Network Working GroupJ. Reschke
Internet-Draftgreenbytes
Intended status: InformationalMay 2002
Expires: November 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.

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This Internet-Draft will expire in November 2002.

Copyright Notice

Copyright © 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 deltaVversioning[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) 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/.

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/.

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 WebDAV versioning deltaV [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 deltaV 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.

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. 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.

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

<?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"
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.

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

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>
</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" ?>
<D:error xmlns:D="DAV:"
  xmlns:cu="http://sapportals.com/xmlns/cm/webdav">
  <cu:cannot-assign-expected-version-URI />
  <cu:expected-version-URI
  >http://repo.webdav.org/his/23/ver/33</cu:expected-version-URI>
</D:error>

>>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
  >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.

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

Appendix 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.

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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