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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.
Intended status: Standards Track                         B. Desruisseaux
Expires: December 21, 2009                                        Oracle
                                                           June 19, 2009


                 CalDAV Scheduling Extensions to WebDAV
                   draft-desruisseaux-caldav-sched-07

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   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
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Abstract

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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  7
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  7
     1.2.  Approach . . . . . . . . . . . . . . . . . . . . . . . . .  8
     1.3.  Limitations  . . . . . . . . . . . . . . . . . . . . . . .  8
     1.4.  Notational Conventions . . . . . . . . . . . . . . . . . .  9
     1.5.  XML Namespaces and Processing  . . . . . . . . . . . . . .  9
   2.  Scheduling Process . . . . . . . . . . . . . . . . . . . . . . 11
   3.  Scheduling Support . . . . . . . . . . . . . . . . . . . . . . 12
   4.  Scheduling Collections . . . . . . . . . . . . . . . . . . . . 13
     4.1.  Scheduling Outbox Collection . . . . . . . . . . . . . . . 13
     4.2.  Scheduling Inbox Collection  . . . . . . . . . . . . . . . 14
     4.3.  Calendaring Reports Extensions . . . . . . . . . . . . . . 16
   5.  Scheduling Transactions  . . . . . . . . . . . . . . . . . . . 17
     5.1.  Identifying Scheduling Object Resources  . . . . . . . . . 17
     5.2.  Handling Scheduling Object Resources . . . . . . . . . . . 17
       5.2.1.  Organizer Scheduling Object Resources  . . . . . . . . 17
         5.2.1.1.  Create . . . . . . . . . . . . . . . . . . . . . . 18
         5.2.1.2.  Modify . . . . . . . . . . . . . . . . . . . . . . 19
         5.2.1.3.  Remove . . . . . . . . . . . . . . . . . . . . . . 20
       5.2.2.  Attendee Scheduling Object Resources . . . . . . . . . 21
         5.2.2.1.  Allowed Attendee Changes . . . . . . . . . . . . . 21
         5.2.2.2.  Create . . . . . . . . . . . . . . . . . . . . . . 22
         5.2.2.3.  Modify . . . . . . . . . . . . . . . . . . . . . . 22
         5.2.2.4.  Remove . . . . . . . . . . . . . . . . . . . . . . 22
       5.2.3.  HTTP Methods . . . . . . . . . . . . . . . . . . . . . 23
         5.2.3.1.  PUT  . . . . . . . . . . . . . . . . . . . . . . . 23
         5.2.3.2.  COPY . . . . . . . . . . . . . . . . . . . . . . . 24
         5.2.3.3.  MOVE . . . . . . . . . . . . . . . . . . . . . . . 24
         5.2.3.4.  DELETE . . . . . . . . . . . . . . . . . . . . . . 25
       5.2.4.  Additional Method Preconditions  . . . . . . . . . . . 25
         5.2.4.1.  CALDAV:unique-scheduling-object-resource
                   Precondition . . . . . . . . . . . . . . . . . . . 25
         5.2.4.2.  CALDAV:same-organizer-in-all-components
                   Precondition . . . . . . . . . . . . . . . . . . . 25
         5.2.4.3.  CALDAV:allowed-organizer-scheduling-object-chan
                   Precondition . . . . . . . . . . . . . . . . . . . 26
         5.2.4.4.  CALDAV:allowed-attendee-scheduling-object-chang
                   Precondition . . . . . . . . . . . . . . . . . . . 27
       5.2.5.  DTSTAMP and SEQUENCE Properties  . . . . . . . . . . . 27



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       5.2.6.  Limit Recurrence Instances Sent to Attendees . . . . . 27
       5.2.7.  Forcing the Server to Send a Scheduling Message  . . . 28
   6.  Processing Incoming Scheduling Messages  . . . . . . . . . . . 29
     6.1.  Processing Attendee Replies  . . . . . . . . . . . . . . . 29
     6.2.  Processing Organizer Requests, Additions, and
           Cancellations  . . . . . . . . . . . . . . . . . . . . . . 30
     6.3.  Default Calendar Collection  . . . . . . . . . . . . . . . 30
       6.3.1.  Additional Method Preconditions  . . . . . . . . . . . 31
         6.3.1.1.  CALDAV:default-calendar-delete-allowed
                   Precondition . . . . . . . . . . . . . . . . . . . 31
         6.3.1.2.  CALDAV:valid-schedule-default-calendar-URL
                   Precondition . . . . . . . . . . . . . . . . . . . 31
     6.4.  Scheduling Messages as Notifications . . . . . . . . . . . 32
   7.  Request for Busy Time Information  . . . . . . . . . . . . . . 33
     7.1.  Status Codes . . . . . . . . . . . . . . . . . . . . . . . 33
     7.2.  Additional Method Preconditions  . . . . . . . . . . . . . 33
       7.2.1.  DAV:need-privileges Precondition . . . . . . . . . . . 33
       7.2.2.  CALDAV:supported-collection Precondition . . . . . . . 34
       7.2.3.  CALDAV:supported-calendar-data Precondition  . . . . . 35
       7.2.4.  CALDAV:valid-calendar-data Precondition  . . . . . . . 35
       7.2.5.  CALDAV:valid-scheduling-message Precondition . . . . . 36
       7.2.6.  CALDAV:organizer-allowed Precondition  . . . . . . . . 36
       7.2.7.  CALDAV:max-resource-size Precondition  . . . . . . . . 37
     7.3.  Response to a POST request . . . . . . . . . . . . . . . . 37
   8.  Conditional Requests on Scheduling Object Resources  . . . . . 38
     8.1.  PUT  . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
     8.2.  DELETE . . . . . . . . . . . . . . . . . . . . . . . . . . 40
     8.3.  COPY or MOVE . . . . . . . . . . . . . . . . . . . . . . . 41
   9.  Other Scheduling Considerations  . . . . . . . . . . . . . . . 42
     9.1.  Attendee Participation Status  . . . . . . . . . . . . . . 42
     9.2.  Schedule Status Values . . . . . . . . . . . . . . . . . . 43
     9.3.  Organizer is an Attendee . . . . . . . . . . . . . . . . . 45
   10. Additional iCalendar Property Parameters . . . . . . . . . . . 46
     10.1. Schedule Agent Parameter . . . . . . . . . . . . . . . . . 46
     10.2. Schedule Force Send Parameter  . . . . . . . . . . . . . . 47
     10.3. Schedule Status Parameter  . . . . . . . . . . . . . . . . 48
   11. Additional Message Header Fields . . . . . . . . . . . . . . . 50
     11.1. Schedule-Reply Request Header  . . . . . . . . . . . . . . 50
     11.2. Schedule-Tag Response Header . . . . . . . . . . . . . . . 50
     11.3. If-Schedule-Tag-Match Request Header . . . . . . . . . . . 51
   12. Additional WebDAV Properties . . . . . . . . . . . . . . . . . 52
     12.1. CALDAV:schedule-calendar-transp Property . . . . . . . . . 52
     12.2. CALDAV:schedule-default-calendar-URL Property  . . . . . . 53
     12.3. CALDAV:schedule-tag Property . . . . . . . . . . . . . . . 54
   13. Scheduling Access Control  . . . . . . . . . . . . . . . . . . 55
     13.1. Scheduling Privileges  . . . . . . . . . . . . . . . . . . 55
       13.1.1. Privileges on Scheduling Inbox Collections . . . . . . 55
         13.1.1.1. CALDAV:schedule-deliver Privilege  . . . . . . . . 55



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         13.1.1.2. CALDAV:schedule-deliver-invite Privilege . . . . . 56
         13.1.1.3. CALDAV:schedule-deliver-reply Privilege  . . . . . 56
         13.1.1.4. CALDAV:schedule-query-freebusy Privilege . . . . . 56
       13.1.2. Privileges on Scheduling Outbox Collections  . . . . . 56
         13.1.2.1. CALDAV:schedule-send Privilege . . . . . . . . . . 56
         13.1.2.2. CALDAV:schedule-send-invite Privilege  . . . . . . 57
         13.1.2.3. CALDAV:schedule-send-reply Privilege . . . . . . . 57
         13.1.2.4. CALDAV:schedule-send-freebusy Privilege  . . . . . 57
       13.1.3. Aggregation of Scheduling Privileges . . . . . . . . . 57
     13.2. Additional Principal Properties  . . . . . . . . . . . . . 58
       13.2.1. CALDAV:schedule-inbox-URL Property . . . . . . . . . . 58
       13.2.2. CALDAV:schedule-outbox-URL Property  . . . . . . . . . 59
       13.2.3. CALDAV:calendar-user-address-set Property  . . . . . . 59
       13.2.4. CALDAV:calendar-user-type Property . . . . . . . . . . 60
   14. XML Element Definitions  . . . . . . . . . . . . . . . . . . . 62
     14.1. CALDAV:schedule-response XML Element . . . . . . . . . . . 62
     14.2. CALDAV:response XML Element  . . . . . . . . . . . . . . . 62
     14.3. CALDAV:recipient XML Element . . . . . . . . . . . . . . . 62
     14.4. CALDAV:request-status XML Element  . . . . . . . . . . . . 63
   15. Security Considerations  . . . . . . . . . . . . . . . . . . . 64
     15.1. Verifying Scheduling Transactions  . . . . . . . . . . . . 64
     15.2. Verifying Busy Time Information Requests . . . . . . . . . 64
     15.3. Privacy Issues . . . . . . . . . . . . . . . . . . . . . . 65
   16. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 66
     16.1. Message Header Field Registrations . . . . . . . . . . . . 66
       16.1.1. Schedule-Reply . . . . . . . . . . . . . . . . . . . . 66
       16.1.2. Schedule-Tag . . . . . . . . . . . . . . . . . . . . . 66
       16.1.3. If-Schedule-Tag-Match  . . . . . . . . . . . . . . . . 66
     16.2. iCalendar Property Parameter Registrations . . . . . . . . 67
     16.3. Additional iCalendar Elements Registries . . . . . . . . . 67
       16.3.1. Schedule Agent Values Registry . . . . . . . . . . . . 67
       16.3.2. Schedule Force Send Values Registry  . . . . . . . . . 67
   17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 69
   18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 70
     18.1. Normative References . . . . . . . . . . . . . . . . . . . 70
     18.2. Informative References . . . . . . . . . . . . . . . . . . 71
   Appendix A.  Scheduling Privileges Summary . . . . . . . . . . . . 72
     A.1.  Scheduling Inbox Privileges  . . . . . . . . . . . . . . . 72
     A.2.  Scheduling Outbox Privileges . . . . . . . . . . . . . . . 72
   Appendix B.  Example Scheduling Transactions . . . . . . . . . . . 74
     B.1.  Example: Organizer Inviting Multiple Attendees . . . . . . 74
     B.2.  Example: Attendee Receiving an Invitation  . . . . . . . . 76
     B.3.  Example: Attendee Replying to an Invitation  . . . . . . . 78
     B.4.  Example: Organizer Receiving a Reply to an Invitation  . . 80
     B.5.  Example: Organizer Requesting Busy Time Information  . . . 82
     B.6.  Example: User Attempting to Invite Attendee on behalf
           of Organizer . . . . . . . . . . . . . . . . . . . . . . . 84
     B.7.  Example: Attendee Declining an Instance of a Recurring



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           Event  . . . . . . . . . . . . . . . . . . . . . . . . . . 85
     B.8.  Example: Attendee Removing an Instance of a Recurring
           Event  . . . . . . . . . . . . . . . . . . . . . . . . . . 89
   Appendix C.  Changes (to be removed by RFC Editor prior to
                publication)  . . . . . . . . . . . . . . . . . . . . 92
     C.1.  Changes in -07 . . . . . . . . . . . . . . . . . . . . . . 92
     C.2.  Changes in -06 . . . . . . . . . . . . . . . . . . . . . . 92
     C.3.  Changes in -05 . . . . . . . . . . . . . . . . . . . . . . 93











































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1.  Introduction

   This document specifies extensions to the CalDAV "calendar-access"
   [RFC4791] feature to enable scheduling of iCalendar-based
   [I-D.ietf-calsify-rfc2445bis] calendar components between Calendar
   Users.  This extension leverages the scheduling methods defined in
   the iCalendar Transport-independent Interoperability Protocol (iTIP)
   [I-D.ietf-calsify-2446bis] to permit Calendar Users to perform
   scheduling transactions such as schedule, reschedule, respond to
   scheduling request or cancel scheduled calendar components, as well
   as search for busy time information.

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

1.1.  Terminology

   This specification uses much of the same terminology as iCalendar
   [I-D.ietf-calsify-rfc2445bis], iTIP [I-D.ietf-calsify-2446bis],
   WebDAV [RFC4918], and CalDAV [RFC4791].  The following definitions
   are provided to aid the reader in understanding this specification.

   Calendar User (CU):  An entity (often a human) that accesses calendar
      information [RFC3283].

   Calendar User Agent (CUA):  Software with which the calendar user
      communicates with a calendar service or local calendar store to
      access calendar information [RFC3283].

   Calendar collection:  A resource that acts as a container of
      references to child calendar object resources [RFC4791].

   Calendar object resource:  A resource representing a calendar object
      (event, to-do, journal entry, or other calendar components)
      [RFC4791].

   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 an Organizer.

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





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   Automatic scheduling transaction:  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 resource that describes a
      scheduling transaction 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.  Approach

   iTIP [I-D.ietf-calsify-2446bis] outlines a model where Calendar Users
   exchange scheduling messages with one another.  Often times, Calendar
   User Agents are made responsible for generating and sending
   scheduling messages as well as processing incoming scheduling
   messages.  This approach yields a number of problems, including:

   o  For most updates to a scheduled calendar component, Calendar User
      Agents need to address a separate scheduling messages to the
      Organizer or the Attendees.

   o  The handling of incoming scheduling messages and the updates to
      calendars impacted by those messages only occurs when Calendar
      User Agents are active.

   o  Due to the update latency, it is possible for calendars of
      different Calendar Users to reflect different, inaccurate states.

   This specification uses an alternative approach where the server is
   made responsible for sending scheduling messages and processing
   incoming scheduling messages.  This approach frees the Calendar User
   Agents from the submission and processing of scheduling messages and
   ensures better consistency of calendar data across users' calendars.
   The operation of creating, modifying or deleting a scheduled calendar
   component in a calendar is enough to trigger the server to deliver
   the necessary scheduling messages to the appropriate Calendar Users.

1.3.  Limitations

   While the scheduling features described in this specification are
   based on iTIP [I-D.ietf-calsify-2446bis], some of its more complex
   features have deliberately been left out in order to keep this
   specification simple.  In particular, the following iTIP



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   [I-D.ietf-calsify-2446bis] features are not covered: publishing,
   countering, delegating, refreshing and forwarding calendar
   components, as well as replacing the Organizer of a calendar
   component.

   The goal of this specification is to provide the essential scheduling
   features needed.  It is expected that future extensions will be
   developed to address the more complex features.

1.4.  Notational Conventions

   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
   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 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].

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

1.5.  XML Namespaces and Processing

   Definitions of XML elements in this document use XML element type
   declarations (as found in XML Document Type Declarations), described
   in Section 3.2 of [W3C.REC-xml-20081126].

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

   The XML declarations used in this document do not include namespace
   information.  Thus, implementers must not use these declarations as
   the only way to create valid CalDAV properties or to validate CalDAV
   XML element type.  Some of the declarations refer to XML elements
   defined by WebDAV [RFC4918] which use the "DAV:" namespace.  Wherever
   such XML elements appear, they are explicitly prefixed with "DAV:" to
   avoid confusion.  Additionally, some of the elements used here are
   defined in CalDAV "calendar-access" [RFC4791].




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

   Processing of XML by CalDAV clients and servers MUST follow the rules
   described in Section 17 of [RFC4918].













































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2.  Scheduling Process

   The process of scheduling an event between different parties often
   involves a series of steps with different actors playing particular
   roles during the whole process.  Typically there is an event
   "Organizer" whose role is to setup an event between one or more
   "Attendees", and this is done by sending out invitations and handling
   responses from each Attendee.

   This process can typically be broken down into two phases.

   In the first phase, the Organizer will query the busy time
   information of each Attendee to determine the most appropriate time
   for the event.  This request is sometimes called a freebusy lookup.

   In the second phase, the Organizer sends out invitations to each
   Attendee using the time previously determined from the freebusy
   lookup.  There then follows exchanges between Organizer and Attendees
   regarding the invitation.  Some Attendees may choose to attend at the
   time proposed by the Organizer, others may decline to attend.  The
   Organizer needs to process each of the replies from the Attendees and
   take appropriate action to confirm the event, reschedule it or
   perhaps cancel it.

   The user expectation as to how a calendaring and scheduling system
   should respond in each of these two phases is somewhat different.  In
   the case of a freebusy lookup, users expect to get back results
   immediately so that they can then move on to the invitation phase as
   quickly as possible.  In the case of invitations, it is expected that
   each Attendee will reply with their participation status in their own
   time, so delays in receiving replies are anticipated.  Thus
   calendaring and scheduling systems should treat these two operational
   phases in different ways to accommodate the user expectations, and
   this specification does that.

   While the scenario described above only covers the case of scheduling
   events between Calendar Users, and requesting busy time information,
   this specification also provides support for the scheduling of to-dos
   between Calendar Users.  For the majority of the following
   discussion, scheduling of events and freebusy lookups will be
   discussed, as these are the more common operations.










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3.  Scheduling Support

   A server that supports the features described in this document MUST
   include "calendar-auto-schedule" as a field in the DAV response
   header from an OPTIONS request on any resource that supports any
   scheduling actions, properties, privileges or methods.

   To advertise support for the CalDAV "calendar-auto-schedule" feature
   a server is REQUIRED to support and advertise support for the CalDAV
   "calendar-access" [RFC4791] feature.

   >> Request <<

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

   >> Response <<

   HTTP/1.1 204 No Content
   Date: Thu, 31 Mar 2005 09:00:00 GMT
   Allow: OPTIONS, GET, HEAD, DELETE, TRACE, PROPFIND
   Allow: PROPPATCH, LOCK, UNLOCK, REPORT, ACL
   DAV: 1, 2, 3, access-control
   DAV: calendar-access, calendar-auto-schedule

   In this example, the OPTIONS response indicates that the server
   supports the "calendar-access" and "calendar-auto-schedule" features
   and that resource "/home/cyrus/calendars/inbox/" supports the
   scheduling actions, properties, privileges and methods defined in
   this specification.





















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4.  Scheduling Collections

   This specification introduces new collection resource types that are
   used to manage scheduling object resources, scheduling privileges as
   well as provide scheduling functionality.

4.1.  Scheduling Outbox Collection

   A scheduling Outbox collection is used as the target for busy time
   information 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>

   New WebDAV ACL [RFC3744] privileges can be set on the scheduling
   Outbox collection to control who is allowed to send scheduling
   messages on behalf of the Calendar User associated with the
   scheduling Outbox collection.  See Section 13.1 for more details.

   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:

      CALDAV:supported-calendar-component-set - when present this
      indicates the allowed calendar component types for scheduling
      messages submitted to the scheduling Outbox collection with the
      POST method.

      CALDAV:supported-calendar-data - when present this indicates the
      allowed media types for scheduling messages submitted to the
      scheduling Outbox collection with the POST method.

      CALDAV:max-resource-size - when present this indicates the maximum
      size of a resource in octets that the server is willing to accept
      for scheduling messages submitted to the scheduling Outbox



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      collection with the POST method.

      CALDAV:min-date-time - when present this indicates the earliest
      date and time (in UTC) that the server is willing to accept for
      any DATE or DATE-TIME value in scheduling messages submitted to
      the scheduling Outbox collection with the POST method.

      CALDAV:max-date-time - when present this indicates the latest date
      and time (in UTC) that the server is willing to accept for any
      DATE or DATE-TIME value in scheduling messages submitted to the
      scheduling Outbox collection with the POST method.

      CALDAV:max-instances - when present this indicates the maximum
      number of recurrence instances in scheduling messages submitted to
      the scheduling Outbox collection with the POST method.

      CALDAV:max-attendees-per-instance - when present this indicates
      the maximum number of ATTENDEE properties in any instance of
      scheduling messages submitted to the scheduling Outbox collection
      with the POST method.

   While there is currently no defined use for child resources in a
   scheduling Outbox collection, a scheduling Outbox collection MAY
   contain child resources.

4.2.  Scheduling Inbox Collection

   A scheduling Inbox collection contains copies of incoming scheduling
   messages.  These may be requests sent by an Organizer, or replies
   sent by an Attendee in response to a request.

   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
   [I-D.ietf-calsify-2446bis].  Consequently, scheduling Inbox



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   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) don't apply to calendar object
   resources contained in a scheduling Inbox collection.  Multiple
   calendar object resources contained in a scheduling Inbox collection
   MAY have the same "UID" property value (i.e., multiple scheduling
   messages for the same calendar component).

   New WebDAV ACL [RFC3744] privileges can be set on the scheduling
   Inbox collection to control who the Calendar User associated with the
   scheduling Inbox collection will accept scheduling messages from.
   See Section 13.1 for more details.

   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:

      CALDAV:calendar-timezone - when present this contains a time zone
      that the server can use when calendar date-time operations are
      carried out, for example when a time-range CALDAV:calendar-query
      REPORT is targeted at a scheduling Inbox collection.

      CALDAV:supported-calendar-component-set - when present this
      indicates the allowed calendar component types for scheduling
      messages delivered to the scheduling Inbox collection.

      CALDAV:supported-calendar-data - when present this indicates the
      allowed media types for scheduling messages delivered to the
      scheduling Inbox collection.

      CALDAV:max-resource-size - when present this indicates the maximum
      size of a resource in octets that the server is willing to accept
      for scheduling messages delivered to the scheduling Inbox
      collection.

      CALDAV:min-date-time - when present this indicates the earliest
      date and time (in UTC) that the server is willing to accept for
      any DATE or DATE-TIME value in scheduling messages delivered to
      the scheduling Inbox collection.

      CALDAV:max-date-time - when present this indicates the latest date
      and time (in UTC) that the server is willing to accept for any
      DATE or DATE-TIME value in scheduling messages delivered to the
      scheduling Inbox collection.




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      CALDAV:max-instances - when present this indicates the maximum
      number of recurrence instances in scheduling messages delivered to
      the scheduling Inbox collection.

      CALDAV:max-attendees-per-instance - when present this indicates
      the maximum number of ATTENDEE properties in any instance of
      scheduling messages delivered to the scheduling Inbox collection.

4.3.  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 the report directly
   targets such a collection.  That is, the Request-URI for a report
   MUST be the URI of the scheduling Inbox collection or of a child
   resource within a scheduling Inbox collection.  A report run on a
   regular collection that includes a scheduling Inbox collection as a
   child resource at any depth MUST NOT examine or return any calendar
   object resources from within any 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
   [I-D.ietf-calsify-2446bis]) 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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5.  Scheduling Transactions

   When a calendar object resource is created, modified or removed from
   a calendar collection (either via a PUT, DELETE, COPY or MOVE HTTP
   request), 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 operation can occur in this case, equivalent to iTIP
   "REQUEST", "REPLY", "CANCEL", and "ADD" operations.

5.1.  Identifying Scheduling Object Resources

   Calendar object resources on which the server performs automatic
   scheduling transactons are refered 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 that at least one of the "ATTENDEE"
   iCalendar property values match 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 stored in an appropriate
   calendar collection.

5.2.  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.

5.2.1.  Organizer Scheduling Object Resources

   An Organizer can create, modify or remove a scheduling object
   resource by issuing HTTP requests with an appropriate method.  The
   create, modify and remove behaviors for the server are each described



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   next, and the way these are invoked via HTTP requests is described in
   Section 5.2.3.

5.2.1.1.  Create

   When a scheduling object resource is created by the Organizer, the
   server will inspect each "ATTENDEE" property to determine if a
   scheduling message should be delivered to this Attendee according to
   the value of the "SCHEDULE-AGENT" property parameter (see
   Section 10.1) as described in the table below:

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

   The attempt to deliver the scheduling message will either succeed or
   fail.  In all cases, the server MUST add a "SCHEDULE-STATUS"
   iCalendar property parameter (see Section 10.3) to the "ATTENDEE"
   iCalendar property in the scheduling object resource being created,
   and set its value as described in Section 9.2.  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 as soon as it is created on 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.

   Restrictions:

   1.  The server MAY 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".  To maintain
       consistency across Organizers and Attendees, a server will
       typically choose to enforce the requirement that only an Attendee
       can change their own "PARTSTAT" to a value other than "NEEDS-
       ACTION".

   2.  The server MAY reject attempts to create a scheduling object
       resource that specifies a "UID" property value already specified



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       in a scheduling object resource contained in another calendar
       collection of the Organizer.

   3.  The server MUST take into account scheduling privileges as
       described in Section 13.1 when handling the creation of a
       scheduling object resource.

   4.  Restrictions on calendar object resources defined in Section 4.1
       of [RFC4791] MUST also be enforced.

5.2.1.2.  Modify

   When a scheduling object resource is modified by the Organizer, the
   server will inspect each "ATTENDEE" property in the new calendar data
   to determine which ones have the "SCHEDULE-AGENT" iCalendar property
   parameter.  It will then need to compare this with the "ATTENDEE"
   properties in the existing calendar object resource that is being
   modified.

   For each Attendee in the old and new calendar data on a per-instance
   basis, and taking into account the addition or removal of Attendees,
   the server will determine whether to deliver a scheduling message to
   the Attendee.  The following table determines whether the server
   needs to deliver a scheduling message, and if so which iTIP
   scheduling method to use.  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 (Old) or is being removed (New).

   +---------------+-----------------------------------------------+
   |               |                     New                       |
   |    ATTENDEE   +-----------+-----------+-----------+-----------+
   |               | <Removed> | SERVER    | CLIENT    | NONE      |
   |               |           | (default) |           |           |
   +===+===========+===========+===========+===========+===========+
   |   | <Absent>  |  --       | REQUEST / | --        | --        |
   |   |           |           | ADD       |           |           |
   |   +-----------+-----------+-----------+-----------+-----------+
   |   | SERVER    |  CANCEL   | REQUEST   | CANCEL    | CANCEL    |
   | O | (default) |           |           |           |           |
   | l +-----------+-----------+-----------+-----------+-----------+
   | d | CLIENT    |  --       | REQUEST / | --        | --        |
   |   |           |           | ADD       |           |           |
   |   +-----------+-----------+-----------+-----------+-----------+
   |   | NONE      |  --       | REQUEST / | --        | --        |
   |   |           |           | ADD       |           |           |
   +---+-----------+-----------+-----------+-----------+-----------+



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   The attempt to deliver the scheduling message will either succeed or
   fail.  In all cases, the server MUST add a "SCHEDULE-STATUS"
   iCalendar property parameter to the "ATTENDEE" iCalendar property in
   the scheduling object resource being modified, and set its value as
   described in Section 9.2.  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 as soon as it is modified on the server in order to update to
   the new server generated state information.

   Restrictions:

   1.  The server MAY 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".  To maintain
       consistency for Organizers and Attendees, a server will typically
       choose to enforce the requirement that only an Attendee can
       change their own "PARTSTAT" to a value other than "NEEDS-ACTION".

   2.  The server MUST take into account scheduling privileges as
       described in Section 13.1 when handling the modification of a
       scheduling object resource.

   3.  Restrictions on calendar object resources defined in Section 4.1
       of [RFC4791] MUST also be enforced.

5.2.1.3.  Remove

   When a scheduling object resource is removed by the Organizer, the
   server will inspect each "ATTENDEE" property in the scheduling object
   resource being removed to determine which ones have the "SCHEDULE-
   AGENT" iCalendar property parameter.

   For each Attendee the server will determine whether to attempt to
   deliver a scheduling message into the Attendee's scheduling Inbox
   collection, based on the table below:

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



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   Restrictions:

   1.  The server MUST take into account scheduling privileges as
       described in Section 13.1 when handling the deletion of a
       scheduling object resource.

5.2.2.  Attendee Scheduling Object Resources

   An Attendee can create, modify or remove a scheduling object resource
   by issuing HTTP requests with an appropriate method.  The create,
   modify and remove behaviors for the server are each described next,
   and the way these are invoked via HTTP requests is described in
   Section 5.2.3.

5.2.2.1.  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.

   The server MUST allow Attendees to:

   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 "VALARM" iCalendar components.

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

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

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

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

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




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5.2.2.2.  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 6).  However, in some cases a scheduling message may get
   delivered directly to the client, and the Attendee may wish to store
   that on the server.  In that case the client creates a scheduling
   object resource in a suitable calendar belonging to the Attendee.
   Once stored, it is then subject to the usual rules for attendee
   scheduling object resources.

   In some cases a server may not be able to process an Attendee
   scheduling object resource that originated from another system (i.e.,
   where the server is unable to deliver scheduling messages to the
   Organizer).  In such cases the server MUST add a "SCHEDULE-AGENT"
   iCalendar property parameter to all "ORGANIZER" iCalendar properties
   in the resource and set the value of each to "NONE".  The server MAY
   reject any attempt by the client to remove the "SCHEDULE-AGENT"
   property parameter or change its value.

5.2.2.3.  Modify

   When a scheduling object resource is modified by an Attendee, the
   server will inspect the changes by comparing it with the existing
   scheduling object resource being replaced.

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

   The attempt to deliver the scheduling message will either succeed or
   fail.  In all cases, the server MUST add a "SCHEDULE-STATUS"
   iCalendar property parameter to the "ORGANIZER" iCalendar property in
   the scheduling object resource being created, and set its value as
   described in Section 9.2.  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 as soon as it is stored in order to update to the new server
   generated state information.

5.2.2.4.  Remove

   When a scheduling object resource is removed by the Attendee, one of
   two possibilities exist:




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   1.  If the HTTP request contains a "Schedule-Reply" request header
       set to the value "T" or there is no "Schedule-Reply" request
       header, then the server MUST attempt to deliver a scheduling
       message to the Organizer indicating that the Attendee has a
       "PARTSTAT" iCalendar property parameter value set to "DECLINED".
       That is, the Attendee has chosen not to attend any instances.  If
       the server is unable to deliver the scheduling message, the
       remove action MUST fail, and an appropriate "SCHEDULE-STATUS"
       iCalendar property parameter set on the "ORGANIZER" property in
       the scheduling object resource stored by the server.

   2.  If the HTTP request contains a request header "Schedule-Reply"
       set to the value "F", the server MUST NOT attempt to deliver a
       scheduling message.  The resource is simply removed.  This
       provides the client a way to silently remove unwanted scheduling
       attempts.

5.2.3.  HTTP Methods

   This section describes how use of various HTTP methods on a
   scheduling object resource will cause a create, modify or remove
   action 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.

5.2.3.1.  PUT

   When a PUT method request is received, the server will execute the
   following actions, provided all appropriate preconditions are met:

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




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   | Scheduling object        | Scheduling object        | Modify      |
   | resource                 | resource                 |             |
   +--------------------------+--------------------------+-------------+

5.2.3.2.  COPY

   When a COPY method request is received, the server will execute the
   following actions based on the source and destination collections in
   the request:

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

   Note 1.  The same rules as used for PUT above are applied for the
   destination of the COPY request.

5.2.3.3.  MOVE

   When a MOVE method request is received, the server will execute the
   following actions based on the source and destination collections in
   the request:

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

   Note 1.  The same rules as used for PUT above are applied for the
   destination of the MOVE request.

   Note 2.  The same rules as used for DELETE below are applied for the
   source of the MOVE request.



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5.2.3.4.  DELETE

   When a DELETE method is targeted at a scheduling object resource the
   server will execute the Remove action.

   When a DELETE method is targeted at a calendar collection the server
   will execute the Remove action on all scheduling object resources
   contained in the calendar collection.

5.2.4.  Additional Method Preconditions

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

5.2.4.1.  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:  409 Conflict

   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>

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







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   Name:  same-organizer-in-all-components

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

   Apply to:  PUT, COPY, and MOVE

   Use with:  409 Conflict

   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>

   Example:

      <C:same-organizer-in-all-components
          xmlns:C="urn:ietf:params:xml:ns:caldav"/>

5.2.4.3.  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:  409 Conflict

   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 5.2.1.

   Definition:

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

   Example:

      <C:allowed-organizer-scheduling-object-change
          xmlns:C="urn:ietf:params:xml:ns:caldav"/>




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5.2.4.4.  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:  409 Conflict

   Purpose:  (precondition) -- Servers MAY impose restrictions on
      modifications allowed by an Attendee.  Attendee modifications that
      servers MUST allow are specified in Section 5.2.2.1.

   Definition:

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

   Example:

      <C:allowed-attendee-scheduling-object-change
          xmlns:C="urn:ietf:params:xml:ns:caldav"/>

5.2.5.  DTSTAMP and SEQUENCE Properties

   Whenever the server generates a scheduling message for delivery to a
   Calendar User, it MUST ensure that a "DTSTAMP" iCalendar property is
   present and MUST set the value to the UTC time that the scheduling
   message was generated (as required by iCalendar).

   iTIP [I-D.ietf-calsify-2446bis] places certain requirements on how
   the "SEQUENCE" iCalendar property value in scheduling messages
   changes.  The server MUST ensure that for each type of scheduling
   operation, the "SEQUENCE" iCalendar property value is appropriately
   updated.  If the client does not update the "SEQUENCE" iCalendar
   property itself when that is required, the server MUST update the
   property.

5.2.6.  Limit Recurrence Instances Sent to Attendees

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

   For example, if an Attendee is invited to a single recurrence
   instance of a recurring event, and no others, the scheduling object
   resource contained in the Organizer's calendar collection will



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   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.  The scheduling message that will be
   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 scheduling object resource
   contained in the calendar collection of the Organizer will include an
   overridden instance with an "ATTENDEE" list that does not include the
   Attendee being excluded.  The scheduling message that will be
   delivered to the Attendee will not specify the overridden instance
   but rather include an "EXDATE" property in the master recurring
   component defining the recurrence set.

5.2.7.  Forcing the Server to Send a Scheduling Message

   The iCalendar property parameter "SCHEDULE-FORCE-SEND" defined in
   Section 10.2 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
   forced to modify the event.
























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6.  Processing Incoming Scheduling Messages

   Scheduling operations can cause the delivery of a scheduling message
   into an Organizer's or Attendee's scheduling Inbox collection.  In
   the former case the scheduling messages are replies from Attendees,
   in the latter case the scheduling messages are requests,
   cancellations or additions from the Organizer.

   The server will automatically process incoming scheduling messages
   and make them available in the scheduling Inbox collection as an
   indicator to the client that a scheduling operation has taken place.

   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.  Additionally, servers MUST
   take into account any scheduling Inbox collection preconditions (see
   Section 4.2) 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.

6.1.  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.

   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 recurrence instances of a
   recurring event).

   The server MUST also update or add the "SCHEDULE-STATUS" property
   parameter on each matching "ATTENDEE" iCalendar property and sets 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



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   replying, subject to the recurrence requirements of Section 5.2.6.

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

6.2.  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 MUST process the scheduling
   message and create a new scheduling object resource in an appropriate
   calendar collection for the Attendee.

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

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

6.3.  Default Calendar Collection

   The server is REQUIRED to process scheduling messages that specify a
   request for a new calendar component received for an Attendee by
   creating a new scheduling object resource in a calendar collection
   belonging to the Attendee.  A Calendar User who can participate as 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 on reception of scheduling messages that specify a
   request for a new calendar component.  The CALDAV:schedule-default-
   calendar-URL WebDAV property, which MAY be defined on the scheduling
   Inbox collection of a Calendar User, specifies if this Calendar User
   has a default calendar collection.  See Section 12.2.

   Servers MUST create new scheduling object resources in the default
   calendar collection, if the CALDAV:schedule-default-calendar-URL
   WebDAV property is set.



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   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, they
   MUST ensure that any new value stored 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.

6.3.1.  Additional Method Preconditions

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

6.3.1.1.  CALDAV:default-calendar-delete-allowed Precondition

   Name:  default-calendar-delete-allowed

   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-delete-allowed EMPTY>

   Example:

      <C:default-calendar-delete-allowed
          xmlns:C="urn:ietf:params:xml:ns:caldav"/>

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

   Name:  valid-schedule-default-calendar-URL







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

   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
      don't 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>

   Example:

      <C:valid-schedule-default-calendar-URL
          xmlns:C="urn:ietf:params:xml:ns:caldav"/>

6.4.  Scheduling Messages as Notifications

   Once the processing of an incoming scheduling message is completed by
   the server, the message is made available as a child resource in the
   scheduling Inbox collection of the Calendar User that received the
   message, to serve as a notification that a change has been made to
   the corresponding scheduling object resource.  Scheduling messages
   are typically removed from the scheduling Inbox collection by the
   client once it has acknowledged the change.



















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7.  Request for Busy Time Information

   The POST method is used to request busy time information of one or
   more Calendar Users by targeting the request at a scheduling Outbox
   collection.  The request body of a POST method MUST contain a
   "VFREEBUSY" calendar compoment with the "METHOD" iCalendar property
   set to the value "REQUEST" as specified in Section 3.3.2 of iTIP
   [I-D.ietf-calsify-2446bis].  The resource identified by the Request-
   URI MUST be a resource collection of type CALDAV:schedule-outbox
   (Section 4.1).

7.1.  Status Codes

   The following are examples of response codes one would expect to be
   used for this method.  Note, however, that unless explicitly
   prohibited any 2/3/4/5xx series response code may be used in a
   response.

      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.

7.2.  Additional Method Preconditions

   This specification defines additional method preconditions for the
   POST method.  Preconditions defined in WebDAV ACL [RFC3744] and
   CalDAV [RFC4791] that applies to the POST method are also listed here
   for completeness.

7.2.1.  DAV:need-privileges Precondition

   Name:  need-privileges







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   Namespace:  DAV:

   Apply to:  POST

   Use with:  403 Forbidden

   Purpose:  (precondition) -- The currently authenticated user MUST be
      granted the CALDAV:schedule-send or CALDAV:schedule-send-freebusy
      privilege on the scheduling Outbox collection being targeted by
      the request.

   Definition:

      <!ELEMENT DAV:need-privileges (DAV:resource)* >
      <!ELEMENT DAV:resource (DAV:href, DAV:privilege) >

   Example:

      <D:need-privileges xmlns:D="DAV:"
                         xmlns:C="urn:ietf:params:xml:ns:caldav"/>
        <D:resource>
          <D:href>/home/bernard/calendars/outbox/</D:href>
          <D:privilege><C:schedule-send-freebusy/></D:privilege>
        </D:resource>
      </D:need-privileges>

7.2.2.  CALDAV:supported-collection Precondition

   Name:  supported-collection

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

   Apply to:  POST

   Use with:  400 Bad Request

   Purpose:  (precondition) -- The Request-URI MUST identify the
      location of a scheduling Outbox collection.

   Definition:

      <!ELEMENT supported-collection EMPTY >

   Example:

      <C:supported-collection xmlns:C="urn:ietf:params:xml:ns:caldav"/>





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7.2.3.  CALDAV:supported-calendar-data Precondition

   Name:  supported-calendar-data

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

   Apply to:  POST

   Use with:  400 Bad Request

   Purpose:  (precondition) -- The resource body submitted in the POST
      request MUST be a supported media type (e.g., text/calendar).

   Definition:

      <!ELEMENT supported-calendar-data EMPTY >

   Example:

      <C:supported-calendar-data
         xmlns:C="urn:ietf:params:xml:ns:caldav"/>

7.2.4.  CALDAV:valid-calendar-data Precondition

   Name:  valid-calendar-data

   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 be valid data for the media type being specified
      (e.g., a valid iCalendar object).

   Definition:

      <!ELEMENT valid-calendar-data EMPTY>

   Example:

      <C:valid-calendar-data xmlns:C="urn:ietf:params:xml:ns:caldav"/>








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7.2.5.  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 restrictions specified for the POST request
      (e.g., the scheduling message follow the restrictions of iTIP).

   Definition:

      <!ELEMENT valid-scheduling-message EMPTY >

   Example:

      <C:valid-scheduling-message
         xmlns:C="urn:ietf:params:xml:ns:caldav"/>

7.2.6.  CALDAV:organizer-allowed Precondition

   Name:  organizer-allowed

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

   Apply to:  POST

   Use with:  409 Conflict

   Purpose:  (precondition) -- The Calendar User identified by the
      "ORGANIZER" property in the POST request's scheduling message MUST
      be the Calendar User (or one of the Calendar Users) associated
      with the scheduling Outbox collection being targeted by the
      request;

   Definition:

      <!ELEMENT organizer-allowed EMPTY >

   Example:

      <C:organizer-allowed xmlns:C="urn:ietf:params:xml:ns:caldav"/>





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7.2.7.  CALDAV:max-resource-size Precondition

   Name:  max-resource-size

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

   Apply to:  POST

   Use with:  403 Forbidden

   Purpose:  (precondition) -- The resource submitted in the POST
      request MUST have an octet size less than or equal to the value of
      the CALDAV:max-resource-size property (defined in Section 5.2.5 of
      [RFC4791]) specified on the scheduling Outbox collection targeted
      by the request.

   Definition:

      <!ELEMENT max-resource-size EMPTY >

   Example:

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

7.3.  Response to a POST request

   A POST request may deliver a scheduling message to one or more
   Calendar Users.  Since the behavior of each recipient may vary, it is
   useful to get response status information for each recipient in the
   overall POST response.  This specification defines a new XML response
   to convey multiple recipient status.

   A response to a POST method that indicates status for one or more
   recipients MUST be a CALDAV:schedule-response XML element.  This MUST
   contain one or more CALDAV:response elements for each recipient, with
   each of those containing elements that indicate which recipient they
   correspond to, the scheduling status for that recipient, any error
   codes and an optional description.  See Section 14.1.

   In the case of a freebusy request, the CALDAV:response elements can
   also contain CALDAV:calendar-data elements which contain freebusy
   information (e.g., an iCalendar VFREEBUSY component) indicating the
   busy state of the corresponding recipient, assuming that the freebusy
   request for that recipient succeeded.  See Appendix B.5 for an
   example freebusy request and response.






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8.  Conditional Requests on Scheduling Object Resources

   Because replies from Attendees and updates from Organizers are
   automatically processed by the server, clients might be in a
   situation where their copy of a calendar resource is different from
   the one currently on the server.  When an Attendee or Organizer makes
   a change to the client's copy of the calendar resource, if the client
   writes the data to the server it could overwrite the changes already
   made there.  Typically, HTTP clients use the ETag value and If-Match
   request header to avoid the "lost update problem".

   Calendar user agents can also use ETag and If-Match to avoid this
   problem.  However, when doing so the client will likely have to
   resolve the differences between the new resource and the original
   one, and the changes made by the Attendee or Organizer in the client.
   This can be a complicated comparison particularly when recurring
   components are present.

   Additionally, the data on the server may change frequently as
   Attendees change their participation status, triggering updates to
   the Organizer and consequently other Attendees' copies of the
   scheduling object resource.  If the ETag/If-Match behavior were used,
   clients would be forced to reconcile their cached copy of a
   scheduling object resource with the updated one on the server in
   order to attempt to write the user's changes back.  This could lead
   to a race condition that can effectively result in a temporary denial
   of service when, for example, there is an event with a large Attendee
   list.  A "storm" of updates will occur if Attendees all start
   responding at the same time, and this would prevent Attendees and the
   Organizer from being able to update their own copies of the
   scheduling object resource as the server copy is changing frequently.

   What would be preferable is having the server determine the best way
   to merge changes made on the server with changes being made by the
   client.  For example, if an Attendee changes their participation
   status and triggers an update to the Organizer's copy of the event,
   but the Organizer also updates their cached copy of the event and
   attempts to write it back, rather than failing on a conditional If-
   Match when the Organizer writes their data, the server would instead
   take the changes made by the Organizer and apply the Attendee changes
   and store the result.  Thus a form of "weak" ETag matching behavior
   is needed such that scheduling changes made automatically on the
   server do not invalidate the tag, so that when clients store data
   conditionally based on the tag value, the server knows it can apply
   the merge behavior.

   In order to do that, this specification introduces a new WebDAV
   resource property CALDAV:schedule-tag with a corresponding response



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   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.  An
   "inconsequential" scheduling message is one which simply updates the
   status information of Attendees due to a reply from an Attendee.

   Servers MUST support conditional requests targeted at scheduling
   object resources using the "If-Schedule-Tag-Match" request header.
   Consequently, the server MUST support the "Schedule-Tag" response
   header and CALDAV:schedule-tag property for scheduling object
   resources.  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 in the same way as
   the If-Match request header.

   Clients SHOULD use conditional requests using the If-Schedule-Tag-
   Match request header.

   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 resource
   identified in the Request-URI.

   The Schedule-Tag feature is designed to be used to address the
   problem of "inconsequential" changes on the server only.  Normal ETag
   operations 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



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          automatically updated by the server with the Attendee's new
          participation status.

      2.  The server MUST change CALDAV:schedule-tag property value when
          the schedulng 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 MUST NOT be changed.

      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).

8.1.  PUT

   Clients can use the If-Schedule-Tag-Match request header to do a
   conditional 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.

8.2.  DELETE

   Clients can use the If-Schedule-Tag-Match request header to do a
   conditional DELETE 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



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   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 request
   processing for the resource.  Otherwise, the server MUST fail the
   request with a 412 Precondition Failed status code.

8.3.  COPY or MOVE

   Clients can use the If-Schedule-Tag-Match request header to do
   conditional COPY or MOVE requests 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 copied or moved.  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 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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9.  Other Scheduling Considerations

9.1.  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.

   Clients SHOULD, and servers MUST reset the "PARTSTAT" property
   parameter value of all "ATTENDEE" properties, except the one that
   corresponds to the Organizer, to "NEEDS-ACTION" when the Organizer
   reschedules an event.

   A reschedule of an event 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.

   +----------+--------------------------------------------------------+
   | Property | Description                                            |
   +----------+--------------------------------------------------------+
   | DTSTART  | Any change to these properties MUST result in          |
   | DTEND    | "PARTSTAT" 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 MUST 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 MUST 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 MUST      |
   |          | result in "PARTSTAT" being reset 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 may be impacted by the change).

9.2.  Schedule Status Values

   When scheduling with an Attendee there are two types of status
   information that can be returned during the transaction.  The first
   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 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 10.3).  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 [I-D.ietf-calsify-rfc2447bis] (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.                                 |
   |          |                                                        |
   |          |                                                        |
   |          |                                                        |
   | 3.8      | The scheduling message was not delivered due to        |
   |          | insufficient privileges.                               |
   |          |                                                        |
   |          |                                                        |
   |          |                                                        |
   | 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 suitable way to deliver  |
   |          | the message.  This is likely a permanent failure, and  |
   |          | the originator should 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 should not try to send the message again.   |
   +----------+--------------------------------------------------------+

   The status code for "reply" status can be any of the valid iTIP
   [I-D.ietf-calsify-2446bis] "REQUEST-STATUS" values.

9.3.  Organizer is an Attendee

   The Organizer of a scheduled event may also be an Attendee of that
   event.  In such cases the server MUST NOT send a scheduling message
   to the Attendee that matches the Organizer.




























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10.  Additional iCalendar Property Parameters

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

10.1.  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 automatic scheduling
                       / x-name        ; Experimental type
                       / iana-token)   ; Other IANA registered type
                                       ;
                                       ; Default is SERVER

   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 an automatic
      scheduling transaction 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 an
      automatic scheduling transaction.  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 an automatic scheduling transaction.

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

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





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   Example:

      ATTENDEE;SCHEDULE-AGENT=SERVER:mailto:bernard@example.com

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

10.2.  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 registered method

   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.

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

      Clients SHOULD 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 [I-D.ietf-calsify-2446bis]) when the
      "SCHEDULE-FORCE-SEND" parameter is set to a x-name or iana-token
      value they don't recognize.




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   Example:

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

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

10.3.  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
      ; [I-D.ietf-calsify-rfc2445bis]. 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 add this property parameter to any "ATTENDEE"
      properties corresponding to Calendar Users who were sent a
      scheduling message via an automatic scheduling transaction.
      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 add this parameter to any "ORGANIZER" properties
      corresponding to Calendar Users who were sent a scheduling message
      reply by an Attendee via an automatic scheduling transaction.
      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 an automatic scheduling transaction.





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

      Suitable values for this property parameter are described in
      Section 9.2.

   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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11.  Additional Message Header Fields

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

11.1.  Schedule-Reply Request Header


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

   Example:

      Schedule-Reply: F

   When an Attendee executes an HTTP DELETE request on a scheduling
   object resource, and the Schedule-Reply header is not present, or
   present and set to the value "T", 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
   automatic scheduling transaction processing.

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

   The Schedule-Reply request header is used by a client to indicate to
   a server whether or not an automatic scheduling transaction should
   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 deletion.  There are situations in
   which unsolicited scheduling messages need to be silently deleted (or
   ignored) for security or privacy reasons.  This request header allows
   the scheduling object resource to be deleted if such a need arises.

   All scheduling object resources MUST support the Schedule-Reply
   request header.

11.2.  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 8.

   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"

11.3.  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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12.  Additional WebDAV Properties

   The CalDAV scheduling extension defines the following new WebDAV
   properties for use with CalDAV.

12.1.  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 freebusy.

   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, but is normally re-initialized when a resource is
      created with a COPY.  It should not be set 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 should contribute to the owner's freebusy or not.  When
      the CALDAV:opaque element is used, all calendar object resources
      in the corresponding calendar collection MUST contribute to
      freebusy, 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 freebusy.

      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>

12.2.  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 6.3.

   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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12.3.  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 is only defined on scheduling
      object resources.  It MUST be preserved when a scheduling object
      resource is copied or moved and the resulting resource is also a
      scheduling object resource.  If the source resource is not a
      scheduling object resource but the destination resource is, this
      property MUST be added to the destination resource.

   Description:  The CALDAV:schedule-tag property MUST be defined on all
      scheduling object resources.  This property is described in
      Section 8.

   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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13.  Scheduling Access Control

13.1.  Scheduling Privileges

   CalDAV servers MUST support and adhere to the requirements of WebDAV
   ACL [RFC3744].  Furthermore, CalDAV servers that advertise support
   for the "calendar-auto-schedule" feature MUST also support the
   scheduling privileges 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.

13.1.1.  Privileges on Scheduling Inbox Collections

   This section defines new WebDAV ACL 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.

13.1.1.1.  CALDAV:schedule-deliver Privilege

   CALDAV:schedule-deliver is an aggregate privilege that contains all
   the scheduling privileges that control the processing and delivery of
   incoming scheduling messages, that is, CALDAV:schedule-deliver-invite
   and CALDAV:schedule-deliver-reply, as well as freebusy requests
   targeted at the owner of the scheduling Inbox collection, that is,
   CALDAV:schedule-query-freebusy.

   <!ELEMENT schedule-deliver EMPTY >



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13.1.1.2.  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 >

13.1.1.3.  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 >

13.1.1.4.  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 >

13.1.2.  Privileges on Scheduling Outbox Collections

   This section defines new WebDAV ACL 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 to send schedule messages to other
   calendar users (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.

13.1.2.1.  CALDAV:schedule-send Privilege

   CALDAV:schedule-send is an aggregate privilege that contains all the
   scheduling privileges that control the use of methods that will cause
   scheduling messages to be delivered to other users, that is, CALDAV-
   schedule-send-invite and CALDAV-schedule-send-reply, as well as
   freebusy requests to be targeted at other users, that is, CALDAV-
   schedule-send-freebusy.

   <!ELEMENT schedule-send EMPTY >







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13.1.2.2.  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 organizer scheduling messages to other
   calendar users.

   <!ELEMENT schedule-send-invite EMPTY >

13.1.2.3.  CALDAV:schedule-send-reply Privilege

   The CALDAV:schedule-send-invite 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 attendee scheduling messages to other
   calendar users.

   <!ELEMENT schedule-send-reply EMPTY >

13.1.2.4.  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 >

13.1.3.  Aggregation of Scheduling Privileges

   Server implementations MUST aggregate the scheduling privileges as
   follows:

      DAV:all MUST contain CALDAV:schedule-send and CALDAV:schedule-
      deliver;




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      CALDAV:schedule-send MUST contain CALDAV:schedule-send-invite,
      CALDAV:schedule-send-reply, and CALDAV:schedule-send-freebusy;

      CALDAV:schedule-deliver MUST contain 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.

         [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]

13.2.  Additional Principal Properties

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

13.2.1.  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]).






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   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 Inbox collection of the current user is located so
      that processing of scheduling messages can occur.

   Definition:

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

13.2.2.  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.

   Definition:

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

13.2.3.  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.






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   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.

   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>

13.2.4.  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
      [I-D.ietf-calsify-rfc2445bis].

   Protected:  This property MAY be protected.






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   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 MAY be defined on principal resources to
      indicate the type of calendar user associated with this 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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14.  XML Element Definitions

14.1.  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 7.3.

   Definition:

       <!ELEMENT schedule-response (response*)>

14.2.  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 7.3.

   Definition:

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

14.3.  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.

   Description:  See Section 7.3.







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   Definition:

       <!ELEMENT recipient (DAV:href)>

14.4.  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 7.3.

   Definition:

       <!ELEMENT request-status (#PCDATA) >


































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15.  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 transactions.

15.1.  Verifying Scheduling Transactions

   When handling a scheduling transaction:

      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.

      Servers MUST verify that the currently authenticated user has the
      CALDAV:schedule-send privilege, or a suitable 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.

      Servers MUST only deliver scheduling messages to recipients when
      the CALDAV:schedule-deliver privilege, or a suitable 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.

      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.

      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.

15.2.  Verifying Busy Time Information Requests

   When handling a POST request on a scheduling Outbox collection:






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      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.

      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.

      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.

15.3.  Privacy Issues

   As noted in Section 11.1, Attendees can use the Schedule-Reply
   request header 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.


























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16.  IANA Considerations

16.1.  Message Header Field Registrations

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

16.1.1.  Schedule-Reply

   Header field name: Schedule-Reply

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document(s): this specification (Section 11.1)

   Related information: none

16.1.2.  Schedule-Tag

   Header field name: Schedule-Tag

   Applicable protocol: http

   Status: standard

   Author/Change controller: IETF

   Specification document(s): this specification (Section 11.2)

   Related information: none

16.1.3.  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 11.3)

   Related information: none



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16.2.  iCalendar Property Parameter Registrations

   The following iCalendar property parameters should be added to the
   iCalendar Property Parameter Registry defined in Section 8.3.3 of
   [I-D.ietf-calsify-rfc2445bis].

         +---------------------+---------+-----------------------+
         | Parameter           | Status  | Reference             |
         +---------------------+---------+-----------------------+
         | SCHEDULE-AGENT      | Current | RFCXXXX, Section 10.1 |
         |                     |         |                       |
         | SCHEDULE-STATUS     | Current | RFCXXXX, Section 10.3 |
         |                     |         |                       |
         | SCHEDULE-FORCE-SEND | Current | RFCXXXX, Section 10.2 |
         +---------------------+---------+-----------------------+

16.3.  Additional iCalendar Elements Registries

   The IANA should create and maintain the following additional
   registries for iCalendar elements with pointers to appropriate
   reference documents.

16.3.1.  Schedule Agent Values Registry

   The following table should be used to initialize the schedule agent
   values registry.

           +----------------+---------+------------------------+
           | Schedule Agent | Status  | Reference              |
           +----------------+---------+------------------------+
           | SERVER         | Current | RFC XXXX, Section 10.1 |
           |                |         |                        |
           | CLIENT         | Current | RFC XXXX, Section 10.1 |
           |                |         |                        |
           | NONE           | Current | RFC XXXX, Section 10.1 |
           +----------------+---------+------------------------+

16.3.2.  Schedule Force Send Values Registry

   The following table should be used to initialize the schedule send
   values registry.

        +---------------------+---------+------------------------+
        | Schedule Force Send | Status  | Reference              |
        +---------------------+---------+------------------------+
        | REQUEST             | Current | RFC XXXX, Section 10.2 |
        |                     |         |                        |




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        | REPLY               | Current | RFC XXXX, Section 10.2 |
        +---------------------+---------+------------------------+

















































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17.  Acknowledgements

   The authors would like to thank the following individuals for
   contributing their ideas and support for writing this specification:
   Mike Douglass, Lisa Dusseault, Helge Hess, Arnaud Quillaud, Julian F.
   Reschke, Wilfredo Sanchez Vega, Simon Vaillancourt, and Jim
   Whitehead.

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








































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18.  References

18.1.  Normative References

   [I-D.ietf-calsify-2446bis]     Daboo, C., "iCalendar Transport-
                                  Independent Interoperability Protocol
                                  (iTIP)", draft-ietf-calsify-2446bis-09
                                  (work in progress), April 2009.

   [I-D.ietf-calsify-rfc2445bis]  Desruisseaux, B., "Internet
                                  Calendaring and Scheduling Core Object
                                  Specification (iCalendar)",
                                  draft-ietf-calsify-rfc2445bis-10 (work
                                  in progress), April 2009.

   [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.

   [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.



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

   [W3C.REC-xml-20081126]         Maler, E., Yergeau, F., Sperberg-
                                  McQueen, C., Paoli, J., 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>.

18.2.  Informative References

   [I-D.ietf-calsify-rfc2447bis]  Melnikov, A., "iCalendar Message-Based
                                  Interoperability Protocol (iMIP)",
                                  draft-ietf-calsify-rfc2447bis-05 (work
                                  in progress), June 2008.

   [RFC3283]                      Mahoney, B., Babics, G., and A. Taler,
                                  "Guide to Internet Calendaring",
                                  RFC 3283, June 2002.





























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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 transaction.  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 Transactions

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

   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 collection 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

   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.  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 Mike.




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   >> Request <<

   GET /home/cyrus/calendars/work/9263504FD3AD.ics HTTP/1.1

   >> 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;Scheduling message has been delivered":mailto:wilfredo@e
    xample.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS="
    1.0;Scheduling message is pending":mailto:bernard@example.net
   ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
    CTION;RSVP=TRUE;SCHEDULE-STATUS="3.7;Invalid calendar user":m
    ailto: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
   new scheduling object resource in his default calendar collection.




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   >> 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's accepts Cyrus's invitation and
   sets a reminder on the event.

   >> 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




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

   >> Request <<

   PUT /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;Scheduling mes
    sage has been delivered":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

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

   >> 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
    ;Reply has been received":mailto:wilfredo@example.com
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
    NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS="
    1.0;Scheduling message is pending":mailto:bernard@example.net
   ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
    CTION;RSVP=TRUE;SCHEDULE-STATUS="3.7;Invalid calendar user":m
    ailto: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
   and Bernard.






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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
   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
   ATTENDEE;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com



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   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: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

   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

   <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>

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 <<



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   PUT /home/bernard/calendars/work/4FD3AD926350.ics 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
   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
   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



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   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























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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

   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
   ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=



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    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






















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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 -07

   a.  Restructured document.

   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.2.  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.





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   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.

   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.3.  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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Internet-Draft        CalDAV Scheduling Extensions             June 2009


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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