fix(dav): wrong comparison method between two events

Old comparison implementation compares each element of the array against each other with no respect for the associated array label, which leads to wrongful removals because one value is accidentally present in a completely different label. New comparison works 'by-label' individually.

Partly fixes #41084 because changes between 'SEQUENCE' not present, 'SEQUENCE:0' and 'SEQUENCE:1' were not detected in the old implementation and thus no email update sent.

Co-authored-by: Christoph Wurst <ChristophWurst@users.noreply.github.com>
Signed-off-by: Robert C. Schaller <gtbc_robert.schaller@rsxc.de>

apps/dav/lib/CalDAV/EventComparisonService.php

@@ -65,7 +65,7 @@ private function removeIfUnchanged(VEvent $filterEvent, array &$eventsToFilter):
 				$eventToFilterData[] = IMipService::readPropertyWithDefault($eventToFilter, $eventDiff, '');
 			}
 			// events are identical and can be removed
-			if (empty(array_diff($filterEventData, $eventToFilterData))) {
+			if ($filterEventData === $eventToFilterData) {
 				unset($eventsToFilter[$k]);
 				return true;
 			}

apps/dav/tests/unit/CalDAV/EventComparisonServiceTest.php

@@ -4,6 +4,7 @@
 
 /**
  * @copyright 2023 Daniel Kesselberg <mail@danielkesselberg.de>
+ * @copyright 2024 Robert C. Schaller <gtbc_robert.schaller@rsxc.de>
  *
  * @author 2023 Daniel Kesselberg <mail@danielkesselberg.de>
  *
@@ -137,4 +138,70 @@ public function testModifiedUnmodifiedEvent(): void {
 		$this->assertEquals([$vEventOld2], $result['old']);
 		$this->assertEquals([$vEventNew2], $result['new']);
 	}
+
+	// First test to certify fix for issue nextcloud/server#41084
+	public function testSequenceNumberIncrementDetectedForFirstModificationToEventWithoutZeroInit(): void {
+		$vCalendarOld = new VCalendar();
+		$vCalendarNew = new VCalendar();
+
+		$vEventOld = $vCalendarOld->add('VEVENT', [
+			'UID' => 'uid-1234',
+			'LAST-MODIFIED' => 123456,
+			// 'SEQUENCE' => 0,			// sequence number may not be set to zero during event creation and instead fully omitted
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-01 00:00:00'),
+			'RRULE' => 'FREQ=DAILY;INTERVAL=1;UNTIL=20160201T000000Z',
+		]);
+		$vEventOld->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$vEventOld->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE', 'CN' => 'Frodo']);
+
+		$vEventNew = $vCalendarNew->add('VEVENT', [
+			'UID' => 'uid-1234',
+			'LAST-MODIFIED' => 123456,
+			'SEQUENCE' => 1,
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-01 00:00:00'),
+			'RRULE' => 'FREQ=DAILY;INTERVAL=1;UNTIL=20160201T000000Z',
+		]);
+		$vEventNew->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$vEventNew->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE', 'CN' => 'Frodo']);
+
+		$result = $this->eventComparisonService->findModified($vCalendarNew, $vCalendarOld);
+		$this->assertEquals([$vEventOld], $result['old']);
+		$this->assertEquals([$vEventNew], $result['new']);
+	}
+
+	// Second test to certify fix for issue nextcloud/server#41084
+	public function testSequenceNumberIncrementDetectedForFirstModificationToEventWithZeroInit(): void {
+		$vCalendarOld = new VCalendar();
+		$vCalendarNew = new VCalendar();
+
+		$vEventOld = $vCalendarOld->add('VEVENT', [
+			'UID' => 'uid-1234',
+			'LAST-MODIFIED' => 123456,
+			'SEQUENCE' => 0,
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-01 00:00:00'),
+			'RRULE' => 'FREQ=DAILY;INTERVAL=1;UNTIL=20160201T000000Z',
+		]);
+		$vEventOld->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$vEventOld->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE', 'CN' => 'Frodo']);
+
+		$vEventNew = $vCalendarNew->add('VEVENT', [
+			'UID' => 'uid-1234',
+			'LAST-MODIFIED' => 123456,
+			'SEQUENCE' => 1,
+			'SUMMARY' => 'Fellowship meeting',
+			'DTSTART' => new \DateTime('2016-01-01 00:00:00'),
+			'RRULE' => 'FREQ=DAILY;INTERVAL=1;UNTIL=20160201T000000Z',
+		]);
+		$vEventNew->add('ORGANIZER', 'mailto:gandalf@wiz.ard');
+		$vEventNew->add('ATTENDEE', 'mailto:' . 'frodo@hobb.it', ['RSVP' => 'TRUE', 'CN' => 'Frodo']);
+
+		$result = $this->eventComparisonService->findModified($vCalendarNew, $vCalendarOld);
+		$this->assertEquals([$vEventOld], $result['old']);
+		$this->assertEquals([$vEventNew], $result['new']);
+	}
+
+
 }