CODESAMPLE

Peer-to-Peer - PHP

Peer-to-Peer PHP

The Peer-to-Peer (P2P) pattern enables direct communication and data exchange between independent components (“peers”) without relying on a central server or intermediary. Each peer acts as both a client and a server, discovering and interacting with other peers directly. This implementation uses simple file-based “discovery” to allow peers to find each other. Each peer writes its address to a shared peers.txt file. Then, another peer reads this file to discover addresses for connection. PHP’s file system functions and basic socket programming are utilized for simplicity—a production system would use more robust discovery mechanisms.

<?php

/**
 * Peer-to-Peer Example in PHP
 */

class Peer {
  private $address;
  private $port;

  public function __construct(string $address, int $port) {
    $this->address = $address;
    $this->port = $port;
  }

  public function publishPeer(string $peersFile): void {
    file_put_contents($peersFile, $this->address . ":" . $this->port . PHP_EOL, FILE_APPEND);
  }

  public function discoverPeers(string $peersFile): array {
    $peers = [];
    $lines = file($peersFile, FILE_IGNORE_NEW_LINES);

    if ($lines) {
      foreach ($lines as $line) {
        list($addr, $port) = explode(":", $line);
        $peers[] = new self($addr, (int)$port);
      }
    }

    return $peers;
  }

  public function communicate(Peer $peer, string $message): string {
    // Simple socket communication (error handling omitted for brevity)
    $socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
    socket_connect($socket, $peer->address, $peer->port);
    socket_send($socket, $message, strlen($message), 0);
    $response = socket_read($socket, 2048);
    socket_close($socket);

    return $response;
  }

  public function getAddress(): string {
      return $this->address . ":" . $this->port;
  }
}

// Example Usage:
$peersFile = 'peers.txt';

// Peer 1 (Publishes itself)
$peer1 = new Peer('127.0.0.1', 8000);
$peer1->publishPeer($peersFile);
echo "Peer 1 published: " . $peer1->getAddress() . PHP_EOL;

// Peer 2 (Publishes itself)
$peer2 = new Peer('127.0.0.1', 8001);
$peer2->publishPeer($peersFile);
echo "Peer 2 published: " . $peer2->getAddress() . PHP_EOL;

// Peer 3 (Discovers and communicates)
$peer3 = new Peer('127.0.0.1', 8002);
$peers = $peer3->discoverPeers($peersFile);
echo "Peer 3 discovered peers: " . PHP_EOL;
foreach($peers as $peer){
    echo "  - " . $peer->getAddress() . PHP_EOL;
}

if ($peers) {
    $response = $peer3->communicate($peers[0], "Hello from Peer 3!");
    echo "Peer 3 received: " . $response . PHP_EOL;
} else {
    echo "No peers discovered." . PHP_EOL;
}

?>