}
    }

    fun listener(listener: Listener) =
      apply {
        this.listener = listener
      }

    fun pushObserver(pushObserver: PushObserver) =
      apply {
        this.pushObserver = pushObserver
      }

    fun pingIntervalMillis(pingIntervalMillis: Int) =
      apply {
        this.pingIntervalMillis = pingIntervalMillis
      }