RFC: UNIX server sockets

[Tronic]

Implement high level API for UNIX server sockets, based on #279

This needs some more work but I'd like to invite others for comments at this point.

[decentral1se]

Just tried to figure out how to serve a unix socket and ended up here, thanks for this effort ... I guess my only capacity to help this along is basically to bump the PR with this comment 😅 There is a whole bunch of stuff here I had no idea that should be taken care of when dealing with sockets...

[decentral1se]

Oh yeah, could also take it for a test drive! Saw the following warning when running serve_unix:

TrioDeprecationWarning: subclassing trio.SocketListener is deprecated since Trio 0.15.0; use composition or delegation instead (#1044) class UnixSocketListener(trio.SocketListener):

Seems to do the job 🌞

from functools import partial
from trio import open_nursery, open_unix_socket, run
from trio_socket import serve_unix  # gh:python-trio/trio/pull/1433

SOCK_PATH = "/tmp/temp.sock"

async def client():
    stream = await open_unix_socket(SOCK_PATH)
    async with stream:
        await stream.send_all(b"hello, world")

async def server(stream):
    async for data in stream:
        print(f"received -> {data}")

async def main():
    async with open_nursery() as server_nursery:
        await server_nursery.start(partial(serve_unix, server, SOCK_PATH))
        async with open_nursery() as client_nursery:
            client_nursery.start_soon(client)
        server_nursery.cancel_scope.cancel()

run(main)

[py-radicz]

I am also bumping this PR as I think it would be nice to have also UDS server support - thank you @Tronic + @decentral1se you saved me ton of time figuring this out

[GalaxySnail]

Why is it necessary here?

[CoolCat467]

Not sure, should we try removing this?

[codecov]

Codecov Report

Attention: Patch coverage is 69.82249% with 51 lines in your changes missing coverage. Please review.

Project coverage is 99.72623%. Comparing base (5ca9662) to head (5091177).

Files with missing lines	Patch %	Lines
src/trio/_highlevel_open_unix_listeners.py	62.22222%	39 Missing and 12 partials ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##                 main       #1433         +/-   ##
====================================================
- Coverage   100.00000%   99.72623%   -0.27377%     
====================================================
  Files             124         126          +2     
  Lines           18460       18629        +169     
  Branches         1216        1234         +18     
====================================================
+ Hits            18460       18578        +118     
- Misses              0          39         +39     
- Partials            0          12         +12     

Files with missing lines	Coverage Δ
src/trio/__init__.py	100.00000% <100.00000%> (ø)
.../trio/_tests/test_highlevel_open_unix_listeners.py	100.00000% <100.00000%> (ø)
src/trio/_highlevel_open_unix_listeners.py	62.22222% <62.22222%> (ø)