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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 6638

Network Working Group                                           C. Daboo
Internet-Draft                                                Apple Inc.
Updates: 4791,5546 (if approved)                         B. Desruisseaux
Intended status: Standards Track                                  Oracle
Expires: October 4, 2012                                   April 2, 2012


                 CalDAV Scheduling Extensions to WebDAV
                   draft-desruisseaux-caldav-sched-12

Abstract

   This document defines extensions to the CalDAV "calendar-access"
   feature to specify a standard way of performing scheduling operations
   with iCalendar-based calendar components.  This document defines the
   "calendar-auto-schedule" feature of CalDAV.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 4, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  7
     1.2.  Notational Conventions . . . . . . . . . . . . . . . . . .  7
     1.3.  XML Namespaces and Processing  . . . . . . . . . . . . . .  8
   2.  Scheduling Support . . . . . . . . . . . . . . . . . . . . . .  9
     2.1.  Scheduling Outbox Collection . . . . . . . . . . . . . . .  9
       2.1.1.  CALDAV:schedule-outbox-URL Property  . . . . . . . . . 10
     2.2.  Scheduling Inbox Collection  . . . . . . . . . . . . . . . 10
       2.2.1.  CALDAV:schedule-inbox-URL Property . . . . . . . . . . 12
     2.3.  Calendaring Reports Extensions . . . . . . . . . . . . . . 12
     2.4.  Additional Principal Properties  . . . . . . . . . . . . . 13
       2.4.1.  CALDAV:calendar-user-address-set Property  . . . . . . 13
       2.4.2.  CALDAV:calendar-user-type Property . . . . . . . . . . 14
   3.  Scheduling Operations  . . . . . . . . . . . . . . . . . . . . 15
     3.1.  Identifying Scheduling Object Resources  . . . . . . . . . 15
     3.2.  Handling Scheduling Object Resources . . . . . . . . . . . 15
       3.2.1.  Organizer Scheduling Object Resources  . . . . . . . . 15
         3.2.1.1.  Create . . . . . . . . . . . . . . . . . . . . . . 16
         3.2.1.2.  Modify . . . . . . . . . . . . . . . . . . . . . . 17
         3.2.1.3.  Remove . . . . . . . . . . . . . . . . . . . . . . 18
       3.2.2.  Attendee Scheduling Object Resources . . . . . . . . . 18
         3.2.2.1.  Allowed Attendee Changes . . . . . . . . . . . . . 18
         3.2.2.2.  Create . . . . . . . . . . . . . . . . . . . . . . 19
         3.2.2.3.  Modify . . . . . . . . . . . . . . . . . . . . . . 20
         3.2.2.4.  Remove . . . . . . . . . . . . . . . . . . . . . . 21
       3.2.3.  HTTP Methods . . . . . . . . . . . . . . . . . . . . . 21
         3.2.3.1.  PUT  . . . . . . . . . . . . . . . . . . . . . . . 22
         3.2.3.2.  DELETE . . . . . . . . . . . . . . . . . . . . . . 22
         3.2.3.3.  COPY . . . . . . . . . . . . . . . . . . . . . . . 22
         3.2.3.4.  MOVE . . . . . . . . . . . . . . . . . . . . . . . 23
       3.2.4.  Additional Method Preconditions  . . . . . . . . . . . 24
         3.2.4.1.  CALDAV:unique-scheduling-object-resource
                   Precondition . . . . . . . . . . . . . . . . . . . 24
         3.2.4.2.  CALDAV:same-organizer-in-all-components



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                   Precondition . . . . . . . . . . . . . . . . . . . 24
         3.2.4.3.  CALDAV:allowed-organizer-scheduling-object-chan
                   Precondition . . . . . . . . . . . . . . . . . . . 25
         3.2.4.4.  CALDAV:allowed-attendee-scheduling-object-chang
                   Precondition . . . . . . . . . . . . . . . . . . . 25
       3.2.5.  DTSTAMP and SEQUENCE Properties  . . . . . . . . . . . 26
       3.2.6.  Restrict Recurrence Instances Sent to Attendees  . . . 26
       3.2.7.  Forcing the Server to Send a Scheduling Message  . . . 26
       3.2.8.  Attendee Participation Status  . . . . . . . . . . . . 27
       3.2.9.  Schedule Status Values . . . . . . . . . . . . . . . . 28
       3.2.10. Avoiding Conflicts when Updating Scheduling Object
               Resources  . . . . . . . . . . . . . . . . . . . . . . 31
         3.2.10.1. PUT  . . . . . . . . . . . . . . . . . . . . . . . 33
         3.2.10.2. DELETE, COPY or MOVE . . . . . . . . . . . . . . . 33
   4.  Processing Incoming Scheduling Messages  . . . . . . . . . . . 34
     4.1.  Processing Organizer Requests, Additions, and
           Cancellations  . . . . . . . . . . . . . . . . . . . . . . 34
     4.2.  Processing Attendee Replies  . . . . . . . . . . . . . . . 35
     4.3.  Default Calendar Collection  . . . . . . . . . . . . . . . 35
       4.3.1.  Additional Method Preconditions  . . . . . . . . . . . 36
         4.3.1.1.  CALDAV:default-calendar-needed Precondition  . . . 36
         4.3.1.2.  CALDAV:valid-schedule-default-calendar-URL
                   Precondition . . . . . . . . . . . . . . . . . . . 36
   5.  Request for Busy Time Information  . . . . . . . . . . . . . . 38
     5.1.  Status Codes . . . . . . . . . . . . . . . . . . . . . . . 38
     5.2.  Additional Method Preconditions  . . . . . . . . . . . . . 39
       5.2.1.  CALDAV:valid-scheduling-message Precondition . . . . . 39
       5.2.2.  CALDAV:valid-organizer Precondition  . . . . . . . . . 39
   6.  Scheduling Privileges  . . . . . . . . . . . . . . . . . . . . 41
     6.1.  Privileges on Scheduling Inbox Collections . . . . . . . . 41
       6.1.1.  CALDAV:schedule-deliver Privilege  . . . . . . . . . . 41
       6.1.2.  CALDAV:schedule-deliver-invite Privilege . . . . . . . 41
       6.1.3.  CALDAV:schedule-deliver-reply Privilege  . . . . . . . 42
       6.1.4.  CALDAV:schedule-query-freebusy Privilege . . . . . . . 42
     6.2.  Privileges on Scheduling Outbox Collections  . . . . . . . 42
       6.2.1.  CALDAV:schedule-send Privilege . . . . . . . . . . . . 42
       6.2.2.  CALDAV:schedule-send-invite Privilege  . . . . . . . . 42
       6.2.3.  CALDAV:schedule-send-reply Privilege . . . . . . . . . 43
       6.2.4.  CALDAV:schedule-send-freebusy Privilege  . . . . . . . 43
     6.3.  Aggregation of Scheduling Privileges . . . . . . . . . . . 43
   7.  Additional iCalendar Property Parameters . . . . . . . . . . . 45
     7.1.  Schedule Agent Parameter . . . . . . . . . . . . . . . . . 45
     7.2.  Schedule Force Send Parameter  . . . . . . . . . . . . . . 46
     7.3.  Schedule Status Parameter  . . . . . . . . . . . . . . . . 47
   8.  Additional Message Header Fields . . . . . . . . . . . . . . . 49
     8.1.  Schedule-Reply Request Header  . . . . . . . . . . . . . . 49
     8.2.  Schedule-Tag Response Header . . . . . . . . . . . . . . . 49
     8.3.  If-Schedule-Tag-Match Request Header . . . . . . . . . . . 50



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   9.  Additional WebDAV Properties . . . . . . . . . . . . . . . . . 51
     9.1.  CALDAV:schedule-calendar-transp Property . . . . . . . . . 51
     9.2.  CALDAV:schedule-default-calendar-URL Property  . . . . . . 52
     9.3.  CALDAV:schedule-tag Property . . . . . . . . . . . . . . . 53
   10. XML Element Definitions  . . . . . . . . . . . . . . . . . . . 54
     10.1. CALDAV:schedule-response XML Element . . . . . . . . . . . 54
     10.2. CALDAV:response XML Element  . . . . . . . . . . . . . . . 54
     10.3. CALDAV:recipient XML Element . . . . . . . . . . . . . . . 54
     10.4. CALDAV:request-status XML Element  . . . . . . . . . . . . 55
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 56
     11.1. Preventing Denial of Service Attacks . . . . . . . . . . . 56
     11.2. Verifying Scheduling Operations  . . . . . . . . . . . . . 56
     11.3. Verifying Busy Time Information Requests . . . . . . . . . 57
     11.4. Privacy Issues . . . . . . . . . . . . . . . . . . . . . . 57
     11.5. Mitigation of iTIP Threats . . . . . . . . . . . . . . . . 58
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 59
     12.1. Message Header Field Registrations . . . . . . . . . . . . 59
       12.1.1. Schedule-Reply . . . . . . . . . . . . . . . . . . . . 59
       12.1.2. Schedule-Tag . . . . . . . . . . . . . . . . . . . . . 59
       12.1.3. If-Schedule-Tag-Match  . . . . . . . . . . . . . . . . 59
     12.2. iCalendar Property Parameter Registrations . . . . . . . . 60
     12.3. iCalendar REQUEST-STATUS Value Registrations . . . . . . . 60
     12.4. Additional iCalendar Elements Registries . . . . . . . . . 60
       12.4.1. Schedule Agent Values Registry . . . . . . . . . . . . 60
       12.4.2. Schedule Force Send Values Registry  . . . . . . . . . 61
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 62
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 63
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 63
     14.2. Informative References . . . . . . . . . . . . . . . . . . 64
   Appendix A.  Scheduling Privileges Summary . . . . . . . . . . . . 65
     A.1.  Scheduling Inbox Privileges  . . . . . . . . . . . . . . . 65
     A.2.  Scheduling Outbox Privileges . . . . . . . . . . . . . . . 65
   Appendix B.  Example Scheduling Operations . . . . . . . . . . . . 67
     B.1.  Example: Organizer Inviting Multiple Attendees . . . . . . 67
     B.2.  Example: Attendee Receiving an Invitation  . . . . . . . . 69
     B.3.  Example: Attendee Replying to an Invitation  . . . . . . . 71
     B.4.  Example: Organizer Receiving a Reply to an Invitation  . . 74
     B.5.  Example: Organizer Requesting Busy Time Information  . . . 76
     B.6.  Example: User Attempting to Invite Attendee on behalf
           of Organizer . . . . . . . . . . . . . . . . . . . . . . . 78
     B.7.  Example: Attendee Declining an Instance of a Recurring
           Event  . . . . . . . . . . . . . . . . . . . . . . . . . . 80
     B.8.  Example: Attendee Removing an Instance of a Recurring
           Event  . . . . . . . . . . . . . . . . . . . . . . . . . . 83
   Appendix C.  Changes (to be removed by RFC Editor prior to
                publication)  . . . . . . . . . . . . . . . . . . . . 86
     C.1.  Changes in -12 . . . . . . . . . . . . . . . . . . . . . . 86
     C.2.  Changes in -11 . . . . . . . . . . . . . . . . . . . . . . 86



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     C.3.  Changes in -10 . . . . . . . . . . . . . . . . . . . . . . 86
     C.4.  Changes in -09 . . . . . . . . . . . . . . . . . . . . . . 87
     C.5.  Changes in -08 . . . . . . . . . . . . . . . . . . . . . . 88
     C.6.  Changes in -07 . . . . . . . . . . . . . . . . . . . . . . 88
     C.7.  Changes in -06 . . . . . . . . . . . . . . . . . . . . . . 89
     C.8.  Changes in -05 . . . . . . . . . . . . . . . . . . . . . . 90













































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1.  Introduction

   This document specifies extensions to the CalDAV "calendar-access"
   [RFC4791] feature to enable scheduling of iCalendar-based [RFC5545]
   calendar components between calendar users.

   This extension leverages the scheduling methods defined in the
   iCalendar Transport-independent Interoperability Protocol (iTIP)
   [RFC5546] to permit calendar users to perform scheduling operations
   such as schedule, reschedule, respond to scheduling request or cancel
   calendar components, as well as search for busy time information.
   However, the following iTIP [RFC5546] features are not covered:
   publishing, countering, delegating, refreshing and forwarding
   calendar components, as well as replacing the Organizer of a calendar
   component.  It is expected that future extensions will be developed
   to address these.

   This specification defines a client/server scheduling protocol, where
   the server is made responsible for sending scheduling messages and
   processing incoming scheduling messages.  The client operations of
   creating, modifying or deleting a calendar component in a calendar is
   enough to trigger the server to deliver the necessary scheduling
   messages to the appropriate calendar users.  This approach is
   sometimes referred to as "implicit scheduling".

   This specification only addresses how scheduling occurs with users on
   a single system (i.e., scheduling between CalDAV servers, or some
   other calendaring and scheduling system, is not defined).  However,
   this specification is compatible with servers being able to send or
   receive scheduling messages with "external" users (e.g., using the
   iCalendar Message-Based Interoperability Protocol iMIP [RFC6047]).

   Section 3 defines the automated "Scheduling Operations", that allow a
   client to store iCalendar data on a CalDAV server, with the server
   taking specific actions in response.  One of three scheduling
   operations can take place: "create", "modify" or "remove", based on
   the HTTP method used for the request, and a comparison between any
   existing and any new iCalendar data.

   Section 4 defines how the server processes scheduling messages sent
   as the result of a scheduling operation.

   Section 5 defines how freebusy requests with an immediate response
   are accomplished.

   Section 6 defines access control privileges for the scheduling
   operations defined in this specification.




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   For the majority of the following discussion, scheduling of events
   will be discussed.  However, scheduling of to-dos is also fully
   supported by this specification.

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

1.1.  Terminology

   This specification reuses much of the same terminology as iCalendar
   [RFC5545], iTIP [RFC5546], WebDAV [RFC4918], and CalDAV [RFC4791].
   Additional terms used by this specification are:

   Scheduling object resource:  A calendar object resource contained in
      a calendar collection for which the server will take care of
      sending scheduling messages on behalf of the owner of the calendar
      collection.

   Organizer scheduling object resource:  A scheduling object resource
      owned by the Organizer.

   Attendee scheduling object resource:  A scheduling object resource
      owned by an Attendee.

   Scheduling operation:  Add, change or remove operations on a
      scheduling object resource for which the server will deliver
      scheduling messages to other calendar users.

   Scheduling message:  A calendar object that describes a scheduling
      operation such as schedule, reschedule, reply, or cancel.

   Scheduling Outbox collection:  A resource at which busy time
      information requests are targeted.

   Scheduling Inbox collection:  A collection in which incoming
      scheduling messages are delivered.

1.2.  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 Augmented BNF (ABNF) syntax used by this document to specify the
   format definition of new iCalendar elements is defined in [RFC5234].

   The Augmented BNF (ABNF) syntax used by this document to specify the



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   format definition of new message header fields to be used with the
   HTTP/1.1 protocol is described in Section 2.1 of [RFC2616].  Since
   this Augmented BNF uses the basic production rules provided in
   Section 2.2 of [RFC2616], these rules apply to this document as well.

   The term "protected" is used in the Conformance field of WebDAV
   property definitions as defined in Section 15 of [RFC4918].

1.3.  XML Namespaces and Processing

   This document uses XML DTD fragments ([W3C.REC-xml-20081126], Section
   3.2) as a purely notational convention.  WebDAV request and response
   bodies cannot be validated by a DTD due to the specific extensibility
   rules defined in Section 17 of [RFC4918] and due to the fact that all
   XML elements defined by that specification use the XML namespace name
   "DAV:".  In particular:

   1.  element names use the "DAV:" namespace,

   2.  element ordering is irrelevant unless explicitly stated,

   3.  extension elements (elements not already defined as valid child
       elements) can be added anywhere, except when explicitly stated
       otherwise,

   4.  extension attributes (attributes not already defined as valid for
       this element) can be added anywhere, except when explicitly
       stated otherwise.

   The XML elements specified in this document are defined in the
   "urn:ietf:params:xml:ns:caldav" XML namespace registered by CalDAV
   [RFC4791].

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

   This document inherits, and sometimes extends, DTD productions from
   Section 14 of [RFC4918].

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







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2.  Scheduling Support

   A server that supports the features described in this document is
   REQUIRED to support the CalDAV "calendar-access" [RFC4791] feature.
   Servers include "calendar-auto-schedule" as a field in the DAV
   response header from an OPTIONS request on any resource that supports
   any scheduling operations, properties, privileges or methods.

   This specification introduces new collection resource types that are
   used to manage scheduling object resources, and scheduling privileges
   (as per Section 6), as well as provide scheduling functionality.  It
   is the server's responsibility to create these collection resources,
   and clients have no way to create or delete them.

2.1.  Scheduling Outbox Collection

   A scheduling Outbox collection is used as the target for busy time
   information requests, and to manage privileges that apply to outgoing
   scheduling requests.

   A scheduling Outbox collection MUST report the DAV:collection and
   CALDAV:schedule-outbox XML elements in the value of the DAV:
   resourcetype property.  The element type declaration for CALDAV:
   schedule-outbox is:

     <!ELEMENT schedule-outbox EMPTY>

   Example:

     <D:resourcetype xmlns:D="DAV:">
       <D:collection/>
       <C:schedule-outbox xmlns:C="urn:ietf:params:xml:ns:caldav"/>
     </D:resourcetype>

   A scheduling Outbox collection MUST NOT be a child (at any depth) of
   a calendar collection resource.

   The following WebDAV properties specified in CalDAV "calendar-access"
   [RFC4791] MAY also be defined on scheduling Outbox collections and
   apply to scheduling messages submitted to the scheduling Outbox
   collection with the POST method:

   o  CALDAV:supported-calendar-component-set

   o  CALDAV:supported-calendar-data

   o  CALDAV:max-resource-size




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   o  CALDAV:min-date-time

   o  CALDAV:max-date-time

   o  CALDAV:max-attendees-per-instance

   The use of child resources in a scheduling Outbox collection is
   reserved for future revisions or extensions of this specification.

   The following WebDAV property is defined on principal resources and
   used to locate the corresponding Outbox collection for the associated
   principal.

2.1.1.  CALDAV:schedule-outbox-URL Property

   Name:  schedule-outbox-URL

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

   Purpose:  Identify the URL of the scheduling Outbox collection owned
      by the associated principal resource.

   Protected:  This property MAY be protected.

   PROPFIND behavior:  This property SHOULD NOT be returned by a
      PROPFIND allprop request (as defined in Section 14.2 of
      [RFC4918]).

   COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
      and MOVE operations.

   Description:  This property is needed for a client to determine where
      the scheduling Outbox collection of the current user is located so
      that sending of scheduling messages can occur.  If not present,
      then the associated calendar user is not enabled for the sending
      of scheduling messages on the server.

   Definition:

     <!ELEMENT schedule-outbox-URL (DAV:href)>

2.2.  Scheduling Inbox Collection

   A scheduling Inbox collection contains copies of incoming scheduling
   messages.  These can be requests sent by an Organizer, or replies
   sent by an Attendee in response to a request.  The scheduling Inbox
   collection is also used to manage scheduling privileges.




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   A scheduling Inbox collection MUST report the DAV:collection and
   CALDAV:schedule-inbox XML elements in the value of the DAV:
   resourcetype property.  The element type declaration for CALDAV:
   schedule-inbox is:

     <!ELEMENT schedule-inbox EMPTY>

   Example:

     <D:resourcetype xmlns:D="DAV:">
       <D:collection/>
       <C:schedule-inbox xmlns:C="urn:ietf:params:xml:ns:caldav"/>
     </D:resourcetype>

   Scheduling Inbox collections MUST only contain calendar object
   resources that obey the restrictions specified in iTIP [RFC5546].
   Consequently, scheduling Inbox collections MUST NOT contain any types
   of collection resources.  Restrictions defined in Section 4.1 of
   CalDAV "calendar-access" [RFC4791] on calendar object resources
   contained in calendar collections (e.g., "UID" uniqueness) do not
   apply to calendar object resources contained in a scheduling Inbox
   collection.  Thus, multiple calendar object resources contained in a
   scheduling Inbox collection can have the same "UID" property value
   (i.e., multiple scheduling messages for the same calendar component).

   A scheduling Inbox collection MUST NOT be a child (at any depth) of a
   calendar collection resource.

   The following WebDAV properties specified in CalDAV "calendar-access"
   [RFC4791] MAY also be defined on scheduling Inbox collections and
   apply to scheduling messages delivered to the collection:

   o  CALDAV:supported-calendar-component-set

   o  CALDAV:supported-calendar-data

   o  CALDAV:max-resource-size

   o  CALDAV:min-date-time

   o  CALDAV:max-date-time

   o  CALDAV:max-instances

   o  CALDAV:max-attendees-per-instance

   o  CALDAV:calendar-timezone




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   The following WebDAV property is defined on principal resources and
   used to locate the corresponding Inbox collection for the associated
   principal.

2.2.1.  CALDAV:schedule-inbox-URL Property

   Name:  schedule-inbox-URL

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

   Purpose:  Identify the URL of the scheduling Inbox collection owned
      by the associated principal resource.

   Protected:  This property MAY be protected.

   PROPFIND behavior:  This property SHOULD NOT be returned by a
      PROPFIND allprop request (as defined in Section 14.2 of
      [RFC4918]).

   COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
      and MOVE operations.

   Description:  This property allows a client to determine where the
      scheduling Inbox collection of the current user is located so that
      processing of scheduling messages can occur.  If not present, then
      the associated calendar user is not enabled for reception of
      scheduling messages on the server.

   Definition:

     <!ELEMENT schedule-inbox-URL (DAV:href)>

2.3.  Calendaring Reports Extensions

   This specification extends the CALDAV:calendar-query and CALDAV:
   calendar-multiget REPORTs to return results for calendar object
   resources in scheduling Inbox collections.

   When a CALDAV:calendar-query REPORT includes a time-range query and
   targets a scheduling Inbox collection, if any calendar object
   resources contain "VEVENT" calendar components that do not include a
   "DTSTART" iCalendar property (as allowed by iTIP [RFC5546]) then such
   components MUST always match the time-range query test.

   Note that the CALDAV:free-busy-query REPORT is not supported on
   scheduling Inbox collections.





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2.4.  Additional Principal Properties

   This section defines new properties for WebDAV principal resources as
   defined in [RFC3744].  These properties are likely to be protected
   but the server MAY allow them to be written by appropriate users.

2.4.1.  CALDAV:calendar-user-address-set Property

   Name:  calendar-user-address-set

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

   Purpose:  Identify the calendar addresses of the associated principal
      resource.

   Protected:  This property MAY be protected.

   PROPFIND behavior:  This property SHOULD NOT be returned by a
      PROPFIND allprop request (as defined in Section 14.2 of
      [RFC4918]).

   COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
      and MOVE operations.

   Description:  Support for this property is REQUIRED.  This property
      is needed to map calendar user addresses in iCalendar data to
      principal resources and their associated scheduling Inbox and
      Outbox collections.  In the event that a user has no well defined
      identifier for their calendar user address, the URI of their
      principal resource can be used.  This property SHOULD be
      searchable using the DAV:principal-property-search REPORT.  The
      DAV:principal-search-property-set REPORT SHOULD identify this
      property as such.  If not present, then the associated calendar
      user is not enabled for scheduling on the server.

   Definition:

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

   Example:

     <C:calendar-user-address-set xmlns:D="DAV:"
         xmlns:C="urn:ietf:params:xml:ns:caldav">
       <D:href>mailto:bernard@example.com</D:href>
       <D:href>mailto:bernard.desruisseaux@example.com</D:href>
     </C:calendar-user-address-set>





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2.4.2.  CALDAV:calendar-user-type Property

   Name:  calendar-user-type

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

   Purpose:  Identifies the calendar user type of the associated
      principal resource.

   Value:  Same values allowed for the iCalendar "CUTYPE" property
      parameter defined in Section 3.2.3 of [RFC5545].

   Protected:  This property MAY be protected.

   PROPFIND behavior:  This property SHOULD NOT be returned by a
      PROPFIND allprop request (as defined in Section 14.2 of
      [RFC4918]).

   COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
      and MOVE operations.

   Description:  Clients can query principal resources in order to
      lookup attendees available on the server.  When doing this, it is
      useful to know, or restrict the query to, certain types of
      calendar user (e.g., only search for "people", or only search for
      "rooms").  This property MAY be defined on principal resources to
      indicate the type of calendar user associated with the principal
      resource.  Its value is the same as the iCalendar "CUTYPE"
      property parameter that can be used on "ATTENDEE" properties.
      This property SHOULD be searchable using the DAV:principal-
      property-search REPORT.  The DAV:principal-search-property-set
      REPORT SHOULD identify this property as such.

   Definition:

     <!ELEMENT calendar-user-type (#PCDATA)>

   Example:

     <C:calendar-user-type
         xmlns:C="urn:ietf:params:xml:ns:caldav">INDIVIDUAL<
     /C:calendar-user-type>









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3.  Scheduling Operations

   When a calendar object resource is created, modified or removed from
   a calendar collection, the server examines the calendar data and
   checks to see whether the data represents a scheduling object
   resource.  If it does, the server will automatically attempt to
   deliver a scheduling message to the appropriate calendar users.
   Several types of scheduling operations can occur in this case,
   equivalent to iTIP "REQUEST", "REPLY", "CANCEL", and "ADD"
   operations.

3.1.  Identifying Scheduling Object Resources

   Calendar object resources on which the server performs scheduling
   operations are referred to as scheduling object resources.  There are
   two types of scheduling object resources: organizer scheduling object
   resources, and attendee scheduling object resources.

   A calendar object resource is considered to be a valid organizer
   scheduling object resource if the "ORGANIZER" iCalendar property is
   present and set in all the calendar components to a value that
   matches one of the calendar user addresses of the owner of the
   calendar collection.

   A calendar object resource is considered to be a valid attendee
   scheduling object resource if the "ORGANIZER" iCalendar property is
   present and set in all the calendar components to the same value and
   doesn't match one of the calendar user addresses of the owner of the
   calendar collection, and at least one of the "ATTENDEE" iCalendar
   property values matches one of the calendar user addresses of the
   owner of the calendar collection.

   The creation of attendee scheduling object resources is typically
   done by the server, with the resource being created in an appropriate
   calendar collection (see Section 4.3).

3.2.  Handling Scheduling Object Resources

   The server's behavior when processing a scheduling object resource
   depends on whether it is owned by the Organizer or an Attendee
   specified in the calendar data.

3.2.1.  Organizer Scheduling Object Resources

   An Organizer can create, modify or remove a scheduling object
   resource, subject to access privileges, pre-conditions, and the
   restrictions defined in Section 4.1 of [RFC4791].  These operations
   are each described next, and how they are invoked via HTTP requests



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   is described in Section 3.2.3.

   The Organizer of a calendar component can also be an Attendee of that
   calendar component.  In such cases the server MUST NOT send a
   scheduling message to the Attendee that matches the Organizer.

   The server SHOULD reject any attempt to set the "PARTSTAT" iCalendar
   property parameter value of the "ATTENDEE" iCalendar property of
   other users in the calendar object resource to a value other than
   "NEEDS-ACTION" if the "SCHEDULE-AGENT" property parameter value is
   not present or set to the value "SERVER".

   The server MAY reject attempts to create a scheduling object resource
   that specifies a "UID" property value already specified in a
   scheduling object resource contained in another calendar collection
   of the Organizer.

3.2.1.1.  Create

   When an Organizer creates a scheduling object resource, the server
   MUST inspect each "ATTENDEE" property to determine whether to send a
   scheduling message.  The table below indicates the appropriate iTIP
   method used by the server, taking into account any "SCHEDULE-AGENT"
   property parameter (see Section 7.1) specified on each "ATTENDEE"
   property.

                    +------------------+-------------+
                    | SCHEDULE-AGENT   | iTIP METHOD |
                    +------------------+-------------+
                    | SERVER (default) | REQUEST     |
                    |                  |             |
                    | CLIENT           | --          |
                    |                  |             |
                    | NONE             | --          |
                    +------------------+-------------+

   "SCHEDULE-STATUS" iCalendar property parameters are added or changed
   on "ATTENDEE" iCalendar properties in the scheduling object resource
   being created as described in Section 7.3, with the value set as
   described in Section 3.2.9.  This will result in the created calendar
   object resource differing from the calendar data sent in the HTTP
   request.  As a result clients MAY reload the calendar data from the
   server in order to update to the new server generated state
   information.

   The server MUST add a "SCHEDULE-STATUS" iCalendar property parameter
   (see Section 7.3) to the "ATTENDEE" iCalendar property in the
   scheduling object resource being created, and set its value as



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   described in Section 3.2.9.  This will result in the created calendar
   object resource differing from the calendar data sent in the HTTP
   request.  As a result clients MAY reload the calendar data from the
   server in order to update to the new server generated state
   information.  Servers MUST NOT set the "SCHEDULE-STATUS" property
   parameter on the "ATTENDEE" property of Attendees for which it did
   not attempt to deliver a scheduling message.

   The server MUST return an error with the CALDAV:allowed-organizer-
   scheduling-object-change precondition code (Section 3.2.4.3) when the
   Organizer attempts to change the iCalendar data in a manner that is
   forbidden.

3.2.1.2.  Modify

   When an Organizer modifies a scheduling object resource, the server
   MUST inspect each "ATTENDEE" property in both the original and
   modified iCalendar data on a per-instance basis to determine whether
   to send a scheduling message.  The table below indicates the
   appropriate iTIP method used by the server, taking into account any
   "SCHEDULE-AGENT" property parameter (see Section 7.1) specified on
   each "ATTENDEE" property.  The values "SERVER", "CLIENT", and "NONE"
   in the top and left titles of the table refer to the "SCHEDULE-AGENT"
   parameter value of the "ATTENDEE" property, and the values "<Absent>"
   and "<Removed>" are used to cover the cases where the "ATTENDEE"
   property is not present (Original) or is being removed (Modified).

   +---------------+-----------------------------------------------+
   |               |                   Modified                    |
   |               +-----------+-----------+-----------+-----------+
   |               | <Removed> | SERVER    | CLIENT    | NONE      |
   |               |           | (default) |           |           |
   +===+===========+===========+===========+===========+===========+
   |   | <Absent>  |  --       | REQUEST / | --        | --        |
   | O |           |           | ADD       |           |           |
   | r +-----------+-----------+-----------+-----------+-----------+
   | i | SERVER    |  CANCEL   | REQUEST   | CANCEL    | CANCEL    |
   | g | (default) |           |           |           |           |
   | i +-----------+-----------+-----------+-----------+-----------+
   | n | CLIENT    |  --       | REQUEST / | --        | --        |
   | a |           |           | ADD       |           |           |
   | l +-----------+-----------+-----------+-----------+-----------+
   |   | NONE      |  --       | REQUEST / | --        | --        |
   |   |           |           | ADD       |           |           |
   +---+-----------+-----------+-----------+-----------+-----------+

   "SCHEDULE-STATUS" iCalendar property parameters are added or changed
   on "ATTENDEE" iCalendar properties in the scheduling object resource



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   being modified as described in Section 7.3, with the value set as
   described in Section 3.2.9.  This will result in the created calendar
   object resource differing from the calendar data sent in the HTTP
   request.  As a result clients MAY reload the calendar data from the
   server in order to update to the new server generated state
   information.

   The server MUST return an error with the CALDAV:allowed-organizer-
   scheduling-object-change precondition code (Section 3.2.4.3) when the
   Organizer attempts to change the iCalendar data in a manner that is
   forbidden.

3.2.1.3.  Remove

   When an Organizer removes a scheduling object resource, the server
   MUST inspect each "ATTENDEE" property to determine whether to send a
   scheduling message.  The table below indicates the appropriate iTIP
   method used by the server, taking into account any "SCHEDULE-AGENT"
   property parameter (see Section 7.1) specified on each "ATTENDEE"
   property.

                    +------------------+-------------+
                    | SCHEDULE-AGENT   | iTIP METHOD |
                    +------------------+-------------+
                    | SERVER (default) | CANCEL      |
                    |                  |             |
                    | CLIENT           | --          |
                    |                  |             |
                    | NONE             | --          |
                    +------------------+-------------+

3.2.2.  Attendee Scheduling Object Resources

   An Attendee can create, modify or remove a scheduling object
   resource.  These operations are each described next, and how they are
   invoked via HTTP requests is described in Section 3.2.3.

3.2.2.1.  Allowed Attendee Changes

   Attendees are allowed to make some changes to a scheduling object
   resource, though key properties such as start time, end time,
   location, and summary are typically under the control of the
   Organizer.

   Servers MUST allow Attendees to make the following iCalendar data
   changes, subject to other restrictions, such as access privileges and
   pre-conditions:




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   1.   change their own "PARTSTAT" iCalendar property parameter value.

   2.   add, modify or remove any "TRANSP" iCalendar properties.

   3.   add, modify or remove any "PERCENT-COMPLETE" iCalendar
        properties.

   4.   add, modify or remove any "COMPLETED" iCalendar properties.

   5.   add, modify or remove any "VALARM" iCalendar components.

   6.   add, modify or remove the "CALSCALE" iCalendar property within
        the top-level "VCALENDAR" component.

   7.   modify the "PRODID" iCalendar property within the top-level
        "VCALENDAR" component.

   8.   add "EXDATE" iCalendar properties and possibly remove components
        for overridden recurrence instances.

   9.   add, modify or remove any "CREATED", "DTSTAMP" and "LAST-
        MODIFIED" iCalendar properties.

   10.  add, modify or remove "SCHEDULE-STATUS" iCalendar property
        parameters on "ATTENDEE" properties that have a "SCHEDULE-AGENT"
        parameter set to "CLIENT".

   11.  add new components to represent overridden recurrence instances,
        provided the only changes to the recurrence instance follow the
        rules above.

   The server MUST return an error with the CALDAV:allowed-attendee-
   scheduling-object-change precondition code (Section 3.2.4.4) when the
   Attendee attempts to change the iCalendar data in a manner forbidden
   by the server.

3.2.2.2.  Create

   Typically an Attendee does not create scheduling object resources, as
   scheduling messages delivered to them on the server are automatically
   processed by the server and placed on one of their calendars (see
   Section 4).  However, in some cases a scheduling message can get
   delivered directly to the client (e.g., via email [RFC6047]), and the
   Attendee might wish to store that on the server.  In that case the
   client creates a scheduling object resource in a calendar belonging
   to the Attendee.  It can then set the "SCHEDULE-AGENT" iCalendar
   property parameter on all "ORGANIZER" iCalendar properties in the
   resource to determine how the server treats the resource.  The value



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   of the "SCHEDULE-AGENT" iCalendar property parameter on all
   "ORGANIZER" iCalendar properties MUST be the same.

   +----------------+--------------------------------------------------+
   | SCHEDULE-AGENT | Action                                           |
   +----------------+--------------------------------------------------+
   | SERVER         | The server will attempt to process changes to    |
   | (default)      | the resource using the normal rules for attendee |
   |                | scheduling object resources.                     |
   |                |                                                  |
   | CLIENT         | The server does no special processing of the     |
   |                | resource.  The client is assumed to be handling  |
   |                | Attendee replies etc.                            |
   |                |                                                  |
   | NONE           | The server does no special processing of the     |
   |                | resource.                                        |
   +----------------+--------------------------------------------------+

   "SCHEDULE-STATUS" iCalendar property parameters are added or changed
   on "ORGANIZER" iCalendar properties in the scheduling object resource
   being created as described in Section 7.3, with the value set as
   described in Section 3.2.9.

3.2.2.3.  Modify

   When a scheduling object resource is modified by an Attendee, the
   server behavior depends on the value of the "SCHEDULE-AGENT"
   iCalendar property parameter on the "ORGANIZER" iCalendar properties:

   +----------------+--------------------------------------------------+
   | SCHEDULE-AGENT | Action                                           |
   +----------------+--------------------------------------------------+
   | SERVER         | The server will attempt to process the update    |
   | (default)      | using the behavior listed below.                 |
   |                |                                                  |
   | CLIENT         | The server does no special processing of the     |
   |                | resource.  The client is assumed to be handling  |
   |                | any Attendee replies etc.                        |
   |                |                                                  |
   | NONE           | The server does no special processing of the     |
   |                | resource.                                        |
   +----------------+--------------------------------------------------+

   The server will inspect the changes by comparing the new scheduling
   object resource with the existing scheduling object resource.

   If the Attendee changes one or more "PARTSTAT" iCalendar property
   values on any component, or adds an overridden component with a



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   changed "PARTSTAT" property, then the server MUST deliver an iTIP
   "REPLY" scheduling message to the Organizer to indicate the new
   participation status of the Attendee.

   If the Attendee adds an "EXDATE" property value to effectively remove
   a recurrence instance, the server MUST deliver an iTIP "REPLY"
   scheduling message to the Organizer to indicate that the Attendee has
   declined the instance.

   "SCHEDULE-STATUS" iCalendar property parameters are added or changed
   on "ORGANIZER" iCalendar properties in the scheduling object resource
   being modified as described in Section 7.3, with the value set as
   described in Section 3.2.9.  This will result in the updated calendar
   object resource differing from the calendar data sent in the HTTP
   request.  As a result clients MAY reload the calendar data from the
   server in order to update to the new server generated state
   information.

3.2.2.4.  Remove

   When a scheduling object resource is removed by an Attendee, the
   server behavior depends on the value of the "SCHEDULE-AGENT"
   iCalendar property parameter on the "ORGANIZER" iCalendar properties:

   +----------------+--------------------------------------------------+
   | SCHEDULE-AGENT | Action                                           |
   +----------------+--------------------------------------------------+
   | SERVER         | The server will attempt to process the removal   |
   | (default)      | taking into account any "Schedule-Reply" request |
   |                | header as per Section 8.1.                       |
   |                |                                                  |
   | CLIENT         | The server does no special processing of the     |
   |                | resource.  The client is assumed to be handling  |
   |                | any Attendee replies etc.                        |
   |                |                                                  |
   | NONE           | The server does no special processing of the     |
   |                | resource.                                        |
   +----------------+--------------------------------------------------+

3.2.3.  HTTP Methods

   This section describes how use of various HTTP [RFC2616] and WebDAV
   [RFC4918] methods on a scheduling object resource will cause a
   create, modify or remove operation on that resource as described
   above.  The use of these methods is subject to the restrictions in
   [RFC4791], in addition to what is described below.





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3.2.3.1.  PUT

   When the server receives a PUT method request it MUST execute the
   following operations, provided all appropriate preconditions are met:

   +------------------------+--------------------------+---------------+
   | Existing Destination   | Resulting Destination    | Server        |
   | Resource               | Resource                 | Operation     |
   +------------------------+--------------------------+---------------+
   | None                   | Calendar object resource | None          |
   |                        |                          |               |
   | None                   | Scheduling object        | Create        |
   |                        | resource                 |               |
   |                        |                          |               |
   | Calendar object        | Calendar object resource | None          |
   | resource               |                          |               |
   |                        |                          |               |
   | Calendar object        | Scheduling object        | Create        |
   | resource               | resource                 |               |
   |                        |                          |               |
   | Scheduling object      | Calendar object resource | Remove        |
   | resource               |                          |               |
   |                        |                          |               |
   | Scheduling object      | Scheduling object        | Modify        |
   | resource               | resource                 |               |
   +------------------------+--------------------------+---------------+

3.2.3.2.  DELETE

   When the server receives a DELETE method request targeted at a
   scheduling object resource it MUST execute the Remove operation.

   When the server receives a DELETE method request targeted at a
   calendar collection it MUST execute the Remove operation on all
   scheduling object resources contained in the calendar collection.

3.2.3.3.  COPY

   When the server receives a COPY method request it MUST execute the
   following operations based on the source and destination collections
   in the request:










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   +-----------------------+------------------------+------------------+
   | Source Collection     | Destination Collection | Server Operation |
   +-----------------------+------------------------+------------------+
   | Non-calendar          | Non-calendar           | None             |
   | collection            | collection             |                  |
   |                       |                        |                  |
   | Non-calendar          | Calendar collection    | (1)              |
   | collection            |                        |                  |
   |                       |                        |                  |
   | Calendar collection   | Non-calendar           | None             |
   |                       | collection             |                  |
   |                       |                        |                  |
   | Calendar collection   | Calendar collection    | (2)              |
   +-----------------------+------------------------+------------------+

   Note 1.  The rules in Section 3.2.3.1 are applied for the destination
   of the COPY request.

   Note 2.  The server MAY reject this as per Section 3.2.4.1, otherwise
   None.

   The behavior of a COPY method request on a calendar collection is
   undefined.

3.2.3.4.  MOVE

   When the server receives a MOVE method request it MUST execute the
   following operations based on the source and destination collections
   in the request:

   +-----------------------+------------------------+------------------+
   | Source Collection     | Destination Collection | Server Operation |
   +-----------------------+------------------------+------------------+
   | Non-calendar          | Non-calendar           | None             |
   | collection            | collection             |                  |
   |                       |                        |                  |
   | Non-calendar          | Calendar collection    | (1)              |
   | collection            |                        |                  |
   |                       |                        |                  |
   | Calendar collection   | Non-calendar           | (2)              |
   |                       | collection             |                  |
   |                       |                        |                  |
   | Calendar collection   | Calendar collection    | None             |
   +-----------------------+------------------------+------------------+

   Note 1.  The rules in Section 3.2.3.1 are applied for the destination
   of the MOVE request.




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   Note 2.  The rules in Section 3.2.3.2 are applied for the source of
   the MOVE request.

   The behavior of a MOVE method request on a calendar collection is
   undefined.

3.2.4.  Additional Method Preconditions

   This specification defines method preconditions (see Section 16 of
   WebDAV [RFC4918]), in addition to the ones in [RFC4791], to provide
   machine-parseable information in error responses.

3.2.4.1.  CALDAV:unique-scheduling-object-resource Precondition

   Name:  unique-scheduling-object-resource

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

   Apply to:  PUT, COPY, and MOVE

   Use with:  403 Forbidden

   Purpose:  (precondition) -- Servers MAY reject requests to create a
      scheduling object resource with an iCalendar "UID" property value
      already in use by another scheduling object resource owned by the
      same user in other calendar collections.  Servers SHOULD report
      the URL of the scheduling object resource that is already making
      use of the same "UID" property value in the DAV:href element.

   Definition:

     <!ELEMENT unique-scheduling-object-resource (DAV:href?)>

   Example:

     <C:unique-scheduling-object-resource xmlns:D="DAV:"
         xmlns:C="urn:ietf:params:xml:ns:caldav">
       <D:href>/home/bernard/calendars/personal/abc123.ics</D:href>
     </C:unique-scheduling-object-resource>

3.2.4.2.  CALDAV:same-organizer-in-all-components Precondition

   Name:  same-organizer-in-all-components

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






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   Apply to:  PUT, COPY, and MOVE

   Use with:  403 Forbidden

   Purpose:  (precondition) -- All the calendar components in a
      scheduling object resource MUST contain the same "ORGANIZER"
      property value when present.

   Definition:

     <!ELEMENT same-organizer-in-all-components EMPTY>

3.2.4.3.  CALDAV:allowed-organizer-scheduling-object-change Precondition

   Name:  allowed-organizer-scheduling-object-change

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

   Apply to:  PUT, COPY, and MOVE

   Use with:  403 Forbidden

   Purpose:  (precondition) -- Servers MAY impose restrictions on
      modifications allowed by an Organizer.  For instance, servers MAY
      prevent the Organizer setting the "PARTSTAT" property parameter to
      a value other than "NEEDS-ACTION" if the corresponding "ATTENDEE"
      property has the "SCHEDULE-AGENT" property parameter set to
      "SERVER", or has no "SCHEDULE-AGENT" property parameter.  See
      Section 3.2.1.

   Definition:

     <!ELEMENT allowed-organizer-scheduling-object-change EMPTY>

3.2.4.4.  CALDAV:allowed-attendee-scheduling-object-change Precondition

   Name:  allowed-attendee-scheduling-object-change

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

   Apply to:  PUT, COPY, and MOVE

   Use with:  403 Forbidden

   Purpose:  (precondition) -- Servers MAY impose restrictions on
      modifications allowed by an Attendee, subject to the allowed
      changes specified in Section 3.2.2.1.




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   Definition:

     <!ELEMENT allowed-attendee-scheduling-object-change EMPTY>

3.2.5.  DTSTAMP and SEQUENCE Properties

   The server MUST ensure that a "DTSTAMP" iCalendar property is present
   and set the value to the UTC time that the scheduling message was
   generated (as required by iCalendar).

   The server MUST ensure that for each type of scheduling operation,
   the "SEQUENCE" iCalendar property value is updated as per iTIP
   [RFC5546].

3.2.6.  Restrict Recurrence Instances Sent to Attendees

   Servers MUST ensure that Attendees only get information about
   recurrence instances that explicitly include them as an Attendee,
   when delivering scheduling messages for recurring calendar
   components.

   For example, if an Attendee is invited to only a single instance of a
   recurring event, the organizer scheduling object resource will
   contain an overridden instance in the form of a separate calendar
   component.  That separate calendar component will include the
   "ATTENDEE" property referencing the "one-off" Attendee.  That
   Attendee will not be listed in any other calendar components in the
   scheduling object resource.  Any scheduling messages delivered to the
   Attendee will only contain information about this overridden
   instance.

   As another example, an Attendee could be excluded from one instance
   of a recurring event.  In that case the organizer scheduling object
   resource will include an overridden instance with an "ATTENDEE" list
   that does not include the Attendee being excluded.  Any scheduling
   messages delivered to the Attendee will not specify the overridden
   instance but rather include an "EXDATE" property in the "master"
   component that defines the recurrence set.

3.2.7.  Forcing the Server to Send a Scheduling Message

   The iCalendar property parameter "SCHEDULE-FORCE-SEND" defined in
   Section 7.2 can be used by a calendar user to force the server to
   send a scheduling message to an Attendee or the Organizer in a
   situation where the server would not normally send a scheduling
   message.  For instance, an Organizer could use this property
   parameter to request an Attendee, that previously declined an
   invitation, to reconsider their participation status without being



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   forced to modify the event.

3.2.8.  Attendee Participation Status

   This section specifies additional requirements on the handling of the
   "PARTSTAT" property parameter when the "SCHEDULE-AGENT" property
   parameter on the corresponding "ATTENDEE" property is set to the
   value "SERVER" or is not present.

   A reschedule occurs when any "DTSTART", "DTEND", "DURATION", "DUE",
   "RRULE", "RDATE", or "EXDATE" property changes in a calendar
   component such that existing recurrence instances are impacted by the
   changes, as shown in the table below.  Servers MUST reset the
   "PARTSTAT" property parameter value of all "ATTENDEE" properties,
   except the one that corresponds to the Organizer, to "NEEDS-ACTION"
   for each calendar component change that causes any instance to be
   rescheduled.

   +-----------+-------------------------------------------------------+
   | Property  | Server Action                                         |
   +-----------+-------------------------------------------------------+
   | DTSTART,  | Any change to these properties result in "PARTSTAT"   |
   | DTEND,    | being set to "NEEDS-ACTION"                           |
   | DURATION, |                                                       |
   | DUE       |                                                       |
   |           |                                                       |
   |           |                                                       |
   |           |                                                       |
   | RRULE     | A change to or addition of this property that results |
   |           | in the addition of new recurring instances or a       |
   |           | change in time for existing recurring instances       |
   |           | result in "PARTSTAT" being reset to "NEEDS-ACTION" on |
   |           | each affected component.                              |
   |           |                                                       |
   |           |                                                       |
   |           |                                                       |
   | RDATE     | A change to or addition of this property that results |
   |           | in the addition of new recurring instances or a       |
   |           | change in time for existing recurring instances       |
   |           | result in "PARTSTAT" being reset to "NEEDS-ACTION" on |
   |           | each affected component.                              |
   |           |                                                       |
   |           |                                                       |
   |           |                                                       |







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   | EXDATE    | A change to or removal of this property that results  |
   |           | in the re-instatement of recurring instances result   |
   |           | in "PARTSTAT" being set to "NEEDS-ACTION" on each     |
   |           | affected component.                                   |
   +-----------+-------------------------------------------------------+

   The server MAY allow the Organizer's client to change an Attendee's
   "PARTSTAT" property parameter value to "NEEDS-ACTION" at any other
   time (e.g., when the "LOCATION" property value changes, an Organizer
   might wish to re-invite Attendees who might be impacted by the
   change).

3.2.9.  Schedule Status Values

   When scheduling with an Attendee there are two types of status
   information that can be returned during the operation.  The first
   type of status information is a "delivery" status that indicates
   whether the scheduling message from the Organizer to the Attendee was
   delivered or not, or what the current status of delivery is.  The
   second type of status information is a "reply" status corresponding
   to the Attendee's own "REQUEST-STATUS" information from the
   scheduling message reply that is sent back to the Organizer.

   Similarly, when an Attendee sends a reply back to the Organizer,
   there will be "delivery" status information for the scheduling
   message sent to the Organizer.  However, there is no "REQUEST-STATUS"
   sent back by the Organizer, so there is no equivalent of the "reply"
   status as per scheduling messages to Attendees.

   The "delivery" status information on an "ORGANIZER" or "ATTENDEE"
   iCalendar property is conveyed in the "SCHEDULE-STATUS" property
   parameter value (Section 7.3).  The status code value for "delivery"
   status can be one of the following:


















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   +----------+--------------------------------------------------------+
   | Delivery | Description                                            |
   | Status   |                                                        |
   | Code     |                                                        |
   +----------+--------------------------------------------------------+
   | 1.0      | The scheduling message is pending. i.e. the server is  |
   |          | still in the process of sending the message.  The      |
   |          | status code value can be expected to change once the   |
   |          | server has completed its sending and delivery          |
   |          | attempts.                                              |
   |          |                                                        |
   |          |                                                        |
   |          |                                                        |
   | 1.1      | The scheduling message has been successfully sent.     |
   |          | However, the server does not have explicit information |
   |          | about whether the scheduling message was successfully  |
   |          | delivered to the recipient.  This state can occur with |
   |          | "store and forward" style scheduling protocols such as |
   |          | iMIP [RFC6047] (iTIP using email).                     |
   |          |                                                        |
   |          |                                                        |
   |          |                                                        |
   | 1.2      | The scheduling message has been successfully           |
   |          | delivered.                                             |
   |          |                                                        |
   |          |                                                        |
   |          |                                                        |
   | 3.7      | The scheduling message was not delivered because the   |
   |          | server did not recognize the calendar user address as  |
   |          | a valid calendar user.  Note that this code applies to |
   |          | both Organizer and Attendee calendar user addresses.   |
   |          |                                                        |
   |          |                                                        |
   |          |                                                        |
   | 3.8      | The scheduling message was not delivered due to        |
   |          | insufficient privileges.  Note that this code applies  |
   |          | to both privileges granted by both the Organizer and   |
   |          | Attendee calendar users.                               |
   |          |                                                        |
   |          |                                                        |
   |          |                                                        |
   | 5.1      | The scheduling message was not delivered because the   |
   |          | server could not complete delivery of the message.     |
   |          | This is likely due to a temporary failure, and the     |
   |          | originator can try to send the message again at a      |
   |          | later time.                                            |
   |          |                                                        |
   |          |                                                        |



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   | 5.2      | The scheduling message was not delivered because the   |
   |          | server was not able to find a way to deliver the       |
   |          | message.  This is likely a permanent failure, and the  |
   |          | originator ought not try to send the message again, at |
   |          | least without verifying/correcting the calendar user   |
   |          | address of the recipient.                              |
   |          |                                                        |
   |          |                                                        |
   |          |                                                        |
   | 5.3      | The scheduling message was not delivered and was       |
   |          | rejected because scheduling with that recipient is not |
   |          | allowed.  This is likely a permanent failure, and the  |
   |          | originator ought not try to send the message again.    |
   +----------+--------------------------------------------------------+

   The status code for "reply" status can be any of the valid iTIP
   [RFC5546] "REQUEST-STATUS" values.

   The 1.xx "REQUEST-STATUS" codes are new.  This specification modifies
   item (2) of Section 3.6 of [RFC5546] by adding the following
   restriction:

      For a 1.xx code, all components MUST have exactly the same code.

   Definition of the new 1.xx codes is as follows:

3.2.9.1.  Status Code 1.0

   Status Code:  1.0

   Status Description:  Pending.

   Status Exception Data:  None.

   Description:  Delivery of the iTIP message is pending.

3.2.9.2.  Status Code 1.1

   Status Code:  1.1

   Status Description:  Sent.

   Status Exception Data:  None.

   Description:  The iTIP message has been sent, though no information
      about successful delivery is known.





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3.2.9.3.  Status Code 1.2

   Status Code:  1.2

   Status Description:  Delivered.

   Status Exception Data:  None.

   Description:  The iTIP message has been sent and delivered.

3.2.10.  Avoiding Conflicts when Updating Scheduling Object Resources

   Scheduling object resources on the server might change frequently as
   Attendees change their participation status, triggering updates to
   the Organizer, and refreshes of other Attendees' copies of the
   scheduling object resource.  This can lead to an "inconsequential"
   change to a calendar user's data - one that does not directly impact
   their own participation status.  When this occurs, clients have to
   reload calendar data and reconcile with changes being made by
   calendar users.  To avoid the need for this, the server can instead
   merge calendar data changes from a client with changes made as a the
   result of a scheduling operation carried out by some other calendar
   user.

   This specification introduces a new WebDAV resource property CALDAV:
   schedule-tag with a corresponding response header "Schedule-Tag", and
   a new "If-Schedule-Tag-Match" request header to allow client changes
   to be appropriately merged with server changes in the case where the
   changes on the server were the result of an "inconsequential"
   scheduling message update (one which simply updates the status
   information of Attendees due to a reply from another Attendee).

   Servers MUST automatically resolve conflicts with "inconsequential"
   changes done to scheduling object resources when the "If-Schedule-
   Tag-Match" request header is specified.  The If-Schedule-Tag-Match
   request header applies only to the Request-URI, and not to the
   Destination of a COPY or MOVE.

   A response to any successful GET or PUT request targeting a
   scheduling object resource MUST include a Schedule-Tag response
   header with the value set to the same value as the CALDAV:schedule-
   tag WebDAV property of the resource.

   A response to any successful COPY or MOVE request that specifies a
   Destination request header targeting a scheduling object resource
   MUST include a Schedule-Tag response header with the value set to the
   same value as the CALDAV:schedule-tag WebDAV property of the
   destination resource.



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   Clients SHOULD use the If-Schedule-Tag-Match header on requests that
   update scheduling object resources, instead of HTTP ETag-based
   precondition tests (e.g., If-Match).  Normal ETag-based precondition
   tests are used in all other cases, e.g., for synchronization.

   The value of the CALDAV:schedule-tag property changes according to
   these rules:

   o  For an Organizer's copy of a scheduling object resource:

      1.  The server MUST NOT change the CALDAV:schedule-tag property
          value when the scheduling object resource is updated as the
          result of automatically processing a scheduling message reply
          from an Attendee.  For instance, when an Attendee replies to
          the Organizer, the CALDAV:schedule-tag property is unchanged
          after the Organizer's scheduling object resource has been
          automatically updated by the server with the Attendee's new
          participation status.

      2.  The server MUST change CALDAV:schedule-tag property value when
          the scheduling object resource is changed directly via an HTTP
          request (e.g., PUT, COPY or MOVE).

   o  For an Attendee's copy of a scheduling object resource:

      1.  The server MUST change the CALDAV:schedule-tag property value
          when the scheduling object resource is changed as the result
          of processing a scheduling message update from an Organizer
          that contains changes other than just the participation status
          of Attendees.

      2.  The server MUST NOT change the CALDAV:schedule-tag property
          value when the scheduling object resource is changed as the
          result of processing a scheduling message update from an
          Organizer that only specify changes in the participation
          status of Attendees.  For instance, when Attendee "A" replies
          to Organizer "O", and Attendee "B" receives a scheduling
          message update from Organizer "O" with the new participation
          status of Attendee "A", the CALDAV:schedule-tag property of
          Attendee "B"s scheduling object resource would remain the
          same.

      3.  The server MUST change the CALDAV:schedule-tag property value
          when the scheduling object resource is changed directly via an
          HTTP request (e.g., PUT, COPY or MOVE).






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3.2.10.1.  PUT

   Clients MAY use the If-Schedule-Tag-Match request header to do a PUT
   request that ensures that "inconsequential" changes on the server do
   not result in a precondition error.  The value of the request header
   is set to the last Schedule-Tag value received for the resource being
   modified.  If the value of the If-Schedule-Tag-Match header matches
   the current value of the CALDAV:schedule-tag property the server MUST
   take any "ATTENDEE" property changes for all Attendees other than the
   owner of the scheduling object resource and apply those to the new
   resource being stored.  Otherwise, the server MUST fail the request
   with a 412 Precondition Failed status code.

3.2.10.2.  DELETE, COPY or MOVE

   Clients MAY use the If-Schedule-Tag-Match request header to do a
   DELETE, COPY or MOVE request that ensures that "inconsequential"
   changes on the server do not result in a precondition error.  The
   value of the request header is set to the last Schedule-Tag value
   received for the resource being deleted.  If the value of the If-
   Schedule-Tag-Match header matches the current value of the CALDAV:
   schedule-tag property the server performs the normal DELETE, COPY or
   MOVE request processing for the resource.  Otherwise, the server MUST
   fail the request with a 412 Precondition Failed status code.



























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4.  Processing Incoming Scheduling Messages

   Scheduling operations can cause the delivery of a scheduling message
   into an Organizer's or Attendee's scheduling Inbox collection.
   Servers MUST automatically process incoming scheduling messages using
   the rules defined by [RFC5546], by creating or updating the
   corresponding scheduling object resources on calendars owned by the
   owner of the scheduling Inbox collection.  In addition, the
   scheduling message is stored in the scheduling Inbox collection as an
   indicator to the client that a scheduling operation has taken place.
   Scheduling messages are typically removed from the scheduling Inbox
   collection by the client once the calendar user has acknowledged the
   change.

   The server MUST take into account privileges on the scheduling Inbox
   collection when processing incoming scheduling messages, to determine
   whether delivery of the scheduling message is allowed.  Privileges on
   calendars containing any matching scheduling object resource are not
   considered in this case (i.e., a schedule message from another user
   can cause modifications to resources in calendar collections that the
   other user would not normally have read or write access to).
   Additionally, servers MUST take into account any scheduling Inbox
   collection preconditions (see Section 2.2) when delivering the
   scheduling message, and it MUST take into account the similar
   preconditions on any calendar collection which contains, or would
   contain, the corresponding scheduling object resource.

4.1.  Processing Organizer Requests, Additions, and Cancellations

   For a scheduling message sent by an Organizer, the server first tries
   to locate a corresponding scheduling object resource belonging to the
   Attendee.  If no matching scheduling object resource exists, the
   server treats the scheduling message as a new message, otherwise it
   is treated as an update.

   In the case of a new message, the server processes the scheduling
   message and creates a new scheduling object resource as per
   Section 4.3.

   In the case of an update, the server processes the scheduling message
   and updates the matching scheduling object resource belonging to the
   Attendee to reflect the changes sent by the Organizer.

   In each case, the scheduling message MUST only appear in the
   Attendee's scheduling Inbox collection once all automatic processing
   has been done.





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4.2.  Processing Attendee Replies

   For a scheduling message reply sent by an Attendee, the server first
   locates the corresponding scheduling object resource belonging to the
   Organizer.  If the corresponding scheduling object resource cannot be
   found, the server SHOULD ignore the scheduling message.

   The server MUST then update the "PARTSTAT" iCalendar property
   parameter value of each "ATTENDEE" iCalendar property in the
   scheduling object resource to match the changes indicated in the
   reply (taking into account the fact that an Attendee could have
   created a new overridden iCalendar component to indicate different
   participation status on one or more instances of a recurring event).

   The server MUST also update or add the "SCHEDULE-STATUS" property
   parameter on each matching "ATTENDEE" iCalendar property and set its
   value to that of the "REQUEST-STATUS" property in the reply, or to
   "2.0" if "REQUEST-STATUS" is not present (also taking into account
   recurrence instances).  If there are multiple "REQUEST-STATUS"
   properties in the reply, the "SCHEDULE-STATUS" property parameter
   value is set to a comma-separated list of status codes, one from each
   "REQUEST-STATUS" property.

   The server SHOULD send scheduling messages to all the other Attendees
   indicating the change in participation status of the Attendee
   replying, subject to the recurrence requirements of Section 3.2.6.

   The scheduling message MUST only appear in the Organizer's scheduling
   Inbox collection once all automatic processing has been done.

4.3.  Default Calendar Collection

   The server processes scheduling messages received for an Attendee by
   creating a new scheduling object resource in a calendar collection
   belonging to the Attendee, when one does not already exist.  A
   calendar user that is an Attendee in a scheduling operation MUST have
   at least one valid calendar collection available.  If there is no
   valid calendar collection, then the server MUST reject the attempt to
   deliver the scheduling message to the Attendee.

   Servers MAY provide support for a default calendar collection, that
   is, the calendar collection in which new scheduling object resources
   will be created.  The CALDAV:schedule-default-calendar-URL WebDAV
   property, which can be present on the scheduling Inbox collection of
   a calendar user, specifies if this calendar user has a default
   calendar collection.  See Section 9.2.

   Servers SHOULD create new scheduling object resources in the default



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   calendar collection, if the CALDAV:schedule-default-calendar-URL
   WebDAV property is set.

   Servers MAY allow clients to change the default calendar collection
   by changing the value of the CALDAV:schedule-default-calendar-URL
   WebDAV property on the scheduling Inbox collection.  However, the
   server MUST ensure that any new value for that property refers to a
   valid calendar collection belonging to the owner of the scheduling
   Inbox collection.

   Servers MUST reject any attempt to delete the default calendar
   collection.

4.3.1.  Additional Method Preconditions

   This specification defines additional method preconditions (see
   Section 16 of WebDAV [RFC4918]) to provide machine-parseable
   information in error responses.

4.3.1.1.  CALDAV:default-calendar-needed Precondition

   Name:  default-calendar-needed

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

   Apply to:  DELETE

   Use with:  403 Forbidden

   Purpose:  (precondition) -- The client attempted to delete the
      calendar collection currently referenced by the CALDAV:schedule-
      default-calendar-URL property, or attempted to remove the CALDAV:
      schedule-default-calendar-URL property on the scheduling Inbox
      collection on a server that doesn't allow such operations.

   Definition:

     <!ELEMENT default-calendar-needed EMPTY>

4.3.1.2.  CALDAV:valid-schedule-default-calendar-URL Precondition

   Name:  valid-schedule-default-calendar-URL

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







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   Apply to:  PROPPATCH

   Use with:  403 Forbidden

   Purpose:  (precondition) -- The client attempted to set the CALDAV:
      schedule-default-calendar-URL property to a DAV:href element that
      doesn't reference a valid calendar collection.  Note: Servers that
      do not allow clients to change the CALDAV:schedule-default-
      calendar-URL property would simply return the DAV:cannot-modify-
      protected-property precondition defined in Section 16 of WebDAV
      [RFC4918].

   Definition:

     <!ELEMENT valid-schedule-default-calendar-URL EMPTY>




































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5.  Request for Busy Time Information

   Busy time information of one or more calendar users can be determined
   by submitting a POST request targeted at the scheduling Outbox
   collection of the calendar user requesting the information (the
   Organizer).  To accomplish this, the request body MUST contain a
   "VFREEBUSY" calendar component with the "METHOD" iCalendar property
   set to the value "REQUEST" as specified in Section 3.3.2 of iTIP
   [RFC5546].  The resource identified by the Request-URI MUST be a
   resource collection of type CALDAV:schedule-outbox (Section 2.1).
   The "ORGANIZER" property value in the "VFREEBUSY" component MUST
   match one of the calendar user addresses of the owner of the Outbox
   collection.

   A response to a busy time request that indicates status for one or
   more calendar users MUST be an XML document with a CALDAV:schedule-
   response XML element as its root element.  This element MUST contain
   one CALDAV:response element for each calendar user, with each of
   those containing elements that indicate which calendar user they
   correspond to, the scheduling status for that calendar user, any
   error codes and an optional description.  For a successful busy time
   request, a CALDAV:calendar-data element is also present for each
   calendar user, containing the actual busy time information (i.e., an
   iCalendar "VFREEBUSY" component).  See Section 10.1 for the detail on
   the child elements.  See Appendix B.5 for an example busy time
   request and response.

5.1.  Status Codes

   The list below summarizes the most common status codes used for this
   method.  However, clients need to be prepared to handle other 2/3/4/
   5xx series status codes as well.

      200 (OK) - The command succeeded.

      204 (No Content) - The command succeeded.

      400 (Bad Request) - The client has provided an invalid scheduling
      message.

      403 (Forbidden) - The client cannot submit a scheduling message to
      the specified Request-URI.

      404 (Not Found) - The URL in the Request-URI was not present.

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



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5.2.  Additional Method Preconditions

   The following are existing preconditions that are reused for the POST
   method on an Outbox collection.

   o  DAV:need-privileges [RFC3744]

   o  CALDAV:supported-calendar-data [RFC4791]

   o  CALDAV:valid-calendar-data [RFC4791]

   o  CALDAV:max-resource-size [RFC4791]

   The following are new method preconditions for the POST method on an
   Outbox collection.

5.2.1.  CALDAV:valid-scheduling-message Precondition

   Name:  valid-scheduling-message

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

   Apply to:  POST

   Use with:  400 Bad Request

   Purpose:  (precondition) -- The resource submitted in the POST
      request MUST obey all the restrictions specified in Section 3.3.2
      of iTIP [RFC5546].

   Definition:

     <!ELEMENT valid-scheduling-message EMPTY>

5.2.2.  CALDAV:valid-organizer Precondition

   Name:  valid-organizer

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

   Apply to:  POST

   Use with:  403 Forbidden

   Purpose:  (precondition) -- The "ORGANIZER" property value in the
      POST request's scheduling message MUST match one of the calendar
      user addresses of the owner of the scheduling Outbox collection
      being targeted by the request;



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   Definition:

     <!ELEMENT valid-organizer EMPTY>
















































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6.  Scheduling Privileges

   New scheduling privileges are defined in this section.  All the
   scheduling privileges MUST be non-abstract and MUST appear in the
   DAV:supported-privilege-set property of scheduling Outbox and Inbox
   collections on which they are defined.

   The tables specified in Appendix A clarify which scheduling methods
   (e.g., "REQUEST", "REPLY", etc.) are controlled by each scheduling
   privilege defined in this section.

6.1.  Privileges on Scheduling Inbox Collections

   This section defines new WebDAV ACL [RFC3744] privileges that are for
   use on scheduling Inbox collections.  These privileges determine
   whether delivery of scheduling messages from a calendar user is
   allowed by the calendar user who "owns" the scheduling Inbox
   collection.  This allows calendar users to choose which other
   calendar users can schedule with them.

   Note that when a scheduling message is delivered to a calendar user,
   in addition to a scheduling object resource being created in the
   calendar user's scheduling Inbox collection, a new scheduling object
   resource might be created or an existing one updated in a calendar
   belonging to the calendar user.  In that case, the ability to create
   or update the scheduling object resource in the calendar is
   controlled by the privileges assigned to the scheduling Inbox
   collection.

   The privileges defined in this section are ignored if applied to a
   resource other than a scheduling Inbox collection.

6.1.1.  CALDAV:schedule-deliver Privilege

   CALDAV:schedule-deliver is an aggregate privilege as per Section 6.3.


     <!ELEMENT schedule-deliver EMPTY>

6.1.2.  CALDAV:schedule-deliver-invite Privilege

   The CALDAV:schedule-deliver-invite privilege controls the processing
   and delivery of scheduling messages coming from an Organizer.


     <!ELEMENT schedule-deliver-invite EMPTY>





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6.1.3.  CALDAV:schedule-deliver-reply Privilege

   The CALDAV:schedule-deliver-reply privilege controls the processing
   and delivery of scheduling messages coming from an Attendee.


     <!ELEMENT schedule-deliver-reply EMPTY>

6.1.4.  CALDAV:schedule-query-freebusy Privilege

   The CALDAV:schedule-query-freebusy privilege controls freebusy
   requests targeted at the owner of the scheduling Inbox collection.


     <!ELEMENT schedule-query-freebusy EMPTY>

6.2.  Privileges on Scheduling Outbox Collections

   This section defines new WebDAV ACL [RFC3744] privileges that are
   defined for use on scheduling Outbox collections.  These privileges
   determine which calendar users are allowed to send scheduling
   messages on behalf of the calendar user who "owns" the scheduling
   Outbox collection.  This allows calendar users to choose other
   calendar users who can act on their behalf (e.g. assistants working
   on behalf of their boss).

   The privileges defined in this section are ignored if applied to a
   resource other than a scheduling Outbox collection.

6.2.1.  CALDAV:schedule-send Privilege

   CALDAV:schedule-send is an aggregate privilege as per Section 6.3.


     <!ELEMENT schedule-send EMPTY>

6.2.2.  CALDAV:schedule-send-invite Privilege

   The CALDAV:schedule-send-invite privilege controls the sending of
   scheduling messages by Organizers.

   Users granted the DAV:bind privilege on a calendar collection, or
   DAV:write privilege on scheduling object resources, will also need
   the CALDAV:schedule-send-invite privilege granted on the scheduling
   Outbox collection of the owner of the calendar collection or
   scheduling object resource in order to be allowed to create, modify
   or delete scheduling object resources in a way that will trigger the
   CalDAV server to deliver scheduling messages to attendees.



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     <!ELEMENT schedule-send-invite EMPTY>

6.2.3.  CALDAV:schedule-send-reply Privilege

   The CALDAV:schedule-send-reply privilege controls the sending of
   scheduling messages by Attendees.

   Users granted the DAV:bind privilege on a calendar collection, or
   DAV:write privilege on scheduling object resources, will also need
   the CALDAV:schedule-send-reply privilege granted on the scheduling
   Outbox collection of the owner of the calendar collection or
   scheduling object resource in order to be allowed to create, modify
   or delete scheduling object resources in a way that will trigger the
   CalDAV server to deliver scheduling message replies to the organizer.


     <!ELEMENT schedule-send-reply EMPTY>

6.2.4.  CALDAV:schedule-send-freebusy Privilege

   The CALDAV:schedule-send-freebusy privilege controls the use of the
   POST method to submit scheduling messages that specify the scheduling
   method "REQUEST" with a "VFREEBUSY" calendar component.


     <!ELEMENT schedule-send-freebusy EMPTY>

6.3.  Aggregation of Scheduling Privileges

   Server implementations MUST aggregate the scheduling privileges as
   follows:

      DAV:all contains CALDAV:schedule-send and CALDAV:schedule-deliver;

      CALDAV:schedule-send contains CALDAV:schedule-send-invite, CALDAV:
      schedule-send-reply, and CALDAV:schedule-send-freebusy;

      CALDAV:schedule-deliver contains CALDAV:schedule-deliver-invite,
      CALDAV:schedule-deliver-reply, and CALDAV:schedule-query-freebusy.

   The following diagram illustrates how scheduling privileges are
   aggregated according to the above requirements.









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   [DAV:all] (aggregate)
       |
       +-- [CALDAV:schedule-deliver] (aggregate)
       |      |
       |      +-- [CALDAV:schedule-deliver-invite]
       |      +-- [CALDAV:schedule-deliver-reply]
       |      +-- [CALDAV:schedule-query-freebusy]
       |
       +-- [CALDAV:schedule-send] (aggregate)
              |
              +-- [CALDAV:schedule-send-invite]
              +-- [CALDAV:schedule-send-reply]
              +-- [CALDAV:schedule-send-freebusy]






































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7.  Additional iCalendar Property Parameters

   This specification defines additional iCalendar property parameters
   to support the CalDAV scheduling extensions.

7.1.  Schedule Agent Parameter

   Parameter Name:  SCHEDULE-AGENT

   Purpose:  To specify the agent expected to deliver scheduling
      messages to the corresponding Organizer or Attendee.

   Format Definition:  This property parameter is defined by the
      following notation:

     scheduleagentparam = "SCHEDULE-AGENT" "="
                      ("SERVER"      ; The server handles scheduling
                     / "CLIENT"      ; The client handles scheduling
                     / "NONE"        ; No scheduling
                     / x-name        ; Experimental type
                     / iana-token)   ; Other IANA registered type
     ;
     ; If the parameter is not present its value defaults to SERVER.
     ; "x-name" and "iana-token" are defined in Section 3.1 of
     ; [RFC5545].

   Description:  This property parameter MAY be specified on "ORGANIZER"
      or "ATTENDEE" iCalendar properties.  In the absence of this
      parameter, the value "SERVER" MUST be used for the default
      behavior.  The value determines whether or not a scheduling
      operation on a server will cause a scheduling message to be sent
      to the corresponding calendar user identified by the "ORGANIZER"
      or "ATTENDEE" property value.  When the value "SERVER" is
      specified, or the parameter is absent, then it is the server's
      responsibility to send a scheduling message as part of a
      scheduling operation.  When the value "CLIENT" is specified, that
      indicates that the client is handling scheduling messages with the
      calendar user itself.  When "NONE" is specified, no scheduling
      messages are being sent to the calendar user.

      Servers MUST NOT include this parameter in any scheduling messages
      sent as the result of a scheduling operation.

      Clients MUST NOT include this parameter in any scheduling messages
      that they themselves send.






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      The parameter value MUST be the same on every "ORGANIZER" property
      in a scheduling object resource.

      The parameter value MUST be the same on each "ATTENDEE" property
      whose values match in a scheduling object resource.

      Servers and clients MUST treat x-name and iana-token values they
      do not recognize the same way as they would the "NONE" value.

   Example:

     ORGANIZER;SCHEDULE-AGENT=SERVER:mailto:bernard@example.com
     ATTENDEE;SCHEDULE-AGENT=NONE:mailto:cyrus@example.com

7.2.  Schedule Force Send Parameter

   Parameter Name:  SCHEDULE-FORCE-SEND

   Purpose:  To force a scheduling message to be sent to the calendar
      user specified by the property.

   Format Definition:  This property parameter is defined by the
      following notation:

     scheduleforcesendparam = "SCHEDULE-FORCE-SEND" "="
                            ("REQUEST"    ; Force a "REQUEST"
                           / "REPLY"      ; Force a "REPLY"
                           / iana-token)
     ;
     ; "iana-token" is defined in Section 3.1 of [RFC5545]. Its value
     ; MUST be an IANA registered iCalendar "METHOD" property value.

   Description:  This property parameter MAY be specified on "ATTENDEE"
      and "ORGANIZER" properties on which the "SCHEDULE-AGENT" property
      parameter is set to the value "SERVER" or is not specified.  This
      property parameter is used to force a server to send a scheduling
      message to a specific calendar user in situations where the server
      would not send a scheduling message otherwise (e.g., when no
      change that warrants the delivery of a new scheduling message was
      performed on the scheduling object resource).  An Organizer MAY
      specify this parameter on an "ATTENDEE" property with the value
      "REQUEST" to force a "REQUEST" scheduling message to be sent to
      this Attendee.  An Attendee MAY specify this parameter on the
      "ORGANIZER" with the value "REPLY" to force a "REPLY" scheduling
      message to be sent to the Organizer.






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      Servers MUST NOT preserve this property parameter in scheduling
      object resources, nor include it in any scheduling messages sent
      as the result of a scheduling operation.

      Clients MUST NOT include this parameter in any scheduling messages
      that they themselves send.

      Servers MUST set the "SCHEDULE-STATUS" parameter of the "ATTENDEE"
      or "ORGANIZER" to 2.3 (i.e., "Success, invalid property parameter
      ignored", see Section 3.6 of [RFC5546]) when the "SCHEDULE-FORCE-
      SEND" parameter is set to an iana-token value they do not
      recognize.

   Example:

     ORGANIZER;SCHEDULE-FORCE-SEND=REPLY:mailto:cyrus@example.com
     ATTENDEE;SCHEDULE-FORCE-SEND=REQUEST:mailto:bernard@example.com

7.3.  Schedule Status Parameter

   Parameter Name:  SCHEDULE-STATUS

   Purpose:  To specify the status codes returned from processing of the
      most recent scheduling message sent to the corresponding Attendee,
      or received from the corresponding Organizer.

   Format Definition:  This property parameter is defined by the
      following notation:

     schedulestatusparam = "SCHEDULE-STATUS" "="
                         ( statcode
                        / DQUOTE statcode *("," statcode) DQUOTE)
     ;
     ; "statcode" is defined in Section 3.8.8.3 of [RFC5545]. Value
     ; is a single "statcode" or a comma-separated list of "statcode"
     ; values.

   Description:  This property parameter MAY be specified on the
      "ATTENDEE" and "ORGANIZER" properties.

      Servers MUST only add or change this property parameter on any
      "ATTENDEE" properties corresponding to calendar users who were
      sent a scheduling message via a scheduling operation.  Clients
      SHOULD NOT change or remove this parameter if it was provided by
      the server.  In the case where the client is handling the
      scheduling, the client MAY add, change or remove this parameter to
      indicate the last scheduling message status it received.




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      Servers MUST add this parameter to any "ORGANIZER" properties
      corresponding to calendar users who were sent a scheduling message
      reply by an Attendee via a scheduling operation.  Clients SHOULD
      NOT change or remove this parameter if it was provided by the
      server.  In the case where the client is handling the scheduling,
      the client MAY add, change or remove this parameter to indicate
      the last scheduling message status it received.

      Servers MUST NOT include this parameter in any scheduling messages
      sent as the result of a scheduling operation.

      Clients MUST NOT include this parameter in any scheduling messages
      that they themselves send.

      Values for this property parameter are described in Section 3.2.9.

   Example:

     ATTENDEE;SCHEDULE-STATUS="2.0":mailto:bernard@example.com
     ATTENDEE;SCHEDULE-STATUS="2.0,2.4":mailto:cyrus@example.com































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8.  Additional Message Header Fields

   This specification defines additional HTTP request and response
   headers for use with CalDAV.

8.1.  Schedule-Reply Request Header


     Schedule-Reply = "Schedule-Reply" ":" ("T" | "F")

   Example:

     Schedule-Reply: F

   When an Attendee removes a scheduling object resource as per
   Section 3.2.2.4, and the Schedule-Reply header is not present, or
   present and set to the value "T" (true), the server MUST send an
   appropriate reply scheduling message with the Attendee's "PARTSTAT"
   iCalendar property parameter value set to "DECLINED" as part of its
   normal scheduling operation processing.

   When the Schedule-Reply header is set to the value "F" (false), the
   server MUST NOT send a scheduling message as part of its normal
   scheduling operation processing.

   The Schedule-Reply request header is used by a client to indicate to
   a server whether or not a scheduling operation ought to occur when an
   Attendee deletes a scheduling object resource.  In particular it
   controls whether a reply scheduling message is sent to the Organizer
   as a result of the removal.  There are situations in which
   unsolicited scheduling messages need to be silently removed (or
   ignored) for security or privacy reasons.  This request header allows
   the scheduling object resource to be removed if such a need arises.

8.2.  Schedule-Tag Response Header

   The Schedule-Tag response header provides the current value of the
   CALDAV:schedule-tag property value.  The behavior of this response
   header is described in Section 3.2.10.

   All scheduling object resources MUST support the Schedule-Tag header.

     Schedule-Tag = "Schedule-Tag" ":" opaque-tag
     ; "opaque-tag" is defined in Section 3.11 of [RFC2616]







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   Example:

     Schedule-Tag: "12ab34-cd56ef"

8.3.  If-Schedule-Tag-Match Request Header

   The If-Schedule-Tag-Match request header field is used with a method
   to make it conditional.  Clients can set this header to the value
   returned in the Schedule-Tag response header, or the CALDAV:schedule-
   tag property, of a scheduling object resource previously retrieved
   from the server to avoid overwriting "consequential" changes to the
   scheduling object resource.

   All scheduling object resources MUST support the If-Schedule-Tag-
   Match header.

     If-Schedule-Tag-Match = "If-Schedule-Tag-Match" ":" opaque-tag
     ; "opaque-tag" is defined in Section 3.11 of [RFC2616]

   Example:

     If-Schedule-Tag-Match: "12ab34-cd56ef"





























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9.  Additional WebDAV Properties

   This specification defines the following new WebDAV properties for
   use with CalDAV.

9.1.  CALDAV:schedule-calendar-transp Property

   Name:  schedule-calendar-transp

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

   Purpose:  Determines whether the calendar object resources in a
      calendar collection will affect the owner's busy time information.

   Protected:  This property MAY be protected and SHOULD NOT be returned
      by a PROPFIND allprop request (as defined in Section 14.2 of
      [RFC4918]).

   COPY/MOVE behavior:  This property value SHOULD be kept during a MOVE
      operation, and SHOULD be copied and preserved in a COPY.

   Description:  This property SHOULD be defined on all calendar
      collections.  If present, it contains one of two XML elements that
      indicate whether the calendar object resources in the calendar
      collection ought to contribute to the owner's busy time.  When the
      CALDAV:opaque element is used, all calendar object resources in
      the corresponding calendar collection MUST contribute to busy
      time, assuming access privileges and other iCalendar properties
      allow it to.  When the CALDAV:transparent XML element is used, the
      calendar object resources in the corresponding calendar collection
      MUST NOT contribute to busy time.

      If this property is not present on a calendar collection, then the
      default value CALDAV:opaque MUST be assumed.

   Definition:

     <!ELEMENT schedule-calendar-transp (opaque | transparent)>

     <!ELEMENT opaque EMPTY>
     <!-- Affect busy time searches -->

     <!ELEMENT transparent EMPTY>
     <!-- Invisible to busy time searches -->







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   Example:

     <C:schedule-calendar-transp
          xmlns:C="urn:ietf:params:xml:ns:caldav">
       <C:opaque/>
     </C:schedule-calendar-transp>

9.2.  CALDAV:schedule-default-calendar-URL Property

   Name:  schedule-default-calendar-URL

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

   Purpose:  Specifies a default calendar for an Attendee where new
      scheduling object resources are created.

   Protected:  This property MAY be protected in the case where a server
      does not support changing the default calendar, or does not
      support a default calendar.

   COPY/MOVE behavior:  This property is only defined on a scheduling
      Inbox collection which cannot be moved or copied.

   Description:  This property MAY be defined on a scheduling Inbox
      collection.  If present, it contains zero or one DAV:href XML
      elements.  When a DAV:href element is present, its value indicates
      a URL to a calendar collection that is used as the default
      calendar.  When no DAV:href element is present, it indicates that
      there is no default calendar.  In the absence of this property
      there is no default calendar.  When there is no default calendar
      the server is free to choose the calendar in which a new
      scheduling object resource is created.  See Section 4.3.

   Definition:

     <!ELEMENT schedule-default-calendar-URL (DAV:href?)>

   Example:

     <C:schedule-default-calendar-URL xmlns:D="DAV:"
         xmlns:C="urn:ietf:params:xml:ns:caldav">
       <D:href>/home/cyrus/calendars/work/</D:href>
     </C:schedule-default-calendar-URL>








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9.3.  CALDAV:schedule-tag Property

   Name:  schedule-tag

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

   Purpose:  Indicates whether a scheduling object resource has had a
      "consequential" change made to it.

   Value:  opaque-tag (defined in Section 3.11 of [RFC2616])

   Protected:  This property MUST be protected as only the server can
      update the value.

   COPY/MOVE behavior:  This property value is determined by the server
      and MAY be different from the value on source resource.

   Description:  The CALDAV:schedule-tag property MUST be defined on all
      scheduling object resources.  This property is described in
      Section 3.2.10.

   Definition:

     <!ELEMENT schedule-tag (#PCDATA)>

   Example:

     <C:schedule-tag xmlns:C="urn:ietf:params:xml:ns:caldav"
     >"12345-67890"</C:schedule-tag>






















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10.  XML Element Definitions

10.1.  CALDAV:schedule-response XML Element

   Name:  schedule-response

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

   Purpose:  Contains the set of responses for a POST method request.

   Description:  See Section 5.

   Definition:

     <!ELEMENT schedule-response (response*)>

10.2.  CALDAV:response XML Element

   Name:  response

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

   Purpose:  Contains a single response for a POST method request.

   Description:  See Section 5.

   Definition:

     <!ELEMENT response (recipient,
                         request-status,
                         calendar-data?,
                         DAV:error?,
                         DAV:responsedescription?)>

     <!-- CALDAV:calendar-data is defined in Section 9.6 of
     RFC 4791 and when used here uses the definition with
     content (#PCDATA) only -->

10.3.  CALDAV:recipient XML Element

   Name:  recipient

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

   Purpose:  The calendar user address that the enclosing response for a
      POST method request is for.





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   Description:  See Section 5.

   Definition:

     <!ELEMENT recipient (DAV:href)>

10.4.  CALDAV:request-status XML Element

   Name:  request-status

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

   Purpose:  The iTIP "REQUEST-STATUS" property value for this response.

   Description:  See Section 5.

   Definition:

     <!ELEMENT request-status (#PCDATA)>
































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11.  Security Considerations

   The process of scheduling involves the sending and receiving of
   scheduling messages.  As a result, the security problems related to
   messaging in general are relevant here.  In particular the
   authenticity of the scheduling messages needs to be verified.
   Servers and clients MUST use an HTTP connection protected with TLS as
   defined in [RFC2818] for all scheduling operations.  Clients MUST use
   the procedures detailed in Section 6 of [RFC6125] to verify the
   authenticity of the server.  Servers MUST make use of HTTP
   authentication [RFC2617] to verify the authenticity of the calendar
   user for whom the client is sending requests.

11.1.  Preventing Denial of Service Attacks

   Servers MUST ensure that clients cannot consume excessive server
   resources by carrying out "large" scheduling operations.  In
   particular, servers SHOULD enforce CALDAV:max-resource-size, CALDAV:
   max-instances and CALDAV:max-attendees-per-instance pre-conditions as
   applicable for scheduling Inbox and Outbox collections.

11.2.  Verifying Scheduling Operations

   When handling a scheduling operation:

   1.  Servers MUST verify that the principal associated with the DAV:
       owner of the calendar collection in which a scheduling object
       resource is being manipulated contains a CALDAV:schedule-outbox-
       URL property value.

   2.  Servers MUST verify that the currently authenticated user has the
       CALDAV:schedule-send privilege, or a sub-privilege aggregated
       under this privilege, on the scheduling Outbox collection of the
       DAV:owner of the calendar collection in which a scheduling object
       resource is being manipulated.

   3.  Servers MUST only deliver scheduling messages to recipients when
       the CALDAV:schedule-deliver privilege, or a sub-privilege
       aggregated under this privilege, is granted on the recipient's
       scheduling Inbox collection for the principal associated with the
       DAV:owner of the calendar collection in which a scheduling object
       resource is being manipulated.

   4.  To prevent impersonation of calendar users, the server MUST
       verify that the "ORGANIZER" property in an organizer scheduling
       object resource matches one of the calendar user addresses of the
       DAV:owner of the calendar collection in which the resource is
       stored.



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   5.  To prevent spoofing of an existing scheduling object resource,
       servers MUST verify that the "UID" iCalendar property value in a
       new scheduling object resource does not match that of an existing
       scheduling object resource with a different "ORGANIZER" property
       value.

11.3.  Verifying Busy Time Information Requests

   When handling a POST request on a scheduling Outbox collection:

   1.  Servers MUST verify that the principal associated with the
       calendar user address specified in the "ORGANIZER" property of
       the scheduling message data in the request contains a CALDAV:
       schedule-outbox-URL property value that matches the scheduling
       Outbox collection targeted by the request.

   2.  Servers MUST verify that the currently authenticated user has the
       CALDAV:schedule-send privilege, or a sub-privilege aggregated
       under this privilege, on the scheduling Outbox collection
       targeted by the request.

   3.  Servers MUST only return valid freebusy information for
       recipients when the CALDAV:schedule-deliver privilege, or a sub-
       privilege aggregated under this privilege, is granted on the
       recipient's scheduling Inbox collection for the principal
       associated with the DAV:owner of the scheduling Outbox collection
       targeted by the request.

11.4.  Privacy Issues

   This specification only defines how calendar users on the same server
   are able to schedule with each other - unauthenticated users have no
   way to carry out scheduling operations.  Access control privileges
   (as per Section 6) can control which of those users can schedule with
   others.  Calendar users not wishing to expose their calendar
   information to other users can do so by denying privileges to
   specific users, or all users, for all scheduling operations, or
   perhaps only freebusy.

   Attendees can also use the Schedule-Reply request header
   (Section 8.1) with the value set to "F" to prevent notification to an
   Organizer that a scheduling object resource was deleted.  This allows
   Attendees to remove unwanted scheduling messages without any response
   to the Organizer.

   Servers MUST NOT expose any private iCalendar data, or WebDAV
   resource state information (URLs, WebDAV properties, etc) for one
   calendar user to another via scheduling messages or error responses



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   to scheduling operations.  In particular, as per Section 8.1 of
   [RFC4918], authorization errors MUST take preference over other
   errors.

11.5.  Mitigation of iTIP Threats

   Section 6.1 of iTIP [RFC5546] defines a set of potential threats in a
   scheduling system, and in Section 6.2 defines recommendations on how
   those can be addressed in protocols using iTIP.  This specification
   addresses the iTIP threats in the following manner:

   Spoofing the Organizer  Addressed by item 4 in Section 11.2.

   Spoofing the Attendee  Addressed by item 2 in Section 11.2 and
      Section 3.2.2.1.

   Unauthorized Replacement of the Organizer  Addressed by item 5 in
      Section 11.2.

   Eavesdropping and Data Integrity  Addressed by requiring TLS.

   Flooding a Calendar  Addressed by requirements in Section 11.1

   Unauthorized REFRESH Requests  This specification does not support
      the REFRESH method.


























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12.  IANA Considerations

12.1.  Message Header Field Registrations

   The message header fields below are to be added to the Permanent
   Message Header Field Registry (see [RFC3864]).

12.1.1.  Schedule-Reply

   Header field name: Schedule-Reply

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document(s): this specification (Section 8.1)

   Related information: none

12.1.2.  Schedule-Tag

   Header field name: Schedule-Tag

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document(s): this specification (Section 8.2)

   Related information: none

12.1.3.  If-Schedule-Tag-Match

   Header field name: If-Schedule-Tag-Match

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document(s): this specification (Section 8.3)

   Related information: none



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12.2.  iCalendar Property Parameter Registrations

   The following iCalendar property parameters are to be added to the
   iCalendar Property Parameter Registry defined in Section 8.3.3 of
   [RFC5545].

         +---------------------+---------+-----------------------+
         | Parameter           | Status  | Reference             |
         +---------------------+---------+-----------------------+
         | SCHEDULE-AGENT      | Current | RFC XXXX, Section 7.1 |
         |                     |         |                       |
         | SCHEDULE-STATUS     | Current | RFC XXXX, Section 7.3 |
         |                     |         |                       |
         | SCHEDULE-FORCE-SEND | Current | RFC XXXX, Section 7.2 |
         +---------------------+---------+-----------------------+

12.3.  iCalendar REQUEST-STATUS Value Registrations

   The following iCalendar "REQUEST-STATUS" values are to be added to
   the iCalendar REQUEST-STATUS Value Registry defined in Section 7.3 of
   [RFC5546].

           +-------------+---------+---------------------------+
           | Status Code | Status  | Reference                 |
           +-------------+---------+---------------------------+
           | 1.0         | Current | RFC XXXX, Section 3.2.9.1 |
           |             |         |                           |
           | 1.1         | Current | RFC XXXX, Section 3.2.9.2 |
           |             |         |                           |
           | 1.2         | Current | RFC XXXX, Section 3.2.9.3 |
           +-------------+---------+---------------------------+

12.4.  Additional iCalendar Elements Registries

   This specification adds two new IANA registries for iCalendar
   elements.  Additional codes MAY be used, provided the process
   described in Section 8.2.1 of [RFC5545] is used to register them.

12.4.1.  Schedule Agent Values Registry

   The following table has been used to initialize the schedule agent
   values registry.









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           +----------------+---------+-----------------------+
           | Schedule Agent | Status  | Reference             |
           +----------------+---------+-----------------------+
           | SERVER         | Current | RFC XXXX, Section 7.1 |
           |                |         |                       |
           | CLIENT         | Current | RFC XXXX, Section 7.1 |
           |                |         |                       |
           | NONE           | Current | RFC XXXX, Section 7.1 |
           +----------------+---------+-----------------------+

12.4.2.  Schedule Force Send Values Registry

   The following table has been used to initialize the schedule send
   values registry.

         +---------------------+---------+-----------------------+
         | Schedule Force Send | Status  | Reference             |
         +---------------------+---------+-----------------------+
         | REQUEST             | Current | RFC XXXX, Section 7.2 |
         |                     |         |                       |
         | REPLY               | Current | RFC XXXX, Section 7.2 |
         +---------------------+---------+-----------------------+





























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13.  Acknowledgements

   The authors would like to thank the following individuals for
   contributing their ideas and support for writing this specification:
   Mike Douglass, Lisa Dusseault, Red Dutta, Jacob Farkas, Jeffrey
   Harris, Helge Hess, Eliot Lear, Andrew McMillan, Alexey Melnikov,
   Arnaud Quillaud, Julian F. Reschke, Wilfredo Sanchez Vega, Simon
   Vaillancourt.

   The authors would also like to thank the Calendaring and Scheduling
   Consortium for advice with this specification, and for organizing
   interoperability testing events to help refine it.







































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14.  References

14.1.  Normative References

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

   [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.

   [RFC2617]               Franks, J., Hallam-Baker, P., Hostetler, J.,
                           Lawrence, S., Leach, P., Luotonen, A., and L.
                           Stewart, "HTTP Authentication: Basic and
                           Digest Access Authentication", RFC 2617,
                           June 1999.

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

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

   [RFC3864]               Klyne, G., Nottingham, M., and J. Mogul,
                           "Registration Procedures for Message Header
                           Fields", BCP 90, RFC 3864, September 2004.

   [RFC4791]               Daboo, C., Desruisseaux, B., and L.
                           Dusseault, "Calendaring Extensions to WebDAV
                           (CalDAV)", RFC 4791, March 2007.

   [RFC4918]               Dusseault, L., "HTTP Extensions for Web
                           Distributed Authoring and Versioning
                           (WebDAV)", RFC 4918, June 2007.

   [RFC5234]               Crocker, D. and P. Overell, "Augmented BNF
                           for Syntax Specifications: ABNF", STD 68,
                           RFC 5234, January 2008.

   [RFC5545]               Desruisseaux, B., "Internet Calendaring and
                           Scheduling Core Object Specification
                           (iCalendar)", RFC 5545, September 2009.

   [RFC5546]               Daboo, C., "iCalendar Transport-Independent



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                           Interoperability Protocol (iTIP)", RFC 5546,
                           December 2009.

   [RFC6125]               Saint-Andre, P. and J. Hodges,
                           "Representation and Verification of Domain-
                           Based Application Service Identity within
                           Internet Public Key Infrastructure Using
                           X.509 (PKIX) Certificates in the Context of
                           Transport Layer Security (TLS)", RFC 6125,
                           March 2011.

   [W3C.REC-xml-20081126]  Yergeau, F., Paoli, J., Sperberg-McQueen, C.,
                           Maler, E., and T. Bray, "Extensible Markup
                           Language (XML) 1.0 (Fifth Edition)", World
                           Wide Web Consortium Recommendation REC-xml-
                           20081126, November 2008,
                           <http://www.w3.org/TR/2008/REC-xml-20081126>.

14.2.  Informative References

   [RFC6047]               Melnikov, A., "iCalendar Message-Based
                           Interoperability Protocol (iMIP)", RFC 6047,
                           December 2010.




























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Appendix A.  Scheduling Privileges Summary

A.1.  Scheduling Inbox Privileges

   The following tables specify which scheduling privileges grant the
   right to a calendar user to deliver a scheduling message to the
   scheduling Inbox collection of another calendar user.  The
   appropriate behavior depends on the calendar component type as well
   as the scheduling "METHOD" specified in the scheduling message.

                                 +--------------------------------+
                                 |  METHOD for VEVENT and VTODO   |
   +-----------------------------+---------+-------+-----+--------+
   | Scheduling Inbox Privilege  | REQUEST | REPLY | ADD | CANCEL |
   +-----------------------------+---------+-------+-----+--------+
   | schedule-deliver            |    *    |   *   |  *  |   *    |
   |   schedule-deliver-invite   |    *    |       |  *  |   *    |
   |   schedule-deliver-reply    |         |   *   |     |        |
   |   schedule-query-freebusy   |         |       |     |        |
   +-----------------------------+---------+-------+-----+--------+


                                 +----------------------+
                                 | METHOD for VFREEBUSY |
   +-----------------------------+----------------------+
   | Scheduling Inbox Privilege  |       REQUEST        |
   +-----------------------------+----------------------+
   | schedule-deliver            |          *           |
   |   schedule-deliver-invite   |                      |
   |   schedule-deliver-reply    |                      |
   |   schedule-query-freebusy   |          *           |
   +-----------------------------+----------------------+

A.2.  Scheduling Outbox Privileges

   The following tables specify which scheduling privileges grant the
   right to a calendar user to perform busy time information requests
   and to submit scheduling messages to other calendar users as the
   result of a scheduling operation.  The appropriate behavior depends
   on the calendar component type as well as the scheduling "METHOD"
   specified in the scheduling message.










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                                 +--------------------------------+
                                 |  METHOD for VEVENT and VTODO   |
   +-----------------------------+---------+-------+-----+--------+
   | Scheduling Outbox Privilege | REQUEST | REPLY | ADD | CANCEL |
   +-----------------------------+---------+-------+-----+--------+
   | schedule-send               |    *    |   *   |  *  |   *    |
   |   schedule-send-invite      |    *    |       |  *  |   *    |
   |   schedule-send-reply       |         |   *   |     |        |
   |   schedule-send-freebusy    |         |       |     |        |
   +-----------------------------+---------+-------+-----+--------+


                                 +----------------------+
                                 | METHOD for VFREEBUSY |
   +-----------------------------+----------------------+
   | Scheduling Outbox Privilege |       REQUEST        |
   +-----------------------------+----------------------+
   | schedule-send               |          *           |
   |   schedule-send-invite      |                      |
   |   schedule-send-reply       |                      |
   |   schedule-send-freebusy    |          *           |
   +-----------------------------+----------------------+





























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Appendix B.  Example Scheduling Operations

   This section describes some example scheduling operations that give a
   general idea of how scheduling is carried out between CalDAV clients
   and servers from the perspective of meeting Organizers and Attendees.

   The server is assumed to be hosted in the "example.com" domain, and
   users whose email address is at the "example.com" domain are assumed
   to be hosted by the server.  In addition, the email addresses in the
   "example.net" domain are also valid email addresses for calendar
   users hosted by the server.  Calendar users with an email address at
   the "example.org" domain are assumed to not be hosted by the server.

   In the following examples the requests and responses are incomplete
   and are only for illustrative purposes.  In particular, HTTP
   authentication headers and behaviors are not shown, even though they
   are required in normal operation.

B.1.  Example: Organizer Inviting Multiple Attendees

   In the following example, Cyrus invites Wilfredo, Bernard and Mike to
   a single instance event by simply creating a new scheduling object
   resource in one of his calendar collections by using the PUT method.




























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   >> Request <<

   PUT /home/cyrus/calendars/work/9263504FD3AD.ics HTTP/1.1
   Host: cal.example.com
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx
   If-None-Match: *

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090602T185254Z
   DTSTART:20090602T160000Z
   DTEND:20090602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com
   ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
    =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@
    example.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
    ample.net
   ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
    CTION;RSVP=TRUE:mailto:mike@example.org
   END:VEVENT
   END:VCALENDAR

   >> Response <<

   HTTP/1.1 201 Created
   Content-Length: 0
   Date: Tue, 02 Jun 2009 18:52:54 GMT
   Last-Modified: Tue, 02 Jun 2009 18:52:54 GMT
   ETag: "d85561cfe74a4e785eb4639451b434fb"
   Schedule-Tag: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"

   Once the event creation has been completed, Cyrus's client will
   retrieve the event back from the server to get the schedule status of
   each Attendee, as well as record the Schedule-Tag value for future
   use.  In this example, the server reports that a scheduling message
   was delivered to Wilfredo, a scheduling message is still pending for
   Bernard, and the server was unable to deliver a scheduling message to



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   Mike.

   >> Request <<

   GET /home/cyrus/calendars/work/9263504FD3AD.ics HTTP/1.1
   Host: cal.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Date: Tue, 02 Jun 2009 18:52:58 GMT
   Last-Modified: Tue, 02 Jun 2009 18:52:58 GMT
   ETag: "eb897deabc8939589da116714bc99265"
   Schedule-Tag: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Server//EN
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090602T185300Z
   DTSTART:20090602T160000Z
   DTEND:20090602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com
   ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
    =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=
    1.2:mailto:wilfredo@e
    xample.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=
    1.0:mailto:bernard@example.net
   ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
    CTION;RSVP=TRUE;SCHEDULE-STATUS=3.7:mailto:mike@example.org
   END:VEVENT
   END:VCALENDAR

B.2.  Example: Attendee Receiving an Invitation

   In the following example, Wilfredo's client retrieves and deletes the
   new scheduling message that appeared in his scheduling Inbox
   collection after the server automatically processed it and created a



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   new scheduling object resource in his default calendar collection.

   >> Request <<

   GET /home/wilfredo/calendars/inbox/27d93fc0a58c.ics HTTP/1.1
   Host: cal.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Date: Tue, 02 Jun 2009 18:59:58 GMT
   Last-Modified: Tue, 02 Jun 2009 18:59:58 GMT
   ETag: "da116714bc9926c89395895eb897deab"
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Server//EN
   METHOD:REQUEST
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090602T185254Z
   DTSTART:20090602T160000Z
   DTEND:20090602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com
   ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
    =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@
    example.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
    ample.net
   ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
    CTION;RSVP=TRUE:mailto:mike@example.org
   END:VEVENT
   END:VCALENDAR

   >> Request <<

   DELETE /home/wilfredo/calendars/inbox/27d93fc0a58c.ics HTTP/1.1
   Host: cal.example.com





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   >> Response <<

   HTTP/1.1 204 No Content
   Date: Tue, 02 Jun 2009 20:40:36 GMT

B.3.  Example: Attendee Replying to an Invitation

   In the following example, Wilfredo accepts Cyrus's invitation and
   sets an alarm reminder on the event.  It uses the If-Schedule-Tag-
   Match precondition behavior to ensure it does not overwrite any
   significant changes from the organizer that might have occurred after
   it retrieved the initial resource data.







































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   >> Request <<

   PUT /home/wilfredo/calendars/work/BB64861C2228.ics HTTP/1.1
   Host: cal.example.com
   If-Schedule-Tag-Match: "e78f23ed-0188-4bab-938d-2aeb3324c7e8"
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090602T185254Z
   DTSTART:20090602T160000Z
   DTEND:20090602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com
   ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
    =ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@exam
    ple.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
    ample.net
   ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
    CTION;RSVP=TRUE:mailto:mike@example.org
   BEGIN:VALARM
   TRIGGER:-PT15M
   ACTION:DISPLAY
   DESCRIPTION:Reminder
   END:VALARM
   END:VEVENT
   END:VCALENDAR

   >> Response <<

   HTTP/1.1 200 OK
   Content-Length: 0
   Date: Tue, 02 Jun 2009 18:57:54 GMT
   Last-Modified: Tue, 02 Jun 2009 18:57:54 GMT
   ETag: "eb4639451b434fbd85561cfe74a4e785"
   Schedule-Tag: "8893ee45-eb9d-428f-b53c-c777daf19e41"

   Once the event modification has been completed, Wilfredo's client



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   will retrieve the event back from the server to get the schedule
   status of the Organizer.

   >> Request <<

   GET /home/wilfredo/calendars/work/BB64861C2228.ics HTTP/1.1
   Host: cal.example.com












































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   >> Response <<

   HTTP/1.1 200 OK
   Date: Tue, 02 Jun 2009 19:03:03 GMT
   Last-Modified: Tue, 02 Jun 2009 19:02:21 GMT
   ETag: "5eb897deabda116714bc9926c8939589"
   Schedule-Tag: "8893ee45-eb9d-428f-b53c-c777daf19e41"
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090602T190221Z
   DTSTART:20090602T160000Z
   DTEND:20090602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Cyrus Daboo";SCHEDULE-STATUS=1.2:mailto:cyrus@ex
    ample.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com
   ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
    =ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@exam
    ple.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
    ample.net
   ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
    CTION;RSVP=TRUE:mailto:mike@example.org
   BEGIN:VALARM
   TRIGGER:-PT15M
   ACTION:DISPLAY
   DESCRIPTION:Reminder
   END:VALARM
   END:VEVENT
   END:VCALENDAR

B.4.  Example: Organizer Receiving a Reply to an Invitation

   On reception of Wilfredo's reply, Cyrus's server will automatically
   update Cyrus's scheduling object resource, make Wilfredo's scheduling
   message available in Cyrus's scheduling Inbox collection, and deliver
   an updated scheduling message to Bernard to share Wilfredo's updated
   participation status.  In this example, Cyrus's client retrieves and



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   deletes this scheduling message in his scheduling Inbox collection.

   >> Request <<

   GET /home/cyrus/calendars/inbox/c0a58c27d93f.ics HTTP/1.1
   Host: cal.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Date: Tue, 02 Jun 2009 19:05:02 GMT
   Last-Modified: Tue, 02 Jun 2009 19:04:20 GMT
   ETag: "9265eb897deabc8939589da116714bc9"
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Server//EN
   METHOD:REPLY
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090602T185754Z
   DTSTART:20090602T160000Z
   DTEND:20090602T170000Z
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Wilfredo Sanchez Vega";PARTSTAT=ACCEPTED:mailto:w
    ilfredo@example.com
   REQUEST-STATUS:2.0;Success
   END:VEVENT
   END:VCALENDAR

   >> Request <<

   DELETE /home/cyrus/calendars/inbox/c0a58c27d93f.ics HTTP/1.1
   Host: cal.example.com

   >> Response <<

   HTTP/1.1 204 No Content
   Date: Tue, 02 Jun 2009 19:05:05 GMT

   Cyrus's client then retrieves the event back from the server with
   Wilfredo's updated participation status.






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   >> Request <<

   GET /home/cyrus/calendars/work/9263504FD3AD.ics HTTP/1.1
   Host: cal.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Date: Tue, 02 Jun 2009 19:05:02 GMT
   Last-Modified: Tue, 02 Jun 2009 19:04:20 GMT
   ETag: "eb897deabc8939589da116714bc99265"
   Schedule-Tag: "132cab27-1fe3-67ab-de13-abd348d1dee3"
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Server//EN
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090602T190420Z
   DTSTART:20090602T160000Z
   DTEND:20090602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com
   ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
    =ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=2.0:
    mailto:wilfredo@example.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=1
    .0:mailto:bernard@example.net
   ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
    CTION;RSVP=TRUE;SCHEDULE-STATUS=3.7:mailto:mike@example.org
   END:VEVENT
   END:VCALENDAR

B.5.  Example: Organizer Requesting Busy Time Information

   In this example, Cyrus requests the busy time information of
   Wilfredo, Bernard and Mike.







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   >> Request <<

   POST /home/cyrus/calendars/outbox/ HTTP/1.1
   Host: cal.example.com
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   METHOD:REQUEST
   BEGIN:VFREEBUSY
   UID:4FD3AD926350
   DTSTAMP:20090602T190420Z
   DTSTART:20090602T000000Z
   DTEND:20090604T000000Z
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com
   ATTENDEE;CN="Bernard Desruisseaux":mailto:bernard@example.net
   ATTENDEE;CN="Mike Douglass":mailto:mike@example.org
   END:VFREEBUSY
   END:VCALENDAR

   >> Response <<

   HTTP/1.1 200 OK
   Date: Tue, 02 Jun 2009 20:07:34 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:schedule-response xmlns:D="DAV:"
          xmlns:C="urn:ietf:params:xml:ns:caldav">
   <C:response>
   <C:recipient>
   <D:href>mailto:wilfredo@example.com</D:href>
   </C:recipient>
   <C:request-status>2.0;Success</C:request-status>
   <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Server//EN
   METHOD:REPLY
   BEGIN:VFREEBUSY
   UID:4FD3AD926350
   DTSTAMP:20090602T200733Z
   DTSTART:20090602T000000Z
   DTEND:20090604T000000Z
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com



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   ATTENDEE;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com
   FREEBUSY;FBTYPE=BUSY:20090602T110000Z/20090602T120000Z
   FREEBUSY;FBTYPE=BUSY:20090603T170000Z/20090603T180000Z
   END:VFREEBUSY
   END:VCALENDAR
   </C:calendar-data>
   </C:response>
   <C:response>
   <C:recipient>
   <D:href>mailto:bernard@example.net</D:href>
   </C:recipient>
   <C:request-status>2.0;Success</C:request-status>
   <C:calendar-data>BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Server//EN
   METHOD:REPLY
   BEGIN:VFREEBUSY
   UID:4FD3AD926350
   DTSTAMP:20090602T200733Z
   DTSTART:20090602T000000Z
   DTEND:20090604T000000Z
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Bernard Desruisseaux":mailto:bernard@example.net
   FREEBUSY;FBTYPE=BUSY:20090602T150000Z/20090602T160000Z
   FREEBUSY;FBTYPE=BUSY:20090603T090000Z/20090603T100000Z
   FREEBUSY;FBTYPE=BUSY:20090603T180000Z/20090603T190000Z
   END:VFREEBUSY
   END:VCALENDAR
   </C:calendar-data>
   </C:response>
   <C:response>
   <C:recipient>
   <D:href>mailto:mike@example.org</D:href>
   </C:recipient>
   <C:request-status>3.7;Invalid calendar user</C:request-status>
   </C:response>
   </C:schedule-response>

B.6.  Example: User Attempting to Invite Attendee on behalf of Organizer

   In the following example, Cyrus attempts to create, on behalf of
   Wilfredo, an event with Bernard specified as an Attendee.  The
   request fails since Wilfredo didn't grant Cyrus the right to invite
   other calendar users on his behalf.







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   >> Request <<

   PUT /home/wilfredo/calendars/work/def456.ics HTTP/1.1
   Host: cal.example.com
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx
   If-None-Match: *

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   UID:3504F926D3AD
   SEQUENCE:0
   DTSTAMP:20090602T190221Z
   DTSTART:20090602T230000Z
   DTEND:20090603T000000Z
   TRANSP:OPAQUE
   SUMMARY:Dinner
   ORGANIZER;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com
   ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT=A
    CCEPTED:mailto:wilfredo@example.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=NE
    EDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
    e.net
   END:VEVENT
   END:VCALENDAR

   >> Response <<

   HTTP/1.1 403 Forbidden
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:error xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:need-privileges>
       <D:resource>
         <D:href>/home/wilfredo/calendars/outbox/</D:href>
         <D:privilege><C:schedule-send-invite/></D:privilege>
       </D:resource>
     </D:need-privileges>
   </D:error>








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B.7.  Example: Attendee Declining an Instance of a Recurring Event

   In the following example, Bernard declines the second recurrence
   instance of a daily recurring event he's been invited to by Cyrus.

   >> Request <<

   PUT /home/bernard/calendars/work/4FD3AD926350.ics HTTP/1.1
   Host: cal.example.com
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx
   If-Schedule-Tag-Match: "7775FB30-7534-489E-A79A-0EA147B933EB"

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   TZID:America/Montreal
   BEGIN:STANDARD
   DTSTART:20071104T020000
   RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   BEGIN:DAYLIGHT
   DTSTART:20070311T020000
   RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   END:VTIMEZONE
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090602T185254Z
   DTSTART;TZID=America/Montreal:20090601T150000
   DTEND;TZID=America/Montreal:20090601T160000
   RRULE:FREQ=DAILY;INTERVAL=1;COUNT=5
   TRANSP:OPAQUE
   SUMMARY:Review Internet-Draft
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
    e.net



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   END:VEVENT
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090603T183823Z
   RECURRENCE-ID;TZID=America/Montreal:20090602T150000
   DTSTART;TZID=America/Montreal:20090602T150000
   DTEND;TZID=America/Montreal:20090602T160000
   TRANSP:TRANSPARENT
   SUMMARY:Review Internet-Draft
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    DECLINED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
    e.net
   END:VEVENT
   END:VCALENDAR

   >> Response <<

   HTTP/1.1 200 OK
   Content-Length: 0
   Date: Tue, 02 Jun 2009 18:52:54 GMT
   Last-Modified: Tue, 02 Jun 2009 18:52:54 GMT
   ETag: "d85561cfe74a4e785eb4639451b434fb"
   Schedule-Tag: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"

   Bernard's participation status update will cause his server to
   deliver a scheduling message to Cyrus.  Cyrus's client will find the
   following reply message from Bernard in Cyrus's scheduling Inbox
   collection:

   >> Request <<

   GET /home/cyrus/calendars/inbox/9263504FD3AD.ics HTTP/1.1
   Host: cal.example.com














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   >> Response <<

   HTTP/1.1 200 OK
   Date: Tue, 02 Jun 2009 18:52:58 GMT
   Last-Modified: Tue, 02 Jun 2009 18:52:58 GMT
   ETag: "eb897deabc8939589da116714bc99265"
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   METHOD:REPLY
   BEGIN:VTIMEZONE
   TZID:America/Montreal
   BEGIN:STANDARD
   DTSTART:20071104T020000
   RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   BEGIN:DAYLIGHT
   DTSTART:20070311T020000
   RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   END:VTIMEZONE
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090603T183823Z
   RECURRENCE-ID;TZID=America/Montreal:20090602T150000
   DTSTART;TZID=America/Montreal:20090602T150000
   DTEND;TZID=America/Montreal:20090602T160000
   SUMMARY:Review Internet-Draft
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Bernard Desruisseaux";PARTSTAT=DECLINED:
    mailto:bernard@example.net
   REQUEST-STATUS:2.0;Success
   END:VEVENT
   END:VCALENDAR







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B.8.  Example: Attendee Removing an Instance of a Recurring Event

   In the following example, Bernard removes from his calendar the third
   recurrence instance of a daily recurring event he's been invited to
   by Cyrus.  This is accomplished by the addition of an "EXDATE"
   property to the scheduling object resource stored by Bernard.

   >> Request <<

   PUT /home/bernard/calendars/work/4FD3AD926350.ics HTTP/1.1
   Host: cal.example.com
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx
   If-Schedule-Tag-Match: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VTIMEZONE
   TZID:America/Montreal
   BEGIN:STANDARD
   DTSTART:20071104T020000
   RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   BEGIN:DAYLIGHT
   DTSTART:20070311T020000
   RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   END:VTIMEZONE
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090602T185254Z
   DTSTART;TZID=America/Montreal:20090601T150000
   DTEND;TZID=America/Montreal:20090601T160000
   RRULE:FREQ=DAILY;INTERVAL=1;COUNT=5
   EXDATE;TZID=America/Montreal:20090603T150000
   TRANSP:OPAQUE
   SUMMARY:Review Internet-Draft
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com



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   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
    e.net
   END:VEVENT
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090603T183823Z
   RECURRENCE-ID;TZID=America/Montreal:20090602T150000
   DTSTART;TZID=America/Montreal:20090602T150000
   DTEND;TZID=America/Montreal:20090602T160000
   TRANSP:TRANSPARENT
   SUMMARY:Review Internet-Draft
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:cyrus@example.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    DECLINED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
    e.net
   END:VEVENT
   END:VCALENDAR

   Bernard's deletion of a recurrence instance will cause his server to
   deliver a scheduling message to Cyrus.  Cyrus's client will find the
   following reply message from Bernard in Cyrus's scheduling Inbox
   collection:

   >> Request <<

   GET /home/cyrus/calendars/inbox/6504923FD3AD.ics HTTP/1.1
   Host: cal.example.com




















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   >> Response <<

   HTTP/1.1 200 OK
   Date: Tue, 02 Jun 2009 18:52:58 GMT
   Last-Modified: Tue, 02 Jun 2009 18:52:58 GMT
   ETag: "eb897deabc8939589da116714bc99265"
   Content-Type: text/calendar; charset="utf-8"
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   METHOD:REPLY
   BEGIN:VTIMEZONE
   TZID:America/Montreal
   BEGIN:STANDARD
   DTSTART:20071104T020000
   RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
   TZNAME:EST
   TZOFFSETFROM:-0400
   TZOFFSETTO:-0500
   END:STANDARD
   BEGIN:DAYLIGHT
   DTSTART:20070311T020000
   RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
   TZNAME:EDT
   TZOFFSETFROM:-0500
   TZOFFSETTO:-0400
   END:DAYLIGHT
   END:VTIMEZONE
   BEGIN:VEVENT
   UID:9263504FD3AD
   SEQUENCE:0
   DTSTAMP:20090603T183823Z
   RECURRENCE-ID;TZID=America/Montreal:20090603T150000
   DTSTART;TZID=America/Montreal:20090603T150000
   DTEND;TZID=America/Montreal:20090603T160000
   SUMMARY:Review Internet-Draft
   ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
   ATTENDEE;CN="Bernard Desruisseaux";PARTSTAT=DECLINED:
    mailto:bernard@example.net
   REQUEST-STATUS:2.0;Success
   END:VEVENT
   END:VCALENDAR







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Appendix C.  Changes (to be removed by RFC Editor prior to publication)

C.1.  Changes in -12

   a.  AppDir: More reworking of various sections for clarity.

   b.  AppDir: Removed terminology items defined in other specs.

   c.  AppDir: Now updates 5546.

   d.  AppDir: MAY instead of can in 3.2.10.1/2.

   e.  Fixed inconsistent whitespace in examples.

   f.  IESG: added x-name and iana-token references in ABNF.

   g.  IESG: clarified that allowed attendee changes are in addition to
       other pre-conditions.

   h.  IESG: added privacy statement to address potential "leakage" of
       private data via scheduling messages or error responses.

   i.  IESG: scrubbed through some RFC2119 language to avoid unnecessary
       use and repetition.

C.2.  Changes in -11

   a.  Major editorial changes to remove "cruft" that built up over
       time, to reduce repetitive statements, and to improve clarity.

   b.  SecDir: Added "Preventing Denial of Service Attacks" security
       sub-section.

   c.  SecDir: Added reference to RFC6125 and clarified how clients and
       server authenticate each other.

   d.  SecDir: Added "Mitigation of iTIP Threats" security sub-section.

   e.  SecDir: Added new text to privacy sub-section.

   f.  Fixed some XML examples.

C.3.  Changes in -10

   a.  Updated to RFC 6047 reference.

   b.  Various minor clarifications to behavior and terminology done.




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   c.  Clarified that Inbox/Outbox are the server's responsibility to
       create.

   d.  Changed MAY to SHOULD for server rejecting organizer PARTSTAT
       changes of attendees.

   e.  Allow COMPLETED as a valid attendee change.

   f.  Allow SCHEDULE-STATUS as a valid attendee change on SCHEDULE-
       AGENT=CLIENT attendee properties.

   g.  COPY or MOVE on a calendar collection now declared to be
       undefined.

   h.  Changed precondition error codes from 409 to 403.

   i.  Clarified that rules 5546 must be used when server processes
       incoming scheduling messages.

   j.  default-calendar-delete-allowed -> default-calendar-needed.

   k.  Clarified that SCHEDULE-AGENT must be the same on all matching
       properties.

   l.  Added more text justifying the need for calendar-user-type
       property.

C.4.  Changes in -09

   a.  Fixed some examples.

   b.  Tweaked XML conventions.

   c.  Removed description in SCHEDULE-STATUS example values.

   d.  Tweaked 3.7 and 3.8 SCHEDULE-STATUS description to indicate it
       applies to the Organizer as well as Attendee.

   e.  Updated to RFC 5545 reference.

   f.  AD Review: clarified text about inbox resource deletion being
       acknowledgment of change.

   g.  AD Review: clarified description of freebusy Outbox POST.

   h.  AD Review: registered new 1.xx request-status codes and added new
       restriction on usage as per iTIP.




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   i.  AD Review: changes SHOULD NOT to MUST NOT for new property
       parameters when clients send scheduling messages.

   j.  AD Review: CALDAV:schedule-calendar-transp now preserved during
       COPY.

   k.  AD Review: changed CALDAV- to CALDAV: in acl descriptions.

   l.  AD Review: fixed various minor typos.

   m.  AD Review: Added text to new principal properties to indicate
       that if they are not present, then the user is not enabled for
       the various scheduling operations.

   n.  AD Review: clarified use of CALDAV:calendar-data element in
       CALDAV:response element.

   o.  AD Review: made reference to 5545 IANA registry procedures for
       the two new element registries.

   p.  AD Review: Fixed description of B5. example.

   q.  Fixed SCHEDULE-AGENT/SCHEDULE-STATUS behavior for Attendee
       replies.

C.5.  Changes in -08

   a.  Added "Updates 4791".

   b.  XML conventions changed to match that in CardDAV spec.

   c.  Reworded child response behavior for Outbox.

   d.  Reworded "octet size".

   e.  If-Schedule-Match descriptions changed to remove implication that
       it is purely a conditional operation.

   f.  Schedule-Reply header descriptions generalized to resource
       removal rather than just HTTP DELETE.

   g.  Fixed various examples.

C.6.  Changes in -07

   a.  Restructured document.





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   b.  Clarified that CALDAV:schedule-calendar-transp only applies to
       calendar collection.

   c.  Removed CALDAV:schedule-state property on scheduling messages in
       the scheduling Inbox collection.

   d.  Added conditional requests on scheduling object resources.

   e.  Added section on handling of PARTSTAT.

   f.  Added SCHEDULE-FORCE-SEND iCalendar property parameter.

   g.  Added clarification on child resources in scheduling Outbox
       collections.

   h.  Clarified Attendee changes that server MUST allow, and removed
       restrictions on changes that Attendee MUST NOT do.

   i.  Added Example Scheduling Transactions appendix.

   j.  Scheduling privileges are no longer required to be non-abstract.

   k.  Removed handling of REFRESH requests.

   l.  Removed handling of VJOURNAL components.

   m.  Completed IANA Considerations section.

   n.  Added references to RFC3283 and RFC5234.

   o.  Updated references to iCalendar, iTIP and iMIP.

C.7.  Changes in -06

   a.  Removed distinction between scheduling calendar collections and
       basic calendar collections - now just have calendar collections.

   b.  Clients now "MAY" reload data rather than "SHOULD" reload data.

   c.  Fixed <C:recipient> in examples.

   d.  Removed CALDAV:attachments-allowed precondition on POST to Outbox
       as that is no longer relevant.

   e.  Added CALDAV:default-calendar-delete-allowed precondition for
       DELETE.





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   f.  Relaxed MUST->MAY for Organizer setting PARTSTAT value.

   g.  Tweaked restrictions on Create/Modify to emphasize that 4791
       restrictions also apply.

   h.  Added comment that 'opaque' is the default when the CALDAV:
       schedule-calendar-transp property is not present.

   i.  Description of Schedule-Reply header changed to reflect that it
       is only relevant for Attendees.

   j.  Minor typos fixed.

C.8.  Changes in -05

   This draft has changed substantially since the -04 version.  The
   primary reason for this change was implementation experience from a
   number of vendors who implemented products based on the earlier
   drafts.  Experience showed that the client/server interaction was not
   reliable in keeping scheduling messages synchronized between
   organizer and attendees.  In addition the latency in updates due to
   clients being offline proved unacceptable to users.  These issues led
   to the redesign of this specification to support a server-based
   processing model that eliminates all the problems seen previously.
   Whilst this adds significant complexity to the server in that it
   needs to be a full blown iTIP processing agent, it does remove a lot
   of the same complexity from clients, opening up the possibility of
   supporting complex scheduling behaviors even with "thin" clients.

   In the judgement of the authors, we consider this new specification
   to be a substantial improvement over the old one and believe it
   represents a stronger protocol that will lead to better
   interoperability.


















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Authors' Addresses

   Cyrus Daboo
   Apple Inc.
   1 Infinite Loop
   Cupertino, CA  95014
   USA

   EMail: cyrus@daboo.name
   URI:   http://www.apple.com/


   Bernard Desruisseaux
   Oracle Corporation
   600 Blvd. de Maisonneuve West
   Suite 1900
   Montreal, QC  H3A 3J2
   CANADA

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






























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