Question

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.

Answer 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")