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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
Expires: October 28, 2006                                B. Desruisseaux
                                                                  Oracle
                                                            L. Dusseault
                                                                    OSAF
                                                          April 26, 2006


               Calendaring Extensions to WebDAV (CalDAV)
                       draft-dusseault-caldav-12

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
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on October 28, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

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 calendar access, calendar management, calendar sharing,



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   and calendar publishing.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   5
     1.2.  XML Namespaces and Processing . . . . . . . . . . . . . .   5
   2.  Requirements Overview . . . . . . . . . . . . . . . . . . . .   6
   3.  Calendaring Data Model  . . . . . . . . . . . . . . . . . . .   7
     3.1.  Calendar Server . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  Recurrence and the Data Model . . . . . . . . . . . . . .   8
   4.  Calendar Resources  . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Calendar Object Resources . . . . . . . . . . . . . . . .   8
     4.2.  Calendar Collection . . . . . . . . . . . . . . . . . . .  10
   5.  Calendar Access Feature . . . . . . . . . . . . . . . . . . .  11
     5.1.  Calendar Access Support . . . . . . . . . . . . . . . . .  11
       5.1.1.  Example: Using OPTIONS for the Discovery of
               Calendar Access Support . . . . . . . . . . . . . . .  11
     5.2.  Calendar Collection Properties  . . . . . . . . . . . . .  11
       5.2.1.  CALDAV:calendar-description Property  . . . . . . . .  11
       5.2.2.  CALDAV:calendar-timezone Property . . . . . . . . . .  12
       5.2.3.  CALDAV:supported-calendar-component-set Property  . .  14
       5.2.4.  CALDAV:supported-calendar-data Property . . . . . . .  15
       5.2.5.  CALDAV:max-resource-size Property . . . . . . . . . .  15
       5.2.6.  CALDAV:min-date-time Property . . . . . . . . . . . .  16
       5.2.7.  CALDAV:max-date-time Property . . . . . . . . . . . .  17
       5.2.8.  CALDAV:max-instances Property . . . . . . . . . . . .  18
       5.2.9.  CALDAV:max-attendees-per-instance Property  . . . . .  19
       5.2.10. Additional Precondition for PROPPATCH . . . . . . . .  19
     5.3.  Creating Resources  . . . . . . . . . . . . . . . . . . .  20
       5.3.1.  MKCALENDAR Method . . . . . . . . . . . . . . . . . .  20
         5.3.1.1.  Status Codes  . . . . . . . . . . . . . . . . . .  21
         5.3.1.2.  Example: Successful MKCALENDAR request  . . . . .  22
       5.3.2.  Creating Calendar Object Resources  . . . . . . . . .  24
         5.3.2.1.  Additional Preconditions for PUT, COPY and MOVE .  25
       5.3.3.  Non-standard components, properties and parameters  .  27
       5.3.4.  Calendar Object Resource Entity Tag . . . . . . . . .  27
   6.  Calendaring Access Control  . . . . . . . . . . . . . . . . .  28
     6.1.  Calendaring Privilege . . . . . . . . . . . . . . . . . .  28
       6.1.1.  CALDAV:read-free-busy Privilege . . . . . . . . . . .  28
     6.2.  Additional Principal Property . . . . . . . . . . . . . .  29
       6.2.1.  CALDAV:calendar-home-set Property . . . . . . . . . .  29
   7.  Calendaring Reports . . . . . . . . . . . . . . . . . . . . .  30
     7.1.  REPORT Method . . . . . . . . . . . . . . . . . . . . . .  30
     7.2.  Ordinary collections  . . . . . . . . . . . . . . . . . .  30
     7.3.  Date and floating time  . . . . . . . . . . . . . . . . .  31
     7.4.  Time range filtering  . . . . . . . . . . . . . . . . . .  31



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     7.5.  Partial Retrieval . . . . . . . . . . . . . . . . . . . .  32
     7.6.  Non-standard components, properties and parameters  . . .  33
     7.7.  CALDAV:calendar-query Report  . . . . . . . . . . . . . .  33
       7.7.1.  Example: Partial retrieval of events by time range  .  35
       7.7.2.  Example: Partial retrieval of recurring events  . . .  39
       7.7.3.  Example: Expanded retrieval of recurring events . . .  42
       7.7.4.  Example: Partial retrieval of stored free busy
               components  . . . . . . . . . . . . . . . . . . . . .  44
       7.7.5.  Example: Retrieval of to-dos by alarm time range  . .  46
       7.7.6.  Example: Retrieval of event by UID  . . . . . . . . .  48
       7.7.7.  Example: Retrieval of events by PARTSTAT  . . . . . .  50
       7.7.8.  Example: Retrieval of events only . . . . . . . . . .  52
       7.7.9.  Example: Retrieval of all pending to-dos  . . . . . .  56
       7.7.10. Example: Attempt to query unsupported property  . . .  59
     7.8.  CALDAV:calendar-multiget Report . . . . . . . . . . . . .  60
       7.8.1.  Example: Successful CALDAV:calendar-multiget Report .  61
     7.9.  CALDAV:free-busy-query Report . . . . . . . . . . . . . .  63
       7.9.1.  Example: Successful CALDAV:free-busy-query Report . .  65
   8.  Guidelines  . . . . . . . . . . . . . . . . . . . . . . . . .  65
     8.1.  Client-to-client Interoperability . . . . . . . . . . . .  66
     8.2.  Synchronization Operations  . . . . . . . . . . . . . . .  66
       8.2.1.  Use of Reports  . . . . . . . . . . . . . . . . . . .  66
         8.2.1.1.  Restrict the Time Range . . . . . . . . . . . . .  66
         8.2.1.2.  Synchronize by Time Range . . . . . . . . . . . .  66
         8.2.1.3.  Synchronization Process . . . . . . . . . . . . .  67
       8.2.2.  Restrict the Properties Returned  . . . . . . . . . .  69
     8.3.  Use of Locking  . . . . . . . . . . . . . . . . . . . . .  69
     8.4.  Finding calendars . . . . . . . . . . . . . . . . . . . .  69
     8.5.  Storing and Using Attachments . . . . . . . . . . . . . .  71
       8.5.1.  Inline attachments  . . . . . . . . . . . . . . . . .  71
       8.5.2.  External attachments  . . . . . . . . . . . . . . . .  72
     8.6.  Storing and Using Alarms  . . . . . . . . . . . . . . . .  73
   9.  XML Element Definitions . . . . . . . . . . . . . . . . . . .  74
     9.1.  CALDAV:calendar XML Element . . . . . . . . . . . . . . .  74
     9.2.  CALDAV:mkcalendar XML Element . . . . . . . . . . . . . .  74
     9.3.  CALDAV:mkcalendar-response XML Element  . . . . . . . . .  74
     9.4.  CALDAV:calendar-query XML Element . . . . . . . . . . . .  75
     9.5.  CALDAV:calendar-data XML Element  . . . . . . . . . . . .  75
       9.5.1.  CALDAV:comp XML Element . . . . . . . . . . . . . . .  76
       9.5.2.  CALDAV:allcomp XML Element  . . . . . . . . . . . . .  77
       9.5.3.  CALDAV:allprop XML Element  . . . . . . . . . . . . .  77
       9.5.4.  CALDAV:prop XML Element . . . . . . . . . . . . . . .  78
       9.5.5.  CALDAV:expand XML Element . . . . . . . . . . . . . .  78
       9.5.6.  CALDAV:limit-recurrence-set XML Element . . . . . . .  79
       9.5.7.  CALDAV:limit-freebusy-set XML Element . . . . . . . .  80
     9.6.  CALDAV:filter XML Element . . . . . . . . . . . . . . . .  81
       9.6.1.  CALDAV:comp-filter XML Element  . . . . . . . . . . .  81
       9.6.2.  CALDAV:prop-filter XML Element  . . . . . . . . . . .  82



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       9.6.3.  CALDAV:param-filter XML Element . . . . . . . . . . .  83
       9.6.4.  CALDAV:is-not-defined XML Element . . . . . . . . . .  83
       9.6.5.  CALDAV:text-match XML Element . . . . . . . . . . . .  84
     9.7.  CALDAV:timezone XML Element . . . . . . . . . . . . . . .  84
     9.8.  CALDAV:time-range XML Element . . . . . . . . . . . . . .  85
     9.9.  CALDAV:calendar-multiget XML Element  . . . . . . . . . .  89
     9.10. CALDAV:free-busy-query XML Element  . . . . . . . . . . .  90
   10. Internationalization Considerations . . . . . . . . . . . . .  90
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  90
   12. IANA Consideration  . . . . . . . . . . . . . . . . . . . . .  91
     12.1. Namespace Registration  . . . . . . . . . . . . . . . . .  91
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  91
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  92
     14.1. Normative References  . . . . . . . . . . . . . . . . . .  92
     14.2. Informative References  . . . . . . . . . . . . . . . . .  93
   Appendix A.  CalDAV Method Privilege Table (Normative)  . . . . .  93
   Appendix B.  Calendar collections used in the examples  . . . . .  93
   Appendix C.  Changes (to be removed prior to publication as an
                RFC) . . . . . . . . . . . . . . . . . . . . . . . . 100
     C.1.  Changes in -12  . . . . . . . . . . . . . . . . . . . . . 100
     C.2.  Changes in -11  . . . . . . . . . . . . . . . . . . . . . 100
     C.3.  Changes in -10  . . . . . . . . . . . . . . . . . . . . . 101
     C.4.  Changes in -09  . . . . . . . . . . . . . . . . . . . . . 102
     C.5.  Changes in -08  . . . . . . . . . . . . . . . . . . . . . 104
     C.6.  Changes in -07  . . . . . . . . . . . . . . . . . . . . . 105
     C.7.  Changes in -06  . . . . . . . . . . . . . . . . . . . . . 105
     C.8.  Changes in -05  . . . . . . . . . . . . . . . . . . . . . 106
     C.9.  Changes in -04  . . . . . . . . . . . . . . . . . . . . . 106
     C.10. Changes in -03  . . . . . . . . . . . . . . . . . . . . . 107
     C.11. Changes in -02  . . . . . . . . . . . . . . . . . . . . . 107
     C.12. Changes in -01  . . . . . . . . . . . . . . . . . . . . . 107
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 108
   Intellectual Property and Copyright Statements  . . . . . . . . . 109


















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1.  Introduction

   The concept of using HTTP [RFC2616] and WebDAV [I-D.ietf-webdav-
   rfc2518bis] as a basis for a calendar access protocol 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 calendar
   access protocols using HTTP to upload and download iCalendar
   [RFC2445] objects, and using WebDAV to get listings of resources.
   However, those implementations do not interoperate because there are
   many small and big decisions to be made in how to model calendaring
   data as WebDAV resources, as well as how to implement required
   features that aren't already part of WebDAV.  This document proposes
   a way to model calendar data in WebDAV, with additional features to
   make an interoperable calendar access protocol.

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

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

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

   When XML element types in the namespaces "DAV:" and
   "urn:ietf:params:xml:ns:caldav" are referenced in this document
   outside of the context of an XML fragment, the string "DAV:" and
   "CALDAV:" will be prefixed to the element type names respectively.

1.2.  XML Namespaces and Processing

   Definitions of XML elements in this document use XML element type
   declarations (as found in XML Document Type Declarations), described
   in Section 3.2 of [W3C.REC-xml-20040204].

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

   The XML declarations used in this document do not include namespace
   information.  Thus, implementers MUST NOT use these declarations as
   the only way to create valid CalDAV properties or to validate CalDAV
   XML element type.  Some of the declarations refer to XML elements



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   defined by WebDAV [I-D.ietf-webdav-rfc2518bis] which use the "DAV:"
   namespace.  Wherever such XML elements appear, they are explicitly
   prefixed with "DAV:" to avoid confusion.

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

   Processing of XML by CalDAV clients and servers MUST follow the rules
   described in [I-D.ietf-webdav-rfc2518bis], in particular Sections 8.2
   and 17, and Appendix A of that specification.


2.  Requirements Overview

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

   o  MUST support iCalendar [RFC2445] as a media type for calendar
      object resource format;

   o  MUST support WebDAV Class 1 and Class 3 [I-D.ietf-webdav-
      rfc2518bis];

   o  MUST support WebDAV ACL [RFC3744] with the additional privilege
      defined in Section 6.1 of this document;

   o  MUST support transport over TLS [RFC2246] as defined in [RFC2818];

   o  MUST support ETags [RFC2616] with additional requirements
      specified in Section 5.3.4 of this document;

   o  MUST support all calendaring REPORTs defined in Section 7 of this
      document; and

   o  MUST advertise support on all calendar collections and calendar
      object resources for the calendaring REPORTs in the DAV:supported-
      report-set property as defined in Versioning Extensions to WebDAV
      [RFC3253].

   In addition, a server:

   o  SHOULD support the MKCALENDAR method defined in Section 5.3.1 of
      this document.







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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 follows the
   same pattern by developing all features based on a well-described
   data model.

   As a brief overview, a CalDAV calendar is modeled as a WebDAV
   collection with a defined structure; each calendar collection
   contains a number of resources representing calendar objects as its
   direct child resource.  Each resource representing a calendar object
   (event or to-do, or journal entry, or other calendar components) is
   called a "calendar object resource".  Each calendar object resource
   and each calendar collection can be individually locked and have
   individual WebDAV properties.  Requirements derived from this model
   are provided in Section 4.1 and Section 4.2.

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://www.example.com/webdav/" may
   contain WebDAV collections and resources, all of which have URLs
   beginning with "http://www.example.com/webdav/".  Note that the root
   URL "http://www.example.com/" may not itself be a WebDAV repository
   (for example, if the WebDAV support is implemented through a servlet
   or other Web server extension).

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

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

   The CalDAV server or repository is the canonical location for



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

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

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


4.  Calendar Resources

4.1.  Calendar Object Resources

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

   Calendar object resources contained in calendar collections MUST NOT



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   specify the iCalendar METHOD property.

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

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

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

   For example, given the following iCalendar object:

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



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

4.2.  Calendar Collection

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

       <!ELEMENT calendar EMPTY>

   A calendar collection can be created through provisioning (e.g.,
   automatically created when a user's account is provisioned), or it
   can be created with the MKCALENDAR method (see Section 5.3.1).  This
   method can be useful for a user to create additional calendars (e.g.,
   soccer schedule) or for users to share a calendar (e.g., team events
   or conference 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 5.2.1 to
   provide such a cue.

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

   a.  Calendar collections MUST only contain calendar object resources
       and collections that are not calendar collections. i.e., the only
       "top-level" non-collection resources allowed in a calendar
       collection are calendar object resources.  This ensures that
       calendar clients do not have to deal with non-calendar data in a
       calendar collection, though they do have to distinguish between
       calendar object resources and collections when using standard
       WebDAV techniques to examine the contents of a collection.

   b.  Collections contained in calendar collections MUST NOT contain
       calendar collections at any depth. i.e., "nesting" of calendar
       collections within other calendar collections at any depth is not
       allowed.  This specification does not define how collections
       contained in a calendar collection are used or how they relate to
       any calendar object resources contained in the calendar
       collection.



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   Multiple calendar collections MAY be children of the same collection.


5.  Calendar Access Feature

5.1.  Calendar Access Support

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

5.1.1.  Example: Using OPTIONS for the Discovery of Calendar Access
        Support

   >> Request <<

   OPTIONS /home/bernard/calendars/ HTTP/1.1
   Host: cal.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE
   Allow: PROPFIND, PROPPATCH, LOCK, UNLOCK, REPORT, ACL
   DAV: 1, 2, 3, access-control, calendar-access
   Date: Fri, 11 Nov 2005 09:32:12 GMT
   Content-Length: 0

   In this example, the OPTIONS method returns the value "calendar-
   access" in the DAV response header to indicate that the collection
   "/home/bernard/calendars/" supports the properties, reports, methods,
   or privileges defined in this specification.

5.2.  Calendar Collection Properties

   This section defines properties that MAY be defined on calendar
   collections.

5.2.1.  CALDAV:calendar-description Property

   Name: calendar-description







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

   Purpose: Provides a human-readable description of the calendar
      collection.

   Conformance: This property MAY be defined on any calendar collection.
      If defined, it MAY be protected and SHOULD NOT be returned by a
      PROPFIND DAV:allprop request (as defined in Section 14.2 of
      [I-D.ietf-webdav-rfc2518bis]).  An xml:lang attribute indicating
      the human language of the description SHOULD be set for this
      property by clients or through server provisioning.  Servers MUST
      return any xml:lang attribute if set for the property.

   Description: If present, the property contains a description of the
      calendar collection that is suitable for presentation to a user.
      If not present, the client should assume no description for the
      calendar collection.

   Definition:

         <!ELEMENT calendar-description (#PCDATA)>
         PCDATA value: string

   Example:

         <C:calendar-description xml:lang="fr-CA"
            xmlns:C="urn:ietf:params:xml:ns:caldav"
         >Calendrier de Mathilde Desruisseaux</C:calendar-description>

5.2.2.  CALDAV:calendar-timezone Property

   Name: calendar-timezone

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

   Purpose: Specifies a time zone on a calendar collection.

   Conformance: This property SHOULD be defined on all calendar
      collections.  If defined, it SHOULD NOT be returned by a PROPFIND
      DAV:allprop request (as defined in Section 14.2 of [I-D.ietf-
      webdav-rfc2518bis]).

   Description: The CALDAV:calendar-timezone property is used to specify
      the time zone the server should rely on to resolve "date" values
      and "date with local time" values (i.e., floating time) to "date
      with UTC time" values.  The server will require this information
      to determine if a calendar component scheduled with "date" values
      or "date with local time" values overlaps a CALDAV:time-range



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      specified in a CALDAV:calendar-query REPORT.  The server will also
      require this information to compute the proper FREEBUSY time
      period as "date with UTC time" in the VFREEBUSY component returned
      in a response to a CALDAV:free-busy-query REPORT request that
      takes into account calendar components scheduled with "date"
      values or "date with local time" values.  In the absence of this
      property the server MAY rely on the time zone of their choice.

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

   Definition:

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

   Example:

   <C:calendar-timezone
       xmlns:C="urn:ietf:params:xml:ns:caldav">BEGIN:VCALENDAR
   PRODID:-//Example Corp.//CalDAV Client//EN
   VERSION:2.0
   BEGIN:VTIMEZONE
   TZID:US-Eastern
   LAST-MODIFIED:19870101T000000Z
   BEGIN:STANDARD
   DTSTART:19671029T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   TZNAME:Eastern Standard Time (US &amp; Canada)
   END:STANDARD
   BEGIN:DAYLIGHT
   DTSTART:19870405T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   TZNAME:Eastern Daylight Time (US &amp; Canada)
   END:DAYLIGHT
   END:VTIMEZONE
   END:VCALENDAR
   </C:calendar-timezone>




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5.2.3.  CALDAV:supported-calendar-component-set Property

   Name: supported-calendar-component-set

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

   Purpose: Specifies the calendar component types (e.g., VEVENT, VTODO,
      etc.) that calendar object resources can contain in the calendar
      collection.

   Conformance: This property MAY be defined on any calendar collection.
      If defined, it MUST be protected and SHOULD NOT be returned by a
      PROPFIND DAV:allprop request (as defined in Section 14.2 of
      [I-D.ietf-webdav-rfc2518bis]).

   Description: The CALDAV:supported-calendar-component-set property is
      used to specify restrictions on the calendar component types that
      calendar object resources may contain in a calendar collection.
      Any attempt by the client to store calendar object resources with
      component types not listed in this property, if it exists, MUST
      result in an error, with the CALDAV:supported-calendar-component
      precondition (Section 5.3.2.1) being violated.  Since this
      property is protected it cannot be changed by clients using a
      PROPPATCH request.  However, clients can initialize the value of
      this property when creating a new calendar collection with
      MKCALENDAR.  The empty-element tag <C:comp name="VTIMEZONE"/> MUST
      only be specified if support for calendar object resources that
      only contain VTIMEZONE components is provided or desired.  Support
      for VTIMEZONE components in calendar object resources that contain
      VEVENT or VTODO components is always assumed.  In the absence of
      this property the server MUST accept all component types, and the
      client can assume that.

   Definition:

         <!ELEMENT supported-calendar-component-set (comp*)>

   Example:

         <C:supported-calendar-component-set
             xmlns:C="urn:ietf:params:xml:ns:caldav">
           <C:comp name="VEVENT"/>
           <C:comp name="VTODO"/>
         </C:supported-calendar-component-set>







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5.2.4.  CALDAV:supported-calendar-data Property

   Name: supported-calendar-data

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

   Purpose: Specifies what media types are allowed for calendar object
      resources in a calendar collection.

   Conformance: This property MAY be defined on any calendar collection.
      If defined, it MUST be protected and SHOULD NOT be returned by a
      PROPFIND DAV:allprop request (as defined in Section 14.2 of
      [I-D.ietf-webdav-rfc2518bis]).

   Description: The CALDAV:supported-calendar-data property is used to
      specify the media type supported for the calendar object resources
      contained in a given calendar collection (e.g., iCalendar version
      2.0).  Any attempt by the client to store calendar object
      resources with a media type not listed in this property MUST
      result in an error, with the CALDAV:supported-calendar-data
      precondition (Section 5.3.2.1) being violated.  In the absence of
      this property the server MUST accept data with the media type
      "text/calendar" and iCalendar version 2.0, and clients can assume
      that.

   Definition:

         <!ELEMENT supported-calendar-data (calendar-data*)>

   Example:

         <C:supported-calendar-data
            xmlns:C="urn:ietf:params:xml:ns:caldav">
           <C:calendar-data content-type="text/calendar" version="2.0"/>
         </C:supported-calendar-data>

5.2.5.  CALDAV:max-resource-size Property

   Name: max-resource-size

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

   Purpose: Provides a numeric value indicating the maximum size of
      resource in octets that the server is willing to accept when a
      calendar object resource is stored in a calendar collection.






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   Conformance: This property MAY be defined on any calendar collection.
      If defined, it MUST be protected and SHOULD NOT be returned by a
      PROPFIND DAV:allprop request (as defined in Section 14.2 of
      [I-D.ietf-webdav-rfc2518bis]).

   Description: The CALDAV:max-resource-size is used to specify a
      numeric value that represents the maximum size in octets that the
      server is willing to accept when a calendar object resource is
      stored in a calendar collection.  Any attempt to store a calendar
      object resource exceeding this size MUST result in an error, with
      the CALDAV:max-resource-size precondition (Section 5.3.2.1) being
      violated.  In the absence of this property the client can assume
      that the server will allow storing a resource of any reasonable
      size.

   Definition:

         <!ELEMENT max-resource-size (#PCDATA)>
         PCDATA value: a numeric value (positive integer)

   Example:

         <C:max-resource-size xmlns:C="urn:ietf:params:xml:ns:caldav"
         >102400</C:max-resource-size>

5.2.6.  CALDAV:min-date-time Property

   Name: min-date-time

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

   Purpose: Provides a date-time value indicating the earliest date and
      time (in UTC) that the server is willing to accept for any date or
      time value in a calendar object resource stored in a calendar
      collection.

   Conformance: This property MAY be defined on any calendar collection.
      If defined, it MUST be protected and SHOULD NOT be returned by a
      PROPFIND DAV:allprop request (as defined in Section 14.2 of
      [I-D.ietf-webdav-rfc2518bis]).

   Description: The CALDAV:min-date-time is used to specify an iCalendar
      DATE-TIME value in UTC that indicates the earliest inclusive date
      that the server is willing to accept for any explicit date or time
      value in a calendar object resource stored in a calendar
      collection.  Any attempt to store a calendar object resource using
      a date or time value earlier than this value MUST result in an
      error, with the CALDAV:min-date-time precondition



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      (Section 5.3.2.1) being violated.  Note that servers MUST accept
      recurring components that specify instances beyond this limit,
      provided none of those instances have been overridden.  In that
      case the server MAY simply ignore those instances outside of the
      acceptable range when processing reports on the calendar object
      resource.  In the absence of this property the client can assume
      any valid iCalendar date may be used at least up to the CALDAV:
      max-date-time value if that is defined.

   Definition:

         <!ELEMENT min-date-time (#PCDATA)>
         PCDATA value: an iCalendar format DATE-TIME value in UTC

   Example:

         <C:min-date-time xmlns:C="urn:ietf:params:xml:ns:caldav"
         >19000101T000000Z</C:min-date-time>

5.2.7.  CALDAV:max-date-time Property

   Name: max-date-time

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

   Purpose: Provides a date-time value indicating the latest date and
      time (in UTC) that the server is willing to accept for any date or
      time value in a calendar object resource stored in a calendar
      collection.

   Conformance: This property MAY be defined on any calendar collection.
      If defined, it MUST be protected and SHOULD NOT be returned by a
      PROPFIND DAV:allprop request (as defined in Section 14.2 of
      [I-D.ietf-webdav-rfc2518bis]).

   Description: The CALDAV:max-date-time is used to specify an iCalendar
      DATE-TIME value in UTC that indicates the inclusive latest date
      that the server is willing to accept for any date or time value in
      a calendar object resource stored in a calendar collection.  Any
      attempt to store a calendar object resource using a date or time
      value later than this value MUST result in an error, with the
      CALDAV:max-date-time precondition (Section 5.3.2.1) being
      violated.  Note that servers MUST accept recurring components that
      specify instances beyond this limit, provided none of those
      instances have been overridden.  In that case the server MAY
      simply ignore those instances outside of the acceptable range when
      processing reports on the calendar object resource.  In the
      absence of this property the client can assume any valid iCalendar



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      date may be used at least down to the CALDAV:min-date-time value
      if that is defined.

   Definition:

         <!ELEMENT max-date-time (#PCDATA)>
         PCDATA value: an iCalendar format DATE-TIME value in UTC

   Example:

         <C:max-date-time xmlns:C="urn:ietf:params:xml:ns:caldav"
         >20491231T235959Z</C:max-date-time>

5.2.8.  CALDAV:max-instances Property

   Name: max-instances

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

   Purpose: Provides a numeric value indicating the maximum number of
      recurrence instances that a calendar object resource stored in a
      calendar collection can generate.

   Conformance: This property MAY be defined on any calendar collection.
      If defined, it MUST be protected and SHOULD NOT be returned by a
      PROPFIND DAV:allprop request (as defined in Section 14.2 of
      [I-D.ietf-webdav-rfc2518bis]).

   Description: The CALDAV:max-instances is used to specify a numeric
      value that indicates the maximum number of recurrence instances
      that a calendar object resource stored in a calendar collection
      can generate.  Any attempt to store a calendar object resource
      with a recurrence pattern that generates more instances than this
      value MUST result in an error, with the CALDAV:max-instances
      precondition (Section 5.3.2.1) being violated.  In the absence of
      this property the client can assume that the server has no limits
      on the number of recurrence instances it can handle or expand.

   Definition:

         <!ELEMENT max-instances (#PCDATA)>
         PCDATA value: a numeric value (integer greater than zero)

   Example:

         <C:max-instances xmlns:C="urn:ietf:params:xml:ns:caldav"
         >100</C:max-instances>




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5.2.9.  CALDAV:max-attendees-per-instance Property

   Name: max-attendees-per-instance

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

   Purpose: Provides a numeric value indicating the maximum number of
      ATTENDEE properties in any instance of a calendar object resource
      stored in a calendar collection.

   Conformance: This property MAY be defined on any calendar collection.
      If defined, it MUST be protected and SHOULD NOT be returned by a
      PROPFIND DAV:allprop request (as defined in Section 14.2 of
      [I-D.ietf-webdav-rfc2518bis]).

   Description: The CALDAV:max-attendees-per-instance is used to specify
      a numeric value that indicates the maximum number of iCalendar
      ATTENDEE properties on any one instance of a calendar object
      resource stored in a calendar collection.  Any attempt to store a
      calendar object resource with more ATTENDEE properties per
      instance than this value MUST result in an error, with the CALDAV:
      max-attendees-per-instance precondition (Section 5.3.2.1) being
      violated.  In the absence of this property the client can assume
      that the server can handle any number of ATTENDEE properties in a
      calendar component.

   Definition:

         <!ELEMENT max-attendees-per-instance (#PCDATA)>
         PCDATA value: a numeric value (integer greater than zero)

   Example:

         <C:max-attendees-per-instance
              xmlns:C="urn:ietf:params:xml:ns:caldav"
         >25</C:max-attendees-per-instance>

5.2.10.  Additional Precondition for PROPPATCH

   This specification requires an additional Precondition (see Section
   16 of [I-D.ietf-webdav-rfc2518bis] for the PROPPATCH method.  The
   precondition is:

      (CALDAV:valid-calendar-data): The time zone specified in CALDAV:
      calendar-timezone property MUST be a valid iCalendar object
      containing a single valid VTIMEZONE component.





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5.3.  Creating Resources

   The creation of calendar collections and calendar object resources
   may be initiated by either a CalDAV client or by the CalDAV server.
   For example, a server might come pre-configured 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.

5.3.1.  MKCALENDAR Method

   An HTTP request using the MKCALENDAR method creates a new calendar
   collection resource.  A server MAY restrict calendar collection
   creation to particular collections.

   Support for MKCALENDAR on the server is only RECOMMENDED and not
   REQUIRED because some calendar stores only support one calendar per
   user (or principal) and those are typically pre-created for each
   account.  However, servers and clients are strongly encouraged to
   support MKCALENDAR whenever possible to allow users to create
   multiple calendar collections to better help organize their data.

   Clients SHOULD use the DAV:displayname property for a human-readable
   name of the calendar.  Clients can either specify the value of the
   DAV:displayname property in the request body of the MKCALENDAR
   request, or alternatively issue a PROPPATCH request to change the
   DAV:displayname property to the appropriate value immediately after
   issuing the MKCALENDAR request.  Clients SHOULD NOT set the DAV:
   displayname property to be the same as any other calendar collection
   at the same URI "level".  When displaying calendar collections to
   users, clients SHOULD check the DAV:displayname property and use that
   value as the name of the calendar.  In the event that the DAV:
   displayname property is empty, the client MAY use the last part of
   the calendar collection URI as the name, however that path segment
   may be "opaque" and not represent any meaningful human-readable text.

   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.  Instruction processing MUST occur in the order
      instructions are received (i.e., from top to bottom).



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      Instructions MUST either all be executed or none executed.  Thus
      if any error occurs during processing, all executed instructions
      MUST be undone and a proper error result returned.  Instruction
      processing details can be found in the definition of the DAV:set
      instruction in Section 14.26 of [I-D.ietf-webdav-rfc2518bis].

         <!ELEMENT mkcalendar (DAV:set)>

      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:valid-calendar-data): The time zone specified in the
      CALDAV:calendar-timezone property MUST be a valid iCalendar object
      containing a single valid VTIMEZONE component;

      (DAV:needs-privilege): The DAV:bind privilege MUST be granted to
      the current user on the parent collection of the Request-URI.

   Postconditions:

      (CALDAV:initialize-calendar-collection): A new calendar collection
      exists at the Request-URI.  The DAV:resourcetype of the calendar
      collection MUST contain both DAV:collection and CALDAV:calendar
      XML elements.

5.3.1.1.  Status Codes

   The following are examples of response codes one would expect to get
   in a response to a MKCALENDAR request.  Note that this list is by no
   means exhaustive.

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

      207 (Multi-Status) - The calendar collection resource was not
      created since one or more DAV:set instructions specified in the



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      request body could not be processed successfully.  The following
      are examples of response codes one would expect to be used in a
      207 (Multi-Status) response in this situation:

         403 (Forbidden) - The client, for reasons the server chooses
         not to specify, cannot alter one of the properties;

         409 (Conflict) - The client has provided a value whose
         semantics are not appropriate for the property.  This includes
         trying to set read-only properties;

         424 (Failed Dependency) - The DAV:set instruction on the
         specified resource would have succeeded if it were not for the
         failure of another DAV:set instruction specified in the request
         body;

         423 (Locked) - The specified resource is locked and the client
         either is not a lock owner or the lock type requires a lock
         token to be submitted and the client did not submit it; and

         507 (Insufficient Storage) - The server did not have sufficient
         space to record the property;

      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;

      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; and

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

5.3.1.2.  Example: Successful MKCALENDAR request

   This example creates a calendar collection called /home/lisa/
   calendars/events/ on the server cal.example.com with specific values
   for the properties DAV:displayname, CALDAV:calendar-description,
   CALDAV:supported-calendar-component-set, and CALDAV:calendar-
   timezone.






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   >> Request <<

   MKCALENDAR /home/lisa/calendars/events/ HTTP/1.1
   Host: cal.example.com
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:mkcalendar xmlns:D="DAV:"
                 xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:set>
       <D:prop>
         <D:displayname>Lisa's Events</D:displayname>
         <C:calendar-description xml:lang="en"
   >Calendar restricted to events.</C:calendar-description>
         <C:supported-calendar-component-set>
           <C:comp name="VEVENT"/>
         </C:supported-calendar-component-set>
         <C:calendar-timezone><![CDATA[BEGIN:VCALENDAR
   PRODID:-//Example Corp.//CalDAV Client//EN
   VERSION:2.0
   BEGIN:VTIMEZONE
   TZID:US-Eastern
   LAST-MODIFIED:19870101T000000Z
   BEGIN:STANDARD
   DTSTART:19671029T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   TZNAME:Eastern Standard Time (US & Canada)
   END:STANDARD
   BEGIN:DAYLIGHT
   DTSTART:19870405T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   TZNAME:Eastern Daylight Time (US & Canada)
   END:DAYLIGHT
   END:VTIMEZONE
   END:VCALENDAR
   ]]></C:calendar-timezone>
       </D:prop>
     </D:set>
   </C:mkcalendar>







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   >> Response <<

   HTTP/1.1 201 Created
   Cache-Control: no-cache
   Date: Fri, 11 Nov 2005 09:32:12 GMT
   Content-Length: 0

5.3.2.  Creating Calendar Object Resources

   Clients populate calendar collections with calendar object resources.
   The URL for each calendar object resource is entirely arbitrary, and
   does not need to bear a specific relationship to the calendar object
   resource's iCalendar properties or other metadata.  New calendar
   object resources MUST be created with a PUT request targeted at an
   unmapped URI.  A PUT request targeted at a mapped URI updates an
   existing calendar object resource.

   When servers create new resources, it's not hard for the server to
   choose an unmapped URI.  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
   resource isn't created with a name collision.  However, there is an
   HTTP feature 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 request 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 "If-None-Match: *" request header ensures
   that the client will not inadvertently overwrite an existing
   resource, if the last path segment turned out to already be used.





















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   >> Request <<

   PUT /home/lisa/calendars/events/qwue23489.ics HTTP/1.1
   If-None-Match: *
   Host: cal.example.com
   Content-Type: text/calendar
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   UID:20010712T182145Z-123401@example.com
   DTSTAMP:20060712T182145Z
   DTSTART:20060714T170000Z
   DTEND:20060715T040000Z
   SUMMARY:Bastille Day Party
   END:VEVENT
   END:VCALENDAR

   >> Response <<

   HTTP/1.1 201 Created
   Content-Length: 0
   Date: Fri, 11 Nov 2005 09:32:12 GMT
   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 [RFC2445], the URL of calendar object
   resources containing (an arbitrary set of) calendaring and scheduling
   information may be suffixed by ".ics", and the URL of calendar object
   resources containing free or busy time information may be suffixed by
   ".ifb".

5.3.2.1.  Additional Preconditions for PUT, COPY and MOVE

   This specification creates additional Preconditions (see Section 16
   of [I-D.ietf-webdav-rfc2518bis] for PUT, COPY and MOVE methods.
   These preconditions apply:

      When a PUT operation of a calendar object resource into a calendar
      collection occurs.

      When a COPY or MOVE operation of a calendar object resource into a
      calendar collection occurs.



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   The new preconditions are:

      (CALDAV:supported-calendar-data): The resource submitted in the
      PUT request, or targeted by a COPY or MOVE request MUST be a
      supported media type (i.e., iCalendar) for calendar object
      resources;

      (CALDAV:valid-calendar-data): The resource submitted in the PUT
      request, or targeted by a COPY or MOVE request MUST be valid data
      for the media type being specified (i.e., MUST contain valid
      iCalendar data);

      (CALDAV:valid-calendar-object-resource): The resource submitted in
      the PUT request, or targeted by a COPY or MOVE request MUST obey
      all restrictions specified in Section 4.1 (e.g., calendar object
      resources MUST NOT contain more than one type of calendar
      component, calendar object resources MUST NOT specify the
      iCalendar METHOD property, etc.);

      (CALDAV:supported-calendar-component): The resource submitted in
      the PUT request, or targeted by a COPY or MOVE request MUST
      contain a type of calendar component that is supported in the
      targeted calendar collection;

      (CALDAV:no-uid-conflict): The resource submitted in the PUT
      request, or targeted by a COPY or MOVE request MUST NOT specify an
      iCalendar UID property value already in use in the targeted
      calendar collection or overwrite an existing calendar object
      resource with one that has a different UID property value.
      Servers SHOULD report the URL of the resource that is already
      making use of the same UID property value in the DAV:href element;

                <!ELEMENT no-uid-conflict (DAV:href)>

      (CALDAV:calendar-collection-location-ok): In a COPY or MOVE
      request, when the Request-URI is a calendar collection, the
      Destination-URI MUST identify a location where a calendar
      collection can be created;

      (CALDAV:max-resource-size): The resource submitted in the PUT
      request, or targeted by a COPY or MOVE request MUST have an octet
      size less than or equal to the value of the CALDAV:max-resource-
      size property value (Section 5.2.5) on the calendar collection
      where the resource will be stored;

      (CALDAV:min-date-time): The resource submitted in the PUT request,
      or targeted by a COPY or MOVE request MUST have all of its
      iCalendar date or time property values (for each recurring



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      instance) greater than or equal to the value of the CALDAV:min-
      date-time property value (Section 5.2.6) on the calendar
      collection where the resource will be stored;

      (CALDAV:max-date-time): The resource submitted in the PUT request,
      or targeted by a COPY or MOVE request MUST have all of its
      iCalendar date or time property values (for each recurring
      instance) less than the value of the CALDAV:max-date-time property
      value (Section 5.2.7) on the calendar collection where the
      resource will be stored;

      (CALDAV:max-instances): The resource submitted in the PUT request,
      or targeted by a COPY or MOVE request MUST generate a number of
      recurring instances less than or equal to the value of the CALDAV:
      max-instances property value (Section 5.2.8) on the calendar
      collection where the resource will be stored;

      (CALDAV:max-attendees-per-instance): The resource submitted in the
      PUT request, or targeted by a COPY or MOVE request MUST have a
      number of ATTENDEE properties on any one instance less than or
      equal to the value of the CALDAV:max-attendees-per-instance
      property value (Section 5.2.9) on the calendar collection where
      the resource will be stored;

5.3.3.  Non-standard components, properties and parameters

   iCalendar provides a "standard mechanism for doing non-standard
   things".  This extension support allows implementers to make use of
   non-standard components, properties and parameters whose names are
   prefixed with the text "X-".

   Servers MUST support the use of non-standard components, properties
   and parameters in calendar object resources stored via the PUT
   method.

   Servers may need to enforce rules for their own "private" components,
   properties or parameters, so servers MAY reject any attempt by the
   client to change those or use values for those outside of any
   restrictions the server may have.  Servers SHOULD ensure that any
   "private" components, properties or parameters it uses follow the
   convention of including a vendor id in the "X-" name as described in
   Section 4.2 of [RFC2445], e.g., "X-ABC-Private".

5.3.4.  Calendar Object Resource Entity Tag

   The DAV:getetag property MUST be defined and set to a strong entity
   tag on all calendar object resources.




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   A response to a GET request targeted at a calendar object resource
   MUST contain an ETag response header field indicating the current
   value of the strong entity tag of the calendar object resource.

   Servers SHOULD return a strong entity tag (ETag header) in a PUT
   response when the stored calendar object resource is equivalent by
   octet equality to the calendar object resource submitted in the body
   of the PUT request.  This allows clients to reliably use the returned
   strong entity tag for data synchronization purposes.  For instance,
   the client can do a PROPFIND request on the stored calendar object
   resource and have the DAV:getetag property returned, and compare that
   value with the strong entity tag it received on the PUT response, and
   know that if they are equal, then the calendar object resource on the
   server has not been changed.

   In the case where the data stored by a server as a result of a PUT
   request is not equivalent by octet equality to the submitted calendar
   object resource, the behavior of the ETag response header is
   undefined, with the exception that a strong entity tag MUST NOT be
   returned in the response.  As a result, clients may need to retrieve
   the modified calendar object resource (and ETag) as a basis for
   further changes, rather than use the calendar object resource it had
   sent with the PUT request.


6.  Calendaring Access Control

6.1.  Calendaring Privilege

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

6.1.1.  CALDAV:read-free-busy Privilege

   Calendar users often wish to allow other users to see their busy time
   information, without viewing the other details of the calendar
   components (e.g., location, summary, attendees).  This allows a
   significant amount of privacy while still allowing other users to
   schedule meetings at times when the user is likely to be free.

   The CALDAV:read-free-busy privilege controls which calendar
   collections, regular collections and calendar object resources are
   examined when a CALDAV:free-busy-query REPORT request is processed
   (see Section 7.9).  This privilege can be granted on calendar
   collections, regular collections or calendar object resources.



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   Servers MUST support this privilege on all calendar collections,
   regular collections and calendar object resources.


           <!ELEMENT read-free-busy EMPTY>

   The CALDAV:read-free-busy privilege MUST be aggregated in the DAV:
   read privilege.  Servers MUST allow the CALDAV:read-free-busy to be
   granted without the DAV:read privilege being granted.

   Clients should note that when only the CALDAV:read-free-busy
   privilege has been granted on a resource, this does not imply access
   to GET, HEAD, OPTIONS and PROPFIND on the resource -- those
   operations are governed by the DAV:read privilege.

6.2.  Additional Principal Property

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

6.2.1.  CALDAV:calendar-home-set Property

   Name: calendar-home-set

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

   Purpose: Identifies the URL of any WebDAV collections that contain
      calendar collections owned by the associated principal resource.

   Conformance: This property MAY be defined in a principal resource.
      If defined, it MAY be protected and SHOULD NOT be returned by a
      PROPFIND DAV:allprop request (as defined in Section 14.2 of
      [I-D.ietf-webdav-rfc2518bis]).  Support for this property is
      RECOMMENDED.

   Description: The CALDAV:calendar-home-set property is meant to allow
      users to easily find the calendar collections owned by the
      principal.  Typically, users will group all the calendar
      collections that they own under a common collection.  This
      property specifies the URL of collections that either are calendar
      collections or ordinary collections that have child or descendant
      calendar collections owned by the principal.

   Definition:

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





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   Example:

       <C:calendar-home-set xmlns:D="DAV:"
                            xmlns:C="urn:ietf:params:xml:ns:caldav">
         <D:href>http://cal.example.com/home/bernard/calendars/</D:href>
       </C:calendar-home-set>


7.  Calendaring Reports

   This section defines the REPORTs that CalDAV servers MUST support on
   calendar collections and calendar object resources.

   CalDAV servers MUST advertise support for these REPORTs on all
   calendar collections and calendar object resources with the DAV:
   supported-report-set property defined in Section 3.1.5 of [RFC3253].
   CalDAV servers MAY also advertise support for these REPORTs on
   ordinary collections.

   Some of these REPORTs allow calendar data (from possibly multiple
   resources) to be returned.

7.1.  REPORT Method

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

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

7.2.  Ordinary collections

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





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7.3.  Date and floating time

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

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

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

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

7.4.  Time range filtering

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

   To determine whether a calendar object resource matches the time
   range filter element, the start and end times for the targeted
   component or property are determined and then compared to the
   requested time range.  If there is an overlap with the requested time
   range, then the calendar object resource matches the filter element.
   The rules defined in [RFC2445] for determining the actual start and
   end times of calendar components MUST be used, and these are fully
   enumerated in Section 9.8 of this document.



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

7.5.  Partial Retrieval

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

   A CalDAV client MAY request particular WebDAV property values, all
   WebDAV property values, or a list of the names of the resource's
   WebDAV properties.  A CalDAV client MAY also request calendar data to
   be returned and whether all calendar components and properties should
   be returned or only particular ones.  See CALDAV:calendar-data in
   Section 9.5.

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

   A CalDAV client only interested in the recurrence instances that
   overlap a specified time range MAY request to receive only the
   "master component" along with the "overridden components" that impact
   the specified time range and thus limit the data returned by the
   server.  See CALDAV:limit-recurrence-set in Section 9.5.6.  An
   overridden component impacts a time range if its current start and
   end times overlap the time range, or if the original start and end
   times - the ones that would have been used if the instance were not
   overridden - overlap the time range.

   A CalDAV client with no support for recurrence properties (i.e.,
   EXDATE, EXRULE, RDATE and RRULE) and possibly VTIMEZONE components,
   or a client not willing to perform recurrence expansion because of
   limited processing capability MAY request to receive only the
   recurrence instances that overlap a specified time range as separate
   calendar components that each define exactly one recurrence instance.
   See CALDAV:expand in Section 9.5.5.

   Finally, in the case of VFREEBUSY components, a CalDAV client MAY
   request to receive only the FREEBUSY property values that overlap a
   specified time range.  See CALDAV:limit-freebusy-set in
   Section 9.5.7.



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7.6.  Non-standard components, properties and parameters

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

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

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

7.7.  CALDAV:calendar-query Report

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

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

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

   Marshalling:

      The request body MUST be a CALDAV:calendar-query XML element as
      defined in Section 9.4.





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      The request MAY include a Depth header.  If no Depth header is
      included, Depth:0 is assumed.

      The response body for a successful request MUST be a DAV:
      multistatus XML element (i.e., the response uses the same format
      as the response for PROPFIND).  In the case where there are no
      response elements, the returned DAV:multistatus XML element is
      empty.

      The response body for a successful CALDAV:calendar-query REPORT
      request MUST contain a DAV:response element for each iCalendar
      object that matched the search filter.  Calendar data is being
      returned in the CALDAV:calendar-data XML element inside the DAV:
      propstat XML element.

   Preconditions:

      (CALDAV:supported-calendar-data): The attributes "content-type"
      and "version" of the CALDAV:calendar-data XML element (see
      Section 9.5) specify a media type supported by the server for
      calendar object resources.

      (CALDAV:valid-filter): The CALDAV:filter XML element (see
      Section 9.6) specified in the REPORT request MUST be valid.  For
      instance, a CALDAV:filter cannot nest a <C:comp name="VEVENT">
      element in a <C:comp name="VTODO"> element, or a CALDAV:filter
      cannot nest a <C:time-range start="..." end="..."> element in a
      <C:prop name="SUMMARY"> element.

      (CALDAV:supported-filter): The CALDAV:comp-filter (see
      Section 9.6.1), CALDAV:prop-filter (see Section 9.6.2) and CALDAV:
      param-filter (see Section 9.6.3) XML elements used in the CALDAV:
      filter XML element (see Section 9.6) in the REPORT request only
      make reference to components, properties and parameters for which
      queries are supported by the server. i.e., if the CALDAV:filter
      element attempts to reference an unsupported component, property
      or parameter, this precondition is violated.  Servers SHOULD
      report the CALDAV:comp-filter, CALDAV:prop-filter or CALDAV:param-
      filter for which it does not provide support.

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

      (CALDAV:valid-calendar-data): The time zone specified in the
      REPORT request MUST be a valid iCalendar object containing a
      single valid VTIMEZONE component.




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      (CALDAV:min-date-time): Any XML element specifying a range of time
      MUST have its start or end date or time values greater than or
      equal to the value of the CALDAV:min-date-time property value
      (Section 5.2.6) on the calendar collections being targeted by the
      REPORT;

      (CALDAV:max-date-time): Any XML element specifying a range of time
      MUST have its start or end date or time values less than or equal
      to the value of the CALDAV:max-date-time property value
      (Section 5.2.7) on the calendar collections being targeted by the
      REPORT;

   Postconditions:

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

7.7.1.  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 January 4th, 2006 at 00:00:00 AM UTC to January 5th,
   2006 at 00:00:00 AM UTC.  In addition the DAV:getetag property is
   also requested and returned as part of the response.  Note that the
   first calendar object returned is a recurring event whose first
   instance lies outside of the requested time range, but whose third
   instance does overlap the time range.  Note that due to the CALDAV:
   calendar-data element restrictions, the DTSTAMP property in VEVENT
   components has not been returned, and the only property returned in
   the VCALENDAR object is VERSION.

   See Appendix B for the calendar data being targeted by this example.
















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   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:D="DAV:"
                 xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop>
       <D:getetag/>
       <C:calendar-data>
         <C:comp name="VCALENDAR">
           <C:prop name="VERSION"/>
           <C:comp name="VEVENT">
             <C:prop name="SUMMARY"/>
             <C:prop name="UID"/>
             <C:prop name="DTSTART"/>
             <C:prop name="DTEND"/>
             <C:prop name="DURATION"/>
             <C:prop name="RRULE"/>
             <C:prop name="RDATE"/>
             <C:prop name="EXRULE"/>
             <C:prop name="EXDATE"/>
             <C:prop name="RECURRENCE-ID"/>
           </C:comp>
           <C:comp name="VTIMEZONE"/>
         </C:comp>
       </C:calendar-data>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:time-range start="20060104T000000Z"
                         end="20060105T000000Z"/>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2005 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx



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   <?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/work/abcd2.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd2"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   DTSTART;TZID=US/Eastern:20060102T120000
   DURATION:PT1H
   RRULE:FREQ=DAILY;COUNT=5
   SUMMARY:Event #2
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   BEGIN:VEVENT
   DTSTART;TZID=US/Eastern:20060104T140000
   DURATION:PT1H
   RECURRENCE-ID;TZID=US/Eastern:20060104T120000
   SUMMARY:Event #2 bis
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   BEGIN:VEVENT
   DTSTART;TZID=US/Eastern:20060106T140000
   DURATION:PT1H
   RECURRENCE-ID;TZID=US/Eastern:20060106T120000
   SUMMARY:Event #2 bis bis
   UID:00959BC664CA650E933C892C@example.com



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   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd3.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd3"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   DTSTART;TZID=US/Eastern:20060104T100000
   DURATION:PT1H
   SUMMARY:Event #3
   UID:DC6C50A017428C5216A2F1CD@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>





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7.7.2.  Example: Partial retrieval of recurring events

   In this example, the client requests the server to return VEVENT
   components that overlap the time range from January 3rd, 2006 at 00:
   00:00 AM UTC to January 5th, 2006 at 00:00:00 AM UTC.  Use of the
   CALDAV:limit-recurrence-set element causes the server to only return
   overridden recurrence components that overlap the time range
   specified in that element, or that affect other instances that
   overlap the time range (e.g., in the case of a "THISANDFUTURE"
   behavior).  In this example the first overridden component in the
   matching resource is returned but the second one is not.

   See Appendix B for the calendar data being targeted by this example.

   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:D="DAV:"
                     xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop>
       <C:calendar-data>
         <C:limit-recurrence-set start="20060103T000000Z"
                                 end="20060105T000000Z"/>
       </C:calendar-data>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:time-range start="20060103T000000Z"
                         end="20060105T000000Z"/>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx




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   <?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/work/abcd2.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd2"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   DTSTAMP:20060206T001121Z
   DTSTART;TZID=US/Eastern:20060102T120000
   DURATION:PT1H
   RRULE:FREQ=DAILY;COUNT=5
   SUMMARY:Event #2
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   BEGIN:VEVENT
   DTSTAMP:20060206T001121Z
   DTSTART;TZID=US/Eastern:20060104T140000
   DURATION:PT1H
   RECURRENCE-ID;TZID=US/Eastern:20060104T120000
   SUMMARY:Event #2 bis
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>



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         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd3.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd3"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   ATTENDEE;PARTSTAT=ACCEPTED;ROLE=CHAIR:mailto:cyrus@example.com
   ATTENDEE;PARTSTAT=NEEDS-ACTION:mailto:lisa@example.com
   DTSTAMP:20060206T001220Z
   DTSTART;TZID=US/Eastern:20060104T100000
   DURATION:PT1H
   LAST-MODIFIED:20060206T001330Z
   ORGANIZER:mailto:cyrus@example.com
   SEQUENCE:1
   STATUS:TENTATIVE
   SUMMARY:Event #3
   UID:DC6C50A017428C5216A2F1CD@example.com
   X-ABC-GUID:E1CX5Dr-0007ym-Hz@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>



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     </D:response>
   </D:multistatus>

7.7.3.  Example: Expanded retrieval of recurring events

   In this example, the client requests the server to return VEVENT
   components that overlap the time range from January 2nd, 2006 at 00:
   00:00 AM UTC to January 5th, 2006 at 00:00:00 AM UTC and to return
   recurring calendar components expanded into individual recurrence
   instance calendar components.  Use of the CALDAV:expand element
   causes the server to only return overridden recurrence instances that
   overlap the time range specified in that element.

   See Appendix B for the calendar data being targeted by this example.

   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:D="DAV:"
                     xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop>
       <C:calendar-data>
         <C:expand start="20060103T000000Z"
                   end="20060105T000000Z"/>
       </C:calendar-data>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:time-range start="20060103T000000Z"
                         end="20060105T000000Z"/>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx



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   <?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/work/abcd2.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd2"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   DTSTAMP:20060206T001121Z
   DTSTART:20060103T170000
   DURATION:PT1H
   RECURRENCE-ID:20060103T170000
   SUMMARY:Event #2
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   BEGIN:VEVENT
   DTSTAMP:20060206T001121Z
   DTSTART:20060104T190000
   DURATION:PT1H
   RECURRENCE-ID:20060104T170000
   SUMMARY:Event #2 bis
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd3.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd3"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   ATTENDEE;PARTSTAT=ACCEPTED;ROLE=CHAIR:mailto:cyrus@example.com
   ATTENDEE;PARTSTAT=NEEDS-ACTION:mailto:lisa@example.com
   DTSTAMP:20060206T001220Z
   DTSTART:20060104T150000
   DURATION:PT1H
   LAST-MODIFIED:20060206T001330Z



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   ORGANIZER:mailto:cyrus@example.com
   SEQUENCE:1
   STATUS:TENTATIVE
   SUMMARY:Event #3
   UID:DC6C50A017428C5216A2F1CD@example.com
   X-ABC-GUID:E1CX5Dr-0007ym-Hz@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

7.7.4.  Example: Partial retrieval of stored free busy components

   In this example, the client requests the server to return the
   VFREEBUSY components that have free busy information that overlap the
   time range from January 2nd, 2006 at 00:00:00 AM UTC (inclusively) to
   January 3rd, 2006 at 00:00:00 AM UTC (exclusively).  Use of the
   CALDAV:limit-freebusy-set element causes the server to only return
   the FREEBUSY property values that overlap the time range specified in
   that element.  Note that this is not an example of discovering when
   the calendar owner is busy.

   See Appendix B for the calendar data being targeted by this example.
























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   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:D="DAV:"
                 xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop>
       <C:calendar-data>
         <C:limit-freebusy-set start="20060102T000000Z"
                                 end="20060103T000000Z"/>
       </C:calendar-data>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VFREEBUSY">
           <C:time-range start="20060102T000000Z"
                           end="20060103T000000Z"/>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

























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   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/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/work/abcd8.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd8"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VFREEBUSY
   ORGANIZER;CN="Bernard Desruisseaux":mailto:bernard@example.com
   UID:76ef34-54a3d2@example.com
   DTSTAMP:20050530T123421Z
   DTSTART:20060101T100000Z
   DTEND:20060108T100000Z
   FREEBUSY;FBTYPE=BUSY-TENTATIVE:20060102T100000Z/20060102T120000Z
   END:VFREEBUSY
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

7.7.5.  Example: Retrieval of to-dos 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.

   See Appendix B for the calendar data being targeted by this example.










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   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
       <C:calendar-data/>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VTODO">
           <C:comp-filter name="VALARM">
             <C:time-range start="20060106T100000Z"
                             end="20060107T100000Z"/>
           </C:comp-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>


























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   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/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/work/abcd4.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd4"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTODO
   DTSTAMP:20060205T235300Z
   DUE;TZID=US/Eastern:20060106T120000
   LAST-MODIFIED:20060205T235308Z
   SEQUENCE:1
   STATUS:NEEDS-ACTION
   SUMMARY:Task #2
   UID:E10BA47467C5C69BB74E8720@example.com
   BEGIN:VALARM
   ACTION:AUDIO
   TRIGGER;RELATED=START:-PT10M
   END:VALARM
   END:VTODO
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

7.7.6.  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
   "DC6C50A017428C5216A2F1CD@example.com".

   See Appendix B for the calendar data being targeted by this example.





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   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
       <C:calendar-data/>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:prop-filter name="UID">
             <C:text-match caseless="no">
              DC6C50A017428C5216A2F1CD@example.com</C:text-match>
           </C:prop-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/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/work/abcd3.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd3"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT



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   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   ATTENDEE;PARTSTAT=ACCEPTED;ROLE=CHAIR:mailto:cyrus@example.com
   ATTENDEE;PARTSTAT=NEEDS-ACTION:mailto:lisa@example.com
   DTSTAMP:20060206T001220Z
   DTSTART;TZID=US/Eastern:20060104T100000
   DURATION:PT1H
   LAST-MODIFIED:20060206T001330Z
   ORGANIZER:mailto:cyrus@example.com
   SEQUENCE:1
   STATUS:TENTATIVE
   SUMMARY:Event #3
   UID:DC6C50A017428C5216A2F1CD@example.com
   X-ABC-GUID:E1CX5Dr-0007ym-Hz@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

7.7.7.  Example: Retrieval of events by PARTSTAT

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

   See Appendix B for the calendar data being targeted by this example.







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   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
       <C:calendar-data/>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:prop-filter name="ATTENDEE">
             <C:text-match
               caseless="yes">mailto:lisa@example.com</C:text-match>
             <C:param-filter name="PARTSTAT">
               <C:text-match caseless="yes">NEEDS-ACTION</C:text-match>
             </C:param-filter>
           </C:prop-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/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/work/abcd3.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd3"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE



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   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   ATTENDEE;PARTSTAT=ACCEPTED;ROLE=CHAIR:mailto:cyrus@example.com
   ATTENDEE;PARTSTAT=NEEDS-ACTION:mailto:lisa@example.com
   DTSTAMP:20060206T001220Z
   DTSTART;TZID=US/Eastern:20060104T100000
   DURATION:PT1H
   LAST-MODIFIED:20060206T001330Z
   ORGANIZER:mailto:cyrus@example.com
   SEQUENCE:1
   STATUS:TENTATIVE
   SUMMARY:Event #3
   UID:DC6C50A017428C5216A2F1CD@example.com
   X-ABC-GUID:E1CX5Dr-0007ym-Hz@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

7.7.8.  Example: Retrieval of events only

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

   See Appendix B for the calendar data being targeted by this example.






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   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
       <C:calendar-data/>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT"/>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/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/work/abcd1.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd1"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400



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   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   DTSTAMP:20060206T001102Z
   DTSTART;TZID=US/Eastern:20060102T100000
   DURATION:PT1H
   SUMMARY:Event #1
   Description:Go Steelers!
   UID:74855313FA803DA593CD579A@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd2.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd2"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD



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   END:VTIMEZONE
   BEGIN:VEVENT
   DTSTAMP:20060206T001121Z
   DTSTART;TZID=US/Eastern:20060102T120000
   DURATION:PT1H
   RRULE:FREQ=DAILY;COUNT=5
   SUMMARY:Event #2
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   BEGIN:VEVENT
   DTSTAMP:20060206T001121Z
   DTSTART;TZID=US/Eastern:20060104T140000
   DURATION:PT1H
   RECURRENCE-ID;TZID=US/Eastern:20060104T120000
   SUMMARY:Event #2 bis
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   BEGIN:VEVENT
   DTSTAMP:20060206T001121Z
   DTSTART;TZID=US/Eastern:20060106T140000
   DURATION:PT1H
   RECURRENCE-ID;TZID=US/Eastern:20060106T120000
   SUMMARY:Event #2 bis bis
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd3.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd3"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400



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   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   ATTENDEE;PARTSTAT=ACCEPTED;ROLE=CHAIR:mailto:cyrus@example.com
   ATTENDEE;PARTSTAT=NEEDS-ACTION:mailto:lisa@example.com
   DTSTAMP:20060206T001220Z
   DTSTART;TZID=US/Eastern:20060104T100000
   DURATION:PT1H
   LAST-MODIFIED:20060206T001330Z
   ORGANIZER:mailto:cyrus@example.com
   SEQUENCE:1
   STATUS:TENTATIVE
   SUMMARY:Event #3
   UID:DC6C50A017428C5216A2F1CD@example.com
   X-ABC-GUID:E1CX5Dr-0007ym-Hz@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

7.7.9.  Example: Retrieval of all pending to-dos

   In this example, the client requests the server to return all VTODO
   components that do not include a "COMPLETED" property and do not have
   a "STATUS" property value matching "CANCELLED". i.e., VTODOs that
   still need to be worked on.

   See Appendix B for the calendar data being targeted by this example.












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   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
       <C:calendar-data/>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VTODO">
           <C:prop-filter name="COMPLETED">
             <C:is-not-defined/>
           </C:prop-filter>
           <C:prop-filter name="STATUS">
             <C:text-match
                negate-condition="yes">CANCELLED</c:text-match>
           </C:prop-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/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/work/abcd4.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd4"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTODO



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   DTSTAMP:20060205T235335Z
   DUE;VALUE=DATE:20060104
   STATUS:NEEDS-ACTION
   SUMMARY:Task #1
   UID:DDDEEB7915FA61233B861457@example.com
   BEGIN:VALARM
   ACTION:AUDIO
   TRIGGER;RELATED=START:-PT10M
   END:VALARM
   END:VTODO
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>

     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd5.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd5"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTODO
   DTSTAMP:20060205T235300Z
   DUE;VALUE=DATE:20060106
   LAST-MODIFIED:20060205T235308Z
   SEQUENCE:1
   STATUS:NEEDS-ACTION
   SUMMARY:Task #2
   UID:E10BA47467C5C69BB74E8720@example.com
   BEGIN:VALARM
   ACTION:AUDIO
   TRIGGER;RELATED=START:-PT10M
   END:VALARM
   END:VTODO
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>






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7.7.10.  Example: Attempt to query unsupported property

   In this example, the client requests the server to return all VEVENT
   components that include an "X-ABC-GUID" property with a value
   matching "ABC".  However, the server does not support querying that
   non-standard property and instead returns and error response.

   See Appendix B for the calendar data being targeted by this example.

   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop xmlns:D="DAV:">
       <D:getetag/>
       <C:calendar-data/>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:prop-filter name="X-ABC-GUID">
             <C:text-match>ABC</C:text-match>
           </C:prop-filter>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

   >> Response <<

   HTTP/1.1 403 Forbidden
   Date: Fri, 11 Nov 2005 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:error>
     <C:supported-filter>
       <C:prop-filter name="X-ABC-GUID"/>
     </C:supported-filter>
   </D:error>




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7.8.  CALDAV:calendar-multiget Report

   The CALDAV:calendar-multiget REPORT is used to retrieve specific
   calendar object resources from within a collection, if the Request-
   URI is a collection, or to retrieve a specific calendar object
   resource, if the Request-URI is a calendar object resource.  This
   REPORT is similar to the CALDAV:calendar-query REPORT (see
   Section 7.7), except that it takes a list of DAV:href elements
   instead of a CALDAV:filter element to determine which calendar object
   resources to return.

   Support for the calendar-multiget REPORT is REQUIRED.

   Marshalling:

      The request body MUST be a CALDAV:calendar-multiget XML element
      (see Section 9.9).  If the Request-URI is a collection resource,
      then the DAV:href elements MUST refer to calendar object resources
      within that collection, and they MAY refer to calendar object
      resources at any depth within the collection.  As a result the
      "Depth" header MUST be ignored by the server and SHOULD NOT be
      sent by the client.  If the Request-URI refers to a non-collection
      resource, then there MUST be a single DAV:href element that is
      equivalent to the Request-URI.

      The response body for a successful request MUST be a DAV:
      multistatus XML element.

      The response body for a successful CALDAV:calendar-multiget REPORT
      request MUST contain a DAV:response element for each calendar
      object resource referenced by the provided set of DAV:href
      elements.  Calendar data is being returned in the CALDAV:calendar-
      data element inside the DAV:prop element.

      In the case of an error accessing any of the provided DAV:href
      resources, the server MUST return the appropriate error status
      code in the DAV:status element of the corresponding DAV:response
      element.

   Preconditions:

      (CALDAV:supported-calendar-data): The attributes "content-type"
      and "version" of the CALDAV:calendar-data XML elements (see
      Section 9.5) specify a media type supported by the server for
      calendar object resources.

      (CALDAV:min-date-time): Any XML element specifying a range of time
      MUST have its start or end date or time values greater than or



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      equal to the value of the CALDAV:min-date-time property value
      (Section 5.2.6) on the calendar collections being targeted by the
      REPORT;

      (CALDAV:max-date-time): Any XML element specifying a range of time
      MUST have its start or end date or time values less than or equal
      to the value of the CALDAV:max-date-time property value
      (Section 5.2.7) on the calendar collections being targeted by the
      REPORT;

   Postconditions:

      None.

7.8.1.  Example: Successful CALDAV:calendar-multiget Report

   In this example, the client requests the server to return specific
   properties of the VEVENT components referenced by specific URIs.  In
   addition the DAV:getetag property is also requested and returned as
   part of the response.  Note that in this example, the resource at
   http://cal.example.com/bernard/work/mtg1.ics does not exist,
   resulting in an error status response.

   See Appendix B for the calendar data being targeted by this example.

   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-multiget xmlns:D="DAV:"
                    xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop>
       <D:getetag/>
       <C:calendar-data/>
     </D:prop>
     <D:href>/bernard/work/abcd1.ics</D:href>
     <D:href>/bernard/work/mtg1.ics</D:href>
   </C:calendar-multiget>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"



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   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/work/abcd1.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd1"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   DTSTAMP:20060206T001102Z
   DTSTART;TZID=US/Eastern:20060102T100000
   DURATION:PT1H
   SUMMARY:Event #1
   Description:Go Steelers!
   UID:74855313FA803DA593CD579A@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>http://cal.example.com/bernard/work/mtg1.ics</D:href>
       <D:status>HTTP/1.1 404 Not Found</D:status>



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     </D:response>
   </D:multistatus>

7.9.  CALDAV:free-busy-query Report

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

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

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

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

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

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




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   Marshalling:

      The request body MUST be a CALDAV:free-busy-query XML element (see
      Section 9.10, which MUST contain exactly one CALDAV:time-range XML
      element, as defined in Section 9.8.

      The request MAY include a Depth header.  If no Depth header is
      included, Depth:0 is assumed.

      The response body for a successful request MUST be an iCalendar
      object that contains exactly one VFREEBUSY component that
      describes the busy time intervals for the calendar object
      resources containing VEVENT or VFREEBUSY components that satisfy
      the Depth value and for which the current user is at least granted
      the CALDAV:read-free-busy privilege.  If no calendar object
      resources are found to satisfy these conditions a VFREEBUSY
      component with no FREEBUSY property MUST be returned.  This REPORT
      only returns busy time information.  Free time information can be
      inferred from the returned busy time information.

      If the current user is not granted the CALDAV:read-free-busy or
      DAV:read privileges on the Request-URI, the CALDAV:free-busy-query
      REPORT request MUST fail and return a 404 (Not Found) status
      value.  This restriction will prevent users from discovering URLs
      of resources for which they are only granted the CALDAV:read-free-
      busy privilege.

      The CALDAV:free-busy-query REPORT request can only be run against
      a collection (either a regular collection or a calendar
      collection).  An attempt to run the report on a calendar object
      resource MUST fail and return a 403 (Forbidden) status value.

   Preconditions:

      None.

   Postconditions:

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







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7.9.1.  Example: Successful CALDAV:free-busy-query Report

   In this example, the client requests the server to return free busy
   information on the calendar collection /bernard/work/, between 9:00
   AM and 5:00 PM EST (2:00 PM and 10:00 PM UTC) on the 4th January
   2006.  The server responds indicating two busy time intervals of one
   hour, one of which is tentative.

   See Appendix B for the calendar data being targeted by this example.

   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:free-busy-query xmlns:C="urn:ietf:params:xml:ns:caldav">
     <C:time-range start="20060104T140000Z"
                     end="20060105T220000Z"/>
   </C:free-busy-query>

   >> Response <<

   HTTP/1.1 200 OK
   Date: Fri, 11 Nov 2006 09:32:12 GMT
   Content-Type: text/calendar
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Server//EN
   BEGIN:VFREEBUSY
   DTSTAMP:20050125T090000Z
   DTSTART:20060104T140000Z
   DTEND:20060105T220000Z
   FREEBUSY;FBTYPE=BUSY-TENTATIVE:20060104T150000Z/PT1H
   FREEBUSY:20060104T190000Z/PT1H
   END:VFREEBUSY
   END:VCALENDAR


8.  Guidelines






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8.1.  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 time zone
   to another time zone.  Although this advice amounts to iCalendar
   interoperability best practices and is not limited only to CalDAV
   usage, interoperability problems are likely to be more evident in
   CalDAV use cases.

8.2.  Synchronization 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.  ETags are the key to
   making this work, but these are not required of all WebDAV servers.
   Since offline functionality is more important to calendar
   applications than to some other WebDAV applications, CalDAV servers
   MUST support ETags as specified in Section 5.3.4.

8.2.1.  Use of Reports

8.2.1.1.  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 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 components from the server using CALDAV:calendar-
   query REPORT combined with a CALDAV:time-range element to limit the
   set of returned components to just those needed to populate the
   current view.

8.2.1.2.  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
   synchronization process by only considering data for the present time



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   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.

8.2.1.3.  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 calendar object resource's URI and ETag along with the
   actual calendar data.  While the URI remains static for the lifetime
   of the calendar object resource, the ETag will change with each
   successive change to the calendar object resource.  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 refreshed.

   In order to properly detect the changes between the server and client
   data, the client will need to keep a record of which calendar object
   resources have been created, changed or deleted since the last
   synchronization operation so that it can reconcile those changes with
   the data on the server.

   Here's an example of how to do that:

   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/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:D="DAV:"
                     xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop>
       <D:getetag/>
     </D:prop>
     <C:filter>
       <C:comp-filter name="VCALENDAR">
         <C:comp-filter name="VEVENT">
           <C:time-range start="20040902T000000Z"
                           end="20040903T000000Z"/>
         </C:comp-filter>
       </C:comp-filter>
     </C:filter>
   </C:calendar-query>

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

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-multiget xmlns:D="DAV:"
                        xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:prop>
       <D:getetag/>
       <C:calendar-data/>
     </D:prop>
     <D:href>/bernard/work/abcd1.ics</D:href>
     <D:href>/bernard/work/mtg1.ics</D:href>
   </C:calendar-multiget>






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8.2.2.  Restrict the Properties Returned

   Clients may not need all the calendar properties of a calendar object
   resource when presenting information to the user.  Since some
   calendar property values can be large (e.g., ATTACH or ATTENDEE)
   clients can choose to restrict the calendar properties to be returned
   in a calendaring REPORT request to those it knows it will use.

   However, if a client needs to make a change to a calendar object
   resource, it can only change the entire calendar object resource via
   a PUT request.  There is currently no way to incrementally make a
   change to a set of calendar properties of a calendar object resource.
   As a result the client will have to get the entire calendar object
   resource that is being changed.

8.3.  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) or wasting time making
   changes that will conflict with another set of changes.  In a multi-
   user calendar system, an interactive calendar client could lock an
   event while the user is editing the event, and unlock the event when
   the user finishes or cancels.  Locks can also be used to prevent
   changes while data is being reorganized.  For example, a calendar
   client might lock two calendar collections prior to moving a bunch of
   calendar resources from one to another.

   Clients are responsible for requesting a lock timeout period that is
   appropriate to the use case.  When the user explicitly decides to
   reserve a resource and prevent other changes, a long timeout might be
   appropriate, but in cases 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.

8.4.  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 copy 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 collection.  The client may
   also be able to browse WebDAV collections to find calendar
   collections.




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

   For calendar sharing and scheduling use cases, one might wish to find
   the calendar belonging to another user.  If the other user has a
   calendar in the same repository, that calendar can be found by using
   the principal namespace required by WebDAV ACL support.  For other
   cases, the authors have no universal solution but implementers can
   consider whether to use vCard [RFC2426] or LDAP [RFC2251] standards
   together with calendar attributes [RFC2739].

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

   In this case, a DAV:principal-match REPORT is used to find a named
   property (the CALDAV:calendar-home-set) on the Principal-URL of the
   current user.  Using this, a WebDAV client can learn "who am I" and
   "where are my calendars".  The REPORT request body looks like this:

   <?xml version="1.0" encoding="utf-8" ?>
   <D:principal-match xmlns:D="DAV:">
     <D:self/>
     <D:prop>
       <C:calendar-home-set
          xmlns:C="urn:ietf:params:xml:ns:caldav"/>
     </D:prop>
   </D:principal-match>

   To find other users calendars, the DAV:principal-property-search
   REPORT can be used to filter on some properties and return others.
   To search for a calendar owned by a user named "Laurie", the REPORT
   request body would look like this:











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   <?xml version="1.0" encoding="utf-8" ?>
   <D:principal-property-search xmlns:D="DAV:">
     <D:property-search>
       <D:prop>
         <D:displayname/>
       </D:prop>
       <D:match>Laurie</D:match>
     </D:property-search>
     <D:prop>
       <C:calendar-home-set
          xmlns:C="urn:ietf:params:xml:ns:caldav"/>
       <D:displayname/>
     </D:prop>
   </D:principal-property-search>

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

8.5.  Storing and Using Attachments

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

8.5.1.  Inline attachments

   CalDAV clients MUST support inline attachments as specified in
   iCalendar [RFC2445].  CalDAV servers MUST support inline attachments,
   so clients can rely on being able to create attachments this way.  On
   the other hand, inline attachments have some drawbacks:

   o  Servers MAY impose limitations on the size of calendar object
      resources (i.e., refusing PUT requests of very large iCalendar
      objects).  Servers that do that MUST use the CALDAV:max-resource-
      size property on a calendar collection to inform the client as to
      what the limitation is (see Section 5.2.5.

   o  Servers MAY impose storage quota limitations on calendar
      collections (See [RFC4331]).

   o  Any change to a calendar object resource containing an attachment
      requires the entire attachment to be re-uploaded.

   o  Clients synchronizing a changed calendar object resource have to
      download the entire calendar object resource even if the



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      attachment is unchanged.

8.5.2.  External attachments

   CalDAV clients MUST support external attachments: if the client
   accesses any calendar object resource it MUST be capable of also
   accessing the external attachment if one exists.  An external
   attachment could be:

   o  In a collection in the calendar collection containing the calendar
      object resource;

   o  Somewhere else in the same repository that hosts the calendar
      collection; or

   o  On an HTTP or FTP server elsewhere.

   CalDAV servers MAY provide support for child collections in calendar
   collections.  CalDAV servers MAY allow the MKCOL method to create
   child collections in calendar collections.  Child collections of
   calendar collections MAY contain any type of resource except calendar
   collections which they MUST NOT contain.  Some CalDAV servers won't
   allow child collections in calendar collections, and it may be
   possible on such a server to discover other locations where
   attachments can be stored.

   Clients are entirely responsible for maintaining reference
   consistency with calendar components that link to external
   attachments.  A client deleting a calendar component with an external
   attachment might therefore also delete the attachment if that's
   appropriate, however appropriateness can be very hard to determine.
   A new component might easily reference some pre-existing Web resource
   which is intended to have independent existence from the calendar
   component (the "attachment" could be a major proposal to be discussed
   in a meeting, for instance).  Best practices will probably emerge and
   should probably be documented but for now clients should be wary of
   engaging in aggressive "cleanup" of external attachments.  A client
   could involve the user in making decisions about removing
   unreferenced documents, or a client could be conservative in only
   deleting attachments it had created.

   Also, clients are responsible for consistency of permissions when
   using external attachments.  One reason for servers to support the
   storage of attachments within child collections of calendar
   collections is that ACL inheritance might make it easier to grant the
   same permissions to attachments that are granted on the calendar
   collection.  Otherwise, it can be very difficult to keep permissions
   synchronized.  With attachments stored on separate repositories, it



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   can be impossible to keep permissions consistent -- the two
   repositories may not support the same permissions or have the same
   set of principals.  Some systems have used tickets or other anonymous
   access control mechanisms to provide partially satisfactory solutions
   to these kinds of problems.

8.6.  Storing and Using Alarms

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

      When the action is "AUDIO", and the client is configured to
      execute the alarm, the client SHOULD play the suggested sound if
      it's available or play another sound, but SHOULD NOT rewrite the
      alarm just to replace the suggested sound with a sound that's
      locally available.

      When the action is "DISPLAY", and the client is configured to
      execute the alarm, the client SHOULD execute a display alarm by
      displaying either according to the suggested description or some
      reasonable replacement, but SHOULD NOT rewrite the alarm for its
      own convenience.

      When the action is "EMAIL", and the client is incapable of sending
      email, it SHOULD ignore the alarm but MUST continue to synchronize
      the alarm itself.

      This specification makes no recommendations about executing alarm
      of type PROCEDURE except to note that clients are advised to take
      care to avoid creating security holes by executing these.

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

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




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


9.  XML Element Definitions

9.1.  CALDAV:calendar XML Element

   Name: calendar

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

   Purpose: Specifies the resource type of a calendar collection.

   Description: See Section 4.2.

   Definition:

         <!ELEMENT calendar EMPTY>

9.2.  CALDAV:mkcalendar XML Element

   Name: mkcalendar

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

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

   Description: See Section 5.3.1.

   Definition:

         <!ELEMENT mkcalendar (DAV:set)>

9.3.  CALDAV:mkcalendar-response XML Element

   Name: mkcalendar-response

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






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   Purpose: Specifies a response body for a successful MKCALENDAR
      request.

   Description: See Section 5.3.1.

   Definition:

         <!ELEMENT mkcalendar-response ANY>

9.4.  CALDAV:calendar-query XML Element

   Name: calendar-query

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

   Purpose: Defines a REPORT for querying calendar object resources.

   Description: See Section 7.7.

   Definition:

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

9.5.  CALDAV:calendar-data XML Element

   Name: calendar-data

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

   Purpose: Used to (1) specify a supported media type for calendar
      object resources when nested in the CALDAV:supported-calendar-data
      property; (2) specify which parts of a calendar object resource
      should be returned by a given calendaring REPORT; and (3) specify
      the content of a calendar object resource in a response to a
      calendaring REPORT.

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

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




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

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

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

   Definition:

         <!ELEMENT calendar-data ((comp?, (expand |
                                           limit-recurrence-set)?,
                                           limit-freebusy-set?) |
                                  #PCDATA)?>
         PCDATA value: iCalendar object

         <!ATTLIST calendar-data content-type CDATA "text/calendar">
                                 version CDATA "2.0">
         content-type value: a MIME media type
         version value: a version string

9.5.1.  CALDAV:comp XML Element

   Name: comp

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






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   Purpose: Defines which component types to return.

   Description: The name value is a calendar component name (e.g.,
      "VEVENT").

   Definition:

         <!ELEMENT comp ((allprop | prop*), (allcomp | comp*))>

         <!ATTLIST comp name CDATA #REQUIRED>
         name value: a calendar component name

   Note: The CALDAV:prop and CALDAV:allprop elements have the same name
      as the DAV:prop and DAV:allprop elements defined in [I-D.ietf-
      webdav-rfc2518bis].  However, the CALDAV:prop and CALDAV:allprop
      element are defined in the "urn:ietf:params:xml:ns:caldav"
      namespace instead of the "DAV:" namespace.

9.5.2.  CALDAV:allcomp XML Element

   Name: allcomp

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

   Purpose: Specifies that all components shall be returned.

   Description: The CALDAV:allcomp XML element can be used when the
      client wants all types of components returned by a calendaring
      REPORT request.

   Definition:

         <!ELEMENT allcomp EMPTY>

9.5.3.  CALDAV:allprop XML Element

   Name: allprop

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

   Purpose: Specifies that all properties shall be returned.

   Description: The CALDAV:allprop XML element can be used when the
      client wants all properties of components returned by a
      calendaring REPORT request.






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   Definition:

         <!ELEMENT allprop EMPTY>

   Note: The CALDAV:allprop element has the same name as the DAV:allprop
      element defined in [I-D.ietf-webdav-rfc2518bis].  However, the
      CALDAV:allprop element is defined in the
      "urn:ietf:params:xml:ns:caldav" namespace instead of the "DAV:"
      namespace.

9.5.4.  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 calendar
      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.

   Definition:

         <!ELEMENT prop EMPTY>

         <!ATTLIST prop name CDATA #REQUIRED
                     novalue (yes | no) "no">
         name value: a calendar property name
         novalue value: "yes" or "no"

   Note: The CALDAV:prop element has the same name as the DAV:prop
      element defined in [I-D.ietf-webdav-rfc2518bis].  However, the
      CALDAV:prop element is defined in the
      "urn:ietf:params:xml:ns:caldav" namespace instead of the "DAV:"
      namespace.

9.5.5.  CALDAV:expand XML Element

   Name: expand







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

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

   Description: The CALDAV:expand XML element specifies that for a given
      calendaring REPORT request the server MUST expand the recurrence
      set into calendar components that define exactly one recurrence
      instance and MUST return only those whose scheduled time intersect
      a specified time range.  The "start" attribute specifies the
      inclusive start of the time range, and the "end" attribute
      specifies the non-inclusive end of the time range.  Both
      attributes are specified as date with UTC time value.  The value
      of the "end" attribute MUST be greater than the value of the
      "start" attribute.  The server MUST use the same logic as defined
      for CALDAV:time-range to determine if a recurrence instance
      intersects the specified time range.  Recurring components, other
      than the initial instance, MUST include a RECURRENCE-ID property
      indicating which instance they refer to.  The returned calendar
      components MUST NOT use recurrence properties (i.e., EXDATE,
      EXRULE, RDATE and RRULE) and MUST NOT have reference to or include
      VTIMEZONE components.  Date and local time with reference to time
      zone information MUST be converted into date with UTC time.

   Definition:

         <!ELEMENT expand EMPTY>

         <!ATTLIST expand start CDATA #REQUIRED
                         end   CDATA #REQUIRED>
         start value: an iCalendar "date with UTC time"
         end value: an iCalendar "date with UTC time"

9.5.6.  CALDAV:limit-recurrence-set XML Element

   Name: limit-recurrence-set

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

   Purpose: Specifies a time range to limit the set of "overridden
      components" returned by the server.

   Description: The CALDAV:limit-recurrence-set XML element specifies
      that for a given calendaring REPORT request the server MUST
      return, in addition to the "master component", only the
      "overridden components" that impact a specified time range.  An
      overridden component impacts a time range if its current start and
      end times overlap the time range, or if the original start and end



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      times - the ones that would have been used if the instance were
      not overridden - overlap the time range.  The "start" attribute
      specifies the inclusive start of the time range, and the "end"
      attribute specifies the non-inclusive end of the time range.  Both
      attributes are specified as date with UTC time value.  The value
      of the "end" attribute MUST be greater than the value of the
      "start" attribute.  The server MUST use the same logic as defined
      for CALDAV:time-range to determine if the current or original
      scheduled time of an "overridden" recurrence instance intersect
      the specified time range.  Overridden components that have a RANGE
      parameter on their RECURRENCE-ID property may specify one or more
      instances in the recurrence set, and some of those instances may
      fall within the specified time range, or may have originally
      fallen within the specified time range prior to being overridden.
      If that is the case, the overridden component MUST be included in
      the results as it has a direct impact on the interpretation of
      instances within the specified time range.

   Definition:

         <!ELEMENT limit-recurrence-set EMPTY>

         <!ATTLIST limit-recurrence-set start CDATA #REQUIRED
                                       end   CDATA #REQUIRED>
         start value: an iCalendar "date with UTC time"
         end value: an iCalendar "date with UTC time"

9.5.7.  CALDAV:limit-freebusy-set XML Element

   Name: limit-freebusy-set

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

   Purpose: Specifies a time range to limit the set of FREEBUSY values
      returned by the server.

   Description: The CALDAV:limit-freebusy-set XML element specifies that
      for a given calendaring REPORT request the server MUST only return
      the FREEBUSY property values of a VFREEBUSY component that
      intersect a specified time range.  The "start" attribute specifies
      the inclusive start of the time range, and the "end" attribute
      specifies the non-inclusive end of the time range.  Both
      attributes are specified as "date with UTC time" value.  The value
      of the "end" attribute MUST be greater than the value of the
      "start" attribute.  The server MUST use the same logic as defined
      for CALDAV:time-range to determine if a FREEBUSY property value
      intersect the specified time range.




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   Definition:

         <!ELEMENT limit-freebusy-set EMPTY>

         <!ATTLIST limit-freebusy-set start CDATA #REQUIRED
                                     end   CDATA #REQUIRED>
         start value: an iCalendar "date with UTC time"
         end value: an iCalendar "date with UTC time"

9.6.  CALDAV:filter XML Element

   Name: filter

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

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

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

   Definition:

         <!ELEMENT filter (comp-filter)>

9.6.1.  CALDAV:comp-filter XML Element

   Name: comp-filter

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

   Purpose: Specifies search criteria on calendar components.

   Description: The CALDAV:comp-filter XML element specifies the queried
      calendar component type (e.g., "VEVENT").  A calendar object
      resource is said to match a CALDAV:comp-filter if:

      *  A component of the type specified by the "name" attribute
         exists, and the CALDAV:comp-filter is empty, or it contains at
         least one recurrence instance scheduled to overlap a given time
         range if a CALDAV:time-range XML element is specified, and that
         any CALDAV:prop-filter and CALDAV:comp-filter child elements
         also match.







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      or:

      *  A component of the type specified by the "name" attribute does
         not exist, and the CALDAV:is-not-defined element is specified.

   Definition:

         <!ELEMENT comp-filter (is-not-defined | (time-range?,
                                prop-filter*, comp-filter*))>

         <!ATTLIST comp-filter name CDATA #REQUIRED>
         name value: a calendar component name (e.g., "VEVENT")

9.6.2.  CALDAV:prop-filter XML Element

   Name: prop-filter

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

   Purpose: Specifies search criteria on calendar properties.

   Description: The CALDAV:prop-filter XML element specifies a search
      criteria on a specific calendar property (e.g., CATEGORIES) in the
      scope of a given CALDAV:comp-filter.  A calendar component is said
      to match a CALDAV:prop-filter if:

      *  A property of the type specified by the "name" attribute
         exists, and the CALDAV:prop-filter is empty, or it matches the
         CALDAV:time-range XML element or CALDAV:text-match conditions
         if specified, and that any CALDAV:param-filter child elements
         also match.

      or:

      *  A property of the type specified by the "name" attribute does
         not exist, and the CALDAV:is-not-defined element is specified.

   Definition:

         <!ELEMENT prop-filter ((is-not-defined |
                                ((time-range | text-match)?,
                                 param-filter*))>

         <!ATTLIST prop-filter name CDATA #REQUIRED>
         name value: a calendar property name (e.g., "ATTENDEE")






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9.6.3.  CALDAV:param-filter XML Element

   Name: param-filter

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

   Purpose: Limits the search to specific parameter values.

   Description: The CALDAV:param-filter XML element specifies a search
      criteria on a specific calendar property parameter (e.g.,
      PARTSTAT) in the scope of a given CALDAV:prop-filter.  A calendar
      property is said to match a CALDAV:param-filter if:

      *  A parameter of the type specified by the "name" attribute
         exists, and the CALDAV:param-filter is empty, or it matches the
         CALDAV:text-match conditions if specified.

      or:

      *  A parameter of the type specified by the "name" attribute does
         not exist, and the CALDAV:is-not-defined element is specified.

   Definition:

         <!ELEMENT param-filter (is-not-defined | text-match)?>

         <!ATTLIST param-filter name CDATA #REQUIRED>
         name value: a property parameter name (e.g., "PARTSTAT")

9.6.4.  CALDAV:is-not-defined XML Element

   Name: is-not-defined

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

   Purpose: Specifies that a match should occur if the enclosing
      component, property or parameter does not exist.

   Description: The CALDAV:is-not-defined XML element specifies that a
      match occurs if the enclosing component, property or parameter
      value specified in a calendaring REPORT request does not exist in
      the calendar data being tested.

   Definition:

         <!ELEMENT is-not-defined EMPTY>





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9.6.5.  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 CALDAV:text-match XML element specifies text used
      for a substring match against the property or parameter value
      specified in a calendaring REPORT request.

      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.  Support for the
      "caseless" attribute is REQUIRED, and implementers of servers are
      strongly encouraged to consult "The Unicode Standard" [UNICODE4],
      especially Section 5.18, Subsection "Caseless Matching", for
      guidance when implementing their case-insensitive matching
      algorithms..  A server MAY ignore the caseless attribute when
      applied to enumerated iCalendar property or parameter values, and
      default to caseless matching for those values, since they are
      defined as being case-insensitive in iCalendar.

      The "negate-condition" attribute is used to indicate that this
      test returns a match if the text matches, when the attribute value
      is set to "no", or return a match if the text does not match, if
      the attribute value is set to "yes".  For example, this can be
      used to match components with a STATUS property not set to
      CANCELLED.

   Definition:

         <!ELEMENT text-match (#PCDATA)>
         PCDATA value: string

         <!ATTLIST text-match caseless         (yes | no) #IMPLIED
                              negate-condition (yes | no) "no">

9.7.  CALDAV:timezone XML Element

   Name: timezone

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






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

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

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

   Definition:

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

9.8.  CALDAV:time-range XML Element

   Name: time-range

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

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

   Description: The CALDAV:time-range XML element specifies that for a
      given calendaring REPORT request the server MUST only return the
      calendar object resources that, depending on the context, have a
      component or property whose value intersect a specified time
      range.  The "start" attribute specifies the inclusive start of the
      time range, and the "end" attribute specifies the non-inclusive
      end of the time range.  Both attributes MUST be specified as "date
      with UTC time" value.  Time ranges open at one end can be
      specified by including only one attribute, however at least one
      attribute MUST always be present in the CALDAV:time-range element.
      If either the "start" or "end" attribute is not specified in the
      CALDAV:time-range XML element, assume "-infinity" and "+infinity"
      as their value respectively.  If both "start" and "end" are



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      present, the value of the "end" attribute MUST be greater than the
      value of the "start" attribute.

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

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

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

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



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      value MUST be a DATE-TIME value equal to or after the DTSTART
      value, if specified.

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

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





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

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

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



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








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

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

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

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

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

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

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

   Definition:

         <!ELEMENT time-range EMPTY>

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

9.9.  CALDAV:calendar-multiget XML Element

   Name: calendar-multiget

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

   Purpose: CalDAV REPORT used to retrieve specific calendar object
      resources.

   Description: See Section 7.8.







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   Definition:

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

9.10.  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 time range.

   Description: See Section 7.9.

   Definition:

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


10.  Internationalization Considerations

   CalDAV allows internationalized strings to be stored and retrieved
   for the description of calendar collections (see Section 5.2.1).


11.  Security Considerations

   HTTP protocol transactions are sent in the clear over the network
   unless protection from snooping is negotiated.  This can be
   accomplished by use of TLS as defined in [RFC2818].  In particular,
   HTTP Basic authentication MUST NOT be used unless TLS is in effect.

   Servers MUST take adequate precautions to ensure malicious clients
   cannot consume excessive server resources (CPU, memory, disk, etc.)
   through carefully crafted reports.  For example, a client could
   upload an event with a recurrence rule that specifies a recurring
   event occurring every second for the next 100 years which would
   result in approximately 3 x 10^9 instances!  A REPORT that asks for
   recurrences to be expanded over that range would likely constitute a
   denial-of-service attack on the server.

   When creating new resources (including calendar collections), clients
   MUST ensure that the resource name (the last path segment of the
   resource URI) assigned to the new resource does not expose any data
   from within the iCalendar resource itself and information about the



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   nature of a calendar collection.  This is required to ensure that the
   presence of a specific iCalendar component or nature of components in
   a collection cannot be inferred based on the name of a resource.

   Security considerations described in iCalendar [RFC2445] and iTIP
   [RFC2446] are also applicable to CalDAV.

   Beyond these, CalDAV does not raise any security considerations that
   are not present in HTTP [RFC2616] and WebDAV [I-D.ietf-webdav-
   rfc2518bis], [RFC3253], [RFC3744], as discussed in those documents.


12.  IANA Consideration

   This document uses one new URN to identify a new XML namespace.  The
   URN conforms to a registry mechanism described in [RFC3688].

12.1.  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.


13.  Acknowledgements

   The authors would like to thank the following individuals for
   contributing their ideas and support for writing this specification:
   Michael Arick, Mario Bonin, Chris Bryant, Scott Carr, Mike Douglass,
   Helge Hess, Dan Mosedale, Kervin L. Pierre, Julian F. Reschke, Mike
   Shaver, Simon Vaillancourt, Wilfredo Sanchez and Jim Whitehead,
   Alexey Melnikov, Jeff McCullough, Brian Moseley, Jari Urpalainen.

   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.


14.  References







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14.1.  Normative References

   [I-D.ietf-webdav-rfc2518bis]
              Dusseault, L., "HTTP Extensions for Distributed Authoring
              - WebDAV", draft-ietf-webdav-rfc2518bis-14 (work in
              progress), February 2006.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

   [RFC2445]  Dawson, F. and Stenerson, D., "Internet Calendaring and
              Scheduling Core Object Specification (iCalendar)",
              RFC 2445, November 1998.

   [RFC2446]  Silverberg, S., Mansour, S., Dawson, F., and R. Hopson,
              "iCalendar Transport-Independent Interoperability Protocol
              (iTIP) Scheduling Events, BusyTime, To-dos and Journal
              Entries", RFC 2446, November 1998.

   [RFC2616]  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.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3253]  Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J.
              Whitehead, "Versioning Extensions to WebDAV (Web
              Distributed Authoring and Versioning)", RFC 3253,
              March 2002.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC3744]  Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
              Distributed Authoring and Versioning (WebDAV) Access
              Control Protocol", RFC 3744, May 2004.

   [UNICODE4]
              The Unicode Consortium, "The Unicode Standard, Version
              4.0", Addison-Wesley, Boston, MA. ISBN 0-321-18578-1,
              August 2003,
              <http://www.unicode.org/versions/Unicode4.0.0/>.

   [W3C.REC-xml-20040204]
              Yergeau, F., Paoli, J., Sperberg-McQueen, C., Bray, T.,



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              and E. Maler, "Extensible Markup Language (XML) 1.0 (Third
              Edition)", W3C REC REC-xml-20040204, February 2004.

14.2.  Informative References

   [RFC2251]  Wahl, M., Howes, T., and S. Kille, "Lightweight Directory
              Access Protocol (v3)", RFC 2251, December 1997.

   [RFC2426]  Dawson, F. and T. Howes, "vCard MIME Directory Profile",
              RFC 2426, September 1998.

   [RFC2739]  Small, T., Hennessy, D., and F. Dawson, "Calendar
              Attributes for vCard and LDAP", RFC 2739, January 2000.

   [RFC4331]  Korver, B. and L. Dusseault, "Quota and Size Properties
              for Distributed Authoring and Versioning (DAV)
              Collections", RFC 4331, February 2006.


Appendix A.  CalDAV Method Privilege Table (Normative)

   The following table extends the WebDAV Method Privilege Table
   specified in Appendix B of [RFC3744].

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


Appendix B.  Calendar collections used in the examples

   This appendix shows the calendar object resources contained in the
   calendar collection queried in the examples throughout this document.

   The content of the calendar collection is being shown as it would be
   returned by a CALDAV:calendar-query REPORT request designed to return
   all the calendar data in the collection:










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   >> Request <<

   REPORT /bernard/work/ HTTP/1.1
   Host: cal.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-query xmlns:D="DAV:"
                    xmlns:C="urn:ietf:params:xml:ns:caldav">
    <D:prop>
      <D:getetag/>
      <C:calendar-data/>
    </D:prop>
    <C:filter>
      <C:comp-filter name="VCALENDAR">
        <C:allprop/>
        <C:allcomp/>
      </C:comp-filter>
    </C:filter>
   </C:calendar-query>

   >> Response <<

   HTTP/1.1 207 Multi-Status
   Content-Type: application/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/work/abcd1.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd1"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT



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   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   DTSTAMP:20060206T001102Z
   DTSTART;TZID=US/Eastern:20060102T100000
   DURATION:PT1H
   SUMMARY:Event #1
   Description:Go Steelers!
   UID:74855313FA803DA593CD579A@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>

     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd2.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd2"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
   TZNAME:EST



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   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   DTSTAMP:20060206T001121Z
   DTSTART;TZID=US/Eastern:20060102T120000
   DURATION:PT1H
   RRULE:FREQ=DAILY;COUNT=5
   SUMMARY:Event #2
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   BEGIN:VEVENT
   DTSTAMP:20060206T001121Z
   DTSTART;TZID=US/Eastern:20060104T140000
   DURATION:PT1H
   RECURRENCE-ID;TZID=US/Eastern:20060104T120000
   SUMMARY:Event #2 bis
   UID:00959BC664CA650E933C892C@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>

     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd3.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd3"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   LAST-MODIFIED:20040110T032845Z
   TZID:US/Eastern
   BEGIN:DAYLIGHT
   DTSTART:20000404T020000
   RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   BEGIN:STANDARD
   DTSTART:20001026T020000
   RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10



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   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   END:VTIMEZONE
   BEGIN:VEVENT
   ATTENDEE;PARTSTAT=ACCEPTED;ROLE=CHAIR:mailto:cyrus@example.com
   ATTENDEE;PARTSTAT=NEEDS-ACTION:mailto:lisa@example.com
   DTSTAMP:20060206T001220Z
   DTSTART;TZID=US/Eastern:20060104T100000
   DURATION:PT1H
   LAST-MODIFIED:20060206T001330Z
   ORGANIZER:mailto:cyrus@example.com
   SEQUENCE:1
   STATUS:TENTATIVE
   SUMMARY:Event #3
   UID:DC6C50A017428C5216A2F1CD@example.com
   END:VEVENT
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>

     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd4.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd4"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTODO
   DTSTAMP:20060205T235335Z
   DUE;VALUE=DATE:20060104
   STATUS:NEEDS-ACTION
   SUMMARY:Task #1
   UID:DDDEEB7915FA61233B861457@example.com
   BEGIN:VALARM
   ACTION:AUDIO
   TRIGGER;RELATED=START:-PT10M
   END:VALARM
   END:VTODO
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>



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       </D:propstat>
     </D:response>

     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd5.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd5"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTODO
   DTSTAMP:20060205T235300Z
   DUE;VALUE=DATE:20060106
   LAST-MODIFIED:20060205T235308Z
   SEQUENCE:1
   STATUS:NEEDS-ACTION
   SUMMARY:Task #2
   UID:E10BA47467C5C69BB74E8720@example.com
   BEGIN:VALARM
   ACTION:AUDIO
   TRIGGER;RELATED=START:-PT10M
   END:VALARM
   END:VTODO
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>

     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd6.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd6"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTODO
   COMPLETED:20051223T122322Z
   DTSTAMP:20060205T235400Z
   DUE;VALUE=DATE:20051225
   LAST-MODIFIED:20060205T235308Z
   SEQUENCE:1
   STATUS:COMPLETED
   SUMMARY:Task #3
   UID:E10BA47467C5C69BB74E8722@example.com



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   END:VTODO
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>

     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd7.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd7"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTODO
   DTSTAMP:20060205T235600Z
   DUE;VALUE=DATE:20060101
   LAST-MODIFIED:20060205T235308Z
   SEQUENCE:1
   STATUS:CANCELLED
   SUMMARY:Task #4
   UID:E10BA47467C5C69BB74E8725@example.com
   END:VTODO
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>

     <D:response>
       <D:href>http://cal.example.com/bernard/work/abcd8.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"fffff-abcd8"</D:getetag>
           <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VFREEBUSY
   ORGANIZER;CN="Bernard Desruisseaux":mailto:bernard@example.com
   UID:76ef34-54a3d2@example.com
   DTSTAMP:20050530T123421Z
   DTSTART:20060101T000000Z
   DTEND:20060108T000000Z
   FREEBUSY:20050531T230000Z/20050601T010000Z
   FREEBUSY;FBTYPE=BUSY-TENTATIVE:20060102T100000Z/20060102T120000Z



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   FREEBUSY:20060103T100000Z/20060103T120000Z
   FREEBUSY:20060104T100000Z/20060104T120000Z
   FREEBUSY;FBTYPE=BUSY-UNAVAILABLE:20060105T100000Z/20060105T120000Z
   FREEBUSY:20060106T100000Z/20060106T120000Z
   END:VFREEBUSY
   END:VCALENDAR
   </C:calendar-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>

   </D:multistatus>


Appendix C.  Changes (to be removed prior to publication as an RFC)

C.1.  Changes in -12

   a.  Changed requirements for ETags on PUT to better reflect the needs
       of CalDAV clients wrt synchronization and reflect what other
       standards define or do not define.

   b.  Changed CALDAV:read-free-busy privilege so that it is also
       defined on regular collections.

C.2.  Changes in -11

   a.  Added statement that calendar-query Depth defaults to zero if
       header is not present.  Fixed one multiget example's Depth
       header.

   b.  Fixed reference to WebDAV Quota RFC.

   c.  Changed DAV:resource to DAV:href in CALDAV:no-uid-conflict
       element.

   d.  Added CALDAV:calendar-collection-location-ok pre-condition for
       COPY and MOVE.

   e.  Added CALDAV:max-resource-size, CALDAV:min-date-time, CALDAV:max-
       date-time, CALDAV:max-instances, CALDAV:max-attendees-per-
       instance properties and preconditions.

   f.  Changed to 2518bis reference.

   g.  Now require 2518bis Class 3 behaviour.




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   h.  Fixed indentation in examples and removed bogus whitespace before
       </C:calendar-data> tags.

   i.  Fixed </C:calendar-data/> typo.

   j.  Added text to <C:calendar-data> element definition as a reminder
       about the need to do XML character data encoding on any iCalendar
       data within that element.

   k.  Major reworking of CALDAV:time-range element description to
       better cover all possibilities for each type of component based
       on which properties are present.

   l.  Added is-not-defined and negate-condition options to reports and
       a new example to illustrate use of those.

   m.  Fixed descriptions of some calendar collection properties.

   n.  Removed section describing preconditions/postconditions as this
       is incorporated into 2518bis.

   o.  Clarified issue about separate component types in separate
       resources.

   p.  Reworded section on servers being allowed to reject changes to
       their own private use iCal values.

   q.  Clarified overridden component 'current' and 'original' time
       range overlap.

   r.  Added more section references for XML element definitions.

   s.  Reworded limit-recurrence-set definition to try and make it clear
       that mast component is always returned, but only some overridden
       one are returned.

   t.  Clarified dependence on UNICODE reference for caseless matching.

C.3.  Changes in -10

   a.  Added new section about support for X- items when storing data.

   b.  Added new precondition to allow servers to reject queries on
       unsupported X- items, and a new example.

   c.  Added new text about always supporting X- in calendar-data.





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   d.  Created new section for PUT, COPY and MOVE preconditions.

   e.  Report examples re-done with full listing of calendar data in
       Appendix.

   f.  Removed description of using UID, SUMMARY etc as resource name.

   g.  Indicate that calendar object resource may contain only
       overridden components.

   h.  Add security consideration about not expose details in resource
       names.

   i.  Add constraint that free-busy-query can only be run on a
       collection.

   j.  Add preconditions for calendar-timezone property/elements in
       MKCALENDAR, PROPPATCH and calendar-query REPORT.

   k.  Fix principal-match example.

C.4.  Changes in -09

   a.   Numerous editorial changes.

   b.   Removed the CALDAV:is-defined XML element.

   c.   Removed section on privilege aggregation.

   d.   Renamed the CALDAV:expand-recurrence-set XML element to CALDAV:
        expand and clarified the server behavior.

   e.   Renamed the CALDAV:calendar-component-restriction-set XML
        element to CALDAV:supported-calendar-component-set.

   f.   Renamed the CALDAV:calendar-restrictions XML element to CALDAV:
        supported-calendar-data.

   g.   Renamed some preconditions as "success conditions" instead of
        "failure causes".  For instance, the precondition CALDAV:
        calendar-collection-location-bad has been renamed to CALDAV:
        calendar-collection-location-ok.

   h.   Reordered some sections.

   i.   Clarified the definition of CALDAV:time-range to specify that a
        repeating VALARM component is said to intersect a given time
        range if at least one of its trigger intersect the time range.



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   j.   Clarified that calendar object resources stored in calendar
        collections MUST NOT specify the iCalendar METHOD property.

   k.   Clarified that CALDAV:calendar-data XML element is not a WebDAV
        property even though it is specified in the DAV:prop XML element
        in both calendaring REPORT requests and responses.

   l.   Clarified CALDAV:limit-recurrence-set with respect to the RANGE
        parameter on the RECURRENCE-ID property.

   m.   Changed the CALDAV:free-busy-query XML element to contain
        exactly one CALDAV:time-range XML element.

   n.   Changed many ELEMENT and ATTLIST declarations to comply with DTD
        syntax.

   o.   Changed XML element CALDAV:calendar-query to allow new XML
        element CALDAV:timezone.

   p.   Changed the XML elements CALDAV:time-range, CALDAV:expand and
        CALDAV:limit-recurrence-set to only allow DATE-TIME with UTC
        time values for the "start" and "end" attributes.

   q.   Changed description of CALDAV:limit-recurrence-set to specify
        that re-scheduled "overridden" recurrence instances whose
        original scheduled time used to overlap the time range specified
        by the "start" and "end" attribute should always be returned in
        a REPORT response.

   r.   Changed the description of the value of CALDAV:calendar-data XML
        element to specify that the CR character (US-ASCII decimal 13)
        MAY be omitted in the iCalendar object specified in this XML
        element.

   s.   Added specific requirements for entity tags support.

   t.   Added more preconditions.

   u.   Added further guidelines about finding calendars.

   v.   Added XML element CALDAV:limit-freebusy-set to limit the set of
        FREEBUSY property values returned in VFREEBUSY components.

   w.   Added property CALDAV:calendar-timezone on calendar collections.

   x.   Added XML element CALDAV:timezone to override the CALDAV:
        calendar-timezone property for a given CALDAV:calendar-query
        REPORT request.



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   y.   Added text on the conversion of "floating date" and "floating
        time" values to date with UTC time values.

   z.   Completed internationalization considerations section.

   aa.  Completed security considerations section.

C.5.  Changes in -08

   a.  Removed statement that said that client SHOULD always request
       DAV:getetag in calendar REPORTs.

   b.  Removed redefiniton of DAV:response.

   c.  Removed XML elements CALDAV:calendar-data-only.

   d.  Removed resource type CALDAV:calendar-home.

   e.  Moved the CALDAV:calendar-data element in the DAV:prop element in
       requests, and in the DAV:propstat element in responses.

   f.  Further defined the request body of MKCALENDAR to allow clients
       to set properties at calendar collection creation time.

   g.  Renamed CALDAV:calendar-home-URL to CALDAV:calendar-home-set

   h.  Clarified the fact that calendar collections may only contain
       calendar object resources and ordinary collections.

   i.  Clarified that calendar REPORTs should only be applied to
       calendar object resources contained in calendar collections.

   j.  Changed the CALDAV:calendar-component-restriction-set and CALDAV:
       calendar-restriction properties to always be protected.

   k.  Changed to use existing postcondition DAV:needs-privileges
       instead of a new CALDAV:insufficient-privilege postcondition.

   l.  Added example for limit-recurrence-set.

   m.  Added example for expand-recurrence-set.

   n.  Moved CALDAV:calendar-address-set in the calendar-schedule draft
       and renamed it to CALDAV:calendar-user-address-set.

   o.  Added guidelines on attachments and alarms.





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C.6.  Changes in -07

   a.  Various editorial changes.

   b.  Added properties calendar-restrictions and calendar-component-
       restriction-set on calendar collections.

   c.  Added properties calendar-home-URL and calendar-address-set on
       principal resources.

   d.  Removed property calendar-URL on principal resources.

   e.  Added pre- and postconditions to reports.

   f.  Added new XML elements calendar-data-only and limit-recurrent-
       set.

   g.  Modified calendar-data XML element to support the attributes
       content-type and version.

   h.  Reorganised sections 3, 4, 5 & 6 into two sections and re-ordered
       sub-sections.

   i.  Added comment about client not setting a duplicate displayname.

   j.  Removed three CalDAV OPTIONS requests.

   k.  Changed "authenticated user" to "user" in various places.

   l.  Rewrote section on calendar object resource restrictions for
       better clarity.

C.7.  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 object 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.



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

C.8.  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.

   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.

C.9.  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.





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   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.

C.10.  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

C.11.  Changes in -02

   Basically still adding major sections of content:

   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

C.12.  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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Authors' Addresses

   Cyrus Daboo

   Email: cyrus@daboo.name


   Bernard Desruisseaux
   Oracle Corporation
   600 Blvd. de Maisonneuve West
   Suite 1900
   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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