[Bug 282251] java/openjdk22: IPv6 / INET6 is broken

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=282251

--- Comment #3 from antonfb@hesiod.org ---
I stand by my comment.

I put your code into a class with imports etc.

This is java22
seine.hesiod.org:anton[1]: java -version
openjdk version "22.0.2" 2024-07-16
OpenJDK Runtime Environment (build 22.0.2+9-1)
OpenJDK 64-Bit Server VM (build 22.0.2+9-1, mixed mode, sharing)


First run (without preferipv4stack=false):
seine.hesiod.org:anton[11]: java bugtest
Connected Socket[addr=seine.hesiod.org/192.168.2.3,port=46994,localport=21181]
to Socket[addr=/192.168.2.3,port=21181,localport=46994]
Connected Socket[addr=/127.0.0.1,port=57640,localport=10314] to
Socket[addr=/127.0.0.1,port=10314,localport=57640]
Failed to connect to localhost with INET6
java.net.SocketException: Protocol family unavailable
        at java.base/sun.nio.ch.Net.bind0(Native Method)
        at java.base/sun.nio.ch.Net.bind(Net.java:565)
        at java.base/sun.nio.ch.Net.bind(Net.java:554)
        at java.base/sun.nio.ch.NioSocketImpl.bind(NioSocketImpl.java:636)
        at java.base/java.net.ServerSocket.bind(ServerSocket.java:390)
        at java.base/java.net.ServerSocket.<init>(ServerSocket.java:277)
        at bugtest.main(bugtest.java:47)

Second run (with java flag):
seine.hesiod.org:anton[12]: java -Djava.net.preferIPv4Stack=false bugtest
Failed to connect to localhost with unspecified protocol
java.net.SocketException: Invalid argument
        at java.base/sun.nio.ch.Net.connect0(Native Method)
        at java.base/sun.nio.ch.Net.connect(Net.java:589)
        at java.base/sun.nio.ch.Net.connect(Net.java:578)
        at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:583)
        at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:327)
        at java.base/java.net.Socket.connect(Socket.java:752)
        at java.base/java.net.Socket.connect(Socket.java:687)
        at java.base/java.net.Socket.<init>(Socket.java:556)
        at java.base/java.net.Socket.<init>(Socket.java:357)
        at bugtest.main(bugtest.java:14)
Failed to connect to localhost with INET
java.net.BindException: Can't assign requested address
        at java.base/sun.nio.ch.Net.bind0(Native Method)
        at java.base/sun.nio.ch.Net.bind(Net.java:565)
        at java.base/sun.nio.ch.Net.bind(Net.java:554)
        at java.base/sun.nio.ch.NioSocketImpl.bind(NioSocketImpl.java:636)
        at java.base/java.net.ServerSocket.bind(ServerSocket.java:390)
        at java.base/java.net.ServerSocket.<init>(ServerSocket.java:277)
        at bugtest.main(bugtest.java:30)
Failed to connect to localhost with INET6
java.net.SocketException: Invalid argument
        at java.base/sun.nio.ch.Net.connect0(Native Method)
        at java.base/sun.nio.ch.Net.connect(Net.java:589)
        at java.base/sun.nio.ch.Net.connect(Net.java:578)
        at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:583)
        at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:327)
        at java.base/java.net.Socket.connect(Socket.java:752)
        at java.base/java.net.Socket.connect(Socket.java:687)
        at java.base/java.net.Socket.<init>(Socket.java:556)
        at java.base/java.net.Socket.<init>(Socket.java:357)
        at bugtest.main(bugtest.java:48)

Third run (with flag & sysctl net.inet6.ip6.v6only=0)
seine.hesiod.org:anton[13]: java -Djava.net.preferIPv4Stack=false bugtest
Connected Socket[addr=seine.hesiod.org/192.168.2.3,port=46531,localport=13926]
to Socket[addr=/192.168.2.3,port=13926,localport=46531]
Connected Socket[addr=/127.0.0.1,port=63268,localport=33512] to
Socket[addr=/127.0.0.1,port=33512,localport=63268]
Connected Socket[addr=seine.hesiod.org/192.168.2.3,port=53154,localport=63501]
to Socket[addr=/192.168.2.3,port=63501,localport=53154]

So as I wrote five years ago the jdk was intentionally broken WRT ipv6.
To make it work, you must pass the -Djava.net.preferIPv4Stack=false to your
java vm AND change the global sysctl net.inet6.ip6.v6only=0

If you want to unbreak this I'm not certain what to do. I would like to see
this fixed and ipv6 cleanly supported without having to set the system wide
level setting. I don't think the code fix is the problem. The problem will be
that the maintainers do not want this fixed.

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