nextcloud · Olen · Feb 9, 2026
@@ -59,6 +59,7 @@
     'OCA\\DAV\\CalDAV\\CalendarImpl' => $baseDir . '/../lib/CalDAV/CalendarImpl.php',
     'OCA\\DAV\\CalDAV\\CalendarManager' => $baseDir . '/../lib/CalDAV/CalendarManager.php',
     'OCA\\DAV\\CalDAV\\CalendarObject' => $baseDir . '/../lib/CalDAV/CalendarObject.php',
+    'OCA\\DAV\\CalDAV\\CalendarObjectEtagHelper' => $baseDir . '/../lib/CalDAV/CalendarObjectEtagHelper.php',
     'OCA\\DAV\\CalDAV\\CalendarProvider' => $baseDir . '/../lib/CalDAV/CalendarProvider.php',
     'OCA\\DAV\\CalDAV\\CalendarRoot' => $baseDir . '/../lib/CalDAV/CalendarRoot.php',
     'OCA\\DAV\\CalDAV\\DefaultCalendarValidator' => $baseDir . '/../lib/CalDAV/DefaultCalendarValidator.php',

@@ -74,6 +74,7 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\CalDAV\\CalendarImpl' => __DIR__ . '/..' . '/../lib/CalDAV/CalendarImpl.php',
         'OCA\\DAV\\CalDAV\\CalendarManager' => __DIR__ . '/..' . '/../lib/CalDAV/CalendarManager.php',
         'OCA\\DAV\\CalDAV\\CalendarObject' => __DIR__ . '/..' . '/../lib/CalDAV/CalendarObject.php',
+        'OCA\\DAV\\CalDAV\\CalendarObjectEtagHelper' => __DIR__ . '/..' . '/../lib/CalDAV/CalendarObjectEtagHelper.php',
         'OCA\\DAV\\CalDAV\\CalendarProvider' => __DIR__ . '/..' . '/../lib/CalDAV/CalendarProvider.php',
         'OCA\\DAV\\CalDAV\\CalendarRoot' => __DIR__ . '/..' . '/../lib/CalDAV/CalendarRoot.php',
         'OCA\\DAV\\CalDAV\\DefaultCalendarValidator' => __DIR__ . '/..' . '/../lib/CalDAV/DefaultCalendarValidator.php',

@@ -1537,7 +1537,7 @@ public function findCalendarObjectByUid(int $calendarId, string $uid, int $calen
 	#[\Override]
 	public function createCalendarObject($calendarId, $objectUri, $calendarData, $calendarType = self::CALENDAR_TYPE_CALENDAR) {
 		$this->cachedObjects = [];
-		$extraData = $this->getDenormalizedData($calendarData);
+		$extraData = $this->getDenormalizedData($calendarData, $calendarType);
 
 		return $this->atomic(function () use ($calendarId, $objectUri, $calendarData, $extraData, $calendarType) {
 			// Try to detect duplicate uids in the target collection
@@ -1615,7 +1615,7 @@ public function createCalendarObject($calendarId, $objectUri, $calendarData, $ca
 	#[\Override]
 	public function updateCalendarObject($calendarId, $objectUri, $calendarData, $calendarType = self::CALENDAR_TYPE_CALENDAR) {
 		$this->cachedObjects = [];
-		$extraData = $this->getDenormalizedData($calendarData);
+		$extraData = $this->getDenormalizedData($calendarData, $calendarType);
 
 		return $this->atomic(function () use ($calendarId, $objectUri, $calendarData, $extraData, $calendarType) {
 			// Read the object before overwriting it so the update event can carry
@@ -3401,18 +3401,22 @@ public function restoreChanges(int $calendarId, int $calendarType = self::CALEND
 	 *   * uid - value of the UID property
 	 *
 	 * @param string $calendarData
+	 * @param int $calendarType
 	 * @return array
 	 */
-	public function getDenormalizedData(string $calendarData): array {
+	public function getDenormalizedData(string $calendarData, int $calendarType = self::CALENDAR_TYPE_CALENDAR): array {
 
-		$derived = [
-			'etag' => md5($calendarData),
-			'size' => strlen($calendarData),
-		];
 		// validate data and extract base component
 		/** @var VCalendar $vObject */
 		$vObject = Reader::read($calendarData);
 
+		$derived = [
+			'etag' => $calendarType === self::CALENDAR_TYPE_SUBSCRIPTION
+				? CalendarObjectEtagHelper::computeWithoutDtstamp($vObject)
+				: md5($calendarData),
+			'size' => strlen($calendarData),
+		];
+
 		// Extracts componentType, uid, classification, firstOccurence and lastOccurence from a single event/todo/journal component.
 		// RECURRENCE-ID is irrelevant here: it plays no part in this computation, so it works just as well on a recurrence exception as
 		// it does on a series master or a non-recurring component.

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\DAV\CalDAV;
+
+use Sabre\VObject\Component\VCalendar;
+
+class CalendarObjectEtagHelper {
+
+	/**
+	 * md5 of the calendar data with DTSTAMP removed from all components
+	 */
+	public static function computeWithoutDtstamp(VCalendar $vObject): string {
+		$vObject = clone $vObject;
+		foreach ($vObject->getComponents() as $component) {
+			unset($component->DTSTAMP);
+		}
+		return md5($vObject->serialize());
+	}
+}
@@ -10,6 +10,7 @@
 namespace OCA\DAV\CalDAV\WebcalCaching;
 
 use OCA\DAV\CalDAV\CalDavBackend;
+use OCA\DAV\CalDAV\CalendarObjectEtagHelper;
 use OCA\DAV\CalDAV\Import\ImportService;
 use OCP\AppFramework\Utility\ITimeFactory;
 use Psr\Log\LoggerInterface;
@@ -113,7 +114,8 @@ public function refreshSubscription(string $principalUri, string $uri) {
 
 				$sObject = $vObject->serialize();
 				$uid = $vBase->UID->getValue();
-				$etag = md5($sObject);
+
+				$etag = CalendarObjectEtagHelper::computeWithoutDtstamp($vObject);
 
 				// No existing object with this UID, create it
 				if (!isset($existingObjects[$uid])) {

@@ -15,6 +15,7 @@
 use DateTimeZone;
 use OCA\DAV\CalDAV\CalDavBackend;
 use OCA\DAV\CalDAV\Calendar;
+use OCA\DAV\CalDAV\CalendarObjectEtagHelper;
 use OCA\DAV\CalDAV\Federation\FederatedCalendarEntity;
 use OCA\DAV\DAV\Sharing\Plugin as SharingPlugin;
 use OCA\DAV\Events\CalendarDeletedEvent;
@@ -27,6 +28,7 @@
 use Sabre\DAV\PropPatch;
 use Sabre\DAV\Xml\Property\Href;
 use Sabre\DAVACL\IACL;
+use Sabre\VObject\Reader;
 use function time;
 
 /**
@@ -1184,6 +1186,39 @@ public function testSameUriSameIdForDifferentCalendarTypes(): void {
 		$this->assertEquals($calData2, $this->backend->getCalendarObject($subscriptionId, $uri, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION)['calendardata']);
 	}
 
+	public function testEtagIgnoresDtstampOnlyForSubscriptions(): void {
+		$calendarId = $this->createTestCalendar();
+		$subscriptionId = $this->createTestSubscription();
+
+		$uri = static::getUniqueID('calobj');
+		$calData = <<<EOD
+BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:Nextcloud Calendar
+BEGIN:VEVENT
+UID:47d15e3ec8
+DTSTAMP;VALUE=DATE-TIME:20130910T125139Z
+SUMMARY:Test Event
+DTSTART;VALUE=DATE-TIME:20130912T130000Z
+DTEND;VALUE=DATE-TIME:20130912T140000Z
+END:VEVENT
+END:VCALENDAR
+EOD;
+		$calDataNewDtstamp = str_replace('20130910T125139Z', '20260209T120000Z', $calData);
+
+		$this->backend->createCalendarObject($calendarId, $uri, $calData);
+		$this->backend->createCalendarObject($subscriptionId, $uri, $calData, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+
+		$this->assertEquals('"' . md5($calData) . '"', $this->backend->getCalendarObject($calendarId, $uri)['etag']);
+		$this->assertEquals('"' . CalendarObjectEtagHelper::computeWithoutDtstamp(Reader::read($calData)) . '"', $this->backend->getCalendarObject($subscriptionId, $uri, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION)['etag']);
+
+		$calendarEtag = $this->backend->updateCalendarObject($calendarId, $uri, $calDataNewDtstamp);
+		$subscriptionEtag = $this->backend->updateCalendarObject($subscriptionId, $uri, $calDataNewDtstamp, CalDavBackend::CALENDAR_TYPE_SUBSCRIPTION);
+
+		$this->assertEquals('"' . md5($calDataNewDtstamp) . '"', $calendarEtag);
+		$this->assertEquals('"' . CalendarObjectEtagHelper::computeWithoutDtstamp(Reader::read($calData)) . '"', $subscriptionEtag);
+	}
+
 	public function testPurgeAllCachedEventsForSubscription(): void {
 		$subscriptionId = $this->createTestSubscription();
 		$uri = static::getUniqueID('calobj');

@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\DAV\Tests\unit\CalDAV;
+
+use OCA\DAV\CalDAV\CalendarObjectEtagHelper;
+use Sabre\VObject\Reader;
+use Test\TestCase;
+
+class CalendarObjectEtagHelperTest extends TestCase {
+	private const CALENDAR_DATA = "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Test//Test//EN\r\nBEGIN:VEVENT\r\nUID:etag-test\r\nDTSTAMP:20260101T080000Z\r\nDTSTART:20260301T100000Z\r\nSUMMARY:Test Event\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n";
+
+	public function testIgnoresDtstamp(): void {
+		$changed = str_replace('DTSTAMP:20260101T080000Z', 'DTSTAMP:20260209T120000Z', self::CALENDAR_DATA);
+
+		$this->assertSame(
+			CalendarObjectEtagHelper::computeWithoutDtstamp(Reader::read(self::CALENDAR_DATA)),
+			CalendarObjectEtagHelper::computeWithoutDtstamp(Reader::read($changed)),
+		);
+	}
+
+	public function testDetectsContentChange(): void {
+		$changed = str_replace('SUMMARY:Test Event', 'SUMMARY:Renamed Event', self::CALENDAR_DATA);
+
+		$this->assertNotSame(
+			CalendarObjectEtagHelper::computeWithoutDtstamp(Reader::read(self::CALENDAR_DATA)),
+			CalendarObjectEtagHelper::computeWithoutDtstamp(Reader::read($changed)),
+		);
+	}
+
+	public function testMatchesAfterSerializeRoundTrip(): void {
+		$vObject = Reader::read("BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Test//Test//EN\r\nBEGIN:VEVENT\r\nUID:etag-test\r\nDTSTAMP;X-VOBJ-ORIGINAL-TZID=America/Argentina/Buenos_Aires:20260209T120000Z\r\nDTSTART:20260301T100000Z\r\nSUMMARY:A summary that is long enough to be folded when the calendar object gets serialized\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n");
+
+		$this->assertSame(
+			CalendarObjectEtagHelper::computeWithoutDtstamp($vObject),
+			CalendarObjectEtagHelper::computeWithoutDtstamp(Reader::read($vObject->serialize())),
+		);
+	}
+
+	public function testDoesNotModifyInput(): void {
+		$vObject = Reader::read(self::CALENDAR_DATA);
+
+		CalendarObjectEtagHelper::computeWithoutDtstamp($vObject);
+
+		$this->assertSame('20260101T080000Z', $vObject->VEVENT->DTSTAMP->getValue());
+	}
+}