RFR: JDK-8313804: JDWP support for -Djava.net.preferIPv6Addresses=system [v3]

[Liam Miller-Cushon]

On Tue, 19 Sep 2023 00:03:27 GMT, Liam Miller-Cushon <cushon at openjdk.org> wrote:

>> Please consider this fix for [JDK-8313804](https://bugs.openjdk.org/browse/JDK-8313804), which adds support to JDWP for `-Djava.net.preferIPv6Addresses=system`. Previously it only handled `-Djava.net.preferIPv6Addresses=true` and `-Djava.net.preferIPv6Addresses=false`.
>
> Liam Miller-Cushon has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Review feedback

The order of the `addInfo`s is determined by `getaddrinfo()`, which is supposed to sort the results according to [RFC 6724](https://datatracker.ietf.org/doc/html/rfc6724). `system` is supposed to [preserve that order](https://docs.oracle.com/en/java/javase/20/docs/api/java.base/java/net/doc-files/net-properties.html) instead of re-ordering them.

There's some related discussion in  [JDK-8170568](https://bugs.openjdk.org/browse/JDK-8170568) about use-cases that IPv4-first and IPv6-first don't support. The bug details some edge cases that still aren't well supported, but in the cases I've seen `-Djava.net.preferIPv6Addresses=system` is usually fine, aside from this issue with JDWP ignoring that setting.

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PR Comment: https://git.openjdk.org/jdk/pull/15796#issuecomment-1724866175