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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 8144

Independent Submission                                      K. Murchison
Internet-Draft                                                       CMU
Updates: 3253, 4918, 5689, 5995 (if                        July 21, 2014
         approved)
Intended status: Standards Track
Expires: January 22, 2015


    Use of the Prefer Header Field in Web Distributed Authoring and
                          Versioning (WebDAV)
                    draft-murchison-webdav-prefer-07

Abstract

   This specification defines how the HTTP Prefer header field can be
   used by a WebDAV client to request that certain behaviors be employed
   by a server while constructing a response to a request.

Editorial Note (To be removed by RFC Editor before publication)

   Please send comments to the Web Distributed Authoring and Versioning
   (WebDAV) mailing list at <mailto:w3c-dist-auth@w3.org> [1], which may
   be joined by sending a message with subject "subscribe" to
   <mailto:w3c-dist-auth-request@w3.org> [2].  This mailing list is
   archived at <http://lists.w3.org/Archives/Public/w3c-dist-auth/> [3].

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 22, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Reducing WebDAV Response Verbosity with
       "return=minimal"  . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Minimal PROPFIND Response . . . . . . . . . . . . . . . .   3
     2.2.  Minimal REPORT Response . . . . . . . . . . . . . . . . .   7
     2.3.  Minimal PROPPATCH Response  . . . . . . . . . . . . . . .  11
     2.4.  Minimal MKCALENDAR / MKCOL Response . . . . . . . . . . .  13
   3.  Reducing WebDAV Round-Trips with
       "return=representation" . . . . . . . . . . . . . . . . . . .  15
   4.  The "depth-noroot" Processing Preference  . . . . . . . . . .  22
   5.  Implementation Status . . . . . . . . . . . . . . . . . . . .  26
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  28
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  29
     9.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  30
   Appendix A.  The Brief and Extended Depth Request Header Fields .  30
   Appendix B.  Change Log (To be removed by RFC Editor before
                publication) . . . . . . . . . . . . . . . . . . . .  31
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  33

1.  Introduction

   [RFC7240] defines the HTTP Prefer request header field and the
   "return=minimal" preference which indicates that a client wishes for
   the server to return a minimal response to a successful request, but
   states that what constitutes an appropriate minimal response is left
   solely to the discretion of the server.  Section 2 of this
   specification defines precisely what is expected of a server when
   constructing minimal responses to successful WebDAV [RFC4918]
   requests.





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   [RFC7240] also defines the "return=representaion" preference which
   indicates that a client wishes for the server to include an entity
   representing the current state of the resource in the response to a
   successful request.  Section 3 of this specification makes
   recommendations on when this preference should be used by clients and
   extends its applicability to 412 (Precondition Failed) [RFC7231]
   responses.

   Finally, Section 4 of this specifcation defines the "depth-noroot"
   preference that can be used with WebDAV methods that support the
   "Depth" header field..

1.1.  Notational Conventions

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

   This document references XML element types in the "DAV:" [RFC4918]
   namespace outside of the context of an XML fragment.  When doing so,
   the string "DAV:" will be prepended to the XML element type.

2.  Reducing WebDAV Response Verbosity with "return=minimal"

   Some payload bodies in responses to WebDAV requests, such as 207
   (Multi-Status) [RFC4918] responses, can be quite verbose or even
   unnecessary at times.  This specification defines how the Prefer
   request header field, in conjunction with its "return=minimal"
   preference, can be used by clients to reduce the verbosity of such
   responses by requesting that the server omit those portions of the
   response that can be inferred by their absence.

2.1.  Minimal PROPFIND Response

   When a PROPFIND [RFC4918] request contains a Prefer header field with
   a preference of "return=minimal", the server SHOULD omit all
   DAV:propstat XML elements containing a DAV:status XML element of
   value 404 (Not Found) [RFC7231] from the 207 (Multi-Status) response.
   If the omission of such a DAV:propstat element would result in a
   DAV:response XML element containing zero DAV:propstat elements, the
   server MUST substitute one of the following in its place:

   o  a DAV:propstat element consisting of an empty DAV:prop element and
      a DAV:status element of value 200 (OK) [RFC7231]

   o  a DAV:status element of value 200 (OK)





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2.1.1.  Example: Typical PROPFIND request/response

   This example tries to fetch an unknown property from a collection.

   >> Request <<


   PROPFIND /container/ HTTP/1.1
   Host: webdav.example.com
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="UTF-8"?>
   <D:propfind xmlns:D="DAV:" xmlns:X="http://ns.example.com/foobar/">
     <D:prop>
       <D:resourcetype/>
       <X:foobar/>
     </D:prop>
   </D:propfind>
































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   >> Response <<


  HTTP/1.1 207 Multi-Status
  Content-Type: application/xml; charset=utf-8
  Content-Length: xxxx

  <?xml version="1.0" encoding="utf-8"?>
  <D:multistatus xmlns:D="DAV:" xmlns:X="http://ns.example.com/foobar/">
    <D:response>
      <D:href>/container/</D:href>
      <D:propstat>
        <D:prop>
          <D:resourcetype>
            <D:collection/>
          </D:resourcetype>
        </D:prop>
        <D:status>HTTP/1.1 200 OK</D:status>
      </D:propstat>
      <D:propstat>
        <D:prop>
          <X:foobar/>
        </D:prop>
        <D:status>HTTP/1.1 404 Not Found</D:status>
      </D:propstat>
    </D:response>
  </D:multistatus>


2.1.2.  Example: Minimal PROPFIND request/response

   This example tries to fetch an unknown property from a collection.



















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   >> Request <<


   PROPFIND /container/ HTTP/1.1
   Host: webdav.example.com
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx
   Prefer: return=minimal

   <?xml version="1.0" encoding="UTF-8"?>
   <D:propfind xmlns:D="DAV:" xmlns:X="http://ns.example.com/foobar/">
     <D:prop>
       <D:resourcetype/>
       <X:foobar/>
     </D:prop>
   </D:propfind>


   >> Response <<


   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx
   Preference-Applied: return=minimal

   <?xml version="1.0" encoding="utf-8"?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>/container/</D:href>
       <D:propstat>
         <D:prop>
           <D:resourcetype>
             <D:collection/>
           </D:resourcetype>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>


2.1.3.  Example: Minimal PROPFIND request/response with an empty
        DAV:propstat element

   This example tries to fetch an unknown property from a collection.





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   >> Request <<


   PROPFIND /container/ HTTP/1.1
   Host: webdav.example.com
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx
   Prefer: return=minimal

   <?xml version="1.0" encoding="UTF-8"?>
   <D:propfind xmlns:D="DAV:" xmlns:X="http://ns.example.com/foobar/">
     <D:prop>
       <X:foobar/>
     </D:prop>
   </D:propfind>


   >> Response <<


   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx
   Preference-Applied: return=minimal

   <?xml version="1.0" encoding="utf-8"?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>/container/</D:href>
       <D:propstat>
         <D:prop/>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>


2.2.  Minimal REPORT Response

   When a REPORT [RFC3253] request, whose report type results in a 207
   (Multi-Status) response, contains a Prefer header field with a
   preference of "return=minimal", the server SHOULD omit all
   DAV:propstat XML elements containing a DAV:status XML element of
   value 404 (Not Found) [RFC7231] from the 207 (Multi-Status) response.
   If the omission of such a DAV:propstat element would result in a
   DAV:response XML element containing zero DAV:propstat elements, the
   server MUST substitute one of the following in its place:




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   o  a DAV:propstat element consisting of an empty DAV:prop element and
      a DAV:status element of value 200 (OK) [RFC7231]

   o  a DAV:status element of value 200 (OK)

2.2.1.  Example: Typical REPORT request/response

   This example tries to fetch an unknown property from several
   resources via the CALDAV:calendar-multiget [RFC4791] REPORT type.

   >> Request <<


   REPORT /murch/work/ HTTP/1.1
   Host: caldav.example.com
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-multiget xmlns:C="urn:ietf:params:xml:ns:caldav"
                xmlns:D="DAV:"
                xmlns:X="http://ns.example.com/foobar/">
     <D:prop>
       <D:getetag/>
       <X:foobar/>
     </D:prop>
     <D:href>/murch/work/abc.ics</D:href>
     <D:href>/murch/work/qrs.ics</D:href>
     <D:href>/murch/work/xyz.ics</D:href>
   </C:calendar-multiget>





















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   >> Response <<


   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8"?>
   <D:multistatus xmlns:D="DAV:"
              xmlns:X="http://ns.example.com/foobar/">
     <D:response>
       <D:href>/murch/work/abc.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"jahsd823ru"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <D:propstat>
         <D:prop>
           <X:foobar/>
         </D:prop>
         <D:status>HTTP/1.1 404 Not Found</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/murch/work/qrs.ics</D:href>
       <D:status>HTTP/1.1 404 Not Found</D:status>
     </D:response>
     <D:response>
       <D:href>/murch/work/xyz.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"p08ulkj"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <D:propstat>
         <D:prop>
           <X:foobar/>
         </D:prop>
         <D:status>HTTP/1.1 404 Not Found</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>






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2.2.2.  Example: Minimal REPORT request/response

   This example tries to fetch an unknown property from several
   resources via the CALDAV:calendar-multiget [RFC4791] REPORT type.

   >> Request <<


   REPORT /murch/work/ HTTP/1.1
   Host: caldav.example.com
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx
   Prefer: return=minimal

   <?xml version="1.0" encoding="utf-8" ?>
   <C:calendar-multiget xmlns:C="urn:ietf:params:xml:ns:caldav"
                xmlns:D="DAV:"
                xmlns:X="http://ns.example.com/foobar/">
     <D:prop>
       <D:getetag/>
       <X:foobar/>
     </D:prop>
     <D:href>/murch/work/abc.ics</D:href>
     <D:href>/murch/work/qrs.ics</D:href>
     <D:href>/murch/work/xyz.ics</D:href>
   </C:calendar-multiget>

























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   >> Response <<


   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx
   Preference-Applied: return=minimal

   <?xml version="1.0" encoding="utf-8"?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>/murch/work/abc.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"jahsd823ru"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/murch/work/qrs.ics</D:href>
       <D:status>HTTP/1.1 404 Not Found</D:status>
     </D:response>
     <D:response>
       <D:href>/murch/work/xyz.ics</D:href>
       <D:propstat>
         <D:prop>
           <D:getetag>"p08ulkj"</D:getetag>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>


2.3.  Minimal PROPPATCH Response

   When a PROPPATCH [RFC4918] request contains a Prefer header field
   with a preference of "return=minimal", and all instructions are
   processed successfully, the server SHOULD return one of the following
   responses rather than a 207 (Multi-Status) response:

   o  204 (No Content) [RFC7231]

   o  200 (OK) [RFC7231] (preferably with a zero-length message body)






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2.3.1.  Example: Typical PROPPATCH request/response

   >> Request <<


   PROPPATCH /container/ HTTP/1.1
   Host: webdav.example.com
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8"?>
   <D:propertyupdate xmlns:D="DAV:">
     <D:set>
       <D:prop>
         <D:displayname>My Container</D:displayname>
       </D:prop>
     </D:set>
   </D:propertyupdate>


   >> Response <<


   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8"?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>/container/</D:href>
       <D:propstat>
         <D:prop>
           <D:displayname/>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>


2.3.2.  Example: Minimal PROPPATCH request/response









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   >> Request <<


   PROPPATCH /container/ HTTP/1.1
   Host: webdav.example.com
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx
   Prefer: return=minimal

   <?xml version="1.0" encoding="utf-8"?>
   <D:propertyupdate xmlns:D="DAV:">
     <D:set>
       <D:prop>
         <D:displayname>My Container</D:displayname>
       </D:prop>
     </D:set>
   </D:propertyupdate>


   >> Response <<


   HTTP/1.1 200 OK
   Content-Length: 0
   Preference-Applied: return=minimal



2.4.  Minimal MKCALENDAR / MKCOL Response

   Both the MKCALENDAR [RFC4791] and Extended MKCOL [RFC5689]
   specifications indicate that a server MAY return a message body in
   response to a successful request.  This specification explicitly
   defines the intended behavior in the presence of the Prefer header
   field.

   When a MKCALENDAR or an Extended MKCOL request contains a Prefer
   header field with a preference of "return=minimal", and the
   collection is created with all requested properties being set
   successfully, the server SHOULD return a 201 (Created) [RFC7231]
   response with an empty (zero-length) message body.

   Note that the rationale for requiring that a minimal success response
   have an empty body is twofold:

   o  [RFC4791] Section 5.3.1 states: "If a response body for a
      successful [MKCALENDAR] request is included, it MUST be a
      CALDAV:mkcalendar-response XML element."



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   o  [RFC5689] Section 3 states: "When an empty response body is
      returned with a success request status code, the client can assume
      that all properties were set."

2.4.1.  Example: Verbose MKCOL request/response

   >> Request <<


   MKCOL /container/ HTTP/1.1
   Host: webdav.example.com
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8"?>
   <D:mkcol xmlns:D="DAV:">
     <D:set>
       <D:prop>
         <D:displayname>My Container</D:displayname>
       </D:prop>
     </D:set>
   </D:mkcol>


   >> Response <<


   HTTP/1.1 201 Created
   Cache-Control: no-cache
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8"?>
   <D:mkcol-response xmlns:D="DAV:">
     <D:propstat>
       <D:prop>
         <D:displayname/>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
   </D:mkcol-response>


2.4.2.  Example: Minimal MKCOL request/response







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   >> Request <<


   MKCOL /container/ HTTP/1.1
   Host: webdav.example.com
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx
   Prefer: return=minimal

   <?xml version="1.0" encoding="utf-8"?>
   <D:mkcol xmlns:D="DAV:">
     <D:set>
       <D:prop>
         <D:displayname>My Container</D:displayname>
       </D:prop>
     </D:set>
   </D:mkcol>


   >> Response <<


   HTTP/1.1 201 Created
   Cache-Control: no-cache
   Content-Length: 0
   Preference-Applied: return=minimal



3.  Reducing WebDAV Round-Trips with "return=representation"

   The PUT, COPY, MOVE, [RFC4918] and POST [RFC5995] methods can be used
   to create or update a resource.  In some instances, such as with
   CalDAV Scheduling [RFC6638], the created or updated resource
   representation may differ from the representation sent in the body of
   the request or referenced by the effective request URI.  In cases
   where the client would normally issue a subsequent GET request to
   retrieve the current representation of the resource, the client
   SHOULD instead include a Prefer header field with the
   "return=representation" preference in the PUT, COPY, MOVE, or POST
   request.  By doing this, the client can coalesce the create/update
   and retrieve operations into one round-trip rather than two.  An
   additional benefit of using "return=representation" in such a request
   is that the client will know that any changes to the resource were
   produced by the server rather than a concurrent client, thus
   providing a level of atomicity to the operation.





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   Frequently, clients using a state-changing method such as those above
   will make them conditional by including either an If-Match or If-
   None-Match [RFC7232] header field in the request.  If the specified
   condition evaluates to false, and the request includes a Prefer
   header field with the "return=representation" preference, the server
   SHOULD include an entity representing the current state of the
   resource in the resulting 412 (Precondition Failed) [RFC7231]
   response.

3.1.  Example: Typical resource creation and retrieval via POST + GET

   Note that this request is not conditional because by using the POST
   [RFC5995] method the client lets the server choose the URI, thereby
   guaranteeing that it will not modify an existing resource.

   >> Request <<


   POST /murch/work;add-member/ HTTP/1.1
   Host: caldav.example.com
   Content-Type: text/calendar; charset=utf-8
   Content-Length: xxxx

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   UID:CD87465FA
   SEQUENCE:0
   DTSTAMP:20120602T185254Z
   DTSTART:20120602T160000Z
   DTEND:20120602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Ken Murchison":mailto:murch@example.com
   ATTENDEE;CN="Ken Murchison";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:murch@example.com
   ATTENDEE;CN="John Doe";CUTYPE=INDIVIDUAL;PARTSTAT
    =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:jdoe@
    example.com
   END:VEVENT
   END:VCALENDAR









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   >> Response <<


   HTTP/1.1 201 Created
   Location: /murch/work/abc.ics
   Content-Length: 0



   Note that the server did not include any validator header fields (e.g
   ETag) in the response, signaling that the created representation
   differs from the representation sent in the body of the request.  The
   client has to send a separate GET request to retrieve the current
   representation:

   >> Request <<


   GET /murch/work/abc.ics HTTP/1.1
   Host: caldav.example.com































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   >> Response <<


   HTTP/1.1 200 OK
   Content-Type: text/calendar; charset=utf-8
   Content-Length: xxxx
   ETag: "nahduyejc"
   Schedule-Tag: "jfd84hgbcn"

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Server//EN
   BEGIN:VEVENT
   UID:CD87465FA
   SEQUENCE:0
   DTSTAMP:20120602T185300Z
   DTSTART:20120602T160000Z
   DTEND:20120602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Ken Murchison":mailto:murch@example.com
   ATTENDEE;CN="Ken Murchison";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:murch@example.com
   ATTENDEE;CN="John Doe";CUTYPE=INDIVIDUAL;PARTSTAT
    =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=
    1.2:mailto:jdoe@example.com
   END:VEVENT
   END:VCALENDAR


3.2.  Example: Streamlined resource creation and retrieval via POST

   Note that this request is not conditional because by using the POST
   [RFC5995] method the client lets the server choose the URI, thereby
   guaranteeing that it will not modify an existing resource.
















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   >> Request <<


   POST /murch/work;add-member/ HTTP/1.1
   Host: caldav.example.com
   Content-Type: text/calendar; charset=utf-8
   Content-Length: xxxx
   Prefer: return=representation

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Client//EN
   BEGIN:VEVENT
   UID:CD87465FA
   SEQUENCE:0
   DTSTAMP:20120602T185254Z
   DTSTART:20120602T160000Z
   DTEND:20120602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Ken Murchison":mailto:murch@example.com
   ATTENDEE;CN="Ken Murchison";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:murch@example.com
   ATTENDEE;CN="John Doe";CUTYPE=INDIVIDUAL;PARTSTAT
    =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:jdoe@
    example.com
   END:VEVENT
   END:VCALENDAR























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   >> Response <<


   HTTP/1.1 201 Created
   Location: /murch/work/abc.ics
   Content-Type: text/calendar; charset=utf-8
   Content-Length: xxxx
   Content-Location: /murch/work/abc.ics
   ETag: "nahduyejc"
   Schedule-Tag: "jfd84hgbcn"
   Preference-Applied: return=representation

   BEGIN:VCALENDAR
   VERSION:2.0
   PRODID:-//Example Corp.//CalDAV Server//EN
   BEGIN:VEVENT
   UID:CD87465FA
   SEQUENCE:0
   DTSTAMP:20120602T185300Z
   DTSTART:20120602T160000Z
   DTEND:20120602T170000Z
   TRANSP:OPAQUE
   SUMMARY:Lunch
   ORGANIZER;CN="Ken Murchison":mailto:murch@example.com
   ATTENDEE;CN="Ken Murchison";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
    mailto:murch@example.com
   ATTENDEE;CN="John Doe";CUTYPE=INDIVIDUAL;PARTSTAT
    =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=
    1.2:mailto:jdoe@example.com
   END:VEVENT
   END:VCALENDAR


3.3.  Example: Typical conditional resource update failure and retrieval
      via PUT + GET

   >> Request <<


   PUT /container/motd.txt HTTP/1.1
   Host: dav.example.com
   Content-Type: text/plain
   Content-Length: xxxx
   If-Match: "asd973"

   Either write something worth reading or do something worth writing.





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   >> Response <<


   HTTP/1.1 412 Precondition Failed
   Content-Length: 0



   The resource has been modified by another user agent (ETag mismatch),
   therefore the client has to send a separate GET request to retrieve
   the current representation:

   >> Request <<


   GET /container/motd.txt HTTP/1.1
   Host: dav.example.com



   >> Response <<


   HTTP/1.1 200 OK
   Content-Type: text/plain
   Content-Length: xxxx
   ETag: "789sdas"

   An investment in knowledge pays the best interest.


3.4.  Example: Streamlined conditional resource update failure and
      retrieval via PUT

   >> Request <<


   PUT /container/motd.txt HTTP/1.1
   Host: dav.example.com
   Content-Type: text/plain
   Content-Length: xxxx
   If-Match: "asd973"
   Prefer: return=representation

   Either write something worth reading or do something worth writing.






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   >> Response <<


   HTTP/1.1 412 Precondition Failed
   Content-Type: text/plain
   Content-Length: xxxx
   Content-Location: /container/motd.txt
   ETag: "789sdas"
   Preference-Applied: return=representation

   An investment in knowledge pays the best interest.


4.  The "depth-noroot" Processing Preference

   The "depth-noroot" preference indicates that the client wishes for
   the server to exclude the target (root) resource from processing by
   the WebDAV method and only apply the WebDAV method to the target
   resource's subordinate resources.

   depth-noroot = "depth-noroot"

   This preference is only intended to be used with WebDAV methods whose
   definitions explicitly provide support for the Depth [RFC4918] header
   field.  Furthermore, this preference only applies when the Depth
   header field has a value of "1" or "infinity" (either implicitly or
   explicitly).

   The "depth-noroot" preference MAY be used in conjunction with the
   "return=minimal" preference in a single request.

4.1.  Example: Typical PROPFIND request/response with Depth:1

   This example fetches the DAV:resourcetype [RFC4918] property for a
   collection and its child resources.
















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   >> Request <<


   PROPFIND /murch/ HTTP/1.1
   Host: webdav.example.com
   Content-Type: text/xml
   Content-Length: xxx
   Depth: 1

   <?xml version="1.0" encoding="UTF-8"?>
   <D:propfind xmlns:D="DAV:">
     <D:prop>
       <D:resourcetype/>
     </D:prop>
   </D:propfind>


   >> Response <<


   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8"?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>/murch/</D:href>
       <D:propstat>
         <D:prop>
           <D:resourcetype>
         <D:collection/>
           </D:resourcetype>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/murch/work/</D:href>
       <D:propstat>
         <D:prop>
           <D:resourcetype>
         <D:collection/>
           </D:resourcetype>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>



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     <D:response>
       <D:href>/murch/home/</D:href>
       <D:propstat>
         <D:prop>
           <D:resourcetype>
         <D:collection/>
           </D:resourcetype>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/murch/foo.txt</D:href>
       <D:propstat>
         <D:prop>
           <D:resourcetype/>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>


4.2.  Example: PROPFIND request/response with Depth:1 and Prefer:depth-
      noroot

   This example fetches the DAV:resourcetype [RFC4918] property for just
   the child resources.

   >> Request <<


   PROPFIND /murch/ HTTP/1.1
   Host: webdav.example.com
   Content-Type: text/xml
   Content-Length: xxx
   Depth: 1
   Prefer: depth-noroot

   <?xml version="1.0" encoding="UTF-8"?>
   <D:propfind xmlns:D="DAV:">
     <D:prop>
       <D:resourcetype/>
     </D:prop>
   </D:propfind>






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   >> Response <<


   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset=utf-8
   Content-Length: xxxx
   Preference-Applied: depth-noroot

   <?xml version="1.0" encoding="utf-8"?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>/murch/work/</D:href>
       <D:propstat>
         <D:prop>
           <D:resourcetype>
         <D:collection/>
           </D:resourcetype>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/murch/home/</D:href>
       <D:propstat>
         <D:prop>
           <D:resourcetype>
         <D:collection/>
           </D:resourcetype>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/murch/foo.txt</D:href>
       <D:propstat>
         <D:prop>
           <D:resourcetype/>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>









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5.  Implementation Status

   [RFC Editor: before publication please remove this section and the
   reference to [RFC6982]]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC6982].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC6982], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

5.1.  Cyrus

   The open source Cyrus [4] project is a highly scalable enterprise
   mail system which also supports calendaring and contacts.  This beta
   level CalDAV/CardDAV implementation supports all of the preferences
   described in this document and successfully interoperates with the
   CalDAVTester and aCal client implementations described below.  This
   implementation is freely distributable under a BSD style license from
   Computing Services at Carnegie Mellon University [5].

5.2.  Calendar and Contacts Server

   The open source Calendar and Contacts Server [6] project is a
   standards-compliant server implementing the CalDAV and CardDAV
   protocols.  This production level implementation supports all of the
   preferences described in this document and successfully interoperates
   with the CalDAVTester client implementation described below.  This
   implementation is freely distributable under the terms of the Apache
   License, Version 2.0 [7].







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5.3.  Bedework

   Bedework [8] is an open-source enterprise calendar system that
   supports public, personal, and group calendaring.  This production
   level implementation supports the "return=minimal" preference
   described in this document and successfully interoperates with the
   CalDAVTester client implementation described below.  This
   implementation is freely distributable under the Jasig Licensing
   Policy [9].

5.4.  DAViCal

   DAViCal [10] is a server for calendar sharing using the CalDAV
   protocol.  This production level implementation supports the
   "return=minimal" preference described in this document and
   successfully interoperates with the CalDAVTester client
   implementation described below.  This implementation is Free Software
   [11] distributable under the General Public License [12].

5.5.  aCal

   aCal [13] is an open source calendar client for Android which uses
   the CalDAV standard for communication.  This implementation makes
   some use of each of the preferences described in this document and
   successfully interoperates with the Cyrus server implementation
   described above.  This implementation is freely distributable under
   the General Public License [14].

5.6.  CalDAVTester

   CalDAVTester [15] is an open source test and performance application
   designed to work with CalDAV and/or CardDAV servers and tests various
   aspects of their protocol handling as well as performance.  This
   widely used implementation supports all of the preferences described
   in this document and successfully interoperates with the server
   implementations described above.  This implementation is freely
   distributable under the terms of the Apache License, Version 2.0
   [16].

6.  Security Considerations

   No new security considerations are introduced by use of the Prefer
   header field with WebDAV request methods, beyond those discussed in
   [RFC7240] and those already inherent in those methods.







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7.  IANA Considerations

   The following preference is to be added to the Preferences Registry
   defined in [RFC7240].

   o  Preference: depth-noroot

   o  Description: The "depth-noroot" preference indicates that the
      client wishes for the server to exclude the target (root) resource
      from processing by the WebDAV method and only apply the WebDAV
      method to the target resource's subordinate resources.

   o  Reference: Section 4

   o  Notes: This preference is only intended to be used with WebDAV
      methods whose definitions explicitly provide support for the
      "Depth" [RFC4918] header field.  Furthermore, this preference only
      applies when the "Depth" header field has a value of "1" or
      "infinity" (either implicitly or explicitly).

8.  Acknowledgements

   The author would like to thank the following individuals for
   contributing their ideas and support for writing this specification:
   Cyrus Daboo, Helge Hess, Andrew McMillan, Arnaud Quillaud, and Julian
   Reschke.

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

9.  References

9.1.  Normative References

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

   [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.

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





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

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

   [RFC5995]  Reschke, J., "Using POST to Add Members to Web Distributed
              Authoring and Versioning (WebDAV) Collections", RFC 5995,
              September 2010.

   [RFC7231]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Semantics and Content", RFC 7231, June 2014.

   [RFC7232]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Conditional Requests", RFC 7232, June 2014.

   [RFC7240]  Snell, J., "Prefer Header for HTTP", RFC 7240, June 2014.

9.2.  Informative References

   [MSDN.aa493854]
              Microsoft Developer Network, "PROPPATCH Method", June
              2006,
              <http://msdn.microsoft.com/en-us/library/aa493854.aspx>.

   [MSDN.aa563501]
              Microsoft Developer Network, "Brief Header", June 2006,
              <http://msdn.microsoft.com/en-us/library/aa563501.aspx>.

   [MSDN.aa563950]
              Microsoft Developer Network, "Depth Header", June 2006,
              <http://msdn.microsoft.com/en-us/library/aa563950.aspx>.

   [MSDN.aa580336]
              Microsoft Developer Network, "PROPFIND Method", June 2006,
              <http://msdn.microsoft.com/en-us/library/aa580336.aspx>.

   [RFC6638]  Daboo, C. and B. Desruisseaux, "Scheduling Extensions to
              CalDAV", RFC 6638, June 2012.

   [RFC6982]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", RFC 6982, July
              2013.








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9.3.  URIs

   [1] http://www.cyrusimap.org/

   [2] http://www.cmu.edu/computing/

   [3] http://calendarserver.org/

   [4] http://www.apache.org/licenses/LICENSE-2.0.html

   [5] http://www.bedework.org/

   [6] http://www.jasig.org/licensing

   [7] http://www.davical.org/

   [8] http://www.gnu.org/philosophy/open-source-misses-the-point.html

   [9] http://www.gnu.org/licenses/gpl.html

   [10] http://www.acal.me/

   [11] http://www.gnu.org/licenses/gpl.html

   [12] http://calendarserver.org/wiki/CalDAVTester

   [13] http://www.apache.org/licenses/LICENSE-2.0.html

Appendix A.  The Brief and Extended Depth Request Header Fields

   This document is based heavily on the Brief [MSDN.aa563501] and
   extended Depth [MSDN.aa563950] request header fields.  The behaviors
   described in Section 2.1 and Section 2.3 are identical to those
   provided by the Brief header field when used with the PROPFIND
   [MSDN.aa580336] and PROPPATCH [MSDN.aa493854] methods respectively.
   The behavior described in Section 4 is identical to that provided by
   the "1,noroot" [MSDN.aa563950] and "infinity,noroot" [MSDN.aa563950]
   Depth header field values.

   Client and server implementations that already support the Brief
   header field can add support for the "return=minimal" preference with
   nominal effort.

   If a server supporting the Prefer header field receives both the
   Brief and Prefer header fields in a request, it MUST ignore the Brief
   header field and only use the Prefer header field preferences.





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Appendix B.  Change Log (To be removed by RFC Editor before publication)

B.1.  Since -06

   o  Updated HTTPbis and Prefer references to published RFCs.

B.2.  Since -05

   o  Allow a minimal PROPFIND/REPORT response to contain a DAV:status
      element rather than an empty DAV:propstat element.

   o  Allow 204 (No Content) as a minimal PROPATCH success response.

   o  Added justification for why a minimal MKCOL/MKCALENDAR success
      response must have an empty body.

   o  Added text and an example of how "return=representation" can be
      employed with a conditional state-changing request and a 412
      (Precondition Failed) response.

   o  Added a note to the POST+GET example bringing attention to the
      lack of a validator header field in the POST response.

   o  Reduced the number of inline references.

   o  Limited most examples to vanilla WebDAV.

   o  Reduced number of items in TOC.

   o  Removed the recommendation that the legacy Brief header
      functionality should be implemented.

   o  Added note about how a server should handle a request that
      contains both Brief and Prefer.

   o  Other editorial tweaks from Julian Reschke.

B.3.  Since -04

   o  Added note stating where to send comments.

B.4.  Since -03

   o  Limited "Updates" to just RFC 4918.

   o  Consensus from CalConnect membership that a "depth-root" option is
      unnecessary at this point.




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   o  Consensus from CalConnect membership to remove Vary header field
      from PROPFIND and REPORT responses since these responses don't
      appear to be cached.

   o  Updated "Implementation Status" section boilerplate to RFC 6982.

   o  Added aCal to "Implementation Status" section.

   o  Added note that servers SHOULD respond with Preference-Applied
      when return=minimal is used with PROPFIND or REPORT.

B.5.  Since -02

   o  Reintroduced "Updates" to header.

   o  Added text noting that "return=representation" provides a level of
      atomicity to the operation.

   o  Added "Implementation Status" section.

   o  Tweaked/corrected some examples..

   o  Updated HTTPbis references.

B.6.  Since -01

   o  Removed "Updates" from header.

   o  Fixed some missing/incorrect references.

   o  Reintroduced Cache-Control:no-cache to MKCOL responses.

B.7.  Since -00

   o  Updated to comply with draft-snell-httpprefer-18.

   o  Reordered "Minimal REPORT Response" and "Minimal PROPPATCH
      Response" sections.

   o  Added some explanatory text to examples.

B.8.  Since CalConnect XXIV

   o  Updated references.

   o  Stated that "depth-noroot" can be used in conjuction with
      "return=minimal".




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   o  Added text mentioning that "depth-noroot" is based on the MSDN
      "1,noroot" and "infinity,noroot" Depth header values.

   o  The server behavior required when "return=minimal" would result in
      zero DAV:propstat elements has been changed

   from:


   <?xml version="1.0" encoding="utf-8"?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>/container/</D:href>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:response>
   </D:multistatus>


   to the slightly more verbose:


   <?xml version="1.0" encoding="utf-8"?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>/container/</D:href>
       <D:propstat>
         <D:prop/>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>


Author's Address

   Kenneth Murchison
   Carnegie Mellon University
   5000 Forbes Avenue
   Pittsburgh, PA  15213
   US

   Email: murch@andrew.cmu.edu









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