Packaged ical4j contains outdated timezones #113

We currently

• use ical4j 3.2.19, which contains outdated timezones, and

• synctools/lib/src/main/kotlin/at/bitfire/synctools/icalendar/validation/ICalPreprocessor.kt

  Lines 33 to 34 in d3f1c22

  	DatePropertyRule(), // These two rules also replace VTIMEZONEs of the iCalendar ...
  	DateListPropertyRule() // ... by the ical4j VTIMEZONE with the same TZID!

  .

This means that some events have wrong times if the timezone definition has been updated and the event contains the new timezone while the packaged ical4j version still has the old version.

On the other side, servers sometimes send invalid VTIMEZONEs while the TZID is correct. This is the reason why we replace the timezone definition.

We should re-think this, especially in the context of the upcoming update to ical4j 4.x.

Hi there,

I'm running baikal as my CalDAV, and I notice that when I create calendar events with specific timezones (using Merkuro Calendar or Thunderbird on desktop), when synced on my Android device via DAVx5, the event doesn't show up with timezones being respected. The event is synced at a different time... which is very bad for people who rely on this for remote meetings.

On Android, I tested with various apps: Etar Calendar, Fossify Calendar and Google Calendar. They all display at the wrong time.

In my test, I created a calendar event in UTC-03:00 for August 27 2025 @ 14:10.

On my Android device, in all three apps I tested, the event shows up at August 27 2025 @ 07:10. In Etar and Fossify I can't see what the timezone selected is, but in Google Calendar it shows as "Coordinated Universal Time" and I do see "14:10" as the original time selected. So not only does DAVx5 not sync the timezone, it's syncing the wrong timezone.

In my baikal sqlite DB, for the event I created, I do see:

BEGIN:VTIMEZONE
TZID:UTC-03:00
END:VTIMEZONE

So I believe it's likely DAVx5 not syncing correctly. But if anyone else has success with timezones syncing and can help me out, that would be greatly appreciated!

Originally posted by @englut in bitfireAT/davx5-ose#1678