software-properties-gtk does not recognize https mirrors under Ubuntu Software

[Alex N.]

How to reproduce:

1. Change main Ubuntu mirrors to https in /etc/apt/sources.list and do "apt update"
2. Run software-properties-gtk
3. Go to "Ubuntu Software" tab

What happens:

The tab "Ubuntu Software" does not list https mirrors. The corresponding boxes are not checked, the correct "Download from" entry is not selected and falls back to "Main server". The correct sources are just listed under "Other Software".

What should happen:

The tab "Ubuntu Software" should recognize the https mirrors from apt and tick the corresponding boxes and select the correct server in the "Download from" list.

Ubuntu 18.04
software-properties-gtk 0.96.24.32.7

[Alex N. (a-nox)]

Ubuntu software tab

[Alex N. (a-nox)]

Other Software tab

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Bryan Quigley (bryanquigley)]

it also does not recognize lines like this:
deb mirror+https://bryanquigley.com/mirrors.txt disco main restricted universe multiverse

[Bryan Quigley (bryanquigley)]

Main source is https://code.launchpad.net/software-properties (I thought upstream was Debian due to versioning)

[Julian Andres Klode (juliank)]

The mirror list is shipped in python-apt and updated with each python-apt update, and with each Ubuntu point release based on the launchpad mirror feed https://launchpad.net/ubuntu/+archivemirrors-rss.

Additional updates to just the mirror list are not made.

The mirror method is supported using the official mirror://mirrors.ubuntu.com/mirrors.txt url. Additional urls are custom modifications and not recognized by aptsources as Ubuntu mirrors.

It might be possible to make aptsources look at Origin field in the Release file if you have downloaded them, however that's prone to breakage if you switch releases, so it's not optimal. In any case this is not a bug in software-properties. Please open a bug against python-apt if you believe we have reasonable means of supporting unofficial mirrors like official ones.