]> CalDAV Scheduling Extensions to WebDAV Apple Inc.
1 Infinite Loop Cupertino CA 95014 USA cyrus@daboo.name http://www.apple.com/
Oracle Corporation
600 Blvd. de Maisonneuve West Suite 1900 Montreal QC H3A 3J2 CANADA bernard.desruisseaux@oracle.com http://www.oracle.com/
Applications calsify calsched calsch caldav calendar calendaring scheduling webcal webdav ical icalendar ischedule itip imip text/calendar http This document defines extensions to the CalDAV "calendar-access" feature to specify a standard way of performing scheduling operations with iCalendar-based calendar components. This document defines the "calendar-auto-schedule" feature of CalDAV.
This document specifies extensions to the CalDAV "calendar-access" feature to enable scheduling of iCalendar-based calendar components between calendar users. This extension leverages the scheduling methods defined in the iCalendar Transport-independent Interoperability Protocol (iTIP) to permit calendar users to perform scheduling operations such as schedule, reschedule, respond to scheduling request or cancel calendar components, as well as search for busy time information. However, the following iTIP features are not covered: publishing, countering, delegating, refreshing and forwarding calendar components, as well as replacing the Organizer of a calendar component. It is expected that future extensions will be developed to address these. This specification defines a client/server scheduling protocol, where the server is made responsible for sending scheduling messages and processing incoming scheduling messages. The client operations of creating, modifying or deleting a calendar component in a calendar is enough to trigger the server to deliver the necessary scheduling messages to the appropriate calendar users. This approach is sometimes referred to as "implicit scheduling". This specification only addresses how scheduling occurs with users on a single system (i.e., scheduling between CalDAV servers, or some other calendaring and scheduling system, is not defined). However, this specification is compatible with servers being able to send or receive scheduling messages with "external" users (e.g., using the iCalendar Message-Based Interoperability Protocol iMIP). defines the automated "Scheduling Operations", that allow a client to store iCalendar data on a CalDAV server, with the server taking specific actions in response. One of three scheduling operations can take place: "create", "modify" or "remove", based on the HTTP method used for the request, and a comparison between any existing and any new iCalendar data. defines how the server processes scheduling messages sent as the result of a scheduling operation. defines how freebusy requests with an immediate response are accomplished. defines access control privileges for the scheduling operations defined in this specification. For the majority of the following discussion, scheduling of events will be discussed. However, scheduling of to-dos is also fully supported by this specification. Discussion of this Internet-Draft is taking place on the mailing lists at <https://www.ietf.org/mailman/listinfo/caldav> and <http://lists.osafoundation.org/pipermail/ietf-caldav>.
This specification reuses much of the same terminology as iCalendar, iTIP, WebDAV, and CalDAV. Additional terms used by this specification are: A calendar object resource contained in a calendar collection for which the server will take care of sending scheduling messages on behalf of the owner of the calendar collection. A scheduling object resource owned by the Organizer. A scheduling object resource owned by an Attendee. Add, change or remove operations on a scheduling object resource for which the server will deliver scheduling messages to other calendar users. A calendar object that describes a scheduling operation such as schedule, reschedule, reply, or cancel. A resource at which busy time information requests are targeted. A collection in which incoming scheduling messages are delivered.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in . The Augmented BNF (ABNF) syntax used by this document to specify the format definition of new iCalendar elements is defined in . The Augmented BNF (ABNF) syntax used by this document to specify the format definition of new message header fields to be used with the HTTP/1.1 protocol is described in Section 2.1 of . Since this Augmented BNF uses the basic production rules provided in Section 2.2 of , these rules apply to this document as well. The term "protected" is used in the Conformance field of WebDAV property definitions as defined in Section 15 of .
This document uses XML DTD fragments (, Section 3.2) as a purely notational convention. WebDAV request and response bodies cannot be validated by a DTD due to the specific extensibility rules defined in Section 17 of [RFC4918] and due to the fact that all XML elements defined by that specification use the XML namespace name "DAV:". In particular: element names use the "DAV:" namespace, element ordering is irrelevant unless explicitly stated, extension elements (elements not already defined as valid child elements) can be added anywhere, except when explicitly stated otherwise, extension attributes (attributes not already defined as valid for this element) can be added anywhere, except when explicitly stated otherwise. The XML elements specified in this document are defined in the "urn:ietf:params:xml:ns:caldav" XML namespace registered by CalDAV. 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 strings "DAV:" and "CALDAV:" will be prefixed to the element types, respectively. This document inherits, and sometimes extends, DTD productions from Section 14 of . Also note that some CalDAV XML element names are identical to WebDAV XML element names, though their namespace differs. Care needs to be taken not to confuse the two sets of names.
A server that supports the features described in this document is REQUIRED to support the CalDAV "calendar-access" feature. Servers include "calendar-auto-schedule" as a field in the DAV response header from an OPTIONS request on any resource that supports any scheduling operations, properties, privileges or methods. This specification introduces new collection resource types that are used to manage scheduling object resources, and scheduling privileges (as per ), as well as provide scheduling functionality. It is the server's responsibility to create these collection resources, and clients have no way to create or delete them.
A scheduling Outbox collection is used as the target for busy time information requests, and to manage privileges that apply to outgoing scheduling requests. A scheduling Outbox collection MUST report the DAV:collection and CALDAV:schedule-outbox XML elements in the value of the DAV:resourcetype property. The element type declaration for CALDAV:schedule-outbox is:
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 A scheduling Outbox collection MUST NOT be a child (at any depth) of a calendar collection resource. The following WebDAV properties specified in CalDAV "calendar-access" MAY also be defined on scheduling Outbox collections and apply to scheduling messages submitted to the scheduling Outbox collection with the POST method: CALDAV:supported-calendar-component-set CALDAV:supported-calendar-data CALDAV:max-resource-size CALDAV:min-date-time CALDAV:max-date-time CALDAV:max-attendees-per-instance The use of child resources in a scheduling Outbox collection is reserved for future revisions or extensions of this specification. The following WebDAV property is defined on principal resources and used to locate the corresponding Outbox collection for the associated principal.
schedule-outbox-URL urn:ietf:params:xml:ns:caldav Identify the URL of the scheduling Outbox collection owned by the associated principal resource. This property MAY be protected. This property SHOULD NOT be returned by a PROPFIND allprop request (as defined in Section 14.2 of ). This property value SHOULD be preserved in COPY and MOVE operations. This property is needed for a client to determine where the scheduling Outbox collection of the current user is located so that sending of scheduling messages can occur. If not present, then the associated calendar user is not enabled for the sending of scheduling messages on the server.
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A scheduling Inbox collection contains copies of incoming scheduling messages. These can be requests sent by an Organizer, or replies sent by an Attendee in response to a request. The scheduling Inbox collection is also used to manage scheduling privileges. A scheduling Inbox collection MUST report the DAV:collection and CALDAV:schedule-inbox XML elements in the value of the DAV:resourcetype property. The element type declaration for CALDAV:schedule-inbox is:
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 Scheduling Inbox collections MUST only contain calendar object resources that obey the restrictions specified in iTIP. Consequently, scheduling Inbox collections MUST NOT contain any types of collection resources. Restrictions defined in Section 4.1 of CalDAV "calendar-access" on calendar object resources contained in calendar collections (e.g., "UID" uniqueness) do not apply to calendar object resources contained in a scheduling Inbox collection. Thus, multiple calendar object resources contained in a scheduling Inbox collection can have the same "UID" property value (i.e., multiple scheduling messages for the same calendar component). A scheduling Inbox collection MUST NOT be a child (at any depth) of a calendar collection resource. The following WebDAV properties specified in CalDAV "calendar-access" MAY also be defined on scheduling Inbox collections and apply to scheduling messages delivered to the collection: CALDAV:supported-calendar-component-set CALDAV:supported-calendar-data CALDAV:max-resource-size CALDAV:min-date-time CALDAV:max-date-time CALDAV:max-instances CALDAV:max-attendees-per-instance CALDAV:calendar-timezone The following WebDAV property is defined on principal resources and used to locate the corresponding Inbox collection for the associated principal.
schedule-inbox-URL urn:ietf:params:xml:ns:caldav Identify the URL of the scheduling Inbox collection owned by the associated principal resource. This property MAY be protected. This property SHOULD NOT be returned by a PROPFIND allprop request (as defined in Section 14.2 of ). This property value SHOULD be preserved in COPY and MOVE operations. This property allows a client to determine where the scheduling Inbox collection of the current user is located so that processing of scheduling messages can occur. If not present, then the associated calendar user is not enabled for reception of scheduling messages on the server.
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This specification extends the CALDAV:calendar-query and CALDAV:calendar-multiget REPORTs to return results for calendar object resources in scheduling Inbox collections. When a CALDAV:calendar-query REPORT includes a time-range query and targets a scheduling Inbox collection, if any calendar object resources contain "VEVENT" calendar components that do not include a "DTSTART" iCalendar property (as allowed by iTIP) then such components MUST always match the time-range query test. Note that the CALDAV:free-busy-query REPORT is not supported on scheduling Inbox collections.
This section defines new properties for WebDAV principal resources as defined in . These properties are likely to be protected but the server MAY allow them to be written by appropriate users.
calendar-user-address-set urn:ietf:params:xml:ns:caldav Identify the calendar addresses of the associated principal resource. This property MAY be protected. This property SHOULD NOT be returned by a PROPFIND allprop request (as defined in Section 14.2 of ). This property value SHOULD be preserved in COPY and MOVE operations. Support for this property is REQUIRED. This property is needed to map calendar user addresses in iCalendar data to principal resources and their associated scheduling Inbox and Outbox collections. In the event that a user has no well defined identifier for their calendar user address, the URI of their principal resource can be used. This property SHOULD be searchable using the DAV:principal-property-search REPORT. The DAV:principal-search-property-set REPORT SHOULD identify this property as such. If not present, then the associated calendar user is not enabled for scheduling on the server.
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calendar-user-type urn:ietf:params:xml:ns:caldav Identifies the calendar user type of the associated principal resource. Same values allowed for the iCalendar "CUTYPE" property parameter defined in Section 3.2.3 of . This property MAY be protected. This property SHOULD NOT be returned by a PROPFIND allprop request (as defined in Section 14.2 of ). This property value SHOULD be preserved in COPY and MOVE operations. Clients can query principal resources in order to lookup attendees available on the server. When doing this, it is useful to know, or restrict the query to, certain types of calendar user (e.g., only search for "people", or only search for "rooms"). This property MAY be defined on principal resources to indicate the type of calendar user associated with the principal resource. Its value is the same as the iCalendar "CUTYPE" property parameter that can be used on "ATTENDEE" properties. This property SHOULD be searchable using the DAV:principal-property-search REPORT. The DAV:principal-search-property-set REPORT SHOULD identify this property as such.
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When a calendar object resource is created, modified or removed from a calendar collection, the server examines the calendar data and checks to see whether the data represents a scheduling object resource. If it does, the server will automatically attempt to deliver a scheduling message to the appropriate calendar users. Several types of scheduling operations can occur in this case, equivalent to iTIP "REQUEST", "REPLY", "CANCEL", and "ADD" operations.
Calendar object resources on which the server performs scheduling operations are referred to as scheduling object resources. There are two types of scheduling object resources: organizer scheduling object resources, and attendee scheduling object resources. A calendar object resource is considered to be a valid organizer scheduling object resource if the "ORGANIZER" iCalendar property is present and set in all the calendar components to a value that matches one of the calendar user addresses of the owner of the calendar collection. A calendar object resource is considered to be a valid attendee scheduling object resource if the "ORGANIZER" iCalendar property is present and set in all the calendar components to the same value and doesn't match one of the calendar user addresses of the owner of the calendar collection, and at least one of the "ATTENDEE" iCalendar property values matches one of the calendar user addresses of the owner of the calendar collection. The creation of attendee scheduling object resources is typically done by the server, with the resource being created in an appropriate calendar collection (see ).
The server's behavior when processing a scheduling object resource depends on whether it is owned by the Organizer or an Attendee specified in the calendar data.
An Organizer can create, modify or remove a scheduling object resource, subject to access privileges, pre-conditions, and the restrictions defined in Section 4.1 of . These operations are each described next, and how they are invoked via HTTP requests is described in . The Organizer of a calendar component can also be an Attendee of that calendar component. In such cases the server MUST NOT send a scheduling message to the Attendee that matches the Organizer. The server SHOULD reject any attempt to set the "PARTSTAT" iCalendar property parameter value of the "ATTENDEE" iCalendar property of other users in the calendar object resource to a value other than "NEEDS-ACTION" if the "SCHEDULE-AGENT" property parameter value is not present or set to the value "SERVER". The server MAY reject attempts to create a scheduling object resource that specifies a "UID" property value already specified in a scheduling object resource contained in another calendar collection of the Organizer.
When an Organizer creates a scheduling object resource, the server MUST inspect each "ATTENDEE" property to determine whether to send a scheduling message. The table below indicates the appropriate iTIP method used by the server, taking into account any "SCHEDULE-AGENT" property parameter (see ) specified on each "ATTENDEE" property. SCHEDULE-AGENT iTIP METHOD SERVER (default) REQUEST CLIENT -- NONE -- "SCHEDULE-STATUS" iCalendar property parameters are added or changed on "ATTENDEE" iCalendar properties in the scheduling object resource being created as described in , with the value set as described in . This will result in the created calendar object resource differing from the calendar data sent in the HTTP request. As a result clients MAY reload the calendar data from the server in order to update to the new server generated state information. The server MUST add a "SCHEDULE-STATUS" iCalendar property parameter (see ) to the "ATTENDEE" iCalendar property in the scheduling object resource being created, and set its value as described in . This will result in the created calendar object resource differing from the calendar data sent in the HTTP request. As a result clients MAY reload the calendar data from the server in order to update to the new server generated state information. Servers MUST NOT set the "SCHEDULE-STATUS" property parameter on the "ATTENDEE" property of Attendees for which it did not attempt to deliver a scheduling message. The server MUST return an error with the CALDAV:allowed-organizer-scheduling-object-change precondition code () when the Organizer attempts to change the iCalendar data in a manner that is forbidden.
When an Organizer modifies a scheduling object resource, the server MUST inspect each "ATTENDEE" property in both the original and modified iCalendar data on a per-instance basis to determine whether to send a scheduling message. The table below indicates the appropriate iTIP method used by the server, taking into account any "SCHEDULE-AGENT" property parameter (see ) specified on each "ATTENDEE" property. The values "SERVER", "CLIENT", and "NONE" in the top and left titles of the table refer to the "SCHEDULE-AGENT" parameter value of the "ATTENDEE" property, and the values "<Absent>" and "<Removed>" are used to cover the cases where the "ATTENDEE" property is not present (Original) or is being removed (Modified).
| SERVER | CLIENT | NONE | | | | (default) | | | +===+===========+===========+===========+===========+===========+ | | | -- | REQUEST / | -- | -- | | O | | | ADD | | | | r +-----------+-----------+-----------+-----------+-----------+ | i | SERVER | CANCEL | REQUEST | CANCEL | CANCEL | | g | (default) | | | | | | i +-----------+-----------+-----------+-----------+-----------+ | n | CLIENT | -- | REQUEST / | -- | -- | | a | | | ADD | | | | l +-----------+-----------+-----------+-----------+-----------+ | | NONE | -- | REQUEST / | -- | -- | | | | | ADD | | | +---+-----------+-----------+-----------+-----------+-----------+ ]]>
"SCHEDULE-STATUS" iCalendar property parameters are added or changed on "ATTENDEE" iCalendar properties in the scheduling object resource being modified as described in , with the value set as described in . This will result in the created calendar object resource differing from the calendar data sent in the HTTP request. As a result clients MAY reload the calendar data from the server in order to update to the new server generated state information. The server MUST return an error with the CALDAV:allowed-organizer-scheduling-object-change precondition code () when the Organizer attempts to change the iCalendar data in a manner that is forbidden.
When an Organizer removes a scheduling object resource, the server MUST inspect each "ATTENDEE" property to determine whether to send a scheduling message. The table below indicates the appropriate iTIP method used by the server, taking into account any "SCHEDULE-AGENT" property parameter (see ) specified on each "ATTENDEE" property. SCHEDULE-AGENT iTIP METHOD SERVER (default) CANCEL CLIENT -- NONE --
An Attendee can create, modify or remove a scheduling object resource. These operations are each described next, and how they are invoked via HTTP requests is described in .
Attendees are allowed to make some changes to a scheduling object resource, though key properties such as start time, end time, location, and summary are typically under the control of the Organizer. Servers MUST allow Attendees to make the following iCalendar data changes, subject to other restrictions, such as access privileges and pre-conditions: change their own "PARTSTAT" iCalendar property parameter value. add, modify or remove any "TRANSP" iCalendar properties. add, modify or remove any "PERCENT-COMPLETE" iCalendar properties. add, modify or remove any "COMPLETED" iCalendar properties. add, modify or remove any "VALARM" iCalendar components. add, modify or remove the "CALSCALE" iCalendar property within the top-level "VCALENDAR" component. modify the "PRODID" iCalendar property within the top-level "VCALENDAR" component. add "EXDATE" iCalendar properties and possibly remove components for overridden recurrence instances. add, modify or remove any "CREATED", "DTSTAMP" and "LAST-MODIFIED" iCalendar properties. add, modify or remove "SCHEDULE-STATUS" iCalendar property parameters on "ATTENDEE" properties that have a "SCHEDULE-AGENT" parameter set to "CLIENT". add new components to represent overridden recurrence instances, provided the only changes to the recurrence instance follow the rules above. The server MUST return an error with the CALDAV:allowed-attendee-scheduling-object-change precondition code () when the Attendee attempts to change the iCalendar data in a manner forbidden by the server.
Typically an Attendee does not create scheduling object resources, as scheduling messages delivered to them on the server are automatically processed by the server and placed on one of their calendars (see ). However, in some cases a scheduling message can get delivered directly to the client (e.g., via email ), and the Attendee might wish to store that on the server. In that case the client creates a scheduling object resource in a calendar belonging to the Attendee. It can then set the "SCHEDULE-AGENT" iCalendar property parameter on all "ORGANIZER" iCalendar properties in the resource to determine how the server treats the resource. The value of the "SCHEDULE-AGENT" iCalendar property parameter on all "ORGANIZER" iCalendar properties MUST be the same. SCHEDULE-AGENT Action SERVER (default) The server will attempt to process changes to the resource using the normal rules for attendee scheduling object resources. CLIENT The server does no special processing of the resource. The client is assumed to be handling Attendee replies etc. NONE The server does no special processing of the resource. "SCHEDULE-STATUS" iCalendar property parameters are added or changed on "ORGANIZER" iCalendar properties in the scheduling object resource being created as described in , with the value set as described in .
When a scheduling object resource is modified by an Attendee, the server behavior depends on the value of the "SCHEDULE-AGENT" iCalendar property parameter on the "ORGANIZER" iCalendar properties: SCHEDULE-AGENT Action SERVER (default) The server will attempt to process the update using the behavior listed below. CLIENT The server does no special processing of the resource. The client is assumed to be handling any Attendee replies etc. NONE The server does no special processing of the resource. The server will inspect the changes by comparing the new scheduling object resource with the existing scheduling object resource. If the Attendee changes one or more "PARTSTAT" iCalendar property values on any component, or adds an overridden component with a changed "PARTSTAT" property, then the server MUST deliver an iTIP "REPLY" scheduling message to the Organizer to indicate the new participation status of the Attendee. If the Attendee adds an "EXDATE" property value to effectively remove a recurrence instance, the server MUST deliver an iTIP "REPLY" scheduling message to the Organizer to indicate that the Attendee has declined the instance. "SCHEDULE-STATUS" iCalendar property parameters are added or changed on "ORGANIZER" iCalendar properties in the scheduling object resource being modified as described in , with the value set as described in . This will result in the updated calendar object resource differing from the calendar data sent in the HTTP request. As a result clients MAY reload the calendar data from the server in order to update to the new server generated state information.
When a scheduling object resource is removed by an Attendee, the server behavior depends on the value of the "SCHEDULE-AGENT" iCalendar property parameter on the "ORGANIZER" iCalendar properties: SCHEDULE-AGENT Action SERVER (default) The server will attempt to process the removal taking into account any "Schedule-Reply" request header as per . CLIENT The server does no special processing of the resource. The client is assumed to be handling any Attendee replies etc. NONE The server does no special processing of the resource.
This section describes how use of various HTTP and WebDAV methods on a scheduling object resource will cause a create, modify or remove operation on that resource as described above. The use of these methods is subject to the restrictions in , in addition to what is described below.
When the server receives a PUT method request it MUST execute the following operations, provided all appropriate preconditions are met: Existing Destination Resource Resulting Destination Resource Server Operation None Calendar object resource None None Scheduling object resource Create Calendar object resource Calendar object resource None Calendar object resource Scheduling object resource Create Scheduling object resource Calendar object resource Remove Scheduling object resource Scheduling object resource Modify
When the server receives a DELETE method request targeted at a scheduling object resource it MUST execute the Remove operation. When the server receives a DELETE method request targeted at a calendar collection it MUST execute the Remove operation on all scheduling object resources contained in the calendar collection.
When the server receives a COPY method request it MUST execute the following operations based on the source and destination collections in the request: Source Collection Destination Collection Server Operation Non-calendar collection Non-calendar collection None Non-calendar collection Calendar collection (1) Calendar collection Non-calendar collection None Calendar collection Calendar collection (2) Note 1. The rules in are applied for the destination of the COPY request. Note 2. The server MAY reject this as per , otherwise None. The behavior of a COPY method request on a calendar collection is undefined.
When the server receives a MOVE method request it MUST execute the following operations based on the source and destination collections in the request: Source Collection Destination Collection Server Operation Non-calendar collection Non-calendar collection None Non-calendar collection Calendar collection (1) Calendar collection Non-calendar collection (2) Calendar collection Calendar collection None Note 1. The rules in are applied for the destination of the MOVE request. Note 2. The rules in are applied for the source of the MOVE request. The behavior of a MOVE method request on a calendar collection is undefined.
This specification defines method preconditions (see Section 16 of WebDAV), in addition to the ones in , to provide machine-parseable information in error responses.
unique-scheduling-object-resource urn:ietf:params:xml:ns:caldav PUT, COPY, and MOVE 403 Forbidden (precondition) -- Servers MAY reject requests to create a scheduling object resource with an iCalendar "UID" property value already in use by another scheduling object resource owned by the same user in other calendar collections. Servers SHOULD report the URL of the scheduling object resource that is already making use of the same "UID" property value in the DAV:href element.
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same-organizer-in-all-components urn:ietf:params:xml:ns:caldav PUT, COPY, and MOVE 403 Forbidden (precondition) -- All the calendar components in a scheduling object resource MUST contain the same "ORGANIZER" property value when present.
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allowed-organizer-scheduling-object-change urn:ietf:params:xml:ns:caldav PUT, COPY, and MOVE 403 Forbidden (precondition) -- Servers MAY impose restrictions on modifications allowed by an Organizer. For instance, servers MAY prevent the Organizer setting the "PARTSTAT" property parameter to a value other than "NEEDS-ACTION" if the corresponding "ATTENDEE" property has the "SCHEDULE-AGENT" property parameter set to "SERVER", or has no "SCHEDULE-AGENT" property parameter. See .
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allowed-attendee-scheduling-object-change urn:ietf:params:xml:ns:caldav PUT, COPY, and MOVE 403 Forbidden (precondition) -- Servers MAY impose restrictions on modifications allowed by an Attendee, subject to the allowed changes specified in .
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The server MUST ensure that a "DTSTAMP" iCalendar property is present and set the value to the UTC time that the scheduling message was generated (as required by iCalendar). The server MUST ensure that for each type of scheduling operation, the "SEQUENCE" iCalendar property value is updated as per iTIP.
Servers MUST ensure that Attendees only get information about recurrence instances that explicitly include them as an Attendee, when delivering scheduling messages for recurring calendar components. For example, if an Attendee is invited to only a single instance of a recurring event, the organizer scheduling object resource will contain an overridden instance in the form of a separate calendar component. That separate calendar component will include the "ATTENDEE" property referencing the "one-off" Attendee. That Attendee will not be listed in any other calendar components in the scheduling object resource. Any scheduling messages delivered to the Attendee will only contain information about this overridden instance. As another example, an Attendee could be excluded from one instance of a recurring event. In that case the organizer scheduling object resource will include an overridden instance with an "ATTENDEE" list that does not include the Attendee being excluded. Any scheduling messages delivered to the Attendee will not specify the overridden instance but rather include an "EXDATE" property in the "master" component that defines the recurrence set.
The iCalendar property parameter "SCHEDULE-FORCE-SEND" defined in can be used by a calendar user to force the server to send a scheduling message to an Attendee or the Organizer in a situation where the server would not normally send a scheduling message. For instance, an Organizer could use this property parameter to request an Attendee, that previously declined an invitation, to reconsider their participation status without being forced to modify the event.
This section specifies additional requirements on the handling of the "PARTSTAT" property parameter when the "SCHEDULE-AGENT" property parameter on the corresponding "ATTENDEE" property is set to the value "SERVER" or is not present. A reschedule occurs when any "DTSTART", "DTEND", "DURATION", "DUE", "RRULE", "RDATE", or "EXDATE" property changes in a calendar component such that existing recurrence instances are impacted by the changes, as shown in the table below. Servers MUST reset the "PARTSTAT" property parameter value of all "ATTENDEE" properties, except the one that corresponds to the Organizer, to "NEEDS-ACTION" for each calendar component change that causes any instance to be rescheduled. Property Server Action DTSTART, DTEND, DURATION, DUE Any change to these properties result in "PARTSTAT" being set to "NEEDS-ACTION"    RRULE A change to or addition of this property that results in the addition of new recurring instances or a change in time for existing recurring instances result in "PARTSTAT" being reset to "NEEDS-ACTION" on each affected component.    RDATE A change to or addition of this property that results in the addition of new recurring instances or a change in time for existing recurring instances result in "PARTSTAT" being reset to "NEEDS-ACTION" on each affected component.    EXDATE A change to or removal of this property that results in the re-instatement of recurring instances result in "PARTSTAT" being set to "NEEDS-ACTION" on each affected component. The server MAY allow the Organizer's client to change an Attendee's "PARTSTAT" property parameter value to "NEEDS-ACTION" at any other time (e.g., when the "LOCATION" property value changes, an Organizer might wish to re-invite Attendees who might be impacted by the change).
When scheduling with an Attendee there are two types of status information that can be returned during the operation. The first type of status information is a "delivery" status that indicates whether the scheduling message from the Organizer to the Attendee was delivered or not, or what the current status of delivery is. The second type of status information is a "reply" status corresponding to the Attendee's own "REQUEST-STATUS" information from the scheduling message reply that is sent back to the Organizer. Similarly, when an Attendee sends a reply back to the Organizer, there will be "delivery" status information for the scheduling message sent to the Organizer. However, there is no "REQUEST-STATUS" sent back by the Organizer, so there is no equivalent of the "reply" status as per scheduling messages to Attendees. The "delivery" status information on an "ORGANIZER" or "ATTENDEE" iCalendar property is conveyed in the "SCHEDULE-STATUS" property parameter value (). The status code value for "delivery" status can be one of the following: Delivery Status Code Description 1.0 The scheduling message is pending. i.e. the server is still in the process of sending the message. The status code value can be expected to change once the server has completed its sending and delivery attempts.     1.1 The scheduling message has been successfully sent. However, the server does not have explicit information about whether the scheduling message was successfully delivered to the recipient. This state can occur with "store and forward" style scheduling protocols such as iMIP (iTIP using email).     1.2 The scheduling message has been successfully delivered.     3.7 The scheduling message was not delivered because the server did not recognize the calendar user address as a valid calendar user. Note that this code applies to both Organizer and Attendee calendar user addresses.     3.8 The scheduling message was not delivered due to insufficient privileges. Note that this code applies to both privileges granted by both the Organizer and Attendee calendar users.     5.1 The scheduling message was not delivered because the server could not complete delivery of the message. This is likely due to a temporary failure, and the originator can try to send the message again at a later time.     5.2 The scheduling message was not delivered because the server was not able to find a way to deliver the message. This is likely a permanent failure, and the originator ought not try to send the message again, at least without verifying/correcting the calendar user address of the recipient.     5.3 The scheduling message was not delivered and was rejected because scheduling with that recipient is not allowed. This is likely a permanent failure, and the originator ought not try to send the message again. The status code for "reply" status can be any of the valid iTIP "REQUEST-STATUS" values. The 1.xx "REQUEST-STATUS" codes are new. This specification modifies item (2) of Section 3.6 of by adding the following restriction: For a 1.xx code, all components MUST have exactly the same code. Definition of the new 1.xx codes is as follows:
1.0 Pending. None. Delivery of the iTIP message is pending.
1.1 Sent. None. The iTIP message has been sent, though no information about successful delivery is known.
1.2 Delivered. None. The iTIP message has been sent and delivered.
Scheduling object resources on the server might change frequently as Attendees change their participation status, triggering updates to the Organizer, and refreshes of other Attendees' copies of the scheduling object resource. This can lead to an "inconsequential" change to a calendar user's data - one that does not directly impact their own participation status. When this occurs, clients have to reload calendar data and reconcile with changes being made by calendar users. To avoid the need for this, the server can instead merge calendar data changes from a client with changes made as a the result of a scheduling operation carried out by some other calendar user. This specification introduces a new WebDAV resource property CALDAV:schedule-tag with a corresponding response header "Schedule-Tag", and a new "If-Schedule-Tag-Match" request header to allow client changes to be appropriately merged with server changes in the case where the changes on the server were the result of an "inconsequential" scheduling message update (one which simply updates the status information of Attendees due to a reply from another Attendee). Servers MUST automatically resolve conflicts with "inconsequential" changes done to scheduling object resources when the "If-Schedule-Tag-Match" request header is specified. The If-Schedule-Tag-Match request header applies only to the Request-URI, and not to the Destination of a COPY or MOVE. A response to any successful GET or PUT request targeting a scheduling object resource MUST include a Schedule-Tag response header with the value set to the same value as the CALDAV:schedule-tag WebDAV property of the resource. A response to any successful COPY or MOVE request that specifies a Destination request header targeting a scheduling object resource MUST include a Schedule-Tag response header with the value set to the same value as the CALDAV:schedule-tag WebDAV property of the destination resource. Clients SHOULD use the If-Schedule-Tag-Match header on requests that update scheduling object resources, instead of HTTP ETag-based precondition tests (e.g., If-Match). Normal ETag-based precondition tests are used in all other cases, e.g., for synchronization. The value of the CALDAV:schedule-tag property changes according to these rules: For an Organizer's copy of a scheduling object resource: The server MUST NOT change the CALDAV:schedule-tag property value when the scheduling object resource is updated as the result of automatically processing a scheduling message reply from an Attendee. For instance, when an Attendee replies to the Organizer, the CALDAV:schedule-tag property is unchanged after the Organizer's scheduling object resource has been automatically updated by the server with the Attendee's new participation status. The server MUST change CALDAV:schedule-tag property value when the scheduling object resource is changed directly via an HTTP request (e.g., PUT, COPY or MOVE). For an Attendee's copy of a scheduling object resource: The server MUST change the CALDAV:schedule-tag property value when the scheduling object resource is changed as the result of processing a scheduling message update from an Organizer that contains changes other than just the participation status of Attendees. The server MUST NOT change the CALDAV:schedule-tag property value when the scheduling object resource is changed as the result of processing a scheduling message update from an Organizer that only specify changes in the participation status of Attendees. For instance, when Attendee "A" replies to Organizer "O", and Attendee "B" receives a scheduling message update from Organizer "O" with the new participation status of Attendee "A", the CALDAV:schedule-tag property of Attendee "B"s scheduling object resource would remain the same. The server MUST change the CALDAV:schedule-tag property value when the scheduling object resource is changed directly via an HTTP request (e.g., PUT, COPY or MOVE).
Clients MAY use the If-Schedule-Tag-Match request header to do a PUT request that ensures that "inconsequential" changes on the server do not result in a precondition error. The value of the request header is set to the last Schedule-Tag value received for the resource being modified. If the value of the If-Schedule-Tag-Match header matches the current value of the CALDAV:schedule-tag property the server MUST take any "ATTENDEE" property changes for all Attendees other than the owner of the scheduling object resource and apply those to the new resource being stored. Otherwise, the server MUST fail the request with a 412 Precondition Failed status code.
Clients MAY use the If-Schedule-Tag-Match request header to do a DELETE, COPY or MOVE request that ensures that "inconsequential" changes on the server do not result in a precondition error. The value of the request header is set to the last Schedule-Tag value received for the resource being deleted. If the value of the If-Schedule-Tag-Match header matches the current value of the CALDAV:schedule-tag property the server performs the normal DELETE, COPY or MOVE request processing for the resource. Otherwise, the server MUST fail the request with a 412 Precondition Failed status code.
Scheduling operations can cause the delivery of a scheduling message into an Organizer's or Attendee's scheduling Inbox collection. Servers MUST automatically process incoming scheduling messages using the rules defined by , by creating or updating the corresponding scheduling object resources on calendars owned by the owner of the scheduling Inbox collection. In addition, the scheduling message is stored in the scheduling Inbox collection as an indicator to the client that a scheduling operation has taken place. Scheduling messages are typically removed from the scheduling Inbox collection by the client once the calendar user has acknowledged the change. The server MUST take into account privileges on the scheduling Inbox collection when processing incoming scheduling messages, to determine whether delivery of the scheduling message is allowed. Privileges on calendars containing any matching scheduling object resource are not considered in this case (i.e., a schedule message from another user can cause modifications to resources in calendar collections that the other user would not normally have read or write access to). Additionally, servers MUST take into account any scheduling Inbox collection preconditions (see ) when delivering the scheduling message, and it MUST take into account the similar preconditions on any calendar collection which contains, or would contain, the corresponding scheduling object resource.
For a scheduling message sent by an Organizer, the server first tries to locate a corresponding scheduling object resource belonging to the Attendee. If no matching scheduling object resource exists, the server treats the scheduling message as a new message, otherwise it is treated as an update. In the case of a new message, the server processes the scheduling message and creates a new scheduling object resource as per . In the case of an update, the server processes the scheduling message and updates the matching scheduling object resource belonging to the Attendee to reflect the changes sent by the Organizer. In each case, the scheduling message MUST only appear in the Attendee's scheduling Inbox collection once all automatic processing has been done.
For a scheduling message reply sent by an Attendee, the server first locates the corresponding scheduling object resource belonging to the Organizer. If the corresponding scheduling object resource cannot be found, the server SHOULD ignore the scheduling message. The server MUST then update the "PARTSTAT" iCalendar property parameter value of each "ATTENDEE" iCalendar property in the scheduling object resource to match the changes indicated in the reply (taking into account the fact that an Attendee could have created a new overridden iCalendar component to indicate different participation status on one or more instances of a recurring event). The server MUST also update or add the "SCHEDULE-STATUS" property parameter on each matching "ATTENDEE" iCalendar property and set its value to that of the "REQUEST-STATUS" property in the reply, or to "2.0" if "REQUEST-STATUS" is not present (also taking into account recurrence instances). If there are multiple "REQUEST-STATUS" properties in the reply, the "SCHEDULE-STATUS" property parameter value is set to a comma-separated list of status codes, one from each "REQUEST-STATUS" property. The server SHOULD send scheduling messages to all the other Attendees indicating the change in participation status of the Attendee replying, subject to the recurrence requirements of . The scheduling message MUST only appear in the Organizer's scheduling Inbox collection once all automatic processing has been done.
The server processes scheduling messages received for an Attendee by creating a new scheduling object resource in a calendar collection belonging to the Attendee, when one does not already exist. A calendar user that is an Attendee in a scheduling operation MUST have at least one valid calendar collection available. If there is no valid calendar collection, then the server MUST reject the attempt to deliver the scheduling message to the Attendee. Servers MAY provide support for a default calendar collection, that is, the calendar collection in which new scheduling object resources will be created. The CALDAV:schedule-default-calendar-URL WebDAV property, which can be present on the scheduling Inbox collection of a calendar user, specifies if this calendar user has a default calendar collection. See . Servers SHOULD create new scheduling object resources in the default calendar collection, if the CALDAV:schedule-default-calendar-URL WebDAV property is set. Servers MAY allow clients to change the default calendar collection by changing the value of the CALDAV:schedule-default-calendar-URL WebDAV property on the scheduling Inbox collection. However, the server MUST ensure that any new value for that property refers to a valid calendar collection belonging to the owner of the scheduling Inbox collection. Servers MUST reject any attempt to delete the default calendar collection.
This specification defines additional method preconditions (see Section 16 of WebDAV) to provide machine-parseable information in error responses.
default-calendar-needed urn:ietf:params:xml:ns:caldav DELETE 403 Forbidden (precondition) -- The client attempted to delete the calendar collection currently referenced by the CALDAV:schedule-default-calendar-URL property, or attempted to remove the CALDAV:schedule-default-calendar-URL property on the scheduling Inbox collection on a server that doesn't allow such operations.
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valid-schedule-default-calendar-URL urn:ietf:params:xml:ns:caldav PROPPATCH 403 Forbidden (precondition) -- The client attempted to set the CALDAV:schedule-default-calendar-URL property to a DAV:href element that doesn't reference a valid calendar collection. Note: Servers that do not allow clients to change the CALDAV:schedule-default-calendar-URL property would simply return the DAV:cannot-modify-protected-property precondition defined in Section 16 of WebDAV.
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Busy time information of one or more calendar users can be determined by submitting a POST request targeted at the scheduling Outbox collection of the calendar user requesting the information (the Organizer). To accomplish this, the request body MUST contain a "VFREEBUSY" calendar component with the "METHOD" iCalendar property set to the value "REQUEST" as specified in Section 3.3.2 of iTIP. The resource identified by the Request-URI MUST be a resource collection of type CALDAV:schedule-outbox. The "ORGANIZER" property value in the "VFREEBUSY" component MUST match one of the calendar user addresses of the owner of the Outbox collection. A response to a busy time request that indicates status for one or more calendar users MUST be an XML document with a CALDAV:schedule-response XML element as its root element. This element MUST contain one CALDAV:response element for each calendar user, with each of those containing elements that indicate which calendar user they correspond to, the scheduling status for that calendar user, any error codes and an optional description. For a successful busy time request, a CALDAV:calendar-data element is also present for each calendar user, containing the actual busy time information (i.e., an iCalendar "VFREEBUSY" component). See for the detail on the child elements. See for an example busy time request and response.
The list below summarizes the most common status codes used for this method. However, clients need to be prepared to handle other 2/3/4/5xx series status codes as well. 200 (OK) - The command succeeded. 204 (No Content) - The command succeeded. 400 (Bad Request) - The client has provided an invalid scheduling message. 403 (Forbidden) - The client cannot submit a scheduling message to the specified Request-URI. 404 (Not Found) - The URL in the Request-URI was not present. 423 (Locked) - The specified resource is locked and the client either is not a lock owner or the lock type requires a lock token to be submitted and the client did not submit it.
The following are existing preconditions that are reused for the POST method on an Outbox collection. DAV:need-privileges CALDAV:supported-calendar-data CALDAV:valid-calendar-data CALDAV:max-resource-size The following are new method preconditions for the POST method on an Outbox collection.
valid-scheduling-message urn:ietf:params:xml:ns:caldav POST 400 Bad Request (precondition) -- The resource submitted in the POST request MUST obey all the restrictions specified in Section 3.3.2 of iTIP.
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valid-organizer urn:ietf:params:xml:ns:caldav POST 403 Forbidden (precondition) -- The "ORGANIZER" property value in the POST request's scheduling message MUST match one of the calendar user addresses of the owner of the scheduling Outbox collection being targeted by the request;
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New scheduling privileges are defined in this section. All the scheduling privileges MUST be non-abstract and MUST appear in the DAV:supported-privilege-set property of scheduling Outbox and Inbox collections on which they are defined. The tables specified in clarify which scheduling methods (e.g., "REQUEST", "REPLY", etc.) are controlled by each scheduling privilege defined in this section.
This section defines new WebDAV ACL privileges that are for use on scheduling Inbox collections. These privileges determine whether delivery of scheduling messages from a calendar user is allowed by the calendar user who "owns" the scheduling Inbox collection. This allows calendar users to choose which other calendar users can schedule with them. Note that when a scheduling message is delivered to a calendar user, in addition to a scheduling object resource being created in the calendar user's scheduling Inbox collection, a new scheduling object resource might be created or an existing one updated in a calendar belonging to the calendar user. In that case, the ability to create or update the scheduling object resource in the calendar is controlled by the privileges assigned to the scheduling Inbox collection. The privileges defined in this section are ignored if applied to a resource other than a scheduling Inbox collection.
CALDAV:schedule-deliver is an aggregate privilege as per .
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The CALDAV:schedule-deliver-invite privilege controls the processing and delivery of scheduling messages coming from an Organizer.
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The CALDAV:schedule-deliver-reply privilege controls the processing and delivery of scheduling messages coming from an Attendee.
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The CALDAV:schedule-query-freebusy privilege controls freebusy requests targeted at the owner of the scheduling Inbox collection.
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This section defines new WebDAV ACL privileges that are defined for use on scheduling Outbox collections. These privileges determine which calendar users are allowed to send scheduling messages on behalf of the calendar user who "owns" the scheduling Outbox collection. This allows calendar users to choose other calendar users who can act on their behalf (e.g. assistants working on behalf of their boss). The privileges defined in this section are ignored if applied to a resource other than a scheduling Outbox collection.
CALDAV:schedule-send is an aggregate privilege as per .
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The CALDAV:schedule-send-invite privilege controls the sending of scheduling messages by Organizers. Users granted the DAV:bind privilege on a calendar collection, or DAV:write privilege on scheduling object resources, will also need the CALDAV:schedule-send-invite privilege granted on the scheduling Outbox collection of the owner of the calendar collection or scheduling object resource in order to be allowed to create, modify or delete scheduling object resources in a way that will trigger the CalDAV server to deliver scheduling messages to attendees.
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The CALDAV:schedule-send-reply privilege controls the sending of scheduling messages by Attendees. Users granted the DAV:bind privilege on a calendar collection, or DAV:write privilege on scheduling object resources, will also need the CALDAV:schedule-send-reply privilege granted on the scheduling Outbox collection of the owner of the calendar collection or scheduling object resource in order to be allowed to create, modify or delete scheduling object resources in a way that will trigger the CalDAV server to deliver scheduling message replies to the organizer.
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The CALDAV:schedule-send-freebusy privilege controls the use of the POST method to submit scheduling messages that specify the scheduling method "REQUEST" with a "VFREEBUSY" calendar component.
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Server implementations MUST aggregate the scheduling privileges as follows: DAV:all contains CALDAV:schedule-send and CALDAV:schedule-deliver; CALDAV:schedule-send contains CALDAV:schedule-send-invite, CALDAV:schedule-send-reply, and CALDAV:schedule-send-freebusy; CALDAV:schedule-deliver contains CALDAV:schedule-deliver-invite, CALDAV:schedule-deliver-reply, and CALDAV:schedule-query-freebusy. The following diagram illustrates how scheduling privileges are aggregated according to the above requirements.
This specification defines additional iCalendar property parameters to support the CalDAV scheduling extensions.
SCHEDULE-AGENT To specify the agent expected to deliver scheduling messages to the corresponding Organizer or Attendee. This property parameter is defined by the following notation:
This property parameter MAY be specified on "ORGANIZER" or "ATTENDEE" iCalendar properties. In the absence of this parameter, the value "SERVER" MUST be used for the default behavior. The value determines whether or not a scheduling operation on a server will cause a scheduling message to be sent to the corresponding calendar user identified by the "ORGANIZER" or "ATTENDEE" property value. When the value "SERVER" is specified, or the parameter is absent, then it is the server's responsibility to send a scheduling message as part of a scheduling operation. When the value "CLIENT" is specified, that indicates that the client is handling scheduling messages with the calendar user itself. When "NONE" is specified, no scheduling messages are being sent to the calendar user. Servers MUST NOT include this parameter in any scheduling messages sent as the result of a scheduling operation. Clients MUST NOT include this parameter in any scheduling messages that they themselves send. The parameter value MUST be the same on every "ORGANIZER" property in a scheduling object resource. The parameter value MUST be the same on each "ATTENDEE" property whose values match in a scheduling object resource. Servers and clients MUST treat x-name and iana-token values they do not recognize the same way as they would the "NONE" value.
SCHEDULE-FORCE-SEND To force a scheduling message to be sent to the calendar user specified by the property. This property parameter is defined by the following notation:
This property parameter MAY be specified on "ATTENDEE" and "ORGANIZER" properties on which the "SCHEDULE-AGENT" property parameter is set to the value "SERVER" or is not specified. This property parameter is used to force a server to send a scheduling message to a specific calendar user in situations where the server would not send a scheduling message otherwise (e.g., when no change that warrants the delivery of a new scheduling message was performed on the scheduling object resource). An Organizer MAY specify this parameter on an "ATTENDEE" property with the value "REQUEST" to force a "REQUEST" scheduling message to be sent to this Attendee. An Attendee MAY specify this parameter on the "ORGANIZER" with the value "REPLY" to force a "REPLY" scheduling message to be sent to the Organizer. Servers MUST NOT preserve this property parameter in scheduling object resources, nor include it in any scheduling messages sent as the result of a scheduling operation. Clients MUST NOT include this parameter in any scheduling messages that they themselves send. Servers MUST set the "SCHEDULE-STATUS" parameter of the "ATTENDEE" or "ORGANIZER" to 2.3 (i.e., "Success, invalid property parameter ignored", see Section 3.6 of ) when the "SCHEDULE-FORCE-SEND" parameter is set to an iana-token value they do not recognize.
SCHEDULE-STATUS To specify the status codes returned from processing of the most recent scheduling message sent to the corresponding Attendee, or received from the corresponding Organizer. This property parameter is defined by the following notation:
This property parameter MAY be specified on the "ATTENDEE" and "ORGANIZER" properties. Servers MUST only add or change this property parameter on any "ATTENDEE" properties corresponding to calendar users who were sent a scheduling message via a scheduling operation. Clients SHOULD NOT change or remove this parameter if it was provided by the server. In the case where the client is handling the scheduling, the client MAY add, change or remove this parameter to indicate the last scheduling message status it received. Servers MUST add this parameter to any "ORGANIZER" properties corresponding to calendar users who were sent a scheduling message reply by an Attendee via a scheduling operation. Clients SHOULD NOT change or remove this parameter if it was provided by the server. In the case where the client is handling the scheduling, the client MAY add, change or remove this parameter to indicate the last scheduling message status it received. Servers MUST NOT include this parameter in any scheduling messages sent as the result of a scheduling operation. Clients MUST NOT include this parameter in any scheduling messages that they themselves send. Values for this property parameter are described in .
This specification defines additional HTTP request and response headers for use with CalDAV.
When an Attendee removes a scheduling object resource as per , and the Schedule-Reply header is not present, or present and set to the value "T" (true), the server MUST send an appropriate reply scheduling message with the Attendee's "PARTSTAT" iCalendar property parameter value set to "DECLINED" as part of its normal scheduling operation processing. When the Schedule-Reply header is set to the value "F" (false), the server MUST NOT send a scheduling message as part of its normal scheduling operation processing. The Schedule-Reply request header is used by a client to indicate to a server whether or not a scheduling operation ought to occur when an Attendee deletes a scheduling object resource. In particular it controls whether a reply scheduling message is sent to the Organizer as a result of the removal. There are situations in which unsolicited scheduling messages need to be silently removed (or ignored) for security or privacy reasons. This request header allows the scheduling object resource to be removed if such a need arises.
The Schedule-Tag response header provides the current value of the CALDAV:schedule-tag property value. The behavior of this response header is described in . All scheduling object resources MUST support the Schedule-Tag header.
The If-Schedule-Tag-Match request header field is used with a method to make it conditional. Clients can set this header to the value returned in the Schedule-Tag response header, or the CALDAV:schedule-tag property, of a scheduling object resource previously retrieved from the server to avoid overwriting "consequential" changes to the scheduling object resource. All scheduling object resources MUST support the If-Schedule-Tag-Match header.
This specification defines the following new WebDAV properties for use with CalDAV.
schedule-calendar-transp urn:ietf:params:xml:ns:caldav Determines whether the calendar object resources in a calendar collection will affect the owner's busy time information. This property MAY be protected and SHOULD NOT be returned by a PROPFIND allprop request (as defined in Section 14.2 of ). This property value SHOULD be kept during a MOVE operation, and SHOULD be copied and preserved in a COPY. This property SHOULD be defined on all calendar collections. If present, it contains one of two XML elements that indicate whether the calendar object resources in the calendar collection ought to contribute to the owner's busy time. When the CALDAV:opaque element is used, all calendar object resources in the corresponding calendar collection MUST contribute to busy time, assuming access privileges and other iCalendar properties allow it to. When the CALDAV:transparent XML element is used, the calendar object resources in the corresponding calendar collection MUST NOT contribute to busy time. If this property is not present on a calendar collection, then the default value CALDAV:opaque MUST be assumed.
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schedule-default-calendar-URL urn:ietf:params:xml:ns:caldav Specifies a default calendar for an Attendee where new scheduling object resources are created. This property MAY be protected in the case where a server does not support changing the default calendar, or does not support a default calendar. This property is only defined on a scheduling Inbox collection which cannot be moved or copied. This property MAY be defined on a scheduling Inbox collection. If present, it contains zero or one DAV:href XML elements. When a DAV:href element is present, its value indicates a URL to a calendar collection that is used as the default calendar. When no DAV:href element is present, it indicates that there is no default calendar. In the absence of this property there is no default calendar. When there is no default calendar the server is free to choose the calendar in which a new scheduling object resource is created. See .
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schedule-tag urn:ietf:params:xml:ns:caldav Indicates whether a scheduling object resource has had a "consequential" change made to it. opaque-tag (defined in Section 3.11 of ) This property MUST be protected as only the server can update the value. This property value is determined by the server and MAY be different from the value on source resource. The CALDAV:schedule-tag property MUST be defined on all scheduling object resources. This property is described in .
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"12345-67890" ]]>
schedule-response urn:ietf:params:xml:ns:caldav Contains the set of responses for a POST method request. See .
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response urn:ietf:params:xml:ns:caldav Contains a single response for a POST method request. See .
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recipient urn:ietf:params:xml:ns:caldav The calendar user address that the enclosing response for a POST method request is for. See .
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request-status urn:ietf:params:xml:ns:caldav The iTIP "REQUEST-STATUS" property value for this response. See .
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The process of scheduling involves the sending and receiving of scheduling messages. As a result, the security problems related to messaging in general are relevant here. In particular the authenticity of the scheduling messages needs to be verified. Servers and clients MUST use an HTTP connection protected with TLS as defined in for all scheduling operations. Clients MUST use the procedures detailed in Section 6 of to verify the authenticity of the server. Servers MUST make use of HTTP authentication to verify the authenticity of the calendar user for whom the client is sending requests.
Servers MUST ensure that clients cannot consume excessive server resources by carrying out "large" scheduling operations. In particular, servers SHOULD enforce CALDAV:max-resource-size, CALDAV:max-instances and CALDAV:max-attendees-per-instance pre-conditions as applicable for scheduling Inbox and Outbox collections.
When handling a scheduling operation: Servers MUST verify that the principal associated with the DAV:owner of the calendar collection in which a scheduling object resource is being manipulated contains a CALDAV:schedule-outbox-URL property value. Servers MUST verify that the currently authenticated user has the CALDAV:schedule-send privilege, or a sub-privilege aggregated under this privilege, on the scheduling Outbox collection of the DAV:owner of the calendar collection in which a scheduling object resource is being manipulated. Servers MUST only deliver scheduling messages to recipients when the CALDAV:schedule-deliver privilege, or a sub-privilege aggregated under this privilege, is granted on the recipient's scheduling Inbox collection for the principal associated with the DAV:owner of the calendar collection in which a scheduling object resource is being manipulated. To prevent impersonation of calendar users, the server MUST verify that the "ORGANIZER" property in an organizer scheduling object resource matches one of the calendar user addresses of the DAV:owner of the calendar collection in which the resource is stored. To prevent spoofing of an existing scheduling object resource, servers MUST verify that the "UID" iCalendar property value in a new scheduling object resource does not match that of an existing scheduling object resource with a different "ORGANIZER" property value.
When handling a POST request on a scheduling Outbox collection: Servers MUST verify that the principal associated with the calendar user address specified in the "ORGANIZER" property of the scheduling message data in the request contains a CALDAV:schedule-outbox-URL property value that matches the scheduling Outbox collection targeted by the request. Servers MUST verify that the currently authenticated user has the CALDAV:schedule-send privilege, or a sub-privilege aggregated under this privilege, on the scheduling Outbox collection targeted by the request. Servers MUST only return valid freebusy information for recipients when the CALDAV:schedule-deliver privilege, or a sub-privilege aggregated under this privilege, is granted on the recipient's scheduling Inbox collection for the principal associated with the DAV:owner of the scheduling Outbox collection targeted by the request.
This specification only defines how calendar users on the same server are able to schedule with each other - unauthenticated users have no way to carry out scheduling operations. Access control privileges (as per ) can control which of those users can schedule with others. Calendar users not wishing to expose their calendar information to other users can do so by denying privileges to specific users, or all users, for all scheduling operations, or perhaps only freebusy. Attendees can also use the Schedule-Reply request header with the value set to "F" to prevent notification to an Organizer that a scheduling object resource was deleted. This allows Attendees to remove unwanted scheduling messages without any response to the Organizer. Servers MUST NOT expose any private iCalendar data, or WebDAV resource state information (URLs, WebDAV properties, etc) for one calendar user to another via scheduling messages or error responses to scheduling operations. In particular, as per Section 8.1 of , authorization errors MUST take preference over other errors.
Section 6.1 of iTIP defines a set of potential threats in a scheduling system, and in Section 6.2 defines recommendations on how those can be addressed in protocols using iTIP. This specification addresses the iTIP threats in the following manner: Addressed by item 4 in . Addressed by item 2 in and . Addressed by item 5 in . Addressed by requiring TLS. Addressed by requirements in This specification does not support the REFRESH method.
The message header fields below are to be added to the Permanent Message Header Field Registry (see ).
Header field name: Schedule-Reply Applicable protocol: http Status: standard Author/Change controller: IETF Specification document(s): this specification () Related information: none
Header field name: Schedule-Tag Applicable protocol: http Status: standard Author/Change controller: IETF Specification document(s): this specification () Related information: none
Header field name: If-Schedule-Tag-Match Applicable protocol: http Status: standard Author/Change controller: IETF Specification document(s): this specification () Related information: none
The following iCalendar property parameters are to be added to the iCalendar Property Parameter Registry defined in Section 8.3.3 of . Parameter Status Reference SCHEDULE-AGENT Current RFC XXXX, SCHEDULE-STATUS Current RFC XXXX, SCHEDULE-FORCE-SEND Current RFC XXXX,
The following iCalendar "REQUEST-STATUS" values are to be added to the iCalendar REQUEST-STATUS Value Registry defined in Section 7.3 of . Status Code Status Reference 1.0 Current RFC XXXX, 1.1 Current RFC XXXX, 1.2 Current RFC XXXX,
This specification adds two new IANA registries for iCalendar elements. Additional codes MAY be used, provided the process described in Section 8.2.1 of is used to register them.
The following table has been used to initialize the schedule agent values registry. Schedule Agent Status Reference SERVER Current RFC XXXX, CLIENT Current RFC XXXX, NONE Current RFC XXXX,
The following table has been used to initialize the schedule send values registry. Schedule Force Send Status Reference REQUEST Current RFC XXXX, REPLY Current RFC XXXX,
The authors would like to thank the following individuals for contributing their ideas and support for writing this specification: Mike Douglass, Lisa Dusseault, Red Dutta, Jacob Farkas, Jeffrey Harris, Helge Hess, Eliot Lear, Andrew McMillan, Alexey Melnikov, Arnaud Quillaud, Julian F. Reschke, Wilfredo Sanchez Vega, Simon Vaillancourt. The authors would also like to thank the Calendaring and Scheduling Consortium for advice with this specification, and for organizing interoperability testing events to help refine it.
&rfc2119; &rfc2616; &rfc2617; &rfc2818; &rfc3744; &rfc3864; &rfc4791; &rfc4918; &rfc5234; &rfc5545; &rfc5546; &rfc6125; &W3C.REC-xml-20081126; &rfc6047;
The following tables specify which scheduling privileges grant the right to a calendar user to deliver a scheduling message to the scheduling Inbox collection of another calendar user. The appropriate behavior depends on the calendar component type as well as the scheduling "METHOD" specified in the scheduling message.
The following tables specify which scheduling privileges grant the right to a calendar user to perform busy time information requests and to submit scheduling messages to other calendar users as the result of a scheduling operation. The appropriate behavior depends on the calendar component type as well as the scheduling "METHOD" specified in the scheduling message.
This section describes some example scheduling operations that give a general idea of how scheduling is carried out between CalDAV clients and servers from the perspective of meeting Organizers and Attendees. The server is assumed to be hosted in the "example.com" domain, and users whose email address is at the "example.com" domain are assumed to be hosted by the server. In addition, the email addresses in the "example.net" domain are also valid email addresses for calendar users hosted by the server. Calendar users with an email address at the "example.org" domain are assumed to not be hosted by the server. In the following examples the requests and responses are incomplete and are only for illustrative purposes. In particular, HTTP authentication headers and behaviors are not shown, even though they are required in normal operation.
In the following example, Cyrus invites Wilfredo, Bernard and Mike to a single instance event by simply creating a new scheduling object resource in one of his calendar collections by using the PUT method.
>> Request <<
>> Response <<
Once the event creation has been completed, Cyrus's client will retrieve the event back from the server to get the schedule status of each Attendee, as well as record the Schedule-Tag value for future use. In this example, the server reports that a scheduling message was delivered to Wilfredo, a scheduling message is still pending for Bernard, and the server was unable to deliver a scheduling message to Mike.
>> Request <<
>> Response <<
In the following example, Wilfredo's client retrieves and deletes the new scheduling message that appeared in his scheduling Inbox collection after the server automatically processed it and created a new scheduling object resource in his default calendar collection.
>> Request <<
>> Response <<
>> Request <<
>> Response <<
In the following example, Wilfredo accepts Cyrus's invitation and sets an alarm reminder on the event. It uses the If-Schedule-Tag-Match precondition behavior to ensure it does not overwrite any significant changes from the organizer that might have occurred after it retrieved the initial resource data.
>> Request <<
>> Response <<
Once the event modification has been completed, Wilfredo's client will retrieve the event back from the server to get the schedule status of the Organizer.
>> Request <<
>> Response <<
On reception of Wilfredo's reply, Cyrus's server will automatically update Cyrus's scheduling object resource, make Wilfredo's scheduling message available in Cyrus's scheduling Inbox collection, and deliver an updated scheduling message to Bernard to share Wilfredo's updated participation status. In this example, Cyrus's client retrieves and deletes this scheduling message in his scheduling Inbox collection.
>> Request <<
>> Response <<
>> Request <<
>> Response <<
Cyrus's client then retrieves the event back from the server with Wilfredo's updated participation status.
>> Request <<
>> Response <<
In this example, Cyrus requests the busy time information of Wilfredo, Bernard and Mike.
>> Request <<
>> Response << mailto:wilfredo@example.com 2.0;Success BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Example Corp.//CalDAV Server//EN METHOD:REPLY BEGIN:VFREEBUSY UID:4FD3AD926350 DTSTAMP:20090602T200733Z DTSTART:20090602T000000Z DTEND:20090604T000000Z ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com ATTENDEE;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com FREEBUSY;FBTYPE=BUSY:20090602T110000Z/20090602T120000Z FREEBUSY;FBTYPE=BUSY:20090603T170000Z/20090603T180000Z END:VFREEBUSY END:VCALENDAR mailto:bernard@example.net 2.0;Success BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Example Corp.//CalDAV Server//EN METHOD:REPLY BEGIN:VFREEBUSY UID:4FD3AD926350 DTSTAMP:20090602T200733Z DTSTART:20090602T000000Z DTEND:20090604T000000Z ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com ATTENDEE;CN="Bernard Desruisseaux":mailto:bernard@example.net FREEBUSY;FBTYPE=BUSY:20090602T150000Z/20090602T160000Z FREEBUSY;FBTYPE=BUSY:20090603T090000Z/20090603T100000Z FREEBUSY;FBTYPE=BUSY:20090603T180000Z/20090603T190000Z END:VFREEBUSY END:VCALENDAR mailto:mike@example.org 3.7;Invalid calendar user ]]>
In the following example, Cyrus attempts to create, on behalf of Wilfredo, an event with Bernard specified as an Attendee. The request fails since Wilfredo didn't grant Cyrus the right to invite other calendar users on his behalf.
>> Request <<
>> Response << /home/wilfredo/calendars/outbox/ ]]>
In the following example, Bernard declines the second recurrence instance of a daily recurring event he's been invited to by Cyrus.
>> Request <<
>> Response <<
Bernard's participation status update will cause his server to deliver a scheduling message to Cyrus. Cyrus's client will find the following reply message from Bernard in Cyrus's scheduling Inbox collection:
>> Request <<
>> Response <<
In the following example, Bernard removes from his calendar the third recurrence instance of a daily recurring event he's been invited to by Cyrus. This is accomplished by the addition of an "EXDATE" property to the scheduling object resource stored by Bernard.
>> Request <<
Bernard's deletion of a recurrence instance will cause his server to deliver a scheduling message to Cyrus. Cyrus's client will find the following reply message from Bernard in Cyrus's scheduling Inbox collection:
>> Request <<
>> Response <<
AppDir: More reworking of various sections for clarity. AppDir: Removed terminology items defined in other specs. AppDir: Now updates 5546. AppDir: MAY instead of can in 3.2.10.1/2. Fixed inconsistent whitespace in examples. IESG: added x-name and iana-token references in ABNF. IESG: clarified that allowed attendee changes are in addition to other pre-conditions. IESG: added privacy statement to address potential "leakage" of private data via scheduling messages or error responses. IESG: scrubbed through some RFC2119 language to avoid unnecessary use and repetition.
Major editorial changes to remove "cruft" that built up over time, to reduce repetitive statements, and to improve clarity. SecDir: Added "Preventing Denial of Service Attacks" security sub-section. SecDir: Added reference to RFC6125 and clarified how clients and server authenticate each other. SecDir: Added "Mitigation of iTIP Threats" security sub-section. SecDir: Added new text to privacy sub-section. Fixed some XML examples.
Updated to RFC 6047 reference. Various minor clarifications to behavior and terminology done. Clarified that Inbox/Outbox are the server's responsibility to create. Changed MAY to SHOULD for server rejecting organizer PARTSTAT changes of attendees. Allow COMPLETED as a valid attendee change. Allow SCHEDULE-STATUS as a valid attendee change on SCHEDULE-AGENT=CLIENT attendee properties. COPY or MOVE on a calendar collection now declared to be undefined. Changed precondition error codes from 409 to 403. Clarified that rules 5546 must be used when server processes incoming scheduling messages. default-calendar-delete-allowed -> default-calendar-needed. Clarified that SCHEDULE-AGENT must be the same on all matching properties. Added more text justifying the need for calendar-user-type property.
Fixed some examples. Tweaked XML conventions. Removed description in SCHEDULE-STATUS example values. Tweaked 3.7 and 3.8 SCHEDULE-STATUS description to indicate it applies to the Organizer as well as Attendee. Updated to RFC 5545 reference. AD Review: clarified text about inbox resource deletion being acknowledgment of change. AD Review: clarified description of freebusy Outbox POST. AD Review: registered new 1.xx request-status codes and added new restriction on usage as per iTIP. AD Review: changes SHOULD NOT to MUST NOT for new property parameters when clients send scheduling messages. AD Review: CALDAV:schedule-calendar-transp now preserved during COPY. AD Review: changed CALDAV- to CALDAV: in acl descriptions. AD Review: fixed various minor typos. AD Review: Added text to new principal properties to indicate that if they are not present, then the user is not enabled for the various scheduling operations. AD Review: clarified use of CALDAV:calendar-data element in CALDAV:response element. AD Review: made reference to 5545 IANA registry procedures for the two new element registries. AD Review: Fixed description of B5. example. Fixed SCHEDULE-AGENT/SCHEDULE-STATUS behavior for Attendee replies.
Added "Updates 4791". XML conventions changed to match that in CardDAV spec. Reworded child response behavior for Outbox. Reworded "octet size". If-Schedule-Match descriptions changed to remove implication that it is purely a conditional operation. Schedule-Reply header descriptions generalized to resource removal rather than just HTTP DELETE. Fixed various examples.
Restructured document. Clarified that CALDAV:schedule-calendar-transp only applies to calendar collection. Removed CALDAV:schedule-state property on scheduling messages in the scheduling Inbox collection. Added conditional requests on scheduling object resources. Added section on handling of PARTSTAT. Added SCHEDULE-FORCE-SEND iCalendar property parameter. Added clarification on child resources in scheduling Outbox collections. Clarified Attendee changes that server MUST allow, and removed restrictions on changes that Attendee MUST NOT do. Added Example Scheduling Transactions appendix. Scheduling privileges are no longer required to be non-abstract. Removed handling of REFRESH requests. Removed handling of VJOURNAL components. Completed IANA Considerations section. Added references to RFC3283 and RFC5234. Updated references to iCalendar, iTIP and iMIP.
Removed distinction between scheduling calendar collections and basic calendar collections - now just have calendar collections. Clients now "MAY" reload data rather than "SHOULD" reload data. Fixed <C:recipient> in examples. Removed CALDAV:attachments-allowed precondition on POST to Outbox as that is no longer relevant. Added CALDAV:default-calendar-delete-allowed precondition for DELETE. Relaxed MUST->MAY for Organizer setting PARTSTAT value. Tweaked restrictions on Create/Modify to emphasize that 4791 restrictions also apply. Added comment that 'opaque' is the default when the CALDAV:schedule-calendar-transp property is not present. Description of Schedule-Reply header changed to reflect that it is only relevant for Attendees. Minor typos fixed.
This draft has changed substantially since the -04 version. The primary reason for this change was implementation experience from a number of vendors who implemented products based on the earlier drafts. Experience showed that the client/server interaction was not reliable in keeping scheduling messages synchronized between organizer and attendees. In addition the latency in updates due to clients being offline proved unacceptable to users. These issues led to the redesign of this specification to support a server-based processing model that eliminates all the problems seen previously. Whilst this adds significant complexity to the server in that it needs to be a full blown iTIP processing agent, it does remove a lot of the same complexity from clients, opening up the possibility of supporting complex scheduling behaviors even with "thin" clients. In the judgement of the authors, we consider this new specification to be a substantial improvement over the old one and believe it represents a stronger protocol that will lead to better interoperability.