Setting mpd/hostname to a DNS address breaks IPV4 if hostname is IPV6 enabled.

[adamcik]

Currently we create a socket using socket.socket(socket.AF_INET6, socket.SOCK_STREAM) and then calling bind. However, if the address given to bind is not an address it gets automatically resolved at which point we have no control over if the IPV4 or IPV6 address is actually used.

Correct way to handle this is to use socket.getaddrinfo(addr, None, socket.AF_UNSPEC, socket.SOCK_STREAM, 0, socket.AI_PASSIVE) and create a socket for each of the addresses we found.

[jodal]

This sounds like exactly how Tornado does this. Maybe we should just use their method?

http://www.tornadoweb.org/en/stable/netutil.html#tornado.netutil.bind_sockets

If we go that path, I also suggest to make an empty mpd/hostname and http/hostname config equal to ::: e.g. bind to all interfaces.

[adamcik]

Correct, that is exactly how they do it, with some details left out for brevity. And yes I did consider just using their code for this.