IPv6 support

[deavmi]

Heya!

Firstly, great work. You have given this here 25 year old a lot of fun things to play around with this year-end and I am only getting started.

I, being an IPv6 MAXI, noticed problems trying to get the TCPServerInterface to bind to [::] or ::. Getting address family errors, which gives me the idea that perhaps some AF_INET hardcoding is present? Or am I doing it wrong?

[deavmi]

Would also be really great if IPv6 worked in such a case because not only can I make it available to all of the IPv6 world on the clearnet but also to Yggdrasil users

[deavmi]

I also did look at the source code, and found myself at ThreadingTCPServer which is sub-typed of some class from some library. I suppose that therein is the problem - and it is not binding to such an address.

It seems that address_family is a member of BaseServer, and Python now treats AF_INET and all those as constants. I presume hinting at the fact they are all multiples or 2 and hence maybe suplying AF_INET|AFINET6 will get it to accept those two address faimiles.

[deavmi]

One other thing I recall from testing last night, this also is affected by outbound code, i.e. code which connect()'s. I think that is two-part. DNS resolution code should prefer AF_INET6 entries, and if none are found then AF_INET.

I think that may be possible with:

self.socket = socket.socket(socket.AF_INET|socket.AF_INET6, socket.SOCK_STREAM)

This solves connecting to raw IPv6 addresses at least. But, I do recall having problems with a domain name that had AAAA record but your code would not play nice with it.

(I am not a Python dev and don't have a proper test environment rn)