How to broadcast the received messages to two different flows - scala

Question

How to broadcast the received messages to two different flows
I am using akka stream websocket client to request and receive the data websocket server.
With the received data from the websocket, I would like to broadcast into two different flows.
The image below, should clarify the scenario:
As you can see on the image, it should be broadcasted to two different flows subsequently to seperate sink.
The websocket client can be created as the following:
import akka.actor.ActorSystem
import akka.Done
import akka.http.scaladsl.Http
import akka.stream.ActorMaterializer
import akka.stream.scaladsl._
import akka.http.scaladsl.model._
import akka.http.scaladsl.model.ws._
import scala.concurrent.Future
object WebSocketClientFlow {
def main(args: Array[String]) = {
implicit val system = ActorSystem()
implicit val materializer = ActorMaterializer()
import system.dispatcher
// Future[Done] is the materialized value of Sink.foreach,
// emitted when the stream completes
val incoming: Sink[Message, Future[Done]] =
Sink.foreach[Message] {
case message: TextMessage.Strict =>
println(message.text)
}
// send this as a message over the WebSocket
val outgoing = Source.single(TextMessage("hello world!"))
// flow to use (note: not re-usable!)
val webSocketFlow = Http().webSocketClientFlow(WebSocketRequest("ws://echo.websocket.org"))
// the materialized value is a tuple with
// upgradeResponse is a Future[WebSocketUpgradeResponse] that
// completes or fails when the connection succeeds or fails
// and closed is a Future[Done] with the stream completion from the incoming sink
val (upgradeResponse, closed) =
outgoing
.viaMat(webSocketFlow)(Keep.right) // keep the materialized Future[WebSocketUpgradeResponse]
.toMat(incoming)(Keep.both) // also keep the Future[Done]
.run()
// just like a regular http request we can access response status which is available via upgrade.response.status
// status code 101 (Switching Protocols) indicates that server support WebSockets
val connected = upgradeResponse.flatMap { upgrade =>
if (upgrade.response.status == StatusCodes.SwitchingProtocols) {
Future.successful(Done)
} else {
throw new RuntimeException(s"Connection failed: ${upgrade.response.status}")
}
}
// in a real application you would not side effect here
connected.onComplete(println)
closed.foreach(_ => println("closed"))
}
}

Answer 1

You can use SinkShape to get the required flow
Sink.fromGraph(GraphDSL.create(){
implicit b =>
val bcast = b.add(Broadcast[Message](2))
val flow1 = b.add(Flow[Message].map(m => m))
val flow2 = b.add(Flow[Message].map(m => m ))
val sink1 = b.add(Sink.foreach(println))
val sink2 = b.add(Sink.foreach(println))
bcast ~> flow1 ~> sink1
bcast ~> flow2 ~> sink2
SinkShape(bcast.in)
})
The entire code is
implicit val system = ActorSystem()
implicit val materializer = ActorMaterializer()
import system.dispatcher
// Future[Done] is the materialized value of Sink.foreach,
// emitted when the stream completes
val incomingSink = Sink.fromGraph(GraphDSL.create() {
implicit b =>
import GraphDSL.Implicits._
val bcast = b.add(Broadcast[Message](2))
val flow1 = b.add(Flow[Message].map(m => m))
val flow2 = b.add(Flow[Message].map(m => m ))
val sink1 = b.add(Sink.head[Message])
val sink2 = b.add(Sink.head[Message])
bcast ~> flow1 ~> sink1
bcast ~> flow2 ~> sink2
SinkShape(bcast.in)
}).mapMaterializedValue(_ => Future(Done))
// send this as a message over the WebSocket
val outgoing = Source.single(TextMessage("hello world!"))
// flow to use (note: not re-usable!)
val webSocketFlow = Http().webSocketClientFlow(WebSocketRequest("ws://echo.websocket.org"))
// the materialized value is a tuple with
// upgradeResponse is a Future[WebSocketUpgradeResponse] that
// completes or fails when the connection succeeds or fails
// and closed is a Future[Done] with the stream completion from the incoming sink
val (upgradeResponse, closed) =
outgoing
.viaMat(webSocketFlow)(Keep.right) // keep the materialized Future[WebSocketUpgradeResponse]
.toMat(incomingSink)(Keep.both) // also keep the Future[Done]
.run()
// just like a regular http request we can access response status which is available via upgrade.response.status
// status code 101 (Switching Protocols) indicates that server support WebSockets
val connected = upgradeResponse.flatMap { upgrade =>
if (upgrade.response.status == StatusCodes.SwitchingProtocols) {
Future.successful(Done)
} else {
throw new RuntimeException(s"Connection failed: ${upgrade.response.status}")
}
}
// in a real application you would not side effect here
connected.onComplete(println)
closed.foreach(_ => println("closed"))