fix(dav): allow multiple organizers if possible

This is very hacky! However, we want to allow saving events with multiple
organizers. Those events are not RFC compliant, but sometimes imported from major
external calendar services (e.g. Google). If the current user is not an organizer of
the event we ignore the exception as no scheduling messages will be sent anyway.

Signed-off-by: Richard Steinmetz <richard@steinmetz.cloud>

apps/dav/lib/CalDAV/Schedule/Plugin.php

@@ -36,11 +36,14 @@ use OCA\DAV\CalDAV\CalendarHome;
 use OCP\IConfig;
 use Psr\Log\LoggerInterface;
 use Sabre\CalDAV\ICalendar;
+use Sabre\CalDAV\ICalendarObject;
+use Sabre\CalDAV\Schedule\ISchedulingObject;
 use Sabre\DAV\INode;
 use Sabre\DAV\IProperties;
 use Sabre\DAV\PropFind;
 use Sabre\DAV\Server;
 use Sabre\DAV\Xml\Property\LocalHref;
+use Sabre\DAVACL\IACL;
 use Sabre\DAVACL\IPrincipal;
 use Sabre\HTTP\RequestInterface;
 use Sabre\HTTP\ResponseInterface;
@@ -50,6 +53,7 @@ use Sabre\VObject\Component\VEvent;
 use Sabre\VObject\DateTimeParser;
 use Sabre\VObject\FreeBusyGenerator;
 use Sabre\VObject\ITip;
+use Sabre\VObject\ITip\SameOrganizerForAllComponentsException;
 use Sabre\VObject\Parameter;
 use Sabre\VObject\Property;
 use Sabre\VObject\Reader;
@@ -161,7 +165,29 @@ class Plugin extends \Sabre\CalDAV\Schedule\Plugin {
 			$this->pathOfCalendarObjectChange = $request->getPath();
 		}
 
-		parent::calendarObjectChange($request, $response, $vCal, $calendarPath, $modified, $isNew);
+		try {
+			parent::calendarObjectChange($request, $response, $vCal, $calendarPath, $modified, $isNew);
+		} catch (SameOrganizerForAllComponentsException $e) {
+			$this->handleSameOrganizerException($e, $vCal, $calendarPath);
+		}
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	public function beforeUnbind($path): void {
+		try {
+			parent::beforeUnbind($path);
+		} catch (SameOrganizerForAllComponentsException $e) {
+			$node = $this->server->tree->getNodeForPath($path);
+			if (!$node instanceof ICalendarObject || $node instanceof ISchedulingObject) {
+				throw $e;
+			}
+
+			/** @var VCalendar $vCal */
+			$vCal = Reader::read($node->get());
+			$this->handleSameOrganizerException($e, $vCal, $path);
+		}
 	}
 
 	/**
@@ -630,4 +656,44 @@ EOF;
 			'{DAV:}displayname' => $displayName,
 		]);
 	}
+
+	/**
+	 * Try to handle the given exception gracefully or throw it if necessary.
+	 *
+	 * @throws SameOrganizerForAllComponentsException If the exception should not be ignored
+	 */
+	private function handleSameOrganizerException(
+		SameOrganizerForAllComponentsException $e,
+		VCalendar $vCal,
+		string $calendarPath,
+	): void {
+		// This is very hacky! However, we want to allow saving events with multiple
+		// organizers. Those events are not RFC compliant, but sometimes imported from major
+		// external calendar services (e.g. Google). If the current user is not an organizer of
+		// the event we ignore the exception as no scheduling messages will be sent anyway.
+
+		// It would be cleaner to patch Sabre to validate organizers *after* checking if
+		// scheduling messages are necessary. Currently, organizers are validated first and
+		// afterwards the broker checks if messages should be scheduled. So the code will throw
+		// even if the organizers are not relevant. This is to ensure compliance with RFCs but
+		// a bit too strict for real world usage.
+
+		if (!isset($vCal->VEVENT)) {
+			throw $e;
+		}
+
+		$calendarNode = $this->server->tree->getNodeForPath($calendarPath);
+		if (!($calendarNode instanceof IACL)) {
+			// Should always be an instance of IACL but just to be sure
+			throw $e;
+		}
+
+		$addresses = $this->getAddressesForPrincipal($calendarNode->getOwner());
+		foreach ($vCal->VEVENT as $vevent) {
+			if (in_array($vevent->ORGANIZER->getNormalizedValue(), $addresses, true)) {
+				// User is an organizer => throw the exception
+				throw $e;
+			}
+		}
+	}
 }