| Network Working Group | C. Daboo |
| Internet-Draft | ISAMET |
| Intended status: Informational | B. Desruisseaux |
| Expires: April 3, 2006 | Oracle |
| L. Dusseault | |
| OSAF | |
| September 30, 2005 |
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Copyright © The Internet Society (2005). All Rights Reserved.¶
This document specifies a set of methods, headers, message bodies, properties, and reports that define calendar access extensions to the WebDAV protocol. The new protocol elements are intended to make WebDAV-based calendaring and scheduling an interoperable standard that supports calendar access, calendar management, calendar sharing, and calendar publishing.¶
The concept of using HTTP [5] and WebDAV [4] as a basis for a calendaring server is by no means a new concept: it was discussed in the IETF CALSCH working group as early as 1997 or 1998. Several companies have implemented calendaring servers using HTTP PUT/GET to upload and download iCalendar [3] objects, and using WebDAV PROPFIND to get listings of resources. However, those implementations do not interoperate because there are many small and big decisions to be made in how to model calendaring data as WebDAV resources, as well as how to implement required features that aren't already part of WebDAV. This document proposes a standard way of modeling calendar data in WebDAV, with additional features to make calendar access work well.¶
Discussion of this Internet-Draft is taking place on the mailing list <http://lists.osafoundation.org/mailman/listinfo/ietf-caldav>.¶
The augmented BNF used by this document to describe protocol elements is described in Section 2.1 of [5]. Because this augmented BNF uses the basic production rules provided in Section 2.2 of [5], those rules apply to this document as well.¶
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 [1].¶
The term "protected" is used in the Conformance field of property definitions as defined in Section 1.4.2 of RFC3253 [7].¶
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 [10].¶
The namespace "urn:ietf:params:xml:ns:caldav" is reserved for the XML elements defined in this specification, its revisions, and related CalDAV specifications. It MUST NOT be used for proprietary extensions.¶
Note that the XML declarations used in this document are incomplete, in that they do not include namespace information. Thus, the reader MUST NOT use these declarations as the only way to create valid CalDAV properties or to validate CalDAV XML element type. Some of the declarations refer to XML elements defined by WebDAV which use the "DAV:" namespace. Wherever such elements appear, they are explicitly given the "DAV:" prefix to help 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.¶
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 be either 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. In a 207 Multi-Status response, the DAV:error element would appear in the appropriate DAV:responsedescription element.¶
This section lists what functionality is required of a CalDAV server. To advertise support for CalDAV, a server: ¶
In addition, a server: ¶
If a server supports the CalDAV features described in this document, it 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, methods, or privilege. A value of "calendar-access" in the DAV header MUST indicate that the server supports all MUST level requirements and REQUIRED features specified in this document.¶
>> Request <<
␉␉␉␉␉␉ OPTIONS /home/bernard/calendars/ HTTP/1.1 Host: cal.example.com
>> Response <<
␉␉␉␉␉␉ HTTP/1.1 200 OK Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE Allow: PROPFIND, PROPPATCH, LOCK, UNLOCK, REPORT, ACL DAV: 1, 2, access-control, calendar-access Content-Length: 0
In this example, the OPTIONS method returns the value "calendar-access" in the DAV header of the response to indicate that the "/home/bernard/calendars/" collection may support properties, reports, methods, or privilege defined in this specification.¶
One of the features which has made WebDAV a successful protocol is its firm data model. This makes it a useful framework for other applications such as calendaring. This specification follows the same pattern by developing all features based on a well-described data model.¶
In the CalDAV data model, every VEVENT, VTODO, VJOURNAL, VTIMEZONE and VFREEBUSY component is contained in an individual resource, referred to as a "calendar object resource". Each calendar object resource may be individually locked and have individual WebDAV properties. These resources are placed into WebDAV collections with a mostly-fixed structure.¶
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. So 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. Both CalDAV servers and clients MUST ensure that the data is consistent and compliant. 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. HTTP ETags and other features help this work.¶
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 patterns, recurrence dates, exception dates, and exception information 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 instances in synch 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 pattern. It makes it easier to create a recurring calendar component, and easier 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 collections are 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 contains calendar object resources that represent iCalendar objects within a calendar. A calendar collection may be created through provisioning (e.g., automatically created when a user's account is created), or it may be created through MKCALENDAR (see Section 4.5.1). This can be useful for a user to create a second calendar (e.g., soccer schedule) or for users to share a calendar (e.g., team events or conference room). Note however that this document doesn't define what extra calendar collections are for, 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 4.3.1 to provide such a cue.¶
Calendar collections MUST only contain calendar object resources and collections that are not calendar collections. Furthermore, collections contained in calendar collections MUST NOT contain calendar collections. This specification does not define how collections contained in calendar collections are used and may relate to the calendar object resources contained in the calendar collections.¶
Multiple calendar collections MAY be children of the same collection.¶
This section defines properties that may be defined on calendar collections.¶
<!ELEMENT calendar-description (#PCDATA) >
<C:calendar-description xml:lang="fr-CA"
xmlns:C="urn:ietf:params:xml:ns:caldav"
>Calendrier de Bernard Desruisseaux</C:calendar-description>
<!ELEMENT calendar-component-restriction-set (comp*)>
<C:calendar-component-restriction-set
xmlns:C="urn:ietf:params:xml:ns:caldav">
<C:comp name="VEVENT"/>
<C:comp name="VTODO"/>
</C:calendar-component-restriction-set>
<!ELEMENT calendar-restrictions (calendar-data?)>
<C:calendar-restrictions xmlns:C="urn:ietf:params:xml:ns:caldav">
<C:calendar-data content-type="text/calendar" version="2.0"/>
</C:calendar-restrictions>
Calendar object resources contained in calendar collections MUST NOT contain more than one type of calendar component (e.g., VEVENT, VTODO, 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 two VEVENT components and one VTIMEZONE component, but it cannot contain one VEVENT component and one VTODO component.¶
The UID property value of the calendar components contained in a calendar object resource MUST be unique in the scope of the calendar collection, and all its descendant collections, in which the calendar object resource is contained.¶
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. In that case there will be one component without a RECURRENCE-ID property (the component that defines the recurrence pattern) and all the rest will have that property (these are the recurrence exceptions).¶
For example, given the following iCalendar object: ¶
␉␉␉␉␉␉ BEGIN:VCALENDAR CALSCALE:GREGORIAN PRODID:-//Example, Inc.\, Inc.//Example App//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 RECURRENCE-ID:20041213T120000Z DTSTAMP:20041210T183838Z DTSTART:20041213T130000Z 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.¶
The creation of calendar collections and calendar object resources may be initiated by either a CalDAV client or by the CalDAV server. For example, a server might come preconfigured with a user's calendar collection, or the CalDAV client might request the server to create a new calendar collection for a given user. Servers might populate events as calendar objects inside a calendar collection, or clients might request the server to create events. Either way, both client and server MUST comply with the requirements in this document, and MUST understand objects appearing in calendar collections or according to the data model defined here.¶
An HTTP request using the MKCALENDAR method creates a new calendar collection resource. A server MAY restrict calendar collection creation to particular collections.¶
Support for MKCALENDAR on the server is only RECOMMENDED and not REQUIRED because some calendar stores only support one calendar per user (or principal) and those are typically pre-created for each account. However, servers and clients are strongly encouraged to support MKCALENDAR whenever possible to allow users to create multiple calendar collections to better help organize their data.¶
Clients SHOULD use the DAV:displayname property for a human-readable name of the calendar. Clients can either specify the value of the DAV:displayname property in the request body of the MKCALENDAR request, or alternatively issue a PROPPATCH request to change the DAV:displayname property to the appropriate value immediately after issuing the MKCALENDAR request. Clients SHOULD NOT set the DAV:displayname property to be the same as any other calendar collection at the same URI "level". When displaying calendar collections to users, clients SHOULD check the DAV:displayname property and use that value as the name of the calendar. In the event that the DAV:displayname property is empty, the client MAY use the last part of the calendar collection URI as the name.¶
If a MKCALENDAR request fails, the server state preceding the request MUST be restored.¶
Marshalling: ¶
<!ELEMENT mkcalendar (DAV:set)>
<!ELEMENT mkcalendar-response ANY>
Preconditions: ¶
Postconditions: ¶
The following are examples of response codes one would expect to get in a response to a MKCALENDAR request. Note that this list is by no mean exhaustive. ¶
This example creates a calendar collection called /home/lisa/tasks/ on the server cal.example.com with specific values for the properties DAV:displayname, CALDAV:calendar-description and CALDAV:calendar-component-restriction-set.¶
>> Request <<
␉␉␉␉␉␉ MKCALENDAR /home/lisa/tasks/ HTTP/1.1 Host: cal.example.com Content-Type: text/xml; charset="utf-8" Content-Length: xxx <?xml version="1.0" encoding="utf-8" ?> <C:mkcalendar xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav"> <D:set> <D:prop> <D:displayname>Lisa's To-dos</D:displayname> <C:calendar-description >Calendar restricted to to-dos.</C:calendar-description> <C:calendar-component-restriction-set> <C:comp name="VTODO"/> </C:calendar-component-restriction-set> </D:prop> </D:set> </C:mkcalendar> ␉␉␉␉␉
>> Response <<
␉␉␉␉␉␉ HTTP/1.1 201 Created Cache-Control: no-cache Content-Length: 0 ␉␉␉␉␉
Clients typically populate calendar collections with calendar object resources. The URL for each calendar object resource is entirely arbitrary, and does not need to bear a specific relationship (but might) to the calendar object resource's subject, scheduled time, UID or other metadata. A new calendar object resource must have a unique URL, otherwise the new component would instead be an update to an existing calendar object resource.¶
When servers create new resources, it's not hard for the server to choose a unique URL. It's slightly tougher for clients, because a client might not want to examine all resources in the collection, and might not want to lock the entire collection to ensure that a new one isn't created with a name collision. However, there are http features to mitigate this. If the client intends to create a new non-collection resource, such as a new VEVENT, the client SHOULD use the HTTP header "If-None-Match: *" on the PUT request. The Request-URI on the PUT request MUST include the target collection, where the resource is to be created, plus the name of the resource in the last path segment. The last path segment could be a random number, or it could be a sequence number, or a string related to the object's SUMMARY property. No matter how the name is chosen, the "If-None-Match" header ensures that the client cannot overwrite an existing resource even if it has accidentally chosen a duplicate resource name.¶
Servers SHOULD return an ETag header containing the actual ETag of the newly created resource on a successful creation.¶
>> Request <<
␉␉␉␉␉ PUT /home/lisa/calendar/newevent.ics HTTP/1.1 If-None-Match: * Host: cal.example.com Content-Type: text/calendar Content-Length: xxx BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Example Corp.//CalDAV Client//EN BEGIN:VEVENT UID:20010712T182145Z-123401@example.com DTSTART:20010714T170000Z DTEND:20010715T040000Z SUMMARY:Bastille Day Party END:VEVENT END:VCALENDAR
>> Response <<
␉␉␉␉␉ HTTP/1.1 201 Created Content-Length: 0 ETag: "123456789-000-111"
The request to change an existing event is the same, but with a specific ETag in the "If-Match" header, rather than the "If-None-Match" header.¶
As indicated in Section 3.10 of RFC 2445 [3], the URL of calendar object resources containing (an arbitrary set of) calendaring and scheduling information may be suffixed by ".ics", and the URL of calendar object resources containing free or busy time information may be suffixed by ".ifb".¶
Preconditions for PUT within calendar collections: ¶
A CalDAV server MUST support WebDAV ACL [9]. WebDAV ACL provides a framework for an extensible list of privileges on WebDAV collections and ordinary resources. A CalDAV server MUST also support the calendaring privilege defined in this section.¶
Calendar users often wish to allow other users to see their busy time information, without viewing the other details of the calendar components (location, summary, attendees). This allows a significant amount of privacy while still allowing those other users to schedule meetings at times when the calendar user is likely to be free.¶
The CALDAV:read-free-busy privilege controls which calendar collections and calendar object resources are examined when a free-busy-query REPORT is run (see Section 6.6). This privilege can be granted on calendar collections or calendar object resources. Servers MUST support this privilege on calendar collections and any calendar object resources within those collections.¶
<!ELEMENT read-free-busy EMPTY>
The CALDAV:read-free-busy privilege is aggregated in the DAV:read privilege. Note that if an ACL grants the privilege CALDAV:read-free-busy, the client may not expect to be granted access to GET, HEAD, OPTIONS and PROPFIND.¶
In the WebDAV ACL standard, servers MUST support the DAV:supported-privilege-set property to show which privileges are abstract, which privileges are supported, how the privileges relate to one another, and to provide text descriptions (particularly useful for custom privileges). The relationships between privileges involves showing which privilege is a subset or a superset of another privilege. For example, because reading the ACL property is considered a more specific privilege than the DAV:read privilege (a subset of the total set of actions are allowed), it may be aggregated under the DAV:read privilege. Although the list of supported privileges MAY vary somewhat from server to server (the WebDAV ACL specification leaves room for a fair amount of diversity in server implementations), the following restriction MUST hold for a CalDAV server: ¶
This is a partial example of how the DAV:supported-privilege-set property could look on a server supporting CalDAV. Note that aggregation is shown in the structure of the DAV:supported-privilege elements containing each other.¶
<D:supported-privilege-set xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:supported-privilege>
<D:privilege><D:all/></D:privilege>
<D:abstract/>
<D:description xml:lang="en"
>Any operation</D:description>
<D:supported-privilege>
<D:privilege><D:read/></D:privilege>
<D:description xml:lang="en"
>Read any object</D:description>
<D:supported-privilege>
<D:privilege><D:read-acl/></D:privilege>
<D:description xml:lang="en"
>Read ACL</D:description>
</D:supported-privilege>
<D:supported-privilege>
<D:privilege><D:read-current-user-privilege-set/>
</D:privilege>
<D:description xml:lang="en"
>Read current user privilege set</D:description>
</D:supported-privilege>
<D:supported-privilege>
<D:privilege>
<C:read-free-busy/>
</D:privilege>
<D:description xml:lang="en"
>Read busy time information</D:description>
</D:supported-privilege>
</D:supported-privilege>
<D:supported-privilege>
<D:privilege><D:write/></D:privilege>
<D:description xml:lang="en"
>Write any object</D:description>
...
</D:supported-privilege>
</D:supported-privilege-set>
This section defines additional properties for WebDAV principal resources as defined in RFC3744 [9].¶
<!ELEMENT calendar-home-set (DAV:href*) >
<C:calendar-home-set xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:href>http://cal.example.com/home/bernard/calendars/</D:href>
</C:calendar-home-set>
This section defines the reports which a CalDAV server MUST support on calendar collections and calendar object resources.¶
CalDAV servers MUST advertise support for those reports with the DAV:supported-report-set property defined in RFC3253 [7].¶
Some of these reports allow calendar data (from possibly multiple resources) to be returned.¶
The REPORT method (defined in Section 3.6 of RFC3253 [7]) provides an extensible mechanism for obtaining information about a resource. 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.¶
Servers MAY support the REPORTs defined in this specification on non-calendar collections. In computing responses to the REPORTs defined in this specification, servers MUST only consider calendar object resources contained in calendar collections, subject also to the value of the Depth request header.¶
If these REPORTs are supported on ordinary collections the server advertises the capability with the DAV:supported-report-set property as already described.¶
Some of the reports defined in CalDAV can be targetted at calendar object resources within a specific time range. To determine whether a calendar object resource matches the time range filter element, the start and end times for the particular type of object are determined and then compared to the requested time range. If the start and end overlap the requested time range, then the calendar object resource matches the filter element. The rules defined in [3] for determining the actual start and end times of calendar components MUST be used.¶
When such time range filtering is used, special consideration must be given to recurring calendar components such as VEVENT and VTODO components. The server MUST expand recurring items to determine whether any one or more recurrence instances overlap the requested time range. If any one instance overlaps the time range, then the calendar object resource matches the filter element.¶
In addition, CalDAV provides three ways to determine which recurrence instances are returned from the recurrence set. The three options are: ¶
The CALDAV:calendar-query REPORT performs a search for all calendar object resources that match a specified search 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 search 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 which does not exist is an error and MUST be noted with a response XML element which contains a 404 (Not Found) status value.¶
Support for the CALDAV:calendar-query REPORT is REQUIRED.¶
Marshalling: ¶
Preconditions: ¶
Postconditions: ¶
In this example, the client requests the server to return specific components and properties of the VEVENT components that overlap the time range from September 2nd, 2004 at 00:00:00 am UTC to September 3rd, 2004 at 00:00:00 am UTC. In addition the DAV:getetag property is also requested and returned as part of the response. Note that the third calendar object returned is a recurring event whose first instance lies outside of the requested time range, but whose second instance does overlap the time range.¶
>> Request <<
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-query xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop>
<D:getetag/>
<C:calendar-data>
<C:comp name="VCALENDAR">
<C:allprop/>
<C:comp name="VEVENT">
<C:prop name="X-ABC-GUID"/>
<C:prop name="UID"/>
<C:prop name="DTSTART"/>
<C:prop name="DTEND"/>
<C:prop name="DURATION"/>
<C:prop name="EXDATE"/>
<C:prop name="EXRULE"/>
<C:prop name="RDATE"/>
<C:prop name="RRULE"/>
<C:prop name="LOCATION"/>
<C:prop name="SUMMARY"/>
</C:comp>
<C:comp name="VTIMEZONE">
<C:allprop/>
<C:allcomp/>
</C:comp>
</C:comp>
</C:calendar-data>
</D:prop>
<C:filter>
<C:comp-filter name="VCALENDAR">
<C:comp-filter name="VEVENT">
<C:time-range start="20040902T000000Z"
end="20040903T000000Z"/>
</C:comp-filter>
</C:comp-filter>
</C:filter>
</C:calendar-query>
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:response>
<D:href
>http://cal.example.com/home/bernard/calendar/ev102.ics</D:href>
<D:propstat>
<D:prop>
<D:getetag>"23ba4d-ff11fb"</D:getetag>
<C:calendar-data>BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Client//EN
BEGIN:VEVENT
DTSTART:20040902T100000Z
DTEND:20040902T120000Z
SUMMARY:Design meeting
UID:34222-232@example.com
X-ABC-GUID:E1CX4zp-0005Ld-21@example.com
END:VEVENT
END:VCALENDAR
</C:calendar-data>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href
>http://cal.example.com/home/bernard/calendar/mtg103.ics</D:href>
<D:propstat>
<D:prop>
<D:getetag>"ff11fb-23ba4d"</D:getetag>
<C:calendar-data>BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Client//EN
BEGIN:VEVENT
DTSTART:20040902T130000Z
DTEND:20040902T150000Z
SUMMARY:Design meeting - Part II
UID:63409-868@example.com
X-ABC-GUID:E1CX5Dr-0007ym-Hz@example.com
END:VEVENT
END:VCALENDAR
</C:calendar-data>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href
>http://cal.example.com/home/bernard/calendar/mtg104.ics</D:href>
<D:propstat>
<D:prop>
<D:getetag>"7834cd-63fd2c"</D:getetag>
<C:calendar-data>BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Client//EN
BEGIN:VEVENT
DTSTART:20040901T130000Z
DTEND:20040901T150000Z
RRULE:FREQ=DAILY;COUNT=2
SUMMARY:Design meeting - Part III
UID:63409-451@example.com
X-ABC-GUID:E1CX5Dr-0008ym-Hz@example.com
END:VEVENT
END:VCALENDAR
</C:calendar-data>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
In this example, the client requests the server to return VEVENT components that overlap the time range from June 1st, 2005 at 00:00:00 am UTC to June 9th, 2005 at 00:00:00 am UTC. Use of the CALDAV:limit-recurrence-set element causes the server to only return overridden recurrence instances that overlap the time range specified in that element.¶
>> Request <<
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-query xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop>
<C:calendar-data>
<C:limit-recurrence-set start="20050601T000000Z"
end="20050609T000000Z"/>
</C:calendar-data>
</D:prop>
<C:filter>
<C:comp-filter name="VCALENDAR">
<C:comp-filter name="VEVENT">
<C:time-range start="20050601T000000Z"
end="20050609T000000Z"/>
</C:comp-filter>
</C:comp-filter>
</C:filter>
</C:calendar-query>
Assuming that only the following recurring VEVENT components contains recurrence instances scheduled to overlap the specified time range:¶
BEGIN:VCALENDAR PRODID:-//Example Corp.//CalDAV Client//EN VERSION:2.0 BEGIN:VEVENT DTSTAMP:20050507T203312Z UID:uid742@example.com DTSTART;TZID=America/Montreal:20050601T100000 RRULE:FREQ=WEEKLY;COUNT=3 DURATION:PT1H SUMMARY:Team Meeting LOCATION:Meeting room 17026 END:VEVENT BEGIN:VEVENT DTSTAMP:20050507T203312Z UID:uid742@example.com RECURRENCE-ID:20050615T050000Z DTSTART:20050615T050000Z DURATION:PT1H SUMMARY:Team Meeting LOCATION:Conference room 18044 END:VEVENT END:VCALENDAR
The server will omit to return the calendar component describing the recurrence instance scheduled on June 15, 2005 in its response to the client.¶
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:response>
<D:href
>http://cal.example.com/home/bernard/calendar/ev204.ics</D:href>
<D:propstat>
<D:prop>
<C:calendar-data>BEGIN:VCALENDAR
PRODID:-//Example Corp.//CalDAV Client//EN
VERSION:2.0
BEGIN:VEVENT
DTSTAMP:20050507T203312Z
UID:uid742@example.com
DTSTART;TZID=America/Montreal:20050601T100000
RRULE:FREQ=WEEKLY;COUNT=3
DURATION:PT1H
SUMMARY:Team Meeting
LOCATION:Meeting room 17026
END:VEVENT
END:VCALENDAR
</C:calendar-data>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
In this example, the client requests the server to return VEVENT components that overlap the time range from June 1st, 2005 at 00:00:00 am UTC to June 9th, 2005 at 00:00:00 am UTC and to return recurring calendar components expanded into individual recurrence instance calendar components. Use of the CALDAV:expand-recurrence-set element causes the server to only return overridden recurrence instances that overlap the time range specified in that element.¶
>> Request <<
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-query xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop>
<C:calendar-data>
<C:expand-recurrence-set start="20050601T000000Z"
end="20050609T000000Z"/>
</C:calendar-data>
</D:prop>
<C:filter>
<C:comp-filter name="VCALENDAR">
<C:comp-filter name="VEVENT">
<C:time-range start="20050601T000000Z"
end="20050609T000000Z"/>
</C:comp-filter>
</C:comp-filter>
</C:filter>
</C:calendar-query>
Assuming that only the following recurring VEVENT components contains recurrence instances scheduled to overlap the specified time range:¶
BEGIN:VCALENDAR PRODID:-//Example Corp.//CalDAV Client//EN VERSION:2.0 BEGIN:VEVENT DTSTAMP:20050507T203312Z UID:uid742@example.com DTSTART;TZID=America/Montreal:20050601T100000 RRULE:FREQ=WEEKLY;COUNT=3 DURATION:PT1H SUMMARY:Team Meeting LOCATION:Meeting room 17026 END:VEVENT BEGIN:VEVENT DTSTAMP:20050507T203312Z UID:uid742@example.com RECURRENCE-ID:20050615T140000Z DTSTART:20050615T140000Z DURATION:PT1H SUMMARY:Team Meeting LOCATION:Conference room 18044 END:VEVENT END:VCALENDAR
The server will return the recurring calendar component expanded into two recurrence instances omitting the recurrence instance scheduled on June 15, 2005 given that it does not overlap the specified time range for the expansion of the recurrence set.¶
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:response>
<D:href
>http://cal.example.com/home/bernard/calendar/ev204.ics</D:href>
<D:propstat>
<D:prop>
<C:calendar-data>BEGIN:VCALENDAR
PRODID:-//Example Corp.//CalDAV Client//EN
VERSION:2.0
BEGIN:VEVENT
DTSTAMP:20050507T203312Z
UID:uid742@example.com
RECURRENCE-ID:20050601T140000Z
DTSTART:20050601T140000Z
DURATION:PT1H
SUMMARY:Team Meeting
LOCATION:Meeting room 17026
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20050507T203312Z
UID:uid742@example.com
RECURRENCE-ID:20050608T140000Z
DTSTART:20050608T140000Z
DURATION:PT1H
SUMMARY:Team Meeting
LOCATION:Meeting room 17026
END:VEVENT
END:VCALENDAR
</C:calendar-data>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
In this example, the client requests the server to return the VTODO components that have an alarm trigger scheduled in the specified time range.¶
>> Request <<
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop xmlns:D="DAV:">
<D:getetag/>
<C:calendar-data/>
</D:prop>
<C:filter>
<C:comp-filter name="VCALENDAR">
<C:comp-filter name="VTODO">
<C:comp-filter name="VALARM">
<C:time-range start="20041121T000000Z"
end="20041122T000000Z"/>
</C:comp-filter>
</C:comp-filter>
</C:comp-filter>
</C:filter>
</C:calendar-query>
In this example, the client requests the server to return the VEVENT component that has the UID property set to "20041121-FEEBDAED@foo.org".¶
>> Request <<
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop xmlns:D="DAV:">
<D:getetag/>
<C:calendar-data/>
</D:prop>
<C:filter>
<C:comp-filter name="VCALENDAR">
<C:comp-filter name="VEVENT">
<C:prop-filter name="UID">
<C:text-match
caseless="no">20041121-FEEBDAED@foo.org</C:text-match>
</C:prop-filter>
</C:comp-filter>
</C:comp-filter>
</C:filter>
</C:calendar-query>
In this example, the client requests the server to return the VEVENT components that have the ATTENDEE property with the value "mailto:bernard@example.com" and for which the PARTSTAT parameter is set to "NEEDS-ACTION".¶
>> Request <<
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop xmlns:D="DAV:">
<D:getetag/>
<C:calendar-data/>
</D:prop>
<C:filter>
<C:comp-filter name="VCALENDAR">
<C:comp-filter name="VEVENT">
<C:prop-filter name="ATTENDEE"/>
<C:text-match
caseless="yes">mailto:bernard@example.com</C:text-match>
<C:param-filter name="PARTSTAT"/>
<C:text-match caseless="yes">NEEDS-ACTION</C:text-match>
</C:param-filter>
</C:prop-filter>
</C:comp-filter>
</C:comp-filter>
</C:filter>
</C:calendar-query>
In this example, the client requests the server to return all VEVENT components.¶
>> Request <<
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop xmlns:D="DAV:">
<D:getetag/>
<C:calendar-data/>
</D:prop>
<C:filter>
<C:comp-filter name="VCALENDAR">
<C:comp-filter name="VEVENT">
<C:is-defined/>
</C:comp-filter>
</C:comp-filter>
</C:filter>
</C:calendar-query>
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 6.4), 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 calendar-multiget REPORT is REQUIRED.¶
Marshalling: ¶
Preconditions: ¶
Postconditions: ¶
In this example, the client requests the server to return specific properties of the VEVENT components referenced by specific URIs. In addition the DAV:getetag property is also requested and returned as part of the response. Note that in this example, the resource at http://cal.example.com/home/bernard/calendar/mtg1.ics does not exist, resulting in an error status response.¶
>> Request <<
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-multiget xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop>
<D:getetag/>
<C:calendar-data>
<C:comp name="VCALENDAR">
<C:allprop/>
<C:comp name="VEVENT">
<C:prop name="UID"/>
<C:prop name="DTSTART"/>
<C:prop name="DTEND"/>
<C:prop name="DURATION"/>
<C:prop name="EXDATE"/>
<C:prop name="EXRULE"/>
<C:prop name="RDATE"/>
<C:prop name="RRULE"/>
<C:prop name="LOCATION"/>
<C:prop name="SUMMARY"/>
</C:comp>
<C:comp name="VTIMEZONE">
<C:allprop/>
<C:allcomp/>
</C:comp>
</C:comp>
</C:calendar-data>
</D:prop>
<D:href
>http://cal.example.com/home/bernard/calendar/ev102.ics</D:href>
<D:href
>http://cal.example.com/home/bernard/calendar/mtg1.ics</D:href>
</C:calendar-multiget>
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:response>
<D:href
>http://cal.example.com/home/bernard/calendar/ev102.ics</D:href>
<D:propstat>
<D:prop>
<D:getetag>"23ba4d-ff11fb"</D:getetag>
<C:calendar-data>BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Client//EN
BEGIN:VEVENT
DTSTART:20040902T100000Z
DTEND:20040902T120000Z
SUMMARY:Design meeting
UID:34222-232@example.com
END:VEVENT
END:VCALENDAR
</C:calendar-data>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href
>http://cal.example.com/home/bernard/calendar/mtg1.ics</D:href>
<D:status>HTTP/1.1 404 Resource not found</D:status>
</D:response>
</D:multistatus>
The CALDAV:free-busy-query REPORT generates a VFREEBUSY component containing free busy information for all relevant calendar components within calendar collections which have the CALDAV:read-free-busy or DAV:read privilege granted for the current user.¶
Only VEVENT components, without a TRANSP property or with the TRANSP property set to a value other than "TRANSPARENT", and VFREEBUSY components are used to generate the free busy time information.¶
Support for the CALDAV:free-busy-query REPORT is REQUIRED.¶
Marshalling: ¶
When the Request-URI for a CALDAV:free-busy-query REPORT is a calendar collection, the free-busy data is implicitly determined from the calendar object resources containing VEVENT and VFREEBUSY components within the calendar collection, irrespective of the value of any Depth header included in the REPORT request. Only calendar object resources containing VEVENT or VFREEBUSY components that have the CALDAV:read-free-busy privilege granted to the current user will be computed in the response.¶
When the Request-URI for a CALDAV:free-busy-query REPORT is a non-calendar collection, the scope of the report is governed by the value of the Depth header in the request as follows: ¶
Note that as per the requirements of Section 6.3 the server MUST expand any recurring items to determine whether any instances contribute to the free busy information in the requested time range.¶
Preconditions: ¶
Postconditions: ¶
In this example, the client requests the server to return free-busy information on the calendar collection /home/bernard/calendar/, between 9:00 AM and 5:00 PM on 2nd September 2004. The server responds indicating three busy time intervals of one hour, two hours and 30 minutes during the course of the time interval being examined.¶
>> Request <<
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:free-busy-query xmlns:C="urn:ietf:params:xml:ns:caldav">
<C:time-range start="20040902T090000Z"
end="20040902T170000Z"/>
</C:free-busy-query>
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:response>
<D:href>http://cal.example.com/home/bernard/calendar/</D:href>
<D:propstat>
<D:prop>
<C:calendar-data>BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Client//EN
BEGIN:VFREEBUSY
DTSTAMP:20050125T090000Z
DTSTART:20040902T090000Z
DTEND:20040902T170000Z
FREEBUSY:20040902T090000Z/PT1H,
20040902T120000Z/PT2H,
20040902T160000Z/PT30M
END:VFREEBUSY
END:VCALENDAR
</C:calendar-data>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
There are a number of actions clients can take which will be legal (the server will not return errors) but which 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 timezone to another timezone. Although these are iCalendar interoperability best practices and 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, make changes offline, and a simple way to resolve conflicts when reconnected. Strong 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 other WebDAV applications, CalDAV servers MUST support strong ETags.¶
The reports provided in CalDAV can be used by clients to optimize their performance in terms of network bandwidth usage, and resource consumption on the local client machine. Both of those issues are certainly major considerations for mobile or handheld devices with limited capacity, but they are also relevant to desktop client applications in cases where the calendar collections contain large amounts of data.¶
Typically clients present calendar data to users in views that span a finite time interval, so whenever possible clients should only retrieve calendar items from the server using CALDAV:calendar-query report combined with a time-range element to limit the scope of returned items to just those needed to populate the current view.¶
Typically in a calendar, historical data (events, to-dos etc. that have completed prior to the current date) do not change, though they may be deleted. As a result, a client can speed up the synchronization process by only considering data for the present time and the future up to a reasonable limit (e.g., one week, one month). If the user then tries to examine a portion of the calendar outside of the range that has been synchronized, the client can perform another synchronization operation on the new time interval being examined. This "just-in-time" synchronization can minimize bandwidth for common user interaction behaviors.¶
If a client wants to support calendar data synchronization, as opposed to downloading calendar data each time it is needed, it needs to cache the component resources URI and ETag along with the actual calendar data. Whilst the URI remains static for the lifetime of the component, the ETag will change with each successive change to the component data. Thus to synchronize a local data cache with the server, the client can first fetch the URI/ETag pairs for the time interval being considered, and compare those results with the cached data. Any cached component whose ETag differs from that on the server needs to be synchronized.¶
In order to properly detect the changes between the server and client data, the client will need to keep a record of which items have been created, changed or deleted since the last synchronization operation so that it can reconcile those changes with the data on the server.¶
An example of how to do that would be the following: ¶
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-query xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop>
<D:getetag/>
</D:prop>
<C:filter>
<C:comp-filter name="VCALENDAR">
<C:comp-filter name="VEVENT">
<C:time-range start="20040902T000000Z"
end="20040903T000000Z"/>
</C:comp-filter>
</C:comp-filter>
</C:filter>
</C:calendar-query>
REPORT /home/bernard/calendar/ HTTP/1.1
Host: cal.example.com
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
<?xml version="1.0" encoding="utf-8" ?>
<C:calendar-multiget xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:prop>
<D:getetag/>
<C:calendar-data>
<C:comp name="VCALENDAR">
<C:allprop/>
<C:comp name="VEVENT">
<C:prop name="UID"/>
<C:prop name="DTSTART"/>
<C:prop name="DTEND"/>
<C:prop name="DURATION"/>
<C:prop name="EXDATE"/>
<C:prop name="EXRULE"/>
<C:prop name="RDATE"/>
<C:prop name="RRULE"/>
<C:prop name="LOCATION"/>
<C:prop name="SUMMARY"/>
</C:comp>
<C:comp name="VTIMEZONE">
<C:allprop/>
<C:allcomp/>
</C:comp>
</C:comp>
</C:calendar-data>
</D:prop>
<D:href
>http://cal.example.com/home/bernard/calendar/evt1.ics</D:href>
<D:href
>http://cal.example.com/home/bernard/calendar/mtg1.ics</D:href>
</C:calendar-multiget>
Clients may not need all the properties in a calendar component when presenting information to the user. Since some property data can be large (e.g., ATTACH or ATTENDEE lists) clients can choose to ignore those by only requesting the specific items it knows it will use, through use of the CALDAV:calendar-data XML element in the relevant reports.¶
However, if a client needs to make a change to a component, it can only change the entire component data via a PUT request. There is no way to incrementally make a change to a set of properties within a calendar component resource. As a result the client will have to cache the entire set of properties on a resource that is being changed.¶
WebDAV locks can be used to prevent two clients modifying the same resource from either overwriting each others' changes (though that problem can also be solved by using ETags) and also to prevent the user from making changes that will conflict with another set of changes. In a multi-user calendar system, the 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 may request 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 when 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. E.g. a user will type his or her own calendar location into client configuration information, or cut and paste a URL from email into the calendar application. The client need only confirm that the URL points to a resource which is a calendar. 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 implementors can consider whether to use vCard [13] or LDAP [12] standards together with calendar attributes [14].¶
CalDAV clients MAY create attachments in calendar components either as inline or external. This section contains some guidelines on creating and managing attachments.¶
CalDAV clients MUST support inline attachments as specified in the iCalendar format. All CalDAV servers MUST support inline attachments, so clients can rely on being able to create attachments this way. On the other hand, inline attachments have some drawbacks:¶
CalDAV clients MUST support external attachments: if the client access any calendar component it MUST be capable of also accessing the external attachment if one exists (subject to virus checking or other security considerations). An external attachment could be:¶
CalDAV servers MAY support the MKCOL method to create sub-collections inside calendar collections. A sub-collection of a calendar collection MUST be able to contain any kind of resource, subject to access and quota control. Some CalDAV servers won't allow sub-collections inside calendar collections, and it may be possible on such a server to discover other locations where attachments can be stored.¶
Clients are entirely responsible for maintaining reference consistency with components that link to external attachments. A client deleting a component with an external attachment might therefore also delete the attachment if that's appropriate, however appropriateness can be very hard to determine. A new component might easily reference some pre-existing Web resource which is intended to have independent existence from the CalDAV component (the "attachment" could be a major proposal to be discussed in a meeting, for instance). Best practices will probably emerge and should probably be documented but for now clients should be wary of engaging in aggressive "cleanup" of external attachments. A client could involve the user in making decisions about removing unreferenced documents, or a client could be conservative in only deleting attachments it had created.¶
Also, clients are responsible for consistency of permissions when using external attachments. One reason for servers to support the storage of attachments within sub-collections of calendar collections is that ACL inheritance might make it easier to grant the same permissions to attachments that are granted on the calendar. Otherwise, it can be very difficult to keep permissions synchronized. With attachments stored on separate repositories, it can be impossible to keep permissions consistent -- the two repositories may not support the same permissions or have the same set of principals. Some systems have used tickets or other anonymous access control mechanisms to provide partially satisfactory solutions to these kinds of problems.¶
Note that all CalDAV calendar collections (including those which the user might treat as public or group calendars) can contain alarm information on events and todos. 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 VALARM types are completely interoperable (e.g., those which name a sound file to play).¶
Non-interoperable alarm information (e.g., should somebody define a color to be used in a display alarm) should be put in custom properties inside the VALARM component in order to keep the basic alarm usable on all devices.¶
Clients that allow offline changes to a calendar MUST synchronize the alarm data that already exists in the calendar collection. 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 who an alarm is intended for. Addressing those issues might require extensions to iCalendar, for example to store alarms per-user or indicate which user a VALARM was intended for. In the meantime, clients might maximize interoperability by generally not uploading alarm information to public, group or resource calendars.¶
<!ELEMENT calendar-query (DAV:allprop | DAV:propname | DAV:prop)?
filter>
<!ELEMENT calendar-data ((comp?, (expand-recurrence-set |
limit-recurrence-set)?) |
#PCDATA)?>
<!ATTLIST calendar-data content-type CDATA "text/calendar">
<!ATTLIST calendar-data version CDATA "2.0">
NOTE: The CALDAV:prop and CALDAV:allprop elements used here have the same name as elements defined in WebDAV. However, the elements used here have the "urn:ietf:params:xml:ns:caldav" namespace, as opposed to the "DAV:" namespace used for elements defined in WebDAV.¶
<!ELEMENT comp ((allcomp, (allprop | prop*)) |
(comp*, (allprop | prop*)))>
<!ATTLIST comp name CDATA #REQUIRED>
<!ELEMENT allcomp EMPTY>
NOTE: The CALDAV:allprop element defined here has the same name as the DAV:allprop element defined in WebDAV. However, the CALDAV:allprop element defined here uses the "urn:ietf:params:xml:ns:caldav" namespace, as opposed to the "DAV:" namespace used for the DAV:allprop element defined in WebDAV.¶
<!ELEMENT allprop EMPTY>
NOTE: The CALDAV:prop element defined here has the same name as the DAV:prop element defined in WebDAV. However, the CALDAV:prop element defined here uses the "urn:ietf:params:xml:ns:caldav" namespace, as opposed to the "DAV:" namespace used for the DAV:prop element defined in WebDAV.¶
<!ELEMENT prop EMPTY>
<!ATTLIST prop name CDATA #REQUIRED
novalue (yes|no) "no">
<!ELEMENT expand-recurrence-set EMPTY>
<!ATTLIST expand-recurrence-set start CDATA #REQUIRED
end CDATA #REQUIRED>
<!ELEMENT limit-recurrence-set EMPTY>
<!ATTLIST limit-recurrence-set start CDATA #REQUIRED
end CDATA #REQUIRED>
<!ELEMENT filter comp-filter>
("no is-defined element" OR "is-defined matches") AND
("no time-range element" OR "time-range matches") AND
("no sub-component filter" OR "all sub-component filters match") AND
("no property filter elements" OR "all property filters match")
<!ELEMENT comp-filter (is-defined | time-range)?
comp-filter* prop-filter*>
<!ATTLIST comp-filter name CDATA #REQUIRED>
("no is-defined element" OR "is-defined matches") AND
("no time-range element" OR "time-range matches") AND
("no text match element" OR "text-match matches") AND
("no parameter filter elements" OR "all parameter filters match")
<!ELEMENT prop-filter (is-defined | time-range | text-match)?
param-filter*>
<!ATTLIST prop-filter name CDATA #REQUIRED>
("is-defined matches" OR "text-match matches")
<!ELEMENT param-filter (is-defined | text-match) >
<!ATTLIST param-filter name CDATA #REQUIRED>
<!ELEMENT is-defined EMPTY>
<!ELEMENT text-match #PCDATA>
<!ATTLIST text-match caseless (yes|no)>
(DTSTART <= start AND DTEND > start) OR
(DTSTART <= start AND DTSTART+DURATION > start) OR
(DTSTART >= start AND DTSTART < end) OR
(DTEND > start AND DTEND <= end)
(DTSTART <= start AND DUE >= start) OR
(DTSTART <= start AND DTSTART+DURATION > start) OR
(DTSTART >= start AND DTSTART < end) OR
(DUE >= start AND DUE < end)
DTSTART >= start AND DTSTART < end
trigger-time >= start AND trigger-time < end
value >= start AND value < end
<!ELEMENT time-range EMPTY>
<!ATTLIST time-range start CDATA
end CDATA>
<!ELEMENT calendar-multiget (DAV:allprop | DAV:propname | DAV:prop)?
DAV:href+>
<!ELEMENT free-busy-query time-range+ >
HTTP protocol transactions are sent in the clear over the network unless protection from snooping is negotiated. This can be accomplished by use of TLS as defined in RFC2818 [6]. In particular, HTTP Basic authentication MUST NOT be used unless TLS is in effect.¶
Servers MUST take adequate precautions to ensure malicious clients cannot consume excessive server resources (CPU, memory, disk, etc.) through carefully crafted reports. For example, a client could upload an event with a recurrence rule that specifies a recurring event occurring every second for the next 100 years which would result in approximately 3 x 10^9 instances! A report that asks for recurrences to be expanded over that range would likely constitute a denial-of-service attack on the server.¶
[rfc.comment.2: We should make an explicit reference to the security considerations mentionned in iCalendar, iTIP and iMIP. --desruisseaux] ¶
In addition to the namespaces defined by RFC2518 [4] for XML elements, this document uses a URN to describe a new XML namespace conforming to a registry mechanism described in RFC3688 [8]. All other IANA considerations mentioned in RFC2518 [4] also apply to this document.¶
Registration request for the CalDAV namespace:¶
URI: urn:ietf:params:xml:ns:caldav¶
Registrant Contact: See the "Author's Address" section of this document.¶
XML: None. Namespace URIs do not represent an XML specification.¶
The authors would like to thank the following individuals for contributing their ideas and support for writing this specification: Michael Arick, Mario Bonin, Chris Bryant, Scott Carr, Mike Douglass, Helge Hess, Dan Mosedale, Kervin L. Pierre, Julian F. Reschke, Mike Shaver, Simon Vaillancourt, and Jim Whitehead.¶
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.¶
The following table extend the WebDAV Method Privilege Table specified in Appendix B of WebDAV ACL [9].¶
| METHOD | PRIVILEGES |
|---|---|
| MKCALENDAR | DAV:bind |
| REPORT | DAV:read or CALDAV:read-free-busy (on all referenced resources) |
Basically still adding major sections of content: ¶
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