Customized Time Zone

[jonnybergdahl]

Describe the bug
I am using Office365, but this library fails to parse my calendar due to TZID being set to "Customized Time Zone" on an event.

To Reproduce
This is the relevant part.

BEGIN:VEVENT
UID:040000008200E00074C5B7101A82E00800000000687C546B5596DA01000000000000000
 010000000309AE93C8C3A94489F90ADBEA30C2F2B
SUMMARY:Uffe
DTSTART;TZID=Customized Time Zone:20240426T140000
DTEND;TZID=Customized Time Zone:20240426T150000
CLASS:PUBLIC
PRIORITY:5
DTSTAMP:20250417T155647Z
TRANSP:OPAQUE
STATUS:CONFIRMED
SEQUENCE:0
LOCATION:
X-MICROSOFT-CDO-APPT-SEQUENCE:0
X-MICROSOFT-CDO-BUSYSTATUS:BUSY
X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY
X-MICROSOFT-CDO-ALLDAYEVENT:FALSE
X-MICROSOFT-CDO-IMPORTANCE:1
X-MICROSOFT-CDO-INSTTYPE:0
X-MICROSOFT-DONOTFORWARDMEETING:FALSE
X-MICROSOFT-DISALLOW-COUNTER:FALSE
X-MICROSOFT-REQUESTEDATTENDANCEMODE:DEFAULT
X-MICROSOFT-ISRESPONSEREQUESTED:FALSE
END:VEVENT

Expected behavior
I expect the ics to be read properly.

Additional context
I don't know what set it to "Customized Time Zone", I am using a mix of iPhone, Mac calendar and Outlook for my calendar.

[allenporter]

Hi,
(1) This is a partial ical file. Does that "Customized Time Zone" exist as a VTIMEZONE block somewhere?
(2) What is the exact error you're seeing?

I would expect this to work if it points to a VTIMEZONE block as required by the rfc5545 spec.

Qouting the block on TZID

Description: This parameter MUST be specified on the "DTSTART",
"DTEND", "DUE", "EXDATE", and "RDATE" properties when either a
DATE-TIME or TIME value type is specified and when the value is
neither a UTC or a "floating" time. Refer to the DATE-TIME or
TIME value type definition for a description of UTC and "floating
time" formats. This property parameter specifies a text value
that uniquely identifies the "VTIMEZONE" calendar component to be
used when evaluating the time portion of the property. The value
of the "TZID" property parameter will be equal to the value of the
"TZID" property for the matching time zone definition. An
individual "VTIMEZONE" calendar component MUST be specified for
each unique "TZID" parameter value specified in the iCalendar
object.

[jonnybergdahl]

This is the start of the ics. There are no other VTIMEZONE declarations in the file.

METHOD:PUBLISH
PRODID:Microsoft Exchange Server 2010
VERSION:2.0
X-WR-CALNAME:Kalender
BEGIN:VTIMEZONE
TZID:W. Europe Standard Time
BEGIN:STANDARD
DTSTART:16010101T030000
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=10
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T020000
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VTIMEZONE
TZID:UTC
BEGIN:STANDARD
DTSTART:16010101T000000
TZOFFSETFROM:+0000
TZOFFSETTO:+0000
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T000000
TZOFFSETFROM:+0000
TZOFFSETTO:+0000
END:DAYLIGHT
END:VTIMEZONE```

[allenporter]

OK, so the error is correct and the TZID does not point to a valid VTIMEZONE. I tried to piece together what I think the calendar looks like and entered it here:
https://icalendar.org/validator.html#results

It gets these two errors:

Invalid TZID value or missing VTIMEZONE component (Customized Time Zone) [near line # 34](javascript:void(0);)
Reference: [3.2.19. Time Zone Identifier](http://icalendar.org/iCalendar-RFC-5545/3-2-19-time-zone-identifier.html)
Invalid TZID value or missing VTIMEZONE component (Customized Time Zone) [near line # 34](javascript:void(0);)
Reference: [3.2.19. Time Zone Identifier](http://icalendar.org/iCalendar-RFC-5545/3-2-19-time-zone-identifier.html)

Here is the calendar I entered:

BEGIN:VCALENDAR
METHOD:PUBLISH
PRODID:Microsoft Exchange Server 2010
VERSION:2.0
X-WR-CALNAME:Kalender
BEGIN:VTIMEZONE
TZID:W. Europe Standard Time
BEGIN:STANDARD
DTSTART:16010101T030000
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=10
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T020000
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VTIMEZONE
TZID:UTC
BEGIN:STANDARD
DTSTART:16010101T000000
TZOFFSETFROM:+0000
TZOFFSETTO:+0000
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T000000
TZOFFSETFROM:+0000
TZOFFSETTO:+0000
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
UID:040000008200E00074C5B7101A82E00800000000687C546B5596DA01000000000000000
 010000000309AE93C8C3A94489F90ADBEA30C2F2B
SUMMARY:Uffe
DTSTART;TZID=Customized Time Zone:20240426T140000
DTEND;TZID=Customized Time Zone:20240426T150000
CLASS:PUBLIC
PRIORITY:5
DTSTAMP:20250417T155647Z
TRANSP:OPAQUE
STATUS:CONFIRMED
SEQUENCE:0
LOCATION:
X-MICROSOFT-CDO-APPT-SEQUENCE:0
X-MICROSOFT-CDO-BUSYSTATUS:BUSY
X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY
X-MICROSOFT-CDO-ALLDAYEVENT:FALSE
X-MICROSOFT-CDO-IMPORTANCE:1
X-MICROSOFT-CDO-INSTTYPE:0
X-MICROSOFT-DONOTFORWARDMEETING:FALSE
X-MICROSOFT-DISALLOW-COUNTER:FALSE
X-MICROSOFT-REQUESTEDATTENDANCEMODE:DEFAULT
X-MICROSOFT-ISRESPONSEREQUESTED:FALSE
END:VEVENT
END:VCALENDAR

Office 365 is creating invalid calendar files.

[jonnybergdahl]

OK, I can confirm this, just tested with another Office365 ics link.

Is there a workaround?

[allenporter]

I'm not sure I want to silently ignore invalid timezones. I generally like that this library is able to stay pretty strict to the spec, so my leaning is to not change the behavior.

• Report the issue to Office 365 given they aren't following the spec (i realize that is not likely very fast approach)
• You can search and replace ";TZID=Customized Time Zone" to remove them and it will fallback to local time
• You can replace with a valid timezone string

[jonnybergdahl]

I have reported it to Microsoft, but as you can guess I am not holding my breath.

I also see where you are coming from, only problem is that ical is used in Home Assistant wich has loads of users. So the chance of users using a non compliant ICS is almost guaranteed.

[allenporter]

Oh yeah but just to be clear, I work on home assistant and created this library so that home assistant could have a local calendar. I'm not saying "no", i'm saying "how"

[allenporter]

This is the fix I am suggesting home-assistant/core#144230 to fix this in remote calendar in Home Assistant. Respectfully, closing.

[allenporter]

OK, I ended up deciding to support this because:
(1) I saw on the home assistant issue there other separate issues, like windows timezones being used. I found the list of windows support windows timezones and how they map to linux timezones and it seemed OK to try to support.
(2) Most other major other calendar makers (Apple, Google) that also had spec conformance issues to resolve, and trying to do them in home-assistant would be to difficult since they may require deeper integration with the parser
(3) I thought about how to do it that wouldn't regress local calendar by introducing a compat module that can enable these features

Thanks for the report and help diagnosing the issues.

[allenporter]

Oh also I found this whole website where Microsoft documents all the standards they are violating:
https://learn.microsoft.com/en-us/openspecs/exchange_standards/ms-stanoical/75767f37-6738-4d09-bf27-a00ada5192b8
so I can see its clearly not a bug, but something intentional they are doing and unlikely to ever change.

[jonnybergdahl]

So Microsoft even document their bugs? Neat!

Anyways, a big thanks for your hard work!