PHP Quake Live ZMQ implementation

// Created by Thomas 'tjone270' Jones - 12-01-17 6:39pm
class QL_Server {
  public $ip, $persistant;
  protected $rconport, $rconpassword;
  private $zmq, $connectionString;

  const IDENTITY = "ControlPanel";
  const WAIT_uS = 1000000;

  public function __construct($ip, $rconpassword, $rconport = "28960", $persistant = true) {
    $this->ip = $ip;
    $this->rconport = $rconport;
    $this->rconpassword = $rconpassword;
    $this->persistant = $persistant;
    $this->connectionString = ("tcp://${ip}:${rconport}");
    $this->zmq = new ZMQSocket(new ZMQContext(), ZMQ::SOCKET_DEALER);
    $this->zmq->setSockOpt(ZMQ::SOCKOPT_PLAIN_USERNAME, "rcon");
    $this->zmq->setSockOpt(ZMQ::SOCKOPT_PLAIN_PASSWORD, $this->rconpassword);
    $this->zmq->setSockOpt(ZMQ::SOCKOPT_IDENTITY, self::IDENTITY);
    $this->zmq->setSockOpt(ZMQ::SOCKOPT_ZAP_DOMAIN, "rcon");
    $this->zmq->connect($this->connectionString);
    $this->zmq->send("register");
  }

  public function __destruct() {
    if (!$this->persistant) {
      $this->zmq->disconnect($this->connectionString);
    }
  }

  public function command($command, $filter = true) {
    $this->zmq->send($command);

    usleep(self::WAIT_uS); // otherwise the server crashes...

    $done = false;
    while (!$done) {
      $recv = $this->zmq->recv();
      if ($recv) {
        $response[] = $recv;
      } else {
        $done = true;
      }
    }

    if ($filter) {
      array_shift($response);
    }

    return implode($response);
  }
}