provide a peeking API to std.io.BufferedReader

[andrewrk]

The point of BufferedInStream is to call read() on the underlying stream in bursts, rather than separate calls. E.g. to make 1 syscall to read() reading 999 bytes, rather than 999 syscalls to read() reading 1 byte each.

The point of PeekStream is to be able to "put back" bytes, so that the next call to read() will get them again. In order to accomplish this, PeekStream needs a buffer. That makes PeekStream also a BufferedInStream.

All we need to unify these two APIs is for BufferedInStream to have a parameter called reserved_buffer_space or something like this, and then it's guaranteed to be able to "put back" this many elements.

Related:

• change std.io.BufferedReader and std.io.BufferedWriter to accept the buffer as a runtime parameter, and use AnyReader / AnyWriter #19298

[pierrec]

Hello,

Since I make use of io.PeekStream and it just got removed, I would like to contribute to this issue.
The idea is to simply implement the old methods on BufferedReader.

pub fn putBackByte(self: *Self, byte: u8) !void { ... }

pub fn putBack(self: *Self, byte: []u8) !void { ... }

Would this be acceptable?

[nektro]

that seems backwards. there should be a peek() function that returns br.buf[br.start] and read() should eat the byte

[travisstaloch]

that seems backwards. there should be a peek()

I agree that it would be nice to have a peek(). How about peek([]u8) !void and peekByte() !u8?

But previously io.PeekStream() had putBackByte(u8) and putBack([]const u8). So maybe we could have both peek() and putBack()?

[septemhill]

I have a question, how do we handle the data after peek ? use read to consume or add one more method discard to ignore the data (byte or slice) ?

Edit: I didn't notice that the putBack maybe the solution of my question, sorry