Akka-http: connect to websocket on localhost - scala

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.