This is the same inconsistent behaviour as I’ve found in which DAVdroid handles contacts and calendars. It’s quite confusing that for calendars, it’s enough to have share permissions to view/modify the calendar in order for it to show up in your available calendars, but for contacts you must “subscribe” for the shared address book to be available to the user.
Maybe it’s because there is are (proposed, but often used) standard for detecting shared calendars using calendar-proxy-read/write (which is used by DAVdroid), but there’s no such standard for address books. If this is the method how your shared calendars are detected, shared addressbooks can’t be detected the same way.
Technical details would be really helpful for deeper insights.
I wouldn’t consider the command (REPORT addressbook-query) “special”. In fact, its the only CardDAV command used. PROPFIND, which was used by previous DAVdroid versions, is only WebDAV and has several problems (for instance, it lists non-addressbook member collections, too).
I see only PROPFIND in my older Sogo logs when it’s about address books. For calendars REPORT is normal. I’ve searched the logfiles with grep.
The bug is now repaired in Sogo when I am right. Maybe you could use the command again in 2 years, with a warning in the readme.
Then you do not have much experience with this kind of problems, I guess.
We just can’t adapt any line of DAVdroid to all potential server bugs and issues for years, especially if they have already been fixed. Please note that we even have workarounds for the REPORT query, but the nature of the SOGo bug makes it impossible to use them here.
I think I must learn from this, and not use programs like Davdroid anymore in combination with F-droid. I want a stable tested platform with security bug-fixes, and no big changes without good testing.
Realize that open source software is a mess, because many developers and organizations are all the time changing their products without much coordination. In Linux you have distro’s what do testing before releasing a new stable version. And I can test it myself, before upgrading. But with F-droid, there is nothing. An app-maker can make a mess of the phone of many people who simple want to do their work.
Maybe you could make a LTS-version when DavDroid 1.0 releases, with only security updates.