Get rid of aiodns gethostbyname()

[weastur]

What do these changes do?

By default aiodns function gethostbyname() (which is actually just a wrapper around c-ares function) resolve host as IPv6 address if socket family set to AF_UNSPEC(default value for TCPConnector). On the other hand ThreadedResolver use asyncio loop function getaddrinfo() which, in accordance with POSIX return both(either IPv4 and IPv6) if socket family set to AF_UNSPEC. So we have unconsistent behavior of ThreadedResolver and AsyncResolver. But c-ares lib doesn't have getaddrinfo() function, so we can't use it in aiohttp resolver. So if I use IPv4 the following simple code does not work for me(if aiodns installed of cause):

 async with aiohttp.ClientSession() as session:
        async with session.get('http://google.com') as resp:
            body = await resp.read()
            print('Done(google.com). status: {}, body len: {}'.format(resp.status, len(body)))

To solve this problem in method resolve() of AsyncResolver I query both types if family set to AF_UNSPEC.

Are there changes in behavior for the user?

No

Related issue number

#559

Checklist

• [ X] I think the code is well written
• [ X] Unit tests for the changes exist
• [ X] Documentation reflects the changes
• [ X] Add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• [ X] Add a new entry to CHANGES.rst
  • Choose any open position to avoid merge conflicts with other PRs.
  • Add a link to the issue you are fixing (if any) using #issue_number format at the end of changelog message. Use Pull Request number if there are no issues for PR or PR covers the issue only partially.

[asvetlov]

No. Until the issue will be fixed by upstream we just should revert back default to use thread pool based solution.

[weastur]

Ok. But what if I want to use aiodns? I think the behavior should be the same as a thread pool. We can set thread pool as default and fix async resolver too. It does not look like they wanted to add getaddrinfo() into c-ares. c-ares/c-ares#70

[asvetlov]

Looks like they are looking for volunteer.
If you want to work via aiodns -- connect it explicitly and use on your own.

[lock]

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