One document matched: draft-ietf-webdav-bind-02.txt
Differences from draft-ietf-webdav-bind-01.txt
INTERNET-DRAFT G. Clemm
draft-ietf-webdav-bind-02 IBM
J. Crawford
IBM Research
J. Reschke
Greenbytes
J. Slein
Xerox
E.J. Whitehead
U.C. Santa Cruz
Expires December 27, 2003 June 27, 2003
Binding Extensions to WebDAV
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of RFC 2026, Section 10.
Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other groups
may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This specification defines bindings, and the BIND method for creating
multiple bindings to the same resource. Creating a new binding to a
resource causes at least one new URI to be mapped to that resource.
Servers are required to insure the integrity of any bindings that they
allow to be created.
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Table of Contents
1 INTRODUCTION............................................3
1.1 Terminology...........................................4
1.2 Rationale for Distinguishing Bindings from URI
Mappings..............................................6
1.3 Method Preconditions and Postconditions...............6
2 OVERVIEW OF BINDINGS....................................7
2.1 Bindings to Collections...............................7
2.2 URI Mappings Created by a new Binding.................8
2.3 COPY and Bindings.....................................9
2.4 DELETE and Bindings..................................10
2.5 MOVE and Bindings....................................10
2.6 Determining Whether Two Bindings Are to the Same
Resource.............................................11
2.7 Discovering the Bindings to a Resource...............12
3 PROPERTIES.............................................12
3.1 DAV:resource-id Property.............................12
3.2 DAV:parent-set Property..............................13
4 BIND METHOD............................................13
4.1 Example: BIND........................................15
5 UNBIND METHOD..........................................15
5.1 Example: UNBIND......................................16
6 REBIND METHOD..........................................17
6.1 Example: REBIND......................................18
7 ADDITIONAL STATUS CODES................................19
7.1 506 Loop Detected....................................19
8 SECURITY CONSIDERATIONS................................20
8.1 Privacy Concerns.....................................20
8.2 Redirect Loops.......................................21
8.3 Bindings, and Denial of Service......................21
8.4 Private Locations May Be Revealed....................21
8.5 DAV:parent-set and Denial of Service.................21
9 INTERNATIONALIZATION CONSIDERATIONS....................21
10 IANA CONSIDERATIONS..................................21
11 INTELLECTUAL PROPERTY................................22
12 ACKNOWLEDGEMENTS.....................................22
13 REFERENCES...........................................22
14 AUTHORS' ADDRESSES...................................23
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1 INTRODUCTION
This specification extends the WebDAV Distributed Authoring
Protocol to enable clients to create new access paths to existing
resources. This capability is useful for several reasons:
URIs of WebDAV-compliant resources are hierarchical and correspond
to a hierarchy of collections in resource space. The WebDAV
Distributed Authoring Protocol makes it possible to organize these
resources into hierarchies, placing them into groupings, known as
collections, which are more easily browsed and manipulated than a
single flat collection. However, hierarchies require
categorization decisions that locate resources at a single location
in the hierarchy, a drawback when a resource has multiple valid
categories. For example, in a hierarchy of vehicle descriptions
containing collections for cars and boats, a description of a
combination car/boat vehicle could belong in either collection.
Ideally, the description should be accessible from both. Allowing
clients to create new URIs that access the existing resource lets
them put that resource into multiple collections.
Hierarchies also make resource sharing more difficult, since
resources that have utility across many collections are still
forced into a single collection. For example, the mathematics
department at one university might create a collection of
information on fractals that contains bindings to some local
resources, but also provides access to some resources at other
universities. For many reasons, it may be undesirable to make
physical copies of the shared resources on the local server: to
conserve disk space, to respect copyright constraints, or to make
any changes in the shared resources visible automatically. Being
able to create new access paths to existing resources in other
collections or even on other servers is useful for this sort of
case.
The BIND method defined here provides a mechanism for allowing
clients to create alternative access paths to existing WebDAV
resources. HTTP and WebDAV methods are able to work because there
are mappings between URIs and resources. A method is addressed to
a URI, and the server follows the mapping from that URI to a
resource, applying the method to that resource. Multiple URIs may
be mapped to the same resource, but until now there has been no way
for clients to create additional URIs mapped to existing resources.
BIND lets clients associate a new URI with an existing WebDAV
resource, and this URI can then be used to submit requests to the
resource. Since URIs of WebDAV resources are hierarchical, and
correspond to a hierarchy of collections in resource space, the
BIND method also has the effect of adding the resource to a
collection. As new URIs are associated with the resource, it
appears in additional collections.
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A BIND request does not create a new resource, but simply makes
available a new URI for submitting requests to an existing
resource. The new URI is indistinguishable from any other URI when
submitting a request to a resource. Only one round trip is needed
to submit a request to the intended target. Servers are required
to enforce the integrity of the relationships between the new URIs
and the resources associated with them. Consequently, it may be
very costly for servers to support BIND requests that cross server
boundaries.
This specification is organized as follows. Section 1.1 defines
terminology used in the rest of the specification, while Section
1.3 overviews bindings. Section 3 defines the new properties
needed to support multiple bindings to the same resource. Section
4 specifies the BIND method, used to create multiple bindings to
the same resource. Section 5 specifies the UNBIND method, used to
remove a binding to a resource. Section 6 specifies the REBIND
method, used to move a binding to another collection.
1.1 Terminology
The terminology used here follows and extends that in the WebDAV
Distributed Authoring Protocol specification [RFC2518].
This document uses XML DTD fragments as a purely notational
convention. WebDAV request and response bodies cannot be validated
due to the specific extensibility rules defined in section 23 of
[RFC2518] and due to the fact that all XML elements defined by this
specification use the XML namespace name "DAV:". In particular:
- Element names use the "DAV:" namespace.
- Element ordering is irrelevant.
- Extension elements/attributes (elements/attributes not already
defined as valid child elements) may be added anywhere, except when
explicitly stated otherwise.
URI Mapping
A relation between an absolute URI and a resource. For an absolute
URI U and the resource it identifies R, the URI mapping can be
thought of as (U => R). 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.
Mapping a resource to an "http" scheme URI makes it possible to
submit HTTP protocol requests to the resource using the URI.
Path Segment
Informally, the characters found between slashes ("/") in a URI.
Formally, as defined in section 3.3 of [RFC2396].
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Binding
A relation between a single path segment (in a collection) and a
resource. A binding is part of the state of a collection. If two
different collections contain a binding between the same path
segment and the same resource, these are two distinct bindings. So
for a collection C, a path segment S, and a resource R, the binding
can be thought of as C:(S -> R). Bindings create URI mappings, and
hence allow requests to be sent to a single resource from multiple
locations in a URI namespace. For example, given a collection C
(accessible through the URI http://www.example.com/CollX), a path
segment S (equal to "foo.html"), and a resource R, then creating
the binding C: (S -> R) makes it possible to use the URI
http://www.example.com/CollX/foo.html to access R.
Collection
A resource that contains, as part of its state, a set of bindings
that identify internal member resources.
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Internal Member URI
The URI that identifies an internal member of a collection, and
that consists of the URI for the collection, followed by a slash
character ('/'), followed by the path segment of the binding for
that internal member.
1.2 Rationale for Distinguishing Bindings from URI Mappings
In [RFC2518], the state of a collection is defined as containing a
list of internal member URIs. If there are multiple mappings to a
collection, then the state of the collection is different when you
refer to it via a different URI. This is undesirable, since ideally
a collection's membership should remain the same, independent of
which URI was used to reference it.
The notion of binding is introduced to separate the final segment
of a URI from its parent collection’s contribution. This done, a
collection can be defined as containing a set of bindings, thus
permitting new mappings to a collection without modifying its
membership. The authors of this specification anticipate and
recommend that future revisions of [RFC2518] will update the
definition of the state of a collection to correspond to the
definition in this document.
1.3 Method Preconditions and Postconditions
A "precondition" of a method describes the state on the server that
must be true for that method to be performed. A "postcondition" of
a method describes the state on the server that must be true after
that method has completed. If a method precondition or
postcondition for a request is not satisfied, the response status
of the request MUST be either 403 (Forbidden) if the request should
not be repeated because it will always fail, or 409 (Conflict) if
it is expected that the user might be able to resolve the conflict
and resubmit the request.
In order to allow better client handling of 403 and 409 responses,
a distinct XML element type is associated with each method
precondition and postcondition of a request. When a particular
precondition is not satisfied or a particular postcondition cannot
be achieved, the appropriate XML element MUST be returned as the
child of a top-level DAV:error element in the response body, unless
otherwise negotiated by the request. In a 207 Multi-Status
response, the DAV:error element would appear in the appropriate
DAV:responsedescription element.
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2 OVERVIEW OF BINDINGS
Bindings are part of the state of a collection. They define the
internal members of the collection, and the names of those internal
members.
Bindings are added and removed by a variety of existing HTTP
methods. A method that creates a new resource, such as PUT, COPY,
and MKCOL, adds a binding. A method that deletes a resource, such
as DELETE, removes a binding. A method that moves a resource (e.g.
MOVE) both adds a binding (in the destination collection) and
removes a binding (in the source collection). The BIND method
introduced here provides a mechanism for adding a second binding to
an existing resource. There is no difference between an initial
binding added by PUT, COPY, or MKCOL, and additional bindings added
with BIND.
It would be very undesirable if one binding could be destroyed as a
side effect of operating on the resource through a different
binding. In particular, the removal of one binding to a resource
(e.g. with a DELETE or a MOVE) MUST NOT disrupt another binding to
that resource, e.g. by turning that binding into a dangling path
segment. The server MUST NOT reclaim system resources after
removing one binding, while other bindings to the resource remain.
In other words, the server MUST maintain the integrity of a
binding.
2.1 Bindings to Collections
Bindings to collections can result in loops, which servers MUST
detect when processing "Depth: infinity" requests. It is sometimes
possible to complete an operation in spite of the presence of a
loop. However, the 506 (Loop Detected) status code is defined in
Section 5 for use in contexts where an operation is terminated
because a loop was encountered.
Creating a new binding to a collection makes each resource
associated with a binding in that collection accessible via a new
URI, and thus creates new URI mappings to those resources but no
new bindings.
For example, suppose a new binding CollY is created for collection
C1 in the figure below. It immediately becomes possible to access
resource R1 using the URI /CollY/x.gif and to access resource R2
using the URI /CollY/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
/CollY/x.gif and /CollY/y.jpg.
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+-------------------------+
| Root Collection |
| bindings: |
| CollX CollY |
+-------------------------+
| /
| /
| /
+------------------+
| Collection C1 |
| bindings: |
| x.gif y.jpg |
+------------------+
| \
| \
| \
+-------------+ +-------------+
| Resource R1 | | Resource R2 |
+-------------+ +-------------+
2.2 URI Mappings Created by a new Binding
Suppose a binding from "Binding-Name" to resource R to be added to
a collection, C. Then if C-MAP is the set of URIs that were mapped
to C before the BIND request, then for each URI "C-URI" in C-MAP,
the URI "C-URI/Binding-Name" is mapped to resource R following the
BIND request.
For example, if a binding from "foo.html" to R is added to a
collection C, and if the following URIs are mapped to C:
http://www.example.com/A/1/
http://example.com/A/one/
then the following new mappings to R are introduced:
http://www.example.com/A/1/foo.html
http://example.com/A/one/foo.html
Note that if R is a collection, additional URI mappings are created
to the descendents of R. Also, note that if a binding is made in
collection C to C itself (or to a parent of C), an infinite number
of mappings are introduced.
For example, if a binding from "myself" to C is then added to C,
the following infinite number of additional mappings to C are
introduced:
http://www.example.com/A/1/myself
http://www.example.com/A/1/myself/myself
...
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and the following infinite number of additional mappings to R are
introduced:
http://www.example.com/A/1/myself/foo.html
http://www.example.com/A/1/myself/myself/foo.html
...
2.3 COPY and Bindings
As defined in Section 8.8 of [RFC2518], 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,
and the destination resource. The new binding is added to its
parent collection, identified by the Destination header minus its
final segment.
The following figure shows an example: Suppose that a COPY is
issued to URI-3 for resource R (which is also mapped to URI-1 and
URI-2), with the Destination header set to URI-X. 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 URI-X and the new resource
(although other URI mappings may also have been created).
URI-1 URI-2 URI-3 URI-X
| | | |
| | | <---- URI Mappings ----> |
| | | |
+---------------------+ +------------------------+
| Resource R | | Resource R' |
+---------------------+ +------------------------+
It might be thought that a COPY request with "Depth: 0" on a
collection would duplicate its bindings, since bindings are part of
the collection's state. This is not the case, however. The
definition of Depth in [RFC2518] makes it clear that a "Depth: 0"
request does not apply to a collection's members. Consequently, a
COPY with "Depth: 0" does not duplicate the bindings contained by
the collection.
If a COPY causes one or more existing resources to be updated, the
bindings to those resources MUST be unaffected by the COPY. Using
the preceding example, suppose that a COPY is issued to URI-X for
resource R', with the Destination header set to URI-2. The content
and dead properties of resource R would be updated to be a copy of
those of resource R', but the mappings from URI-1, URI-2, and URI-3
to resource R remain unaffected.
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2.4 DELETE and Bindings
When there are multiple bindings to a resource, a DELETE applied to
that resource MUST NOT remove any bindings to that resource other
than the one identified by the request URI. For example, suppose
the collection identified by the URI "/a" has a binding named "x"
to a resource R, and another collection identified by "/b" has a
binding named "y" to the same resource R. Then a DELETE applied to
"/a/x" removes the binding named "x" from "/a" but MUST NOT remove
the binding named "y" from "/b" (i.e. after the DELETE, "/y/b"
continues to identify the resource R). In particular, although
Section 8.6.1 of [RFC2518] 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", a
server that supports the binding protocol MUST NOT follow this
requirement.
When DELETE is applied to a collection, it MUST NOT modify the
membership of any other collection that is not itself a member of
the collection being deleted. For example, if both "/a/.../x" and
"/b/.../y" identify the same collection, C, then applying DELETE to
"/a" MUST NOT delete an internal member from C or from any other
collection that is a member of C, because that would modify the
membership of "/b".
If a collection supports the UNBIND method (see Section 5), a
DELETE of an internal member of a collection MAY be implemented as
an UNBIND request. In this case, applying DELETE to a Request-URI
has the effect of removing the binding identified by the final
segment of the Request-URI from the collection identified by the
Request-URI minus its final segment. Although [RFC2518] allows a
DELETE to be a non-atomic operation, when the DELETE operation is
implemented as an UNBIND, the operation is atomic. In particular,
a DELETE on a hierarchy of resources is simply the removal of a
binding to the collection identified by the Request-URI.
2.5 MOVE and Bindings
When MOVE is applied to a resource, the other bindings to that
resource MUST be unaffected, and if the resource being moved is a
collection, the bindings to any members of that collection MUST be
unaffected. Also, if MOVE is used with Overwrite:T to delete an
existing resource, the constraints specified for DELETE apply.
If the destination collection of a MOVE request supports the REBIND
method (see Section 6), a MOVE of a resource into that collection
MAY be implemented as a REBIND request. Although [RFC2518] allows
a MOVE to be a non-atomic operation, when the MOVE operation is
implemented as a REBIND, the operation is atomic. In particular,
applying a MOVE to a Request-URI and a Destination URI has the
effect of removing a binding to a resource (at the Request-URI),
and creating a new binding to that resource (at the Destination
URI).
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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 URI-X. After successful completion of
the MOVE operation, a new binding has been created which creates
the URI mapping between URI-X and resource R. 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. If
resource R were a collection, old URI-3 based mappings to members
of R would have been removed, and new URI-X based mappings to
members of R would have been created.
>> Before Request:
URI-1 URI-2 URI-3
| | |
| | | <---- URI Mappings
| | |
+---------------------+
| Resource R |
+---------------------+
>> After Request:
URI-1 URI-2 URI-X
| | |
| | | <---- URI Mappings
| | |
+---------------------+
| Resource R |
+---------------------+
Although [RFC2518] allows a MOVE on a collection to be a non-atomic
operation, a MOVE implemented as a REBIND MUST be atomic. Even
when the Request-URI identifies a collection, the MOVE operation
involves only removing one binding to that collection and adding
another. There are no operations on bindings to any of its
children, so the case of MOVE on a collection is the same as the
case of MOVE on a non-collection resource. Both are atomic.
2.6 Determining Whether Two Bindings Are to the Same Resource
It is useful to have some way of determining whether two bindings
are to the same resource. Two resources might have identical
contents and properties, but not be the same resource (e.g. an
update to one resource does not affect the other resource).
The REQUIRED DAV:resource-id property defined in Section 3.1 is a
resource identifier, which MUST be unique across all resources for
all time. If the values of DAV:resource-id returned by PROPFIND
requests through two bindings are identical, the client can be
assured that the two bindings are to the same resource.
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The DAV:resource-id property is created, and its value assigned,
when the resource is created. The value of DAV:resource-id MUST
NOT be changed. Even after the resource is no longer accessible
through any URI, that value MUST NOT be reassigned to another
resource's DAV:resource-id property.
Any method that creates a new resource MUST assign a new, unique
value to its DAV:resource-id property. For example, a PUT or a
COPY that creates a new resource must assign a new, unique value to
the DAV:resource-id property of that new resource.
On the other hand, any method that affects an existing resource
MUST NOT change the value of its DAV:resource-id property. For
example, a PUT or a COPY that updates an existing resource must not
change the value of its DAV:resource-id property. A MOVE, since it
does not create a new resource, but only changes the location of an
existing resource, must not change the value of the DAV:resource-id
property.
2.7 Discovering the Bindings to a Resource
An OPTIONAL DAV:parent-set property on a resource provides a list
of the bindings that associate a collection and a URI segment with
that resource. If the DAV:parent-set property exists on a given
resource, it MUST contain a complete list of all bindings to that
resource that the client is authorized to see. When deciding
whether to support the DAV:parent-set property, server implementers
/ administrators should balance the benefits it provides against
the cost of maintaining the property and the security risks
enumerated in Sections 8.4 and 8.5.
3 PROPERTIES
The bind feature introduces the following properties for a
resource.
A DAV:allprop PROPFIND request SHOULD NOT return any of the
properties defined by this document. This allows a binding server
to perform efficiently when a naive client, which does not
understand the cost of asking a server to compute all possible live
properties, issues a DAV:allprop PROPFIND request.
3.1 DAV:resource-id Property
The DAV:resource-id property is a REQUIRED property that enables
clients to determine whether two bindings are to the same resource.
The value of DAV:resource-id is a URI, and may use any registered
URI scheme that guarantees the uniqueness of the value across all
resources for all time (e.g. the opaquelocktoken: scheme defined in
[RFC2518]).
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<!ELEMENT resource-id (href)>
3.2 DAV:parent-set Property
The DAV:parent-set property is an OPTIONAL property that enables
clients to discover what collections contain a binding to this
resource (i.e. what collections have that resource as an internal
member). It contains an of href/segment pair for each collection
that has a binding to the resource. The href identifies the
collection, and the segment identifies the binding name of that
resource in that collection.
A given collection MUST appear only once in the DAV:parent-set for
any given binding, even if there are multiple URI mappings to that
collection. For example, if collection C1 is mapped to both /CollX
and /CollY, and C1 contains a binding named "x.gif" to a resource
R1, then either [/CollX, x.gif] or [/CollY, x.gif] can appear in
the DAV:parent-set of R1, but not both. But if C1 also had a
binding named "y.gif" to R1, then there would be two entries for C1
in the DAV:binding-set of R1 (i.e. either both [/CollX, x.gif] and
[/CollX, y.gif] or alternatively, both [/CollY, x.gif] and [/CollY,
y.gif]).
<!ELEMENT parent-set (parent)*>
<!ELEMENT parent (href, segment)>
<!ELEMENT segment (#PCDATA)>
PCDATA value: segment, as defined in section 3.3 of [RFC2396]
4 BIND METHOD
The BIND method modifies the collection identified by the Request-
URI, by adding a new binding from the segment specified in the BIND
body to the resource identified in the BIND body.
If a server cannot guarantee the integrity of the binding, the BIND
request MUST fail. Note that 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 make
it inaccessible without notifying another server that manages a
binding to the resource. 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. Status code 507 (Cross-server Binding
Forbidden) is defined in Section 7.1 for cases where servers fail
cross-server BIND requests because they cannot guarantee the
integrity of cross-server bindings.
By default, if there already is a binding for the specified segment
in the collection, the new binding replaces the existing binding.
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This default binding replacement behavior can be overridden using
the Overwrite header defined in Section 9.6 of [RFC2518].
Marshalling:
The request MAY include an Overwrite header.
The request body MUST be a DAV:bind XML element.
<!ELEMENT bind (segment, href)>
If the request succeeds, the server MUST return 201 (Created) when
a new binding was created and 200 (OK) when an existing binding was
replaced.
If a response body for a successful request is included, it MUST be
a DAV:bind-response XML element. Note that this document does not
define any elements for the BIND response body, but the DAV:bind-
response element is defined to ensure interoperability between
future extensions that do define elements for the BIND response
body.
<!ELEMENT bind-response ANY>
Preconditions:
(DAV:bind-into-collection): The Request-URI MUST identify a
collection.
(DAV:bind-source-exists): The DAV:href element MUST identify a
resource.
(DAV:binding-allowed): The resource identified by the DAV:href
supports multiple bindings to it.
(DAV:cross-server-binding): If the resource identified by the
DAV:href element in the request body is on another server from the
collection identified by the request-URI, the server MUST support
cross-server bindings.
(DAV:name-allowed): The name specified by the DAV:segment is
available for use as a new binding name.
(DAV:can-overwrite): If the collection already contains a binding
with the specified path segment, and if an Overwrite header is
included, the value of the Overwrite header MUST be "T".
(DAV:cycle-allowed): If the DAV:href element identifies a
collection, and if the request-URI identifies a collection that is
a member of that collection, the server MUST support cycles in the
URI namespace.
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(DAV:locked-update-allowed): If the collection identified by the
Request-URI is write-locked, then the appropriate token MUST be
specified in an If request header.
(DAV:locked-overwrite-allowed): If the collection already contains
a binding with the specified path segment, and if that binding is
protected by a write-lock, then the appropriate token MUST be
specified in an If request header.
Postconditions:
(DAV:new-binding): The collection MUST have a binding that maps the
segment specified in the DAV:segment element in the request body,
to the resource identified by the DAV:href element in the request
body.
4.1 Example: BIND
>> Request:
BIND /CollY HTTP/1.1
Host: www.example.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
<?xml version="1.0" encoding="utf-8" ?>
<D:bind xmlns:D="DAV:">
<D:segment>bar.html</D:segment>
<D:href>http://www.example.com/CollX/foo.html</D:href>
</D:bind>
>> Response:
HTTP/1.1 201 Created
The server added a new binding to the collection,
"http://www.example.com/CollY", associating "bar.html" with the
resource identified by the URI
"http://www.example.com/CollX/foo.html". Clients can now use the
URI "http://www.example.com/CollY/bar.html", to submit requests to
that resource.
5 UNBIND METHOD
The UNBIND method modifies the collection identified by the
Request-URI, by removing the binding identified by the segment
specified in the UNBIND body.
Once a resource is unreachable by any URI mapping, the server MAY
reclaim system resources associated with that resource. If UNBIND
removes a binding to a resource, but there remain URI mappings to
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that resource, the server MUST NOT reclaim system resources
associated with the resource.
Marshalling:
The request body MUST be a DAV:unbind XML element.
<!ELEMENT unbind (segment)>
If the request succeeds, the server MUST return 200 (OK) when the
binding was successfully deleted.
If a response body for a successful request is included, it MUST be
a DAV:unbind-response XML element. Note that this document does
not define any elements for the UNBIND response body, but the
DAV:unbind-response element is defined to ensure interoperability
between future extensions that do define elements for the UNBIND
response body.
<!ELEMENT unbind-response ANY>
Preconditions:
(DAV:unbind-from-collection): The Request-URI MUST identify a
collection.
(DAV:unbind-source-exists): The DAV:segment element MUST identify a
binding in the collection identified by the Request-URI.
(DAV:locked-update-allowed): If the collection identified by the
Request-URI is write-locked, then the appropriate token MUST be
specified in the request.
(DAV:protected-url-deletion-allowed): If the binding identified by
the segment is protected by a write-lock, then the appropriate
token MUST be specified in the request.
Postconditions:
(DAV:binding-deleted): The collection MUST NOT have a binding for
the segment specified in the DAV:segment element in the request
body.
5.1 Example: UNBIND
>> Request:
UNBIND /CollX HTTP/1.1
Host: www.example.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
<?xml version="1.0" encoding="utf-8" ?>
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<D:unbind xmlns:D="DAV:">
<D:segment>foo.html</D:segment>
</D:unbind>
>> Response:
HTTP/1.1 200 OK
The server removed the binding named "foo.html" from the
collection, "http://www.example.com/CollX". A request to the
resource named "http://www.example.com/CollX/foo.html" will return
a 404 (Not Found) response.
6 REBIND METHOD
The REBIND method removes a binding to a resource from one
collection, and adds a binding to that resource into another
collection. It is effectively an atomic form of a MOVE request.
Marshalling:
The request MAY include an Overwrite header.
The request body MUST be a DAV:rebind XML element.
<!ELEMENT rebind (segment, href)>
If the request succeeds, the server MUST return 201 (Created) when
a new binding was created and 200 (OK) when an existing binding was
replaced.
If a response body for a successful request is included, it MUST be
a DAV:rebind-response XML element. Note that this document does
not define any elements for the REBIND response body, but the
DAV:rebind-response element is defined to ensure interoperability
between future extensions that do define elements for the REBIND
response body.
<!ELEMENT rebind-response ANY>
Preconditions:
(DAV:rebind-into-collection): The Request-URI MUST identify a
collection.
(DAV:rebind-source-exists): The DAV:href element MUST identify a
resource.
(DAV:binding-allowed): The resource identified by the DAV:href
supports multiple bindings to it.
(DAV:cross-server-binding): If the resource identified by the
DAV:href element in the request body is on another server from the
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collection identified by the request-URI, the server MUST support
cross-server bindings.
(DAV:name-allowed): The name specified by the DAV:segment is
available for use as a new binding name.
(DAV:can-overwrite): If the collection already contains a binding
with the specified path segment, and if an Overwrite header is
included, the value of the Overwrite header MUST be "T".
(DAV:cycle-allowed): If the DAV:href element identifies a
collection, and if the request-URI identifies a collection that is
a member of that collection, the server MUST support cycles in the
URI namespace.
(DAV:locked-update-allowed): If the collection identified by the
Request-URI is write-locked, then the appropriate token MUST be
specified in the request.
(DAV:protected-url-modification-allowed): If the collection
identified by the Request-URI already contains a binding with the
specified path segment, and if that binding is protected by a
write-lock, then the appropriate token MUST be specified in the
request.
(DAV:locked-source-collection-update-allowed): If the collection
identified by the parent collection prefix of the DAV:href URI is
write-locked, then the appropriate token MUST be specified in the
request.
(DAV:protected-source-url-deletion-allowed): If the DAV:href URI is
protected by a write lock, then the appropriate token MUST be
specified in the request.
Postconditions:
(DAV:new-binding): The collection MUST have a binding that maps the
segment specified in the DAV:segment element in the request body,
to the resource that was identified by the DAV:href element in the
request body.
(DAV:binding-deleted): The URL specified in the DAV:href element in
the request body MUST NOT be mapped to a resource.
6.1 Example: REBIND
>> Request:
REBIND /CollX HTTP/1.1
Host: www.example.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
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<?xml version="1.0" encoding="utf-8" ?>
<D:rebind xmlns:D="DAV:">
<D:segment>foo.html</D:segment>
<D:href>http://www.example.com/CollY/bar.html</D:href>
</D:rebind>
>> Response:
HTTP/1.1 200 OK
The server added a new binding to the collection,
"http://www.example.com/CollX", associating "foo.html" with the
resource identified by the URI
"http://www.example.com/CollY/bar.html", and removes the binding
named "bar.html" from the collection identified by the URI
"http://www.example.com/CollY". Clients can now use the URI
"http://www.example.com/CollX/foo.html" to submit requests to that
resource, and requests on the URI
"http://www.example.com/CollY/bar.html" will fail with a 404 (Not
Found) response.
7 ADDITIONAL STATUS CODES
7.1 506 Loop Detected
The 506 (Loop Detected) status code indicates that the server
terminated an operation because it encountered an infinite loop
while processing a request with "Depth: infinity".
When this status code is the top-level status code for the
operation, it indicates that the entire operation failed.
When this status code occurs inside a multi-status response, it
indicates only that a loop is being terminated, but does not
indicate failure of the operation as a whole.
For example, consider a PROPFIND request on /Coll (bound to
collection C), where the members of /Coll are /Coll/Foo (bound to
resource R) and /Coll/Bar (bound to collection C).
>> Request:
PROPFIND /Coll/ HTTP/1.1
Host: www.example.com
Depth: infinity
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:prop> <D:displayname/> </D:prop>
</D:propfind>
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>> Response:
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
<?xml version="1.0" encoding="utf-8" ?>
<D:multistatus xmlns:D="DAV:">
<D:response>
<D:href>http://www.example.com/Coll/</D:href>
<D:propstat>
<D:prop>
<D:displayname>Loop Demo</D:displayname>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>http://www.example.com/Coll/Foo</D:href>
<D:propstat>
<D:prop>
<D:displayname>Bird Inventory</D:displayname>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>http://www.example.com/Coll/Bar</D:href>
<D:status>HTTP/1.1 506 Loop Detected</D:status>
</D:response>
</D:multistatus>
8 SECURITY CONSIDERATIONS
This section is provided to make WebDAV applications aware of the
security implications of this protocol.
All of the security considerations of HTTP/1.1 and the WebDAV
Distributed Authoring Protocol specification also apply to this
protocol specification. In addition, bindings introduce several
new security concerns and increase the risk of some existing
threats. These issues are detailed below.
8.1 Privacy Concerns
In a context where cross-server bindings are supported, creating
bindings on a trusted server may make it possible for a hostile
agent to induce users to send private information to a target on a
different server.
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8.2 Redirect Loops
Although redirect loops were already possible in HTTP 1.1, the
introduction of the BIND method creates a new avenue for clients to
create loops accidentally or maliciously. If the binding and its
target are on the same server, the server may be able to detect
BIND requests that would create loops. Servers are required to
detect loops that are caused by bindings to collections during the
processing of any requests with "Depth: infinity".
8.3 Bindings, and Denial of Service
Denial of service attacks were already possible by posting URIs
that were intended for limited use at heavily used Web sites. The
introduction of BIND creates a new avenue for similar denial of
service attacks. If cross-server bindings are supported, clients
can now create bindings at heavily used sites to target locations
that were not designed for heavy usage.
8.4 Private Locations May Be Revealed
If the DAV:parent-set property is maintained on a resource, the
owners of the bindings risk revealing private locations. The
directory structures where bindings are located are available to
anyone who has access to the DAV:parent-set property on the
resource. Moving a binding may reveal its new location to anyone
with access to DAV:parent-set on its resource.
8.5 DAV:parent-set and Denial of Service
If the server maintains the DAV:parent-set 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.
9 INTERNATIONALIZATION CONSIDERATIONS
All internationalization considerations mentioned in [RFC2518] also
apply to this document.
10 IANA CONSIDERATIONS
All IANA considerations mentioned in [RFC2518] also apply to this
document.
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11 INTELLECTUAL PROPERTY
The following notice is copied from RFC 2026, Section 10.4, and
describes the position of the IETF concerning intellectual property
claims made against this document.
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use other technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on
the procedures of the IETF with respect to rights in standards-
track and standards-related documentation can be found in BCP-11.
Copies of claims of rights made available for publication and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use
of such proprietary rights by implementers or users of this
specification can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to practice
this standard. Please address the information to the IETF
Executive Director.
12 ACKNOWLEDGEMENTS
This draft is the collaborative product of the authors and Tyson
Chihaya, Jim Davis, and Chuck Fay. This draft has benefited from
thoughtful discussion by Jim Amsden, Peter Carlson, Steve Carter,
Ken Coar, Ellis Cohen, Dan Connolly, Bruce Cragun, Spencer Dawkins,
Mark Day, Rajiv Dulepet, David Durand, Roy Fielding, Yaron Goland,
Fred Hitt, Alex Hopmann, James Hunt, Marcus Jager, Chris Kaler,
Manoj Kasichainula, Rohit Khare, Daniel LaLiberte, Steve Martin,
Larry Masinter, Jeff McAffer, Surendra Koduru Reddy, Max Rible, Sam
Ruby, Bradley Sergeant, Nick Shelness, John Stracke, John Tigue,
John Turner, Kevin Wiggen, and other members of the WebDAV working
group.
13 REFERENCES
[RFC2026] S.Bradner, "The Internet Standards Process", RFC 2026,
October 1996.
[RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2277] H.Alvestrand, "IETF Policy on Character Sets and
Languages." RFC 2277, January 1998.
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[RFC2396] T. Berners-Lee, R. Fielding, L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax." RFC 2396, August 1998.
[RFC2518] Y.Goland, E.Whitehead, A.Faizi, S.R.Carter, D.Jensen,
"HTTP Extensions for Distributed Authoring - WEBDAV", RFC 2518,
February 1999.
[RFC2616] R.Fielding, J.Gettys, J.C.Mogul, H.Frystyk, L.Masinter,
P.Leach, and T.Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[XML] T. Bray, J. Paoli, C.M. Sperberg-McQueen, "Extensible Markup
Language (XML) 1.0 (Second Edition)" W3C Recommendation 6 October
2000. http://www.w3.org/TR/2000/REC-xml-20001006.
14 AUTHORS' ADDRESSES
Geoffrey Clemm
Rational Software Corporation
20 Maguire Road
Lexington, MA 02173-3104
Email: geoffrey.clemm@us.ibm.com
Jason Crawford
IBM Research
P.O. Box 704
Yorktown Heights, NY 10598
Email: ccjason@us.ibm.com
Julian F. Reschke
greenbytes GmbH
Salzmannstrasse 152
Muenster, NW 48159, Germany
Email: julian.reschke@greenbytes.de
Judy Slein
Xerox Corporation
800 Phillips Road, 105-50C
Webster, NY 14580
Email: jslein@crt.xerox.com
Jim Whitehead
UC Santa Cruz, Dept. of Computer Science
1156 High Street, Santa Cruz, CA 95064
Email: ejw@cse.ucsc.edu
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