Calendaring Extensions to WebDAV (CalDAV)

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 [RFC2119].¶

The term "protected" is used in the Conformance field of property definitions as defined in Section 1.4.2 of [RFC3253].¶

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.¶

Definitions of XML elements in this document use XML element type declarations (as found in XML Document Type Declarations), described in Section 3.2 of [W3C.REC-xml-20060816].¶

The namespace "urn:ietf:params:xml:ns:caldav" is reserved for the XML elements defined in this specification, its revisions, and related CalDAV specifications. XML elements defined by individual implementations MUST NOT use the "urn:ietf:params:xml:ns:caldav" namespace, and instead should use a namespace that they control.¶

The XML declarations used in this document do not include namespace information. Thus, implementers must not use these declarations as the only way to create valid CalDAV properties or to validate CalDAV XML element types. Some of the declarations refer to XML elements defined by WebDAV [RFC2518], which use the "DAV:" namespace. Wherever such XML elements appear, they are explicitly prefixed with "DAV:" to avoid confusion.¶

Also note that some CalDAV XML element names are identical to WebDAV XML element names, though their namespace differs. Care must be taken not to confuse the two sets of names.¶

Processing of XML by CalDAV clients and servers MUST follow the rules described in [RFC2518]; in particular, Section 14, and Appendix 3 of that specification.¶

A "precondition" of a method describes the state of the server that must be true for that method to be performed. A "postcondition" of a method describes the state of the server that must be true after that method has been completed. If a method precondition or postcondition for a request is not satisfied, the response status of the request MUST either be 403 (Forbidden), if the request should not be repeated because it will always fail, or 409 (Conflict), if it is expected that the user might be able to resolve the conflict and resubmit the request.¶

In order to allow better client handling of 403 and 409 responses, a distinct XML element type is associated with each method precondition and postcondition of a request. When a particular precondition is not satisfied or a particular postcondition cannot be achieved, the appropriate XML element MUST be returned as the child of a top-level DAV:error element in the response body, unless otherwise negotiated by the request. ¶

A CalDAV server is a calendaring-aware engine combined with a WebDAV repository. A WebDAV repository is a set of WebDAV collections, containing other WebDAV resources, within a unified URL namespace. For example, the repository "http://www.example.com/webdav/" may contain WebDAV collections and resources, all of which have URLs beginning with "http://www.example.com/webdav/". Note that the root URL, "http://www.example.com/", may not itself be a WebDAV repository (for example, if the WebDAV support is implemented through a servlet or other Web server extension).¶

A WebDAV repository MAY include calendar data in some parts of its URL namespace, and non-calendaring data in other parts.¶

A WebDAV repository can advertise itself as a CalDAV server if it supports the functionality defined in this specification at any point within the root of the repository. That might mean that calendaring data is spread throughout the repository and mixed with non-calendar data in nearby collections (e.g., calendar data may be found in /home/lisa/calendars/ as well as in /home/bernard/calendars/, and non-calendar data in /home/lisa/contacts/). Or, it might mean that calendar data can be found only in certain sections of the repository (e.g., /calendar/). Calendaring features are only required in the repository sections that are or contain calendar object resources. Therefore, a repository confining calendar data to the /calendar/ collection would only need to support the CalDAV required features within that collection.¶

The CalDAV server or repository is the canonical location for calendar data and state information. Clients may submit requests to change data or download data. Clients may store calendar objects offline and attempt to synchronize at a later time. However, clients MUST be prepared for calendar data on the server to change between the time of last synchronization and when attempting an update, as calendar collections may be shared and accessible via multiple clients. Entity tags and other features make this possible.¶

Recurrence is an important part of the data model because it governs how many resources are expected to exist. This specification models a recurring calendar component and its recurrence exceptions as a single resource. In this model, recurrence rules, recurrence dates, exception rules, and exception dates are all part of the data in a single calendar object resource. This model avoids problems of limiting how many recurrence instances to store in the repository, how to keep recurrence instances in sync with the recurring calendar component, and how to link recurrence exceptions with the recurring calendar component. It also results in less data to synchronize between client and server, and makes it easier to make changes to all recurrence instances or to a recurrence rule. It makes it easier to create a recurring calendar component and to delete all recurrence instances.¶

Clients are not forced to retrieve information about all recurrence instances of a recurring component. The CALDAV:calendar-query and CALDAV:calendar-multiget reports defined in this document allow clients to retrieve only recurrence instances that overlap a given time range.¶

Calendar object resources contained in calendar collections MUST NOT contain more than one type of calendar component (e.g., VEVENT, VTODO, VJOURNAL, VFREEBUSY, etc.) with the exception of VTIMEZONE components, which MUST be specified for each unique TZID parameter value specified in the iCalendar object. For instance, a calendar object resource can contain one VEVENT component and one VTIMEZONE component, but it cannot contain one VEVENT component and one VTODO component. Instead, the VEVENT and VTODO components would have to be stored in separate calendar object resources in the same collection.¶

Calendar object resources contained in calendar collections MUST NOT specify the iCalendar METHOD property.¶

The UID property value of the calendar components contained in a calendar object resource MUST be unique in the scope of the calendar collection in which they are stored.¶

Calendar components in a calendar collection that have different UID property values MUST be stored in separate calendar object resources.¶

Calendar components with the same UID property value, in a given calendar collection, MUST be contained in the same calendar object resource. This ensures that all components in a recurrence "set" are contained in the same calendar object resource. It is possible for a calendar object resource to just contain components that represent "overridden" instances (ones that modify the behavior of a regular instance, and thus include a RECURRENCE-ID property) without also including the "master" recurring component (the one that defines the recurrence "set" and does not contain any RECURRENCE-ID property).¶

For example, given the following iCalendar object: ¶

BEGIN:VCALENDAR
PRODID:-//Example Corp.//CalDAV Client//EN
VERSION:2.0
BEGIN:VEVENT
UID:1@example.com
SUMMARY:One-off Meeting
DTSTAMP:20041210T183904Z
DTSTART:20041207T120000Z
DTEND:20041207T130000Z
END:VEVENT
BEGIN:VEVENT
UID:2@example.com
SUMMARY:Weekly Meeting
DTSTAMP:20041210T183838Z
DTSTART:20041206T120000Z
DTEND:20041206T130000Z
RRULE:FREQ=WEEKLY
END:VEVENT
BEGIN:VEVENT
UID:2@example.com
SUMMARY:Weekly Meeting
RECURRENCE-ID:20041213T120000Z
DTSTAMP:20041210T183838Z
DTSTART:20041213T130000Z
DTEND:20041213T140000Z
END:VEVENT
END:VCALENDAR

The VEVENT component with the UID value "1@example.com" would be stored in its own calendar object resource. The two VEVENT components with the UID value "2@example.com", which represent a recurring event where one recurrence instance has been overridden, would be stored in the same calendar object resource.¶

A calendar collection contains calendar object resources that represent calendar components within a calendar. A calendar collection is manifested to clients as a WebDAV resource collection identified by a URL. A calendar collection MUST report the DAV:collection and CALDAV:calendar XML elements in the value of the DAV:resourcetype property. The element type declaration for CALDAV:calendar is:¶

    <!ELEMENT calendar EMPTY>

A calendar collection can be created through provisioning (i.e., automatically created when a user's account is provisioned), or it can be created with the MKCALENDAR method (see Section 5.3.1). This method can be useful for a user to create additional calendars (e.g., soccer schedule) or for users to share a calendar (e.g., team events or conference rooms). However, note that this document doesn't define the purpose of extra calendar collections. Users must rely on non-standard cues to find out what a calendar collection is for, or use the CALDAV:calendar-description property defined in Section 5.2.1 to provide such a cue.¶

The following restrictions are applied to the resources within a calendar collection: ¶

1. Calendar collections MUST only contain calendar object resources and collections that are not calendar collections, i.e., the only "top-level" non-collection resources allowed in a calendar collection are calendar object resources. This ensures that calendar clients do not have to deal with non-calendar data in a calendar collection, though they do have to distinguish between calendar object resources and collections when using standard WebDAV techniques to examine the contents of a collection.
2. Collections contained in calendar collections MUST NOT contain calendar collections at any depth, i.e., "nesting" of calendar collections within other calendar collections at any depth is not allowed. This specification does not define how collections contained in a calendar collection are used or how they relate to any calendar object resources contained in the calendar collection.

Multiple calendar collections MAY be children of the same collection.¶

A server supporting the features described in this document MUST include "calendar-access" 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-access" in the DAV response header MUST indicate that the server supports all MUST level requirements specified in this document.¶

This section defines properties for calendar collections.¶

Calendar collections and calendar object resources may be created by either a CalDAV client or by the CalDAV server. This specification defines restrictions and a data model that both clients and servers MUST adhere to when manipulating such calendar data.¶

CalDAV servers MUST support and adhere to the requirements of WebDAV ACL [RFC3744]. WebDAV ACL provides a framework for an extensible set of privileges that can be applied to WebDAV collections and ordinary resources. CalDAV servers MUST also support the calendaring privilege defined in this section.¶

This section defines an additional property for WebDAV principal resources, as defined in [RFC3744].¶

The REPORT method (defined in Section 3.6 of [RFC3253]) provides an extensible mechanism for obtaining information about one or more resources. Unlike the PROPFIND method, which returns the value of one or more named properties, the REPORT method can involve more complex processing. REPORT is valuable in cases where the server has access to all of the information needed to perform the complex request (such as a query), and where it would require multiple requests for the client to retrieve the information needed to perform the same request.¶

CalDAV servers MUST support the DAV:expand-property REPORT defined in Section 3.8 of [RFC3253].¶

Servers MAY support the reports defined in this document on ordinary collections (collections that are not calendar collections), in addition to calendar collections or calendar object resources. In computing responses to the reports on ordinary collections, servers MUST only consider calendar object resources contained in calendar collections that are targeted by the REPORT request, based on the value of the Depth request header.¶

iCalendar provides a way to specify DATE and DATE-TIME values that are not bound to any time zone in particular, hereafter called "floating date" and "floating time", respectively. These values are used to represent the same day, hour, minute, and second value, regardless of which time zone is being observed. For instance, the DATE value "20051111", represents November 11, 2005 in no specific time zone, while the DATE-TIME value "20051111T111100" represents November 11, 2005, at 11:11 A.M. in no specific time zone.¶

CalDAV servers may need to convert "floating date" and "floating time" values in date with UTC time values in the processing of calendaring REPORT requests.¶

For the CALDAV:calendar-query REPORT, CalDAV servers MUST rely on the value of the CALDAV:timezone XML element, if specified as part of the request body, to perform the proper conversion of "floating date" and "floating time" values to date with UTC time values. If the CALDAV:timezone XML element is not specified in the request body, CalDAV servers MUST rely on the value of the CALDAV:calendar-timezone property, if defined, or else the CalDAV servers MAY rely on the time zone of their choice.¶

For the CALDAV:free-busy-query REPORT, CalDAV servers MUST rely on the value of the CALDAV:calendar-timezone property, if defined, to compute the proper FREEBUSY time period value as date with UTC time for calendar components scheduled with "floating date" or "floating time". If the CALDAV:calendar-timezone property is not defined, CalDAV servers MAY rely on the time zone of their choice.¶

Some of the reports defined in this section can include a time range filter that is used to restrict the set of calendar object resources returned to just those that overlap the specified time range. The time range filter can be applied to a calendar component as a whole, or to specific calendar component properties with DATE or DATE-TIME value types.¶

To determine whether a calendar object resource matches the time range filter element, the start and end times for the targeted component or property are determined and then compared to the requested time range. If there is an overlap with the requested time range, then the calendar object resource matches the filter element. The rules defined in [RFC2445] for determining the actual start and end times of calendar components MUST be used, and these are fully enumerated in Section 9.9 of this document.¶

When such time range filtering is used, special consideration must be given to recurring calendar components, such as VEVENT and VTODO. The server MUST expand recurring components to determine whether any recurrence instances overlap the specified time range. If one or more recurrence instances overlap the time range, then the calendar object resource matches the filter element.¶

Some of the reports defined in this section do text matches of character strings provided by the client and are compared to stored calendar data. Since iCalendar data is, by default, encoded in the UTF-8 charset and may include characters outside the US-ASCII charset range in some property and parameter values, there is a need to ensure that text matching follows well-defined rules.¶

To deal with this, this specification makes use of the IANA Collation Registry defined in [RFC4790] to specify collations that may be used to carry out the text comparison operations with a well-defined rule.¶

The comparisons used in CalDAV are all "substring" matches, as per [RFC4790], Section 4.2. Collations supported by the server MUST support "substring" match operations.¶

CalDAV servers are REQUIRED to support the "i;ascii-casemap" and "i;octet" collations, as described in [RFC4790], and MAY support other collations.¶

Servers MUST advertise the set of collations that they support via the CALDAV:supported-collation-set property defined on any resource that supports reports that use collations.¶

Clients MUST only use collations from the list advertised by the server.¶

In the absence of a collation explicitly specified by the client, or if the client specifies the "default" collation identifier (as defined in [RFC4790], Section 3.1), the server MUST default to using "i;ascii-casemap" as the collation.¶

Wildcards (as defined in [RFC4790], Section 3.2) MUST NOT be used in the collation identifier.¶

If the client chooses a collation not supported by the server, the server MUST respond with a CALDAV:supported-collation precondition error response.¶

Some calendaring reports defined in this document allow partial retrieval of calendar object resources. A CalDAV client can specify what information to return in the body of a calendaring REPORT request.¶

A CalDAV client can request particular WebDAV property values, all WebDAV property values, or a list of the names of the resource's WebDAV properties. A CalDAV client can also request calendar data to be returned and specify whether all calendar components and properties should be returned, or only particular ones. See CALDAV:calendar-data in Section 9.6.¶

By default, the returned calendar data will include the component that defines the recurrence set, referred to as the "master component", as well as the components that define exceptions to the recurrence set, referred to as the "overridden components".¶

A CalDAV client that is only interested in the recurrence instances that overlap a specified time range can request to receive only the "master component", along with the "overridden components" that impact the specified time range, and thus, limit the data returned by the server (see CALDAV:limit-recurrence-set in Section 9.6.6). An overridden component impacts a time range if its current start and end times overlap the time range, or if the original start and end times -- the ones that would have been used if the instance were not overridden -- overlap the time range, or if it affects other instances that overlap the time range.¶

A CalDAV client with no support for recurrence properties (i.e., EXDATE, EXRULE, RDATE, and RRULE) and possibly VTIMEZONE components, or a client unwilling to perform recurrence expansion because of limited processing capability, can request to receive only the recurrence instances that overlap a specified time range as separate calendar components that each define exactly one recurrence instance (see CALDAV:expand in Section 9.6.5.)¶

Finally, in the case of VFREEBUSY components, a CalDAV client can request to receive only the FREEBUSY property values that overlap a specified time range (see CALDAV:limit-freebusy-set in Section 9.6.7.)¶

Servers MUST support the use of non-standard component, property, or parameter names in the CALDAV:calendar-data XML element in calendaring REPORT requests to allow clients to request that non-standard components, properties, and parameters be returned in the calendar data provided in the response.¶

Servers MAY support the use of non-standard component, property, or parameter names in the CALDAV:comp-filter, CALDAV:prop-filter, and CALDAV:param-filter XML elements specified in the CALDAV:filter XML element of calendaring REPORT requests.¶

Servers MUST fail with the CALDAV:supported-filter precondition if a calendaring REPORT request uses a CALDAV:comp-filter, CALDAV:prop-filter, or CALDAV:param-filter XML element that makes reference to a non-standard component, property, or parameter name on which the server does not support queries.¶

The CALDAV:calendar-query REPORT performs a search for all calendar object resources that match a specified filter. The response of this report will contain all the WebDAV properties and calendar object resource data specified in the request. In the case of the CALDAV:calendar-data XML element, one can explicitly specify the calendar components and properties that should be returned in the calendar object resource data that matches the filter.¶

The format of this report is modeled on the PROPFIND method. The request and response bodies of the CALDAV:calendar-query REPORT use XML elements that are also used by PROPFIND. In particular, the request can include XML elements to request WebDAV properties to be returned. When that occurs, the response should follow the same behavior as PROPFIND with respect to the DAV:multistatus response elements used to return specific property results. For instance, a request to retrieve the value of a property that does not exist is an error and MUST be noted with a response XML element that contains a 404 (Not Found) status value.¶

Support for the CALDAV:calendar-query REPORT is REQUIRED.¶

Marshalling: ¶

• The request body MUST be a CALDAV:calendar-query XML element, as defined in Section 9.5.
• The request MAY include a Depth header. If no Depth header is included, Depth:0 is assumed.
• The response body for a successful request MUST be a DAV:multistatus XML element (i.e., the response uses the same format as the response for PROPFIND). In the case where there are no response elements, the returned DAV:multistatus XML element is empty.
• The response body for a successful CALDAV:calendar-query REPORT request MUST contain a DAV:response element for each iCalendar object that matched the search filter. Calendar data is being returned in the CALDAV:calendar-data XML element inside the DAV:propstat XML element.

Preconditions: ¶

• (CALDAV:supported-calendar-data): The attributes "content-type" and "version" of the CALDAV:calendar-data XML element (see Section 9.6) specify a media type supported by the server for calendar object resources.
• (CALDAV:valid-filter): The CALDAV:filter XML element (see Section 9.7) specified in the REPORT request MUST be valid. For instance, a CALDAV:filter cannot nest a <C:comp name="VEVENT"> element in a <C:comp name="VTODO"> element, and a CALDAV:filter cannot nest a <C:time-range start="..." end="..."> element in a <C:prop name="SUMMARY"> element.
• (CALDAV:supported-filter): The CALDAV:comp-filter (see Section 9.7.1), CALDAV:prop-filter (see Section 9.7.2), and CALDAV:param-filter (see Section 9.7.3) XML elements used in the CALDAV:filter XML element (see Section 9.7) in the REPORT request only make reference to components, properties, and parameters for which queries are supported by the server, i.e., if the CALDAV:filter element attempts to reference an unsupported component, property, or parameter, this precondition is violated. Servers SHOULD report the CALDAV:comp-filter, CALDAV:prop-filter, or CALDAV:param-filter for which it does not provide support.

           <!ELEMENT supported-filter (comp-filter*,
                                       prop-filter*,
                                       param-filter*)>

• (CALDAV:valid-calendar-data): The time zone specified in the REPORT request MUST be a valid iCalendar object containing a single valid VTIMEZONE component.
• (CALDAV:min-date-time): Any XML element specifying a range of time MUST have its start or end DATE or DATE-TIME values greater than or equal to the value of the CALDAV:min-date-time property value (Section 5.2.6) on the calendar collections being targeted by the REPORT request;
• (CALDAV:max-date-time): Any XML element specifying a range of time MUST have its start or end DATE or DATE-TIME values less than or equal to the value of the CALDAV:max-date-time property value (Section 5.2.7) on the calendar collections being targeted by the REPORT request;
• (CALDAV:supported-collation): Any XML attribute specifying a collation MUST specify a collation supported by the server as described in Section 7.5.

Postconditions: ¶

• (DAV:number-of-matches-within-limits): The number of matching calendar object resources must fall within server-specific, predefined limits. For example, this condition might be triggered if a search specification would cause the return of an extremely large number of responses.

The CALDAV:calendar-multiget REPORT is used to retrieve specific calendar object resources from within a collection, if the Request-URI is a collection, or to retrieve a specific calendar object resource, if the Request-URI is a calendar object resource. This report is similar to the CALDAV:calendar-query REPORT (see Section 7.8), except that it takes a list of DAV:href elements, instead of a CALDAV:filter element, to determine which calendar object resources to return.¶

Support for the CALDAV:calendar-multiget REPORT is REQUIRED.¶

Marshalling: ¶

• The request body MUST be a CALDAV:calendar-multiget XML element (see Section 9.10). If the Request-URI is a collection resource, then the DAV:href elements MUST refer to calendar object resources within that collection, and they MAY refer to calendar object resources at any depth within the collection. As a result, the "Depth" header MUST be ignored by the server and SHOULD NOT be sent by the client. If the Request-URI refers to a non-collection resource, then there MUST be a single DAV:href element that is equivalent to the Request-URI.
• The response body for a successful request MUST be a DAV:multistatus XML element.
• The response body for a successful CALDAV:calendar-multiget REPORT request MUST contain a DAV:response element for each calendar object resource referenced by the provided set of DAV:href elements. Calendar data is being returned in the CALDAV:calendar-data element inside the DAV:prop element.
• In the case of an error accessing any of the provided DAV:href resources, the server MUST return the appropriate error status code in the DAV:status element of the corresponding DAV:response element.

Preconditions: ¶

• (CALDAV:supported-calendar-data): The attributes "content-type" and "version" of the CALDAV:calendar-data XML elements (see Section 9.6) specify a media type supported by the server for calendar object resources.
• (CALDAV:min-date-time): Any XML element specifying a range of time MUST have its start or end DATE or DATE-TIME values greater than or equal to the value of the CALDAV:min-date-time property value (Section 5.2.6) on the calendar collections being targeted by the REPORT request;
• (CALDAV:max-date-time): Any XML element specifying a range of time MUST have its start or end DATE or DATE-TIME values less than or equal to the value of the CALDAV:max-date-time property value (Section 5.2.7) on the calendar collections being targeted by the REPORT request;

Postconditions: ¶

• None.

The CALDAV:free-busy-query REPORT generates a VFREEBUSY component containing free busy information for all the calendar object resources targeted by the request and that have the CALDAV:read-free-busy or DAV:read privilege granted to the current user.¶

Only VEVENT components without a TRANSP property or with the TRANSP property set to OPAQUE, and VFREEBUSY components SHOULD be considered in generating the free busy time information.¶

In the case of VEVENT components, the free or busy time type (FBTYPE) of the FREEBUSY properties in the returned VFREEBUSY component SHOULD be derived from the value of the TRANSP and STATUS properties, as outlined in the table below:¶

      +---------------------------++------------------+
      |          VEVENT           ||    VFREEBUSY     |
      +-------------+-------------++------------------+
      | TRANSP      | STATUS      || FBTYPE           |
      +=============+=============++==================+
      |             | CONFIRMED   || BUSY             |
      |             | (default)   ||                  |
      | OPAQUE      +-------------++------------------+
      | (default)   | CANCELLED   || FREE             |
      |             +-------------++------------------+
      |             | TENTATIVE   || BUSY-TENTATIVE   |
      |             +-------------++------------------+
      |             | x-name      || BUSY or          |
      |             |             || x-name           |
      +-------------+-------------++------------------+ 
      |             | CONFIRMED   ||                  |
      | TRANSPARENT | CANCELLED   || FREE             |
      |             | TENTATIVE   ||                  |
      |             | x-name      ||                  |
      +-------------+-------------++------------------+
        

Duplicate busy time periods with the same FBTYPE parameter value SHOULD NOT be specified in the returned VFREEBUSY component. Servers SHOULD coalesce consecutive or overlapping busy time periods of the same type. Busy time periods with different FBTYPE parameter values MAY overlap.¶

Support for the CALDAV:free-busy-query REPORT is REQUIRED.¶

Marshalling: ¶

• The request body MUST be a CALDAV:free-busy-query XML element (see Section 9.11), which MUST contain exactly one CALDAV:time-range XML element, as defined in Section 9.9.
• The request MAY include a Depth header. If no Depth header is included, Depth:0 is assumed.
• The response body for a successful request MUST be an iCalendar object that contains exactly one VFREEBUSY component that describes the busy time intervals for the calendar object resources containing VEVENT, or VFREEBUSY components that satisfy the Depth value and for which the current user is at least granted the CALDAV:read-free-busy privilege. If no calendar object resources are found to satisfy these conditions, a VFREEBUSY component with no FREEBUSY property MUST be returned. This report only returns busy time information. Free time information can be inferred from the returned busy time information.
• If the current user is not granted the CALDAV:read-free-busy or DAV:read privileges on the Request-URI, the CALDAV:free-busy-query REPORT request MUST fail and return a 404 (Not Found) status value. This restriction will prevent users from discovering URLs of resources for which they are only granted the CALDAV:read-free-busy privilege.
• The CALDAV:free-busy-query REPORT request can only be run against a collection (either a regular collection or a calendar collection). An attempt to run the report on a calendar object resource MUST fail and return a 403 (Forbidden) status value.

Preconditions: ¶

• None.

Postconditions: ¶

• (DAV:number-of-matches-within-limits): The number of matching calendar object resources must fall within server-specific, predefined limits. For example, this postcondition might fail if the specified CALDAV:time-range would cause an extremely large number of calendar object resources to be considered in computing the response.

There are a number of actions clients can take that will be legal (the server will not return errors), but that can degrade interoperability with other client implementations accessing the same data. For example, a recurrence rule could be replaced with a set of recurrence dates, a single recurring event could be replaced with a set of independent resources to represent each recurrence, or the start/end time values can be translated from the original time zone to another time zone. Although this advice amounts to iCalendar interoperability best practices and is not limited only to CalDAV usage, interoperability problems are likely to be more evident in CalDAV use cases.¶

WebDAV already provides functionality required to synchronize a collection or set of collections, to make changes offline, and provides a simple way to resolve conflicts when reconnected. ETags are the key to making this work, but these are not required of all WebDAV servers. Since offline functionality is more important to calendar applications than to some other WebDAV applications, CalDAV servers MUST support ETags, as specified in Section 5.3.4.¶

WebDAV locks can be used to prevent two clients that are modifying the same resource from either overwriting each others' changes (though that problem can also be solved by using ETags) or wasting time making changes that will conflict with another set of changes. In a multi-user calendar system, an interactive calendar client could lock an event while the user is editing the event, and unlock the event when the user finishes or cancels. Locks can also be used to prevent changes while data is being reorganized. For example, a calendar client might lock two calendar collections prior to moving a bunch of calendar resources from one to another.¶

Clients are responsible for requesting a lock timeout period that is appropriate to the use case. When the user explicitly decides to reserve a resource and prevent other changes, a long timeout might be appropriate, but in cases where the client automatically decides to lock the resource, the timeout should be short (and the client can always refresh the lock should it need to). A short lock timeout means that if the client is unable to remove the lock, the other calendar users aren't prevented from making changes.¶

Much of the time, a calendar client (or agent) will discover a new calendar's location by being provided directly with the URL. For example, a user will type his or her own calendar location into client configuration information or copy and paste a URL from email into the calendar application. The client need only confirm that the URL points to a resource that is a calendar collection. The client may also be able to browse WebDAV collections to find calendar collections.¶

The choice of HTTP URLs means that calendar object resources are backward compatible with existing software, but does have the disadvantage that existing software does not usually know to look at the OPTIONS response to that URL to determine what can be done with it. This is somewhat of a barrier for WebDAV usage as well as with CalDAV usage. This specification does not offer a way through this other than making the information available in the OPTIONS response should this be requested.¶

For calendar sharing and scheduling use cases, one might wish to find the calendar belonging to another user. If the other user has a calendar in the same repository, that calendar can be found by using the principal namespace required by WebDAV ACL support. For other cases, the authors have no universal solution, but implementers can consider whether to use vCard [RFC2426] or LDAP [RFC4511] standards together with calendar attributes [RFC2739].¶

Because CalDAV requires servers to support WebDAV ACL [RFC3744], including principal namespaces, and with the addition of the CALDAV:calendar-home-set property, there are a couple options for CalDAV clients to find one's own calendar or another user's calendar.¶

The server performs a case-sensitive or caseless search for a matching string subset of "Laurie" within the DAV:displayname property. Thus, the server might return "Laurie Dusseault", "Laurier Desruisseaux", or "Wilfrid Laurier" as matching DAV:displayname values, and return the calendars for each of these.¶

CalDAV clients MAY create attachments in calendar components either as inline or external. This section contains some guidelines for creating and managing attachments.¶

Note that all CalDAV calendar collections (including those the user might treat as public or group calendars) can contain alarm information on events and to-dos. Users can synchronize a calendar between multiple devices and decide to have alarms execute on a different device than the device that created the alarm. Not all alarm action types are completely interoperable (e.g., those that name a sound file to play).¶

• When the action is AUDIO and the client is configured to execute the alarm, the client SHOULD play the suggested sound if it's available or play another sound, but SHOULD NOT rewrite the alarm just to replace the suggested sound with a sound that's locally available.
• When the action is DISPLAY and the client is configured to execute the alarm, the client SHOULD execute a display alarm by displaying according to the suggested description or some reasonable replacement, but SHOULD NOT rewrite the alarm for its own convenience.
• When the action is EMAIL and the client is incapable of sending email, it SHOULD ignore the alarm, but it MUST continue to synchronize the alarm itself.
• This specification makes no recommendations about executing alarms of type PROCEDURE, except to note that clients are advised to take care to avoid creating security holes by executing these.

Non-interoperable alarm information (e.g., should somebody define a color to be used in a display alarm) should be put in non-standard properties inside the VALARM component in order to keep the basic alarm usable on all devices.¶

Clients that allow changes to calendar object resources MUST synchronize the alarm data that already exists in the resources. Clients MAY execute alarms that are downloaded in this fashion, possibly based on user preference. If a client is only doing read operations on a calendar and there is no risk of losing alarm information, then the client MAY discard alarm information.¶

This specification makes no attempt to provide multi-user alarms on group calendars or to find out for whom an alarm is intended. Addressing those issues might require extensions to iCalendar; for example, to store alarms per-user, or to indicate for which user a VALARM was intended. In the meantime, clients might maximize interoperability by generally not uploading alarm information to public, group, or resource calendars.¶

Name:

calendar

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Specifies the resource type of a calendar collection.

Description:

See Section 4.2.

Definition:

      <!ELEMENT calendar EMPTY>

Name:

mkcalendar

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Specifies a request that includes the WebDAV property values to be set for a calendar collection resource when it is created.

Description:

See Section 5.3.1.

Definition:

      <!ELEMENT mkcalendar (DAV:set)>

Name:

mkcalendar-response

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Specifies a response body for a successful MKCALENDAR request.

Description:

See Section 5.3.1.

Definition:

      <!ELEMENT mkcalendar-response ANY>

Name:

supported-collation

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Identifies a single collation via its collation identifier, as defined by [RFC4790].

Description:

The CALDAV:supported-collation contains the text of a collation identifier, as described in Section 7.5.1.

Definition:

      <!ELEMENT supported-collation (#PCDATA)>
      PCDATA value: collation identifier

Name:

calendar-query

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Defines a report for querying calendar object resources.

Description:

See Section 7.8.

Definition:

      <!ELEMENT calendar-query ((DAV:allprop |
                                 DAV:propname |
                                 DAV:prop)?, filter, timezone?)>

Name:

calendar-data

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Specified one of the following:

1. A supported media type for calendar object resources when nested in the CALDAV:supported-calendar-data property;
2. The parts of a calendar object resource should be returned by a calendaring report;
3. The content of a calendar object resource in a response to a calendaring report.

Description:

When nested in the CALDAV:supported-calendar-data property, the CALDAV:calendar-data XML element specifies a media type supported by the CalDAV server for calendar object resources.

When used in a calendaring REPORT request, the CALDAV:calendar-data XML element specifies which parts of calendar object resources need to be returned in the response. If the CALDAV:calendar-data XML element doesn't contain any CALDAV:comp element, calendar object resources will be returned in their entirety.

Finally, when used in a calendaring REPORT response, the CALDAV:calendar-data XML element specifies the content of a calendar object resource. Given that XML parsers normalize the two-character sequence CRLF (US-ASCII decimal 13 and US-ASCII decimal 10) to a single LF character (US-ASCII decimal 10), the CR character (US-ASCII decimal 13) MAY be omitted in calendar object resources specified in the CALDAV:calendar-data XML element. Furthermore, calendar object resources specified in the CALDAV:calendar-data XML element MAY be invalid per their media type specification if the CALDAV:calendar-data XML element part of the calendaring REPORT request did not specify required properties (e.g., UID, DTSTAMP, etc.), or specified a CALDAV:prop XML element with the "novalue" attribute set to "yes".

Note:

The CALDAV:calendar-data XML element is specified in requests and responses inside the DAV:prop XML element as if it were a WebDAV property. However, the CALDAV:calendar-data XML element is not a WebDAV property and, as such, is not returned in PROPFIND responses, nor used in PROPPATCH requests.

Note:

The iCalendar data embedded within the CALDAV:calendar-data XML element MUST follow the standard XML character data encoding rules, including use of &lt;, &gt;, &amp; etc. entity encoding or the use of a <![CDATA[ ... ]]> construct. In the later case, the iCalendar data cannot contain the character sequence "]]>", which is the end delimiter for the CDATA section.

Definition:

      <!ELEMENT calendar-data EMPTY>

      when nested in the CALDAV:supported-calendar-data property
      to specify a supported media type for calendar object
      resources;

      <!ELEMENT calendar-data (comp?,
                               (expand | limit-recurrence-set)?,
                               limit-freebusy-set?)>

      when nested in the DAV:prop XML element in a calendaring
      REPORT request to specify which parts of calendar object
      resources should be returned in the response;

      <!ELEMENT calendar-data (#PCDATA)>
      PCDATA value: iCalendar object

      when nested in the DAV:prop XML element in a calendaring
      REPORT response to specify the content of a returned
      calendar object resource.

      <!ATTLIST calendar-data content-type CDATA "text/calendar"
                              version CDATA "2.0">
      content-type value: a MIME media type
      version value: a version string
      
      attributes can be used on all three variants of the
      CALDAV:calendar-data XML element.

Name:

filter

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Specifies a filter to limit the set of calendar components returned by the server.

Description:

The CALDAV:filter XML element specifies the search filter used to limit the calendar components returned by a calendaring REPORT request.

Definition:

      <!ELEMENT filter (comp-filter)>

Name:

timezone

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Specifies the time zone component to use when determining the results of a report.

Description:

The CALDAV:timezone XML element specifies that for a given calendaring REPORT request, the server MUST rely on the specified VTIMEZONE component instead of the CALDAV:calendar-timezone property of the calendar collection, in which the calendar object resource is contained to resolve "date" values and "date with local time" values (i.e., floating time) to "date with UTC time" values. The server will require this information to determine if a calendar component scheduled with "date" values or "date with local time" values intersects a CALDAV:time-range specified in a CALDAV:calendar-query REPORT.

Note:

The iCalendar data embedded within the CALDAV:timezone XML element MUST follow the standard XML character data encoding rules, including use of &lt;, &gt;, &amp; etc. entity encoding or the use of a <![CDATA[ ... ]]> construct. In the later case, the iCalendar data cannot contain the character sequence "]]>", which is the end delimiter for the CDATA section.

Definition:

      <!ELEMENT timezone (#PCDATA)>
      PCDATA value: an iCalendar object with exactly one VTIMEZONE
              

Name:

time-range

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Specifies a time range to limit the set of calendar components returned by the server.

Description:

The CALDAV:time-range XML element specifies that for a given calendaring REPORT request, the server MUST only return the calendar object resources that, depending on the context, have a component or property whose value intersects a specified time range.

The "start" attribute specifies the inclusive start of the time range, and the "end" attribute specifies the non-inclusive end of the time range. Both attributes MUST be specified as "date with UTC time" value. Time ranges open at one end can be specified by including only one attribute; however, at least one attribute MUST always be present in the CALDAV:time-range element. If either the "start" or "end" attribute is not specified in the CALDAV:time-range XML element, assume "-infinity" and "+infinity" as their value, respectively. If both "start" and "end" are present, the value of the "end" attribute MUST be greater than the value of the "start" attribute.

Time range tests MUST consider every recurrence instance when testing the time range condition; if any one instance matches, then the test returns true. Testing recurrence instances requires the server to infer an effective value for DTSTART, DTEND, DURATION, and DUE properties for an instance based on the recurrence patterns and any overrides.

A VEVENT component overlaps a given time range if the condition for the corresponding component state specified in the table below is satisfied. Note that, as specified in [RFC2445], the DTSTART property is REQUIRED in the VEVENT component. The conditions depend on the presence of the DTEND and DURATION properties in the VEVENT component. Furthermore, the value of the DTEND property MUST be later in time than the value of the DTSTART property. The duration of a VEVENT component with no DTEND and DURATION properties is 1 day (+P1D) when the DTSTART is a DATE value, and 0 seconds when the DTSTART is a DATE-TIME value.

   +---------------------------------------------------------------+
   | VEVENT has the DTEND property?                                |
   |   +-----------------------------------------------------------+
   |   | VEVENT has the DURATION property?                         |
   |   |   +-------------------------------------------------------+
   |   |   | DURATION property value is greater than 0 seconds?    |
   |   |   |   +---------------------------------------------------+
   |   |   |   | DTSTART property is a DATE-TIME value?            |
   |   |   |   |   +-----------------------------------------------+
   |   |   |   |   | Condition to evaluate                         |
   +---+---+---+---+-----------------------------------------------+
   | Y | N | N | * | (start <  DTEND AND end > DTSTART)            |
   +---+---+---+---+-----------------------------------------------+
   | N | Y | Y | * | (start <  DTSTART+DURATION AND end > DTSTART) |
   |   |   +---+---+-----------------------------------------------+
   |   |   | N | * | (start <= DTSTART AND end > DTSTART)          |
   +---+---+---+---+-----------------------------------------------+
   | N | N | N | Y | (start <= DTSTART AND end > DTSTART)          |
   +---+---+---+---+-----------------------------------------------+
   | N | N | N | N | (start <  DTSTART+P1D AND end > DTSTART)      |
   +---+---+---+---+-----------------------------------------------+
              

A VTODO component is said to overlap a given time range if the condition for the corresponding component state specified in the table below is satisfied. The conditions depend on the presence of the DTSTART, DURATION, DUE, COMPLETED, and CREATED properties in the VTODO component. Note that, as specified in [RFC2445], the DUE value MUST be a DATE-TIME value equal to or after the DTSTART value if specified.

+-------------------------------------------------------------------+
| VTODO has the DTSTART property?                                   |
|   +---------------------------------------------------------------+
|   |   VTODO has the DURATION property?                            |
|   |   +-----------------------------------------------------------+
|   |   | VTODO has the DUE property?                               |
|   |   |   +-------------------------------------------------------+
|   |   |   | VTODO has the COMPLETED property?                     |
|   |   |   |   +---------------------------------------------------+
|   |   |   |   | VTODO has the CREATED property?                   |
|   |   |   |   |   +-----------------------------------------------+
|   |   |   |   |   | Condition to evaluate                         |
+---+---+---+---+---+-----------------------------------------------+
| Y | Y | N | * | * | (start  <= DTSTART+DURATION)  AND             |
|   |   |   |   |   | ((end   >  DTSTART)  OR                       |
|   |   |   |   |   |  (end   >= DTSTART+DURATION))                 |
+---+---+---+---+---+-----------------------------------------------+
| Y | N | Y | * | * | ((start <  DUE)      OR  (start <= DTSTART))  |
|   |   |   |   |   | AND                                           |
|   |   |   |   |   | ((end   >  DTSTART)  OR  (end   >= DUE))      |
+---+---+---+---+---+-----------------------------------------------+
| Y | N | N | * | * | (start  <= DTSTART)  AND (end >  DTSTART)     |
+---+---+---+---+---+-----------------------------------------------+
| N | N | Y | * | * | (start  <  DUE)      AND (end >= DUE)         |
+---+---+---+---+---+-----------------------------------------------+
| N | N | N | Y | Y | ((start <= CREATED)  OR  (start <= COMPLETED))|
|   |   |   |   |   | AND                                           |
|   |   |   |   |   | ((end   >= CREATED)  OR  (end   >= COMPLETED))|
+---+---+---+---+---+-----------------------------------------------+
| N | N | N | Y | N | (start  <= COMPLETED) AND (end  >= COMPLETED) |
+---+---+---+---+---+-----------------------------------------------+
| N | N | N | N | Y | (end    >  CREATED)                           |
+---+---+---+---+---+-----------------------------------------------+
| N | N | N | N | N | TRUE                                          |
+---+---+---+---+---+-----------------------------------------------+
              

A VJOURNAL component overlaps a given time range if the condition for the corresponding component state specified in the table below is satisfied. The conditions depend on the presence of the DTSTART property in the VJOURNAL component and on whether the DTSTART is a DATE-TIME or DATE value. The effective "duration" of a VJOURNAL component is 1 day (+P1D) when the DTSTART is a DATE value, and 0 seconds when the DTSTART is a DATE-TIME value.

   +----------------------------------------------------+
   | VJOURNAL has the DTSTART property?                 |
   |   +------------------------------------------------+
   |   | DTSTART property is a DATE-TIME value?         |
   |   |   +--------------------------------------------+
   |   |   | Condition to evaluate                      |
   +---+---+--------------------------------------------+
   | Y | Y | (start <= DTSTART)     AND (end > DTSTART) |
   +---+---+--------------------------------------------+
   | Y | N | (start <  DTSTART+P1D) AND (end > DTSTART) |
   +---+---+--------------------------------------------+
   | N | * | FALSE                                      |
   +---+---+--------------------------------------------+
              

A VFREEBUSY component overlaps a given time range if the condition for the corresponding component state specified in the table below is satisfied. The conditions depend on the presence in the VFREEBUSY component of the DTSTART and DTEND properties, and any FREEBUSY properties in the absence of DTSTART and DTEND. Any DURATION property is ignored, as it has a special meaning when used in a VFREEBUSY component.

When only FREEBUSY properties are used, each period in each FREEBUSY property is compared against the time range, irrespective of the type of free busy information (free, busy, busy-tentative, busy-unavailable) represented by the property.

   +------------------------------------------------------+
   | VFREEBUSY has both the DTSTART and DTEND properties? |
   |   +--------------------------------------------------+
   |   | VFREEBUSY has the FREEBUSY property?             |
   |   |   +----------------------------------------------+
   |   |   | Condition to evaluate                        |
   +---+---+----------------------------------------------+
   | Y | * | (start <= DTEND) AND (end > DTSTART)         |
   +---+---+----------------------------------------------+
   | N | Y | (start <  freebusy-period-end) AND           |
   |   |   | (end   >  freebusy-period-start)             |
   +---+---+----------------------------------------------+
   | N | N | FALSE                                        |
   +---+---+----------------------------------------------+
              

A VALARM component is said to overlap a given time range if the following condition holds:

      (start <= trigger-time) AND (end > trigger-time)

A VALARM component can be defined such that it triggers repeatedly. Such a VALARM component is said to overlap a given time range if at least one of its triggers overlaps the time range.

The calendar properties COMPLETED, CREATED, DTEND, DTSTAMP, DTSTART, DUE, and LAST-MODIFIED overlap a given time range if the following condition holds:

       (start <= date-time) AND (end > date-time)

Note that if DTEND is not present in a VEVENT, but DURATION is, then the test should instead operate on the 'effective' DTEND, i.e., DTSTART+DURATION. Similarly, if DUE is not present in a VTODO, but DTSTART and DURATION are, then the test should instead operate on the 'effective' DUE, i.e., DTSTART+DURATION.

The semantic of CALDAV:time-range is not defined for any other calendar components and properties.

Definition:

      <!ELEMENT time-range EMPTY>

      <!ATTLIST time-range start CDATA #IMPLIED
                           end   CDATA #IMPLIED>
      start value: an iCalendar "date with UTC time"
      end value: an iCalendar "date with UTC time"
              

Name:

calendar-multiget

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

CalDAV report used to retrieve specific calendar object resources.

Description:

See Section 7.9.

Definition:

      <!ELEMENT calendar-multiget ((DAV:allprop |
                                   DAV:propname |
                                   DAV:prop)?, DAV:href+)>
              

Name:

free-busy-query

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

CalDAV report used to generate a VFREEBUSY to determine busy time over a specific time range.

Description:

See Section 7.10.

Definition:

      <!ELEMENT free-busy-query (time-range)>
              

URI: urn:ietf:params:xml:ns:caldav¶

Registrant Contact: See the "Authors' Addresses" section of this document.¶

XML: None. Namespace URIs do not represent an XML specification.¶