[Bug]: No iMIP response sent when accepting an invitation from Outlook through Nextcloud Mail

[kesselb]

Bug description

When accepting an invitation from Outlook in Nextcloud Mail, no iMIP response is sent to the organizer, and the status in Outlook isn't updated. However, when the event is deleted, a decline message is sent successfully.

Steps to reproduce

1. Add your email account to Nextcloud Mail.
2. Configure Nextcloud to send iMIP responses through your email account in Nextcloud Mail.
3. Invite yourself to an event using Outlook Calendar.
4. Accept the invitation in Nextcloud Mail.
5. Observe that the status in Outlook isn’t updated and no email is sent.
6. Delete the event in Nextcloud Mail.
7. Observe that a decline message is sent to the organizer, updating the status.

Expected behavior

When accepting an invitation in Nextcloud Mail, an iMIP response should be sent to the organizer, updating the status in Outlook.

Nextcloud Server version

master

Nextcloud Mail version

main

Additional info

Accepting an invitation from Google Calendar triggers a response email to the organizer.

The EventComparisonService.findModified method returns null for the Outlook event, and as a result, no response is sent.

server/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php

Lines 132 to 134 in 1407a1d

	$modified = $this->eventComparisonService->findModified($newEvents, $oldEvents);
	/** @var VEvent $vEvent */
	$vEvent = array_pop($modified['new']);

[kesselb]

cc @SebastianKrupinski @st3iny

[SebastianKrupinski]

@kesselb

I am wondering how you accepted the invitation, Outlook.com invitations do not get discovered properly.

This is due to the iMip message being Base64 encoded.

--_000_CY4PR0401MB36678BE7D5F3B935DF4B16D4D9F72CY4PR0401MB3667_

Content-Type: text/calendar; charset="utf-8"; method=REQUEST
Content-Transfer-Encoding: base64

QkVHSU46VkNBTEVOREFSDQpNRVRIT0Q6UkVRVUVTVA0KUFJPRElEOk1pY3Jvc29mdCBFeGNoYW5n
ZSBTZXJ2ZXIgMjAxMA0KVkVSU0lPTjoyLjANCkJFR0lOOlZUSU1FWk9ORQ0KVFpJRDpFYXN0ZXJu
IFN0YW5kYXJkIFRpbWUNCkJFR0lOOlNUQU5EQVJEDQpEVFNUQVJUOjE2MDEwMTAxVDAyMDAwMA0K
VFpPRkZTRVRGUk9NOi0wNDAwDQpUWk9GRlNFVFRPOi0wNTAwDQpSUlVMRTpGUkVRPVlFQVJMWTtJ
TlRFUlZBTD0xO0JZREFZPTFTVTtCWU1PTlRIPTExDQpFTkQ6U1RBTkRBUkQNCkJFR0lOOkRBWUxJ
R0hU

[SebastianKrupinski]

@kesselb

Thanks for forwarding the outlook invite, you where working with, with that invite I was able to reproduce this...

When accepting a calendar invitation there is first a PUT request to create the event, this is then followed by a secondary PUT for the same event to update the status to ACCEPT. The second request triggers the iMIP process but this fails when we try to find a Uri for a external user...