Recipe Chat Server

Recipe — Chat Server

A TCP server that supports named clients and directed messages. The protocol is line-oriented:

Command	Effect
REGISTER alice	Claim the name alice for the rest of the session.
SEND @bob hello bob	Direct-message bob.
quit / exit	Disconnect.
anything else	Broadcast to every connected client.

Server

chat-server.php:

<?php
require __DIR__ . '/vendor/autoload.php';

use InitPHP\Socket\Socket;
use InitPHP\Socket\Enum\Transport;
use InitPHP\Socket\Interfaces\{SocketServerInterface, SocketConnectionInterface};

$server = Socket::server(Transport::TCP, '127.0.0.1', 8080);
$server->listen();

echo "Chat server listening on 127.0.0.1:8080\n";

$server->live(function (SocketServerInterface $srv, SocketConnectionInterface $conn) {
    $line = $conn->read(4096);
    if ($line === null) {
        return;
    }
    $line = trim($line);
    if ($line === '') {
        return;
    }

    if (in_array($line, ['quit', 'exit'], true)) {
        $conn->write("Goodbye!\n");
        $conn->close();
        return;
    }

    if (preg_match('/^REGISTER\s+([\w-]{3,})$/i', $line, $m) === 1) {
        $srv->register($m[1], $conn);
        $conn->write("Registered as {$m[1]}\n");
        return;
    }

    if (preg_match('/^SEND\s+@([\w-]+)\s+(.+)$/i', $line, $m) === 1) {
        $sender = $conn->getId() ?? 'guest';
        $srv->broadcast("[{$sender} → {$m[1]}] {$m[2]}\n", $m[1]);
        return;
    }

    $sender = $conn->getId() ?? 'guest';
    $srv->broadcast("[{$sender}] {$line}\n");
});

Try it

Run the server:

php chat-server.php

Open two more terminals and connect with nc:

$ nc 127.0.0.1 8080                              # terminal A
REGISTER alice
Registered as alice

$ nc 127.0.0.1 8080                              # terminal B
REGISTER bob
Registered as bob
SEND @alice hey there
                                                  # terminal A sees:
                                                  # [bob → alice] hey there

hello room                                        # terminal B
                                                  # both terminals see:
                                                  # [bob] hello room

How it works

Registering an id

SocketServerInterface::register(int|string, SocketConnectionInterface) does two things:

1. Calls setId() on the connection so future code can identify it.
2. Updates the server's internal clientIdMap so broadcast() can address the connection by id.

Until register() is called, $conn->getId() returns null and broadcast(msg, 'alice') will skip the connection.

Broadcasting

broadcast() accepts three shapes:

$srv->broadcast('mass');                  // every alive client
$srv->broadcast('alice-only', 'alice');   // single id
$srv->broadcast('vips', ['alice','bob']); // multiple ids

Unknown ids are silently skipped — the loop short-circuits with a isset($this->clientIdMap[$id]) check.

close() from inside the callback

$conn->close() is safe to call from inside the callback. The server's loop checks isAlive() on every iteration before invoking the callback, so the closed connection is evicted on the next tick() and never receives a message again.

Race-condition note

The "register" workflow is application-level — the server does not enforce uniqueness, nor does it verify the registering client is the rightful owner of the name. Add your own auth on top if that matters.

Variations

Refuse unregistered users from broadcasting

if ($conn->getId() === null) {
    $conn->write("REGISTER first.\n");
    return;
}

Slot that at the top of the broadcast branches.

Per-room dispatch

register() accepts both int and string. Use composite ids like "room1#alice" and target a room with a list:

$srv->broadcast('hi room', array_filter(
    array_map(
        fn ($c) => $c->getId(),
        $srv->getClients(),
    ),
    fn ($id) => is_string($id) && str_starts_with($id, 'room1#'),
));

Drop dead peers proactively

The server already evicts disconnected clients on the next loop iteration. To do it more eagerly (e.g. when running this on UDP where there is no kernel close signal), call $conn->isAlive() in your callback and $conn->close() if you decide the peer is gone.

See also

• Recipe Broadcast — the dispatch patterns isolated.
• Connection and Channel — what setId() / getId() actually do.
• Server Lifecycle — register() / broadcast() semantics across states.