[Kolab-devel] issue with custom timezones in invitations

[Christian Schwamborn]

Hello Aleksander,

recently I got an invitation with a custom timezone. Curious as I am, I
tested it on the roundcube calendar plugin (with the new caldav driver)
and got not quite the intended result.

The event was shown in the roundcube preview with
2024-10-22 9:30 - 10:00 (UTC)

Accepting the event it was entered as
2024-10-22 11:30 - 12:00 local time, my timezone is CEST (UTC+2)

which makes sense on first glance, but looking at the original ics there
is a somewhat unconventional but I think valid timezone definition:

(stripped out the superfluous stuff i.e. the X-MICROSOFT and the private
data)

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:Microsoft Exchange Server 2010
VERSION:2.0
BEGIN:VTIMEZONE
TZID:Customized Time Zone
BEGIN:STANDARD
DTSTART:16010101T030000
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=4SU;BYMONTH=10
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T020000
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
ORGANIZER...
ATTENDEE...
...
DESCRIPTION...
UID...
SUMMARY...
DTSTART;TZID=Customized Time Zone:20241022T093000
DTEND;TZID=Customized Time Zone:20241022T100000
CLASS:PUBLIC
PRIORITY:5
DTSTAMP:20241015T055003Z
TRANSP:OPAQUE
STATUS:CONFIRMED
SEQUENCE:2
LOCATION...
BEGIN:VALARM
DESCRIPTION:REMINDER
TRIGGER;RELATED=START:-PT15M
ACTION:DISPLAY
END:VALARM
...
END:VEVENT
END:VCALENDAR

I honestly don't know why that server just used a standard time zone
(cest in this case) and if that timezone definition is a general
Microsoft thing, or if its just the strange configuration on this host
(might be able to get a hold on the hosts admins).

The calendars interpretation as UTC is incorrect, it doesn't know what
exactly it is. Might be an easy solution just to say something like
'unknown timezone' and let the user guess and pick it, or it should be
handled somehow but not just falling back to UTC.


There where some other connected issues:

1. (I don't know if the client can influence this) even if you switch
off the sender notification, systems like the nextcloud will send
something to the organizer.

2. As the plugin offers the possibility to edit the event, I tried to
change the time (with the warning that it's just a local change and the
organizer would not be notified), but after the save the event was
reloaded and appeared with the old (wrong) time.
My guess: Nextcloud refuses to modify such events, usually that's the
behavior I would expect, as an invitation can either be accepted, accept
with reservation, or declined.

3. I finally deleted the invitation with switched off organizer
notification, but a decline was sent anyway (again: I don't know if the
client can influence this, if the caldav server handles the notifications)

Is there some configuration how to handle invitations and notifications?

Best regards
Christian