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CardDAV: vCard Extensions to Web Distributed Authoring and Versioning (WebDAV)
RFC 6352

Internet Engineering Task Force (IETF)                          C. Daboo
Request for Comments: 6352                                         Apple
Category: Standards Track                                    August 2011
ISSN: 2070-1721

                      CardDAV: vCard Extensions to
           Web Distributed Authoring and Versioning (WebDAV)

Abstract

   This document defines extensions to the Web Distributed Authoring and
   Versioning (WebDAV) protocol to specify a standard way of accessing,
   managing, and sharing contact information based on the vCard format.

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/rfc6352.

Copyright Notice

   Copyright (c) 2011 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.

   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

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   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 and Overview  . . . . . . . . . . . . . . . . . .  4
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Requirements Overview  . . . . . . . . . . . . . . . . . . . .  6
   4.  Address Book Data Model  . . . . . . . . . . . . . . . . . . .  7
     4.1.  Address Book Server  . . . . . . . . . . . . . . . . . . .  7
   5.  Address Book Resources . . . . . . . . . . . . . . . . . . . .  7
     5.1.  Address Object Resources . . . . . . . . . . . . . . . . .  7
       5.1.1.  Data Type Conversion . . . . . . . . . . . . . . . . .  8
         5.1.1.1.  Additional Precondition for GET  . . . . . . . . .  8
     5.2.  Address Book Collections . . . . . . . . . . . . . . . . .  9
   6.  Address Book Feature . . . . . . . . . . . . . . . . . . . . . 10
     6.1.  Address Book Support . . . . . . . . . . . . . . . . . . . 10
       6.1.1.  Example: Using OPTIONS for the Discovery of
               Support for CardDAV  . . . . . . . . . . . . . . . . . 10
     6.2.  Address Book Properties  . . . . . . . . . . . . . . . . . 10
       6.2.1.  CARDDAV:addressbook-description Property . . . . . . . 10
       6.2.2.  CARDDAV:supported-address-data Property  . . . . . . . 11
       6.2.3.  CARDDAV:max-resource-size Property . . . . . . . . . . 12
     6.3.  Creating Resources . . . . . . . . . . . . . . . . . . . . 13
       6.3.1.  Extended MKCOL Method  . . . . . . . . . . . . . . . . 13
         6.3.1.1.  Example - Successful MKCOL Request . . . . . . . . 14
       6.3.2.  Creating Address Object Resources  . . . . . . . . . . 15
         6.3.2.1.  Additional Preconditions for PUT, COPY, and
                   MOVE . . . . . . . . . . . . . . . . . . . . . . . 16
         6.3.2.2.  Non-Standard vCard Properties and Parameters . . . 17
         6.3.2.3.  Address Object Resource Entity Tag . . . . . . . . 18
   7.  Address Book Access Control  . . . . . . . . . . . . . . . . . 18
     7.1.  Additional Principal Properties  . . . . . . . . . . . . . 18
       7.1.1.  CARDDAV:addressbook-home-set Property  . . . . . . . . 19
       7.1.2.  CARDDAV:principal-address Property . . . . . . . . . . 19
   8.  Address Book Reports . . . . . . . . . . . . . . . . . . . . . 20
     8.1.  REPORT Method  . . . . . . . . . . . . . . . . . . . . . . 20
     8.2.  Ordinary Collections . . . . . . . . . . . . . . . . . . . 21
     8.3.  Searching Text: Collations . . . . . . . . . . . . . . . . 21
       8.3.1.  CARDDAV:supported-collation-set Property . . . . . . . 22
     8.4.  Partial Retrieval  . . . . . . . . . . . . . . . . . . . . 23
     8.5.  Non-Standard Properties and Parameters . . . . . . . . . . 23

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     8.6.  CARDDAV:addressbook-query Report . . . . . . . . . . . . . 23
       8.6.1.  Limiting Results . . . . . . . . . . . . . . . . . . . 25
       8.6.2.  Truncation of Results  . . . . . . . . . . . . . . . . 25
       8.6.3.  Example: Partial Retrieval of vCards Matching
               NICKNAME . . . . . . . . . . . . . . . . . . . . . . . 26
       8.6.4.  Example: Partial Retrieval of vCards Matching a
               Full Name or Email Address . . . . . . . . . . . . . . 27
       8.6.5.  Example: Truncated Results . . . . . . . . . . . . . . 29
     8.7.  CARDDAV:addressbook-multiget Report  . . . . . . . . . . . 31
       8.7.1.  Example: CARDDAV:addressbook-multiget Report . . . . . 32
       8.7.2.  Example: CARDDAV:addressbook-multiget Report . . . . . 33
   9.  Client Guidelines  . . . . . . . . . . . . . . . . . . . . . . 34
     9.1.  Restrict the Properties Returned . . . . . . . . . . . . . 34
     9.2.  Avoiding Lost Updates  . . . . . . . . . . . . . . . . . . 35
     9.3.  Client Configuration . . . . . . . . . . . . . . . . . . . 35
     9.4.  Finding Other Users' Address Books . . . . . . . . . . . . 35
   10. XML Element Definitions  . . . . . . . . . . . . . . . . . . . 36
     10.1. CARDDAV:addressbook XML Element  . . . . . . . . . . . . . 36
     10.2. CARDDAV:supported-collation XML Element  . . . . . . . . . 36
     10.3. CARDDAV:addressbook-query XML Element  . . . . . . . . . . 37
     10.4. CARDDAV:address-data XML Element . . . . . . . . . . . . . 37
       10.4.1. CARDDAV:allprop XML Element  . . . . . . . . . . . . . 39
       10.4.2. CARDDAV:prop XML Element . . . . . . . . . . . . . . . 39
     10.5. CARDDAV:filter XML Element . . . . . . . . . . . . . . . . 40
       10.5.1. CARDDAV:prop-filter XML Element  . . . . . . . . . . . 40
       10.5.2. CARDDAV:param-filter XML Element . . . . . . . . . . . 41
       10.5.3. CARDDAV:is-not-defined XML Element . . . . . . . . . . 42
       10.5.4. CARDDAV:text-match XML Element . . . . . . . . . . . . 42
     10.6. CARDDAV:limit XML Element  . . . . . . . . . . . . . . . . 43
       10.6.1. CARDDAV:nresults XML Element . . . . . . . . . . . . . 44
     10.7. CARDDAV:addressbook-multiget XML Element . . . . . . . . . 44
   11. Service Discovery via SRV Records  . . . . . . . . . . . . . . 45
   12. Internationalization Considerations  . . . . . . . . . . . . . 45
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 45
   14. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 46
     14.1. Namespace Registration . . . . . . . . . . . . . . . . . . 46
   15. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 46
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 47
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 47
     16.2. Informative References . . . . . . . . . . . . . . . . . . 48

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1.  Introduction and Overview

   Address books containing contact information are a key component of
   personal information management tools, such as email, calendaring and
   scheduling, and instant messaging clients.  To date several protocols
   have been used for remote access to contact data, including the
   Lightweight Directory Access Protocol (LDAP) [RFC4510], Internet
   Message Support Protocol [IMSP], and Application Configuration Access
   Protocol (ACAP) [RFC2244], together with SyncML used for
   synchronization of such data.

   WebDAV [RFC4918] offers a number of advantages as a framework or
   basis for address book access and management.  Most of these
   advantages boil down to a significant reduction in the costs of
   design, implementation, interoperability testing, and deployment.

   The key features of address book support with WebDAV are:

   1.  Ability to use multiple address books with hierarchical layout.

   2.  Ability to control access to individual address books and address
       entries as per WebDAV Access Control List (ACL) [RFC3744].

   3.  Principal collections can be used to enumerate and query other
       users on the system as per WebDAV ACL [RFC3744].

   4.  Server-side searching of address data, avoiding the need for
       clients to download an entire address book in order to do a quick
       address 'expansion' operation.

   5.  Well-defined internationalization support through WebDAV's use of
       XML.

   6.  Use of vCards [RFC2426] for well-defined address schema to
       enhance client interoperability.

   7.  Many limited clients (e.g., mobile devices) contain an HTTP stack
       that makes implementing WebDAV much easier than other protocols.

   The key disadvantage of address book support in WebDAV is:

   1.  Lack of change notification.  Many of the alternative protocols
       also lack this ability.  However, an extension for push
       notifications could easily be developed.

   vCard is a MIME directory profile aimed at encapsulating personal
   addressing and contact information about people.  The specification
   of vCard was originally done by the Versit consortium, with a

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   subsequent 3.0 version standardized by the IETF [RFC2426]. vCard is
   in widespread use in email clients and mobile devices as a means of
   encapsulating address information for transport via email or for
   import/export and synchronization operations.

   An update to vCard -- vCard v4 -- is currently being developed
   [RFC6350] and is compatible with this specification.

2.  Conventions

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

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

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

   1.  Element names use the "DAV:" namespace.

   2.  Element ordering is irrelevant unless explicitly stated.

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

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

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

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

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

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

3.  Requirements Overview

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

   o  MUST support vCard v3 [RFC2426] as a media type for the address
      object resource format;

   o  MUST support WebDAV Class 3 [RFC4918];

   o  MUST support WebDAV ACL [RFC3744];

   o  MUST support secure transport as defined in [RFC2818] using
      Transport Layer Security (TLS) [RFC5246] and using the certificate
      validation procedures described in [RFC5280];

   o  MUST support ETags [RFC2616] with additional requirements
      specified in Section 6.3.2.3 of this document;

   o  MUST support all address book reports defined in Section 8 of this
      document; and

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

   In addition, a server:

   o  SHOULD support vCard v4 [RFC6350] as a media type for the address
      object resource format;

   o  SHOULD support the extended MKCOL method [RFC5689] to create
      address book collections as defined in Section 6.3.1 of this
      document.

   o  SHOULD support the DAV:current-user-principal-URL property as
      defined in [RFC5397] to give clients a fast way to locate user
      principals.

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4.  Address Book Data Model

   As a brief overview, a CardDAV address book is modeled as a WebDAV
   collection with a well-defined structure; each of these address book
   collections contains a number of resources representing address
   objects as their direct child resources.  Each resource representing
   an address object is called an "address object resource".  Each
   address object resource and each address book collection can be
   individually locked and have individual WebDAV properties.
   Requirements derived from this model are provided in Sections 5.1 and
   5.2.

4.1.  Address Book Server

   A CardDAV server is an address-aware engine combined with a WebDAV
   server.  The server may include address data in some parts of its URL
   namespace and non-address data in other parts.

   A WebDAV server can advertise itself as a CardDAV server if it
   supports the functionality defined in this specification at any point
   within the root of its repository.  That might mean that address data
   is spread throughout the repository and mixed with non-address data
   in nearby collections (e.g., address data may be found in /lisa/
   addressbook/ as well as in /bernard/addressbook/, and non-address
   data in /lisa/calendars/).  Or, it might mean that address data can
   be found only in certain sections of the repository (e.g.,
   /addressbooks/user/).  Address book features are only required in the
   repository sections that are or contain address objects.  So, a
   repository confining address data to the /carddav/ collection would
   only need to support the CardDAV required features within that
   collection.

   The CardDAV server is the canonical location for address data and
   state information.  Clients may submit requests to change data or
   download data.  Clients may store address objects offline and attempt
   to synchronize at a later time.  Address data on the server can
   change between the time of last synchronization and when attempting
   an update, as address book collections may be shared and accessible
   via multiple clients.  Entity tags and locking help this work.

5.  Address Book Resources

5.1.  Address Object Resources

   This specification uses vCard as the default format for address or
   contact information being stored on the server.  However, this
   specification does allow other formats for address data provided that
   the server advertises support for those additional formats as

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   described below.  The requirements in this section pertain to vCard
   address data or formats that follow the semantics of vCard data.

   Address object resources contained in address book collections MUST
   contain a single vCard component only.

   vCard components in an address book collection MUST have a UID
   property value that MUST be unique in the scope of the address book
   collection in which it is contained.

5.1.1.  Data Type Conversion

   Servers might support more than one primary media type for address
   object resources, for example, vCard v3.0 and vCard v4.0.  In such
   cases, servers have to accept all media types that they advertise via
   the CARDDAV:supported-address-data WebDAV property (see
   Section 6.2.2).

   However, clients can use standard HTTP content negotiation behavior
   (the Accept request header defined in Section 14.1 of [RFC2616]) to
   request that an address object resource's data be returned in a
   specific media type format.  For example, a client merely capable of
   handling vCard v3.0 would only want to have address object resources
   returned in v3.0 format.

   Additionally, REPORT requests, defined later in this specification,
   allow for the return of address object resource data within an XML
   response body.  Again, the client can use content negotiation to
   request that data be returned in a specific media type by specifying
   appropriate attributes on the CARDDAV:address-data XML element used
   in the request body (see Section 10.4).

   In some cases, it might not be possible for a server to convert from
   one media type to another.  When that happens, the server MUST return
   the CARDDAV:supported-address-data-conversion precondition (see
   below) in the response body (when the failure to convert applies to
   the entire response) or use that same precondition code in the
   DAV:response XML element in the response for the targeted address
   object resource when one of the REPORTs defined below is used.  See
   Section 8.7.2 for an example of this.

5.1.1.1.  Additional Precondition for GET

   This specification creates additional preconditions for the GET
   method.

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   The new precondition is:

      (CARDDAV:supported-address-data-conversion): The resource targeted
      by the GET request can be converted to the media type specified in
      the Accept request header included with the request.

5.2.  Address Book Collections

   Address book collections appear to clients as a WebDAV collection
   resource, identified by a URL.  An address book collection MUST
   report the DAV:collection and CARDDAV:addressbook XML elements in the
   value of the DAV:resourcetype property.  The element type declaration
   for CARDDAV:addressbook is:

       <!ELEMENT addressbook EMPTY>

   An address book collection can be created through provisioning (e.g.,
   automatically created when a user's account is provisioned), or it
   can be created with the extended MKCOL method (see Section 6.3.1).
   This can be used by a user to create additional address books (e.g.,
   "soccer team members") or for users to share an address book (e.g.,
   "sales team contacts").  However, note that this document doesn't
   define what extra address book collections are for.  Users must rely
   on non-standard cues to find out what an address book collection is
   for, or use the CARDDAV:addressbook-description property defined in
   Section 6.2.1 to provide such a cue.

   The following restrictions are applied to the resources within an
   address book collection:

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

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

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   Multiple address book collections MAY be children of the same
   collection.

6.  Address Book Feature

6.1.  Address Book Support

   A server supporting the features described in this document MUST
   include "addressbook" as a field in the DAV response header from an
   OPTIONS request on any resource that supports any address book
   properties, reports, or methods.  A value of "addressbook" in the DAV
   response header MUST indicate that the server supports all MUST level
   requirements and REQUIRED features specified in this document.

6.1.1.  Example: Using OPTIONS for the Discovery of Support for CardDAV

   >> Request <<

   OPTIONS /addressbooks/users/ HTTP/1.1
   Host: addressbook.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE
   Allow: MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, REPORT, ACL
   DAV: 1, 2, 3, access-control, addressbook
   DAV: extended-mkcol
   Date: Sat, 11 Nov 2006 09:32:12 GMT
   Content-Length: 0

   In this example, the OPTIONS response indicates that the server
   supports CardDAV in this namespace; therefore, the '/addressbooks/
   users/' collection may be used as a parent for address book
   collections as the extended MKCOL method is available and as a
   possible target for REPORT requests for address book reports.

6.2.  Address Book Properties

6.2.1.  CARDDAV:addressbook-description Property

   Name:  addressbook-description

   Namespace:  urn:ietf:params:xml:ns:carddav

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

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   Value:  Any text.

   Protected:  SHOULD NOT be protected so that users can specify a
      description.

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

   allprop behavior:  SHOULD NOT be returned by a PROPFIND DAV:allprop
      request.

   Description:  This property contains a description of the address
      book collection that is suitable for presentation to a user.  The
      xml:lang attribute can be used to add a language tag for the value
      of this property.

   Definition:

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

   Example:

       <C:addressbook-description xml:lang="fr-CA"
          xmlns:C="urn:ietf:params:xml:ns:carddav"
       >Adresses de Oliver Daboo</C:addressbook-description>

6.2.2.  CARDDAV:supported-address-data Property

   Name:  supported-address-data

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Specifies what media types are allowed for address object
      resources in an address book collection.

   Protected:  MUST be protected as it indicates the level of support
      provided by the server.

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

   allprop behavior:  SHOULD NOT be returned by a PROPFIND DAV:allprop
      request.

   Description:  The CARDDAV:supported-address-data property is used to
      specify the media type supported for the address object resources
      contained in a given address book collection (e.g., vCard version

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      3.0).  Any attempt by the client to store address object resources
      with a media type not listed in this property MUST result in an
      error, with the CARDDAV:supported-address-data precondition
      (Section 6.3.2.1) being violated.  In the absence of this
      property, the server MUST only accept data with the media type
      "text/vcard" and vCard version 3.0, and clients can assume that is
      all the server will accept.

   Definition:

       <!ELEMENT supported-address-data (address-data-type+)>

       <!ELEMENT address-data-type EMPTY>
       <!ATTLIST address-data-type content-type CDATA "text/vcard"
                             version CDATA "3.0">
       <!-- content-type value: a MIME media type -->
       <!-- version value: a version string -->

   Example:

       <C:supported-address-data
          xmlns:C="urn:ietf:params:xml:ns:carddav">
         <C:address-data-type content-type="text/vcard" version="3.0"/>
       </C:supported-address-data>

6.2.3.  CARDDAV:max-resource-size Property

   Name:  max-resource-size

   Namespace:  urn:ietf:params:xml:ns:carddav

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

   Value:  Any text representing a numeric value.

   Protected:  MUST be protected as it indicates limits provided by the
      server.

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

   allprop behavior:  SHOULD NOT be returned by a PROPFIND DAV:allprop
      request.

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   Description:  The CARDDAV:max-resource-size is used to specify a
      numeric value that represents the maximum size in octets that the
      server is willing to accept when an address object resource is
      stored in an address book collection.  Any attempt to store an
      address book object resource exceeding this size MUST result in an
      error, with the CARDDAV:max-resource-size precondition
      (Section 6.3.2.1) being violated.  In the absence of this
      property, the client can assume that the server will allow storing
      a resource of any reasonable size.

   Definition:

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

   Example:

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

6.3.  Creating Resources

   Address book collections and address object resources may be created
   by either a CardDAV client or the CardDAV server.  This specification
   defines restrictions and a data model that both clients and servers
   MUST adhere to when manipulating such address data.

6.3.1.  Extended MKCOL Method

   An HTTP request using the extended MKCOL method [RFC5689] can be used
   to create a new address book collection resource.  A server MAY
   restrict address book collection creation to particular collections.

   To create an address book, the client sends an extended MKCOL request
   to the server and in the body of the request sets the
   DAV:resourcetype property to the resource type for an address book
   collection as defined in Section 5.2.

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

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   The DAV:displayname property can be used for a human-readable name of
   the address book.  Clients can either specify the value of the
   DAV:displayname property in the request body of the extended MKCOL
   request or, alternatively, issue a PROPPATCH request to change the
   DAV:displayname property to the appropriate value immediately after
   using the extended MKCOL request.  When displaying address book
   collections to users, clients SHOULD check the DAV:displayname
   property and use that value as the name of the address book.  In the
   event that the DAV:displayname property is not set, the client MAY
   use the last part of the address book collection URI as the name;
   however, that path segment may be "opaque" and not represent any
   meaningful human-readable text.

6.3.1.1.  Example - Successful MKCOL Request

   This example creates an address book collection called /home/lisa/
   addressbook/ on the server addressbook.example.com with specific
   values for the properties DAV:resourcetype, DAV:displayname, and
   CARDDAV:addressbook-description.

   >> Request <<

   MKCOL /home/lisa/addressbook/ HTTP/1.1
   Host: addressbook.example.com
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:mkcol xmlns:D="DAV:"
                 xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:set>
       <D:prop>
         <D:resourcetype>
           <D:collection/>
           <C:addressbook/>
         </D:resourcetype>
         <D:displayname>Lisa's Contacts</D:displayname>
         <C:addressbook-description xml:lang="en"
   >My primary address book.</C:addressbook-description>
       </D:prop>
     </D:set>
   </D:mkcol>

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   >> Response <<

   HTTP/1.1 201 Created
   Cache-Control: no-cache
   Date: Sat, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:mkcol-response xmlns:D="DAV:"
                 xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:propstat>
       <D:prop>
         <D:resourcetype/>
         <D:displayname/>
         <C:addressbook-description/>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
   </D:mkcol-response>

6.3.2.  Creating Address Object Resources

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

   When servers create new resources, it's not hard for the server to
   choose a unique URL.  It's slightly tougher for clients, because a
   client might not want to examine all resources in the collection and
   might not want to lock the entire collection to ensure that a new one
   isn't created with a name collision.  However, there is an HTTP
   feature to mitigate this.  If the client intends to create a new
   address resource, the client SHOULD use the HTTP header "If-None-
   Match: *" on the PUT request.  The Request-URI on the PUT request
   MUST include the target collection, where the resource is to be
   created, plus the name of the resource in the last path segment.  The
   "If-None-Match" header ensures that the client will not inadvertently
   overwrite an existing resource even if the last path segment turned
   out to already be used.

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   >> Request <<

   PUT /lisa/addressbook/newvcard.vcf HTTP/1.1
   If-None-Match: *
   Host: addressbook.example.com
   Content-Type: text/vcard
   Content-Length: xxx

   BEGIN:VCARD
   VERSION:3.0
   FN:Cyrus Daboo
   N:Daboo;Cyrus
   ADR;TYPE=POSTAL:;2822 Email HQ;Suite 2821;RFCVille;PA;15213;USA
   EMAIL;TYPE=INTERNET,PREF:cyrus@example.com
   NICKNAME:me
   NOTE:Example VCard.
   ORG:Self Employed
   TEL;TYPE=WORK,VOICE:412 605 0499
   TEL;TYPE=FAX:412 605 0705
   URL:http://www.example.com
   UID:1234-5678-9000-1
   END:VCARD

   >> Response <<

   HTTP/1.1 201 Created
   Date: Thu, 02 Sep 2004 16:53:32 GMT
   Content-Length: 0
   ETag: "123456789-000-111"

   The request to change an existing address object resource without
   overwriting a change made on the server uses a specific ETag in an
   "If-Match" header, rather than the "If-None-Match" header.

   File names for vCards are commonly suffixed by ".vcf", and clients
   may choose to use the same convention for URLs.

6.3.2.1.  Additional Preconditions for PUT, COPY, and MOVE

   This specification creates additional preconditions for the PUT,
   COPY, and MOVE methods.  These preconditions apply:

   o  When a PUT operation of an address object resource into an address
      book collection occurs.

   o  When a COPY or MOVE operation of an address object resource into
      an address book collection occurs.

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   The new preconditions are:

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

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

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

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

      (CARDDAV:addressbook-collection-location-ok): In a COPY or MOVE
      request, when the Request-URI is an address book collection, the
      URI targeted by the Destination HTTP Request header MUST identify
      a location where an address book collection can be created.

      (CARDDAV:max-resource-size): The resource submitted in the PUT
      request, or targeted by a COPY or MOVE request, MUST have a size
      in octets less than or equal to the value of the
      CARDDAV:max-resource-size property value (Section 6.2.3) on the
      address book collection where the resource will be stored.

6.3.2.2.  Non-Standard vCard Properties and Parameters

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

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

   Servers may need to enforce rules for their own "private" properties
   or parameters, so servers MAY reject any attempt by the client to
   change those or use values for those outside of any restrictions the
   server may have.  A server SHOULD ensure that any "private"

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   properties or parameters it uses follow the convention of including a
   vendor ID in the "X-" name, as described in Section 3.8 of [RFC2426],
   e.g., "X-ABC-PRIVATE".

6.3.2.3.  Address Object Resource Entity Tag

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

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

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

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

7.  Address Book Access Control

   CardDAV servers MUST support and adhere to the requirements of WebDAV
   ACL [RFC3744].  WebDAV ACL provides a framework for an extensible set
   of privileges that can be applied to WebDAV collections and ordinary
   resources.

7.1.  Additional Principal Properties

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

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7.1.1.  CARDDAV:addressbook-home-set Property

   Name:  addressbook-home-set

   Namespace:  urn:ietf:params:xml:ns:carddav

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

   Protected:  MAY be protected if the server has fixed locations in
      which address books are created.

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

   allprop behavior:  SHOULD NOT be returned by a PROPFIND DAV:allprop
      request.

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

   Definition:

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

   Example:

       <C:addressbook-home-set xmlns:D="DAV:"
          xmlns:C="urn:ietf:params:xml:ns:carddav">
         <D:href>/bernard/addresses/</D:href>
       </C:addressbook-home-set>

7.1.2.  CARDDAV:principal-address Property

   Name:  principal-address

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Identifies the URL of an address object resource that
      corresponds to the user represented by the principal.

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   Protected:  MAY be protected if the server provides a fixed location
      for principal addresses.

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

   allprop behavior:  SHOULD NOT be returned by a PROPFIND DAV:allprop
      request.

   Description:  The CARDDAV:principal-address property is meant to
      allow users to easily find contact information for users
      represented by principals on the system.  This property specifies
      the URL of the resource containing the corresponding contact
      information.  The resource could be an address object resource in
      an address book collection, or it could be a resource in a
      "regular" collection.

   Definition:

       <!ELEMENT principal-address (DAV:href)>

   Example:

       <C:principal-address xmlns:D="DAV:"
          xmlns:C="urn:ietf:params:xml:ns:carddav">
          <D:href>/system/cyrus.vcf</D:href>
       </C:principal-address>

8.  Address Book Reports

   This section defines the reports that CardDAV servers MUST support on
   address book collections and address object resources.

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

   Some of these reports allow address data (from possibly multiple
   resources) to be returned.

8.1.  REPORT Method

   The REPORT method (defined in Section 3.6 of [RFC3253]) provides an
   extensible mechanism for obtaining information about a resource.
   Unlike the PROPFIND method, which returns the value of one or more
   named properties, the REPORT method can involve more complex

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   processing.  REPORT is valuable in cases where the server has access
   to all of the information needed to perform the complex request (such
   as a query), and where it would require multiple requests for the
   client to retrieve the information needed to perform the same
   request.

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

8.2.  Ordinary Collections

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

8.3.  Searching Text: Collations

   Some of the reports defined in this section do text matches of
   character strings provided by the client and compared to stored
   address data.  Since vCard data is by default encoded in the UTF-8
   charset and may include characters outside of the US-ASCII charset
   range in some property and parameter values, there is a need to
   ensure that text matching follows well-defined rules.

   To deal with this, this specification makes use of the IANA Collation
   Registry defined in [RFC4790] to specify collations that may be used
   to carry out the text comparison operations with a well-defined rule.

   Collations supported by the server MUST support "equality" and
   "substring" match operations as per [RFC4790], Section 4.2, including
   the "prefix" and "suffix" options for "substring" matching.  CardDAV
   uses these match options for "equals", "contains", "starts-with", and
   "ends-with" match operations.

   CardDAV servers are REQUIRED to support the "i;ascii-casemap"
   [RFC4790] and "i;unicode-casemap" [RFC5051] collations and MAY
   support other collations.

   Servers MUST advertise the set of collations that they support via
   the CARDDAV:supported-collation-set property defined on any resource
   that supports reports that use collations.

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   In the absence of a collation explicitly specified by the client, or
   if the client specifies the "default" collation identifier (as
   defined in [RFC4790], Section 3.1), the server MUST default to using
   "i;unicode-casemap" as the collation.

   Wildcards (as defined in [RFC4790], Section 3.2) MUST NOT be used in
   the collation identifier.

   If the client chooses a collation not supported by the server, the
   server MUST respond with a CARDDAV:supported-collation precondition
   error response.

8.3.1.  CARDDAV:supported-collation-set Property

   Name:  supported-collation-set

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Identifies the set of collations supported by the server
      for text matching operations.

   Protected:  MUST be protected as it indicates support provided by the
      server.

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

   allprop behavior:  SHOULD NOT be returned by a PROPFIND DAV:allprop
      request.

   Description:  The CARDDAV:supported-collation-set property contains
      two or more CARDDAV:supported-collation elements that specify the
      identifiers of the collations supported by the server.

   Definition:

         <!ELEMENT supported-collation-set (
               supported-collation
               supported-collation
               supported-collation*)>
         <!-- Both "i;ascii-casemap" and "i;unicode-casemap"
              will be present -->

         <!ELEMENT supported-collation (#PCDATA)>

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   Example:

      <C:supported-collation-set
        xmlns:C="urn:ietf:params:xml:ns:carddav">
        <C:supported-collation>i;ascii-casemap</C:supported-collation>
        <C:supported-collation>i;octet</C:supported-collation>
        <C:supported-collation>i;unicode-casemap</C:supported-collation>
      </C:supported-collation-set>

8.4.  Partial Retrieval

   Some address book reports defined in this document allow partial
   retrieval of address object resources.  A CardDAV client can specify
   what information to return in the body of an address book REPORT
   request.

   A CardDAV client can request particular WebDAV property values, all
   WebDAV property values, or a list of the names of the resource's
   WebDAV properties.  A CardDAV client can also request address data to
   be returned and whether all vCard properties should be returned or
   only particular ones.  See CARDDAV:address-data in Section 10.4.

8.5.  Non-Standard Properties and Parameters

   Servers MUST support the use of non-standard vCard property or
   parameter names in the CARDDAV:address-data XML element in address
   book REPORT requests to allow clients to request that non-standard
   properties and parameters be returned in the address data provided in
   the response.

   Servers MAY support the use of non-standard vCard property or
   parameter names in the CARDDAV:prop-filter and CARDDAV:param-filter
   XML elements specified in the CARDDAV:filter XML element of address
   book REPORT requests.

   Servers MUST fail with the CARDDAV:supported-filter precondition if
   an address book REPORT request uses a CARDDAV:prop-filter or
   CARDDAV:param-filter XML element that makes reference to a non-
   standard vCard property or parameter name on which the server does
   not support queries.

8.6.  CARDDAV:addressbook-query Report

   The CARDDAV:addressbook-query REPORT performs a search for all
   address object resources that match a specified filter.  The response
   of this report will contain all the WebDAV properties and address
   object resource data specified in the request.  In the case of the

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   CARDDAV:address-data XML element, one can explicitly specify the
   vCard properties that should be returned in the address object
   resource data that matches the filter.

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

   Support for the CARDDAV:addressbook-query REPORT is REQUIRED.

   Marshalling:

      The request body MUST be a CARDDAV:addressbook-query XML element
      as defined in Section 10.3.

      The request MUST include a Depth header.  The scope of the query
      is determined by the value of the Depth header.  For example, to
      query all address object resources in an address book collection,
      the REPORT would use the address book collection as the Request-
      URI and specify a Depth of 1 or infinity.

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

      The response body for a successful CARDDAV:addressbook-query
      REPORT request MUST contain a DAV:response element for each
      address object that matched the search filter.  Address data is
      returned in the CARDDAV:address-data XML element inside the
      DAV:propstat XML element.

   Preconditions:

      (CARDDAV:supported-address-data): The attributes "content-type"
      and "version" of the CARDDAV:address-data XML element (see
      Section 10.4) specify a media type supported by the server for
      address object resources.

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      (CARDDAV:supported-filter): The CARDDAV:prop-filter (see
      Section 10.5.1) and CARDDAV:param-filter (see Section 10.5.2) XML
      elements used in the CARDDAV:filter XML element (see Section 10.5)
      in the REPORT request only make reference to vCard properties and
      parameters for which queries are supported by the server.  That
      is, if the CARDDAV:filter element attempts to reference an
      unsupported vCard property or parameter, this precondition is
      violated.  A server SHOULD report the CARDDAV:prop-filter or
      CARDDAV:param-filter for which it does not provide support.

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

      (CARDDAV:supported-collation): Any XML attribute specifying a
      collation MUST specify a collation supported by the server as
      described in Section 8.3.

   Postconditions:

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

8.6.1.  Limiting Results

   A client can limit the number of results returned by the server
   through use of the CARDDAV:limit element in the request body.  This
   is useful when clients are only interested in a few matches or only
   have limited space to display results to users and thus don't need
   the overhead of receiving more than that.  When the results are
   truncated by the server, the server MUST follow the rules below for
   indicating a result set truncation to the client.

8.6.2.  Truncation of Results

   A server MAY limit the number of resources in a response, for
   example, to limit the amount of work expended in processing a query,
   or as the result of an explicit limit set by the client.  If the
   result set is truncated because of such a limit, the response MUST
   use status code 207 (Multi-Status), return a DAV:multistatus response
   body, and indicate a status of 507 (Insufficient Storage) for the
   Request-URI.  That DAV:response element SHOULD include a DAV:error
   element with the DAV:number-of-matches-within-limits precondition, as
   defined in [RFC3744], Section 9.2.

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   The server SHOULD also include the partial results in additional
   DAV:response elements.  If a client-requested limit is being applied,
   the 507 response for the Request-URI MUST NOT be included in
   calculating the limit (e.g., if the client requests that only a
   single result be returned, and multiple matches are present, then the
   DAV:multistatus response will include one DAV:response for the
   matching resource and one DAV:response for the 507 status on the
   Request-URI).

8.6.3.  Example: Partial Retrieval of vCards Matching NICKNAME

   In this example, the client requests that the server search for
   address object resources that contain a NICKNAME property whose value
   equals some specific text and return specific vCard properties for
   those vCards found.  In addition, the DAV:getetag property is also
   requested and returned as part of the response.

   >> Request <<

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

   <?xml version="1.0" encoding="utf-8" ?>
   <C:addressbook-query xmlns:D="DAV:"
                     xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:prop>
       <D:getetag/>
       <C:address-data>
         <C:prop name="VERSION"/>
         <C:prop name="UID"/>
         <C:prop name="NICKNAME"/>
         <C:prop name="EMAIL"/>
         <C:prop name="FN"/>
       </C:address-data>
     </D:prop>
     <C:filter>
       <C:prop-filter name="NICKNAME">
         <C:text-match collation="i;unicode-casemap"
                       match-type="equals"
         >me</C:text-match>
       </C:prop-filter>
     </C:filter>
   </C:addressbook-query>

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   >> Response <<

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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:"
                  xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:response>
       <D:href>/home/bernard/addressbook/v102.vcf</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fb"</D:getetag>
           <C:address-data>BEGIN:VCARD
   VERSION:3.0
   NICKNAME:me
   UID:34222-232@example.com
   FN:Cyrus Daboo
   EMAIL:daboo@example.com
   END:VCARD
   </C:address-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

8.6.4.  Example: Partial Retrieval of vCards Matching a Full Name or
        Email Address

   In this example, the client requests that the server search for
   address object resources that contain a FN property whose value
   contains some specific text or that contain an EMAIL property whose
   value contains other text and return specific vCard properties for
   those vCards found.  In addition, the DAV:getetag property is also
   requested and returned as part of the response.

   >> Request <<

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

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   <?xml version="1.0" encoding="utf-8" ?>
   <C:addressbook-query xmlns:D="DAV:"
                     xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:prop>
       <D:getetag/>
       <C:address-data>
         <C:prop name="VERSION"/>
         <C:prop name="UID"/>
         <C:prop name="NICKNAME"/>
         <C:prop name="EMAIL"/>
         <C:prop name="FN"/>
       </C:address-data>
     </D:prop>
     <C:filter test="anyof">
       <C:prop-filter name="FN">
         <C:text-match collation="i;unicode-casemap"
                       match-type="contains"
         >daboo</C:text-match>
       </C:prop-filter>
       <C:prop-filter name="EMAIL">
         <C:text-match collation="i;unicode-casemap"
                       match-type="contains"
         >daboo</C:text-match>
       </C:prop-filter>
     </C:filter>
   </C:addressbook-query>

   >> Response <<

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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:"
                  xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:response>
       <D:href>/home/bernard/addressbook/v102.vcf</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fb"</D:getetag>
           <C:address-data>BEGIN:VCARD
   VERSION:3.0
   NICKNAME:me
   UID:34222-232@example.com
   FN:David Boo
   EMAIL:daboo@example.com

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   END:VCARD
   </C:address-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/home/bernard/addressbook/v104.vcf</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fc"</D:getetag>
           <C:address-data>BEGIN:VCARD
   VERSION:3.0
   NICKNAME:oliver
   UID:34222-23222@example.com
   FN:Oliver Daboo
   EMAIL:oliver@example.com
   END:VCARD
   </C:address-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

8.6.5.  Example: Truncated Results

   In this example, the client requests that the server search for
   address object resources that contain a FN property whose value
   contains some specific text and return the DAV:getetag property for
   two results only.  The server response includes a 507 status for the
   Request-URI indicating that there were more than two resources that
   matched the query, but that the server truncated the result set as
   requested by the client.

   >> Request <<

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

   <?xml version="1.0" encoding="utf-8" ?>
   <C:addressbook-query xmlns:D="DAV:"
                     xmlns:C="urn:ietf:params:xml:ns:carddav">

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     <D:prop>
       <D:getetag/>
     </D:prop>
     <C:filter test="anyof">
       <C:prop-filter name="FN">
         <C:text-match collation="i;unicode-casemap"
                       match-type="contains"
         >daboo</C:text-match>
       </C:prop-filter>
     </C:filter>
     <C:limit>
       <C:nresults>2</C:nresults>
     </C:limit>
   </C:addressbook-query>

   >> Response <<

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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:"
                  xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:response>
       <D:href>/home/bernard/addressbook/</D:href>
       <D:status>HTTP/1.1 507 Insufficient Storage</D:status>
       <D:error><D:number-of-matches-within-limits/></D:error>
       <D:responsedescription xml:lang="en">
         Only two matching records were returned
       </D:responsedescription>
     </D:response>
     <D:response>
       <D:href>/home/bernard/addressbook/v102.vcf</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fb"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/home/bernard/addressbook/v104.vcf</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fc"</D:getetag>
         </D:prop>

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         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

8.7.  CARDDAV:addressbook-multiget Report

   The CARDDAV:addressbook-multiget REPORT is used to retrieve specific
   address object resources from within a collection, if the Request-URI
   is a collection, or to retrieve a specific address object resource,
   if the Request-URI is an address object resource.  This report is
   similar to the CARDDAV:addressbook-query REPORT (see Section 8.6),
   except that it takes a list of DAV:href elements instead of a
   CARDDAV:filter element to determine which address object resources to
   return.

   Support for the addressbook-multiget REPORT is REQUIRED.

   Marshalling:

      The request body MUST be a CARDDAV:addressbook-multiget XML
      element (see Section 10.7), which MUST contain at least one
      DAV:href XML element and one optional CARDDAV:address-data element
      as defined in Section 10.4.  If DAV:href elements are present, the
      scope of the request is the set of resources identified by these
      elements, which all need to be members (not necessarily internal
      members) of the resource identified by the Request-URI.
      Otherwise, the scope is the resource identified by the Request-URI
      itself.

      The request MUST include a Depth: 0 header; however, the actual
      scope of the REPORT is determined as described above.

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

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

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

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   Preconditions:

      (CARDDAV:supported-address-data): The attributes "content-type"
      and "version" of the CARDDAV:address-data XML elements (see
      Section 10.4) specify a media type supported by the server for
      address object resources.

   Postconditions:

      None.

8.7.1.  Example: CARDDAV:addressbook-multiget Report

   In this example, the client requests the server to return specific
   vCard properties of the address components referenced by specific
   URIs.  In addition, the DAV:getetag property is also requested and
   returned as part of the response.  Note that, in this example, the
   resource at
   http://addressbook.example.com/home/bernard/addressbook/vcf1.vcf does
   not exist, resulting in an error status response.

   >> Request <<

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

   <?xml version="1.0" encoding="utf-8" ?>
   <C:addressbook-multiget xmlns:D="DAV:"
                        xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:prop>
       <D:getetag/>
       <C:address-data>
         <C:prop name="VERSION"/>
         <C:prop name="UID"/>
         <C:prop name="NICKNAME"/>
         <C:prop name="EMAIL"/>
         <C:prop name="FN"/>
       </C:address-data>
     </D:prop>
     <D:href>/home/bernard/addressbook/vcf102.vcf</D:href>
     <D:href>/home/bernard/addressbook/vcf1.vcf</D:href>
   </C:addressbook-multiget>

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   >> Response <<

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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:"
                  xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:response>
       <D:href>/home/bernard/addressbook/vcf102.vcf</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"23ba4d-ff11fb"</D:getetag>
           <C:address-data>BEGIN:VCARD
   VERSION:3.0
   NICKNAME:me
   UID:34222-232@example.com
   FN:Cyrus Daboo
   EMAIL:daboo@example.com
   END:VCARD
   </C:address-data>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/home/bernard/addressbook/vcf1.vcf</D:href>
       <D:status>HTTP/1.1 404 Resource not found</D:status>
     </D:response>
   </D:multistatus>

8.7.2.  Example: CARDDAV:addressbook-multiget Report

   In this example, the client requests the server to return vCard v4.0
   data of the address components referenced by specific URIs.  In
   addition, the DAV:getetag property is also requested and returned as
   part of the response.  Note that, in this example, the resource at
   http://addressbook.example.com/home/bernard/addressbook/vcf3.vcf
   exists but in a media type format that the server is unable to
   convert, resulting in an error status response.

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   >> Request <<

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

   <?xml version="1.0" encoding="utf-8" ?>
   <C:addressbook-multiget xmlns:D="DAV:"
                        xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:prop>
       <D:getetag/>
       <C:address-data content-type='text/vcard' version='4.0'/>
     </D:prop>
     <D:href>/home/bernard/addressbook/vcf3.vcf</D:href>
   </C:addressbook-multiget>

   >> Response <<

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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:"
                  xmlns:C="urn:ietf:params:xml:ns:carddav">
     <D:response>
       <D:href>/home/bernard/addressbook/vcf3.vcf</D:href>
       <D:status>HTTP/1.1 415 Unsupported Media Type</D:status>
       <D:error><C:supported-address-data-conversion/></D:error>
       <D:responsedescription>Unable to convert from vCard v3.0
       to vCard v4.0</D:responsedescription>
     </D:response>
   </D:multistatus>

9.  Client Guidelines

9.1.  Restrict the Properties Returned

   Clients may not need all the properties in a vCard object when
   presenting information to the user, or looking up specific items for
   their email address, for example.  Since some property data can be
   large (e.g., PHOTO or SOUND with in-line content) clients can choose
   to ignore those by only requesting the specific items it knows it
   will use, through use of the CARDDAV:address-data XML element in the
   relevant reports.

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

9.2.  Avoiding Lost Updates

   When resources are accessed by multiple clients, the possibility of
   clients overwriting each other's changes exists.  To alleviate this,
   clients SHOULD use the If-Match request header on PUT requests with
   the ETag of the previously retrieved resource data to check whether
   the resource was modified since it was previously retrieved.  If a
   precondition failure occurs, clients need to reload the resource and
   go through their own merge or conflict resolution process before
   writing back the data (again using the If-Match check).

9.3.  Client Configuration

   When CardDAV clients need to be configured, the key piece of
   information that they require is the principal-URL of the user whose
   address book information is desired.  Servers SHOULD support the
   DAV:current-user-principal-URL property as defined in [RFC5397] to
   give clients a fast way to locate user principals.

   Given support for SRV records (Section 11) and DAV:current-user-
   principal-URL [RFC5397], users only need enter a user identifier,
   host name, and password to configure their client.  The client would
   take the host name and do an SRV lookup to locate the CardDAV server,
   then execute an authenticated PROPFIND on the root/resource looking
   for the DAV:current-user-principal-URL property.  The value returned
   gives the client direct access to the user's principal-URL and from
   there all the related CardDAV properties needed to locate address
   books.

9.4.  Finding Other Users' Address Books

   For use cases of address book sharing, one might wish to find the
   address book belonging to another user.  To find other users' address
   books on the same server, the DAV:principal-property-search REPORT
   [RFC3744] can be used to search principals for matching properties
   and return specified properties for the matching principal resources.
   To search for an address book owned by a user named "Laurie", the
   REPORT request body would look like this:

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

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

10.  XML Element Definitions

10.1.  CARDDAV:addressbook XML Element

   Name:  addressbook

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Specifies the resource type of an address book collection.

   Description:  See Section 5.2.

   Definition:

       <!ELEMENT addressbook EMPTY>

10.2.  CARDDAV:supported-collation XML Element

   Name:  supported-collation

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Identifies a single collation via its collation identifier
      as defined by [RFC4790].

   Description:  The CARDDAV:supported-collation contains the text of a
      collation identifier as described in Section 8.3.1.

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   Definition:

       <!ELEMENT supported-collation (#PCDATA)>
       <!-- PCDATA value: collation identifier -->

10.3.  CARDDAV:addressbook-query XML Element

   Name:  addressbook-query

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Defines a report for querying address book data

   Description:  See Section 8.6.

   Definition:

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

10.4.  CARDDAV:address-data XML Element

   Name:  address-data

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Specifies one of the following:

      1.  The parts of an address object resource that should be
          returned by a given address book REPORT request, and the media
          type and version for the returned data; or

      2.  The content of an address object resource in a response to an
          address book REPORT request.

   Description:  When used in an address book REPORT request, the
      CARDDAV:address-data XML element specifies which parts of address
      object resources need to be returned in the response.  If the
      CARDDAV:address-data XML element doesn't contain any CARDDAV:prop
      elements, address object resources will be returned in their
      entirety.  Additionally, a media type and version can be specified
      to request that the server return the data in that format if
      possible.

      Finally, when used in an address book REPORT response, the
      CARDDAV:address-data XML element specifies the content of an
      address object resource.  Given that XML parsers normalize the

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      two-character sequence CRLF (US-ASCII decimal 13 and US-ASCII
      decimal 10) to a single LF character (US-ASCII decimal 10), the CR
      character (US-ASCII decimal 13) MAY be omitted in address object
      resources specified in the CARDDAV:address-data XML element.
      Furthermore, address object resources specified in the
      CARDDAV:address-data XML element MAY be invalid per their media
      type specification if the CARDDAV:address-data XML element part of
      the address book REPORT request did not specify required vCard
      properties (e.g., UID, etc.) or specified a CARDDAV:prop XML
      element with the "novalue" attribute set to "yes".

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

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

   Definition:

       <!ELEMENT address-data (allprop | prop*)>

       when nested in the DAV:prop XML element in an address book
       REPORT request to specify which parts of address object
       resources should be returned in the response;

       <!ELEMENT address-data (#PCDATA)>
       <!-- PCDATA value: address data -->

       when nested in the DAV:prop XML element in an address book
       REPORT response to specify the content of a returned
       address object resource.

       <!ATTLIST address-data content-type CDATA "text/vcard"
                             version CDATA "3.0">
       <!-- content-type value: a MIME media type -->
       <!-- version value: a version string -->

       attributes can be used on each variant of the
       CALDAV:address-data XML element.

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10.4.1.  CARDDAV:allprop XML Element

   Name:  allprop

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Specifies that all vCard properties shall be returned.

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

   Definition:

       <!ELEMENT allprop EMPTY>

   Note: The CARDDAV:allprop element defined here has the same name as
   the DAV:allprop element defined in WebDAV.  However, the
   CARDDAV:allprop element defined here uses the
   "urn:ietf:params:xml:ns:carddav" namespace, as opposed to the "DAV:"
   namespace used for the DAV:allprop element defined in WebDAV.

10.4.2.  CARDDAV:prop XML Element

   Name:  prop

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Defines which vCard properties to return in the response.

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

      vCard allows a "group" prefix to appear before a property name in
      the vCard data.  When the "name" attribute does not specify a
      group prefix, it MUST match properties in the vCard data without a
      group prefix or with any group prefix.  When the "name" attribute
      includes a group prefix, it MUST match properties that have
      exactly the same group prefix and name.  For example, a "name" set
      to "TEL" will match "TEL", "X-ABC.TEL", and "X-ABC-1.TEL" vCard
      properties.  A "name" set to "X-ABC.TEL" will match an "X-ABC.TEL"
      vCard property only; it will not match "TEL" or "X-ABC-1.TEL".

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   Definition:

       <!ELEMENT prop EMPTY>

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

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

10.5.  CARDDAV:filter XML Element

   Name:  filter

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Determines which matching objects are returned.

   Description:  The "filter" element specifies the search filter used
      to match address objects that should be returned by a report.  The
      "test" attribute specifies whether any (logical OR) or all
      (logical AND) of the prop-filter tests need to match in order for
      the overall filter to match.

   Definition:

       <!ELEMENT filter (prop-filter*)>

       <!ATTLIST filter test (anyof | allof) "anyof">
       <!-- test value:
                 anyof logical OR for prop-filter matches
                 allof logical AND for prop-filter matches -->

10.5.1.  CARDDAV:prop-filter XML Element

   Name:  prop-filter

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Limits the search to specific vCard properties.

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   Description:  The CARDDAV:prop-filter XML element specifies search
      criteria on a specific vCard property (e.g., "NICKNAME").  An
      address object is said to match a CARDDAV:prop-filter if:

      *  A vCard property of the type specified by the "name" attribute
         exists, and the CARDDAV:prop-filter is empty, or it matches any
         specified CARDDAV:text-match or CARDDAV:param-filter
         conditions.  The "test" attribute specifies whether any
         (logical OR) or all (logical AND) of the text-filter and param-
         filter tests need to match in order for the overall filter to
         match.

      or:

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

      vCard allows a "group" prefix to appear before a property name in
      the vCard data.  When the "name" attribute does not specify a
      group prefix, it MUST match properties in the vCard data without a
      group prefix or with any group prefix.  When the "name" attribute
      includes a group prefix, it MUST match properties that have
      exactly the same group prefix and name.  For example, a "name" set
      to "TEL" will match "TEL", "X-ABC.TEL", "X-ABC-1.TEL" vCard
      properties.  A "name" set to "X-ABC.TEL" will match an "X-ABC.TEL"
      vCard property only, it will not match "TEL" or "X-ABC-1.TEL".

   Definition:

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

       <!ATTLIST prop-filter name CDATA #REQUIRED
                             test (anyof | allof) "anyof">
       <!-- name value: a vCard property name (e.g., "NICKNAME")
         test value:
             anyof logical OR for text-match/param-filter matches
             allof logical AND for text-match/param-filter matches -->

10.5.2.  CARDDAV:param-filter XML Element

   Name:  param-filter

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Limits the search to specific parameter values.

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

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

      or:

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

   Definition:

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

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

10.5.3.  CARDDAV:is-not-defined XML Element

   Name:  is-not-defined

   Namespace:  urn:ietf:params:xml:ns:carddav

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

   Description:  The CARDDAV:is-not-defined XML element specifies that a
      match occurs if the enclosing vCard property or parameter value
      specified in an address book REPORT request does not exist in the
      address data being tested.

   Definition:

       <!ELEMENT is-not-defined EMPTY>

10.5.4.  CARDDAV:text-match XML Element

   Name:  text-match

   Namespace:  urn:ietf:params:xml:ns:carddav

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

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   Description:  The CARDDAV:text-match XML element specifies text used
      for a substring match against the vCard property or parameter
      value specified in an address book REPORT request.

      The "collation" attribute is used to select the collation that the
      server MUST use for character string matching.  In the absence of
      this attribute, the server MUST use the "i;unicode-casemap"
      collation.

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

      The "match-type" attribute is used to indicate the type of match
      operation to use.  Possible choices are:

         "equals" - an exact match to the target string

         "contains" - a substring match, matching anywhere within the
         target string

         "starts-with" - a substring match, matching only at the start
         of the target string

         "ends-with" - a substring match, matching only at the end of
         the target string

   Definition:

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

       <!ATTLIST text-match
          collation        CDATA "i;unicode-casemap"
          negate-condition (yes | no) "no"
          match-type (equals|contains|starts-with|ends-with) "contains">

10.6.  CARDDAV:limit XML Element

   Name:  limit

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Specifies different types of limits that can be applied to
      the results returned by the server.

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   Description:  The CARDDAV:limit XML element can be used to specify
      different types of limits that the client can request the server
      to apply to the results returned by the server.  Currently, only
      the CARDDAV:nresults limit can be used; other types of limit could
      be defined in the future.

   Definition:

       <!ELEMENT limit (nresults)>

10.6.1.  CARDDAV:nresults XML Element

   Name:  nresults

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  Specifies a limit on the number of results returned by the
      server.

   Description:  The CARDDAV:nresults XML element contains a requested
      maximum number of DAV:response elements to be returned in the
      response body of a query.  The server MAY disregard this limit.
      The value of this element is an unsigned integer.

   Definition:

       <!ELEMENT nresults (#PCDATA)>
       <!-- nresults value: unsigned integer, must be digits -->

10.7.  CARDDAV:addressbook-multiget XML Element

   Name:  addressbook-multiget

   Namespace:  urn:ietf:params:xml:ns:carddav

   Purpose:  CardDAV report used to retrieve specific address objects
      via their URIs.

   Description:  See Section 8.7.

   Definition:

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

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11.  Service Discovery via SRV Records

   [RFC2782] defines a DNS-based service discovery protocol that has
   been widely adopted as a means of locating particular services within
   a local area network and beyond, using SRV RRs.

   This specification adds two service types for use with SRV records:

   carddav:  Identifies a CardDAV server that uses HTTP without TLS
      [RFC2818].

   carddavs:  Identifies a CardDAV server that uses HTTP with TLS
      [RFC2818].

   Example: non-TLS service record

       _carddav._tcp     SRV 0 1 80 addressbook.example.com.

   Example: TLS service

       _carddavs._tcp    SRV 0 1 443 addressbook.example.com.

12.  Internationalization Considerations

   CardDAV allows internationalized strings to be stored and retrieved
   for the description of address book collections (see Section 6.2.1).

   The CARDDAV:addressbook-query REPORT (Section 8.6) includes a text
   searching option controlled by the CARDDAV:text-match element and
   details of character handling are covered in the description of that
   element (see Section 10.5.4).

13.  Security Considerations

   HTTP protocol transactions are sent in the clear over the network
   unless protection from snooping is negotiated.  This can be
   accomplished by use of TLS as defined in [RFC2818].  In particular,
   if HTTP Basic authentication [RFC2617] is available, the server MUST
   allow TLS to be used at the same time, and it SHOULD prevent use of
   Basic authentication when TLS is not in use.  Clients SHOULD use TLS
   whenever possible.

   With the ACL extension [RFC3744] present, WebDAV allows control over
   who can access (read or write) any resource on the WebDAV server.  In
   addition, WebDAV ACL provides for an "inheritance" mechanism, whereby
   resources may inherit access privileges from other resources.  Often,
   the "other" resource is a parent collection of the resource itself.
   Servers are able to support address books that are "private"

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   (accessible only to the "owner"), "shared" (accessible to the owner
   and other specified authenticated users), and "public" (accessible to
   any authenticated or unauthenticated users).  When provisioning
   address books of a particular type, servers MUST ensure that the
   correct privileges are applied on creation.  In particular, private
   and shared address books MUST NOT be accessible by unauthenticated
   users (to prevent data from being automatically searched or indexed
   by web "crawlers").

   Clients SHOULD warn users in an appropriate fashion when they copy or
   move address data from a private address book to a shared address
   book or public address book.  Clients SHOULD provide a clear
   indication as to which address books are private, shared, or public.
   Clients SHOULD provide an appropriate warning when changing access
   privileges for a private or shared address book with data so as to
   allow unauthenticated users access.

   This specification currently relies on standard HTTP authentication
   mechanisms for identifying users.  These comprise Basic and Digest
   authentication [RFC2617] as well as TLS [RFC2818] using client-side
   certificates.

14.  IANA Consideration

   This document uses a URN to describe a new XML namespace conforming
   to the registry mechanism described in [RFC3688].

14.1.  Namespace Registration

   Registration request for the carddav namespace:

   URI: urn:ietf:params:xml:ns:carddav

   Registrant Contact: The IESG <iesg@ietf.org>

   XML: None - not applicable for namespace registrations.

15.  Acknowledgments

   Thanks go to Lisa Dusseault and Bernard Desruisseaux for their work
   on CalDAV, on which CardDAV is heavily based.  The following
   individuals contributed their ideas and support for writing this
   specification: Mike Douglass, Stefan Eissing, Helge Hess, Arnaud
   Quillaud, Julian Reschke, Elias Sinderson, Greg Stein, Wilfredo
   Sanchez, and Simon Vaillancourt.

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16.  References

16.1.  Normative References

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

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

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [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.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

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

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

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

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

   [RFC4790]  Newman, C., Duerst, M., and A. Gulbrandsen, "Internet
              Application Protocol Collation Registry", RFC 4790,
              March 2007.

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

   [RFC5051]  Crispin, M., "i;unicode-casemap - Simple Unicode Collation
              Algorithm", RFC 5051, October 2007.

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   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5397]  Sanchez, W. and C. Daboo, "WebDAV Current Principal
              Extension", RFC 5397, December 2008.

   [RFC5689]  Daboo, C., "Extended MKCOL for Web Distributed Authoring
              and Versioning (WebDAV)", RFC 5689, September 2009.

   [RFC6350]  Perreault, S., "vCard Format Specification", RFC 6350,
              August 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>.

16.2.  Informative References

   [IMSP]     Myers, J., "IMSP - Internet Message Support Protocol",
              Work in Progress, June 1995.

   [RFC2244]  Newman, C. and J. Myers, "ACAP -- Application
              Configuration Access Protocol", RFC 2244, November 1997.

   [RFC4510]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP): Technical Specification Road Map", RFC 4510,
              June 2006.

Author's Address

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

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

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