What is the proper way of acknowledging SQS message in Akka streams - scala

Question

Let say I have a constant stream of SQS message from AWS. I have a flow which take messages and perform some side effects that is possibly unsafe.
I want to ACK all the messages, if the process failed for any reason I want to push the message to another queue. If the process succeded I want to delete it. I don't want to have not ACK messages.
Also I want to be able to dispatch the incoming messages into parallelized workers.
What is the proper way of doing such a thing ?
I devised that this is working but I wonder if it is a "good" solution:
val flow = Flow[String]
.map { value =>
if (value == "global")
throw new Exception("Unexpected failure parsing global")
println(value)
}
val result = Source(
Seq("coucou", "baba", "global", "obvious", "test", "lol", "supercool")
)
.mapAsync(2) { el =>
Source
.single(el)
.via(flow)
.recover {
case ex: Throwable =>
println(s"SEND message ${el} to another queue")
}
.runWith(Sink.foreach { _ =>
println(s"DELETE message ${el}")
})
}
.runWith(Sink.ignore)
What do you think?

Answer 1

In flow, instead of performing side effects, maybe you can simply wrap it in an Either so that you can handle left and right differently with nok and ok.
import akka.actor.ActorSystem
import akka.stream.SinkShape
import akka.stream.scaladsl.{Flow, GraphDSL, Partition, Sink, Source}
import scala.concurrent.ExecutionContext
object PartitionStream {
def main(args: Array[String]): Unit = {
implicit val system: ActorSystem = ActorSystem("PartitionStream")
implicit val ec: ExecutionContext = system.dispatcher
val flow = Flow[String].map { value =>
if (value == "global")
Left(MyException("Unexpected failure parsing global"))
else Right(value)
}
val sink = Sink.fromGraph(GraphDSL.create() { implicit b =>
import GraphDSL.Implicits._
val partition = b.add(
Partition[Either[MyException, String]](2, el => if (el.isLeft) 0 else 1)
)
val collectNok = Flow[Either[MyException, String]].collect {
case Left(ex) => ex
}
val collectOk = Flow[Either[MyException, String]].collect {
case Right(value) => value
}
val nok = b.add(Sink.foreach[MyException](x => println(x.msg)))
val ok = b.add(Sink.foreach[String](println))
partition.out(0) ~> collectNok ~> nok
partition.out(1) ~> collectOk ~> ok
SinkShape(partition.in)
})
Source(
List("coucou", "baba", "global", "obvious", "test", "lol", "supercool")
).via(flow).runWith(sink)
}
case class MyException(msg: String)
}