Re: IPv6-only testing

[Jakub Wilk <jwilk@jwilk.net>]

* Julien Puydt <julien.puydt@gmail.com>, 2022-02-04, 12:34:
> I got an RC bug on python-anyio, because its testsuite fails when run 
> on an IPv6-only host [1].

I'm pretty sure "IPv6-only" means "the only non-loopback addresses this 
host has are IPv6", rather than "it doesn't have any IPv4, not even 
127.0.0.1."

This project uses AI_ADDRCONFIG: "IPv4 addresses are returned […] if the 
local system has at least one IPv4 address configured, […] The loopback 
address is not considered for this case as valid as a configured 
address."

Somewhat surprisingly, this means that getaddrinfo("127.0.0.1", ...) can 
fail even when the 127.0.0.1 address exists.

To reproduce this, unshare the network ("unshare -c -r --keep-caps" or 
"sudo unshare -n") and run:

$ ip link set lo up

$ ip link add dum0 type dummy

$ ip link set dum0 up

$ ip -br addr
lo               UNKNOWN        127.0.0.1/8 ::1/128
dum0             UNKNOWN        fe80::50aa:f3ff:fe1a:e828/64

$ python3 -c 'from socket import *; getaddrinfo("127.0.0.1", port=1, flags=AI_ADDRCONFIG)'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3.9/socket.py", line 954, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -9] Address family for hostname not supported

--
Jakub Wilk