fix: prevent CalDAV duplicate invitations with RFC-compliant SCHEDULE-AGENT by yuvrajangadsingh · Pull Request #22434 · calcom/cal.com

yuvrajangadsingh · 2025-07-11T19:55:50Z

Summary

Adds SCHEDULE-AGENT=CLIENT to ATTENDEE lines in CalDAV createEvent and updateEvent operations per RFC 6638 Section 7.1. This tells CalDAV servers (Fastmail, NextCloud, etc.) that the client handles scheduling, preventing duplicate invitation emails.

Implementation Details

This implementation includes full RFC compliance:

RFC 5545 line folding: Lines exceeding 75 octets are properly folded with CRLF + space
UTF-8 aware byte counting: Correctly handles international characters in attendee names
Proper ATTENDEE parsing: Handles :mailto: format correctly
Idempotent: Skips lines that already have SCHEDULE-AGENT parameter

What Changed

Added foldLine() helper for RFC 5545 compliant line folding
Added addScheduleAgentClient() helper that adds the parameter with proper folding
Applied to both createEvent and updateEvent in CalendarService.ts

Test Plan

Create CalDAV event with attendees - verify no duplicate emails from server
Update CalDAV event - verify no duplicate emails
Test with long attendey names (international characters) - verify line folding works
Verify existing SCHEDULE-AGENT parameters are preserved

/claim #9485

vercel · 2025-07-11T19:55:56Z

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yuvrajangadsingh · 2025-07-11T20:16:23Z

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anikdhabal

Thanks for your work

yuvrajangadsingh · 2026-01-22T14:59:35Z

Thanks @anikdhabal for reviewing and merging! Really appreciate the time you put into this.

saschafoerster · 2026-01-25T12:10:51Z

I just tested it with "Kerio", connected via CalDAV. Kerio still sends a secondary invitation. What makes this bad is that the timezone is different in the mails from Cal.com and from Kerio calendar invitation, so poeple show up to GMT, when they should be in Europe/Berlin timezone.

Maybe in relation to https://github.com/calcom/cal.com/discussions/24473

yuvrajangadsingh · 2026-02-05T07:24:29Z

@PeerRich @keithwillcode My PR #22434 was merged and closed issue #9485. I forgot to include /claim #9485 in the PR body at the time. Could you please manually award the $500 bounty? Thank you!

anikdhabal · 2026-02-21T05:25:32Z

@yuvrajangadsingh We will ask our team to tip you, but this isn't a complete fix—it looks like two remaining issues were not addressed. Please check this: #28112

Kindly try to address them in the best possible way in a separate pr

yuvrajangadsingh · 2026-02-21T08:30:41Z

@anikdhabal done — opened #28115 addressing both remaining issues (UID consistency + missing VTIMEZONE). thanks for flagging #28112, used it as reference for the fixes.

PeerRich · 2026-02-21T17:02:47Z

/tip 500

algora-pbc · 2026-02-21T17:03:01Z

🎉🎈 @yuvrajangadsingh has been awarded $500 by Cal.com, Inc.! 🎈🎊

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volnei mentioned this pull request Jan 22, 2026

fix: merge main to resolve lint errors for caldav-duplicate-invites PR #27119

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Merge branch 'main' into fix/caldav-duplicate-invites

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anikdhabal merged commit 45ea59c into calcom:main Jan 22, 2026
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yuvrajangadsingh deleted the fix/caldav-duplicate-invites branch January 22, 2026 14:53

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fix(caldav): consistent UID and VTIMEZONE in iCalendar output #28112

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fix(caldav): consistent UIDs and VTIMEZONE in iCalendar output #28115

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Summary

Implementation Details

What Changed

Test Plan

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