Play2 Framework proxy streaming content to client

问题:

The below code does streaming back to client, in, what I gather is a more idiomatic way than using Java's IO Streams. It, however, has an issue: connection is kept open after stream is done.

def getImage() = Action { request =>
  val imageUrl = "http://hereandthere.com/someimageurl.png"
  Ok.stream({ content: Iteratee[Array[Byte], Unit] => 
    WS.url(imageUrl).withHeaders("Accept"->"image/png").get { response => content }
    return
  }).withHeaders("Content-Type"->"image/png")
}

this is intended for streaming large (>1 mb) files from internal API to requester.

The question is, why does it keep the connection open? Is there something it expects from upstream server? I tested the upstream server using curl, and the connection does close - it just doesn't close when passed through this proxy.

回答1:

The reason that the stream doesn't finish is because an EOF isn't sent to the iteratee that comes back from WS.get() call. Without this explicit EOF, the connection stays open - as it's in chunked mode, and potentially a long-running, comet-like connection.

Here's the fixed code:

Ok.stream({ content: Iteratee[Array[Byte], Unit] => 
  WS.url(imageUrl)
    .withHeaders("Accept"->"image/png")
    .get { response => content }
    .onRedeem { ii =>
       ii.feed(Input.EOF)
    }
}).withHeaders("Content-Type"->"image/png")

回答2:

Here is a modified version for play 2.1.0. See https://groups.google.com/forum/#!msg/play-framework/HwoRR-nipCc/gUKs9NexCx4J

Thanks Anatoly G for sharing.

def proxy = Action {

   val url = "..."

   Async {
     val iterateePromise = Promise[Iteratee[Array[Byte], Unit]]
     val resultPromise = Promise[ChunkedResult[Array[Byte]]]

     WS.url(url).get { responseHeaders =>
       resultPromise.success {
         new Status(responseHeaders.status).stream({ content: Iteratee[Array[Byte], Unit] =>
           iterateePromise.success(content)
         }).withHeaders(
           "Content-Type" -> responseHeaders.headers.getOrElse("Content-Type", Seq("application/octet-stream")).head,
           "Connection" -> "Close")
       }
       Iteratee.flatten(iterateePromise.future)
     }.onComplete {
       case Success(ii) => ii.feed(Input.EOF)
       case Failure(t) => resultPromise.failure(t)
     }

     resultPromise.future
   }

}

回答3:

Update for play 2.2.x:

def proxy = Action.async {
  val url = "http://localhost:9000"

  def enumerator(chunks: Iteratee[Array[Byte], Unit] => _) = {
    new Enumerator[Array[Byte]] {
      def apply[C](i: Iteratee[Array[Byte], C]): Future[Iteratee[Array[Byte], C]] = {
        val doneIteratee = Promise[Iteratee[Array[Byte], C]]()
        chunks(i.map {
          done =>
            doneIteratee.success(Done[Array[Byte], C](done)).asInstanceOf[Unit]
        })
        doneIteratee.future
      }
    }
  }

  val iterateePromise = Promise[Iteratee[Array[Byte], Unit]]()
  val resultPromise = Promise[SimpleResult]()

  WS.url(url).get {
    responseHeaders =>

      resultPromise.success(new Status(responseHeaders.status).chunked(
        enumerator({
          content: Iteratee[Array[Byte], Unit] => iterateePromise.success(content)
        }
        )).withHeaders(
        "Content-Type" -> responseHeaders.headers.getOrElse("Content-Type", Seq("application/octet-stream")).head,
        "Connection" -> "Close"))

      Iteratee.flatten(iterateePromise.future)
  }.onComplete {
    case Success(ii) => ii.feed(Input.EOF)
    case Failure(t) => throw t
  }

  resultPromise.future
}

if anyone has a better solution, it interests me greatly!