[Bug]: Cannot add attendee to occurrence of an repeating event

[odzhychko]

Steps to reproduce

1. As User A create event Event X
   • let it repeat daily
   • add User B as attendee
2. As User A edit the second occurrence
   • add User C as attendee
   • save as "Update this occurrence"

Expected behavior

User C is invited to the second occurrence.

Actual behavior

400 response from server

<?xml version="1.0" encoding="utf-8"?>
<d:error xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns">
  <s:exception>Sabre\DAV\Exception\BadRequest</s:exception>
  <s:message>A valid calendar object must contain at least one VJOURNAL, VEVENT, or VTODO component type</s:message>
</d:error>

Calendar app version

6.6.0-rc.2 and main (3d5f6086c)

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

35.0.0 RC4

Updated from an older installed version or fresh install

None

List of activated apps

Nextcloud configuration

Web server error log

{
    "reqId": "W9L7hQew8Txrmn5IPx1z",
    "level": 1,
    "time": "2026-09-11T18:05:13+00:00",
    "remoteAddr": "127.0.0.1",
    "user": "UserA",
    "app": "no app in context",
    "method": "PUT",
    "url": "/remote.php/dav/calendars/UserA/personal/e655465e-3cff-450a-993b-d8ed5d81a02e.ics",
    "scriptName": "/remote.php",
    "message": "Uncaught exception",
    "userAgent": "Mozilla/5.0 (X11; Linux x86_64; rv:155.0) Gecko/20100101 Thunderbird/155.0",
    "version": "35.0.0.9",
    "exception": {
        "Exception": "Sabre\\DAV\\Exception\\BadRequest",
        "Message": "A valid calendar object must contain at least one VJOURNAL, VEVENT, or VTODO component type",
        "Code": 0,
        "Trace": [
            {
                "file": "/var/www/html/apps/dav/lib/CalDAV/CalDavBackend.php",
                "line": 1551,
                "function": "getDenormalizedData",
                "class": "OCA\\DAV\\CalDAV\\CalDavBackend",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/dav/lib/CalDAV/Calendar.php",
                "line": 199,
                "function": "createCalendarObject",
                "class": "OCA\\DAV\\CalDAV\\CalDavBackend",
                "type": "->",
                "args": [
                    "*** sensitive parameters replaced ***"
                ]
            },
            {
                "file": "/var/www/html/3rdparty/sabre/dav/lib/CalDAV/Schedule/Plugin.php",
                "line": 526,
                "function": "createFile",
                "class": "Sabre\\CalDAV\\Calendar",
                "type": "->",
                "args": [
                    "*** sensitive parameters replaced ***"
                ]
            },
            {
                "file": "/var/www/html/apps/dav/lib/CalDAV/Schedule/Plugin.php",
                "line": 265,
                "function": "scheduleLocalDelivery",
                "class": "Sabre\\CalDAV\\Schedule\\Plugin",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php",
                "line": 89,
                "function": "scheduleLocalDelivery",
                "class": "OCA\\DAV\\CalDAV\\Schedule\\Plugin",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/dav/lib/CalDAV/Schedule/Plugin.php",
                "line": 351,
                "function": "emit",
                "class": "Sabre\\DAV\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/dav/lib/CalDAV/Schedule/Plugin.php",
                "line": 627,
                "function": "deliver",
                "class": "Sabre\\CalDAV\\Schedule\\Plugin",
                "type": "->"
            },
            {
                "file": "/var/www/html/apps/dav/lib/CalDAV/Schedule/Plugin.php",
                "line": 214,
                "function": "processICalendarChange",
                "class": "Sabre\\CalDAV\\Schedule\\Plugin",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php",
                "line": 89,
                "function": "calendarObjectChange",
                "class": "OCA\\DAV\\CalDAV\\Schedule\\Plugin",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/dav/lib/CalDAV/Plugin.php",
                "line": 889,
                "function": "emit",
                "class": "Sabre\\DAV\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/dav/lib/CalDAV/Plugin.php",
                "line": 733,
                "function": "validateICalendar",
                "class": "Sabre\\CalDAV\\Plugin",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php",
                "line": 89,
                "function": "beforeWriteContent",
                "class": "Sabre\\CalDAV\\Plugin",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php",
                "line": 1133,
                "function": "emit",
                "class": "Sabre\\DAV\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/dav/lib/DAV/CorePlugin.php",
                "line": 492,
                "function": "updateFile",
                "class": "Sabre\\DAV\\Server",
                "type": "->",
                "args": [
                    "*** sensitive parameters replaced ***"
                ]
            },
            {
                "file": "/var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php",
                "line": 89,
                "function": "httpPut",
                "class": "Sabre\\DAV\\CorePlugin",
                "type": "->"
            },
            {
                "file": "/var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php",
                "line": 472,
                "function": "emit",
                "class": "Sabre\\DAV\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/html/apps/dav/lib/Connector/Sabre/Server.php",
                "line": 216,
                "function": "invokeMethod",
                "class": "Sabre\\DAV\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/html/apps/dav/lib/Server.php",
                "line": 436,
                "function": "start",
                "class": "OCA\\DAV\\Connector\\Sabre\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/html/apps/dav/appinfo/v2/remote.php",
                "line": 25,
                "function": "exec",
                "class": "OCA\\DAV\\Server",
                "type": "->"
            },
            {
                "file": "/var/www/html/remote.php",
                "line": 158,
                "args": [
                    "/var/www/html/apps/dav/appinfo/v2/remote.php"
                ],
                "function": "require"
            },
            {
                "file": "/var/www/html/lib/OC.php",
                "line": 1397,
                "function": "{closure:/var/www/html/remote.php:102}",
                "args": [
                    "*** sensitive parameters replaced ***"
                ]
            },
            {
                "file": "/var/www/html/remote.php",
                "line": 102,
                "function": "handleRequests",
                "class": "OC",
                "type": "::"
            }
        ],
        "File": "/var/www/html/apps/dav/lib/CalDAV/CalDavBackend.php",
        "Line": 3429,
        "message": "Uncaught exception",
        "exception": "{\"class\":\"Sabre\\DAV\\Exception\\BadRequest\",\"message\":\"A valid calendar object must contain at least one VJOURNAL, VEVENT, or VTODO component type\",\"code\":0,\"file\":\"/var/www/html/apps/dav/lib/CalDAV/CalDavBackend.php:3429\",\"trace\":\"#0 /var/www/html/apps/dav/lib/CalDAV/CalDavBackend.php(1551): OCA\\DAV\\CalDAV\\CalDavBackend->getDenormalizedData()\\n#1 /var/www/html/3rdparty/sabre/dav/lib/CalDAV/Calendar.php(199): OCA\\DAV\\CalDAV\\CalDavBackend->createCalendarObject()\\n#2 /var/www/html/3rdparty/sabre/dav/lib/CalDAV/Schedule/Plugin.php(526): Sabre\\CalDAV\\Calendar->createFile()\\n#3 /var/www/html/apps/dav/lib/CalDAV/Schedule/Plugin.php(265): Sabre\\CalDAV\\Schedule\\Plugin->scheduleLocalDelivery()\\n#4 /var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php(89): OCA\\DAV\\CalDAV\\Schedule\\Plugin->scheduleLocalDelivery()\\n#5 /var/www/html/3rdparty/sabre/dav/lib/CalDAV/Schedule/Plugin.php(351): Sabre\\DAV\\Server->emit()\\n#6 /var/www/html/3rdparty/sabre/dav/lib/CalDAV/Schedule/Plugin.php(627): Sabre\\CalDAV\\Schedule\\Plugin->deliver()\\n#7 /var/www/html/apps/dav/lib/CalDAV/Schedule/Plugin.php(214): Sabre\\CalDAV\\Schedule\\Plugin->processICalendarChange()\\n#8 /var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php(89): OCA\\DAV\\CalDAV\\Schedule\\Plugin->calendarObjectChange()\\n#9 /var/www/html/3rdparty/sabre/dav/lib/CalDAV/Plugin.php(889): Sabre\\DAV\\Server->emit()\\n#10 /var/www/html/3rdparty/sabre/dav/lib/CalDAV/Plugin.php(733): Sabre\\CalDAV\\Plugin->validateICalendar()\\n#11 /var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\\CalDAV\\Plugin->beforeWriteContent()\\n#12 /var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php(1133): Sabre\\DAV\\Server->emit()\\n#13 /var/www/html/3rdparty/sabre/dav/lib/DAV/CorePlugin.php(492): Sabre\\DAV\\Server->updateFile()\\n#14 /var/www/html/3rdparty/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\\DAV\\CorePlugin->httpPut()\\n#15 /var/www/html/3rdparty/sabre/dav/lib/DAV/Server.php(472): Sabre\\DAV\\Server->emit()\\n#16 /var/www/html/apps/dav/lib/Connector/Sabre/Server.php(216): Sabre\\DAV\\Server->invokeMethod()\\n#17 /var/www/html/apps/dav/lib/Server.php(436): OCA\\DAV\\Connector\\Sabre\\Server->start()\\n#18 /var/www/html/apps/dav/appinfo/v2/remote.php(25): OCA\\DAV\\Server->exec()\\n#19 /var/www/html/remote.php(158): require('...')\\n#20 /var/www/html/lib/OC.php(1397): {closure:/var/www/html/remote.php:102}()\\n#21 /var/www/html/remote.php(102): OC::handleRequests()\\n#22 {main}\"}",
        "CustomMessage": "Uncaught exception"
    }
}

Log file

Browser log

Additional info

No response

[odzhychko]

Still in triage, because I want to test if this also happens without calendar app.

[SebastianKrupinski]

Still in triage, because I want to test if this also happens without calendar app.

Just post the ICS file that's being saved after the change

[odzhychko]

Adding User C and as described above does not change the event. This is how the event looks before and after the failed action.

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//IDN nextcloud.com//Calendar app 6.7.0-dev.1//EN
CALSCALE:GREGORIAN
BEGIN:VEVENT
CREATED:20260911T170829Z
DTSTAMP:20260911T170849Z
LAST-MODIFIED:20260911T170849Z
SEQUENCE:3
UID:185f6ab7-f4e9-4354-bbcf-b24068e6d116
DTSTART;VALUE=DATE:20260920
DTEND;VALUE=DATE:20260921
TRANSP:OPAQUE
STATUS:CONFIRMED
SUMMARY:EventX
ATTENDEE;CN=UserB;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION;ROLE=REQ-PARTICIP
 ANT;RSVP=TRUE;SCHEDULE-STATUS=1.1:mailto:userb@userb.userb
ORGANIZER;CN=UserA:mailto:usera@usera.usera
RRULE:FREQ=DAILY
END:VEVENT
END:VCALENDAR

[odzhychko]

And this is the payload of the failing PUT request http://localhost:36033/remote.php/dav/calendars/UserA/personal/1CEB4BC6-1D14-499C-9317-C3A7B0C53FCB.ics

BEGIN:VCALENDAR
CALSCALE:GREGORIAN
VERSION:2.0
PRODID:-//IDN nextcloud.com//Calendar app 6.7.0-dev.1//EN

BEGIN:VEVENT
CREATED:20260911T170829Z
DTSTAMP:20260911T170849Z
LAST-MODIFIED:20260911T170849Z
SEQUENCE:3
UID:185f6ab7-f4e9-4354-bbcf-b24068e6d116
DTSTART;VALUE=DATE:20260920
DTEND;VALUE=DATE:20260921
TRANSP:OPAQUE
STATUS:CONFIRMED
SUMMARY:EventX
ATTENDEE;CN=UserB;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION;ROLE=REQ-PARTICIP
 ANT;RSVP=TRUE;SCHEDULE-STATUS=1.1:mailto:userb@userb.userb
ORGANIZER;CN=UserA:mailto:usera@usera.usera
RRULE:FREQ=DAILY
END:VEVENT

BEGIN:VEVENT
CREATED:20260911T171226Z
DTSTAMP:20260911T171226Z
LAST-MODIFIED:20260911T171226Z
SEQUENCE:1
UID:185f6ab7-f4e9-4354-bbcf-b24068e6d116
DTSTART;VALUE=DATE:20260921
DTEND;VALUE=DATE:20260922
TRANSP:OPAQUE
STATUS:CONFIRMED
SUMMARY:EventX
ATTENDEE;CN=UserB;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION;ROLE=REQ-PARTICIP
 ANT;RSVP=TRUE;SCHEDULE-STATUS=1.1:mailto:userb@userb.userb
ATTENDEE;CN=UserC;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION;ROLE=REQ-PARTICIP
 ANT;RSVP=TRUE:mailto:userc@userc.userc
ORGANIZER;CN=UserA:mailto:usera@usera.usera
RECURRENCE-ID;VALUE=DATE:20260921
END:VEVENT

END:VCALENDAR

[SebastianKrupinski]

And this is the payload of the failing PUT request http://localhost:36033/remote.php/dav/calendars/UserA/personal/1CEB4BC6-1D14-499C-9317-C3A7B0C53FCB.ics

The event is correct, one main event and one modified occurance.

[odzhychko]

Still in triage, because I want to test if this also happens without calendar app.

Following the described steps I could reproduce the same error in Thunderbird.
Also just added the relevant server log.

This is the $calendarData in getDenormalizedDate for which it fails.
There is only the exception but not the master event.

VERSION:2.0
PRODID:-//Sabre//Sabre VObject 4.5.6//EN
CALSCALE:GREGORIAN
BEGIN:VEVENT
CREATED:20260911T181426Z
DTSTAMP:20260911T181426Z
LAST-MODIFIED:20260911T181426Z
SEQUENCE:1
UID:77da3c2b-be01-4c2a-949a-ade3a6bdf0c7 (had to recreate the event to test, so this UID not matching with UIDs above might be only caused by that and not relevant for the bug)
DTSTART;VALUE=DATE:20260908
DTEND;VALUE=DATE:20260909
TRANSP:OPAQUE
STATUS:CONFIRMED
SUMMARY:EventA
ATTENDEE;CN=UserB;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION;ROLE=REQ-PARTICIP
 ANT;RSVP=TRUE:mailto:userb@userb.userb
ATTENDEE;CN=UserC;CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-ACTION;ROLE=REQ-PARTICIP
 ANT;RSVP=TRUE:mailto:userc@userc.userc
ORGANIZER;CN=UserA:mailto:usera@usera.usera
RECURRENCE-ID;VALUE=DATE:20260908
END:VEVENT
END:VCALENDAR