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MS timezone "Central America Standard Time" is transformed with DST #157

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ArnyminerZ opened this issue Jul 8, 2024 · 5 comments
Open

MS timezone "Central America Standard Time" is transformed with DST #157

ArnyminerZ opened this issue Jul 8, 2024 · 5 comments
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@rfc2822 @ArnyminerZ
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3rd party related to a third-party product (library, …) bug Something isn't working dependent

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@ArnyminerZ
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ArnyminerZ commented Jul 8, 2024 •
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ICS files with the timezone "Central America Standard Time", which should be the one used in Guatemala. It looks like it gets converted to Chicago, which may break summer time I think.

The problem seems to come from files generated from Outlook.

Example ICS file: internal

BEGIN:VCALENDAR
PRODID:-//Microsoft Corporation//Outlook 16.0 MIMEDIR//EN
VERSION:2.0
METHOD:REQUEST
X-MS-OLK-FORCEINSPECTOROPEN:TRUE
BEGIN:VTIMEZONE
TZID:Central America Standard Time
BEGIN:STANDARD
DTSTART:16010101T000000
TZOFFSETFROM:-0600
TZOFFSETTO:-0600
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
ATTENDEE;CN="Richard Martinez";RSVP=TRUE:mailto:[email protected]
CLASS:PUBLIC
CREATED:20240703T151754Z
DESCRIPTION:test 2 \n\n
DTEND;TZID="Central America Standard Time":20240703T103000
DTSTAMP:20240703T151352Z
DTSTART;TZID="Central America Standard Time":20240703T100000
LAST-MODIFIED:20240703T151754Z
LOCATION:remoto
ORGANIZER;CN="Jose de San Martin Juarez":mailto:[email protected]
PRIORITY:5
SEQUENCE:0
SUMMARY;LANGUAGE=es-gt:Reunion prueba 2 Calendario Outlook
TRANSP:OPAQUE
UID:040000008200E00074C5B7101A82E00800000000C08BCB4229CDDA01000000000000000
	010000000D3656D305AAF6A448B2B7D02C21E2448
X-ALT-DESC;FMTTYPE=text/html:<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//E
	N">\n<HTML>\n<HEAD>\n\n<META NAME="Generator" CONTENT="MS Exchange Server 
	version 16.0.17726.20016">\n<TITLE></TITLE>\n</HEAD>\n<BODY>\n<!-- Convert
	ed from text/rtf format -->\n\n<P><FONT FACE="Aptos">test 2</FONT>\n</P>\n
	\n</BODY>\n</HTML>
X-MICROSOFT-CDO-BUSYSTATUS:BUSY
X-MICROSOFT-CDO-IMPORTANCE:1
X-MICROSOFT-DISALLOW-COUNTER:FALSE
X-MS-OLK-APPTSEQTIME:20240703T151352Z
X-MS-OLK-AUTOFILLLOCATION:FALSE
X-MS-OLK-CONFTYPE:0
BEGIN:VALARM
TRIGGER:-PT10M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR

Depends on ical4j/ical4j#709
@ArnyminerZ ArnyminerZ added the bug Something isn't working label Jul 8, 2024
@ArnyminerZ
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ArnyminerZ commented Jul 8, 2024 •
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To reproduce:

@Test
fun testGuatemala() {
    javaClass.classLoader!!.getResourceAsStream("events/guatemala.ics").use { stream ->
        val events = Event.eventsFromReader(InputStreamReader(stream, Charsets.UTF_8))
        assertEquals(1, events.size)
        val event = events[0]
        event.dtStart!!.let { start ->
            val instant = Instant.ofEpochMilli(start.date.time)
            val dateTime = instant.atZone(ZoneId.of("America/Guatemala"))
            println(start.timeZone.id)
            assertEquals(
                ZonedDateTime.of(2024, 7, 3, 10, 0, 0, 0, ZoneId.of("America/Guatemala")),
                dateTime
            )
        }
    }
}

Fails with:

expected:<2024-07-03T10:00-06:00[America/Guatemala]>
but was: <2024-07-03T09:00-06:00[America/Guatemala]>

@ArnyminerZ
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In any case, I think the timezone is directly not correctly defined in the ics. It doesn't specify any daylight saving, and "Central America Standard Time" is ambiguous I think, so that may be the issue here.

@rfc2822
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rfc2822 commented Jul 9, 2024 •
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I agree:

  1. Central America Standard Time is mapped to US/Central by the MS timezone transformation rules. The transformation happens before evaluating the actual MS timezone.
  2. US/Central is an alias for America/Chicago. So the DTSTART is treated as if would have America/Chicago timezone.
  3. America/Chicago has DST, while Central America Standard Time apparently doesn't (at least given the original VTIMEZONE and some non 100% reliable information on the Web).
  4. So this causes the one-hour difference because the event is in summer so DST is applied.

I also found a table on unicode.org that suggests these mappings:

Central America Standard Time	001	America/Guatemala
Central America Standard Time	BZ	America/Belize
Central America Standard Time	CR	America/Costa_Rica
Central America Standard Time	EC	Pacific/Galapagos
Central America Standard Time	GT	America/Guatemala
Central America Standard Time	HN	America/Tegucigalpa
Central America Standard Time	NI	America/Managua
Central America Standard Time	SV	America/El_Salvador
Central America Standard Time	ZZ	Etc/GMT+6

I think Etc/GMT+6 would be the best choice because it's generic (although Etc/GMT+6 with plus actually means -06:00), or one of the cities/countries if it must be a city/country.

So as I understand it, this would have to be updated in ical4j in the MS outlook mapping file. @ArnyminerZ Can you please prepare an issue/PR for ical4j and link it as dependency?

@rfc2822 rfc2822 added the 3rd party related to a third-party product (library, …) label Jul 9, 2024
@rfc2822 rfc2822 changed the title Timezone for Guatemala is not converted properly MS timezone "Central America Standard Time" is transformed with DST Jul 9, 2024
@ArnyminerZ
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Okay, I'll open a PR for that, however, I don't know if it will be released on 3.* knowing that 4.* is already stable...

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github-actions bot commented Jul 9, 2024

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