Events with RRULE get imported into the incorrect day with different timezones (enough for the day to differ from the inviter's TZ)

[shtrom]

(This discussion was initiated as nextcloud/calendar#6459, but I am now wondering if this is instead an issue with DavX5; this post is to help determine where the root cause is).

When receiving an invitation with an RRULE from GCalendar in UTC-0400 when my Nextloud instance is in UTC+1000. When importing the ICS into Nexctloud, and getting it back out with vdirsyncer, I can see that the timezone in the ICS file has been updated to my local TZ, but the RRULE hasn't been updated accordingly, even if the event would be the next day for me.

Recurring events get created, and shown at the correct (TZ-adjusted) time, BUT the days of the week are those in the original timezone (i.e., day before).

More details on the workflow:

1. I get the invites by email, which I open on my mobile with K9 Mail (an attached invite.ics)
2. I import it into my local calendar with the stock Android (14) app
3. It gets synced via DavX5 to Nextcloud (where it's already showing wrong)
4. I then fetch it using vdirsyncer on my laptop, and can see the mismatched data.

Here's an example:

1. invite.ics attached to the email

BEGIN:VCALENDAR
PRODID:-//Google Inc//Google Calendar 70.9054//EN
VERSION:2.0
CALSCALE:GREGORIAN
METHOD:REQUEST
BEGIN:VTIMEZONE
TZID:America/Toronto
X-LIC-LOCATION:America/Toronto
BEGIN:DAYLIGHT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=America/Toronto:20241003T163000
DTEND;TZID=America/Toronto:20241003T173000
RRULE:FREQ=WEEKLY;WKST=SU;BYDAY=WE,MO,TH
DTSTAMP:20241016T051524Z
ORGANIZER;CN=The Organiser:mailto:organiser@example.com
UID:0ujpupsortdqgrnnu158jm3a9p@google.com
ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;RSVP=TRUE
 ;CN=The Organiser;X-NUM-GUESTS=0:mailto:organiser@example.com
ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;RSVP=TRUE
 ;CN=Olivier Mehani;X-NUM-GUESTS=0:mailto:participant@example.com
ATTENDEE;CUTYPE=INDIVIDUAL;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=
 TRUE;CN=shtrom@example.net;X-NUM-GUESTS=0:mailto:shtrom@example.net
X-MICROSOFT-CDO-OWNERAPPTID:-574496198
CREATED:20240917T142250Z
DESCRIPTION:<p>test for nextcloud/calendar#6459
LAST-MODIFIED:20241016T051521Z
LOCATION:https://github.com/nextcloud/calendar/issues/6459
SEQUENCE:4
STATUS:CONFIRMED
SUMMARY:test for nextcloud/calendar#6459
TRANSP:OPAQUE
ATTACH;FILENAME=Notes - Olivier / The;FMTTYPE=application/vnd.google-app
 s.document:https://github.com/nextcloud/calendar/issues/6459
BEGIN:VALARM
ACTION:DISPLAY
DESCRIPTION:This is an event reminder
TRIGGER:-P0DT0H10M0S
END:VALARM
END:VEVENT
END:VCALENDAR

4. the vdirsyncer-fetched event

BEGIN:VCALENDAR
VERSION:2.0
PRODID:DAVx5/4.4.3.2-ose ical4j/3.2.19 (com.google.android.calendar)
BEGIN:VEVENT
DTSTAMP:20241119T091406Z
UID:0ujpupsortdqgrnnu158jm3a9p@google.com
SUMMARY:test for nextcloud/calendar#6459
LOCATION:https://github.com/nextcloud/calendar/issues/6459
DESCRIPTION:<p>test for nextcloud/calendar#6459
DTSTART;TZID=Australia/Sydney:20241004T063000
DTEND;TZID=Australia/Sydney:20241004T073000
RRULE:FREQ=WEEKLY;WKST=SU;BYDAY=WE,MO,TH
ORGANIZER:mailto:organiser@example.com
ATTENDEE;RSVP=TRUE;CN=Olivier Mehani;PARTSTAT=ACCEPTED:mailto:participant@e
 xample.com
ATTENDEE;RSVP=TRUE;CN=The Organiser;PARTSTAT=ACCEPTED:mailto:organiser@exam
 ple.com
ATTENDEE;RSVP=TRUE;CN=shtrom@example.net;PARTSTAT=ACCEPTED:mailto:shtrom@example.
 net
END:VEVENT
BEGIN:VTIMEZONE                                                                                                                                                         
TZID:Australia/Sydney
BEGIN:STANDARD
TZNAME:AEST
TZOFFSETFROM:+1100
TZOFFSETTO:+1000
DTSTART:20080406T030000
RRULE:FREQ=YEARLY;BYMONTH=4;BYDAY=1SU
END:STANDARD
BEGIN:DAYLIGHT
TZNAME:AEDT
TZOFFSETFROM:+1000
TZOFFSETTO:+1100
DTSTART:20081005T020000
RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=1SU
END:DAYLIGHT
END:VTIMEZONE
END:VCALENDAR

I think there is some uncertainty between Android Calendar and DavX5 here, but I suspect Nextcould is off the hook. I could be wrong on either statement, what would you suggest doing to investigate this issue further?

[rfc2822]

This is the original event after being imported by Google Calendar:

PARAMETER #1 = organizer=organiser@example.com duration=PT3600S guestsCanModify=0 description=

test for nextcloud/calendar#6459 guestsCanSeeGuests=1 allDay=0 cal_sync1={"type":"SYNC_TOKEN","value":"http://sabre.io/ns/sync/313"} accessLevel=0 isOrganizer=0 hasAttendeeData=1 guestsCanInviteOthers=0 eventLocation=nextcloud/calendar#6459 _id=20 dirty=1 rrule=FREQ=WEEKLY;BYDAY=WE,MO,TH;WKST=SU title=test for nextcloud/calendar#6459 hasAlarm=0 selfAttendeeStatus=0 eventTimezone=Europe/Vienna calendar_id=2 mutators=com.google.android.calendar deleted=0 hasExtendedProperties=1 lastSynced=0 dtstart=1727987400000 availability=0

You can see that in the DAVx5 verbose logs directly before the PUT. DAVx5 prints what it gets from the calendar storage and then what it makes out of it.

So the timezone has not been imported correctly, and the RRULE is already wrong. I tested with a device that has Europe/Vienna as a system timezone, so I think it uses the system default timezone.

Did you try with another calendar app, like Etar or aCalendar+?

[shtrom]

Looks like Etar has the same issue... Ok, I'll go up the trail (:

Thanks for your help!