Incorrect Timezone Handling in CalDAV Synchronization Causes Time Shifts

[sandro-byte32]

Description:

When syncing events with CalDAV, there is a recurring issue where event times are shifted by one hour. This happens because the synchronization process incorrectly assumes that DTSTART and DTEND values are in UTC, even when they are actually in the local timezone (e.g., Europe/Vienna).

Steps to Reproduce:

Create an event in the calendar with a start time of 09:00 in Europe/Vienna. Synchronize the event with CalDAV.
Observe that the start time in the synchronized system is incorrectly shifted to 10:00. Root Cause Analysis:

The issue arises in the convert_caldav_event_to_array_event method:

private function convert_caldav_event_to_array_event(VEvent $vevent, DateTimeZone $timezone_object): array {
    $utc_timezone_object = new DateTimeZone('UTC'); // UTC is incorrectly assumed here
    
    $start_date_time_object = new DateTime((string) $vevent->DTSTART, $utc_timezone_object);
    $start_date_time_object->setTimezone($timezone_object);
}

This method assumes all DTSTART and DTEND values are in UTC. However, in many cases:

The DTSTART value contains a timezone identifier (e.g., TZID=Europe/Vienna). The value is implicitly in the local timezone, but this is not indicated in the data. As a result, the synchronization logic performs an unnecessary conversion from UTC to the local timezone, causing an unwanted shift.

[alextselegidis]

Hello!

Thanks for this PR.

I will review and merge accordingly.

Alex Tselegidis, Easy!Appointments Creator Need a customization? Get a free quote!

[alextselegidis]

Hello!

I had to make some minor adjustments but did merge the logic for parsing the timezone values.

Thanks for providing this PR.

Alex Tselegidis, Easy!Appointments Creator Need a customization? Get a free quote!