Allow accessing websocket connections via protocol

[thekid]

This allows writing a websocket-based chat, including running it with the development webserver.

use io\redis\RedisProtocol;
use web\Application;
use web\handler\WebSocket;

class Chat extends Application {

  public function initialize($kernel) {
    $redis= new RedisProtocol('redis://localhost');
    $redis->command('SUBSCRIBE', 'chat');

    $kernel->server->select($redis->socket(), function($socket) use($redis, $kernel) {
      $websocket= $kernel->protocol('websocket');
      while (!$socket->eof()) {
        yield 'read' => null;
        [, , $payload]= $redis->receive();
        $input= json_decode($payload, true);
        $output= /* ...shortened for brevity */;
        
        $websocket->broadcast($output, prioritize: [$input['id']]);
      }
    });
  }

  public function routes() {
    $redis= new RedisProtocol('redis://localhost');
    return [
      '/ws' => new WebSocket(function($conn, $payload) use($redis) {
        if ($input= json_decode($payload, true)) {
          $redis->command('PUBLISH', 'chat', json_encode(['id' => $conn->id()] + $input));
        }
      }),
      '/' => function($request, $response) {
        // ...shortened for brevity: output HTML / CSS / JavaScript to connect
      }
    ];
  }
}