[ruby-core:99851] [Ruby master Feature#15628] init_inetsock_internal should fallback to IPv4 if IPv6 is unreachable

[deivid.rodriguez@riseup.net]

Issue #15628 has been updated by deivid (David Rodríguez).


Hi!

Any feedback about this? We're considering implementing "Happy Eyeballs" in rubygems by monkeypatching `TCPSocket.new`, in order to fix longstanding issues with `gem install` timing out on ipv6-capable clients. But it would feel much better if this was built in.

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Feature #15628: init_inetsock_internal should fallback to IPv4 if IPv6 is unreachable
https://bugs.ruby-lang.org/issues/15628#change-87378

* Author: sonalkr132 (Aditya Prakash)
* Status: Open
* Priority: Normal
----------------------------------------
Hi,

This is not really bug but more of a missing feature. Let me layout steps to reproduce what I am trying to achieve:
* Add local entries for `example.com` 

```
$ echo "::1     example.com www.example.com
127.0.0.1 example.com www.example.com" | sudo tee  --append /etc/hosts
```
* Add rule to `DROP` ipv6 packets: `sudo ip6tables -P INPUT DROP`
* Start a server: `ruby -rwebrick -e 'WEBrick::HTTPServer.new(Port: 8000).start'`
* Making request using Net:HTTP with timeout (`Net::OpenTimeout`) after after 60 seconds: `ruby -rnet/http -e "Net::HTTP.get(URI('http://example.com:8000'))"`


As far as I understand, [init_inetsock_internal](https://github.com/ruby/ruby/blob/4444025d16ae1a586eee6a0ac9bdd09e33833f3c/ext/socket/ipsocket.c#L42) needs to fallback to ipv4 for Net::HTTP.get to work. IPv6 route being broke is expected and hence, [RFC8305](https://tools.ietf.org/html/rfc8305) recommends fallback to IPv4.
Support for IPv6 fallback is spotty across languages and http clients, for example, [golang supports it](https://github.com/golang/go/blob/master/src/net/dial.go#L47) but python doesn't, making request with `curl` works but `wget` hangs.



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