Exception in the inner observable of flatMap not rethrown

[dvtomas]

Hi all,
I'm trying to figure out, how errors are handled in RxJava (0.19.1). Basically, I'd expect the fundamental rule to be something like: Any exception thrown within an operator is either handed to the onError handler of subscribe if one is provided, or rethrown if none is provided.

This works for the map operator:

def throwOnB2(prefix: String) = Observable.from(List(1, 2, 3))
  .map(x ⇒ prefix + x.toString)
  .map(s ⇒ if (s == "b2") throw new Exception("Bang!") else s)

throwOnB2("b").subscribe(next ⇒ println(next))

throws a rx.exceptions.OnErrorNotImplementedException: Bang! as expected.

throwOnB2("b").subscribe(
  next ⇒ println(next),
  err ⇒ println(s"error: ${err}"),
  () ⇒ println("completed")
)

prints error: java.lang.Exception: Bang! as expected.

For nested observables joined using flatMap

def nested = Observable
  .from(List("a", "b", "c"))
  .flatMap(prefix ⇒ throwOnB2(prefix))

nested
  .subscribe(
    next ⇒ println(next),
    err ⇒ println(s"error: ${err}"),
    () ⇒ println("completed")
  )

prints error: java.lang.Exception: Bang! as expected,

But:

nested.subscribe(next ⇒ println(next))

prints

a1
a2
a3
b1

and finishes without throwing any exception.

Is this the intended behavior? For me it is quite unfortunate, since bugs in my code can easily slip away unnoticed, but perhaps there is something I don't see.

Thank you, best regards

[headinthebox]

@dvtomas Good catch.