[Bug]: Apps outlive installations

[eeejay]

Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a bug that matches the one I want to file, without success.
• If this is an issue with a particular app, I have tried filing it in the appropriate issue tracker for the app (e.g. under https://github.com/flathub/) and determined that it is an issue with Flatpak itself.
• This issue is not a report of a security vulnerability (see here if you need to report a security issue).

Flatpak version

1.15.6

What Linux distribution are you using?

Fedora Linux

Linux distribution version

39

What architecture are you using?

x86_64

How to reproduce

1. Spawn a D-Bus service exported by a flatpak
2. Uninstall the flatpak

Expected Behavior

Service should be shut down.

Actual Behavior

Service is still running

Additional Information

This happens with apps too, but is more acute with services since the user does not have visibility into the fact that a stale service is still running. This introduces also safety concerns since the user believes that they removed a malicious flatpak only to still have it running in the background.

There is also the problem that a user might upgrade a flatpak with an exported service, but the older one is still running until the user exits the session.

I propose that services either be forcibly killed, or that they expose a special interface with a Shutdown() method in order to do any cleanup. This method should make the service quit in-line so the method will ultimately "fail".

The first solution is good for legacy apps, the second solution could be opted in to if needed.