Recurring events with timezone

[Hendrik Helwich]

Hi,

thank you for the active discussion on the kolab tz issue :-)
I think some interesting thoughts where argued here. But unfortunately i have 
to act now and i don't have the feeling something is going to change in the 
kolab format and the kolab clients with regard to the tz problem in the near 
future.
So i think we will implement it like it is described below to be most 
interoperable between the kolab format and the iCalendar format.

Unfortunately the shown times in evolution and kontact/outlook will be 
different for many recurring events due to the tz restrictions in the kolab 
format and also because of the discussed tz bug in kontact/toltec.


Conversion iCalendar -> Kolab

* convert the stored time & stored tz from iCalendar to an UTC time and store 
it in the kolab item.
* Store the tz from the iCalendar in the kolab item. I created an attached an 
XML schema document which describes the structure and constraints of this 
timezone element.
E.g. for the german tz:

<timezone>
        <id>Europe/Berlin</id>
        <standard-time name="CET">
                <offset>+0100</offset>
        </standard-time>
        <daylight-saving-time name="CEST">
                <offset>+0200</offset>
                <start-date>
                        <month>march</month>
                        <day>sunday</day>
                        <daynumber>-1</daynumber>
                </start-date>
                <end-date>
                        <month>october</month>
                        <day>sunday</day>
                        <daynumber>-1</daynumber>
                </end-date>
        </daylight-saving-time>
</timezone>

* So at least the time is shown correctly in kolab clients until the DST rules 
of the events tz or the users local tz does change.
* timezone tag must be preserved by other kolab clients according to the kolab 
format specification [1].

Conversion Kolab -> iCalendar

* If the kolab format contains a timezone tag then convert it to an iCalendar 
timezone else use UTC timezone.
* No conversion loss for kolab format here but we have a problem even for UTC 
timezone because of the discussed bug in the kolab clients. The shown time in 
the kolab clients and evolution can be different until the bug is not fixed.
* Convert the stored UTC time to a time which has the stored tz.

Best Regards,

Hendrik



[1] http://kolab.org/doc/kolabformat-2.0rc7-html/x123.html
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