Build a UDP Server with Swoole in PHP – Step‑by‑Step Guide

Swoole\Server provides a simple way to build high‑performance UDP servers in PHP. The example creates a server that listens on 127.0.0.1:9502 using the SWOOLE_SOCK_UDP socket type.

<?php
// Create a Server object listening on 127.0.0.1:9502 with UDP socket
$serv = new Swoole\Server("127.0.0.1", 9502, SWOOLE_PROCESS, SWOOLE_SOCK_UDP);

// Register the packet‑receive event handler
$serv->on('Packet', function ($serv, $data, $clientInfo) {
    // Send a response back to the client
    $serv->sendto($clientInfo['address'], $clientInfo['port'], "Server " . $data);
    // Dump client information for debugging
    var_dump($clientInfo);
});

// Start the server
$serv->start();

The $clientInfo variable is an associative array containing the client’s IP address ( 'address') and port ( 'port'). Inside the on('Packet') callback, the sendto method is used to send data back to the client.

Running the Server

Save the code above as udp_server.php and start it from the command line: php udp_server.php After the server starts, you can verify that it is listening on port 9502 with tools such as netstat.

Testing with Netcat

Because UDP is connection‑less, a client can send packets directly without a prior connect. Use netcat (or nc) to send a test message:

netcat -u 127.0.0.1 9502
hello Server

The server will echo back the received data prefixed with "Server ". The callback also prints the $clientInfo array, allowing you to see the client’s address and port.

$clientInfo holds the client’s IP and port information.

Use $serv->sendto to reply to a specific UDP client.

This example illustrates the essential steps for building, running, and testing a UDP server with Swoole, which can be extended for more complex networking scenarios.