icalendar-implementations

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iCalendar implementations

This is a list of calendar programs, applications and services that support the iCalendar RFC2445 standard.

In addition, please note any quirks or bugs with implementations' handling of iCalendar - we've already discovered some in the development of hCalendar and proxies like X2V.

libraries

libical

Open source C-based implementation of iCalendar.

Python iCalendar

Python implementation of iCalendar.

services

Google Calendar

http://calendar.google.com/

  • supports subscribing to "webcal:" and "http:" URLs to iCalendar

products

Apple Calendar.app

Apple Calendar.app, formerly known as iCal.

  • platform: OSX
  • handles "webcal:" URLs and supports subscribing to events.

Apple iCal 2.0.5

Apple iCal.app 2.0.5 build 1069 (AppleiCal205)

iCal 2.0.5 notes
  • Requires dates and date-times without separators. Apple iCal 2.0.5 (and probably other versions) appears to require dates without "-" and times without ":" which appears to be consistent with the iCalendar spec due to:
    • iCalendar section 4.3.4 Date - "date-value = date-fullyear date-month date-mday" (no separators)
    • iCalendar section 4.3.12 Time - "time = time-hour time-minute time-second [time-utc]" (no separators)

As a result Apple iCal 2.0.5 ignores date and date-time properties (e.g. DTSTART, DTEND, etc.) when date components (year, month, day) are separated by "-" or when time components (hours, minutes, seconds) are separated by ":" (both as allowed by ISO8601 and required by RFC3339).

However per accessibility research, dates and times with separators are more readable and accessible, and consequently explicitly allowed by hCalendar.

Thus hCalendar processors which generate iCalendar files MUST handle parsing hCalendar date and date-time properties (e.g. DTSTART, DTEND, etc.) with separators, and remove separators when converting to iCalendar.

  • Requires date-times with seconds explicitly specified. Apple iCal 2.0.5 (and probably other versions) appears to require date-times with the seconds explicitly specified, which appears to be consistent with the iCalendar spec:
    • iCalendar section 4.3.12 Time - "time = time-hour time-minute time-second [time-utc]" (no separators)

However in practice (see hcalendar-examples-in-wild) hCalendar date-time properties often omit the seconds because when they are "00" for simplicity and easier/quicker readability.

Thus hCalendar processors which generate iCalendar files MUST handle parsing hCalendar date-time properties (e.g. DTSTART, DTEND, etc.) without the seconds explicitly specified, and imply "00" seconds when converting to iCalendar.

  • Requires floating or UTC date-times. Apple iCal 2.0.5 (and probably other versions) appears to require date-times which are either floating (no time zone) or explicitly specified to be UTC and ignores date-times which use timezone offsets, which appears to be consistent with the iCalendar spec:
    • iCalendar section 4.3.12 Time - "time = time-hour time-minute time-second [time-utc]" (no separators) and:

      The form of time with UTC offset MUST NOT be used. For example, the following is NOT VALID for a time value:

      230000-0800        ;Invalid time format

However, in practice (see hcalendar-examples-in-wild) hCalendar date-time properties often state the timezone offset in order to make the human visible time consistent with the machine readable time for easier verification (minimize DRY divergence probability).

Thus hCalendar processors which generate iCalendar files MUST handle parsing hCalendar date-time properties (e.g. DTSTART, DTEND, etc.) with an explicit timezone offset, and convert the specified date-time value to a UTC value when converting to iCalendar.

All hCalendar processor requirements above should be documented thoroughly in hcalendar-parsing.

Apple Calendar.app 8.0 (2092.3)

Timezone handling: Calendar.app is incompatible with timezone-aware dates produced by the Python iCalendar implementation which puts quotation marks around TZIDs. See this gist for details.

KOrganizer

  • platforms: All Linux, *BSD, etc. (Wherever KDE runs)
  • supports the "webcal:" protocol, as well as "http:", "ftp:", "fish:", etc.

Evolution

  • platform: Fedora Core 3
  • supports "webcal:" protocol

Sunbird

Mozilla Sunbird

  • platforms: Windows XP, others?
  • supports "webcal:" protocol

Microsoft Outlook

Microsoft Outlook 2007

Microsoft Outlook 2007 (MSOutlook2k7)

  • platforms: Windows
  • supports importing and subscribing to .ics files, "webcal:" URLs, etc.

Microsoft Outlook 2003

Microsoft Outlook 2003 (MSOutlook2k3)

  • platforms: Windows
  • supports importing .ics files
MSOutlook2k3 general comments

For importing, MSOutlook2k3 apparently requires VEVENTS to have UID, DTSTAMP, and METHOD properties. (citation/platform/date tested info needed). If any of the three is not present, returns this message: 

This error can appear if you have attempted to save a recurring Lunar appointment in iCalendar format.
To avoid this error, set the appointment option to Gregorian instead of Lunar.

After some testing, this seems to be the generic message to indicate a problem with event import.

No such restriction is placed on vCalendar 1.0 events. So, if VERSION:1.0 is output instead of VERSION:2.0, the only required field is DTSTART. Note that VERSION property may be omitted. In this case, value inferred as 1.0.

  • UID and DTSTAMP is required for Outlook to import. GeoffWebb 14:03, 9 Dec 2005 (PST)


Potential Security Related Issue w/ Outlook 2003 and Standard Account

I've been all over the web tracing the "Lunar" exception. I believe I'm come across another lunar permutation. I have an XP box running Outlook 2003 SP3 with Admin privileges, and I have an XP box running Outlook 2003 SP3 (same build number) running under a standard account. The .ics will try to import correctly under the Admin account (aka, it will prompt you for acceptance, everything working as expected). HOWEVER, the same .ics file will throw the "lunar" exception on the ~standard~ account.

Here is my environment information just in case you're bumping your head on this issue.

Outlook 2003 with SP3 Build Number : 11.8325.8329

.ics file contents (aka, "known to work" file contents under the Admin account) 

BEGIN:VCALENDAR
VERSION:2.0
PRODID:www.testMeiCalendar.net
METHOD:REQUEST
BEGIN:VEVENT
DTSTART:20101231T230000
DTEND:20110101T010000
SUMMARY:New Years Eve Reminder
LOCATION:Downtown
DESCRIPTION:Let's get together for New Years Eve
UID:ABCD1234
SEQUENCE:0
DTSTAMP:20101125T112600
END:VEVENT
END:VCALENDAR

To be honest, I probably will just abandon trying to use it for this project because of this issue. But I wanted to report it, so someone doesn't waste a day thinking the issue is the contents of the .ics file.

MSOutlook2k3 sample importable iCalendar
BEGIN:VCALENDAR
VERSION:2.0
METHOD:PUBLISH
BEGIN:VEVENT
UID:0
DTSTAMP:20060601T080000
DTSTART:20060601T080000
END:VEVENT
END:VCALENDAR
MSOutlook2k3 sample importable vCalendar
BEGIN:VCALENDAR
BEGIN:VEVENT
DTSTART:20060601T080000
END:VEVENT
END:VCALENDAR

Fantastical

  • Platform: Mac and iOS
  • supports importing ICS files and subscribing using webcal (tested using Facebok URL)
  • Implemented using libical

notes

  • the "webcal:" URL protocol scheme is non-standard.

contributors

related pages

This specification is a work in progress. As additional aspects are discussed, understood, and written, they will be added. These thoughts, issues, and questions are kept in separate pages.

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