Environment Information

• JRuby 9.4.7.0 (jruby 9.4.7.0 (3.1.4) 2024-04-29 597ff08 OpenJDK 64-Bit Server VM 25.412-b08 on 1.8.0_412-b08 +jit [arm64-darwin])
• macOS 14.4.1

I've observed the same behavior on Ubuntu 22.04.4 with the same version of JRuby.

Expected Behavior

IPv6 addresses can mix the formatting of IPv6 and IPv4 in one address (e.g. ::ffff:192.0.2.128), as defined in RFC4291:

An alternative form that is sometimes more convenient when dealing
with a mixed environment of IPv4 and IPv6 nodes is
x:x:x:x:x:x:d.d.d.d, where the 'x's are the hexadecimal values of
the six high-order 16-bit pieces of the address, and the 'd's are
the decimal values of the four low-order 8-bit pieces of the
address (standard IPv4 representation). Examples:

0:0:0:0:0:0:13.1.68.3

0:0:0:0:0:FFFF:129.144.52.38

or in compressed form:

::13.1.68.3

::FFFF:129.144.52.38

MRI 3.1.5 correctly parses these types of IPv6 addresses:

$ ruby -v
ruby 3.1.5p252 (2024-04-23 revision 1945f8dc0e) [arm64-darwin23]
$ irb -r socket
irb(main):001:0> IPSocket.getaddress('::ffff:192.0.2.128')
=> "::ffff:192.0.2.128"

Actual Behavior

JRuby 9.4.7.0 incorrectly parses the same address as an IPv4 address:

$ ruby -v
jruby 9.4.7.0 (3.1.4) 2024-04-29 597ff08ac1 OpenJDK 64-Bit Server VM 25.412-b08 on 1.8.0_412-b08 +jit [arm64-darwin]
$ irb -r socket
irb(main):001:0> IPSocket.getaddress('::ffff:192.0.2.128')
=> "192.0.2.128"

Note that when JRuby drops the hex characters and :: syntax at the start of the address.

This can have knock-on effects for things like Addrinfo:

irb(main):002:0> Addrinfo.new(['AF_INET6', 0, nil, '::ffff:192.0.2.128'], :INET6)
org/jruby/ext/socket/Addrinfo.java:139:in `initialize': getaddrinfo: Address family for hostname not supported (SocketError)