akka流消耗web套接字

Question

开始使用akka-streams，我想构建一个简单的示例。在chrome中，使用web套接字插件，我可以通过wss：//ws.blockchain.info/inv并发送2个命令，简单地连接到这样的流https://blockchain.info/api/apiwebsocket

• {“op”：“ping”}
• {“op”：“unconfirmed_sub”}将在chromes web socket插件窗口中传输结果。

我试图在akka流中实现相同的功能,但面临一些问题：

• 执行了2个命令，但我实际上没有获得流输出
• 同一命令执行两次（ping命令）

在学习http://doc.akka.io/docs/akka/2.4.7/scala/http/client-side/websocket-support.html或http://doc.akka.io/docs/akka-http/10.0.0/scala/http/client-side/websocket-support.html#half-closed-client-websockets教程时，以下是我的修改：

object SingleWebSocketRequest extends App {

implicit val system = ActorSystem()
implicit val materializer = ActorMaterializer()

import system.dispatcher

// print each incoming strict text message
val printSink: Sink[Message, Future[Done]] =
    Sink.foreach {
      case message: TextMessage.Strict =>
        println(message.text)
    }

      val commandMessages = Seq(TextMessage("{\"op\":\"ping\"}"), TextMessage("{\"op\":\"unconfirmed_sub\"}"))
      val helloSource: Source[Message, NotUsed] = Source(commandMessages.to[scala.collection.immutable.Seq])

      // the Future[Done] is the materialized value of Sink.foreach
      // and it is completed when the stream completes
      val flow: Flow[Message, Message, Future[Done]] =
      Flow.fromSinkAndSourceMat(printSink, helloSource)(Keep.left)

      // upgradeResponse is a Future[WebSocketUpgradeResponse] that
      // completes or fails when the connection succeeds or fails
      // and closed is a Future[Done] representing the stream completion from above
      val (upgradeResponse, closed) =
      Http().singleWebSocketRequest(WebSocketRequest("wss://ws.blockchain.info/inv"), flow)

      val connected = upgradeResponse.map { upgrade =>
        // 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
        if (upgrade.response.status == StatusCodes.SwitchingProtocols) {
          Done
        } else {
          throw new RuntimeException(s"Connection failed: ${upgrade.response.status}")
        }
      }

      // in a real application you would not side effect here
      // and handle errors more carefully
      connected.onComplete(println) // TODO why do I not get the same output as in chrome?
      closed.foreach(_ => println("closed"))
    }

{"op":"pong"}
{"op":"pong"}

请参阅代码：

object WebSocketClientFlow extends App {
  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 commandMessages = Seq(TextMessage("{\"op\":\"ping\"}"), TextMessage("{\"op\":\"unconfirmed_sub\"}"))
  val outgoing: Source[Message, NotUsed] = Source(commandMessages.to[scala.collection.immutable.Seq])
  //  val outgoing = Source.single(TextMessage("hello world!"))

  // flow to use (note: not re-usable!)
  val webSocketFlow = Http().webSocketClientFlow(WebSocketRequest("wss://ws.blockchain.info/inv"))

  // 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")
    system.terminate
  })
}

如何才能达到与chrome相同结果

• 显示订阅流的打印
• 最好通过{“op”：“ping”}消息
定期发送https://blockchain.info/api/api中列出的更新（ping语句）

Answer 1

我注意到的几件事是：

1）您需要使用所有类型的传入消息，而不仅仅是textmessage.strict类型。blockchain流绝对是一个流消息，因为它包含大量文本，并且将在网络上以块形式传递。更完整的传入接收器可以是：

  val incoming: Sink[Message, Future[Done]] =
    Flow[Message].mapAsync(4) {
      case message: TextMessage.Strict =>
        println(message.text)
        Future.successful(Done)
      case message: TextMessage.Streamed =>
        message.textStream.runForeach(println)
      case message: BinaryMessage =>
        message.dataStream.runWith(Sink.ignore)
    }.toMat(Sink.last)(Keep.right)

2）您的2个元素的源可能完成得太早，即在websocket响应返回之前。您可以通过执行以下操作来连接源.maybe

val outgoing: Source[Strict, Promise[Option[Nothing]]] =
    Source(commandMessages.to[scala.collection.immutable.Seq]).concatMat(Source.maybe)(Keep.right)

  val ((completionPromise, upgradeResponse), closed) =
    outgoing
      .viaMat(webSocketFlow)(Keep.both)
      .toMat(incoming)(Keep.both)
      .run()