warp: Use custom exception on listen socket closure

[shlevy]

Currently, my custom uncaught exception logger needs:

onException Nothing e
  | Just (ioeGetErrorType -> et) <- fromException e
  , et == ResourceVanished || et == InvalidArgument = pure ()

in order to avoid logging the invalid argument error that results from the listen socket being closed (to start graceful shutdown). It would be nice to have a custom exception type passed to the uncaught exception handler in this case, as it's an internal implementation detail if there could be other cases of ResourceVanished or InvalidArgument thrown prior to the construction of the Request which we actually do want to log.

[snoyberg]

Making such a change would end up silently breaking lots of existing code that's doing exactly what you've done here.

[shlevy]

Hmm so options here:

1. Do nothing
2. Accept the breakage
3. Have some new interface generalizing setOnException with a richer context

Probably 1 is the right answer for the library but I wouldn't say no to 3.

[snoyberg]

An option (4) that I think would work here: provide predicate functions that test for the common cases people care about, e.g. isListenSocketClosedException :: SomeException -> Bool