localhost proxy resolved to IPv6 (in version 2.3.1)

[CheViana]

Long story short

I'm using aiohttp to make calls via proxy "http://localhost:9999". "etc/hosts" maps localhost to IPv4 and IPv6 addresses.
aiohttp version 2.2.5 resolves that proxy value to "127.0.0.1:9999", aiohttp version 2.3.1 - to value "::1:9999".
I can't pinpoint changes in 2.3.1 that caused this behavior.
I found a workaround, but I think IPv4 should be used by default in this case.

Expected behavior

Proxy "http://localhost:9999" got resolved to "127.0.0.1:9999" (IPv4 is default).

Actual behavior

Proxy "http://localhost:9999" got resolved to "::1:9999" (IPv6 is used for some reason).

Steps to reproduce

    async with aiohttp.ClientSession() as session:
            async with session.get(
                'https://github.com/aio-libs/aiohttp',
                proxy='http://localhost:9999'
            ) as response:
                response.raise_for_status()
                result = await response.read()
                return result

As far as I nailed it, line 785 in connector.py does host resolution:
hosts = yield from self._resolve_host(req.url.raw_host, req.port)

In version 2.2.5 hosts[0] equals:

{'hostname': 'localhost',
 'host': '127.0.0.1',
 'port': 9999,
 'family': <AddressFamily.AF_INET: 2>,
 'proto': 6,
 'flags': <AddressInfo.AI_NUMERICHOST: 4>}

In version 2.3.1 hosts[0] equals:

{'family': <AddressFamily.AF_INET6: 10>,
 'flags': <AddressInfo.AI_NUMERICHOST: 4>,
 'host': '::1',
 'hostname': 'localhost',
 'port': 9999,
 'proto': 6}

(aiodns is not used)

I've tried to call directly socket.getaddrinfo (AFAIK that is the function that does resolution under the hood):

>>> import socket
>>> socket.getaddrinfo('localhost', 9999, type=socket.SOCK_STREAM, family=socket.AF_INET)
[(<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('127.0.0.1', 4140)), (<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('127.0.0.1', 4140))]
>>> socket.getaddrinfo('localhost', 9999, type=socket.SOCK_STREAM, family=socket.AF_INET6)
[(<AddressFamily.AF_INET6: 10>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('::1', 4140, 0, 0))]

family parameter is the trick, but I'm not modifying it in request code and I don't see where in aiohttp code it's value changed...

Your environment

Linux. Python 3.6.
Contents of /etc/hosts:

127.0.0.1 localhost ...
::1 localhost ...

(aiodns is not used)

Workaround

Specify socket family explicitly:

    connector = aiohttp.TCPConnector(family=socket.AF_INET)
    async with aiohttp.ClientSession(connector=connector) as session:
            async with session.get(
                'https://github.com/aio-libs/aiohttp',
                proxy='http://localhost:9999'
            ) as response:
                response.raise_for_status()
                result = await response.read()
                return result

[asvetlov]

I pretty sure aiohttp has no changes for it.
What is hosts list content? Not only hosts[0] but the whole list?

[johnlockwood-wf]

I hit this issue too

[asvetlov]

The issue should be fixed by #2424
aiohttp will connect to all resolved IPs: IPv4 and IPv6 should be processed in parallel.

[asvetlov]

Fixed by #2447

[johnlockwood-wf]

That did indeed fix it for me. Thanks!

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a [new issue] for related bugs.
If you feel like there's important points made in this discussion, please include those exceprts into that [new issue].
[new issue]: https://github.com/aio-libs/aiohttp/issues/new