WEBDAV Working Group J. Whitehead
Internet-Draft U.C. Santa Cruz
Expires: April 5, 2005 G. Clemm
IBM
J. Reschke, Ed.
greenbytes
October 5, 2004
Web Distributed Authoring and Versioning (WebDAV) Redirect Reference
Resources
draft-ietf-webdav-redirectref-protocol-latest-09
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This specification defines redirect reference resources. A redirect
reference resource is a resource whose default response is an
HTTP/1.1 3xx (Redirection) status code (see RFC2616, Section 10.3),
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redirecting the client to a different resource, the target resource.
A redirect reference makes it possible to access the target resource
indirectly, through any URI mapped to the redirect reference
resource. There are no integrity guarantees associated with redirect
reference resources.
Editorial Note (To be removed by RFC Editor before publication)
Distribution of this document is unlimited. Please send comments to
the Distributed Authoring and Versioning (WebDAV) working group at
<mailto:w3c-dist-auth@w3.org>, which may be joined by sending a
message with subject "subscribe" to
<mailto:w3c-dist-auth-request@w3.org>. Discussions of the WEBDAV
working group are archived at
<http://lists.w3.org/Archives/Public/w3c-dist-auth/>.
An issues list and XML and HTML versions of this draft are available
from
<http://greenbytes.de/tech/webdav/#draft-ietf-webdav-redirectref-prot
ocol>.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 6
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Overview of Redirect Reference Resources . . . . . . . . . . 7
5. MKREDIRECTREF Method . . . . . . . . . . . . . . . . . . . . 8
5.1 Example: Creating a Redirect Reference Resource with
MKREDIRECTREF . . . . . . . . . . . . . . . . . . . . . . 9
6. Operations on Redirect Reference Resources . . . . . . . . . 10
7. Operations on Collections That Contain Redirect Reference
Resources . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1 LOCK on a Collection That Contains Redirect References . . 11
7.2 Example: PROPFIND on a Collection with Redirect
Reference Resources . . . . . . . . . . . . . . . . . . . 11
7.3 Example: PROPFIND with Apply-To-Redirect-Ref on a
Collection with Redirect Reference Resources . . . . . . . 13
7.4 Example: COPY on a Collection That Contains a Redirect
Reference Resource . . . . . . . . . . . . . . . . . . . . 14
7.5 Example: LOCK on a Collection That Contains a Redirect
Reference Resource . . . . . . . . . . . . . . . . . . . . 15
8. Operations on Targets of Redirect Reference Resources . . . 17
9. Relative URIs in DAV:reftarget . . . . . . . . . . . . . . . 17
9.1 Example: Resolving a Relative URI in a Multi-Status
Response . . . . . . . . . . . . . . . . . . . . . . . . . 17
10. Redirect References to Collections . . . . . . . . . . . . . 18
11. Headers . . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1 Redirect-Ref Response Header . . . . . . . . . . . . . . 20
11.2 Apply-To-Redirect-Ref Request Header . . . . . . . . . . 20
12. Redirect Reference Resource Properties . . . . . . . . . . . 20
12.1 DAV:redirect-lifetime (protected) . . . . . . . . . . . 20
12.2 DAV:reftarget (protected) . . . . . . . . . . . . . . . 21
13. XML Elements . . . . . . . . . . . . . . . . . . . . . . . . 21
13.1 redirectref XML Element . . . . . . . . . . . . . . . . 21
14. Extensions to the DAV:response XML Element for
Multi-Status Responses . . . . . . . . . . . . . . . . . . . 21
15. Capability Discovery . . . . . . . . . . . . . . . . . . . . 21
15.1 Example: Discovery of Support for Redirect Reference
Resources . . . . . . . . . . . . . . . . . . . . . . . 22
16. Security Considerations . . . . . . . . . . . . . . . . . . 22
16.1 Privacy Concerns . . . . . . . . . . . . . . . . . . . . 22
16.2 Redirect Loops . . . . . . . . . . . . . . . . . . . . . 23
16.3 Redirect Reference Resources and Denial of Service . . . 23
16.4 Revealing Private Locations . . . . . . . . . . . . . . 23
17. Internationalization Considerations . . . . . . . . . . . . 23
18. IANA Considerations . . . . . . . . . . . . . . . . . . . . 24
19. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 24
20. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
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21. Normative References . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 25
A. Changes to the WebDAV Document Type Definition . . . . . . . 25
B. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . . . . 26
B.1 Since draft-ietf-webdav-redirectref-protocol-02 . . . . . 26
B.2 Since draft-ietf-webdav-redirectref-protocol-03 . . . . . 26
B.3 Since draft-ietf-webdav-redirectref-protocol-04 . . . . . 26
B.4 Since draft-ietf-webdav-redirectref-protocol-05 . . . . . 26
B.5 Since draft-ietf-webdav-redirectref-protocol-06 . . . . . 26
B.6 Since draft-ietf-webdav-redirectref-protocol-07 . . . . . 26
B.7 Since draft-ietf-webdav-redirectref-protocol-08 . . . . . 27
C. Resolved issues (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . . . . 27
C.1 lc-85-301 . . . . . . . . . . . . . . . . . . . . . . . . 27
C.2 specify_safeness . . . . . . . . . . . . . . . . . . . . . 28
D. Open issues (to be removed by RFC Editor prior to
publication) . . . . . . . . . . . . . . . . . . . . . . . . 28
D.1 edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
D.2 old_clients . . . . . . . . . . . . . . . . . . . . . . . 28
D.3 lc-36-server . . . . . . . . . . . . . . . . . . . . . . . 29
D.4 lc-33-forwarding . . . . . . . . . . . . . . . . . . . . . 29
D.5 3-terminology-redirectref . . . . . . . . . . . . . . . . 29
D.6 lc-58-update . . . . . . . . . . . . . . . . . . . . . . . 29
D.7 lc-48-s6 . . . . . . . . . . . . . . . . . . . . . . . . . 30
D.8 lc-57-noautoupdate . . . . . . . . . . . . . . . . . . . . 30
D.9 12.1-property-name . . . . . . . . . . . . . . . . . . . . 30
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Intellectual Property and Copyright Statements . . . . . . . 33
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1. Introduction
This specification extends the Web Distributed Authoring Protocol
(WebDAV) to enable clients to create new access paths to existing
resources. This capability is useful for several reasons:
WebDAV makes it possible to organize HTTP resources into hierarchies,
placing them into groupings, known as collections, which are more
easily browsed and manipulated than a single flat collection.
However, hierarchies require categorization decisions that locate
resources at a single location in the hierarchy, a drawback when a
resource has multiple valid categories. For example, in a hierarchy
of vehicle descriptions containing collections for cars and boats, a
description of a combination car/boat vehicle could belong in either
collection. Ideally, the description should be accessible from both.
Allowing clients to create new URIs that access the existing resource
lets them put that resource into multiple collections.
Hierarchies also make resource sharing more difficult, since
resources that have utility across many collections are still forced
into a single collection. For example, the mathematics department at
one university might create a collection of information on fractals
that contains bindings to some local resources, but also provides
access to some resources at other universities. For many reasons, it
may be undesirable to make physical copies of the shared resources on
the local server: to conserve disk space, to respect copyright
constraints, or to make any changes in the shared resources visible
automatically. Being able to create new access paths to existing
resources in other collections or even on other servers is useful for
this sort of case.
The redirect reference resources defined here provide a mechanism for
creating alternative access paths to existing resources. A redirect
reference resource is a resource in one collection whose purpose is
to forward requests to another resource (its target), possibly in a
different collection. In this way, it allows clients to submit
requests to the target resource from another collection. It
redirects most requests to the target resource using a HTTP status
code from the 3xx range (Redirection), thereby providing a form of
mediated access to the target resource.
A redirect reference is a resource with properties but no body of its
own. Properties of a redirect reference resource can contain such
information as who created the reference, when, and why. Since
redirect reference resources are implemented using HTTP 3xx
responses, it generally takes two round trips to submit a request to
the intended resource. Redirect references work equally well for
local resources and for resources that reside on a different server
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from the reference.
The remainder of this document is structured as follows: Section 3
defines terms that will be used throughout the specification.
Section 4 provides an overview of redirect reference resources.
Section 5 discusses how to create a redirect reference resource.
Section 6 defines the semantics of existing methods when applied to
redirect reference resources, and Section 7 discusses their semantics
when applied to collections that contain redirect reference
resources. Sections 8 through 10 discuss several other issues raised
by the existence of redirect reference resources. Sections 11
through 14 define the new headers, properties, and XML elements
required to support redirect reference resources. Section 15
discusses capability discovery. Sections 16 through 18 present the
security, internationalization, and IANA concerns raised by this
specification. The remaining sections provide a variety of
supporting information.
2. Notational Conventions
Since this document describes a set of extensions to the WebDAV
Distributed Authoring Protocol [RFC2518], itself an extension to the
HTTP/1.1 protocol, the augmented BNF used here to describe protocol
elements is exactly the same as described in Section 2.1 of
[RFC2616]. Since this augmented BNF uses the basic production rules
provided in Section 2.2 of [RFC2616], these rules apply to this
document as well.
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].
3. Terminology
The terminology used here follows and extends that in the WebDAV
Distributed Authoring Protocol specification [RFC2518]. Definitions
of the terms resource, Uniform Resource Identifier (URI), and Uniform
Resource Locator (URL) are provided in [RFC2396].
Redirect Reference Resource
A resource created to redirect all requests made to it, using an
HTTP status code from the 3xx range, to a defined target resource.
Non-Reference Resource
A resource that is not a reference to another resource.
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Target Resource
The resource to which requests are forwarded by a reference
resource. A target resource can be anything that can be
identified by an absolute URI (see [RFC2396], "absoluteURI").
This document uses the terms "precondition", "postcondition" and
"protected property" as defined in [RFC3253]. Servers MUST report
pre-/postcondition failures as described in section 1.6 of this
document.
4. Overview of Redirect Reference Resources
For all operations submitted to a redirect reference resource, the
default response is a 302 (Found), accompanied by the Redirect-Ref
header (defined in Section 11.1 below) and the Location header set to
the URI of the target resource. With this information, the client
can resubmit the request to the URI of the target resource.
A redirect reference resource never automatically forwards requests
to its target resource. Redirect resources bring the same benefits
as links in HTML documents. They can be created and maintained
without the involvement or even knowledge of their target resource.
This reduces the cost of linking between resources."
If the client is aware that it is operating on a redirect reference
resource, it can resolve the reference by retrieving the reference
resource's DAV:reftarget property (defined in Section 12.2 below),
whose value contains the URI of the target resource. It can then
submit requests to the target resource.
A redirect reference resource is a new type of resource. To
distinguish redirect reference resources from non-reference
resources, a new value of the DAV:resourcetype property (defined in
[RFC2518]), DAV:redirectref, is defined in Section 13.1 below.
Since a redirect reference resource is a resource, methods can be
applied to the reference resource as well as to its target resource.
The Apply-To-Redirect-Ref request header (defined in Section 11.2
below) is provided so that referencing-aware clients can control
whether an operation is applied to the redirect reference resource or
standard HTTP/WebDAV behaviour (redirection with a 3xx status code)
should occur. The Apply-To-Redirect-Ref header can be used with most
requests to redirect reference resources. This header is
particularly useful with PROPFIND, to retrieve the reference
resource's own properties.
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5. MKREDIRECTREF Method
The MKREDIRECTREF method requests the creation of a redirect
reference resource.
If a MKREDIRECTREF request fails, the server state preceding the
request MUST be restored.
Responses from a MKREDIRECTREF request MUST NOT be cached, as
MKREDIRECTREF has non-idempotent and non-safe semantics (see
[RFC2616], section 9.1)..
Marshalling:
The request body MUST be a DAV:mkredirectref XML element.
<!ELEMENT mkredirectref (reftarget, redirect-lifetime?)>
<!ELEMENT reftarget (href)>
<!ELEMENT redirect-lifetime (permanent | temporary)>
<!ELEMENT permanent EMPTY>
<!ELEMENT temporary EMPTY>
The DAV:href element is defined in [RFC2518] (Section 12.3) and
MUST contain either an absoluteURI or a relativeURI (see
[RFC2396], Section 3 and 5).
If no DAV:redirect-lifetime element is specified, the server MUST
behave as if a value of DAV:temporary was specified.
If the request succeeds, the server MUST return 201 (Created)
status.
If a response body for a successful request is included, it MUST
be a DAV:mkredirectref-response XML element. Note that this
document does not define any elements for the MKREDIRECTREF
response body, but the DAV:mkredirectref-response element is
defined to ensure interoperability between future extensions that
do define elements for the MKREDIRECTREF response body.
<!ELEMENT mkredirectref-response ANY>
Preconditions:
(DAV:resource-must-be-null): A resource MUST NOT exist at the
request-URL.
(DAV:parent-resource-must-be-non-null): The request-URL minus the
last past segment MUST identify a collection.
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(DAV:name-allowed): The last segment of the request URL is
available for use as a resource name.
(DAV:locked-update-allowed): If the collection identified by the
Request-URL minus the last path segment is write-locked, then the
appropriate token MUST be specified in an If request header.
(DAV:redirect-lifetime-supported): If the request body contains a
DAV:redirect-lifetime element, the server MUST support the
specified lifetime. Support for DAV:temporary is REQUIRED, while
support for DAV:permanent is OPTIONAL.
Postconditions:
(DAV:new-redirectref): a new redirect reference resource is
created whose DAV:reftarget property has the value specified in
the request body.
5.1 Example: Creating a Redirect Reference Resource with MKREDIRECTREF
>> Request:
MKREDIRECTREF /~whitehead/dav/spec08.ref HTTP/1.1
Host: www.example.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
<?xml version="1.0" encoding="utf-8" ?>
<D:mkredirectref xmlns:D="DAV:">
<D:reftarget>
<D:href>/i-d/draft-webdav-protocol-08.txt</D:href>
</D:reftarget>
</D:mkredirectref>
>> Response:
HTTP/1.1 201 Created
This request resulted in the creation of a new redirect reference
resource at http://www.example.com/~whitehead/dav/spec08.ref, which
points to the resource identified by the DAV:reftarget property. In
this example, the target resource is identified by the URI
http://www.example.com/i-d/draft-webdav-protocol-08.txt. The
redirect reference resource's DAV:resourcetype property is set to
DAV:redirectref and it's DAV:redirect-lifetime property has the value
DAV:temporary.
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6. Operations on Redirect Reference Resources
Although non-referencing-aware clients cannot create reference
resources, they should be able to submit requests through the
reference resources created by reference-aware WebDAV clients. They
should be able to follow any references to their targets. To make
this possible, a server that receives any request made via a redirect
reference resource MUST return a 3xx range (Redirection) status code,
unless the request includes an Apply-To-Redirect-Ref header
specifying "T". The client and server MUST follow [RFC2616] Section
10.3, but with these additional rules:
o The Location response header MUST contain an absolute URI that
identifies the target of the reference resource.
o The response MUST include the Redirect-Ref header. This header
allows reference-aware WebDAV clients to recognize the resource as
a reference resource and understand the reason for the
redirection.
A reference-aware WebDAV client can, like a non-referencing client,
resubmit the request to the URI in the Location header in order to
operate on the target resource. Alternatively, it can resubmit the
request to the URI of the redirect reference resource with the
"Apply-To-Redirect-Ref: T" header in order to operate on the
reference resource itself. In this case, the request MUST be applied
to the reference resource itself, and a 3xx response MUST NOT be
returned.
As redirect references do not have bodies, GET and PUT requests with
"Apply-To-Redirect-Ref: T" MUST fail with status 403 (forbidden).
7. Operations on Collections That Contain Redirect Reference Resources
Consistent with the rules in Section 6, the response for each
redirect reference encountered while processing a collection MUST be
a 3xx (Redirection) unless a "Apply-To-Redirect-Ref: T" header is
included with the request. The overall response will therefore be a
207 (Multi-Status). For each DAV:response element representing a
redirect reference, the server MUST include an additional
DAV:location element, specifying the value of the "Location" header
that would be returned otherwise. The extension is defined in
Section 14 below.
The Apply-To-Redirect-Ref header (defined in Section 11.2) MAY be
used with any request on a collection. If present, it will be
applied to all redirect reference resources encountered while
processing the collection.
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7.1 LOCK on a Collection That Contains Redirect References
An attempt to lock (with Depth: infinity) a collection that contains
redirect references without specifying "Apply-To-Redirect-Ref: T"
will always fail. The Multi-Status response will contain a 3xx
response for each redirect reference.
Reference-aware clients can lock the collection by using
Apply-To-Redirect-Ref, and, if desired, lock the targets of the
redirect references individually.
Non-referencing clients must resort to locking each resource
individually.
7.2 Example: PROPFIND on a Collection with Redirect Reference Resources
Suppose a PROPFIND request with Depth: infinity is submitted to the
following collection, with the members shown here:
/MyCollection/
(non-reference resource) diary.html
(redirect reference resource) nunavut
>> Request:
PROPFIND /MyCollection/ HTTP/1.1
Host: example.com
Depth: infinity
Apply-To-Redirect-Ref: F
Content-Type: text/xml
Content-Length: xxxx
<?xml version="1.0" ?>
<D:propfind xmlns:D="DAV: ">
<D:prop xmlns:J="http://example.com/jsprops/">
<D:resourcetype/>
<J:keywords/>
</D:prop>
</D:propfind>
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>> Response:
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxx
<?xml version="1.0" ?>
<D:multistatus xmlns:D="DAV:" xmlns:J="http://example.com/jsprops/">
<D:response>
<D:href>/MyCollection/</D:href>
<D:propstat>
<D:prop>
<D:resourcetype><D:collection/></D:resourcetype>
<J:keywords>diary, interests, hobbies</J:keywords>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>/MyCollection/diary.html</D:href>
<D:propstat>
<D:prop>
<D:resourcetype/>
<J:keywords>diary, travel, family, history</J:keywords>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>/MyCollection/nunavut</D:href>
<D:status>HTTP/1.1 302 Found</D:status>
<D:location>
<D:href>http://example.ca/art/inuit/</D:href>
</D:location>
</D:response>
</D:multistatus>
In this example the Depth header is set to infinity, and the
Apply-To-Redirect-Ref header is set to "F". The collection contains
one URI that identifies a redirect reference resource. The response
element for the redirect reference resource has a status of 302
(Found), and includes a DAV:location extension element to allow
clients to retrieve the properties of its target resource. (The
response element for the redirect reference resource does not include
the requested properties. The client can submit another PROPFIND
request to the URI in the DAV:location pseudo-property to retrieve
those properties.)
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7.3 Example: PROPFIND with Apply-To-Redirect-Ref on a Collection with
Redirect Reference Resources
Suppose a PROPFIND request with "Apply-To-Redirect-Ref: T" and Depth:
infinity is submitted to the following collection, with the members
shown here:
/MyCollection/
(non-reference resource) diary.html
(redirect reference resource) nunavut
>> Request:
PROPFIND /MyCollection/ HTTP/1.1
Host: example.com
Depth: infinity
Apply-To-Redirect-Ref: T
Content-Type: text/xml
Content-Length: xxxx
<?xml version="1.0" ?>
<D:propfind xmlns:D="DAV:">
<D:prop>
<D:resourcetype/>
<D:reftarget/>
<D:redirect-lifetime/>
</D:prop>
</D:propfind>
>> Response:
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxx
<?xml version="1.0" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>/MyCollection/</D:href>
<D:propstat>
<D:prop>
<D:resourcetype><D:collection/></D:resourcetype>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
<D:propstat>
<D:prop>
<D:reftarget/>
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<D:redirect-lifetime/>
</D:prop>
<D:status>HTTP/1.1 404 Not Found</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>/MyCollection/diary.html</D:href>
<D:propstat>
<D:prop>
<D:resourcetype/>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
<D:propstat>
<D:prop>
<D:reftarget/>
<D:redirect-lifetime/>
</D:prop>
<D:status>HTTP/1.1 404 Not Found</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>/MyCollection/nunavut</D:href>
<D:propstat>
<D:prop>
<D:resourcetype><D:redirectref/></D:resourcetype>
<D:reftarget>
<D:href>http://example.ca/art/inuit/</D:href>
</D:reftarget>
<D:redirect-lifetime><D:temporary/></D:redirect-lifetime>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
Since the "Apply-To-Redirect-Ref: T" header is present, the response
shows the properties of the redirect reference resource in the
collection rather than reporting a 302 status.
7.4 Example: COPY on a Collection That Contains a Redirect Reference
Resource
Suppose a COPY request is submitted to the following collection, with
the members shown:
/MyCollection/
(non-reference resource) diary.html
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(redirect reference resource) nunavut with target
/Someplace/nunavut.map
>> Request:
COPY /MyCollection/ HTTP/1.1
Host: example.com
Depth: infinity
Destination: http://example.com/OtherCollection/
>> Response:
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>/MyCollection/nunavut</D:href>
<D:status>HTTP/1.1 302 Found</D:status>
<D:location>
<D:href>http://example.com//Someplace/nunavut.map</D:href>
</D:location>
</D:response>
</D:multistatus>
In this case, since /MyCollection/nunavut is a redirect reference
resource, the COPY operation was only a partial success. The
redirect reference resource was not copied, but a 302 response was
returned for it. So the resulting collection is as follows:
/OtherCollection/
(non-reference resource) diary.html
7.5 Example: LOCK on a Collection That Contains a Redirect Reference
Resource
Suppose a LOCK request is submitted to the following collection, with
the members shown:
/MyCollection/
(non-reference resource) diary.html
(redirect reference resource) nunavut
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>> Request:
LOCK /MyCollection/ HTTP/1.1
Host: example.com
Apply-To-Redirect-Ref: F
Content-Type: text/xml
<?xml version="1.0" ?>
<D:lockinfo xmlns:D="DAV:">
<D:lockscope><D:exclusive/></D:lockscope>
<D:locktype><D:write/></D:locktype>
</D:lockinfo>
>> Response:
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: nnnn
<?xml version="1.0" ?>
<D:multistatus xmlns:D="Dav:">
<D:response>
<D:href>/MyCollection/</D:href>
<D:status>HTTP/1.1 424 Failed Dependency</D:status>
</D:response>
<D:response>
<D:href>/MyCollection/diary.html</D:href>
<D:status>HTTP/1.1 424 Failed Dependency</D:status>
</D:response>
<D:response>
<D:href>/MyCollection/nunavut</D:href>
<D:status>HTTP/1.1 302 Found</D:status>
<D:location>
<D:href>http://example.ca/art/inuit/</D:href>
</D:location>
</D:response>
</D:multistatus>
The server returns a 302 response code for the redirect reference
resource in the collection. Consequently, neither the collection nor
any of the resources identified by its internal member URIs were
locked. A referencing-aware client can submit a separate LOCK
request to the URI in the DAV:location element returned for the
redirect reference resource, and can resubmit the LOCK request with
the Apply-To-Redirect-Ref header to the collection. At that point
both the reference resource and its target resource will be locked
(as well as the collection and all the resources identified by its
other members).
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8. Operations on Targets of Redirect Reference Resources
Operations on targets of redirect reference resources have no effect
on the reference resource.
9. Relative URIs in DAV:reftarget
The URI in the href in a DAV:reftarget property MAY be a relative
URI. In this case, the base URI to be used for resolving the
relative URI to absolute form is the URI used in the HTTP message to
identify the redirect reference resource to which the DAV:reftarget
property belongs.
When DAV:reftarget appears in the context of a Multi-Status response,
it is in a DAV:response element that contains a single DAV:href
element. The value of this DAV:href element serves as the base URI
for resolving a relative URI in DAV:reftarget. The value of DAV:href
may itself be relative, in which case it must be resolved first in
order to serve as the base URI for the relative URI in DAV:reftarget.
If the DAV:href element is relative, its base URI is constructed from
the scheme component "http", the value of the Host header in the
request, and the request-URI.
9.1 Example: Resolving a Relative URI in a Multi-Status Response
>> Request:
PROPFIND /geog/ HTTP/1.1
Host: example.com
Apply-To-Redirect-Ref: T
Depth: 1
Content-Type: text/xml
Content-Length: nnn
<?xml version="1.0" ?>
<D:propfind xmlns:D="DAV:">
<D:prop>
<D:resourcetype/>
<D:reftarget/>
</D:prop>
</D:propfind>
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>> Response:
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: nnn
<?xml version="1/0" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>/geog/</D:href>
<D:propstat>
<D:prop>
<D:resourcetype><D:collection/></D:resourcetype>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
<D:propstat>
<D:prop><D:reftarget/></D:prop>
<D:status>HTTP/1.1 404 Not Found</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>/geog/stats.html</D:href>
<D:propstat>
<D:prop>
<D:resourcetype><D:redirectref/></D:resourcetype>
<D:reftarget>
<D:href>statistics/population/1997.html</D:href>
</D:reftarget>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
</D:multistatus>
In this example, the relative URI statistics/population/1997.html is
returned as the value of reftarget for the reference resource
identified by href /geog/stats.html. The href is itself a relative
URI, which resolves to http://example.com/geog/stats.html. This is
the base URI for resolving the relative URI in reftarget. The
absolute URI of reftarget is
http://example.com/geog/statistics/population/1997.html.
10. Redirect References to Collections
In a Request-URI /segment1/segment2/segment3, any of the three
segments may identify a redirect reference resource. (See [RFC2396],
Section 3.3, for definitions of "path" and "segment".) If any
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segment in a Request-URI identifies a redirect reference resource,
the response SHOULD be a 3xx. The value of the Location header in
the response is as follows:
The leftmost path segment of the request-URI that identifies a
redirect reference resource, together with all path segments and
separators to the left of it, is replaced by the value of the
redirect reference resource's DAV:reftarget property (resolved to an
absolute URI). The remainder of the request-URI is concatenated to
this path.
Note: If the DAV:reftarget property ends with a "/" and the remainder
of the Request-URI is non-empty (and therefore must begin with a
"/"), the final "/" in the DAV:reftarget property is dropped before
the remainder of the Request-URI is appended.
Consider Request-URI /x/y/z.html. Suppose that /x/ is a redirect
reference resource whose target resource is collection /a/, which
contains redirect reference resource y whose target resource is
collection /b/, which contains redirect reference resource z.html
whose target resource is /c/d.html.
/x/y/z.html
|
| /x -> /a
|
v
/a/y/z.html
|
| /a/y -> /b
|
v
/b/z.html
|
| /b/z.html -> /c/d.html
|
v
/c/d.html
In this case the client must follow up three separate 3xx responses
before finally reaching the target resource. The server responds to
the initial request with a 3xx with Location: /a/y/z.html, and the
client resubmits the request to /a/y/z.html. The server responds to
this request with a 3xx with Location: /b/z.html, and the client
resubmits the request to /b/z.html. The server responds to this
request with a 3xx with Location: /c/d.html, and the client resubmits
the request to /c/d.html. This final request succeeds.
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Note: the behavior described above may have a very serious impact
on the efficiency of mapping Request-URIs to resources in HTTP
request processing. Therefore servers MAY respond with a 404
status code if the cost of checking all leading path segments for
redirect references seems prohibitive.
11. Headers
11.1 Redirect-Ref Response Header
Redirect-Ref = "Redirect-Ref:" (absoluteURI | relativeURI)
; see sections 3 and 5 of [RFC2396]
The Redirect-Ref header is used in all 3xx responses from redirect
reference resources. The value is the (possibly relative) URI of the
link target as specified during redirect reference resource creation.
11.2 Apply-To-Redirect-Ref Request Header
Apply-To-Redirect-Ref = "Apply-To-Redirect-Ref" ":" ("T" | "F")
The optional Apply-To-Redirect-Ref header can be used on any request
to a redirect reference resource. When it is present and set to "T",
the request MUST be applied to the reference resource itself, and a
3xx response MUST NOT be returned.
If the Apply-To-Redirect-Ref header is used on a request to any other
sort of resource besides a redirect reference resource, the server
MUST ignore it.
12. Redirect Reference Resource Properties
The properties defined below are REQUIRED on redirect reference
resources.
12.1 DAV:redirect-lifetime (protected)
This property provides information about the lifetime of a redirect.
It can either be DAV:permanent (HTTP status 301) or DAV:temporary
(HTTP status 302). Future protocols MAY define additional values.
<!ELEMENT redirect-lifetime (permanent | temporary)>
<!ELEMENT permanent EMPTY>
<!ELEMENT temporary EMPTY>
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12.2 DAV:reftarget (protected)
This property provides an efficient way for clients to discover the
URI of the target resource. This is a read-only property after its
initial creation. Its value can only be set in a MKREDIRECTREF
request. The value is a DAV:href element containing the URI of the
target resource.
<!ELEMENT reftarget href >
13. XML Elements
13.1 redirectref XML Element
Name: redirectref
Namespace: DAV:
Purpose: Used as the value of the DAV:resourcetype property to
specify that the resource type is a redirect reference resource.
<!ELEMENT redirectref EMPTY >
14. Extensions to the DAV:response XML Element for Multi-Status
Responses
As described in Section 7, the DAV:location element may be returned
in the DAV:response element of a 207 Multi-Status response, to allow
clients to resubmit their requests to the target resource of a
redirect reference resource.
Consequently, the definition of the DAV:response XML element changes
to the following:
<!ELEMENT response (href, ((href*, status)|(propstat+)),
responsedescription?, location?) >
<!ELEMENT location (href) >
15. Capability Discovery
Sections 9.1 and 15 of [RFC2518] describe the use of compliance
classes with the DAV header in responses to OPTIONS, to indicate
which parts of the WebDAV Distributed Authoring protocols the
resource supports. This specification defines an OPTIONAL extension
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to [RFC2518]. It defines a new compliance class, called
redirectrefs, for use with the DAV header in responses to OPTIONS
requests. If a resource does support redirect references, its
response to an OPTIONS request may indicate that it does, by listing
the new redirectrefs compliance class in the DAV header and by
listing the MKREDIRECTREF method as one it supports.
When responding to an OPTIONS request, any type of resource can
include redirectrefs in the value of the DAV header. Doing so
indicates that the server permits a redirect reference resource at
the request URI.
15.1 Example: Discovery of Support for Redirect Reference Resources
>> Request:
OPTIONS /somecollection/someresource HTTP/1.1
Host: example.org
>> Response:
HTTP/1.1 200 OK
Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE
Allow: MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, MKREDIRECTREF
DAV: 1, 2, redirectrefs
The DAV header in the response indicates that the resource
/somecollection/someresource is level 1 and level 2 compliant, as
defined in [RFC2518]. In addition, /somecollection/someresource
supports redirect reference resources. The Allow header indicates
that MKREDIRECTREF requests can be submitted to
/somecollection/someresource.
16. Security Considerations
This section is provided to make applications that implement this
protocol aware of the security implications of this protocol.
All of the security considerations of HTTP/1.1 and the WebDAV
Distributed Authoring Protocol specification also apply to this
protocol specification. In addition, redirect reference resources
introduce several new security concerns and increase the risk of some
existing threats. These issues are detailed below.
16.1 Privacy Concerns
By creating redirect reference resources on a trusted server, it is
possible for a hostile agent to induce users to send private
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information to a target on a different server. This risk is
mitigated somewhat, since clients are required to notify the user of
the redirection for any request other than GET or HEAD. (See
[RFC2616], Section 10.3.3 302 Found.)
16.2 Redirect Loops
Although redirect loops were already possible in HTTP 1.1, the
introduction of the MKREDIRECTREF method creates a new avenue for
clients to create loops accidentally or maliciously. If the
reference resource and its target are on the same server, the server
may be able to detect MKREDIRECTREF requests that would create loops.
See also [RFC2616], Section 10.3 "Redirection 3xx."
16.3 Redirect Reference Resources and Denial of Service
Denial of service attacks were already possible by posting URLs that
were intended for limited use at heavily used Web sites. The
introduction of MKREDIRECTREF creates a new avenue for similar denial
of service attacks. Clients can now create redirect reference
resources at heavily used sites to target locations that were not
designed for heavy usage.
16.4 Revealing Private Locations
There are several ways that redirect reference resources may reveal
information about collection structures. First, the DAV:reftarget
property of every redirect reference resource contains the URI of the
target resource. Anyone who has access to the reference resource can
discover the collection path that leads to the target resource. The
owner of the target resource may have wanted to limit knowledge of
this collection structure.
Sufficiently powerful access control mechanisms can control this risk
to some extent. Property-level access control could prevent users
from examining the DAV:reftarget property. (The Location header
returned in responses to requests on redirect reference resources
reveals the same information, however.)
This risk is no greater than the similar risk posed by HTML links.
17. Internationalization Considerations
All internationalization considerations mentioned in [RFC2518] also
apply to this document.
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18. IANA Considerations
All IANA considerations mentioned in [RFC2518] also apply to this
document.
19. Contributors
Many thanks to Jason Crawford, Jim Davis, Chuck Fay and Judith Slein
who can take credit for big parts of the original design of this
specification.
20. Acknowledgements
This document has benefited from thoughtful discussion by Jim Amsden,
Peter Carlson, Steve Carter, Tyson Chihaya, Ken Coar, Ellis Cohen,
Bruce Cragun, Spencer Dawkins, Mark Day, Rajiv Dulepet, David Durand,
Lisa Dusseault, Stefan Eissing, Roy Fielding, Yaron Goland, Fred
Hitt, Alex Hopmann, James Hunt, Marcus Jager, Chris Kaler, Manoj
Kasichainula, Rohit Khare, Daniel LaLiberte, Steve Martin, Larry
Masinter, Jeff McAffer, Joe Orton, Surendra Koduru Reddy, Juergen
Reuter, Max Rible, Sam Ruby, Bradley Sergeant, Nick Shelness, John
Stracke, John Tigue, John Turner, Kevin Wiggen, and others.
21 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D.
Jensen, "HTTP Extensions for Distributed Authoring --
WEBDAV", RFC 2518, February 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3253] Clemm, G., Amsden, J., Ellison, T., Kaler, C. and J.
Whitehead, "Versioning Extensions to WebDAV (Web
Distributed Authoring and Versioning)", RFC 3253, March
2002.
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Authors' Addresses
Jim Whitehead
UC Santa Cruz, Dept. of Computer Science
1156 High Street
Santa Cruz, CA 95064
US
EMail: ejw@cse.ucsc.edu
Geoff Clemm
IBM
20 Maguire Road
Lexington, MA 02421
US
EMail: geoffrey.clemm@us.ibm.com
Julian F. Reschke (editor)
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/
Appendix A. Changes to the WebDAV Document Type Definition
<!-- Property Elements from Section 12 -->
<!ELEMENT reftarget href>
<!ELEMENT location href>
<!-- XML Elements from Section 13 -->
<!ELEMENT redirectref EMPTY >
<!-- Changes to the DAV:response Element from Section 14 -->
<!ELEMENT response (href, ((href*, status)|(propstat+)),
responsedescription?, location?) >
<!ELEMENT location (href) >
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Appendix B. Change Log (to be removed by RFC Editor before publication)
B.1 Since draft-ietf-webdav-redirectref-protocol-02
Julian Reschke takes editorial role (added to authors list). Cleanup
XML indentation. Start adding all unresolved last call issues.
Update some author's contact information. Update references, split
into "normative" and "informational". Remove non-RFC2616 headers
("Public") from examples. Fixed width problems in artwork. Start
resolving editorial issues.
B.2 Since draft-ietf-webdav-redirectref-protocol-03
Added Joe Orton and Juergen Reuter to Acknowledgements section.
Close more editorial issues. Remove dependencies on BIND spec.
B.3 Since draft-ietf-webdav-redirectref-protocol-04
More editorial fixes. Clarify that MKRESOURCE can only be used to
create redirect references (switch to new method in a future draft).
Clarify that redirect references do not have bodies.
B.4 Since draft-ietf-webdav-redirectref-protocol-05
Close (accept) issue "lc-79-accesscontrol". Add issue
"rfc2606-compliance". Close issues "lc-50-blindredirect",
"lc-71-relative", "lc-74-terminology". Update contact info for Geoff
Clemm. Moved some of the original authors names to new Contributors
section. Add and close issue "9-MKRESOURCE-vs-relative-URI". Close
issue "lc-72-trailingslash". Close issue "lc-60-ex". Update issue
"lc-85-301" with proposal. Close issue "lc-06-reftarget-relative"
(9-MKRESOURCE-vs-relative-URI was a duplicate of this one). Also
remove section 9.1 (example for MKRESOURCE vs relative URIs). Add
and resolve issue "11.2-apply-to-redirect-ref-syntax" (header now has
values "T" and "F"). Also some cleanup for "rfc2606-compliance".
Typo fixes. Add and resolve "15.1-options-response".
B.5 Since draft-ietf-webdav-redirectref-protocol-06
Resolve issues "lc-19-direct-ref", "lc-28-lang", "lc-29-lang",
"lc-44-pseudo", "lc-53-s10", "lc-61-pseudo", "lc-63-move",
"lc-80-i18n" and "rfc2606-compliance". Start work on index. Add new
issue "old_clients".
B.6 Since draft-ietf-webdav-redirectref-protocol-07
Closed issue "lc-38-not-hierarchical". Cleaned up DTD fragments in
appendix. Close (reject) issues "lc-55-iana" and "lc-41-no-webdav".
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Add issue "5_mkresource" and start work on MKREDIRECTREF (issue
closed, but more work on MKREDIRECTREF needs to be done for updates
and status codes other than 302). Start resolution of "lc-85-301",
replacing "302" by more generic language. Update issue
"lc-57-noautoupdate". Close issue "lc-37-integrity" (duplicate of
"lc-57-autoupdate"). Started work on "lc-85-301". Add L. Dusseault
and S. Eissing to Acknowledgments section.
B.7 Since draft-ietf-webdav-redirectref-protocol-08
Fix index entries for conditions. Open and resolve issue
"specify_safeness". Rewrite editorial section and parts of intro.
Add more clarifications for issue "lc-85-301" and close it.
Appendix C. Resolved issues (to be removed by RFC Editor before
publication)
Issues that were either rejected or resolved in this version of this
document.
C.1 lc-85-301
Type: change
ejw@cse.ucsc.edu (2000-01-03): Support creation of other than 302
redirects, especially 301.
julian.reschke@greenbytes.de (2003-10-13): HTTP seems to distinguish
the following use cases: (a) permanent redirect (301), (b) temporary
redirect (302 or 307), (c) redirect to a GET location after POST
(303) and (d) agent-driven negotiation (300). Among these, (a) and
(b) seem to be well understood, so we should support both. (c)
doesn't seem to be applicable. (d) may become interesting when user
agents start supporting it, so the spec should be flexible enough to
support a feature extension for that. For now I propose that the
client is able to specify the redirection type as a resource type,
such as "DAV:permanent-redirect-reference" and
"DAV:temporary-redirect-reference". This spec would only define the
behaviour for these two resource types and would allow future
extensions using new resource types and suggested response codes.
Resolution (2004-10-05): Support creation of both permanent (301,
optional) and temporary (302, required) redirects. Keep protocol
extensible for other types. Make lifetime visible as protected
property.
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C.2 specify_safeness
Type: edit
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2004JulSep/0196.ht
ml>
julian.reschke@greenbytes.de (2004-09-19): Specify safeness and
idempotence of new methods.
Resolution (2004-09-20): Done.
Appendix D. Open issues (to be removed by RFC Editor prior to
publication)
D.1 edit
Type: edit
julian.reschke@greenbytes.de (2004-10-03): Umbrella issue for
editorial changes.
D.2 old_clients
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2003OctDec/0180.ht
ml>
julian.reschke@greenbytes.de (2003-11-10): There are (at least) two
major design goals, but unfortunately both are in direct
contradiction: #1: Maximum consistency with HTTP/1.1 (RFC2616). This
means that any request that addresses a redirect reference resource
MUST result in a 3xx status code (obviously the whole point is that
GET MUST result in a redirection, and if it does, it's hard to say
why other methods such as PUT or DELETE should behave differently).
Therefore, the redirect reference protocol introduces a new request
header ("Apply-To-Redirect-Ref") through which a client can indicate
that the request indeed should be applied to the redirect reference
resource itself. #2: Maximum usability with existing clients. For
instance, the Microsoft Webfolder client will not be able to DELETE a
redirect reference resource unless the server deviates from #1.
Right now I'm not sure about the best way to resolve this. Currently
the spec chooses #1 (back when this decision was made, there was
probably the assumption that existing clients would quickly be
updated -- something that probably isn't true today). However this
may result in implementers either just ignoring these rules, or
adding special workarounds based on "User Agent" detection.
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D.3 lc-36-server
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2000JanMar/0285.ht
ml>
yarong@Exchange.Microsoft.com (2000-02-11): Servers: Replace "server"
with "unrelated system" throughout.
Resolution: Try replacing "server" with "host" in some contexts,
rephrasing in passive voice in others. See also issue 40.
D.4 lc-33-forwarding
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2000JanMar/0284.ht
ml>
yarong@Exchange.Microsoft.com (2000-02-11): Forwarding: Replace
"forward" with "redirect" throughout.
Resolution: Use "redirect" for the behavior redirect resources do
exhibit. Use "forward" for the contrasting behavior (passing a
method on to the target with no client action needed). Define these
two terms. See also issue 40.
D.5 3-terminology-redirectref
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2000JanMar/0290.ht
ml>
julian.reschke@greenbytes.de (2003-07-27): Consider global rename of
"redirect reference resource" to "redirect resource".
D.6 lc-58-update
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2000JanMar/0308.ht
ml>
yarong@Exchange.Microsoft.com (2000-02-11): There needs to be a way
to update the target of a redirect reference.
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Resolution: Agreed. See also issues 6, 43.
D.7 lc-48-s6
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2000JanMar/0298.ht
ml>
yarong@Exchange.Microsoft.com (2000-02-11): Replace all of section 6
with just this: A redirect resource, upon receiving a request without
an Apply-To-Redirect-Ref header, MUST respond with a 302 (Found)
response. The 302 (Found) response MUST include a location header
identifying the target and a Redirect-Ref header. If a redirect
resource receives a request with an Apply-To-Redirect-Ref header then
the redirect reference resource MUST apply the method to itself
rather than blindly returning a 302 (Found) response.
Resolution: Keep a summary along the lines of Yaron's proposal (don't
use the word "blindly"). Keep the bullets detailing the headers to
be returned. Delete the rest, including the examples. See also
issue 28, 29, 30, 31, 32.
D.8 lc-57-noautoupdate
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2000JanMar/0307.ht
ml>
yarong@Exchange.Microsoft.com (2000-02-11): Add language to forbid
servers from automatically updating redirect resources when their
targets move.
julian.reschke@greenbytes.de (2004-01-05): I don't think we can
forbid that. This spec consists of (a) clarifications of how a
server that supports redirects should behave for specific WebDAV
methods, and (b) extensions to explicitly create them (or to apply a
method to the redirect itself). As such, we shouldn't add any
requirements that HTTP doesn't add. What we could do is (1) note why
auto-update may be a bad idea, and possibly (2) define that redirects
created by MKREDIRECTREF should not behave that way (or alternatively
define more specific resource types).
D.9 12.1-property-name
Type: change
Whitehead, et al. Expires April 5, 2005 [Page 30]
Internet-Draft WebDAV Redirect Reference Resources October 2004
julian.reschke@greenbytes.de (2003-10-06): Sync names for
DAV:reftarget property and "Redirect-Ref" response headers.
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Internet-Draft WebDAV Redirect Reference Resources October 2004
Index
A
Apply-To-Redirect-Ref header 20
C
Condition Names
DAV:locked-update-allowed (pre) 9
DAV:name-allowed (pre) 9
DAV:new-redirectref (post) 9
DAV:parent-resource-must-be-non-null (pre) 8
DAV:redirect-lifetime-supported (pre) 9
DAV:resource-must-be-null (pre) 8
D
DAV header
compliance class 'redirectrefs' 21
DAV:locked-update-allowed precondition 9
DAV:name-allowed precondition 9
DAV:new-redirectref postcondition 9
DAV:parent-resource-must-be-non-null precondition 8
DAV:redirect-lifetime property 20
DAV:redirect-lifetime-supported precondition 9
DAV:redirectref resource type 21
DAV:reftarget property 21
DAV:resource-must-be-null precondition 8
H
Headers
Apply-To-Redirect-Ref 20
Redirect-Ref 20
M
Methods
MKREDIRECTREF 8
MKREDIRECTREF method 8
P
Properties
DAV:redirect-lifetime 20
DAV:reftarget 21
R
Redirect-Ref header 20
Resource Types
DAV:redirectref 21
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