Akka(36): Http:Client-side-Api,Client-Connections

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   Akka-http的客户端Api应该是以HttpRequest操作为主轴的网上消息交换模式编程工具。我们知道:Akka-http是搭建在Akka-stream之上的。所以,Akka-http在客户端构建与服务器的连接通道也可以用Akka-stream的Flow来表示。这个Flow可以通过调用Http.outgoingConnection来获取:

 /**

* Creates a [[akka.stream.scaladsl.Flow]] representing a prospective HTTP client connection to the given endpoint.

* Every materialization of the produced flow will attempt to establish a new outgoing connection.

*

* To configure additional settings for requests made using this method,

* use the `akka.http.client` config section or pass in a [[akka.http.scaladsl.settings.ClientConnectionSettings]] explicitly.

*/

def outgoingConnection(host: String, port: Int = 80,

localAddress: Option[InetSocketAddress] = None,

settings: ClientConnectionSettings = ClientConnectionSettings(system),

log: LoggingAdapter = system.log): Flow[HttpRequest, HttpResponse, Future[OutgoingConnection]] =

_outgoingConnection(host, port, settings.withLocalAddressOverride(localAddress), ConnectionContext.noEncryption(), ClientTransport.TCP, log)

我们看到:这个函数实现了对Server端地址host+port的设定,返回的结果类型是Flow[HttpRequest,HttpResponse,Future[OutgoingConnection]]。这个Flow代表将输入的HttpRequest转换成输出的HttpResponse。这个转换过程包括了与Server之间的Request,Response消息交换。下面我们试着用这个Flow来向Server端发送request,并获取response:

 val connFlow: Flow[HttpRequest,HttpResponse,Future[Http.OutgoingConnection]] =

Http().outgoingConnection("akka.io")

def sendHttpRequest(req: HttpRequest) = {

Source.single(req)

.via(connFlow)

.runWith(Sink.head)

}

sendHttpRequest(HttpRequest(uri="/"))

.andThen{

case Success(resp) => println(s"got response: ${resp.status.intValue()}")

case Failure(err) => println(s"request failed: ${err.getMessage}")

}

.andThen {case _ => sys.terminate()}

上面的这种模式就是所谓Connection-Level-Client-Side-Api。这种模式可以让用户有更大程度的自由度控制connection的构建、使用及在connection上发送request的方式。一般来讲,当返回response的entity被完全消耗后系统会自动close connection,这套api还提供了一些手动方法可以在有需要的情况下手动进行connection close,如下:

 //close connection by cancelling response entity

resp.entity.dataBytes.runWith(Sink.cancelled)

//close connection by receiving response with close header

Http().bindAndHandleSync(

{ req ⇒ HttpResponse(headers = headers.Connection("close") :: Nil) },

"akka.io",

80)(mat)

Akka-http客户端api还有一种实用的Host-Level-Client-Side-Api模式。这套api能自动针对每个端点维护一个连接池(connection-pool),用户只需对连接池进行配置。系统按照连接池配置自动维护池内线程的生、死、动、停。akka-http.host-connection-pool配置中max-connections,max-open-requests,pipelining-limit等控制着connection、在途request的数量,需要特别注意。针对某个端点的连接池是通过Http().cachedHostConnectionPool(endPoint)获取的。同样,获取的也是一个client-flow实例。因为系统自动维护着线程池,所以client-flow实例可以任意引用,无论调用次数与调用时间间隔。cachedHostConnectionPool()函数定义如下:

 /**

* Same as [[#cachedHostConnectionPool]] but for encrypted (HTTPS) connections.

*

* If an explicit [[ConnectionContext]] is given then it rather than the configured default [[ConnectionContext]] will be used

* for encryption on the connections.

*

* To configure additional settings for the pool (and requests made using it),

* use the `akka.http.host-connection-pool` config section or pass in a [[ConnectionPoolSettings]] explicitly.

*/

def cachedHostConnectionPoolHttps[T](host: String, port: Int = 443,

connectionContext: HttpsConnectionContext = defaultClientHttpsContext,

settings: ConnectionPoolSettings = defaultConnectionPoolSettings,

log: LoggingAdapter = system.log)(implicit fm: Materializer): Flow[(HttpRequest, T), (Try[HttpResponse], T), HostConnectionPool] = {

val cps = ConnectionPoolSetup(settings, connectionContext, log)

val setup = HostConnectionPoolSetup(host, port, cps)

cachedHostConnectionPool(setup)

}

函数返回结果类型:Flow[(HttpRequest,T),(Try[HttpResponse],T),HostConnectionPool]。因为线程池内的线程是异步构建request和接收response的,而返回response的顺序未必按照发送request的顺序,所以需要一个tuple2的T类型标示request与返回的response进行匹配。线程池会根据idle-timeout自动终止,也可以手动通过HostConnectionPool.shutDown()实现:

 /**

* Represents a connection pool to a specific target host and pool configuration.

*/

final case class HostConnectionPool private[http] (setup: HostConnectionPoolSetup)(

private[http] val gateway: PoolGateway) { // enable test access

/**

* Asynchronously triggers the shutdown of the host connection pool.

*

* The produced [[scala.concurrent.Future]] is fulfilled when the shutdown has been completed.

*/

def shutdown()(implicit ec: ExecutionContextExecutor): Future[Done] = gateway.shutdown()

private[http] def toJava = new akka.http.javadsl.HostConnectionPool {

override def setup = HostConnectionPool.this.setup

override def shutdown(executor: ExecutionContextExecutor): CompletionStage[Done] = HostConnectionPool.this.shutdown()(executor).toJava

}

}

也可以通过Http().shutdownAllConnectionPools()一次性终止ActorSystem内所有线程池:

 /**

* Triggers an orderly shutdown of all host connections pools currently maintained by the [[akka.actor.ActorSystem]].

* The returned future is completed when all pools that were live at the time of this method call

* have completed their shutdown process.

*

* If existing pool client flows are re-used or new ones materialized concurrently with or after this

* method call the respective connection pools will be restarted and not contribute to the returned future.

*/

def shutdownAllConnectionPools(): Future[Unit] = {

val shutdownCompletedPromise = Promise[Done]()

poolMasterActorRef ! ShutdownAll(shutdownCompletedPromise)

shutdownCompletedPromise.future.map(_ ⇒ ())(system.dispatcher)

}

我们用cachedHostConnectionPool获取一个client-flow实例:

Flow[(HttpRequest,T),(Try[HttpResponse],T),HostConnectionPool]后就可以进行输入HttpRequest到HttpResponse的转换处理。如下面的例子:

 val pooledFlow: Flow[(HttpRequest,Int),(Try[HttpResponse],Int),Http.HostConnectionPool] =

Http().cachedHostConnectionPool[Int](host="akka.io",port=80)

def sendPoolRequest(req: HttpRequest, marker: Int) = {

Source.single(req -> marker)

.via(pooledFlow)

.runWith(Sink.head)

}

sendPoolRequest(HttpRequest(uri="/"), 1)

.andThen{

case Success((tryResp, mk)) =>

tryResp match {

case Success(resp) => println(s"got response: ${resp.status.intValue()}")

case Failure(err) => println(s"request failed: ${err.getMessage}")

}

case Failure(err) => println(s"request failed: ${err.getMessage}")

}

.andThen {case _ => sys.terminate()}

在以上这个例子里实际同样会遇到Connection-Level-Api所遇的的问题,这是因为获取的线程池内的线程还是有限的,只能缓解因为request速率超出response速率所造成的request积压。目前最有效的方法还是通过使用一个queue来暂存request后再逐个处理:

 val QueueSize = 10

// This idea came initially from this blog post:

// http://kazuhiro.github.io/scala/akka/akka-http/akka-streams/2016/01/31/connection-pooling-with-akka-http-and-source-queue.html

val poolClientFlow = Http().cachedHostConnectionPool[Promise[HttpResponse]]("akka.io")

val queue =

Source.queue[(HttpRequest, Promise[HttpResponse])](QueueSize, OverflowStrategy.dropNew)

.via(poolClientFlow)

.toMat(Sink.foreach({

case ((Success(resp), p)) => p.success(resp)

case ((Failure(e), p)) => p.failure(e)

}))(Keep.left)

.run()

def queueRequest(request: HttpRequest): Future[HttpResponse] = {

val responsePromise = Promise[HttpResponse]()

queue.offer(request -> responsePromise).flatMap {

case QueueOfferResult.Enqueued => responsePromise.future

case QueueOfferResult.Dropped => Future.failed(new RuntimeException("Queue overflowed. Try again later."))

case QueueOfferResult.Failure(ex) => Future.failed(ex)

case QueueOfferResult.QueueClosed => Future.failed(new RuntimeException("Queue was closed (pool shut down) while running the request. Try again later."))

}

}

val responseFuture: Future[HttpResponse] = queueRequest(HttpRequest(uri = "/"))

responseFuture.andThen {

case Success(resp) => println(s"got response: ${resp.status.intValue()}")

case Failure(err) => println(s"request failed: ${err.getMessage}")

}.andThen {case _ => sys.terminate()}

下面是本次Akka-http-client-side-connection讨论的示范源代码:

import akka.actor._

import akka.http.javadsl.{HostConnectionPool, OutgoingConnection}

import akka.stream._

import akka.stream.scaladsl._

import akka.http.scaladsl.Http

import akka.http.scaladsl.model._

import scala.concurrent._

import scala.util._

object ClientApiDemo extends App {

implicit val sys = ActorSystem("ClientSys")

implicit val mat = ActorMaterializer()

implicit val ec = sys.dispatcher

/*

val connFlow: Flow[HttpRequest,HttpResponse,Future[Http.OutgoingConnection]] =

Http().outgoingConnection("www.sina.com")

def sendHttpRequest(req: HttpRequest) = {

Source.single(req)

.via(connFlow)

.runWith(Sink.head)

}

sendHttpRequest(HttpRequest(uri="/"))

.andThen{

case Success(resp) =>

//close connection by cancelling response entity

resp.entity.dataBytes.runWith(Sink.cancelled)

println(s"got response: ${resp.status.intValue()}")

case Failure(err) => println(s"request failed: ${err.getMessage}")

}

// .andThen {case _ => sys.terminate()}

//close connection by receiving response with close header

Http().bindAndHandleSync(

{ req ⇒ HttpResponse(headers = headers.Connection("close") :: Nil) },

"akka.io",

80)(mat)

val pooledFlow: Flow[(HttpRequest,Int),(Try[HttpResponse],Int),Http.HostConnectionPool] =

Http().cachedHostConnectionPool[Int](host="akka.io",port=80)

def sendPoolRequest(req: HttpRequest, marker: Int) = {

Source.single(req -> marker)

.via(pooledFlow)

.runWith(Sink.head)

}

sendPoolRequest(HttpRequest(uri="/"), 1)

.andThen{

case Success((tryResp, mk)) =>

tryResp match {

case Success(resp) => println(s"got response: ${resp.status.intValue()}")

case Failure(err) => println(s"request failed: ${err.getMessage}")

}

case Failure(err) => println(s"request failed: ${err.getMessage}")

}

.andThen {case _ => sys.terminate()}

*/

val QueueSize = 10

// This idea came initially from this blog post:

// http://kazuhiro.github.io/scala/akka/akka-http/akka-streams/2016/01/31/connection-pooling-with-akka-http-and-source-queue.html

val poolClientFlow = Http().cachedHostConnectionPool[Promise[HttpResponse]]("akka.io")

val queue =

Source.queue[(HttpRequest, Promise[HttpResponse])](QueueSize, OverflowStrategy.dropNew)

.via(poolClientFlow)

.toMat(Sink.foreach({

case ((Success(resp), p)) => p.success(resp)

case ((Failure(e), p)) => p.failure(e)

}))(Keep.left)

.run()

def queueRequest(request: HttpRequest): Future[HttpResponse] = {

val responsePromise = Promise[HttpResponse]()

queue.offer(request -> responsePromise).flatMap {

case QueueOfferResult.Enqueued => responsePromise.future

case QueueOfferResult.Dropped => Future.failed(new RuntimeException("Queue overflowed. Try again later."))

case QueueOfferResult.Failure(ex) => Future.failed(ex)

case QueueOfferResult.QueueClosed => Future.failed(new RuntimeException("Queue was closed (pool shut down) while running the request. Try again later."))

}

}

val responseFuture: Future[HttpResponse] = queueRequest(HttpRequest(uri = "/"))

responseFuture.andThen {

case Success(resp) => println(s"got response: ${resp.status.intValue()}")

case Failure(err) => println(s"request failed: ${err.getMessage}")

}.andThen {case _ => sys.terminate()}

}

 

 

 

 

 

 

 

 

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