Why is Akka Streams swallowing my exceptions?

Question

Why is the exception in

import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import akka.stream.scaladsl.Source

object TestExceptionHandling {
  d         


        

Answer 1

I had a different issue with Akka Streams swallowing my exceptions. I'll post it here since this is the top Google result.

In a case like this, where source is a Source[ByteString, Any]:

source.runWith(StreamConverters.fromOutputStream(() => outputStream))

This returns a Future[IOResult]. If the write to the output stream fails (for example, the source fails), then the Future will still return a Success. In this case, you actually have to check the IOResult for the error:

source.runWith(StreamConverters.fromOutputStream(() => output)).
      map(ior => {
        if (!ior.wasSuccessful) 
          throw new RuntimeException(ior.getError)
      })

The result of this will be a failed Future with the correct exception.