Migration from Play Websocket to Akka HTTP Websocket

Question

I am migrating from Play to Akka HTTP. I have jar dependency code which I am not able to change which accepts a

Flow[Array[Byte],Array[Byte],Any]

which is what is provided by Play for a WebSocket connection. In Akka HTTP the definition is

Flow[Message,Message,Any]

I need a translation between the 2 definitions. I am new to Akka http so I am not exactly sure how to proceed. In play I was also using ActorFlow.actorRef

handleWebSocketMessages(wsFlow)

def wsFlow: Flow[Message, Message, Any] = {
 ActorFlow.actorRef(websocket => MyBridgeActor.props(websocket))
}

ActorFlow code only has a dependency on akka so I have just copied the file to my own code base. https://github.com/playframework/playframework/blob/master/framework/src/play-streams/src/main/scala/play/api/libs/streams/ActorFlow.scala

I guess a solution would be to create a CustomActorFlow which will includes the conversion from Message to Array[Byte]. MyBridgeActor accepts the websocket in Flow[Array[Byte],Array[Byte],Any] format.

PH88 PH88 · Accepted Answer · 2018-06-29T03:00:38

Using akka stream api, you can convert the flow like:

import akka.http.scaladsl.model.ws.{BinaryMessage, Message, TextMessage}
import akka.stream.Materializer
import akka.stream.scaladsl.{Flow, Sink}
import akka.util.ByteString

import scala.concurrent.Future

handleWebSocketMessages(msgFlow)

def msgFlow: Flow[Message, Message, Any] = convertFlow(bytesFlow)

def bytesFlow: Flow[Array[Byte], Array[Byte], Any] = {
  // Can just copy ActorFlow over, no need to customize
  ActorFlow.actorRef[Array[Byte], Array[Byte]](...)
}

def covertFlow(msgs: Flow[Array[Byte], Array[Byte], Any])(implicit materializer: Materializer): Flow[Message, Message, Any] =
  Flow[Message]
    .mapAsync(2)(msgToBytes)
    .via(msgs)
    .map(bytesToMsg)


def bytesToMsg(bytes: Array[Byte]): Message = {
  // This depends on your application:
  //   is the outgoing message text or binary?
  val isText = true
  if (isText) {
    TextMessage(new String(bytes, "UTF-8"))
  } else {
    BinaryMessage(ByteString(bytes))
  }
}

def msgToBytes(msg: Message)(implicit materializer: Materializer): Future[Array[Byte]] = {
  msg match {
    case TextMessage.Strict(data) =>
      Future.successful(data.getBytes("UTF-8"))
    case TextMessage.Streamed(stream) =>
      stream.fold("")(_ + _).map(_.getBytes("UTF-8")).runWith(Sink.head)
    case BinaryMessage.Strict(data) =>
      Future.successful(data.toArray[Byte])
    case BinaryMessage.Streamed(stream) =>
      stream.fold(ByteString.empty)(_ ++ _).map(_.toArray[Byte]).runWith(Sink.head)
  }
}

Migration from Play Websocket to Akka HTTP Websocket

1 Answers