Network Working Group J. F. Reschke
Internet Draft greenbytes
Expires: August 2003 February 2003
Computing the CHECKIN URI in WebDAV versioning
draft-reschke-deltav-compute-checkin-uri-04
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
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This Internet-Draft will expire in August 2003.
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
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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 . . . . . . . . . . . . . . . . . . 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
A.3 Since 'draft-reschke-deltav-compute-checkin-uri-02' . . . . 18
A.4 Since 'draft-reschke-deltav-compute-checkin-uri-03' . . . . 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
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:"
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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>
<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>
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>>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.
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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.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>
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</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
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.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
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<?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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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://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.
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".
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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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
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included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
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Acknowledgement
Funding for the RFC editor function is currently provided by the
Internet Society.
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