    d.add(res);

    // Now run the handler function in the domain.
    d.run(function() {
      handleRequest(req, res);
    });
  });
  server.listen(PORT);
}

// This part isn't important.  Just an example routing thing.
// You'd put your fancy application logic here.
function handleRequest(req, res) {
  switch(req.url) {
    case '/error':
      // We do some async stuff, and then...
      setTimeout(function() {
        // Whoops!
        flerb.bark();
      });
      break;
    default:
      res.end('ok');
  }
}

Additions to Error objects

Any time an Error object is routed through a domain, a few extra fields are added to it.

error.domain The domain that first handled the error.

error.domainEmitter The event emitter that emitted an ‘error’ event with the error object.

error.domainBound The callback function which was bound to the domain, and passed an error as its first argument.

error.domainThrown A boolean indicating whether the error was thrown, emitted, or passed to a bound callback function.

Implicit Binding

If domains are in use, then all new EventEmitter objects (including Stream objects, requests, responses, etc.) will be implicitly bound to the active domain at the time of their creation.

Additionally, callbacks passed to lowlevel event loop requests (such as to fs.open, or other callback-taking methods) will automatically be bound to the active domain. If they throw, then the domain will catch the error.

In order to prevent excessive memory usage, Domain objects themselves are not implicitly added as children of the active domain. If they were, then it would be too easy to prevent request and response objects from being properly garbage collected.

If you want to nest Domain objects as children of a parent Domain, then you must explicitly add them.

Implicit binding routes thrown errors and 'error' events to the Domain’s error event, but does not register the EventEmitter on the Domain, so domain.dispose() will not shut down the EventEmitter. Implicit binding only takes care of thrown errors and 'error' events.

Explicit Binding

Sometimes, the domain in use is not the one that ought to be used for a specific event emitter. Or, the event emitter could have been created in the context of one domain, but ought to instead be bound to some other domain.

For example, there could be one domain in use for an HTTP server, but perhaps we would like to have a separate domain to use for each request.

That is possible via explicit binding.

For example:

// create a top-level domain for the server
var serverDomain = domain.create();

serverDomain.run(function() {
  // server is created in the scope of serverDomain
  http.createServer(function(req, res) {
    // req and res are also created in the scope of serverDomain
    // however, we'd prefer to have a separate domain for each request.
    // create it first thing, and add req and res to it.
    var reqd = domain.create();
    reqd.add(req);
    reqd.add(res);
    reqd.on('error', function(er) {
      console.error('Error', er, req.url);
      try {
        res.writeHead(500);
        res.end('Error occurred, sorry.');
      } catch (er) {
        console.error('Error sending 500', er, req.url);
      }
    });
  }).listen(1337);
});

domain.create()

return: {Domain}

Returns a new Domain object.

Class: Domain

The Domain class encapsulates the functionality of routing errors and uncaught exceptions to the active Domain object.

Domain is a child class of EventEmitter. To handle the errors that it catches, listen to its error event.

domain.run(fn)

fn {Function}

Run the supplied function in the context of the domain, implicitly binding all event emitters, timers, and lowlevel requests that are created in that context.

This is the most basic way to use a domain.

Example:

var d = domain.create();
d.on('error', function(er) {
  console.error('Caught error!', er);
});
d.run(function() {
  process.nextTick(function() {
    setTimeout(function() { // simulating some various async stuff
      fs.open('non-existent file', 'r', function(er, fd) {
        if (er) throw er;
        // proceed...
      });
    }, 100);
  });
});

In this example, the d.on('error') handler will be triggered, rather than crashing the program.

domain.members

{Array}

An array of timers and event emitters that have been explicitly added to the domain.

domain.add(emitter)

emitter {EventEmitter | Timer} emitter or timer to be added to the domain

Explicitly adds an emitter to the domain. If any event handlers called by the emitter throw an error, or if the emitter emits an error event, it will be routed to the domain’s error event, just like with implicit binding.

This also works with timers that are returned from setInterval and setTimeout. If their callback function throws, it will be caught by the domain ‘error’ handler.

If the Timer or EventEmitter was already bound to a domain, it is removed from that one, and bound to this one instead.

domain.remove(emitter)

emitter {EventEmitter | Timer} emitter or timer to be removed from the domain

The opposite of domain.add(emitter). Removes domain handling from the specified emitter.

domain.bind(callback)

callback {Function} The callback function

return: {Function} The bound function

The returned function will be a wrapper around the supplied callback function. When the returned function is called, any errors that are thrown will be routed to the domain’s error event.

Example

var d = domain.create();

function readSomeFile(filename, cb) {
  fs.readFile(filename, 'utf8', d.bind(function(er, data) {
    // if this throws, it will also be passed to the domain
    return cb(er, data ? JSON.parse(data) : null);
  }));
}

d.on('error', function(er) {
  // an error occurred somewhere.
  // if we throw it now, it will crash the program
  // with the normal line number and stack message.
});

domain.intercept(callback)

callback {Function} The callback function

return: {Function} The intercepted function

This method is almost identical to domain.bind(callback). However, in addition to catching thrown errors, it will also intercept Error objects sent as the first argument to the function.

In this way, the common if (er) return callback(er); pattern can be replaced with a single error handler in a single place.

Example

var d = domain.create();

function readSomeFile(filename, cb) {
  fs.readFile(filename, 'utf8', d.intercept(function(data) {
    // note, the first argument is never passed to the
    // callback since it is assumed to be the 'Error' argument
    // and thus intercepted by the domain.

    // if this throws, it will also be passed to the domain
    // so the error-handling logic can be moved to the 'error'
    // event on the domain instead of being repeated throughout
    // the program.
    return cb(null, JSON.parse(data));
  }));
}

d.on('error', function(er) {
  // an error occurred somewhere.
  // if we throw it now, it will crash the program
  // with the normal line number and stack message.
});

domain.enter()

The enter method is plumbing used by the run, bind, and intercept methods to set the active domain. It sets domain.active and process.domain to the domain, and implicitly pushes the domain onto the domain stack managed by the domain module (see domain.exit() for details on the domain stack). The call to enter delimits the beginning of a chain of asynchronous calls and I/O operations bound to a domain.

Calling enter changes only the active domain, and does not alter the domain itself. Enter and exit can be called an arbitrary number of times on a single domain.

If the domain on which enter is called has been disposed, enter will return without setting the domain.

domain.exit()

The exit method exits the current domain, popping it off the domain stack. Any time execution is going to switch to the context of a different chain of asynchronous calls, it’s important to ensure that the current domain is exited. The call to exit delimits either the end of or an interruption to the chain of asynchronous calls and I/O operations bound to a domain.

If there are multiple, nested domains bound to the current execution context, exit will exit any domains nested within this domain.

Calling exit changes only the active domain, and does not alter the domain itself. Enter and exit can be called an arbitrary number of times on a single domain.

If the domain on which exit is called has been disposed, exit will return without exiting the domain.

domain.dispose()

Stability: 0 - Deprecated.  Please recover from failed IO actions
explicitly via error event handlers set on the domain.

Once dispose has been called, the domain will no longer be used by callbacks bound into the domain via run, bind, or intercept, and a dispose event is emitted.

Events

Stability: 4 - API Frozen

Many objects in Node emit events: a net.Server emits an event each time a peer connects to it, a fs.readStream emits an event when the file is opened. All objects which emit events are instances of events.EventEmitter. You can access this module by doing: require("events");

Typically, event names are represented by a camel-cased string, however, there aren’t any strict restrictions on that, as any string will be accepted.

Functions can then be attached to objects, to be executed when an event is emitted. These functions are called listeners. Inside a listener function, this refers to the EventEmitter that the listener was attached to.

Class: events.EventEmitter

To access the EventEmitter class, require('events').EventEmitter.

When an EventEmitter instance experiences an error, the typical action is to emit an 'error' event. Error events are treated as a special case in node. If there is no listener for it, then the default action is to print a stack trace and exit the program.

All EventEmitters emit the event 'newListener' when new listeners are added and 'removeListener' when a listener is removed.

emitter.addListener(event, listener)

emitter.on(event, listener)

Adds a listener to the end of the listeners array for the specified event. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of event and listener will result in the listener being added multiple times.

server.on('connection', function (stream) {
  console.log('someone connected!');
});

Returns emitter, so calls can be chained.

emitter.once(event, listener)

Adds a one time listener for the event. This listener is invoked only the next time the event is fired, after which it is removed.

server.once('connection', function (stream) {
  console.log('Ah, we have our first user!');
});

Returns emitter, so calls can be chained.

emitter.removeListener(event, listener)

Remove a listener from the listener array for the specified event. Caution: changes array indices in the listener array behind the listener.

var callback = function(stream) {
  console.log('someone connected!');
};
server.on('connection', callback);
// ...
server.removeListener('connection', callback);

removeListener will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified event, then removeListener must be called multiple times to remove each instance.

Returns emitter, so calls can be chained.

emitter.removeAllListeners([event])

Removes all listeners, or those of the specified event. It’s not a good idea to remove listeners that were added elsewhere in the code, especially when it’s on an emitter that you didn’t create (e.g. sockets or file streams).

Returns emitter, so calls can be chained.

emitter.setMaxListeners(n)

By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default which helps finding memory leaks. Obviously not all Emitters should be limited to 10. This function allows that to be increased. Set to zero for unlimited.

Returns emitter, so calls can be chained.

EventEmitter.defaultMaxListeners

emitter.setMaxListeners(n) sets the maximum on a per-instance basis. This class property lets you set it for all EventEmitter instances, current and future, effective immediately. Use with care.

Note that emitter.setMaxListeners(n) still has precedence over EventEmitter.defaultMaxListeners.

emitter.listeners(event)

Returns an array of listeners for the specified event.

server.on('connection', function (stream) {
  console.log('someone connected!');
});
console.log(util.inspect(server.listeners('connection'))); // [ [Function] ]

emitter.emit(event[, arg1][, arg2][, …])

Execute each of the listeners in order with the supplied arguments.

Returns true if event had listeners, false otherwise.

Class Method: EventEmitter.listenerCount(emitter, event)

Return the number of listeners for a given event.

Event: ‘newListener’

event {String} The event name

listener {Function} The event handler function

This event is emitted any time a listener is added. When this event is triggered, the listener may not yet have been added to the array of listeners for the event.

Event: ‘removeListener’

event {String} The event name

listener {Function} The event handler function

This event is emitted any time someone removes a listener. When this event is triggered, the listener may not yet have been removed from the array of listeners for the event.

File System

Stability: 3 - Stable

File I/O is provided by simple wrappers around standard POSIX functions. To use this module do require('fs'). All the methods have asynchronous and synchronous forms.

The asynchronous form always take a completion callback as its last argument. The arguments passed to the completion callback depend on the method, but the first argument is always reserved for an exception. If the operation was completed successfully, then the first argument will be null or undefined.

When using the synchronous form any exceptions are immediately thrown. You can use try/catch to handle exceptions or allow them to bubble up.

Here is an example of the asynchronous version:

var fs = require('fs');

fs.unlink('/tmp/hello', function (err) {
  if (err) throw err;
  console.log('successfully deleted /tmp/hello');
});

Here is the synchronous version:

var fs = require('fs');

fs.unlinkSync('/tmp/hello');
console.log('successfully deleted /tmp/hello');

With the asynchronous methods there is no guaranteed ordering. So the following is prone to error:

fs.rename('/tmp/hello', '/tmp/world', function (err) {
  if (err) throw err;
  console.log('renamed complete');
});
fs.stat('/tmp/world', function (err, stats) {
  if (err) throw err;
  console.log('stats: ' + JSON.stringify(stats));
});

It could be that fs.stat is executed before fs.rename. The correct way to do this is to chain the callbacks.

fs.rename('/tmp/hello', '/tmp/world', function (err) {
  if (err) throw err;
  fs.stat('/tmp/world', function (err, stats) {
    if (err) throw err;
    console.log('stats: ' + JSON.stringify(stats));
  });
});

In busy processes, the programmer is strongly encouraged to use the asynchronous versions of these calls. The synchronous versions will block the entire process until they complete–halting all connections.

Relative path to filename can be used, remember however that this path will be relative to process.cwd().

Most fs functions let you omit the callback argument. If you do, a default callback is used that rethrows errors. To get a trace to the original call site, set the NODE_DEBUG environment variable:

$ cat script.js
function bad() {
  require('fs').readFile('/');
}
bad();

$ env NODE_DEBUG=fs node script.js
fs.js:66
        throw err;
              ^
Error: EISDIR, read
    at rethrow (fs.js:61:21)
    at maybeCallback (fs.js:79:42)
    at Object.fs.readFile (fs.js:153:18)
    at bad (/path/to/script.js:2:17)
    at Object.<anonymous> (/path/to/script.js:5:1)
    <etc.>

fs.rename(oldPath, newPath, callback)

Asynchronous rename(2). No arguments other than a possible exception are given to the completion callback.

fs.renameSync(oldPath, newPath)

Synchronous rename(2). Returns undefined.

fs.ftruncate(fd, len, callback)

Asynchronous ftruncate(2). No arguments other than a possible exception are given to the completion callback.

fs.ftruncateSync(fd, len)

Synchronous ftruncate(2). Returns undefined.

fs.truncate(path, len, callback)

Asynchronous truncate(2). No arguments other than a possible exception are given to the completion callback. A file descriptor can also be passed as the first argument. In this case, fs.ftruncate() is called.

fs.truncateSync(path, len)

Synchronous truncate(2). Returns undefined.

fs.chown(path, uid, gid, callback)

Asynchronous chown(2). No arguments other than a possible exception are given to the completion callback.

fs.chownSync(path, uid, gid)

Synchronous chown(2). Returns undefined.

fs.fchown(fd, uid, gid, callback)

Asynchronous fchown(2). No arguments other than a possible exception are given to the completion callback.

fs.fchownSync(fd, uid, gid)

Synchronous fchown(2). Returns undefined.

fs.lchown(path, uid, gid, callback)

Asynchronous lchown(2). No arguments other than a possible exception are given to the completion callback.

fs.lchownSync(path, uid, gid)

Synchronous lchown(2). Returns undefined.

fs.chmod(path, mode, callback)

Asynchronous chmod(2). No arguments other than a possible exception are given to the completion callback.

fs.chmodSync(path, mode)

Synchronous chmod(2). Returns undefined.

fs.fchmod(fd, mode, callback)

Asynchronous fchmod(2). No arguments other than a possible exception are given to the completion callback.

fs.fchmodSync(fd, mode)

Synchronous fchmod(2). Returns undefined.

fs.lchmod(path, mode, callback)

Asynchronous lchmod(2). No arguments other than a possible exception are given to the completion callback.

Only available on Mac OS X.

fs.lchmodSync(path, mode)

Synchronous lchmod(2). Returns undefined.

fs.stat(path, callback)

Asynchronous stat(2). The callback gets two arguments (err, stats) where stats is a fs.Stats object. See the fs.Stats section below for more information.

fs.lstat(path, callback)

Asynchronous lstat(2). The callback gets two arguments (err, stats) where stats is a fs.Stats object. lstat() is identical to stat(), except that if path is a symbolic link, then the link itself is stat-ed, not the file that it refers to.

fs.fstat(fd, callback)

Asynchronous fstat(2). The callback gets two arguments (err, stats) where stats is a fs.Stats object. fstat() is identical to stat(), except that the file to be stat-ed is specified by the file descriptor fd.

fs.statSync(path)

Synchronous stat(2). Returns an instance of fs.Stats.

fs.lstatSync(path)

Synchronous lstat(2). Returns an instance of fs.Stats.

fs.fstatSync(fd)

Synchronous fstat(2). Returns an instance of fs.Stats.

fs.link(srcpath, dstpath, callback)

Asynchronous link(2). No arguments other than a possible exception are given to the completion callback.

fs.linkSync(srcpath, dstpath)

Synchronous link(2). Returns undefined.

fs.symlink(srcpath, dstpath[, type], callback)

Asynchronous symlink(2). No arguments other than a possible exception are given to the completion callback. The type argument can be set to 'dir', 'file', or 'junction' (default is 'file') and is only available on Windows (ignored on other platforms). Note that Windows junction points require the destination path to be absolute. When using 'junction', the destination argument will automatically be normalized to absolute path.

fs.symlinkSync(srcpath, dstpath[, type])

Synchronous symlink(2). Returns undefined.

fs.readlink(path, callback)

Asynchronous readlink(2). The callback gets two arguments (err, linkString).

fs.readlinkSync(path)

Synchronous readlink(2). Returns the symbolic link’s string value.

fs.realpath(path[, cache], callback)

Asynchronous realpath(2). The callback gets two arguments (err, resolvedPath). May use process.cwd to resolve relative paths. cache is an object literal of mapped paths that can be used to force a specific path resolution or avoid additional fs.stat calls for known real paths.

Example:

var cache = {'/etc':'/private/etc'};
fs.realpath('/etc/passwd', cache, function (err, resolvedPath) {
  if (err) throw err;
  console.log(resolvedPath);
});

fs.realpathSync(path[, cache])

Synchronous realpath(2). Returns the resolved path.

fs.unlink(path, callback)

Asynchronous unlink(2). No arguments other than a possible exception are given to the completion callback.

fs.unlinkSync(path)

Synchronous unlink(2). Returns undefined.

fs.rmdir(path, callback)

Asynchronous rmdir(2). No arguments other than a possible exception are given to the completion callback.

fs.rmdirSync(path)

Synchronous rmdir(2). Returns undefined.

fs.mkdir(path[, mode], callback)

Asynchronous mkdir(2). No arguments other than a possible exception are given to the completion callback. mode defaults to 0777.

fs.mkdirSync(path[, mode])

Synchronous mkdir(2). Returns undefined.

fs.readdir(path, callback)

Asynchronous readdir(3). Reads the contents of a directory. The callback gets two arguments (err, files) where files is an array of the names of the files in the directory excluding '.' and '..'.

fs.readdirSync(path)

Synchronous readdir(3). Returns an array of filenames excluding '.' and '..'.

fs.close(fd, callback)

Asynchronous close(2). No arguments other than a possible exception are given to the completion callback.

fs.closeSync(fd)

Synchronous close(2). Returns undefined.

fs.open(path, flags[, mode], callback)

Asynchronous file open. See open(2). flags can be:

'r' - Open file for reading. An exception occurs if the file does not exist.

'r+' - Open file for reading and writing. An exception occurs if the file does not exist.

'rs' - Open file for reading in synchronous mode. Instructs the operating system to bypass the local file system cache.

This is primarily useful for opening files on NFS mounts as it allows you to skip the potentially stale local cache. It has a very real impact on I/O performance so don’t use this flag unless you need it.

Note that this doesn’t turn fs.open() into a synchronous blocking call. If that’s what you want then you should be using fs.openSync()

'rs+' - Open file for reading and writing, telling the OS to open it synchronously. See notes for 'rs' about using this with caution.

'w' - Open file for writing. The file is created (if it does not exist) or truncated (if it exists).

'wx' - Like 'w' but fails if path exists.

'w+' - Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists).

'wx+' - Like 'w+' but fails if path exists.

'a' - Open file for appending. The file is created if it does not exist.

'ax' - Like 'a' but fails if path exists.

'a+' - Open file for reading and appending. The file is created if it does not exist.

'ax+' - Like 'a+' but fails if path exists.

mode sets the file mode (permission and sticky bits), but only if the file was created. It defaults to 0666, readable and writeable.

The callback gets two arguments (err, fd).

The exclusive flag 'x' (O_EXCL flag in open(2)) ensures that path is newly created. On POSIX systems, path is considered to exist even if it is a symlink to a non-existent file. The exclusive flag may or may not work with network file systems.

On Linux, positional writes don’t work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.

fs.openSync(path, flags[, mode])

Synchronous version of fs.open(). Returns an integer representing the file descriptor.

fs.utimes(path, atime, mtime, callback)

Change file timestamps of the file referenced by the supplied path.

fs.utimesSync(path, atime, mtime)

Synchronous version of fs.utimes(). Returns undefined.

fs.futimes(fd, atime, mtime, callback)

Change the file timestamps of a file referenced by the supplied file descriptor.

fs.futimesSync(fd, atime, mtime)

Synchronous version of fs.futimes(). Returns undefined.

fs.fsync(fd, callback)

Asynchronous fsync(2). No arguments other than a possible exception are given to the completion callback.

fs.fsyncSync(fd)

Synchronous fsync(2). Returns undefined.

fs.write(fd, buffer, offset, length[, position], callback)

Write buffer to the file specified by fd.

offset and length determine the part of the buffer to be written.

position refers to the offset from the beginning of the file where this data should be written. If typeof position !== 'number', the data will be written at the current position. See pwrite(2).

The callback will be given three arguments (err, written, buffer) where written specifies how many bytes were written from buffer.

Note that it is unsafe to use fs.write multiple times on the same file without waiting for the callback. For this scenario, fs.createWriteStream is strongly recommended.

On Linux, positional writes don’t work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.

fs.write(fd, data[, position[, encoding]], callback)

Write data to the file specified by fd. If data is not a Buffer instance then the value will be coerced to a string.

position refers to the offset from the beginning of the file where this data should be written. If typeof position !== 'number' the data will be written at the current position. See pwrite(2).

encoding is the expected string encoding.

The callback will receive the arguments (err, written, string) where written specifies how many bytes the passed string required to be written. Note that bytes written is not the same as string characters. See Buffer.byteLength.

Unlike when writing buffer, the entire string must be written. No substring may be specified. This is because the byte offset of the resulting data may not be the same as the string offset.

Note that it is unsafe to use fs.write multiple times on the same file without waiting for the callback. For this scenario, fs.createWriteStream is strongly recommended.

On Linux, positional writes don’t work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.

fs.writeSync(fd, buffer, offset, length[, position])

fs.writeSync(fd, data[, position[, encoding]])

Synchronous versions of fs.write(). Returns the number of bytes written.

fs.read(fd, buffer, offset, length, position, callback)

Read data from the file specified by fd.

buffer is the buffer that the data will be written to.

offset is the offset in the buffer to start writing at.

length is an integer specifying the number of bytes to read.

position is an integer specifying where to begin reading from in the file. If position is null, data will be read from the current file position.

The callback is given the three arguments, (err, bytesRead, buffer).

fs.readSync(fd, buffer, offset, length, position)

Synchronous version of fs.read. Returns the number of bytesRead.

fs.readFile(filename[, options], callback)

filename {String}

options {Object}

encoding {String | Null} default = null

flag {String} default = 'r'

callback {Function}

Asynchronously reads the entire contents of a file. Example:

fs.readFile('/etc/passwd', function (err, data) {
  if (err) throw err;
  console.log(data);
});

The callback is passed two arguments (err, data), where data is the contents of the file.

If no encoding is specified, then the raw buffer is returned.

fs.readFileSync(filename[, options])

Synchronous version of fs.readFile. Returns the contents of the filename.

If the encoding option is specified then this function returns a string. Otherwise it returns a buffer.

fs.writeFile(filename, data[, options], callback)

filename {String}

data {String | Buffer}

options {Object}

encoding {String | Null} default = 'utf8'

mode {Number} default = 438 (aka 0666 in Octal)

flag {String} default = 'w'

callback {Function}

Asynchronously writes data to a file, replacing the file if it already exists. data can be a string or a buffer.

The encoding option is ignored if data is a buffer. It defaults to 'utf8'.

Example:

fs.writeFile('message.txt', 'Hello Node', function (err) {
  if (err) throw err;
  console.log('It\'s saved!');
});

fs.writeFileSync(filename, data[, options])

The synchronous version of fs.writeFile. Returns undefined.

fs.appendFile(filename, data[, options], callback)

filename {String}

data {String | Buffer}

options {Object}

encoding {String | Null} default = 'utf8'

mode {Number} default = 438 (aka 0666 in Octal)

flag {String} default = 'a'

callback {Function}

Asynchronously append data to a file, creating the file if it not yet exists. data can be a string or a buffer.

Example:

fs.appendFile('message.txt', 'data to append', function (err) {
  if (err) throw err;
  console.log('The "data to append" was appended to file!');
});

fs.appendFileSync(filename, data[, options])

The synchronous version of fs.appendFile. Returns undefined.

fs.watchFile(filename[, options], listener)

Stability: 2 - Unstable.  Use fs.watch instead, if possible.

Watch for changes on filename. The callback listener will be called each time the file is accessed.

The second argument is optional. The options if provided should be an object containing two members a boolean, persistent, and interval. persistent indicates whether the process should continue to run as long as files are being watched. interval indicates how often the target should be polled, in milliseconds. The default is { persistent: true, interval: 5007 }.

The listener gets two arguments the current stat object and the previous stat object:

fs.watchFile('message.text', function (curr, prev) {
  console.log('the current mtime is: ' + curr.mtime);
  console.log('the previous mtime was: ' + prev.mtime);
});

These stat objects are instances of fs.Stat.

If you want to be notified when the file was modified, not just accessed you need to compare curr.mtime and prev.mtime.

fs.unwatchFile(filename[, listener])

Stability: 2 - Unstable.  Use fs.watch instead, if possible.

Stop watching for changes on filename. If listener is specified, only that particular listener is removed. Otherwise, all listeners are removed and you have effectively stopped watching filename.

Calling fs.unwatchFile() with a filename that is not being watched is a no-op, not an error.

fs.watch(filename[, options][, listener])

Stability: 2 - Unstable.

Watch for changes on filename, where filename is either a file or a directory. The returned object is a fs.FSWatcher.

The second argument is optional. The options if provided should be an object. The supported boolean members are persistent and recursive. persistent indicates whether the process should continue to run as long as files are being watched. recursive indicates whether all subdirectories should be watched, or only the current directory. This applies when a directory is specified, and only on supported platforms (See Caveats below).

The default is { persistent: true, recursive: false }.

The listener callback gets two arguments (event, filename). event is either ‘rename’ or ‘change’, and filename is the name of the file which triggered the event.

Caveats

The fs.watch API is not 100% consistent across platforms, and is unavailable in some situations.

The recursive option is currently supported on OS X. Only FSEvents supports this type of file watching so it is unlikely any additional platforms will be added soon.

Availability

This feature depends on the underlying operating system providing a way to be notified of filesystem changes.

On Linux systems, this uses inotify.

On BSD systems, this uses kqueue.

On OS X, this uses kqueue for files and ‘FSEvents’ for directories.

On SunOS systems (including Solaris and SmartOS), this uses event ports.

On Windows systems, this feature depends on ReadDirectoryChangesW.

If the underlying functionality is not available for some reason, then fs.watch will not be able to function. For example, watching files or directories on network file systems (NFS, SMB, etc.) often doesn’t work reliably or at all.

You can still use fs.watchFile, which uses stat polling, but it is slower and less reliable.

Filename Argument

Providing filename argument in the callback is not supported on every platform (currently it’s only supported on Linux and Windows). Even on supported platforms filename is not always guaranteed to be provided. Therefore, don’t assume that filename argument is always provided in the callback, and have some fallback logic if it is null.

fs.watch('somedir', function (event, filename) {
  console.log('event is: ' + event);
  if (filename) {
    console.log('filename provided: ' + filename);
  } else {
    console.log('filename not provided');
  }
});

fs.exists(path, callback)

Test whether or not the given path exists by checking with the file system. Then call the callback argument with either true or false. Example:

fs.exists('/etc/passwd', function (exists) {
  util.debug(exists ? "it's there" : "no passwd!");
});

fs.exists() is an anachronism and exists only for historical reasons. There should almost never be a reason to use it in your own code.

In particular, checking if a file exists before opening it is an anti-pattern that leaves you vulnerable to race conditions: another process may remove the file between the calls to fs.exists() and fs.open(). Just open the file and handle the error when it’s not there.

fs.exists() will be deprecated.

fs.existsSync(path)

Synchronous version of fs.exists(). Returns true if the file exists, false otherwise.

fs.existsSync() will be deprecated.

fs.access(path[, mode], callback)

Tests a user’s permissions for the file specified by path. mode is an optional integer that specifies the accessibility checks to be performed. The following constants define the possible values of mode. It is possible to create a mask consisting of the bitwise OR of two or more values.

fs.F_OK - File is visible to the calling process. This is useful for determining if a file exists, but says nothing about rwx permissions. Default if no mode is specified.

fs.R_OK - File can be read by the calling process.

fs.W_OK - File can be written by the calling process.

fs.X_OK - File can be executed by the calling process. This has no effect on Windows (will behave like fs.F_OK).

The final argument, callback, is a callback function that is invoked with a possible error argument. If any of the accessibility checks fail, the error argument will be populated. The following example checks if the file /etc/passwd can be read and written by the current process.

fs.access('/etc/passwd', fs.R_OK | fs.W_OK, function(err) {
  util.debug(err ? 'no access!' : 'can read/write');
});

fs.accessSync(path[, mode])

Synchronous version of fs.access. This throws if any accessibility checks fail, and does nothing otherwise.

Class: fs.Stats

Objects returned from fs.stat(), fs.lstat() and fs.fstat() and their synchronous counterparts are of this type.

stats.isFile()

stats.isDirectory()

stats.isBlockDevice()

stats.isCharacterDevice()

stats.isSymbolicLink() (only valid with fs.lstat())

stats.isFIFO()

stats.isSocket()

For a regular file util.inspect(stats) would return a string very similar to this:

{ dev: 2114,
  ino: 48064969,
  mode: 33188,
  nlink: 1,
  uid: 85,
  gid: 100,
  rdev: 0,
  size: 527,
  blksize: 4096,
  blocks: 8,
  atime: Mon, 10 Oct 2011 23:24:11 GMT,
  mtime: Mon, 10 Oct 2011 23:24:11 GMT,
  ctime: Mon, 10 Oct 2011 23:24:11 GMT,
  birthtime: Mon, 10 Oct 2011 23:24:11 GMT }

Please note that atime, mtime, birthtime, and ctime are instances of Date object and to compare the values of these objects you should use appropriate methods. For most general uses getTime() will return the number of milliseconds elapsed since 1 January 1970 00:00:00 UTC and this integer should be sufficient for any comparison, however there are additional methods which can be used for displaying fuzzy information. More details can be found in the MDN JavaScript Reference page.

Stat Time Values

The times in the stat object have the following semantics:

atime “Access Time” - Time when file data last accessed. Changed by the mknod(2), utimes(2), and read(2) system calls.

mtime “Modified Time” - Time when file data last modified. Changed by the mknod(2), utimes(2), and write(2) system calls.

ctime “Change Time” - Time when file status was last changed (inode data modification). Changed by the chmod(2), chown(2), link(2), mknod(2), rename(2), unlink(2), utimes(2), read(2), and write(2) system calls.

birthtime “Birth Time” - Time of file creation. Set once when the file is created. On filesystems where birthtime is not available, this field may instead hold either the ctime or 1970-01-01T00:00Z (ie, unix epoch timestamp 0). On Darwin and other FreeBSD variants, also set if the atime is explicitly set to an earlier value than the current birthtime using the utimes(2) system call.

Prior to Node v0.12, the ctime held the birthtime on Windows systems. Note that as of v0.12, ctime is not “creation time”, and on Unix systems, it never was.

fs.createReadStream(path[, options])

Returns a new ReadStream object (See Readable Stream).

options is an object with the following defaults:

{ flags: 'r',
  encoding: null,
  fd: null,
  mode: 0666,
  autoClose: true
}

options can include start and end values to read a range of bytes from the file instead of the entire file. Both start and end are inclusive and start at 0. The encoding can be 'utf8', 'ascii', or 'base64'.

If fd is specified, ReadStream will ignore the path argument and will use the specified file descriptor. This means that no open event will be emitted.

If autoClose is false, then the file descriptor won’t be closed, even if there’s an error. It is your responsibility to close it and make sure there’s no file descriptor leak. If autoClose is set to true (default behavior), on error or end the file descriptor will be closed automatically.

mode sets the file mode (permission and sticky bits), but only if the file was created.

An example to read the last 10 bytes of a file which is 100 bytes long:

fs.createReadStream('sample.txt', {start: 90, end: 99});

Class: fs.ReadStream

ReadStream is a Readable Stream.

Event: ‘open’

fd {Integer} file descriptor used by the ReadStream.

Emitted when the ReadStream’s file is opened.

fs.createWriteStream(path[, options])

Returns a new WriteStream object (See Writable Stream).

options is an object with the following defaults:

{ flags: 'w',
  defaultEncoding: 'utf8',
  fd: null,
  mode: 0666 }

options may also include a start option to allow writing data at some position past the beginning of the file. Modifying a file rather than replacing it may require a flags mode of r+ rather than the default mode w.

Like ReadStream above, if fd is specified, WriteStream will ignore the path argument and will use the specified file descriptor. This means that no open event will be emitted.

Class: fs.WriteStream

WriteStream is a Writable Stream.

Event: ‘open’

fd {Integer} file descriptor used by the WriteStream.

Emitted when the WriteStream’s file is opened.

file.bytesWritten

The number of bytes written so far. Does not include data that is still queued for writing.

Class: fs.FSWatcher

Objects returned from fs.watch() are of this type.

watcher.close()

Stop watching for changes on the given fs.FSWatcher.

Event: ‘change’

event {String} The type of fs change

filename {String} The filename that changed (if relevant/available)

Emitted when something changes in a watched directory or file. See more details in fs.watch.

Event: ‘error’

error {Error object}

Emitted when an error occurs.

Global Objects

These objects are available in all modules. Some of these objects aren’t actually in the global scope but in the module scope - this will be noted.

global

{Object} The global namespace object.

In browsers, the top-level scope is the global scope. That means that in browsers if you’re in the global scope var something will define a global variable. In Node this is different. The top-level scope is not the global scope; var something inside a Node module will be local to that module.

process

{Object}

The process object. See the process object section.

console

{Object}

Used to print to stdout and stderr. See the console section.

Class: Buffer

{Function}

Used to handle binary data. See the buffer section

require()

{Function}

To require modules. See the Modules section. require isn’t actually a global but rather local to each module.

require.resolve()

Use the internal require() machinery to look up the location of a module, but rather than loading the module, just return the resolved filename.

require.cache

{Object}

Modules are cached in this object when they are required. By deleting a key value from this object, the next require will reload the module.

require.extensions

Stability: 0 - Deprecated

{Object}

Instruct require on how to handle certain file extensions.

Process files with the extension .sjs as .js:

require.extensions['.sjs'] = require.extensions['.js'];

Deprecated In the past, this list has been used to load non-JavaScript modules into Node by compiling them on-demand. However, in practice, there are much better ways to do this, such as loading modules via some other Node program, or compiling them to JavaScript ahead of time.

Since the Module system is locked, this feature will probably never go away. However, it may have subtle bugs and complexities that are best left untouched.

__filename

{String}

The filename of the code being executed. This is the resolved absolute path of this code file. For a main program this is not necessarily the same filename used in the command line. The value inside a module is the path to that module file.

Example: running node example.js from /Users/mjr

console.log(__filename);
// /Users/mjr/example.js

__filename isn’t actually a global but rather local to each module.

__dirname

{String}

The name of the directory that the currently executing script resides in.

Example: running node example.js from /Users/mjr

console.log(__dirname);
// /Users/mjr

__dirname isn’t actually a global but rather local to each module.

module

{Object}

A reference to the current module. In particular module.exports is used for defining what a module exports and makes available through require().

module isn’t actually a global but rather local to each module.

See the module system documentation for more information.

exports

A reference to the module.exports that is shorter to type. See module system documentation for details on when to use exports and when to use module.exports.

exports isn’t actually a global but rather local to each module.

See the module system documentation for more information.

See the module section for more information.

setTimeout(cb, ms)

Run callback cb after at least ms milliseconds. The actual delay depends on external factors like OS timer granularity and system load.

The timeout must be in the range of 1-2,147,483,647 inclusive. If the value is outside that range, it’s changed to 1 millisecond. Broadly speaking, a timer cannot span more than 24.8 days.

Returns an opaque value that represents the timer.

clearTimeout(t)

Stop a timer that was previously created with setTimeout(). The callback will not execute.

setInterval(cb, ms)

Run callback cb repeatedly every ms milliseconds. Note that the actual interval may vary, depending on external factors like OS timer granularity and system load. It’s never less than ms but it may be longer.

The interval must be in the range of 1-2,147,483,647 inclusive. If the value is outside that range, it’s changed to 1 millisecond. Broadly speaking, a timer cannot span more than 24.8 days.

Returns an opaque value that represents the timer.

clearInterval(t)

Stop a timer that was previously created with setInterval(). The callback will not execute.

The timer functions are global variables. See the timers section.

HTTP

Stability: 3 - Stable

To use the HTTP server and client one must require('http').

The HTTP interfaces in Node are designed to support many features of the protocol which have been traditionally difficult to use. In particular, large, possibly chunk-encoded, messages. The interface is careful to never buffer entire requests or responses–the user is able to stream data.

HTTP message headers are represented by an object like this:

{ 'content-length': '123',
  'content-type': 'text/plain',
  'connection': 'keep-alive',
  'host': 'mysite.com',
  'accept': '*/*' }

Keys are lowercased. Values are not modified.

In order to support the full spectrum of possible HTTP applications, Node’s HTTP API is very low-level. It deals with stream handling and message parsing only. It parses a message into headers and body but it does not parse the actual headers or the body.

Defined headers that allow multiple values are concatenated with a , character, except for the set-cookie and cookie headers which are represented as an array of values. Headers such as content-length which can only have a single value are parsed accordingly, and only a single value is represented on the parsed object.

The raw headers as they were received are retained in the rawHeaders property, which is an array of [key, value, key2, value2, ...]. For example, the previous message header object might have a rawHeaders list like the following:

[ 'ConTent-Length', '123456',
  'content-LENGTH', '123',
  'content-type', 'text/plain',
  'CONNECTION', 'keep-alive',
  'Host', 'mysite.com',
  'accepT', '*/*' ]

http.METHODS

{Array}

A list of the HTTP methods that are supported by the parser.

http.STATUS_CODES

{Object}

A collection of all the standard HTTP response status codes, and the short description of each. For example, http.STATUS_CODES[404] === 'Not Found'.

http.createServer([requestListener])

Returns a new instance of http.Server.

The requestListener is a function which is automatically added to the 'request' event.

http.createClient([port][, host])

This function is deprecated; please use http.request() instead. Constructs a new HTTP client. port and host refer to the server to be connected to.

Class: http.Server

This is an EventEmitter with the following events:

Event: ‘request’

function (request, response) { }

Emitted each time there is a request. Note that there may be multiple requests per connection (in the case of keep-alive connections). request is an instance of http.IncomingMessage and response is an instance of http.ServerResponse.

Event: ‘connection’

function (socket) { }

When a new TCP stream is established. socket is an object of type net.Socket. Usually users will not want to access this event. In particular, the socket will not emit readable events because of how the protocol parser attaches to the socket. The socket can also be accessed at request.connection.

Event: ‘close’

function () { }

Emitted when the server closes.

Event: ‘checkContinue’

function (request, response) { }

Emitted each time a request with an http Expect: 100-continue is received. If this event isn’t listened for, the server will automatically respond with a 100 Continue as appropriate.

Handling this event involves calling response.writeContinue() if the client should continue to send the request body, or generating an appropriate HTTP response (e.g., 400 Bad Request) if the client should not continue to send the request body.

Note that when this event is emitted and handled, the request event will not be emitted.

Event: ‘connect’

function (request, socket, head) { }

Emitted each time a client requests a http CONNECT method. If this event isn’t listened for, then clients requesting a CONNECT method will have their connections closed.

request is the arguments for the http request, as it is in the request event.

socket is the network socket between the server and client.

head is an instance of Buffer, the first packet of the tunneling stream, this may be empty.

After this event is emitted, the request’s socket will not have a data event listener, meaning you will need to bind to it in order to handle data sent to the server on that socket.

Event: ‘upgrade’

function (request, socket, head) { }

Emitted each time a client requests a http upgrade. If this event isn’t listened for, then clients requesting an upgrade will have their connections closed.

request is the arguments for the http request, as it is in the request event.

socket is the network socket between the server and client.

head is an instance of Buffer, the first packet of the upgraded stream, this may be empty.

After this event is emitted, the request’s socket will not have a data event listener, meaning you will need to bind to it in order to handle data sent to the server on that socket.

Event: ‘clientError’

function (exception, socket) { }

If a client connection emits an ‘error’ event, it will be forwarded here.

socket is the net.Socket object that the error originated from.

server.listen(port[, hostname][, backlog][, callback])

Begin accepting connections on the specified port and hostname. If the hostname is omitted, the server will accept connections directed to any IPv4 address (INADDR_ANY).

To listen to a unix socket, supply a filename instead of port and hostname.

Backlog is the maximum length of the queue of pending connections. The actual length will be determined by your OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on linux. The default value of this parameter is 511 (not 512).

This function is asynchronous. The last parameter callback will be added as a listener for the ‘listening’ event. See also net.Server.listen(port).

server.listen(path[, callback])

Start a UNIX socket server listening for connections on the given path.

This function is asynchronous. The last parameter callback will be added as a listener for the ‘listening’ event. See also net.Server.listen(path).

server.listen(handle[, callback])

handle {Object}

callback {Function}

The handle object can be set to either a server or socket (anything with an underlying _handle member), or a {fd: <n>} object.

This will cause the server to accept connections on the specified handle, but it is presumed that the file descriptor or handle has already been bound to a port or domain socket.

Listening on a file descriptor is not supported on Windows.

This function is asynchronous. The last parameter callback will be added as a listener for the ‘listening’ event. See also net.Server.listen().

server.close([callback])

Stops the server from accepting new connections. See net.Server.close().

server.maxHeadersCount

Limits maximum incoming headers count, equal to 1000 by default. If set to 0 - no limit will be applied.

server.setTimeout(msecs, callback)

msecs {Number}

callback {Function}

Sets the timeout value for sockets, and emits a 'timeout' event on the Server object, passing the socket as an argument, if a timeout occurs.

If there is a 'timeout' event listener on the Server object, then it will be called with the timed-out socket as an argument.

By default, the Server’s timeout value is 2 minutes, and sockets are destroyed automatically if they time out. However, if you assign a callback to the Server’s 'timeout' event, then you are responsible for handling socket timeouts.

server.timeout

{Number} Default = 120000 (2 minutes)

The number of milliseconds of inactivity before a socket is presumed to have timed out.

Note that the socket timeout logic is set up on connection, so changing this value only affects new connections to the server, not any existing connections.

Set to 0 to disable any kind of automatic timeout behavior on incoming connections.

Class: http.ServerResponse

This object is created internally by a HTTP server–not by the user. It is passed as the second parameter to the 'request' event.

The response implements the Writable Stream interface. This is an EventEmitter with the following events:

Event: ‘close’

function () { }

Indicates that the underlying connection was terminated before response.end() was called or able to flush.

Event: ‘finish’

function () { }

Emitted when the response has been sent. More specifically, this event is emitted when the last segment of the response headers and body have been handed off to the operating system for transmission over the network. It does not imply that the client has received anything yet.

After this event, no more events will be emitted on the response object.

response.writeContinue()

Sends a HTTP/1.1 100 Continue message to the client, indicating that the request body should be sent. See the ‘checkContinue’ event on Server.

response.writeHead(statusCode[, statusMessage][, headers])

Sends a response header to the request. The status code is a 3-digit HTTP status code, like 404. The last argument, headers, are the response headers. Optionally one can give a human-readable statusMessage as the second argument.

Example:

var body = 'hello world';
response.writeHead(200, {
  'Content-Length': body.length,
  'Content-Type': 'text/plain' });

This method must only be called once on a message and it must be called before response.end() is called.

If you call response.write() or response.end() before calling this, the implicit/mutable headers will be calculated and call this function for you.

Note that Content-Length is given in bytes not characters. The above example works because the string 'hello world' contains only single byte characters. If the body contains higher coded characters then Buffer.byteLength() should be used to determine the number of bytes in a given encoding. And Node does not check whether Content-Length and the length of the body which has been transmitted are equal or not.

response.setTimeout(msecs, callback)

msecs {Number}

callback {Function}

Sets the Socket’s timeout value to msecs. If a callback is provided, then it is added as a listener on the 'timeout' event on the response object.

If no 'timeout' listener is added to the request, the response, or the server, then sockets are destroyed when they time out. If you assign a handler on the request, the response, or the server’s 'timeout' events, then it is your responsibility to handle timed out sockets.

response.statusCode

When using implicit headers (not calling response.writeHead() explicitly), this property controls the status code that will be sent to the client when the headers get flushed.

Example:

response.statusCode = 404;

After response header was sent to the client, this property indicates the status code which was sent out.

response.statusMessage

When using implicit headers (not calling response.writeHead() explicitly), this property controls the status message that will be sent to the client when the headers get flushed. If this is left as undefined then the standard message for the status code will be used.

Example:

response.statusMessage = 'Not found';

After response header was sent to the client, this property indicates the status message which was sent out.

response.setHeader(name, value)

Sets a single header value for implicit headers. If this header already exists in the to-be-sent headers, its value will be replaced. Use an array of strings here if you need to send multiple headers with the same name.

Example:

response.setHeader("Content-Type", "text/html");

or

response.setHeader("Set-Cookie", ["type=ninja", "language=javascript"]);

response.headersSent

Boolean (read-only). True if headers were sent, false otherwise.

response.sendDate

When true, the Date header will be automatically generated and sent in the response if it is not already present in the headers. Defaults to true.

This should only be disabled for testing; HTTP requires the Date header in responses.

response.getHeader(name)

Reads out a header that’s already been queued but not sent to the client. Note that the name is case insensitive. This can only be called before headers get implicitly flushed.

Example:

var contentType = response.getHeader('content-type');

response.removeHeader(name)

Removes a header that’s queued for implicit sending.

Example:

response.removeHeader("Content-Encoding");

response.write(chunk[, encoding][, callback])

If this method is called and response.writeHead() has not been called, it will switch to implicit header mode and flush the implicit headers.

This sends a chunk of the response body. This method may be called multiple times to provide successive parts of the body.

chunk can be a string or a buffer. If chunk is a string, the second parameter specifies how to encode it into a byte stream. By default the encoding is 'utf8'. The last parameter callback will be called when this chunk of data is flushed.

Note: This is the raw HTTP body and has nothing to do with higher-level multi-part body encodings that may be used.

The first time response.write() is called, it will send the buffered header information and the first body to the client. The second time response.write() is called, Node assumes you’re going to be streaming data, and sends that separately. That is, the response is buffered up to the first chunk of body.

Returns true if the entire data was flushed successfully to the kernel buffer. Returns false if all or part of the data was queued in user memory. 'drain' will be emitted when the buffer is free again.

response.addTrailers(headers)

This method adds HTTP trailing headers (a header but at the end of the message) to the response.

Trailers will only be emitted if chunked encoding is used for the response; if it is not (e.g., if the request was HTTP/1.0), they will be silently discarded.

Note that HTTP requires the Trailer header to be sent if you intend to emit trailers, with a list of the header fields in its value. E.g.,

response.writeHead(200, { 'Content-Type': 'text/plain',
                          'Trailer': 'Content-MD5' });
response.write(fileData);
response.addTrailers({'Content-MD5': "7895bf4b8828b55ceaf47747b4bca667"});
response.end();

response.end([data][, encoding][, callback])

This method signals to the server that all of the response headers and body have been sent; that server should consider this message complete. The method, response.end(), MUST be called on each response.

If data is specified, it is equivalent to calling response.write(data, encoding) followed by response.end(callback).

If callback is specified, it will be called when the response stream is finished.

http.request(options[, callback])

Node maintains several connections per server to make HTTP requests. This function allows one to transparently issue requests.

options can be an object or a string. If options is a string, it is automatically parsed with url.parse().

Options:

host: A domain name or IP address of the server to issue the request to. Defaults to 'localhost'.

hostname: To support url.parse() hostname is preferred over host

port: Port of remote server. Defaults to 80.

localAddress: Local interface to bind for network connections.

socketPath: Unix Domain Socket (use one of host:port or socketPath)

method: A string specifying the HTTP request method. Defaults to 'GET'.

path: Request path. Defaults to '/'. Should include query string if any. E.G. '/index.html?page=12'. An exception is thrown when the request path contains illegal characters. Currently, only spaces are rejected but that may change in the future.

headers: An object containing request headers.

auth: Basic authentication i.e. 'user:password' to compute an Authorization header.

agent: Controls Agent behavior. When an Agent is used request will default to Connection: keep-alive. Possible values:

undefined (default): use global Agent for this host and port.

Agent object: explicitly use the passed in Agent.

false: opts out of connection pooling with an Agent, defaults request to Connection: close.

keepAlive: {Boolean} Keep sockets around in a pool to be used by other requests in the future. Default = false

keepAliveMsecs: {Integer} When using HTTP KeepAlive, how often to send TCP KeepAlive packets over sockets being kept alive. Default = 1000. Only relevant if keepAlive is set to true.

The optional callback parameter will be added as a one time listener for the ‘response’ event.

http.request() returns an instance of the http.ClientRequest class. The ClientRequest instance is a writable stream. If one needs to upload a file with a POST request, then write to the ClientRequest object.

Example:

var postData = querystring.stringify({
  'msg' : 'Hello World!'
});

var options = {
  hostname: 'www.google.com',
  port: 80,
  path: '/upload',
  method: 'POST',
  headers: {
    'Content-Type': 'application/x-www-form-urlencoded',
    'Content-Length': postData.length
  }
};

var req = http.request(options, function(res) {
  console.log('STATUS: ' + res.statusCode);
  console.log('HEADERS: ' + JSON.stringify(res.headers));
  res.setEncoding('utf8');
  var data = '';
  res.on('data', function (chunk) {
    console.log('PARTIAL BODY: ' + chunk);
    data += chunk;
  });
  res.on('end', function() {
    console.log('COMPLETE BODY: ' + data);
  });
});

req.on('error', function(e) {
  console.log('problem with request: ' + e.message);
});

// write data to request body
req.write(postData);
req.end();

The res object handed off to the callback function passed into to http.request is an instance of http.IncomingMessage, which is an instance of a Readable Stream. The content of a successful response will be delivered using zero or more data events followed by a closing end event.

Note that in the example req.end() was called. With http.request() one must always call req.end() to signify that you’re done with the request - even if there is no data being written to the request body.

If any error is encountered during the request (be that with DNS resolution, TCP level errors, or actual HTTP parse errors) an 'error' event is emitted on the returned request object.

There are a few special headers that should be noted.

Sending a ‘Connection: keep-alive’ will notify Node that the connection to the server should be persisted until the next request.

Sending a ‘Content-length’ header will disable the default chunked encoding.

Sending an ‘Expect’ header will immediately send the request headers. Usually, when sending ‘Expect: 100-continue’, you should both set a timeout and listen for the continue event. See RFC2616 Section 8.2.3 for more information.

Sending an Authorization header will override using the auth option to compute basic authentication.

http.get(options[, callback])

Since most requests are GET requests without bodies, Node provides this convenience method. The only difference between this method and http.request() is that it sets the method to GET and calls req.end() automatically.

Example:

http.get("http://www.google.com/index.html", function(res) {
  console.log("Got response: " + res.statusCode);
  // consume response body
  res.resume();
}).on('error', function(e) {
  console.log("Got error: " + e.message);
});

Class: http.Agent

The HTTP Agent is used for pooling sockets used in HTTP client requests.

The HTTP Agent also defaults client requests to using Connection:keep-alive. If no pending HTTP requests are waiting on a socket to become free the socket is closed. This means that Node’s pool has the benefit of keep-alive when under load but still does not require developers to manually close the HTTP clients using KeepAlive.

If you opt into using HTTP KeepAlive, you can create an Agent object with that flag set to true. (See the constructor options below.) Then, the Agent will keep unused sockets in a pool for later use. They will be explicitly marked so as to not keep the Node process running. However, it is still a good idea to explicitly destroy() KeepAlive agents when they are no longer in use, so that the Sockets will be shut down.

Sockets are removed from the agent’s pool when the socket emits either a “close” event or a special “agentRemove” event. This means that if you intend to keep one HTTP request open for a long time and don’t want it to stay in the pool you can do something along the lines of:

http.get(options, function(res) {
  // Do stuff
}).on("socket", function (socket) {
  socket.emit("agentRemove");
});

Alternatively, you could just opt out of pooling entirely using agent:false:

http.get({
  hostname: 'localhost',
  port: 80,
  path: '/',
  agent: false  // create a new agent just for this one request
}, function (res) {
  // Do stuff with response
})

new Agent([options])

options {Object} Set of configurable options to set on the agent. Can have the following fields:

keepAlive {Boolean} Keep sockets around in a pool to be used by other requests in the future. Default = false

keepAliveMsecs {Integer} When using HTTP KeepAlive, how often to send TCP KeepAlive packets over sockets being kept alive. Default = 1000. Only relevant if keepAlive is set to true.

maxSockets {Number} Maximum number of sockets to allow per host. Default = Infinity.

maxFreeSockets {Number} Maximum number of sockets to leave open in a free state. Only relevant if keepAlive is set to true. Default = 256.

The default http.globalAgent that is used by http.request has all of these values set to their respective defaults.

To configure any of them, you must create your own Agent object.

var http = require('http');
var keepAliveAgent = new http.Agent({ keepAlive: true });
options.agent = keepAliveAgent;
http.request(options, onResponseCallback);

agent.maxSockets

By default set to Infinity. Determines how many concurrent sockets the agent can have open per origin. Origin is either a ‘host:port’ or ‘host:port:localAddress’ combination.

agent.maxFreeSockets

By default set to 256. For Agents supporting HTTP KeepAlive, this sets the maximum number of sockets that will be left open in the free state.

agent.sockets

An object which contains arrays of sockets currently in use by the Agent. Do not modify.

agent.freeSockets

An object which contains arrays of sockets currently awaiting use by the Agent when HTTP KeepAlive is used. Do not modify.

agent.requests

An object which contains queues of requests that have not yet been assigned to sockets. Do not modify.

agent.destroy()

Destroy any sockets that are currently in use by the agent.

It is usually not necessary to do this. However, if you are using an agent with KeepAlive enabled, then it is best to explicitly shut down the agent when you know that it will no longer be used. Otherwise, sockets may hang open for quite a long time before the server terminates them.

agent.getName(options)

Get a unique name for a set of request options, to determine whether a connection can be reused. In the http agent, this returns host:port:localAddress. In the https agent, the name includes the CA, cert, ciphers, and other HTTPS/TLS-specific options that determine socket reusability.

http.globalAgent

Global instance of Agent which is used as the default for all http client requests.

Class: http.ClientRequest

This object is created internally and returned from http.request(). It represents an in-progress request whose header has already been queued. The header is still mutable using the setHeader(name, value), getHeader(name), removeHeader(name) API. The actual header will be sent along with the first data chunk or when closing the connection.

To get the response, add a listener for 'response' to the request object. 'response' will be emitted from the request object when the response headers have been received. The 'response' event is executed with one argument which is an instance of http.IncomingMessage.

During the 'response' event, one can add listeners to the response object; particularly to listen for the 'data' event.

If no 'response' handler is added, then the response will be entirely discarded. However, if you add a 'response' event handler, then you must consume the data from the response object, either by calling response.read() whenever there is a 'readable' event, or by adding a 'data' handler, or by calling the .resume() method. Until the data is consumed, the 'end' event will not fire. Also, until the data is read it will consume memory that can eventually lead to a ‘process out of memory’ error.

Note: Node does not check whether Content-Length and the length of the body which has been transmitted are equal or not.

The request implements the Writable Stream interface. This is an EventEmitter with the following events:

Event: ‘response’

function (response) { }

Emitted when a response is received to this request. This event is emitted only once. The response argument will be an instance of http.IncomingMessage.

Options:

host: A domain name or IP address of the server to issue the request to.

port: Port of remote server.

socketPath: Unix Domain Socket (use one of host:port or socketPath)

Event: ‘socket’

function (socket) { }

Emitted after a socket is assigned to this request.

Event: ‘connect’

function (response, socket, head) { }

Emitted each time a server responds to a request with a CONNECT method. If this event isn’t being listened for, clients receiving a CONNECT method will have their connections closed.

A client server pair that show you how to listen for the connect event.

var http = require('http');
var net = require('net');
var url = require('url');

// Create an HTTP tunneling proxy
var proxy = http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('okay');
});
proxy.on('connect', function(req, cltSocket, head) {
  // connect to an origin server
  var srvUrl = url.parse('http://' + req.url);
  var srvSocket = net.connect(srvUrl.port, srvUrl.hostname, function() {
    cltSocket.write('HTTP/1.1 200 Connection Established\r\n' +
                    'Proxy-agent: Node-Proxy\r\n' +
                    '\r\n');
    srvSocket.write(head);
    srvSocket.pipe(cltSocket);
    cltSocket.pipe(srvSocket);
  });
});

// now that proxy is running
proxy.listen(1337, '127.0.0.1', function() {

  // make a request to a tunneling proxy
  var options = {
    port: 1337,
    hostname: '127.0.0.1',
    method: 'CONNECT',
    path: 'www.google.com:80'
  };

  var req = http.request(options);
  req.end();

  req.on('connect', function(res, socket, head) {
    console.log('got connected!');

    // make a request over an HTTP tunnel
    socket.write('GET / HTTP/1.1\r\n' +
                 'Host: www.google.com:80\r\n' +
                 'Connection: close\r\n' +
                 '\r\n');
    socket.on('data', function(chunk) {
      console.log(chunk.toString());
    });
    socket.on('end', function() {
      proxy.close();
    });
  });
});

Event: ‘upgrade’

function (response, socket, head) { }

Emitted each time a server responds to a request with an upgrade. If this event isn’t being listened for, clients receiving an upgrade header will have their connections closed.

A client server pair that show you how to listen for the upgrade event.

var http = require('http');

// Create an HTTP server
var srv = http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('okay');
});
srv.on('upgrade', function(req, socket, head) {
  socket.write('HTTP/1.1 101 Web Socket Protocol Handshake\r\n' +
               'Upgrade: WebSocket\r\n' +
               'Connection: Upgrade\r\n' +
               '\r\n');

  socket.pipe(socket); // echo back
});

// now that server is running
srv.listen(1337, '127.0.0.1', function() {

  // make a request
  var options = {
    port: 1337,
    hostname: '127.0.0.1',
    headers: {
      'Connection': 'Upgrade',
      'Upgrade': 'websocket'
    }
  };

  var req = http.request(options);
  req.end();

  req.on('upgrade', function(res, socket, upgradeHead) {
    console.log('got upgraded!');
    socket.end();
    process.exit(0);
  });
});

Event: ‘continue’

function () { }

Emitted when the server sends a ‘100 Continue’ HTTP response, usually because the request contained ‘Expect: 100-continue’. This is an instruction that the client should send the request body.

request.flushHeaders()

Flush the request headers.

For efficiency reasons, node.js normally buffers the request headers until you call request.end() or write the first chunk of request data. It then tries hard to pack the request headers and data into a single TCP packet.

That’s usually what you want (it saves a TCP round-trip) but not when the first data isn’t sent until possibly much later. request.flush() lets you bypass the optimization and kickstart the request.

request.write(chunk[, encoding][, callback])

Sends a chunk of the body. By calling this method many times, the user can stream a request body to a server–in that case it is suggested to use the ['Transfer-Encoding', 'chunked'] header line when creating the request.

The chunk argument should be a Buffer or a string.

The encoding argument is optional and only applies when chunk is a string. Defaults to 'utf8'.

The callback argument is optional and will be called when this chunk of data is flushed.

request.end([data][, encoding][, callback])

Finishes sending the request. If any parts of the body are unsent, it will flush them to the stream. If the request is chunked, this will send the terminating '0\r\n\r\n'.

If data is specified, it is equivalent to calling request.write(data, encoding) followed by request.end(callback).

If callback is specified, it will be called when the request stream is finished.

request.abort()

Marks the request as aborting. Calling this will cause remaining data in the response to be dropped and the socket to be destroyed.

request.setTimeout(timeout[, callback])

Once a socket is assigned to this request and is connected socket.setTimeout() will be called.

request.setNoDelay([noDelay])

Once a socket is assigned to this request and is connected socket.setNoDelay() will be called.

request.setSocketKeepAlive([enable][, initialDelay])

Once a socket is assigned to this request and is connected socket.setKeepAlive() will be called.

http.IncomingMessage

An IncomingMessage object is created by http.Server or http.ClientRequest and passed as the first argument to the 'request' and 'response' event respectively. It may be used to access response status, headers and data.

It implements the Readable Stream interface, as well as the following additional events, methods, and properties.

Event: ‘close’

function () { }

Indicates that the underlying connection was closed. Just like 'end', this event occurs only once per response.

message.httpVersion

In case of server request, the HTTP version sent by the client. In the case of client response, the HTTP version of the connected-to server. Probably either '1.1' or '1.0'.

Also response.httpVersionMajor is the first integer and response.httpVersionMinor is the second.

message.headers

The request/response headers object.

Read only map of header names and values. Header names are lower-cased. Example:

// Prints something like:
//
// { 'user-agent': 'curl/7.22.0',
//   host: '127.0.0.1:8000',
//   accept: '*/*' }
console.log(request.headers);

message.rawHeaders

The raw request/response headers list exactly as they were received.

Note that the keys and values are in the same list. It is not a list of tuples. So, the even-numbered offsets are key values, and the odd-numbered offsets are the associated values.

Header names are not lowercased, and duplicates are not merged.

// Prints something like:
//
// [ 'user-agent',
//   'this is invalid because there can be only one',
//   'User-Agent',
//   'curl/7.22.0',
//   'Host',
//   '127.0.0.1:8000',
//   'ACCEPT',
//   '*/*' ]
console.log(request.rawHeaders);

message.trailers

The request/response trailers object. Only populated at the ‘end’ event.

message.rawTrailers

The raw request/response trailer keys and values exactly as they were received. Only populated at the ‘end’ event.

message.setTimeout(msecs, callback)

msecs {Number}

callback {Function}

Calls message.connection.setTimeout(msecs, callback).

message.method

Only valid for request obtained from http.Server.

The request method as a string. Read only. Example: 'GET', 'DELETE'.

message.url

Only valid for request obtained from http.Server.

Request URL string. This contains only the URL that is present in the actual HTTP request. If the request is:

GET /status?name=ryan HTTP/1.1\r\n
Accept: text/plain\r\n
\r\n

Then request.url will be:

'/status?name=ryan'

If you would like to parse the URL into its parts, you can use require('url').parse(request.url). Example:

node> require('url').parse('/status?name=ryan')
{ href: '/status?name=ryan',
  search: '?name=ryan',
  query: 'name=ryan',
  pathname: '/status' }

If you would like to extract the params from the query string, you can use the require('querystring').parse function, or pass true as the second argument to require('url').parse. Example:

node> require('url').parse('/status?name=ryan', true)
{ href: '/status?name=ryan',
  search: '?name=ryan',
  query: { name: 'ryan' },
  pathname: '/status' }

message.statusCode

Only valid for response obtained from http.ClientRequest.

The 3-digit HTTP response status code. E.G. 404.

message.statusMessage

Only valid for response obtained from http.ClientRequest.

The HTTP response status message (reason phrase). E.G. OK or Internal Server Error.

message.socket

The net.Socket object associated with the connection.

With HTTPS support, use request.connection.verifyPeer() and request.connection.getPeerCertificate() to obtain the client’s authentication details.

HTTPS

Stability: 3 - Stable

HTTPS is the HTTP protocol over TLS/SSL. In Node this is implemented as a separate module.

Class: https.Server

This class is a subclass of tls.Server and emits events same as http.Server. See http.Server for more information.

server.setTimeout(msecs, callback)

See http.Server#setTimeout().

server.timeout

See http.Server#timeout.

https.createServer(options[, requestListener])

Returns a new HTTPS web server object. The options is similar to tls.createServer(). The requestListener is a function which is automatically added to the 'request' event.

Example:

// curl -k https://localhost:8000/
var https = require('https');
var fs = require('fs');

var options = {
  key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
  cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};

https.createServer(options, function (req, res) {
  res.writeHead(200);
  res.end("hello world\n");
}).listen(8000);

Or

var https = require('https');
var fs = require('fs');

var options = {
  pfx: fs.readFileSync('server.pfx')
};

https.createServer(options, function (req, res) {
  res.writeHead(200);
  res.end("hello world\n");
}).listen(8000);

server.listen(port[, host][, backlog][, callback])

server.listen(path[, callback])

server.listen(handle[, callback])

See http.listen() for details.

server.close([callback])

See http.close() for details.

https.request(options, callback)

Makes a request to a secure web server.

options can be an object or a string. If options is a string, it is automatically parsed with url.parse().

All options from http.request() are valid.

Example:

var https = require('https');

var options = {
  hostname: 'encrypted.google.com',
  port: 443,
  path: '/',
  method: 'GET'
};

var req = https.request(options, function(res) {
  console.log("statusCode: ", res.statusCode);
  console.log("headers: ", res.headers);

  res.on('data', function(d) {
    process.stdout.write(d);
  });
});
req.end();

req.on('error', function(e) {
  console.error(e);
});

The options argument has the following options

host: A domain name or IP address of the server to issue the request to. Defaults to 'localhost'.

hostname: To support url.parse() hostname is preferred over host

port: Port of remote server. Defaults to 443.

method: A string specifying the HTTP request method. Defaults to 'GET'.

path: Request path. Defaults to '/'. Should include query string if any. E.G. '/index.html?page=12'

headers: An object containing request headers.

auth: Basic authentication i.e. 'user:password' to compute an Authorization header.

agent: Controls Agent behavior. When an Agent is used request will default to Connection: keep-alive. Possible values:

undefined (default): use globalAgent for this host and port.

Agent object: explicitly use the passed in Agent.

false: opts out of connection pooling with an Agent, defaults request to Connection: close.

The following options from tls.connect() can also be specified. However, a globalAgent silently ignores these.

pfx: Certificate, Private key and CA certificates to use for SSL. Default null.

key: Private key to use for SSL. Default null.

passphrase: A string of passphrase for the private key or pfx. Default null.

cert: Public x509 certificate to use. Default null.

ca: An authority certificate or array of authority certificates to check the remote host against.

ciphers: A string describing the ciphers to use or exclude. Consult http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT for details on the format.

rejectUnauthorized: If true, the server certificate is verified against the list of supplied CAs. An 'error' event is emitted if verification fails. Verification happens at the connection level, before the HTTP request is sent. Default true.

secureProtocol: The SSL method to use, e.g. TLSv1_method to force TLS version 1. The possible values depend on your installation of OpenSSL and are defined in the constant SSL_METHODS.

In order to specify these options, use a custom Agent.

Example:

var options = {
  hostname: 'encrypted.google.com',
  port: 443,
  path: '/',
  method: 'GET',
  key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
  cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem')
};
options.agent = new https.Agent(options);

var req = https.request(options, function(res) {
  ...
}

Or does not use an Agent.

Example:

var options = {
  hostname: 'encrypted.google.com',
  port: 443,
  path: '/',
  method: 'GET',
  key: fs.readFileSync('test/fixtures/keys/agent2-key.pem'),
  cert: fs.readFileSync('test/fixtures/keys/agent2-cert.pem'),
  agent: false
};

var req = https.request(options, function(res) {
  ...
}

https.get(options, callback)

Like http.get() but for HTTPS.

options can be an object or a string. If options is a string, it is automatically parsed with url.parse().

Example:

var https = require('https');

https.get('https://encrypted.google.com/', function(res) {
  console.log("statusCode: ", res.statusCode);
  console.log("headers: ", res.headers);

  res.on('data', function(d) {
    process.stdout.write(d);
  });

}).on('error', function(e) {
  console.error(e);
});

Class: https.Agent

An Agent object for HTTPS similar to http.Agent. See https.request() for more information.

https.globalAgent

Global instance of https.Agent for all HTTPS client requests.

Modules

Stability: 5 - Locked

Node has a simple module loading system. In Node, files and modules are in one-to-one correspondence. As an example, foo.js loads the module circle.js in the same directory.

The contents of foo.js:

var circle = require('./circle.js');
console.log( 'The area of a circle of radius 4 is '
           + circle.area(4));

The contents of circle.js:

var PI = Math.PI;

exports.area = function (r) {
  return PI * r * r;
};

exports.circumference = function (r) {
  return 2 * PI * r;
};

The module circle.js has exported the functions area() and circumference(). To add functions and objects to the root of your module, you can add them to the special exports object.

Variables local to the module will be private, as though the module was wrapped in a function. In this example the variable PI is private to circle.js.

If you want the root of your module’s export to be a function (such as a constructor) or if you want to export a complete object in one assignment instead of building it one property at a time, assign it to module.exports instead of exports.

Below, bar.js makes use of the square module, which exports a constructor:

var square = require('./square.js');
var mySquare = square(2);
console.log('The area of my square is ' + mySquare.area());

The square module is defined in square.js:

// assigning to exports will not modify module, must use module.exports
module.exports = function(width) {
  return {
    area: function() {
      return width * width;
    }
  };
}

The module system is implemented in the require("module") module.

Cycles

When there are circular require() calls, a module might not have finished executing when it is returned.

Consider this situation:

a.js:

console.log('a starting');
exports.done = false;
var b = require('./b.js');
console.log('in a, b.done = %j', b.done);
exports.done = true;
console.log('a done');

b.js:

console.log('b starting');
exports.done = false;
var a = require('./a.js');
console.log('in b, a.done = %j', a.done);
exports.done = true;
console.log('b done');

main.js:

console.log('main starting');
var a = require('./a.js');
var b = require('./b.js');
console.log('in main, a.done=%j, b.done=%j', a.done, b.done);

When main.js loads a.js, then a.js in turn loads b.js. At that point, b.js tries to load a.js. In order to prevent an infinite loop, an unfinished copy of the a.js exports object is returned to the b.js module. b.js then finishes loading, and its exports object is provided to the a.js module.

By the time main.js has loaded both modules, they’re both finished. The output of this program would thus be:

$ node main.js
main starting
a starting
b starting
in b, a.done = false
b done
in a, b.done = true
a done
in main, a.done=true, b.done=true

If you have cyclic module dependencies in your program, make sure to plan accordingly.

Core Modules

Node has several modules compiled into the binary. These modules are described in greater detail elsewhere in this documentation.

The core modules are defined in node’s source in the lib/ folder.

Core modules are always preferentially loaded if their identifier is passed to require(). For instance, require('http') will always return the built in HTTP module, even if there is a file by that name.

File Modules

If the exact filename is not found, then node will attempt to load the required filename with the added extension of .js, .json, and then .node.

.js files are interpreted as JavaScript text files, and .json files are parsed as JSON text files. .node files are interpreted as compiled addon modules loaded with dlopen.

A module prefixed with '/' is an absolute path to the file. For example, require('/home/marco/foo.js') will load the file at /home/marco/foo.js.

A module prefixed with './' is relative to the file calling require(). That is, circle.js must be in the same directory as foo.js for require('./circle') to find it.

Without a leading ‘/’ or ‘./’ to indicate a file, the module is either a “core module” or is loaded from a node_modules folder.

If the given path does not exist, require() will throw an Error with its code property set to 'MODULE_NOT_FOUND'.

Loading from node_modules Folders

If the module identifier passed to require() is not a native module, and does not begin with '/', '../', or './', then node starts at the parent directory of the current module, and adds /node_modules, and attempts to load the module from that location.

If it is not found there, then it moves to the parent directory, and so on, until the root of the file system is reached.

For example, if the file at '/home/ry/projects/foo.js' called require('bar.js'), then node would look in the following locations, in this order:

/home/ry/projects/node_modules/bar.js

/home/ry/node_modules/bar.js

/home/node_modules/bar.js

/node_modules/bar.js

This allows programs to localize their dependencies, so that they do not clash.

You can require specific files or sub modules distributed with a module by including a path suffix after the module name. For instance require('example-module/path/to/file') would resolve path/to/file relative to where example-module is located. The suffixed path follows the same module resolution semantics.

Folders as Modules

It is convenient to organize programs and libraries into self-contained directories, and then provide a single entry point to that library. There are three ways in which a folder may be passed to require() as an argument.

The first is to create a package.json file in the root of the folder, which specifies a main module. An example package.json file might look like this:

{ "name" : "some-library",
  "main" : "./lib/some-library.js" }

If this was in a folder at ./some-library, then require('./some-library') would attempt to load ./some-library/lib/some-library.js.

This is the extent of Node’s awareness of package.json files.

If there is no package.json file present in the directory, then node will attempt to load an index.js or index.node file out of that directory. For example, if there was no package.json file in the above example, then require('./some-library') would attempt to load:

./some-library/index.js

./some-library/index.node

Caching

Modules are cached after the first time they are loaded. This means (among other things) that every call to require('foo') will get exactly the same object returned, if it would resolve to the same file.

Multiple calls to require('foo') may not cause the module code to be executed multiple times. This is an important feature. With it, “partially done” objects can be returned, thus allowing transitive dependencies to be loaded even when they would cause cycles.

If you want to have a module execute code multiple times, then export a function, and call that function.

Module Caching Caveats

Modules are cached based on their resolved filename. Since modules may resolve to a different filename based on the location of the calling module (loading from node_modules folders), it is not a guarantee that require('foo') will always return the exact same object, if it would resolve to different files.

The module Object

{Object}

In each module, the module free variable is a reference to the object representing the current module. For convenience, module.exports is also accessible via the exports module-global. module isn’t actually a global but rather local to each module.

module.exports

{Object}

The module.exports object is created by the Module system. Sometimes this is not acceptable; many want their module to be an instance of some class. To do this, assign the desired export object to module.exports. Note that assigning the desired object to exports will simply rebind the local exports variable, which is probably not what you want to do.

For example suppose we were making a module called a.js

var EventEmitter = require('events').EventEmitter;

module.exports = new EventEmitter();

// Do some work, and after some time emit
// the 'ready' event from the module itself.
setTimeout(function() {
  module.exports.emit('ready');
}, 1000);

Then in another file we could do

var a = require('./a');
a.on('ready', function() {
  console.log('module a is ready');
});

Note that assignment to module.exports must be done immediately. It cannot be done in any callbacks. This does not work:

x.js:

setTimeout(function() {
  module.exports = { a: "hello" };
}, 0);

y.js:

var x = require('./x');
console.log(x.a);

exports alias

The exports variable that is available within a module starts as a reference to module.exports. As with any variable, if you assign a new value to it, it is no longer bound to the previous value.

To illustrate the behaviour, imagine this hypothetical implementation of require():

function require(...) {
  // ...
  function (module, exports) {
    // Your module code here
    exports = some_func;        // re-assigns exports, exports is no longer
                                // a shortcut, and nothing is exported.
    module.exports = some_func; // makes your module export 0
  } (module, module.exports);
  return module;
}

As a guideline, if the relationship between exports and module.exports seems like magic to you, ignore exports and only use module.exports.

module.require(id)

id {String}

Return: {Object} module.exports from the resolved module

The module.require method provides a way to load a module as if require() was called from the original module.

Note that in order to do this, you must get a reference to the module object. Since require() returns the module.exports, and the module is typically only available within a specific module’s code, it must be explicitly exported in order to be used.

module.id

{String}

The identifier for the module. Typically this is the fully resolved filename.

module.filename

{String}

The fully resolved filename to the module.

module.loaded

{Boolean}

Whether or not the module is done loading, or is in the process of loading.

module.parent

{Module Object}

The module that required this one.

module.children

{Array}

The module objects required by this one.

All Together…

To get the exact filename that will be loaded when require() is called, use the require.resolve() function.

Putting together all of the above, here is the high-level algorithm in pseudocode of what require.resolve does:

require(X) from module at path Y
1. If X is a core module,
   a. return the core module
   b. STOP
2. If X begins with './' or '/' or '../'
   a. LOAD_AS_FILE(Y + X)
   b. LOAD_AS_DIRECTORY(Y + X)
3. LOAD_NODE_MODULES(X, dirname(Y))
4. THROW "not found"

LOAD_AS_FILE(X)
1. If X is a file, load X as JavaScript text.  STOP
2. If X.js is a file, load X.js as JavaScript text.  STOP
3. If X.json is a file, parse X.json to a JavaScript Object.  STOP
4. If X.node is a file, load X.node as binary addon.  STOP

LOAD_AS_DIRECTORY(X)
1. If X/package.json is a file,
   a. Parse X/package.json, and look for "main" field.
   b. let M = X + (json main field)
   c. LOAD_AS_FILE(M)
2. If X/index.js is a file, load X/index.js as JavaScript text.  STOP
3. If X/index.json is a file, parse X/index.json to a JavaScript object. STOP
4. If X/index.node is a file, load X/index.node as binary addon.  STOP

LOAD_NODE_MODULES(X, START)
1. let DIRS=NODE_MODULES_PATHS(START)
2. for each DIR in DIRS:
   a. LOAD_AS_FILE(DIR/X)
   b. LOAD_AS_DIRECTORY(DIR/X)

NODE_MODULES_PATHS(START)
1. let PARTS = path split(START)
2. let I = count of PARTS - 1
3. let DIRS = []
4. while I >= 0,
   a. if PARTS[I] = "node_modules" CONTINUE
   c. DIR = path join(PARTS[0 .. I] + "node_modules")
   b. DIRS = DIRS + DIR
   c. let I = I - 1
5. return DIRS

Loading from the global folders

If the NODE_PATH environment variable is set to a colon-delimited list of absolute paths, then node will search those paths for modules if they are not found elsewhere. (Note: On Windows, NODE_PATH is delimited by semicolons instead of colons.)

Additionally, node will search in the following locations:

1: $HOME/.node_modules

2: $HOME/.node_libraries

3: $PREFIX/lib/node

Where $HOME is the user’s home directory, and $PREFIX is node’s configured node_prefix.

These are mostly for historic reasons. You are highly encouraged to place your dependencies locally in node_modules folders. They will be loaded faster, and more reliably.

Accessing the main module

When a file is run directly from Node, require.main is set to its module. That means that you can determine whether a file has been run directly by testing

require.main === module

For a file foo.js, this will be true if run via node foo.js, but false if run by require('./foo').

Because module provides a filename property (normally equivalent to __filename), the entry point of the current application can be obtained by checking require.main.filename.

Addenda: Package Manager Tips

The semantics of Node’s require() function were designed to be general enough to support a number of sane directory structures. Package manager programs such as dpkg, rpm, and npm will hopefully find it possible to build native packages from Node modules without modification.

Below we give a suggested directory structure that could work:

Let’s say that we wanted to have the folder at /usr/lib/node/<some-package>/<some-version> hold the contents of a specific version of a package.

Packages can depend on one another. In order to install package foo, you may have to install a specific version of package bar. The bar package may itself have dependencies, and in some cases, these dependencies may even collide or form cycles.

Since Node looks up the realpath of any modules it loads (that is, resolves symlinks), and then looks for their dependencies in the node_modules folders as described above, this situation is very simple to resolve with the following architecture:

/usr/lib/node/foo/1.2.3/ - Contents of the foo package, version 1.2.3.

/usr/lib/node/bar/4.3.2/ - Contents of the bar package that foo depends on.

/usr/lib/node/foo/1.2.3/node_modules/bar - Symbolic link to /usr/lib/node/bar/4.3.2/.

/usr/lib/node/bar/4.3.2/node_modules/* - Symbolic links to the packages that bar depends on.

Thus, even if a cycle is encountered, or if there are dependency conflicts, every module will be able to get a version of its dependency that it can use.

When the code in the foo package does require('bar'), it will get the version that is symlinked into /usr/lib/node/foo/1.2.3/node_modules/bar. Then, when the code in the bar package calls require('quux'), it’ll get the version that is symlinked into /usr/lib/node/bar/4.3.2/node_modules/quux.

Furthermore, to make the module lookup process even more optimal, rather than putting packages directly in /usr/lib/node, we could put them in /usr/lib/node_modules/<name>/<version>. Then node will not bother looking for missing dependencies in /usr/node_modules or /node_modules.

In order to make modules available to the node REPL, it might be useful to also add the /usr/lib/node_modules folder to the $NODE_PATH environment variable. Since the module lookups using node_modules folders are all relative, and based on the real path of the files making the calls to require(), the packages themselves can be anywhere.

net

Stability: 3 - Stable

The net module provides you with an asynchronous network wrapper. It contains methods for creating both servers and clients (called streams). You can include this module with require('net');

net.createServer([options][, connectionListener])

Creates a new TCP server. The connectionListener argument is automatically set as a listener for the ‘connection’ event.

options is an object with the following defaults:

{
  allowHalfOpen: false,
  pauseOnConnect: false
}

If allowHalfOpen is true, then the socket won’t automatically send a FIN packet when the other end of the socket sends a FIN packet. The socket becomes non-readable, but still writable. You should call the end() method explicitly. See ‘end’ event for more information.

If pauseOnConnect is true, then the socket associated with each incoming connection will be paused, and no data will be read from its handle. This allows connections to be passed between processes without any data being read by the original process. To begin reading data from a paused socket, call resume().

Here is an example of an echo server which listens for connections on port 8124:

var net = require('net');
var server = net.createServer(function(c) { //'connection' listener
  console.log('client connected');
  c.on('end', function() {
    console.log('client disconnected');
  });
  c.write('hello\r\n');
  c.pipe(c);
});
server.listen(8124, function() { //'listening' listener
  console.log('server bound');
});

Test this by using telnet:

telnet localhost 8124

To listen on the socket /tmp/echo.sock the third line from the last would just be changed to

server.listen('/tmp/echo.sock', function() { //'listening' listener

Use nc to connect to a UNIX domain socket server:

nc -U /tmp/echo.sock

net.connect(options[, connectionListener])

net.createConnection(options[, connectionListener])

A factory method, which returns a new ‘net.Socket’ and connects to the supplied address and port.

When the socket is established, the ‘connect’ event will be emitted.

Has the same events as ‘net.Socket’.

For TCP sockets, options argument should be an object which specifies:

port: Port the client should connect to (Required).

host: Host the client should connect to. Defaults to 'localhost'.

localAddress: Local interface to bind to for network connections.

localPort: Local port to bind to for network connections.

family : Version of IP stack. Defaults to 4.

For local domain sockets, options argument should be an object which specifies:

path: Path the client should connect to (Required).

Common options are:

allowHalfOpen: if true, the socket won’t automatically send a FIN packet when the other end of the socket sends a FIN packet. Defaults to false. See ‘end’ event for more information.

The connectListener parameter will be added as an listener for the ‘connect’ event.

Here is an example of a client of echo server as described previously:

var net = require('net');
var client = net.connect({port: 8124},
    function() { //'connect' listener
  console.log('connected to server!');
  client.write('world!\r\n');
});
client.on('data', function(data) {
  console.log(data.toString());
  client.end();
});
client.on('end', function() {
  console.log('disconnected from server');
});

To connect on the socket /tmp/echo.sock the second line would just be changed to

var client = net.connect({path: '/tmp/echo.sock'});

net.connect(port[, host][, connectListener])

net.createConnection(port[, host][, connectListener])

Creates a TCP connection to port on host. If host is omitted, 'localhost' will be assumed. The connectListener parameter will be added as an listener for the ‘connect’ event.

Is a factory method which returns a new ‘net.Socket’.

net.connect(path[, connectListener])

net.createConnection(path[, connectListener])

Creates unix socket connection to path. The connectListener parameter will be added as an listener for the ‘connect’ event.

A factory method which returns a new ‘net.Socket’.

Class: net.Server

This class is used to create a TCP or local server.

server.listen(port[, host][, backlog][, callback])

Begin accepting connections on the specified port and host. If the host is omitted, the server will accept connections directed to any IPv4 address (INADDR_ANY). A port value of zero will assign a random port.

Backlog is the maximum length of the queue of pending connections. The actual length will be determined by your OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on linux. The default value of this parameter is 511 (not 512).

This function is asynchronous. When the server has been bound, ‘listening’ event will be emitted. The last parameter callback will be added as an listener for the ‘listening’ event.

One issue some users run into is getting EADDRINUSE errors. This means that another server is already running on the requested port. One way of handling this would be to wait a second and then try again. This can be done with

server.on('error', function (e) {
  if (e.code == 'EADDRINUSE') {
    console.log('Address in use, retrying...');
    setTimeout(function () {
      server.close();
      server.listen(PORT, HOST);
    }, 1000);
  }
});

(Note: All sockets in Node set SO_REUSEADDR already)

server.listen(path[, callback])

path {String}

callback {Function}

Start a local socket server listening for connections on the given path.

This function is asynchronous. When the server has been bound, ‘listening’ event will be emitted. The last parameter callback will be added as an listener for the ‘listening’ event.

On UNIX, the local domain is usually known as the UNIX domain. The path is a filesystem path name. It is subject to the same naming conventions and permissions checks as would be done on file creation, will be visible in the filesystem, and will persist until unlinked.

On Windows, the local domain is implemented using a named pipe. The path must refer to an entry in \\?\pipe\ or \\.\pipe\. Any characters are permitted, but the latter may do some processing of pipe names, such as resolving .. sequences. Despite appearances, the pipe name space is flat. Pipes will not persist, they are removed when the last reference to them is closed. Do not forget javascript string escaping requires paths to be specified with double-backslashes, such as:

net.createServer().listen(
    path.join('\\\\?\\pipe', process.cwd(), 'myctl'))

server.listen(handle[, callback])

handle {Object}

callback {Function}

The handle object can be set to either a server or socket (anything with an underlying _handle member), or a {fd: <n>} object.

This will cause the server to accept connections on the specified handle, but it is presumed that the file descriptor or handle has already been bound to a port or domain socket.

Listening on a file descriptor is not supported on Windows.

This function is asynchronous. When the server has been bound, ‘listening’ event will be emitted. the last parameter callback will be added as an listener for the ‘listening’ event.

server.listen(options[, callback])

options {Object} - Required. Supports the following properties:

port {Number} - Optional.

host {String} - Optional.

backlog {Number} - Optional.

path {String} - Optional.

exclusive {Boolean} - Optional.

callback {Function} - Optional.

The port, host, and backlog properties of options, as well as the optional callback function, behave as they do on a call to server.listen(port, [host], [backlog], [callback]). Alternatively, the path option can be used to specify a UNIX socket.

If exclusive is false (default), then cluster workers will use the same underlying handle, allowing connection handling duties to be shared. When exclusive is true, the handle is not shared, and attempted port sharing results in an error. An example which listens on an exclusive port is shown below.

server.listen({
  host: 'localhost',
  port: 80,
  exclusive: true
});

server.close([callback])

Stops the server from accepting new connections and keeps existing connections. This function is asynchronous, the server is finally closed when all connections are ended and the server emits a 'close' event. Optionally, you can pass a callback to listen for the 'close' event. If present, the callback is invoked with any potential error as the first and only argument.

server.address()

Returns the bound address, the address family name and port of the server as reported by the operating system. Useful to find which port was assigned when giving getting an OS-assigned address. Returns an object with three properties, e.g. { port: 12346, family: 'IPv4', address: '127.0.0.1' }

Example:

var server = net.createServer(function (socket) {
  socket.end("goodbye\n");
});

// grab a random port.
server.listen(function() {
  address = server.address();
  console.log("opened server on %j", address);
});

Don’t call server.address() until the 'listening' event has been emitted.

server.unref()

Calling unref on a server will allow the program to exit if this is the only active server in the event system. If the server is already unrefd calling unref again will have no effect.

server.ref()

Opposite of unref, calling ref on a previously unrefd server will not let the program exit if it’s the only server left (the default behavior). If the server is refd calling ref again will have no effect.

server.maxConnections

Set this property to reject connections when the server’s connection count gets high.

It is not recommended to use this option once a socket has been sent to a child with child_process.fork().

server.connections

This function is deprecated; please use server.getConnections() instead. The number of concurrent connections on the server.

This becomes null when sending a socket to a child with child_process.fork(). To poll forks and get current number of active connections use asynchronous server.getConnections instead.

server.getConnections(callback)

Asynchronously get the number of concurrent connections on the server. Works when sockets were sent to forks.

Callback should take two arguments err and count.

net.Server is an EventEmitter with the following events:

Event: ‘listening’

Emitted when the server has been bound after calling server.listen.

Event: ‘connection’

{Socket object} The connection object

Emitted when a new connection is made. socket is an instance of net.Socket.

Event: ‘close’

Emitted when the server closes. Note that if connections exist, this event is not emitted until all connections are ended.

Event: ‘error’

{Error Object}

Emitted when an error occurs. The 'close' event will be called directly following this event. See example in discussion of server.listen.

Class: net.Socket

This object is an abstraction of a TCP or local socket. net.Socket instances implement a duplex Stream interface. They can be created by the user and used as a client (with connect()) or they can be created by Node and passed to the user through the 'connection' event of a server.

new net.Socket([options])

Construct a new socket object.

options is an object with the following defaults:

{ fd: null
  allowHalfOpen: false,
  readable: false,
  writable: false
}

fd allows you to specify the existing file descriptor of socket. Set readable and/or writable to true to allow reads and/or writes on this socket (NOTE: Works only when fd is passed). About allowHalfOpen, refer to createServer() and 'end' event.

socket.connect(port[, host][, connectListener])

socket.connect(path[, connectListener])

Opens the connection for a given socket. If port and host are given, then the socket will be opened as a TCP socket, if host is omitted, localhost will be assumed. If a path is given, the socket will be opened as a unix socket to that path.

Normally this method is not needed, as net.createConnection opens the socket. Use this only if you are implementing a custom Socket.

This function is asynchronous. When the ‘connect’ event is emitted the socket is established. If there is a problem connecting, the 'connect' event will not be emitted, the 'error' event will be emitted with the exception.

The connectListener parameter will be added as an listener for the ‘connect’ event.

socket.bufferSize

net.Socket has the property that socket.write() always works. This is to help users get up and running quickly. The computer cannot always keep up with the amount of data that is written to a socket - the network connection simply might be too slow. Node will internally queue up the data written to a socket and send it out over the wire when it is possible. (Internally it is polling on the socket’s file descriptor for being writable).

The consequence of this internal buffering is that memory may grow. This property shows the number of characters currently buffered to be written. (Number of characters is approximately equal to the number of bytes to be written, but the buffer may contain strings, and the strings are lazily encoded, so the exact number of bytes is not known.)

Users who experience large or growing bufferSize should attempt to “throttle” the data flows in their program with pause() and resume().

socket.setEncoding([encoding])

Set the encoding for the socket as a Readable Stream. See stream.setEncoding() for more information.

socket.write(data[, encoding][, callback])

Sends data on the socket. The second parameter specifies the encoding in the case of a string–it defaults to UTF8 encoding.

Returns true if the entire data was flushed successfully to the kernel buffer. Returns false if all or part of the data was queued in user memory. 'drain' will be emitted when the buffer is again free.

The optional callback parameter will be executed when the data is finally written out - this may not be immediately.

socket.end([data][, encoding])

Half-closes the socket. i.e., it sends a FIN packet. It is possible the server will still send some data.

If data is specified, it is equivalent to calling socket.write(data, encoding) followed by socket.end().

socket.destroy()

Ensures that no more I/O activity happens on this socket. Only necessary in case of errors (parse error or so).

socket.pause()

Pauses the reading of data. That is, 'data' events will not be emitted. Useful to throttle back an upload.

socket.resume()

Resumes reading after a call to pause().

socket.setTimeout(timeout[, callback])

Sets the socket to timeout after timeout milliseconds of inactivity on the socket. By default net.Socket do not have a timeout.

When an idle timeout is triggered the socket will receive a 'timeout' event but the connection will not be severed. The user must manually end() or destroy() the socket.

If timeout is 0, then the existing idle timeout is disabled.

The optional callback parameter will be added as a one time listener for the 'timeout' event.

socket.setNoDelay([noDelay])

Disables the Nagle algorithm. By default TCP connections use the Nagle algorithm, they buffer data before sending it off. Setting true for noDelay will immediately fire off data each time socket.write() is called. noDelay defaults to true.

socket.setKeepAlive([enable][, initialDelay])

Enable/disable keep-alive functionality, and optionally set the initial delay before the first keepalive probe is sent on an idle socket. enable defaults to false.

Set initialDelay (in milliseconds) to set the delay between the last data packet received and the first keepalive probe. Setting 0 for initialDelay will leave the value unchanged from the default (or previous) setting. Defaults to 0.

socket.address()

Returns the bound address, the address family name and port of the socket as reported by the operating system. Returns an object with three properties, e.g. { port: 12346, family: 'IPv4', address: '127.0.0.1' }

socket.unref()

Calling unref on a socket will allow the program to exit if this is the only active socket in the event system. If the socket is already unrefd calling unref again will have no effect.

socket.ref()

Opposite of unref, calling ref on a previously unrefd socket will not let the program exit if it’s the only socket left (the default behavior). If the socket is refd calling ref again will have no effect.

socket.remoteAddress

The string representation of the remote IP address. For example, '74.125.127.100' or '2001:4860:a005::68'.

socket.remoteFamily

The string representation of the remote IP family. 'IPv4' or 'IPv6'.

socket.remotePort

The numeric representation of the remote port. For example, 80 or 21.

socket.localAddress

The string representation of the local IP address the remote client is connecting on. For example, if you are listening on '0.0.0.0' and the client connects on '192.168.1.1', the value would be '192.168.1.1'.

socket.localPort

The numeric representation of the local port. For example, 80 or 21.

socket.bytesRead

The amount of received bytes.

socket.bytesWritten

The amount of bytes sent.

net.Socket instances are EventEmitter with the following events:

Event: ‘lookup’

Emitted after resolving the hostname but before connecting. Not applicable to UNIX sockets.

err {Error | Null} The error object. See dns.lookup().

address {String} The IP address.

family {String | Null} The address type. See dns.lookup().

Event: ‘connect’

Emitted when a socket connection is successfully established. See connect().

Event: ‘data’

{Buffer object}

Emitted when data is received. The argument data will be a Buffer or String. Encoding of data is set by socket.setEncoding(). (See the Readable Stream section for more information.)

Note that the data will be lost if there is no listener when a Socket emits a 'data' event.

Event: ‘end’

Emitted when the other end of the socket sends a FIN packet.

By default (allowHalfOpen == false) the socket will destroy its file descriptor once it has written out its pending write queue. However, by setting allowHalfOpen == true the socket will not automatically end() its side allowing the user to write arbitrary amounts of data, with the caveat that the user is required to end() their side now.

Event: ‘timeout’

Emitted if the socket times out from inactivity. This is only to notify that the socket has been idle. The user must manually close the connection.

See also: socket.setTimeout()

Event: ‘drain’

Emitted when the write buffer becomes empty. Can be used to throttle uploads.

See also: the return values of socket.write()

Event: ‘error’

{Error object}

Emitted when an error occurs. The 'close' event will be called directly following this event.

Event: ‘close’

had_error {Boolean} true if the socket had a transmission error

Emitted once the socket is fully closed. The argument had_error is a boolean which says if the socket was closed due to a transmission error.

net.isIP(input)

Tests if input is an IP address. Returns 0 for invalid strings, returns 4 for IP version 4 addresses, and returns 6 for IP version 6 addresses.

net.isIPv4(input)

Returns true if input is a version 4 IP address, otherwise returns false.

net.isIPv6(input)

Returns true if input is a version 6 IP address, otherwise returns false.

os

Stability: 4 - API Frozen

Provides a few basic operating-system related utility functions.

Use require('os') to access this module.

os.tmpdir()

Returns the operating system’s default directory for temp files.

os.endianness()

Returns the endianness of the CPU. Possible values are "BE" or "LE".

os.hostname()

Returns the hostname of the operating system.

os.type()

Returns the operating system name.

os.platform()

Returns the operating system platform.

os.arch()

Returns the operating system CPU architecture. Possible values are "x64", "arm" and "ia32".

os.release()

Returns the operating system release.

os.uptime()

Returns the system uptime in seconds.

os.loadavg()

Returns an array containing the 1, 5, and 15 minute load averages.

The load average is a measure of system activity, calculated by the operating system and expressed as a fractional number. As a rule of thumb, the load average should ideally be less than the number of logical CPUs in the system.

The load average is a very UNIX-y concept; there is no real equivalent on Windows platforms. That is why this function always returns [0, 0, 0] on Windows.

os.totalmem()

Returns the total amount of system memory in bytes.

os.freemem()

Returns the amount of free system memory in bytes.

os.cpus()

Returns an array of objects containing information about each CPU/core installed: model, speed (in MHz), and times (an object containing the number of milliseconds the CPU/core spent in: user, nice, sys, idle, and irq).

Example inspection of os.cpus:

[ { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 252020,
       nice: 0,
       sys: 30340,
       idle: 1070356870,
       irq: 0 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 306960,
       nice: 0,
       sys: 26980,
       idle: 1071569080,
       irq: 0 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 248450,
       nice: 0,
       sys: 21750,
       idle: 1070919370,
       irq: 0 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 256880,
       nice: 0,
       sys: 19430,
       idle: 1070905480,
       irq: 20 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 511580,
       nice: 20,
       sys: 40900,
       idle: 1070842510,
       irq: 0 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 291660,
       nice: 0,
       sys: 34360,
       idle: 1070888000,
       irq: 10 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 308260,
       nice: 0,
       sys: 55410,
       idle: 1071129970,
       irq: 880 } },
  { model: 'Intel(R) Core(TM) i7 CPU         860  @ 2.80GHz',
    speed: 2926,
    times:
     { user: 266450,
       nice: 1480,
       sys: 34920,
       idle: 1072572010,
       irq: 30 } } ]

os.networkInterfaces()

Get a list of network interfaces:

{ lo:
   [ { address: '127.0.0.1',
       netmask: '255.0.0.0',
       family: 'IPv4',
       mac: '00:00:00:00:00:00',
       internal: true },
     { address: '::1',
       netmask: 'ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff',
       family: 'IPv6',
       mac: '00:00:00:00:00:00',
       internal: true } ],
  eth0:
   [ { address: '192.168.1.108',
       netmask: '255.255.255.0',
       family: 'IPv4',
       mac: '01:02:03:0a:0b:0c',
       internal: false },
     { address: 'fe80::a00:27ff:fe4e:66a1',
       netmask: 'ffff:ffff:ffff:ffff::',
       family: 'IPv6',
       mac: '01:02:03:0a:0b:0c',
       internal: false } ] }

os.EOL

A constant defining the appropriate End-of-line marker for the operating system.

Path

Stability: 3 - Stable

This module contains utilities for handling and transforming file paths. Almost all these methods perform only string transformations. The file system is not consulted to check whether paths are valid.

Use require('path') to use this module. The following methods are provided:

path.normalize(p)

Normalize a string path, taking care of '..' and '.' parts.

When multiple slashes are found, they’re replaced by a single one; when the path contains a trailing slash, it is preserved. On Windows backslashes are used.

Example:

path.normalize('/foo/bar//baz/asdf/quux/..')
// returns
'/foo/bar/baz/asdf'

path.join([path1][, path2][, …])

Join all arguments together and normalize the resulting path.

Arguments must be strings. In v0.8, non-string arguments were silently ignored. In v0.10 and up, an exception is thrown.

Example:

path.join('/foo', 'bar', 'baz/asdf', 'quux', '..')
// returns
'/foo/bar/baz/asdf'

path.join('foo', {}, 'bar')
// throws exception
TypeError: Arguments to path.join must be strings

path.resolve([from …], to)

Resolves to to an absolute path.

If to isn’t already absolute from arguments are prepended in right to left order, until an absolute path is found. If after using all from paths still no absolute path is found, the current working directory is used as well. The resulting path is normalized, and trailing slashes are removed unless the path gets resolved to the root directory. Non-string from arguments are ignored.

Another way to think of it is as a sequence of cd commands in a shell.

path.resolve('foo/bar', '/tmp/file/', '..', 'a/../subfile')

Is similar to:

cd foo/bar
cd /tmp/file/
cd ..
cd a/../subfile
pwd

The difference is that the different paths don’t need to exist and may also be files.

Examples:

path.resolve('/foo/bar', './baz')
// returns
'/foo/bar/baz'

path.resolve('/foo/bar', '/tmp/file/')
// returns
'/tmp/file'

path.resolve('wwwroot', 'static_files/png/', '../gif/image.gif')
// if currently in /home/myself/node, it returns
'/home/myself/node/wwwroot/static_files/gif/image.gif'

path.isAbsolute(path)

Determines whether path is an absolute path. An absolute path will always resolve to the same location, regardless of the working directory.

Posix examples:

path.isAbsolute('/foo/bar') // true
path.isAbsolute('/baz/..')  // true
path.isAbsolute('qux/')     // false
path.isAbsolute('.')        // false

Windows examples:

path.isAbsolute('//server')  // true
path.isAbsolute('C:/foo/..') // true
path.isAbsolute('bar\\baz')   // false
path.isAbsolute('.')         // false

path.relative(from, to)

Solve the relative path from from to to.

At times we have two absolute paths, and we need to derive the relative path from one to the other. This is actually the reverse transform of path.resolve, which means we see that:

path.resolve(from, path.relative(from, to)) == path.resolve(to)

Examples:

path.relative('C:\\orandea\\test\\aaa', 'C:\\orandea\\impl\\bbb')
// returns
'..\\..\\impl\\bbb'

path.relative('/data/orandea/test/aaa', '/data/orandea/impl/bbb')
// returns
'../../impl/bbb'

path.dirname(p)

Return the directory name of a path. Similar to the Unix dirname command.

Example:

path.dirname('/foo/bar/baz/asdf/quux')
// returns
'/foo/bar/baz/asdf'

path.basename(p[, ext])

Return the last portion of a path. Similar to the Unix basename command.

Example:

path.basename('/foo/bar/baz/asdf/quux.html')
// returns
'quux.html'

path.basename('/foo/bar/baz/asdf/quux.html', '.html')
// returns
'quux'

path.extname(p)

Return the extension of the path, from the last ‘.’ to end of string in the last portion of the path. If there is no ‘.’ in the last portion of the path or the first character of it is ‘.’, then it returns an empty string. Examples:

path.extname('index.html')
// returns
'.html'

path.extname('index.coffee.md')
// returns
'.md'

path.extname('index.')
// returns
'.'

path.extname('index')
// returns
''

path.sep

The platform-specific file separator. '\\' or '/'.

An example on *nix:

'foo/bar/baz'.split(path.sep)
// returns
['foo', 'bar', 'baz']

An example on Windows:

'foo\\bar\\baz'.split(path.sep)
// returns
['foo', 'bar', 'baz']

path.delimiter

The platform-specific path delimiter, ; or ':'.

An example on *nix:

console.log(process.env.PATH)
// '/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin'

process.env.PATH.split(path.delimiter)
// returns
['/usr/bin', '/bin', '/usr/sbin', '/sbin', '/usr/local/bin']

An example on Windows:

console.log(process.env.PATH)
// 'C:\Windows\system32;C:\Windows;C:\Program Files\nodejs\'

process.env.PATH.split(path.delimiter)
// returns
['C:\\Windows\\system32', 'C:\\Windows', 'C:\\Program Files\\nodejs\\']

path.parse(pathString)

Returns an object from a path string.

An example on *nix:

path.parse('/home/user/dir/file.txt')
// returns
{
    root : "/",
    dir : "/home/user/dir",
    base : "file.txt",
    ext : ".txt",
    name : "file"
}

An example on Windows:

path.parse('C:\\path\\dir\\index.html')
// returns
{
    root : "C:\\",
    dir : "C:\\path\\dir",
    base : "index.html",
    ext : ".html",
    name : "index"
}

path.format(pathObject)

Returns a path string from an object, the opposite of path.parse above.

path.format({
    root : "/",
    dir : "/home/user/dir",
    base : "file.txt",
    ext : ".txt",
    name : "file"
})
// returns
'/home/user/dir/file.txt'

path.posix

Provide access to aforementioned path methods but always interact in a posix compatible way.

path.win32

Provide access to aforementioned path methods but always interact in a win32 compatible way.

process

The process object is a global object and can be accessed from anywhere. It is an instance of EventEmitter.

Exit Codes

Node will normally exit with a 0 status code when no more async operations are pending. The following status codes are used in other cases:

1 Uncaught Fatal Exception - There was an uncaught exception, and it was not handled by a domain or an uncaughtException event handler.

2 - Unused (reserved by Bash for builtin misuse)

3 Internal JavaScript Parse Error - The JavaScript source code internal in Node’s bootstrapping process caused a parse error. This is extremely rare, and generally can only happen during development of Node itself.

4 Internal JavaScript Evaluation Failure - The JavaScript source code internal in Node’s bootstrapping process failed to return a function value when evaluated. This is extremely rare, and generally can only happen during development of Node itself.

5 Fatal Error - There was a fatal unrecoverable error in V8. Typically a message will be printed to stderr with the prefix FATAL ERROR.

6 Non-function Internal Exception Handler - There was an uncaught exception, but the internal fatal exception handler function was somehow set to a non-function, and could not be called.

7 Internal Exception Handler Run-Time Failure - There was an uncaught exception, and the internal fatal exception handler function itself threw an error while attempting to handle it. This can happen, for example, if a process.on('uncaughtException') or domain.on('error') handler throws an error.

8 - Unused. In previous versions of Node, exit code 8 sometimes indicated an uncaught exception.

9 - Invalid Argument - Either an unknown option was specified, or an option requiring a value was provided without a value.

10 Internal JavaScript Run-Time Failure - The JavaScript source code internal in Node’s bootstrapping process threw an error when the bootstrapping function was called. This is extremely rare, and generally can only happen during development of Node itself.

12 Invalid Debug Argument - The --debug and/or --debug-brk options were set, but an invalid port number was chosen.

>128 Signal Exits - If Node receives a fatal signal such as SIGKILL or SIGHUP, then its exit code will be 128 plus the value of the signal code. This is a standard Unix practice, since exit codes are defined to be 7-bit integers, and signal exits set the high-order bit, and then contain the value of the signal code.

Event: ‘exit’

Emitted when the process is about to exit. There is no way to prevent the exiting of the event loop at this point, and once all exit listeners have finished running the process will exit. Therefore you must only perform synchronous operations in this handler. This is a good hook to perform checks on the module’s state (like for unit tests). The callback takes one argument, the code the process is exiting with.

Example of listening for exit:

process.on('exit', function(code) {
  // do *NOT* do this
  setTimeout(function() {
    console.log('This will not run');
  }, 0);
  console.log('About to exit with code:', code);
});

Event: ‘beforeExit’

This event is emitted when node empties it’s event loop and has nothing else to schedule. Normally, node exits when there is no work scheduled, but a listener for ‘beforeExit’ can make asynchronous calls, and cause node to continue.

‘beforeExit’ is not emitted for conditions causing explicit termination, such as process.exit() or uncaught exceptions, and should not be used as an alternative to the ‘exit’ event unless the intention is to schedule more work.

Event: ‘uncaughtException’

Emitted when an exception bubbles all the way back to the event loop. If a listener is added for this exception, the default action (which is to print a stack trace and exit) will not occur.

Example of listening for uncaughtException:

process.on('uncaughtException', function(err) {
  console.log('Caught exception: ' + err);
});

setTimeout(function() {
  console.log('This will still run.');
}, 500);

// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');

Note that uncaughtException is a very crude mechanism for exception handling.

Don’t use it, use domains instead. If you do use it, restart your application after every unhandled exception!

Do not use it as the node.js equivalent of On Error Resume Next. An unhandled exception means your application - and by extension node.js itself - is in an undefined state. Blindly resuming means anything could happen.

Think of resuming as pulling the power cord when you are upgrading your system. Nine out of ten times nothing happens - but the 10th time, your system is bust.

You have been warned.

Signal Events

Emitted when the processes receives a signal. See sigaction(2) for a list of standard POSIX signal names such as SIGINT, SIGHUP, etc.

Example of listening for SIGINT:

// Start reading from stdin so we don't exit.
process.stdin.resume();

process.on('SIGINT', function() {
  console.log('Got SIGINT.  Press Control-D to exit.');
});

An easy way to send the SIGINT signal is with Control-C in most terminal programs.

Note:

SIGUSR1 is reserved by node.js to start the debugger. It’s possible to install a listener but that won’t stop the debugger from starting.

SIGTERM and SIGINT have default handlers on non-Windows platforms that resets the terminal mode before exiting with code 128 + signal number. If one of these signals has a listener installed, its default behaviour will be removed (node will no longer exit).

SIGPIPE is ignored by default, it can have a listener installed.

SIGHUP is generated on Windows when the console window is closed, and on other platforms under various similar conditions, see signal(7). It can have a listener installed, however node will be unconditionally terminated by Windows about 10 seconds later. On non-Windows platforms, the default behaviour of SIGHUP is to terminate node, but once a listener has been installed its default behaviour will be removed.

SIGTERM is not supported on Windows, it can be listened on.

SIGINT from the terminal is supported on all platforms, and can usually be generated with CTRL+C (though this may be configurable). It is not generated when terminal raw mode is enabled.

SIGBREAK is delivered on Windows when CTRL+BREAK is pressed, on non-Windows platforms it can be listened on, but there is no way to send or generate it.

SIGWINCH is delivered when the console has been resized. On Windows, this will only happen on write to the console when the cursor is being moved, or when a readable tty is used in raw mode.

SIGKILL cannot have a listener installed, it will unconditionally terminate node on all platforms.

SIGSTOP cannot have a listener installed.

Note that Windows does not support sending Signals, but node offers some emulation with process.kill(), and child_process.kill(): - Sending signal 0 can be used to search for the existence of a process - Sending SIGINT, SIGTERM, and SIGKILL cause the unconditional exit of the target process.

process.stdout

A Writable Stream to stdout (on fd 1).

Example: the definition of console.log

console.log = function(d) {
  process.stdout.write(d + '\n');
};

process.stderr and process.stdout are unlike other streams in Node in that they cannot be closed (end() will throw), they never emit the finish event and that writes are usually blocking.

They are blocking in the case that they refer to regular files or TTY file descriptors.

In the case they refer to pipes:

They are blocking in Linux/Unix.

They are non-blocking like other streams in Windows.

To check if Node is being run in a TTY context, read the isTTY property on process.stderr, process.stdout, or process.stdin:

$ node -p "Boolean(process.stdin.isTTY)"
true
$ echo "foo" | node -p "Boolean(process.stdin.isTTY)"
false

$ node -p "Boolean(process.stdout.isTTY)"
true
$ node -p "Boolean(process.stdout.isTTY)" | cat
false

See the tty docs for more information.

process.stderr

A writable stream to stderr (on fd 2).

process.stderr and process.stdout are unlike other streams in Node in that they cannot be closed (end() will throw), they never emit the finish event and that writes are usually blocking.

They are blocking in the case that they refer to regular files or TTY file descriptors.

In the case they refer to pipes:

They are blocking in Linux/Unix.

They are non-blocking like other streams in Windows.

process.stdin

A Readable Stream for stdin (on fd 0).

Example of opening standard input and listening for both events:

process.stdin.setEncoding('utf8');

process.stdin.on('readable', function() {
  var chunk = process.stdin.read();
  if (chunk !== null) {
    process.stdout.write('data: ' + chunk);
  }
});

process.stdin.on('end', function() {
  process.stdout.write('end');
});

As a Stream, process.stdin can also be used in “old” mode that is compatible with scripts written for node prior v0.10. For more information see Stream compatibility.

In “old” Streams mode the stdin stream is paused by default, so one must call process.stdin.resume() to read from it. Note also that calling process.stdin.resume() itself would switch stream to “old” mode.

If you are starting a new project you should prefer a more recent “new” Streams mode over “old” one.

process.argv

An array containing the command line arguments. The first element will be ‘node’, the second element will be the name of the JavaScript file. The next elements will be any additional command line arguments.

// print process.argv
process.argv.forEach(function(val, index, array) {
  console.log(index + ': ' + val);
});

This will generate:

$ node process-2.js one two=three four
0: node
1: /Users/mjr/work/node/process-2.js
2: one
3: two=three
4: four

process.execPath

This is the absolute pathname of the executable that started the process.

Example:

/usr/local/bin/node

process.execArgv

This is the set of node-specific command line options from the executable that started the process. These options do not show up in process.argv, and do not include the node executable, the name of the script, or any options following the script name. These options are useful in order to spawn child processes with the same execution environment as the parent.

Example:

$ node --harmony script.js --version

results in process.execArgv:

['--harmony']

and process.argv:

['/usr/local/bin/node', 'script.js', '--version']

process.abort()

This causes node to emit an abort. This will cause node to exit and generate a core file.

process.chdir(directory)

Changes the current working directory of the process or throws an exception if that fails.

console.log('Starting directory: ' + process.cwd());
try {
  process.chdir('/tmp');
  console.log('New directory: ' + process.cwd());
}
catch (err) {
  console.log('chdir: ' + err);
}

process.cwd()

Returns the current working directory of the process.

console.log('Current directory: ' + process.cwd());

process.env

An object containing the user environment. See environ(7).

An example of this object looks like:

{ TERM: 'xterm-256color',
  SHELL: '/usr/local/bin/bash',
  USER: 'maciej',
  PATH: '~/.bin/:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin',
  PWD: '/Users/maciej',
  EDITOR: 'vim',
  SHLVL: '1',
  HOME: '/Users/maciej',
  LOGNAME: 'maciej',
  _: '/usr/local/bin/node' }

You can write to this object, but changes won’t be reflected outside of your process. That means that the following won’t work:

node -e 'process.env.foo = "bar"' && echo $foo

But this will:

process.env.foo = 'bar';
console.log(process.env.foo);

process.exit([code])

Ends the process with the specified code. If omitted, exit uses the ‘success’ code 0.

To exit with a ‘failure’ code:

process.exit(1);

The shell that executed node should see the exit code as 1.

process.exitCode

A number which will be the process exit code, when the process either exits gracefully, or is exited via process.exit() without specifying a code.

Specifying a code to process.exit(code) will override any previous setting of process.exitCode.

process.getgid()

Note: this function is only available on POSIX platforms (i.e. not Windows, Android)

Gets the group identity of the process. (See getgid(2).) This is the numerical group id, not the group name.

if (process.getgid) {
  console.log('Current gid: ' + process.getgid());
}

process.setgid(id)

Note: this function is only available on POSIX platforms (i.e. not Windows, Android)

Sets the group identity of the process. (See setgid(2).) This accepts either a numerical ID or a groupname string. If a groupname is specified, this method blocks while resolving it to a numerical ID.

if (process.getgid && process.setgid) {
  console.log('Current gid: ' + process.getgid());
  try {
    process.setgid(501);
    console.log('New gid: ' + process.getgid());
  }
  catch (err) {
    console.log('Failed to set gid: ' + err);
  }
}

process.getuid()

Note: this function is only available on POSIX platforms (i.e. not Windows, Android)

Gets the user identity of the process. (See getuid(2).) This is the numerical userid, not the username.

if (process.getuid) {
  console.log('Current uid: ' + process.getuid());
}

process.setuid(id)

Note: this function is only available on POSIX platforms (i.e. not Windows, Android)

Sets the user identity of the process. (See setuid(2).) This accepts either a numerical ID or a username string. If a username is specified, this method blocks while resolving it to a numerical ID.

if (process.getuid && process.setuid) {
  console.log('Current uid: ' + process.getuid());
  try {
    process.setuid(501);
    console.log('New uid: ' + process.getuid());
  }
  catch (err) {
    console.log('Failed to set uid: ' + err);
  }
}

process.getgroups()

Note: this function is only available on POSIX platforms (i.e. not Windows, Android)

Returns an array with the supplementary group IDs. POSIX leaves it unspecified if the effective group ID is included but node.js ensures it always is.

process.setgroups(groups)

Note: this function is only available on POSIX platforms (i.e. not Windows, Android)

Sets the supplementary group IDs. This is a privileged operation, meaning you need to be root or have the CAP_SETGID capability.

The list can contain group IDs, group names or both.

process.initgroups(user, extra_group)

Note: this function is only available on POSIX platforms (i.e. not Windows, Android)

Reads /etc/group and initializes the group access list, using all groups of which the user is a member. This is a privileged operation, meaning you need to be root or have the CAP_SETGID capability.

user is a user name or user ID. extra_group is a group name or group ID.

Some care needs to be taken when dropping privileges. Example:

console.log(process.getgroups());         // [ 0 ]
process.initgroups('bnoordhuis', 1000);   // switch user
console.log(process.getgroups());         // [ 27, 30, 46, 1000, 0 ]
process.setgid(1000);                     // drop root gid
console.log(process.getgroups());         // [ 27, 30, 46, 1000 ]

process.version

A compiled-in property that exposes NODE_VERSION.

console.log('Version: ' + process.version);

process.versions

A property exposing version strings of node and its dependencies.

console.log(process.versions);

Will print something like:

{ http_parser: '1.0',
  node: '0.10.4',
  v8: '3.14.5.8',
  ares: '1.9.0-DEV',
  uv: '0.10.3',
  zlib: '1.2.3',
  modules: '11',
  openssl: '1.0.1e' }

process.config

An Object containing the JavaScript representation of the configure options that were used to compile the current node executable. This is the same as the “config.gypi” file that was produced when running the ./configure script.

An example of the possible output looks like:

{ target_defaults:
   { cflags: [],
     default_configuration: 'Release',
     defines: [],
     include_dirs: [],
     libraries: [] },
  variables:
   { host_arch: 'x64',
     node_install_npm: 'true',
     node_prefix: '',
     node_shared_cares: 'false',
     node_shared_http_parser: 'false',
     node_shared_libuv: 'false',
     node_shared_v8: 'false',
     node_shared_zlib: 'false',
     node_use_dtrace: 'false',
     node_use_openssl: 'true',
     node_shared_openssl: 'false',
     strict_aliasing: 'true',
     target_arch: 'x64',
     v8_use_snapshot: 'true' } }

process.kill(pid[, signal])

Send a signal to a process. pid is the process id and signal is the string describing the signal to send. Signal names are strings like ‘SIGINT’ or ‘SIGHUP’. If omitted, the signal will be ‘SIGTERM’. See Signal Events and kill(2) for more information.

Will throw an error if target does not exist, and as a special case, a signal of 0 can be used to test for the existence of a process.

Note that just because the name of this function is process.kill, it is really just a signal sender, like the kill system call. The signal sent may do something other than kill the target process.

Example of sending a signal to yourself:

process.on('SIGHUP', function() {
  console.log('Got SIGHUP signal.');
});

setTimeout(function() {
  console.log('Exiting.');
  process.exit(0);
}, 100);

process.kill(process.pid, 'SIGHUP');

Note: When SIGUSR1 is received by Node.js it starts the debugger, see Signal Events.

process.pid

The PID of the process.

console.log('This process is pid ' + process.pid);

process.title

Getter/setter to set what is displayed in ‘ps’.

When used as a setter, the maximum length is platform-specific and probably short.

On Linux and OS X, it’s limited to the size of the binary name plus the length of the command line arguments because it overwrites the argv memory.

v0.8 allowed for longer process title strings by also overwriting the environ memory but that was potentially insecure/confusing in some (rather obscure) cases.

process.arch

What processor architecture you’re running on: 'arm', 'ia32', or 'x64'.

console.log('This processor architecture is ' + process.arch);

process.platform

What platform you’re running on: 'darwin', 'freebsd', 'linux', 'sunos' or 'win32'

console.log('This platform is ' + process.platform);

process.memoryUsage()

Returns an object describing the memory usage of the Node process measured in bytes.

var util = require('util');

console.log(util.inspect(process.memoryUsage()));

This will generate:

{ rss: 4935680,
  heapTotal: 1826816,
  heapUsed: 650472 }

heapTotal and heapUsed refer to V8’s memory usage.

process.nextTick(callback)

callback {Function}

Once the current event loop turn runs to completion, call the callback function.

This is not a simple alias to setTimeout(fn, 0), it’s much more efficient. It runs before any additional I/O events (including timers) fire in subsequent ticks of the event loop.

console.log('start');
process.nextTick(function() {
  console.log('nextTick callback');
});
console.log('scheduled');
// Output:
// start
// scheduled
// nextTick callback

This is important in developing APIs where you want to give the user the chance to assign event handlers after an object has been constructed, but before any I/O has occurred.

function MyThing(options) {
  this.setupOptions(options);

  process.nextTick(function() {
    this.startDoingStuff();
  }.bind(this));
}

var thing = new MyThing();
thing.getReadyForStuff();

// thing.startDoingStuff() gets called now, not before.

It is very important for APIs to be either 100% synchronous or 100% asynchronous. Consider this example:

// WARNING!  DO NOT USE!  BAD UNSAFE HAZARD!
function maybeSync(arg, cb) {
  if (arg) {
    cb();
    return;
  }

  fs.stat('file', cb);
}

This API is hazardous. If you do this:

maybeSync(true, function() {
  foo();
});
bar();

then it’s not clear whether foo() or bar() will be called first.

This approach is much better:

function definitelyAsync(arg, cb) {
  if (arg) {
    process.nextTick(cb);
    return;
  }

  fs.stat('file', cb);
}

Note: the nextTick queue is completely drained on each pass of the event loop before additional I/O is processed. As a result, recursively setting nextTick callbacks will block any I/O from happening, just like a while(true); loop.

process.umask([mask])

Sets or reads the process’s file mode creation mask. Child processes inherit the mask from the parent process. Returns the old mask if mask argument is given, otherwise returns the current mask.

var oldmask, newmask = 0022;

oldmask = process.umask(newmask);
console.log('Changed umask from: ' + oldmask.toString(8) +
            ' to ' + newmask.toString(8));

process.uptime()

Number of seconds Node has been running.

process.hrtime()

Returns the current high-resolution real time in a [seconds, nanoseconds] tuple Array. It is relative to an arbitrary time in the past. It is not related to the time of day and therefore not subject to clock drift. The primary use is for measuring performance between intervals.

You may pass in the result of a previous call to process.hrtime() to get a diff reading, useful for benchmarks and measuring intervals:

var time = process.hrtime();
// [ 1800216, 25 ]

setTimeout(function() {
  var diff = process.hrtime(time);
  // [ 1, 552 ]

  console.log('benchmark took %d nanoseconds', diff[0] * 1e9 + diff[1]);
  // benchmark took 1000000527 nanoseconds
}, 1000);

process.mainModule

Alternate way to retrieve require.main. The difference is that if the main module changes at runtime, require.main might still refer to the original main module in modules that were required before the change occurred. Generally it’s safe to assume that the two refer to the same module.

As with require.main, it will be undefined if there was no entry script.

punycode

Stability: 2 - Unstable

Punycode.js is bundled with Node.js v0.6.2+. Use require('punycode') to access it. (To use it with other Node.js versions, use npm to install the punycode module first.)

punycode.decode(string)

Converts a Punycode string of ASCII-only symbols to a string of Unicode symbols.

// decode domain name parts
punycode.decode('maana-pta'); // 'mañana'
punycode.decode('--dqo34k'); // '☃-⌘'

punycode.encode(string)

Converts a string of Unicode symbols to a Punycode string of ASCII-only symbols.

// encode domain name parts
punycode.encode('mañana'); // 'maana-pta'
punycode.encode('☃-⌘'); // '--dqo34k'

punycode.toUnicode(domain)

Converts a Punycode string representing a domain name to Unicode. Only the Punycoded parts of the domain name will be converted, i.e. it doesn’t matter if you call it on a string that has already been converted to Unicode.

// decode domain names
punycode.toUnicode('xn--maana-pta.com'); // 'mañana.com'
punycode.toUnicode('xn----dqo34k.com'); // '☃-⌘.com'

punycode.toASCII(domain)

Converts a Unicode string representing a domain name to Punycode. Only the non-ASCII parts of the domain name will be converted, i.e. it doesn’t matter if you call it with a domain that’s already in ASCII.

// encode domain names
punycode.toASCII('mañana.com'); // 'xn--maana-pta.com'
punycode.toASCII('☃-⌘.com'); // 'xn----dqo34k.com'

punycode.ucs2

punycode.ucs2.decode(string)

Creates an array containing the numeric code point values of each Unicode symbol in the string. While JavaScript uses UCS-2 internally, this function will convert a pair of surrogate halves (each of which UCS-2 exposes as separate characters) into a single code point, matching UTF-16.

punycode.ucs2.decode('abc'); // [0x61, 0x62, 0x63]
// surrogate pair for U+1D306 tetragram for centre:
punycode.ucs2.decode('\uD834\uDF06'); // [0x1D306]

punycode.ucs2.encode(codePoints)

Creates a string based on an array of numeric code point values.

punycode.ucs2.encode([0x61, 0x62, 0x63]); // 'abc'
punycode.ucs2.encode([0x1D306]); // '\uD834\uDF06'

punycode.version

A string representing the current Punycode.js version number.

Query String

Stability: 3 - Stable

This module provides utilities for dealing with query strings. It provides the following methods:

querystring.stringify(obj[, sep][, eq][, options])

Serialize an object to a query string. Optionally override the default separator ('&') and assignment ('=') characters.

Options object may contain encodeURIComponent property (querystring.escape by default), it can be used to encode string with non-utf8 encoding if necessary.

Example:

querystring.stringify({ foo: 'bar', baz: ['qux', 'quux'], corge: '' })
// returns
'foo=bar&baz=qux&baz=quux&corge='

querystring.stringify({foo: 'bar', baz: 'qux'}, ';', ':')
// returns
'foo:bar;baz:qux'

// Suppose gbkEncodeURIComponent function already exists,
// it can encode string with `gbk` encoding
querystring.stringify({ w: '中文', foo: 'bar' }, null, null,
  { encodeURIComponent: gbkEncodeURIComponent })
// returns
'w=%D6%D0%CE%C4&foo=bar'

querystring.parse(str[, sep][, eq][, options])

Deserialize a query string to an object. Optionally override the default separator ('&') and assignment ('=') characters.

Options object may contain maxKeys property (equal to 1000 by default), it’ll be used to limit processed keys. Set it to 0 to remove key count limitation.

Options object may contain decodeURIComponent property (querystring.unescape by default), it can be used to decode a non-utf8 encoding string if necessary.

Example:

querystring.parse('foo=bar&baz=qux&baz=quux&corge')
// returns
{ foo: 'bar', baz: ['qux', 'quux'], corge: '' }

// Suppose gbkDecodeURIComponent function already exists,
// it can decode `gbk` encoding string
querystring.parse('w=%D6%D0%CE%C4&foo=bar', null, null,
  { decodeURIComponent: gbkDecodeURIComponent })
// returns
{ w: '中文', foo: 'bar' }

querystring.escape

The escape function used by querystring.stringify, provided so that it could be overridden if necessary.

querystring.unescape

The unescape function used by querystring.parse, provided so that it could be overridden if necessary.

It will try to use decodeURIComponent in the first place, but if that fails it falls back to a safer equivalent that doesn’t throw on malformed URLs.

Readline

Stability: 2 - Unstable

To use this module, do require('readline'). Readline allows reading of a stream (such as process.stdin) on a line-by-line basis.

Note that once you’ve invoked this module, your node program will not terminate until you’ve closed the interface. Here’s how to allow your program to gracefully exit:

var readline = require('readline');

var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

rl.question("What do you think of node.js? ", function(answer) {
  // TODO: Log the answer in a database
  console.log("Thank you for your valuable feedback:", answer);

  rl.close();
});

readline.createInterface(options)

Creates a readline Interface instance. Accepts an “options” Object that takes the following values:

input - the readable stream to listen to (Required).

output - the writable stream to write readline data to (Optional).

completer - an optional function that is used for Tab autocompletion. See below for an example of using this.

terminal - pass true if the input and output streams should be treated like a TTY, and have ANSI/VT100 escape codes written to it. Defaults to checking isTTY on the output stream upon instantiation.

The completer function is given the current line entered by the user, and is supposed to return an Array with 2 entries:

An Array with matching entries for the completion.

The substring that was used for the matching.

Which ends up looking something like: [[substr1, substr2, ...], originalsubstring].

Example:

function completer(line) {
  var completions = '.help .error .exit .quit .q'.split(' ')
  var hits = completions.filter(function(c) { return c.indexOf(line) == 0 })
  // show all completions if none found
  return [hits.length ? hits : completions, line]
}

Also completer can be run in async mode if it accepts two arguments:

function completer(linePartial, callback) {
  callback(null, [['123'], linePartial]);
}

createInterface is commonly used with process.stdin and process.stdout in order to accept user input:

var readline = require('readline');
var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

Once you have a readline instance, you most commonly listen for the "line" event.

If terminal is true for this instance then the output stream will get the best compatibility if it defines an output.columns property, and fires a "resize" event on the output if/when the columns ever change (process.stdout does this automatically when it is a TTY).

Class: Interface

The class that represents a readline interface with an input and output stream.

rl.setPrompt(prompt)

Sets the prompt, for example when you run node on the command line, you see >, which is node’s prompt.

rl.prompt([preserveCursor])

Readies readline for input from the user, putting the current setPrompt options on a new line, giving the user a new spot to write. Set preserveCursor to true to prevent the cursor placement being reset to 0.

This will also resume the input stream used with createInterface if it has been paused.

If output is set to null or undefined when calling createInterface, the prompt is not written.

rl.question(query, callback)

Prepends the prompt with query and invokes callback with the user’s response. Displays the query to the user, and then invokes callback with the user’s response after it has been typed.

This will also resume the input stream used with createInterface if it has been paused.

If output is set to null or undefined when calling createInterface, nothing is displayed.

Example usage:

interface.question('What is your favorite food?', function(answer) {
  console.log('Oh, so your favorite food is ' + answer);
});

rl.pause()

Pauses the readline input stream, allowing it to be resumed later if needed.

Note that this doesn’t immediately pause the stream of events. Several events may be emitted after calling pause, including line.

rl.resume()

Resumes the readline input stream.

rl.close()

Closes the Interface instance, relinquishing control on the input and output streams. The “close” event will also be emitted.

rl.write(data[, key])

Writes data to output stream, unless output is set to null or undefined when calling createInterface. key is an object literal to represent a key sequence; available if the terminal is a TTY.

This will also resume the input stream if it has been paused.

Example:

rl.write('Delete me!');
// Simulate ctrl+u to delete the line written previously
rl.write(null, {ctrl: true, name: 'u'});

Events

Event: ‘line’

function (line) {}

Emitted whenever the input stream receives a \n, usually received when the user hits enter, or return. This is a good hook to listen for user input.

Example of listening for line:

rl.on('line', function (cmd) {
  console.log('You just typed: '+cmd);
});

Event: ‘pause’

function () {}

Emitted whenever the input stream is paused.

Also emitted whenever the input stream is not paused and receives the SIGCONT event. (See events SIGTSTP and SIGCONT)

Example of listening for pause:

rl.on('pause', function() {
  console.log('Readline paused.');
});

Event: ‘resume’

function () {}

Emitted whenever the input stream is resumed.

Example of listening for resume:

rl.on('resume', function() {
  console.log('Readline resumed.');
});

Event: ‘close’

function () {}

Emitted when close() is called.

Also emitted when the input stream receives its “end” event. The Interface instance should be considered “finished” once this is emitted. For example, when the input stream receives ^D, respectively known as EOT.

This event is also called if there is no SIGINT event listener present when the input stream receives a ^C, respectively known as SIGINT.

Event: ‘SIGINT’

function () {}

Emitted whenever the input stream receives a ^C, respectively known as SIGINT. If there is no SIGINT event listener present when the input stream receives a SIGINT, pause will be triggered.

Example of listening for SIGINT:

rl.on('SIGINT', function() {
  rl.question('Are you sure you want to exit?', function(answer) {
    if (answer.match(/^y(es)?$/i)) rl.pause();
  });
});

Event: ‘SIGTSTP’

function () {}

This does not work on Windows.

Emitted whenever the input stream receives a ^Z, respectively known as SIGTSTP. If there is no SIGTSTP event listener present when the input stream receives a SIGTSTP, the program will be sent to the background.

When the program is resumed with fg, the pause and SIGCONT events will be emitted. You can use either to resume the stream.

The pause and SIGCONT events will not be triggered if the stream was paused before the program was sent to the background.

Example of listening for SIGTSTP:

rl.on('SIGTSTP', function() {
  // This will override SIGTSTP and prevent the program from going to the
  // background.
  console.log('Caught SIGTSTP.');
});

Event: ‘SIGCONT’

function () {}

This does not work on Windows.

Emitted whenever the input stream is sent to the background with ^Z, respectively known as SIGTSTP, and then continued with fg(1). This event only emits if the stream was not paused before sending the program to the background.

Example of listening for SIGCONT:

rl.on('SIGCONT', function() {
  // `prompt` will automatically resume the stream
  rl.prompt();
});

Example: Tiny CLI

Here’s an example of how to use all these together to craft a tiny command line interface:

var readline = require('readline'),
    rl = readline.createInterface(process.stdin, process.stdout);

rl.setPrompt('OHAI> ');
rl.prompt();

rl.on('line', function(line) {
  switch(line.trim()) {
    case 'hello':
      console.log('world!');
      break;
    default:
      console.log('Say what? I might have heard `' + line.trim() + '`');
      break;
  }
  rl.prompt();
}).on('close', function() {
  console.log('Have a great day!');
  process.exit(0);
});

readline.cursorTo(stream, x, y)

Move cursor to the specified position in a given TTY stream.

readline.moveCursor(stream, dx, dy)

Move cursor relative to it’s current position in a given TTY stream.

readline.clearLine(stream, dir)

Clears current line of given TTY stream in a specified direction. dir should have one of following values:

-1 - to the left from cursor

1 - to the right from cursor

0 - the entire line

readline.clearScreenDown(stream)

Clears the screen from the current position of the cursor down.

REPL

Stability: 3 - Stable

A Read-Eval-Print-Loop (REPL) is available both as a standalone program and easily includable in other programs. The REPL provides a way to interactively run JavaScript and see the results. It can be used for debugging, testing, or just trying things out.

By executing node without any arguments from the command-line you will be dropped into the REPL. It has simplistic emacs line-editing.

mjr:~$ node
Type '.help' for options.
> a = [ 1, 2, 3];
[ 1, 2, 3 ]
> a.forEach(function (v) {
...   console.log(v);
...   });
1
2
3

For advanced line-editors, start node with the environmental variable NODE_NO_READLINE=1. This will start the main and debugger REPL in canonical terminal settings which will allow you to use with rlwrap.

For example, you could add this to your bashrc file:

alias node="env NODE_NO_READLINE=1 rlwrap node"

repl.start(options)

Returns and starts a REPLServer instance, that inherits from [Readline Interface][]. Accepts an “options” Object that takes the following values:

prompt - the prompt and stream for all I/O. Defaults to >.

input - the readable stream to listen to. Defaults to process.stdin.

output - the writable stream to write readline data to. Defaults to process.stdout.

terminal - pass true if the stream should be treated like a TTY, and have ANSI/VT100 escape codes written to it. Defaults to checking isTTY on the output stream upon instantiation.

eval - function that will be used to eval each given line. Defaults to an async wrapper for eval(). See below for an example of a custom eval.

useColors - a boolean which specifies whether or not the writer function should output colors. If a different writer function is set then this does nothing. Defaults to the repl’s terminal value.

useGlobal - if set to true, then the repl will use the global object, instead of running scripts in a separate context. Defaults to false.

ignoreUndefined - if set to true, then the repl will not output the return value of command if it’s undefined. Defaults to false.

writer - the function to invoke for each command that gets evaluated which returns the formatting (including coloring) to display. Defaults to util.inspect.

You can use your own eval function if it has following signature:

function eval(cmd, context, filename, callback) {
  callback(null, result);
}

Multiple REPLs may be started against the same running instance of node. Each will share the same global object but will have unique I/O.

Here is an example that starts a REPL on stdin, a Unix socket, and a TCP socket:

var net = require("net"),
    repl = require("repl");

connections = 0;

repl.start({
  prompt: "node via stdin> ",
  input: process.stdin,
  output: process.stdout
});

net.createServer(function (socket) {
  connections += 1;
  repl.start({
    prompt: "node via Unix socket> ",
    input: socket,
    output: socket
  }).on('exit', function() {
    socket.end();
  })
}).listen("/tmp/node-repl-sock");

net.createServer(function (socket) {
  connections += 1;
  repl.start({
    prompt: "node via TCP socket> ",
    input: socket,
    output: socket
  }).on('exit', function() {
    socket.end();
  });
}).listen(5001);

Running this program from the command line will start a REPL on stdin. Other REPL clients may connect through the Unix socket or TCP socket. telnet is useful for connecting to TCP sockets, and socat can be used to connect to both Unix and TCP sockets.

By starting a REPL from a Unix socket-based server instead of stdin, you can connect to a long-running node process without restarting it.

For an example of running a “full-featured” (terminal) REPL over a net.Server and net.Socket instance, see: https://gist.github.com/2209310

For an example of running a REPL instance over curl(1), see: https://gist.github.com/2053342

Event: ‘exit’

function () {}

Emitted when the user exits the REPL in any of the defined ways. Namely, typing .exit at the repl, pressing Ctrl+C twice to signal SIGINT, or pressing Ctrl+D to signal “end” on the input stream.

Example of listening for exit:

r.on('exit', function () {
  console.log('Got "exit" event from repl!');
  process.exit();
});

Event: ‘reset’

function (context) {}

Emitted when the REPL’s context is reset. This happens when you type .clear. If you start the repl with { useGlobal: true } then this event will never be emitted.

Example of listening for reset:

// Extend the initial repl context.
r = repl.start({ options ... });
someExtension.extend(r.context);

// When a new context is created extend it as well.
r.on('reset', function (context) {
  console.log('repl has a new context');
  someExtension.extend(context);
});

REPL Features

Inside the REPL, Control+D will exit. Multi-line expressions can be input. Tab completion is supported for both global and local variables.

The special variable _ (underscore) contains the result of the last expression.

> [ "a", "b", "c" ]
[ 'a', 'b', 'c' ]
> _.length
3
> _ += 1
4

The REPL provides access to any variables in the global scope. You can expose a variable to the REPL explicitly by assigning it to the context object associated with each REPLServer. For example:

// repl_test.js
var repl = require("repl"),
    msg = "message";

repl.start("> ").context.m = msg;

Things in the context object appear as local within the REPL:

mjr:~$ node repl_test.js
> m
'message'

There are a few special REPL commands:

.break - While inputting a multi-line expression, sometimes you get lost or just don’t care about completing it. .break will start over.

.clear - Resets the context object to an empty object and clears any multi-line expression.

.exit - Close the I/O stream, which will cause the REPL to exit.

.help - Show this list of special commands.

.save - Save the current REPL session to a file >.save ./file/to/save.js

.load - Load a file into the current REPL session. >.load ./file/to/load.js

The following key combinations in the REPL have these special effects:

<ctrl>C - Similar to the .break keyword. Terminates the current command. Press twice on a blank line to forcibly exit.

<ctrl>D - Similar to the .exit keyword.

Smalloc

Stability: 1 - Experimental

Class: smalloc

Buffers are backed by a simple allocator that only handles the assignation of external raw memory. Smalloc exposes that functionality.

smalloc.alloc(length[, receiver][, type])

length {Number} <= smalloc.kMaxLength

receiver {Object} Default: new Object

type {Enum} Default: Uint8

Returns receiver with allocated external array data. If no receiver is passed then a new Object will be created and returned.

This can be used to create your own Buffer-like classes. No other properties are set, so the user will need to keep track of other necessary information (e.g. length of the allocation).

function SimpleData(n) {
  this.length = n;
  smalloc.alloc(this.length, this);
}

SimpleData.prototype = { /* ... */ };

It only checks if the receiver is an Object, and also not an Array. Because of this it is possible to allocate external array data to more than a plain Object.

function allocMe() { }
smalloc.alloc(3, allocMe);

// { [Function allocMe] '0': 0, '1': 0, '2': 0 }

v8 does not support allocating external array data to an Array, and if passed will throw.

It’s possible to specify the type of external array data you would like. All possible options are listed in smalloc.Types. Example usage:

var doubleArr = smalloc.alloc(3, smalloc.Types.Double);

for (var i = 0; i < 3; i++)
  doubleArr = i / 10;

// { '0': 0, '1': 0.1, '2': 0.2 }

It is not possible to freeze, seal and prevent extensions of objects with external data using Object.freeze, Object.seal and Object.preventExtensions respectively.

smalloc.copyOnto(source, sourceStart, dest, destStart, copyLength);

source {Object} with external array allocation

sourceStart {Number} Position to begin copying from

dest {Object} with external array allocation

destStart {Number} Position to begin copying onto

copyLength {Number} Length of copy

Copy memory from one external array allocation to another. No arguments are optional, and any violation will throw.

var a = smalloc.alloc(4);
var b = smalloc.alloc(4);

for (var i = 0; i < 4; i++) {
  a[i] = i;
  b[i] = i * 2;
}

// { '0': 0, '1': 1, '2': 2, '3': 3 }
// { '0': 0, '1': 2, '2': 4, '3': 6 }

smalloc.copyOnto(b, 2, a, 0, 2);

// { '0': 4, '1': 6, '2': 2, '3': 3 }

copyOnto automatically detects the length of the allocation internally, so no need to set any additional properties for this to work.

smalloc.dispose(obj)

obj Object

Free memory that has been allocated to an object via smalloc.alloc.

var a = {};
smalloc.alloc(3, a);

// { '0': 0, '1': 0, '2': 0 }

smalloc.dispose(a);

// {}

This is useful to reduce strain on the garbage collector, but developers must be careful. Cryptic errors may arise in applications that are difficult to trace.

var a = smalloc.alloc(4);
var b = smalloc.alloc(4);

// perform this somewhere along the line
smalloc.dispose(b);

// now trying to copy some data out
smalloc.copyOnto(b, 2, a, 0, 2);

// now results in:
// RangeError: copy_length > source_length

After dispose() is called object still behaves as one with external data, for example smalloc.hasExternalData() returns true. dispose() does not support Buffers, and will throw if passed.

smalloc.hasExternalData(obj)

obj {Object}

Returns true if the obj has externally allocated memory.

smalloc.kMaxLength

Size of maximum allocation. This is also applicable to Buffer creation.

smalloc.Types

Enum of possible external array types. Contains:

Int8

Uint8

Int16

Uint16

Int32

Uint32

Float

Double

Uint8Clamped

Stream

Stability: 2 - Unstable

A stream is an abstract interface implemented by various objects in Node. For example a request to an HTTP server is a stream, as is stdout. Streams are readable, writable, or both. All streams are instances of EventEmitter

You can load the Stream base classes by doing require('stream'). There are base classes provided for Readable streams, Writable streams, Duplex streams, and Transform streams.

This document is split up into 3 sections. The first explains the parts of the API that you need to be aware of to use streams in your programs. If you never implement a streaming API yourself, you can stop there.

The second section explains the parts of the API that you need to use if you implement your own custom streams yourself. The API is designed to make this easy for you to do.

The third section goes into more depth about how streams work, including some of the internal mechanisms and functions that you should probably not modify unless you definitely know what you are doing.

API for Stream Consumers

Streams can be either Readable, Writable, or both (Duplex).

All streams are EventEmitters, but they also have other custom methods and properties depending on whether they are Readable, Writable, or Duplex.

If a stream is both Readable and Writable, then it implements all of the methods and events below. So, a Duplex or Transform stream is fully described by this API, though their implementation may be somewhat different.

It is not necessary to implement Stream interfaces in order to consume streams in your programs. If you are implementing streaming interfaces in your own program, please also refer to API for Stream Implementors below.

Almost all Node programs, no matter how simple, use Streams in some way. Here is an example of using Streams in a Node program:

var http = require('http');

var server = http.createServer(function (req, res) {
  // req is an http.IncomingMessage, which is a Readable Stream
  // res is an http.ServerResponse, which is a Writable Stream

  var body = '';
  // we want to get the data as utf8 strings
  // If you don't set an encoding, then you'll get Buffer objects
  req.setEncoding('utf8');

  // Readable streams emit 'data' events once a listener is added
  req.on('data', function (chunk) {
    body += chunk;
  });

  // the end event tells you that you have entire body
  req.on('end', function () {
    try {
      var data = JSON.parse(body);
    } catch (er) {
      // uh oh!  bad json!
      res.statusCode = 400;
      return res.end('error: ' + er.message);
    }

    // write back something interesting to the user:
    res.write(typeof data);
    res.end();
  });
});

server.listen(1337);

// $ curl localhost:1337 -d '{}'
// object
// $ curl localhost:1337 -d '"foo"'
// string
// $ curl localhost:1337 -d 'not json'
// error: Unexpected token o

Class: stream.Readable

The Readable stream interface is the abstraction for a source of data that you are reading from. In other words, data comes out of a Readable stream.

A Readable stream will not start emitting data until you indicate that you are ready to receive it.

Readable streams have two “modes”: a flowing mode and a paused mode. When in flowing mode, data is read from the underlying system and provided to your program as fast as possible. In paused mode, you must explicitly call stream.read() to get chunks of data out. Streams start out in paused mode.

Note: If no data event handlers are attached, and there are no pipe() destinations, and the stream is switched into flowing mode, then data will be lost.

You can switch to flowing mode by doing any of the following:

Adding a 'data' event handler to listen for data.

Calling the resume() method to explicitly open the flow.

Calling the pipe() method to send the data to a Writable.

You can switch back to paused mode by doing either of the following:

If there are no pipe destinations, by calling the pause() method.

If there are pipe destinations, by removing any 'data' event handlers, and removing all pipe destinations by calling the unpipe() method.

Note that, for backwards compatibility reasons, removing 'data' event handlers will not automatically pause the stream. Also, if there are piped destinations, then calling pause() will not guarantee that the stream will remain paused once those destinations drain and ask for more data.

Examples of readable streams include:

http responses, on the client

http requests, on the server

fs read streams

zlib streams

crypto streams

tcp sockets

child process stdout and stderr

process.stdin

Event: ‘readable’

When a chunk of data can be read from the stream, it will emit a 'readable' event.

In some cases, listening for a 'readable' event will cause some data to be read into the internal buffer from the underlying system, if it hadn’t already.

var readable = getReadableStreamSomehow();
readable.on('readable', function() {
  // there is some data to read now
});

Once the internal buffer is drained, a readable event will fire again when more data is available.

The readable event is not emitted in the “flowing” mode with the sole exception of the last one, on end-of-stream.

Event: ‘data’

chunk {Buffer | String} The chunk of data.

Attaching a data event listener to a stream that has not been explicitly paused will switch the stream into flowing mode. Data will then be passed as soon as it is available.

If you just want to get all the data out of the stream as fast as possible, this is the best way to do so.

var readable = getReadableStreamSomehow();
readable.on('data', function(chunk) {
  console.log('got %d bytes of data', chunk.length);
});

Note that the readable event should not be used together with data because the assigning the latter switches the stream into “flowing” mode, so the readable event will not be emitted.

Event: ‘end’

This event fires when there will be no more data to read.

Note that the end event will not fire unless the data is completely consumed. This can be done by switching into flowing mode, or by calling read() repeatedly until you get to the end.

var readable = getReadableStreamSomehow();
readable.on('data', function(chunk) {
  console.log('got %d bytes of data', chunk.length);
});
readable.on('end', function() {
  console.log('there will be no more data.');
});

Event: ‘close’

Emitted when the underlying resource (for example, the backing file descriptor) has been closed. Not all streams will emit this.

Event: ‘error’

{Error Object}

Emitted if there was an error receiving data.

readable.read([size])

size {Number} Optional argument to specify how much data to read.

Return {String | Buffer | null}

The read() method pulls some data out of the internal buffer and returns it. If there is no data available, then it will return null.

If you pass in a size argument, then it will return that many bytes. If size bytes are not available, then it will return null.

If you do not specify a size argument, then it will return all the data in the internal buffer.

This method should only be called in paused mode. In flowing mode, this method is called automatically until the internal buffer is drained.

var readable = getReadableStreamSomehow();
readable.on('readable', function() {
  var chunk;
  while (null !== (chunk = readable.read())) {
    console.log('got %d bytes of data', chunk.length);
  }
});

If this method returns a data chunk, then it will also trigger the emission of a 'data' event.

readable.setEncoding(encoding)

encoding {String} The encoding to use.

Return: this

Call this function to cause the stream to return strings of the specified encoding instead of Buffer objects. For example, if you do readable.setEncoding('utf8'), then the output data will be interpreted as UTF-8 data, and returned as strings. If you do readable.setEncoding('hex'), then the data will be encoded in hexadecimal string format.

This properly handles multi-byte characters that would otherwise be potentially mangled if you simply pulled the Buffers directly and called buf.toString(encoding) on them. If you want to read the data as strings, always use this method.

var readable = getReadableStreamSomehow();
readable.setEncoding('utf8');
readable.on('data', function(chunk) {
  assert.equal(typeof chunk, 'string');
  console.log('got %d characters of string data', chunk.length);
});

readable.resume()

Return: this

This method will cause the readable stream to resume emitting data events.

This method will switch the stream into flowing mode. If you do not want to consume the data from a stream, but you do want to get to its end event, you can call readable.resume() to open the flow of data.

var readable = getReadableStreamSomehow();
readable.resume();
readable.on('end', function(chunk) {
  console.log('got to the end, but did not read anything');
});

readable.pause()

Return: this

This method will cause a stream in flowing mode to stop emitting data events, switching out of flowing mode. Any data that becomes available will remain in the internal buffer.

var readable = getReadableStreamSomehow();
readable.on('data', function(chunk) {
  console.log('got %d bytes of data', chunk.length);
  readable.pause();
  console.log('there will be no more data for 1 second');
  setTimeout(function() {
    console.log('now data will start flowing again');
    readable.resume();
  }, 1000);
});

readable.isPaused()

Return: Boolean

This method returns whether or not the readable has been explicitly paused by client code (using readable.pause() without a corresponding readable.resume()).

var readable = new stream.Readable

readable.isPaused() // === false
readable.pause()
readable.isPaused() // === true
readable.resume()
readable.isPaused() // === false

readable.pipe(destination[, options])

destination {Writable Stream} The destination for writing data

options {Object} Pipe options

end {Boolean} End the writer when the reader ends. Default = true

This method pulls all the data out of a readable stream, and writes it to the supplied destination, automatically managing the flow so that the destination is not overwhelmed by a fast readable stream.

Multiple destinations can be piped to safely.

var readable = getReadableStreamSomehow();
var writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt'
readable.pipe(writable);

This function returns the destination stream, so you can set up pipe chains like so:

var r = fs.createReadStream('file.txt');
var z = zlib.createGzip();
var w = fs.createWriteStream('file.txt.gz');
r.pipe(z).pipe(w);

For example, emulating the Unix cat command:

process.stdin.pipe(process.stdout);

By default end() is called on the destination when the source stream emits end, so that destination is no longer writable. Pass { end: false } as options to keep the destination stream open.

This keeps writer open so that “Goodbye” can be written at the end.

reader.pipe(writer, { end: false });
reader.on('end', function() {
  writer.end('Goodbye\n');
});

Note that process.stderr and process.stdout are never closed until the process exits, regardless of the specified options.

readable.unpipe([destination])

destination {Writable Stream} Optional specific stream to unpipe

This method will remove the hooks set up for a previous pipe() call.

If the destination is not specified, then all pipes are removed.

If the destination is specified, but no pipe is set up for it, then this is a no-op.

var readable = getReadableStreamSomehow();
var writable = fs.createWriteStream('file.txt');
// All the data from readable goes into 'file.txt',
// but only for the first second
readable.pipe(writable);
setTimeout(function() {
  console.log('stop writing to file.txt');
  readable.unpipe(writable);
  console.log('manually close the file stream');
  writable.end();
}, 1000);

readable.unshift(chunk)

chunk {Buffer | String} Chunk of data to unshift onto the read queue

This is useful in certain cases where a stream is being consumed by a parser, which needs to “un-consume” some data that it has optimistically pulled out of the source, so that the stream can be passed on to some other party.

If you find that you must often call stream.unshift(chunk) in your programs, consider implementing a Transform stream instead. (See API for Stream Implementors, below.)

// Pull off a header delimited by \n\n
// use unshift() if we get too much
// Call the callback with (error, header, stream)
var StringDecoder = require('string_decoder').StringDecoder;
function parseHeader(stream, callback) {
  stream.on('error', callback);
  stream.on('readable', onReadable);
  var decoder = new StringDecoder('utf8');
  var header = '';
  function onReadable() {
    var chunk;
    while (null !== (chunk = stream.read())) {
      var str = decoder.write(chunk);
      if (str.match(/\n\n/)) {
        // found the header boundary
        var split = str.split(/\n\n/);
        header += split.shift();
        var remaining = split.join('\n\n');
        var buf = new Buffer(remaining, 'utf8');
        if (buf.length)
          stream.unshift(buf);
        stream.removeListener('error', callback);
        stream.removeListener('readable', onReadable);
        // now the body of the message can be read from the stream.
        callback(null, header, stream);
      } else {
        // still reading the header.
        header += str;
      }
    }
  }
}

readable.wrap(stream)

stream {Stream} An “old style” readable stream

Versions of Node prior to v0.10 had streams that did not implement the entire Streams API as it is today. (See “Compatibility” below for more information.)

If you are using an older Node library that emits 'data' events and has a pause() method that is advisory only, then you can use the wrap() method to create a Readable stream that uses the old stream as its data source.

You will very rarely ever need to call this function, but it exists as a convenience for interacting with old Node programs and libraries.

For example:

var OldReader = require('./old-api-module.js').OldReader;
var oreader = new OldReader;
var Readable = require('stream').Readable;
var myReader = new Readable().wrap(oreader);

myReader.on('readable', function() {
  myReader.read(); // etc.
});

Class: stream.Writable

The Writable stream interface is an abstraction for a destination that you are writing data to.

Examples of writable streams include:

http requests, on the client

http responses, on the server

fs write streams

zlib streams

crypto streams

tcp sockets

child process stdin

process.stdout, process.stderr

writable.write(chunk[, encoding][, callback])

chunk {String | Buffer} The data to write

encoding {String} The encoding, if chunk is a String

callback {Function} Callback for when this chunk of data is flushed

Returns: {Boolean} True if the data was handled completely.

This method writes some data to the underlying system, and calls the supplied callback once the data has been fully handled.

The return value indicates if you should continue writing right now. If the data had to be buffered internally, then it will return false. Otherwise, it will return true.

This return value is strictly advisory. You MAY continue to write, even if it returns false. However, writes will be buffered in memory, so it is best not to do this excessively. Instead, wait for the drain event before writing more data.

Event: ‘drain’

If a writable.write(chunk) call returns false, then the drain event will indicate when it is appropriate to begin writing more data to the stream.

// Write the data to the supplied writable stream 1MM times.
// Be attentive to back-pressure.
function writeOneMillionTimes(writer, data, encoding, callback) {
  var i = 1000000;
  write();
  function write() {
    var ok = true;
    do {
      i -= 1;
      if (i === 0) {
        // last time!
        writer.write(data, encoding, callback);
      } else {
        // see if we should continue, or wait
        // don't pass the callback, because we're not done yet.
        ok = writer.write(data, encoding);
      }
    } while (i > 0 && ok);
    if (i > 0) {
      // had to stop early!
      // write some more once it drains
      writer.once('drain', write);
    }
  }
}

writable.cork()

Forces buffering of all writes.

Buffered data will be flushed either at .uncork() or at .end() call.

writable.uncork()

Flush all data, buffered since .cork() call.

writable.setDefaultEncoding(encoding)

encoding {String} The new default encoding

Return: Boolean

Sets the default encoding for a writable stream. Returns true if the encoding is valid and is set. Otherwise returns false.

writable.end([chunk][, encoding][, callback])

chunk {String | Buffer} Optional data to write

encoding {String} The encoding, if chunk is a String

callback {Function} Optional callback for when the stream is finished

Call this method when no more data will be written to the stream. If supplied, the callback is attached as a listener on the finish event.

// write 'hello, ' and then end with 'world!'
var file = fs.createWriteStream('example.txt');
file.write('hello, ');
file.end('world!');

Calling write() after calling end() will raise an error:

// end with 'world!' and then write with 'hello, ' will raise an error
var file = fs.createWriteStream('example.txt');
file.end('world!');
file.write('hello, ');

Event: ‘finish’

When the end() method has been called, and all data has been flushed to the underlying system, this event is emitted.

var writer = getWritableStreamSomehow();
for (var i = 0; i < 100; i ++) {
  writer.write('hello, #' + i + '!\n');
}
writer.end('this is the end\n');
writer.on('finish', function() {
  console.error('all writes are now complete.');
});

Event: ‘pipe’

src {Readable Stream} source stream that is piping to this writable

This is emitted whenever the pipe() method is called on a readable stream, adding this writable to its set of destinations.

var writer = getWritableStreamSomehow();
var reader = getReadableStreamSomehow();
writer.on('pipe', function(src) {
  console.error('something is piping into the writer');
  assert.equal(src, reader);
});
reader.pipe(writer);

Event: ‘unpipe’

src {Readable Stream} The source stream that unpiped this writable

This is emitted whenever the unpipe() method is called on a readable stream, removing this writable from its set of destinations.

var writer = getWritableStreamSomehow();
var reader = getReadableStreamSomehow();
writer.on('unpipe', function(src) {
  console.error('something has stopped piping into the writer');
  assert.equal(src, reader);
});
reader.pipe(writer);
reader.unpipe(writer);

Event: ‘error’

{Error object}

Emitted if there was an error when writing or piping data.

Class: stream.Duplex

Duplex streams are streams that implement both the Readable and Writable interfaces. See above for usage.

Examples of Duplex streams include:

tcp sockets

zlib streams

crypto streams

Class: stream.Transform

Transform streams are Duplex streams where the output is in some way computed from the input. They implement both the Readable and Writable interfaces. See above for usage.

Examples of Transform streams include:

zlib streams

crypto streams

API for Stream Implementors

To implement any sort of stream, the pattern is the same:

Extend the appropriate parent class in your own subclass. (The util.inherits method is particularly helpful for this.)

Call the appropriate parent class constructor in your constructor, to be sure that the internal mechanisms are set up properly.

Implement one or more specific methods, as detailed below.

The class to extend and the method(s) to implement depend on the sort of stream class you are writing:

<tr>
  <th>
    <p>Use-case</p>
  </th>
  <th>
    <p>Class</p>
  </th>
  <th>
    <p>Method(s) to implement</p>
  </th>
</tr>

<td>
  <p>Reading only</p>
</td>
<td>
  <p>[Readable](#stream_class_stream_readable_1)</p>
</td>
<td>
  <p><code>[_read][]</code></p>
</td>

<td>
  <p>Writing only</p>
</td>
<td>
  <p>[Writable](#stream_class_stream_writable_1)</p>
</td>
<td>
  <p><code>[_write][]</code></p>
</td>

<td>
  <p>Reading and writing</p>
</td>
<td>
  <p>[Duplex](#stream_class_stream_duplex_1)</p>
</td>
<td>
  <p><code>[_read][]</code>, <code>[_write][]</code></p>
</td>

<td>
  <p>Operate on written data, then read the result</p>
</td>
<td>
  <p>[Transform](#stream_class_stream_transform_1)</p>
</td>
<td>
  <p><code>_transform</code>, <code>_flush</code></p>
</td>

In your implementation code, it is very important to never call the methods described in API for Stream Consumers above. Otherwise, you can potentially cause adverse side effects in programs that consume your streaming interfaces.

Class: stream.Readable

stream.Readable is an abstract class designed to be extended with an underlying implementation of the _read(size) method.

Please see above under API for Stream Consumers for how to consume streams in your programs. What follows is an explanation of how to implement Readable streams in your programs.

Example: A Counting Stream

This is a basic example of a Readable stream. It emits the numerals from 1 to 1,000,000 in ascending order, and then ends.

var Readable = require('stream').Readable;
var util = require('util');
util.inherits(Counter, Readable);

function Counter(opt) {
  Readable.call(this, opt);
  this._max = 1000000;
  this._index = 1;
}

Counter.prototype._read = function() {
  var i = this._index++;
  if (i > this._max)
    this.push(null);
  else {
    var str = '' + i;
    var buf = new Buffer(str, 'ascii');
    this.push(buf);
  }
};

Example: SimpleProtocol v1 (Sub-optimal)

This is similar to the parseHeader function described above, but implemented as a custom stream. Also, note that this implementation does not convert the incoming data to a string.

However, this would be better implemented as a Transform stream. See below for a better implementation.

// A parser for a simple data protocol.
// The "header" is a JSON object, followed by 2 \n characters, and
// then a message body.
//
// NOTE: This can be done more simply as a Transform stream!
// Using Readable directly for this is sub-optimal.  See the
// alternative example below under the Transform section.

var Readable = require('stream').Readable;
var util = require('util');

util.inherits(SimpleProtocol, Readable);

function SimpleProtocol(source, options) {
  if (!(this instanceof SimpleProtocol))
    return new SimpleProtocol(source, options);

  Readable.call(this, options);
  this._inBody = false;
  this._sawFirstCr = false;

  // source is a readable stream, such as a socket or file
  this._source = source;

  var self = this;
  source.on('end', function() {
    self.push(null);
  });

  // give it a kick whenever the source is readable
  // read(0) will not consume any bytes
  source.on('readable', function() {
    self.read(0);
  });

  this._rawHeader = [];
  this.header = null;
}

SimpleProtocol.prototype._read = function(n) {
  if (!this._inBody) {
    var chunk = this._source.read();

    // if the source doesn't have data, we don't have data yet.
    if (chunk === null)
      return this.push('');

    // check if the chunk has a \n\n
    var split = -1;
    for (var i = 0; i < chunk.length; i++) {
      if (chunk[i] === 10) { // '\n'
        if (this._sawFirstCr) {
          split = i;
          break;
        } else {
          this._sawFirstCr = true;
        }
      } else {
        this._sawFirstCr = false;
      }
    }

    if (split === -1) {
      // still waiting for the \n\n
      // stash the chunk, and try again.
      this._rawHeader.push(chunk);
      this.push('');
    } else {
      this._inBody = true;
      var h = chunk.slice(0, split);
      this._rawHeader.push(h);
      var header = Buffer.concat(this._rawHeader).toString();
      try {
        this.header = JSON.parse(header);
      } catch (er) {
        this.emit('error', new Error('invalid simple protocol data'));
        return;
      }
      // now, because we got some extra data, unshift the rest
      // back into the read queue so that our consumer will see it.
      var b = chunk.slice(split);
      this.unshift(b);

      // and let them know that we are done parsing the header.
      this.emit('header', this.header);
    }
  } else {
    // from there on, just provide the data to our consumer.
    // careful not to push(null), since that would indicate EOF.
    var chunk = this._source.read();
    if (chunk) this.push(chunk);
  }
};

// Usage:
// var parser = new SimpleProtocol(source);
// Now parser is a readable stream that will emit 'header'
// with the parsed header data.

new stream.Readable([options])

options {Object}

highWaterMark {Number} The maximum number of bytes to store in the internal buffer before ceasing to read from the underlying resource. Default=16kb, or 16 for objectMode streams

encoding {String} If specified, then buffers will be decoded to strings using the specified encoding. Default=null

objectMode {Boolean} Whether this stream should behave as a stream of objects. Meaning that stream.read(n) returns a single value instead of a Buffer of size n. Default=false

In classes that extend the Readable class, make sure to call the Readable constructor so that the buffering settings can be properly initialized.

readable._read(size)

size {Number} Number of bytes to read asynchronously

Note: Implement this function, but do NOT call it directly.

This function should NOT be called directly. It should be implemented by child classes, and only called by the internal Readable class methods.

All Readable stream implementations must provide a _read method to fetch data from the underlying resource.

This method is prefixed with an underscore because it is internal to the class that defines it, and should not be called directly by user programs. However, you are expected to override this method in your own extension classes.

When data is available, put it into the read queue by calling readable.push(chunk). If push returns false, then you should stop reading. When _read is called again, you should start pushing more data.

The size argument is advisory. Implementations where a “read” is a single call that returns data can use this to know how much data to fetch. Implementations where that is not relevant, such as TCP or TLS, may ignore this argument, and simply provide data whenever it becomes available. There is no need, for example to “wait” until size bytes are available before calling stream.push(chunk).

readable.push(chunk[, encoding])

chunk {Buffer | null | String} Chunk of data to push into the read queue

encoding {String} Encoding of String chunks. Must be a valid Buffer encoding, such as 'utf8' or 'ascii'

return {Boolean} Whether or not more pushes should be performed

Note: This function should be called by Readable implementors, NOT by consumers of Readable streams.

The _read() function will not be called again until at least one push(chunk) call is made.

The Readable class works by putting data into a read queue to be pulled out later by calling the read() method when the 'readable' event fires.

The push() method will explicitly insert some data into the read queue. If it is called with null then it will signal the end of the data (EOF).

This API is designed to be as flexible as possible. For example, you may be wrapping a lower-level source which has some sort of pause/resume mechanism, and a data callback. In those cases, you could wrap the low-level source object by doing something like this:

// source is an object with readStop() and readStart() methods,
// and an `ondata` member that gets called when it has data, and
// an `onend` member that gets called when the data is over.

util.inherits(SourceWrapper, Readable);

function SourceWrapper(options) {
  Readable.call(this, options);

  this._source = getLowlevelSourceObject();
  var self = this;

  // Every time there's data, we push it into the internal buffer.
  this._source.ondata = function(chunk) {
    // if push() returns false, then we need to stop reading from source
    if (!self.push(chunk))
      self._source.readStop();
  };

  // When the source ends, we push the EOF-signaling `null` chunk
  this._source.onend = function() {
    self.push(null);
  };
}

// _read will be called when the stream wants to pull more data in
// the advisory size argument is ignored in this case.
SourceWrapper.prototype._read = function(size) {
  this._source.readStart();
};

Class: stream.Writable

stream.Writable is an abstract class designed to be extended with an underlying implementation of the _write(chunk, encoding, callback) method.

Please see above under API for Stream Consumers for how to consume writable streams in your programs. What follows is an explanation of how to implement Writable streams in your programs.

new stream.Writable([options])

options {Object}

highWaterMark {Number} Buffer level when write() starts returning false. Default=16kb, or 16 for objectMode streams

decodeStrings {Boolean} Whether or not to decode strings into Buffers before passing them to _write(). Default=true

objectMode {Boolean} Whether or not the write(anyObj) is a valid operation. If set you can write arbitrary data instead of only Buffer / String data. Default=false

In classes that extend the Writable class, make sure to call the constructor so that the buffering settings can be properly initialized.

writable._write(chunk, encoding, callback)

chunk {Buffer | String} The chunk to be written. Will always be a buffer unless the decodeStrings option was set to false.

encoding {String} If the chunk is a string, then this is the encoding type. Ignore if chunk is a buffer. Note that chunk will always be a buffer unless the decodeStrings option is explicitly set to false.

callback {Function} Call this function (optionally with an error argument) when you are done processing the supplied chunk.

All Writable stream implementations must provide a _write() method to send data to the underlying resource.

Note: This function MUST NOT be called directly. It should be implemented by child classes, and called by the internal Writable class methods only.

Call the callback using the standard callback(error) pattern to signal that the write completed successfully or with an error.

If the decodeStrings flag is set in the constructor options, then chunk may be a string rather than a Buffer, and encoding will indicate the sort of string that it is. This is to support implementations that have an optimized handling for certain string data encodings. If you do not explicitly set the decodeStrings option to false, then you can safely ignore the encoding argument, and assume that chunk will always be a Buffer.

This method is prefixed with an underscore because it is internal to the class that defines it, and should not be called directly by user programs. However, you are expected to override this method in your own extension classes.

writable._writev(chunks, callback)

chunks {Array} The chunks to be written. Each chunk has following format: { chunk: ..., encoding: ... }.

callback {Function} Call this function (optionally with an error argument) when you are done processing the supplied chunks.

Note: This function MUST NOT be called directly. It may be implemented by child classes, and called by the internal Writable class methods only.

This function is completely optional to implement. In most cases it is unnecessary. If implemented, it will be called with all the chunks that are buffered in the write queue.

Class: stream.Duplex

A “duplex” stream is one that is both Readable and Writable, such as a TCP socket connection.

Note that stream.Duplex is an abstract class designed to be extended with an underlying implementation of the _read(size) and _write(chunk, encoding, callback) methods as you would with a Readable or Writable stream class.

Since JavaScript doesn’t have multiple prototypal inheritance, this class prototypally inherits from Readable, and then parasitically from Writable. It is thus up to the user to implement both the lowlevel _read(n) method as well as the lowlevel _write(chunk, encoding, callback) method on extension duplex classes.

new stream.Duplex(options)

options {Object} Passed to both Writable and Readable constructors. Also has the following fields:

allowHalfOpen {Boolean} Default=true. If set to false, then the stream will automatically end the readable side when the writable side ends and vice versa.

readableObjectMode {Boolean} Default=false. Sets objectMode for readable side of the stream. Has no effect if objectMode is true.

writableObjectMode {Boolean} Default=false. Sets objectMode for writable side of the stream. Has no effect if objectMode is true.

In classes that extend the Duplex class, make sure to call the constructor so that the buffering settings can be properly initialized.

Class: stream.Transform

A “transform” stream is a duplex stream where the output is causally connected in some way to the input, such as a zlib stream or a crypto stream.

There is no requirement that the output be the same size as the input, the same number of chunks, or arrive at the same time. For example, a Hash stream will only ever have a single chunk of output which is provided when the input is ended. A zlib stream will produce output that is either much smaller or much larger than its input.

Rather than implement the _read() and _write() methods, Transform classes must implement the _transform() method, and may optionally also implement the _flush() method. (See below.)

new stream.Transform([options])

options {Object} Passed to both Writable and Readable constructors.

In classes that extend the Transform class, make sure to call the constructor so that the buffering settings can be properly initialized.

transform._transform(chunk, encoding, callback)

chunk {Buffer | String} The chunk to be transformed. Will always be a buffer unless the decodeStrings option was set to false.

encoding {String} If the chunk is a string, then this is the encoding type. (Ignore if decodeStrings chunk is a buffer.)

callback {Function} Call this function (optionally with an error argument and data) when you are done processing the supplied chunk.

Note: This function MUST NOT be called directly. It should be implemented by child classes, and called by the internal Transform class methods only.

All Transform stream implementations must provide a _transform method to accept input and produce output.

_transform should do whatever has to be done in this specific Transform class, to handle the bytes being written, and pass them off to the readable portion of the interface. Do asynchronous I/O, process things, and so on.

Call transform.push(outputChunk) 0 or more times to generate output from this input chunk, depending on how much data you want to output as a result of this chunk.

Call the callback function only when the current chunk is completely consumed. Note that there may or may not be output as a result of any particular input chunk. If you supply a data chunk as the second argument to the callback function it will be passed to push method, in other words the following are equivalent:

transform.prototype._transform = function (data, encoding, callback) {
  this.push(data);
  callback();
}

transform.prototype._transform = function (data, encoding, callback) {
  callback(null, data);
}

This method is prefixed with an underscore because it is internal to the class that defines it, and should not be called directly by user programs. However, you are expected to override this method in your own extension classes.

transform._flush(callback)

callback {Function} Call this function (optionally with an error argument) when you are done flushing any remaining data.

Note: This function MUST NOT be called directly. It MAY be implemented by child classes, and if so, will be called by the internal Transform class methods only.

In some cases, your transform operation may need to emit a bit more data at the end of the stream. For example, a Zlib compression stream will store up some internal state so that it can optimally compress the output. At the end, however, it needs to do the best it can with what is left, so that the data will be complete.

In those cases, you can implement a _flush method, which will be called at the very end, after all the written data is consumed, but before emitting end to signal the end of the readable side. Just like with _transform, call transform.push(chunk) zero or more times, as appropriate, and call callback when the flush operation is complete.

This method is prefixed with an underscore because it is internal to the class that defines it, and should not be called directly by user programs. However, you are expected to override this method in your own extension classes.

Events: ‘finish’ and ‘end’

The finish and end events are from the parent Writable and Readable classes respectively. The finish event is fired after .end() is called and all chunks have been processed by _transform, end is fired after all data has been output which is after the callback in _flush has been called.

Example: SimpleProtocol parser v2

The example above of a simple protocol parser can be implemented simply by using the higher level Transform stream class, similar to the parseHeader and SimpleProtocol v1 examples above.

In this example, rather than providing the input as an argument, it would be piped into the parser, which is a more idiomatic Node stream approach.

var util = require('util');
var Transform = require('stream').Transform;
util.inherits(SimpleProtocol, Transform);

function SimpleProtocol(options) {
  if (!(this instanceof SimpleProtocol))
    return new SimpleProtocol(options);

  Transform.call(this, options);
  this._inBody = false;
  this._sawFirstCr = false;
  this._rawHeader = [];
  this.header = null;
}

SimpleProtocol.prototype._transform = function(chunk, encoding, done) {
  if (!this._inBody) {
    // check if the chunk has a \n\n
    var split = -1;
    for (var i = 0; i < chunk.length; i++) {
      if (chunk[i] === 10) { // '\n'
        if (this._sawFirstCr) {
          split = i;
          break;
        } else {
          this._sawFirstCr = true;
        }
      } else {
        this._sawFirstCr = false;
      }
    }

    if (split === -1) {
      // still waiting for the \n\n
      // stash the chunk, and try again.
      this._rawHeader.push(chunk);
    } else {
      this._inBody = true;
      var h = chunk.slice(0, split);
      this._rawHeader.push(h);
      var header = Buffer.concat(this._rawHeader).toString();
      try {
        this.header = JSON.parse(header);
      } catch (er) {
        this.emit('error', new Error('invalid simple protocol data'));
        return;
      }
      // and let them know that we are done parsing the header.
      this.emit('header', this.header);

      // now, because we got some extra data, emit this first.
      this.push(chunk.slice(split));
    }
  } else {
    // from there on, just provide the data to our consumer as-is.
    this.push(chunk);
  }
  done();
};

// Usage:
// var parser = new SimpleProtocol();
// source.pipe(parser)
// Now parser is a readable stream that will emit 'header'
// with the parsed header data.

Class: stream.PassThrough

This is a trivial implementation of a Transform stream that simply passes the input bytes across to the output. Its purpose is mainly for examples and testing, but there are occasionally use cases where it can come in handy as a building block for novel sorts of streams.

Streams: Under the Hood

Buffering

Both Writable and Readable streams will buffer data on an internal object called _writableState.buffer or _readableState.buffer, respectively.

The amount of data that will potentially be buffered depends on the highWaterMark option which is passed into the constructor.

Buffering in Readable streams happens when the implementation calls stream.push(chunk). If the consumer of the Stream does not call stream.read(), then the data will sit in the internal queue until it is consumed.

Buffering in Writable streams happens when the user calls stream.write(chunk) repeatedly, even when write() returns false.

The purpose of streams, especially with the pipe() method, is to limit the buffering of data to acceptable levels, so that sources and destinations of varying speed will not overwhelm the available memory.

stream.read(0)

There are some cases where you want to trigger a refresh of the underlying readable stream mechanisms, without actually consuming any data. In that case, you can call stream.read(0), which will always return null.

If the internal read buffer is below the highWaterMark, and the stream is not currently reading, then calling read(0) will trigger a low-level _read call.

There is almost never a need to do this. However, you will see some cases in Node’s internals where this is done, particularly in the Readable stream class internals.

stream.push('')

Pushing a zero-byte string or Buffer (when not in Object mode) has an interesting side effect. Because it is a call to stream.push(), it will end the reading process. However, it does not add any data to the readable buffer, so there’s nothing for a user to consume.

Very rarely, there are cases where you have no data to provide now, but the consumer of your stream (or, perhaps, another bit of your own code) will know when to check again, by calling stream.read(0). In those cases, you may call stream.push('').

So far, the only use case for this functionality is in the tls.CryptoStream class, which is deprecated in Node v0.12. If you find that you have to use stream.push(''), please consider another approach, because it almost certainly indicates that something is horribly wrong.

Compatibility with Older Node Versions

In versions of Node prior to v0.10, the Readable stream interface was simpler, but also less powerful and less useful.

Rather than waiting for you to call the read() method, 'data' events would start emitting immediately. If you needed to do some I/O to decide how to handle data, then you had to store the chunks in some kind of buffer so that they would not be lost.

The pause() method was advisory, rather than guaranteed. This meant that you still had to be prepared to receive 'data' events even when the stream was in a paused state.

In Node v0.10, the Readable class described below was added. For backwards compatibility with older Node programs, Readable streams switch into “flowing mode” when a 'data' event handler is added, or when the resume() method is called. The effect is that, even if you are not using the new read() method and 'readable' event, you no longer have to worry about losing 'data' chunks.

Most programs will continue to function normally. However, this introduces an edge case in the following conditions:

No 'data' event handler is added.

The resume() method is never called.

The stream is not piped to any writable destination.

For example, consider the following code:

// WARNING!  BROKEN!
net.createServer(function(socket) {

  // we add an 'end' method, but never consume the data
  socket.on('end', function() {
    // It will never get here.
    socket.end('I got your message (but didnt read it)\n');
  });

}).listen(1337);

In versions of node prior to v0.10, the incoming message data would be simply discarded. However, in Node v0.10 and beyond, the socket will remain paused forever.

The workaround in this situation is to call the resume() method to start the flow of data:

// Workaround
net.createServer(function(socket) {

  socket.on('end', function() {
    socket.end('I got your message (but didnt read it)\n');
  });

  // start the flow of data, discarding it.
  socket.resume();

}).listen(1337);

In addition to new Readable streams switching into flowing mode, pre-v0.10 style streams can be wrapped in a Readable class using the wrap() method.

Object Mode

Normally, Streams operate on Strings and Buffers exclusively.

Streams that are in object mode can emit generic JavaScript values other than Buffers and Strings.

A Readable stream in object mode will always return a single item from a call to stream.read(size), regardless of what the size argument is.

A Writable stream in object mode will always ignore the encoding argument to stream.write(data, encoding).

The special value null still retains its special value for object mode streams. That is, for object mode readable streams, null as a return value from stream.read() indicates that there is no more data, and stream.push(null) will signal the end of stream data (EOF).

No streams in Node core are object mode streams. This pattern is only used by userland streaming libraries.

You should set objectMode in your stream child class constructor on the options object. Setting objectMode mid-stream is not safe.

For Duplex streams objectMode can be set exclusively for readable or writable side with readableObjectMode and writableObjectMode respectively. These options can be used to implement parsers and serializers with Transform streams.

var util = require('util');
var StringDecoder = require('string_decoder').StringDecoder;
var Transform = require('stream').Transform;
util.inherits(JSONParseStream, Transform);

// Gets \n-delimited JSON string data, and emits the parsed objects
function JSONParseStream() {
  if (!(this instanceof JSONParseStream))
    return new JSONParseStream();

  Transform.call(this, { readableObjectMode : true });

  this._buffer = '';
  this._decoder = new StringDecoder('utf8');
}

JSONParseStream.prototype._transform = function(chunk, encoding, cb) {
  this._buffer += this._decoder.write(chunk);
  // split on newlines
  var lines = this._buffer.split(/\r?\n/);
  // keep the last partial line buffered
  this._buffer = lines.pop();
  for (var l = 0; l < lines.length; l++) {
    var line = lines[l];
    try {
      var obj = JSON.parse(line);
    } catch (er) {
      this.emit('error', er);
      return;
    }
    // push the parsed object out to the readable consumer
    this.push(obj);
  }
  cb();
};

JSONParseStream.prototype._flush = function(cb) {
  // Just handle any leftover
  var rem = this._buffer.trim();
  if (rem) {
    try {
      var obj = JSON.parse(rem);
    } catch (er) {
      this.emit('error', er);
      return;
    }
    // push the parsed object out to the readable consumer
    this.push(obj);
  }
  cb();
};

StringDecoder

Stability: 3 - Stable

To use this module, do require('string_decoder'). StringDecoder decodes a buffer to a string. It is a simple interface to buffer.toString() but provides additional support for utf8.

var StringDecoder = require('string_decoder').StringDecoder;
var decoder = new StringDecoder('utf8');

var cent = new Buffer([0xC2, 0xA2]);
console.log(decoder.write(cent));

var euro = new Buffer([0xE2, 0x82, 0xAC]);
console.log(decoder.write(euro));

Class: StringDecoder

Accepts a single argument, encoding which defaults to utf8.

decoder.write(buffer)

Returns a decoded string.

decoder.end()

Returns any trailing bytes that were left in the buffer.

Timers

Stability: 5 - Locked

All of the timer functions are globals. You do not need to require() this module in order to use them.

setTimeout(callback, delay[, arg][, …])

To schedule execution of a one-time callback after delay milliseconds. Returns a timeoutObject for possible use with clearTimeout(). Optionally you can also pass arguments to the callback.

It is important to note that your callback will probably not be called in exactly delay milliseconds - Node.js makes no guarantees about the exact timing of when the callback will fire, nor of the ordering things will fire in. The callback will be called as close as possible to the time specified.

clearTimeout(timeoutObject)

Prevents a timeout from triggering.

setInterval(callback, delay[, arg][, …])

To schedule the repeated execution of callback every delay milliseconds. Returns a intervalObject for possible use with clearInterval(). Optionally you can also pass arguments to the callback.

clearInterval(intervalObject)

Stops an interval from triggering.

unref()

The opaque value returned by setTimeout and setInterval also has the method timer.unref() which will allow you to create a timer that is active but if it is the only item left in the event loop won’t keep the program running. If the timer is already unrefd calling unref again will have no effect.

In the case of setTimeout when you unref you create a separate timer that will wakeup the event loop, creating too many of these may adversely effect event loop performance – use wisely.

ref()

If you had previously unref()d a timer you can call ref() to explicitly request the timer hold the program open. If the timer is already refd calling ref again will have no effect.

setImmediate(callback[, arg][, …])

To schedule the “immediate” execution of callback after I/O events callbacks and before setTimeout and setInterval . Returns an immediateObject for possible use with clearImmediate(). Optionally you can also pass arguments to the callback.

Callbacks for immediates are queued in the order in which they were created. The entire callback queue is processed every event loop iteration. If you queue an immediate from inside an executing callback, that immediate won’t fire until the next event loop iteration.

clearImmediate(immediateObject)

Stops an immediate from triggering.

TLS (SSL)

Stability: 3 - Stable

Use require('tls') to access this module.

The tls module uses OpenSSL to provide Transport Layer Security and/or Secure Socket Layer: encrypted stream communication.

TLS/SSL is a public/private key infrastructure. Each client and each server must have a private key. A private key is created like this:

openssl genrsa -out ryans-key.pem 2048

All servers and some clients need to have a certificate. Certificates are public keys signed by a Certificate Authority or self-signed. The first step to getting a certificate is to create a “Certificate Signing Request” (CSR) file. This is done with:

openssl req -new -sha256 -key ryans-key.pem -out ryans-csr.pem

To create a self-signed certificate with the CSR, do this:

openssl x509 -req -in ryans-csr.pem -signkey ryans-key.pem -out ryans-cert.pem

Alternatively you can send the CSR to a Certificate Authority for signing.

For Perfect Forward Secrecy, it is required to generate Diffie-Hellman parameters:

openssl dhparam -outform PEM -out dhparam.pem 2048

To create .pfx or .p12, do this:

openssl pkcs12 -export -in agent5-cert.pem -inkey agent5-key.pem \
    -certfile ca-cert.pem -out agent5.pfx

in: certificate

inkey: private key

certfile: all CA certs concatenated in one file like cat ca1-cert.pem ca2-cert.pem > ca-cert.pem

Protocol support

Node.js is compiled with SSLv2 and SSLv3 protocol support by default, but these protocols are disabled. They are considered insecure and could be easily compromised as was shown by CVE-2014-3566. However, in some situations, it may cause problems with legacy clients/servers (such as Internet Explorer 6). If you wish to enable SSLv2 or SSLv3, run node with the --enable-ssl2 or --enable-ssl3 flag respectively. In future versions of Node.js SSLv2 and SSLv3 will not be compiled in by default.

There is a way to force node into using SSLv3 or SSLv2 only mode by explicitly specifying secureProtocol to 'SSLv3_method' or 'SSLv2_method'.

The default protocol method Node.js uses is SSLv23_method which would be more accurately named AutoNegotiate_method. This method will try and negotiate from the highest level down to whatever the client supports. To provide a secure default, Node.js (since v0.10.33) explicitly disables the use of SSLv3 and SSLv2 by setting the secureOptions to be SSL_OP_NO_SSLv3|SSL_OP_NO_SSLv2 (again, unless you have passed --enable-ssl3, or --enable-ssl2, or SSLv3_method as secureProtocol).

If you have set secureOptions to anything, we will not override your options.

The ramifications of this behavior change:

If your application is behaving as a secure server, clients who are SSLv3 only will now not be able to appropriately negotiate a connection and will be refused. In this case your server will emit a clientError event. The error message will include 'wrong version number'.

If your application is behaving as a secure client and communicating with a server that doesn’t support methods more secure than SSLv3 then your connection won’t be able to negotiate and will fail. In this case your client will emit a an error event. The error message will include 'wrong version number'.

Client-initiated renegotiation attack mitigation

The TLS protocol lets the client renegotiate certain aspects of the TLS session. Unfortunately, session renegotiation requires a disproportional amount of server-side resources, which makes it a potential vector for denial-of-service attacks.

To mitigate this, renegotiations are limited to three times every 10 minutes. An error is emitted on the tls.TLSSocket instance when the threshold is exceeded. The limits are configurable:

tls.CLIENT_RENEG_LIMIT: renegotiation limit, default is 3.

tls.CLIENT_RENEG_WINDOW: renegotiation window in seconds, default is 10 minutes.

Don’t change the defaults unless you know what you are doing.

To test your server, connect to it with openssl s_client -connect address:port and tap R<CR> (that’s the letter R followed by a carriage return) a few times.

NPN and SNI

NPN (Next Protocol Negotiation) and SNI (Server Name Indication) are TLS handshake extensions allowing you:

NPN - to use one TLS server for multiple protocols (HTTP, SPDY)

SNI - to use one TLS server for multiple hostnames with different SSL certificates.

Perfect Forward Secrecy

The term “Forward Secrecy” or “Perfect Forward Secrecy” describes a feature of key-agreement (i.e. key-exchange) methods. Practically it means that even if the private key of a (your) server is compromised, communication can only be decrypted by eavesdroppers if they manage to obtain the key-pair specifically generated for each session.

This is achieved by randomly generating a key pair for key-agreement on every handshake (in contrary to the same key for all sessions). Methods implementing this technique, thus offering Perfect Forward Secrecy, are called “ephemeral”.

Currently two methods are commonly used to achieve Perfect Forward Secrecy (note the character “E” appended to the traditional abbreviations):

DHE - An ephemeral version of the Diffie Hellman key-agreement protocol.

ECDHE - An ephemeral version of the Elliptic Curve Diffie Hellman key-agreement protocol.

Ephemeral methods may have some performance drawbacks, because key generation is expensive.

Modifying the Default Cipher Suite

Node.js is built with a default suite of enabled and disabled ciphers. Currently, the default cipher suite is:

ECDHE-RSA-AES256-SHA384:DHE-RSA-AES256-SHA384:ECDHE-RSA-AES256-SHA256:
DHE-RSA-AES256-SHA256:ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:
HIGH:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!SRP:!CAMELLIA

This default can be overridden entirely using the --cipher-list command line switch or NODE_CIPHER_LIST environment variable. For instance:

node --cipher-list=ECDHE-RSA-AES256-SHA384:DHE-RSA-AES256-SHA384

Setting the environment variable would have the same effect:

NODE_CIPHER_LIST=ECDHE-RSA-AES256-SHA384:DHE-RSA-AES256-SHA384

CAUTION: The default cipher suite has been carefully selected to reflect current security best practices and risk mitigation. Changing the default cipher suite can have a significant impact on the security of an application. The --cipher-list and NODE_CIPHER_LIST options should only be used if absolutely necessary.

Using Legacy Default Cipher Suite

It is possible for the built-in default cipher suite to change from one release of Node.js to another. For instance, v0.10.38 uses a different default than v0.12.2. Such changes can cause issues with applications written to assume certain specific defaults. To help buffer applications against such changes, the --enable-legacy-cipher-list command line switch or NODE_LEGACY_CIPHER_LIST environment variable can be set to specify a specific preset default:

# Use the v0.10.38 defaults
node --enable-legacy-cipher-list=v0.10.38
// or
NODE_LEGACY_CIPHER_LIST=v0.10.38

# Use the v0.12.2 defaults
node --enable-legacy-cipher-list=v0.12.2
// or
NODE_LEGACY_CIPHER_LIST=v0.12.2

Currently, the values supported for the enable-legacy-cipher-list switch and NODE_LEGACY_CIPHER_LIST environment variable include:

v0.10.38 - To enable the default cipher suite used in v0.10.38

  ECDHE-RSA-AES128-SHA256:AES128-GCM-SHA256:RC4:HIGH:!MD5:!aNULL:!EDH

v0.10.39 - To enable the default cipher suite used in v0.10.39

  ECDHE-RSA-AES128-SHA256:AES128-GCM-SHA256:HIGH:!RC4:!MD5:!aNULL:!EDH

v0.12.2 - To enable the default cipher suite used in v0.12.2

  ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:AES128-GCM-SHA256:RC4:
  HIGH:!MD5:!aNULL

v.0.12.3 - To enable the default cipher suite used in v0.12.3

  ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:AES128-GCM-SHA256:HIGH:
  !RC4:!MD5:!aNULL

These legacy cipher suites are also made available for use via the getLegacyCiphers() method:

var tls = require('tls');
console.log(tls.getLegacyCiphers('v0.10.38'));

CAUTION: Changes to the default cipher suite are typically made in order to strengthen the default security for applications running within Node.js. Reverting back to the defaults used by older releases can weaken the security of your applications. The legacy cipher suites should only be used if absolutely necessary.

tls.getCiphers()

Returns an array with the names of the supported SSL ciphers.

Example:

var ciphers = tls.getCiphers();
console.log(ciphers); // ['AES128-SHA', 'AES256-SHA', ...]

tls.getLegacyCiphers(version)

Returns the legacy default cipher suite for the specified Node.js release.

Example: var cipher_suite = tls.getLegacyCiphers(‘v0.10.38’);

tls.createServer(options[, secureConnectionListener])

Creates a new tls.Server. The connectionListener argument is automatically set as a listener for the secureConnection event. The options object has these possibilities:

pfx: A string or Buffer containing the private key, certificate and CA certs of the server in PFX or PKCS12 format. (Mutually exclusive with the key, cert and ca options.)

key: A string or Buffer containing the private key of the server in PEM format. (Could be an array of keys). (Required)

passphrase: A string of passphrase for the private key or pfx.

cert: A string or Buffer containing the certificate key of the server in PEM format. (Could be an array of certs). (Required)

ca: An array of strings or Buffers of trusted certificates in PEM format. If this is omitted several well known “root” CAs will be used, like VeriSign. These are used to authorize connections.

crl : Either a string or list of strings of PEM encoded CRLs (Certificate Revocation List)

ciphers: A string describing the ciphers to use or exclude, separated by :. The default cipher suite is:

ECDHE-RSA-AES256-SHA384:DHE-RSA-AES256-SHA384:ECDHE-RSA-AES256-SHA256:
DHE-RSA-AES256-SHA256:ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:
HIGH:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!SRP:!CAMELLIA

The default cipher suite prefers ECDHE and DHE ciphers for Perfect Forward secrecy, while offering some backward compatibility. Old clients which rely on insecure and deprecated RC4 or DES-based ciphers (like Internet Explorer 6) aren’t able to complete the handshake with the default configuration. If you absolutely must support these clients, the TLS recommendations may offer a compatible cipher suite. For more details on the format, see the OpenSSL cipher list format documentation.

ecdhCurve: A string describing a named curve to use for ECDH key agreement or false to disable ECDH.

Defaults to prime256v1. Consult RFC 4492 for more details.

dhparam: DH parameter file to use for DHE key agreement. Use openssl dhparam command to create it. If the file is invalid to load, it is silently discarded.

handshakeTimeout: Abort the connection if the SSL/TLS handshake does not finish in this many milliseconds. The default is 120 seconds.

A 'clientError' is emitted on the tls.Server object whenever a handshake times out.

honorCipherOrder : When choosing a cipher, use the server’s preferences instead of the client preferences. Default: true.

Although, this option is disabled by default, it is recommended that you use this option in conjunction with the ciphers option to mitigate BEAST attacks.

Note: If SSLv2 is used, the server will send its list of preferences to the client, and the client chooses the cipher. Support for SSLv2 is disabled unless node.js was configured with ./configure --with-sslv2.

requestCert: If true the server will request a certificate from clients that connect and attempt to verify that certificate. Default: false.

rejectUnauthorized: If true the server will reject any connection which is not authorized with the list of supplied CAs. This option only has an effect if requestCert is true. Default: false.

checkServerIdentity(servername, cert): Provide an override for checking server’s hostname against the certificate. Should return an error if verification fails. Return undefined if passing.

NPNProtocols: An array or Buffer of possible NPN protocols. (Protocols should be ordered by their priority).

SNICallback(servername, cb): A function that will be called if client supports SNI TLS extension. Two argument will be passed to it: servername, and cb. SNICallback should invoke cb(null, ctx), where ctx is a SecureContext instance. (You can use tls.createSecureContext(...) to get proper SecureContext). If SNICallback wasn’t provided - default callback with high-level API will be used (see below).

sessionTimeout: An integer specifying the seconds after which TLS session identifiers and TLS session tickets created by the server are timed out. See SSL_CTX_set_timeout for more details.

ticketKeys: A 48-byte Buffer instance consisting of 16-byte prefix, 16-byte hmac key, 16-byte AES key. You could use it to accept tls session tickets on multiple instances of tls server.

NOTE: Automatically shared between cluster module workers.

sessionIdContext: A string containing an opaque identifier for session resumption. If requestCert is true, the default is MD5 hash value generated from command-line. Otherwise, the default is not provided.

secureProtocol: The SSL method to use, e.g. SSLv3_method to force SSL version 3. The possible values depend on your installation of OpenSSL and are defined in the constant SSL_METHODS.

secureOptions: Set server options. For example, to disable the SSLv3 protocol set the SSL_OP_NO_SSLv3 flag. See SSL_CTX_set_options for all available options.

Here is a simple example echo server:

var tls = require('tls');
var fs = require('fs');

var options = {
  key: fs.readFileSync('server-key.pem'),
  cert: fs.readFileSync('server-cert.pem'),

  // This is necessary only if using the client certificate authentication.
  requestCert: true,

  // This is necessary only if the client uses the self-signed certificate.
  ca: [ fs.readFileSync('client-cert.pem') ]
};

var server = tls.createServer(options, function(socket) {
  console.log('server connected',
              socket.authorized ? 'authorized' : 'unauthorized');
  socket.write("welcome!\n");
  socket.setEncoding('utf8');
  socket.pipe(socket);
});
server.listen(8000, function() {
  console.log('server bound');
});

Or

var tls = require('tls');
var fs = require('fs');

var options = {
  pfx: fs.readFileSync('server.pfx'),

  // This is necessary only if using the client certificate authentication.
  requestCert: true,

};

var server = tls.createServer(options, function(socket) {
  console.log('server connected',
              socket.authorized ? 'authorized' : 'unauthorized');
  socket.write("welcome!\n");
  socket.setEncoding('utf8');
  socket.pipe(socket);
});
server.listen(8000, function() {
  console.log('server bound');
});

You can test this server by connecting to it with openssl s_client:

openssl s_client -connect 127.0.0.1:8000

tls.connect(options[, callback])

tls.connect(port[, host][, options][, callback])

Creates a new client connection to the given port and host (old API) or options.port and options.host. (If host is omitted, it defaults to localhost.) options should be an object which specifies:

host: Host the client should connect to

port: Port the client should connect to

socket: Establish secure connection on a given socket rather than creating a new socket. If this option is specified, host and port are ignored.

path: Creates unix socket connection to path. If this option is specified, host and port are ignored.

ciphers: A string describing the ciphers to use or exclude.

Defaults to ECDHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA256:AES128-GCM-SHA256:HIGH:!RC4:!MD5:!aNULL. Consult the OpenSSL cipher list format documentation for details on the format.

The full list of available ciphers can be obtained via tls.getCiphers.

ECDHE-RSA-AES128-SHA256, DHE-RSA-AES128-SHA256 and AES128-GCM-SHA256 are TLS v1.2 ciphers and used when Node.js is linked against OpenSSL 1.0.1 or newer, such as the bundled version of OpenSSL.

pfx: A string or Buffer containing the private key, certificate and CA certs of the client in PFX or PKCS12 format.

key: A string or Buffer containing the private key of the client in PEM format. (Could be an array of keys).

passphrase: A string of passphrase for the private key or pfx.

cert: A string or Buffer containing the certificate key of the client in PEM format. (Could be an array of certs).

ca: An array of strings or Buffers of trusted certificates in PEM format. If this is omitted several well known “root” CAs will be used, like VeriSign. These are used to authorize connections.

rejectUnauthorized: If true, the server certificate is verified against the list of supplied CAs. An 'error' event is emitted if verification fails; err.code contains the OpenSSL error code. Default: true.

NPNProtocols: An array of strings or Buffers containing supported NPN protocols. Buffers should have following format: 0x05hello0x05world, where first byte is next protocol name’s length. (Passing array should usually be much simpler: ['hello', 'world'].)

servername: Servername for SNI (Server Name Indication) TLS extension.

secureProtocol: The SSL method to use, e.g. SSLv3_method to force SSL version 3. The possible values depend on your installation of OpenSSL and are defined in the constant SSL_METHODS.

session: A Buffer instance, containing TLS session.

The callback parameter will be added as a listener for the ‘secureConnect’ event.

tls.connect() returns a tls.TLSSocket object.

Here is an example of a client of echo server as described previously:

var tls = require('tls');
var fs = require('fs');

var options = {
  // These are necessary only if using the client certificate authentication
  key: fs.readFileSync('client-key.pem'),
  cert: fs.readFileSync('client-cert.pem'),

  // This is necessary only if the server uses the self-signed certificate
  ca: [ fs.readFileSync('server-cert.pem') ]
};

var socket = tls.connect(8000, options, function() {
  console.log('client connected',
              socket.authorized ? 'authorized' : 'unauthorized');
  process.stdin.pipe(socket);
  process.stdin.resume();
});
socket.setEncoding('utf8');
socket.on('data', function(data) {
  console.log(data);
});
socket.on('end', function() {
  server.close();
});

Or

var tls = require('tls');
var fs = require('fs');

var options = {
  pfx: fs.readFileSync('client.pfx')
};

var socket = tls.connect(8000, options, function() {
  console.log('client connected',
              socket.authorized ? 'authorized' : 'unauthorized');
  process.stdin.pipe(socket);
  process.stdin.resume();
});
socket.setEncoding('utf8');
socket.on('data', function(data) {
  console.log(data);
});
socket.on('end', function() {
  server.close();
});

Class: tls.TLSSocket

Wrapper for instance of net.Socket, replaces internal socket read/write routines to perform transparent encryption/decryption of incoming/outgoing data.

new tls.TLSSocket(socket, options)

Construct a new TLSSocket object from existing TCP socket.

socket is an instance of net.Socket

options is an object that might contain following properties:

secureContext: An optional TLS context object from tls.createSecureContext( ... )

isServer: If true - TLS socket will be instantiated in server-mode

server: An optional net.Server instance

requestCert: Optional, see tls.createSecurePair

rejectUnauthorized: Optional, see tls.createSecurePair

NPNProtocols: Optional, see tls.createServer

SNICallback: Optional, see tls.createServer

session: Optional, a Buffer instance, containing TLS session

requestOCSP: Optional, if true - OCSP status request extension would be added to client hello, and OCSPResponse event will be emitted on socket before establishing secure communication

tls.createSecureContext(details)

Creates a credentials object, with the optional details being a dictionary with keys:

pfx : A string or buffer holding the PFX or PKCS12 encoded private key, certificate and CA certificates

key : A string holding the PEM encoded private key

passphrase : A string of passphrase for the private key or pfx

cert : A string holding the PEM encoded certificate

ca : Either a string or list of strings of PEM encoded CA certificates to trust.

crl : Either a string or list of strings of PEM encoded CRLs (Certificate Revocation List)

ciphers: A string describing the ciphers to use or exclude. Consult http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT for details on the format.

honorCipherOrder : When choosing a cipher, use the server’s preferences instead of the client preferences. For further details see tls module documentation.

If no ‘ca’ details are given, then node.js will use the default publicly trusted list of CAs as given in http://mxr.mozilla.org/mozilla/source/security/nss/lib/ckfw/builtins/certdata.txt.

tls.createSecurePair([context][, isServer][, requestCert][, rejectUnauthorized])

Creates a new secure pair object with two streams, one of which reads/writes encrypted data, and one reads/writes cleartext data. Generally the encrypted one is piped to/from an incoming encrypted data stream, and the cleartext one is used as a replacement for the initial encrypted stream.

context: A secure context object from tls.createSecureContext( … )

isServer: A boolean indicating whether this tls connection should be opened as a server or a client.

requestCert: A boolean indicating whether a server should request a certificate from a connecting client. Only applies to server connections.

rejectUnauthorized: A boolean indicating whether a server should automatically reject clients with invalid certificates. Only applies to servers with requestCert enabled.

tls.createSecurePair() returns a SecurePair object with cleartext and encrypted stream properties.

NOTE: cleartext has the same APIs as tls.TLSSocket

Class: SecurePair

Returned by tls.createSecurePair.

Event: ‘secure’

The event is emitted from the SecurePair once the pair has successfully established a secure connection.

Similarly to the checking for the server ‘secureConnection’ event, pair.cleartext.authorized should be checked to confirm whether the certificate used properly authorized.

Class: tls.Server

This class is a subclass of net.Server and has the same methods on it. Instead of accepting just raw TCP connections, this accepts encrypted connections using TLS or SSL.

Event: ‘secureConnection’

function (tlsSocket) {}

This event is emitted after a new connection has been successfully handshaked. The argument is an instance of tls.TLSSocket. It has all the common stream methods and events.

socket.authorized is a boolean value which indicates if the client has verified by one of the supplied certificate authorities for the server. If socket.authorized is false, then socket.authorizationError is set to describe how authorization failed. Implied but worth mentioning: depending on the settings of the TLS server, you unauthorized connections may be accepted. socket.npnProtocol is a string containing selected NPN protocol. socket.servername is a string containing servername requested with SNI.

Event: ‘clientError’

function (exception, tlsSocket) { }

When a client connection emits an ‘error’ event before secure connection is established - it will be forwarded here.

tlsSocket is the tls.TLSSocket that the error originated from.

Event: ‘newSession’

function (sessionId, sessionData, callback) { }

Emitted on creation of TLS session. May be used to store sessions in external storage. callback must be invoked eventually, otherwise no data will be sent or received from secure connection.

NOTE: adding this event listener will have an effect only on connections established after addition of event listener.

Event: ‘resumeSession’

function (sessionId, callback) { }

Emitted when client wants to resume previous TLS session. Event listener may perform lookup in external storage using given sessionId, and invoke callback(null, sessionData) once finished. If session can’t be resumed (i.e. doesn’t exist in storage) one may call callback(null, null). Calling callback(err) will terminate incoming connection and destroy socket.

NOTE: adding this event listener will have an effect only on connections established after addition of event listener.

Event: ‘OCSPRequest’

function (certificate, issuer, callback) { }

Emitted when the client sends a certificate status request. You could parse server’s current certificate to obtain OCSP url and certificate id, and after obtaining OCSP response invoke callback(null, resp), where resp is a Buffer instance. Both certificate and issuer are a Buffer DER-representations of the primary and issuer’s certificates. They could be used to obtain OCSP certificate id and OCSP endpoint url.

Alternatively, callback(null, null) could be called, meaning that there is no OCSP response.

Calling callback(err) will result in a socket.destroy(err) call.

Typical flow:

Client connects to server and sends OCSPRequest to it (via status info extension in ClientHello.)

Server receives request and invokes OCSPRequest event listener if present

Server grabs OCSP url from either certificate or issuer and performs an OCSP request to the CA

Server receives OCSPResponse from CA and sends it back to client via callback argument

Client validates the response and either destroys socket or performs a handshake.

NOTE: issuer could be null, if the certificate is self-signed or if the issuer is not in the root certificates list. (You could provide an issuer via ca option.)

NOTE: adding this event listener will have an effect only on connections established after addition of event listener.

NOTE: you may want to use some npm module like asn1.js to parse the certificates.

server.listen(port[, host][, callback])

Begin accepting connections on the specified port and host. If the host is omitted, the server will accept connections directed to any IPv4 address (INADDR_ANY).

This function is asynchronous. The last parameter callback will be called when the server has been bound.

See net.Server for more information.

server.close()

Stops the server from accepting new connections. This function is asynchronous, the server is finally closed when the server emits a 'close' event.

server.address()

Returns the bound address, the address family name and port of the server as reported by the operating system. See net.Server.address() for more information.

server.addContext(hostname, context)

Add secure context that will be used if client request’s SNI hostname is matching passed hostname (wildcards can be used). context can contain key, cert, ca and/or any other properties from tls.createSecureContext options argument.

server.maxConnections

Set this property to reject connections when the server’s connection count gets high.

server.connections

The number of concurrent connections on the server.

Class: CryptoStream

Stability: 0 - Deprecated. Use tls.TLSSocket instead.

This is an encrypted stream.

cryptoStream.bytesWritten

A proxy to the underlying socket’s bytesWritten accessor, this will return the total bytes written to the socket, including the TLS overhead.

Class: CleartextStream

The CleartextStream class in Node.js version v0.10.39 and prior has been deprecated and removed.

Class: tls.TLSSocket

This is a wrapped version of net.Socket that does transparent encryption of written data and all required TLS negotiation.

This instance implements a duplex Stream interfaces. It has all the common stream methods and events.

Event: ‘secureConnect’

This event is emitted after a new connection has been successfully handshaked. The listener will be called no matter if the server’s certificate was authorized or not. It is up to the user to test tlsSocket.authorized to see if the server certificate was signed by one of the specified CAs. If tlsSocket.authorized === false then the error can be found in tlsSocket.authorizationError. Also if NPN was used - you can check tlsSocket.npnProtocol for negotiated protocol.

Event: ‘OCSPResponse’

function (response) { }

This event will be emitted if requestOCSP option was set. response is a buffer object, containing server’s OCSP response.

Traditionally, the response is a signed object from the server’s CA that contains information about server’s certificate revocation status.

tlsSocket.encrypted

Static boolean value, always true. May be used to distinguish TLS sockets from regular ones.

tlsSocket.authorized

A boolean that is true if the peer certificate was signed by one of the specified CAs, otherwise false

tlsSocket.authorizationError

The reason why the peer’s certificate has not been verified. This property becomes available only when tlsSocket.authorized === false.

tlsSocket.getPeerCertificate([ detailed ])

Returns an object representing the peer’s certificate. The returned object has some properties corresponding to the field of the certificate. If detailed argument is true - the full chain with issuer property will be returned, if false - only the top certificate without issuer property.

Example:

{ subject:
   { C: 'UK',
     ST: 'Acknack Ltd',
     L: 'Rhys Jones',
     O: 'node.js',
     OU: 'Test TLS Certificate',
     CN: 'localhost' },
  issuerInfo:
   { C: 'UK',
     ST: 'Acknack Ltd',
     L: 'Rhys Jones',
     O: 'node.js',
     OU: 'Test TLS Certificate',
     CN: 'localhost' },
  issuer:
   { ... another certificate ... },
  raw: < RAW DER buffer >,
  valid_from: 'Nov 11 09:52:22 2009 GMT',
  valid_to: 'Nov  6 09:52:22 2029 GMT',
  fingerprint: '2A:7A:C2:DD:E5:F9:CC:53:72:35:99:7A:02:5A:71:38:52:EC:8A:DF',
  serialNumber: 'B9B0D332A1AA5635' }

If the peer does not provide a certificate, it returns null or an empty object.

tlsSocket.getCipher()

Returns an object representing the cipher name and the SSL/TLS protocol version of the current connection.

Example: { name: ‘AES256-SHA’, version: ‘TLSv1/SSLv3’ }

See SSL_CIPHER_get_name() and SSL_CIPHER_get_version() in http://www.openssl.org/docs/ssl/ssl.html#DEALING_WITH_CIPHERS for more information.

tlsSocket.renegotiate(options, callback)

Initiate TLS renegotiation process. The options may contain the following fields: rejectUnauthorized, requestCert (See tls.createServer for details). callback(err) will be executed with null as err, once the renegotiation is successfully completed.

NOTE: Can be used to request peer’s certificate after the secure connection has been established.

ANOTHER NOTE: When running as the server, socket will be destroyed with an error after handshakeTimeout timeout.

tlsSocket.setMaxSendFragment(size)

Set maximum TLS fragment size (default and maximum value is: 16384, minimum is: 512). Returns true on success, false otherwise.

Smaller fragment size decreases buffering latency on the client: large fragments are buffered by the TLS layer until the entire fragment is received and its integrity is verified; large fragments can span multiple roundtrips, and their processing can be delayed due to packet loss or reordering. However, smaller fragments add extra TLS framing bytes and CPU overhead, which may decrease overall server throughput.

tlsSocket.getSession()

Return ASN.1 encoded TLS session or undefined if none was negotiated. Could be used to speed up handshake establishment when reconnecting to the server.

tlsSocket.getTLSTicket()

NOTE: Works only with client TLS sockets. Useful only for debugging, for session reuse provide session option to tls.connect.

Return TLS session ticket or undefined if none was negotiated.

tlsSocket.address()

Returns the bound address, the address family name and port of the underlying socket as reported by the operating system. Returns an object with three properties, e.g. { port: 12346, family: 'IPv4', address: '127.0.0.1' }

tlsSocket.remoteAddress

The string representation of the remote IP address. For example, '74.125.127.100' or '2001:4860:a005::68'.

tlsSocket.remoteFamily

The string representation of the remote IP family. 'IPv4' or 'IPv6'.

tlsSocket.remotePort

The numeric representation of the remote port. For example, 443.

tlsSocket.localAddress

The string representation of the local IP address.

tlsSocket.localPort

The numeric representation of the local port.

Tracing

Stability: 1 - Experimental

The tracing module is designed for instrumenting your Node application. It is not meant for general purpose use.

Be very careful with callbacks used in conjunction with this module

Many of these callbacks interact directly with asynchronous subsystems in a synchronous fashion. That is to say, you may be in a callback where a call to console.log() could result in an infinite recursive loop. Also of note, many of these callbacks are in hot execution code paths. That is to say your callbacks are executed quite often in the normal operation of Node, so be wary of doing CPU bound or synchronous workloads in these functions. Consider a ring buffer and a timer to defer processing.

require('tracing') to use this module.

v8

The v8 property is an EventEmitter, it exposes events and interfaces specific to the version of v8 built with node. These interfaces are subject to change by upstream and are therefore not covered under the stability index.

Event: ‘gc’

function (before, after) { }

Emitted each time a GC run is completed.

before and after are objects with the following properties:

{
  type: 'mark-sweep-compact',
  flags: 0,
  timestamp: 905535650119053,
  total_heap_size: 6295040,
  total_heap_size_executable: 4194304,
  total_physical_size: 6295040,
  used_heap_size: 2855416,
  heap_size_limit: 1535115264
}

getHeapStatistics()

Returns an object with the following properties

{
  total_heap_size: 7326976,
  total_heap_size_executable: 4194304,
  total_physical_size: 7326976,
  used_heap_size: 3476208,
  heap_size_limit: 1535115264
}

Async Listeners

The AsyncListener API is the JavaScript interface for the AsyncWrap class which allows developers to be notified about key events in the lifetime of an asynchronous event. Node performs a lot of asynchronous events internally, and significant use of this API may have a significant performance impact on your application.

tracing.createAsyncListener(callbacksObj[, userData])

callbacksObj {Object} Contains optional callbacks that will fire at specific times in the life cycle of the asynchronous event.

userData {Value} a value that will be passed to all callbacks.

Returns a constructed AsyncListener object.

To begin capturing asynchronous events pass either the callbacksObj or pass an existing AsyncListener instance to tracing.addAsyncListener(). The same AsyncListener instance can only be added once to the active queue, and subsequent attempts to add the instance will be ignored.

To stop capturing pass the AsyncListener instance to tracing.removeAsyncListener(). This does not mean the AsyncListener previously added will stop triggering callbacks. Once attached to an asynchronous event it will persist with the lifetime of the asynchronous call stack.

Explanation of function parameters:

callbacksObj: An Object which may contain several optional fields:

create(userData): A Function called when an asynchronous event is instantiated. If a Value is returned then it will be attached to the event and overwrite any value that had been passed to tracing.createAsyncListener()’s userData argument. If an initial userData was passed when created, then create() will receive that as a function argument.

before(context, userData): A Function that is called immediately before the asynchronous callback is about to run. It will be passed both the context (i.e. this) of the calling function and the userData either returned from create() or passed during construction (if either occurred).

after(context, userData): A Function called immediately after the asynchronous event’s callback has run. Note this will not be called if the callback throws and the error is not handled.

error(userData, error): A Function called if the event’s callback threw. If this registered callback returns true then Node will assume the error has been properly handled and resume execution normally. When multiple error() callbacks have been registered only one of those callbacks needs to return true for AsyncListener to accept that the error has been handled, but all error() callbacks will always be run.

userData: A Value (i.e. anything) that will be, by default, attached to all new event instances. This will be overwritten if a Value is returned by create().

Here is an example of overwriting the userData:

tracing.createAsyncListener({
  create: function listener(value) {
    // value === true
    return false;
}, {
  before: function before(context, value) {
    // value === false
  }
}, true);

Note: The EventEmitter, while used to emit status of an asynchronous event, is not itself asynchronous. So create() will not fire when an event is added, and before()/after() will not fire when emitted callbacks are called.

tracing.addAsyncListener(callbacksObj[, userData])

tracing.addAsyncListener(asyncListener)

Returns a constructed AsyncListener object and immediately adds it to the listening queue to begin capturing asynchronous events.

Function parameters can either be the same as tracing.createAsyncListener(), or a constructed AsyncListener object.

Example usage for capturing errors:

var fs = require('fs');

var cntr = 0;
var key = tracing.addAsyncListener({
  create: function onCreate() {
    return { uid: cntr++ };
  },
  before: function onBefore(context, storage) {
    // Write directly to stdout or we'll enter a recursive loop
    fs.writeSync(1, 'uid: ' + storage.uid + ' is about to run\n');
  },
  after: function onAfter(context, storage) {
    fs.writeSync(1, 'uid: ' + storage.uid + ' ran\n');
  },
  error: function onError(storage, err) {
    // Handle known errors
    if (err.message === 'everything is fine') {
      // Writing to stderr this time.
      fs.writeSync(2, 'handled error just threw:\n');
      fs.writeSync(2, err.stack + '\n');
      return true;
    }
  }
});

process.nextTick(function() {
  throw new Error('everything is fine');
});

// Output:
// uid: 0 is about to run
// handled error just threw:
// Error: really, it's ok
//     at /tmp/test2.js:27:9
//     at process._tickCallback (node.js:583:11)
//     at Function.Module.runMain (module.js:492:11)
//     at startup (node.js:123:16)
//     at node.js:1012:3

tracing.removeAsyncListener(asyncListener)

Removes the AsyncListener from the listening queue.

Removing the AsyncListener from the active queue does not mean the asyncListener callbacks will cease to fire on the events they’ve been registered. Subsequently, any asynchronous events fired during the execution of a callback will also have the same asyncListener callbacks attached for future execution. For example:

var fs = require('fs');

var key = tracing.createAsyncListener({
  create: function asyncListener() {
    // Write directly to stdout or we'll enter a recursive loop
    fs.writeSync(1, 'You summoned me?\n');
  }
});

// We want to begin capturing async events some time in the future.
setTimeout(function() {
  tracing.addAsyncListener(key);

  // Perform a few additional async events.
  setTimeout(function() {
    setImmediate(function() {
      process.nextTick(function() { });
    });
  });

  // Removing the listener doesn't mean to stop capturing events that
  // have already been added.
  tracing.removeAsyncListener(key);
}, 100);

// Output:
// You summoned me?
// You summoned me?
// You summoned me?
// You summoned me?

The fact that we logged 4 asynchronous events is an implementation detail of Node’s Timers.

To stop capturing from a specific asynchronous event stack tracing.removeAsyncListener() must be called from within the call stack itself. For example:

var fs = require('fs');

var key = tracing.createAsyncListener({
  create: function asyncListener() {
    // Write directly to stdout or we'll enter a recursive loop
    fs.writeSync(1, 'You summoned me?\n');
  }
});

// We want to begin capturing async events some time in the future.
setTimeout(function() {
  tracing.addAsyncListener(key);

  // Perform a few additional async events.
  setImmediate(function() {
    // Stop capturing from this call stack.
    tracing.removeAsyncListener(key);

    process.nextTick(function() { });
  });
}, 100);

// Output:
// You summoned me?

The user must be explicit and always pass the AsyncListener they wish to remove. It is not possible to simply remove all listeners at once.

TTY

Stability: 2 - Unstable

The tty module houses the tty.ReadStream and tty.WriteStream classes. In most cases, you will not need to use this module directly.

When node detects that it is being run inside a TTY context, then process.stdin will be a tty.ReadStream instance and process.stdout will be a tty.WriteStream instance. The preferred way to check if node is being run in a TTY context is to check process.stdout.isTTY:

$ node -p -e "Boolean(process.stdout.isTTY)"
true
$ node -p -e "Boolean(process.stdout.isTTY)" | cat
false

tty.isatty(fd)

Returns true or false depending on if the fd is associated with a terminal.

tty.setRawMode(mode)

Deprecated. Use tty.ReadStream#setRawMode() (i.e. process.stdin.setRawMode()) instead.

Class: ReadStream

A net.Socket subclass that represents the readable portion of a tty. In normal circumstances, process.stdin will be the only tty.ReadStream instance in any node program (only when isatty(0) is true).

rs.isRaw

A Boolean that is initialized to false. It represents the current “raw” state of the tty.ReadStream instance.

rs.setRawMode(mode)

mode should be true or false. This sets the properties of the tty.ReadStream to act either as a raw device or default. isRaw will be set to the resulting mode.

Class: WriteStream

A net.Socket subclass that represents the writable portion of a tty. In normal circumstances, process.stdout will be the only tty.WriteStream instance ever created (and only when isatty(1) is true).

ws.columns

A Number that gives the number of columns the TTY currently has. This property gets updated on “resize” events.

ws.rows

A Number that gives the number of rows the TTY currently has. This property gets updated on “resize” events.

Event: ‘resize’

function () {}

Emitted by refreshSize() when either of the columns or rows properties has changed.

process.stdout.on('resize', function() {
  console.log('screen size has changed!');
  console.log(process.stdout.columns + 'x' + process.stdout.rows);
});

UDP / Datagram Sockets

Stability: 3 - Stable

Datagram sockets are available through require('dgram').

Important note: the behavior of dgram.Socket#bind() has changed in v0.10 and is always asynchronous now. If you have code that looks like this:

var s = dgram.createSocket('udp4');
s.bind(1234);
s.addMembership('224.0.0.114');

You have to change it to this:

var s = dgram.createSocket('udp4');
s.bind(1234, function() {
  s.addMembership('224.0.0.114');
});

dgram.createSocket(type[, callback])

type String. Either ‘udp4’ or ‘udp6’

callback Function. Attached as a listener to message events. Optional

Returns: Socket object

Creates a datagram Socket of the specified types. Valid types are udp4 and udp6.

Takes an optional callback which is added as a listener for message events.

Call socket.bind() if you want to receive datagrams. socket.bind() will bind to the “all interfaces” address on a random port (it does the right thing for both udp4 and udp6 sockets). You can then retrieve the address and port with socket.address().address and socket.address().port.

dgram.createSocket(options[, callback])

options Object

callback Function. Attached as a listener to message events.

Returns: Socket object

The options object should contain a type field of either udp4 or udp6 and an optional boolean reuseAddr field.

When reuseAddr is true socket.bind() will reuse the address, even if another process has already bound a socket on it. reuseAddr defaults to false.

Takes an optional callback which is added as a listener for message events.

Call socket.bind() if you want to receive datagrams. socket.bind() will bind to the “all interfaces” address on a random port (it does the right thing for both udp4 and udp6 sockets). You can then retrieve the address and port with socket.address().address and socket.address().port.

Class: dgram.Socket

The dgram Socket class encapsulates the datagram functionality. It should be created via dgram.createSocket(...)

Event: ‘message’

msg Buffer object. The message

rinfo Object. Remote address information

Emitted when a new datagram is available on a socket. msg is a Buffer and rinfo is an object with the sender’s address information:

socket.on('message', function(msg, rinfo) {
  console.log('Received %d bytes from %s:%d\n',
              msg.length, rinfo.address, rinfo.port);
});

Event: ‘listening’

Emitted when a socket starts listening for datagrams. This happens as soon as UDP sockets are created.

Event: ‘close’

Emitted when a socket is closed with close(). No new message events will be emitted on this socket.

Event: ‘error’

exception Error object

Emitted when an error occurs.

socket.send(buf, offset, length, port, address[, callback])

buf Buffer object or string. Message to be sent

offset Integer. Offset in the buffer where the message starts.

length Integer. Number of bytes in the message.

port Integer. Destination port.

address String. Destination hostname or IP address.

callback Function. Called when the message has been sent. Optional.

For UDP sockets, the destination port and address must be specified. A string may be supplied for the address parameter, and it will be resolved with DNS.

If the address is omitted or is an empty string, '0.0.0.0' or '::0' is used instead. Depending on the network configuration, those defaults may or may not work; it’s best to be explicit about the destination address.

If the socket has not been previously bound with a call to bind, it gets assigned a random port number and is bound to the “all interfaces” address ('0.0.0.0' for udp4 sockets, '::0' for udp6 sockets.)

An optional callback may be specified to detect DNS errors or for determining when it’s safe to reuse the buf object. Note that DNS lookups delay the time to send for at least one tick. The only way to know for sure that the datagram has been sent is by using a callback.

With consideration for multi-byte characters, offset and length will be calculated with respect to byte length and not the character position.

Example of sending a UDP packet to a random port on localhost;

var dgram = require('dgram');
var message = new Buffer("Some bytes");
var client = dgram.createSocket("udp4");
client.send(message, 0, message.length, 41234, "localhost", function(err) {
  client.close();
});

A Note about UDP datagram size

The maximum size of an IPv4/v6 datagram depends on the MTU (Maximum Transmission Unit) and on the Payload Length field size.

The Payload Length field is 16 bits wide, which means that a normal payload cannot be larger than 64K octets including internet header and data (65,507 bytes = 65,535 − 8 bytes UDP header − 20 bytes IP header); this is generally true for loopback interfaces, but such long datagrams are impractical for most hosts and networks.

The MTU is the largest size a given link layer technology can support for datagrams. For any link, IPv4 mandates a minimum MTU of 68 octets, while the recommended MTU for IPv4 is 576 (typically recommended as the MTU for dial-up type applications), whether they arrive whole or in fragments.

For IPv6, the minimum MTU is 1280 octets, however, the mandatory minimum fragment reassembly buffer size is 1500 octets. The value of 68 octets is very small, since most current link layer technologies have a minimum MTU of 1500 (like Ethernet).

Note that it’s impossible to know in advance the MTU of each link through which a packet might travel, and that generally sending a datagram greater than the (receiver) MTU won’t work (the packet gets silently dropped, without informing the source that the data did not reach its intended recipient).

socket.bind(port[, address][, callback])

port Integer

address String, Optional

callback Function with no parameters, Optional. Callback when binding is done.

For UDP sockets, listen for datagrams on a named port and optional address. If address is not specified, the OS will try to listen on all addresses. After binding is done, a “listening” event is emitted and the callback(if specified) is called. Specifying both a “listening” event listener and callback is not harmful but not very useful.

A bound datagram socket keeps the node process running to receive datagrams.

If binding fails, an “error” event is generated. In rare case (e.g. binding a closed socket), an Error may be thrown by this method.

Example of a UDP server listening on port 41234:

var dgram = require("dgram");

var server = dgram.createSocket("udp4");

server.on("error", function (err) {
  console.log("server error:\n" + err.stack);
  server.close();
});

server.on("message", function (msg, rinfo) {
  console.log("server got: " + msg + " from " +
    rinfo.address + ":" + rinfo.port);
});

server.on("listening", function () {
  var address = server.address();
  console.log("server listening " +
      address.address + ":" + address.port);
});

server.bind(41234);
// server listening 0.0.0.0:41234

socket.bind(options[, callback])

options {Object} - Required. Supports the following properties:

port {Number} - Required.

address {String} - Optional.

exclusive {Boolean} - Optional.

callback {Function} - Optional.

The port and address properties of options, as well as the optional callback function, behave as they do on a call to socket.bind(port, [address], [callback]).

If exclusive is false (default), then cluster workers will use the same underlying handle, allowing connection handling duties to be shared. When exclusive is true, the handle is not shared, and attempted port sharing results in an error. An example which listens on an exclusive port is shown below.

socket.bind({
  address: 'localhost',
  port: 8000,
  exclusive: true
});

socket.close()

Close the underlying socket and stop listening for data on it.

socket.address()

Returns an object containing the address information for a socket. For UDP sockets, this object will contain address , family and port.

socket.setBroadcast(flag)

flag Boolean

Sets or clears the SO_BROADCAST socket option. When this option is set, UDP packets may be sent to a local interface’s broadcast address.

socket.setTTL(ttl)

ttl Integer

Sets the IP_TTL socket option. TTL stands for “Time to Live,” but in this context it specifies the number of IP hops that a packet is allowed to go through. Each router or gateway that forwards a packet decrements the TTL. If the TTL is decremented to 0 by a router, it will not be forwarded. Changing TTL values is typically done for network probes or when multicasting.

The argument to setTTL() is a number of hops between 1 and 255. The default on most systems is 64.

socket.setMulticastTTL(ttl)

ttl Integer

Sets the IP_MULTICAST_TTL socket option. TTL stands for “Time to Live,” but in this context it specifies the number of IP hops that a packet is allowed to go through, specifically for multicast traffic. Each router or gateway that forwards a packet decrements the TTL. If the TTL is decremented to 0 by a router, it will not be forwarded.

The argument to setMulticastTTL() is a number of hops between 0 and 255. The default on most systems is 1.

socket.setMulticastLoopback(flag)

flag Boolean

Sets or clears the IP_MULTICAST_LOOP socket option. When this option is set, multicast packets will also be received on the local interface.

socket.addMembership(multicastAddress[, multicastInterface])

multicastAddress String

multicastInterface String, Optional

Tells the kernel to join a multicast group with IP_ADD_MEMBERSHIP socket option.

If multicastInterface is not specified, the OS will try to add membership to all valid interfaces.

socket.dropMembership(multicastAddress[, multicastInterface])

multicastAddress String

multicastInterface String, Optional

Opposite of addMembership - tells the kernel to leave a multicast group with IP_DROP_MEMBERSHIP socket option. This is automatically called by the kernel when the socket is closed or process terminates, so most apps will never need to call this.

If multicastInterface is not specified, the OS will try to drop membership to all valid interfaces.

socket.unref()

Calling unref on a socket will allow the program to exit if this is the only active socket in the event system. If the socket is already unrefd calling unref again will have no effect.

socket.ref()

Opposite of unref, calling ref on a previously unrefd socket will not let the program exit if it’s the only socket left (the default behavior). If the socket is refd calling ref again will have no effect.

URL

Stability: 3 - Stable

This module has utilities for URL resolution and parsing. Call require('url') to use it.

Parsed URL objects have some or all of the following fields, depending on whether or not they exist in the URL string. Any parts that are not in the URL string will not be in the parsed object. Examples are shown for the URL

'http://user:pass@host.com:8080/p/a/t/h?query=string#hash'

href: The full URL that was originally parsed. Both the protocol and host are lowercased.

Example: 'http://user:pass@host.com:8080/p/a/t/h?query=string#hash'

protocol: The request protocol, lowercased.

Example: 'http:'

slashes: The protocol requires slashes after the colon

Example: true or false

host: The full lowercased host portion of the URL, including port information.

Example: 'host.com:8080'

auth: The authentication information portion of a URL.

Example: 'user:pass'

hostname: Just the lowercased hostname portion of the host.

Example: 'host.com'

port: The port number portion of the host.

Example: '8080'

pathname: The path section of the URL, that comes after the host and before the query, including the initial slash if present.

Example: '/p/a/t/h'

search: The ‘query string’ portion of the URL, including the leading question mark.

Example: '?query=string'

path: Concatenation of pathname and search.

Example: '/p/a/t/h?query=string'

query: Either the ‘params’ portion of the query string, or a querystring-parsed object.

Example: 'query=string' or {'query':'string'}

hash: The ‘fragment’ portion of the URL including the pound-sign.

Example: '#hash'

The following methods are provided by the URL module:

url.parse(urlStr[, parseQueryString][, slashesDenoteHost])

Take a URL string, and return an object.

Pass true as the second argument to also parse the query string using the querystring module. If true then the query property will always be assigned an object, and the search property will always be a (possibly empty) string. Defaults to false.

Pass true as the third argument to treat //foo/bar as { host: 'foo', pathname: '/bar' } rather than { pathname: '//foo/bar' }. Defaults to false.

url.format(urlObj)

Take a parsed URL object, and return a formatted URL string.

Here’s how the formatting process works:

href will be ignored.

protocol is treated the same with or without the trailing : (colon).

The protocols http, https, ftp, gopher, file will be postfixed with :// (colon-slash-slash).

All other protocols mailto, xmpp, aim, sftp, foo, etc will be postfixed with : (colon)

slashes set to true if the protocol requires :// (colon-slash-slash)

Only needs to be set for protocols not previously listed as requiring slashes, such as mongodb://localhost:8000/

auth will be used if present.

hostname will only be used if host is absent.

port will only be used if host is absent.

host will be used in place of hostname and port

pathname is treated the same with or without the leading / (slash).

search will be used in place of query.

It is treated the same with or without the leading ? (question mark)

query (object; see querystring) will only be used if search is absent.

hash is treated the same with or without the leading # (pound sign, anchor).

url.resolve(from, to)

Take a base URL, and a href URL, and resolve them as a browser would for an anchor tag. Examples:

url.resolve('/one/two/three', 'four')         // '/one/two/four'
url.resolve('http://example.com/', '/one')    // 'http://example.com/one'
url.resolve('http://example.com/one', '/two') // 'http://example.com/two'

util

Stability: 4 - API Frozen

These functions are in the module 'util'. Use require('util') to access them.

The util module is primarily designed to support the needs of Node’s internal APIs. Many of these utilities are useful for your own programs. If you find that these functions are lacking for your purposes, however, you are encouraged to write your own utilities. We are not interested in any future additions to the util module that are unnecessary for Node’s internal functionality.

util.debuglog(section)

section {String} The section of the program to be debugged

Returns: {Function} The logging function

This is used to create a function which conditionally writes to stderr based on the existence of a NODE_DEBUG environment variable. If the section name appears in that environment variable, then the returned function will be similar to console.error(). If not, then the returned function is a no-op.

For example:

var debuglog = util.debuglog('foo');

var bar = 123;
debuglog('hello from foo [%d]', bar);

If this program is run with NODE_DEBUG=foo in the environment, then it will output something like:

FOO 3245: hello from foo [123]

where 3245 is the process id. If it is not run with that environment variable set, then it will not print anything.

You may separate multiple NODE_DEBUG environment variables with a comma. For example, NODE_DEBUG=fs,net,tls.

util.format(format[, …])

Returns a formatted string using the first argument as a printf-like format.

The first argument is a string that contains zero or more placeholders. Each placeholder is replaced with the converted value from its corresponding argument. Supported placeholders are:

%s - String.

%d - Number (both integer and float).

%j - JSON. Replaced with the string '[Circular]' if the argument contains circular references.

%% - single percent sign ('%'). This does not consume an argument.

If the placeholder does not have a corresponding argument, the placeholder is not replaced.

util.format('%s:%s', 'foo'); // 'foo:%s'

If there are more arguments than placeholders, the extra arguments are converted to strings with util.inspect() and these strings are concatenated, delimited by a space.

util.format('%s:%s', 'foo', 'bar', 'baz'); // 'foo:bar baz'

If the first argument is not a format string then util.format() returns a string that is the concatenation of all its arguments separated by spaces. Each argument is converted to a string with util.inspect().

util.format(1, 2, 3); // '1 2 3'

util.log(string)

Output with timestamp on stdout.

require('util').log('Timestamped message.');

util.inspect(object[, options])

Return a string representation of object, which is useful for debugging.

An optional options object may be passed that alters certain aspects of the formatted string:

showHidden - if true then the object’s non-enumerable properties will be shown too. Defaults to false.

depth - tells inspect how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. Defaults to 2. To make it recurse indefinitely pass null.

colors - if true, then the output will be styled with ANSI color codes. Defaults to false. Colors are customizable, see below.

customInspect - if false, then custom inspect(depth, opts) functions defined on the objects being inspected won’t be called. Defaults to true.

Example of inspecting all properties of the util object:

var util = require('util');

console.log(util.inspect(util, { showHidden: true, depth: null }));

Values may supply their own custom inspect(depth, opts) functions, when called they receive the current depth in the recursive inspection, as well as the options object passed to util.inspect().

Customizing util.inspect colors

Color output (if enabled) of util.inspect is customizable globally via util.inspect.styles and util.inspect.colors objects.

util.inspect.styles is a map assigning each style a color from util.inspect.colors. Highlighted styles and their default values are: * number (yellow) * boolean (yellow) * string (green) * date (magenta) * regexp (red) * null (bold) * undefined (grey) * special - only function at this time (cyan) * name (intentionally no styling)

Predefined color codes are: white, grey, black, blue, cyan, green, magenta, red and yellow. There are also bold, italic, underline and inverse codes.

Custom inspect() function on Objects

Objects also may define their own inspect(depth) function which util.inspect() will invoke and use the result of when inspecting the object:

var util = require('util');

var obj = { name: 'nate' };
obj.inspect = function(depth) {
  return '{' + this.name + '}';
};

util.inspect(obj);
  // "{nate}"

You may also return another Object entirely, and the returned String will be formatted according to the returned Object. This is similar to how JSON.stringify() works:

var obj = { foo: 'this will not show up in the inspect() output' };
obj.inspect = function(depth) {
  return { bar: 'baz' };
};

util.inspect(obj);
  // "{ bar: 'baz' }"

util.isArray(object)

Internal alias for Array.isArray.

Returns true if the given “object” is an Array. false otherwise.

var util = require('util');

util.isArray([])
  // true
util.isArray(new Array)
  // true
util.isArray({})
  // false

util.isRegExp(object)

Returns true if the given “object” is a RegExp. false otherwise.

var util = require('util');

util.isRegExp(/some regexp/)
  // true
util.isRegExp(new RegExp('another regexp'))
  // true
util.isRegExp({})
  // false

util.isDate(object)

Returns true if the given “object” is a Date. false otherwise.

var util = require('util');

util.isDate(new Date())
  // true
util.isDate(Date())
  // false (without 'new' returns a String)
util.isDate({})
  // false

util.isError(object)

Returns true if the given “object” is an Error. false otherwise.

var util = require('util');

util.isError(new Error())
  // true
util.isError(new TypeError())
  // true
util.isError({ name: 'Error', message: 'an error occurred' })
  // false

util.inherits(constructor, superConstructor)

Inherit the prototype methods from one constructor into another. The prototype of constructor will be set to a new object created from superConstructor.

As an additional convenience, superConstructor will be accessible through the constructor.super_ property.

var util = require("util");
var events = require("events");

function MyStream() {
    events.EventEmitter.call(this);
}

util.inherits(MyStream, events.EventEmitter);

MyStream.prototype.write = function(data) {
    this.emit("data", data);
}

var stream = new MyStream();

console.log(stream instanceof events.EventEmitter); // true
console.log(MyStream.super_ === events.EventEmitter); // true

stream.on("data", function(data) {
    console.log('Received data: "' + data + '"');
})
stream.write("It works!"); // Received data: "It works!"

util.deprecate(function, string)

Marks that a method should not be used any more.

exports.puts = exports.deprecate(function() {
  for (var i = 0, len = arguments.length; i < len; ++i) {
    process.stdout.write(arguments[i] + '\n');
  }
}, 'util.puts: Use console.log instead')

It returns a modified function which warns once by default. If --no-deprecation is set then this function is a NO-OP. If --throw-deprecation is set then the application will throw an exception if the deprecated API is used.

util.debug(string)

Stability: 0 - Deprecated: use console.error() instead.

Deprecated predecessor of console.error.

util.error([…])

Stability: 0 - Deprecated: Use console.error() instead.

Deprecated predecessor of console.error.

util.puts([…])

Stability: 0 - Deprecated: Use console.log() instead.

Deprecated predecessor of console.log.

util.print([…])

Stability: 0 - Deprecated: Use `console.log` instead.

Deprecated predecessor of console.log.

util.pump(readableStream, writableStream[, callback])

Stability: 0 - Deprecated: Use readableStream.pipe(writableStream)

Deprecated predecessor of stream.pipe().

Executing JavaScript

Stability: 3 - Stable

You can access this module with:

var vm = require('vm');

JavaScript code can be compiled and run immediately or compiled, saved, and run later.

vm.runInThisContext(code[, options])

vm.runInThisContext() compiles code, runs it and returns the result. Running code does not have access to local scope, but does have access to the current global object.

Example of using vm.runInThisContext and eval to run the same code:

var localVar = 'initial value';

var vmResult = vm.runInThisContext('localVar = "vm";');
console.log('vmResult: ', vmResult);
console.log('localVar: ', localVar);

var evalResult = eval('localVar = "eval";');
console.log('evalResult: ', evalResult);
console.log('localVar: ', localVar);

// vmResult: 'vm', localVar: 'initial value'
// evalResult: 'eval', localVar: 'eval'

vm.runInThisContext does not have access to the local scope, so localVar is unchanged. eval does have access to the local scope, so localVar is changed.

In this way vm.runInThisContext is much like an indirect eval call, e.g. (0,eval)('code'). However, it also has the following additional options:

filename: allows you to control the filename that shows up in any stack traces produced.

displayErrors: whether or not to print any errors to stderr, with the line of code that caused them highlighted, before throwing an exception. Will capture both syntax errors from compiling code and runtime errors thrown by executing the compiled code. Defaults to true.

timeout: a number of milliseconds to execute code before terminating execution. If execution is terminated, an Error will be thrown.

vm.createContext([sandbox])

If given a sandbox object, will “contextify” that sandbox so that it can be used in calls to vm.runInContext or script.runInContext. Inside scripts run as such, sandbox will be the global object, retaining all its existing properties but also having the built-in objects and functions any standard global object has. Outside of scripts run by the vm module, sandbox will be unchanged.

If not given a sandbox object, returns a new, empty contextified sandbox object you can use.

This function is useful for creating a sandbox that can be used to run multiple scripts, e.g. if you were emulating a web browser it could be used to create a single sandbox representing a window’s global object, then run all <script> tags together inside that sandbox.

vm.isContext(sandbox)

Returns whether or not a sandbox object has been contextified by calling vm.createContext on it.

vm.runInContext(code, contextifiedSandbox[, options])

vm.runInContext compiles code, then runs it in contextifiedSandbox and returns the result. Running code does not have access to local scope. The contextifiedSandbox object must have been previously contextified via vm.createContext; it will be used as the global object for code.

vm.runInContext takes the same options as vm.runInThisContext.

Example: compile and execute different scripts in a single existing context.

var util = require('util');
var vm = require('vm');

var sandbox = { globalVar: 1 };
vm.createContext(sandbox);

for (var i = 0; i < 10; ++i) {
    vm.runInContext('globalVar *= 2;', sandbox);
}
console.log(util.inspect(sandbox));

// { globalVar: 1024 }

Note that running untrusted code is a tricky business requiring great care. vm.runInContext is quite useful, but safely running untrusted code requires a separate process.

vm.runInNewContext(code[, sandbox][, options])

vm.runInNewContext compiles code, contextifies sandbox if passed or creates a new contextified sandbox if it’s omitted, and then runs the code with the sandbox as the global object and returns the result.

vm.runInNewContext takes the same options as vm.runInThisContext.

Example: compile and execute code that increments a global variable and sets a new one. These globals are contained in the sandbox.

var util = require('util');
var vm = require('vm'),

var sandbox = {
  animal: 'cat',
  count: 2
};

vm.runInNewContext('count += 1; name = "kitty"', sandbox);
console.log(util.inspect(sandbox));

// { animal: 'cat', count: 3, name: 'kitty' }

Note that running untrusted code is a tricky business requiring great care. vm.runInNewContext is quite useful, but safely running untrusted code requires a separate process.

vm.runInDebugContext(code)

vm.runInDebugContext compiles and executes code inside the V8 debug context. The primary use case is to get access to the V8 debug object:

var Debug = vm.runInDebugContext('Debug');
Debug.scripts().forEach(function(script) { console.log(script.name); });

Note that the debug context and object are intrinsically tied to V8’s debugger implementation and may change (or even get removed) without prior warning.

The debug object can also be exposed with the --expose_debug_as= switch.

Class: Script

A class for holding precompiled scripts, and running them in specific sandboxes.

new vm.Script(code, options)

Creating a new Script compiles code but does not run it. Instead, the created vm.Script object represents this compiled code. This script can be run later many times using methods below. The returned script is not bound to any global object. It is bound before each run, just for that run.

The options when creating a script are:

filename: allows you to control the filename that shows up in any stack traces produced from this script.

displayErrors: whether or not to print any errors to stderr, with the line of code that caused them highlighted, before throwing an exception. Applies only to syntax errors compiling the code; errors while running the code are controlled by the options to the script’s methods.

script.runInThisContext([options])

Similar to vm.runInThisContext but a method of a precompiled Script object. script.runInThisContext runs script’s compiled code and returns the result. Running code does not have access to local scope, but does have access to the current global object.

Example of using script.runInThisContext to compile code once and run it multiple times:

var vm = require('vm');

global.globalVar = 0;

var script = new vm.Script('globalVar += 1', { filename: 'myfile.vm' });

for (var i = 0; i < 1000; ++i) {
  script.runInThisContext();
}

console.log(globalVar);

// 1000

The options for running a script are:

displayErrors: whether or not to print any runtime errors to stderr, with the line of code that caused them highlighted, before throwing an exception. Applies only to runtime errors executing the code; it is impossible to create a Script instance with syntax errors, as the constructor will throw.

timeout: a number of milliseconds to execute the script before terminating execution. If execution is terminated, an Error will be thrown.

script.runInContext(contextifiedSandbox[, options])

Similar to vm.runInContext but a method of a precompiled Script object. script.runInContext runs script’s compiled code in contextifiedSandbox and returns the result. Running code does not have access to local scope.

script.runInContext takes the same options as script.runInThisContext.

Example: compile code that increments a global variable and sets one, then execute the code multiple times. These globals are contained in the sandbox.

var util = require('util');
var vm = require('vm');

var sandbox = {
  animal: 'cat',
  count: 2
};

var script = new vm.Script('count += 1; name = "kitty"');

for (var i = 0; i < 10; ++i) {
  script.runInContext(sandbox);
}

console.log(util.inspect(sandbox));

// { animal: 'cat', count: 12, name: 'kitty' }

Note that running untrusted code is a tricky business requiring great care. script.runInContext is quite useful, but safely running untrusted code requires a separate process.

script.runInNewContext([sandbox][, options])

Similar to vm.runInNewContext but a method of a precompiled Script object. script.runInNewContext contextifies sandbox if passed or creates a new contextified sandbox if it’s omitted, and then runs script’s compiled code with the sandbox as the global object and returns the result. Running code does not have access to local scope.

script.runInNewContext takes the same options as script.runInThisContext.

Example: compile code that sets a global variable, then execute the code multiple times in different contexts. These globals are set on and contained in the sandboxes.

var util = require('util');
var vm = require('vm');

var sandboxes = [{}, {}, {}];

var script = new vm.Script('globalVar = "set"');

sandboxes.forEach(function (sandbox) {
  script.runInNewContext(sandbox);
});

console.log(util.inspect(sandboxes));

// [{ globalVar: 'set' }, { globalVar: 'set' }, { globalVar: 'set' }]

Note that running untrusted code is a tricky business requiring great care. script.runInNewContext is quite useful, but safely running untrusted code requires a separate process.

Zlib

Stability: 3 - Stable

You can access this module with:

var zlib = require('zlib');

This provides bindings to Gzip/Gunzip, Deflate/Inflate, and DeflateRaw/InflateRaw classes. Each class takes the same options, and is a readable/writable Stream.

Examples

Compressing or decompressing a file can be done by piping an fs.ReadStream into a zlib stream, then into an fs.WriteStream.

var gzip = zlib.createGzip();
var fs = require('fs');
var inp = fs.createReadStream('input.txt');
var out = fs.createWriteStream('input.txt.gz');

inp.pipe(gzip).pipe(out);

Compressing or decompressing data in one step can be done by using the convenience methods.

var input = '.................................';
zlib.deflate(input, function(err, buffer) {
  if (!err) {
    console.log(buffer.toString('base64'));
  }
});

var buffer = new Buffer('eJzT0yMAAGTvBe8=', 'base64');
zlib.unzip(buffer, function(err, buffer) {
  if (!err) {
    console.log(buffer.toString());
  }
});

To use this module in an HTTP client or server, use the accept-encoding on requests, and the content-encoding header on responses.

Note: these examples are drastically simplified to show the basic concept. Zlib encoding can be expensive, and the results ought to be cached. See Memory Usage Tuning below for more information on the speed/memory/compression tradeoffs involved in zlib usage.

// client request example
var zlib = require('zlib');
var http = require('http');
var fs = require('fs');
var request = http.get({ host: 'izs.me',
                         path: '/',
                         port: 80,
                         headers: { 'accept-encoding': 'gzip,deflate' } });
request.on('response', function(response) {
  var output = fs.createWriteStream('izs.me_index.html');

  switch (response.headers['content-encoding']) {
    // or, just use zlib.createUnzip() to handle both cases
    case 'gzip':
      response.pipe(zlib.createGunzip()).pipe(output);
      break;
    case 'deflate':
      response.pipe(zlib.createInflate()).pipe(output);
      break;
    default:
      response.pipe(output);
      break;
  }
});

// server example
// Running a gzip operation on every request is quite expensive.
// It would be much more efficient to cache the compressed buffer.
var zlib = require('zlib');
var http = require('http');
var fs = require('fs');
http.createServer(function(request, response) {
  var raw = fs.createReadStream('index.html');
  var acceptEncoding = request.headers['accept-encoding'];
  if (!acceptEncoding) {
    acceptEncoding = '';
  }

  // Note: this is not a conformant accept-encoding parser.
  // See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.3
  if (acceptEncoding.match(/\bdeflate\b/)) {
    response.writeHead(200, { 'content-encoding': 'deflate' });
    raw.pipe(zlib.createDeflate()).pipe(response);
  } else if (acceptEncoding.match(/\bgzip\b/)) {
    response.writeHead(200, { 'content-encoding': 'gzip' });
    raw.pipe(zlib.createGzip()).pipe(response);
  } else {
    response.writeHead(200, {});
    raw.pipe(response);
  }
}).listen(1337);

zlib.createGzip([options])

Returns a new Gzip object with an options.

zlib.createGunzip([options])

Returns a new Gunzip object with an options.

zlib.createDeflate([options])

Returns a new Deflate object with an options.

zlib.createInflate([options])

Returns a new Inflate object with an options.

zlib.createDeflateRaw([options])

Returns a new DeflateRaw object with an options.

zlib.createInflateRaw([options])

Returns a new InflateRaw object with an options.

zlib.createUnzip([options])

Returns a new Unzip object with an options.

Class: zlib.Zlib

Not exported by the zlib module. It is documented here because it is the base class of the compressor/decompressor classes.

zlib.flush([kind], callback)

kind defaults to zlib.Z_FULL_FLUSH.

Flush pending data. Don’t call this frivolously, premature flushes negatively impact the effectiveness of the compression algorithm.

zlib.params(level, strategy, callback)

Dynamically update the compression level and compression strategy. Only applicable to deflate algorithm.

zlib.reset()

Reset the compressor/decompressor to factory defaults. Only applicable to the inflate and deflate algorithms.

Class: zlib.Gzip

Compress data using gzip.

Class: zlib.Gunzip

Decompress a gzip stream.

Class: zlib.Deflate

Compress data using deflate.

Class: zlib.Inflate

Decompress a deflate stream.

Class: zlib.DeflateRaw

Compress data using deflate, and do not append a zlib header.

Class: zlib.InflateRaw

Decompress a raw deflate stream.

Class: zlib.Unzip

Decompress either a Gzip- or Deflate-compressed stream by auto-detecting the header.

Convenience Methods

All of these take a string or buffer as the first argument, an optional second argument to supply options to the zlib classes and will call the supplied callback with callback(error, result).

Every method has a *Sync counterpart, which accept the same arguments, but without a callback.

zlib.deflate(buf[, options], callback)

zlib.deflateSync(buf[, options])

Compress a string with Deflate.

zlib.deflateRaw(buf[, options], callback)

zlib.deflateRawSync(buf[, options])

Compress a string with DeflateRaw.

zlib.gzip(buf[, options], callback)

zlib.gzipSync(buf[, options])

Compress a string with Gzip.

zlib.gunzip(buf[, options], callback)

zlib.gunzipSync(buf[, options])

Decompress a raw Buffer with Gunzip.

zlib.inflate(buf[, options], callback)

zlib.inflateSync(buf[, options])

Decompress a raw Buffer with Inflate.

zlib.inflateRaw(buf[, options], callback)

zlib.inflateRawSync(buf[, options])

Decompress a raw Buffer with InflateRaw.

zlib.unzip(buf[, options], callback)

zlib.unzipSync(buf[, options])

Decompress a raw Buffer with Unzip.

Options

Each class takes an options object. All options are optional.

Note that some options are only relevant when compressing, and are ignored by the decompression classes.

flush (default: zlib.Z_NO_FLUSH)

chunkSize (default: 16*1024)

windowBits

level (compression only)

memLevel (compression only)

strategy (compression only)

dictionary (deflate/inflate only, empty dictionary by default)

See the description of deflateInit2 and inflateInit2 at http://zlib.net/manual.html#Advanced for more information on these.

Memory Usage Tuning

From zlib/zconf.h, modified to node’s usage:

The memory requirements for deflate are (in bytes):

(1 << (windowBits+2)) +  (1 << (memLevel+9))

that is: 128K for windowBits=15 + 128K for memLevel = 8 (default values) plus a few kilobytes for small objects.

For example, if you want to reduce the default memory requirements from 256K to 128K, set the options to:

{ windowBits: 14, memLevel: 7 }

Of course this will generally degrade compression (there’s no free lunch).

The memory requirements for inflate are (in bytes)

1 << windowBits

that is, 32K for windowBits=15 (default value) plus a few kilobytes for small objects.

This is in addition to a single internal output slab buffer of size chunkSize, which defaults to 16K.

The speed of zlib compression is affected most dramatically by the level setting. A higher level will result in better compression, but will take longer to complete. A lower level will result in less compression, but will be much faster.

In general, greater memory usage options will mean that node has to make fewer calls to zlib, since it’ll be able to process more data in a single write operation. So, this is another factor that affects the speed, at the cost of memory usage.

Constants

All of the constants defined in zlib.h are also defined on require('zlib'). In the normal course of operations, you will not need to ever set any of these. They are documented here so that their presence is not surprising. This section is taken almost directly from the zlib documentation. See http://zlib.net/manual.html#Constants for more details.

Allowed flush values.

zlib.Z_NO_FLUSH

zlib.Z_PARTIAL_FLUSH

zlib.Z_SYNC_FLUSH

zlib.Z_FULL_FLUSH

zlib.Z_FINISH

zlib.Z_BLOCK

zlib.Z_TREES

Return codes for the compression/decompression functions. Negative values are errors, positive values are used for special but normal events.

zlib.Z_OK

zlib.Z_STREAM_END

zlib.Z_NEED_DICT

zlib.Z_ERRNO

zlib.Z_STREAM_ERROR

zlib.Z_DATA_ERROR

zlib.Z_MEM_ERROR

zlib.Z_BUF_ERROR

zlib.Z_VERSION_ERROR

Compression levels.

zlib.Z_NO_COMPRESSION

zlib.Z_BEST_SPEED

zlib.Z_BEST_COMPRESSION

zlib.Z_DEFAULT_COMPRESSION

Compression strategy.

zlib.Z_FILTERED

zlib.Z_HUFFMAN_ONLY

zlib.Z_RLE

zlib.Z_FIXED

zlib.Z_DEFAULT_STRATEGY

Possible values of the data_type field.

zlib.Z_BINARY

zlib.Z_TEXT

zlib.Z_ASCII

zlib.Z_UNKNOWN

The deflate compression method (the only one supported in this version).

zlib.Z_DEFLATED

For initializing zalloc, zfree, opaque.

zlib.Z_NULL