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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 4791

Network Working Group                                           C. Daboo
Internet-Draft                                                    ISAMET
Expires: November 25, 2005                               B. Desruisseaux
                                                                  Oracle
                                                            L. Dusseault
                                                                    OSAF
                                                            May 24, 2005


               Calendaring Extensions to WebDAV (CalDAV)
                       draft-dusseault-caldav-06

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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   This Internet-Draft will expire on November 25, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   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 single-user calendar access, calendar sharing, and



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   calendar publishing.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1   XML Namespaces . . . . . . . . . . . . . . . . . . . . . .  5
     1.2   Notational Conventions . . . . . . . . . . . . . . . . . .  5
     1.3   Method Preconditions and Postconditions  . . . . . . . . .  6
   2.  CalDAV Requirements Overview . . . . . . . . . . . . . . . . .  7
   3.  Calendaring Data Model . . . . . . . . . . . . . . . . . . . .  8
     3.1   Calendar Server  . . . . . . . . . . . . . . . . . . . . .  8
     3.2   Recurrence and the Data Model  . . . . . . . . . . . . . .  9
   4.  New Resource Types . . . . . . . . . . . . . . . . . . . . . . 10
     4.1   Calendar Collection  . . . . . . . . . . . . . . . . . . . 10
     4.2   Calendar Resources Restrictions in Calendar Collections  . 10
   5.  Creating Resources . . . . . . . . . . . . . . . . . . . . . . 13
     5.1   MKCALENDAR Method  . . . . . . . . . . . . . . . . . . . . 13
       5.1.1   Status Codes . . . . . . . . . . . . . . . . . . . . . 14
       5.1.2   Example - MKCALENDAR . . . . . . . . . . . . . . . . . 15
     5.2   Additional OPTIONS Semantics . . . . . . . . . . . . . . . 15
       5.2.1   Capability Discovery . . . . . . . . . . . . . . . . . 15
         5.2.1.1   Example: Using OPTIONS for the Discovery of
                   Support for CalDAV . . . . . . . . . . . . . . . . 15
       5.2.2   CALDAV:calendar-collection-set OPTIONS request . . . . 16
       5.2.3   CALDAV:current-user-calendar-collection-set
               OPTIONS request  . . . . . . . . . . . . . . . . . . . 16
       5.2.4   Example - OPTIONS  . . . . . . . . . . . . . . . . . . 17
     5.3   Creating calendar resources  . . . . . . . . . . . . . . . 18
   6.  Calendaring Properties . . . . . . . . . . . . . . . . . . . . 20
     6.1   CALDAV:calendar-description Property . . . . . . . . . . . 20
   7.  Calendaring Access Control . . . . . . . . . . . . . . . . . . 21
     7.1   Calendaring Privileges . . . . . . . . . . . . . . . . . . 21
       7.1.1   CALDAV:view-free-busy Privilege  . . . . . . . . . . . 21
       7.1.2   Privilege aggregation and the
               DAV:supported-privilege-set property . . . . . . . . . 21
         7.1.2.1   Partial example of DAV:supported-privilege-set
                   property . . . . . . . . . . . . . . . . . . . . . 22
     7.2   Additional Principal Properties  . . . . . . . . . . . . . 23
       7.2.1   CALDAV:calendar-URL Property . . . . . . . . . . . . . 23
   8.  Calendaring Reports  . . . . . . . . . . . . . . . . . . . . . 25
     8.1   REPORT Method  . . . . . . . . . . . . . . . . . . . . . . 25
     8.2   Reports on collections containing calendar collections . . 25
     8.3   CALDAV:calendar-query Report . . . . . . . . . . . . . . . 25
       8.3.1   Example: Partial retrieval of events by time range . . 26
       8.3.2   Example: Retrieval of todos by alarm time range  . . . 29
       8.3.3   Example: Retrieval of event by UID . . . . . . . . . . 29
       8.3.4   Example: Retrieval of events by participation
               status . . . . . . . . . . . . . . . . . . . . . . . . 30



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       8.3.5   Example: Retrieval of events only  . . . . . . . . . . 31
     8.4   CALDAV:calendar-multiget Report  . . . . . . . . . . . . . 32
       8.4.1   Example: CALDAV:calendar-multiget Report . . . . . . . 33
     8.5   CALDAV:free-busy-query Report  . . . . . . . . . . . . . . 35
       8.5.1   Example: CALDAV:free-busy-query Report . . . . . . . . 37
   9.  Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . 39
     9.1   Client-to-client Interoperability  . . . . . . . . . . . . 39
     9.2   Sychronization Operations  . . . . . . . . . . . . . . . . 39
       9.2.1   Use of Reports . . . . . . . . . . . . . . . . . . . . 39
         9.2.1.1   Restrict the Time Range  . . . . . . . . . . . . . 39
         9.2.1.2   Synchronize by Time Range  . . . . . . . . . . . . 39
         9.2.1.3   Synchronization Process  . . . . . . . . . . . . . 40
       9.2.2   Restrict the Properties Returned . . . . . . . . . . . 42
     9.3   Use of Locking . . . . . . . . . . . . . . . . . . . . . . 43
     9.4   Finding calendars  . . . . . . . . . . . . . . . . . . . . 43
   10.   XML Element Definitions  . . . . . . . . . . . . . . . . . . 45
     10.1  CALDAV:calendar-query XML Element  . . . . . . . . . . . . 45
     10.2  CALDAV:calendar-data XML Element . . . . . . . . . . . . . 45
       10.2.1  CALDAV:comp XML Element  . . . . . . . . . . . . . . . 45
       10.2.2  CALDAV:allcomp XML Element . . . . . . . . . . . . . . 46
       10.2.3  CALDAV:allprop XML Element . . . . . . . . . . . . . . 46
       10.2.4  CALDAV:prop XML Element  . . . . . . . . . . . . . . . 47
       10.2.5  CALDAV:expand-recurrence-set XML Element . . . . . . . 47
     10.3  CALDAV:filter XML Element  . . . . . . . . . . . . . . . . 48
       10.3.1  CALDAV:comp-filter XML Element . . . . . . . . . . . . 48
       10.3.2  CALDAV:prop-filter XML Element . . . . . . . . . . . . 49
       10.3.3  CALDAV:param-filter XML Element  . . . . . . . . . . . 49
       10.3.4  CALDAV:is-defined XML Element  . . . . . . . . . . . . 50
       10.3.5  CALDAV:text-match XML Element  . . . . . . . . . . . . 50
     10.4  CALDAV:time-range XML Element  . . . . . . . . . . . . . . 50
     10.5  DAV:response XML Element . . . . . . . . . . . . . . . . . 52
     10.6  CALDAV:calendar-multiget XML Element . . . . . . . . . . . 52
     10.7  CALDAV:free-busy-query XML Element . . . . . . . . . . . . 52
   11.   Internationalization Considerations  . . . . . . . . . . . . 53
   12.   Security Considerations  . . . . . . . . . . . . . . . . . . 54
     12.1  Authentication of Clients  . . . . . . . . . . . . . . . . 54
     12.2  Denial of Service  . . . . . . . . . . . . . . . . . . . . 54
   13.   IANA Consideration . . . . . . . . . . . . . . . . . . . . . 55
     13.1  Namespace Registration . . . . . . . . . . . . . . . . . . 55
   14.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 56
   15.   References . . . . . . . . . . . . . . . . . . . . . . . . . 57
     15.1  Normative References . . . . . . . . . . . . . . . . . . . 57
     15.2  Informative References . . . . . . . . . . . . . . . . . . 57
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 58
   A.  CalDAV Method Privilege Table (Normative)  . . . . . . . . . . 59
   B.  Changes  . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
     B.1   Changes in -06 . . . . . . . . . . . . . . . . . . . . . . 60
     B.2   Changes in -05 . . . . . . . . . . . . . . . . . . . . . . 60



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     B.3   Changes in -04 . . . . . . . . . . . . . . . . . . . . . . 61
     B.4   Changes in -03 . . . . . . . . . . . . . . . . . . . . . . 61
     B.5   Changes in -02 . . . . . . . . . . . . . . . . . . . . . . 61
     B.6   Changes in -01 . . . . . . . . . . . . . . . . . . . . . . 62
       Intellectual Property and Copyright Statements . . . . . . . . 63














































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1.  Introduction

   The concept of using HTTP [4] and WebDAV [3] 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 [2] 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 is therefore intended to propose a standard
   way of modeling calendar data in WebDAV, plus some additional
   features to make calendar access work well.

   Discussion of this Internet-Draft is being done on the mailing list
   <http://lists.osafoundation.org/mailman/listinfo/ietf-caldav>.

1.1  XML Namespaces

   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 [8].

   The namespace "urn:ietf:params:xml:ns:caldav" is reserved for the XML
   elements defined in this specification, or in other Standards Track
   IETF RFCs written to extend CalDAV.  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.

1.2  Notational Conventions

   The augmented BNF used by this document to describe protocol elements
   is described in Section 2.1 of [4].  Because this augmented BNF uses
   the basic production rules provided in Section 2.2 of [4], those
   rules apply to this document as well.




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   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].

   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 types respectively.

1.3  Method Preconditions and Postconditions

   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.





















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2.  CalDAV Requirements Overview

   This section lists what functionality is required of a CalDAV server.
   To advertise support for CalDAV, a server:

   o  MUST support WebDAV Class 1.

   o  MUST support WebDAV ACL [7] with the privilege defined in
      Section 7.1 of this document.

   o  MUST support SSL.

   o  MUST support strong ETags to support disconnected operations.

   o  MUST support all required calendaring REPORTs defined in this
      document.

   o  MUST advertise calendaring REPORTs via the DAV:supported-report-
      set property as defined in DeltaV [5].

   In addition, a server:

   o  SHOULD support MKCALENDAR.




























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3.  Calendaring Data Model

   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 attempts to
   follow the same pattern by developing all new features based on a
   well-described data model.

   In the CalDAV data model, every iCalendar VEVENT, VJOURNAL, VTODO and
   VFREEBUSY component is stored as an individual HTTP/WebDAV resource.
   That means each calendar resource may be individually locked and have
   individual WebDAV properties.  These resources are placed into WebDAV
   collections with a mostly-fixed structure.

3.1  Calendar Server

   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://example.org/webdav/" may contain
   WebDAV collections and resources, all of which have URLs beginning
   with "http://example.org/webdav/".  Note that the root URL
   "http://example.org/" 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 may 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
   /lisa/calendar/ as well as in /bernard/calendar/, and non-calendar
   data in /lisa/contacts/).  Or, it might mean that calendar data can
   be found only in certain sections of the repository (e.g.,
   /calendars/user/).  Calendaring features are only required in the
   repository sections that are or contain calendaring objects.  So a
   repository confining calendar data to the /caldav/ 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.



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   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 tools help this work.

3.2  Recurrence and the Data Model

   Recurrence is an important part of the data model because it governs
   how many resources are expected to exist.  This proposal models a
   recurring resource and its recurrence exceptions as a single WebDAV
   resource.  In this model, recurrence patterns, recurrence dates,
   exception dates, and exception information are all part of the data
   in a single master event.  This decision avoids problems of limiting
   how many recurrence instances to store in the repository, how to keep
   instances in synch with the master, and how to link recurrence
   exceptions with the master.  It also results in less data to
   synchronize between client and server, and makes it easier to make
   changes to all recurrences or to a recurrence pattern.  It makes it
   easier to create a recurring component, and easier to delete all
   recurrences.

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


























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4.  New Resource Types

   CalDAV defines the following new resource types for use in WebDAV
   repositories holding calendar data.

4.1  Calendar Collection

   Calendar collections are manifested to clients as a WebDAV resource
   collection, identified by a URL.  A calendar collection MUST have a
   non-empty DAV:displayname property (defined in Section 13.2 of
   RFC2518 [3]), and a DAV:resourcetype property (defined in Section
   13.9 of RFC2518 [3]).  Additionally, 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 resources that represent the 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.  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 6.1 to
   provide such a cue.

   Calendar collections MUST NOT contain other calendar collections.
   Multiple calendar collections MAY be children of the same WebDAV
   collection.

   A calendar collection MAY contain additional collections and non-
   collection resources of types not defined here.  How such items are
   used is not defined by this specification.  However, additional
   collections contained in a calendar collection MUST NOT contain
   calendar collections.

4.2  Calendar Resources Restrictions in Calendar Collections

   Calendar 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 resource may contain two VEVENT
   components and one VTIMEZONE component, but it may not contain one



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   VEVENT component and one VTODO component.

   Calendar resources that contain more than one calendar components of
   the same type (e.g., VEVENT), with the exception of VTIMEZONE
   components, are REQUIRED to have the same UID property value.  For
   instance, a calendar resource with two VEVENT components MUST specify
   the same UID property value in the two VEVENT components.  One of the
   two VEVENT components could define the recurrence rule of an event,
   and the other one could define an exception to the same event.

   Calendar components with the same UID property value, in a given
   calendar collection, MUST be contained in the same calendar resource.
   All the recurrence instances of the same recurring calendar
   component, that is, calendar components with the same UID property
   value but with different RECURRENCE-ID property value MUST be
   contained in the same calendar resource.

   The UID property value of the calendar components contained in a
   calendar resource MUST be unique in the scope of the calendar
   collection, and all its descendant collections, in which the calendar
   resource is contained.

   For example, given the following iCalendar object:




























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   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 need
   to be stored in its own calendar 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 need to be
   stored in the same calendar resource.



















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5.  Creating Resources

   The creation of calendar collections and calendar 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.

5.1  MKCALENDAR Method

   A MKCALENDAR request creates a new calendar collection resource.  A
   server MAY restrict calendar collection creation to particular
   collections, but a client can determine the location of these
   collections from a CALDAV:calendar-collection-set OPTIONS request
   (see Section 5.2.2).

   Support for MKCALENDAR on the server is OPTIONAL 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.  This requires the clients to issue a PROPPATCH
   request to change the DAV:displayname property to the appropriate
   value immediately after issuing the MKCALENDAR request.  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:

      If a request body is included, it MUST be a CALDAV:mkcalendar XML
      element.

   <!ELEMENT mkcalendar ANY>




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      If a response body for a successful request is included, it MUST
      be a CALDAV:mkcalendar-response XML element.

   <!ELEMENT mkcalendar-response ANY>

      The response MUST include a Cache-Control:no-cache header.

   Preconditions:

      (DAV:resource-must-be-null): A resource MUST NOT exist at the
      Request-URI.

      (CALDAV:calendar-collection-location-ok): The Request-URI MUST
      identify a location where a calendar collection can be created.

      (CALDAV:insufficient-privilege): The DAV:bind privilege MUST be
      granted to the current authenticated user.

   Postconditions:

      (CALDAV:initialize-calendar-collection): A new calendar collection
      exists at the Request-URI.  The DAV:resourcetype of the calendar
      collection MUST be DAV:collection.  Additionally, a calendar
      collection MUST report the CALDAV:calendar XML element in the
      value of the DAV:resourcetype property.


5.1.1  Status Codes

   201 (Created) - The calendar collection resource was created in its
   entirety.

   403 (Forbidden) - This indicates at least one of two conditions: 1)
   the server does not allow the creation of calendar collections at the
   given location in its namespace, or 2) the parent collection of the
   Request-URI exists but cannot accept members.

   405 (Method Not Allowed) - MKCALENDAR can only be executed on a null
   resource.

   409 (Conflict) - A collection cannot be made at the Request-URI until
   one or more intermediate collections have been created.

   415 (Unsupported Media Type)- The server does not support the request
   type of the body.

   507 (Insufficient Storage) - The resource does not have sufficient
   space to record the state of the resource after the execution of this



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   method.

5.1.2  Example - MKCALENDAR

   >> Request <<

   MKCALENDAR /calendars/user/lisa/ HTTP/1.1
   Host: cal.example.com
   Content-Length: 0

   >> Response <<

   HTTP/1.1 201 Created
   Date: Fri, 22 Oct 2004 12:17:08 GMT
   Content-Length: 0
   Cache-Control: no-cache

   In this example, a new calendar collection is created at
   http://cal.example.com/calendars/user/lisa/

5.2  Additional OPTIONS Semantics

5.2.1  Capability Discovery

   If the server supports the calendar-access feature, 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, or methods.  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.

5.2.1.1  Example: Using OPTIONS for the Discovery of Support for CalDAV

   >> Request <<

   OPTIONS /calendars/users/ HTTP/1.1
   Host: cal.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE
   Allow: MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, REPORT
   Allow: MKCALENDAR, ACL
   DAV: 1, 2, access-control, calendar-access
   Content-Length: 0

   In this example, the OPTIONS response indicates that the server



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   supports CalDAV in this namespace, therefore the '/calendars/users/'
   collection may be used as a parent for calendar collections as the
   MKCALENDAR method is available, and as a possible target for REPORT
   requests for calendaring reports.

5.2.2  CALDAV:calendar-collection-set OPTIONS request

   A CALDAV:calendar-collection-set element MAY be included in the
   request body to identify collections that may contain calendar
   collection resources.

   Additional Marshalling:

      If an XML request body is included, it MUST be a DAV:options XML
      element.

     <!ELEMENT options ANY>
     ANY value: A sequence of elements with at most one
     calendar-collection-set element.

      If an XML response body for a successful request is included, it
      MUST be a DAV:options-response XML element.

     <!ELEMENT options-response ANY>
     ANY value: A sequence of elements with at most one
     calendar-collection-set element.

     <!ELEMENT calendar-collection-set (href*)>

      If CALDAV:calendar-collection-set is included in the request body,
      the response body for a successful request MUST contain a CALDAV:
      calendar-collection-set element identifying collections that may
      contain calendar collections.  An identified collection MAY be the
      root collection of a tree of collections, all of which may contain
      calendar collections.  Since different servers can control
      different parts of the URL namespace, different resources on the
      same host MAY have different CALDAV:calendar-collection-set
      values.  The identified collections MAY be located on different
      hosts from the resource.


5.2.3  CALDAV:current-user-calendar-collection-set OPTIONS request

   A CALDAV:current-user-calendar-collection-set element MAY be included
   in the request body to identify the calendar collections owned by the
   current authenticated user.

   Additional Marshalling:



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      If an XML request body is included, it MUST be a DAV:options XML
      element.

     <!ELEMENT options ANY>
     ANY value: A sequence of elements with at most one
     current-user-calendar-collection-set element.

      If an XML response body for a successful request is included, it
      MUST be a DAV:options-response XML element.

     <!ELEMENT options-response ANY>
     ANY value: A sequence of elements with at most one
     current-user-calendar-collection-set element.

     <!ELEMENT current-user-calendar-collection-set (href*)>

      If CALDAV:current-user-calendar-collection-set is included in the
      request body, the response body for a successful request MUST
      contain a CALDAV:current-user-calendar-collection-set element
      identifying calendar collections owned by the current
      authenticated user.


5.2.4  Example - OPTIONS

   >> Request <<

   OPTIONS /caldav-root/ HTTP/1.1
   Host: cal.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:options xmlns:D="DAV:">
     <C:calendar-collection-set
       xmlns:C="urn:ietf:params:xml:ns:caldav"/>
   </D:options>














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   >> Response <<

   HTTP/1.1 200 OK
   DAV: 1, calendar-access
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:options-response xmlns:D="DAV:">
     <C:calendar-collection-set
       xmlns:C="urn:ietf:params:xml:ns:caldav">
       <D:href>http://cal.example.com/calendars/user/</D:href>
       <D:href>http://cal.example.com/calendars/public/</D:href>
     </C:calendar-collection-set>
   </D:options-response>

   In this example, the server indicates that it provides Class 1 DAV
   support and calendar-access support.  In addition, the server
   indicates the requested locations of the calendar collection
   resources.  Naturally, the server may also have done an
   authentication step (not shown) to ensure this operation was allowed.

5.3  Creating calendar resources

   Clients typically populate calendar collections with calendar
   resources.  The URL for each calendar resource is entirely arbitrary,
   and does not need to bear a specific relationship (but might) to the
   calendar resource's subject, scheduled time, UID or other metadata.
   A new calendar resource must have a new URL, otherwise the new
   component would instead be an update to an existing calendar
   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 tools 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.




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   Servers SHOULD return an ETag header containing the actual ETag of
   the newly created resource on a successful creation.

   >> Request <<

   PUT /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:20010715T035959Z
   SUMMARY:Bastille Day Party
   END:VEVENT
   END:VCALENDAR

   >> Response <<

   HTTP/1.1 201 Created
   Date: Thu, 02 Sep 2004 16:53:32 GMT
   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 [2], the URL of calendar
   resources containing (an arbitrary set of) calendaring and scheduling
   information may be suffixed by ".ics", and the URL of calendar
   resources containing free or busy time information may be suffixed by
   ".ifb".

   Preconditions for PUT within calendar collections:

      (CALDAV:uid-already-exists): The component UID chosen is not
      unique and the client must choose another if it attempts again.

      (CALDAV:invalid-calendar-resource): The iCalendar object syntax or
      structure was invalid.  (Note that the server MAY support upload
      formats other than iCalendar but then the server MUST validate
      each component uploaded according to the chosen format syntax.)



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6.  Calendaring Properties

   This specification defines new properties for WebDAV resources.
   Calendar access properties may be retrieved just like other WebDAV
   properties, using the PROPFIND method.

   A DAV:allprop PROPFIND request SHOULD NOT return any of the
   properties defined in this section.

6.1  CALDAV:calendar-description Property

   Name: calendar-description

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Provides a description for the resource that is suitable for
      presentation to a user.

   Description: The CALDAV:calendar-description property MAY be defined
      on all calendar collection resources.  If present, the property
      contains a description of the resource that is suitable for
      presentation layer.


     <!ELEMENT calendar-description (#PCDATA) >


























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7.  Calendaring Access Control

7.1  Calendaring Privileges

   A CalDAV server MUST support WebDAV  ACL [7].  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.

7.1.1  CALDAV:view-free-busy Privilege

   Calendar users often wish to allow other users to see their free-busy
   time intervals, without viewing the other details of the calendar
   components (location, subject, 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:view-free-busy privilege controls access to view the start
   times and end times of free and busy time intervals.  This privilege
   may be granted on an entire calendar collection.  It may also make
   sense to grant this privilege on individual calendar resources (in
   which case the time allocated to those calendar resources would show
   up as free in the free-busy rollup to an unauthorized viewer), but a
   server MAY forbid the CALDAV:view-free-busy privilege from being used
   on individual calendar resources.  A CalDAV server MUST support the
   CALDAV:view-free-busy privilege on calendar collections.


     <!ELEMENT view-free-busy EMPTY>

   The CALDAV:view-free-busy privilege is aggregated in the DAV:read
   privilege.  Clients can discover support for various privileges using
   the DAV:supported-privilege-set property defined in RFC3744 [7].

7.1.2  Privilege aggregation and the DAV:supported-privilege-set
       property

   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 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 is aggregated under the DAV:read
   privilege.  Although the list of supported privileges MAY vary
   somewhat from server to server (the WebDAV ACL specification leaves



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   room for a fair amount of diversity in server implementations), some
   relationships MUST hold for a CalDAV server:

   o  The server MUST support the CALDAV:view-free-busy privilege.  The
      CALDAV:view-free-busy privilege MUST be non-abstract, and MUST be
      aggregated under the DAV:read privilege.


7.1.2.1  Partial example of DAV:supported-privilege-set property

   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.





































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   <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:view-free-busy/>
           </D:privilege>
           <D:description xml:lang="en">View free-busy rollup
           </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>


7.2  Additional Principal Properties

   This section defines a new property for WebDAV principal resources as
   defined in RFC3744 [7].

7.2.1  CALDAV:calendar-URL Property







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   Name: calendar-URL

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Identify the URL of any calendar collections owned by the
      associated principal resource.

   Description:


     <!ELEMENT calendar-URL (DAV:href*) >

   Support for this property is RECOMMENDED.






































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8.  Calendaring Reports

   This section defines the reports which a CalDAV server MUST support
   on calendar collections and calendar resources.

   CalDAV servers MUST advertise support for those reports with the DAV:
   supported-report-set property defined in DeltaV [5].

   Some of these reports allow calendar data (from possibly multiple
   resources) to be returned.  Clients SHOULD request the DAV:getetag
   property whenever executing reports that return calendar data, to
   ensure that any local cache used for synchronization is kept up to
   date with the latest changes on the server

8.1  REPORT Method

   The REPORT method (defined in Section 3.6 of RFC3253 [5]) 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.

   A server that supports calendar-access MUST support the DAV:expand-
   property report (defined in Section 3.8 of RFC3253 [5]).

8.2  Reports on collections containing calendar collections

   A WebDAV collection which contains one or more calendar collections
   is not a new type of resource, but it may support these new REPORT.
   If so, then the REPORT is expected to have the semantics of including
   information from all the calendar data contained in the collection,
   and its children, recursively.  These collections may contain more
   than only calendar related resources.  It's up to the server, if it
   supports this REPORT on a normal WebDAV collection, to find calendar
   resources and decide what to do with non-calendar resources and
   whether those may also appear in the collection or its children.

   If these reports are supported on ordinary collections the server
   advertises the capability with the DAV:supported-report-set property
   as already described.

8.3  CALDAV:calendar-query Report

   The CALDAV:calendar-query REPORT performs a search for all calendar



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   resources (e.g., iCalendar objects) that match a specified search
   filter.  The response of this report will contain all the WebDAV
   properties and calendar 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 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 calendar-query REPORT is REQUIRED.

   Marshalling:

      The request body MUST be a CALDAV:calendar-query XML element as
      defined in Section 10.1.

      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 multistatus XML element is empty.

      The response body for a successful calendar-query REPORT request
      MUST contain a DAV:response element for each iCalendar object that
      matched the search filter.  The declaration of the DAV:response
      element from Section 12.9.1 of RFC2518 [3] has been modified as
      follow to allow the CALDAV:calendar-data element within the DAV:
      response element, see Section 10.5

   [[Comment.1: We need to define the role of the Depth request header
   when applied to a collection resource.  We need to specify
   preconditions and postconditions. (e.g., DAV:number-of-matches-
   within-limits). --desruisseaux]]

8.3.1  Example: Partial retrieval of events by time range

   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



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   2nd, 2004 at 11:59:59 pm UTC.  In addition the DAV:getetag property
   is also requested and returned as part of the response.

   >> Request <<

   REPORT /bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml
   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: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>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:time-range start="20040902T000000Z"
                         end="20040902T235959Z"/>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>



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   >> 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/bernard/calendar/ev102.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fb"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <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:response>
     <D:response>
       <D:href
   >http://cal.example.com/bernard/calendar/mtg103.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"ff11fb-23ba4d"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <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



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   X-ABC-GUID:E1CX5Dr-0007ym-Hz@example.com
   END:VEVENT
   END:VCALENDAR
       </C:calendar-data>
     </D:response>
   </D:multistatus>


8.3.2  Example: Retrieval of todos by alarm time range

   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 /bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml
   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/>
     </D:prop>
     <C:calendar-data/>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VTODO">
           <C:comp-filter name="VALARM">
             <C:time-range start="20041121T000000Z"
                           end="20041121T235959Z"/>
           </C:comp-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>


8.3.3  Example: Retrieval of event by UID

   In this example, the client requests the server to return the VEVENT
   component that has the UID property set to
   "20041121-FEEBDAED@foo.org".





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   >> Request <<

   REPORT /bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml
   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/>
     </D:prop>
     <C:calendar-data/>
     <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>


8.3.4  Example: Retrieval of events by participation status

   In this example, the client requests the server to return the VEVENT
   components that have the ATTENDEE property with the value
   "mailto:jsmith@example.org" and for which the PARTSTAT parameter is
   set to "NEEDS-ACTION".


















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   >> Request <<

   REPORT /bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml
   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/>
     </D:prop>
     <C:calendar-data/>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:prop-filter name="ATTENDEE"/>
             <C:text-match
                caseless="yes">mailto:jsmith@foo.org</C:text-match>
             <C:param-filter name="PARTSTAT"/>
               <C:text-match caseless="no">NEEDS-ACTION</C:text-match>
             </C:param-filter>
           </C:prop-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>


8.3.5  Example: Retrieval of events only

   In this example, the client requests the server to return all VEVENT
   components.

















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   >> Request <<

     REPORT /bernard/calendar/ HTTP/1.1
     Host: cal.example.com
     Depth: 1
     Content-Type: text/xml
     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/>
       </D:prop>
       <C:calendar-data/>
       <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>


8.4  CALDAV:calendar-multiget Report

   The CALDAV:calendar-multiget REPORT is used to retrieve specific
   calendar resources from within a collection, if the Request-URI is a
   collection, or to retrieve a specific calendar resource, if the
   Request-URI is a calendar resource.  This report is similar to the
   CALDAV:calendar-query REPORT (see Section 8.3), except that it takes
   a list of DAV:href elements instead of a CALDAV:filter element to
   determine which calendar resources to return.

   Support for the calendar-multiget REPORT is REQUIRED.

   Marshalling:

      The request body MUST be a CALDAV:calendar-multiget XML element
      (see Section 10.6, which MUST contain at least one DAV:href XML
      element, and one optional CALDAV:calendar-data element as defined
      in Section 10.2.  If the Request-URI is a collection resource,
      then the DAV:href elements MUST refer to resources within that
      collection, and they MAY refer to 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 equal to the Request-URI.



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      The response body for a successful request MUST be a DAV:
      multistatus XML element.  In the case where there are no response
      elements, the returned multistatus XML element is empty.

      The response body for a successful CALDAV:calendar-multiget REPORT
      request MUST contain a DAV:response element for each calendar
      resource referenced by the provided set of DAV:href elements.  The
      DAV:response element is as defined in Section 10.5.

      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.


8.4.1  Example: CALDAV:calendar-multiget Report

   In this example, the client requests the server to return specific
   properties of the VEVENT components references 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/bernard/calendar/mtg1.ics does not exist,
   resulting in an error status response.




























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   >> Request <<

   REPORT /bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Content-Type: text/xml
   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/>
     </D:prop>
     <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:href>http://cal.example.com/bernard/calendar/ev102.ics</D:href>
     <D:href>http://cal.example.com/bernard/calendar/mtg1.ics</D:href>
   </C:calendar-multiget>














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   >> 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/bernard/calendar/ev102.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fb"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <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:response>
     <D:response>
       <D:href>http://cal.example.com/bernard/calendar/mtg1.ics</D:href>
       <D:status>HTTP/1.1 404 Resource not found</D:status>
     </D:response>
   </D:multistatus>


8.5  CALDAV:free-busy-query Report

   The CALDAV:free-busy-query REPORT generates an iCalendar VFREEBUSY
   component containing free busy information for all relevant
   components within calendar collections which have the CALDAV:view-
   free-busy or DAV:read privilege granted for the current authenticated
   user.

   Only the VEVENT components, with the TRANSP property set to a value
   different from "TRANSPARENT", and the VFREEBUSY components will be
   considered to generate the free busy time information.




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   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 10.7, which MUST contain at least one CALDAV:time-range
      XML element, as defined in Section 10.4.

      The response body for a successful request MUST be a DAV:
      multistatus XML element.  In the case where there are no response
      elements, the returned multistatus XML element is empty.

      The response body for a successful CALDAV:free-busy-query REPORT
      request MUST contains a DAV:response element for each calendar
      collection for which free-busy information has been computed.
      Each DAV:response element contains a single CALDAV:calendar-data
      XML element as defined in Section 10.2.  The CALDAV:calendar-data
      XML element MUST contain an iCalendar object with a single
      VFREEBUSY component, with zero or more FREEBUSY property values
      that describe the busy time intervals for the calendar resources
      being targeted, and with other properties set according to the
      rules of iCalendar.  This report only returns busy time
      information.  Applications desiring free time information MUST
      infer this from available busy time information.

   When the Request-URI for a CALDAV:free-busy-query REPORT is a
   calendar collection, the free-busy data is implicitly determined from
   the "text/calendar" VEVENT resources within the calendar collection,
   irrespective of the value of any Depth header included in the REPORT
   request.  Only calendar resources containing VEVENT or VFREEBUSY
   components that have the CALDAV:view-free-busy privilege granted to
   the current authenticated 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:



      'Depth: 0' - an empty VFREEBUSY component will be returned as
      there is no valid calendar data to be scanned on the collection.



      'Depth: 1' - free-busy data for any calendar collections
      immediately within the target collection is returned.





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      'Depth: infinity' - free-busy data for all calendar collections
      within any sub-collections of the target collection is returned.


8.5.1  Example: CALDAV:free-busy-query Report

   In this example, the client requests the server to return free-busy
   information on the calendar collection /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 /bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml
   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>
























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   >> 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/bernard/calendar/</D:href>
       <D:status>HTTP/1.1 200 OK</D:status>
       <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:response>
   </D:multistatus>
























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9.  Guidelines

9.1  Client-to-client Interoperability

   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.

9.2  Sychronization Operations

   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.

9.2.1  Use of Reports

9.2.1.1  Restrict the Time Range

   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.

9.2.1.2  Synchronize by Time Range

   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



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   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.

9.2.1.3  Synchronization Process

   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:



      The client issues a CALDAV:calendar-query REPORT request for a
      specific time range, and asks for only the DAV:getetag property to
      be returned:


















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   REPORT /bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml
   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="20040902T235959Z"/>
        </C:comp-filter>
      </C:comp-filter>
    </C:filter>
   </C:calendar-query>

      The client then uses the results to determine which components
      have changed, been created or deleted on the server and how those
      relate to locally cached components that may have changed, been
      created or deleted.  If the client determines that there are items
      on the server that need to be fetched, the client issues a CALDAV:
      calendar-multiget report to fetch the actual data:























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   REPORT /bernard/calendar/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: text/xml
   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/>
    </D:prop>
    <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:href>http://cal.example.com/bernard/calendar/evt1.ics</D:href>
    <D:href>http://cal.example.com/bernard/calendar/mtg1.ics</D:href>
   </C:calendar-multiget>


9.2.2  Restrict the Properties Returned

   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



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   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.

9.3  Use of Locking

   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.

9.4  Finding calendars

   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 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



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   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 [11] or LDAP [10] standards together
   with calendar attributes [12].













































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10.  XML Element Definitions

10.1  CALDAV:calendar-query XML Element

   Name: calendar-query

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Defines a report for querying calendar data

   Description See Section 8.3.


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


10.2  CALDAV:calendar-data XML Element

   Name: calendar-data

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Used to define which parts of a calendar component object
      should be returned by the report that uses this element.

   Description: When used in a request, the CALDAV:calendar-data element
      specifies the iCalendar components and properties to be returned
      in the iCalendar objects part of the response.  If this element
      doesn't contain any CALDAV:comp element, iCalendar objects will be
      returned with all their components and properties.

   Value: When used inside a response, the CALDAV:calendar-data element
      contains an iCalendar object that matched the search filter
      specified in the request.


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

   <!ATTLIST calendar-data return-content-type CDATA
                   "text/calendar">


10.2.1  CALDAV:comp XML Element






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   Name: comp

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Defines which component types to return

   Description: The name value is an iCalendar component name (e.g.,
      "VEVENT")

   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>


10.2.2  CALDAV:allcomp XML Element

   Name: allcomp

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies that all components shall be returned

   Description: This element can be used when the client wants all types
      of components returned by a report.


   <!ELEMENT allcomp EMPTY>


10.2.3  CALDAV:allprop XML Element

   Name: allprop

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies that all properties shall be returned.

   Description: This element can be used when the client wants all
      properties of components returned by a report.

   NOTE: The 'allprop' element defined here has the same name as the
   'allprop' element defined in WebDAV.  However, the 'allprop' element



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   defined here uses the "urn:ietf:params:xml:ns:caldav" namespace, as
   opposed to the "DAV:" namespace used for the 'allprop' element
   defined in WebDAV.

   <!ELEMENT allprop EMPTY>


10.2.4  CALDAV:prop XML Element

   Name: prop

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Defines which properties to return in the response.

   Description: The "name" attribute specifies the name of the iCalendar
      property to return (e.g., "ATTENDEE").  The "novalue" attribute
      can be used by clients to request that the actual value of the
      property not be returned (if the "novalue" attribute is set to
      "yes").  In that case the server will return just the iCalendar
      property name and any iCalendar parameters and a trailing ":"
      without the subsequent value data.

   NOTE: The 'prop' element defined here has the same name as the 'prop'
   element defined in WebDAV.  However, the 'prop' element defined here
   uses the "urn:ietf:params:xml:ns:caldav" namespace, as opposed to the
   "DAV:" namespace used for the 'prop' element defined in WebDAV.

   <!ELEMENT prop EMPTY>

   <!ATTLIST prop name CDATA #REQUIRED
                  novalue (yes|no) "no">


10.2.5  CALDAV:expand-recurrence-set XML Element

   Name: expand-recurrence-set

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Forces the server to expand recurring components into
      separate instances.

   Description: The expand-recurrence-set element specifies that
      recurring components shall be returned as multiple components with
      no recurrence properties (i.e., EXDATE, EXRULE, RDATE and RRULE).
      The required "start" and "end" attributes contain iCalendar format
      DATE-TIME (always specified in UTC) or DATE values that define the



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      time interval over which the recurrence expansion should take
      place.  The start value is inclusive and the end value is
      exclusive of the interval as per iCalendar DTSTART and DTEND
      properties.  The server MUST return only those expanded components
      whose time interval intersects the interval specified by the start
      and end attributes.


   <!ELEMENT expand-recurrence-set EMPTY>
   <!ATTLIST expand-recurrence-set start CDATA #REQUIRED
                                   end CDATA #REQUIRED>


10.3  CALDAV:filter XML Element

   Name: filter

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Determines which matching components are returned.

   Description: The "filter" element specifies the search filter used to
      match components that should be returned by a report.


   <!ELEMENT filter comp-filter>


10.3.1  CALDAV:comp-filter XML Element

   Name: comp-filter

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Limits the search to only the chosen component types.

   Description: The "name" attribute is an iCalendar component type
      (e.g., "VEVENT").  When this element is present, the server should
      only return a component if it matches the filter, which is to say:

   ("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")







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   <!ELEMENT comp-filter (is-defined | time-range)?
                         comp-filter* prop-filter*>

   <!ATTLIST comp-filter name CDATA #REQUIRED>


10.3.2  CALDAV:prop-filter XML Element

   Name: prop-filter

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Limits the search to specific properties.

   Description: The "name" attribute MUST contain an iCalendar property
      name (e.g., "ATTENDEE").  When the 'prop-filter' executes, a
      property matches if:

   ("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>


10.3.3  CALDAV:param-filter XML Element

   Name: param-filter

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Limits the search to specific parameters.

   Description: The "param-filter" element limits the search result to
      the set of resources containing properties with parameters that
      meet the parameter filter rules.  When this filter executes, a
      parameter matches if:

   ("is-defined matches" OR "text-match matches")


   <!ELEMENT param-filter (is-defined | text-match) >




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   <!ATTLIST param-filter name CDATA #REQUIRED>


10.3.4  CALDAV:is-defined XML Element

   Name: is-defined

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Causes a search to match a resource if a component type,
      property or parameter name exists.

   Description: The CALDAV:is-defined XML element limits the filter to
      resources where the named component, property or parameter is
      defined.


   <!ELEMENT is-defined EMPTY>


10.3.5  CALDAV:text-match XML Element

   Name: text-match

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies a substring match on a property or parameter
      value.

   Description: The specified text is used for a substring match against
      the property or parameter value specified in a report.  The
      "caseless" attribute indicates whether the match is case-sensitive
      (value set to "no") or case-insensitive (value set to "yes").  The
      default value is server-specified.  Caseless matching SHOULD be
      implemented as defined in section 5.18 of the Unicode Standard
      ([9]).  Support for the "caseless" attribute is optional.  A
      server should respond with a status of 422 if it is used but
      cannot be supported.


   <!ELEMENT text-match #PCDATA>

   <!ATTLIST text-match caseless (yes|no)>


10.4  CALDAV:time-range XML Element





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   Name: time-range

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: Specifies a time interval for testing components against.

   Description: The CALDAV:time-range element allows for a single time
      range to be defined, in order to limit all the results of the
      search to the set of resources that contain a component which
      falls into that time range.  The value of the "start" and "end"
      attributes MUST follow the syntax of the DATE or DATE-TIME
      iCalendar value type, with any time specified in UTC.

      A VEVENT component falls in a given time-range if:

   (DTSTART <= start AND DTEND > start) OR
   (DTSTART <= start AND DTSTART+DURATION > start) OR
   (DTSTART >= start AND DTSTART < end) OR
   (DTEND   > start AND DTEND <= end)

      A VTODO component falls in a given time-range if:

   (DTSTART <= start AND DUE >= start) OR
   (DTSTART <= start AND DTSTART+DURATION > start) OR
   (DTSTART >= start AND DTSTART < end) OR
   (DUE     >= start AND DUE < end)

      A VJOURNAL component falls in a given time-range if:

   DTSTART >= start AND DTSTART < end

      A VALARM component falls in a given time-range if:

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

      Any property of value type DATE-TIME or DATE (e.g., DTSTAMP) will
      match a given time-range if:

   value >= start AND value < end


   <!ELEMENT time-range EMPTY>

   <!ATTLIST time-range start CDATA
                        end CDATA>






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10.5  DAV:response XML Element

   Name: response

   Namespace: DAV:

   Purpose: Response that includes calendar data.

   Description: Modifies the standard WebDAV response element to include
      calendar data in the response if required by the report type.


   <!ELEMENT DAV:response (DAV:href,
                           ((DAV:href*, DAV:status)|(DAV:propstat+)),
                           calendar-data?,
                           DAV:responsedescription?) >


10.6  CALDAV:calendar-multiget XML Element

   Name: calendar-multiget

   Namespace: urn:ietf:params:xml:ns:caldav

   Purpose: CalDAV report used to retrieve specific calendar component
      items via their URIs.

   Description: See Section 8.4.


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


10.7  CALDAV:free-busy-query XML Element

   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 set of time ranges.

   Description: See Section 8.5.


   <!ELEMENT free-busy-query time-range+ >




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11.  Internationalization Considerations


















































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12.  Security Considerations

12.1  Authentication of Clients

   CalDAV relies on HTTP authentication to authenticate users to the
   server.  As a result the security considerations for use of HTTP
   authentication also apply to CalDAV.  In particular, the HTTP Basic
   authentication method MUST NOT be used without adequate transport
   layer security.

12.2  Denial of Service

   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.

   [[Comment.2: We should make an explicit reference to the security
   considerations mentionned in iCalendar, iTIP and iMIP.  We should
   also specify if there is any semantic defined in CalDAV for the
   iCalendar property CLASS (access classification). --desruisseaux]]


























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13.  IANA Consideration

   In addition to the namespaces defined by RFC2518 [3] for XML
   elements, this document uses a URN to describe a new XML namespace
   conforming to a registry mechanism described in RFC3688 [6].  All
   other IANA considerations mentioned in RFC2518 [3] also apply to this
   document.

13.1  Namespace Registration

   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.

































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14.  Acknowledgements

   The authors would like to thank the following individuals for
   contributing their ideas and support for writing this specification:
   Michael Arick, Mario Bonin, Scott Carr, Mike Douglass, Helge Hess,
   Dan Mosedale, 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.








































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15.  References

15.1  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Dawson, F. and Stenerson, D., "Internet Calendaring and
        Scheduling Core Object Specification (iCalendar)", RFC 2445,
        November 1998.

   [3]  Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D. Jensen,
        "HTTP Extensions for Distributed Authoring -- WEBDAV", RFC 2518,
        February 1999.

   [4]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
        Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
        HTTP/1.1", RFC 2616, June 1999.

   [5]  Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead,
        "Versioning Extensions to WebDAV (Web Distributed Authoring and
        Versioning)", RFC 3253, March 2002.

   [6]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
        January 2004.

   [7]  Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
        Distributed Authoring and Versioning (WebDAV) Access Control
        Protocol", RFC 3744, May 2004.

   [8]  Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and F.
        Yergeau, "Extensible Markup Language (XML) 1.0 (Third Edition)",
        W3C REC-xml-20040204, February 2004,
        <http://www.w3.org/TR/2004/REC-xml-20040204>.

   [9]  The Unicode Consortium, "The Unicode Standard - Version 4.0",
        Addison-Wesley , August 2003,
        <http://www.unicode.org/versions/Unicode4.0.0/>.

        ISBN 0321185781

15.2  Informative References

   [10]  Wahl, M., Howes, T., and S. Kille, "Lightweight Directory
         Access Protocol (v3)", RFC 2251, December 1997.

   [11]  Dawson, F. and T. Howes, "vCard MIME Directory Profile",
         RFC 2426, September 1998.



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   [12]  Small, T., Hennessy, D., and F. Dawson, "Calendar Attributes
         for vCard and LDAP", RFC 2739, January 2000.


Authors' Addresses

   Cyrus Daboo
   ISAMET Inc.
   5001 Baum Blvd.
   Suite 650
   Pittsburgh, PA  15213
   US

   Email: daboo@isamet.com
   URI:   http://www.isamet.com/


   Bernard Desruisseaux
   Oracle Corporation
   600 Blvd. de Maisonneuve West
   10th Floor
   Montreal, QC  H3A 3J2
   CA

   Email: bernard.desruisseaux@oracle.com
   URI:   http://www.oracle.com/


   Lisa Dusseault
   Open Source Application  Foundation
   2064 Edgewood Dr.
   Palo Alto, CA  94303
   US

   Email: lisa@osafoundation.org
   URI:   http://www.osafoundation.org/















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Appendix A.  CalDAV Method Privilege Table (Normative)

   The following table extend the WebDAV Method Privilege Table
   specified in Appendix B of WebDAV ACL [7].

   +---------------------------------+---------------------------------+
   | METHOD                          | PRIVILEGES                      |
   +---------------------------------+---------------------------------+
   | MKCALENDAR                      | DAV:bind                        |
   |                                 |                                 |
   | REPORT                          | DAV:read or                     |
   |                                 | CALDAV:view-free-busy (on all   |
   |                                 | referenced resources)           |
   +---------------------------------+---------------------------------+





































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Appendix B.  Changes

B.1  Changes in -06

   a.  Reworded section "Recurrence and the Data Model".

   b.  Removed timezone collection feature.

   c.  Removed ability for a server to return the Location header on a
       successful PUT request.

   d.  Clarified restrictions on calendar resources contained in
       calendar collections.

   e.  Added preconditions on PUT in calendar collections.

   f.  Added informative "Guidelines" section, with information on
       locking and how to find calendar collections.

   g.  Moved "Sychronization Operations" section in the "Guidelines"
       section.


B.2  Changes in -05

   a.  Removed a lot of non-normative text.

   b.  Removed property promotion/demotion requirements.

   c.  Removed calendar-owner and cal-scale properties.

   d.  Removed 'ical' prefix/text from element names.

   e.  Relaxed WebDAV Class 2 (locking) requirement to a MAY.

   f.  Relaxed MKCALENDAR requirement to a SHOULD.

   g.  Moved the XML Namespace section in the Introduction.

   h.  Added CALDAV: prefix to CalDAV XML elements in the text.

   i.  Added CALDAV:calendar-multiget report.

   j.  Added CALDAV:free-busy-query report.

   k.  Added CALDAV:calendar-description property.





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   l.  Changed CALDAV:calendar-query-result element name to CALDAV:
       calendar-data

   m.  Added description and examples of handling timezones.

   n.  Added mandatory "start" and "end" attributes to the CALDAV:
       expand-recurrence-set element.

   o.  Added three CalDAV OPTIONS requests.

   p.  Grouped XML Element declarations in a separate section.


B.3  Changes in -04

   a.  Added a note about the HTTP Location response header.

   b.  Added report calendar-query.

   c.  Removed reports calendar-property-search and calendar-time-range.

   d.  Removed section on CalDAV and timezones.

   e.  Added requirement to return ETag on creation.

   f.  Revised data model to remove sub-collections from calendar
       collection.

   g.  Added informative references section.

   h.  Removed dependencies on DASL.


B.4  Changes in -03

   a.  Removed Calendar Containers (simplification that doesn't seem to
       remove much functionality)

   b.  Added MKCALENDAR to create calendars and all sub-collections

   c.  Added cal-scale property to calendars


B.5  Changes in -02

   Basically still adding major sections of content:





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   a.  Defined new field values to the OPTIONS "DAV:" response header

   b.  Added new resource properties

   c.  Added new principal properties

   d.  Added new SCHEDULE method and related headers

   e.  Added new privileges for scheduling


B.6  Changes in -01

   a.  Added section on privileges for calendaring, extending WebDAV ACL
       privilege set

   b.  Defined what to do with unrecognized properties in the bodies of
       iCalendar events, with respect to property promotion/demotion

































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