[dev] Thunderbird/CalDAV: Snoozing events may lead to Itip spam (introducing ical storage)

[Ralf Lang]

I had some user reports for a scenario where external attendees
complained about event update spam scenarios:

1) Minor, irrelevant updates caused event update mails (like for example
snoozing an alert)

2) Kronolith and Thunderbird kept modifying an event due to kronolith
"forgetting" some X-attribute thunderbird kept adding on parsing. This
was especially annoying for events already past.


This commit would restrict itips

https://github.com/maintaina-com/kronolith/commit/71510e8d7f24ab944637d0d62be914b8b307b452

- No iTips sent out for past events
- No iTips sent out if not at least one relevant attribute has been changed

Another commit introduces storing the whole incoming iCalendar event for
further use.
https://github.com/maintaina-com/kronolith/commit/3d585423a4cf484f4e31c25a4f13139f356a47a7

Storing is optional, there is also a Null driver.

That feature is still incomplete, iCalendars are not deleted on
deleting/moving events.

I'm not sure if we should explicitly whitelist specific X- attributes
for re-applying on caldav get or if we only should blacklist those horde
recognizes/handles itself (like X-MOZ-LASTACK)
Or if the administrator should configure this.

The icalendar storage may be useful for other applications of external
or expensive to re-get icalendars.

Any suggestions welcome.

-- 
Ralf Lang
Linux Consultant / Developer
Tel.: +49-170-6381563
Mail: lang at b1-systems.de
B1 Systems GmbH
Osterfeldstraße 7 / 85088 Vohburg / http://www.b1-systems.de
GF: Ralph Dehner / Unternehmenssitz: Vohburg / AG: Ingolstadt,HRB 3537