How to listen websocket server close events using akka-http websocket client - scala

Question

I have websocket client connected to akka-http websocket server , how can i listen to connection close events happened on server( i.e server shutdown/ server closed websocket connection) ?
object Client extends App {
implicit val actorSystem = ActorSystem("akka-system")
implicit val flowMaterializer = ActorMaterializer()
val config = actorSystem.settings.config
val interface = config.getString("app.interface")
val port = config.getInt("app.port")
// print each incoming strict text message
val printSink: Sink[Message, Future[Done]] =
Sink.foreach {
case message: TextMessage.Strict =>
println(message.text)
case _ => {
sourceQueue.map(q => {
println(s"offering message on client")
q.offer(TextMessage("received unknown"))
})
println(s"received unknown message format")
}
}
val (source, sourceQueue) = {
val p = Promise[SourceQueue[Message]]
val s = Source.queue[Message](Int.MaxValue, OverflowStrategy.backpressure).mapMaterializedValue(m => {
p.trySuccess(m)
m
})
.keepAlive(FiniteDuration(1, TimeUnit.SECONDS), () => TextMessage.Strict("Heart Beat"))
(s, p.future)
}
val flow =
Flow.fromSinkAndSourceMat(printSink, source)(Keep.right)
val (upgradeResponse, sourceClose) =
Http().singleWebSocketRequest(WebSocketRequest("ws://localhost:8080/ws-echo"), flow)
val connected = upgradeResponse.map { upgrade =>
// just like a regular http request we can get 404 NotFound,
// with a response body, that will be available from upgrade.response
if (upgrade.response.status == StatusCodes.SwitchingProtocols || upgrade.response.status == StatusCodes.SwitchingProtocols) {
Done
} else {
throw new RuntimeException(s"Connection failed: ${upgrade.response.status}")
}
}
connected.onComplete(println)
}

Answer 1

Websocket connection termination is modeled as a regular stream completion, therefore in your case you can use the materialized Future[Done] yielded by Sink.foreach:
val flow = Flow.fromSinkAndSourceMat(printSink, source)(Keep.both)
val (upgradeResponse, (sinkClose, sourceClose)) =
Http().singleWebSocketRequest(..., flow)
sinkClose.onComplete {
case Success(_) => println("Connection closed gracefully")
case Failure(e) => println("Connection closed with an error: $e")
}