TCP connection fails on systems without IPv6 support when connecting to a host that has an IPv6 address

[lilydjwg]

getaddrinfo will return IPv6 addresses when the system doesn't support it, and Tornado will then fail to connect to the IPv6 address with this error (I get a report for my project here):

OSError: [Errno 97] Address family not supported by protocol

I see in #593 AI_ADDRCONFIG was removed from bind_sockets, and in #823 Tornado just ignores the unsupported protocol. But this is about connect, not bind. What do you think, to use AI_ADDRCONFIG or just ignore the error? There's currently no way to pass the flags to resolvers though.

[bdarnell]

It sounds like the resolver is configured incorrectly if it is returning ipv6 addresses on a machine that doesn't support it. But if someone gets themselves into that state, I guess we should catch and ignore the error in TCPClient as in #823.

Even though AI_ADDRCONFIG makes more sense for connect() than for bind(), the arguments against it in #593 still mostly apply, so I don't think we should introduce a way to pass it to the resolvers for client-side use.

[lilydjwg]

I've created pr #1821 to fix this.

PS: I've found no way for glibc to not query for AAAA when IPv6 is disabled.

[bdarnell]

FYI you could also do AsyncHTTPClient.configure(None, defaults=dict(allow_ipv6=False))

[lilydjwg]

@bdarnell no, I won't do that. It's those users who has disabled IPv6 should do that :-)