Deleting a single occurrence of a recurring event cancels entire series for attendees

[alphadawn]

Steps to reproduce

1.Create a recurring event in Nextcloud Calendar (e.g. weekly event with multiple occurrences)
2.Invite one or more participants via email
3.Participants accept the invitation
4. As organizer, delete only one occurrence of the recurring event (not the entire series)
5.Wait for sync / refresh attendee calendars

Expected behavior

• Only the specific deleted occurrence should be removed from attendee calendars
• Remaining events in the recurrence series should remain active
• No full-series cancellation should be triggered

Actual behavior

• In organizer calendar:
  • The selected occurrence is correctly removed
  • Remaining recurring events are still present (correct)
• In attendee calendars:
  • The entire recurring event series becomes cancelled (strikethrough)
  • All occurrences appear cancelled, not just the deleted one

Calendar app version

6.2.2 (even in newer versions)

CalDAV-clients used

No response

Browser

No response

Client operating system

No response

Server operating system

No response

Web server

None

Database engine version

None

PHP engine version

None

Nextcloud version

latest

Updated from an older installed version or fresh install

Fresh install

List of activated apps

Nextcloud configuration

Web server error log

Log file

Browser log

Additional info

It appears that when a single occurrence is deleted, the CalDAV/iTIP message sent to attendees is interpreted as a series-level CANCEL instead of a recurrence exception update, causing the entire UID series to be marked as cancelled.

this is the attendee calendar after they accpeted the invite for a recurring event

This is the organizer calendar (cancels an event)

This is the attendee calendar after ONE event was deleted (all are canceled)

[SebastianKrupinski]

Hi @alphadawn

This was a issue... But should be resolved now with the following fix:

nextcloud/server#50843

[SebastianKrupinski]

What version of the server are you using?

[alphadawn]

i am using Nextcloud AIO v12.9.2 Nextcloud Hub 26 Winter(33.0.2). is there a beta version that has fixed this?

[alphadawn]

So, i have updated my calendar to the newst version (4.6.0) and updated nextcloud to version 33.0.3 and the problem seems to be somewhat fixed, but not fully. here are some tests i made and their results:

1. When creating a recurring appointment in Outlook and the invitation is accepted by Nextcloud participants, all appointments are displayed correctly.

   • However, if a single appointment of the series is cancelled by the organizer, all appointments in the series are struck through in Nextcloud.

2. When creating a recurring appointment in Nextcloud and the invitation is accepted by Nextcloud participants, all appointments are displayed correctly.

   • If a single appointment is deleted by the organizer, this appointment is also correctly deleted for the participant (instead of being struck through).
   • If an appointment is marked as "cancelled" by the organizer, it is neither deleted nor struck through in the participants' calendars.

3. When creating a single appointment in Nextcloud and the invitation is accepted by the participants, the appointment is displayed correctly.

   • If this appointment is marked as "cancelled" by the organizer, it is struck through in the participants' calendars after a certain amount of time.

[SebastianKrupinski]

Hi @alphadawn

So the imip messages are handled by the server it self, updating the calendar has no effect on this, the cancellation was addressed in

nextcloud/server#50843

As for you test,

1. I would need to see the inbound ics file, this should work properly, as it was fixed by the above PR

2. I will need to test the second scenario to see what is happening

3. The event sync on the calendar is not instant, it on a polling cycle of 1 min, hence the delay

Thank you for the in depth analyses

[alphadawn]

Thanks for the quick reply, but I have tested the fix proposed in nextcloud/server#50843 but tbh I am not really a PHP professional. After I modified the apps/dav/lib/CalDAV/TipBroker.php file inside the container (as was explained in the commit), I started getting errors (I saw them in the administration overview tab) and the calendar itself stopped working properly. As in, I couldn't see any events and couldn't create any; it said something was wrong with my email or something, I forgot the error since I just restored a backup I made before I changed anything. I tried fixing the errors myself since some of them were syntactic errors (e.g. it gave me an error in line 30 saying that there is a comma that shouldn't be there).
As I said, I am not professional with PHP so it could be that I have done something wrong.

[SebastianKrupinski]

Hi @alphadawn

So it took me a minute to figure out what happened there, this patch was not applied to NC 33 yet, it will be out with the release of 34, This was done on purpose as it was a major logic rewrite and I want to make sure there is no major issues before applying it to all supported version.

If you want to test it. You can replace the entire file, instead of patching it. Backup the current file then download the raw version of the new file and replace the existing one.

https://github.com/nextcloud/server/blob/master/apps/dav/lib/CalDAV/TipBroker.php

[alphadawn]

hi @SebastianKrupinski,
thanks for the reply. i have downloaded the raw file and put it in the correct place inside the container, and i have to say, it works better than before. so i went back to stable version of nextcloud (33.0.2) and started testing the calendar, and here are the results i found:

now with NC version 33.0.2 with TipBroker.php file updated, and calendar version 6.4.0:

Nextcloud -> Nextcloud

• organizer creates recurring event from nextcloud and invites attendees
• attendees accept, events are shown correctly in their calendar
• if the organizer deletes one of the events:
  • the attendees get an email that the event was canceled the event is thus deleted from the calendar of the attendees
• if the organizer marks an event as canceled
  • the event is marked as canceled in the organizer calendar (strike through) but the attendees dont recieve an email that the event was canceled and nothing happens with the calendar of the attendees (edit: i have tested this with another account, and it seems to be working fine, as in the attendees get the cancelation email and get the event strike-throughed. i need to test this more to be 100% sure)
• BUT; if the organizer marks an event as canceled AND quickly deletes another event :
  • all events are marked as canceled (strike through) in the attendee calendar. (not sure if this has to do with Nextcloud version 33.0.2 or if nextcloud version is irrelevent)

Outlook -> Nextcloud

• if organizer creates recurring event from outlook and invites attendees
• if the attendees accept, the events are shown correctly on the calendar
• if the organizer cancels an event (outlook):
  • the event is correctly marked as canceled, BUT i have seen that the attendees somehow automatically withdraw their acceptance from the rest of the meetings, making them either need to go to the original invite email they recieved from the organizer and accept again (so all of them are accepted again) or they would have to accept the events one by one in the calendar.

Nextcloud -> Outlook

• if Organizer creates an occuring event in Nextcloud and invites attendees (outlook)
• if attendees from outlook accept the invite, the event is correctly shown in their calendar
• if the organizer cancels one of the events (nextcloud):
  • the attendees recieve an email that the event on the date X got canceled and the event gets removed from heir calendar
• if the organizer deletes an event (not cancels):
  • attendees on outlook dont get an email saying that the event was deleted, but it gets deleted from their calendar. (they may recieve a notification on teams app that the calendar was updated)

[alphadawn]

This seems to be fixed after the newest update. thanks for your work devs!