Akka queue stream recover and drop element back in top

[scal...@twitter.com]

Hey all,

In my example below I have a source queue. In the middle I have a flow that can fail for a few different network related reason and all I want to do is drop the request back in the top of the funnel. But I am not entirely sure how I can get access to the element that went into the flow and caused the failure.

val queue = Source.queue[ArchiveValidationRequest](50, OverflowStrategy.fail)

queue.via(alwaysOnFlow).recover {

  case ex: Throwable =>
    error("Element failed. Reinserting back into queue to be processed")
    queue.offer(???)       

}

This seems like a fairly basic pattern but its not super obvious how to get that failed request. recoverWithRetries doesn't seem to be what I want here as I just want to capture the failed element and just try to process it later.

[Akka Team]

Recover will catch an exception coming from upstream and continue by emitting a single element before completing. Indeed does not sound like what you are after. 

Maybe the retry stream in akka-stream-contrib could give you some inspiration on how to solve your problem: https://github.com/akka/akka-stream-contrib/blob/master/contrib/src/main/scala/akka/stream/contrib/Retry.scala

--

Johan 

Akka Team

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