Recipe Echo Server

Recipe — Echo Server

The smallest server that demonstrates accept, read and write. We do it twice — once over TCP, once over UDP — so the differences are visible side by side.

TCP echo

tcp-echo-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', 9000);
$server->listen();

echo "TCP echo on 127.0.0.1:9000\n";

$server->live(function (SocketServerInterface $srv, SocketConnectionInterface $conn) {
    $payload = $conn->read(1024);
    if ($payload === null) {
        return;
    }
    $conn->write("echo: {$payload}");
});

php tcp-echo-server.php

From another terminal:

$ nc 127.0.0.1 9000
hi
echo: hi

A matching TCP client

tcp-echo-client.php:

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

use InitPHP\Socket\Socket;
use InitPHP\Socket\Enum\Transport;

$client = Socket::client(Transport::TCP, '127.0.0.1', 9000);
$client->connect();

$client->write("hello\n");
echo $client->read(1024);   // -> "echo: hello\n"

$client->disconnect();

UDP echo

udp-echo-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::UDP, '127.0.0.1', 9001);
$server->listen();

echo "UDP echo on 127.0.0.1:9001\n";

$server->live(function (SocketServerInterface $srv, SocketConnectionInterface $conn) {
    $payload = $conn->read(65535);
    if ($payload === null) {
        return;
    }
    $conn->write("echo: {$payload}");
});

php udp-echo-server.php

From another terminal:

$ echo -n 'ping' | nc -u -w1 127.0.0.1 9001
echo: ping

A matching UDP client

udp-echo-client.php:

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

use InitPHP\Socket\Socket;
use InitPHP\Socket\Enum\Transport;

$client = Socket::client(Transport::UDP, '127.0.0.1', 9001);
$client->connect();

$client->write('ping');
echo $client->read(65535);

$client->disconnect();

What changes between TCP and UDP

• The transport enum case (TCP vs UDP).
• Read buffer size: 1 KiB is plenty for ad-hoc TCP framing; UDP needs to be big enough for one whole datagram (UdpChannel::MAX_DATAGRAM = 65535).
• UDP has no half-close and no notion of disconnection on the server side. If a client stops talking, the server still keeps its UdpChannel. Evict idle peers with an application-level TTL — see Transport UDP.

What stays the same

• Lifecycle: listen() → live(callback) → close() (clean shutdown).
• The callback signature (SocketServerInterface, SocketConnectionInterface).
• $conn->read() returns ?string, $conn->write() returns ?int.

See also

• Transport TCP / Transport UDP — transport-specific details.
• Recipe Broadcast — fan out a message to multiple peers.
• Event Loop Integration — drive the same server from tick() instead of live().