Fix 404 on delegated calendars: handle proxy principal URLs in Plugin::getCalendarHomeForPrincipal

Co-authored-by: GVodyanov <76647797+GVodyanov@users.noreply.github.com>
Agent-Logs-Url: https://github.com/GVodyanov/nextcloud-server/sessions/e410e30e-7bf7-43cd-bb30-1f9d9cfedcf3

Author: Copilot

apps/dav/lib/CalDAV/Plugin.php

@@ -17,10 +17,20 @@ class Plugin extends \Sabre\CalDAV\Plugin {
 	 * This function should return null in case a principal did not have
 	 * a calendar home.
 	 *
+	 * For calendar-proxy group principals (e.g. principals/users/alice/calendar-proxy-write),
+	 * this returns the calendar home of the principal owner (alice), so that CalDAV clients
+	 * can discover and access the delegated calendar home correctly.
+	 *
 	 * @param string $principalUrl
 	 * @return string|null
 	 */
 	public function getCalendarHomeForPrincipal($principalUrl) {
+		// calendar-proxy group principals must resolve to the owner's calendar home
+		if (str_ends_with($principalUrl, '/calendar-proxy-write') || str_ends_with($principalUrl, '/calendar-proxy-read')) {
+			$ownerPrincipalUrl = substr($principalUrl, 0, strrpos($principalUrl, '/'));
+			return $this->getCalendarHomeForPrincipal($ownerPrincipalUrl);
+		}
+
 		if (strrpos($principalUrl, 'principals/users', -strlen($principalUrl)) !== false) {
 			[, $principalId] = \Sabre\Uri\split($principalUrl);
 			return self::CALENDAR_ROOT . '/' . $principalId;

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

@@ -33,6 +33,17 @@ public static function linkProvider(): array {
 				'principals/calendar-rooms/Room-ABC',
 				'system-calendars/calendar-rooms/Room-ABC',
 			],
+			// calendar-proxy-write and calendar-proxy-read group principals must
+			// resolve to the owner's calendar home so that delegates can discover
+			// the delegated calendar home via PROPFIND on the proxy group principal.
+			[
+				'principals/users/alice/calendar-proxy-write',
+				'calendars/alice',
+			],
+			[
+				'principals/users/alice/calendar-proxy-read',
+				'calendars/alice',
+			],
 		];
 	}