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'XML' Summary: 6 errors (**), 0 flaws (~~), 9 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 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