设置如下:我希望能够通过 tcp 连接将消息(json 转换为字节串)从发布者流式传输到远程服务器订阅者。
理想情况下,发布者应该是接收内部消息、将它们排队然后将它们流式传输到订阅者服务器的角色,当然如果有突出的需求。我知道这样做的必要条件是扩展 ActorPublisher
类,以便在需要时 onNext()
消息。
我的问题是,到目前为止,我只能向服务器发送(正确接收和解码)一次 消息,每次都打开一个新连接。我没有设法理解 akka 文档,也无法使用 ActorPublisher
设置正确的 tcp Flow
。
这是发布者的代码:
def send(message: Message): Unit = {
val system = Akka.system()
implicit val sys = system
import system.dispatcher
implicit val materializer = ActorMaterializer()
val address = Play.current.configuration.getString("eventservice.location").getOrElse("localhost")
val port = Play.current.configuration.getInt("eventservice.port").getOrElse(9000)
/*** Try with actorPublisher ***/
//val result = Source.actorPublisher[Message] (Props[EventActor]).via(Flow[Message].map(Json.toJson(_).toString.map(ByteString(_))))
/*** Try with actorRef ***/
/*val source = Source.actorRef[Message](0, OverflowStrategy.fail).map(
m => {
Logger.info(s"Sending message: ${m.toString}")
ByteString(Json.toJson(m).toString)
}
)
val ref = Flow[ByteString].via(Tcp().outgoingConnection(address, port)).to(Sink.ignore).runWith(source)*/
val result = Source(Json.toJson(message).toString.map(ByteString(_))).
via(Tcp().outgoingConnection(address, port)).
runFold(ByteString.empty) { (acc, in) ⇒ acc ++ in }//Handle the future
}
最后是相当标准的 Actor 代码:
import akka.actor.Actor
import akka.stream.actor.ActorSubscriberMessage.{OnComplete, OnError}
import akka.stream.actor.{ActorPublisherMessage, ActorPublisher}
import models.events.Message
import play.api.Logger
import scala.collection.mutable
class EventActor extends Actor with ActorPublisher[Message] {
import ActorPublisherMessage._
var queue: mutable.Queue[Message] = mutable.Queue.empty
def receive = {
case m: Message =>
Logger.info(s"EventActor - message received and queued: ${m.toString}")
queue.enqueue(m)
publish()
case Request => publish()
case Cancel =>
Logger.info("EventActor - cancel message received")
context.stop(self)
case OnError(err: Exception) =>
Logger.info("EventActor - error message received")
onError(err)
context.stop(self)
case OnComplete =>
Logger.info("EventActor - onComplete message received")
onComplete()
context.stop(self)
}
def publish() = {
while (queue.nonEmpty && isActive && totalDemand > 0) {
Logger.info("EventActor - message published")
onNext(queue.dequeue())
}
}
如有必要,我可以提供订阅者的代码:
def connect(system: ActorSystem, address: String, port: Int): Unit = {
implicit val sys = system
import system.dispatcher
implicit val materializer = ActorMaterializer()
val handler = Sink.foreach[Tcp.IncomingConnection] { conn =>
Logger.info("Event server connected to: " + conn.remoteAddress)
// Get the ByteString flow and reconstruct the msg for handling and then output it back
// that is how handleWith work apparently
conn.handleWith(
Flow[ByteString].fold(ByteString.empty)((acc, b) => acc ++ b).
map(b => handleIncomingMessages(system, b.utf8String)).
map(ByteString(_))
)
}
val connections = Tcp().bind(address, port)
val binding = connections.to(handler).run()
binding.onComplete {
case Success(b) =>
Logger.info("Event server started, listening on: " + b.localAddress)
case Failure(e) =>
Logger.info(s"Event server could not bind to $address:$port: ${e.getMessage}")
system.terminate()
}
}
提前感谢您的提示。
最佳答案
我的第一个建议是不要编写自己的队列逻辑。 Akka 提供了这个开箱即用的功能。您也不需要编写自己的 Actor,Akka Streams 也可以提供。
首先,我们可以创建 Flow,通过 Tcp 将您的发布者连接到您的订阅者。在您的发布者代码中,您只需创建一次 ActorSystem
并连接到外部服务器一次:
//this code is at top level of your application
implicit val actorSystem = ActorSystem()
implicit val actorMaterializer = ActorMaterializer()
import actorSystem.dispatcher
val host = Play.current.configuration.getString("eventservice.location").getOrElse("localhost")
val port = Play.current.configuration.getInt("eventservice.port").getOrElse(9000)
val publishFlow = Tcp().outgoingConnection(host, port)
publishFlow
是一个 Flow
将输入要发送给外部订阅者的 ByteString
数据,并输出来自订阅者的 ByteString 数据:
// data to subscriber ----> publishFlow ----> data returned from subscriber
下一步是发布者来源。您可以使用 Source.actorRef
而不是编写自己的 Actor。至 "materialize" Stream 到 ActorRef
。本质上,Stream 将成为我们稍后使用的 ActorRef:
//these values control the buffer
val bufferSize = 1024
val overflowStrategy = akka.stream.OverflowStrategy.dropHead
val messageSource = Source.actorRef[Message](bufferSize, overflowStrategy)
我们还需要一个 Flow 来将 Messages 转换成 ByteString
val marshalFlow =
Flow[Message].map(message => ByteString(Json.toJson(message).toString))
最后我们可以连接所有的部分。由于您没有收到来自外部订阅者的任何数据,我们将忽略来自连接的任何数据:
val subscriberRef : ActorRef = messageSource.via(marshalFlow)
.via(publishFlow)
.runWith(Sink.ignore)
我们现在可以把这个流当作一个 Actor 来对待:
val message1 : Message = ???
subscriberRef ! message1
val message2 : Message = ???
subscriberRef ! message2
关于scala - akka 通过 tcp 传输,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/35830401/