UNIX socket and SOCK_DGRAM

[Victor Stinner]

Hi,

I see that new methods were added to support the AF_UNIX family. The
socket type is hardcoded to SOCK_STREAM. It looks like AF_UNIX can be
used with SOCK_DGRAM.
http://stackoverflow.com/questions/18711996/using-abstract-sockets-with-af-unix-sock-dgram

Why not adding an option to make the user choose the socket type?

Victor

[Guido van Rossum]

Because that would require duplicating the logic in create_datagram_endpoint(), which is totally separate (all the way down to the I/O callbacks).

Feel free to add a feature request to the tracker for this though. Be sure to indicate an actual use case (rather than just abstract interest). E.g. do you expect to need this in OpenStack? How?

--
--Guido van Rossum (python.org/~guido)

[Yury Selivanov]

On 2/19/2014, 10:55 AM, Guido van Rossum wrote:
> Because that would require duplicating the logic in
> create_datagram_endpoint(), which is totally separate (all the way down to
> the I/O callbacks).

Exactly. I was hesitant to do that myself because my experience
with UDP is fairly limited.

Yury

[Victor Stinner]

2014-02-19 16:55 GMT+01:00 Guido van Rossum <gu...@python.org>:
> Because that would require duplicating the logic in
> create_datagram_endpoint(), which is totally separate (all the way down to
> the I/O callbacks).

Oh, I didn't notice that TCP and UDP are handled differently. I only
expected to pass type=SOCK_DGRAM and it would just work :-D

> Feel free to add a feature request to the tracker for this though. Be sure
> to indicate an actual use case (rather than just abstract interest). E.g. do
> you expect to need this in OpenStack? How?

The new UNIX methods were not documented. When I wrote the
documentation, I noticed that only SOCK_STREAM was supported. That's
why I asked the question. I don't need UNIX+SSL nor UNIX on UDP :-)

Victor

[Guido van Rossum]

Cool. Since we do have UNIX + SSL, maybe we should provide an example?

[Ludovic Gasc]

On Wednesday, February 19, 2014 at 4:55:03 PM UTC+1, Guido van Rossum wrote:

Because that would require duplicating the logic in create_datagram_endpoint(), which is totally separate (all the way down to the I/O callbacks).

Feel free to add a feature request to the tracker for this though. Be sure to indicate an actual use case (rather than just abstract interest). E.g. do you expect to need this in OpenStack? How?

Hi everybody,

I would wake-up this thread because I have a concrete use case to have that in AsyncIO, even if it would the only one concrete use case from a production environment:

systemd has a watchdog mechanism and a way to communicate between a daemon and systemd.

It uses a UNIX socket with DGRAM, the mechanism is named sd_notify.

For example, a Python that implements sd_notify: https://github.com/bb4242/sdnotify/blob/master/sdnotify/__init__.py#L35

Another example in Python: https://gist.github.com/Spindel/1d07533ef94a4589d348#file-watchdogged-py-L78

More technical documentation about sd_notify protocol: https://www.freedesktop.org/software/systemd/man/sd_notify.html

In fact, if somebody has a workaround or a way to implement that gently with AsyncIO, it would be awesome, because I need to ping-pong with systemd to say that my daemon is still alive.

Thanks for your help.

I have tried to find a way with loop.create_datagram_endpoint() that would be the most closer what I want and a custom socket, I have this error:

   File "/usr/local/pythonz/pythons/CPython-3.6.2/lib/python3.6/asyncio/base_events.py", line 951, in create_datagram_endpoint
     yield from waiter
 AssertionError: yield from wasn't used with future

My piece of code:

sock = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
sock.setblocking(False)
sock.connect(os.environ["NOTIFY_SOCKET"])
transport, protocol = loop.create_datagram_endpoint(
    lambda: WatchDogClientProtocol(loop),
    sock=sock)

[Guido van Rossum]

OK, that looks like a real use case and proof that UNIX sockets used as datagrams are actually used. If you submit a PR (to CPython -- the separate asyncio repo is dead) it should be possible to get this into Python 3.7.

[Ludovic Gasc]

Except if the implementation is a candy for somebody's else (please raise your hand ;-) ), I will follow the official process to contribute in CPython to add that.

Thanks Guido for your response. 

[Ludovic Gasc]

2017-08-17 10:51 GMT+02:00 Victor Stinner <victor....@gmail.com>:

Hi Ludo,

2017-08-17 9:21 GMT+02:00 Ludovic Gasc <gml...@gmail.com>:
> I will follow the official process to contribute in CPython to add that.

I can help you on that part if you want ;-)

Thank you a lot Victor, I will contact you directly when I have something to show :-)

[Ludovic Gasc]

Hi,

Finally, it became a candy for one of my developers, he has made an issue+PR:

http://bugs.python.org/issue31245

Thanks a lot Victor for your code review.

All automatic checks are green now, thanks for your feedbacks.

Have a nice week.