RFC 6352 - CardDAV: vCard Extensions to Web Distributed Authoring and Versioning (WebDAV)
Author: Cyrus Daboo <cyrus@daboo.name>

[Docs] [txt|pdf] [draft-ietf-vcardd...] [Diff1] [Diff2]
PROPOSED STANDARD

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    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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    RFC 6352                         CardDAV                     August 2011

       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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    RFC 6352                         CardDAV                     August 2011

       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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    RFC 6352                         CardDAV                     August 2011

       >> 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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    RFC 6352                         CardDAV                     August 2011

       >> 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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    RFC 6352                         CardDAV                     August 2011

       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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    RFC 6352                         CardDAV                     August 2011

       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].

    Daboo                        Standards Track                   [Page 18]

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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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    RFC 6352                         CardDAV                     August 2011

       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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    RFC 6352                         CardDAV                     August 2011

       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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    RFC 6352                         CardDAV                     August 2011

       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)>

    Daboo                        Standards Track                   [Page 22]

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    RFC 6352                         CardDAV                     August 2011

       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

    Daboo                        Standards Track                   [Page 23]

    RFC 6352                         CardDAV                     August 2011

       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.

    Daboo                        Standards Track                   [Page 24]

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    RFC 6352                         CardDAV                     August 2011

          (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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    RFC 6352                         CardDAV                     August 2011

       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>

    Daboo                        Standards Track                   [Page 32]

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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.

    Daboo                        Standards Track                   [Page 33]

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    RFC 6352                         CardDAV                     August 2011

       >> 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.

    Daboo                        Standards Track                   [Page 34]

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    RFC 6352                         CardDAV                     August 2011

       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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    RFC 6352                         CardDAV                     August 2011

       <?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.

    Daboo                        Standards Track                   [Page 36]

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    RFC 6352                         CardDAV                     August 2011

       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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    RFC 6352                         CardDAV                     August 2011

          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.

    Daboo                        Standards Track                   [Page 38]

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    RFC 6352                         CardDAV                     August 2011

    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".

    Daboo                        Standards Track                   [Page 39]

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    RFC 6352                         CardDAV                     August 2011

       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.

    Daboo                        Standards Track                   [Page 40]

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    RFC 6352                         CardDAV                     August 2011

       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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    RFC 6352                         CardDAV                     August 2011

       (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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    RFC 6352                         CardDAV                     August 2011

       [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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