Recurring rule: COUNT=0 added to endless custom rules

[grisumedia]

If you define a custom recurrence rule like "every week on Wednesday, forever", the recurrence rule created by tasks will contain COUNT=0, which creates problems with other consumers like the ICAL.NET library that check for COUNT>=1.

BEGIN:VTODO
DTSTAMP:20230301T105803Z
UID:922187406211724545
CREATED:20230301T105234Z
LAST-MODIFIED:20230301T105759Z
SUMMARY:Weekly on Wed
PRIORITY:5
RRULE:FREQ=WEEKLY;COUNT=0;INTERVAL=1;BYDAY=WE
X-APPLE-SORT-ORDER:625234142
DUE;VALUE=DATE:20230301
DTSTART;VALUE=DATE:20230301
BEGIN:VALARM
TRIGGER;RELATED=END:PT0S
ACTION:DISPLAY
DESCRIPTION:Default Tasks.org description
END:VALARM
END:VTODO

The problem is quite easy to solve by leaving COUNT=0 out.
I'm not absolutely sure if COUNT=0 is really forbidden, as RFC 5545 says

       recur-rule-part = ( "FREQ" "=" freq )
                       / ( "UNTIL" "=" enddate )
                       / ( "COUNT" "=" 1*DIGIT )

Checked with Tasks 13.1.1

[grisumedia]

By the way, Thunderbird with Lightning seems to entirely remove the faulty recurrence rule:

RRULE:FREQ=WEEKLY;COUNT=0;INTERVAL=1;BYDAY=FR
X-LIC-ERROR;X-LIC-ERRORTYPE=VALUE-PARSE-ERROR:Can't parse as RECUR value in
  RRULE property. Removing entire property: FREQ=WEEKLY\;COUNT=0\;INTERVAL=
 1\;BYDAY=SA

Which leads to recurring events not being recurrent any more and so they are gone once they are done.

[abaker]

Thanks for bringing this to my attention. Tasks previously used google's rfc-2445 library for processing recurrence rules, and I think COUNT=0 was a hack to get it to play nice with iCal4j recurrence. I removed the rfc-2445 library long ago, but didn't remove this hack

32eed65

[andrewrothman]

I am seeing similar today, synced via DAVx5.

I am able to reliably reproduce the issue by deleting the task and creating another.

Let me know if there is any other information or assistance I can provide. Thanks!

Tasks v13.1.2 on a Samsung Galaxy s10e, Android 12, One UI 4.1

HTTP REQUEST
Request{method=PUT, url=REDACTED, headers=[If-None-Match:*, User-Agent:DAVx5/4.3.5.2-gplay (2023/08/07; dav4jvm; okhttp/4.11.0) Android/12, Accept-Language:en-US, en;q=0.7, *;q=0.5]}
BEGIN:VCALENDAR
VERSION:2.0
PRODID:DAVx5/4.3.5.2-gplay ical4j/3.2.11 (org.tasks)
BEGIN:VTODO
DTSTAMP:20230825T195744Z
UID:315556882140164719
CREATED:20230825T195729Z
LAST-MODIFIED:20230825T195729Z
SUMMARY:Example recurring task
STATUS:NEEDS-ACTION
RRULE:FREQ=WEEKLY;COUNT=0;INTERVAL=1;BYDAY=FR
X-APPLE-SORT-ORDER:709724834
END:VTODO
END:VCALENDAR


HTTP RESPONSE
Response{protocol=http/1.1, code=403, message=Forbidden, url=REDACTED
<?xml version="1.0" encoding="utf-8"?>
<D:error xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
  <C:valid-calendar-data/>
  <D:responsedescription>Can't parse as RECUR value in RRULE property. Removing entire property: FREQ=WEEKLY;COUNT=0;INTERVAL=1;BYDAY=FR</D:responsedescription>
</D:error>

[abaker]

Can you update your app? This fix went into v13.2, and the latest version is v13.5.1

[andrewrothman]

Nevermind. I checked and realized that F-Droid wasn't updating Tasks.org. I am no longer seeing the above issue on v13.5.1.