"[Dom0] Choose Preferred Application" improvement

[RefinedSoftwareLLC]

If this change is not desired, please refer to "General notes".

Qubes OS version:

R4.0

Affected component(s):

dom0

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Steps to reproduce the behavior:

Right click the taskbar audio widget.
Select "About".
Left click "Website".
"[Dom0] Choose Preferred Application" displays.
Dropdown "No application selected" only has "Other..." option which drops you into a select file popup.
Unable to even see the link it is trying to open in a browser.

Expected behavior:

• In "[Dom0] Choose Preferred Application" popup, it needs to have the same list as the file manager's "Open with another Application..." list which include Applications from other VMs, especially DispVMs.
• For security, future openings of that file extension should ALWAYS ask for permission (like websites do, when a link will take you somewhere outside their website). This includes file extension defaults set by "Open with another Application...".

Copying this file/link to this Qube then this application opening it,
can leak information like passwords or ways to identify you.
This is not recommended, are you sure you want to continue?
<filename/sterilized-url>
<vm-name>
<application-name>
[Cancel]    [Open with another Application...]    [Continue]

• For security, the file needs to be read only and never bring back any changes into dom0.
• Should this copy the file with qvm-copy-to-vm <dest-vm> <file> then open it up in the other VM?
• Sterilize urls, removing any non-web characters, invisible Unicode characters, only allowing select prefixes like http/https, and disallowing any port numbers.

Actual behavior:

In "[Dom0] Choose Preferred Application" popup,
Dropdown "No application selected" only has "Other..." option which drops you into a select file popup.
Unable to even see the link it is trying to open in a browser.

General notes:

If this change is not desired because opening dom0 files in another VM is a security risk, then shouldn't "Open with another Application..." not even display Applications from another VM?
Currently, when I select an Application from another VM, it doesn't open the file. Shouldn't dom0 at least display a notification, instead of silently failing? In this case, clicking a website link in the about page of a widget should default to opening a text editor with the website link in a new file.

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Related issues: