only support IPv6 socket?

[lastpepole]

in aioquic/asyncio/client.py file, line 70

# explicitly enable IPv4/IPv6 dual stack
sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)         // **only support IPv6 socket ?**
completed = False
try:
    sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
    sock.bind((local_host, local_port, 0, 0))
    completed = True
finally:
    if not completed:
        sock.close()

[rthalley]

This is not v6-only. IPv6 can do both v4 and v6 on one socket via IPv4-mapped IPv6 addresses provided it's enabled. This code is explicitly enabling the IPv4 mapped addresses just in case the default has been set to off on a platform. Basically it's ensuring the IPv6-only option is off. If you look a bit above, you can see it constructing an IPv4 mapped address if needed:

if len(addr) == 2:
        addr = ("::ffff:" + addr[0], addr[1], 0, 0)

So, all is ok!

[catap]

@rthalley I'd like you to reconsider this issue. I'm porting it to OpenBSD and OpenBSD has different stack for IPv4 and IPv6.

So, current code is really IPv6 only on OpenBSD and on machine which has only IPv4 it fails as:

aioquic $ python3 examples/http3_client.py https://google.com/     
Traceback (most recent call last):
  File "/home/catap/src/aioquic/examples/http3_client.py", line 564, in <module>
    asyncio.run(
  File "/usr/local/lib/python3.11/asyncio/runners.py", line 190, in run
    return runner.run(main)
           ^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/asyncio/base_events.py", line 654, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "/home/catap/src/aioquic/examples/http3_client.py", line 387, in main
    async with connect(
  File "/usr/local/lib/python3.11/contextlib.py", line 210, in __aenter__
    return await anext(self.gen)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/aioquic/asyncio/client.py", line 73, in connect
    sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
OSError: [Errno 22] Invalid argument
aioquic $ 

A PR which fixes it: #516