The _exception() -> close() change seems to be wrong. The third set of
select() is supposed to represent oob data, so the previous use in the
select-based loop should have been correct?

Other than that, i can't see anything wrong with it.

Maybe handle_expt_event should be reverted to the old one, that just
calls handle_expt, too? The current version seems to assume that it is
called on socket error conditions.