Recurring events with timezone

Hendrik Helwich h.helwich at
Wed Oct 20 09:34:07 CEST 2010

Am 20.10.2010 08:46, schrieb Joon Radley:
> Hi Hendrik,
> This is an excellent example. Your argument is that the incorrect conversion in the client of UTC ->  local time can be fixed by adding time zone information to the object.
> Lets run a use case with this. User A is the creator of the object and is situated in Johannesburg. User B that shares the folder is situated in Germany (for the daylight savings time).
> The problem is: UTC ->  User B local time is incorrect.
> Your suggested solution is: User A Time Zone + User A Local Time ->  UTC ->  User B local time
> UTC ->  User B local time conversion will still be broken, as you need User B TZ to fix the incorrect calculation. Thus by adding the User A TZ information to the object no problem is solved.
> The only time when the TZ information will help is when User A and User B is in the same time zone and they both know it. All other user cases do not benefit from User A’s TZ information.
> You are trying to fix a client “bug” by providing it with information, which will only be valid/helpful in very limited cases.
> By fixing the UTC->  locale conversion you will fix all the use cases. The localtime function has never failed me. Is there a problem with it on your OS?

Hi Joon,

timzones are working fine on my OS :-) the UTC time can surely be used 
for single events/tasks. But it is possible to code recurring events in 
kolab so you must add timezones to the format even if they are complex. 
This is obvious i think. Otherwise it is not possible to fix this problem.

To the example:
The correct way would be to make the kolab xml with timezone e.g. like this:

<?xml version="1.0" encoding="UTF-8"?>
<event version="1.0">
<product-id>KOrganizer 3.5.9 (enterprise35 20100805.1161816), Kolab
	<standard-time name="CET">
	<daylight-saving-time name="CEST">
			<day count="-1">sunday</day>
			<day count="-1">sunday</day>
<recurrence cycle="monthly" type="daynumber">
	<range type="none"></range>

(I added the timezone block and changed start-date and end-date to the 
local times)
My Kontact now can see that i am in the same time zone as it is stored 
in the event and does not need to convert the local times. It can show 
me the 10 o'clock start-time for all the year. It also can do the stored 
local -> UTC -> local conversion but this would be an identity function 
and will cause the same result.

If i am in Johannesburg my Kontact can convert each start-time to the 
UTC time by using the stored time zone from germany and then convert it 
to the system local time.
In october:
german local 10 -> UTC 8 -> south africa local 10
in november:
german local 10 -> UTC 9 -> south africa local 11

So this example could be calculated correctly. Without storing the time 
zone information of germany that could not be possible.



> [..]

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