Question

我有以下无法编译的代码段：

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._
import scala.concurrent.duration._


object Main 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)
  }


  // flow to use (note: not re-usable!)
  val sourceSocketFlow = RestartSource.withBackoff(
    minBackoff = 3.seconds,
    maxBackoff = 30.seconds,
    randomFactor = 0.2,
    maxRestarts = 3
  ) { () =>
    Source.tick(2.seconds, 2.seconds, TextMessage("Hello world!!!"))
        .viaMat(Http().webSocketClientFlow(WebSocketRequest("ws://127.0.0.1:8080/")))(Keep.right)
  }
  // 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) =
    sourceSocketFlow
    .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}")
    }
  }

  connected.onComplete(println)
  closed.foreach(_ => println("closed"))

}

这里的问题是：

  // 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) =
    sourceSocketFlow
    .toMat(incoming)(Keep.both) // also keep the Future[Done]
    .run()

不在元组的第一个位置返回Future[WebSocketUpgradeResponse]，而是返回NotUsed。

问题是，如何获取返回类型Future[WebSocketUpgradeResponse]来确定连接是否成功。

Answer 1

RestartSource#withBackoff接受类型为sourceFactory的{{1}}并返回类型为() => Source[T, _]的新源。因此，不可能从包装的源中提取物化值。这可能是因为在每次RestartSource重新启动时，物化值都会有所不同。

问题是，如何获取返回类型Future [WebSocketUpgradeResponse]来确定连接成功。

如果要检查是否已建立连接，并且WebSockets握手是否成功，则可以使用Source#preMaterialize预先实现源。经过稍微修改的代码版本如下所示：

Source[T, NotUsed]

如果连接失败或websocket handshake fails，则无需执行任何操作。这两种情况都将由RestartSource处理。

协议切换成功与否

1 个答案: