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rfc:rfc6638

Internet Engineering Task Force (IETF) C. Daboo Request for Comments: 6638 Apple Inc. Updates: 4791, 5546 B. Desruisseaux Category: Standards Track Oracle ISSN: 2070-1721 June 2012

                  Scheduling Extensions to CalDAV

Abstract

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

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6638.

Copyright Notice

 Copyright (c) 2012 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Daboo & Desruisseaux Standards Track [Page 1] RFC 6638 CalDAV Scheduling June 2012

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

Table of Contents

 1. Introduction ....................................................5
    1.1. Terminology ................................................6
    1.2. Notational Conventions .....................................7
    1.3. XML Namespaces and Processing ..............................7
 2. Scheduling Support ..............................................8
    2.1. Scheduling Outbox Collection ...............................9
         2.1.1. CALDAV:schedule-outbox-URL Property ................10
    2.2. Scheduling Inbox Collection ...............................10
         2.2.1. CALDAV:schedule-inbox-URL Property .................11
    2.3. Calendaring Reports Extensions ............................12
    2.4. Additional Principal Properties ...........................12
         2.4.1. CALDAV:calendar-user-address-set Property ..........12
         2.4.2. CALDAV:calendar-user-type Property .................13
 3. Scheduling Operations ..........................................14
    3.1. Identifying Scheduling Object Resources ...................14
    3.2. Handling Scheduling Object Resources ......................15
         3.2.1. Organizer Scheduling Object Resources ..............15
                3.2.1.1. Create ....................................16
                3.2.1.2. Modify ....................................17
                3.2.1.3. Remove ....................................18
         3.2.2. Attendee Scheduling Object Resources ...............18
                3.2.2.1. Allowed "Attendee" Changes ................18
                3.2.2.2. Create ....................................19
                3.2.2.3. Modify ....................................20
                3.2.2.4. Remove ....................................21
         3.2.3. HTTP Methods .......................................21
                3.2.3.1. PUT .......................................22
                3.2.3.2. DELETE ....................................22
                3.2.3.3. COPY ......................................23
                3.2.3.4. MOVE ......................................24

Daboo & Desruisseaux Standards Track [Page 2] RFC 6638 CalDAV Scheduling June 2012

         3.2.4. Additional Method Preconditions ....................24
                3.2.4.1. CALDAV:unique-scheduling-object-resource
                         Precondition ..............................24
                3.2.4.2. CALDAV:same-organizer-in-all-components
                         Precondition ..............................25
                3.2.4.3. CALDAV:allowed-organizer-scheduling-
                            object-change Precondition .............25
                3.2.4.4. CALDAV:allowed-attendee-scheduling-
                            object-change Precondition .............26
         3.2.5. DTSTAMP and SEQUENCE Properties ....................26
         3.2.6. Restrict Recurrence Instances Sent to "Attendees" ..27
         3.2.7. Forcing the Server to Send a Scheduling Message ....27
         3.2.8. "Attendee" Participation Status ....................28
         3.2.9. Schedule Status Values .............................29
         3.2.10. Avoiding Conflicts when Updating Scheduling Object
                 Resources .........................................31
                 3.2.10.1. PUT .....................................33
                 3.2.10.2. DELETE, COPY, or MOVE ...................33
 4. Processing Incoming Scheduling Messages ........................34
    4.1. Processing "Organizer" Requests, Additions, and
         Cancellations .............................................34
    4.2. Processing "Attendee" Replies .............................35
    4.3. Default Calendar Collection ...............................35
         4.3.1. Additional Method Preconditions ....................36
                4.3.1.1. CALDAV:default-calendar-needed
                         Precondition ..............................36
                4.3.1.2. CALDAV:valid-schedule-default-calendar-URL
                         Precondition ..............................36
 5. Request for Busy Time Information ..............................37
    5.1. Status Codes ..............................................38
    5.2. Additional Method Preconditions ...........................38
         5.2.1. CALDAV:valid-scheduling-message Precondition .......38
         5.2.2. CALDAV:valid-organizer Precondition ................39
 6. Scheduling Privileges ..........................................39
    6.1. Privileges on Scheduling Inbox Collections ................39
         6.1.1. CALDAV:schedule-deliver Privilege ..................40
         6.1.2. CALDAV:schedule-deliver-invite Privilege ...........40
         6.1.3. CALDAV:schedule-deliver-reply Privilege ............40
         6.1.4. CALDAV:schedule-query-freebusy Privilege ...........40
    6.2. Privileges on Scheduling Outbox Collections ...............40
         6.2.1. CALDAV:schedule-send Privilege .....................41
         6.2.2. CALDAV:schedule-send-invite Privilege ..............41
         6.2.3. CALDAV:schedule-send-reply Privilege ...............41
         6.2.4. CALDAV:schedule-send-freebusy Privilege ............41
    6.3. Aggregation of Scheduling Privileges ......................42

Daboo & Desruisseaux Standards Track [Page 3] RFC 6638 CalDAV Scheduling June 2012

 7. Additional iCalendar Property Parameters .......................42
    7.1. Schedule Agent Parameter ..................................42
    7.2. Schedule Force Send Parameter .............................44
    7.3. Schedule Status Parameter .................................45
 8. Additional Message Header Fields ...............................46
    8.1. Schedule-Reply Request Header .............................46
    8.2. Schedule-Tag Response Header ..............................46
    8.3. If-Schedule-Tag-Match Request Header ......................47
 9. Additional WebDAV Properties ...................................47
    9.1. CALDAV:schedule-calendar-transp Property ..................47
    9.2. CALDAV:schedule-default-calendar-URL Property .............48
    9.3. CALDAV:schedule-tag Property ..............................49
 10. XML Element Definitions .......................................50
    10.1. CALDAV:schedule-response XML Element .....................50
    10.2. CALDAV:response XML Element ..............................50
    10.3. CALDAV:recipient XML Element .............................50
    10.4. CALDAV:request-status XML Element ........................51
 11. Security Considerations .......................................51
    11.1. Preventing Denial-of-Service Attacks .....................51
    11.2. Verifying Scheduling Operations ..........................52
    11.3. Verifying Busy Time Information Requests .................52
    11.4. Privacy Issues ...........................................53
    11.5. Mitigation of iTIP Threats ...............................53
 12. IANA Considerations ...........................................54
    12.1. Message Header Field Registrations .......................54
         12.1.1. Schedule-Reply ....................................54
         12.1.2. Schedule-Tag ......................................54
         12.1.3. If-Schedule-Tag-Match .............................54
    12.2. iCalendar Property Parameter Registrations ...............55
    12.3. iCalendar REQUEST-STATUS Value Registrations .............55
    12.4. Additional iCalendar Elements Registries .................55
         12.4.1. Schedule Agent Values Registry ....................56
         12.4.2. Schedule Force Send Values Registry ...............56
 13. Acknowledgements ..............................................56
 14. References ....................................................57
    14.1. Normative References .....................................57
    14.2. Informative References ...................................58

Daboo & Desruisseaux Standards Track [Page 4] RFC 6638 CalDAV Scheduling June 2012

 Appendix A. Scheduling Privileges Summary .........................59
   A.1. Scheduling Inbox Privileges ................................59
   A.2. Scheduling Outbox Privileges ...............................60
 Appendix B. Example Scheduling Operations .........................60
   B.1. Example: "Organizer" Inviting Multiple "Attendees" .........61
   B.2. Example: "Attendee" Receiving an Invitation ................63
   B.3. Example: "Attendee" Replying to an Invitation ..............64
   B.4. Example: "Organizer" Receiving a Reply to an Invitation ....66
   B.5. Example: "Organizer" Requesting Busy Time Information ......69
   B.6. Example: User Attempting to Invite "Attendee" on
        Behalf of "Organizer" ......................................71
   B.7. Example: "Attendee" Declining an Instance of a
        Recurring Event ............................................72
   B.8. Example: "Attendee" Removing an Instance of a
        Recurring Event ............................................75

1. Introduction

 This document specifies extensions to the CalDAV "calendar-access"
 [RFC4791] feature to enable scheduling of iCalendar-based [RFC5545]
 calendar components between calendar users.
 This extension leverages the scheduling methods defined in the
 iCalendar Transport-independent Interoperability Protocol (iTIP)
 [RFC5546] to permit calendar users to perform scheduling operations
 such as schedule, reschedule, respond to scheduling request, or
 cancel calendar components, as well as search for busy time
 information.  However, the following iTIP [RFC5546] features are not
 covered: publishing, countering, delegating, refreshing, and
 forwarding calendar components, as well as replacing the "Organizer"
 of a calendar component.  It is expected that future extensions will
 be developed to address these.
 This specification defines a client/server scheduling protocol, where
 the server is made responsible for sending scheduling messages and
 processing incoming scheduling messages.  The client operations of
 creating, modifying, or deleting a calendar component in a calendar
 are enough to trigger the server to deliver the necessary scheduling
 messages to the appropriate calendar users.  This approach is
 sometimes referred to as "implicit scheduling".
 This specification only addresses how scheduling occurs with users on
 a single system (i.e., scheduling between CalDAV servers, or some
 other calendaring and scheduling system, is not defined).  However,
 this specification is compatible with servers being able to send or
 receive scheduling messages with "external" users (e.g., using the
 iCalendar Message-Based Interoperability Protocol (iMIP) [RFC6047]).

Daboo & Desruisseaux Standards Track [Page 5] RFC 6638 CalDAV Scheduling June 2012

 Section 3 defines the automated "Scheduling Operations" that allow a
 client to store iCalendar data on a CalDAV server, with the server
 taking specific actions in response.  One of three scheduling
 operations can take place -- "create", "modify", or "remove", based
 on the HTTP method used for the request -- in addition to a
 comparison between any existing and any new iCalendar data.
 Section 4 defines how the server processes scheduling messages sent
 as the result of a scheduling operation.
 Section 5 defines how freebusy requests with an immediate response
 are accomplished.
 Section 6 defines access control privileges for the scheduling
 operations defined in this specification.
 For the majority of the following discussion, scheduling of events
 will be discussed.  However, scheduling of to-dos is also fully
 supported by this specification.
 This specification has been under development for a number of years,
 and most current implementations of CalDAV support it.  With the
 publication of this document, it is expected that all new CalDAV
 implementations will support it by default.  Interoperability tests
 have been performed regularly.  Significant issues with incompatible
 CalDAV implementations are not anticipated.

1.1. Terminology

 This specification reuses much of the same terminology as iCalendar
 [RFC5545], iTIP [RFC5546], WebDAV [RFC4918], and CalDAV [RFC4791].
 Additional terms used by this specification are as follows:
 Scheduling object resource:  A calendar object resource contained in
    a calendar collection for which the server will take care of
    sending scheduling messages on behalf of the owner of the calendar
    collection.
 Organizer scheduling object resource:  A scheduling object resource
    owned by the "Organizer".
 Attendee scheduling object resource:  A scheduling object resource
    owned by an "Attendee".
 Scheduling operation:  Add, change, or remove operations on a
    scheduling object resource for which the server will deliver
    scheduling messages to other calendar users.

Daboo & Desruisseaux Standards Track [Page 6] RFC 6638 CalDAV Scheduling June 2012

 Scheduling message:  A calendar object that describes a scheduling
    operation such as schedule, reschedule, reply, or cancel.
 Scheduling Outbox collection:  A resource at which busy time
    information requests are targeted.
 Scheduling Inbox collection:  A collection in which incoming
    scheduling messages are delivered.

1.2. Notational Conventions

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].
 The Augmented BNF (ABNF) syntax used by this document to specify the
 format definition of new iCalendar elements is defined in [RFC5234].
 The 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 term "protected" is used in the Conformance field of WebDAV
 property definitions as defined in Section 15 of [RFC4918].
 Calendaring and scheduling roles are referred to in quoted-strings of
 text with the first character of each word in uppercase.  For
 example, "Organizer" refers to a role of a calendar user within the
 scheduling protocol defined by [RFC5546].

1.3. XML Namespaces and Processing

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

Daboo & Desruisseaux Standards Track [Page 7] RFC 6638 CalDAV Scheduling June 2012

 3.  extension elements (elements not already defined as valid child
     elements) can be added anywhere, except when explicitly stated
     otherwise, and
 4.  extension attributes (attributes not already defined as valid for
     this element) can be added anywhere, except when explicitly
     stated otherwise.
 The XML elements specified in this document are defined in the
 "urn:ietf:params:xml:ns:caldav" XML namespace registered by CalDAV
 [RFC4791].
 When XML element types in the namespaces "DAV:" and
 "urn:ietf:params:xml:ns:caldav" are referenced in this document
 outside of the context of an XML fragment, the strings "DAV:" and
 "CALDAV:" will be prefixed to the element types, respectively.
 This document inherits, and sometimes extends, DTD productions from
 Section 14 of [RFC4918].
 Also note that some CalDAV XML element names are identical to WebDAV
 XML element names, though their namespace differs.  Care needs to be
 taken not to confuse the two sets of names.

2. Scheduling Support

 A server that supports the features described in this document is
 REQUIRED to support the CalDAV "calendar-access" [RFC4791] feature.
 Servers include "calendar-auto-schedule" as a field in the DAV
 response header from an OPTIONS request on any resource that supports
 any scheduling operations, properties, privileges, or methods.
 This specification introduces new collection resource types that are
 used to manage scheduling object resources, and scheduling privileges
 (as per Section 6), as well as provide scheduling functionality.  It
 is the server's responsibility to create these collection resources,
 and clients have no way to create or delete them.

Daboo & Desruisseaux Standards Track [Page 8] RFC 6638 CalDAV Scheduling June 2012

2.1. Scheduling Outbox Collection

 A scheduling Outbox collection is used as the target for busy time
 information requests, and to manage privileges that apply to outgoing
 scheduling requests.
 A scheduling Outbox collection MUST report the DAV:collection and
 CALDAV:schedule-outbox XML elements in the value of the DAV:
 resourcetype property.  The element type declaration for CALDAV:
 schedule-outbox is
   <!ELEMENT schedule-outbox EMPTY>
 Example:
   <D:resourcetype xmlns:D="DAV:">
     <D:collection/>
     <C:schedule-outbox xmlns:C="urn:ietf:params:xml:ns:caldav"/>
   </D:resourcetype>
 A scheduling Outbox collection MUST NOT be a child (at any depth) of
 a calendar collection resource.
 The following WebDAV properties specified in CalDAV "calendar-access"
 [RFC4791] MAY also be defined on scheduling Outbox collections and
 apply to scheduling messages submitted to the scheduling Outbox
 collection with the POST method:
 o  CALDAV:supported-calendar-component-set
 o  CALDAV:supported-calendar-data
 o  CALDAV:max-resource-size
 o  CALDAV:min-date-time
 o  CALDAV:max-date-time
 o  CALDAV:max-attendees-per-instance
 The use of child resources in a scheduling Outbox collection is
 reserved for future revisions or extensions of this specification.
 The following WebDAV property is defined on principal resources and
 used to locate the corresponding Outbox collection for the associated
 principal.

Daboo & Desruisseaux Standards Track [Page 9] RFC 6638 CalDAV Scheduling June 2012

2.1.1. CALDAV:schedule-outbox-URL Property

 Name:  schedule-outbox-URL
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  Identify the URL of the scheduling Outbox collection owned
    by the associated principal resource.
 Protected:  This property MAY be protected.
 PROPFIND behavior:  This property SHOULD NOT be returned by a
    PROPFIND DAV:allprop request (as defined in Section 14.2 of
    [RFC4918]).
 COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
    and MOVE operations.
 Description:  This property is needed for a client to determine where
    the scheduling Outbox collection of the current user is located so
    that sending of scheduling messages can occur.  If not present,
    then the associated calendar user is not enabled for the sending
    of scheduling messages on the server.
 Definition:
   <!ELEMENT schedule-outbox-URL (DAV:href)>

2.2. Scheduling Inbox Collection

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

Daboo & Desruisseaux Standards Track [Page 10] RFC 6638 CalDAV Scheduling June 2012

 Scheduling Inbox collections MUST only contain calendar object
 resources that obey the restrictions specified in iTIP [RFC5546].
 Consequently, scheduling Inbox collections MUST NOT contain any types
 of collection resources.  Restrictions defined in Section 4.1 of
 CalDAV "calendar-access" [RFC4791] on calendar object resources
 contained in calendar collections (e.g., Unique Identifier ("UID")
 uniqueness) do not apply to calendar object resources contained in a
 scheduling Inbox collection.  Thus, multiple calendar object
 resources contained in a scheduling Inbox collection can have the
 same "UID" property value (i.e., multiple scheduling messages for the
 same calendar component).
 A scheduling Inbox collection MUST NOT be a child (at any depth) of a
 calendar collection resource.
 The following WebDAV properties specified in CalDAV "calendar-access"
 [RFC4791] MAY also be defined on scheduling Inbox collections and
 apply to scheduling messages delivered to the collection:
 o  CALDAV:supported-calendar-component-set
 o  CALDAV:supported-calendar-data
 o  CALDAV:max-resource-size
 o  CALDAV:min-date-time
 o  CALDAV:max-date-time
 o  CALDAV:max-instances
 o  CALDAV:max-attendees-per-instance
 o  CALDAV:calendar-timezone
 The following WebDAV property is defined on principal resources and
 used to locate the corresponding Inbox collection for the associated
 principal.

2.2.1. CALDAV:schedule-inbox-URL Property

 Name:  schedule-inbox-URL
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  Identify the URL of the scheduling Inbox collection owned
    by the associated principal resource.

Daboo & Desruisseaux Standards Track [Page 11] RFC 6638 CalDAV Scheduling June 2012

 Protected:  This property MAY be protected.
 PROPFIND behavior:  This property SHOULD NOT be returned by a
    PROPFIND DAV:allprop request (as defined in Section 14.2 of
    [RFC4918]).
 COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
    and MOVE operations.
 Description:  This property allows a client to determine where the
    scheduling Inbox collection of the current user is located so that
    processing of scheduling messages can occur.  If not present, then
    the associated calendar user is not enabled for reception of
    scheduling messages on the server.
 Definition:
   <!ELEMENT schedule-inbox-URL (DAV:href)>

2.3. Calendaring Reports Extensions

 This specification extends the CALDAV:calendar-query and CALDAV:
 calendar-multiget REPORTs to return results for calendar object
 resources in scheduling Inbox collections.
 When a CALDAV:calendar-query REPORT includes a time-range query and
 targets a scheduling Inbox collection, if any calendar object
 resources contain "VEVENT" calendar components that do not include a
 "DTSTART" iCalendar property (as allowed by iTIP [RFC5546]) then such
 components MUST always match the time-range query test.
 Note that the CALDAV:free-busy-query REPORT is not supported on
 scheduling Inbox collections.

2.4. Additional Principal Properties

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

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

 Name:  calendar-user-address-set
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  Identify the calendar addresses of the associated principal
    resource.

Daboo & Desruisseaux Standards Track [Page 12] RFC 6638 CalDAV Scheduling June 2012

 Protected:  This property MAY be protected.
 PROPFIND behavior:  This property SHOULD NOT be returned by a
    PROPFIND DAV: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 his calendar user address, the URI of his principal
    resource can be used.  This property SHOULD be searchable using
    the DAV:principal-property-search REPORT.  The DAV:principal-
    search-property-set REPORT SHOULD identify this property as such.
    If not present, then the associated calendar user is not enabled
    for scheduling on the server.
 Definition:
   <!ELEMENT calendar-user-address-set (DAV:href*)>
 Example:
   <C:calendar-user-address-set xmlns:D="DAV:"
       xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:href>mailto:bernard@example.com</D:href>
     <D:href>mailto:bernard.desruisseaux@example.com</D:href>
   </C:calendar-user-address-set>

2.4.2. CALDAV:calendar-user-type Property

 Name:  calendar-user-type
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  Identifies the calendar user type of the associated
    principal resource.
 Value:  Same values allowed for the iCalendar "CUTYPE" property
    parameter defined in Section 3.2.3 of [RFC5545].
 Protected:  This property MAY be protected.

Daboo & Desruisseaux Standards Track [Page 13] RFC 6638 CalDAV Scheduling June 2012

 PROPFIND behavior:  This property SHOULD NOT be returned by a
    PROPFIND DAV:allprop request (as defined in Section 14.2 of
    [RFC4918]).
 COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
    and MOVE operations.
 Description:  Clients can query principal resources in order to look
    up "Attendees" available on the server.  When doing this, it is
    useful to know, or restrict the query to, certain types of
    calendar users (e.g., only search for "people", or only search for
    "rooms").  This property MAY be defined on principal resources to
    indicate the type of calendar user associated with the principal
    resource.  Its value is the same as the iCalendar "CUTYPE"
    property parameter that can be used on "ATTENDEE" properties.
    This property SHOULD be searchable using the DAV:principal-
    property-search REPORT.  The DAV:principal-search-property-set
    REPORT SHOULD identify this property as such.
 Definition:
   <!ELEMENT calendar-user-type (#PCDATA)>
 Example:
   <C:calendar-user-type
       xmlns:C="urn:ietf:params:xml:ns:caldav">INDIVIDUAL<
   /C:calendar-user-type>

3. Scheduling Operations

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

3.1. Identifying Scheduling Object Resources

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

Daboo & Desruisseaux Standards Track [Page 14] RFC 6638 CalDAV Scheduling June 2012

 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 if at least one of the "ATTENDEE" iCalendar
 property values matches one of the calendar user addresses of the
 owner of the calendar collection.
 The creation of attendee scheduling object resources is typically
 done by the server, with the resource being created in an appropriate
 calendar collection (see Section 4.3).

3.2. Handling Scheduling Object Resources

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

3.2.1. Organizer Scheduling Object Resources

 An "Organizer" can create, modify, or remove a scheduling object
 resource, subject to access privileges, preconditions, and the
 restrictions defined in Section 4.1 of [RFC4791].  These operations
 are each described next, and how they are invoked via HTTP requests
 is described in Section 3.2.3.
 The "Organizer" of a calendar component can also be an "Attendee" of
 that calendar component.  In such cases, the server MUST NOT send a
 scheduling message to the "Attendee" that matches the "Organizer".
 The server SHOULD reject any attempt to set the "PARTSTAT" iCalendar
 property parameter value of the "ATTENDEE" iCalendar property of
 other users in the calendar object resource to a value other than
 "NEEDS-ACTION" if the "SCHEDULE-AGENT" property parameter value is
 not present or set to the value "SERVER".
 The server MAY reject attempts to create a scheduling object resource
 that specifies a "UID" property value already specified in a
 scheduling object resource contained in another calendar collection
 of the "Organizer".

Daboo & Desruisseaux Standards Track [Page 15] RFC 6638 CalDAV Scheduling June 2012

3.2.1.1. Create

 When an "Organizer" creates a scheduling object resource, the server
 MUST inspect each "ATTENDEE" property to determine whether to send a
 scheduling message.  The table below indicates the appropriate iTIP
 method used by the server, taking into account any "SCHEDULE-AGENT"
 property parameter (see Section 7.1) specified on each "ATTENDEE"
 property.
                  +------------------+-------------+
                  | SCHEDULE-AGENT   | iTIP METHOD |
                  +------------------+-------------+
                  | SERVER (default) | REQUEST     |
                  |                  |             |
                  | CLIENT           | --          |
                  |                  |             |
                  | NONE             | --          |
                  +------------------+-------------+
 "SCHEDULE-STATUS" iCalendar property parameters are added or changed
 on "ATTENDEE" iCalendar properties in the scheduling object resource
 being created as described in Section 7.3, with the value set as
 described in Section 3.2.9.  This will result in the created calendar
 object resource differing from the calendar data sent in the HTTP
 request.  As a result, clients MAY reload the calendar data from the
 server in order to update to the new server-generated state
 information.
 The server MUST add a "SCHEDULE-STATUS" iCalendar property parameter
 (see Section 7.3) to the "ATTENDEE" iCalendar property in the
 scheduling object resource being created, and set its value as
 described in Section 3.2.9.  This will result in the created calendar
 object resource differing from the calendar data sent in the HTTP
 request.  As a result, clients MAY reload the calendar data from the
 server in order to update to the new server-generated state
 information.  Servers MUST NOT set the "SCHEDULE-STATUS" property
 parameter on the "ATTENDEE" property of "Attendees" for which it did
 not attempt to deliver a scheduling message.
 The server MUST return an error with the CALDAV:allowed-organizer-
 scheduling-object-change precondition code (Section 3.2.4.3) when the
 "Organizer" attempts to change the iCalendar data in a manner that is
 forbidden.

Daboo & Desruisseaux Standards Track [Page 16] RFC 6638 CalDAV Scheduling June 2012

3.2.1.2. Modify

 When an "Organizer" modifies a scheduling object resource, the server
 MUST inspect each "ATTENDEE" property in both the original and
 modified iCalendar data on a per-instance basis to determine whether
 to send a scheduling message.  The table below indicates the
 appropriate iTIP method used by the server, taking into account any
 "SCHEDULE-AGENT" property parameter (see Section 7.1) specified on
 each "ATTENDEE" property.  The values "SERVER", "CLIENT", and "NONE"
 in the top and left titles of the table refer to the "SCHEDULE-AGENT"
 parameter value of the "ATTENDEE" property, and the values "<Absent>"
 and "<Removed>" are used to cover the cases where the "ATTENDEE"
 property is not present (Original) or is being removed (Modified).
 +---------------+-----------------------------------------------+
 |               |                   Modified                    |
 |               +-----------+-----------+-----------+-----------+
 |               | <Removed> | SERVER    | CLIENT    | NONE      |
 |               |           | (default) |           |           |
 +===+===========+===========+===========+===========+===========+
 |   | <Absent>  |  --       | REQUEST / | --        | --        |
 | O |           |           | ADD       |           |           |
 | r +-----------+-----------+-----------+-----------+-----------+
 | i | SERVER    |  CANCEL   | REQUEST   | CANCEL    | CANCEL    |
 | g | (default) |           |           |           |           |
 | i +-----------+-----------+-----------+-----------+-----------+
 | n | CLIENT    |  --       | REQUEST / | --        | --        |
 | a |           |           | ADD       |           |           |
 | l +-----------+-----------+-----------+-----------+-----------+
 |   | NONE      |  --       | REQUEST / | --        | --        |
 |   |           |           | ADD       |           |           |
 +---+-----------+-----------+-----------+-----------+-----------+
 "SCHEDULE-STATUS" iCalendar property parameters are added or changed
 on "ATTENDEE" iCalendar properties in the scheduling object resource
 being modified as described in Section 7.3, with the value set as
 described in Section 3.2.9.  This will result in the created calendar
 object resource differing from the calendar data sent in the HTTP
 request.  As a result, clients MAY reload the calendar data from the
 server in order to update to the new server-generated state
 information.
 The server MUST return an error with the CALDAV:allowed-organizer-
 scheduling-object-change precondition code (Section 3.2.4.3) when the
 "Organizer" attempts to change the iCalendar data in a manner that is
 forbidden.

Daboo & Desruisseaux Standards Track [Page 17] RFC 6638 CalDAV Scheduling June 2012

3.2.1.3. Remove

 When an "Organizer" removes a scheduling object resource, the server
 MUST inspect each "ATTENDEE" property to determine whether to send a
 scheduling message.  The table below indicates the appropriate iTIP
 method used by the server, taking into account any "SCHEDULE-AGENT"
 property parameter (see Section 7.1) specified on each "ATTENDEE"
 property.
                  +------------------+-------------+
                  | SCHEDULE-AGENT   | iTIP METHOD |
                  +------------------+-------------+
                  | SERVER (default) | CANCEL      |
                  |                  |             |
                  | CLIENT           | --          |
                  |                  |             |
                  | NONE             | --          |
                  +------------------+-------------+

3.2.2. Attendee Scheduling Object Resources

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

3.2.2.1. Allowed "Attendee" Changes

 "Attendees" are allowed to make some changes to a scheduling object
 resource, though key properties such as start time, end time,
 location, and summary are typically under the control of the
 "Organizer".
 Servers MUST allow "Attendees" to make the following iCalendar data
 changes, subject to other restrictions, such as access privileges and
 preconditions:
 1.   change their own "PARTSTAT" iCalendar property parameter value.
 2.   add, modify, or remove any "TRANSP" iCalendar properties.
 3.   add, modify, or remove any "PERCENT-COMPLETE" iCalendar
      properties.
 4.   add, modify, or remove any "COMPLETED" iCalendar properties.
 5.   add, modify, or remove any "VALARM" iCalendar components.

Daboo & Desruisseaux Standards Track [Page 18] RFC 6638 CalDAV Scheduling June 2012

 6.   add, modify, or remove the "CALSCALE" iCalendar property within
      the top-level "VCALENDAR" component.
 7.   modify the "PRODID" iCalendar property within the top-level
      "VCALENDAR" component.
 8.   add "EXDATE" iCalendar properties and possibly remove components
      for overridden recurrence instances.
 9.   add, modify, or remove any "CREATED", "DTSTAMP", and
      "LAST-MODIFIED" iCalendar properties.
 10.  add, modify, or remove "SCHEDULE-STATUS" iCalendar property
      parameters on "ATTENDEE" properties that have a "SCHEDULE-AGENT"
      parameter set to "CLIENT".
 11.  add new components to represent overridden recurrence instances,
      provided the only changes to the recurrence instance follow the
      rules above.
 The server MUST return an error with the CALDAV:allowed-attendee-
 scheduling-object-change precondition code (Section 3.2.4.4) when the
 "Attendee" attempts to change the iCalendar data in a manner
 forbidden by the server.

3.2.2.2. Create

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

Daboo & Desruisseaux Standards Track [Page 19] RFC 6638 CalDAV Scheduling June 2012

 +----------------+--------------------------------------------------+
 | SCHEDULE-AGENT | Action                                           |
 +----------------+--------------------------------------------------+
 | SERVER         | The server will attempt to process changes to    |
 | (default)      | the resource using the normal rules for attendee |
 |                | scheduling object resources.                     |
 |                |                                                  |
 | CLIENT         | The server does no special processing of the     |
 |                | resource.  The client is assumed to be handling  |
 |                | "Attendee" replies, etc.                         |
 |                |                                                  |
 | NONE           | The server does no special processing of the     |
 |                | resource.                                        |
 +----------------+--------------------------------------------------+
 "SCHEDULE-STATUS" iCalendar property parameters are added or changed
 on "ORGANIZER" iCalendar properties in the scheduling object resource
 being created as described in Section 7.3, with the value set as
 described in Section 3.2.9.

3.2.2.3. Modify

 When a scheduling object resource is modified by an "Attendee", the
 server's behavior depends on the value of the "SCHEDULE-AGENT"
 iCalendar property parameter on the "ORGANIZER" iCalendar properties:
 +----------------+--------------------------------------------------+
 | SCHEDULE-AGENT | Action                                           |
 +----------------+--------------------------------------------------+
 | SERVER         | The server will attempt to process the update    |
 | (default)      | using the behavior listed below.                 |
 |                |                                                  |
 | CLIENT         | The server does no special processing of the     |
 |                | resource.  The client is assumed to be handling  |
 |                | any "Attendee" replies, etc.                     |
 |                |                                                  |
 | NONE           | The server does no special processing of the     |
 |                | resource.                                        |
 +----------------+--------------------------------------------------+
 The server will inspect the changes by comparing the new scheduling
 object resource with the existing scheduling object resource.
 If the "Attendee" changes one or more "PARTSTAT" iCalendar property
 values on any component, or adds an overridden component with a
 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".

Daboo & Desruisseaux Standards Track [Page 20] RFC 6638 CalDAV Scheduling June 2012

 If the "Attendee" adds an "EXDATE" property value to effectively
 remove a recurrence instance, the server MUST deliver an iTIP "REPLY"
 scheduling message to the "Organizer" to indicate that the "Attendee"
 has declined the instance.
 "SCHEDULE-STATUS" iCalendar property parameters are added or changed
 on "ORGANIZER" iCalendar properties in the scheduling object resource
 being modified as described in Section 7.3, with the value set as
 described in Section 3.2.9.  This will result in the updated calendar
 object resource differing from the calendar data sent in the HTTP
 request.  As a result, clients MAY reload the calendar data from the
 server in order to update to the new server-generated state
 information.

3.2.2.4. Remove

 When a scheduling object resource is removed by an "Attendee", the
 server's behavior depends on the value of the "SCHEDULE-AGENT"
 iCalendar property parameter on the "ORGANIZER" iCalendar properties:
 +----------------+--------------------------------------------------+
 | SCHEDULE-AGENT | Action                                           |
 +----------------+--------------------------------------------------+
 | SERVER         | The server will attempt to process the removal,  |
 | (default)      | taking into account any "Schedule-Reply" request |
 |                | header as per Section 8.1.                       |
 |                |                                                  |
 | CLIENT         | The server does no special processing of the     |
 |                | resource.  The client is assumed to be handling  |
 |                | any "Attendee" replies, etc.                     |
 |                |                                                  |
 | NONE           | The server does no special processing of the     |
 |                | resource.                                        |
 +----------------+--------------------------------------------------+

3.2.3. HTTP Methods

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

Daboo & Desruisseaux Standards Track [Page 21] RFC 6638 CalDAV Scheduling June 2012

3.2.3.1. PUT

 When the server receives a PUT method request, it MUST execute the
 following operations, provided all appropriate preconditions are met:
 +------------------------+--------------------------+---------------+
 | Existing Destination   | Resulting Destination    | Server        |
 | Resource               | Resource                 | Operation     |
 +------------------------+--------------------------+---------------+
 | None                   | Calendar object resource | None          |
 |                        |                          |               |
 | None                   | Scheduling object        | Create        |
 |                        | resource                 |               |
 |                        |                          |               |
 | Calendar object        | Calendar object resource | None          |
 | resource               |                          |               |
 |                        |                          |               |
 | Calendar object        | Scheduling object        | Create        |
 | resource               | resource                 |               |
 | Scheduling object      | Calendar object resource | Remove        |
 | resource               |                          |               |
 |                        |                          |               |
 | Scheduling object      | Scheduling object        | Modify        |
 | resource               | resource                 |               |
 +------------------------+--------------------------+---------------+

3.2.3.2. DELETE

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

Daboo & Desruisseaux Standards Track [Page 22] RFC 6638 CalDAV Scheduling June 2012

3.2.3.3. COPY

 When the server receives a COPY method request, it MUST execute the
 following operations based on the source and destination collections
 in the request:
 +-----------------------+------------------------+------------------+
 | Source Collection     | Destination Collection | Server Operation |
 +-----------------------+------------------------+------------------+
 | Non-calendar          | Non-calendar           | None             |
 | collection            | collection             |                  |
 |                       |                        |                  |
 | Non-calendar          | Calendar collection    | (1)              |
 | collection            |                        |                  |
 |                       |                        |                  |
 | Calendar collection   | Non-calendar           | None             |
 |                       | collection             |                  |
 |                       |                        |                  |
 | Calendar collection   | Calendar collection    | (2)              |
 +-----------------------+------------------------+------------------+
 Note (1):  The rules in Section 3.2.3.1 are applied for the
            destination of the COPY request.
 Note (2):  The server MAY reject this as per Section 3.2.4.1;
            otherwise, None.
 The behavior of a COPY method request on a calendar collection is
 undefined.

Daboo & Desruisseaux Standards Track [Page 23] RFC 6638 CalDAV Scheduling June 2012

3.2.3.4. MOVE

 When the server receives a MOVE method request, it MUST execute the
 following operations based on the source and destination collections
 in the request:
 +-----------------------+------------------------+------------------+
 | Source Collection     | Destination Collection | Server Operation |
 +-----------------------+------------------------+------------------+
 | Non-calendar          | Non-calendar           | None             |
 | collection            | collection             |                  |
 |                       |                        |                  |
 | Non-calendar          | Calendar collection    | (1)              |
 | collection            |                        |                  |
 |                       |                        |                  |
 | Calendar collection   | Non-calendar           | (2)              |
 |                       | collection             |                  |
 |                       |                        |                  |
 | Calendar collection   | Calendar collection    | None             |
 +-----------------------+------------------------+------------------+
 Note (1):  The rules in Section 3.2.3.1 are applied for the
            destination of the MOVE request.
 Note (2):  The rules in Section 3.2.3.2 are applied for the source of
            the MOVE request.
 The behavior of a MOVE method request on a calendar collection is
 undefined.

3.2.4. Additional Method Preconditions

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

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

 Name:  unique-scheduling-object-resource
 Namespace:  urn:ietf:params:xml:ns:caldav
 Apply to:  PUT, COPY, and MOVE
 Use with:  403 Forbidden

Daboo & Desruisseaux Standards Track [Page 24] RFC 6638 CalDAV Scheduling June 2012

 Purpose:  (precondition) -- Servers MAY reject requests to create a
    scheduling object resource with an iCalendar "UID" property value
    already in use by another scheduling object resource owned by the
    same user in other calendar collections.  Servers SHOULD report
    the URL of the scheduling object resource that is already making
    use of the same "UID" property value in the DAV:href element.
 Definition:
   <!ELEMENT unique-scheduling-object-resource (DAV:href?)>
 Example:
   <C:unique-scheduling-object-resource xmlns:D="DAV:"
       xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:href>/home/bernard/calendars/personal/abc123.ics</D:href>
   </C:unique-scheduling-object-resource>

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

 Name:  same-organizer-in-all-components
 Namespace:  urn:ietf:params:xml:ns:caldav
 Apply to:  PUT, COPY, and MOVE
 Use with:  403 Forbidden
 Purpose:  (precondition) -- All the calendar components in a
    scheduling object resource MUST contain the same "ORGANIZER"
    property value when present.
 Definition:
   <!ELEMENT same-organizer-in-all-components EMPTY>

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

 Name:  allowed-organizer-scheduling-object-change
 Namespace:  urn:ietf:params:xml:ns:caldav
 Apply to:  PUT, COPY, and MOVE
 Use with:  403 Forbidden

Daboo & Desruisseaux Standards Track [Page 25] RFC 6638 CalDAV Scheduling June 2012

 Purpose:  (precondition) -- Servers MAY impose restrictions on
    modifications allowed by an "Organizer".  For instance, servers
    MAY prevent the "Organizer" from 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 does not have the
    "SCHEDULE-AGENT" property parameter.  See Section 3.2.1.
 Definition:
   <!ELEMENT allowed-organizer-scheduling-object-change EMPTY>

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

 Name:  allowed-attendee-scheduling-object-change
 Namespace:  urn:ietf:params:xml:ns:caldav
 Apply to:  PUT, COPY, and MOVE
 Use with:  403 Forbidden
 Purpose:  (precondition) -- Servers MAY impose restrictions on
    modifications allowed by an "Attendee", subject to the allowed
    changes specified in Section 3.2.2.1.
 Definition:
   <!ELEMENT allowed-attendee-scheduling-object-change EMPTY>

3.2.5. DTSTAMP and SEQUENCE Properties

 The server MUST ensure that a "DTSTAMP" iCalendar property is present
 and set the value to the UTC time that the scheduling message was
 generated (as required by iCalendar).
 The server MUST ensure that for each type of scheduling operation,
 the "SEQUENCE" iCalendar property value is updated as per iTIP
 [RFC5546].

Daboo & Desruisseaux Standards Track [Page 26] RFC 6638 CalDAV Scheduling June 2012

3.2.6. Restrict Recurrence Instances Sent to "Attendees"

 Servers MUST ensure that "Attendees" only get information about
 recurrence instances that explicitly include them as an "Attendee",
 when delivering scheduling messages for recurring calendar
 components.
 For example, if an "Attendee" is invited to only a single instance of
 a recurring event, the organizer scheduling object resource will
 contain an overridden instance in the form of a separate calendar
 component.  That separate calendar component will include the
 "ATTENDEE" property referencing the "one-off" "Attendee".  That
 "Attendee" will not be listed in any other calendar components in the
 scheduling object resource.  Any scheduling messages delivered to the
 "Attendee" will only contain information about this overridden
 instance.
 As another example, an "Attendee" could be excluded from one instance
 of a recurring event.  In that case, the organizer scheduling object
 resource will include an overridden instance with an "ATTENDEE" list
 that does not include the "Attendee" being excluded.  Any scheduling
 messages delivered to the "Attendee" will not specify the overridden
 instance but rather will include an "EXDATE" property in the "master"
 component that defines the recurrence set.

3.2.7. Forcing the Server to Send a Scheduling Message

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

Daboo & Desruisseaux Standards Track [Page 27] RFC 6638 CalDAV Scheduling June 2012

3.2.8. "Attendee" Participation Status

 This section specifies additional requirements on the handling of the
 "PARTSTAT" property parameter when the "SCHEDULE-AGENT" property
 parameter on the corresponding "ATTENDEE" property is set to the
 value "SERVER" or is not present.
 A reschedule occurs when any "DTSTART", "DTEND", "DURATION", "DUE",
 "RRULE", "RDATE", or "EXDATE" property changes in a calendar
 component such that existing recurrence instances are impacted by the
 changes, as shown in the table below.  Servers MUST reset the
 "PARTSTAT" property parameter value of all "ATTENDEE" properties,
 except the one that corresponds to the "Organizer", to "NEEDS-ACTION"
 for each calendar component change that causes any instance to be
 rescheduled.
 +-----------+-------------------------------------------------------+
 | Property  | Server Action                                         |
 +-----------+-------------------------------------------------------+
 | DTSTART,  | Any change to these properties results in "PARTSTAT"  |
 | DTEND,    | being set to "NEEDS-ACTION".                          |
 | DURATION, |                                                       |
 | DUE       |                                                       |
 |           |                                                       |
 | RRULE     | A change to or addition of this property that results |
 |           | in the addition of new recurring instances or a       |
 |           | change in time for existing recurring instances       |
 |           | results 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       |
 |           | results in "PARTSTAT" being reset to "NEEDS-ACTION"   |
 |           | on each affected component.                           |
 |           |                                                       |
 | EXDATE    | A change to or removal of this property that results  |
 |           | in the reinstatement of recurring instances results   |
 |           | in "PARTSTAT" being set to "NEEDS-ACTION" on each     |
 |           | affected component.                                   |
 +-----------+-------------------------------------------------------+
 The server MAY allow the "Organizer's" client to change an
 "Attendee's" "PARTSTAT" property parameter value to "NEEDS-ACTION" at
 any other time (e.g., when the "LOCATION" property value changes, an
 "Organizer" might wish to re-invite "Attendees" who might be impacted
 by the change).

Daboo & Desruisseaux Standards Track [Page 28] RFC 6638 CalDAV Scheduling June 2012

3.2.9. Schedule Status Values

 When scheduling with an "Attendee", there are two types of status
 information that can be returned during the operation.  The first
 type of status information is a "delivery" status that indicates
 whether the scheduling message from the "Organizer" to the "Attendee"
 was delivered or not, or what the current status of delivery is.  The
 second type of status information is a "reply" status corresponding
 to the "Attendee's" own "REQUEST-STATUS" information from the
 scheduling message reply that is sent back to the "Organizer".
 Similarly, when an "Attendee" sends a reply back to the "Organizer",
 there will be "delivery" status information for the scheduling
 message sent to the "Organizer".  However, there is no
 "REQUEST-STATUS" sent back by the "Organizer", so there is no
 equivalent of the "reply" status as per scheduling messages to
 "Attendees".
 The "delivery" status information on an "ORGANIZER" or "ATTENDEE"
 iCalendar property is conveyed in the "SCHEDULE-STATUS" property
 parameter value (Section 7.3).  The status code value for "delivery"
 status can be one of the following:
 +----------+--------------------------------------------------------+
 | Delivery | Description                                            |
 | Status   |                                                        |
 | Code     |                                                        |
 +----------+--------------------------------------------------------+
 | 1.0      | The scheduling message is pending.  That is, the       |
 |          | server is still in the process of sending the message. |
 |          | The status code value can be expected to change once   |
 |          | the server has completed its sending and delivery      |
 |          | attempts.                                              |
 |          |                                                        |
 | 1.1      | The scheduling message has been successfully sent.     |
 |          | However, the server does not have explicit information |
 |          | about whether the scheduling message was successfully  |
 |          | delivered to the recipient.  This state can occur with |
 |          | "store and forward" style scheduling protocols such as |
 |          | iMIP [RFC6047] (iTIP using email).                     |
 |          |                                                        |
 | 1.2      | The scheduling message has been successfully           |
 |          | delivered.                                             |
 |          |                                                        |

Daboo & Desruisseaux Standards Track [Page 29] RFC 6638 CalDAV Scheduling June 2012

 | 3.7      | The scheduling message was not delivered because the   |
 |          | server did not recognize the calendar user address as  |
 |          | a valid calendar user.  Note that this code applies to |
 |          | both "Organizer" and "Attendee" calendar user          |
 |          | addresses.                                             |
 |          |                                                        |
 | 3.8      | The scheduling message was not delivered due to        |
 |          | insufficient privileges.  Note that this code applies  |
 |          | to privileges granted by both the "Organizer" and      |
 |          | "Attendee" calendar users.                             |
 |          |                                                        |
 | 5.1      | The scheduling message was not delivered because the   |
 |          | server could not complete delivery of the message.     |
 |          | This is likely due to a temporary failure, and the     |
 |          | originator can try to send the message again at a      |
 |          | later time.                                            |
 |          |                                                        |
 | 5.2      | The scheduling message was not delivered because the   |
 |          | server was not able to find a way to deliver the       |
 |          | message.  This is likely a permanent failure, and the  |
 |          | originator ought not try to send the message again, at |
 |          | least without verifying/correcting the calendar user   |
 |          | address of the recipient.                              |
 |          |                                                        |
 | 5.3      | The scheduling message was not delivered and was       |
 |          | rejected because scheduling with that recipient is not |
 |          | allowed.  This is likely a permanent failure, and the  |
 |          | originator ought not try to send the message again.    |
 +----------+--------------------------------------------------------+
 The status code for "reply" status can be any of the valid iTIP
 [RFC5546] "REQUEST-STATUS" values.
 The 1.xx "REQUEST-STATUS" codes are new.  This specification modifies
 item (2) of Section 3.6 of [RFC5546] by adding the following
 restriction:
    For a 1.xx code, all components MUST have exactly the same code.

Daboo & Desruisseaux Standards Track [Page 30] RFC 6638 CalDAV Scheduling June 2012

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

3.2.9.1. Status Code 1.0

 Status Code:  1.0
 Status Description:  Pending.
 Status Exception Data:  None.
 Description:  Delivery of the iTIP message is pending.

3.2.9.2. Status Code 1.1

 Status Code:  1.1
 Status Description:  Sent.
 Status Exception Data:  None.
 Description:  The iTIP message has been sent, though no information
    about successful delivery is known.

3.2.9.3. Status Code 1.2

 Status Code:  1.2
 Status Description:  Delivered.
 Status Exception Data:  None.
 Description:  The iTIP message has been sent and delivered.

3.2.10. Avoiding Conflicts when Updating Scheduling Object Resources

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

Daboo & Desruisseaux Standards Track [Page 31] RFC 6638 CalDAV Scheduling June 2012

 This specification introduces a new WebDAV resource property CALDAV:
 schedule-tag with a corresponding response header "Schedule-Tag", and
 a new "If-Schedule-Tag-Match" request header to allow client changes
 to be appropriately merged with server changes in the case where the
 changes on the server were the result of an "inconsequential"
 scheduling message update (one that simply updates the status
 information of "Attendees" due to a reply from another "Attendee").
 Servers MUST automatically resolve conflicts with "inconsequential"
 changes done to scheduling object resources when the "If-Schedule-
 Tag-Match" request header is specified.  The If-Schedule-Tag-Match
 request header applies only to the Request-URI, and not to the
 destination of a COPY or MOVE.
 A response to any successful GET or PUT request targeting a
 scheduling object resource MUST include a Schedule-Tag response
 header with the value set to the same value as the CALDAV:schedule-
 tag WebDAV property of the resource.
 A response to any successful COPY or MOVE request that specifies a
 Destination request header targeting a scheduling object resource
 MUST include a Schedule-Tag response header with the value set to the
 same value as the CALDAV:schedule-tag WebDAV property of the
 destination resource.
 Clients SHOULD use the If-Schedule-Tag-Match header on requests that
 update scheduling object resources, instead of HTTP ETag-based
 precondition tests (e.g., If-Match).  Normal ETag-based precondition
 tests are used in all other cases, e.g., for synchronization.
 The value of the CALDAV:schedule-tag property changes according to
 these rules:
 o  For an "Organizer's" copy of a scheduling object resource:
    1.  The server MUST NOT change the CALDAV:schedule-tag property
        value when the scheduling object resource is updated as the
        result of automatically processing a scheduling message reply
        from an "Attendee".  For instance, when an "Attendee" replies
        to the "Organizer", the CALDAV:schedule-tag property is
        unchanged after the "Organizer's" scheduling object resource
        has been automatically updated by the server with the
        "Attendee's" new participation status.
    2.  The server MUST change the CALDAV:schedule-tag property value
        when the scheduling object resource is changed directly via an
        HTTP request (e.g., PUT, COPY, or MOVE).

Daboo & Desruisseaux Standards Track [Page 32] RFC 6638 CalDAV Scheduling June 2012

 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 specifies changes in the participation
        status of "Attendees".  For instance, when "Attendee" "A"
        replies to "Organizer" "O", and "Attendee" "B" receives a
        scheduling message update from "Organizer" "O" with the new
        participation status of "Attendee" "A", the CALDAV:schedule-
        tag property of "Attendee" "B"'s scheduling object resource
        would remain the same.
    3.  The server MUST change the CALDAV:schedule-tag property value
        when the scheduling object resource is changed directly via an
        HTTP request (e.g., PUT, COPY, or MOVE).

3.2.10.1. PUT

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

3.2.10.2. DELETE, COPY, or MOVE

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

Daboo & Desruisseaux Standards Track [Page 33] RFC 6638 CalDAV Scheduling June 2012

4. Processing Incoming Scheduling Messages

 Scheduling operations can cause the delivery of a scheduling message
 into an "Organizer's" or "Attendee's" scheduling Inbox collection.
 Servers MUST automatically process incoming scheduling messages using
 the rules defined by [RFC5546], by creating or updating the
 corresponding scheduling object resources on calendars owned by the
 owner of the scheduling Inbox collection.  In addition, the
 scheduling message is stored in the scheduling Inbox collection as an
 indicator to the client that a scheduling operation has taken place.
 Scheduling messages are typically removed from the scheduling Inbox
 collection by the client once the calendar user has acknowledged the
 change.
 The server MUST take into account privileges on the scheduling Inbox
 collection when processing incoming scheduling messages, to determine
 whether delivery of the scheduling message is allowed.  Privileges on
 calendars containing any matching scheduling object resource are not
 considered in this case (i.e., a schedule message from another user
 can cause modifications to resources in calendar collections that the
 other user would not normally have read or write access to).
 Additionally, servers MUST take into account any scheduling Inbox
 collection preconditions (see Section 2.2) when delivering the
 scheduling message, and MUST take into account the similar
 preconditions on any calendar collection that contains, or would
 contain, the corresponding scheduling object resource.

4.1. Processing "Organizer" Requests, Additions, and Cancellations

 For a scheduling message sent by an "Organizer", the server first
 tries to locate a corresponding scheduling object resource belonging
 to the "Attendee".  If no matching scheduling object resource exists,
 the server treats the scheduling message as a new message; otherwise,
 it is treated as an update.
 In the case of a new message, the server processes the scheduling
 message and creates a new scheduling object resource as per
 Section 4.3.
 In the case of an update, the server processes the scheduling message
 and updates the matching scheduling object resource belonging to the
 "Attendee" to reflect the changes sent by the "Organizer".
 In each case, the scheduling message MUST only appear in the
 "Attendee's" scheduling Inbox collection once all automatic
 processing has been done.

Daboo & Desruisseaux Standards Track [Page 34] RFC 6638 CalDAV Scheduling June 2012

4.2. Processing "Attendee" Replies

 For a scheduling message reply sent by an "Attendee", the server
 first locates the corresponding scheduling object resource belonging
 to the "Organizer".  If the corresponding scheduling object resource
 cannot be found, the server SHOULD ignore the scheduling message.
 The server MUST then update the "PARTSTAT" iCalendar property
 parameter value of each "ATTENDEE" iCalendar property in the
 scheduling object resource to match the changes indicated in the
 reply (taking into account the fact that an "Attendee" could have
 created a new overridden iCalendar component to indicate different
 participation status on one or more instances of a recurring event).
 The server MUST also update or add the "SCHEDULE-STATUS" property
 parameter on each matching "ATTENDEE" iCalendar property and set its
 value to that of the "REQUEST-STATUS" property in the reply, or to
 "2.0" if "REQUEST-STATUS" is not present (also taking into account
 recurrence instances).  If there are multiple "REQUEST-STATUS"
 properties in the reply, the "SCHEDULE-STATUS" property parameter
 value is set to a comma-separated list of status codes, one from each
 "REQUEST-STATUS" property.
 The server SHOULD send scheduling messages to all the other
 "Attendees" indicating the change in participation status of the
 "Attendee" replying, subject to the recurrence requirements of
 Section 3.2.6.
 The scheduling message MUST only appear in the "Organizer's"
 scheduling Inbox collection once all automatic processing has been
 done.

4.3. Default Calendar Collection

 The server processes scheduling messages received for an "Attendee"
 by creating a new scheduling object resource in a calendar collection
 belonging to the "Attendee", when one does not already exist.  A
 calendar user that is an "Attendee" in a scheduling operation MUST
 have at least one valid calendar collection available.  If there is
 no valid calendar collection, then the server MUST reject the attempt
 to deliver the scheduling message to the "Attendee".
 Servers MAY provide support for a default calendar collection -- that
 is, the calendar collection in which new scheduling object resources
 will be created.  The CALDAV:schedule-default-calendar-URL WebDAV
 property, which can be present on the scheduling Inbox collection of
 a calendar user, specifies whether this calendar user has a default
 calendar collection.  See Section 9.2.

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 Servers SHOULD create new scheduling object resources in the default
 calendar collection, if the CALDAV:schedule-default-calendar-URL
 WebDAV property is set.
 Servers MAY allow clients to change the default calendar collection
 by changing the value of the CALDAV:schedule-default-calendar-URL
 WebDAV property on the scheduling Inbox collection.  However, the
 server MUST ensure that any new value for that property refers to a
 valid calendar collection belonging to the owner of the scheduling
 Inbox collection.
 Servers MUST reject any attempt to delete the default calendar
 collection.

4.3.1. Additional Method Preconditions

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

4.3.1.1. CALDAV:default-calendar-needed Precondition

 Name:  default-calendar-needed
 Namespace:  urn:ietf:params:xml:ns:caldav
 Apply to:  DELETE
 Use with:  403 Forbidden
 Purpose:  (precondition) -- The client attempted to delete the
    calendar collection currently referenced by the CALDAV:schedule-
    default-calendar-URL property, or attempted to remove the CALDAV:
    schedule-default-calendar-URL property on the scheduling Inbox
    collection on a server that doesn't allow such operations.
 Definition:
   <!ELEMENT default-calendar-needed EMPTY>

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

 Name:  valid-schedule-default-calendar-URL
 Namespace:  urn:ietf:params:xml:ns:caldav
 Apply to:  PROPPATCH

Daboo & Desruisseaux Standards Track [Page 36] RFC 6638 CalDAV Scheduling June 2012

 Use with:  403 Forbidden
 Purpose:  (precondition) -- The client attempted to set the CALDAV:
    schedule-default-calendar-URL property to a DAV:href element that
    doesn't reference a valid calendar collection.  Note: Servers that
    do not allow clients to change the CALDAV:schedule-default-
    calendar-URL property would simply return the DAV:cannot-modify-
    protected-property precondition defined in Section 16 of WebDAV
    [RFC4918].
 Definition:
   <!ELEMENT valid-schedule-default-calendar-URL EMPTY>

5. Request for Busy Time Information

 Busy time information of one or more calendar users can be determined
 by submitting a POST request targeted at the scheduling Outbox
 collection of the calendar user requesting the information (the
 "Organizer").  To accomplish this, the request body MUST contain a
 "VFREEBUSY" calendar component with the "METHOD" iCalendar property
 set to the value "REQUEST" as specified in Section 3.3.2 of iTIP
 [RFC5546].  The resource identified by the Request-URI MUST be a
 resource collection of type CALDAV:schedule-outbox (Section 2.1).
 The "ORGANIZER" property value in the "VFREEBUSY" component MUST
 match one of the calendar user addresses of the owner of the Outbox
 collection.
 A response to a busy time request that indicates status for one or
 more calendar users MUST be an XML document with a CALDAV:schedule-
 response XML element as its root element.  This element MUST contain
 one CALDAV:response element for each calendar user, with each such
 element in turn containing elements that indicate which calendar user
 they correspond to, the scheduling status for that calendar user, any
 error codes, and an optional description.  For a successful busy time
 request, a CALDAV:calendar-data element is also present for each
 calendar user, containing the actual busy time information (i.e., an
 iCalendar "VFREEBUSY" component).  See Section 10 for details on the
 child elements.  See Appendix B.5 for an example busy time request
 and response.

Daboo & Desruisseaux Standards Track [Page 37] RFC 6638 CalDAV Scheduling June 2012

5.1. Status Codes

 The list below summarizes the most common status codes used for this
 method.  However, clients need to be prepared to handle other
 2/3/4/5xx series status codes as well.
    200 (OK) - The command succeeded.
    204 (No Content) - The command succeeded.
    400 (Bad Request) - The client has provided an invalid scheduling
    message.
    403 (Forbidden) - The client cannot submit a scheduling message to
    the specified Request-URI.
    404 (Not Found) - The URL in the Request-URI was not present.
    423 (Locked) - The specified resource is locked, and the client
    either is not a lock owner or the lock type requires a lock token
    to be submitted and the client did not submit it.

5.2. Additional Method Preconditions

 The following are existing preconditions that are reused for the POST
 method on an Outbox collection.
 o  DAV:need-privileges [RFC3744]
 o  CALDAV:supported-calendar-data [RFC4791]
 o  CALDAV:valid-calendar-data [RFC4791]
 o  CALDAV:max-resource-size [RFC4791]
 The following are new method preconditions for the POST method on an
 Outbox collection.

5.2.1. CALDAV:valid-scheduling-message Precondition

 Name:  valid-scheduling-message
 Namespace:  urn:ietf:params:xml:ns:caldav
 Apply to:  POST
 Use with:  400 Bad Request

Daboo & Desruisseaux Standards Track [Page 38] RFC 6638 CalDAV Scheduling June 2012

 Purpose:  (precondition) -- The resource submitted in the POST
    request MUST obey all the restrictions specified in Section 3.3.2
    of iTIP [RFC5546].
 Definition:
   <!ELEMENT valid-scheduling-message EMPTY>

5.2.2. CALDAV:valid-organizer Precondition

 Name:  valid-organizer
 Namespace:  urn:ietf:params:xml:ns:caldav
 Apply to:  POST
 Use with:  403 Forbidden
 Purpose:  (precondition) -- The "ORGANIZER" property value in the
    POST request's scheduling message MUST match one of the calendar
    user addresses of the owner of the scheduling Outbox collection
    being targeted by the request.
 Definition:
   <!ELEMENT valid-organizer EMPTY>

6. Scheduling Privileges

 New scheduling privileges are defined in this section.  All the
 scheduling privileges MUST be non-abstract and MUST appear in the
 DAV:supported-privilege-set property of scheduling Outbox and Inbox
 collections on which they are defined.
 The tables specified in Appendix A clarify which scheduling methods
 (e.g., "REQUEST", "REPLY", etc.) are controlled by each scheduling
 privilege defined in this section.

6.1. Privileges on Scheduling Inbox Collections

 This section defines new WebDAV Access Control List (ACL) [RFC3744]
 privileges that are defined 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.

Daboo & Desruisseaux Standards Track [Page 39] RFC 6638 CalDAV Scheduling June 2012

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

6.1.1. CALDAV:schedule-deliver Privilege

 CALDAV:schedule-deliver is an aggregate privilege as per Section 6.3.
   <!ELEMENT schedule-deliver EMPTY>

6.1.2. CALDAV:schedule-deliver-invite Privilege

 The CALDAV:schedule-deliver-invite privilege controls the processing
 and delivery of scheduling messages coming from an "Organizer".
   <!ELEMENT schedule-deliver-invite EMPTY>

6.1.3. CALDAV:schedule-deliver-reply Privilege

 The CALDAV:schedule-deliver-reply privilege controls the processing
 and delivery of scheduling messages coming from an "Attendee".
   <!ELEMENT schedule-deliver-reply EMPTY>

6.1.4. CALDAV:schedule-query-freebusy Privilege

 The CALDAV:schedule-query-freebusy privilege controls freebusy
 requests targeted at the owner of the scheduling Inbox collection.
   <!ELEMENT schedule-query-freebusy EMPTY>

6.2. Privileges on Scheduling Outbox Collections

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

Daboo & Desruisseaux Standards Track [Page 40] RFC 6638 CalDAV Scheduling June 2012

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

6.2.1. CALDAV:schedule-send Privilege

 CALDAV:schedule-send is an aggregate privilege as per Section 6.3.
   <!ELEMENT schedule-send EMPTY>

6.2.2. CALDAV:schedule-send-invite Privilege

 The CALDAV:schedule-send-invite privilege controls the sending of
 scheduling messages by "Organizers".
 Users granted the DAV:bind privilege on a calendar collection, or the
 DAV:write privilege on scheduling object resources, will also need
 the CALDAV:schedule-send-invite privilege granted on the scheduling
 Outbox collection of the owner of the calendar collection or
 scheduling object resource in order to be allowed to create, modify,
 or delete scheduling object resources in a way that will trigger the
 CalDAV server to deliver scheduling messages to "Attendees".
   <!ELEMENT schedule-send-invite EMPTY>

6.2.3. CALDAV:schedule-send-reply Privilege

 The CALDAV:schedule-send-reply privilege controls the sending of
 scheduling messages by "Attendees".
 Users granted the DAV:bind privilege on a calendar collection, or the
 DAV:write privilege on scheduling object resources, will also need
 the CALDAV:schedule-send-reply privilege granted on the scheduling
 Outbox collection of the owner of the calendar collection or
 scheduling object resource in order to be allowed to create, modify,
 or delete scheduling object resources in a way that will trigger the
 CalDAV server to deliver scheduling message replies to the
 "Organizer".
   <!ELEMENT schedule-send-reply EMPTY>

6.2.4. CALDAV:schedule-send-freebusy Privilege

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

Daboo & Desruisseaux Standards Track [Page 41] RFC 6638 CalDAV Scheduling June 2012

6.3. Aggregation of Scheduling Privileges

 Server implementations MUST aggregate the scheduling privileges as
 follows:
    DAV:all contains CALDAV:schedule-deliver and CALDAV:schedule-send;
    CALDAV:schedule-deliver contains CALDAV:schedule-deliver-invite,
    CALDAV:schedule-deliver-reply, and CALDAV:schedule-query-freebusy;
    CALDAV:schedule-send contains CALDAV:schedule-send-invite, CALDAV:
    schedule-send-reply, and CALDAV:schedule-send-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]

7. Additional iCalendar Property Parameters

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

7.1. Schedule Agent Parameter

 Parameter Name:  SCHEDULE-AGENT
 Purpose:  To specify the agent expected to deliver scheduling
    messages to the corresponding "Organizer" or "Attendee".

Daboo & Desruisseaux Standards Track [Page 42] RFC 6638 CalDAV Scheduling June 2012

 Format Definition:  This property parameter is defined by the
    following notation:
   scheduleagentparam = "SCHEDULE-AGENT" "="
                    ("SERVER"      ; The server handles scheduling
                   / "CLIENT"      ; The client handles scheduling
                   / "NONE"        ; No scheduling
                   / x-name        ; Experimental type
                   / iana-token)   ; Other IANA-registered type
   ;
   ; If the parameter is not present, its value defaults to SERVER.
   ; "x-name" and "iana-token" are defined in Section 3.1 of
   ; [RFC5545].
 Description:  This property parameter MAY be specified on "ORGANIZER"
    or "ATTENDEE" iCalendar properties.  In the absence of this
    parameter, the value "SERVER" MUST be used for the default
    behavior.  The value determines whether or not a scheduling
    operation on a server will cause a scheduling message to be sent
    to the corresponding calendar user identified by the "ORGANIZER"
    or "ATTENDEE" property value.  When the value "SERVER" is
    specified, or the parameter is absent, then it is the server's
    responsibility to send a scheduling message as part of a
    scheduling operation.  When the value "CLIENT" is specified, that
    indicates that the client is handling scheduling messages with the
    calendar user itself.  When "NONE" is specified, no scheduling
    messages are being sent to the calendar user.
    Servers MUST NOT include this parameter in any scheduling messages
    sent as the result of a scheduling operation.
    Clients MUST NOT include this parameter in any scheduling messages
    that they themselves send.
    The parameter value MUST be the same on every "ORGANIZER" property
    in a scheduling object resource.
    The parameter value MUST be the same on each "ATTENDEE" property
    whose values match in a scheduling object resource.
    Servers and clients MUST treat x-name and iana-token values they
    do not recognize the same way as they would the "NONE" value.
 Example:
   ORGANIZER;SCHEDULE-AGENT=SERVER:mailto:bernard@example.com
   ATTENDEE;SCHEDULE-AGENT=NONE:mailto:cyrus@example.com

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7.2. Schedule Force Send Parameter

 Parameter Name:  SCHEDULE-FORCE-SEND
 Purpose:  To force a scheduling message to be sent to the calendar
    user specified by the property.
 Format Definition:  This property parameter is defined by the
    following notation:
   scheduleforcesendparam = "SCHEDULE-FORCE-SEND" "="
                          ("REQUEST"    ; Force a "REQUEST"
                         / "REPLY"      ; Force a "REPLY"
                         / iana-token)
   ;
   ; "iana-token" is defined in Section 3.1 of [RFC5545].  Its value
   ; MUST be an IANA-registered iCalendar "METHOD" property value.
 Description:  This property parameter MAY be specified on "ATTENDEE"
    and "ORGANIZER" properties on which the "SCHEDULE-AGENT" property
    parameter is set to the value "SERVER" or is not specified.  This
    property parameter is used to force a server to send a scheduling
    message to a specific calendar user in situations where the server
    would not send a scheduling message otherwise (e.g., when no
    change that warrants the delivery of a new scheduling message was
    performed on the scheduling object resource).  An "Organizer" MAY
    specify this parameter on an "ATTENDEE" property with the value
    "REQUEST" to force a "REQUEST" scheduling message to be sent to
    this "Attendee".  An "Attendee" MAY specify this parameter on the
    "ORGANIZER" with the value "REPLY" to force a "REPLY" scheduling
    message to be sent to the "Organizer".
    Servers MUST NOT preserve this property parameter in scheduling
    object resources, nor include it in any scheduling messages sent
    as the result of a scheduling operation.
    Clients MUST NOT include this parameter in any scheduling messages
    that they themselves send.
    Servers MUST set the "SCHEDULE-STATUS" parameter of the "ATTENDEE"
    or "ORGANIZER" to 2.3 (i.e., "Success; invalid property parameter
    ignored"; see Section 3.6 of [RFC5546]) when the "SCHEDULE-FORCE-
    SEND" parameter is set to an iana-token value they do not
    recognize.

Daboo & Desruisseaux Standards Track [Page 44] RFC 6638 CalDAV Scheduling June 2012

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

7.3. Schedule Status Parameter

 Parameter Name:  SCHEDULE-STATUS
 Purpose:  To specify the status codes returned from processing of the
    most recent scheduling message sent to the corresponding
    "Attendee", or received from the corresponding "Organizer".
 Format Definition:  This property parameter is defined by the
    following notation:
   schedulestatusparam = "SCHEDULE-STATUS" "="
                       ( statcode
                      / DQUOTE statcode *("," statcode) DQUOTE)
   ;
   ; "statcode" is defined in Section 3.8.8.3 of [RFC5545].  The
   ; value is a single "statcode" or a comma-separated list of
   ; "statcode" values.
 Description:  This property parameter MAY be specified on the
    "ATTENDEE" and "ORGANIZER" properties.
    Servers MUST only add or change this property parameter on any
    "ATTENDEE" properties corresponding to calendar users who were
    sent a scheduling message via a scheduling operation.  Clients
    SHOULD NOT change or remove this parameter if it was provided by
    the server.  In the case where the client is handling the
    scheduling, the client MAY add, change, or remove this parameter
    to indicate the last scheduling message status it received.
    Servers MUST add this parameter to any "ORGANIZER" properties
    corresponding to calendar users who were sent a scheduling message
    reply by an "Attendee" via a scheduling operation.  Clients SHOULD
    NOT change or remove this parameter if it was provided by the
    server.  In the case where the client is handling the scheduling,
    the client MAY add, change, or remove this parameter to indicate
    the last scheduling message status it received.
    Servers MUST NOT include this parameter in any scheduling messages
    sent as the result of a scheduling operation.
    Clients MUST NOT include this parameter in any scheduling messages
    that they themselves send.

Daboo & Desruisseaux Standards Track [Page 45] RFC 6638 CalDAV Scheduling June 2012

    Values for this property parameter are described in Section 3.2.9.
 Example:
   ATTENDEE;SCHEDULE-STATUS="2.0":mailto:bernard@example.com
   ATTENDEE;SCHEDULE-STATUS="2.0,2.4":mailto:cyrus@example.com

8. Additional Message Header Fields

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

8.1. Schedule-Reply Request Header

   Schedule-Reply = "Schedule-Reply" ":" ("T" | "F")
 Example:
   Schedule-Reply: F
 When an "Attendee" removes a scheduling object resource as per
 Section 3.2.2.4, and the Schedule-Reply header is set to the value
 "T" (true) or is not present, the server MUST send an appropriate
 reply scheduling message with the "Attendee's" "PARTSTAT" iCalendar
 property parameter value set to "DECLINED" as part of its normal
 scheduling operation processing.
 When the Schedule-Reply header is set to the value "F" (false), the
 server MUST NOT send a scheduling message as part of its normal
 scheduling operation processing.
 The Schedule-Reply request header is used by a client to indicate to
 a server whether or not a scheduling operation ought to occur when an
 "Attendee" deletes a scheduling object resource.  In particular, it
 controls whether a reply scheduling message is sent to the
 "Organizer" as a result of the removal.  There are situations in
 which unsolicited scheduling messages need to be silently removed (or
 ignored) for security or privacy reasons.  This request header allows
 the scheduling object resource to be removed if such a need arises.

8.2. Schedule-Tag Response Header

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

Daboo & Desruisseaux Standards Track [Page 46] RFC 6638 CalDAV Scheduling June 2012

   Schedule-Tag = "Schedule-Tag" ":" opaque-tag
   ; "opaque-tag" is defined in Section 3.11 of [RFC2616].
 Example:
   Schedule-Tag: "12ab34-cd56ef"

8.3. If-Schedule-Tag-Match Request Header

 The If-Schedule-Tag-Match request header field is used with a method
 to make it conditional.  Clients can set this header to the value
 returned in the Schedule-Tag response header, or the CALDAV:schedule-
 tag property, of a scheduling object resource previously retrieved
 from the server to avoid overwriting "consequential" changes to the
 scheduling object resource.
 All scheduling object resources MUST support the If-Schedule-Tag-
 Match header.
   If-Schedule-Tag-Match = "If-Schedule-Tag-Match" ":" opaque-tag
   ; "opaque-tag" is defined in Section 3.11 of [RFC2616].
 Example:
   If-Schedule-Tag-Match: "12ab34-cd56ef"

9. Additional WebDAV Properties

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

9.1. CALDAV:schedule-calendar-transp Property

 Name:  schedule-calendar-transp
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  Determines whether the calendar object resources in a
    calendar collection will affect the owner's busy time information.
 Protected:  This property MAY be protected and SHOULD NOT be returned
    by a PROPFIND DAV:allprop request (as defined in Section 14.2 of
    [RFC4918]).
 COPY/MOVE behavior:  This property value SHOULD be kept during a MOVE
    operation, and SHOULD be copied and preserved in a COPY.

Daboo & Desruisseaux Standards Track [Page 47] RFC 6638 CalDAV Scheduling June 2012

 Description:  This property SHOULD be defined on all calendar
    collections.  If present, it contains one of two XML elements that
    indicate whether the calendar object resources in the calendar
    collection ought to contribute to the owner's busy time.  When the
    CALDAV:opaque element is used, all calendar object resources in
    the corresponding calendar collection MUST contribute to busy
    time, assuming that access privileges and other iCalendar
    properties allow it to.  When the CALDAV:transparent XML element
    is used, the calendar object resources in the corresponding
    calendar collection MUST NOT contribute to busy time.
    If this property is not present on a calendar collection, then the
    default value CALDAV:opaque MUST be assumed.
 Definition:
   <!ELEMENT schedule-calendar-transp (opaque | transparent)>
   <!ELEMENT opaque EMPTY>
   <!-- Affects busy time searches -->
   <!ELEMENT transparent EMPTY>
   <!-- Invisible to busy time searches -->
 Example:
   <C:schedule-calendar-transp
        xmlns:C="urn:ietf:params:xml:ns:caldav">
     <C:opaque/>
   </C:schedule-calendar-transp>

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

 Name:  schedule-default-calendar-URL
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  Specifies a default calendar for an "Attendee" where new
    scheduling object resources are created.
 Protected:  This property MAY be protected in the case where a server
    does not support changing the default calendar, or does not
    support a default calendar.
 COPY/MOVE behavior:  This property is only defined on a scheduling
    Inbox collection that cannot be moved or copied.

Daboo & Desruisseaux Standards Track [Page 48] RFC 6638 CalDAV Scheduling June 2012

 Description:  This property MAY be defined on a scheduling Inbox
    collection.  If present, it contains zero or one DAV:href XML
    elements.  When a DAV:href element is present, its value indicates
    a URL to a calendar collection that is used as the default
    calendar.  When no DAV:href element is present, it indicates that
    there is no default calendar.  In the absence of this property,
    there is no default calendar.  When there is no default calendar,
    the server is free to choose the calendar in which a new
    scheduling object resource is created.  See Section 4.3.
 Definition:
   <!ELEMENT schedule-default-calendar-URL (DAV:href?)>
 Example:
   <C:schedule-default-calendar-URL xmlns:D="DAV:"
       xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:href>/home/cyrus/calendars/work/</D:href>
   </C:schedule-default-calendar-URL>

9.3. CALDAV:schedule-tag Property

 Name:  schedule-tag
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  Indicates whether a scheduling object resource has had a
    "consequential" change made to it.
 Value:  opaque-tag (defined in Section 3.11 of [RFC2616])
 Protected:  This property MUST be protected, as only the server can
    update the value.
 COPY/MOVE behavior:  This property value is determined by the server
    and MAY be different from the value on the source resource.
 Description:  The CALDAV:schedule-tag property MUST be defined on all
    scheduling object resources.  This property is described in
    Section 3.2.10.
 Definition:
   <!ELEMENT schedule-tag (#PCDATA)>

Daboo & Desruisseaux Standards Track [Page 49] RFC 6638 CalDAV Scheduling June 2012

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

10. XML Element Definitions

10.1. CALDAV:schedule-response XML Element

 Name:  schedule-response
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  Contains the set of responses for a POST method request.
 Description:  See Section 5.
 Definition:
   <!ELEMENT schedule-response (response*)>

10.2. CALDAV:response XML Element

 Name:  response
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  Contains a single response for a POST method request.
 Description:  See Section 5.
 Definition:
   <!ELEMENT response (recipient,
                       request-status,
                       calendar-data?,
                       DAV:error?,
                       DAV:responsedescription?)>
   <!-- CALDAV:calendar-data is defined in Section 9.6 of
   RFC 4791 and when used here uses the definition with
   content (#PCDATA) only. -->

10.3. CALDAV:recipient XML Element

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

Daboo & Desruisseaux Standards Track [Page 50] RFC 6638 CalDAV Scheduling June 2012

 Purpose:  The calendar user address that the enclosing response for a
    POST method request is for.
 Description:  See Section 5.
 Definition:
   <!ELEMENT recipient (DAV:href)>

10.4. CALDAV:request-status XML Element

 Name:  request-status
 Namespace:  urn:ietf:params:xml:ns:caldav
 Purpose:  The iTIP "REQUEST-STATUS" property value for this response.
 Description:  See Section 5.
 Definition:
   <!ELEMENT request-status (#PCDATA)>

11. Security Considerations

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

11.1. Preventing Denial-of-Service Attacks

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

Daboo & Desruisseaux Standards Track [Page 51] RFC 6638 CalDAV Scheduling June 2012

11.2. Verifying Scheduling Operations

 When handling a scheduling operation:
 1.  Servers MUST verify that the principal associated with the DAV:
     owner of the calendar collection in which a scheduling object
     resource is being manipulated contains a CALDAV:schedule-outbox-
     URL property value.
 2.  Servers MUST verify that the currently authenticated user has the
     CALDAV:schedule-send privilege, or a sub-privilege aggregated
     under this privilege, on the scheduling Outbox collection of the
     DAV:owner of the calendar collection in which a scheduling object
     resource is being manipulated.
 3.  Servers MUST only deliver scheduling messages to recipients when
     the CALDAV:schedule-deliver privilege, or a sub-privilege
     aggregated under this privilege, is granted on the recipient's
     scheduling Inbox collection for the principal associated with the
     DAV:owner of the calendar collection in which a scheduling object
     resource is being manipulated.
 4.  To prevent impersonation of calendar users, the server MUST
     verify that the "ORGANIZER" property in an organizer scheduling
     object resource matches one of the calendar user addresses of the
     DAV:owner of the calendar collection in which the resource is
     stored.
 5.  To prevent spoofing of an existing scheduling object resource,
     servers MUST verify that the "UID" iCalendar property value in a
     new scheduling object resource does not match that of an existing
     scheduling object resource with a different "ORGANIZER" property
     value.

11.3. Verifying Busy Time Information Requests

 When handling a POST request on a scheduling Outbox collection:
 1.  Servers MUST verify that the principal associated with the
     calendar user address specified in the "ORGANIZER" property of
     the scheduling message data in the request contains a CALDAV:
     schedule-outbox-URL property value that matches the scheduling
     Outbox collection targeted by the request.
 2.  Servers MUST verify that the currently authenticated user has the
     CALDAV:schedule-send privilege, or a sub-privilege aggregated
     under this privilege, on the scheduling Outbox collection
     targeted by the request.

Daboo & Desruisseaux Standards Track [Page 52] RFC 6638 CalDAV Scheduling June 2012

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

11.4. Privacy Issues

 This specification only defines how calendar users on the same server
 are able to schedule with each other -- unauthenticated users have no
 way to carry out scheduling operations.  Access control privileges
 (as per Section 6) can control which of those users can schedule with
 others.  Calendar users not wishing to expose their calendar
 information to other users can do so by denying privileges to
 specific users, or all users, for all scheduling operations, or
 perhaps only freebusy.
 "Attendees" can also use the Schedule-Reply request header
 (Section 8.1) with the value set to "F" to prevent notification to an
 "Organizer" that a scheduling object resource was deleted.  This
 allows "Attendees" to remove unwanted scheduling messages without any
 response to the "Organizer".
 Servers MUST NOT expose any private iCalendar data, or WebDAV
 resource state information (URLs, WebDAV properties, etc.) for one
 calendar user to another via scheduling messages or error responses
 to scheduling operations.  In particular, as per Section 8.1 of
 [RFC4918], authorization errors MUST take preference over other
 errors.

11.5. Mitigation of iTIP Threats

 Section 6.1 of iTIP [RFC5546] defines a set of potential threats in a
 scheduling system, and Section 6.2 of [RFC5546] defines
 recommendations on how those can be addressed in protocols using
 iTIP.  This specification addresses the iTIP threats in the following
 manner:
 Spoofing the "Organizer":  Addressed by item 4 in Section 11.2.
 Spoofing the "Attendee":  Addressed by Section 3.2.2.1 and item 2 in
    Section 11.2.
 Unauthorized Replacement of the "Organizer":  Addressed by item 5 in
    Section 11.2.
 Eavesdropping and Data Integrity:  Addressed by requiring TLS.

Daboo & Desruisseaux Standards Track [Page 53] RFC 6638 CalDAV Scheduling June 2012

 Flooding a Calendar:  Addressed by requirements in Section 11.1.
 Unauthorized REFRESH Requests:  This specification does not support
    the REFRESH method.

12. IANA Considerations

12.1. Message Header Field Registrations

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

12.1.1. Schedule-Reply

 Header field name: Schedule-Reply
 Applicable protocol: http
 Status: standard
 Author/Change controller: IETF
 Specification document(s): this specification (Section 8.1)
 Related information: none

12.1.2. Schedule-Tag

 Header field name: Schedule-Tag
 Applicable protocol: http
 Status: standard
 Author/Change controller: IETF
 Specification document(s): this specification (Section 8.2)
 Related information: none

12.1.3. If-Schedule-Tag-Match

 Header field name: If-Schedule-Tag-Match
 Applicable protocol: http
 Status: standard

Daboo & Desruisseaux Standards Track [Page 54] RFC 6638 CalDAV Scheduling June 2012

 Author/Change controller: IETF
 Specification document(s): this specification (Section 8.3)
 Related information: none

12.2. iCalendar Property Parameter Registrations

 The following iCalendar property parameter names have been added to
 the iCalendar Parameters Registry defined in Section 8.3.3 of
 [RFC5545].
       +---------------------+---------+-----------------------+
       | Parameter           | Status  | Reference             |
       +---------------------+---------+-----------------------+
       | SCHEDULE-AGENT      | Current | RFC 6638, Section 7.1 |
       |                     |         |                       |
       | SCHEDULE-STATUS     | Current | RFC 6638, Section 7.3 |
       |                     |         |                       |
       | SCHEDULE-FORCE-SEND | Current | RFC 6638, Section 7.2 |
       +---------------------+---------+-----------------------+

12.3. iCalendar REQUEST-STATUS Value Registrations

 The following iCalendar "REQUEST-STATUS" values have been added to
 the iCalendar REQUEST-STATUS Value Registry defined in Section 7.3 of
 [RFC5546].
         +-------------+---------+---------------------------+
         | Status Code | Status  | Reference                 |
         +-------------+---------+---------------------------+
         | 1.0         | Current | RFC 6638, Section 3.2.9.1 |
         |             |         |                           |
         | 1.1         | Current | RFC 6638, Section 3.2.9.2 |
         |             |         |                           |
         | 1.2         | Current | RFC 6638, Section 3.2.9.3 |
         +-------------+---------+---------------------------+

12.4. Additional iCalendar Elements Registries

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

Daboo & Desruisseaux Standards Track [Page 55] RFC 6638 CalDAV Scheduling June 2012

12.4.1. Schedule Agent Values Registry

 The following table has been used to initialize the Schedule Agent
 Values Registry.
         +----------------+---------+-----------------------+
         | Schedule Agent | Status  | Reference             |
         +----------------+---------+-----------------------+
         | SERVER         | Current | RFC 6638, Section 7.1 |
         |                |         |                       |
         | CLIENT         | Current | RFC 6638, Section 7.1 |
         |                |         |                       |
         | NONE           | Current | RFC 6638, Section 7.1 |
         +----------------+---------+-----------------------+

12.4.2. Schedule Force Send Values Registry

 The following table has been used to initialize the Schedule Force
 Send Values Registry.
       +---------------------+---------+-----------------------+
       | Schedule Force Send | Status  | Reference             |
       +---------------------+---------+-----------------------+
       | REQUEST             | Current | RFC 6638, Section 7.2 |
       |                     |         |                       |
       | REPLY               | Current | RFC 6638, Section 7.2 |
       +---------------------+---------+-----------------------+

13. Acknowledgements

 The authors would like to thank the following individuals for
 contributing their ideas and support for writing this specification:
 Mike Douglass, Lisa Dusseault, Red Dutta, Jacob Farkas, Jeffrey
 Harris, Helge Hess, Eliot Lear, Andrew McMillan, Alexey Melnikov,
 Arnaud Quillaud, Julian F. Reschke, Wilfredo Sanchez Vega, and Simon
 Vaillancourt.
 The authors would also like to thank the Calendaring and Scheduling
 Consortium for advice with this specification, and for organizing
 interoperability testing events to help refine it.

Daboo & Desruisseaux Standards Track [Page 56] RFC 6638 CalDAV Scheduling June 2012

14. References

14.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
            Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
            Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
 [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
            Leach, P., Luotonen, A., and L. Stewart, "HTTP
            Authentication: Basic and Digest Access Authentication",
            RFC 2617, June 1999.
 [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
 [RFC3744]  Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
            Distributed Authoring and Versioning (WebDAV)
            Access Control Protocol", RFC 3744, May 2004.
 [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
            Procedures for Message Header Fields", BCP 90, RFC 3864,
            September 2004.
 [RFC4791]  Daboo, C., Desruisseaux, B., and L. Dusseault,
            "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
            March 2007.
 [RFC4918]  Dusseault, L., Ed., "HTTP Extensions for Web Distributed
            Authoring and Versioning (WebDAV)", RFC 4918, June 2007.
 [RFC5234]  Crocker, D., Ed., and P. Overell, "Augmented BNF for
            Syntax Specifications: ABNF", STD 68, RFC 5234,
            January 2008.
 [RFC5545]  Desruisseaux, B., Ed., "Internet Calendaring and
            Scheduling Core Object Specification (iCalendar)",
            RFC 5545, September 2009.
 [RFC5546]  Daboo, C., Ed., "iCalendar Transport-Independent
            Interoperability Protocol (iTIP)", RFC 5546,
            December 2009.

Daboo & Desruisseaux Standards Track [Page 57] RFC 6638 CalDAV Scheduling June 2012

 [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
            Verification of Domain-Based Application Service Identity
            within Internet Public Key Infrastructure Using X.509
            (PKIX) Certificates in the Context of Transport Layer
            Security (TLS)", RFC 6125, March 2011.
 [W3C.REC-xml-20081126]
            Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E.,
            and F. Yergeau, "Extensible Markup Language (XML) 1.0
            (Fifth Edition)", World Wide Web Consortium
            Recommendation REC-xml-20081126, November 2008,
            <http://www.w3.org/TR/2008/REC-xml-20081126>.

14.2. Informative References

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

Daboo & Desruisseaux Standards Track [Page 58] RFC 6638 CalDAV Scheduling June 2012

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   |          *           |
 +-----------------------------+----------------------+

Daboo & Desruisseaux Standards Track [Page 59] RFC 6638 CalDAV Scheduling June 2012

A.2. Scheduling Outbox Privileges

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

Appendix B. Example Scheduling Operations

 This section describes some example scheduling operations that give a
 general idea of how scheduling is carried out between CalDAV clients
 and servers from the perspective of meeting "Organizers" and
 "Attendees".
 The server is assumed to be hosted in the "example.com" domain, and
 users whose email addresses are at the "example.com" domain are
 assumed to be hosted by the server.  In addition, the email addresses
 in the "example.net" domain are also valid email addresses for
 calendar users hosted by the server.  Calendar users with an email
 address at the "example.org" domain are assumed to not be hosted by
 the server.

Daboo & Desruisseaux Standards Track [Page 60] RFC 6638 CalDAV Scheduling June 2012

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

B.1. Example: "Organizer" Inviting Multiple "Attendees"

 In the following example, Cyrus invites Wilfredo, Bernard, and Mike
 to a single instance event by simply creating a new scheduling object
 resource in one of his calendar collections by using the PUT method.
 >> Request <<
 PUT /home/cyrus/calendars/work/9263504FD3AD.ics HTTP/1.1
 Host: cal.example.com
 Content-Type: text/calendar; charset="utf-8"
 Content-Length: xxxx
 If-None-Match: *
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//Example Corp.//CalDAV Client//EN
 BEGIN:VEVENT
 UID:9263504FD3AD
 SEQUENCE:0
 DTSTAMP:20090602T185254Z
 DTSTART:20090602T160000Z
 DTEND:20090602T170000Z
 TRANSP:OPAQUE
 SUMMARY:Lunch
 ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
 ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
  mailto:cyrus@example.com
 ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
  =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@
  example.com
 ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
  NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
  ample.net
 ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
  CTION;RSVP=TRUE:mailto:mike@example.org
 END:VEVENT
 END:VCALENDAR
 >> Response <<
 HTTP/1.1 201 Created
 Content-Length: 0

Daboo & Desruisseaux Standards Track [Page 61] RFC 6638 CalDAV Scheduling June 2012

 Date: Tue, 02 Jun 2009 18:52:54 GMT
 Last-Modified: Tue, 02 Jun 2009 18:52:54 GMT
 ETag: "d85561cfe74a4e785eb4639451b434fb"
 Schedule-Tag: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"
 Once the event creation has been completed, Cyrus's client will
 retrieve the event back from the server to get the schedule status of
 each "Attendee", as well as record the Schedule-Tag value for future
 use.  In this example, the server reports that a scheduling message
 was delivered to Wilfredo, a scheduling message is still pending for
 Bernard, and the server was unable to deliver a scheduling message to
 Mike.
 >> Request <<
 GET /home/cyrus/calendars/work/9263504FD3AD.ics HTTP/1.1
 Host: cal.example.com
 >> Response <<
 HTTP/1.1 200 OK
 Date: Tue, 02 Jun 2009 18:52:58 GMT
 Last-Modified: Tue, 02 Jun 2009 18:52:58 GMT
 ETag: "eb897deabc8939589da116714bc99265"
 Schedule-Tag: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"
 Content-Type: text/calendar; charset="utf-8"
 Content-Length: xxxx
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//Example Corp.//CalDAV Server//EN
 BEGIN:VEVENT
 UID:9263504FD3AD
 SEQUENCE:0
 DTSTAMP:20090602T185300Z
 DTSTART:20090602T160000Z
 DTEND:20090602T170000Z
 TRANSP:OPAQUE
 SUMMARY:Lunch
 ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
 ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
  mailto:cyrus@example.com
 ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
  =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=
  1.2:mailto:wilfredo@e
  xample.com

Daboo & Desruisseaux Standards Track [Page 62] RFC 6638 CalDAV Scheduling June 2012

 ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
  NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=
  1.0:mailto:bernard@example.net
 ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
  CTION;RSVP=TRUE;SCHEDULE-STATUS=3.7:mailto:mike@example.org
 END:VEVENT
 END:VCALENDAR

B.2. Example: "Attendee" Receiving an Invitation

 In the following example, Wilfredo's client retrieves and deletes the
 new scheduling message that appeared in his scheduling Inbox
 collection after the server automatically processed it and created a
 new scheduling object resource in his default calendar collection.
 >> Request <<
 GET /home/wilfredo/calendars/inbox/27d93fc0a58c.ics HTTP/1.1
 Host: cal.example.com
 >> Response <<
 HTTP/1.1 200 OK
 Date: Tue, 02 Jun 2009 18:59:58 GMT
 Last-Modified: Tue, 02 Jun 2009 18:59:58 GMT
 ETag: "da116714bc9926c89395895eb897deab"
 Content-Type: text/calendar; charset="utf-8"
 Content-Length: xxxx
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//Example Corp.//CalDAV Server//EN
 METHOD:REQUEST
 BEGIN:VEVENT
 UID:9263504FD3AD
 SEQUENCE:0
 DTSTAMP:20090602T185254Z
 DTSTART:20090602T160000Z
 DTEND:20090602T170000Z
 TRANSP:OPAQUE
 SUMMARY:Lunch
 ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
 ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
  mailto:cyrus@example.com
 ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
  =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@
  example.com

Daboo & Desruisseaux Standards Track [Page 63] RFC 6638 CalDAV Scheduling June 2012

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

B.3. Example: "Attendee" Replying to an Invitation

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

Daboo & Desruisseaux Standards Track [Page 64] RFC 6638 CalDAV Scheduling June 2012

 ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
  =ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@exam
  ple.com
 ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
  NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
  ample.net
 ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
  CTION;RSVP=TRUE:mailto:mike@example.org
 BEGIN:VALARM
 TRIGGER:-PT15M
 ACTION:DISPLAY
 DESCRIPTION:Reminder
 END:VALARM
 END:VEVENT
 END:VCALENDAR
 >> Response <<
 HTTP/1.1 200 OK
 Content-Length: 0
 Date: Tue, 02 Jun 2009 18:57:54 GMT
 Last-Modified: Tue, 02 Jun 2009 18:57:54 GMT
 ETag: "eb4639451b434fbd85561cfe74a4e785"
 Schedule-Tag: "8893ee45-eb9d-428f-b53c-c777daf19e41"
 Once the event modification has been completed, Wilfredo's client
 will retrieve the event back from the server to get the schedule
 status of the "Organizer".
 >> Request <<
 GET /home/wilfredo/calendars/work/BB64861C2228.ics HTTP/1.1
 Host: cal.example.com
 >> 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

Daboo & Desruisseaux Standards Track [Page 65] RFC 6638 CalDAV Scheduling June 2012

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

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

 On reception of Wilfredo's reply, Cyrus's server will automatically
 update Cyrus's scheduling object resource, make Wilfredo's scheduling
 message available in Cyrus's scheduling Inbox collection, and deliver
 an updated scheduling message to Bernard to share Wilfredo's updated
 participation status.  In this example, Cyrus's client retrieves and
 deletes this scheduling message in his scheduling Inbox collection.
 >> Request <<
 GET /home/cyrus/calendars/inbox/c0a58c27d93f.ics HTTP/1.1
 Host: cal.example.com

Daboo & Desruisseaux Standards Track [Page 66] RFC 6638 CalDAV Scheduling June 2012

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

Daboo & Desruisseaux Standards Track [Page 67] RFC 6638 CalDAV Scheduling June 2012

 >> Response <<
 HTTP/1.1 200 OK
 Date: Tue, 02 Jun 2009 19:05:02 GMT
 Last-Modified: Tue, 02 Jun 2009 19:04:20 GMT
 ETag: "eb897deabc8939589da116714bc99265"
 Schedule-Tag: "132cab27-1fe3-67ab-de13-abd348d1dee3"
 Content-Type: text/calendar; charset="utf-8"
 Content-Length: xxxx
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//Example Corp.//CalDAV Server//EN
 BEGIN:VEVENT
 UID:9263504FD3AD
 SEQUENCE:0
 DTSTAMP:20090602T190420Z
 DTSTART:20090602T160000Z
 DTEND:20090602T170000Z
 TRANSP:OPAQUE
 SUMMARY:Lunch
 ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
 ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
  mailto:cyrus@example.com
 ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
  =ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=2.0:
  mailto:wilfredo@example.com
 ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
  NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=1
  .0:mailto:bernard@example.net
 ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
  CTION;RSVP=TRUE;SCHEDULE-STATUS=3.7:mailto:mike@example.org
 END:VEVENT
 END:VCALENDAR

Daboo & Desruisseaux Standards Track [Page 68] RFC 6638 CalDAV Scheduling June 2012

B.5. Example: "Organizer" Requesting Busy Time Information

 In this example, Cyrus requests the busy time information of
 Wilfredo, Bernard, and Mike.
 >> Request <<
 POST /home/cyrus/calendars/outbox/ HTTP/1.1
 Host: cal.example.com
 Content-Type: text/calendar; charset="utf-8"
 Content-Length: xxxx
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//Example Corp.//CalDAV Client//EN
 METHOD:REQUEST
 BEGIN:VFREEBUSY
 UID:4FD3AD926350
 DTSTAMP:20090602T190420Z
 DTSTART:20090602T000000Z
 DTEND:20090604T000000Z
 ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
 ATTENDEE;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com
 ATTENDEE;CN="Bernard Desruisseaux":mailto:bernard@example.net
 ATTENDEE;CN="Mike Douglass":mailto:mike@example.org
 END:VFREEBUSY
 END:VCALENDAR
 >> Response <<
 HTTP/1.1 200 OK
 Date: Tue, 02 Jun 2009 20:07:34 GMT
 Content-Type: application/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>
 <C:schedule-response xmlns:D="DAV:"
        xmlns:C="urn:ietf:params:xml:ns:caldav">
 <C:response>
 <C:recipient>
 <D:href>mailto:wilfredo@example.com</D:href>
 </C:recipient>
 <C:request-status>2.0;Success</C:request-status>
 <C:calendar-data>BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//Example Corp.//CalDAV Server//EN
 METHOD:REPLY
 BEGIN:VFREEBUSY

Daboo & Desruisseaux Standards Track [Page 69] RFC 6638 CalDAV Scheduling June 2012

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

Daboo & Desruisseaux Standards Track [Page 70] RFC 6638 CalDAV Scheduling June 2012

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.
 >> Request <<
 PUT /home/wilfredo/calendars/work/def456.ics HTTP/1.1
 Host: cal.example.com
 Content-Type: text/calendar; charset="utf-8"
 Content-Length: xxxx
 If-None-Match: *
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//Example Corp.//CalDAV Client//EN
 BEGIN:VEVENT
 UID:3504F926D3AD
 SEQUENCE:0
 DTSTAMP:20090602T190221Z
 DTSTART:20090602T230000Z
 DTEND:20090603T000000Z
 TRANSP:OPAQUE
 SUMMARY:Dinner
 ORGANIZER;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com
 ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT=A
  CCEPTED:mailto:wilfredo@example.com
 ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=NE
  EDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
  e.net
 END:VEVENT
 END:VCALENDAR

Daboo & Desruisseaux Standards Track [Page 71] RFC 6638 CalDAV Scheduling June 2012

 >> Response <<
 HTTP/1.1 403 Forbidden
 Content-Type: application/xml; charset="utf-8"
 Content-Length: xxxx
 <?xml version="1.0" encoding="utf-8" ?>
 <D:error xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
   <D:need-privileges>
     <D:resource>
       <D:href>/home/wilfredo/calendars/outbox/</D:href>
       <D:privilege><C:schedule-send-invite/></D:privilege>
     </D:resource>
   </D:need-privileges>
 </D:error>

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

 In the following example, Bernard declines the second recurrence
 instance of a daily recurring event he's been invited to by Cyrus.
 >> Request <<
 PUT /home/bernard/calendars/work/4FD3AD926350.ics HTTP/1.1
 Host: cal.example.com
 Content-Type: text/calendar; charset="utf-8"
 Content-Length: xxxx
 If-Schedule-Tag-Match: "7775FB30-7534-489E-A79A-0EA147B933EB"
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//Example Corp.//CalDAV Client//EN
 BEGIN:VTIMEZONE
 TZID:America/Montreal
 BEGIN:STANDARD
 DTSTART:20071104T020000
 RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
 TZNAME:EST
 TZOFFSETFROM:-0400
 TZOFFSETTO:-0500
 END:STANDARD
 BEGIN:DAYLIGHT
 DTSTART:20070311T020000
 RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
 TZNAME:EDT
 TZOFFSETFROM:-0500
 TZOFFSETTO:-0400
 END:DAYLIGHT

Daboo & Desruisseaux Standards Track [Page 72] RFC 6638 CalDAV Scheduling June 2012

 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
 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"

Daboo & Desruisseaux Standards Track [Page 73] RFC 6638 CalDAV Scheduling June 2012

 Bernard's participation status update will cause his server to
 deliver a scheduling message to Cyrus.  Cyrus's client will find the
 following reply message from Bernard in Cyrus's scheduling Inbox
 collection:
 >> Request <<
 GET /home/cyrus/calendars/inbox/9263504FD3AD.ics HTTP/1.1
 Host: cal.example.com
 >> 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

Daboo & Desruisseaux Standards Track [Page 74] RFC 6638 CalDAV Scheduling June 2012

 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

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

 In the following example, Bernard removes from his calendar the third
 recurrence instance of a daily recurring event he's been invited to
 by Cyrus.  This is accomplished by the addition of an "EXDATE"
 property to the scheduling object resource stored by Bernard.
 >> Request <<
 PUT /home/bernard/calendars/work/4FD3AD926350.ics HTTP/1.1
 Host: cal.example.com
 Content-Type: text/calendar; charset="utf-8"
 Content-Length: xxxx
 If-Schedule-Tag-Match: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"
 BEGIN:VCALENDAR
 VERSION:2.0
 PRODID:-//Example Corp.//CalDAV Client//EN
 BEGIN:VTIMEZONE
 TZID:America/Montreal
 BEGIN:STANDARD
 DTSTART:20071104T020000
 RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
 TZNAME:EST
 TZOFFSETFROM:-0400
 TZOFFSETTO:-0500
 END:STANDARD
 BEGIN:DAYLIGHT
 DTSTART:20070311T020000
 RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
 TZNAME:EDT
 TZOFFSETFROM:-0500
 TZOFFSETTO:-0400
 END:DAYLIGHT
 END:VTIMEZONE
 BEGIN:VEVENT
 UID:9263504FD3AD
 SEQUENCE:0
 DTSTAMP:20090602T185254Z
 DTSTART;TZID=America/Montreal:20090601T150000
 DTEND;TZID=America/Montreal:20090601T160000

Daboo & Desruisseaux Standards Track [Page 75] RFC 6638 CalDAV Scheduling June 2012

 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=
  ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
  e.net
 END:VEVENT
 BEGIN:VEVENT
 UID:9263504FD3AD
 SEQUENCE:0
 DTSTAMP:20090603T183823Z
 RECURRENCE-ID;TZID=America/Montreal:20090602T150000
 DTSTART;TZID=America/Montreal:20090602T150000
 DTEND;TZID=America/Montreal:20090602T160000
 TRANSP:TRANSPARENT
 SUMMARY:Review Internet-Draft
 ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
 ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
  mailto:cyrus@example.com
 ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
  DECLINED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
  e.net
 END:VEVENT
 END:VCALENDAR
 Bernard's deletion of a recurrence instance will cause his server to
 deliver a scheduling message to Cyrus.  Cyrus's client will find the
 following reply message from Bernard in Cyrus's scheduling Inbox
 collection:
 >> Request <<
 GET /home/cyrus/calendars/inbox/6504923FD3AD.ics HTTP/1.1
 Host: cal.example.com
 >> 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
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Daboo & Desruisseaux Standards Track [Page 76] RFC 6638 CalDAV Scheduling June 2012

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Daboo & Desruisseaux Standards Track [Page 77] RFC 6638 CalDAV Scheduling June 2012

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/

Daboo & Desruisseaux Standards Track [Page 78]

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