jamulus-server: -6 makes server IPv6 only on FreeBSD

[yurivict]

Describe the bug

Description is from this downstream bug report:

Adding -6 to the jamulus_server_flags does enable IPv6, but drops the socket for IPv4.

I believe this is due to different defaults between Linux and (Free)BSD. The code opening the socket should specify the correct flag to get a socket that supports both IPv4 and IPv6.

To Reproduce

See subject.

Expected behavior

-6 should only enable IPv6 and not disable IPv4.

Operating system

FreeBSD 14.2

[softins]

Thank you for the report. There is some relevant information from an unrelated project here.

It would appear it is possible to configure a FreeBSD system to support IPv4-to-IPv6 address mapping in the same way as it works under Linux, Windows and macOS, but that on OpenBSD that possibility does not even exist, deliberately. At present, it is impossible to determine how many xxxxBSD Jamulus servers there are in public directories, because they will report their OS type as Linux. However, I suspect the number is very small. I don't believe any of the core developers uses a BSD variant.

It looks like the proper way to solve it portably would be to have separate sockets for IPv4 and IPv6 within the Jamulus application. That won't happen in the 3.x series of Jamulus releases, but we can consider it for Jamulus 4.0, for which significant enhancements to IPv6 support are planned. There is no timescale yet.

[ann0see]

Definitely not good. Can we at least add some documentation somewhere?

[ann0see]

Suggestion:

• Add (default disabled) compile time option to open two sockets
• Document that FreeBSD needs this to be set in COMPILING.md
• Enable IPv6 by default

[softins]

Suggestion:

• Add (default disabled) compile time option to open two sockets

As well as opening two sockets, the code that currently receives the incoming UDP via a single socket would need to be enhanced to do a poll() or select() on both sockets, and code that sends outbound messages would need to check via which socket it should send.

• Document that FreeBSD needs this to be set in COMPILING.md

If all the work to do the above had been done, it may as well be enabled for all architectures, as it would be upwards compatible.

• Enable IPv6 by default

In 4.0.0, I agree.