rust async: Currently cancelling a stream/future read/write discards the intrinsic return value #1188

Currently cancelling a stream/future read/write discards the return value from the imported intrinsic. According to this it might even be possible for the intrinsic to not actually complete and return that nothing was cancelled. My hunch is that something needs to be handled here, so I wanted to file an issue to come back and take a look at this.