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zlib: fix decompression of empty data streams #17042

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zlib: fix decompression of empty data streams #17042

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5 changes: 5 additions & 0 deletions lib/zlib.js
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Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,8 @@ function zlibBufferOnEnd() {
var err;
if (this.nread >= kMaxLength) {
err = new errors.RangeError('ERR_BUFFER_TOO_LARGE');
} else if (this.nread === 0) {
buf = Buffer.alloc(0);
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I don't know if there is any performance penalty to use Buffer.alloc(0) vs Buffer.allocUnsafe(0). However, as it's 0 I would use allocUnsafe.

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alloc() has what is essentially a fast path for 0, allocUnsafe() doesn’t.

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This is very interesting. thanks!

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I mean, I don’t think it’s that way on purpose. :) It just happens to align nicely with how we can use basically new Uint8Array(n) for the Buffer.alloc() fast path, whereas Buffer.allocUnsafe() needs a bit of setup.

} else {
var bufs = this.buffers;
buf = (bufs.length === 1 ? bufs[0] : Buffer.concat(bufs, this.nread));
Expand Down Expand Up @@ -485,6 +487,9 @@ function processChunkSync(self, chunk, flushFlag) {

_close(self);

if (nread === 0)
return Buffer.alloc(0);

return (buffers.length === 1 ? buffers[0] : Buffer.concat(buffers, nread));
}

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26 changes: 26 additions & 0 deletions test/parallel/test-zlib-empty-buffer.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
'use strict';
const common = require('../common');
const zlib = require('zlib');
const { inspect, promisify } = require('util');
const assert = require('assert');
const emptyBuffer = new Buffer(0);

common.crashOnUnhandledRejection();

(async function() {
for (const [ compress, decompress, method ] of [
[ zlib.deflateRawSync, zlib.inflateRawSync, 'raw sync' ],
[ zlib.deflateSync, zlib.inflateSync, 'deflate sync' ],
[ zlib.gzipSync, zlib.gunzipSync, 'gzip sync' ],
[ promisify(zlib.deflateRaw), promisify(zlib.inflateRaw), 'raw' ],
[ promisify(zlib.deflate), promisify(zlib.inflate), 'deflate' ],
[ promisify(zlib.gzip), promisify(zlib.gunzip), 'gzip' ]
]) {
const compressed = await compress(emptyBuffer);
const decompressed = await decompress(compressed);
assert.deepStrictEqual(
emptyBuffer, decompressed,
`Expected ${inspect(compressed)} to match ${inspect(decompressed)} ` +
`to match for ${method}`);
}
})();