[Jack-Devel] Fwd: Possible error codes for jack_midi_event_get()?

[Matthias Geier]

Dear list.

I'm the author of one of the Python bindings for JACK:
https://jackclient-python.readthedocs.io/

I was a bit lazy when implementing a generator function that's
supposed to yield all incoming MIDI events one-by-one.

Here's the code if somebody is interested (it's using CFFI and the
_lib object is a wrapper for the JACK API):


    def incoming_midi_events(self):
        event = self._event
        buf = _lib.jack_port_get_buffer(
            self._ptr, self._client.blocksize)
        for i in range(_lib.jack_midi_get_event_count(buf)):
            err = _lib.jack_midi_event_get(event, buf, i)
            # TODO: proper error handling if this ever happens:
            assert not err, err
            yield event.time, _ffi.buffer(event.buffer, event.size)


As you can see, I didn't check the return value of
jack_midi_event_get(), I just added an "assert" statement hoping that
somebody would report it if the call to jack_midi_event_get() would
ever fail.

I didn't hear anything for a long time, but recently I got a bug
report where the assertion was violated:
https://github.com/spatialaudio/jackclient-python/issues/54

This shows that jack_midi_event_get() can raise an error, even if I
check with jack_midi_get_event_count() beforehand.

My question is now: how should I react to this error?

Shall I ...

* discard the current event and continue reading further events?

* discard the current and all following events in this block?

* raise an error?

* do something else?

Can I guarantee that no incoming MIDI events get lost?

Another related question: what error code is supposed to be returned?
The documentation
(http://www.jackaudio.org/api/group__MIDIAPI.html#ga838c794bd1451bfd47edde1c7cd1ff4f)
mentions ENODATA, but according to my bug report, ENOBUFS (-105) was
returned.

Is this a bug in JACK or an omission in the documentation?

I don't know which JACK version was used, the OS was Ubuntu 18.04 LTS 64 bits.

cheers,
Matthias