WEBDAV Working Group                                     J. Slein, Xerox
INTERNET DRAFT                             E.J. Whitehead Jr., UC Irvine
<draft-ietf-webdav-redirectref-protocol-00.txt>      J. Davis, CourseNet
                                                      G. Clemm, Rational
                                                         C. Fay, FileNet
                                                        J. Crawford, IBM
                                                 T. Chihaya, DataChannel
                                                         August 20, 1999
Expires February 20, 2000

                        WebDAV Redirect Reference Resources

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
documents of the Internet Engineering Task Force (IETF), its areas, and
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Abstract

The WebDAV Distributed Authoring Protocol provides basic support for
collections, offering the ability to create and list unordered
collections.

This specification is one of a group of three specifications that
supplement the WebDAV Distributed Authoring Protocol to increase the
power of WebDAV collections. This specification defines redirect
reference resources, one mechanism for allowing a single resource to
appear in more than one collection.  A redirect reference resource is a
resource in one collection that responds to most requests by redirecting
the request (using an HTTP 1.1 302 Moved Temporarily response) to a
different resource, possibly in a different collection.  [B] defines
bindings, another approach to allowing a single resource to be accessed
from multiple collections.  [OC] provides ordered collections.

Table of Contents

1       Notational Conventions.......................................3
2       Introduction.................................................3

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3       Terminology..................................................4
4       Overview of Redirect Reference Resources.....................5
5       MKREF Method.................................................5
5.1     Overview of MKREF............................................5
5.2     Status Codes.................................................6
5.3     Example: MKREF...............................................6
6       Listing the Redirect Reference Resources in a Collection.....6
6.1     Example: PROPFIND on a Collection with Redirect Reference
        Resources....................................................7
6.2     Example: PROPFIND with Passthrough: F on a Collection with
        Redirect Reference Resources.................................9
7       Copying Redirect Reference Resources........................10
7.1     Example: COPY on a Redirect Reference Resource..............11
7.2     Example: COPY on a Collection That Contains a Redirect
        Reference Resource..........................................11
8       Deleting and Moving Redirect Reference Resources............12
9       Locking Redirect Reference Resources........................12
9.1     Example: LOCK on a Redirect Reference Resource..............14
9.2     Example: LOCK on a Collection That Contains a Redirect
        Reference Resource, with Passthrough: T.....................15
10      Other Operations on Redirect Reference Resources............16
10.1    Example: GET on a Redirect Reference Resource...............17
10.2    Example: PUT on a Redirect Reference Resource with
        "Passthrough: F"............................................18
10.3    Example: PROPPATCH on a Redirect Reference Resource.........18
11      Operations on Targets of Redirect Reference Resources.......19
12      Relative URIs in Ref-Target and DAV:reftarget...............19
12.1    Example: Resolving a Relative URI in Ref-Target.............19
12.2    Example: Resolving a Relative URI in DAV:reftarget..........20
13      Redirect References to Collections..........................21
14      Headers.....................................................21
14.1    Ref-Target Entity Header....................................21
14.2    Resource-Type Entity Header.................................22
14.3    Passthrough Request Header..................................22
15      Properties..................................................22
15.1    reftarget Property..........................................22
15.2    location Pseudo-Property....................................23
16      XML Elements................................................23
16.1    redirectref XML Element.....................................23
      Extensions to the DAV:response XML Element for Multi-Status
        Responses...................................................23
18      Capability Discovery........................................23
18.1    Example: Discovery of Support for Redirect Reference
        Resources...................................................24
19      Security Considerations.....................................24
19.1    Privacy Concerns............................................24
19.2    Redirect Loops..............................................25
19.3    Redirect Reference Resources and Denial of Service..........25
19.4    Private Locations May Be Revealed...........................25
20      Internationalization Considerations.........................25
21      IANA Considerations.........................................26
22      Copyright...................................................26
23      Intellectual Property.......................................26
24      Acknowledgements............................................26
25      References..................................................26

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26      Authors' Addresses..........................................27
27      Appendices..................................................28
27.1    Appendix 1: Extensions to the WebDAV Document Type
        Definition..................................................28

 Notational Conventions

Since this document describes a set of extensions 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 [HTTP].  Since this
augmented BNF uses the basic production rules provided in Section 2.2 of
[HTTP], 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].

 Introduction

The simple collections that the WebDAV Distributed Authoring Protocol
specification supports are powerful enough to be widely useful.  They
provide for the hierarchical organization of resources, with mechanisms
for creating and deleting collections, copying and moving them, locking
them, adding members to them and removing members from them, and getting
listings of their members.  Delete, copy, move, list, and lock
operations can be applied recursively, so that a client can operate on
whole hierarchies with a single request.

This specification is one of a family of three specifications that build
on the infrastructure defined in [HTTP] and [WebDAV] to extend the
capabilities of collections.  The companion specification [OC] defines
protocol extensions to support ordered collections.  The present
specification and the companion specification [B] define mechanisms for
allowing the same resource to appear in multiple collections.  This
capability is useful for several reasons:

Organizing resources into hierarchies places them into smaller
groupings, known as collections, which are more easily browsed and
manipulated than a flat namespace.  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.

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.

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The BIND method defined in [B] provides one mechanism for allowing a
single resource to appear in multiple collections.  It lets clients
associate a new URI with an existing resource.  This URI can then be
used to submit requests to the resource.  Since URIs in WebDAV are
hierarchical, and correspond to a hierarchy of collections in resource
space, the BIND method also has the effect of adding the resource to a
collection.  As new URIs are associated with the resource, it appears in
additional collections.

The redirect reference resources defined here are a different mechanism
for allowing a single resource to appear in multiple collections.  A
redirect reference resource is a resource in one collection whose
purpose is to forward requests to another resource (its target), usually
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 the HTTP 302 (Moved
Temporarily) status code, thereby providing a form of mediated access to
the target resource.

These two approaches to allowing clients to add a single resource to
multiple collections have very different characteristics:

A redirect reference is a resource, and so can have properties of its
own.  Such information as who created the reference, when, and why can
be stored on the redirect reference resource.  Since redirect references
are implemented using HTTP 302 responses, it generally takes two round
trips to submit a request to the intended resource.  Servers are not
required to enforce the integrity of redirect references.  Redirect
references work equally well for local resources and for resources that
reside on a different server from the reference.

By contrast, a BIND request does not create a new resource, but simply
makes available a new URI for submitting requests to an existing
resource.  The new URI can be used like any other URI to submit a
request to a resource.  Only one round trip is needed to submit a
request to the intended target.  Servers are required to enforce the
integrity of the relationships between the new URIs clients create and
the resources associated with them.  Consequently, it is unlikely that
servers will support BIND requests that cross server boundaries.

 Terminology

The terminology used here follows and extends that in the WebDAV
Distributed Authoring Protocol specification [WebDAV]. Definitions of
the terms resource, Uniform Resource Identifier (URI), and Uniform
Resource Locator (URL) are provided in [URI].

Reference Resource
     A resource whose purpose is to forward requests to another
     resource.  Reference resources are an alternative mechanism to
     bindings (defined in [B]) for allowing clients to create multiple
     URIs that can be used to submit requests to the same resource.

Redirect Reference Resource

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     A resource that forwards requests to another resource using the
     HTTP 1.1 302 (Moved Temporarily) response mechanism.  The client
     is aware that this type of reference resource is mediating between
     it and the target resource.

Non-Reference Resource
     A resource that is not a reference to another resource.

Target Resource
     The resource to which requests are forwarded by a reference
     resource.

 Overview of Redirect Reference Resources

For most operations submitted to a redirect reference resource, the
response is a 302 (Moved Temporarily), accompanied by the Resource-Type
header (defined in Section 14.2 below) set to "DAV:redirectref" 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.  The methods COPY (for collections containing redirect
reference resources), DELETE, MOVE, and LOCK, for reasons that will be
explained, are exceptions to this general behavior. These exceptional
operations are applied to the reference resource itself and do not
result in a 302 response.

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 15.1 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 [WebDAV]), DAV:redirectref,
is defined in Section 16.1 below.

Since a redirect reference resource is a resource, it is possible to
apply methods to the reference resource rather than to its target
resource.  The Passthrough request header (defined in Section 14.3
below) is provided so that referencing-aware clients can control whether
an operation is applied to the redirect reference resource or to its
target resource.  The Passthrough 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.

 MKREF Method

5.1 Overview of MKREF

The MKREF method creates a redirect reference resource identified by the
Request-URI, whose target is identified by the REQUIRED Ref-Target
header. MKREF sets the value of the REQUIRED DAV:reftarget property to
the value of the Ref-Target header.

The MKREF method creates a new binding between the new redirect

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reference resource and the last path segment of the Request-URI.  The
new binding is added to its parent collection, identified by the
Request-URI minus its trailing slash (if present) and final segment.

MKREF requests MAY include an entity body.  This specification does not
define the action to be taken if a request entity body is present, but
allows it for extensibility.

By default, if the Request-URI of the MKREF request identifies an
existing resource, the request MUST fail with a 405 (Method Not Allowed)
response code. This default behavior can be overridden using the
Overwrite header defined in Section 9.6 of [WebDAV].

5.2 Status Codes

 (Created): The redirect reference resource was successfully created.

 (Bad Request): The client set an invalid value for the Ref-Target
header.

 (Method Not Allowed): A resource already exists at the Request-URI.

 (Conflict): Several conditions may produce this response.  There may
be no resource at the location specified in Ref-Target, on a server that
prohibits dangling reference resources.  The request may be attempting
to create the reference resource in a collection that does not exist.

 (Precondition Failed): The Overwrite header is "F" or absent, and a
resource already exists at the request-URI.

5.3 Example: MKREF

>> Request:

MKREF /~whitehead/dav/spec08.ref HTTP/1.1
Host: www.ics.uci.edu
Ref-Target: </i-d/draft-webdav-protocol-08.txt>

>> Response:

HTTP/1.1 201 Created

This request resulted in the creation of a new redirect reference
resource at www.ics.uci.edu/~whitehead/dav/spec08.ref, which points to
the resource identified by the Ref-Target header. In this example, the
target resource of the referential resource is identified by the URI
http://www.ics.uci.edu/~whitehead/dav/i-d/draft-webdav-protocol-08.txt.
The referential resource's DAV:resourcetype property is set to
DAV:redirectref.  Its DAV:reftarget property is set to the value of the
Ref-Target header, "/i-d/draft-webdav-protocol-08.txt".

 Listing the Redirect Reference Resources in a Collection

A URI of a redirect reference resource can be an internal member URI of
a collection just as the URI of a non-reference resource can.  A listing

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of the internal member URIs of a collection shows all of the URIs that
are internal members of the collection, whether they identify redirect
reference resources or non-reference resources.  That is, a WebDAV
PROPFIND request on a collection resource with the Depth header set to 1
or infinity MUST return a response XML element for each member URI in
the collection, whether it identifies a non-reference resource or a
redirect reference resource.

For each redirect reference resource, the response element MUST contain
a 302 (Moved Temporarily) status code unless a Passthrough header with
the value "F" is included with the PROPFIND request.  The DAV:location
pseudo-property and the DAV:resourcetype property MUST be included with
the 302 status code, extending the syntax of the DAV:response element
that was defined in [WebDAV] as described in Section 17 below.  A
referencing-aware client can tell from the DAV:resourcetype property
that the collection contains a redirect reference resource.  The
DAV:location pseudo-property contains the absolute URI of the target
resource.  A referencing-aware client can either use the URI value of
the DAV:location pseudo-property to retrieve the properties of the
target resource, or it can submit a PROPFIND to the redirect reference
resource with "Passthrough: F" to retrieve its properties.  It is
recommended that future editors of [WebDAV] define the DAV:location
pseudo-property in [WebDAV], so that non-referencing clients will also
be able to use the response to retrieve the properties of the target
resource.

If the Depth header is set to infinity in the PROPFIND request, the
server MUST NOT follow redirect reference resources into any collections
to which they may refer.

The Passthrough header (defined in Section 14.3) MAY be used with a
PROPFIND request on a collection.

6.1 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:

http://www.svr.com/MyCollection/
     (non-reference resource) diary.html
     (redirect reference resource) nunavut

>> Request:

PROPFIND /MyCollection/ HTTP/1.1
Host: www.svr.com
Depth: infinity
Content-Type: text/xml
Content-Length: xxxx

<?xml version="1.0" ?>
<D:propfind xmlns:D="DAV: ">
   <D:prop xmlns:J="http://www.svr.com/jsprops/">
      <D:resourcetype/>
      <J:keywords/>

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   </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:"
               xmlns:J="http://www.svr.com/jsprops/">
   <D:response>
      <D:href>http://www.svr.com/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>http://www.svr.com/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>http://www.svr.com/MyCollection/nunavut</D:href>
      <D:status>HTTP/1.1 302 Moved Temporarily</D:status>
      <D:prop>
         <D:location>
            <D:href>http://www.inac.gc.ca/art/inuit/</D:href>
         </D:location>
         <D:resourcetype><D:redirectref/></D:resourcetype>
      </D:prop>
   </D:response>
</D:multistatus>

In this example the Depth header is set to infinity, and the Passthrough
header is not used.  The collection contains one URI that identifies a
redirect reference resource.  The response element for the redirect
reference resource has a status of 302 (Moved Temporarily), and includes
a DAV:prop element with the DAV:location pseudo-property and the
DAV:resourcetype property 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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6.2 Example: PROPFIND with Passthrough: F on a Collection with Redirect
    Reference Resources

Suppose a PROPFIND request with Passthrough = F 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: www.svr.com
Depth: infinity
Passthrough: F
Content-Type: text/xml
Content-Length: xxxx

<?xml version="1.0" ?>
<D:propfind xmlns:D="DAV:">
   <D:prop>
      <D:resourcetype/>
      <D:reftarget/>
   </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>http://www.svr.com/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/> </D:prop>
         <D:status>HTTP/1.1 404 Not Found</D:status>
      </D:propstat>
   </D:response>
<D:response>
      <D:href>http://www.svr.com/MyCollection/diary.html</D:href>
      <D:propstat>
         <D:prop>
            <D:resourcetype/>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>

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      </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>http://www.svr.com/MyCollection/nunavut</D:href>
      <D:propstat>
         <D:prop>
            <D:resourcetype><D:redirectref/></D:resourcetype>
            <D:reftarget>
               <D:href>http://www.inac.gc.ca/art/inuit/</D:href>
            </D:reftarget>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
      </D:propstat>
   </D:response>
</D:multistatus>

Since the Passthrough header has the value "F", the response shows the
properties of the redirect reference resource in the collection rather
than the properties of its target. The value of the Passthrough header
also prevents a 302 response from being returned for the redirect
reference resource.

 Copying Redirect Reference Resources

A client's intent in performing a COPY operation is to create a new
resource that is similar to the original resource and behaves like the
original resource, and that can be modified without affecting the
original resource.  For a COPY request to a redirect reference resource,
the expectation would be a 302 response that the client could use to
copy the target resource.  This would yield an independent resource that
could be modified without affecting the original resource.  For COPY
requests to collections that contain redirect reference resources, the
situation is less clear.  There is tension between two expectations. On
the one hand, the client may expect the new copy of the collection to
behave like the old one (which implies having reference resources where
the old one had reference resources).  On the other hand, the client may
expect that it will be possible to modify the resources in the new
collection without affecting the resources in the old collection (which
implies having copies of the target resources where the original
collection had reference resources).

For a COPY request on an individual reference resource, the response
MUST be a 302 (Moved Temporarily) status code, with the URI of the
target resource in the Location header, and "Resource-Type:
DAV:redirectref" to distinguish the response from an ordinary HTTP
redirect.  This is the normal behavior for redirect reference resources,
allowing the client to resubmit the request to the target resource
identified in the Location header.  This also yields intuitively correct
behavior for a COPY request to an individual reference resource.
Reference-aware clients can use the Passthrough header with the value
"F" to copy the redirect reference resource itself.

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For COPY on a collection containing redirect reference resources,
different semantics may be desirable in different scenarios.
Consequently, this specification makes a fairly arbitrary choice to take
the simplest path.  When a COPY request is submitted to a collection
containing redirect reference resources, the server MUST copy the
redirect reference resources to the new collection rather than returning
 status codes for them.  This will result in a new collection that
behaves like the old one, and avoids responding with multiple 302 status
codes, each of which the client would have to process separately.
Reference-aware clients can force the server to respond with 302 status
codes rather than copying the reference resources by using the
Passthrough header with the value "T".

7.1 Example: COPY on a Redirect Reference Resource

>> Request:

COPY /MyCollection/tuva HTTP/1.1
Host: www.svr.com
Destination: http://www.svr.com/OtherCollection/tuva.html

>> Response:

HTTP/1.1 302 Moved Temporarily
Location: http://www.svr.com/Asia/History/tuva.html
Resource-Type: DAV:redirectref

In this example, the request-URI identifies a redirect reference
resource whose target resource is identified by
http://www.svr.com/Asia/History/tuva.html.  In this case, the server
responded with a 302, and provided the URL of the target resource in the
Location header.  The Resource-Type header indicates to a reference-
aware client that this is not an HTTP 1.1 redirect, but a reference to
the resource identified by the Location header.  The client can now
resubmit the COPY request to the target resource, producing the desired
result: a duplicate of the original target resource that can be modified
independently of the original.

7.2 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
     (redirect reference resource) nunavut with target
                                /Someplace/nunavut.map

>> Request:

COPY /MyCollection/ HTTP/1.1
Host: www.svr.com
Destination: http://www.svr.com/OtherCollection/

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>> Response:

HTTP/1.1 201 Created

In this case, since /MyCollection/nunavut is a redirect reference
resource, the reference resource itself, and not its target resource,
was copied into the new collection.  So the resulting collection is as
follows:

/OtherCollection/
      (non-reference resource) diary.html
      (redirect reference resource) nunavut with target
                                 /Someplace/nunavut.map

 Deleting and Moving Redirect Reference Resources

The DELETE method is used to delete bindings to redirect reference
resources. DELETE MUST affect bindings to the reference resource itself,
unless "Passthrough: T" is used, in which case it generates a 302 (Moved
Temporarily) response.  Similarly, when a DELETE on a collection
encounters a redirect reference resource in the subtree under that
collection, it MUST delete bindings to the reference resource, unless
"Passthrough: T" is used, in which case it generates a 302 (Moved
Temporarily) response. Whether deleting an individual resource or a
collection, DELETE on a redirect reference resource does not affect the
target of the reference resource.

A MOVE operation on a redirect reference resource MUST move the
reference resource to a different location, and MUST NOT change the
location of its target resource, unless "Passthrough: T" is used, in
which case a 302 (Moved Temporarily) response is generated. The
DAV:reftarget property is unchanged after a MOVE.  Similarly, when a
MOVE on a collection encounters a redirect reference resource in the
subtree under that collection, it MUST move the reference resource, and
not its target, unless "Passthrough: T" is used, in which case a 302
(Moved Temporarily) response is generated.

DELETE and MOVE differ from other methods in that they do not alter the
resource that is being deleted or moved, but rather the collection that
contains its binding.  They change the membership of that collection.

When a redirect reference resource is added to a collection, the aim is
to make it look as if the target resource were a member of that
collection.  When the reference resource is removed from that
collection, the aim is to change the membership of that collection.
Membership of the target resource in any other collections, either
internally or by reference, should not be affected.  Consequently,
DELETE and MOVE do not follow the normal rules of behavior for reference
resources.  Instead, they are applied by default to the reference
resource itself, not to its target resource, and by default do not
result in 302 status codes.

 Locking Redirect Reference Resources


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The semantics of LOCK described here resulted from balancing a set of
incompatible considerations:

o Ideally, a LOCK on a redirect reference resource should lock both the
  reference resource and its target resource.  The owner of an
  exclusive write lock, for example, would be surprised if anyone else
  could modify the content of the target resource while he held the
  lock.  He would also be surprised if anyone else could delete the
  reference to it, or replace the reference resource with one pointing
  to a different target resource.
o Non-referencing clients should be able to use redirect reference
  resources without encountering surprising results.
o The basic characteristics of redirect reference resources should be
  honored.  Redirect reference resources should be simple for servers
  to implement. In particular, a server should never have to resolve a
  redirect reference.  A server should not have to provide proxy
  capabilities in order to implement redirect references.
o There should be consistency between the behavior of LOCK on a single
  redirect reference resource and the behavior of LOCK on a collection
  that contains redirect reference resources.
o The behavior of all requests to redirect reference resources should
  be as consistent as possible. In the absence of a Passthrough header,
  all methods should return a 302 when sent to a redirect reference
  resource.
o LOCK semantics for redirect reference resources should be consistent
  with the LOCK semantics defined in [WebDAV].

We have compromised the intuitive locking behavior and support for non-
referencing clients in order to preserve various sorts of consistency.

The behavior of LOCK for redirect reference resources was determined by
what is possible for the case of locking collections that contain
redirect reference resources.

The default behavior for any operation on a redirect reference resource
is that a 302 (Moved Temporarily) response will be returned, unless the
Passthrough header with a value of "F" is used.  However, this policy
has unacceptable consequences when locking a collection that contains
redirect reference resources.  Since [WebDAV] requires LOCK on a
collection to be an atomic operation, if a 302 response is received for
any member of the collection, the entire LOCK must fail.  This would
make it impossible to lock any collection that contained a redirect
reference resource.

To avoid this result, a LOCK with Depth > 0 on a collection MUST lock
any redirect reference resources it encounters, and not return 302
responses for them, unless the Passthrough header with a value of "T" is
used.  Use of the Passthrough header with a value of "T" in a LOCK
request on a collection will cause the entire lock to fail if a redirect
reference resource is encountered.

This gives part of the expected default lock behavior without forcing
the server to resolve the redirect reference or become a proxy server in
cases where the target resides on a different server.


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There will be no hint in any response code that there are redirect
reference resources whose targets need to be locked.  The client will
most likely not lock any target resources until it attempts an operation
on the target resource and gets a 302 response.  It is possible that a
non-referencing client may never realize that the reference resource's
target has not been locked.

Clearly, a LOCK with Depth = infinity on a collection MUST NOT follow
any redirect reference resources whose targets are collections into the
target collections; it MUST NOT cause any resources in those target
collections to be locked.

The behavior of LOCK for individual redirect reference resources is
designed to be consistent with LOCK behavior for collections that
contain redirect reference resources.  By default a LOCK on a redirect
reference resource MUST lock only the reference resource, not its target
resource, and it MUST NOT return a 302 response.  A reference-aware
client can use the Passthrough header with a value of "T" to get a 302
response with the URI of the target resource in the Location header.

UNLOCK behaves as specified in [WebDAV], unlocking all resources
included in the lock identified by the Lock-Token header.

9.1 Example: LOCK on a Redirect Reference Resource

>> Request:

LOCK /MyCollection/tuva HTTP/1.1
Host: www.svr.com
Content-Type: text/xml
Content-Length: nnnn
Authorizaton: Digest username="jas",
   realm=jas@webdav.sb.aol.com, nonce=". . . ",
   uri="/MyCollection/tuva",
   response=". . . ", opaque=". . . "

<?xml version="1.0" ?>
<D:lockinfo xmlns:D="DAV:">
   <D:lockscope><D:exclusive/></D:lockscope>
   <D:locktype><D:write/></D:locktype>
   <D:owner>
      <D:href>http://www.svr.com/~jas/contact.html</D:href>
   </D:owner>
</D:lockinfo>

>> Response:

HTTP/1.1 200 OK
Content-Type: text/xml
Content-Length: nnnn

<?xml version="1.0" ?>
<D:prop xmlns:D="DAV:">
   <D:lockdiscovery>
      <D:activelock>

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         <D:lockscope><D:exclusive/></D:lockscope>
         <D:locktype><D:write/></D:locktype>
         <D:depth>0</D:depth>
         <D:owner>
            <D:href>http://www.svr.com/~jas/contact.html</D:href>
         </D:owner>
         <D:locktoken>
            opaquelocktoken:e71dfae-5dec-22d6-fea5-00a0c91e6be4
         </D:locktoken>
      </D:activelock>
   </D:lockdiscovery>
</D:prop>

The request and response look exactly as specified in [WebDAV].  In this
example, the request-URI, http://www.svr.com/MyCollection/tuva,
identifies a redirect reference resource, which was successfully locked.
The target resource of the redirect reference resource is not locked.

9.2 Example: LOCK on a Collection That Contains a Redirect Reference
    Resource, with Passthrough: T

Suppose a LOCK request is submitted to the following collection, with
the members shown:

/MyCollection/
     (non-reference resource) diary.html
     (redirect reference resource) nunavut

>> Request:

LOCK /MyCollection/ HTTP/1.1
Host: www.svr.com
Passthrough: T
Content-Type: text/xml
Content-Length: nnnn
Authorizaton: Digest username="jas",
   realm=jas@webdav.sb.aol.com, nonce=". . . ",
   uri="/MyCollection/tuva",
   response=". . . ", opaque=". . . "

<?xml version="1.0" ?>
<D:lockinfo xmlns:D="DAV:">
   <D:lockscope><D:exclusive/></D:lockscope>
   <D:locktype><D:write/></D:locktype>
   <D:owner>
      <D:href>http://www.svr.com/~jas/contact.html</D:href>
   </D:owner>
</D:lockinfo>

>> Response:

HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: nnnn


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<?xml version="1.0" ?>
<D:multistatus xmlns:D="Dav:">
   <D:response>
      <D:href>http://www.svr.com/MyCollection/</D:href>
      <D:propstat>
         <D:prop><D:lockdiscovery/></D:prop>
         <D:status>HTTP/1.1 424 Failed Dependency</D:status>
      </D:propstat>
   </D:response>
   <D:response>
      <D:href>http://www.svr.com/MyCollection/diary.html</D:href>
      <D:status>HTTP/1.1 424 Failed Dependency</D:status>
   </D:response>
   <D:response>
      <D:href>http://www.svr.com/MyCollection/nunavut</D:href>
      <D:status>HTTP/1.1 302 Moved Temporarily</D:status>
      <D:prop>
         <D:location>
            <D:href>http://www.inac.gc.ca/art/inuit/</D:href>
         </D:location>
         <D:resourcetype><D:redirectref/></D:resourcetype>
      </D:prop>
   </D:response>
</D:multistatus>

The "Passthrough: T" header caused the server to return 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 pseudo-
property returned for the redirect reference resource, and can resubmit
the LOCK request with "Passthrough: F" 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).

 Other 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 a GET, HEAD, PUT, POST, OPTIONS, PROPFIND,
PROPPATCH, MKCOL, MKREF, BIND, or ORDERPATCH request made via a redirect
reference resource MUST return a 302 (Moved Temporarily) status code.
The client and server MUST follow [HTTP] Section 10.3.3 "302 Moved
Temporarily," but with these additional rules:

o The Location response header MUST contain the absolute target URI of
  the reference resource.

o The response MUST include the Resource-Type header.  This header
  allows reference-aware WebDAV clients to recognize the resource as a
  reference resource and understand the reason for the redirection.


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A reference-aware WebDAV client can act on this response in one of two
ways.  It 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 Passthrough header set to "F" in
order to operate on the reference resource itself.  If the Passthrough
header is present with a value of "F", the request MUST be applied to
the reference resource itself, and a 302 response MUST NOT be returned.

If a reference-aware client knows before submitting its request that the
request-URI identifies a redirect reference resource, and if the client
wants to apply the method to the reference resource, it can save the
round trip caused by the 302 response by using "Passthrough: F" in its
initial request to the URI.

"Passthrough: F" can be used with GET or HEAD to retrieve the entity
headers of a redirect reference resource.  When "Passthrough: F" is used
with GET or HEAD, the referencing entity headers (Ref-Type and Ref-
Target) MUST be returned, along with all HTTP headers that make sense
for reference resources (for example, Cache-Control, Age, ETag, Expires,
and Last-Modified).

"Passthrough: F" can be used with PUT to replace the redirect reference
resource with a non-reference resource.  It can be used with OPTIONS to
retrieve the capabilities of a redirect reference resource.

Clients MUST NOT, however, use "Passthrough: F" with POST. Since a
reference resource cannot accept another entity as its subordinate, an
attempt to POST to a reference resource with "Passthrough: F" will also
fail.  If a server receives a POST request with "Passthrough: F" on a
redirect reference resource, it MUST fail the request with a 400 (Bad
Request) status code.

Since MKCOL fails when applied to existing resources, if the client
attempts to resubmit the request to the target resource, the request
MUST fail (unless the reference resource is a dangling reference).
Similarly, if the client attempts to resubmit the request to the
reference resource with "Passthrough: F", the request MUST fail.

Since ORDERPATCH applies only to collections, an ORDERPATCH request with
a Passthrough header with the value "F" on a redirect reference resource
MUST fail.

10.1 Example: GET on a Redirect Reference Resource

>> Request:

GET /bar.html HTTP/1.1
Host: www.foo.com

>> Response:

HTTP/1.1 302 Moved Temporarily
Location: http://www.svr.com/Internet/xxspec08.html
Resource-Type: DAV:redirectref

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Since /bar.html is a redirect reference resource and the Passthrough
header is not included in the request, the response is a 302 (Moved
Temporarily).  The Resource-Type header informs a reference-aware client
that this is not an ordinary HTTP 1.1 redirect, but is a redirect
reference resource.  The URI of the target resource is provided in the
Location header so that the client can resubmit the request to the
target resource.

10.2 Example: PUT on a Redirect Reference Resource with "Passthrough: F"

>> Request:

PUT /bar.html HTTP/1.1
Host: www.foo.com
Passthrough: F
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx

. . . some content . . .

>> Response:

HTTP/1.1 200 OK

Although /bar.html is a redirect reference resource, the presence of the
"Passthrough: F" header prevents a 302 response, and instead causes the
request to be applied to the reference resource.  The result in this
case is that the reference resource is replaced by a non-reference
resource having the content submitted with the request.

10.3 Example: PROPPATCH on a Redirect Reference Resource

Request:

PROPPATCH /bar.html HTTP/1.1
Host: www.foo.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propertyupdate xmlns:D="DAV:"
   xmlns:Z="http://www.w3.com/standards/z39.50/">
     <D:set>
          <D:prop>
               <Z:authors>
                    <Z:Author>Jim Whitehead</Z:Author>
                    <Z:Author>Roy Fielding</Z:Author>
               </Z:authors>
          </D:prop>
     </D:set>
     <D:remove>
          <D:prop><Z:Copyright-Owner/></D:prop>
     </D:remove>
   </D:propertyupdate>

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Response:

HTTP/1.1 302 Moved Temporarily
Location: http://www.svr.com/Internet/xxspec08.html
Resource-Type: DAV:redirectref

Since /bar.html is a redirect reference resource and the Passthrough
header is not included in the request, the response is a 302 (Moved
Temporarily).  The Resource-Type header informs a reference-aware client
that this is not an ordinary HTTP 1.1 redirect, but is a redirect
reference resource.  The URI of the target resource is provided in the
Location header so that the client can resubmit the request to the
target resource.

 Operations on Targets of Redirect Reference Resources

Operations on targets of redirect reference resources have no effect on
the reference resource.

 Relative URIs in Ref-Target and DAV:reftarget

The URI in a Ref-Target header MAY be a relative URI.  Similarly, the
href in a DAV:reftarget property MAY be a relative URI.  In both cases,
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 Ref-Target entity header or DAV:reftarget property
belongs.

In the case of a Ref-Target header, the base URI is constructed as
follows: Its scheme component is "http", its authority component is the
value of the Host header in the request, and its path component is the
request-URI in the request.  See Section 5 of [URI] for a discussion of
relative URI references and how to resolve them.

The DAV:reftarget property appears in the protocol in the context of a
Multi-Status response, 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.

12.1 Example: Resolving a Relative URI in Ref-Target

>> Request:

MKREF /north/inuvik HTTP/1.1
Host: www.somehost.edu
Ref-Target: <mapcollection/inuvik.gif>

>> Response:


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HTTP/1.1 201 Created

In this example, the base URI is http://www.somehost.edu/north/inuvik.
Then, following the rules in [URI] Section 5, the relative URI in Ref-
Target resolves to the absolute URI
http://www.somehost.edu/north/mapcollection/inuvik.gif.

12.2 Example: Resolving a Relative URI in DAV:reftarget

>> Request:

PROPFIND /geog/ HTTP/1.1
Host: www.xxsvr.com
Passthrough: F
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>

>> 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>

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         <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://www.xxsrv.com/geog/stats.html.  This is the base URI
for resolving the relative URI in reftarget.  The absolute URI of
reftarget is http://www.xxsrv.com/geog/statistics/population/1997.html.

 Redirect References to Collections

In a Request-URI /segment1/segment2/segment3, any of the three segments
may identify a redirect reference resource.  (See [URI], Section 3.3,
for definitions of "path" and "segment".)  If any segment in a Request-
URI identifies a redirect reference resource, the response is a 302.
The value of the Location header in the 302 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/ -----> /a/
           /a/y/ -----> /b/
                        /b/z.html -----> /c/d.html

In this case the client must follow up three separate 302 responses
before finally reaching the target resource.  The server responds to the
initial request with a 302 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 302 with Location: /b/z.html, and the client resubmits
the request to /b/z.html.  The server responds to this request with a
 with Location: /c/d.html, and the client resubmits the request to
/c/d.html.  This final request succeeds.

 Headers

14.1 Ref-Target Entity Header

Ref-Target = "Ref-Target" ":" Generic-Coded-url

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Generic-Coded-url = "<" (absoluteURI | relativeURI) ">"
absoluteURI is defined in Section 3 of [URI].
relativeURI is defined in Section 5 of [URI].

The Ref-Target header is defined primarily for use with MKREF requests
to identify the target resource of the new redirect reference resource
being created.

14.2 Resource-Type Entity Header

Resource-Type = "Resource-Type" ":" ("DAV:redirectref" |
                                      ext-resource-type)
ext-resource-type = coded-URL

The Resource-Type header is defined primarily for use in 302 responses,
to allow reference-aware clients to distinguish between HTTP 1.1
redirects and 302 responses for redirect reference resources.  The
possible values of this header are DAV:redirectref, and ext-resource-
type. The ext-resource-type production is provided for extensibility.

14.3 Passthrough Request Header

Passthrough = "Passthrough" ":" ("T" | "F")

The optional Passthrough header can be used on any request to a redirect
reference resource.  If the Passthrough header has the value "F", the
request MUST be applied to the reference resource itself, and a 302
response MUST NOT be returned.  If the Passthrough header has the value
"T", a 302 response MUST be returned, with the URI of the target
resource in the Location header and the Resource-Type header with a
value "DAV:redirectref".

If the Passthrough header is used on a request to any other sort of
resource besides a reference resource, the server SHOULD ignore it.  If
the Passthrough header with the value "F" appears in a POST or
ORDERPATCH request to a reference resource, the server MUST respond with
a 400 (Bad Request).

 Properties

15.1 reftarget Property

Name:       reftarget
Namespace:  DAV:
Purpose:    A property of redirect reference resources that provides an
            efficient way for clients to discover the URI of the target
            resource.  This is a read-only property, whose value can
            only be set by using the Ref-Target header with a MKREF
            request.
Value:      href containing the URI of the target resource.  This value
            MAY be a relative URI.  The reftarget property can occur in
            the entity bodies of responses to PROPFIND requests.

<!ELEMENT reftarget href >


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15.2 location Pseudo-Property

Name:       location
Namespace:  DAV:
Purpose:    For use with 302 (Moved Temporarily) response codes in
            Multi-Status responses.  It contains the absolute URI of the
            temporary location of the resource.  In the context of
            redirect reference resources, this value is the absolute URI
            of the target resource.  It is analogous to the Location
            header in HTTP 302 responses defined in [HTTP] Section
            10.3.3 "302 Moved Temporarily."  Including the location
            pseudo-property in a Multi-Status response requires an
            extension to the syntax of the DAV:response element defined
            in [WebDAV], which is defined in Section 17 below.  This
            pseudo-property is not expected to be stored on the
            reference resource. It is modeled as a property only so that
            it can be returned inside a DAV:prop element in a Multi-
            Status response.
Value:      href containing the absolute URI of the target resource.

<!ELEMENT location href >

 XML Elements

16.1 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 >

 Extensions to the DAV:response XML Element for Multi-Status Responses

As described in Sections 6 and 9, the DAV:location pseudo-property and
the DAV:reftype property 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.

Whenever these properties are included in a Multi-Status response, they
are placed in a DAV:prop element associated with the href to which they
apply.  This structure provides a framework for future extensions by
other standards that may need to include additional properties in their
responses.

Consequently, the definition of the DAV:response XML element changes to
the following:

<!ELEMENT response (href, ((href*, status, prop?) | (propstat+)),
responsedescription?) >

 Capability Discovery


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Sections 9.1 and 15 of [WebDAV] describe the use of compliance classes
with the DAV header in responses to OPTIONS, to indicate which parts of
the Web Distributed Authoring protocols the resource supports. This
specification defines an OPTIONAL extension to [WebDAV].  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 MUST indicate that it
does, by listing the new MKREF method as one it supports, and by listing
the new redirectrefs compliance class in the DAV header.

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.

18.1 Example: Discovery of Support for Redirect Reference Resources

>> Request:

OPTIONS /somecollection/someresource HTTP/1.1
HOST: somehost.org

>> Response:

HTTP/1.1 200 OK
Date: Tue, 20 Jan 1998 20:52:29 GMT
Connection: close
Accept-Ranges: none
Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE, MKCOL,
PROPFIND, PROPPATCH, LOCK, UNLOCK, MKREF
Public: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE, MKCOL,
PROPFIND, PROPPATCH, LOCK, UNLOCK, BIND, MKREF, ORDERPATCH
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 [WebDAV].  In addition, /somecollection/someresource supports
redirect reference resources.  The Allow header indicates that MKREF
requests can be submitted to /somecollection/someresource.  The Public
header shows that other Request-URIs on the server support additional
methods.

 Security Considerations

This section is provided to make WebDAV applications 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.

19.1 Privacy Concerns

By creating redirect reference resources on a trusted server, it is

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possible for a hostile agent to induce users to send private 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 [HTTP], Section 10.3.3 Moved
Temporarily.)

19.2 Redirect Loops

Although redirect loops were already possible in HTTP 1.1, the
introduction of the MKREF 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
MKREF requests that would create loops. See also [HTTP], Section 10.3
"Redirection 3xx."

19.3 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 MKREF 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.

19.4 Private Locations May Be Revealed

There are several ways that redirect reference resources may reveal
information about directory 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 directory path that leads to the target resource.   The
owner of the target resource may have wanted to limit knowledge of this
directory 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 Ref-Target and Location
headers, which are returned in some responses to requests on redirect
reference resources, reveal the same information, however.)  In some
environments, the owner of a resource might be able to use access
control to prevent others from creating references to that resource.

 Internationalization Considerations

This specification follows the practices of [WebDAV] in encoding all
human-readable content using XML [XML] and in the treatment of names.
Consequently, this specification complies with the IETF Character Set
Policy [Alvestrand].

WebDAV applications MUST support the character set tagging, character
set encoding, and the language tagging functionality of the XML
specification.  This constraint ensures that the human-readable content
of this specification complies with [Alvestrand].

As in [WebDAV}, names in this specification fall into three categories:
names of protocol elements such as methods and headers, names of XML

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elements, and names of properties.  Naming of protocol elements follows
the precedent of HTTP, using English names encoded in USASCII for
methods and headers.  The names of XML elements used in this
specification are English names encoded in UTF-8.

For error reporting, [WebDAV] follows the convention of HTTP/1.1 status
codes, including with each status code a short, English description of
the code (e.g., 423 Locked).  Internationalized applications will ignore
this message, and display an appropriate message in the user's language
and character set.

For rationales for these decisions and advice for application
implementors, see [WebDAV].

 IANA Considerations

This document uses the namespaces defined by [WebDAV] for properties and
XML elements.  All other IANA considerations mentioned in [WebDAV] also
apply to this document.

 Copyright

To be supplied by the RFC Editor.

 Intellectual Property

To be supplied by the RFC Editor.

 Acknowledgements

This draft has benefited from thoughtful discussion by Jim Amsden, Steve
Carter, Ken Coar, Ellis Cohen, Bruce Cragun, Spencer Dawkins, Mark Day,
Rajiv Dulepet, David Durand, Roy Fielding, Yaron Goland, Fred Hitt, Alex
Hopmann, Marcus Jager, Chris Kaler, Manoj Kasichainula, Rohit Khare,
Daniel LaLiberte, Steve Martin, Larry Masinter, Jeff McAffer, Surendra
Koduru Reddy, Max Rible, Sam Ruby, Bradley Sergeant, Nick Shelness, John
Stracke, John Tigue, John Turner, and others.

 References

[URI] T. Berners-Lee, R. Fielding, L. Masinter, "Uniform Resource
Identifiers (URI): Generic Syntax." RFC 2396. MIT/LCS, U.C. Irvine,
Xerox. August, 1998.

[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels."  RFC 2119, BCP 14.  Harvard University.  March, 1997.

[XML] T. Bray, J. Paoli, C.M. Sperberg-McQueen, "Extensible Markup
Language (XML)."  World Wide Web Consortium Recommendation REC-xml-
. http://www.w3.org/TR/1998/REC-xml-19980210.

[HTTP] R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P.
Leach, T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1." RFC
.  UC Irvine, Compaq, W3C, Xerox, Microsoft.  June, 1999.


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[WebDAV] Y. Y. Goland, E. J. Whitehead, Jr., A. Faizi, S. R. Carter, D.
Jensen, "HTTP Extensions for Distributed Authoring - WebDAV." RFC 2518.
Microsoft, U.C. Irvine, Netscape, Novell.  February, 1999.

[B] J. Slein, E.J. Whitehead Jr., J. Davis, G. Clemm, C. Fay, J.
Crawford, T. Chihaya, "WebDAV Bindings." Internet Draft (work in
progress) draft-ietf-webdav-binding-protocol-00. Xerox, UC Irvine,
CourseNet, Rational, FileNet, IBM, DataChannel. August, 1999.

[OC] J. Slein, E.J. Whitehead Jr., J. Davis, G. Clemm, C. Fay, J.
Crawford, T. Chihaya, "WebDAV Ordered Collections." Internet Draft (work
in progress) draft-ietf-webdav-ordering-protocol-00. Xerox, UC Irvine,
CourseNet, Rational, FileNet, IBM, DataChannel. August, 1999.

 Authors' Addresses

J. Slein
Xerox Corporation
 Phillips Road, 105-50C
Webster, NY 14580
Email: jslein@crt.xerox.com

E. J. Whitehead, Jr.
Dept. of Information and Computer Science
University of California, Irvine
Irvine, CA 92697-3425
Email: ejw@ics.uci.edu

J. Davis
CourseNet Systems
 Capp Street
San Francisco, CA 94110
Email: jrd3@alum.mit.edu

G. Clemm
Rational Software Corporation
 Maguire Road
Lexington, MA 02173-3104
Email: gclemm@rational.com

C. Fay
FileNet Corporation
 Harbor Boulevard
Costa Mesa, CA 92626-1420
Email: cfay@filenet.com

J. Crawford
IBM
Email: ccjason@us.ibm.com

T. Chihaya
DataChannel, Inc.
 108th Ave. N.E., Suite 400
Bellevue, WA 98004
Email: Tyson@DataChannel.com

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 Appendices

27.1 Appendix 1: Extensions to the WebDAV Document Type Definition

<!--============= XML Elements from Section 16 ================-->
<!ELEMENT redirectref EMPTY >
<!--============= Property Elements from Section 15 =================-->
<!ELEMENT reftarget href>
<!ELEMENT location href>
<!--====== Changes to the DAV:response Element from Section 17 ====-->
<!ELEMENT response (href, ((href*, status, prop?) | (propstat+)),
responsedescription?) >

Expires February 20, 2000

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