Akka-http：连接到本地主机上的websocket

Question

I am trying to connect to some server through websocket on localhost. When I try to do it in JS by

ws = new WebSocket('ws://localhost:8137');

it succeeds. However, when I use akka-http and akka-streams I get "connection failed" error.

object Transmitter {
    implicit val system: ActorSystem = ActorSystem()
    implicit val materializer: ActorMaterializer = ActorMaterializer()

    import system.dispatcher

    object Rec extends Actor {
        override def receive: Receive = {
            case TextMessage.Strict(msg) =>
                Log.info("Recevied signal " + msg)
        }
    }

    //  val host = "ws://echo.websocket.org"
    val host = "ws://localhost:8137"

    val sink: Sink[Message, NotUsed] = Sink.actorRef[Message](system.actorOf(Props(Rec)), PoisonPill)


    val source: Source[Message, NotUsed] = Source(List("test1", "test2") map (TextMessage(_)))


    val flow: Flow[Message, Message, Future[WebSocketUpgradeResponse]] =
        Http().webSocketClientFlow(WebSocketRequest(host))

    val (upgradeResponse, closed) =
        source
        .viaMat(flow)(Keep.right) // keep the materialized Future[WebSocketUpgradeResponse]
        .toMat(sink)(Keep.both) // also keep the Future[Done]
        .run()

    val connected: Future[Done.type] = upgradeResponse.flatMap { upgrade =>
        if (upgrade.response.status == StatusCodes.SwitchingProtocols) {
            Future.successful(Done)
        } else {
            Future.failed(new Exception(s"Connection failed: ${upgrade.response.status}")
        }
    }

    def test(): Unit = {
        connected.onComplete(Log.info)
    }
}

It works completely OK with ws://echo.websocket.org.

I think attaching code of my server is reasonless, because it works with JavaScript client and problem is only with connection, however if you would like to look at it I may show it.

What am I doing wrong?

Answer 1

I have tested your client implementation with a websocket server from akka documentation , and I did not get any connection error. Your websocket client connects successfully. That is why I am guessing the problem is with your server implementation.

object WebSocketServer extends App {
  implicit val system = ActorSystem()
  implicit val materializer = ActorMaterializer()
  import Directives._

  val greeterWebSocketService = Flow[Message].collect {
    case tm: TextMessage => TextMessage(Source.single("Hello ") ++ tm.textStream)
  }

  val route =
    get {
      handleWebSocketMessages(greeterWebSocketService)
    }

  val bindingFuture = Http().bindAndHandle(route, "localhost", 8137)

  println(s"Server online at http://localhost:8137/\nPress RETURN to stop...")
  StdIn.readLine()

  import system.dispatcher // for the future transformations
  bindingFuture
    .flatMap(_.unbind()) // trigger unbinding from the port
    .onComplete(_ => system.terminate()) // and shutdown when done
}

By the way, I noticed that your actor's receive method does not cover all possible messages. According to that akka issue , every message, even very small, can end up as Streamed . If you want to print all text messages a better implementation of the actor would be:

object Rec extends Actor {
  override def receive: Receive = {
    case TextMessage.Strict(text)             ⇒ println(s"Received signal $text")
    case TextMessage.Streamed(textStream)     ⇒ textStream.runFold("")(_ + _).foreach(msg => println(s"Received streamed signal: $msg"))
  }
}

Please find a working project on my github .

Answer 2

I found the solution: the server I used was running on IPv6 (as ::1), but akka-http treats localhost as 127.0.0.1 and ignores ::1. I had to rewrite server to force it to use IPv4 and it worked.