Time of Event not correct with Events from Wordpress Events Manager

[ArnyminerZ]

Describe the bug
When using events provided from the Wordpress' Events Manager plugin, start time is parsed incorrectly.

To Reproduce
Steps to reproduce the behavior:

1. Try parsing the following ical:

   BEGIN:VCALENDAR
   VERSION:2.0
   BEGIN:VEVENT
   UID:xxx@xxx.de
   DTSTART;TZID=Europe/Berlin:20230905T200000
   DTEND;TZID=Europe/Berlin:20230905T210000
   SUMMARY:xxxxxxxxxxxxxxxxxxx
   END:VEVENT
   BEGIN:VTIMEZONE
   TZID:Europe/Berlin
   BEGIN:DAYLIGHT
   DTSTART:20230326T030000
   TZOFFSETFROM:+0100
   TZOFFSETTO:+0200
   TZNAME:CEST
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20231029T020000
   TZOFFSETFROM:+0200
   TZOFFSETTO:+0100
   TZNAME:CET
   END:STANDARD
   BEGIN:DAYLIGHT
   DTSTART:20240331T030000
   TZOFFSETFROM:+0100
   TZOFFSETTO:+0200
   TZNAME:CEST
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20241027T020000
   TZOFFSETFROM:+0200
   TZOFFSETTO:+0100
   TZNAME:CET
   END:STANDARD
   END:VTIMEZONE
   END:VCALENDAR
   

2. Example test code:

   import net.fortuna.ical4j.data.CalendarBuilder
   import net.fortuna.ical4j.model.Component
   import net.fortuna.ical4j.model.component.VEvent
   import org.junit.Test
   import java.io.StringReader
   
   class WordpressEventsManagerTest {
       @Test
       fun test_parsing() {
           val calendar = CalendarBuilder().build(
               StringReader(
                   "BEGIN:VCALENDAR\n" +
                       "VERSION:2.0\n" +
                       "BEGIN:VEVENT\n" +
                       "UID:xxx@xxx.de\n" +
                       "DTSTART;TZID=Europe/Berlin:20230905T200000\n" +
                       "DTEND;TZID=Europe/Berlin:20230905T210000\n" +
                       "SUMMARY:xxxxxxxxxxxxxxxxxxx\n" +
                       "END:VEVENT\n" +
                       "BEGIN:VTIMEZONE\n" +
                       "TZID:Europe/Berlin\n" +
                       "BEGIN:DAYLIGHT\n" +
                       "DTSTART:20230326T030000\n" +
                       "TZOFFSETFROM:+0100\n" +
                       "TZOFFSETTO:+0200\n" +
                       "TZNAME:CEST\n" +
                       "END:DAYLIGHT\n" +
                       "BEGIN:STANDARD\n" +
                       "DTSTART:20231029T020000\n" +
                       "TZOFFSETFROM:+0200\n" +
                       "TZOFFSETTO:+0100\n" +
                       "TZNAME:CET\n" +
                       "END:STANDARD\n" +
                       "BEGIN:DAYLIGHT\n" +
                       "DTSTART:20240331T030000\n" +
                       "TZOFFSETFROM:+0100\n" +
                       "TZOFFSETTO:+0200\n" +
                       "TZNAME:CEST\n" +
                       "END:DAYLIGHT\n" +
                       "BEGIN:STANDARD\n" +
                       "DTSTART:20241027T020000\n" +
                       "TZOFFSETFROM:+0200\n" +
                       "TZOFFSETTO:+0100\n" +
                       "TZNAME:CET\n" +
                       "END:STANDARD\n" +
                       "END:VTIMEZONE\n" +
                       "END:VCALENDAR"
               )
           )
   
           val event = calendar.getComponent<VEvent>(Component.VEVENT)
           assert(event.startDate.value == "20230905T200000") {
               "Start date does not match. Expected: <20230905T200000>. Actual: <${event.startDate.value}>"
           }
       }
   }

3. Assertion fails with Start date does not match. Expected: <20230905T200000>. Actual: <20230905T010000>.

Expected behavior
DTSTART should be 20230905T200000 and not 20230905T010000

Environment (please complete the following information):

• OS: Android
• Java Version: 17
• iCal4j Version: 3.2.12

[odin568]

Issue not only happening with Wordpress Events Manager, also have a case with eluceo/ical

Coming from bitfireAT/icsx5#198

[cbix]

I'm observing the same issue with iCal generated by the Wordpress Event Calendar Plugin. Two calendar feeds using the Europe/Berlin timezone to validate:

• Example 1
• Example 2

[cbix]

Issue seems to be related to timezone definition.
This (for example) causes the issue:

BEGIN:VTIMEZONE
TZID:Europe/Berlin
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:20240331T010000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:20241027T010000
END:STANDARD
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:20250330T010000
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:20251026T010000
END:STANDARD
END:VTIMEZONE

While this works as expected:

BEGIN:VTIMEZONE
TZID:Europe/Berlin
BEGIN:DAYLIGHT
DTSTART:19810329T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
TZNAME:CEST
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:19961027T030000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZNAME:CET
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
END:STANDARD
END:VTIMEZONE

[benfortuna]

Issue seems to be related to timezone definition. This (for example) causes the issue:

If I'm not mistaken, that first example doesn't include any current timezone information as the DTSTART values are all in the future.

[cbix]

the DTSTART values are all in the future

Good catch, I just reported this to the plugin's support forum. Seems like a few php-based generators use DateTimeZone::getTransitions($start, $end) which gives you a fixed set of tz transitions as opposed to proper rrules.

What's still weird is that while all timezone DTSTARTs are in the future, it also causes later events within those intervals to be parsed with the wrong time.