Network Working Group G. Clemm
Internet-Draft IBM
Expires: June 10, 2004 J. Crawford
IBM Research
J. Reschke
greenbytes
J. Slein
Xerox
J. Whitehead
U.C. Santa Cruz
December 11, 2003
Binding Extensions to Web Distributed Authoring and Versioning
(WebDAV)
draft-ietf-webdav-bind-03
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on June 10, 2004.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
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
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they allow to be created.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Rationale for Distinguishing Bindings from URI Mappings . . . 6
1.3 Method Preconditions and Postconditions . . . . . . . . . . . 7
2. Overview of Bindings . . . . . . . . . . . . . . . . . . . . . 7
2.1 Bindings to Collections . . . . . . . . . . . . . . . . . . . 8
2.2 URI Mappings Created by a new Binding . . . . . . . . . . . . 9
2.3 COPY and Bindings . . . . . . . . . . . . . . . . . . . . . . 10
2.4 DELETE and Bindings . . . . . . . . . . . . . . . . . . . . . 11
2.5 MOVE and Bindings . . . . . . . . . . . . . . . . . . . . . . 12
2.6 Determining Whether Two Bindings Are to the Same Resource . . 13
2.7 Discovering the Bindings to a Resource . . . . . . . . . . . . 14
3. Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1 DAV:resource-id Property . . . . . . . . . . . . . . . . . . . 14
3.2 DAV:parent-set Property . . . . . . . . . . . . . . . . . . . 14
4. BIND Method . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1 Example: BIND . . . . . . . . . . . . . . . . . . . . . . . . 17
5. UNBIND Method . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1 Example: UNBIND . . . . . . . . . . . . . . . . . . . . . . . 19
6. REBIND Method . . . . . . . . . . . . . . . . . . . . . . . . 19
6.1 Example: REBIND . . . . . . . . . . . . . . . . . . . . . . . 21
7. Additional Status Codes . . . . . . . . . . . . . . . . . . . 21
7.1 208 Already Reported . . . . . . . . . . . . . . . . . . . . . 21
7.2 506 Loop Detected . . . . . . . . . . . . . . . . . . . . . . 23
8. Security Considerations . . . . . . . . . . . . . . . . . . . 24
8.1 Privacy Concerns . . . . . . . . . . . . . . . . . . . . . . . 24
8.2 Redirect Loops . . . . . . . . . . . . . . . . . . . . . . . . 24
8.3 Bindings, and Denial of Service . . . . . . . . . . . . . . . 24
8.4 Private Locations May Be Revealed . . . . . . . . . . . . . . 24
8.5 DAV:parent-set and Denial of Service . . . . . . . . . . . . . 25
9. Internationalization Considerations . . . . . . . . . . . . . 25
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
Normative References . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 26
A. Change Log (to be removed by RFC Editor before publication) . 27
A.1 Since draft-ietf-webdav-bind-02 . . . . . . . . . . . . . . . 27
B. Resolved issues (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . . . . . 27
B.1 ED_references . . . . . . . . . . . . . . . . . . . . . . . . 27
B.2 2.3_COPY_SHARED_BINDINGS . . . . . . . . . . . . . . . . . . . 27
B.3 2.3_MULTIPLE_COPY . . . . . . . . . . . . . . . . . . . . . . 28
B.4 4_507_status . . . . . . . . . . . . . . . . . . . . . . . . . 28
C. Open issues (to be removed by RFC Editor before
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publication) . . . . . . . . . . . . . . . . . . . . . . . . . 28
C.1 5.1_LOOP_STATUS . . . . . . . . . . . . . . . . . . . . . . . 28
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . . 31
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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 [RFC2616] and WebDAV [RFC2518] 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
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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.
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 2
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].
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].
This document uses XML DTD fragments ([XML]) 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:
o Element names use the "DAV:" namespace.
o Element ordering is irrelevant.
o 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
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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].
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.
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
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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.
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.
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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 7
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.
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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
...
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
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collection.
If a COPY request causes an existing resource to be updated, the
bindings to that resource MUST be unaffected by the COPY request.
Using the preceding example, suppose that a COPY request 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. If because of multiple
bindings to a resource, more than one source resource updates a
single destination resource, the order of the updates is server
defined.
If a COPY request would cause a new resource to be created as a copy
of an existing resource, and that COPY request has already created a
copy of that existing resource, the COPY request instead creates
another binding to the previous copy, instead of creating a new
resource.
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
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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).
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 |
+---------------------+
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>> 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.
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.
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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]).
<!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,
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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. The precondition DAV:cross-server-binding is defined below
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.
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)>
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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.
(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
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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
that resource, the server MUST NOT reclaim system resources
associated with the resource.
Marshalling:
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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.
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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" ?>
<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.
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<!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
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.
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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
<?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
7.1 208 Already Reported
The 208 (Already Reported) status code can be used inside a
DAV:propstat response element to indicate that information about the
resource has already been reported in a previous DAV:propstat element
in that response. The members of the 208 status resource are omitted
from the response.
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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:propstat>
<D:prop>
<D:displayname>Loop Demo</D:displayname>
</D:prop>
<D:status>HTTP/1.1 208 Already Reported</D:status>
</D:propstat>
</D:response>
</D:multistatus>
A client can request the DAV:resourceid property in a PROPFIND
request to guarantee that they can accurately reconstruct the binding
structure of a collection with multiple bindings to a single
resource.
7.2 506 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". This status indicates
that the entire operation failed.
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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.
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.
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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.
11. 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.
Normative References
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D.
Jensen, "HTTP Extensions for Distributed Authoring --
WEBDAV", RFC 2518, February 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
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Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (2nd ed)", W3C
REC-xml, October 2000, <http://www.w3.org/TR/2000/
REC-xml-20001006>.
Authors' Addresses
Geoffrey Clemm
IBM
20 Maguire Road
Lexington, MA 02421
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
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Jim Whitehead
UC Santa Cruz, Dept. of Computer Science
1156 High Street
Santa Cruz, CA 95064
EMail: ejw@cse.ucsc.edu
Appendix A. Change Log (to be removed by RFC Editor before publication)
A.1 Since draft-ietf-webdav-bind-02
Add and resolve issues "2.3_COPY_SHARED_BINDINGS" and
"2.3_MULTIPLE_COPY". Add issue "5.1_LOOP_STATUS" and proposed
resolution, but keep it open. Add issues "ED_references" and
"4_507_status". Started work on index. Rename document to "Binding
Extensions to Web Distributed Authoring and Versioning (WebDAV)".
Rename "References" to "Normative References". Close issue
"ED_references". CLose issue "4_507_status".
Appendix B. Resolved issues (to be removed by RFC Editor before
publication)
Issues that were either rejected or resolved in this version of this
document.
B.1 ED_references
Type: edit
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2003OctDec/
0283.html>
julian.reschke@greenbytes.de (2003-12-09): (1) Distinguish normative
and informative references, (2) text referring to RFC2119 is missing,
(3) references to RFC2277, RFC2616 and XML not needed.
Resolution (2003-12-11): Editorial changes applied.
B.2 2.3_COPY_SHARED_BINDINGS
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2003JulSep/
0010.html>
Peter.Nevermann@softwareag.com (2003-07-10): What if a copied
collection has two bindings to the same resource.
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Resolution (2003-08-21): Recommend that only one resource with
multiple bindings to it be created by the COPY.
B.3 2.3_MULTIPLE_COPY
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2003JulSep/
0124.html>
Peter.Nevermann@softwareag.com (2003-08-17): What two resources are
copied to the same resource by a single COPY.
Resolution (2003-08-21): Server decides order of updates.
B.4 4_507_status
Type: change
<http://lists.w3.org/Archives/Public/w3c-dist-auth/2003OctDec/
0282.html>
julian.reschke@greenbytes.de (2003-12-09): Section 4 refers to a
definition of a 507 status code in Section 7.1, which doesn't exist.
Should this text be replaced by a reference to the
DAV:cross-server-binding precondition?
Resolution (2003-12-11): Change wording to refer to precondition
name.
Appendix C. Open issues (to be removed by RFC Editor before publication)
C.1 5.1_LOOP_STATUS
Type: change
julian.reschke@greenbytes.de (2002-10-11): Should the 506 status in a
PROPFIND be handled differently?
geoffrey.clemm@us.ibm.com (2003-08-03): Use new 208 status to report
cycles in PROPFIND.
julian.reschke@greenbytes.de (2003-11-16): Proposal: a) import DAV
request header definition from rfc2518bis (note that the definition
in the latest draft probably needs some more work) b) define a DAV
compliance class for the BIND spec c) clarify that 208 should only be
returned when the client specifies compliance to the BIND spec in the
PROPFIND request (otherwise fail the complete request).
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Index
2
208 Already Reported (status code) 21
5
506 Loop Detected (status code) 23
B
BIND method 15
C
Condition Names
DAV:bind-into-collection (pre) 16
DAV:bind-source-exists (pre) 16
DAV:binding-allowed (pre) 16, 20
DAV:binding-deleted (post) 18, 21
DAV:can-overwrite (pre) 16, 20
DAV:cross-server-binding (pre) 16, 20
DAV:cycle-allowed (pre) 16, 20
DAV:locked-overwrite-allowed (pre) 16
DAV:locked-source-collection-update-allowed (pre) 20
DAV:locked-update-allowed (pre) 16, 18, 20
DAV:name-allowed (pre) 16, 20
DAV:new-binding (post) 17, 21
DAV:protected-source-url-deletion-allowed (pre) 20
DAV:protected-url-deletion-allowed (pre) 18
DAV:protected-url-modification-allowed (pre) 20
DAV:rebind-into-collection (pre) 20
DAV:rebind-source-exists (pre) 20
DAV:unbind-from-collection (pre) 18
DAV:unbind-source-exists (pre) 18
D
DAV:bind-into-collection precondition 16
DAV:bind-source-exists precondition 16
DAV:binding-allowed precondition 16, 20
DAV:binding-deleted postcondition 18, 21
DAV:can-overwrite precondition 16, 20
DAV:cross-server-binding precondition 16, 20
DAV:cycle-allowed precondition 16, 20
DAV:locked-overwrite-allowed precondition 16
DAV:locked-source-collection-update-allowed precondition 20
DAV:locked-update-allowed precondition 16, 18, 20
DAV:name-allowed precondition 16, 20
DAV:new-binding postcondition 17, 21
DAV:parent-set property 14
DAV:protected-source-url-deletion-allowed precondition 20
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DAV:protected-url-deletion-allowed precondition 18
DAV:protected-url-modification-allowed precondition 20
DAV:rebind-into-collection precondition 20
DAV:rebind-source-exists precondition 20
DAV:resource-id property 14
DAV:unbind-from-collection precondition 18
DAV:unbind-source-exists precondition 18
M
Methods
BIND 15
REBIND 19
UNBIND 17
P
Properties
DAV:parent-set 14
DAV:resource-id 14
R
REBIND method 19
S
Status Codes
208 Already Reported 21
506 Loop Detected 23
U
UNBIND method 17
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Intellectual Property Statement
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The IETF invites any interested party to bring to its attention any
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
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