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Network Working Group                                      J. F. Reschke
Internet Draft                                                greenbytes
Expires: November 2002                                          May 2002


             Computing the CHECKIN URI in WebDAV versioning
              draft-reschke-deltav-compute-checkin-uri-02



Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups may also distribute
   working documents as Internet-Drafts.

   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".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

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

   This Internet-Draft will expire in November 2002.


Copyright Notice

   Copyright (C) The Internet Society (2002). All Rights Reserved.


Abstract

   In many cases, a versioning-aware client might want to
   display/include the URI of the version it's editing while it's being
   edited. For instance, an editor might include this as meta
   information, or the author of a document might want to know the URI
   of the version before it's checked in. A well-known example is the
   W3C way of referring to document versions in recommendations: it
   contains references to "the current version", to "this version" and
   to the "previous version". Something like this is currently
   impossible with WebDAV versioning [RFC3253], as the version URI is



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   determined at the time of CHECKIN.

   Distribution of this document is unlimited. Please send comments to
   the WebDAV versioning (delta-V) mailing list at ietf-dav-
   versioning@w3.org, which may be joined by sending a message with
   subject "subscribe" to ietf-dav-versioning-request@w3.org.
   Discussions of the delta-V mailing list are archived at URL:
   http://lists.w3.org/Archives/Public/ietf-dav-versioning/.











































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Table of Contents

   Abstract  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   1
   Table of Contents . . . . . . . . . . . . . . . . . . . . . . . .   3
   1 Notational Conventions  . . . . . . . . . . . . . . . . . . . .   4
   2 Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3 Changes for CHECKOUT method (when applied to a version-
   controlled resource)  . . . . . . . . . . . . . . . . . . . . . .   6
     3.1 Example for successful CHECKOUT with computed version URI
   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2 Example for successful CHECKOUT without computed version
   URI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   4 Changes for CHECKIN method (when applied to a version-
   controlled resource)  . . . . . . . . . . . . . . . . . . . . . .   9
     4.1 Example for successful CHECKIN with computed version URI  .   9
     4.2 Example for failed CHECKIN with computed version URI  . . .  10
   5 Compatibility Considerations  . . . . . . . . . . . . . . . . .  12
   6 Internationalization Considerations . . . . . . . . . . . . . .  13
   7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  14
   8 Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
   9 Intellectual Property . . . . . . . . . . . . . . . . . . . . .  16
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  17
   A Change Log  . . . . . . . . . . . . . . . . . . . . . . . . . .  18
     A.1 Since 'draft-reschke-deltav-compute-checkin-uri-00' . . . .  18
     A.2 Since 'draft-reschke-deltav-compute-checkin-uri-01' . . . .  18

























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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].














































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2 Introduction

   In many cases, a versioning-aware client might want to
   display/include the URI of the version it's editing while it's being
   edited. For instance, an editor might include this as meta
   information, or the author of a document might want to know the URI
   of the version before it's checked in. A well-known example is the
   W3C way of referring to document versions in recommendations: it
   contains references to "the current version", to "this version" and
   to the "previous version". Something like this is currently
   impossible with WebDAV versioning[RFC3253], as the version URI is
   determined at the time of CHECKIN.

   This specification builds on the infrastructure provided by the
   WebDAV Versioning Protocol, adding support for servers willing to
   compute an "expected version URI" upon CHECKOUT, and using this URI
   at time of CHECKIN.

   This document defines an extension element that could ultimately
   become part of the WebDAV versioning protocol. Being just an
   individual submission, it currently defines it in the proprietary
   namespace




      http://sapportals.com/xmlns/cm/webdav



   instead of the "DAV:" namespace. It uses a prefix of "cu:" for
   referring to elements in this namespace. However, WebDAV server and
   clients are free to use any prefix, provided that there is a
   namespace declaration that binds the prefix to the URI of the same
   namespace.
















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3 Changes for CHECKOUT method (when applied to a version-controlled
resource)

   A client may ask for an "expected version URI" upon CHECKOUT. This is
   done by placing cu:compute-expected-version-URI as top-level element
   into the request body.

   Additional Marshalling:

      Presence of the cu:compute-expected-version-URI as top-level
      element in the request body indicates that the server SHOULD
      compute the "expected version URI". The server is free to either
      ignore the request, or to return it's best guess about what the
      URI for a version resource created upon CHECKIN would be.

      The client can detect the "expected version URI" by parsing the
      response body for a top-level element called cu:expected-version-
      URI. Absence of this element (or absence of a response body)
      indicates that the server is not able to compute the URI.



3.1 Example for successful CHECKOUT with computed version URI


   >>Request

   CHECKOUT /foo.html HTTP/1.1
   Host: www.webdav.org
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:checkout xmlns:D="DAV:"
     xmlns:cu="http://sapportals.com/xmlns/cm/webdav">
     <cu:compute-expected-version-URI />
   </D:checkout>




   >>Response

   HTTP/1.1 200 OK
   Cache-Control: no-cache
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx




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   <?xml version="1.0" encoding="utf-8" ?>
   <D:checkout-response xmlns:D="DAV:"
     xmlns:cu="http://sapportals.com/xmlns/cm/webdav">
     <cu:expected-version-URI
     >http://repo.webdav.org/his/23/ver/32</cu:expected-version-URI>
   </D:checkout-response>



   In this example, the server was able to compute the "expected version
   URI" and returned it in the cu:expected-version-URI element.


3.2 Example for successful CHECKOUT without computed version URI


   >>Request

   CHECKOUT /foo.html HTTP/1.1
   Host: www.webdav.org
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:checkout xmlns:D="DAV:"
     xmlns:cu="http://sapportals.com/xmlns/cm/webdav">
     <cu:compute-expected-version-URI />
   </D:checkout>




   >>Response

   HTTP/1.1 200 OK
   Cache-Control: no-cache



   In this case, no response body was returned, and thus no "expected
   version URI" is available. Simarily, the server may also return


   >>Response

   HTTP/1.1 200 OK
   Cache-Control: no-cache
   Content-Type: text/xml; charset="utf-8"



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   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:checkout-response xmlns:D="DAV:">
       ...other content...
   </D:checkout-response>



   where a response body is available, but it doesn't contain the
   cu:expected-version-URI element.








































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4 Changes for CHECKIN method (when applied to a version-controlled
resource)

   A client may submit the "expected version URI" (obtained during
   CHECKOUT) upon a CHECKIN by placing it into a top-level cu:expected-
   version-URI element in the request body. A server may

   o  simply ignore the presence of this information or

   o  use the information and try to checkin the resource using the
      "expected version URI" as location for the version resource. A
      failure to create a version resource at the "expected version URI"
      MUST cause the operation to fail.

   Additional Marshalling:

      A top-level element cu:expected-version-URI, when present,
      indicates the client's expectation about the URI of the version
      that will be created by the CHECKIN operation.

      Upon failure, the server MAY return a new "expected version URI"
      in the DAV:error response body using the element cu:expected-
      version-URI.


   Additional Preconditions:

      (cu:can-assign-expected-version-URI): the server must be able to
      use the specified URI for the version that is going to be created
      by the CHECKIN operation.



4.1 Example for successful CHECKIN with computed version URI


   >>Request

   CHECKIN /foo.html HTTP/1.1
   Host: www.webdav.org
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:checkin xmlns:D="DAV:"
     xmlns:cu="http://sapportals.com/xmlns/cm/webdav">
     <cu:expected-version-URI
     >http://repo.webdav.org/his/23/ver/32</cu:expected-version-URI>



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   </D:checkin>




   >>Response

   HTTP/1.1 201 Created
   Location: http://repo.webdav.org/his/23/ver/32
   Cache-Control: no-cache



   Note that the client can not rely on the server signaling an error if
   the expected version URI could not be applied. It will have to
   compare the URI returned in the HTTP "Location" header with the
   requested version URI, and in the case of mismatch it MAY have to
   report the situation to the user.


4.2 Example for failed CHECKIN with computed version URI


   >>Request

   CHECKIN /foo.html HTTP/1.1
   Host: www.webdav.org
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:checkin xmlns:D="DAV:"
     xmlns:cu="http://sapportals.com/xmlns/cm/webdav">
     <cu:expected-version-URI
     >http://repo.webdav.org/his/23/ver/32</cu:expected-version-URI>
   </D:checkin>




   >>Response

   HTTP/1.1 403 Forbidden
   Cache-Control: no-cache
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>



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   <D:error xmlns:D="DAV:"
     xmlns:cu="http://sapportals.com/xmlns/cm/webdav">
     <cu:can-assign-expected-version-URI />
     <cu:expected-version-URI
     >http://repo.webdav.org/his/23/ver/33</cu:expected-version-URI>
   </D:error>



   Note that 403 (Forbidden) is returned because subsequent request with
   the same expected version URI will always fail.








































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5 Compatibility Considerations

   This specification does introduce new protocol elements for the
   request and response bodies for CHECKIN and CHECKOUT.

   Clients not aware of this specification will never submit the new
   protocol elements in a request and therefore never will see the new
   response elements.

   Servers not aware of this specification will ignore the additional
   two request body elements which is legal behaviour according to this
   protocol (indicating that the protocol extension is not available).







































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6 Internationalization Considerations

   This proposal builds on [RFC3253], and inherits its
   internationalizability.















































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7 IANA Considerations

   This proposal does not introduce any new IANA considerations, since
   it does not specify any new namespaces (in the general sense), but
   merely uses existing ones.














































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8 Copyright

   To be supplied by the RFC Editor.
















































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9 Intellectual Property

   To be supplied by the RFC Editor.
















































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References


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

   [RFC2518]  Goland, Y., Whitehead, E., Faizi, A., Carter, S.R. and
              Jensen, D., "HTTP Extensions for Distributed Authoring --
              WEBDAV", RFC 2518, February 1999.

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


Author's Address

   Julian F. Reschke
   greenbytes GmbH
   Salzmannstrasse 152
   Muenster, NW 48159
   Germany

   Phone: +49 251 2807760
   Fax:   +49 251 2807761
   EMail: julian.reschke@greenbytes.de
   URI:   http://www.greenbytes.de/tech/webdav/
























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A Change Log


A.1 Since 'draft-reschke-deltav-compute-checkin-uri-00'

   Made the document element for responses upon failed CHECKIN DAV:error
   rather than DAV:checkin-response.
   Updated reference to [RFC3253].
   Moved extension elements out of DAV: namespace.
   Changed examples to explicitly use utf-8 encoding for HTTP content
   type and XML encoding.
   Globally replaced the term "CHECKIN URI" by "version URI"
   Added note about how to discover whether the server actually applied
   the expected version URI.
   Made sure artwork (figures) fits into 72 columns.


A.2 Since 'draft-reschke-deltav-compute-checkin-uri-01'

   Updated abstract not to refer to DeltaV WG anymore. Use "WebDAV
   versioning" instead of "deltaV".
   Changed descriptions to use RFC3253's Marshalling/Precondition
   format. Changed name of cu:cannot-assign-expected-version-URI to
   cu:can-assign-expected-version-URI as this is a precondition.


Full Copyright Statement

   Copyright (C) The Internet Society (2002). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.





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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgement

   Funding for the RFC editor function is currently provided by the
   Internet Society.







































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