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Versions: 00 01 02 03 04 05 06 07 08 RFC 6578

Network Working Group                                           C. Daboo
Internet-Draft                                               Apple, Inc.
Intended status: Standards Track                             A. Quillaud
Expires: September 9, 2010                              Sun Microsystems
                                                           March 8, 2010


                 Collection Synchronization for WebDAV
                       draft-daboo-webdav-sync-03

Abstract

   This specification defines an extension to WebDAV that allows
   efficient synchronization of the contents of a WebDAV collection.

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

   Please send comments to the Distributed Authoring and Versioning
   (WebDAV) working group at <mailto:w3c-dist-auth@w3.org>, which may be
   joined by sending a message with subject "subscribe" to
   <mailto:w3c-dist-auth-request@w3.org>.  Discussions of the WEBDAV
   working group are archived at
   <http://lists.w3.org/Archives/Public/w3c-dist-auth/>.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on September 9, 2010.

Copyright Notice



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   Copyright (c) 2010 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
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   This document may contain material from IETF Documents or IETF
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   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.



























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  4
   3.  WebDAV Synchronization . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  DAV:sync-collection Report . . . . . . . . . . . . . . . .  6
     3.3.  Types of Changes Reported on Initial Synchronization . . .  7
     3.4.  Types of Changes Reported on Subsequent
           Synchronizations . . . . . . . . . . . . . . . . . . . . .  7
       3.4.1.  Changed Resource . . . . . . . . . . . . . . . . . . .  8
       3.4.2.  Removed Resource . . . . . . . . . . . . . . . . . . .  8
     3.5.  Truncation of Results  . . . . . . . . . . . . . . . . . .  8
     3.6.  Limiting Results . . . . . . . . . . . . . . . . . . . . .  9
     3.7.  Example: Initial DAV:sync-collection Report  . . . . . . .  9
     3.8.  Example: DAV:sync-collection Report with Token . . . . . . 11
     3.9.  Example: Initial DAV:sync-collection Report with
           Truncation . . . . . . . . . . . . . . . . . . . . . . . . 14
     3.10. Example: Initial DAV:sync-collection Report with Limit . . 15
     3.11. Example: DAV:sync-collection Report with Unsupported
           Limit  . . . . . . . . . . . . . . . . . . . . . . . . . . 17
   4.  DAV:sync-token Property  . . . . . . . . . . . . . . . . . . . 17
   5.  XML Element Definitions  . . . . . . . . . . . . . . . . . . . 18
     5.1.  DAV:sync-collection XML Element  . . . . . . . . . . . . . 18
     5.2.  DAV:sync-token XML Element . . . . . . . . . . . . . . . . 19
     5.3.  DAV:multistatus XML Element  . . . . . . . . . . . . . . . 19
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 20
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 21
   Appendix A.  Change History (to be removed prior to
                publication as an RFC)  . . . . . . . . . . . . . . . 21

















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1.  Introduction

   WebDAV [RFC4918] defines the concept of 'collections' which are
   hierarchical groupings of WebDAV resources on an HTTP [RFC2616]
   server.  Collections can be of arbitrary size and depth (i.e.,
   collections within collections).  WebDAV clients that cache resource
   content need a way to synchronize that data with the server (i.e.,
   detect what has changed and update their cache).  This can currently
   be done using a WebDAV PROPFIND request on a collection to list all
   members of a collection along with their DAV:getetag property values,
   which allows the client to determine which resources were changed,
   added or deleted.  However, this does not scale well to large
   collections as the XML response to the PROPFIND request will grow
   with the collection size.

   This specification defines a new WebDAV report that results in the
   server returning to the client only information about those resources
   which have changed, are new or were deleted since a previous
   execution of the report on the collection.

   Additionally, a new property is added to collection resources that is
   used to convey a "synchronization token" that is guaranteed to change
   when resources within the collection have changed.

2.  Conventions Used in This Document

   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 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 this 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.



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   When an XML element type in the "DAV:" namespace is referenced in
   this document outside of the context of an XML fragment, the string
   "DAV:" will be prefixed to the element type.

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

3.  WebDAV Synchronization

3.1.  Overview

   One way to synchronize data between two entities is to use some form
   of synchronization token.  The token defines the state of the data
   being synchronized at a particular point in time.  It can then be
   used to determine what has changed since one point in time and
   another.

   This specification defines a new WebDAV report that is used to enable
   client-server collection synchronization based on such a token.

   In order to synchronize the contents of a collection between a server
   and client, the server provides the client with a synchronization
   token each time the synchronization report is executed.  That token
   represents the state of the data being synchronized at that point in
   time.  The client can then present that same token back to the server
   at some later time and the server will return only those items that
   are new, have changed or were deleted since that token was generated.
   The server also returns a new token representing the new state at the
   time the report was run.

   Typically the first time a client connects to the server it will need
   to be informed of the entire state of the collection (i.e., a full
   list of all resources that are currently contained in the
   collection).  That is done by the client sending an empty token value
   to the server.  This indicates to the server that a full listing is
   required.

   As an alternative, the client may choose to do its first
   synchronization using some other mechanism on the collection (e.g.
   some other form of batch resource information retrieval such as
   PROPFIND, SEARCH [RFC5323], or specialized REPORTs such as those
   defined in CalDAV [RFC4791] and CardDAV [I-D.ietf-vcarddav-carddav])
   and ask for the DAV:sync-token property to be returned.  This
   property (defined in Section 4) contains the same token that can be
   used later on to issue a DAV:sync-collection report.

   In some cases a server may only wish to maintain a limited amount of
   history about changes to a collection.  In that situation it will



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   return an error to the client when the client presents a token that
   is "out of date".  At that point the client has to fall back to
   synchronizing the entire collection by re-running the report request
   using an empty token value.

3.2.  DAV:sync-collection Report

   This specification defines the DAV:sync-collection report.

   If this report is implemented by a WebDAV server, then the server
   MUST list the report in the "DAV:supported-report-set" property on
   any collection supporting synchronization.

   To implement the behavior for this report a server needs to keep
   track of changes to any resources in a collection.  This includes
   noting the addition of new resources, changes to existing resources
   and removal of resources.  Only internal members of the collection
   (as defined in [RFC4918]) are to be considered.  The server will
   track each change and provide a synchronization "token" to the client
   that describes the state of the server at a specific point in time.
   This "token" is returned as part of the response to the "sync-
   collection" report.  Clients include the last token they got from the
   server in the next "sync-collection" report that they execute and the
   server provides the changes from the previous state, represented by
   the token, to the current state, represented by the new token
   returned.

   The synchronization token itself is an "opaque" string - i.e., the
   actual string data has no specific meaning or syntax.  A simple
   implementation of such a token would be a numeric counter that counts
   each change as it occurs and relates that change to the specific
   object that changed.

   Marshalling:

      The request URI MUST identify a collection.  The request body MUST
      be a DAV:sync-collection XML element (see Section 5.1), which MUST
      contain one DAV:sync-token XML element, and one DAV:prop XML
      element.

      The request MUST include a Depth header with a value of "1".

      The response body for a successful request MUST be a DAV:
      multistatus XML element, which MUST contain one DAV:sync-token
      element in addition to one DAV:response element for each resource
      that was created, has changed or been deleted since the last
      synchronization operation as specified by the DAV:sync-token
      provided in the request.  A given resource MUST appear only once



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      in the response.

      The content of each DAV:response element differs depending on how
      the resource was altered:

         For resources that have changed (i.e. are new or have been
         modified) the DAV:response MUST contain at least one DAV:
         propstat element and MUST NOT contain any DAV:status element.

         For resources that have been removed, the DAV:response MUST
         contain one DAV:status with a value set to '404 Not Found' and
         MUST NOT contain any DAV:propstat element.

      The conditions under which each type of change may occur is
      further described in Section 3.4.

   Preconditions:

      (DAV:valid-sync-token): The DAV:sync-token element value MUST map
      to a valid token previously returned by the server.  A token may
      become invalid as the result of being "out of date" (out of the
      range of change history maintained by the server), or for other
      reasons (e.g. collection deleted, then recreated, ACL changes,
      etc...).

   Postconditions:

      (DAV:number-of-matches-within-limits): The number of changes
      reported in the response must fall within the client specified
      limit.  This condition might be triggered if a client requests a
      limit on the number of responses (as per Section 3.6) but the
      server is unable to truncate the result set at or below that
      limit.

3.3.  Types of Changes Reported on Initial Synchronization

   When the DAV:sync-collection request does not contain a sync-token,
   the server MUST return all internal members of the collection and it
   MUST NOT return any removed resource.

3.4.  Types of Changes Reported on Subsequent Synchronizations

   When the DAV:sync-collection request contains a valid sync-token, two
   types of resource state changes can be returned (changed or removed).
   This section defines what triggers each of these to be returned.  It
   also clarifies the case where a resource may have undergone multiple
   changes in between two synchronizations.




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3.4.1.  Changed Resource

   A resource MUST be reported as changed if it has been mapped directly
   under the target collection since the request sync token was
   generated.  This includes resources that have been mapped as the
   result of a COPY, MOVE or BIND ([I-D.ietf-webdav-bind]) operation.
   This also includes collection resources that have been created.

   In the case where a mapping between a resource and the target
   collection was removed, then a new mapping with the same URI created,
   the new resource MUST be reported as changed while the old resource
   MUST NOT be reported as removed.  For example, if a resource was
   deleted, then recreated using the same URI, it should be reported as
   a changed resource only.

   A resource MUST be reported as changed if its entity tag value
   (defined in [RFC2616]) has changed since the request sync token was
   generated.

   A resource MAY be reported as changed if the user issuing the request
   was granted access to this resource, due to access control changes.

   Collection resources MUST NOT be returned as changed, except in the
   case stated above.  Instead clients are expected to synchronize
   changes in child collection resources on an individual basis.

3.4.2.  Removed Resource

   A resource MUST be reported as removed if its mapping under the
   target collection has been removed since the request sync token was
   generated, and it has not been re-mapped since it was removed.  This
   includes resources that have been unmapped as the result of a MOVE or
   UNBIND ([I-D.ietf-webdav-bind]) operation.  This also includes
   collection resources that have been removed.

   If a resource was created (and possibly modified), then removed in
   between two synchronizations, it MUST be reported as removed.

   A resource MAY be reported as removed if the user issuing the request
   no longer has access to this resource, due to access control changes.

3.5.  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
   request, or as the result of an explicit limit set by the client.  If
   the result set is truncated, the response MUST use status code 207,
   return a DAV:multistatus response body, and indicate a status of 507



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   (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).  DAV:response elements for all the changes being reported are
   also included.

   When truncation occurs, the DAV:sync-token value returned in the
   response MUST represent the correct state for the partial set of
   changes returned.  That allows the client to use the returned DAV:
   sync-token to fetch the next set of changes.  In this way the client
   can effectively "page" through the entire set of changes in a
   consistent manner.

   Clients MUST handle the 507 status on the request-URI in the response
   to the report.

   For example, consider a server that records changes using a
   monotonically increasing integer to represent a "revision number" and
   uses that quantity as the DAV:sync-token value.  Assume the last DAV:
   sync-token used by the client was "10", and since then 20 additional
   changes have occurred.  If the client executes a DAV:sync-collection
   request with a DAV:sync-token of "10", without a limit the server
   would return 20 DAV:response elements and a DAV:sync-token with value
   "30".  But if the server choose to limit responses to at most 10
   changes, then it would return only 10 DAV:response elements and a
   DAV:sync-token with value "20", together with an addition DAV:
   response element for the request-URI with a status code of 507.
   Subsequently, the client can re-issue the request with the DAV:sync-
   token value returned from the server and fetch the remaining 10
   changes.

3.6.  Limiting Results

   A client can limit the number of results returned by the server
   through use of the DAV:limit element ([RFC5323], Section 5.17) in the
   request body.  This is useful when clients have limited space or
   bandwidth for the results.  If a server is unable to truncate the
   result at or below the requested number, then it MUST fail the
   request with a DAV:number-of-matches-within-limits post-condition
   error.  When the results can be correctly limited by the server, the
   server MUST follow the rules above for indicating a result set
   truncation to the client.

3.7.  Example: Initial DAV:sync-collection Report

   In this example, the client is making its first synchronization
   request to the server, so the DAV:sync-token element in the request
   is empty.  It also asks for the DAV:getetag property and for a



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   proprietary property.  The server responds with the items currently
   in the targeted collection.  The current synchronization token is
   also returned.

   >> Request <<


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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:sync-collection xmlns:D="DAV:">
     <D:sync-token/>
     <D:prop xmlns:R="urn:ns.example.com:boxschema">
       <D:getetag/>
       <R:bigbox/>
     </D:prop>
   </D:sync-collection>


   >> Response <<


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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
     <D:href
   >http://webdav.example.com/home/cyrusdaboo/test.doc</D:href>
     <D:propstat>
       <D:prop>
         <D:getetag>"00001-abcd1"</D:getetag>
         <R:bigbox xmlns:R="urn:ns.example.com:boxschema">
           <R:BoxType>Box type A</R:BoxType>
         </R:bigbox>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
     </D:response>
     <D:response>
     <D:href
   >http://webdav.example.com/home/cyrusdaboo/vcard.vcf</D:href>



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     <D:propstat>
       <D:prop>
         <D:getetag>"00002-abcd1"</D:getetag>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
     <D:propstat>
       <D:prop>
         <R:bigbox xmlns:R="urn:ns.example.com:boxschema"/>
       </D:prop>
       <D:status>HTTP/1.1 404 Not Found</D:status>
     </D:propstat>
     </D:response>
     <D:response>
     <D:href
   >http://webdav.example.com/home/cyrusdaboo/calendar.ics</D:href>
     <D:propstat>
       <D:prop>
         <D:getetag>"00003-abcd1"</D:getetag>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
     <D:propstat>
       <D:prop>
         <R:bigbox xmlns:R="urn:ns.example.com:boxschema"/>
       </D:prop>
       <D:status>HTTP/1.1 404 Not Found</D:status>
     </D:propstat>
     </D:response>
     <D:sync-token>1234</D:sync-token>
   </D:multistatus>


3.8.  Example: DAV:sync-collection Report with Token

   In this example, the client is making a synchronization request to
   the server and is using the DAV:sync-token element returned from the
   last report it ran on this collection.  The server responds, listing
   the items that have been added, changed or removed.  The (new)
   current synchronization token is also returned.











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   >> Request <<


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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:sync-collection xmlns:D="DAV:">
     <D:sync-token>1234</D:sync-token>
     <D:prop xmlns:R="urn:ns.example.com:boxschema">
       <D:getetag/>
       <R:bigbox/>
     </D:prop>
   </D:sync-collection>


































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   >> Response <<


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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
     <D:href
   >http://webdav.example.com/home/cyrusdaboo/file.xml</D:href>
     <D:propstat>
       <D:prop>
         <D:getetag>"00004-abcd1"</D:getetag>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
     <D:propstat>
       <D:prop>
         <R:bigbox xmlns:R="urn:ns.example.com:boxschema"/>
       </D:prop>
       <D:status>HTTP/1.1 404 Not Found</D:status>
     </D:propstat>
     </D:response>
     <D:response>
     <D:href
   >http://webdav.example.com/home/cyrusdaboo/vcard.vcf</D:href>
     <D:propstat>
       <D:prop>
         <D:getetag>"00002-abcd2"</D:getetag>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
     <D:propstat>
       <D:prop>
         <R:bigbox xmlns:R="urn:ns.example.com:boxschema"/>
       </D:prop>
       <D:status>HTTP/1.1 404 Not Found</D:status>
     </D:propstat>
     </D:response>
     <D:response>
     <D:href
   >http://webdav.example.com/home/cyrusdaboo/test.doc</D:href>
     <D:status>HTTP/1.1 404 Not Found</D:status>
     </D:response>
     <D:sync-token>1238</D:sync-token>
   </D:multistatus>



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3.9.  Example: Initial DAV:sync-collection Report with Truncation

   In this example, the client is making its first synchronization
   request to the server, so the DAV:sync-token element in the request
   is empty.  It also asks for the DAV:getetag property.  The server
   responds with the items currently in the targeted collection, but
   truncated at two items.  The synchronization token for the truncated
   result set is returned.

   >> Request <<


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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:sync-collection xmlns:D="DAV:">
     <D:sync-token/>
     <D:prop>
       <D:getetag/>
     </D:prop>
   </D:sync-collection>


























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   >> Response <<


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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
     <D:href
   >http://webdav.example.com/home/cyrusdaboo/test.doc</D:href>
     <D:propstat>
       <D:prop>
         <D:getetag>"00001-abcd1"</D:getetag>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
     </D:response>
     <D:response>
     <D:href
   >http://webdav.example.com/home/cyrusdaboo/vcard.vcf</D:href>
     <D:propstat>
       <D:prop>
         <D:getetag>"00002-abcd1"</D:getetag>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
     </D:response>
     <D:response>
       <D:href
   >http://webdav.example.com/home/cyrusdaboo/</D:href>
       <D:status>HTTP/1.1 507 Insufficient Storage</D:status>
     </D:response>
     <D:sync-token>1233</D:sync-token>
   </D:multistatus>


3.10.  Example: Initial DAV:sync-collection Report with Limit

   In this example, the client is making its first synchronization
   request to the server, so the DAV:sync-token element in the request
   is empty.  It requests a limit of 1 for the responses returned by the
   server.  It also asks for the DAV:getetag property.  The server
   responds with the items currently in the targeted collection, but
   truncated at one item.  The synchronization token for the truncated
   result set is returned.




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   >> Request <<


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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:sync-collection xmlns:D="DAV:">
     <D:sync-token/>
     <D:limit>
       <D:nresults>1</D:nresults>
     </D:limit>
     <D:prop>
       <D:getetag/>
     </D:prop>
   </D:sync-collection>


   >> Response <<


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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
     <D:href
   >http://webdav.example.com/home/cyrusdaboo/test.doc</D:href>
     <D:propstat>
       <D:prop>
         <D:getetag>"00001-abcd1"</D:getetag>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
     </D:response>
     <D:response>
       <D:href
   >http://webdav.example.com/home/cyrusdaboo/</D:href>
       <D:status>HTTP/1.1 507 Insufficient Storage</D:status>
     </D:response>
     <D:sync-token>1232</D:sync-token>
   </D:multistatus>




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3.11.  Example: DAV:sync-collection Report with Unsupported Limit

   In this example, the client is making a synchronization request to
   the server with a valid DAV:sync-token element value.  It requests a
   limit of 100 for the responses returned by the server.  It also asks
   for the DAV:getetag property.  The server is unable to limit the
   results to the maximum specified by the client, so it responds with a
   507 status code and appropriate post-condition error code.

   >> Request <<


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

   <?xml version="1.0" encoding="utf-8" ?>
   <D:sync-collection xmlns:D="DAV:">
     <D:sync-token>1232</D:sync-token>
     <D:limit>
       <D:nresults>100</D:nresults>
     </D:limit>
     <D:prop>
       <D:getetag/>
     </D:prop>
   </D:sync-collection>


   >> Response <<


   HTTP/1.1 507 Insufficient Storage
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:error xmlns:D="DAV:">
     <D:number-of-matches-within-limits/>
   </D:error>


4.  DAV:sync-token Property







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   Name:  sync-token

   Namespace:  DAV:

   Purpose:  Contains the value of the synchronization token as it would
      be returned by a DAV:sync-collection report.

   Value:  Any text.

   Protected:  MUST be protected because this value is created and
      controlled by the server.

   COPY/MOVE behavior:  This property value is dependent on the final
      state of the destination resource, not the value of the property
      on the source resource.

   Description:  The DAV:sync-token property MUST be defined on all
      resources that support the DAV:sync-collection report.  It
      contains the value of the synchronization token as it would be
      returned by a DAV:sync-collection report on that resource at the
      same point in time.  It SHOULD NOT be returned by a PROPFIND DAV:
      allprop request (as defined in [RFC4918]).

   Definition:


   <!ELEMENT sync-token #PCDATA>


5.  XML Element Definitions

5.1.  DAV:sync-collection XML Element

   Name:  sync-collection

   Namespace:  DAV:

   Purpose:  WebDAV report used to synchronize data between client and
      server.

   Description:  See Section 3.



   <!ELEMENT sync-collection (sync-token, DAV:limit?, DAV:prop)>

   <!-- DAV:limit defined in RFC 5323, Section 5.17 -->
   <!-- DAV:prop defined in RFC 4918, Section 14.18 -->



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5.2.  DAV:sync-token XML Element

   Name:  sync-token

   Namespace:  DAV:

   Purpose:  The synchronization token provided by the server and
      returned by the client.

   Description:  See Section 3.



   <!ELEMENT sync-token CDATA>


5.3.  DAV:multistatus XML Element

   Name:  multistatus

   Namespace:  DAV:

   Purpose:  Extends the DAV:multistatus element to include
      synchronization details.

   Description:  See Section 3.



   <!ELEMENT multistatus (DAV:response*, DAV:responsedescription?,
                          sync-token?) >

   <!-- DAV:multistatus originally defined in RFC 4918, Section 14.16
        but overridden here to add the DAV:sync-token element -->
   <!-- DAV:response defined in RFC 4918, Section 14.24 -->
   <!-- DAV:responsedescription defined in RFC 4918, Section 14.25 -->


6.  Security Considerations

   This extension does not introduce any new security concerns than
   those already described in HTTP and WebDAV.

7.  IANA Considerations

   This document does not require any actions on the part of IANA.





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8.  Acknowledgments

   The following individuals contributed their ideas and support for
   writing this specification: Bernard Desruisseaux, Mike Douglass, Ciny
   Joy, Andrew McMillan, Julian Reschke, and Wilfredo Sanchez.  We would
   like to thank the Calendaring and Scheduling Consortium for
   facilitating interoperability testing for early implementations of
   this specification.

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.

   [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.

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

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

   [RFC5323]                    Reschke, J., Reddy, S., Davis, J., and
                                A. Babich, "Web Distributed Authoring
                                and Versioning (WebDAV) SEARCH",
                                RFC 5323, November 2008.

   [W3C.REC-xml-20081126]       Maler, E., Yergeau, F., Sperberg-
                                McQueen, C., Paoli, J., and T. Bray,
                                "Extensible Markup Language (XML) 1.0
                                (Fifth Edition)", World Wide Web
                                Consortium Recommendation REC-xml-
                                20081126, November 2008, <http://
                                www.w3.org/TR/2008/REC-xml-20081126>.






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9.2.  Informative References

   [I-D.ietf-vcarddav-carddav]  Daboo, C., "vCard Extensions to WebDAV
                                (CardDAV)",
                                draft-ietf-vcarddav-carddav-10 (work in
                                progress), November 2009.

   [I-D.ietf-webdav-bind]       Clemm, G., Crawford, J., Reschke, J.,
                                and J. Whitehead, "Binding Extensions to
                                Web Distributed Authoring and Versioning
                                (WebDAV)", draft-ietf-webdav-bind-27
                                (work in progress), December 2009.

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

Appendix A.  Change History (to be removed prior to publication as an
             RFC)

   Changes in -03:

   1.  Changed D:propstat to D:prop in marshalling.

   2.  Added request for dead property in examples.

   3.  Made D:prop mandatory in request so that D:response always
       contains at least one D:propstat as per WebDAV definition.

   4.  Removed DAV:status from response when resource is created/
       modified, thus allowing to get rid of DAV:sync-response in favor
       of a regular DAV:response.  As a consequence, there is no longer
       any difference in the report between created and modified
       resources.

   5.  Resource created, then removed between 2 sync MUST be returned as
       removed.

   6.  Added ability for server to truncate results and indicate such to
       the client.

   7.  Added ability for client to request the server to limit the
       result set.

   Changes in -02:

   1.  Added definition of sync-token WebDAV property.




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   2.  Added references to SEARCH, CalDAV, CardDAV as alternative ways
       to first synchronize a collection.

   3.  Added section defining under which condition each state change
       (new, modified, removed) should be reported.  Added reference to
       BIND.

   4.  Incorporated feedback from Julian Reschke and Ciny Joy.

   5.  More details on the use of the DAV:valid-sync-token precondition.

   Changes in -01:

   1.  Updated to 4918 reference.

   2.  Fixed examples to properly include DAV:status in DAV:propstat

   3.  Switch to using XML conventions text from RFC5323.

Authors' Addresses

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

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


   Arnaud Quillaud
   Sun Microsystems
   180, Avenue de l'Europe
   Saint Ismier cedex,   38334
   France

   EMail: arnaud.quillaud@sun.com
   URI:   http://www.sun.com/












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