socket.getsockname() type mismatch with AF_UNIX on Linux

[giampaolo]

BPO	30205
Nosy	@ronaldoussoren, @pitrou, @vstinner, @giampaolo, @tiran, @ned-deily
PRs	bpo-30205: Fix getsockname() for unbound AF_UNIX sockets on Linux #1370 Backport bpo-30205 to 3.5 #1404 Backport bpo-30205 to 3.6 #1403

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2017-05-02.22:23:04.258>
created_at = <Date 2017-04-29.08:55:10.959>
labels = ['3.7', 'type-bug', 'library']
title = 'socket.getsockname() type mismatch with AF_UNIX on Linux'
updated_at = <Date 2017-05-02.22:23:04.257>
user = 'https://github.com/giampaolo'

bugs.python.org fields:

activity = <Date 2017-05-02.22:23:04.257>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2017-05-02.22:23:04.258>
closer = 'pitrou'
components = ['Library (Lib)']
creation = <Date 2017-04-29.08:55:10.959>
creator = 'giampaolo.rodola'
dependencies = []
files = []
hgrepos = []
issue_num = 30205
keywords = []
message_count = 11.0
messages = ['292580', '292581', '292702', '292776', '292781', '292806', '292807', '292809', '292810', '292818', '292819']
nosy_count = 7.0
nosy_names = ['ronaldoussoren', 'pitrou', 'vstinner', 'giampaolo.rodola', 'christian.heimes', 'ned.deily', 'neologix']
pr_nums = ['1370', '1404', '1403']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue30205'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']

[giampaolo]

>>> import socket
>>> s = socket.socket(socket.AF_UNIX)
>>> s.getsockname()
b''
>>> s.bind('foo')
>>> s.getsockname()
'foo'

[giampaolo]

The change was introduced here:
b10c71d

[pitrou]

Amusingly, binding to the empty string produces something different:

>>> s = socket.socket(socket.AF_UNIX)
>>> s.getsockname()
b''
>>> s.bind(b'')
>>> s.getsockname()
b'\x000005d'

while binding to the nul byte string produces the expected result:

>>> s = socket.socket(socket.AF_UNIX)
>>> s.bind(b'\x00')
>>> s.getsockname()
b'\x00'

[pitrou]

New changeset 495b502 by Antoine Pitrou in branch 'master':
bpo-30205: Fix getsockname() for unbound AF_UNIX sockets on Linux (bpo-1370)
495b502

[giampaolo]

Thanks.

[vstinner]

Test fails on x86 Tiger 3.x:

http://buildbot.python.org/all/builders/x86%20Tiger%203.x/builds/600/steps/test/logs/stdio

======================================================================
FAIL: testUnbound (test.test_socket.TestUnixDomain)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/Users/db3l/buildarea/3.x.bolen-tiger/build/Lib/test/test_socket.py", line 4687, in testUnbound
    self.assertEqual(self.sock.getsockname(), '')
AssertionError: None != ''

[vstinner]

Maybe restrict the unit test to Linux since the change was specific to Linux?

[pitrou]

Oh, yuck.

Maybe restrict the unit test to Linux since the change was specific to Linux?

That sounds reasonable. I didn't know getsockname() could return None...

[vstinner]

I didn't know getsockname() could return None...

Me neither. Maybe it's a bug? makesockaddr() returns None if addrlen equals 0:                                   
             
    if (addrlen == 0) {                                                           
        /* No address -- may be recvfrom() from known socket */                   
        Py_RETURN_NONE;                                                           
    }

[pitrou]

New changeset 0c2ff08 by Antoine Pitrou in branch '3.6':
Backport bpo-30205 to 3.6 (bpo-1403)
0c2ff08

[pitrou]

New changeset 0d9d618 by Antoine Pitrou in branch '3.5':
Backport bpo-30205 to 3.5 (bpo-1404)
0d9d618