A byte buffer in PHP? - php

Question

I am working with a project which uses a custom TCP protocol. I have everything down the line, except for one thing: The protocol requires 4 bites before the message, that determine the length of the package. In NodeJS, this is done via:
var b = new Buffer(4);
b.writeUInt32BE(data.length, 0);
But is there such a way in PHP also? I was considering using pack() - but I have no experience with this function. I also need to read a package of the same format, so I also need to be able to obtain the integer from the first 4 bites too.

Answer 1

Using pack is the correct way to go in PHP and here is an example of how to use it to return the information you require:
<?php
$string = 'hello world';
$bytes = pack ( 'N', strlen ( $string ) ); // unsigned 32 bit big endian byte order
?>
To parse the first 4 raw bytes back into a number, this is assuming the a variable named $rawBytes contains the data read from the tcp packet.
<?php
$decoded = unpack ( 'N', substr ( $rawBytes, 0, 4 ); );
$length = end ( $decoded );
?>
One unfortunate gotcha within PHP is that the binary only understands 32bit signed integers on Windows machines and on 32bit Linux/Macintosh/Unix machines.
−2,147,483,648 to 2,147,483,647
64bit PHP binaries running on Linux/Macintosh/Unix machines have the maximum integer value of a signed 64bit integer.
−9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
But using 64bit binary on a Windows machine still has an integer size of a 32bit signed integer.
Anything outside of the integer bounds will be cast to a floating point number.