A simple example of responding to a websocket message with backpressure using Akka

WsPingPong.scala

class WsPingPong extends Actor {
  import WsPingPong._

  private implicit val materializer = ActorMaterializer()

  private val queue =
    Source.queue[Message](Int.MaxValue, OverflowStrategy.backpressure)
      .via(Http().webSocketClientFlow(WebSocketRequest("wss://pingpongsockets.org")))
      .to(Sink.actorRefWithAck(self, Init, Ack, Complete))
      .run()

  override def receive: Receive = {
    case Init =>
      sender ! Ack
    case TextMessage.Strict("ping") =>
      queue.offer(TextMessage("pong"))
      sender ! Ack
    case TextMessage.Strict("pong") =>
      queue.offer(TextMessage("ping"))
      sender ! Ack
    case Complete =>
      context.stop(self)
  }
}

object WsPingPong {
  private case object Init
  private case object Ack
  private case object Complete
}