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+.TH ICAL 4
+.SH NAME
+ical \- calendar file system
+.SH SYNOPSIS
+.B ical/fs
+[
+.B -n
+] [
+.B -c
+.I config
+] [
+.B -d
+.I dir
+] [
+.B -s
+.I service
+] [
+.B -M
+.I mtpt
+] [
+.B -w
+.I days
+] [
+.B -u
+.I url
+] [
+.B -U
+.I file
+] [
+.B -a
+.I addr
+]
+.SH DESCRIPTION
+.I Ical/fs
+presents a calendar as a file tree.
+It reads iCalendar
+.RB ( .ics )
+files from
+.I dir
+(default
+.BR . ),
+expands recurring events, and posts a service file descriptor in
+.BR /srv/\fIservice .
+.PP
+The default service name is
+.BI ical. user . pid\fR,
+as
+.IR rio (1)
+and
+.IR plumb (1)
+name theirs, so that several may run at once.
+A name given with
+.B -s
+is used unchanged, for a singleton something else expects to find by
+name.
+The name posted is written to standard error.
+.I Ical/fs
+does not mount itself; a start script would say
+.IP
+.EX
+ical/fs &
+mount /srv/ical.$user.$apid /mnt/pim
+.EE
+.PP
+Calendars named in
+.I config
+(default
+.BR $home/lib/pim )
+are fetched over HTTP and kept current without being asked.
+Each line is a tuple of attribute-value pairs in the syntax of
+.IR ndb (6):
+.IP
+.EX
+cal=work url=https://... refresh=15m
+.EE
+.PP
+.B Refresh
+defaults to 15 minutes.
+A fetch whose content is unchanged rebuilds nothing.
+The
+.B -u
+and
+.B -U
+flags name a single url directly, the latter reading it from
+.IR file ;
+the url of a private calendar is a secret and belongs in a file
+rather than in the arguments, where
+.IR ps (1)
+would show it.
+.PP
+The
+.B -w
+flag sets how many days either side of now recurrences are expanded
+into, default 400.
+.B -M
+is the mount point reported in query answers, default
+.BR /mnt/pim .
+.B -a
+also serves 9P on a TCP address.
+.B -n
+loads the calendars, reports what was found, and exits.
+.PP
+The top level contains the files
+.BR ctl ,
+.BR query ,
+.BR alarm ,
+.BR changed ,
+and the directory
+.BR events .
+.SS Events
+.B Events/date
+holds one file per occurrence, at
+.BI events/date/ yyyy/mm/dd/hhmm-summary\fR.
+Times are local, zero filled, and four digits wide, so that a day
+sorts by name.
+All day events are named
+.BI 0000-allday- summary\fR.
+Each file holds a header of
+.BI attribute :\ value
+lines, a blank line, and the description:
+.IP
+.EX
+summary: API WG
+start: 2026-08-19T10:00:00-04:00
+end: 2026-08-19T11:05:00-04:00
+epoch: 1787148000
+epochend: 1787151900
+uid: 1avg0u8b0k5v4bqokqfvgr157v@google.com
+event: ../../../../uuid/1avg0u8b0k5v4bqokqfvgr157v_google.com
+.EE
+.PP
+.B Epoch
+and
+.B epochend
+are seconds, for
+.IR date (1).
+.B Event
+is the path of the event this occurrence belongs to; 9P has no
+symbolic links.
+.PP
+.B Events/uuid
+holds one directory per event, named for its
+.BR uid ,
+containing the files
+.BR summary ,
+.BR start ,
+.BR end ,
+.BR location ,
+.BR description ,
+.BR rrule ,
+.BR organizer ,
+.BR attendees ,
+.BR uid ,
+and
+.BR raw .
+Absent values have no file.
+.B Attendees
+holds one line per attendee: participation status, name, and address,
+separated by tabs.
+.B Raw
+is the event as it arrived.
+.SS Ctl
+Reading
+.B ctl
+reports the source directory, the expansion window, the number of
+events, and one line per calendar giving its refresh interval and the
+time of its last fetch.
+Writing to it accepts:
+.TF "\fLwindow\fI n\fL"
+.TP
+.B refresh
+Reload from
+.IR dir .
+.TP
+.BI window \ n
+Expand recurrences
+.I n
+days either side of now, and reload.
+.SS Query
+.B Query
+answers questions the tree does not index.
+Write a query, then read the answer, as with
+.IR cs (8);
+one path is returned per line.
+A query is a list of
+.IB attribute = value
+terms, all of which must match:
+.BR summary ,
+.BR attendee ,
+.BR organizer ,
+.BR location ,
+and
+.B uid
+match a substring, without regard to case;
+.B from
+and
+.B to
+bound the occurrence time and are written
+.BR yyyy-mm-dd .
+.IP
+.EX
+% echo 'attendee=michael from=2026-08-19' >/mnt/pim/query
+% cat /mnt/pim/query
+.EE
+.PP
+Holding one file descriptor across the write and the read is correct
+usage.
+The last answer is also returned to a descriptor that has none of its
+own, so that
+.B echo
+and
+.B cat
+work.
+.SS Alarm and changed
+A read of
+.B alarm
+blocks until an alarm is due and returns the alarm time, the start of
+the event, and its summary, separated by tabs.
+Only
+.B VALARM
+triggers relative to the start are honoured.
+.PP
+A read of
+.B changed
+blocks until the tree has been rebuilt.
+A program displaying a calendar should walk the tree again when it
+returns rather than poll.
+The whole tree is rebuilt, so open file descriptors should not be
+assumed to remain valid.
+.SH EXAMPLE
+Serve the calendars named in the config and mount them:
+.IP
+.EX
+% ical/fs -s pim
+% mount /srv/pim /mnt/pim
+% pim/agenda
+.EE
+.SH SOURCE
+.B /sys/src/pim
+.SH "SEE ALSO"
+.IR agenda (1),
+.IR date (1),
+.IR ndb (6),
+.IR cs (8)
+.PP
+Desruisseaux,
+``Internet Calendaring and Scheduling Core Object Specification'',
+RFC 5545.
+.SH BUGS
+Embedded
+.B VTIMEZONE
+definitions are ignored;
+.B TZID
+is resolved by IANA name.
+.PP
+.B RECURRENCE-ID
+overrides are applied, but
+.B METHOD:CANCEL
+is not.
+.PP
+Absolute alarm triggers,
+.BR RELATED=END ,
+and repeating alarms are ignored.
+.PP
+Nothing can be written but
+.B ctl
+and
+.BR query .
+Replying to an invitation is not yet possible.