Network Working GroupJ. Reschke
Internet-Draftgreenbytes
Intended status: InformationalOctober 2001
Expires: April 2002

Computing the CHECKIN URI in WebDAV versioning

draft-reschke-deltav-compute-checkin-uri-00

Status of this Memo

This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026.

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Copyright Notice

Copyright © The Internet Society (2001). 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 the current draft version of WebDAV deltaV [deltaV], 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) working group 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 working group are archived at URL: http://lists.w3.org/Archives/Public/ietf-dav-versioning/.



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].


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 the current draft version of WebDAV deltaV [deltaV], 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 CHECKIN URI" upon CHECKOUT, and using this URI at time of CHECKIN.


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

A client may ask for an "expected CHECKIN URI" upon CHECKOUT. This is done by placing DAV:compute-expected-checkin-URI as top-level element into the request body. 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 CHECKIN URI" by parsing the response body for a top-level element called DAV:expected-checkin-URI.

3.1. Example for successful CHECKOUT with computed-checkin-URI

>>Request

   CHECKOUT /foo.html HTTP/1.1 
   Host: www.webdav.org
   Content-Type: text/xml
   Content-Length: xxxx

   <D:checkout xmlns:D="DAV:">
     <D:compute-expected-version-URI />
   </D:checkout>

>>Response

   HTTP/1.1 200 OK
   Cache-Control: no-cache
   Content-Type: text/xml
   Content-Length: xxxx

   <D:checkout-response xmlns:D="DAV:">
     <D:expected-version-URI>http://repo.webdav.org/his/23/ver/32</D:expected-version-URI>
   </D:checkout-response>

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

3.2. Example for successful CHECKOUT without computed-checkin-URI

>>Request

   CHECKOUT /foo.html HTTP/1.1 
   Host: www.webdav.org
   Content-Type: text/xml
   Content-Length: xxxx

   <D:checkout xmlns:D="DAV:">
     <D: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 CHECKIN URI" is available. Simarily, the server may also return

>>Response

   HTTP/1.1 200 OK
   Cache-Control: no-cache
   Content-Type: text/xml
   Content-Length: xxxx

   <D:checkout-response xmlns:D="DAV:">
       ...other content...
   </D:checkout-response>

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


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

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

4.1. Example for successful CHECKIN with computed-checkin-URI

>>Request

  CHECKIN /foo.html HTTP/1.1 
  Host: www.webdav.org
  Content-Type: text/xml
  Content-Length: xxxx

  <D:checkin xmlns:D="DAV:">
    <D:expected-version-URI>http://repo.webdav.org/his/23/ver/32</D:expected-version-URI>
  </D:checkin>

>>Response

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

4.2. Example for failed CHECKIN with computed-checkin-URI

>>Request

  CHECKIN /foo.html HTTP/1.1 
  Host: www.webdav.org
  Content-Type: text/xml
  Content-Length: xxxx

  <D:checkin xmlns:D="DAV:">
    <D:expected-version-URI>http://repo.webdav.org/his/23/ver/32</D:expected-version-URI>
  </D:checkin>

>>Response

  HTTP/1.1 403 Forbidden
  Cache-Control: no-cache
  Content-Type: text/xml
  Content-Length: xxxx

  <D:checkin-response xmlns:D="DAV:">
    <D:cannot-assign-expected-version-URI />
    <D:expected-version-URI>http://repo.webdav.org/his/23/ver/33</D:expected-version-URI>
  </D:checkin-response>

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).


6. Internationalization Considerations

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


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.



9. Intellectual Property

To be supplied by the RFC Editor.

10. 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.
[deltaV]
Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV”, ID draft-ietf-deltav-versioning-18, September 2001, <http://www.webdav.org/deltav/protocol/draft-ietf-deltav-versioning-18.htm>.

Author's Address

Julian F. Reschke
greenbytes GmbH
Salzmannstrasse 152
Muenster, NW 48159
Germany
EMail: julian.reschke@greenbytes.de

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