WEBDAV Working Group J. Slein, Xerox
INTERNET DRAFT E.J. Whitehead Jr., UC Irvine
J. Davis, CourseNet
G. Clemm, Rational
C. Fay, FileNet
J. Crawford, IBM
T. Chihaya, DataChannel
June 18, 1999
Expires December 18, 1999
WebDAV Advanced Collections Protocol
draft-ietf-webdav-collection-protocol-04.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. Internet-Drafts are working
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Abstract
The WebDAV Distributed Authoring Protocol provides basic support for
collections, offering the ability to create and list unordered
collections. Many applications, however, need more powerful
collections, especially for resource sharing and collection ordering.
This specification defines HTTP methods, headers, and XML elements that
supplement the WebDAV Distributed Authoring Protocol to support resource
sharing and collection orderings. Resource sharing is provided by
bindings and redirect references. Bindings create new mappings of URIs
to resources, while redirect references respond to most requests with an
HTTP Redirection (i.e., a 302 status code). An ordered collection
always returns a listing of its members in a specific order. Together,
these capabilities are referred to as WebDAV Advanced Collections.
Table of Contents
1 Notational Conventions......................................3
2 Terminology.................................................4
3 Introduction................................................5
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4 Shared Resources............................................6
4.1 Overview....................................................6
4.2 Bindings....................................................7
4.2.1 BIND Method.................................................8
4.2.2 Bindings to Collections.....................................9
4.2.3 URI Mappings Created by BIND...............................10
4.2.4 Example: Generating the Set of URI Mappings................10
4.2.5 Status Codes...............................................11
4.2.6 Example: BIND..............................................11
4.2.7 Example: BIND Conflict.....................................12
4.2.8 DELETE and Bindings........................................12
4.2.9 COPY and Bindings..........................................13
4.2.10 MOVE and Bindings..........................................13
4.2.11 LOCK and UNLOCK............................................15
4.2.12 Bindings and Other Methods.................................16
4.2.13 Discovering the Bindings to a Resource.....................16
4.3 Redirect References........................................17
4.3.1 MKREF Method...............................................17
4.3.2 Listing the Redirect References in a Collection............19
4.3.3 Copying Redirect References................................22
4.3.4 Deleting and Moving Redirect References....................24
4.3.5 Locking Redirect References................................24
4.3.6 LOCK on Redirect References................................25
4.3.7 Other Operations on Redirect References....................28
4.3.8 Operations on Targets of Redirect References...............30
4.3.9 Relative URIs in Ref-Target and DAV:reftarget..............31
4.3.10 Redirect References to Collections.........................32
5 Ordered Collections........................................33
5.1 Overview...................................................33
5.2 Creating an Ordered Collection.............................34
5.2.1 Overview...................................................34
5.2.2 Example: Creating an Ordered Collection....................34
5.3 Setting the Position of a Collection Member................35
5.3.1 Overview...................................................35
5.3.2 Status Codes...............................................35
5.3.3 Examples: Setting the Position of a Collection Member......35
5.4 Changing the Semantics of a Collection Ordering............36
5.5 Changing the Position of a Collection Member...............36
5.5.1 ORDERPATCH Method..........................................36
5.5.2 Status Codes...............................................36
5.5.3 Example: Changing Positions in an Ordered Collection.......37
5.5.4 Example: Failure of an ORDERPATCH Request..................38
6 Headers....................................................39
6.1 All-Bindings Request Header................................39
6.2 Ref-Target Entity Header...................................39
6.3 Resource-Type Entity Header................................40
6.4 Passthrough Request Header.................................40
6.5 Ordered Entity Header......................................40
6.6 Position Request Header....................................40
7 Status Codes...............................................41
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7.1 506 Loop Detected..........................................41
7.2 425 Unordered Collection...................................41
8 Properties.................................................41
8.1 reftarget Property.........................................41
8.2 location Property..........................................42
8.3 bindings Property..........................................42
8.4 orderingtype Property......................................42
9 XML Elements...............................................43
9.1 redirectref XML Element....................................43
9.2 segment XML Element........................................43
9.3 unordered XML Element......................................43
9.4 custom XML Element.........................................43
9.5 order XML Element..........................................44
9.6 ordermember XML Element....................................44
9.7 position XML Element.......................................44
9.8 first XML Element..........................................44
9.9 last XML Element...........................................44
9.10 before XML Element.........................................45
9.11 after XML Element..........................................45
9.12 options XML Element........................................45
9.13 orderingoptions XML Element................................45
10 Extensions to the DAV:response XML Element for Multi-Status
Responses..................................................45
11 Capability Discovery.......................................46
11.1 Compliance Classes.........................................46
11.2 Example: Discovery of Compliance Classes...................46
11.3 Additional Advanced Collections Capabilities...............47
11.4 Example: Discovery of Ordering Options.....................47
12 Security Considerations....................................48
12.1 Privacy Concerns...........................................48
12.2 Redirect Loops.............................................48
12.3 Redirect References, Bindings, and Denial of Service.......48
12.4 Private Locations May Be Revealed..........................49
12.5 DAV:bindings and Denial of Service.........................49
12.6 Denial of Service and DAV:orderingtype.....................49
13 Internationalization Considerations........................49
14 IANA Considerations........................................50
15 Copyright..................................................50
16 Intellectual Property......................................50
17 Acknowledgements...........................................50
18 References.................................................50
18.1 Normative References.......................................50
18.2 Informational References...................................51
19 Authors' Addresses.........................................51
20 Appendices.................................................52
20.1 Appendix 1: Extensions to the WebDAV Document Type
Definition.................................................52
1 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.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2 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].
Association
A direct or indirect connection between a resource and a namespace
element that supports resource sharing. The bindings, URI
mappings, and redirect references defined in this specification
are types of associations.
URI Mapping
An association between an absolute URL or URI and a resource.
Since a resource can represent items that are not network
retrievable, as well as those that are, it is possible for a
resource to have zero, one, or many URI mappings to URLs or URIs.
Mapping a resource to an "http" scheme URL makes it possible to
submit HTTP protocol requests to the resource using the URL.
Path Segment
Informally, the characters found between slashes ("/") in a URL or
URI. Formally, as defined in section 3.3 of [URI].
Binding
An association between a single path segment (in a collection) and
a resource. A binding creates one or more URI mappings, and hence
is a mechanism for resource sharing, allowing a single resource to
be accessed from multiple locations in a URI namespace.
Collection
A resource that contains, as part of its state, a set of bindings
which identify member resources.
Internal Member URI
The URI mapping, created by a binding that is contained in a
collection. While, in general, bindings can create multiple URI
mappings to a resource, for a given request, only one of these URI
mappings is referred to as the internal member. The URI of the
parent collection used in a given request determines the base URI
for internal member URI calculation.
In [WebDAV], a collection is defined as containing a list of
internal member URIs, where an internal member URI is the URI of
the collection, plus a single path segment. This definition
combines the two concepts of binding and mapping that are
separated in this specification. As a result, this specification
redefines a collection's state to be a set of bindings, and
redefines an internal member URI to be a mapping derived from a
binding. After this redefinition, an internal member URI can be
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used when reading [WebDAV] without loss of meaning. For purposes
of interpretation, when [WebDAV] discusses a collection
"containing" an internal member URI, this should be read as the
collection containing a binding whose mapping to a URI creates an
internal member URI, in this sense "containing" the internal
member URI. The authors of this specification anticipate and
recommend that future revisions of [WebDAV] perform a full
reconciliation of terms between these two specifications.
Reference
A resource whose purpose is to provide access to another resource.
Redirect Reference
A resource whose purpose is to provide access to another resource,
and that requires client action before it can be resolved. The
client is aware that this type of reference is mediating between
it and the target resource.
Ordinary Resource
A resource that is not a reference to another resource.
Target Resource
The resource referenced by a referential resource.
Referential Integrity
The integrity of a reference is preserved as long as it points to
the same resource it pointed to when it was created. Its
integrity may be destroyed if the target resource is moved without
updating the reference to reflect its new location, or if the
target resource is deleted while a reference to it still exists.
3 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.
Many applications, however, need more powerful collections. There are
two areas in particular where more powerful functionality is often
needed: shared resources and ordering. This specification defines
extensions to [WebDAV] in both these areas.
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
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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.
This protocol provides two mechanisms for allowing resources to appear
in multiple places in an http URL hierarchy, and for sharing resources:
bindings and redirect references.
The WebDAV Distributed Authoring Protocol added to the Web the ability
to navigate Web resources hierarchically, complementing existing
hypertext navigation facilities. In hypertext navigation, links appear
in a specific order in a document. By contrast, hierarchical navigation
has fewer mechanisms for expressing the ordering of a set of resources.
There are many scenarios where it is useful to impose an ordering on a
collection, such as expressing a recommended access order, or a revision
history order. Orderings may be based on property values, but they may
be completely independent of any properties on the resources identified
by the collection's internal member URIs. Orderings based on properties
can be obtained using a search protocol [DASL], but orderings not based
on properties need some other mechanism. These orderings generally need
to be maintained by a human user. The ordering protocol defined here
focuses on support for such human-maintained orderings, but also allows
for server-maintained orderings.
4 Shared Resources
4.1 Overview
Shared resources make the same resource accessible from multiple
locations in http URL namespaces. This protocol provides two mechanisms
for sharing resources: bindings and redirect references.
The binding mechanism defined in this specification provides a way for
clients to add new URI mappings to existing resources. A URI mapping is
an association between an absolute URI and a resource, which makes it
possible to submit requests to the resource using that URI as the
Request-URI. Bindings, and the URI mappings based on them, are appealing
mechanisms for resource sharing because:
o Once URI mappings are created with a BIND request, clients need do
nothing special to use them. They behave just like any other URI
mappings, transparently applying operations to the target resource.
o HTTP and WebDAV servers already provide URI mappings, so there is
little extra work involved in allowing clients to create them.
o The integrity of bindings is guaranteed. MOVE and DELETE operations
cannot leave bindings in an inconsistent state.
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A limitation of bindings is that a server would need proxy capabilities
in order to support bindings to resources on another server. In light
of this complexity, support for cross-server bindings is OPTIONAL.
A redirect reference is a resource whose purpose is to provide access to
another resource. It redirects most requests on the reference to
another resource, thereby providing a form of mediated access to the
other resource. Since the HTTP 302 (Moved Temporarily) status code is
used to redirect client requests on a redirect reference, from the
clientÆs point of view redirect references are less convenient to use
than bindings. Redirect references require action by the client before
they can be resolved. Moreover, the server is not required to enforce
the integrity of redirect references. However, redirect references have
a number of advantages:
o They are simple for servers to implement. Servers already provide
redirect resources in the form of 301 / 302 redirection control, and
the same mechanism can be used for redirect references.
o The same simple implementation works equally well for target
resources that reside on the same server and for target resources
that reside on a different server.
o Redirect references have only limited security implications.
o Since redirect references are resources, they can carry properties of
their own.
Ideally, non-referencing clients should be able to use both bindings and
redirect references. This goal is more difficult to meet for redirect
references, since client action is required to resolve them. The
strategy of having redirect references respond to most requests with a
302 (Moved Temporarily), accompanied by the URI of the target resource
in the Location header, fulfills this goal in most cases.
4.2 Bindings
Bindings are part of the state of a collection. In general, there is a
one-to-one correspondence between a collection's bindings and its
internal member URIs. The URI segment associated with a resource by one
of a collection's bindings is also the final segment of one of the
collection's internal member URIs. The final segment of each internal
member URI identifies one of the bindings that is part of the
collection's state, unless the internal member URI is not bound to a
resource.
Even though a binding is just an association between a path segment and
a resource, a binding creates one or more URI mappings of a URI to a
resource. For example, if the segment "index.html" is being bound to a
resource in a collection with URL "http://www.foo.net/A/", the binding
creates a URI mapping of URL "http://www.foo.net/A/index.html" to the
HTML resource. If the parent collection is then bound to the segment
"B", this creates two URI mappings, "http://www.foo.net/B/" to the
collection resource, and "http://www.foo.net/B/index.html" to the HTML
resource. Both the collection and the HTML resource are now accessible
via two URLs apiece.
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For a resource implemented by a computer, the relationship between a URI
mapping and a resource is highlighted in the following diagram:
URI 1 URI 2 ... URI N
| | |
| | | <------- URI Mappings
| | |
+---------------------+
| Resource R |
+---------------------+
As discussed in [URI], a resource is an abstraction that maps a URI to
an entity or set of entities. This resource can have multiple URIs/URLs
mapped to it.
The identity of a binding is determined by the URI segment (in its
collection) and the resource that the binding associates. If the
resource is destroyed, the binding also goes out of existence. If the
URI segment comes to be associated with a different resource, the
original binding ceases to exist and another binding is created.
Bindings are not unique to advanced collections, although the BIND
method for explicitly creating bindings is introduced here. Existing
methods that create resources, such as PUT, MOVE, COPY, and MKCOL,
implicitly create bindings. There is no difference between implicitly
created bindings and bindings created with BIND.
Since a binding is an association between a path segment and a resource,
it would be very undesirable if one binding could be destroyed as a side
effect of operating on the resource through a different binding. It is
not acceptable for a DELETE or MOVE through a different binding to
destroy the resource or fail to update one binding, turning that binding
into a dangling path segment. As a result, implementations MUST act to
ensure the integrity of bindings.
It is especially difficult to maintain the integrity of cross-server
bindings. Unless the server where the resource resides knows about all
bindings on all servers to that resource, it may unwittingly destroy the
resource or move it without notifying a server where a binding resides.
For example, if server A permits creation of a binding to a resource on
server B, server A must notify server B about its binding and must have
an agreement with B that B will not destroy the resource while A's
binding exists. Otherwise server B may receive a DELETE request that it
thinks removes the last binding to the resource and destroy the resource
while A's binding still exists.
Consequently, support for cross-server bindings is OPTIONAL.
4.2.1 BIND Method
The BIND method creates a new binding from the final segment of the
Request-URI (minus any trailing slash) to the resource identified
by the Destination header. This binding is added to the collection
identified by the Request-URI minus its trailing slash (if present) and
final segment. The Destination header is defined in Section 9.3 of
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[WebDAV].
If a server cannot guarantee the binding behavior specified for GET
(Section 4.2.12), DELETE (Section 4.2.8), and MOVE (Section 4.2.10), the
BIND request MUST fail with a 501 (Not Implemented) status code.
If the Request-URI ends in a slash ("/") (i.e., the Request-URI
identifies a collection), the resource identified by the Destination
header MUST be a collection resource, or the request fails with a 409
(Conflict) status code. This ensures that URIs ending in a slash are
always bound to collections. If the Request-URI does not contain a path
segment (i.e., it consists simply of a slash "/"), the BIND operation
MUST fail and report a 409 (Conflict) status code.
After successful processing of a BIND request, it MUST be possible for
clients to use the Request-URI to submit requests to the resource
identified by the Destination header.
By default, if the Request-URI identifies an existing binding, the new
binding replaces the existing binding. This default binding replacement
behavior can be overridden using the Overwrite header defined in Section
9.6 of [WebDAV].
The Position request header (defined in Section 6.6) MAY be used in BIND
requests.
A server MAY allow the BIND method to be used to create bindings to
resources that support content negotiation or to resources that
dynamically generate response entities.
4.2.2 Bindings to Collections
BIND can create a binding to a collection resource. A collection
accessed through such a binding behaves exactly as would a collection
accessed through any other binding. Bindings to collections can result
in loops, which servers MUST detect when processing "Depth: infinity"
requests. When a loop is detected, the server MUST respond with a 506
(Loop Detected) status code (defined in Section 7.1).
Creating a new binding to a collection makes each resource associated
with a binding in that collection accessible via a new URI, but does not
result in the creation of a new binding for each of these resources.
For example, suppose a new binding COLLX is created for collection C1 in
the figure below. It immediately becomes possible to access resource R1
using the URI /COLLX/x.gif and to access resource R2 using the URI
/COLLX/y.jpg, but no new bindings for these child resources were
created. This is because bindings are part of the state of a
collection, and associate a URI that is *relative to that collection*
with its target resource. No change to the bindings in Collection C1 is
needed to make its children accessible using /COLLX/x.gif and
/COLLX/y.jpg.
+-------------------------+
| Root Collection |
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| (properties) |
| bindings: |
| coll1 COLLX |
+-------------------------+
| /
| /
| /
+------------------+
| Collection C1 |
| (properties) |
| bindings: |
| x.gif y.jpg |
+------------------+
| \
| \
| \
+-------------+ +-------------+
| Resource R1 | | Resource R2 |
+-------------+ +-------------+
4.2.3 URI Mappings Created by BIND
The set of URI mappings created by a successful BIND operation MUST be
determined as follows:
1. Start with an empty set of URLs, called U.
2. Take the Request-URI and remove path segments (and associated "/"
characters) from the right until either (a) a non-WebDAV collection, or
a non-WebDAV advanced collection is found, or (b) the root, "/" is
reached (i.e., no characters after the scheme and authority parts of the
URL). This is the base URL B.
3. Add B, and all possible domain name variants of B (i.e., all other
domain names which can be substituted for the domain name in B, and
still retrieve the resource mapped to B), to URL set U.
4. Calculate the next path segment of the Request-URI, going from right
to left, and call it S, which is bound to resource R.
5. For each member of URL set U, called Um, remove Um, then for every
possible binding to R, create a new URL by adding the binding's path
segment to Um, then add this new URL to U.
6. If there is no further path segment, then U has the complete set of
URI mappings. Otherwise, go back to step 4.
4.2.4 Example: Generating the Set of URI Mappings
Assume a server responds to two domain names, www.fuzz.com, and
fuzz.com, and has a top level that is not WebDAV-aware, called A/.
Below A/ is an advanced collection that is bound to both 1/ and one/. In
collection one/ there is a resource called index.html.
>> Request:
BIND /A/1/info.html HTTP/1.1
Host: www.fuzz.com
Destination: http://www.fuzz.com/A/one/index.html
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>> Response:
HTTP/1.1 201 Created
The set of all possible URI mappings to the resource identified by
http://www.fuzz.com/A/one/index.html is calculated as follows:
1. U is empty.
2. The base URL, B, is http://www.fuzz.com/A/, since A/ is not WebDAV-
aware.
3. Since there are two domain names for this server, the domain name
variations of B are added to U, making U contain: http://www.fuzz.com/A/
and http://fuzz.com/A/.
4. (iteration 1) The next path segment of the Request-URI is 1/, which
is bound to an advanced collection resource, R.
5. (iteration 1) Since the advanced collection resource R is bound to 1/
and one/, the value of U after the operation is:
http://www.fuzz.com/A/1/, http://www.fuzz.com/A/one/,
http://fuzz.com/A/1/, and http://fuzz.com/A/one/.
6. Go back to step 4, since there is one more path segment in the
Request-URI.
4. (iteration 2) The next path segment of the Request-URI is info.html,
which is bound to an HTML resource, R.
5. (iteration 2) Since the HTML resource is bound to info.html and
index.html, the value of U after the operation is:
http://www.fuzz.com/A/1/index.html, http://www.fuzz.com/A/1/info.html,
http://www.fuzz.com/A/one/index.html,
http://www.fuzz.com/A/one/info.html, http://fuzz.com/A/1/index.html,
http://fuzz.com/A/1/info.html, http://fuzz.com/A/one/index.html,
http://fuzz.com/A/one/info.html.
6. Since there are no further path segments in the Request-URI, U now
has the complete set of URI mappings for the resource identified by the
Destination header.
4.2.5 Status Codes
201 (Created): The binding was successfully created.
400 (Bad Request): The client set an invalid value for the Destination
or Position header.
409 (Conflict): Several conditions may produce this response. The URI
in the Destination header is not mapped to a resource. The request is
attempting to create a binding in a collection that does not exist. The
request is attempting to position the binding in an unordered
collection. The request is attempting to re-bind the top-level
collection.
412 (Precondition Failed): The Overwrite header is "F", and a binding
already exists for the request-URI.
4.2.6 Example: BIND
>> Request:
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BIND /~whitehead/dav/spec08.txt HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/pub/i-d/draft-webdav-protocol-08.txt
>> Response:
HTTP/1.1 201 Created
The server created a new binding, associating "spec08.txt" with the
resource identified by the URL "http://www.ics.uci.edu/pub/i-d/draft-
webdav-protocol-08.txt". Clients can now use the Request-URI,
"http://www.ics.uci.edu/~whitehead/dav/spec08.txt", to submit requests
to that resource. As part of this operation, the server added the
binding "spec08.txt" to collection /~whitehead/dav/.
4.2.7 Example: BIND Conflict
>> Request:
BIND /press/prlogo.gif HTTP/1.1
Host: www.softcorp.com
Destination: http://www.softcorp.com/logos/
>> Response:
HTTP/1.1 409 Conflict
The client requested the server to create a binding between "prlogo.gif"
and the resource identified by the URL "http://www.softcorp.com/logos/".
Since the Destination does end in a slash, while the Request-URI does
not, the server failed the request, returning a 409 (Conflict) status
code.
4.2.8 DELETE and Bindings
The DELETE method requests that the server remove the binding between
the resource identified by the Request-URI and the binding name, the
last path segment of the Request-URI. The binding MUST be removed from
its parent collection, identified by the Request-URI minus its trailing
slash (if present) and final segment. The All-Bindings header may be
used with DELETE to request that the server remove all bindings to the
resource identified by the Request-URI.
Once all bindings to the resource are removed, the server MAY reclaim
system resources associated with the resource. If DELETE removes a
binding to a resource, but there remain other bindings to that resource,
the server MUST NOT reclaim system resources associated with the
resource.
Since DELETE as specified in [WebDAV] is not an atomic operation, it may
happen that parts of the hierarchy under the request-URI cannot be
deleted. In this case, the response is as described in [WebDAV].
[HTTP] states that "the DELETE method requests that the origin server
delete the resource identified by the Request-URI." Because [HTTP] did
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not distinguish between bindings and resources, the intent of its
definition of DELETE is unclear. We consider the definition presented
here to be a clarification of the definition in [HTTP].
Section 8.6.1 of [WebDAV] states that during DELETE processing, a server
"MUST remove any URI for the resource identified by the Request-URI from
collections which contain it as a member." Servers that support
bindings SHOULD NOT follow this requirement.
4.2.9 COPY and Bindings
As defined in Section 8.8 of [WebDAV], COPY causes the resource
identified by the Request-URI to be duplicated, and makes the new
resource accessible using the URI specified in the Destination header.
Upon successful completion of a COPY, a new binding is created between
the last path segment of the Destination header (including trailing "/",
if present), and the destination resource. The new binding is added to
its parent collection, identified by the Destination header minus its
trailing slash (if present) and final segment.
A COPY with "Depth: 0" MUST NOT duplicate the bindings contained by the
collection.
As an example, suppose that a COPY is issued to URI 3 for resource R
below (which is also mapped to URI 1 and URI 2), with the Destination
header set to URIX. After successful completion of the COPY operation,
resource R is duplicated to create resource R', and a new binding has
been created which creates at least the URI mapping between URIX and the
new resource (although other URI mappings may also have been created).
URI 1 URI 2 URI 3 URIX
| | | |
| | | <---- URI Mappings ----> |
| | | |
+---------------------+ +------------------------+
| Resource R | | Resource RÆ |
+---------------------+ +------------------------+
4.2.10 MOVE and Bindings
The MOVE method has the effect of creating a new binding to a resource
(at the Destination), and removing an existing binding (at the Request-
URI). The name of the new binding is the last path segment of the
Destination header, and the new binding is added to its parent
collection, identified by the Destination header minus its trailing
slash (if present) and final segment.
As an example, suppose that a MOVE is issued to URI 3 for resource R
below (which is also mapped to URI 1 and URI 2), with the Destination
header set to URIX. After successful completion of the MOVE operation,
a new binding has been created which creates at least the URI mapping
between URIX and resource R (although other URI mappings may also have
been created). The binding corresponding to the final segment of URI 3
has been removed, which also causes the URI mapping between URI 3 and R
to be removed.
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>> Before Request:
URI 1 URI 2 URI 3
| | |
| | | <---- URI Mappings
| | |
+---------------------+
| Resource R |
+---------------------+
>> After Request:
URI 1 URI 2 URIX
| | |
| | | <---- URI Mappings
| | |
+---------------------+
| Resource R |
+---------------------+
Since MOVE as specified in [WebDAV] is not an atomic operation, it may
happen that parts of the hierarchy under the request-URI can be moved.
In this case, the response is as described in [WebDAV].
4.2.10.1 Implementation Note
In some situations, particularly when the destination is on a different
server from the original resource, the server may implement MOVE by
performing a COPY, performing some consistency maintenance on bindings
and properties, and then performing a DELETE. In the end, all of the
original bindings except the one corresponding to the Request-URI will
be associated with the new resource. The binding corresponding to the
URI in the Destination header will be associated with the new resource.
And the original resource together with the binding corresponding to the
Request-URI will have been deleted. This implementation is in accord
with the definition of MOVE in [WebDAV], and is logically equivalent to
the definition given above.
The consistency maintenance processing that is required for this
implementation is as follows:
The DAV:creationdate property of the new resource SHOULD have the same
value as the DAV:creationdate property of the old resource.
The DAV:getlastmodified property of the new resource SHOULD have the
same value as the DAV:getlastmodified property of the old resource.
All URIs that were bound to the original resource except for the
Request-URI MUST be bound instead to the new resource.
Consider again the case where a MOVE is issued to URI 3 for resource R
(which is also mapped to URI 1 and URI 2), with the Destination header
set to URIX. Unlike the previous example, in this implementation, after
successful completion of the MOVE operation, resource R has been
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duplicated as resource R'. The original bindings corresponding to URI 1
and URI2 are now associated with R'. The binding corresponding to the
Request-URI (URI 3) has been removed. And a new binding has been
created which creates at least the URI mapping between URIX and resource
R'. Note that the server may reclaim the storage associated with
resource R once the MOVE operation has finished.
>> Before Request:
URI 1 URI 2 URI 3
| | |
| | | <---- URI Mappings
| | |
+---------------------+
| Resource R |
+---------------------+
>> After Request:
URI1 URI2 --------------------------------- URIX
| | |
----------------------------------------- | |
| | |
+---------------------+ +------------------------+
| Resource R | | Resource RÆ |
+---------------------+ +------------------------+
4.2.11 LOCK and UNLOCK
Bindings do not affect the semantics of locks, as specified in [WebDAV].
Specifically, the requirement in section 8.10.3 that "a LOCK request on
a resource MUST NOT succeed if it can not be honored by all the URIs
through which the resource is accessible" still holds. The LOCK method
locks the resource, and a lock is visible via all URIs mapped to that
resource. Similarly, a successful UNLOCK issued via any URI mapping to a
resource removes the lock from the resource, and this lock removal is
visible via all URI mappings.
When a resource is locked, the lock owner expects to be able to access
the resource -- using the same Request-URI that he used to lock the
resource -- for as long as he holds the lock. This would not be
possible if another user could move or delete any of the collections
corresponding to segments of the request-URI.
Consequently, for the duration of a lock, it MUST NOT be possible for a
principal other than the lock owner to make a locked resource
inaccessible via the URI mapping used to lock the resource. Only the
lock owner can move or delete any of the collections corresponding to
segments of the Request-URI. This restriction does not prevent others
from modifying those collections, by adding members to them, removing
members from them, or changing their property values.
For example, if a user locks /plants/herbs/rosemary.html, it is not
possible for another user to move /plants/herbs/ to
/plants/flowering/herbs/, or to completely delete /plants/herbs/, though
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it is possible this delete operation may succeed in deleting everything
except for /plants/herbs/rosemary.html and /plants/herbs/.
4.2.12 Bindings and Other Methods
This section describes the interaction of bindings with those HTTP
methods not yet explicitly discussed. The semantics of the methods GET,
HEAD, PUT, POST and OPTIONS are specified in [HTTP]. The semantics of
PROPFIND, PROPPATCH, and MKCOL are specified in [WebDAV].
For most of these methods, no new complexities are introduced by
allowing explicit creation of multiple bindings to the same resource.
For the access operations (GET, HEAD, OPTIONS, and PROPFIND), it is
simply the case that no matter which URI mapping to a given resource is
used as the Request-URI, the response is mediated by that same resource.
The responses may, however, vary depending upon which Request-URI was
used. For example, the response to a GET request may contain the
Request-URI in its entity.
The same is true for POST. No matter which URI mapping to a given
resource is used as the Request-URI, the response is mediated by that
same resource. The changes made on the server and the responses may,
however, vary depending upon which Request-URI was used.
If the Request-URI of a PUT identifies an existing resource, then a PUT
via one URI mapping to this resource MUST produce the same result as a
PUT with the same headers and request entity body via any other URI
mapping to the same resource. The change made by a PUT via one URI
mapping MUST affect the resource that generates the GET response for all
URI mappings to the same resource.
A PROPPATCH through one URI mapping to a resource MUST produce the same
changes to its properties as the same PROPPATCH request through a
different URI mapping to the same resource.
As specified in [WebDAV], MKCOL cannot overwrite an existing resource.
MKCOL through any URI mapping to an existing resource must fail.
The semantics of MKREF are specified in Section 4.5.1 below. A MKREF
through one URI mapping to a resource MUST produce the same result as a
MKREF with the same headers through any other URI mapping to the same
resource. By default, it overwrites the resource with a new redirect
reference.
The semantics of ORDERPATCH are specified in 5.5.1 below. An ORDERPATCH
through one URI mapping to a collection MUST produce the same changes to
its ordering as the same ORDERPATCH request through any other URI
mapping to the same collection.
4.2.13 Discovering the Bindings to a Resource
An OPTIONAL DAV:bindings property on a resource provides a list of the
bindings that associate URI segments with that resource. By retrieving
this property, a client can discover the bindings that point to the
resource and the collections that contain bindings to the resource. As
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for all DAV: properties, this specification is silent as to how the
DAV:bindings property is implemented on the server.
Rationale: A number of scenarios require clients to navigate from a
resource to the bindings that point to it, and to the collections that
contain those bindings. This capability is particularly important for
Document Management Systems. Their clients may need to determine, for
any object in the DMS, what collections contain bindings to that object.
This information can be used for upward navigation through a hierarchy
or to discover related documents in other collections.
Risks: When deciding whether to support the DAV:bindings property,
server implementers / administrators should balance the benefits it
provides against the cost of maintaining the property and the security
risks enumerated in Sections 12.5 and 12.6.
4.3 Redirect References
For most operations submitted to a redirect reference, the response is a
302 (Moved Temporarily), accompanied by the Resource-Type header
(defined in Section 6.2 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 references),
DELETE, MOVE, and LOCK, for reasons that will be explained, are
exceptions to this general behavior. These exceptional operations are
applied to the reference itself and do not result in a 302 response.
If the client is aware that it is operating on a redirect reference, it
can resolve the reference by retrieving the reference's DAV:reftarget
property (defined in Section 7.1 below), whose value is the URI of the
target resource. It can then submit requests to the target resource.
A redirect reference is a new type of resource. To distinguish redirect
references from ordinary resources, a new value of the DAV:resourcetype
property (defined in [WebDAV]), DAV:redirectref, is defined in Section
8.1 below.
Since a redirect reference is a resource, it is possible to apply
methods to the reference rather than to its target. The Passthrough
request header (defined in Section 6.4 below) is provided so that
referencing-aware clients can control whether an operation is applied to
the redirect reference or to its target resource. The Passthrough
header can be used with most requests to redirect references. This
header is particularly useful with PROPFIND, to retrieve the reference's
own properties.
4.3.1 MKREF Method
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.
The Position request header (defined in Section 6.6) MAY be used in
MKREF requests.
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 server MUST perform a delete operation on the
existing resource before performing the MKREF. This default behavior can
be overridden using the Overwrite header defined in Section 9.6 of
[WebDAV].
4.3.1.1 Status Codes
201 (Created): The redirect reference resource was successfully created.
400 (Bad Request): The client set an invalid value for the Ref-Target or
Position header.
409 (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 references. The request may be attempting to create
the reference in a collection that does not exist. The request may be
attempting to position the reference before or after a resource that is
not in the collection, or before or after itself. The request may be
attempting to position the reference in an unordered collection.
412 (Precondition Failed): The Overwrite header is "F", and a resource
already exists at the request-URI.
4.3.1.2 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 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".
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4.3.2 Listing the Redirect References in a Collection
A URI of a redirect reference can be an internal member URI of a
collection just as the URI of an ordinary resource can. A listing of
the internal member URIs of a collection shows all of the URIs that are
internal members of the collection, whether they identify redirect
references or ordinary 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 an ordinary resource or a redirect reference.
For each redirect reference, 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 and
DAV:resourcetype properties 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 9 below. A referencing-aware client
can tell from the DAV:resourcetype property that the collection contains
a redirect reference. The DAV:location property contains the absolute
URI of the target resource. A referencing-aware client can either use
the URI value of the DAV:location property to retrieve the properties of
the target resource, or it can submit a PROPFIND to the redirect
reference with "Passthrough: F" to retrieve its properties. It is
recommended that future editors of [WebDAV] define the DAV:location
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 references into any collections to which
they may refer.
The Passthrough header (defined in Section 6.4) MAY be used with a
PROPFIND request on a collection.
4.3.2.1 Example: PROPFIND on a Collection with Redirect References
Suppose a PROPFIND request with Depth = infinity is submitted to the
following collection, with the members shown here:
http://www.svr.com/MyCollection/
(ordinary resource) diary.html
(redirect reference) 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/">
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<D:resourcetype/>
<J:keywords/>
</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. The response element for the redirect reference has
a status of 302 (Moved Temporarily), and includes a DAV:prop element
with the DAV:location and DAV:resourcetype properties to allow clients
to retrieve the properties of its target resource. (The response
element for the redirect reference does not include the requested
properties. The client can submit another PROPFIND request to the URI
in the DAV:location property to retrieve those properties.)
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4.3.2.2 Example: PROPFIND with Passthrough: F on a Collection with
Redirect References
Suppose a PROPFIND request with Passthrough = F and Depth = infinity is
submitted to the following collection, with the members shown here:
/MyCollection/
(ordinary resource) diary.html
(redirect reference) 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>
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<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/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 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.
4.3.3 Copying Redirect References
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, 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 references, 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 references where the old one had
references). 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
targets where the original collection had references).
For a COPY request on an individual reference, 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 references, 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. Reference-aware clients can use the Passthrough
header with the value "F" to copy the redirect reference itself.
For COPY on a collection containing redirect references, different
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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
references, the server MUST copy the redirect references to the new
collection rather than returning 302 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
references by using the Passthrough header with the value "T".
4.3.3.1 Example: COPY on a Redirect Reference
>> 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 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.
4.3.3.2 Example: COPY on a Collection That Contains a Redirect Reference
Suppose a COPY request is submitted to the following collection, with
the members shown:
/MyCollection/
(ordinary resource) diary.html
(redirect reference) nunavut with target /Someplace/nunavut.map
>> Request:
COPY /MyCollection/ HTTP/1.1
Host: www.svr.com
Destination: http://www.svr.com/OtherCollection/
>> Response:
HTTP/1.1 201 Created
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In this case, since /MyCollection/nunavut is a redirect reference, the
reference itself, and not its target, was copied into the new
collection. So the resulting collection is as follows:
/OtherCollection/
(ordinary resource) diary.html
(redirect reference) nunavut with target /Someplace/nunavut.map
4.3.4 Deleting and Moving Redirect References
The DELETE method is used to delete bindings to redirect references.
DELETE MUST affect bindings to the reference 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 in the subtree under that collection, it
MUST delete bindings to the reference, 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 does not affect the target of the reference.
A MOVE operation on a redirect reference MUST move the reference to a
different location, and MUST NOT change the location of its target,
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 in the subtree under that collection, it MUST move the
reference, 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 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 is removed from that collection, the aim is to change
the membership of that collection. Membership of the target 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 references. Instead, they are applied by default to the
reference itself, not to its target, and by default do not result in 302
status codes.
4.3.5 Locking Redirect References
The semantics of LOCK described here resulted from balancing a set of
incompatible considerations:
o Ideally, a LOCK on a redirect reference should lock both the
reference 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 with one pointing to a different target.
o Non-referencing clients should be able to use redirect references
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without encountering surprising results.
o The basic characteristics of redirect references should be honored.
Redirect references 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 and the behavior of LOCK on a collection that
contains redirect references.
o The behavior of all requests to redirect references 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.
o LOCK semantics for redirect references 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.
4.3.6 LOCK on Redirect References
The behavior of LOCK for redirect references was determined by what is
possible for the case of locking collections that contain redirect
references.
The default behavior for any operation on a redirect reference 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 references. 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.
To avoid this result, a LOCK with Depth > 0 on a collection MUST lock
any redirect references 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 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.
There will be no hint in any response code that there are redirect
references whose targets need to be locked. The client will most likely
not lock any targets until it attempts an operation on the target and
gets a 302 response. It is possible that a non-referencing client may
never realize that the reference's target has not been locked.
Clearly, a LOCK with Depth = infinity on a collection MUST NOT follow
any redirect references whose targets are collections into the target
collections; it MUST NOT cause any resources in those target collections
to be locked.
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The behavior of LOCK for individual redirect references is designed to
be consistent with LOCK behavior for collections that contain redirect
references. By default a LOCK on a redirect reference MUST lock only
the reference, not its target, 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.
4.3.6.1 Example: LOCK on a Redirect Reference
>> 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>
<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>
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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, which was successfully locked. The
target resource of the redirect reference is not locked.
4.3.6.2 Example: LOCK on a Collection That Contains a Redirect
Reference, with Passthrough: T
Suppose a LOCK request is submitted to the following collection, with
the members shown:
/MyCollection/
(ordinary resource) diary.html
(redirect reference) 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
<?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>
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</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 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 property returned
for the redirect reference, and can resubmit the LOCK request with
"Passthrough: F" to the collection. At that point both the reference
and its target will be locked (as well as the collection and all the
resources identified by its other members).
4.3.7 Other Operations on Redirect References
Although non-referencing-aware clients cannot create referential
resources, they should be able to use the references 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 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.
o The response MUST include the Resource-Type header. This header
allows reference-aware WebDAV clients to recognize the resource as a
reference and understand the reason for the redirection.
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 with the Passthrough header set to "F" in order to
operate on the reference itself. If the Passthrough header is present
with a value of "F", the request MUST be applied to the reference
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, and if the client wants to
apply the method to the reference, it can save the round trip caused by
the 302 response by using "Passthrough: F" in its initial request to the
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URI.
"Passthrough: F" can be used with GET or HEAD to retrieve the entity
headers of a redirect reference. 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 references
(at a minimum, Cache-Control, Age, ETag, Expires, and Last-Modified).
"Passthrough: F" can be used with PUT to replace the redirect reference
with an ordinary resource. It can be used with OPTIONS to retrieve the
capabilities of a redirect reference.
Clients MUST NOT, however, use "Passthrough: F" with POST. Since a
reference cannot accept another entity as its subordinate, an attempt to
POST to a reference with "Passthrough: F" will also fail. If a server
receives a POST request with "Passthrough: F" on a redirect reference,
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 is a dangling reference). Similarly, if
the client attempts to resubmit the request to the reference 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 MUST
fail.
4.3.7.1 Example: GET on a Redirect Reference
>> 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
Since /bar.html is a redirect reference 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. The URI
of the target resource is provided in the Location header so that the
client can resubmit the request to the target resource.
4.3.7.2 Example: PUT on a Redirect Reference with "Passthrough: F"
>> Request:
PUT /bar.html HTTP/1.1
Host: www.foo.com
Passthrough: F
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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, the presence of the
"Passthrough: F" header prevents a 302 response, and instead causes the
request to be applied to the reference. The result in this case is that
the reference is replaced by an ordinary resource having the content
submitted with the request.
4.3.7.3 Example: PROPPATCH on a Redirect Reference
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>
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 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. The URI
of the target resource is provided in the Location header so that the
client can resubmit the request to the target resource.
4.3.8 Operations on Targets of Redirect References
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Operations on targets of redirect references have no effect on the
reference.
4.3.9 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
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.
4.3.9.1 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:
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.
4.3.9.2 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
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<?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>statistics/population/1997.html</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 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.
4.3.10 Redirect References to Collections
In a Request-URI /segment1/segment2/segment3, any of the three segments
may identify a redirect reference. (See [URI], Section 3.3, for
definitions of "path" and "segment".) If any segment in a Request-URI
identifies a redirect reference, the response is a 302. The value of
the Location header in the 302 response is as follows:
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The leftmost path segment of the request-URI that identifies a redirect
reference, together with all path segments and separators to the left of
it, is replaced by the value of the redirect reference'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 whose target is collection /a/, which contains redirect
reference y whose target is collection /b/, which contains redirect
reference z.html whose target 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
302 with Location: /c/d.html, and the client resubmits the request to
/c/d.html. This final request succeeds.
5 Ordered Collections
5.1 Overview
Collections on a compliant server may be ordered, but need not be. It
is up to the client to decide whether a given collection is ordered and,
if so, to specify the semantics to be used for ordering its bindings.
If a collection is ordered, each of its bindings, and hence internal
member URIs, MUST be in the ordering exactly once, and the ordering MUST
NOT include any binding that is not contained by the collection. Only
one ordering can be attached to any collection. An ordering is
considered to be part of the state of a collection resource, and hence
is the same across all URI mappings to the collection. Multiple
orderings of the same resources can be achieved by creating multiple
collections referencing those resources, and attaching a different
ordering to each collection.
The server is responsible for enforcing these constraints on orderings.
The server MUST remove a binding (and its derived internal member URI)
from the ordering when it is removed from the collection. The server
MUST add a binding (and its derived internal member URI) to the ordering
when it is added to the collection.
When responding to a PROPFIND on a collection, the server MUST order the
response elements according to the ordering defined on the collection.
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If the collection is unordered, the client cannot depend on the
repeatability of the ordering of results from a PROPFIND request.
Orderings may be client-maintained or server-maintained. This protocol
provides support for both types of orderings.
5.2 Creating an Ordered Collection
5.2.1 Overview
When a collection is created, the client MAY request that it be ordered
and specify the semantics of the ordering by using the new Ordered
header (defined in Section 6.5) with a MKCOL request.
For collections that are ordered, the client SHOULD identify the
semantics of the ordering with a URI in the Ordered header. This URI
may identify a server-maintained ordering. Clients can discover the
available server-maintained orderings using the mechanism defined in
Section 11.3. The URI may identify a semantics for a client-maintained
ordering, providing the information a human user or software package
needs to insert new collection members into the ordering intelligently.
Although the URI in the Ordered header MAY point to a resource that
contains a definition of the semantics of the ordering, clients are
discouraged from accessing that resource, in order to avoid
overburdening its server. The client MAY set the header value to
DAV:custom to indicate that the collection is ordered, but the semantics
of the ordering are not being advertised. If the client does not want
the collection to be ordered, it may omit the Ordered header, or use it
with the value DAV:unordered.
If the server does not recognize the value of the Ordered header as one
of its server-maintained orderings, it MUST assume that a client-
maintained ordering is intended. If the value of the Ordered header is
one of the server-maintained orderings that the server supports, it MUST
maintain the collection's ordering according to that ordering semantics
as new members are added.
Every collection MUST have a DAV:orderingtype property (defined in
Section 7.5), which indicates whether the collection is ordered and, if
so, identifies the semantics of the ordering. The server sets the
initial value of this property based on the value of the Ordering header
in the MKCOL request. If the collection is unordered, the
DAV:orderingtype property MUST have the value DAV:unordered. An
ordering-aware client interacting with an ordering-unaware server (e.g.,
one that is implemented only according to [WebDAV]) SHOULD assume that
if a collection does not have the DAV:orderingtype property, the
collection is unordered.
5.2.2 Example: Creating an Ordered Collection
>>Request:
MKCOL /theNorth/ HTTP/1.1
Host: www.server.org
Ordered: http://www.server.org/orderings/compass.html
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>>Response:
HTTP/1.1 201 Created
In this example a new, ordered collection was created. Its
DAV:orderingtype property has as its value the URI from the Ordered
header, http://www.server.org/orderings/compass.html. In this case, the
URI identifies the semantics governing a client-maintained ordering. As
new members are added to the collection, clients or end users can use
the semantics to determine where to position the new members in the
ordering.
5.3 Setting the Position of a Collection Member
5.3.1 Overview
When a new member is added to a collection with a client-maintained
ordering (for example, with PUT, MKREF, or MKCOL), its position in the
ordering can be set with the new Position header (defined in Section
6.6). The Position header allows the client to specify that the member
should be first in the collection's ordering, last in the collection's
ordering, immediately before some other binding in the collection's
ordering, or immediately after some other binding in the collection's
ordering.
5.3.2 Status Codes
409 (Conflict): The request specifies a position that is before or after
a URI that is not an internal member URI of the collection, or before or
after itself.
425 (Unordered Collection): The request specifies a collection position
in an unordered collection or in a collection with a server-maintained
ordering.
5.3.3 Examples: Setting the Position of a Collection Member
>>Request:
MKREF /~whitehead/dav/spec08.ref HTTP/1.1
HOST: www.ics.uci.edu
Ref-Target: http://www.ics.uci.edu/i-d/draft-webdav-protocol-08.txt
Position: After <requirements.html>
>>Response:
HTTP/1.1 201 Created
This request resulted in the creation of a new referential resource at
www.ics.uci.edu/~whitehead/dav/spec08.ref, which points to the resource
identified by the Ref-Target header. The Position header in this
example caused the server to set its position in the ordering of the
/~whitehead/dav/ collection immediately after requirements.html.
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>>Request:
MOVE /i-d/draft-webdav-protocol-08.txt HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/~whitehead/dav/draft-webdav-
protocol-08.txt
Position: First
>>Response:
HTTP/1.1 425 Unordered Collection
In this case, the server returned a 425 (Unordered Collection) status
code because the /~whitehead/dav/ collection is an unordered collection.
Consequently, the server was unable to satisfy the Position header.
5.4 Changing the Semantics of a Collection Ordering
After a collection has been created, a client can change its ordering
semantics, or change an ordered collection to an unordered collection or
vice versa, by using PROPPATCH to change the value of its
DAV:orderingtype property (defined in Section 7.5). If the new value
identifies a client-maintained ordering, the client is then responsible
for updating the collection's ordering according to the new semantics.
If it identifies a server-maintained ordering, the server MUST reorder
the collection according to the new semantics. PROPPATCH is defined in
[WebDAV], Section 7.2.
5.5 Changing the Position of a Collection Member
5.5.1 ORDERPATCH Method
The ORDERPATCH method alters the ordering of bindings in the collection
identified by the Request-URI, based on instructions in the order XML
element. The order XML element identifies the bindings whose positions
are to be changed, and describes their new positions in the ordering.
Each new position can be specified as first in the ordering, last in the
ordering, immediately before some other binding, or immediately after
some other binding.
The server MUST apply the changes in the order they appear in the order
XML element. The server MUST either apply all the changes or apply none
of them. If any error occurs during processing, all executed changes
MUST be undone and a proper error result returned.
5.5.2 Status Codes
Since multiple changes can be requested in a single ORDERPATCH request,
the server MUST return a 207 (Multi-Status) response, as defined in
[WebDAV].
The following are examples of response codes one would expect to be used
in a 207 (Multi-Status) response for this method:
200 (OK): The change in ordering was successfully made.
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409 (Conflict): The request specifies a position that is before or after
a URI that is not an internal member URI of the collection, or before or
after itself.
425 (Unordered Collection): The request specifies a collection position
in an unordered collection or in a collection with a server-maintained
ordering.
A request to reposition a binding at the same place in the ordering is
not an error.
5.5.3 Example: Changing Positions in an Ordered Collection
Consider a collection /coll-1/ with bindings ordered as follows:
nunavut.map
nunavut.img
baffin.map
baffin.desc
baffin.img
iqaluit.map
nunavut.desc
iqaluit.img
iqaluit.desc
>> Request:
ORDERPATCH /coll-1/ HTTP/1.1
Host: www.nunanet.com
Content-Type: text/xml
Content-Length: xxx
<?xml version="1.0" ?>
<d:order xmlns:d="DAV:">
<d:ordermember>
<d:href>nunavut.desc</d:href>
<d:position>
<d:after>
<d:href>nunavut.map</d:href>
</d:after>
</d:position>
</d:ordermember>
<d:ordermember>
<d:href>iqaluit.img</d:href>
<d:position>
<d:last/>
</d:position>
</d:ordermember>
</d:order>
>> Response:
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
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Content-Length: xxx
<?xml version="1.0" ?>
<d:multistatus xmlns:d="DAV:">
<d:response>
<d:href>http://www.nunanet.com/coll-1/nunavut.desc</d:href>
<d:status>HTTP/1.1 200 OK</d:status>
</d:response>
<d:response>
<d:href>http://www.nunanet.com/coll-1/iqaluit.img</d:href>
<d:status>HTTP/1.1 200 OK</d:status>
</d:response>
</d:multistatus>
If the href elements are relative URIs, as in this example, they are
interpreted relative to the collection that is being reordered. In this
example, after the request has been processed, the collection's ordering
is as follows:
nunavut.map
nunavut.desc
nunavut.img
baffin.map
baffin.desc
baffin.img
iqaluit.map
iqaluit.desc
iqaluit.img
5.5.4 Example: Failure of an ORDERPATCH Request
Consider a collection /coll-1/ with bindings ordered as follows:
nunavut.map
nunavut.img
baffin.map
baffin.desc
baffin.img
iqaluit.map
nunavut.desc
iqaluit.img
iqaluit.desc
>> Request:
ORDERPATCH /coll-1/ HTTP/1.1
Host: www.nunanet.com
Content-Type: text/xml
Content-Length: xxx
<?xml version="1.0" ?>
<d:order xmlns:d="DAV:">
<d:ordermember>
<d:href>nunavut.desc</d:href>
<d:position>
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<d:after>
<d:href>nunavut.map</d:href>
</d:after>
</d:position>
</d:ordermember>
<d:ordermember>
<d:href>iqaluit.map</d:href>
<d:position>
<d:after>
<d:href>pangnirtung.img</d:href>
</d:after>
</d:position>
</d:ordermember>
</d:order>
>> Response:
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxx
<?xml version="1.0" ?>
<d:multistatus xmlns:d="DAV:">
<d:response>
<d:href>http://www.nunanet.com/coll-1/nunavut.desc</d:href>
<d:status>HTTP/1.1 424 Failed Dependency</d:status>
</d:response>
<d:response>
<d:href>http://www.nunanet.com/coll-1/iqaluit.map</d:href>
<d:status>HTTP/1.1 409 Conflict</d:status>
<d:responsedescription>pangnirtung.img is not a collection
member.</d:responsedescription>
</d:response>
</d:multistatus>
In this example, the client attempted to position iqaluit.map after a
binding that is not contained in the collection /coll-1/. The server
responded to this client error with a 409 (Conflict) status code.
Because ORDERPATCH is an atomic method, the request to reposition
nunavut.desc (which would otherwise have succeeded) failed with a 424
(Failed Dependency) status code.
6 Headers
6.1 All-Bindings Request Header
All-Bindings = "All-Bindings" ":"
The All-Bindings request header may be used with DELETE requests to
instruct the server to remove all bindings to the resource identified by
the Request-URI.
6.2 Ref-Target Entity Header
Ref-Target = "Ref-Target" ":" (absoluteURI | relativeURI)
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The Ref-Target header is defined primarily for use with MKREF requests
to identify the target resource of the new redirect reference being
created.
6.3 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 references (see Sections 4.1,
and 4.3.7). The possible values of this header are DAV:redirectref, and
ext-resource-type. The ext-resource-type production is provided for
extensibility.
6.4 Passthrough Request Header
Passthrough = "Passthrough" ":" ("T" | "F")
The optional Passthrough header can be used on any request to a redirect
reference. If the Passthrough header has the value "F", the request
MUST be applied to the reference 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, the server SHOULD ignore it. If the
Passthrough header with the value "F" appears in a POST or ORDERPATCH
request to a reference, the server MUST respond with a 400 (Bad
Request).
6.5 Ordered Entity Header
Ordered = "Ordered" ":" ("DAV:unordered" | "DAV:custom" | absoluteURI)
The Ordered header may be used with MKCOL to request that the new
collection be ordered and to specify its ordering semantics. A value of
"DAV:unordered" indicates that the collection is not ordered. A value of
"DAV:custom" indicates that the collection is to be ordered, but the
semantics of the ordering is not being advertised. Any other
absoluteURI value indicates that the collection is ordered, and
identifies the semantics of the ordering.
6.6 Position Request Header
Position = "Position" ":" ("First" | "Last" |
(("Before" | "After") Generic-Coded-url))
Generic-Coded-url = "<" (absoluteURI | relativeURI) ">"
absoluteURI and relativeURI are defined in [URI].
The Position header may be used with any method that adds a binding to a
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collection with a client-maintained ordering, to tell the server where
in the collection ordering to position the new binding being added to
the collection.
If the Generic-Coded-url is a relative URL, it is interpreted relative
to the collection to which the new binding is being added.
The server MUST insert the new binding into the ordering at the location
specified in the Position header, if one is present (and if the
collection has a client-maintained ordering).
The "First" keyword indicates the new binding is put in the beginning
position in the collection's ordering, while "Last" indicates the new
binding is put in the final position in the collection's ordering. The
"Before" keyword indicates the new binding is added to the collection's
ordering immediately prior to the position of the binding identified in
the Generic-Coded-url. Likewise, the "After" keyword indicates the new
binding is added to the collection's ordering immediately following the
position of the binding identified in the Generic-Coded-url.
If the request is replacing an existing resource, and the Position
header is present, the server MUST remove the binding from its previous
position, and then insert it at the requested position.
If the Position request header is not used when adding a binding to a
collection with a client-maintained ordering, then:
o If the request is replacing an existing resource, the server MUST
preserve the present ordering.
o If the request is adding a new binding to the collection, the server
MUST append the new binding to the end of the ordering.
If an attempt is made to use the Position header on a collection that is
unordered or that has a server-maintained ordering, the server MUST fail
the request with a 409 (Conflict) status code.
7 Status Codes
7.1 506 Loop Detected
The 506 (Loop Detected) status code indicates that the server detected
an infinite loop while processing a request with "Depth: infinity".
7.2 425 Unordered Collection
The 425 (Unordered Collection) status code indicates that the client
attempted to set the position of an internal collection member in an
unordered collection or in a collection with a server-maintained
ordering.
8 Properties
8.1 reftarget Property
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Name: reftarget
Namespace: DAV:
Purpose: A property of redirect references 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: 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 (#PCDATA)>
8.2 location 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 references, 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 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 9 below. This property is not expected
to be stored on the reference. 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 >
8.3 bindings Property
Name: bindings
Namespace: DAV:
Purpose: Enables clients to discover, for any resource, what bindings
point to it and what collections contain those bindings.
This is an optional property. If present, it is a read-only
property, maintained by the server.
Value: List of href / segment pairs for all of the bindings that
associate URI segments with the resource. The href is an
absolute URI for one URI mapping of the collection
containing the binding. The segment is the URI segment that
identifies the binding within that collection. If a binding
belongs to a collection that has multiple URI mappings, only
one URI mapping for that collection should be reported.
<!ELEMENT bindings ((href, segment)*)>
8.4 orderingtype Property
Name: orderingtype
Namespace: DAV:
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Purpose: Indicates whether the collection is ordered and, if so,
uniquely identifies the semantics of the ordering being
used. May also point to an explanation of the semantics in
human and / or machine-readable form. At a minimum, this
allows human users who add members to the collection to
understand where to position them in the ordering.
Value: unordered for an unordered collection, or a URI that
uniquely identifies the semantics of the collection's
ordering. The value custom indicates that the collection is
ordered, but the semantics are not being advertised.
<!ELEMENT orderingtype (unordered | custom | href) >
9 XML Elements
9.1 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.
<!ELEMENT redirectref EMPTY >
9.2 segment XML Element
Name: segment
Namespace: DAV:
Purpose: The segment that names a binding, used in the DAV:bindings
property.
Value: segment ; as defined in section 3.3 of [URI].
<!ELEMENT segment (#PCDATA)>
9.3 unordered XML Element
Name: unordered
Namespace: DAV:
Purpose: A value of the DAV:orderingtype property that indicates that
the collection is not ordered. That is, the client cannot
depend on the repeatability of the ordering of results from
a PROPFIND request.
<!ELEMENT unordered EMPTY >
9.4 custom XML Element
Name: custom
Namespace: DAV:
Purpose: A value of the DAV:orderingtype property that indicates that
the collection is ordered, but the semantics of the ordering
are not being advertised.
<!ELEMENT custom EMPTY >
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9.5 order XML Element
Name: order
Namespace: DAV:
Purpose: For use with the new ORDERPATCH method. Describes a change
to be made in a collection ordering.
Value: A description of the new positions of the bindings a
collection contains in its ordering.
<!ELEMENT order (ordermember+) >
9.6 ordermember XML Element
Name: ordermember
Namespace: DAV:
Purpose: Occurs in the order XML Element, and describes the new
position of a single binding in the collection's ordering.
Value: An href containing a binding's path segment, and a
description of its new position in the ordering. The href
XML element is defined in [WebDAV], Section 11.3.
<!ELEMENT ordermember (href, position) >
9.7 position XML Element
Name: position
Namespace: DAV:
Purpose: Occurs in the ordermember XML element. Describes the new
position in a collection's ordering of one of the bindings
it contains.
Value: The new position can be described as first in the
collection's ordering, last in the collection's ordering,
immediately before some other binding, or immediately after
some other binding.
<!ELEMENT position (first | last | before | after)>
9.8 first XML Element
Name: first
Namespace: DAV:
Purpose: Occurs in the position XML element. Specifies that the
binding should be placed first in the collection's ordering.
<!ELEMENT first EMPTY >
9.9 last XML Element
Name: last
Namespace: DAV:
Purpose: Occurs in the position XML element. Specifies that the
binding should be placed last in the collection's ordering.
<!ELEMENT last EMPTY >
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9.10 before XML Element
Name: before
Namespace: DAV:
Purpose: Occurs in the position XML element. Specifies that the
binding should be placed immediately before the binding in
the enclosed href XML element in the collection's ordering.
Value: href of the member it precedes in the ordering
<!ELEMENT before href >
9.11 after XML Element
Name: after
Namespace: DAV:
Purpose: Occurs in the position XML element. Specifies that the
binding should be placed immediately after the binding in
the enclosed href XML element in the collection's ordering.
Value: href of the member it follows in the ordering
<!ELEMENT after href >
9.12 options XML Element
Name: options
Namespace: DAV:
Purpose: Used in OPTIONS requests to ask for more detailed
information about capabilities than can be provided in the
DAV: response header. Used in OPTIONS responses to provide
that information.
Value: List of elements identifying or providing the additional
information desired.
<!ELEMENT options (orderingoptions | ANY)+ >
9.13 orderingoptions XML Element
Name: orderingoptions
Namespace: DAV:
Purpose: Used in OPTIONS requests to ask for the list of server-
maintained orderings that can be supported at the request-
URI. Used in OPTIONS responses to provide that information.
These values can be used in the Ordered header or the
DAV:orderingtype property to request that a particular
server-maintained ordering be applied to the collection.
Value: EMPTY on requests. On responses, it is the list of server-
maintained orderings available for the request-URI.
<!ELEMENT orderingoptions ( (#PCDATA)+ | EMPTY) >
10 Extensions to the DAV:response XML Element for Multi-Status Responses
As described in Sections 4.6 and 4.9, the DAV:location 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
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INTERNET-DRAFT WebDAV Collections Protocol June 1999
to the target resource of a redirect reference.
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?) >
11 Capability Discovery
11.1 Compliance Classes
This specification defines OPTIONAL extensions to [WebDAV]. Since
resource sharing and ordering are independent capabilities, a resource
MAY support either, both, or neither of these capabilities. A resource
that provides resource sharing MUST support both bindings and redirect
references. A response to an OPTIONS request MUST indicate which of
these capabilities the resource supports.
This specification defines three new methods: BIND and MKREF in support
of shared resources, and ORDERPATCH in support of ordering. The
response MUST indicate which of these methods the resource allows. In
addition, the response MUST include the DAV header, as described in
Sections 9.1 and 15 of [WebDAV]. Two new compliance classes are defined
here for use with the DAV header: sharing and orderedcoll.
When responding to an OPTIONS request, only a collection or a null
resource can include orderedcoll in the value of the DAV header. By
including orderedcoll, the resource indicates that its bindings can be
ordered. It implies nothing about whether any collections identified by
its internal member URIs can be ordered.
When responding to an OPTIONS request, any type of resource can include
sharing in the value of the DAV header. Including sharing indicates
that the server permits a redirect reference or a binding at the request
URI.
11.2 Example: Discovery of Compliance Classes
>> Request:
OPTIONS /somecollection/ HTTP/1.1
HOST: somehost.org
>> Response:
HTTP/1.1 200 OK
Date: Tue, 20 Jan 1998 20:52:29 GMT
Connection: close
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Accept-Ranges: none
Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE, MKCOL,
PROPFIND, PROPPATCH, LOCK, UNLOCK, BIND, ORDERPATCH
Public: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE, MKCOL,
PROPFIND, PROPPATCH, LOCK, UNLOCK, BIND, MKREF, ORDERPATCH
DAV: 1, 2, sharing, orderedcoll
The DAV header in the response indicates that the resource
/somecollection/ is level 1 and level 2 compliant, as defined in
[WebDAV]. In addition, /somecollection/ supports ordering and resource
sharing. The Allow header indicates that BIND and ORDERPATCH requests
can be submitted to /somecollection/. Since a redirect reference is not
a collection, a MKREF request with /somecollection/ as its Request-URI
would fail, but the Public header shows that other Request-URIs on the
server do support MKREF.
11.3 Additional Advanced Collections Capabilities
Clients may need detailed information about specific areas of advanced
collections functionality. This information can be requested by sending
an OPTIONS request with an XML body that includes a DAV:options element.
The DAV:options element contains a list of empty elements identifying
the information the client needs.
As described in Section 5.2, servers may offer a set of server-
maintained orderings on collections. Clients can discover the list of
server-maintained orderings available for the request-URI by including
an empty DAV:orderingoptions element in the DAV:options element. The
response will include a DAV:orderingoptions element with the list of
supported server-maintained orderings. Servers SHOULD advertise the
server-maintained orderings available using this mechanism.
11.4 Example: Discovery of Ordering Options
>> Request:
OPTIONS /somecollection/ HTTP/1.1
HOST: somehost.org
<?xml version="1.0" ?>
<D:options xmlns:D="DAV:">
<D:orderingoptions/>
</D:options>
>> 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, BIND, ORDERPATCH
Public: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE, MKCOL,
PROPFIND, PROPPATCH, LOCK, UNLOCK, BIND, MKREF, ORDERPATCH
DAV: 1, sharing, orderedcoll
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<?xml version="1.0" ?>
<D:options xmlns:D="DAV:">
<D:orderingoptions xmlns:X="Xerox:">
<X:author-ascending/>
<X:title-ascending/>
<X:date-descending/>
</D:orderingoptions>
</D:options>
This response indicates that the resource /somecollection/ is level 1
compliant, as defined in [WebDAV]. In addition, /somecollection/
supports ordering and resource sharing. The client also asked for a
list of the server-maintained orderings that are supported for
/somecollection/. The response indicates that the orderings
Xerox:author-ascending, Xerox:title-ascending, and Xerox:date-descending
are supported.
12 Security Considerations
This section is provided to detail issues concerning security
implications of which WebDAV applications need to be aware.
All of the security considerations of HTTP/1.1 and the WebDAV
Distributed Authoring Protocol specification also apply to WebDAV
collections. In addition, resource sharing and ordered collections
introduce several new security concerns and increase the risk of some
existing threats. These issues are detailed below.
12.1 Privacy Concerns
By creating redirect references on a trusted server, it is 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.)
The same risk exists for bindings, although it is less likely that
servers will support cross-server bindings.
12.2 Redirect Loops
Although redirect loops were already possible in HTTP 1.1, the
introduction of the BIND and MKREF methods creates a new avenue for
clients to create loops accidentally or maliciously. If the binding or
reference and its target are on the same server, the server may be able
to detect MKREF and BIND requests that would create loops. See also
[HTTP], Section 10.3 "Redirection 3xx." Servers are required to detect
loops caused by bindings to collections during the processing of any
requests with "Depth: infinity".
12.3 Redirect References, Bindings, 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
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introduction of BIND and MKREF creates a new avenue for similar denial
of service attacks. Clients can now create bindings and redirect
references at heavily used sites to target locations that were not
designed for heavy usage.
12.4 Private Locations May Be Revealed
There are several ways that redirect references may reveal information
about directory structures. First, the DAV:reftarget property of every
redirect reference contains the URI of the target resource. Anyone who
has access to the reference 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
references, 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.
In addition, if backpointers are maintained on the target resource, the
owners of bindings face these same risks. The directory structures
where bindings are located are revealed to anyone who has access to the
DAV:bindings property on a target resource. Moving a binding may reveal
its new location to anyone with access to DAV:bindings on its target
resource.
12.5 DAV:bindings and Denial of Service
If the server maintains the DAV:bindings property in response to
bindings created in other administrative domains, it is exposed to
hostile attempts to make it devote resources to adding bindings to the
list.
12.6 Denial of Service and DAV:orderingtype
There may be some risk of denial of service at sites that are advertised
in the DAV:orderingtype property of collections. However, it is
anticipated that widely-deployed applications will use hard-coded values
for frequently-used ordering semantics rather than looking up the
semantics at the location specified by DAV:orderingtype. In addition,
Section 5.2 discourages clients from looking up the semantics at that
location.
13 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
Slein et al. Page 49
INTERNET-DRAFT WebDAV Collections Protocol June 1999
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
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].
14 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.
15 Copyright
To be supplied by the RFC Editor.
16 Intellectual Property
To be supplied by the RFC Editor.
17 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.
18 References
18.1 Normative 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
Slein et al. Page 50
INTERNET-DRAFT WebDAV Collections Protocol June 1999
Language (XML)." World Wide Web Consortium Recommendation REC-xml-
19980210. http://www.w3.org/TR/1998/REC-xml-19980210.
[HTTP] R. Fielding, J. Gettys, J. Mogul, H. Frystyk, T. Berners-Lee,
"Hypertext Transfer Protocol -- HTTP/1.1." RFC 2068. UC Irvine, DEC,
MIT/LCS. January, 1997.
[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.
18.2 Informational References
[DASL] Saveen Reddy, D. Jensen, Surendra Reddy, R. Henderson, J. Davis,
A. Babich, "DAV Searching & Locating." Draft-reddy-dasl-protocol-03.
Internet Draft, work in progress. Microsoft, Novell, Oracle, Netscape,
Xerox, Filenet. November, 1998.
[CollReq] J. Slein, J. Davis, "Requirements for Advanced Collection
Functionality in WebDAV." Draft-ietf-webdav-collection-reqts-02.
Internet Draft, work in progress. Xerox. February, 1999.
19 Authors' Addresses
J. Slein
Xerox Corporation
800 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
170 Capp Street
San Francisco, CA 94110
Email: jrd3@alum.mit.edu
G. Clemm
Rational Software Corporation
20 Maguire Road
Lexington, MA 02173-3104
Email: gclemm@rational.com
C. Fay
FileNet Corporation
3565 Harbor Boulevard
Costa Mesa, CA 92626-1420
Email: cfay@filenet.com
J. Crawford
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INTERNET-DRAFT WebDAV Collections Protocol June 1999
IBM
Email: ccjason@us.ibm.com
T. Chihaya
DataChannel, Inc.
155 108th Ave. N.E., Suite 400
Bellevue, WA 98004
Email: Tyson@DataChannel.com
20 Appendices
20.1 Appendix 1: Extensions to the WebDAV Document Type Definition
<!--============= XML Elements from Section 8 ================-->
<!ELEMENT redirectref EMPTY >
<!ELEMENT segment (#PCDATA)>
<!ELEMENT unordered EMPTY >
<!ELEMENT custom EMPTY >
<!ELEMENT order (ordermember+) >
<!ELEMENT ordermember (href, position) >
<!ELEMENT position (first | last | before | after)>
<!ELEMENT first EMPTY >
<!ELEMENT last EMPTY >
<!ELEMENT before href >
<!ELEMENT after href >
<!ELEMENT options (refintegrityoptions | orderingoptions)+ >
<!ELEMENT orderingoptions ( (#PCDATA)+ | EMPTY) >
<!--============= Property Elements from Section 7 ==================-->
<!ELEMENT reftarget (#PCDATA)>
<!ELEMENT location href>
<!ELEMENT bindings ((href, segment)*)>
<!ELEMENT orderingtype (arbitrary | custom | href) >
<!--====== Changes to the DAV:response Element from Section 9 ====-->
<!ELEMENT response (href, ((href*, status, prop?) | (propstat+)),
responsedescription?) >
Expires December 18, 1999
Slein et al. Page 52
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| Authors |
Jim Whitehead
,
Judith Slein
,
Jim Davis
,
Alan Babich
,
Charles R. Fay
,
Geoffrey M. Clemm
,
T. Chihaya
Email authors |
||
| RFC stream |
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| Intended RFC status | (None) | ||
| Other formats | |||
| Additional resources | Mailing list discussion |