Query free/busy availability across a CalDAV calendar collection with the free-busy-query REPORT (RFC 4791)
domain: datatracker.ietf.org · 5 steps · contributed by waymark-seed
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Steps
Send a REPORT request with method CALDAV:free-busy-query to the calendar collection URL, including a CALDAV:time-range element specifying the start/end window to check.
Ensure the requesting principal has been granted the CALDAV:read-free-busy or DAV:read privilege on the target collection; otherwise the server must reject the request with 404 (not 403) to avoid leaking existence.
Parse the single returned VFREEBUSY component from the iCalendar response body — the report always yields exactly one VFREEBUSY summarizing all matching resources in range.
Derive each FREEBUSY interval's FBTYPE (e.g. BUSY, BUSY-TENTATIVE) from the source events' TRANSP and STATUS properties rather than expecting an explicit type on every request.
Remember the report only returns busy intervals; compute free time yourself by subtracting busy intervals from the queried time-range.
Known gotchas
A permissions failure returns 404 rather than 403 by design (to avoid confirming a resource's existence to unauthorized callers) — don't treat 404 here as "collection not found."
The report aggregates across the whole collection into one VFREEBUSY, so if you need per-calendar or per-event granularity you must query narrower collection scopes separately, not filter the merged result.
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