Calendar invites sent through mail providers have incorrect headers for the ics attachment

[ChristophWurst]

Steps to reproduce

1. Invite another user to an event

Expected behavior

I receive an email where my mail client offers to import an event and respond to the RSVP

Content-Type: text/calendar; method=REQUEST; name=event.ics
Content-Transfer-Encoding: base64
Content-Disposition: inline; name=event.ics; filename=event.ics

^ from an invite before we had mail providers.

Actual behavior

Content-Type: text/calendar; name=event.ics; method=REQUEST
Content-Disposition: attachment; filename=event.ics
Content-Transfer-Encoding: 8bit

^ at least for Gnome Evolution, this doesn't make the ics file show as invite. It shows as attachment.

Mail app version

4.1.0-beta2

Nextcloud version

No response

Mailserver or service

No response

Operating system

No response

PHP engine version

None

Nextcloud memory caching

No response

Web server

None

Database

None

Additional info

No response

[SebastianKrupinski]

Tested

Confirmed

Issue

Mail app sending does not have support for inline attachments

Resolution

Alter OCA\Mail\Service\MailTransmission::sendMessage() line 88 and 124 to handle inline attachments
Alter OCA\Mail\Db\LocalMessageAttachement to handle inline attachments
Alter OCA\Mail\Provider\Command\MessageSend::perform() to handle inline attachments

[ChristophWurst]

This is a blocker for the release of v4.1.0

[SebastianKrupinski]

After doing some extensive testing and RFC reading, calendar invitations should NOT be sent as inline attachments.

RFC Examples
https://datatracker.ietf.org/doc/html/rfc2447#section-4

Therefore the current implementation is correct and the previous implementation with inline attachments seems to have been flawed.

[ChristophWurst]

^ at least for Gnome Evolution, this doesn't make the ics file show as invite. It shows as attachment.

@SebastianKrupinski can you explain why previous invitations were recognized as such by Evolution and the ones sent through the provider mechanism aren't?

[SebastianKrupinski]

Please see #10851 for a possible solution.

After testing several other software suites, I noticed that the content disposition on 'text/calendar' event attachments is not set to nothing (missing). Although according to the RFC a missing Content-Disposition should be treated as Content-Disposition: attachment some clients seem to treat a missing disposition differently which in turn causes the event attachments to not be recognized properly.