AMQP Source acknowledges messages too early

[irishshagua]

Currently the AMQP source sends an acknowledgement back to the RabbitMQ server as soon as it sends the received message to the outlet.
https://github.com/akka/alpakka/blob/master/amqp/src/main/scala/akka/stream/alpakka/amqp/AmqpSourceStage.scala#L126

If anything happens to the message during the flow which would cause the flow to explode then the message will not be re-queued (although other messages that were in the buffer will). It should be possible to reserve the acknowledgement of the message until it has reached the sink. This way there would be no possibility of losing a message due to some non related runtime exception.

I haven't fully thought out how this would deal with invalid messages which could cause repeated exceptions, but it'd be cool to see if acking after the flow had been considered.

[johanandren]

It's not a bug, it was a design decision when it was written to keep the scope reasonable.

[johanandren]

Relevant ticket #104

[johanandren]

I should add that such functionality would be great to have.

[kennedyoliveira]

Is this feature going to be worked on? Is there are "best practice" to get around the problem of losing messages?

[johanandren]

It was worked on in #292, but I think it may be stalled. If you would like to pick it up, please ping the original author of that PR and check what is happening.

[kennedyoliveira]

I see, i'll check the pr and get in touch with the author, thanks @johanandren.