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--------------------------------------------------------------------------------
2 INTERNET-DRAFT G. Clemm
3 draft-ietf-webdav-bind-02 IBM
4 J. Crawford
5 IBM Research
6 J. Reschke
7 Greenbytes
8 J. Slein
9 Xerox
10 E.J. Whitehead
11 U.C. Santa Cruz
13 Expires December 27, 2003 June 27, 2003
15 Binding Extensions to WebDAV
17 Status of this Memo
18 This document is an Internet-Draft and is in full conformance with all
19 provisions of RFC 2026, Section 10.
21 Internet-Drafts are working documents of the Internet Engineering Task
22 Force (IETF), its areas, and its working groups. Note that other groups
23 may also distribute working documents as Internet-Drafts.
25 Internet-Drafts are draft documents valid for a maximum of six months
26 and may be updated, replaced, or obsoleted by other documents at any
27 time. It is inappropriate to use Internet-Drafts as reference material
28 or to cite them other than as "work in progress."
30 The list of current Internet-Drafts can be accessed at
31 http://www.ietf.org/ietf/1id-abstracts.txt
33 The list of Internet-Draft Shadow Directories can be accessed at
34 http://www.ietf.org/shadow.html.
36 Abstract
37 This specification defines bindings, and the BIND method for creating
38 multiple bindings to the same resource. Creating a new binding to a
39 resource causes at least one new URI to be mapped to that resource.
40 Servers are required to insure the integrity of any bindings that they
41 allow to be created.
43 Table of Contents
45 1 INTRODUCTION............................................3
46 1.1 Terminology...........................................4
47 1.2 Rationale for Distinguishing Bindings from URI
48 Mappings..............................................6
49 1.3 Method Preconditions and Postconditions...............6
51 2 OVERVIEW OF BINDINGS....................................7
52 2.1 Bindings to Collections...............................7
53 2.2 URI Mappings Created by a new Binding.................8
54 2.3 COPY and Bindings.....................................9
55 2.4 DELETE and Bindings..................................10
56 2.5 MOVE and Bindings....................................10
57 2.6 Determining Whether Two Bindings Are to the Same
58 Resource.............................................11
59 2.7 Discovering the Bindings to a Resource...............12
61 3 PROPERTIES.............................................12
62 3.1 DAV:resource-id Property.............................12
63 3.2 DAV:parent-set Property..............................13
65 4 BIND METHOD............................................13
66 4.1 Example: BIND........................................15
68 5 UNBIND METHOD..........................................15
69 5.1 Example: UNBIND......................................16
71 6 REBIND METHOD..........................................17
72 6.1 Example: REBIND......................................18
74 7 ADDITIONAL STATUS CODES................................19
75 7.1 506 Loop Detected....................................19
77 8 SECURITY CONSIDERATIONS................................20
78 8.1 Privacy Concerns.....................................20
79 8.2 Redirect Loops.......................................21
80 8.3 Bindings, and Denial of Service......................21
81 8.4 Private Locations May Be Revealed....................21
82 8.5 DAV:parent-set and Denial of Service.................21
84 9 INTERNATIONALIZATION CONSIDERATIONS....................21
86 10 IANA CONSIDERATIONS..................................21
88 11 INTELLECTUAL PROPERTY................................22
90 12 ACKNOWLEDGEMENTS.....................................22
92 13 REFERENCES...........................................22
94 14 AUTHORS' ADDRESSES...................................23
95 1 INTRODUCTION
97 This specification extends the WebDAV Distributed Authoring
98 Protocol to enable clients to create new access paths to existing
99 resources. This capability is useful for several reasons:
101 URIs of WebDAV-compliant resources are hierarchical and correspond
102 to a hierarchy of collections in resource space. The WebDAV
103 Distributed Authoring Protocol makes it possible to organize these
104 resources into hierarchies, placing them into groupings, known as
105 collections, which are more easily browsed and manipulated than a
106 single flat collection. However, hierarchies require
107 categorization decisions that locate resources at a single location
108 in the hierarchy, a drawback when a resource has multiple valid
109 categories. For example, in a hierarchy of vehicle descriptions
110 containing collections for cars and boats, a description of a
111 combination car/boat vehicle could belong in either collection.
112 Ideally, the description should be accessible from both. Allowing
113 clients to create new URIs that access the existing resource lets
114 them put that resource into multiple collections.
116 Hierarchies also make resource sharing more difficult, since
117 resources that have utility across many collections are still
118 forced into a single collection. For example, the mathematics
119 department at one university might create a collection of
120 information on fractals that contains bindings to some local
121 resources, but also provides access to some resources at other
122 universities. For many reasons, it may be undesirable to make
123 physical copies of the shared resources on the local server: to
124 conserve disk space, to respect copyright constraints, or to make
125 any changes in the shared resources visible automatically. Being
126 able to create new access paths to existing resources in other
127 collections or even on other servers is useful for this sort of
128 case.
130 The BIND method defined here provides a mechanism for allowing
131 clients to create alternative access paths to existing WebDAV
132 resources. HTTP and WebDAV methods are able to work because there
133 are mappings between URIs and resources. A method is addressed to
134 a URI, and the server follows the mapping from that URI to a
135 resource, applying the method to that resource. Multiple URIs may
136 be mapped to the same resource, but until now there has been no way
137 for clients to create additional URIs mapped to existing resources.
139 BIND lets clients associate a new URI with an existing WebDAV
140 resource, and this URI can then be used to submit requests to the
141 resource. Since URIs of WebDAV resources are hierarchical, and
142 correspond to a hierarchy of collections in resource space, the
143 BIND method also has the effect of adding the resource to a
144 collection. As new URIs are associated with the resource, it
145 appears in additional collections.
147 A BIND request does not create a new resource, but simply makes
148 available a new URI for submitting requests to an existing
149 resource. The new URI is indistinguishable from any other URI when
150 submitting a request to a resource. Only one round trip is needed
151 to submit a request to the intended target. Servers are required
152 to enforce the integrity of the relationships between the new URIs
153 and the resources associated with them. Consequently, it may be
154 very costly for servers to support BIND requests that cross server
155 boundaries.
157 This specification is organized as follows. Section 1.1 defines
158 terminology used in the rest of the specification, while Section
159 1.3 overviews bindings. Section 3 defines the new properties
160 needed to support multiple bindings to the same resource. Section
161 4 specifies the BIND method, used to create multiple bindings to
162 the same resource. Section 5 specifies the UNBIND method, used to
163 remove a binding to a resource. Section 6 specifies the REBIND
164 method, used to move a binding to another collection.
166 1.1 Terminology
168 The terminology used here follows and extends that in the WebDAV
169 Distributed Authoring Protocol specification [RFC2518].
171 This document uses XML DTD fragments as a purely notational
172 convention. WebDAV request and response bodies cannot be validated
173 due to the specific extensibility rules defined in section 23 of
174 [RFC2518] and due to the fact that all XML elements defined by this
175 specification use the XML namespace name "DAV:". In particular:
176 - Element names use the "DAV:" namespace.
177 - Element ordering is irrelevant.
178 - Extension elements/attributes (elements/attributes not already
179 defined as valid child elements) may be added anywhere, except when
180 explicitly stated otherwise.
182 URI Mapping
184 A relation between an absolute URI and a resource. For an absolute
185 URI U and the resource it identifies R, the URI mapping can be
186 thought of as (U => R). Since a resource can represent items that
187 are not network retrievable, as well as those that are, it is
188 possible for a resource to have zero, one, or many URI mappings.
189 Mapping a resource to an "http" scheme URI makes it possible to
190 submit HTTP protocol requests to the resource using the URI.
192 Path Segment
194 Informally, the characters found between slashes ("/") in a URI.
195 Formally, as defined in section 3.3 of [RFC2396].
197 Binding
199 A relation between a single path segment (in a collection) and a
200 resource. A binding is part of the state of a collection. If two
201 different collections contain a binding between the same path
202 segment and the same resource, these are two distinct bindings. So
203 for a collection C, a path segment S, and a resource R, the binding
204 can be thought of as C:(S -> R). Bindings create URI mappings, and
205 hence allow requests to be sent to a single resource from multiple
206 locations in a URI namespace. For example, given a collection C
207 (accessible through the URI http://www.example.com/CollX), a path
208 segment S (equal to "foo.html"), and a resource R, then creating
209 the binding C: (S -> R) makes it possible to use the URI
210 http://www.example.com/CollX/foo.html to access R.
212 Collection
214 A resource that contains, as part of its state, a set of bindings
215 that identify internal member resources.
217 Internal Member URI
219 The URI that identifies an internal member of a collection, and
220 that consists of the URI for the collection, followed by a slash
221 character ('/'), followed by the path segment of the binding for
222 that internal member.
224 1.2 Rationale for Distinguishing Bindings from URI Mappings
226 In [RFC2518], the state of a collection is defined as containing a
227 list of internal member URIs. If there are multiple mappings to a
228 collection, then the state of the collection is different when you
229 refer to it via a different URI. This is undesirable, since ideally
230 a collection's membership should remain the same, independent of
231 which URI was used to reference it.
233 The notion of binding is introduced to separate the final segment
234 of a URI from its parent collection�s contribution. This done, a
235 collection can be defined as containing a set of bindings, thus
236 permitting new mappings to a collection without modifying its
237 membership. The authors of this specification anticipate and
238 recommend that future revisions of [RFC2518] will update the
239 definition of the state of a collection to correspond to the
240 definition in this document.
242 1.3 Method Preconditions and Postconditions
244 A "precondition" of a method describes the state on the server that
245 must be true for that method to be performed. A "postcondition" of
246 a method describes the state on the server that must be true after
247 that method has completed. If a method precondition or
248 postcondition for a request is not satisfied, the response status
249 of the request MUST be either 403 (Forbidden) if the request should
250 not be repeated because it will always fail, or 409 (Conflict) if
251 it is expected that the user might be able to resolve the conflict
252 and resubmit the request.
254 In order to allow better client handling of 403 and 409 responses,
255 a distinct XML element type is associated with each method
256 precondition and postcondition of a request. When a particular
257 precondition is not satisfied or a particular postcondition cannot
258 be achieved, the appropriate XML element MUST be returned as the
259 child of a top-level DAV:error element in the response body, unless
260 otherwise negotiated by the request. In a 207 Multi-Status
261 response, the DAV:error element would appear in the appropriate
262 DAV:responsedescription element.
264 2 OVERVIEW OF BINDINGS
266 Bindings are part of the state of a collection. They define the
267 internal members of the collection, and the names of those internal
268 members.
270 Bindings are added and removed by a variety of existing HTTP
271 methods. A method that creates a new resource, such as PUT, COPY,
272 and MKCOL, adds a binding. A method that deletes a resource, such
273 as DELETE, removes a binding. A method that moves a resource (e.g.
274 MOVE) both adds a binding (in the destination collection) and
275 removes a binding (in the source collection). The BIND method
276 introduced here provides a mechanism for adding a second binding to
277 an existing resource. There is no difference between an initial
278 binding added by PUT, COPY, or MKCOL, and additional bindings added
279 with BIND.
281 It would be very undesirable if one binding could be destroyed as a
282 side effect of operating on the resource through a different
283 binding. In particular, the removal of one binding to a resource
284 (e.g. with a DELETE or a MOVE) MUST NOT disrupt another binding to
285 that resource, e.g. by turning that binding into a dangling path
286 segment. The server MUST NOT reclaim system resources after
287 removing one binding, while other bindings to the resource remain.
288 In other words, the server MUST maintain the integrity of a
289 binding.
291 2.1 Bindings to Collections
293 Bindings to collections can result in loops, which servers MUST
294 detect when processing "Depth: infinity" requests. It is sometimes
295 possible to complete an operation in spite of the presence of a
296 loop. However, the 506 (Loop Detected) status code is defined in
297 Section 5 for use in contexts where an operation is terminated
298 because a loop was encountered.
300 Creating a new binding to a collection makes each resource
301 associated with a binding in that collection accessible via a new
302 URI, and thus creates new URI mappings to those resources but no
303 new bindings.
305 For example, suppose a new binding CollY is created for collection
306 C1 in the figure below. It immediately becomes possible to access
307 resource R1 using the URI /CollY/x.gif and to access resource R2
308 using the URI /CollY/y.jpg, but no new bindings for these child
309 resources were created. This is because bindings are part of the
310 state of a collection, and associate a URI that is relative to that
311 collection with its target resource. No change to the bindings in
312 Collection C1 is needed to make its children accessible using
313 /CollY/x.gif and /CollY/y.jpg.
315 +-------------------------+
316 | Root Collection |
317 | bindings: |
318 | CollX CollY |
319 +-------------------------+
320 | /
321 | /
322 | /
323 +------------------+
324 | Collection C1 |
325 | bindings: |
326 | x.gif y.jpg |
327 +------------------+
328 | \
329 | \
330 | \
331 +-------------+ +-------------+
332 | Resource R1 | | Resource R2 |
333 +-------------+ +-------------+
335 2.2 URI Mappings Created by a new Binding
337 Suppose a binding from "Binding-Name" to resource R to be added to
338 a collection, C. Then if C-MAP is the set of URIs that were mapped
339 to C before the BIND request, then for each URI "C-URI" in C-MAP,
340 the URI "C-URI/Binding-Name" is mapped to resource R following the
341 BIND request.
343 For example, if a binding from "foo.html" to R is added to a
344 collection C, and if the following URIs are mapped to C:
346 http://www.example.com/A/1/
347 http://example.com/A/one/
349 then the following new mappings to R are introduced:
351 http://www.example.com/A/1/foo.html
352 http://example.com/A/one/foo.html
354 Note that if R is a collection, additional URI mappings are created
355 to the descendents of R. Also, note that if a binding is made in
356 collection C to C itself (or to a parent of C), an infinite number
357 of mappings are introduced.
359 For example, if a binding from "myself" to C is then added to C,
360 the following infinite number of additional mappings to C are
361 introduced:
363 http://www.example.com/A/1/myself
364 http://www.example.com/A/1/myself/myself
365 ...
367 and the following infinite number of additional mappings to R are
368 introduced:
370 http://www.example.com/A/1/myself/foo.html
371 http://www.example.com/A/1/myself/myself/foo.html
372 ...
374 2.3 COPY and Bindings
376 As defined in Section 8.8 of [RFC2518], COPY causes the resource
377 identified by the Request-URI to be duplicated, and makes the new
378 resource accessible using the URI specified in the Destination
379 header. Upon successful completion of a COPY, a new binding is
380 created between the last path segment of the Destination header,
381 and the destination resource. The new binding is added to its
382 parent collection, identified by the Destination header minus its
383 final segment.
385 The following figure shows an example: Suppose that a COPY is
386 issued to URI-3 for resource R (which is also mapped to URI-1 and
387 URI-2), with the Destination header set to URI-X. After successful
388 completion of the COPY operation, resource R is duplicated to
389 create resource R', and a new binding has been created which
390 creates at least the URI mapping between URI-X and the new resource
391 (although other URI mappings may also have been created).
393 URI-1 URI-2 URI-3 URI-X
394 | | | |
395 | | | <---- URI Mappings ----> |
396 | | | |
397 +---------------------+ +------------------------+
398 | Resource R | | Resource R' |
399 +---------------------+ +------------------------+
401 It might be thought that a COPY request with "Depth: 0" on a
402 collection would duplicate its bindings, since bindings are part of
403 the collection's state. This is not the case, however. The
404 definition of Depth in [RFC2518] makes it clear that a "Depth: 0"
405 request does not apply to a collection's members. Consequently, a
406 COPY with "Depth: 0" does not duplicate the bindings contained by
407 the collection.
409 If a COPY causes one or more existing resources to be updated, the
410 bindings to those resources MUST be unaffected by the COPY. Using
411 the preceding example, suppose that a COPY is issued to URI-X for
412 resource R', with the Destination header set to URI-2. The content
413 and dead properties of resource R would be updated to be a copy of
414 those of resource R', but the mappings from URI-1, URI-2, and URI-3
415 to resource R remain unaffected.
417 2.4 DELETE and Bindings
419 When there are multiple bindings to a resource, a DELETE applied to
420 that resource MUST NOT remove any bindings to that resource other
421 than the one identified by the request URI. For example, suppose
422 the collection identified by the URI "/a" has a binding named "x"
423 to a resource R, and another collection identified by "/b" has a
424 binding named "y" to the same resource R. Then a DELETE applied to
425 "/a/x" removes the binding named "x" from "/a" but MUST NOT remove
426 the binding named "y" from "/b" (i.e. after the DELETE, "/y/b"
427 continues to identify the resource R). In particular, although
428 Section 8.6.1 of [RFC2518] states that during DELETE processing, a
429 server "MUST remove any URI for the resource identified by the
430 Request-URI from collections which contain it as a member", a
431 server that supports the binding protocol MUST NOT follow this
432 requirement.
434 When DELETE is applied to a collection, it MUST NOT modify the
435 membership of any other collection that is not itself a member of
436 the collection being deleted. For example, if both "/a/.../x" and
437 "/b/.../y" identify the same collection, C, then applying DELETE to
438 "/a" MUST NOT delete an internal member from C or from any other
439 collection that is a member of C, because that would modify the
440 membership of "/b".
442 If a collection supports the UNBIND method (see Section 5), a
443 DELETE of an internal member of a collection MAY be implemented as
444 an UNBIND request. In this case, applying DELETE to a Request-URI
445 has the effect of removing the binding identified by the final
446 segment of the Request-URI from the collection identified by the
447 Request-URI minus its final segment. Although [RFC2518] allows a
448 DELETE to be a non-atomic operation, when the DELETE operation is
449 implemented as an UNBIND, the operation is atomic. In particular,
450 a DELETE on a hierarchy of resources is simply the removal of a
451 binding to the collection identified by the Request-URI.
453 2.5 MOVE and Bindings
455 When MOVE is applied to a resource, the other bindings to that
456 resource MUST be unaffected, and if the resource being moved is a
457 collection, the bindings to any members of that collection MUST be
458 unaffected. Also, if MOVE is used with Overwrite:T to delete an
459 existing resource, the constraints specified for DELETE apply.
461 If the destination collection of a MOVE request supports the REBIND
462 method (see Section 6), a MOVE of a resource into that collection
463 MAY be implemented as a REBIND request. Although [RFC2518] allows
464 a MOVE to be a non-atomic operation, when the MOVE operation is
465 implemented as a REBIND, the operation is atomic. In particular,
466 applying a MOVE to a Request-URI and a Destination URI has the
467 effect of removing a binding to a resource (at the Request-URI),
468 and creating a new binding to that resource (at the Destination
469 URI).
471 As an example, suppose that a MOVE is issued to URI-3 for resource
472 R below (which is also mapped to URI-1 and URI-2), with the
473 Destination header set to URI-X. After successful completion of
474 the MOVE operation, a new binding has been created which creates
475 the URI mapping between URI-X and resource R. The binding
476 corresponding to the final segment of URI-3 has been removed, which
477 also causes the URI mapping between URI-3 and R to be removed. If
478 resource R were a collection, old URI-3 based mappings to members
479 of R would have been removed, and new URI-X based mappings to
480 members of R would have been created.
482 >> Before Request:
484 URI-1 URI-2 URI-3
485 | | |
486 | | | <---- URI Mappings
487 | | |
488 +---------------------+
489 | Resource R |
490 +---------------------+
492 >> After Request:
494 URI-1 URI-2 URI-X
495 | | |
496 | | | <---- URI Mappings
497 | | |
498 +---------------------+
499 | Resource R |
500 +---------------------+
502 Although [RFC2518] allows a MOVE on a collection to be a non-atomic
503 operation, a MOVE implemented as a REBIND MUST be atomic. Even
504 when the Request-URI identifies a collection, the MOVE operation
505 involves only removing one binding to that collection and adding
506 another. There are no operations on bindings to any of its
507 children, so the case of MOVE on a collection is the same as the
508 case of MOVE on a non-collection resource. Both are atomic.
510 2.6 Determining Whether Two Bindings Are to the Same Resource
512 It is useful to have some way of determining whether two bindings
513 are to the same resource. Two resources might have identical
514 contents and properties, but not be the same resource (e.g. an
515 update to one resource does not affect the other resource).
517 The REQUIRED DAV:resource-id property defined in Section 3.1 is a
518 resource identifier, which MUST be unique across all resources for
519 all time. If the values of DAV:resource-id returned by PROPFIND
520 requests through two bindings are identical, the client can be
521 assured that the two bindings are to the same resource.
523 The DAV:resource-id property is created, and its value assigned,
524 when the resource is created. The value of DAV:resource-id MUST
525 NOT be changed. Even after the resource is no longer accessible
526 through any URI, that value MUST NOT be reassigned to another
527 resource's DAV:resource-id property.
529 Any method that creates a new resource MUST assign a new, unique
530 value to its DAV:resource-id property. For example, a PUT or a
531 COPY that creates a new resource must assign a new, unique value to
532 the DAV:resource-id property of that new resource.
534 On the other hand, any method that affects an existing resource
535 MUST NOT change the value of its DAV:resource-id property. For
536 example, a PUT or a COPY that updates an existing resource must not
537 change the value of its DAV:resource-id property. A MOVE, since it
538 does not create a new resource, but only changes the location of an
539 existing resource, must not change the value of the DAV:resource-id
540 property.
542 2.7 Discovering the Bindings to a Resource
544 An OPTIONAL DAV:parent-set property on a resource provides a list
545 of the bindings that associate a collection and a URI segment with
546 that resource. If the DAV:parent-set property exists on a given
547 resource, it MUST contain a complete list of all bindings to that
548 resource that the client is authorized to see. When deciding
549 whether to support the DAV:parent-set property, server implementers
550 / administrators should balance the benefits it provides against
551 the cost of maintaining the property and the security risks
552 enumerated in Sections 8.4 and 8.5.
554 3 PROPERTIES
556 The bind feature introduces the following properties for a
557 resource.
559 A DAV:allprop PROPFIND request SHOULD NOT return any of the
560 properties defined by this document. This allows a binding server
561 to perform efficiently when a naive client, which does not
562 understand the cost of asking a server to compute all possible live
563 properties, issues a DAV:allprop PROPFIND request.
565 3.1 DAV:resource-id Property
567 The DAV:resource-id property is a REQUIRED property that enables
568 clients to determine whether two bindings are to the same resource.
569 The value of DAV:resource-id is a URI, and may use any registered
570 URI scheme that guarantees the uniqueness of the value across all
571 resources for all time (e.g. the opaquelocktoken: scheme defined in
572 [RFC2518]).
574
576 3.2 DAV:parent-set Property
578 The DAV:parent-set property is an OPTIONAL property that enables
579 clients to discover what collections contain a binding to this
580 resource (i.e. what collections have that resource as an internal
581 member). It contains an of href/segment pair for each collection
582 that has a binding to the resource. The href identifies the
583 collection, and the segment identifies the binding name of that
584 resource in that collection.
586 A given collection MUST appear only once in the DAV:parent-set for
587 any given binding, even if there are multiple URI mappings to that
588 collection. For example, if collection C1 is mapped to both /CollX
589 and /CollY, and C1 contains a binding named "x.gif" to a resource
590 R1, then either [/CollX, x.gif] or [/CollY, x.gif] can appear in
591 the DAV:parent-set of R1, but not both. But if C1 also had a
592 binding named "y.gif" to R1, then there would be two entries for C1
593 in the DAV:binding-set of R1 (i.e. either both [/CollX, x.gif] and
594 [/CollX, y.gif] or alternatively, both [/CollY, x.gif] and [/CollY,
595 y.gif]).
597
598
599
600 PCDATA value: segment, as defined in section 3.3 of [RFC2396]
602 4 BIND METHOD
604 The BIND method modifies the collection identified by the Request-
605 URI, by adding a new binding from the segment specified in the BIND
606 body to the resource identified in the BIND body.
608 If a server cannot guarantee the integrity of the binding, the BIND
609 request MUST fail. Note that it is especially difficult to
610 maintain the integrity of cross-server bindings. Unless the server
611 where the resource resides knows about all bindings on all servers
612 to that resource, it may unwittingly destroy the resource or make
613 it inaccessible without notifying another server that manages a
614 binding to the resource. For example, if server A permits creation
615 of a binding to a resource on server B, server A must notify server
616 B about its binding and must have an agreement with B that B will
617 not destroy the resource while A's binding exists. Otherwise
618 server B may receive a DELETE request that it thinks removes the
619 last binding to the resource and destroy the resource while A's
620 binding still exists. Status code 507 (Cross-server Binding
621 Forbidden) is defined in Section 7.1 for cases where servers fail
622 cross-server BIND requests because they cannot guarantee the
623 integrity of cross-server bindings.
625 By default, if there already is a binding for the specified segment
626 in the collection, the new binding replaces the existing binding.
628 This default binding replacement behavior can be overridden using
629 the Overwrite header defined in Section 9.6 of [RFC2518].
631 Marshalling:
633 The request MAY include an Overwrite header.
635 The request body MUST be a DAV:bind XML element.
637
639 If the request succeeds, the server MUST return 201 (Created) when
640 a new binding was created and 200 (OK) when an existing binding was
641 replaced.
643 If a response body for a successful request is included, it MUST be
644 a DAV:bind-response XML element. Note that this document does not
645 define any elements for the BIND response body, but the DAV:bind-
646 response element is defined to ensure interoperability between
647 future extensions that do define elements for the BIND response
648 body.
650
652 Preconditions:
654 (DAV:bind-into-collection): The Request-URI MUST identify a
655 collection.
657 (DAV:bind-source-exists): The DAV:href element MUST identify a
658 resource.
660 (DAV:binding-allowed): The resource identified by the DAV:href
661 supports multiple bindings to it.
663 (DAV:cross-server-binding): If the resource identified by the
664 DAV:href element in the request body is on another server from the
665 collection identified by the request-URI, the server MUST support
666 cross-server bindings.
668 (DAV:name-allowed): The name specified by the DAV:segment is
669 available for use as a new binding name.
671 (DAV:can-overwrite): If the collection already contains a binding
672 with the specified path segment, and if an Overwrite header is
673 included, the value of the Overwrite header MUST be "T".
675 (DAV:cycle-allowed): If the DAV:href element identifies a
676 collection, and if the request-URI identifies a collection that is
677 a member of that collection, the server MUST support cycles in the
678 URI namespace.
680 (DAV:locked-update-allowed): If the collection identified by the
681 Request-URI is write-locked, then the appropriate token MUST be
682 specified in an If request header.
684 (DAV:locked-overwrite-allowed): If the collection already contains
685 a binding with the specified path segment, and if that binding is
686 protected by a write-lock, then the appropriate token MUST be
687 specified in an If request header.
689 Postconditions:
691 (DAV:new-binding): The collection MUST have a binding that maps the
692 segment specified in the DAV:segment element in the request body,
693 to the resource identified by the DAV:href element in the request
694 body.
696 4.1 Example: BIND
698 >> Request:
700 BIND /CollY HTTP/1.1
701 Host: www.example.com
702 Content-Type: text/xml; charset="utf-8"
703 Content-Length: xxx
705
706
707 bar.html
708 http://www.example.com/CollX/foo.html
709
711 >> Response:
713 HTTP/1.1 201 Created
715 The server added a new binding to the collection,
716 "http://www.example.com/CollY", associating "bar.html" with the
717 resource identified by the URI
718 "http://www.example.com/CollX/foo.html". Clients can now use the
719 URI "http://www.example.com/CollY/bar.html", to submit requests to
720 that resource.
722 5 UNBIND METHOD
724 The UNBIND method modifies the collection identified by the
725 Request-URI, by removing the binding identified by the segment
726 specified in the UNBIND body.
728 Once a resource is unreachable by any URI mapping, the server MAY
729 reclaim system resources associated with that resource. If UNBIND
730 removes a binding to a resource, but there remain URI mappings to
731 that resource, the server MUST NOT reclaim system resources
732 associated with the resource.
734 Marshalling:
736 The request body MUST be a DAV:unbind XML element.
738
740 If the request succeeds, the server MUST return 200 (OK) when the
741 binding was successfully deleted.
743 If a response body for a successful request is included, it MUST be
744 a DAV:unbind-response XML element. Note that this document does
745 not define any elements for the UNBIND response body, but the
746 DAV:unbind-response element is defined to ensure interoperability
747 between future extensions that do define elements for the UNBIND
748 response body.
750
752 Preconditions:
754 (DAV:unbind-from-collection): The Request-URI MUST identify a
755 collection.
757 (DAV:unbind-source-exists): The DAV:segment element MUST identify a
758 binding in the collection identified by the Request-URI.
760 (DAV:locked-update-allowed): If the collection identified by the
761 Request-URI is write-locked, then the appropriate token MUST be
762 specified in the request.
764 (DAV:protected-url-deletion-allowed): If the binding identified by
765 the segment is protected by a write-lock, then the appropriate
766 token MUST be specified in the request.
768 Postconditions:
770 (DAV:binding-deleted): The collection MUST NOT have a binding for
771 the segment specified in the DAV:segment element in the request
772 body.
774 5.1 Example: UNBIND
776 >> Request:
778 UNBIND /CollX HTTP/1.1
779 Host: www.example.com
780 Content-Type: text/xml; charset="utf-8"
781 Content-Length: xxx
783
784
785 foo.html
786
788 >> Response:
790 HTTP/1.1 200 OK
792 The server removed the binding named "foo.html" from the
793 collection, "http://www.example.com/CollX". A request to the
794 resource named "http://www.example.com/CollX/foo.html" will return
795 a 404 (Not Found) response.
797 6 REBIND METHOD
799 The REBIND method removes a binding to a resource from one
800 collection, and adds a binding to that resource into another
801 collection. It is effectively an atomic form of a MOVE request.
803 Marshalling:
805 The request MAY include an Overwrite header.
807 The request body MUST be a DAV:rebind XML element.
809
811 If the request succeeds, the server MUST return 201 (Created) when
812 a new binding was created and 200 (OK) when an existing binding was
813 replaced.
815 If a response body for a successful request is included, it MUST be
816 a DAV:rebind-response XML element. Note that this document does
817 not define any elements for the REBIND response body, but the
818 DAV:rebind-response element is defined to ensure interoperability
819 between future extensions that do define elements for the REBIND
820 response body.
822
824 Preconditions:
826 (DAV:rebind-into-collection): The Request-URI MUST identify a
827 collection.
829 (DAV:rebind-source-exists): The DAV:href element MUST identify a
830 resource.
832 (DAV:binding-allowed): The resource identified by the DAV:href
833 supports multiple bindings to it.
835 (DAV:cross-server-binding): If the resource identified by the
836 DAV:href element in the request body is on another server from the
837 collection identified by the request-URI, the server MUST support
838 cross-server bindings.
840 (DAV:name-allowed): The name specified by the DAV:segment is
841 available for use as a new binding name.
843 (DAV:can-overwrite): If the collection already contains a binding
844 with the specified path segment, and if an Overwrite header is
845 included, the value of the Overwrite header MUST be "T".
847 (DAV:cycle-allowed): If the DAV:href element identifies a
848 collection, and if the request-URI identifies a collection that is
849 a member of that collection, the server MUST support cycles in the
850 URI namespace.
852 (DAV:locked-update-allowed): If the collection identified by the
853 Request-URI is write-locked, then the appropriate token MUST be
854 specified in the request.
856 (DAV:protected-url-modification-allowed): If the collection
857 identified by the Request-URI already contains a binding with the
858 specified path segment, and if that binding is protected by a
859 write-lock, then the appropriate token MUST be specified in the
860 request.
862 (DAV:locked-source-collection-update-allowed): If the collection
863 identified by the parent collection prefix of the DAV:href URI is
864 write-locked, then the appropriate token MUST be specified in the
865 request.
867 (DAV:protected-source-url-deletion-allowed): If the DAV:href URI is
868 protected by a write lock, then the appropriate token MUST be
869 specified in the request.
871 Postconditions:
873 (DAV:new-binding): The collection MUST have a binding that maps the
874 segment specified in the DAV:segment element in the request body,
875 to the resource that was identified by the DAV:href element in the
876 request body.
878 (DAV:binding-deleted): The URL specified in the DAV:href element in
879 the request body MUST NOT be mapped to a resource.
881 6.1 Example: REBIND
883 >> Request:
885 REBIND /CollX HTTP/1.1
886 Host: www.example.com
887 Content-Type: text/xml; charset="utf-8"
888 Content-Length: xxx
889
890
891 foo.html
892 http://www.example.com/CollY/bar.html
893
895 >> Response:
897 HTTP/1.1 200 OK
899 The server added a new binding to the collection,
900 "http://www.example.com/CollX", associating "foo.html" with the
901 resource identified by the URI
902 "http://www.example.com/CollY/bar.html", and removes the binding
903 named "bar.html" from the collection identified by the URI
904 "http://www.example.com/CollY". Clients can now use the URI
905 "http://www.example.com/CollX/foo.html" to submit requests to that
906 resource, and requests on the URI
907 "http://www.example.com/CollY/bar.html" will fail with a 404 (Not
908 Found) response.
910 7 ADDITIONAL STATUS CODES
912 7.1 506 Loop Detected
914 The 506 (Loop Detected) status code indicates that the server
915 terminated an operation because it encountered an infinite loop
916 while processing a request with "Depth: infinity".
918 When this status code is the top-level status code for the
919 operation, it indicates that the entire operation failed.
921 When this status code occurs inside a multi-status response, it
922 indicates only that a loop is being terminated, but does not
923 indicate failure of the operation as a whole.
925 For example, consider a PROPFIND request on /Coll (bound to
926 collection C), where the members of /Coll are /Coll/Foo (bound to
927 resource R) and /Coll/Bar (bound to collection C).
929 >> Request:
931 PROPFIND /Coll/ HTTP/1.1
932 Host: www.example.com
933 Depth: infinity
934 Content-Type: text/xml; charset="utf-8"
935 Content-Length: xxx
937
938
939
940
941 >> Response:
943 HTTP/1.1 207 Multi-Status
944 Content-Type: text/xml; charset="utf-8"
945 Content-Length: xxx
947
948
949
950 http://www.example.com/Coll/
951
952
953 Loop Demo
954
955 HTTP/1.1 200 OK
956
957
958
959 http://www.example.com/Coll/Foo
960
961
962 Bird Inventory
963
964 HTTP/1.1 200 OK
965
966
967
968 http://www.example.com/Coll/Bar
969 HTTP/1.1 506 Loop Detected
970
971
973 8 SECURITY CONSIDERATIONS
975 This section is provided to make WebDAV applications aware of the
976 security implications of this protocol.
978 All of the security considerations of HTTP/1.1 and the WebDAV
979 Distributed Authoring Protocol specification also apply to this
980 protocol specification. In addition, bindings introduce several
981 new security concerns and increase the risk of some existing
982 threats. These issues are detailed below.
984 8.1 Privacy Concerns
986 In a context where cross-server bindings are supported, creating
987 bindings on a trusted server may make it possible for a hostile
988 agent to induce users to send private information to a target on a
989 different server.
991 8.2 Redirect Loops
993 Although redirect loops were already possible in HTTP 1.1, the
994 introduction of the BIND method creates a new avenue for clients to
995 create loops accidentally or maliciously. If the binding and its
996 target are on the same server, the server may be able to detect
997 BIND requests that would create loops. Servers are required to
998 detect loops that are caused by bindings to collections during the
999 processing of any requests with "Depth: infinity".
1001 8.3 Bindings, and Denial of Service
1003 Denial of service attacks were already possible by posting URIs
1004 that were intended for limited use at heavily used Web sites. The
1005 introduction of BIND creates a new avenue for similar denial of
1006 service attacks. If cross-server bindings are supported, clients
1007 can now create bindings at heavily used sites to target locations
1008 that were not designed for heavy usage.
1010 8.4 Private Locations May Be Revealed
1012 If the DAV:parent-set property is maintained on a resource, the
1013 owners of the bindings risk revealing private locations. The
1014 directory structures where bindings are located are available to
1015 anyone who has access to the DAV:parent-set property on the
1016 resource. Moving a binding may reveal its new location to anyone
1017 with access to DAV:parent-set on its resource.
1019 8.5 DAV:parent-set and Denial of Service
1021 If the server maintains the DAV:parent-set property in response to
1022 bindings created in other administrative domains, it is exposed to
1023 hostile attempts to make it devote resources to adding bindings to
1024 the list.
1026 9 INTERNATIONALIZATION CONSIDERATIONS
1028 All internationalization considerations mentioned in [RFC2518] also
1029 apply to this document.
1031 10 IANA CONSIDERATIONS
1033 All IANA considerations mentioned in [RFC2518] also apply to this
1034 document.
1036 11 INTELLECTUAL PROPERTY
1038 The following notice is copied from RFC 2026, Section 10.4, and
1039 describes the position of the IETF concerning intellectual property
1040 claims made against this document.
1042 The IETF takes no position regarding the validity or scope of any
1043 intellectual property or other rights that might be claimed to
1044 pertain to the implementation or use other technology described in
1045 this document or the extent to which any license under such rights
1046 might or might not be available; neither does it represent that it
1047 has made any effort to identify any such rights. Information on
1048 the procedures of the IETF with respect to rights in standards-
1049 track and standards-related documentation can be found in BCP-11.
1050 Copies of claims of rights made available for publication and any
1051 assurances of licenses to be made available, or the result of an
1052 attempt made to obtain a general license or permission for the use
1053 of such proprietary rights by implementers or users of this
1054 specification can be obtained from the IETF Secretariat.
1056 The IETF invites any interested party to bring to its attention any
1057 copyrights, patents or patent applications, or other proprietary
1058 rights that may cover technology that may be required to practice
1059 this standard. Please address the information to the IETF
1060 Executive Director.
1062 12 ACKNOWLEDGEMENTS
1064 This draft is the collaborative product of the authors and Tyson
1065 Chihaya, Jim Davis, and Chuck Fay. This draft has benefited from
1066 thoughtful discussion by Jim Amsden, Peter Carlson, Steve Carter,
1067 Ken Coar, Ellis Cohen, Dan Connolly, Bruce Cragun, Spencer Dawkins,
1068 Mark Day, Rajiv Dulepet, David Durand, Roy Fielding, Yaron Goland,
1069 Fred Hitt, Alex Hopmann, James Hunt, Marcus Jager, Chris Kaler,
1070 Manoj Kasichainula, Rohit Khare, Daniel LaLiberte, Steve Martin,
1071 Larry Masinter, Jeff McAffer, Surendra Koduru Reddy, Max Rible, Sam
1072 Ruby, Bradley Sergeant, Nick Shelness, John Stracke, John Tigue,
1073 John Turner, Kevin Wiggen, and other members of the WebDAV working
1074 group.
1076 13 REFERENCES
1078 [RFC2026] S.Bradner, "The Internet Standards Process", RFC 2026,
1079 October 1996.
1081 [RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
1082 Requirement Levels", RFC 2119, March 1997.
1084 [RFC2277] H.Alvestrand, "IETF Policy on Character Sets and
1085 Languages." RFC 2277, January 1998.
1087 [RFC2396] T. Berners-Lee, R. Fielding, L. Masinter, "Uniform
1088 Resource Identifiers (URI): Generic Syntax." RFC 2396, August 1998.
1090 [RFC2518] Y.Goland, E.Whitehead, A.Faizi, S.R.Carter, D.Jensen,
1091 "HTTP Extensions for Distributed Authoring - WEBDAV", RFC 2518,
1092 February 1999.
1094 [RFC2616] R.Fielding, J.Gettys, J.C.Mogul, H.Frystyk, L.Masinter,
1095 P.Leach, and T.Berners-Lee, "Hypertext Transfer Protocol --
1096 HTTP/1.1", RFC 2616, June 1999.
1098 [XML] T. Bray, J. Paoli, C.M. Sperberg-McQueen, "Extensible Markup
1099 Language (XML) 1.0 (Second Edition)" W3C Recommendation 6 October
1100 2000. http://www.w3.org/TR/2000/REC-xml-20001006.
1102 14 AUTHORS' ADDRESSES
1104 Geoffrey Clemm
1105 Rational Software Corporation
1106 20 Maguire Road
1107 Lexington, MA 02173-3104
1108 Email: geoffrey.clemm@us.ibm.com
1110 Jason Crawford
1111 IBM Research
1112 P.O. Box 704
1113 Yorktown Heights, NY 10598
1114 Email: ccjason@us.ibm.com
1116 Julian F. Reschke
1117 greenbytes GmbH
1118 Salzmannstrasse 152
1119 Muenster, NW 48159, Germany
1120 Email: julian.reschke@greenbytes.de
1122 Judy Slein
1123 Xerox Corporation
1124 800 Phillips Road, 105-50C
1125 Webster, NY 14580
1126 Email: jslein@crt.xerox.com
1128 Jim Whitehead
1129 UC Santa Cruz, Dept. of Computer Science
1130 1156 High Street, Santa Cruz, CA 95064
1131 Email: ejw@cse.ucsc.edu