fix(dav): send reply email to organizer when attendee responds via invitation link

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Nico Donath <ndo84bw@gmx.de>

Author: ndo84bw

apps/dav/lib/CalDAV/InvitationResponse/InvitationResponseServer.php

@@ -12,6 +12,7 @@
 use OCA\DAV\CalDAV\Auth\PublicPrincipalPlugin;
 use OCA\DAV\CalDAV\DefaultCalendarValidator;
 use OCA\DAV\CalDAV\Publishing\PublishPlugin;
+use OCA\DAV\CalDAV\Schedule\IMipPlugin;
 use OCA\DAV\Connector\Sabre\AnonymousOptionsPlugin;
 use OCA\DAV\Connector\Sabre\BlockLegacyClientPlugin;
 use OCA\DAV\Connector\Sabre\CachingTree;
@@ -113,6 +114,11 @@ public function __construct(bool $public = true) {
 	 * @return void
 	 */
 	public function handleITipMessage(Message $iTipMessage) {
+		// Register the iMIP plugin only for the invitation-link flow, it must stay absent for createFromStringMinimal() and CalendarImpl
+		if ($this->server->getPlugin('imip') === null) {
+			$this->server->addPlugin(Server::get(IMipPlugin::class));
+		}
+
 		/** @var \OCA\DAV\CalDAV\Schedule\Plugin $schedulingPlugin */
 		$schedulingPlugin = $this->server->getPlugin('caldav-schedule');
 		$schedulingPlugin->scheduleLocalDelivery($iTipMessage);

apps/dav/tests/unit/CalDAV/InvitationResponse/InvitationResponseServerTest.php

@@ -0,0 +1,51 @@
+<?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\InvitationResponse;
+
+use OCA\DAV\CalDAV\InvitationResponse\InvitationResponseServer;
+use OCA\DAV\CalDAV\Schedule\IMipPlugin;
+use PHPUnit\Framework\Attributes\Group;
+use Sabre\VObject\ITip\Message;
+use Sabre\VObject\Reader;
+use Test\TestCase;
+
+#[Group(name: 'DB')]
+class InvitationResponseServerTest extends TestCase {
+	public function testIMipPluginIsOnlyRegisteredWhenHandlingITipMessages(): void {
+		$server = new InvitationResponseServer();
+
+		// Not registered by the constructor: other flows (e.g. createFromStringMinimal) must not send emails
+		$this->assertNull($server->getServer()->getPlugin('imip'));
+
+		$message = new Message();
+		$message->uid = 'fb1bc04c-ac3e-4f5d-8329-7a1e0b07a1e0';
+		$message->component = 'VEVENT';
+		$message->method = 'REPLY';
+		$message->sequence = 0;
+		$message->sender = 'mailto:attendee@example.com';
+		$message->recipient = 'mailto:unknown-organizer@example.com';
+		$message->message = Reader::read(<<<EOF
+			BEGIN:VCALENDAR
+			VERSION:2.0
+			METHOD:REPLY
+			BEGIN:VEVENT
+			ATTENDEE;PARTSTAT=ACCEPTED:mailto:attendee@example.com
+			ORGANIZER:mailto:unknown-organizer@example.com
+			UID:fb1bc04c-ac3e-4f5d-8329-7a1e0b07a1e0
+			SEQUENCE:0
+			DTSTAMP:20260611T120000Z
+			END:VEVENT
+			END:VCALENDAR
+			EOF);
+
+		$server->handleITipMessage($message);
+
+		$this->assertInstanceOf(IMipPlugin::class, $server->getServer()->getPlugin('imip'));
+	}
+}