Enable ipv6 client side support by default

[stevie2sheds]

Current behaviour and why should it be changed?

IPv6 client support currently has to be enabled at the command line using the -6 option. This requires the user either to edit the shortcuts/links or start the client from the command line. This varies in complexity depending on the OS, but it is a major barrier to IPv6 adoption when trying to support large groups having to make the required changes to client startup. Having IPv6 support enabled by default would remove this barrier.

Describe possible approaches
Another approach could be to enable IPv6 support using a checkbox within the UI. This would allow the user to elect to enable IPv6, and perhaps there is a very marginal resource saving in not starting a feature that may not be used.

Describe the solution you'd like
Enable ipv6 client side support by default with no additional checkbox in the UI. That solution means no action needs to be taken at the client side at all for IPv6.

Has this feature been discussed and generally agreed?

The topic has been discussed here: https://github.com/orgs/jamulussoftware/discussions/3291

[softins]

If we did make it a checkbox in Settings, it should also be stored in the ini file, to remember the setting.

In that case, rather than the complication of changing the open socket on the fly when the checkbox is toggled, it may well be sufficient to request a restart, like it does when the language setting is changed.

Would also need to make sure the ini file is loaded before the socket is created.

[stevie2sheds]

That sounds as if the checkbox option is of greater complexity than enabling by default and therefore the always on option is preferable.

[pljones]

I've tagged this as Release 4.0.0 as it'll probably get picked up alongside #3242.

[ann0see]

We'll need to keep #3478 in mind.

But I'd like to get default IPv6 support early in 4.0.0.

• Default enable IPv6 on client and server starting from 4.0.0.
• Disable IPv6 via CLI argument "-6 off" or similar and issue a warning message on the CLI.