AKKA HTTP源流与未来

Question

我的服务代码如下所示,

def getShards(id: String, shards: Int) = {
  def getShardsInternal(shardNo: Int, shards: Future[Array[Byte]]): Future[Array[Byte]] = {
    if (shardNo == 0) shards
    else getShardsInternal(shardNo - 1, shards.flatMap(x => Database.ShardModel.find(id, shardNo)))
  }
  getShardsInternal(shards, Future.successful(Array()))
}

在我的AKKA HTTP路由中,我尝试从返回的未来构建源,如下所示,

def getAsset = get {
  pathPrefix("asset") {
    parameters('id) { id =>
      complete {
        val f = mediaService.getMetadata(id).flatMap { x =>
          mediaService.getShards(id, x.shards)
        }
        Source.fromFuture(f)
      }
    }
  }
}

我不确定source.fromfuture如何提交给响应。被传递的未来实质上是一系列预期按顺序执行的平面映射的未来。但是，我不相信这会作为分块字节流返回到客户端。

get {
  pathPrefix("asset") {
    parameters('id) { id =>
      complete {
        Source.fromFuture {
          Future.successful("Hello".getBytes()).flatMap(x => Future.successful("World".getBytes()))
        }
      }
    }
  }
}

[72,101,108,108,111,32,87,111,114,108,100]

然而,我只得到最后一个未来的结果如下,

[[87,111,114,108,100]]

亲切地问候Meeraj

Answer 1

将源[Array[Byte],NotUsed]转换为源[ByteString,NotUsed]，并将HttpEntity与ContentTypes:

import akka.util.ByteString

def getAsset = get {
  pathPrefix("asset") {
    parameters('id) { id =>
      val f = mediaService.getMetadata(id).flatMap { x =>
        mediaService.getShards(id, x.shards)
      }
      val source = Source.fromFuture(f).map(ByteString.apply)
      complete(HttpEntity(ContentTypes.`application/octet-stream`, source))
    }
  }
}

这里我使用application/octet-stream作为示例。由于您正在对视频进行流式传输，因此可能需要使用ContentType.Binary以及适当的媒体类型。例如：

complete(HttpEntity(ContentType.Binary(MediaTypes.`video/mpeg`), source))    

处理您的注释和更新时，您似乎想要在getshards中连接未来的结果：正如您所发现的，flatmap不会这样做。改用future.reduceLeft:

def getShards(id: String, shards: Int): Future[Array[Byte]] = {
  val futures = (1 to shards).map(Database.ShardModel.find(id, _))
  Future.reduceLeft(futures)(_ ++ _)
}

def getShards(id: String, shards: Int): Future[List[Array[Byte]]] = {
  val futures = (1 to shards).map(Database.ShardModel.find(id, _)).toList
  Future.sequence(futures)
}

def getAsset = get {
  pathPrefix("asset") {
    parameters('id) { id =>
      val f = mediaService.getMetadata(id).flatMap { x =>
        mediaService.getShards(id, x.shards)
      }
      val source =
        Source.fromFuture(f)
              .flatMapConcat(Source.apply)
              .map(ByteString.apply)
      complete(HttpEntity(/* a content type */, source))
    }
  }
}