Issue Summary

When we subscribe 2 way sync team calendar via F-Droid (Android app) which recommended by our documentation, we get an 500 error saying the remote resource is invalid.

• The calendars show up while adding on the mobile app, however the problem comes when we try to synchronise.
• The problem is replicable with the android phone, however there are no issue with iphone IOS calendar following the steps in this documentation. Performing the steps in the documentation allow us to successfully synchronise the team calendar to our iPhone IOS calendar without any issue.

This is reproducible on Data Center: Yes

Steps to Reproduce

Step-1. Install the DAVdroid app on your device.

Step-2. Grab your Team Calendars URL
In Confluence:

• Choose the Subscribe button at the top of your calendar.
• Select Google Calendar (Android) from the Calendar app dropdown.
• Make a note of the Calendar URL.

Step-2. Subscribe to the calendar in the DAVdroid app
On your Android device:

• In DAVdroid, go to Add account > Login with URL and user name.
• Enter the Confluence URL you copied earlier.
• Enter your Confluence username and password.
• Follow the prompts to name your account. 
• Select the calendars you want to display in the Android Calendar app.
• Open the Calendar app on your device. Your Team Calendars will be listed under the account name. 
• Click Synchronize now

We used android phone to replicate the behavior and captured below screenshot and recording.

Screen_Recording.mp4

Expected Results

Team Calendars events synchronize successfully with DAVdroid app for Android

Actual Results

Team Calendars events doesn't synchronize with DAVdroid app for Android

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available.

Note

• In the logs, we are able to see the set of stack trace after enable the calendar debug (com.atlassian.confluence.extra.calendar3) in atlassian-confluence.log and the F-Droid(Adroid app) debug log
  atlassian-confluence.log

  Caused by: java.lang.UnsupportedOperationException
      at com.atlassian.confluence.extra.calendar3.caldav.configuration.CalendarCalDAVAuthProperties.getMaxUserEntitySize(CalendarCalDAVAuthProperties.java:19)
      at org.bedework.caldav.server.CaldavBWIntf.generatePropValue(CaldavBWIntf.java:1944)
      ... 383 more
  

  F-Droid(Adroid app) debug log

  EXCEPTION
  at.bitfire.dav4jvm.exception.HttpException: HTTP 500 
  	at at.bitfire.dav4jvm.DavResource.checkStatus(DavResource.kt:3)
  

• After looking into the exception from Confluence and a debug log from DavDroid, we could see that DavDroid request properties from Team Calendars.
• Then in Confluence there is an exception as above stacktrace.

  <?xml version='1.0' encoding='UTF-8' ?>
  <propfind xmlns="DAV:" xmlns:CAL="urn:ietf:params:xml:ns:caldav" xmlns:CARD="urn:ietf:params:xml:ns:carddav">
     <prop>
         <CAL:max-resource-size />
         <supported-report-set />
         <n0:getctag xmlns:n0="http://calendarserver.org/ns/" />
         <sync-token />
     </prop>
  </propfind> 
  

• As we can see Team Calendars was trying to serve the request but hit UnsupportedOperationException.
• It seem that in Team Calendars it does not support property "max-resource-size" (property description) which then linked to the method.