resolving hostnames for bind

[wanneut]

gunicorn takes a list of hostnames, checks for everyone if it is a IPv6 address and if it is not, it binds to the IPv4 address of the hostname.
The relevant parts are:

gunicorn/gunicorn/config.py

Line 125 in d1f5268

return [util.parse_address(_compat.bytes_to_str(bind)) for bind in s]

gunicorn/gunicorn/sock.py

Line 132 in d1f5268

if util.is_ipv6(addr[0]):

gunicorn/gunicorn/util.py

Line 227 in d1f5268

socket.inet_pton(socket.AF_INET6, addr)

This makes two wrong assumptions:

• Every hostname has exact one IP-address.
• A hostname can not resolve to an IPv6 address.

Even for the most common example localhost this assumptions are not true:
localhost resolves on the most systems to ::1 and 127.0.0.1. But gunicorn binds only to 127.0.0.1 (the first IPv4 address)
If a standards-compliant software tries to connect to gunicorn on localhost it will at first try to connect to ::1 and only after that times out to 127.0.0.1.
So most of my clients disable IPv6 to make gunicorn react faster…

A much better approach would be to loop over all results of getaddrinfo and just bind to whatever family it returns:
https://docs.python.org/2.5/lib/socket-example.html

[tilgovi]

Thank you for reporting this issue! If you would like to make a PR, I'd be happy to review it with you.

[tilgovi]

It seems like we might have to change that first comprehension to complex comprehension and have parse_address yield one or multiple addresses. I am open to other approaches, but that seems the least invasive.

[wanneut]

Tried to make a nicer approach to handle different family types there https://github.com/wanneut/gunicorn
But there is still a little work to do. (Some former tests fail, because they are still using is_ipv6... And I still don't understand how you close sockets.)
I am not that fit in python programming. Can you have a look?

[tilgovi]

@wanneut I took a look and left some style comments, but I like your approach! I won't be able to look at tests until later today, but this is great. Thank you. You should be able to close sockets with .close().

[tilgovi]

We also have a helper in gunicorn.util to close a socket and catch any error when you don't care about errors.

[wanneut]

I start adopting the tests.

[gozdal]

I've stumbled upon exact this problem and see that the old PR was abandoned. I've created a minimal change which allows gunicorn to listen on IPv6 addresses specified as hostnames. Unfortunately the GitHub check on AppVeyor seems to be broken currently. Not sure how I could proceed with this #2689, @tilgovi maybe you can advise?

[gozdal]

I've run the tests locally and they seem to pass (apart from pylint, although it's not something broken by this PR)