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Network Working Group                                           G. Clemm
Internet-Draft                                                       IBM
Updates: 2518 (if approved)                                  J. Crawford
Expires: July 6, 2005                                       IBM Research
                                                              J. Reschke
                                                              greenbytes
                                                            J. Whitehead
                                                         U.C. Santa Cruz
                                                         January 5, 2005


     Binding Extensions to Web Distributed Authoring and Versioning
                                (WebDAV)
                       draft-ietf-webdav-bind-10

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

   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.

   This Internet-Draft will expire on July 6, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This specification defines bindings, and the BIND method for creating



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   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.

Editorial Note (To be removed by RFC Editor before publication)

   Please send comments to the Distributed Authoring and Versioning
   (WebDAV) working group at <mailto:w3c-dist-auth@w3.org>, which may be
   joined by sending a message with subject "subscribe" to
   <mailto:w3c-dist-auth-request@w3.org>.  Discussions of the WEBDAV
   working group are archived at
   <http://lists.w3.org/Archives/Public/w3c-dist-auth/>.

   <http://www.webdav.org/bind/draft-ietf-webdav-bind-issues.html> lists
   all registered issues since draft 02.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1   Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
     1.2   Rationale for Distinguishing Bindings from URI Mappings  .  7
     1.3   Method Preconditions and Postconditions  . . . . . . . . .  8
   2.  Overview of Bindings . . . . . . . . . . . . . . . . . . . . .  8
     2.1   Bindings to Collections  . . . . . . . . . . . . . . . . .  9
       2.1.1   Bind loops . . . . . . . . . . . . . . . . . . . . . . 10
     2.2   URI Mappings Created by a new Binding  . . . . . . . . . . 10
     2.3   COPY and Bindings  . . . . . . . . . . . . . . . . . . . . 11
       2.3.1   Example: COPY with 'Depth: infinity' in presence
               of bind loops  . . . . . . . . . . . . . . . . . . . . 12
       2.3.2   Example: COPY with 'Depth: infinity' with multiple
               bindings to a leaf resource  . . . . . . . . . . . . . 14
     2.4   DELETE and Bindings  . . . . . . . . . . . . . . . . . . . 15
     2.5   MOVE and Bindings  . . . . . . . . . . . . . . . . . . . . 15
     2.6   PROPFIND and Bindings  . . . . . . . . . . . . . . . . . . 16
     2.7   Determining Whether Two Bindings Are to the Same
           Resource . . . . . . . . . . . . . . . . . . . . . . . . . 16
     2.8   Discovering the Bindings to a Resource . . . . . . . . . . 17
   3.  Properties . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     3.1   DAV:resource-id Property . . . . . . . . . . . . . . . . . 18
     3.2   DAV:parent-set Property  . . . . . . . . . . . . . . . . . 18
       3.2.1   Example for DAV:parent-set property  . . . . . . . . . 18
   4.  BIND Method  . . . . . . . . . . . . . . . . . . . . . . . . . 19
     4.1   Example: BIND  . . . . . . . . . . . . . . . . . . . . . . 22
   5.  UNBIND Method  . . . . . . . . . . . . . . . . . . . . . . . . 22
     5.1   Example: UNBIND  . . . . . . . . . . . . . . . . . . . . . 24
   6.  REBIND Method  . . . . . . . . . . . . . . . . . . . . . . . . 24
     6.1   Example: REBIND  . . . . . . . . . . . . . . . . . . . . . 26
     6.2   Example: REBIND in presence of locks and bind loops  . . . 27
   7.  Additional Status Codes  . . . . . . . . . . . . . . . . . . . 29
     7.1   208 Already Reported . . . . . . . . . . . . . . . . . . . 29
       7.1.1   Example: PROPFIND by bind-aware client . . . . . . . . 30
       7.1.2   Example: PROPFIND by non-bind-aware client . . . . . . 31
     7.2   506 Loop Detected  . . . . . . . . . . . . . . . . . . . . 32
   8.  Capability discovery . . . . . . . . . . . . . . . . . . . . . 32
     8.1   OPTIONS method . . . . . . . . . . . . . . . . . . . . . . 32
     8.2   'DAV' request header . . . . . . . . . . . . . . . . . . . 32
       8.2.1   Generic syntax . . . . . . . . . . . . . . . . . . . . 32
       8.2.2   Client compliance class 'bind' . . . . . . . . . . . . 33
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 33
     9.1   Privacy Concerns . . . . . . . . . . . . . . . . . . . . . 33
     9.2   Bind Loops . . . . . . . . . . . . . . . . . . . . . . . . 33
     9.3   Bindings, and Denial of Service  . . . . . . . . . . . . . 33
     9.4   Private Locations May Be Revealed  . . . . . . . . . . . . 34
     9.5   DAV:parent-set and Denial of Service . . . . . . . . . . . 34



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   10.   Internationalization Considerations  . . . . . . . . . . . . 34
   11.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . 34
   12.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 34
   13.   References . . . . . . . . . . . . . . . . . . . . . . . . . 35
   13.1  Normative References . . . . . . . . . . . . . . . . . . . . 35
   13.2  Informative References . . . . . . . . . . . . . . . . . . . 35
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 35
   A.  Change Log (to be removed by RFC Editor before publication)  . 36
     A.1   Since draft-ietf-webdav-bind-02  . . . . . . . . . . . . . 36
     A.2   Since draft-ietf-webdav-bind-03  . . . . . . . . . . . . . 36
     A.3   Since draft-ietf-webdav-bind-04  . . . . . . . . . . . . . 36
     A.4   Since draft-ietf-webdav-bind-05  . . . . . . . . . . . . . 37
     A.5   Since draft-ietf-webdav-bind-06  . . . . . . . . . . . . . 37
     A.6   Since draft-ietf-webdav-bind-07  . . . . . . . . . . . . . 37
     A.7   Since draft-ietf-webdav-bind-08  . . . . . . . . . . . . . 37
     A.8   Since draft-ietf-webdav-bind-09  . . . . . . . . . . . . . 37
   B.  Resolved issues (to be removed by RFC Editor before
       publication) . . . . . . . . . . . . . . . . . . . . . . . . . 37
     B.1   uri_draft_ref  . . . . . . . . . . . . . . . . . . . . . . 37
     B.2   2.6_bindings_vs_properties . . . . . . . . . . . . . . . . 38
     B.3   2.6_when_do_ids_change . . . . . . . . . . . . . . . . . . 38
     B.4   6.1_rebind_vs_locks  . . . . . . . . . . . . . . . . . . . 38
   C.  Open issues (to be removed by RFC Editor prior to
       publication) . . . . . . . . . . . . . . . . . . . . . . . . . 39
     C.1   edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
     C.2   3.1_uuids  . . . . . . . . . . . . . . . . . . . . . . . . 39
       Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
       Intellectual Property and Copyright Statements . . . . . . . . 42























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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
      [draft-fielding-uri-rfc2396bis].

   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



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   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.

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.



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   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.  It is permissible,
   however, for future method definitions (e.g., a DESTROY method) to
   have semantics that explicitly remove all bindings and/or immediately
   reclaim system resources.

2.1  Bindings to Collections

   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.

   +-------------------------+
   | Root Collection         |
   |  bindings:              |
   |  CollX          CollY   |
   +-------------------------+
       |            /
       |           /
       |          /
   +------------------+
   | Collection C1    |
   | bindings:        |
   | x.gif     y.jpg  |
   +------------------+
       |          \
       |           \
       |            \
   +-------------+   +-------------+



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   | Resource R1 |   | Resource R2 |
   +-------------+   +-------------+


2.1.1  Bind loops

   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.
   For instance, a PROPFIND can still succeed if the server uses the new
   status code 208 (Already Reported) defined in Section 7.1.

   However, the 506 (Loop Detected) status code is defined in Section
   7.2 for use in contexts where an operation is terminated because a
   loop was encountered.

2.2  URI Mappings Created by a new Binding

   Suppose a binding from "Binding-Name" to resource R is 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 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



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   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.

2.3.1  Example: COPY with 'Depth: infinity' in presence of bind loops

   As an example of how COPY with Depth infinity would work in the
   presence of bindings, consider the following collection:

   +------------------+
   | Root Collection  |
   |  bindings:       |
   |  CollX           |
   +------------------+
       |
       |
   +-------------------------------+
   | Collection C1                 |<-------+
   | bindings:                     |        |
   | x.gif      CollY              |        |
   +-------------------------------+        |
       |            \        (creates loop) |
       |             \                      |
   +-------------+   +------------------+   |
   | Resource R1 |   | Collection C2    |   |
   +-------------+   | bindings:        |   |
                     | y.gif     CollZ  |   |
                     +------------------+   |
                         |         |        |
                         |         +--------+
                         |
                     +-------------+
                     | Resource R2 |
                     +-------------+

   If a COPY with Depth inifinity is submitted to /CollX, with
   destination of /CollA, the outcome of the copy operation is:

   +------------------+
   | Root Collection  |



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   |  bindings:       |
   |  CollX     CollA |
   +------------------+
      |           |
      |           +---------------------------+
      |                                       |
   +-------------------+                      |
   | Collection C1     |<------------------+  |
   | bindings:         |                   |  |
   | x.gif      CollY  |                   |  |
   +-------------------+                   |  |
      |            \        (creates loop) |  |
      |             \                      |  |
   +-------------+   +-----------------+   |  |
   | Resource R1 |   | Collection C2   |   |  |
   +-------------+   | bindings:       |   |  |
                     | y.gif     CollZ |   |  |
                     +-----------------+   |  |
                         |         |       |  |
                         |         +-------+  |
                         |                    |
                     +-------------+          |
                     | Resource R2 |          |
                     +-------------+          |
                                              |
              +-------------------------------+
              |
   +-------------------+
   | Collection C3     |<------------------+
   | bindings:         |                   |
   | x.gif      CollY  |                   |
   +-------------------+                   |
      |            \        (creates loop) |
      |             \                      |
   +-------------+   +-----------------+   |
   | Resource R3 |   | Collection C4   |   |
   +-------------+   | bindings:       |   |
                     | y.gif     CollZ |   |
                     +-----------------+   |
                         |         |       |
                         |         +-------+
                         |
                     +-------------+
                     | Resource R4 |
                     +-------------+






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2.3.2  Example: COPY with 'Depth: infinity' with multiple bindings to a
      leaf resource

   Given the following collection hierarchy:

   +------------------+
   | Root Collection  |
   |  bindings:       |
   |  CollX           |
   +------------------+
      |
      |
      |
   +----------------+
   | Collection C1  |
   | bindings:      |
   | x.gif    y.gif |
   +----------------+
      |         |
      |         |
    +-------------+
    | Resource R1 |
    +-------------+

   A COPY of /CollX with Depth infinity to /CollY results in the
   following collection hierarchy:

   +------------------+
   | Root Collection  |
   |  bindings:       |
   |  CollX     CollY |
   +------------------+
      |              \
      |               \
      |                \
   +----------------+  +-----------------+
   | Collection C1  |  | Collection C2   |
   | bindings:      |  | bindings:       |
   | x.gif    y.gif |  | x.gif     y.gif |
   +----------------+  +-----------------+
      |         |          |         |
      |         |          |         |
    +-------------+      +-------------+
    | Resource R1 |      | Resource R2 |
    +-------------+      +-------------+






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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



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   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).  Even when the
   Request-URI identifies a collection, the MOVE operation involves only
   removing one binding to that collection and adding another.

   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      |
   +---------------------+


2.6  PROPFIND and Bindings

   Consistent with [RFC2518] the value of a dead property MUST be, and
   the value of a live property SHOULD be, independent of the number of
   bindings to its host resource or of the path submitted to PROPFIND.

2.7  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



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   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 character by character,
   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 applied to
   a null resource, COPY (when not overwriting an existing target) and
   CHECKIN (see [RFC3253], section 4.4) must assign a new, unique value
   to the DAV:resource-id property of the new resource they create.

   On the other hand, any method that affects an existing resource must
   not change the value of its DAV:resource-id property.  Specifically,
   a PUT or a COPY that updates an existing resource must not change the
   value of its DAV:resource-id property.  A REBIND, 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.

2.8  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 9.4 and 9.5.

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



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   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.

   <!ELEMENT parent-set (parent)*>
   <!ELEMENT parent (href, segment)>
   <!ELEMENT segment (#PCDATA)>
   <!-- PCDATA value: segment, as defined in section 3.3 of
        [draft-fielding-uri-rfc2396bis] -->



3.2.1  Example for DAV:parent-set property

   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.  both [/CollX, x.gif] and [/CollX, y.gif] or, alternatively,
   both [/CollY, x.gif] and [/CollY, y.gif]).





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   +-------------------------+
   | Root Collection         |
   |  bindings:              |
   |  CollX          CollY   |
   +-------------------------+
       |            /
       |           /
       |          /
   +-----------------+
   | Collection C1   |
   | bindings:       |
   | x.gif    y.gif  |
   +-----------------+
        |      |
        |      |
        |      |
    +--------------+
    | Resource  R1 |
    +--------------+

   In this case, one possible value for DAV:parent-set property on
   "/CollX/x.gif" would be:

     <parent-set xmlns="DAV:">
       <parent>
         <href>/CollX</href>
         <segment>x.gif</segment>
       </parent>
       <parent>
         <href>/CollX</href>
         <segment>y.gif</segment>
       </parent>
     </parent-set>


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



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   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].

   If a BIND request fails, the server state preceding the request MUST
   be restored.  This method is unsafe and idempotent (see [RFC2616],
   section 9.1).

   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



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      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
      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.

















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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.

   If an UNBIND request fails, the server state preceding the request
   MUST be restored.  This method is unsafe and idempotent (see
   [RFC2616], section 9.1).

   Marshalling:

      The request body MUST be a DAV:unbind XML element.

      <!ELEMENT unbind (segment)>




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      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.

      (DAV:lock-deleted): If the internal member URI of the binding
      specified by the Request-URI and the DAV:segment element in the
      request body was protected by a write-lock at the time of the
      request, that write-lock must have been deleted by the request.













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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 a collection,
   and adds a binding to that resource into the collection identified by
   the Request-URI.  The request body specifies the binding to be added
   (segment) and the old binding to be removed (href).  It is
   effectively an atomic form of a MOVE request, and MUST be treated the
   same way as MOVE for the purpose of determining access permissions.

   If a REBIND request fails, the server state preceding the request
   MUST be restored.  This method is unsafe and idempotent (see
   [RFC2616], section 9.1).

   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.




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      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: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.



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      (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.

      (DAV:lock-deleted): If the URL specified in the DAV:href element
      in the request body was protected by a write-lock at the time of
      the request, that write-lock must have been deleted by the
      request.


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



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   Found) response.

6.2  Example: REBIND in presence of locks and bind loops

   To illustrate the effects of locks and bind loops on a REBIND
   operation, consider the following collection:

   +------------------+
   | Root Collection  |
   |  bindings:       |
   |  CollW           |
   +------------------+
        |
        |
        |
   +-------------------------------+
   | Collection C1                 |<--------+
   | LOCKED infinity               |         |
   | (lock token L1)               |         |
   | bindings:                     |         |
   | CollX               CollY     |         |
   +-------------------------------+         |
        |                  |                 |
        |                  |  (creates loop) |
        |                  |                 |
   +-----------------+  +------------------+ |
   | Collection C2   |  | Collection C3    | |
   | (inherit lock)  |  | (inherit lock)   | |
   | (lock token L1) |  | (lock token L1)  | |
   | bindings:       |  | bindings:        | |
   |  {none}         |  | y.gif     CollZ  | |
   +-----------------+  +------------------+ |
                          |            |     |
                          |            +-----+
                          |
                      +---------------------------+
                      | Resource R2               |
                      | (lock inherited from C1)  |
                      | (lock token L1)           |
                      +---------------------------+

   (where L1 is "opaquelocktoken:f92d4fae-7012-11ab-a765-00c0ca1f6bf9").

   Note that the binding between CollZ and C1 creates a loop in the
   containment hierarchy.  Servers are not required to support such
   loops, though the server in this example does.





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   The REBIND request below will remove the segment "CollZ" from C3 and
   add a new binding from "CollA" to the collection C2.

   REBIND /CollW/CollX HTTP/1.1
   Host: www.example.com
   If: (<opaquelocktoken:f92d4fae-7012-11ab-a765-00c0ca1f6bf9>)
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:rebind xmlns:D="DAV:">
     <D:segment>CollA</D:segment>
     <D:href>/CollW/CollY/CollZ</D:href>
   </D:rebind>





































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   The outcome of the REBIND operation is:

   +------------------+
   | Root Collection  |
   |  bindings:       |
   |  CollW           |
   +------------------+
        |
        |
        |
   +-------------------------------+
   | Collection C1                 |
   | LOCKED infinity               |
   | (lock token L1)               |
   | bindings:                     |
   | CollX                  CollY  |
   +-------------------------------+
        |              ^      |
        |              |      |
   +-----------------+ | +------------------+
   | Collection C2   | | | Collection C3    |
   |(inherited lock) | | | (inherited lock) |
   |(lock token L1)  | | | (lock token L1)  |
   | bindings:       | | | bindings:        |
   | CollA           | | | y.gif            |
   +-----------------+ | +------------------+
       |               |    |
       +---------------+    |
        (creates loop)      |
                      +---------------------------+
                      | Resource R2               |
                      | (inherited lock from C1)  |
                      | (lock token L1)           |
                      +---------------------------+


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 avoid enumerating the internal
   members of multiple bindings to the same collection repeatedly.  For
   each binding to a collection inside the request's scope, only one
   will be reported with a 200 status, while subsequent DAV:response
   elements for all other bindings will use the 208 status, and no
   DAV:response elements for their descendants are included.




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   Note that the 208 status will only occur for "Depth: infinity"
   requests, and that it is of particular importance when the multiple
   collection bindings cause a bind loop as discussed in Section 2.2.

   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.

   For backward compatibility with clients not aware of the 208 status
   code appearing in multistatus response bodies, it SHOULD NOT be used
   unless the client has signalled support for this specification using
   the "DAV" request header (see Section 8.2).  Instead, a 506 status
   should be returned when a binding loop is discovered.  This allows
   the server to return the 506 as the top level return status, if it
   discovers it before it started the response, or in the middle of a
   multistatus, if it discovers it in the middle of streaming out a
   multistatus response.

7.1.1  Example: PROPFIND by bind-aware client

   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
   DAV: bind
   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:resource-id/>
     </D:prop>
   </D:propfind>

   >> Response:

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxx




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   <?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:resource-id>
             <D:href
   >opaquelocktoken:f81d4fae-7dec-11d0-a765-00a0c91e6bf8</D:href>
           </D:resource-id>
         </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:resource-id>
             <D:href
   >opaquelocktoken:f81d4fae-7dec-11d0-a765-00a0c91e6bf9</D:href>
           </D:resource-id>
         </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:resource-id>
             <D:href
   >opaquelocktoken:f81d4fae-7dec-11d0-a765-00a0c91e6bf8</D:href>
           </D:resource-id>
         </D:prop>
         <D:status>HTTP/1.1 208 Already Reported</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>


7.1.2  Example: PROPFIND by non-bind-aware client

   In this example, the client isn't aware of the 208 status code
   introduced by this specification.  As the "Depth: infinity" PROPFIND



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   request would cause a loop condition, the whole request is rejected
   with a 506 status.

   >> 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>

   >> Response:

   HTTP/1.1 506 Loop Detected


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.

8.  Capability discovery

8.1  OPTIONS method

   If the server supports bindings, it MUST return the compliance class
   name "bind" as a field in the "DAV" response header (see [RFC2518],
   section 9.1) from an OPTIONS request on any resource implemented by
   that server.  A value of "bind" in the "DAV" header MUST indicate
   that the server supports all MUST level requirements and REQUIRED
   features specified in this document.

8.2  'DAV' request header

8.2.1  Generic syntax

   This specification introduces the 'DAV' request header that allows
   clients to signal compliance to specific WebDAV features.  It has the
   same syntax as the response header defined in [RFC2518], section 9.1,
   but MAY be used with any method.




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   Note that clients MUST NOT submit a specific compliance class name in
   the request header unless the specification defining this compliance
   class specifically defines its semantics for clients.

   Note that if a server chooses to vary the result of a request based
   on values in the "DAV" header, the response either MUST NOT be
   cacheable or the server MUST mark the response accordingly using the
   "Vary" header (see [RFC2616], section 14.44).

8.2.2  Client compliance class 'bind'

   Clients SHOULD signal support for all MUST level requirements and
   REQUIRED features by submitting a "DAV" request header containing the
   compliance class name "bind".  In particular, the client MUST
   understand the 208 status code defined in Section 7.1.

9.  Security Considerations

   This section is provided to make WebDAV implementors 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.

9.1  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.

9.2  Bind Loops

   Although bind 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".

9.3  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



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   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.

9.4  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.

9.5  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.

10.  Internationalization Considerations

   All internationalization considerations mentioned in [RFC2518] also
   apply to this document.

11.  IANA Considerations

   All IANA considerations mentioned in [RFC2518] also apply to this
   document.

12.  Acknowledgements

   This document is the collaborative product of the authors and Tyson
   Chihaya, Jim Davis, Chuck Fay and Judith Slein.  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, Lisa
   Dusseault, Stefan Eissing, Roy Fielding, Yaron Goland, Joe
   Hildebrand, Fred Hitt, Alex Hopmann, James Hunt, Marcus Jager, Chris
   Kaler, Manoj Kasichainula, Rohit Khare, Brian Korver, 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.






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13.  References

13.1  Normative References

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

   [RFC2518]  Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D.
              Jensen, "HTTP Extensions for Distributed Authoring --
              WEBDAV", RFC 2518, February 1999.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [XML]      Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E. and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Third
              Edition)", W3C REC-xml-20040204, February 2004,
              <http://www.w3.org/TR/2004/REC-xml-20040204>.

   [draft-fielding-uri-rfc2396bis]
              Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax",
              draft-fielding-uri-rfc2396bis-07 (work in progress),
              September 2004.

13.2  Informative References

   [RFC3253]  Clemm, G., Amsden, J., Ellison, T., Kaler, C. and J.
              Whitehead, "Versioning Extensions to WebDAV (Web
              Distributed Authoring and Versioning)", RFC 3253, March
              2002.


Authors' Addresses

   Geoffrey Clemm
   IBM
   20 Maguire Road
   Lexington, MA  02421

   EMail: geoffrey.clemm@us.ibm.com









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   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


   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".

A.2  Since draft-ietf-webdav-bind-03

   Add and close issues "9.2_redirect_loops", "ED_authors" and
   "ED_updates".  Add section about capability discovery (DAV header).
   Close issues "5.1_LOOP_STATUS".  Add and resolve new issue
   "5.1_506_STATUS_STREAMING".  Update XML spec reference.  Add issue
   "locking" and resolve as invalid.

A.3  Since draft-ietf-webdav-bind-04

   Add and close issues "6_precondition_binding_allowed" and
   "6_lock_behaviour".  Add mailing list and issues list pointers to



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   front.

A.4  Since draft-ietf-webdav-bind-05

   Editorial fixes.  Add and resolve issues "1.3_error_negotiation",
   "2.5_language" and "7.1.1_add_resource_id".  Add historical issue
   "4_LOCK_BEHAVIOR" and it's resolution for better tracking.

A.5  Since draft-ietf-webdav-bind-06

   Rewrite Editorial Note.  Open and resolve issues "2.6_identical",
   "specify_safeness_and_idempotence" and "ED_rfc2026_ref".

A.6  Since draft-ietf-webdav-bind-07

   Add more index items (no change tracking).  Add and resolve issues
   "2.3_copy_to_same", "bind_properties", "bind_vs_ACL",
   "6_rebind_intro" and "rfc2396bis" (actually an action item).  Fix XML
   DTD fragment in section 3.3.  Make spelling of "Request-URI"
   consistent.

A.7  Since draft-ietf-webdav-bind-08

   Resolved editorial issues raised by Jim Whitehead in
   <http://lists.w3.org/Archives/Public/w3c-dist-auth/2004OctDec/0129.ht
   ml>.  Add and resolve issues "atomicity", "2_allow_destroy",
   "2.1_separate_loop_discussion", "2.1.1_bind_loops_vs_locks",
   "2.3_copy_depth_infinity", "2.3_copy_example", "2.3_copy_vs_loops",
   "2.6_resource-id_vs_versions", "3.2_example" and
   "6_rebind_premissions".  Add issue "2.6_when_do_ids_change".  Re-open
   and resolve "6_rebind_intro".

A.8  Since draft-ietf-webdav-bind-09

   Add and resolve issue "6.1_rebind_vs_locks", adding proposed example
   text.  Add action item "3.1_uuids".  Close issue
   "2.6_when_do_ids_change".  Add and resolve issues
   "2.6_bindings_vs_properties" and "uri_draft_ref".

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  uri_draft_ref

   Type: edit



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   julian.reschke@greenbytes.de (2005-01-01): Fix reference to
   draft-fielding-uri-rfc2396bis-07

B.2  2.6_bindings_vs_properties

   Type: change

   <http://lists.w3.org/Archives/Public/w3c-dist-auth/2004OctDec/0248.ht
   ml>

   ejw@cs.ucsc.edu (2004-12-06): I think it would be good to include the
   following language in the bind specification: Note that, consistent
   with [RFC2518], the value of a dead property is independent of the
   number of bindings to its host resource, and of the path submitted to
   PROPFIND.  Since live properties can be aribtrary computational
   processes, they MAY vary depending on path or number of bindings, but
   SHOULD NOT do this unless the definition of the live property
   explicitly includes this dependency.  Here I avoided adding new
   requirements in areas already covered by 2518, but did add
   requirements for the new situation raised by the BIND specification.

   Resolution (2004-12-14): Add that statement (see
   http://lists.w3.org/Archives/Public/w3c-dist-auth/2004OctDec/0299.htm
   l and subsequent messages).

B.3  2.6_when_do_ids_change

   Type: change

   <http://lists.w3.org/Archives/Public/w3c-dist-auth/2004OctDec/0129.ht
   ml>

   ejw@cs.ucsc.edu (2004-11-29): Change "must not" to "MUST NOT" (and
   eliminate the "For example" at the start of the sentence -- perhaps
   change to "Specifically,"

   julian.reschke@greenbytes.de (2004-11-30): Fix language, replace MOVE
   by REBIND (because MOVE may be implemented as COPY/DELETE).  Unclear
   whether we need more changes.

   Resolution (2004-12-13): Closed (see
   http://lists.w3.org/Archives/Public/w3c-dist-auth/2004OctDec/0300.htm
   l).

B.4  6.1_rebind_vs_locks

   Type: change




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   <http://lists.w3.org/Archives/Public/w3c-dist-auth/2004OctDec/0281.ht
   ml>

   ejw@cs.ucsc.edu (2004-12-09): (Request to add a REBIND example that
   requires submitting a lock token)

   Resolution (2004-12-21): Example added.

Appendix C.  Open issues (to be removed by RFC Editor prior to
            publication)

C.1  edit

   Type: edit

   julian.reschke@greenbytes.de (2004-05-30): Umbrella issue for
   editorial fixes/enhancements.

C.2  3.1_uuids

   Type: edit

   julian.reschke@greenbytes.de (2004-12-11): Action item: if
   draft-mealling-uuid-urn gets accepted in time, consider referencing
   it and using urn:uuid URIs instead of opaquelocktoken URIs.  See IETF
   I-D Tracker.

























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Index

2
   208 Already Reported (status code)  29

5
   506 Loop Detected (status code)  32

B
   BIND method  19
   Binding  7

C
   Collection  7
   Condition Names
      DAV:bind-into-collection (pre)  20
      DAV:bind-source-exists (pre)  20
      DAV:binding-allowed (pre)  20
      DAV:binding-deleted (post)  23, 26
      DAV:can-overwrite (pre)  21, 25
      DAV:cross-server-binding (pre)  21, 25
      DAV:cycle-allowed (pre)  21, 25
      DAV:lock-deleted (post)  23, 26
      DAV:locked-overwrite-allowed (pre)  21
      DAV:locked-source-collection-update-allowed (pre)  25
      DAV:locked-update-allowed (pre)  21, 23, 25
      DAV:name-allowed (pre)  21, 25
      DAV:new-binding (post)  21, 26
      DAV:protected-source-url-deletion-allowed (pre)  26
      DAV:protected-url-deletion-allowed (pre)  23
      DAV:protected-url-modification-allowed (pre)  25
      DAV:rebind-from-collection (pre)  25
      DAV:rebind-source-exists (pre)  25
      DAV:unbind-from-collection (pre)  23
      DAV:unbind-source-exists (pre)  23

D
   DAV header
      compliance class 'bind'  32
   DAV:bind-into-collection precondition  20
   DAV:bind-source-exists precondition  20
   DAV:binding-allowed precondition  20
   DAV:binding-deleted postcondition  23, 26
   DAV:can-overwrite precondition  21, 25
   DAV:cross-server-binding precondition  21, 25
   DAV:cycle-allowed precondition  21, 25
   DAV:lock-deleted postcondition  23, 26
   DAV:locked-overwrite-allowed precondition  21



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   DAV:locked-source-collection-update-allowed precondition  25
   DAV:locked-update-allowed precondition  21, 23, 25
   DAV:name-allowed precondition  21, 25
   DAV:new-binding postcondition  21, 26
   DAV:parent-set property  18
   DAV:protected-source-url-deletion-allowed precondition  26
   DAV:protected-url-deletion-allowed precondition  23
   DAV:protected-url-modification-allowed precondition  25
   DAV:rebind-from-collection precondition  25
   DAV:rebind-source-exists precondition  25
   DAV:resource-id property  18
   DAV:unbind-from-collection precondition  23
   DAV:unbind-source-exists precondition  23

I
   Internal Member URI  7

M
   Methods
      BIND  19
      REBIND  24
      UNBIND  22

P
   Path Segment  7
   Properties
      DAV:parent-set  18
      DAV:resource-id  18

R
   REBIND method  24

S
   Status Codes
      208 Already Reported  29
      506 Loop Detected  32

U
   UNBIND method  22
   URI Mapping  6











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Intellectual Property Statement

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Disclaimer of Validity

   This document and the information contained herein are provided on an
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   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




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