21 tests fail when run on an IPv6-only host

[gpshead]

BPO	37901
Nosy	@gpshead, @vstinner
PRs	gh-82082: Make our test suite pass on an IPv6-only Linux host #26225

^{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 = 'https://github.com/gpshead'
closed_at = None
created_at = <Date 2019-08-20.22:41:23.434>
labels = ['3.7', '3.8', 'type-bug', 'tests', '3.9']
title = '21 tests fail when run on an IPv6-only host'
updated_at = <Date 2022-03-23.00:04:55.105>
user = 'https://github.com/gpshead'

bugs.python.org fields:

activity = <Date 2022-03-23.00:04:55.105>
actor = 'gregory.p.smith'
assignee = 'gregory.p.smith'
closed = False
closed_date = None
closer = None
components = ['Tests']
creation = <Date 2019-08-20.22:41:23.434>
creator = 'gregory.p.smith'
dependencies = []
files = []
hgrepos = []
issue_num = 37901
keywords = ['patch']
message_count = 4.0
messages = ['350039', '350059', '350063', '415841']
nosy_count = 2.0
nosy_names = ['gregory.p.smith', 'vstinner']
pr_nums = ['26225']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37901'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[gpshead]

21 tests failed:
test_asynchat test_asyncore test_docxmlrpc test_eintr test_epoll
test_ftplib test_httplib test_imaplib
test_multiprocessing_forkserver test_multiprocessing_spawn
test_nntplib test_os test_poplib test_robotparser test_smtplib
test_socket test_ssl test_support test_telnetlib
test_urllib2_localnet test_wsgiref

This is a rollup tracking issue. I've got an IPv6-only future buildbot host with which to run an diagnose these for fixes. Of note there is no IPv4 localhost.

If there are larger problems I may spawn child bugs for specific issues off of this one. (I already filed separate issues about 5 other tests that hang rather than fail)

[vstinner]

How do you configure a Linux box to disable IPv4? At least, disable IPv4 localhost?

[vstinner]

(I already filed separate issues about 5 other tests that hang rather than fail)

Maybe use this issue as a meta-issue for IPv6-only issues? I saw:

• bpo-37895: test_logging hangs on an IPv6-only host
• bpo-37896: test_multiprocessing_fork hangs on an IPv6-only host
• bpo-37897: test_asyncio hangs on an IPv6-only host
• bpo-37898: test_httpservers hangs on an IPv6-only host
• bpo-37899: test_xmlrpc hangs on an IPv6-only host

[gpshead]

Here's how I created an IPv6-only host: https://gist.github.com/gpshead/f4f394593674e5f7a58e9424b4dba989