IO-TCP logs unnecessary error message on flow termination

[anpin]

Version Information
Version of Akka.NET? 1.5.13
Which Akka.NET Modules? Akka and Akka.Streams

On net472 target TcpStreams extensions logs out unnecessary error message when attached TCP flow is terminated. The message is not produced when target runs net7.0.

[ERROR][09/27/2023 13:15:59.865Z][Thread 0035][akka://my-system/system/IO-TCP/$a] Monitored actor [[akka://my-system/user/$a/StreamSupervisor-1/$$a#549811830]] terminated
Cause: Akka.Actor.DeathPactException: Monitored actor [[akka://my-system/user/$a/StreamSupervisor-1/$$a#549811830]] terminated
  at Akka.Actor.ActorBase.Unhandled (System.Object message) [0x00015] in <d180930ef5f34340b9af3303aa68102d>:0 
  at Akka.Actor.ActorBase.AroundReceive (Akka.Actor.Receive receive, System.Object message) [0x00096] in <d180930ef5f34340b9af3303aa68102d>:0 
  at Akka.Actor.ActorCell.ReceiveMessage (System.Object message) [0x00023] in <d180930ef5f34340b9af3303aa68102d>:0 
  at Akka.Actor.ActorCell.ReceivedTerminated (Akka.Actor.Terminated t) [0x00042] in <d180930ef5f34340b9af3303aa68102d>:0 
  at Akka.Actor.ActorCell.AutoReceiveMessage (Akka.Actor.Envelope envelope) [0x000af] in <d180930ef5f34340b9af3303aa68102d>:0 
  at Akka.Actor.ActorCell.Invoke (Akka.Actor.Envelope envelope) [0x0006d] in <d180930ef5f34340b9af3303aa68102d>:0 

To Reproduce
Steps to reproduce the behavior:

1. git clone https://github.com/anpin/akka-mergehub-and-socket-repro
2. cd akka-mergehub-and-socket-repro/ConsoleApp1
3. dotnet run --framework net472
4. depending on the random condition inside the loop the server might terminate with exception, regardless of it press Ctrl-C to close the app and observe the above exception
5. Run the same example with dotnet run --framework net7.0 and see no error after Ctrl-C

Note: the exception inside the server code was planted to illustrate another error message logged when MergeHub source is failing

Expected behavior
The Monitored actor terminated message is not emitted on both platforms

Actual behavior
The Monitored actor terminated message is emitted on net472, but not on dotnet

Environment
Both Linux and Windows

.NET SDK:
Version: 7.0.400
Commit: 73bf45718d

[Aaronontheweb]

This is definitely a long-standing bug with Akka.IO - we're using a very sloppy technique for ensuring the mutual destruction of actors inside of here, hence the useless spam in the error logs. We should handle this more appropriately so it doesn't cast off unnecessary exceptions.

[anpin]

Hi @Aaronontheweb, I created a draft which uses pattern matching on upstream exception to complete MergeHub.Sink gracefully if it was NormalShutdownException. Do you think it is a feasible approach to eliminate the noise in our logs?

BTW my original report mentions that errors are not logged on net7.0 yet they are appearing for me now on net8.0

[Aaronontheweb]

Thanks @anpin - I'd be happy to check this out.

[He-Pin]

But seems the ActorPublisher.NormalShutdownReason is only been used in the FanoutProcessorImpl?
Seems like there is nothing to do with the MergeHub