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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 2616 (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235) -- Possible downref: Non-RFC (?) normative reference: ref. 'XML' Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Reschke 3 Internet-Draft greenbytes 4 Intended status: Standards Track December 7, 2008 5 Expires: June 10, 2009 7 Using POST to add Members to Web Distributed Authoring and Versioning 8 (WebDAV) Collections 9 draft-reschke-webdav-post-03 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on June 10, 2009. 36 Abstract 38 The Hypertext Transfer Protocol (HTTP) Extensions for the Web 39 Distributed Authoring and Versioning (WebDAV) do not define the 40 behavior for the "POST" method when applied to collections, as the 41 base specification (HTTP) leaves implementers lots of freedom for the 42 semantics of "POST". 44 This has led to a situation where many WebDAV servers do not 45 implement POST for collections at all, although it is well suited to 46 be used for the purpose of adding new members to a collection, where 47 the server remains in control of the newly assigned URL. As a matter 48 of fact, the Atom Publishing Protocol (AtomPub) uses POST exactly for 49 that purpose. On the other hand, WebDAV-based protocols such as the 50 Calendar Extensions to WebDAV (CalDAV) frequently require clients to 51 pick a unique URL, although the server could easily perform that 52 task. 54 This specification defines a discovery mechanism through which 55 servers can advertise support for POST requests with the 56 aforementioned "add collection member" semantics. 58 Editorial Note (To be removed by RFC Editor before publication) 60 Please send comments to the Distributed Authoring and Versioning 61 (WebDAV) working group at , which may be 62 joined by sending a message with subject "subscribe" to 63 . Discussions of the WEBDAV 64 working group are archived at 65 . 67 Note that although discussion takes place on the WebDAV working 68 group's mailing list, this is not a working group document. 70 XML versions, latest edits and the issues list for this document are 71 available from 72 . 74 Table of Contents 76 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 77 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 78 3. Protocol Extension . . . . . . . . . . . . . . . . . . . . . . 5 79 3.1. Definition of 'Add-Member' URI . . . . . . . . . . . . . . 6 80 3.2. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 7 81 3.2.1. DAV:add-member property . . . . . . . . . . . . . . . 7 82 3.2.2. Example . . . . . . . . . . . . . . . . . . . . . . . 7 83 3.3. Relation to AtomPub's 'Slug' Header . . . . . . . . . . . 8 84 3.4. Example Operation . . . . . . . . . . . . . . . . . . . . 8 85 4. Additional Semantics for existing Methods . . . . . . . . . . 9 86 4.1. Additional Preconditions . . . . . . . . . . . . . . . . . 9 87 4.2. Example: Failed PUT Request . . . . . . . . . . . . . . . 9 88 5. Relationship to WebDAV Access Control Protocol . . . . . . . . 10 89 6. Internationalization Considerations . . . . . . . . . . . . . 10 90 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 91 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 92 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 93 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 94 10.1. Normative References . . . . . . . . . . . . . . . . . . . 11 95 10.2. Informative References . . . . . . . . . . . . . . . . . . 12 96 Appendix A. Change Log (to be removed by RFC Editor before 97 publication) . . . . . . . . . . . . . . . . . . . . 12 98 A.1. since draft-reschke-webdav-post-00 . . . . . . . . . . . . 12 99 A.2. since draft-reschke-webdav-post-01 . . . . . . . . . . . . 12 100 A.3. since draft-reschke-webdav-post-02 . . . . . . . . . . . . 12 101 Appendix B. Resolved issues (to be removed by RFC Editor 102 before publication) . . . . . . . . . . . . . . . . . 13 103 B.1. link-header . . . . . . . . . . . . . . . . . . . . . . . 13 104 B.2. ns . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 105 Appendix C. Open issues (to be removed by RFC Editor prior to 106 publication) . . . . . . . . . . . . . . . . . . . . 13 107 C.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 108 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 109 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 110 Intellectual Property and Copyright Statements . . . . . . . . . . 15 112 1. Introduction 114 The Hypertext Transfer Protocol (HTTP) Extensions for the Web 115 Distributed Authoring and Versioning (WebDAV) ([RFC4918], Section 116 9.5) do not define the behavior for the "POST" method when applied to 117 collections, as the base specification (HTTP) leaves implementers 118 lots of freedom for the semantics of "POST": 120 9.5 POST for Collections 122 Since by definition the actual function performed by POST is 123 determined by the server and often depends on the particular 124 resource, the behavior of POST when applied to collections cannot 125 be meaningfully modified because it is largely undefined. Thus, 126 the semantics of POST are unmodified when applied to a collection. 128 This has led to a situation where many WebDAV servers do not 129 implement POST for collections at all, although it is well suited to 130 be used for the purpose of adding new members to a collection, where 131 the server remains in control of the newly assigned URL. As a matter 132 of fact, the Atom Publishing Protocol (AtomPub) uses POST exactly for 133 that purpose ([RFC5023], Section 9.2): 135 9.2 Creating Resources with POST 137 To add members to a Collection, clients send POST requests to the 138 URI of the Collection. 140 On the other hand, WebDAV-based protocols such as Calendaring 141 Extensions to WebDAV (CalDAV) frequently require clients to pick a 142 unique URL, although the server could easily perform that task 143 ([RFC4791], Section 5.3.2): 145 5.3.2 Creating Calendar Object Resources 147 ... 149 When servers create new resources, it's not hard for the server to 150 choose an unmapped URI. It's slightly tougher for clients, 151 because a client might not want to examine all resources in the 152 collection and might not want to lock the entire collection to 153 ensure that a new resource isn't created with a name collision. 154 (...) 156 As a matter of fact, letting the server choose the member URI not 157 only is a simplification for certain types of clients, but can also 158 reduce the complexity of the server (in that it doesn't need to 159 persist an additional client-supplied identifier where it already has 160 an internal one like a UUID or a primary key). 162 Note: the vCard Extensions to WebDAV (CardDAV) 163 ([draft-ietf-vcarddav-carddav]) suffer from the same issue, and 164 may be able to take advantage of this specification. 166 This specification defines a discovery mechanism through which 167 servers can advertise support for POST requests with the 168 aforementioned "add collection member" semantics. 170 Note: the author previously proposed a new HTTP method for exactly 171 this purpose ([draft-reschke-http-addmember]), but quite a few 172 reviewers pointed out that this would duplicate the original 173 semantics of POST. Thus this proposal that avoids adding a new 174 HTTP method is made. 176 2. Terminology 178 The terminology used here follows that in the WebDAV specification 179 ([RFC4918]). 181 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 182 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 183 document are to be interpreted as described in [RFC2119]. 185 This document uses XML DTD fragments ([XML]) as a purely notational 186 convention. In particular: 188 o Element ordering is irrelevant. 190 o Extension elements/attributes (elements/attributes not already 191 defined as valid child elements) may be added anywhere, except 192 when explicitly stated otherwise. 194 Note: this specification defines new properties and precondition 195 names in the "DAV:" namespace, which the WebDAV specification 196 reserves for use by the IETF ([RFC4918], Section 21.1). However, 197 there was rough consensus in the WebDAV community that the 198 specification is of general applicability to other WebDAV related 199 standards efforts, and thus deserves inclusion into the base 200 namespace. 202 3. Protocol Extension 204 Due to the reasons stated in Section 1, clients can not rely on a 205 specific server behavior when POST is applied to a collection. This 206 problem is addressed by this specification by allowing servers to 207 advertise a URI that has the desired "add member" semantics. 209 Note that servers that already use POST for a different purpose can 210 just expose a separate URI. Other servers can just advertise the 211 collection's own URI, thus avoiding minting another URI for a limited 212 purpose. 214 3.1. Definition of 'Add-Member' URI 216 The "Add-Member" URI of a WebDAV collection is a URI that will accept 217 HTTP POST requests, and will interpret these as requests to store the 218 enclosed entity as a new internal member of the collection (see 219 Section 3 of [RFC4918] for the definition of "internal member"). It 220 MUST identify a resource on the same server as the WebDAV collection 221 (the host and port components ([RFC2616], Section 3.2.2) of the URIs 222 must match). 224 If there are pre-conditions related to creating a resource in the 225 collection using a PUT request, then those same pre-conditions apply 226 to the new POST request behavior, and the same HTTP response body 227 will returned on failure. 229 The URI of the newly created resource is returned in the HTTP 230 Location response header ([RFC2616], Section 14.30). 232 Note: the fact that a server advertises an "Add-Member" URI does 233 not imply any special semantics of the collection itself. For 234 instance, member URIs assigned by the server are not necessarily 235 unique over time (a member URI may be assigned again to a new 236 resource when it previously was removed). 238 Note: the "Add-Member" URI can be the identical to the 239 collection's URI (in which case the server just advertises the 240 fact that POST to the WebDAV collection's URI is supported as 241 defined within this specification). But it can also be different 242 from it, in which case it doesn't need to have any relation to the 243 collection's URI. 245 Given a collection URI of 247 /docs/collection/ 248 all of the URIs below might occur as "Add-Member" URIs: 250 /docs/collection/ 251 /docs/collection/;post 252 /docs/collection;post/ 253 /docs/collection/&post 254 /post-service?path=/collection/ 256 The remainder of the document uses the same format just for 257 reasons of consistency; any other HTTP URI on the same server 258 would do as well. 260 3.2. Discovery 262 3.2.1. DAV:add-member property 264 The DAV:add-member property is defined on WebDAV collections, and 265 contains the "Add-Member" URI for that collection (embedded inside a 266 DAV:href element). 268 269 271 A PROPFIND/allprop request SHOULD NOT return this property (see 272 [RFC4918], Section 9.1). Servers MUST implement the DAV:supported- 273 live-property-set property defined in Section 3.1.4 of [RFC3253], and 274 report the property DAV:add-member as a supported live property. 276 3.2.2. Example 278 >>Request 280 PROPFIND /collection/ HTTP/1.1 281 Host: example.com 282 Content-Type: application/xml; charset="utf-8" 283 Content-Length: 118 285 286 287 288 289 290 291 >>Response 293 HTTP/1.1 207 Multi-Status 294 Content-Type: application/xml; charset="utf-8" 295 Content-Length: 340 297 298 299 300 /collection/ 301 302 303 304 /collection;add-member/ 305 306 307 HTTP/1.1 200 OK 308 309 310 312 Note that in this case, the server has minted a separate URI for the 313 purpose of adding new content. 315 3.3. Relation to AtomPub's 'Slug' Header 317 In the AtomPub protocol, clients can use the entity header "Slug" to 318 suggest parts of the URI to be created (see [RFC5023], Section 9.7). 319 Note that servers are free to ignore this suggestion, or to use 320 whatever algorithm that makes sense to generate the new URI. 322 The same applies to the extension defined here: clients can use the 323 "Slug" header as by its definition of a generic HTTP header. Servers 324 should process it exactly the way defined by AtomPub. 326 3.4. Example Operation 328 >>Request 330 POST /collection;add-member/ HTTP/1.1 331 Host: example.com 332 Content-Type: text/plain 333 Slug: Sample Text 334 Content-Length: 12 336 Sample text. 338 >>Response 340 HTTP/1.1 201 Created 341 Location: http://example.com/collection/sample%20text 343 4. Additional Semantics for existing Methods 345 One important use case for this specification are collections that 346 act as WebDAV collections for the purpose of read access (PROPFIND 347 Depth 1/Infinity), but which only support internal member URIs 348 assigned by the server. These collections will not allow a client to 349 create a new member using methods like PUT, MKCOL, LOCK, COPY or 350 MOVE. Therefore, this specification defines a new precondition name 351 ([RFC4918], Section 16) that can be used to provide the client with 352 additional information about why exactly the request failed. 354 4.1. Additional Preconditions 356 (DAV:allow-client-defined-URI): the server allows clients to specify 357 the last path segment for newly created resources. 359 The precondition element MAY contain a add-member-uri XML element 360 specifying the "Add-Member" URI associated with the collection, on 361 which the creation of a new child resource was attempted: 363 365 4.2. Example: Failed PUT Request 367 In this example, the client tries to use PUT to create a new internal 368 member of /collection/. 370 >>Request 372 PUT /collection/new.txt HTTP/1.1 373 Host: example.com 374 Content-Type: text/plain 375 Content-Length: 12 377 Sample text. 379 >>Response 381 HTTP/1.1 405 Method Not Allowed 382 Allow: GET, HEAD, TRACE, PROPFIND, COPY, MOVE 383 Content-Type: application/xml; charset=UTF-8 384 Content-Length: 172 386 387 388 389 /collection;add-member/ 390 391 392 394 The request fails with a 405 (Method Not Allowed) status, but also 395 provides the reason, and a pointer to the "Add-Member" URI in the 396 response body. 398 5. Relationship to WebDAV Access Control Protocol 400 The WebDAV ACL specification requires the DAV:bind privilege to be 401 granted on a collection for the client to able add new collection 402 members ([RFC3744], Section 3.9). Consistent with that, a server 403 MUST reject a POST request to the Add-Member URI of a collection 404 unless the authenticated principal is granted DAV:bind privilege on 405 the associated WebDAV collection resource. 407 6. Internationalization Considerations 409 This document does not introduce any new internationalization 410 considerations beyond those discussed in Section 20 of [RFC4918]. 412 7. IANA Considerations 414 This specification does not require any actions from IANA. 416 8. Security Considerations 418 All security considerations connected to HTTP/WebDAV and XML apply 419 for this specification as well, namely, [RFC4918] (Section 20) and 420 [RFC3470] (Section 7). 422 Furthermore, servers should be aware that deriving the member path 423 from the data being stored in the resource could potentially expose 424 confidential information. This could even be the case when only a 425 hash code of the content is used. 427 In addition, on servers that do not support this specification, a 428 malevolent user could set the DAV:add-member URI as a custom 429 property, tricking other users to post content to an entirely 430 different URI. Clients can protect themselves against this scenario 431 by 433 o not following DAV:add-member URIs to different servers, and/or 435 o verifying that the DAV:add-member property is indeed a live 436 property (this can be achieved by testing the DAV:supported-live- 437 property-set property, or by checking whether DAV:add-member is 438 returned upon PROPFIND/allprop) 440 9. Acknowledgements 442 This document has benefited from thoughtful discussion by Cyrus Daboo 443 and Bernard Desruissaux. 445 10. References 447 10.1. Normative References 449 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 450 Requirement Levels", BCP 14, RFC 2119, March 1997. 452 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 453 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 454 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 456 [RFC3253] Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. 457 Whitehead, "Versioning Extensions to WebDAV", RFC 3253, 458 March 2002. 460 [RFC3744] Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web 461 Distributed Authoring and Versioning (WebDAV) Access 462 Control Protocol", RFC 3744, May 2004. 464 [RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed 465 Authoring and Versioning (WebDAV)", RFC 4918, June 2007. 467 [XML] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and 468 F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth 469 Edition)", W3C REC-xml-20081126, November 2008, 470 . 472 10.2. Informative References 474 [RFC3470] Hollenbeck, S., Rose, M., and L. Masinter, "Guidelines for 475 the Use of Extensible Markup Language (XML) within IETF 476 Protocols", RFC 3470, BCP 70, January 2003. 478 [RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault, 479 "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791, 480 March 2007. 482 [RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing 483 Protocol", RFC 5023, October 2007. 485 [draft-ietf-vcarddav-carddav] 486 Daboo, C., "vCard Extensions to WebDAV (CardDAV)", 487 draft-ietf-vcarddav-carddav-03 (work in progress), 488 November 2008. 490 [draft-reschke-http-addmember] 491 Reschke, J., "The HTTP ADDMEMBER Method", 492 draft-reschke-http-addmember-00 (work in progress), 493 February 2005. 495 Appendix A. Change Log (to be removed by RFC Editor before publication) 497 A.1. since draft-reschke-webdav-post-00 499 Added Acknowledgements. 501 Added and resolved issues "acl", "forbidden-put", "member-uri- 502 content", "post-error-semantics", "property-trust", "rational-server- 503 uri", ""remote-uri", "uri-format" and "uri-uniqueness". 505 A.2. since draft-reschke-webdav-post-01 507 Add and resolve issue "containment". 509 Update draft-ietf-vcarddav-carddav reference. 511 A.3. since draft-reschke-webdav-post-02 513 Update XML, draft-ietf-vcarddav-carddav and 514 draft-nottingham-http-link-header references. 516 Add and resolve issues "link-header" and "ns". 518 Appendix B. Resolved issues (to be removed by RFC Editor before 519 publication) 521 Issues that were either rejected or resolved in this version of this 522 document. 524 B.1. link-header 526 Type: edit 528 julian.reschke@greenbytes.de (2008-12-01): Restructure text so that 529 link header reference becomes informative. 531 Resolution (2008-12-06): Change of plan: leave out discussion of the 532 Link header for now. See http://lists.w3.org/Archives/Public/ 533 w3c-dist-auth/2008OctDec/0038.html. 535 B.2. ns 537 Type: change 539 julian.reschke@greenbytes.de (2008-12-01): Put elements into DAV: 540 namespace. See http://lists.w3.org/Archives/Public/w3c-dist-auth/ 541 2008OctDec/0035.html. 543 Resolution (2008-12-04): Done. 545 Appendix C. Open issues (to be removed by RFC Editor prior to 546 publication) 548 C.1. edit 550 Type: edit 552 julian.reschke@greenbytes.de (2008-09-22): Umbrella issue for 553 editorial fixes/enhancements. 555 Index 557 A 558 Add-Member URI 6 560 C 561 Condition Names 562 DAV:allow-client-defined-URI (pre) 9 563 COPY method 564 Additional Preconditions 9 566 D 567 DAV:allow-client-defined-URI 9 569 L 570 LOCK method 571 Additional Preconditions 9 573 M 574 MKCOL method 575 Additional Preconditions 9 576 MOVE method 577 Additional Preconditions 9 579 P 580 PUT method 581 Additional Preconditions 9 583 Author's Address 585 Julian F. Reschke 586 greenbytes GmbH 587 Hafenweg 16 588 Muenster, NW 48155 589 Germany 591 Phone: +49 251 2807760 592 Email: julian.reschke@greenbytes.de 593 URI: http://greenbytes.de/tech/webdav/ 595 Full Copyright Statement 597 Copyright (C) The IETF Trust (2008). 599 This document is subject to the rights, licenses and restrictions 600 contained in BCP 78, and except as set forth therein, the authors 601 retain all their rights. 603 This document and the information contained herein are provided on an 604 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 605 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 606 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 607 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 608 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 609 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 611 Intellectual Property 613 The IETF takes no position regarding the validity or scope of any 614 Intellectual Property Rights or other rights that might be claimed to 615 pertain to the implementation or use of the technology described in 616 this document or the extent to which any license under such rights 617 might or might not be available; nor does it represent that it has 618 made any independent effort to identify any such rights. 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