What causes "Could not create new calendar event: {message}" in nextcloud/server?

Generate a unique object name per event (e.g. the event UID plus a random suffix) before calling createFromString().

nextcloud/server · error · CalendarException

Could not create new calendar event: {message}

Error message

Could not create new calendar event: {message}

What it means

Thrown as OCA\DAV\CalDAV\CalendarException by CalendarImpl::createFromStringInServer() when the embedded sabre/dav server rejects $server->createFile() with a Conflict while writing a new event object. The original sabre Conflict message is appended, so the CalendarException text is a wrapper around the underlying DAV conflict reason. It surfaces through the public ICalendar API methods createFromString() and createFromStringMinimal().

Source

Thrown at apps/dav/lib/CalDAV/CalendarImpl.php:223

			throw new CalendarException('Could not write to calendar as URI parameter is missing');
		}

		// Build full calendar path
		[, $user] = uriSplit($this->calendar->getPrincipalURI());
		$fullCalendarFilename = sprintf('calendars/%s/%s/%s', $user, $this->calendarInfo['uri'], $name);

		// Force calendar change URI
		/** @var Schedule\Plugin $schedulingPlugin */
		$schedulingPlugin = $server->getPlugin('caldav-schedule');
		$schedulingPlugin->setPathOfCalendarObjectChange($fullCalendarFilename);

		$stream = fopen('php://memory', 'rb+');
		fwrite($stream, $calendarData);
		rewind($stream);
		try {
			$server->createFile($fullCalendarFilename, $stream);
		} catch (Conflict $e) {
			throw new CalendarException('Could not create new calendar event: ' . $e->getMessage(), 0, $e);
		} finally {
			fclose($stream);
		}
	}

	#[\Override]
	public function createFromString(string $name, string $calendarData): void {
		$server = new EmbeddedCalDavServer(false);
		$this->createFromStringInServer($name, $calendarData, $server->getServer());
	}

	#[\Override]
	public function createFromStringMinimal(string $name, string $calendarData): void {
		$server = new InvitationResponseServer(false);
		$this->createFromStringInServer($name, $calendarData, $server->getServer());
	}

	/**

View on GitHub (pinned to ecdeb153ff)

Solutions

Generate a unique object name per event (e.g. the event UID plus a random suffix) before calling createFromString().
Before creating, check whether an object with that name already exists (calendarQuery/search on the ICalendar or the CalDAV backend) and update instead of create.
Catch CalendarException around createFromString(), inspect the chained Conflict via getPrevious(), and decide skip/update/rename on collision.
For imports, track which UIDs were already written so re-runs are idempotent.

Example fix

// before
$calendar->createFromString('event.ics', $calendarData);

// after
$name = $eventUid . '-' . bin2hex(random_bytes(4)) . '.ics';
try {
	$calendar->createFromString($name, $calendarData);
} catch (CalendarException $e) {
	// object name collision or scheduling conflict; inspect $e->getPrevious()
	$logger->warning('Event create failed: ' . $e->getMessage());
}

Defensive patterns

Strategy: try-catch

Validate before calling

// derive a collision-free name before creating
$objectName = $eventUid . '.ics';
$existing = $calendar->search('', ['UID'], ['uid' => $eventUid]); // or calendarQuery via backend
if ($existing !== []) {
    $objectName = $eventUid . '-' . bin2hex(random_bytes(4)) . '.ics';
}

Try / catch

try {
    $calendar->createFromString($name, $calendarData);
} catch (\OCA\DAV\CalDAV\CalendarException $e) {
    if ($e->getPrevious() instanceof \Sabre\DAV\Exception\Conflict) {
        // name collision or scheduling conflict -> rename and retry once, or update existing
    }
    throw $e;
}

Prevention

Always derive object filenames from a unique UID instead of constants like 'event.ics'.
Make import scripts idempotent by recording written UIDs.
Log the chained Conflict message (getPrevious()) to distinguish collision from other createFile conflicts.

When it happens

Trigger: Calling $calendar->createFromString($name, $calendarData) (or createFromStringMinimal) on an OCA\DAV\CalDAV\CalendarImpl when an object with the same filename already exists under calendars/<user>/<calendarUri>/<name>, or when the CalDAV scheduling/plugin layer reports a conflict during the PUT into the embedded server. Typical from calendar import scripts that reuse a fixed object name or re-run after a partial failure.

Common situations: Bulk iCalendar imports that derive the object name from a UID and hit the same UID twice; retrying an import after a timeout without skipping already-created events; concurrent requests creating the same event name; testing event creation in a loop with a hardcoded '.ics' filename.

Related errors

AI-assisted analysis of nextcloud/server@ecdeb153ff (2026-08-17). Data as JSON: /api/errors/805807daf4d0d604. Report an issue: GitHub.