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
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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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