Akka（37）： Http：客户端操作模式

   Akka-http的客户端连接模式除Connection-Level和Host-Level之外还有一种非常便利的模式：Request-Level-Api。这种模式免除了连接Connection的概念，任何时候可以直接调用singleRequest来与服务端沟通。下面我们用几个例子来示范singleRequest的用法：

  (for {    response <- Http().singleRequest(HttpRequest(method=HttpMethods.GET,uri="http://localhost:8011/message"))    message <- Unmarshal(response.entity).to[String]  } yield message).andThen {    case Success(msg) => println(s"Received message: $msg")    case Failure(err) => println(s"Error: ${err.getMessage}")  }.andThen {case _ => sys.terminate()}

这是一个GET操作：用Http().singleRequest直接把HttpRequest发送给服务端uri并获取返回的HttpResponse。我们看到，整组函数的返回类型都是Future[?]，所以用for-comprehension来把所有实际运算包嵌在Future运算模式内（context)。下面这个例子是客户端上传数据示范：

  (for {    entity <- Marshal("Wata hell you doing?").to[RequestEntity]    response <- Http().singleRequest(HttpRequest(method=HttpMethods.PUT,uri="http://localhost:8011/message",entity=entity))    message <- Unmarshal(response.entity).to[String]  } yield message).andThen {    case Success(msg) => println(s"Received message: $msg")    case Failure(err) => println(s"Error: ${err.getMessage}")  }.andThen {case _ => sys.terminate()}

以上是个PUT操作。我们需要先构建数据载体HttpEntity。格式转换函数Marshal也返回Future[HttpEntity]，所以也可以包含在for语句内。关注一下这个andThen，它可以连接一串多个monadic运算，在不影响上游运算结果的情况下实现一些副作用计算。

值得注意的是上面这两个例子虽然表现形式很简洁，但我们无法对数据转换过程中的异常及response的状态码等进行监控。所以我们应该把整个过程拆分成两部分：先获取response，再具体处理response,包括核对状态，处理数据等：

  case class Item(id: Int, name: String, price: Double)  def getItem(itemId: Int): Future[HttpResponse] = for {    response <- Http().singleRequest(HttpRequest(method=HttpMethods.GET,uri = s"http://localhost:8011/item/$itemId"))  } yield response  def extractEntity[T](futResp: Future[HttpResponse])(implicit um: Unmarshaller[ResponseEntity,T]) = {    futResp.andThen {      case Success(HttpResponse(StatusCodes.OK, _, entity, _)) =>        Unmarshal(entity).to[T]          .onComplete {            case Success(t) => println(s"Got response entity: ${t}")            case Failure(e) => println(s"Unmarshalling failed: ${e.getMessage}")          }      case Success(_) => println("Exception in response!")      case Failure(err) => println(s"Response Failed: ${err.getMessage}")    }  }  extractEntity[Item](getItem(13))

现在这个extractEntity[Item](getItem(13))可以实现全过程的监控管理了。用同样的模式实现PUT操作：

  def putItem(item: Item): Future[HttpResponse] =   for {    reqEntity <- Marshal(item).to[RequestEntity]    response <- Http().singleRequest(HttpRequest(method=HttpMethods.PUT,uri="http://localhost:8011/item",entity=reqEntity))   } yield response  extractEntity[Item](putItem(Item(23,"Item#23", 46.0)))     .andThen { case _ => sys.terminate()}

当然，我们还是使用了前面几篇讨论里的Marshalling方式来进行数据格式的自动转换：

import de.heikoseeberger.akkahttpjson4s.Json4sSupportimport org.json4s.jackson...trait JsonCodec extends Json4sSupport {  import org.json4s.DefaultFormats  import org.json4s.ext.JodaTimeSerializers  implicit val serilizer = jackson.Serialization  implicit val formats = DefaultFormats ++ JodaTimeSerializers.all}object JsConverters extends JsonCodec...  import JsConverters._  implicit val jsonStreamingSupport = EntityStreamingSupport.json()    .withParallelMarshalling(parallelism = 8, unordered = false)

如果我们需要对数据交换过程进行更细致的管控，用Host-Level-Api会更加适合。下面我们就针对Host-Level-Api构建一个客户端的工具库：

class PooledClient(host: String, port: Int, poolSettings: ConnectionPoolSettings)                  (implicit sys: ActorSystem, mat: ActorMaterializer) {  import sys.dispatcher  private val cnnPool: Flow[(HttpRequest, Int), (Try[HttpResponse], Int), Http.HostConnectionPool] =    Http().cachedHostConnectionPool[Int](host = host, port = port, settings = poolSettings)//单一request  def requestSingleResponse(req: HttpRequest): Future[HttpResponse] = {    Source.single(req -> 1)      .via(cnnPool)      .runWith(Sink.head).flatMap {      case (Success(resp), _) => Future.successful(resp)      case (Failure(fail), _) => Future.failed(fail)    }  }//组串request  def orderedResponses(reqs: Iterable[HttpRequest]): Future[Iterable[HttpResponse]] = {    Source(reqs.zipWithIndex.toMap)      .via(cnnPool)      .runFold(SortedMap[Int, Future[HttpResponse]]()) {        case (m, (Success(r), idx)) => m + (idx -> Future.successful(r))        case (m, (Failure(f), idx)) => m + (idx -> Future.failed(f))      }.flatMap { m => Future.sequence(m.values) }  }}

下面是一种比较安全的模式：使用了queue来暂存request从而解决因发送方与接收方速率不同所产生的问题：

class QueuedRequestsClient(host: String, port: Int, poolSettings: ConnectionPoolSettings)                          (qsize: Int = 10, overflowStrategy: OverflowStrategy = OverflowStrategy.dropNew)                  (implicit sys: ActorSystem, mat: ActorMaterializer) {  import sys.dispatcher  private val cnnPool: Flow[(HttpRequest,Promise[HttpResponse]),(Try[HttpResponse],Promise[HttpResponse]),Http.HostConnectionPool] =    Http().cachedHostConnectionPool[Promise[HttpResponse]](host=host,port=port,settings=poolSettings)  val queue =    Source.queue[(HttpRequest, Promise[HttpResponse])](qsize, overflowStrategy)      .via(cnnPool)      .to(Sink.foreach({        case ((Success(resp), p)) => p.success(resp)        case ((Failure(e), p))    => p.failure(e)      })).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."))      }  }}

下面是这些工具函数的具体使用示范：

  val settings = ConnectionPoolSettings(sys)    .withMaxConnections(8)    .withMaxOpenRequests(8)    .withMaxRetries(3)    .withPipeliningLimit(4)  val pooledClient = new PooledClient("localhost",8011,settings)  def getItemByPool(itemId: Int): Future[HttpResponse] = for {    response <- pooledClient.requestSingleResponse(HttpRequest(method=HttpMethods.GET,uri = s"http://localhost:8011/item/$itemId"))  } yield response  extractEntity[Item](getItemByPool(13))  def getItemsByPool(itemIds: List[Int]): Future[Iterable[HttpResponse]] = {    val reqs = itemIds.map { id =>      HttpRequest(method = HttpMethods.GET, uri = s"http://localhost:8011/item/$id")    }    val rets = (for {      responses <- pooledClient.orderedResponses(reqs)    } yield responses)    rets  }  val futResps = getItemsByPool(List(3,5,7))  futResps.andThen {    case Success(listOfResps) => {      listOfResps.foreach { r =>        r match {          case HttpResponse(StatusCodes.OK, _, entity, _) =>            Unmarshal(entity).to[Item]              .onComplete {                case Success(t) => println(s"Got response entity: ${t}")                case Failure(e) => println(s"Unmarshalling failed: ${e.getMessage}")              }          case _ => println("Exception in response!")        }      }    }    case _ => println("Failed to get list of responses!")  }  val queuedClient = new QueuedRequestsClient("localhost",8011,settings)()  def putItemByQueue(item: Item): Future[HttpResponse] =    for {      reqEntity <- Marshal(item).to[RequestEntity]      response <- queuedClient.queueRequest(HttpRequest(method=HttpMethods.PUT,uri="http://localhost:8011/item",entity=reqEntity))    } yield response  extractEntity[Item](putItemByQueue(Item(23,"Item#23", 46.0)))    .andThen { case _ => sys.terminate()}

下面是本次讨论的示范源代码：

服务端代码：

import akka.actor._import akka.stream._import akka.http.scaladsl.Httpimport akka.http.scaladsl.server.Directives._import de.heikoseeberger.akkahttpjson4s.Json4sSupportimport org.json4s.jacksontrait JsonCodec extends Json4sSupport {  import org.json4s.DefaultFormats  import org.json4s.ext.JodaTimeSerializers  implicit val serilizer = jackson.Serialization  implicit val formats = DefaultFormats ++ JodaTimeSerializers.all}object JsConverters extends JsonCodecobject TestServer extends App with JsonCodec {  implicit val httpSys = ActorSystem("httpSystem")  implicit val httpMat = ActorMaterializer()  implicit val httpEC = httpSys.dispatcher  import JsConverters._  case class Item(id: Int, name: String, price: Double)  val messages = path("message") {    get {      complete("hello, how are you?")    } ~    put {      entity(as[String]) {msg =>        complete(msg)      }    }  }  val items =    (path("item" / IntNumber) & get) { id =>       get {         complete(Item(id, s"item#$id", id * 2.0))       }    } ~      (path("item") & put) {        entity(as[Item]) {item =>          complete(item)        }     }  val route = messages ~ items  val (host, port) = ("localhost", 8011)  val bindingFuture = Http().bindAndHandle(route,host,port)  println(s"Server running at $host $port. Press any key to exit ...")  scala.io.StdIn.readLine()  bindingFuture.flatMap(_.unbind())    .onComplete(_ => httpSys.terminate())}

客户端源代码：

import akka.actor._import akka.http.scaladsl.settings.ConnectionPoolSettingsimport akka.stream._import akka.stream.scaladsl._import akka.http.scaladsl.Httpimport akka.http.scaladsl.model._import scala.util._import de.heikoseeberger.akkahttpjson4s.Json4sSupportimport org.json4s.jacksonimport scala.concurrent._import akka.http.scaladsl.unmarshalling.Unmarshalimport akka.http.scaladsl.unmarshalling._import akka.http.scaladsl.marshalling.Marshalimport scala.collection.SortedMapimport akka.http.scaladsl.common._trait JsonCodec extends Json4sSupport {  import org.json4s.DefaultFormats  import org.json4s.ext.JodaTimeSerializers  implicit val serilizer = jackson.Serialization  implicit val formats = DefaultFormats ++ JodaTimeSerializers.all}object JsConverters extends JsonCodecclass PooledClient(host: String, port: Int, poolSettings: ConnectionPoolSettings)                  (implicit sys: ActorSystem, mat: ActorMaterializer) {  import sys.dispatcher  private val cnnPool: Flow[(HttpRequest, Int), (Try[HttpResponse], Int), Http.HostConnectionPool] =    Http().cachedHostConnectionPool[Int](host = host, port = port, settings = poolSettings)  def requestSingleResponse(req: HttpRequest): Future[HttpResponse] = {    Source.single(req -> 1)      .via(cnnPool)      .runWith(Sink.head).flatMap {      case (Success(resp), _) => Future.successful(resp)      case (Failure(fail), _) => Future.failed(fail)    }  }  def orderedResponses(reqs: Iterable[HttpRequest]): Future[Iterable[HttpResponse]] = {    Source(reqs.zipWithIndex.toMap)      .via(cnnPool)      .runFold(SortedMap[Int, Future[HttpResponse]]()) {        case (m, (Success(r), idx)) => m + (idx -> Future.successful(r))        case (m, (Failure(f), idx)) => m + (idx -> Future.failed(f))      }.flatMap { m => Future.sequence(m.values) }  }}class QueuedRequestsClient(host: String, port: Int, poolSettings: ConnectionPoolSettings)                          (qsize: Int = 10, overflowStrategy: OverflowStrategy = OverflowStrategy.dropNew)                  (implicit sys: ActorSystem, mat: ActorMaterializer) {  import sys.dispatcher  private val cnnPool: Flow[(HttpRequest,Promise[HttpResponse]),(Try[HttpResponse],Promise[HttpResponse]),Http.HostConnectionPool] =    Http().cachedHostConnectionPool[Promise[HttpResponse]](host=host,port=port,settings=poolSettings)  val queue =    Source.queue[(HttpRequest, Promise[HttpResponse])](qsize, overflowStrategy)      .via(cnnPool)      .to(Sink.foreach({        case ((Success(resp), p)) => p.success(resp)        case ((Failure(e), p))    => p.failure(e)      })).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."))      }  }}object ClientRequesting extends App {  import JsConverters._  implicit val sys = ActorSystem("sysClient")  implicit val mat = ActorMaterializer()  implicit val ec = sys.dispatcher  implicit val jsonStreamingSupport = EntityStreamingSupport.json()    .withParallelMarshalling(parallelism = 8, unordered = false)  case class Item(id: Int, name: String, price: Double)  def extractEntity[T](futResp: Future[HttpResponse])(implicit um: Unmarshaller[ResponseEntity,T]) = {    futResp.andThen {      case Success(HttpResponse(StatusCodes.OK, _, entity, _)) =>        Unmarshal(entity).to[T]          .onComplete {            case Success(t) => println(s"Got response entity: ${t}")            case Failure(e) => println(s"Unmarshalling failed: ${e.getMessage}")          }      case Success(_) => println("Exception in response!")      case Failure(err) => println(s"Response Failed: ${err.getMessage}")    }  }    (for {    response <- Http().singleRequest(HttpRequest(method=HttpMethods.GET,uri="http://localhost:8011/message"))    message <- Unmarshal(response.entity).to[String]  } yield message).andThen {    case Success(msg) => println(s"Received message: $msg")    case Failure(err) => println(s"Error: ${err.getMessage}")  }  //.andThen {case _ => sys.terminate()}  (for {    entity <- Marshal("Wata hell you doing?").to[RequestEntity]    response <- Http().singleRequest(HttpRequest(method=HttpMethods.PUT,uri="http://localhost:8011/message",entity=entity))    message <- Unmarshal(response.entity).to[String]  } yield message).andThen {    case Success(msg) => println(s"Received message: $msg")    case Failure(err) => println(s"Error: ${err.getMessage}")  } //.andThen {case _ => sys.terminate()}  def getItem(itemId: Int): Future[HttpResponse] = for {    response <- Http().singleRequest(HttpRequest(method=HttpMethods.GET,uri = s"http://localhost:8011/item/$itemId"))  } yield response  extractEntity[Item](getItem(13))  def putItem(item: Item): Future[HttpResponse] =   for {    reqEntity <- Marshal(item).to[RequestEntity]    response <- Http().singleRequest(HttpRequest(method=HttpMethods.PUT,uri="http://localhost:8011/item",entity=reqEntity))   } yield response  extractEntity[Item](putItem(Item(23,"Item#23", 46.0)))     .andThen { case _ => sys.terminate()}    val settings = ConnectionPoolSettings(sys)    .withMaxConnections(8)    .withMaxOpenRequests(8)    .withMaxRetries(3)    .withPipeliningLimit(4)  val pooledClient = new PooledClient("localhost",8011,settings)  def getItemByPool(itemId: Int): Future[HttpResponse] = for {    response <- pooledClient.requestSingleResponse(HttpRequest(method=HttpMethods.GET,uri = s"http://localhost:8011/item/$itemId"))  } yield response  extractEntity[Item](getItemByPool(13))  def getItemsByPool(itemIds: List[Int]): Future[Iterable[HttpResponse]] = {    val reqs = itemIds.map { id =>      HttpRequest(method = HttpMethods.GET, uri = s"http://localhost:8011/item/$id")    }    val rets = (for {      responses <- pooledClient.orderedResponses(reqs)    } yield responses)    rets  }  val futResps = getItemsByPool(List(3,5,7))  futResps.andThen {    case Success(listOfResps) => {      listOfResps.foreach { r =>        r match {          case HttpResponse(StatusCodes.OK, _, entity, _) =>            Unmarshal(entity).to[Item]              .onComplete {                case Success(t) => println(s"Got response entity: ${t}")                case Failure(e) => println(s"Unmarshalling failed: ${e.getMessage}")              }          case _ => println("Exception in response!")        }      }    }    case _ => println("Failed to get list of responses!")  }  val queuedClient = new QueuedRequestsClient("localhost",8011,settings)()    def putItemByQueue(item: Item): Future[HttpResponse] =    for {      reqEntity <- Marshal(item).to[RequestEntity]      response <- queuedClient.queueRequest(HttpRequest(method=HttpMethods.PUT,uri="http://localhost:8011/item",entity=reqEntity))    } yield response  extractEntity[Item](putItemByQueue(Item(23,"Item#23", 46.0)))    .andThen { case _ => sys.terminate()}  }