PHP WebSockets

WebSockets keep an open line between the browser and the server, like a phone call instead of sending letters. Both sides can talk any time, which is great for chat and live updates.

In this page:

Introduction to WebSockets
Socket Server Initialization
Handling Handshake Requests
Formatting Data Frames
Client Connection Manager

Introduction to WebSockets

WebSockets keep a single connection open between browser and server for as long as needed, allowing both sides to push data at any time -- unlike HTTP, where the server can only respond after the client asks.

Example: Introduction to WebSockets

php

<?php
// Print "WebSockets keep one connection open so either side can push data anytime" to the output
echo "WebSockets keep one connection open so either side can push data anytime";
?>

Socket Server Initialization

stream_socket_server() opens a raw socket that listens for incoming connections, forming the low-level foundation a PHP WebSocket server is built on top of.

Example: Socket Server Initialization

php

<?php
// Declare `$socket`, set to `stream_socket_server("tcp://127.0.0.1:0", $errno, $errstr)`
$socket = stream_socket_server("tcp://127.0.0.1:0", $errno, $errstr);
// Print `$socket ? "Socket server listening" : "Failed: $errstr"` to the output
echo $socket ? "Socket server listening" : "Failed: $errstr";
if ($socket) fclose($socket);
?>

Handling Handshake Requests

Establishing a WebSocket connection requires a specific handshake: the server takes the client's Sec-WebSocket-Key, combines it with a fixed magic string, hashes it, and returns the result to confirm the upgrade.

Example: Handling Handshake Requests

php

<?php
// Declare `$key`, set to "dGhlIHNhbXBsZSBub25jZQ=="
$key = "dGhlIHNhbXBsZSBub25jZQ==";
// Declare `$magic`, set to "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
$magic = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
// Declare `$accept`, set to `base64_encode(sha1($key . $magic, true))`
$accept = base64_encode(sha1($key . $magic, true));
// Print `$accept` to the output
echo $accept;
?>

Formatting Data Frames

WebSocket messages travel as binary-framed packets rather than plain text, so outgoing strings must be wrapped in the correct frame format before being written to the socket.

Example: Formatting Data Frames

php

<?php
// Define the function `encodeFrame` taking `$message`
function encodeFrame($message) {
    // Declare `$length`, set to `strlen($message)`
    $length = strlen($message);
    // Return `chr(129) . chr($length) . $message` from this function
    return chr(129) . chr($length) . $message;
}
// Print `bin2hex(encodeFrame("hi"))` to the output
echo bin2hex(encodeFrame("hi"));
?>

Client Connection Manager

Because a WebSocket server may serve many clients at once, keeping open connections in an array registry lets you broadcast to all of them, message a specific one, or clean up connections that have disconnected.

Example: Client Connection Manager

php

<?php
// Declare `$clients` as an empty array
$clients = [];
// Set `$clients['conn1']` to "socket_resource_1"
$clients['conn1'] = "socket_resource_1";
// Set `$clients['conn2']` to "socket_resource_2"
$clients['conn2'] = "socket_resource_2";
// Loop over `$clients`, binding each item to `$id => $conn`
foreach ($clients as $id => $conn) {
    // Print "Broadcasting to $id\n" to the output
    echo "Broadcasting to $id\n";
}
?>

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