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serve_tcp() fails out-of-the-box on systems with disabled IPv6 #853

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oremanj opened this issue Jan 11, 2019 · 1 comment
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serve_tcp() fails out-of-the-box on systems with disabled IPv6 #853

oremanj opened this issue Jan 11, 2019 · 1 comment

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@oremanj
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oremanj commented Jan 11, 2019

I recently had occasion to run a Trio server on a Linux system that had ipv6.disable=1 in the kernel command line. I don't know why it was configured this way, but some Googling suggests that this is not such a very uncommon configuration. In this configuration, getaddrinfo(None, ...) still returns an IPv6 option, but socket(AF_INET6, ...) fails with [Errno 97] Address family not supported by protocol. This also affects several tests in trio's test suite.

I can work around this by explicitly serving on "0.0.0.0", but it feels like a rough edge. As an alternative, maybe trio could suppress EAFNOSUPPORT errors from IPv6 socket creation in open_tcp_listeners if the IPv4 socket was created OK. Thoughts?
@njsmith
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njsmith commented Jan 11, 2019

Oh yeah, we should do that.

There are also increasing numbers of systems out there with only ipv6, no ipv4, so we should handle that too.

oremanj added a commit to oremanj/trio that referenced this issue Jan 14, 2019
@oremanj
Improve support for systems with IPv4 or IPv6 administratively disabled
7f3304c 
Closes python-trio#853.

- Some such systems return both address families from `getaddrinfo` but fail with `EAFNOSUPPORT` in `socket`. Allow `open_tcp_listeners()` to ignore `EAFNOSUPPORT` as long as at least one listener is created successfully.
- Fix socket tests to be more careful about not even trying to create an IPv6 socket on systems that don't support IPv6.
@oremanj oremanj mentioned this issue Jan 14, 2019
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@njsmith @oremanj