JMS: txSource should report rollbacks

[ennru]

Short description

When a JMS transactional message is rolled back, this should be inspectable by the user at least via log messages with a hint to the ack-timeout setting.

Possibly, the users should be able to let the stream fail if the ACK timeout is hit and a message is rolled back.

Details

The current JMS.txSource automatically calls rollback when the ack-timeout (default 1 s) is hit, but this can't be noticed by the consumer.

alpakka/jms/src/main/scala/akka/stream/alpakka/jms/impl/JmsTxSourceStage.scala

Lines 53 to 58 in 85f65b1

	val action = Await.result(envelope.commitFuture, settings.ackTimeout)
	action()
	} catch {
	case _: TimeoutException => session.session.rollback()
	case e: IllegalArgumentException => handleError.invoke(e) // Invalid envelope. Fail the stage.
	case e: jms.JMSException => handleError.invoke(e)

See #1831

[WellingR]

Actually, just a log message may not be enough. I would rather see that the commit (and maybe also rollback) methods on the TxEvenlope would throw an exception to make it clear that the message was already rolled back.

[ennru]

Yes, that makes sense and would be expected. Changing it would break backwards compatibility for code that handles duplicated messages correctly today, though.

[WellingR]

Perhaps an alternative could be for the commit/rollback method to return a future which completes when the commit/rollback has actually been handled

[ennru]

In #1857 I suggest a backwards-compatible way to improve this.
For Alpakka 2.0 we could look into further improvements.

[ennru]

Improved with #1857.