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fix(dav): Strip DTSTAMP before etag comparison in webcal refresh #58193

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fix(dav): Strip DTSTAMP before etag comparison in webcal refresh #58193

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8 changes: 7 additions & 1 deletion apps/dav/lib/CalDAV/WebcalCaching/RefreshWebcalService.php
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,13 @@ public function refreshSubscription(string $principalUri, string $uri) {

$sObject = $vObject->serialize();
$uid = $vBase->UID->getValue();
$etag = md5($sObject);
// Strip DTSTAMP lines for etag computation only.
// Many providers (Google Calendar, Outlook, itslearning) set DTSTAMP
// to the current time on every feed request per RFC 5545, causing
// every event to appear modified on every refresh.
// DTSTAMP is kept in the stored data as it is a required property.
$sObjectForEtag = preg_replace('/^DTSTAMP[;:].*\r?\n([ \t].*\r?\n)*/m', '', $sObject);
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@kesselb kesselb Feb 10, 2026

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That seems a bit odd. I think we should rather use the data from $vObject to calculate an etag instead of altering the serialized object with regex.

I'm also seeing the changing dtstamp with my google test account:

Request 1

BEGIN:VEVENT
DTSTART:20250905T163000Z
DTEND:20250905T173000Z
DTSTAMP:20260210T144443Z
UID:1234-1234-1234-1234
CREATED:20250904T204927Z
LAST-MODIFIED:20250904T204927Z
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:Testing 3
TRANSP:OPAQUE
END:VEVENT

Request 2 (a few seconds later)

BEGIN:VEVENT
DTSTART:20250905T163000Z
DTEND:20250905T173000Z
DTSTAMP:20260210T144446Z
UID:1234-1234-1234-1234
CREATED:20250904T204927Z
LAST-MODIFIED:20250904T204927Z
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:Testing 3
TRANSP:OPAQUE
END:VEVENT

What do you think to calculate the etag from "UID + Last-Modified + Sequence + DTSTART + DTSEND" @tcitworld @SebastianKrupinski?

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@SebastianKrupinski SebastianKrupinski Feb 10, 2026

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@kesselb

I think that approach would work... as long as the source updates those fields properly... which is a big IF...

My idea would be to just serialize the object twice... once with the DTSTAMP once with out... But you idea is more efficient

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@Olen Olen Feb 10, 2026

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Just let me know if you decide you want to build the etag differently. I will update the PR to match what you think is best. I only noticed because the table was growing huge with updates for some of my calendars.

$etag = md5($sObjectForEtag);

// No existing object with this UID, create it
if (!isset($existingObjects[$uid])) {
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135 changes: 134 additions & 1 deletion apps/dav/tests/unit/CalDAV/WebcalCaching/RefreshWebcalServiceTest.php
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Expand Up @@ -460,9 +460,142 @@ public function testRunCreateCalendarBadRequest(string $body, string $format, st
$refreshWebcalService->refreshSubscription('principals/users/testuser', 'sub123');
}

public function testDtstampChangeDoesNotTriggerUpdate(): void {
$refreshWebcalService = new RefreshWebcalService(
$this->caldavBackend,
$this->logger,
$this->connection,
$this->timeFactory,
$this->importService
);

$this->caldavBackend->expects(self::once())
->method('getSubscriptionsForUser')
->with('principals/users/testuser')
->willReturn([
[
'id' => '42',
'uri' => 'sub123',
RefreshWebcalService::STRIP_TODOS => '1',
RefreshWebcalService::STRIP_ALARMS => '1',
RefreshWebcalService::STRIP_ATTACHMENTS => '1',
'source' => 'webcal://foo.bar/bla2',
'lastmodified' => 0,
],
]);

// Feed body has a new DTSTAMP (as happens on every fetch from Google/Outlook)
$body = "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Test//Test//EN\r\nBEGIN:VEVENT\r\nUID:dtstamp-test\r\nDTSTAMP:20260209T120000Z\r\nDTSTART:20260301T100000Z\r\nSUMMARY:Test Event\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n";
$stream = $this->createStreamFromString($body);

$this->connection->expects(self::once())
->method('queryWebcalFeed')
->willReturn(['data' => $stream, 'format' => 'ical']);

// The stored etag was computed from the DTSTAMP-stripped serialization
$existingEtag = md5(preg_replace('/^DTSTAMP[;:].*\r?\n([ \t].*\r?\n)*/m', '', $body));

$this->caldavBackend->expects(self::once())
->method('getLimitedCalendarObjects')
->willReturn([
'dtstamp-test' => [
'id' => 1,
'uid' => 'dtstamp-test',
'etag' => $existingEtag,
'uri' => 'dtstamp-test.ics',
],
]);

$vCalendar = VObject\Reader::read($body);
$generator = function () use ($vCalendar) {
yield $vCalendar;
};

$this->importService->expects(self::once())
->method('importText')
->willReturn($generator());

// DTSTAMP-only change must NOT trigger an update
$this->caldavBackend->expects(self::never())
->method('updateCalendarObject');

$this->caldavBackend->expects(self::never())
->method('createCalendarObject');

$refreshWebcalService->refreshSubscription('principals/users/testuser', 'sub123');
}

public function testFoldedDtstampChangeDoesNotTriggerUpdate(): void {
$refreshWebcalService = new RefreshWebcalService(
$this->caldavBackend,
$this->logger,
$this->connection,
$this->timeFactory,
$this->importService
);

$this->caldavBackend->expects(self::once())
->method('getSubscriptionsForUser')
->with('principals/users/testuser')
->willReturn([
[
'id' => '42',
'uri' => 'sub123',
RefreshWebcalService::STRIP_TODOS => '1',
RefreshWebcalService::STRIP_ALARMS => '1',
RefreshWebcalService::STRIP_ATTACHMENTS => '1',
'source' => 'webcal://foo.bar/bla2',
'lastmodified' => 0,
],
]);

// DTSTAMP with TZID parameter exceeds 75 bytes, triggering RFC 5545 content line folding
$body = "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Test//Test//EN\r\nBEGIN:VEVENT\r\nUID:folded-dtstamp-test\r\nDTSTAMP;X-VOBJ-ORIGINAL-TZID=America/Argentina/Buenos_Aires:20260209T120000Z\r\nDTSTART:20260301T100000Z\r\nSUMMARY:Test Event\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n";
$stream = $this->createStreamFromString($body);

$this->connection->expects(self::once())
->method('queryWebcalFeed')
->willReturn(['data' => $stream, 'format' => 'ical']);

// Compute etag from the serialized output (which will be folded) minus DTSTAMP
$vCalForEtag = VObject\Reader::read($body);
$serialized = $vCalForEtag->serialize();
$existingEtag = md5(preg_replace('/^DTSTAMP[;:].*\r?\n([ \t].*\r?\n)*/m', '', $serialized));

$this->caldavBackend->expects(self::once())
->method('getLimitedCalendarObjects')
->willReturn([
'folded-dtstamp-test' => [
'id' => 1,
'uid' => 'folded-dtstamp-test',
'etag' => $existingEtag,
'uri' => 'folded-dtstamp-test.ics',
],
]);

$vCalendar = VObject\Reader::read($body);
$generator = function () use ($vCalendar) {
yield $vCalendar;
};

$this->importService->expects(self::once())
->method('importText')
->willReturn($generator());

// Folded DTSTAMP change must NOT trigger an update
$this->caldavBackend->expects(self::never())
->method('updateCalendarObject');

$this->caldavBackend->expects(self::never())
->method('createCalendarObject');

$refreshWebcalService->refreshSubscription('principals/users/testuser', 'sub123');
}

public static function identicalDataProvider(): array {
$icalBody = "BEGIN:VCALENDAR\r\nVERSION:2.0\r\nPRODID:-//Sabre//Sabre VObject " . VObject\Version::VERSION . "//EN\r\nCALSCALE:GREGORIAN\r\nBEGIN:VEVENT\r\nUID:12345\r\nDTSTAMP:20160218T133704Z\r\nDTSTART;VALUE=DATE:19000101\r\nDTEND;VALUE=DATE:19000102\r\nRRULE:FREQ=YEARLY\r\nSUMMARY:12345's Birthday (1900)\r\nTRANSP:TRANSPARENT\r\nEND:VEVENT\r\nEND:VCALENDAR\r\n";
$etag = md5($icalBody);
// Etag is computed from DTSTAMP-stripped serialization
$etag = md5(preg_replace('/^DTSTAMP[;:].*\r?\n([ \t].*\r?\n)*/m', '', $icalBody));

return [
[
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