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Applications availability calendaring free-busy iCalendar CalDAV This document specifies a new iCalendar calendar component that allows the publication of available and unavailable time periods associated with a calendar user. This component can be used in standard iCalendar free-busy lookups, including iTIP free-busy requests, to generate repeating blocks of available or busy time with exceptions as needed. This document also defines extensions to CalDAV calendar-access and calendar-auto-schedule which specify how this new calendar component should be used when doing free-busy time evaluation in CalDAV. Discussion of this specification is taking place on the mailing list http://lists.osafoundation.org/mailman/listinfo/ietf-caldav .

Often calendar users have regular periods of time when they are either available to be scheduled or always unavailable. For example, an office worker will often wish to only appear free to their work colleagues during normal 'office hours' (e.g., Monday through Friday, 9 am through 5 pm). Or, a university professor may only be available to students during a set period of time (e.g., Thursday afternoons, 2 pm through 5 pm during term time only). Ideally users should be able to specify such periods directly via their calendar user agent, and have them automatically considered as part of the normal free-busy lookup for that user. In addition it should be possible to present different periods of available time depending on which user is making the request. iCalendar defines a "VFREEBUSY" component that can be used to represent fixed busy time periods, but it does does not provide a way to specify a repeating period of available or unavailable time. Since repeating patterns are often the case, "VFREEBUSY" components are not sufficient to solve this problem. This specification defines a new type of iCalendar calendar component that can be used to publish user availability. CalDAV provides a way for calendar users to access and manage calendar data and exchange this data via scheduling operations. As part of this, the CalDAV calendar-access feature provides a CALDAV:free-busy-query REPORT that returns free-busy information for a calendar collection or hierarchy of calendar collections. Also, the CalDAV calendar-auto-schedule feature allows free-busy information for a calendar user to be determined. Both of these operations involve examining user calendars for events that 'block time', with the blocked out periods being returned in a "VFREEBUSY" component. This specification extends the CalDAV calendar-access and CalDAV calendar-auto-schedule features to allow the new iCalendar availability components to be stored and manipulated, and to allow free-busy lookups to use the information from any such components, if present.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in . When XML element types in the namespaces "DAV:" and "urn:ietf:params:xml:ns:caldav" are referenced in this document outside of the context of an XML fragment, the string "DAV:" and "CALDAV:" will be prefixed to the element type names respectively.

This specification adds a new "VAVAILABILITY" calendar component to iCalendar. The "VAVAILABILITY" component is itself a container for new "AVAILABLE" sub-components. The purpose of the "VAVAILABILITY" calendar component is to provide a grouping of available time information over a specific range of time. Within that there are specific time ranges that are marked as available via a set of "AVAILABLE" calendar sub-components. Together these can be used to specify available time that can repeat over set periods of time, and which can vary over time.

VAVAILABILITY Provide a grouping of component properties that describe the availability associated with a calendar user. A "VAVAILABILITY" calendar component is defined by the following notation:

availabilityc = "BEGIN" ":" "VAVAILABILITY" CRLF availabilityprop *availablec "END" ":" "VAVAILABILITY" CRLF availabilityprop = *( ; ; the following are REQUIRED, ; but MUST NOT occur more than once ; dtstamp / uid ; ; the following are OPTIONAL, ; but MUST NOT occur more than once ; busytype / class / created / description / dtstart / last-mod / organizer / priority / seq / summary / url / ; ; either 'dtend' or 'duration' MAY appear ; once, but 'dtend' and 'duration' MUST ; NOT occur in the same 'availabilityprop'. ; dtend / duration / ; ; the following are OPTIONAL, ; and MAY occur more than once ; categories / comment / contact / x-prop / iana-prop ; ) availablec = "BEGIN" ":" "AVAILABLE" CRLF availableprop "END" ":" "AVAILABLE" CRLF availableprop = *( ; ; the following are REQUIRED, ; but MUST NOT occur more than once ; dtstamp / dtstart / uid / ; ; either 'dtend' or 'duration' MAY appear ; once, but 'dtend' and 'duration' MUST NOT ; occur in the same 'availableprop'. ; 'duration' MUST NOT be present if 'dtstart' ; is not present ; dtend / duration / ; ; the following are OPTIONAL, ; but MUST NOT occur more than once ; created / description / last-mod / recurid / rrule / summary / ; ; the following are OPTIONAL, ; and MAY occur more than once ; categories / comment / contact / exdate / rdate / x-prop / iana-prop )

A "VAVAILABILITY" component indicates a period of time within which availability information is provided. A "VAVAILABILITY" component can specify a start time and an end time or duration. If "DTSTART" is not present, then the start time is unbounded. If "DTEND" or "DURATION" are not present, then the end time is unbounded. Within the specified time period, availability defaults to a free-busy type of "BUSY-UNAVAILABLE", except for any time periods corresponding to "AVAILABLE" sub-components. "AVAILABLE" sub-components are used to indicate periods of free time within the time range of the enclosing "VAVAILABILITY" component. "AVAILABLE" sub-components MAY include recurrence properties to specify recurring periods of time, which may be overridden using normal recurrence behavior (i.e., use of the "RECURRENCE-ID" property). If specified, the "DTSTART" and "DTEND" properties in "VAVAILABILITY" components and "AVAILABLE" sub-components MUST be "DATE-TIME" values specified as either date with UTC time or date with local time and a time zone reference. If any property with a "DATE-TIME" value is present in a "VAVAILABILITY" component or any of its "AVAILABLE" sub-components, and that property includes a "TZID" parameter, then the iCalendar object containing the "VAVAILABILITY" component MUST contain "VTIMEZONE" components corresponding to each unique "TZID" parameter value. When used to publish available time, the "ORGANIZER" property specifies the calendar user associated with the published available time. If the "PRIORITY" property is specified in "VAVAILABILITY" components it is used to determine how that component is combined with other "VAVAILABILITY" components. See Other calendar properties MAY be specified in "VAVAILABILITY" or "AVAILABLE" components and are considered attributes of the marked block of time. Their usage is application specific. For example, the "LOCATION" property may be used to indicate that a person is available in one location for part of the week and another location for another part. The following is an example of a "VAVAILABILITY" calendar component used to represent the availability of a user always available Monday through Friday, 9:00 AM to 5:00 PM in the America/Montreal time zone:

BEGIN:VAVAILABILITY ORGANIZER:mailto:bernard@example.com UID:vavail-1@example.com DTSTAMP:20111005T133225Z BEGIN:AVAILABLE UID:avail-1-A@example.com SUMMARY:Monday to Friday from 9:00 to 17:00 DTSTART;TZID=America/Montreal:20111002T090000 DTEND;TZID=America/Montreal:20111002T170000 RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR END:AVAILABLE END:VAVAILABILITY

The following is an example of a "VAVAILABILITY" calendar component used to represent the availability of a user available Monday through Thursday, 9:00 AM to 5:00 PM at the main office, and Friday 9:00 AM to 12:00 PM in the branch office in the America/Montreal time zone between October 2nd and December 2nd 2011:

BEGIN:VAVAILABILITY ORGANIZER:mailto:bernard@example.com UID:vavail-1@example.com DTSTAMP:20111005T133225Z DTSTART;TZID=America/Montreal:20111002T000000 DTEND;TZID=America/Montreal:20111202T000000 BEGIN:AVAILABLE UID:avail-1-A@example.com SUMMARY:Monday to Thursday from 9:00 to 17:00 DTSTART;TZID=America/Montreal:20111002T090000 DTEND;TZID=America/Montreal:20111002T170000 RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH LOCATION:Main Office END:AVAILABLE BEGIN:AVAILABLE UID:avail-1-B@example.com SUMMARY:Friday from 9:00 to 12:00 DTSTART;TZID=America/Montreal:20111006T090000 DTEND;TZID=America/Montreal:20111006T120000 RRULE:FREQ=WEEKLY LOCATION:Branch Office END:AVAILABLE END:VAVAILABILITY

The following is an example of three "VAVAILABILITY" calendar components used to represent the availability of a traveling worker: Monday through Friday, 9:00 AM to 5:00 PM each day. However, for three weeks the calendar user is working in Montreal, then one week in Los Angeles, then back to Montreal. Note that each overall period is covered by separate "VAVAILABILITY" components. The last of these has no DTEND so continues on "for ever". This example shows one way "blocks" of available time can be represented. See for another approach using priority.

BEGIN:VAVAILABILITY ORGANIZER:mailto:bernard@example.com UID:vavail-1@example.com DTSTAMP:20111005T133225Z DTSTART;TZID=America/Montreal:20111002T000000 DTEND;TZID=America/Montreal:20111023T030000 BEGIN:AVAILABLE UID:avail-1-A@example.com SUMMARY:Monday to Friday from 9:00 to 17:00 DTSTART;TZID=America/Montreal:20111002T090000 DTEND;TZID=America/Montreal:20111002T170000 RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR LOCATION:Montreal END:AVAILABLE END:VAVAILABILITY BEGIN:VAVAILABILITY ORGANIZER:mailto:bernard@example.com UID:vavail-2@example.com DTSTAMP:20111005T133225Z DTSTART;TZID=America/Los_Angeles:20111023T000000 DTEND;TZID=America/Los_Angeles:20111030T000000 BEGIN:AVAILABLE UID:avail-2-A@example.com SUMMARY:Monday to Friday from 9:00 to 17:00 DTSTART;TZID=America/Los_Angeles:20111023T090000 DTEND;TZID=America/Los_Angeles:20111023T170000 RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR LOCATION:Los Angeles END:AVAILABLE END:VAVAILABILITY BEGIN:VAVAILABILITY ORGANIZER:mailto:bernard@example.com UID:vavail-3@example.com DTSTAMP:20111005T133225Z DTSTART;TZID=America/Montreal:20111030T030000 BEGIN:AVAILABLE UID:avail-3-A@example.com SUMMARY:Monday to Friday from 9:00 to 17:00 DTSTART;TZID=America/Montreal:20111030T090000 DTEND;TZID=America/Montreal:20111030T170000 RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR LOCATION:Montreal END:AVAILABLE END:VAVAILABILITY

BUSYTYPE This property specifies the default busy time type. TEXT IANA and non-standard property parameters can be specified on this property. This property can be specified within "VAVAILABILITY" calendar components. This property is defined by the following notation:

busytype = "BUSYTYPE" busytypeparam ":" busytypevalue CRLF busytypeparam = *(";" other-param) busytypevalue = "BUSY" / "BUSY-UNAVAILABLE" / "BUSY-TENTATIVE" / iana-token / x-name ; Default is "BUSY-UNAVAILABLE".

This property is used to specify the default busy time type. The values correspond to those used by the "FBTYPE" parameter used on a "FREEBUSY" property, with the exception that the "FREE" value is not used in this property. If not specified on a component that allows this property, the default is "BUSY-UNAVAILABLE". The following is an example of this property:

BUSYTYPE:BUSY

The Vavailability component allows a calendar user to describe their availability over extended periods of time through the use of recurrence patterns. This availability may be relatively constant from year to year. However, there is usually some degree of irregularity, as people take vacations or perhaps spend a few weeks at a different office. For that period of time there can be a need to redefine their availability. Rather than modify their existing vavailability, the "PRIORITY" property allows new vavailability components to be provided which override others of lower ordinal priority. Note that iCalendar defines the "PRIORITY" property such that a value of 0 is undefined, 1 is the highest priority and 9 is the lowest. When combining vavailability components, an absence of a "PRIORITY" property or a value of 0 implies the lowest level of priority. If two or more vavailability components have the same PRIORITY value, then their AVAILABILITY components which fall within the date range of interest are combined. It is up to the creator of such components to ensure that combining them produces a consistent and expected result. To calculate the available time, order the intersecting "VAVAILABILITY" components by priority, those with no "PRIORITY" or a priority value of 0 first, then in decreasing order of priority that is, an increasing "PRIORITY" value. Step through the resulting list of "VAVAILABILITY" components. For each, the time range covered by the "VAVAILABILITY" component is set to busy and then portions of it defined by the "AVAILABLE" components in the "VAVAILABILITY" component are set to free. Note that, if any VAVAILABILITY component completely covers the date range of interest, then any lower priority VAVAILABILITY components may be ignored.

This section describes how free-busy time information for a calendar user is calculated in the presence of "VAVAILABILITY" calendar components. An iCalendar "VFREEBUSY" component is used to convey "rolled-up" free-busy time information for a calendar user. This can be generated as the result of an iTIP free-busy request or through some other mechanism (e.g., a CalDAV calendar-access CALDAV:free-busy-query REPORT). When one or more "VAVAILABILITY" components are present and intersect the time-range for the free-busy request, first available time is calculated, as outlined in . Once that is done, regular "VEVENT" and "VFREEBUSY" components can be "overlaid" in the usual way to block out additional time. An example procedure for this is as follows: Initially mark the entire period of the free-busy request as free. For each "VAVAILABILITY" component ordered by PRIORITY: Determine if the "VAVAILABILITY" intersects the time-range of the free-busy request. If not ignore it. Determine if the "VAVAILABILITY" is completely overridden by a higher priority component. If so ignore it. For the time period covered by the "VAVAILABILITY" component, mark time in the free-busy request result set as busy, using the busy time type derived from the "BUSYTYPE" property in the "VAVAILABILITY" component. For each remaining "VAVAILABILITY" component in the same order: For each "AVAILABLE" component in the "VAVAILABILITY" component: Expand all recurring instances, taking into account overridden instances, ignoring instances or parts of instances that fall outside of the free-busy request time-range or the time period specified by the "VAVAILABILITY" component. For each instance, mark the corresponding time in the free-busy request result set as free. For each "VEVENT" or "VFREEBUSY" component apply normal free-busy processing within the free-busy request time-range.

In the examples below a table is used to represent time slots for the period of a free-busy request. Each time slot is two hours long. The column header represents the hours from midnight local time. Each row below the column headers represents a step in the free-busy result set determination, following the procedure outlined above. Each cell in the rows below the column header contains a single character that represents the free-busy type for the corresponding time period at the end of the process step represented by the row. The characters in the row are: Character Meaning F Represents "FREE" time in that slot. B Represents "BUSY" time in that slot. U Represents "BUSY-UNAVAILABLE" time in that slot. T Represents "BUSY-TENTATIVE" time in that slot.

A free-busy request for Monday, 6th November 2011, midnight to midnight in the America/Montreal timezone. The user's calendar is as shown in . This includes one "VAVAILABILITY" component giving available time within the requested time-range of 8:00 AM to 6:00 PM, together with one "VEVENT" component representing a two hour meeting starting at 12:00 PM. Step  0  2  4  6  8 10 12 14 16 18 20 22 1. F F F F F F F F F F F F 2. U U U U U U U U U U U U 3. U U U U F F F F F U U U 4. U U U U F F B F F U U U

The following is another way to represent the availability of the traveling worker shown above. Here we represent their base availability of Monday through Friday, 9:00 AM to 5:00 PM each day with a "VAVAILABILITY" with defaulted PRIORITY. For the three weeks the calendar user is working in Montreal we represent it with an overriding "VAVAILABILITY" component with priority 1.

BEGIN:VAVAILABILITY ORGANIZER:mailto:bernard@example.com UID:vavail-1@example.com DTSTAMP:20111005T133225Z DTSTART;TZID=America/Montreal:20111002T000000 BEGIN:AVAILABLE UID:avail-1-A@example.com SUMMARY:Monday to Friday from 9:00 to 17:00 DTSTART;TZID=America/Montreal:20111002T090000 DTEND;TZID=America/Montreal:20111002T170000 RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR LOCATION:Montreal END:AVAILABLE END:VAVAILABILITY BEGIN:VAVAILABILITY ORGANIZER:mailto:bernard@example.com UID:vavail-2@example.com DTSTAMP:20111005T133225Z DTSTART;TZID=America/Los_Angeles:20111023T000000 DTEND;TZID=America/Los_Angeles:20111030T000000 BEGIN:AVAILABLE UID:avail-2-A@example.com SUMMARY:Monday to Friday from 9:00 to 17:00 DTSTART;TZID=America/Los_Angeles:20111023T090000 DTEND;TZID=America/Los_Angeles:20111023T170000 PRIORITY:1 RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR LOCATION:Los Angeles END:AVAILABLE END:VAVAILABILITY

This section lists what functionality is required of a CalDAV server which supports this extension. A server: MUST support "VAVAILABILITY" components in a calendar collection resource if the CALDAV calendar-access feature is supported, which includes advertising it in CALDAV;supported-calendar-component-set properties on calendars; MUST support CALDAV:free-busy-query REPORTs that aggregate the information in any "VAVAILABILITY" components in the calendar collections targeted by the request; MUST support "VAVAILABILITY" components stored in a CALDAV:calendar-availability WebDAV property on a CALDAV scheduling inbox collection if the CALDAV calendar-auto-schedule feature is supported; MUST support iTIP free-busy requests that aggregate the information in any "VAVAILABILITY" components in calendar collections that contribute to free-busy, or in any "VAVAILABILITY" components stored in the CALDAV:calendar-availability in the CALDAV scheduling inbox collection of the calendar user targeted by the iTIP free-busy request, if the CalDAV calendar-auto-schedule feature is available.

A server supporting the features described in this document MUST include "calendar-availability" as a field in the DAV response header from an OPTIONS request on any resource that supports any calendar properties, reports, method, or privilege. A value of "calendar-availability" in the DAV response header MUST indicate that the server supports all MUST level requirements specified in this document.

>> Request <<

>> Response <<

In this example, the OPTIONS method returns the value "calendar-availability" in the DAV response header to indicate that the collection "/home/bernard/calendars/" supports the new features defined in this specification.

A CALDAV:free-busy-query REPORT can be executed on a calendar collection that contains iCalendar "VAVAILABILITY" components. When that is done, the server MUST aggregate the information in any "VAVAILABILITY" components when generating the free-busy response, as described in .

calendar-availability urn:ietf:params:xml:ns:caldav Defines a "VAVAILABILITY" component that will be used in calculating free-busy time when an iTIP free-busy request is targeted at the calendar user who owns the Inbox. This property MAY be protected and SHOULD NOT be returned by a PROPFIND DAV:allprop request. Support for this property is REQUIRED. The value of this property MUST be a valid iCalendar object containing "VAVAILABILITY" components and "VTIMEZONE" components (if required) only. This property allows a user to specify their availability by including "VAVAILABILITY" components in the value of this property. If present, the server MUST use these "VAVAILABILITY" components when determining free-busy information as part of an iTIP free-busy request being handled by the server.

; Data value MUST be iCalendar object containing ; "VAVAILABILITY" or "VTIMEZONE" components. ]]>

BEGIN:VCALENDAR CALSCALE:GREGORIAN PRODID:-//example.com//iCalendar 2.0//EN VERSION:2.0 BEGIN:VTIMEZONE LAST-MODIFIED:20040110T032845Z TZID:America/Montreal BEGIN:DAYLIGHT DTSTART:20000404T020000 RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4 TZNAME:EDT TZOFFSETFROM:-0500 TZOFFSETTO:-0400 END:DAYLIGHT BEGIN:STANDARD DTSTART:20001026T020000 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10 TZNAME:EST TZOFFSETFROM:-0400 TZOFFSETTO:-0500 END:STANDARD END:VTIMEZONE BEGIN:VAVAILABILITY UID:vavail-1@example.com DTSTAMP:20111005T133225Z DTSTART;TZID=America/Montreal:20111002T000000 BEGIN:AVAILABLE UID:avail-1-A@example.com SUMMARY:Monday to Friday from 9:00 to 18:00 DTSTART;TZID=America/Montreal:20111002T090000 DTEND;TZID=America/Montreal:20111002T180000 RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR END:AVAILABLE END:VAVAILABILITY END:VCALENDAR ]]>

The processing of an iTIP free-busy request targeted at the owner of the CALDAV:schedule-inbox will include free-busy information derived from "VAVAILABILITY" components in any calendar collection targeted during the request, as described in . In addition, any "VAVAILABILITY" components specified in the CALDAV:calendar-availability property on the owner's Inbox, MUST be included in the free-busy calculation.

Free-busy information generated from "VAVAILABILITY" components MUST NOT include information other than busy or free time periods. In particular, user specified property values such as "SUMMARY" and "DESCRIPTION" MUST NOT be copied into the free-busy result data. Beyond this, this specification does not add any additional security issues that are not already present in and .

This documents defines the following new iCalendar components to be added to the registry defined in Section 8.2.2 of : Component Status Reference VAVAILABILITY Current RFCXXXX, AVAILABLE Current RFCXXXX,

This documents defines the following new iCalendar properties to be added to the registry defined in Section 8.2.3 of : Property Status Reference BUSYTYPE Current RFCXXXX,

Thanks to the following for providing feedback: Toby Considine and Dave Thewlis. Particular thanks go to Bernard Desruisseaux. This specification came about via discussions at the Calendaring and Scheduling Consortium.

&rfc2119; &rfc4791; &rfc5545; &rfc5546; &rfc6638;

iCalendar object

Changes in -05: Small typos. Fix explanation of priority. Change uid values to make legal and easier to follow. Changes in -04: Small typos. Add prioritized example. Changes in -03: Switch authors. CalDAV scheduling is now rfc6638. List priority as a vavailability property and define its use. Changes in -02: Updated to 5545/5546 references. Fixed some examples. Added some more properties to the components Fixed text that said dtstart was required in VAVAILABILITY Changes in -01: Allow property on Inbox for caldav-schedule. Clarify that DURATION can only be present in VAVAILABILITY if DTSTART is also present, and DTEND is not. Updated references. Added templates.