Tuesday, December 22, 2015

Calendar sharing between Google and iCloud is very confusing: webcal vs http vs. https

A book project forced me to dig into a perennially painful topic — Calendar sharing and subscription in iOS and OS X (MacOS Yosemite) for Google and Apple.

I discovered:

  • iCloud uses Webcal protocol links to share public calendars among iCloud users. Google can parse these, but it in my tests no events appeared. Old web pages say Apple blocks Google access to public iCloud calendars (robots.txt).
  • Google uses https links to an ICS file to share public calendars. Yosemite Calendar.app can use these links and iOS Calendar.app can use these URLs [1], but iCloud.com Calendar can’t. At least in my testing, with Yosemite, Calendar.app on MacOS and Calendar.app on iOS don’t share these calendar subscriptions.
  • Safari.app on iOS will pass an iCloud webcal URL link to Calendar.app and this will trigger a calendar subscription. Google ICS file (https) links won’t work, renaming them to webcal doesn’t work either (I think it might have in the past).
This confusing situation is reminiscent of the complex hoops required to support CalDAV sync for multiple Google Calendars in iOS and MacOS. Apple and Google have very different models for calendaring and they also appear to have different approaches to implementing CalDAV (and they’re probably on different CalDAV versions too).
On balance I much prefer Google’s approach to managing Calendars. On the other hand, if one stays entirely within iCloud and ignores Google calendar sharing, then Apple’s Calendars are simpler to use and understand and are better documented.
Don’t bother trying to share a public iCloud Calendar to the world, when Apple says “public” they really mean “iCloud”. If you do want to subscribe to a Google Calendar on your iPhone or MacOS, you will have to do it separately on every device you use (it my testing these subscriptions do not sync, I do hope they are backed up).
If you are sharing a Google Calendar, you’ll want to provide directions for iOS and MacOS users and you’ll need to explain that they won’t be able to see the calendar using iCloud.com.
Sample links used in my testing:
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[1] Documentation: Subscribe to a calendar. Go to Settings > Mail, Contacts, Calendars, then tap Add Account. Tap Other, then tap Add Subscribed Calendar. Enter the server and filename of the .ics file to subscribe to. You can also subscribe to an iCalendar (.ics) calendar published on the web, by tapping a link to the calendar. The second part of this documentation is incorrect, you can only subscribe for a webcal URL and only iCloud seems to produce the “right” ones.

See also (references)

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