From: "datibbaw (Tjerk Meesters) via ruby-core" <ruby-core@...>
Date: 2026-11-13T08:03:10+00:00
Subject: [ruby-core:127460] [Ruby Bug#22538] require 'socket' raises NameError for builds with --disable-ipv6, and IPv6 addresses leak from the resolver

Issue #22538 has been updated by datibbaw (Tjerk Meesters).


nobu (Nobuyoshi Nakada) wrote in #note-1:
> Applied in changeset commit:git|c99813a8d8484058987c968923cd814e99aa6dd3.
> 
> ----------
> [Bug #22538] Fix failures when IPv6 is disabled

Thanks for that, but that only fixes a small part of the issue; the rest involves the Happy Eyeballs implementation that causes hangs and otherwise undesirable behaviour ... in fact, the test suite doesn't pass with `--disable-ipv6` on a system that _does_ support it.

I've drafted my proposed change here: https://github.com/ruby/ruby/compare/master...datibbaw:ruby:disable-ipv6-consistency

----------------------------------------
Bug #22538: require 'socket' raises NameError for builds with --disable-ipv6, and IPv6 addresses leak from the resolver
https://bugs.ruby-lang.org/issues/22538#change-119921

* Author: datibbaw (Tjerk Meesters)
* Status: Closed
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
On a Ruby built with `./configure --disable-ipv6`, `require 'socket'` fails:

```
$ ruby -rsocket -e0
.../socket.rb:622:in '<class:Socket>': uninitialized constant Socket::AF_INET6 (NameError)
	from .../socket.rb:478:in '<top (required)>'
```

Reproduced with:

* ruby 3.4.10 (2026-06-30 revision 2b0b7728dc) +PRISM [arm64-darwin25]
* ruby 4.1.0dev (2026-11-12T01:39:13Z master 0738c9dfaa) +PRISM [arm64-darwin25]

## Cause

With `--disable-ipv6`, `INET6` is not defined, so `mkconstants.rb` omits
`AF_INET6`, `PF_INET6` and `IPV6_*`. Since Happy Eyeballs v2 was added to
`Socket.tcp` (Ruby 3.4), `socket.rb` defines a class-level constant that
references `Socket::AF_INET6` without a `defined?` check:

```ruby
ADDRESS_FAMILIES = {
  ipv6: Socket::AF_INET6,
  ipv4: Socket::AF_INET
}.freeze
```

## Further problems once the require is fixed

`--disable-ipv6` only removes the Ruby-level IPv6 constants. The system
resolver still returns IPv6 addresses (with `AF_UNSPEC` hints), and
`getifaddrs` still reports IPv6 interface addresses. Code that skips IPv6
handling with `defined?(Socket::AF_INET6)` then gets IPv6 sockets anyway:

* `Socket.tcp_server_sockets(0)` never returns. `getaddrinfo(nil, 0, ..., AI_PASSIVE)`
  returns `::` and `0.0.0.0`; `ipv6only!` is a no-op because
  `Socket::IPV6_V6ONLY` is not defined, so the `[::]:P` socket is
  dual-stack, binding `0.0.0.0:P` fails with `EADDRINUSE`, and
  `ip_sockets_port0` retries forever. This also hangs
  `TestSocket#test_accept_loop_with_unix`.
* `Socket.tcp(host, port, nil, 0)` (local port only) resolves `::1` and
  `127.0.0.1` locally; `ADDRESS_FAMILIES.key(AF_INET6)` is `nil`, so the
  resolver thread runs with a `nil` family.
* `Addrinfo#connect_address` does not turn `[::]` into `[::1]` (that branch
  is guarded by `defined?(Socket::AF_INET6)`), and connecting to it fails
  with `ENOBUFS` on macOS.
* `Socket.ip_address_list` and `Socket.udp_server_sockets` return IPv6
  addresses.
* `TCPSocket.new` (C Happy Eyeballs) starts an IPv6 resolver thread and then
  discards its results.

## Proposed fix

Make `--disable-ipv6` consistently IPv4-only:

* `socket.rb`: only add `:ipv6` to `ADDRESS_FAMILIES` when `Socket::AF_INET6`
  is defined.
* `raddrinfo.c` (`rsock_getaddrinfo`, which every Ruby-level lookup goes
  through): when `INET6` is not defined, change `PF_UNSPEC` hints to `PF_INET`
  and reject `PF_INET6` with `EAI_FAMILY`.
* `ipsocket.c`: resolve only IPv4 in the `TCPSocket.new` fast fallback path.
* `socket.c`: skip `AF_INET6` in the getifaddrs and ioctl implementations of
  `Socket.ip_address_list`. The Windows implementation already does this.
* Tests: skip tests that need IPv6 (`::1` servers, IPv6 addresses); make
  stubbed `Socket.tcp` and `TCPSocket.new` tests work when `Socket::AF_INET6`
  is undefined.

User-visible change, only in `--disable-ipv6` builds: IPv6 literals such as
`Addrinfo.ip("::1")` or `TCPSocket.new("::1", port)` raise
`Socket::ResolutionError` instead of partly working.

I will open a pull request.

## Note on backporting to 3.4

On 3.4, fixing `ADDRESS_FAMILIES` alone is not enough. With only one family
to resolve, `Socket.tcp_with_fast_fallback` passes the Symbol `:ipv4` to
`Addrinfo.getaddrinfo`, which raises `unknown socket domain: ipv4`
(#21512). A 3.4 backport also needs both fixes for that issue:
b896f80598 and its follow-up f33766720c. The first commit alone passes
`ADDRESS_FAMILIES[:family_name]`, i.e. `nil`, so it silently resolves all
families.



-- 
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