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Network Working Group                                         J. Reschke
Internet-Draft                                                greenbytes
Expires: February 18, 2004                               August 20, 2003


             Computing the CHECKIN URI in WebDAV versioning
              draft-reschke-deltav-compute-checkin-uri-05

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

   The list of current Internet-Drafts can be accessed at http://
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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 February 18, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003). 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 determined at the
   time of CHECKIN.

   Distribution of this document is unlimited. Please send comments to
   the WebDAV versioning (delta-V) mailing list at



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   ietf-dav-versioning@w3.org [1], which may be joined by sending a
   message with subject "subscribe" to
   ietf-dav-versioning-request@w3.org [2]. Discussions of the delta-V
   mailing list are archived at URL: http://lists.w3.org/Archives/
   Public/ietf-dav-versioning/.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Notational Conventions . . . . . . . . . . . . . . . . . . . .  4
   3.  Changes for CHECKOUT method  . . . . . . . . . . . . . . . . .  5
   3.1 Example for successful CHECKOUT with computed version URI  . .  5
   3.2 Example for successful CHECKOUT without computed version
       URI  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Changes for CHECKIN method (when applied to a
       version-controlled resource) . . . . . . . . . . . . . . . . .  8
   4.1 Example for successful CHECKIN with computed version URI . . .  8
   4.2 Example for failed CHECKIN with computed version URI . . . . .  9
   5.  Compatibility Considerations . . . . . . . . . . . . . . . . . 10
   6.  Internationalization Considerations  . . . . . . . . . . . . . 11
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
       References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 13
   A.  Change Log (to be removed by RFC Editor before publication)  . 14
   A.1 Since 'draft-reschke-deltav-compute-checkin-uri-00'  . . . . . 14
   A.2 Since 'draft-reschke-deltav-compute-checkin-uri-01'  . . . . . 14
   A.3 Since 'draft-reschke-deltav-compute-checkin-uri-02'  . . . . . 14
   A.4 Since 'draft-reschke-deltav-compute-checkin-uri-03'  . . . . . 14
   A.5 Since 'draft-reschke-deltav-compute-checkin-uri-04'  . . . . . 14
   B.  Resolved issues (to be removed by RFC Editor before
       publication) . . . . . . . . . . . . . . . . . . . . . . . . . 15
   B.1 required-checkin-behaviour . . . . . . . . . . . . . . . . . . 15
       Intellectual Property and Copyright Statements . . . . . . . . 16


















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1. 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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2. 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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3. Changes for CHECKOUT method

   A client may ask for an "expected version URI" upon CHECKOUT (and the
   CHECKIN variant with DAV:keep-checked-out request element). 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.



   <!ELEMENT cu:compute-expected-version-URI EMPTY >

      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.



   <!ELEMENT cu:expected-version-URI (href) >


3.1 Example for successful CHECKOUT with computed version URI

   >>Request

   CHECKOUT /foo.html HTTP/1.1
   Host: www.example.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



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

   <?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>
       <D:href>http://repo.example.org/his/23/ver/32</D:href>
     </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.example.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"
   Content-Length: xxxx

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



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   </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.

   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): if the server does support
      the cu:compute-expected-version-URI extension upon CHECKOUT, it
      MUST create the new version at the URI specified in the
      cu:expected-version-URI or otherwise fail the request.


4.1 Example for successful CHECKIN with computed version URI

   >>Request

   CHECKIN /foo.html HTTP/1.1
   Host: www.example.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>
       <D:href>http://repo.example.org/his/23/ver/32</D:href>
     </cu:expected-version-URI>
   </D:checkin>

   >>Response

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




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4.2 Example for failed CHECKIN with computed version URI

   >>Request

   CHECKIN /foo.html HTTP/1.1
   Host: www.example.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>
       <D:href>http://repo.example.org/his/23/ver/32</D:href>
     </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" ?>
   <D:error xmlns:D="DAV:"
     xmlns:cu="http://sapportals.com/xmlns/cm/webdav">
     <cu:can-assign-expected-version-URI />
     <cu:expected-version-URI>
       <D:href>http://repo.example.org/his/23/ver/33</D:href>
     </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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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. and D.
              Jensen, "HTTP Extensions for Distributed Authoring --
              WEBDAV", RFC 2518, February 1999.

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

   [1]  <mailto:ietf-dav-versioning@w3.org>

   [2]  <mailto:ietf-dav-versioning-request@w3.org?subject=subscribe>


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://greenbytes.de/tech/webdav/





















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Appendix A. Change Log (to be removed by RFC Editor before publication)

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.

A.3 Since 'draft-reschke-deltav-compute-checkin-uri-02'

   Update marshalling to use DAV:href as container for URIs.
   Clarify that the extension applies to CHECKOUT on version resources
   and to CHECKIN/DAV:keep-checked-out as well.

A.4 Since 'draft-reschke-deltav-compute-checkin-uri-03'

   Replaced domain names in examples according to RFC2606: "webdav.org"
   by "example.org".

A.5 Since 'draft-reschke-deltav-compute-checkin-uri-04'

   Remove superfluous IP and copyright sections. Swap "Introduction" and
   "Notation" sections. Require server to support both extensions to
   make behaviour more predictable.












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Appendix B. Resolved issues (to be removed by RFC Editor before
            publication)

   Issues that were either rejected or resolved in this version of this
   document.

B.1 required-checkin-behaviour

   Type: change

   julian.reschke@greebytes.de (2003-08-20): The CHECKIN extension is of
   little value if the client can not detect beforehand whether it will
   be respected.

   Resolution: Require support for CHECKIN extension if the server does
   support the CHECKOUT extension.



































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Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights. Information on the
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   standards-related documentation can be found in BCP-11. Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
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   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive
   Director.


Full Copyright Statement

   Copyright (C) The Internet Society (2003). All Rights Reserved.

   This document and translations of it may be copied and furnished to
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   The limited permissions granted above are perpetual and will not be
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   "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



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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgment

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











































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