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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) ** Obsolete normative reference: RFC 2818 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 4627 (Obsoleted by RFC 7158, RFC 7159) ** Obsolete normative reference: RFC 5785 (Obsoleted by RFC 8615) ** Obsolete normative reference: RFC 5988 (Obsoleted by RFC 8288) -- Possible downref: Non-RFC (?) normative reference: ref. '1' Summary: 6 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Hammer-Lahav 3 Internet-Draft Yahoo! 4 Intended status: Standards Track B. Cook 5 Expires: November 10, 2011 May 9, 2011 7 Web Host Metadata 8 draft-hammer-hostmeta-15 10 Abstract 12 This specification describes a method for locating host metadata as 13 well as information about individual resources controlled by the 14 host. 16 Editorial Note (to be removed by RFC Editor) 18 Please discuss this draft on the apps-discuss@ietf.org [1] mailing 19 list. 21 Status of this Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on November 10, 2011. 38 Copyright Notice 40 Copyright (c) 2011 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 1.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 1.1.1. Processing Resource-Specific Information . . . . . . . 5 58 1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 6 59 2. Obtaining host-meta Documents . . . . . . . . . . . . . . . . 6 60 3. The host-meta Document . . . . . . . . . . . . . . . . . . . . 7 61 3.1. XML Document format . . . . . . . . . . . . . . . . . . . 8 62 3.1.1. The 'Link' Element . . . . . . . . . . . . . . . . . . 8 63 4. Processing host-meta Documents . . . . . . . . . . . . . . . . 10 64 4.1. Host-Wide Information . . . . . . . . . . . . . . . . . . 10 65 4.2. Resource-Specific Information . . . . . . . . . . . . . . 10 66 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 67 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 68 6.1. The 'host-meta' Well-Known URI . . . . . . . . . . . . . . 12 69 6.2. The 'lrdd' Relation Type . . . . . . . . . . . . . . . . . 12 70 Appendix A. JRD Document Format . . . . . . . . . . . . . . . . . 13 71 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 16 72 7. Normative References . . . . . . . . . . . . . . . . . . . . . 16 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 75 1. Introduction 77 Web-based protocols often require the discovery of host policy or 78 metadata, where "host" is not a single resource but the entity 79 controlling the collection of resources identified by Uniform 80 Resource Identifiers (URI) with a common URI host [RFC3986]. 82 While web protocols have a wide range of metadata needs, they often 83 use metadata that is concise, has simple syntax requirements, and can 84 benefit from storing their metadata in a common location used by 85 other related protocols. 87 Because there is no URI or representation available to describe a 88 host, many of the methods used for associating per-resource metadata 89 (such as HTTP headers) are not available. This often leads to the 90 overloading of the root HTTP resource (e.g. 'http://example.com/') 91 with host metadata that is not specific or relevant to the root 92 resource itself. 94 This specification registers the well-known URI suffix "host-meta" in 95 the Well-Known URI Registry established by [RFC5785], and specifies a 96 simple, general-purpose metadata document format for hosts, to be 97 used by multiple web-based protocols. 99 In addition, there are times when a host-wide scope for policy or 100 metadata is too coarse-grained. host-meta provides two mechanisms for 101 providing resource-specific information: 103 o Link Templates - links using a URI template instead of a fixed 104 target URI, providing a way to define generic rules for generating 105 resource-specific links by applying the individual resource URI to 106 the template. 108 o Link-based Resource Descriptor Documents (LRDD, pronounced 'lard') 109 - descriptor documents providing resource-specific information, 110 typically information that cannot be expressed using link 111 templates. LRDD documents are linked to resources or host-meta 112 documents using link templates with the "lrdd" relation type. 114 1.1. Example 116 The following is a simple host-meta document including both host-wide 117 and resource-specific information for the 'example.com' host: 119 120 122 124 1.0 126 129 131 134 138 141 143 The host-wide information which applies to host in its entirety 144 provided by the document includes: 146 o A "http://protocol.example.net/version" host property with a value 147 of "1.0". 149 o A link to the host's copyright policy ("copyright"). 151 The resource-specific information provided by the document includes: 153 o A link template for receiving real-time updates ("hub") about 154 individual resources. Since the template does not include a 155 template variable, the target URI is identical for all resources. 157 o A LRDD document link template ("lrdd") for obtaining additional 158 resource-specific information contained in a separate document for 159 each individual resource. 161 o A link template for finding information about the author of 162 individual resources ("author"). 164 1.1.1. Processing Resource-Specific Information 166 When looking for information about the an individual resource, for 167 example, the resource identified by 'http://example.com/xy', the 168 resource URI is applied to the templates found, producing the 169 following links: 171 174 178 181 The LRDD document for 'http://example.com/xy' is obtained using an 182 HTTP "GET" request: 184 185 187 http://example.com/xy 189 red 191 194 196 198 Together, the information available about the individual resource 199 (presented as an XRD document for illustration purposes) is: 201 202 204 http://example.com/xy 206 red 208 211 214 217 220 222 Note that the order of links matters and is based on their original 223 order in the host-meta and LRDD documents. For example, the "hub" 224 link obtained from the host-meta link template has a higher priority 225 than the link found in the LRDD document because the host-meta link 226 appears before the "lrdd" link. 228 On the other hand, the "author" link found in the LRDD document has a 229 higher priority than the link found in the host-meta document because 230 it appears after the "lrdd" link. 232 1.2. Notational Conventions 234 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 235 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 236 document are to be interpreted as described in [RFC2119]. 238 This document uses the Augmented Backus-Naur Form (ABNF) notation of 239 [RFC5234]. Additionally, the following rules are included from 240 [RFC3986]: reserved, unreserved, and pct-encoded. 242 2. Obtaining host-meta Documents 244 The client obtains the host-meta document for a given host by sending 245 an HTTP [RFC2616] or an HTTPS [RFC2818] GET request to the host for 246 the "/.well-known/host-meta" path, using the default ports defined 247 for each protocol (e.g. port 80 for HTTP and port 443 for HTTPS). 248 The scope and meaning of host-meta documents obtained via other 249 protocols or ports is undefined. 251 The server MUST support at least one protocol but MAY support both. 252 If both protocols are supported, they MUST produce the same document. 254 The decision which protocol is used to obtain the host-meta document 255 have significant security ramifications as described in Section 5. 257 For example, the following request is used to obtain the host-meta 258 document for the 'example.com' host: 260 GET /.well-known/host-meta HTTP/1.1 261 Host: example.com 263 If the server response indicates that the host-meta resource is 264 located elsewhere (a 301, 302, or 307 response status code), the 265 client MUST try to obtain the resource from the location provided in 266 the response. This means that the host-meta document for one host 267 MAY be retrieved from another host. Likewise, if the resource is not 268 available or does not exist (e.g. a 404 or 410 response status codes) 269 using both the HTTP and HTTPS protocols, the client should infer that 270 metadata is not available via this mechanism. 272 The host-meta document SHOULD be served with the 273 "application/xrd+xml" media type. [[ media type registration pending 274 ]] 276 3. The host-meta Document 278 The host-meta document uses the XRD 1.0 document format as defined by 279 [OASIS.XRD-1.0], which provides a simple and extensible XML-based 280 schema for describing resources. This specification defines 281 additional processing rules needed to describe hosts. Documents MAY 282 include any XRD element not explicitly excluded. 284 The server MAY offer alternative representations of any XRD document 285 it serves (host-meta, LRDD, or other XRD-based documents). The 286 client MAY request a particular representation using the HTTP 287 "Accept" request header field. If no "Accept" request header field 288 is included with the request, or if the client requests a 289 "application/xrd+xml" representation, the server MUST respond using 290 the REQUIRED XRD 1.0 XML representation described in Section 3.1. 292 The XRD 1.0 XML representation is the only canonical representation 293 for any XRD document. If there is any discrepancy between the 294 content of the XRD 1.0 XML representation and any other 295 representation for the same resource, the client MUST only use the 296 XRD 1.0 XML representation. 298 Applications using the host-meta document MAY require the server to 299 provide a specific alternative representation in addition to the XRD 300 1.0 XML representation when explicitly requested by the client. 302 A JavaScript Object Notation (JSON) XRD 1.0 representation is 303 described in Appendix A. 305 3.1. XML Document format 307 The host-meta document root MUST be an "XRD" element. The document 308 SHOULD NOT include a "Subject" element, as at this time no URI is 309 available to identify hosts. The use of the "Alias" element in host- 310 meta is undefined and NOT RECOMMENDED. 312 The subject (or "context resource" as defined by [RFC5988]) of the 313 XRD "Property" and "Link" elements is the host described by the host- 314 meta document. However, the subject of "Link" elements with a 315 "template" attribute is the individual resource whose URI is applied 316 to the link template as described in Section 3.1.1. 318 3.1.1. The 'Link' Element 320 The XRD "Link" element, when used with the "href" attribute, conveys 321 a link relation between the host described by the document and a 322 common target URI. 324 For example, the following link declares a common copyright license 325 for the entire scope: 327 329 However, a "Link" element with a "template" attribute conveys a 330 relation whose context is an individual resource within the host-meta 331 document scope, and whose target is constructed by applying the 332 context resource URI to the template. The template string MAY 333 contain a URI string without any variables to represent a resource- 334 level relation that is identical for every individual resource. 336 For example, a blog with multiple authors can provide information 337 about each article's author by providing an endpoint with a parameter 338 set to the URI of each article. Each article has a unique author, 339 but all share the same pattern of where that information is located: 341 344 3.1.1.1. Template Syntax 346 This specification defines a simple template syntax for URI 347 transformation. A template is a string containing brace-enclosed 348 ("{}") variable names marking the parts of the string that are to be 349 substituted by the corresponding variable values. 351 Before substituting template variables, values MUST be encoded using 352 UTF-8 and any character other than unreserved (as defined by 353 [RFC3986]) MUST be percent-encoded per [RFC3986]. 355 This specification defines a single variable - "uri" - as the entire 356 context resource URI. Protocols MAY define additional relation- 357 specific variables and syntax rules, but SHOULD only do so for 358 protocol-specific relation types, and MUST NOT change the meaning of 359 the "uri" variable. If a client is unable to successfully process a 360 template (e.g. unknown variable names, unknown or incompatible 361 syntax) the parent "Link" element SHOULD be ignored. 363 The template syntax ABNF: 365 URI-Template = *( uri-char / variable ) 366 variable = "{" var-name "}" 367 uri-char = ( reserved / unreserved / pct-encoded ) 368 var-name = %x75.72.69 / ( 1*var-char ) ; "uri" or other names 369 var-char = ALPHA / DIGIT / "." / "_" 371 For example: 373 Input: http://example.com/r?f=1 374 Template: http://example.org/?q={uri} 375 Output: http://example.org/?q=http%3A%2F%2Fexample.com%2Fr%3Ff%3D1 377 4. Processing host-meta Documents 379 Once the host-meta document has been obtained, the client processes 380 its content based on the type of information desired: host-wide or 381 resource-specific. 383 Clients usually look for a link with a specific relation type or 384 other attributes. In such cases, the client does not need to process 385 the entire host-meta document and all linked LRDD documents, but 386 instead, process the various documents in their prescribed order 387 until the desired information is found. 389 Protocols using host-meta must indicate whether the information they 390 seek is host-wide or resource-specific. For example, "obtain the 391 first host-meta resource-specific link using the 'author' relation 392 type". If both types are used for the same purpose (e.g. first look 393 for resource-specific, then look for host-wide), the protocol must 394 specify the processing order. 396 4.1. Host-Wide Information 398 When looking for host-wide information, the client MUST ignore any 399 "Link" elements with a "template" attribute, as well as any link 400 using the "lrdd" relation type. All other elements are scoped as 401 host-wide. 403 4.2. Resource-Specific Information 405 Unlike host-wide information which is contained solely within the 406 host-meta document, resource-specific information is obtained from 407 host-meta link templates, as well as from linked LRDD documents. 409 When looking for resource-specific information, the client constructs 410 a resource descriptor by collecting and processing all the host-meta 411 link templates. For each link template: 413 1. The client applies the URI of the desired resource to the 414 template, producing a resource-specific link. 416 2. If the link's relation type is other than "lrdd", the client adds 417 the link to the resource descriptor in order. 419 3. If the link's relation type is "lrdd": 421 3.1 The client obtains the LRDD document by following the 422 scheme-specific rules for the LRDD document URI. If the 423 document URI scheme is "http" or "https", the document is 424 obtained via an HTTP "GET" request to the identified URI. 426 If the HTTP response status code is 301, 302, or 307, the 427 client MUST follow the redirection response and repeat the 428 request with the provided location. 430 3.2 The client adds any links found in the LRDD document to the 431 resource descriptor in order, except for any link using the 432 "lrdd" relation type (processing is limited to a single 433 level of inclusion). When adding links, the client SHOULD 434 retain any extension attributes and child elements if 435 present (e.g. or elements). 437 3.3 The client adds any resource properties found in the LRDD 438 document to the resource descriptor in order (e.g. <Alias> 439 or <Property> child elements of the LRDD document <XRD> root 440 element). 442 5. Security Considerations 444 The host-meta document is designed to be used by other applications 445 explicitly "opting-in" to use the facility. Therefore, any such 446 application MUST review the specific security implications of using 447 host-meta documents. By itself, this specification does not provide 448 any protections or guarantees that any given host-meta document is 449 under the control of the appropriate entity as required by each 450 application. 452 The metadata returned by the host-meta resource is presumed to be 453 under the control of the appropriate authority and representative of 454 all the resources described by it. If this resource is compromised 455 or otherwise under the control of another party, it may represent a 456 risk to the security of the server and data served by it, depending 457 on the applications using it. 459 Applications utilizing the host-meta document for sensitive or 460 security related information MUST require the use of the HTTPS 461 protocol and MUST NOT produce a host-meta document using other means. 462 In addition, such applications MUST require that any redirection 463 leading to the retrieval of a host-meta document also utilize the 464 HTTPS protocol. 466 Since the host-meta document is authoritative for the entire host, 467 not just the authority (combination of scheme, host, and port) of the 468 host-meta document server, applications MUST ensure that using a 469 host-meta document for another URI authority does not represent a 470 potential security exploit. 472 Protocols using host-meta templates must evaluate the construction of 473 their templates as well as any protocol-specific variables or syntax 474 to ensure that the templates cannot be abused by an attacker. For 475 example, a client can be tricked into following a malicious link due 476 to a poorly constructed template which produces unexpected results 477 when its variable values contain unexpected characters. 479 6. IANA Considerations 481 6.1. The 'host-meta' Well-Known URI 483 This specification registers the "host-meta" well-known URI in the 484 Well-Known URI Registry as defined by [RFC5785]. 486 URI suffix: host-meta 488 Change controller: IETF 490 Specification document(s): [[ this document ]] 492 Related information: The "host-meta" documents obtained from the 493 same host using the HTTP and HTTPS protocols (using default ports) 494 MUST be identical. 496 6.2. The 'lrdd' Relation Type 498 This specification registers the "lrdd" relation type in the Link 499 Relation Type Registry defined by [RFC5988]: 501 Relation Name: lrdd 503 Description: "lrdd" (pronounced 'lard') is an acronym for Link-based 504 Resource Descriptor Document. It is used by the host-meta 505 document processor to locate resource-specific information about 506 individual resources. When used elsewhere (e.g. in HTTP "Link" 507 header fields or in HTML <LINK> elements), it operates as an 508 include directive, identifying the location of additional links 509 and other metadata. Multiple links with the 'lrdd' relation 510 indicate multiple sources to include, not alternative sources of 511 the same information. An "application/xrd+xml" representation 512 MUST be available, and this media type MAY appear in a link's 513 "type" attribute. Additional representations MAY be available 514 (using the HTTP "Accept" request header field), in which case the 515 link's "type" attribute SHOULD be omitted. 517 Reference: [[ This specification ]] 519 Appendix A. JRD Document Format 521 The JRD document format - a general purpose XRD 1.0 represenation - 522 uses the JavaScript Object Notation (JSON) format defined in 523 [RFC4627]. JRD uses the same elements and processing rules described 524 in Section 3.1. The JRD format is designed to include the same base 525 functionality provided by the XML format with the exception of 526 extensibility which is beyond the scope of this specification. 528 The client MAY requst a JRD representation using the HTTP "Accept" 529 request header field with value of "application/json". The server 530 MUST include the HTTP "Content-Type" response header field with value 531 of "application/json". Any other "Content-Type" value (or lack of) 532 indicates that the server does not support the JRD format. 534 XRD elements are serialized into a JSON structure as follows: 536 o The XML document declaration and "XRD" element are discarded. 538 o The "Subject" element is included as name/value pair with the name 539 'subject', and value included as a string. 541 o The "Expires" element is included as name/value pair with the name 542 'expires', and value included as a string. 544 o "Alias" elements are included as a single name/value pair with the 545 name 'alias', and value a string array containing the values of 546 each element in order. 548 o "Property" elements are included as a single object with the name 549 'properties', and value an object with each element included as a 550 name/value pair with the value of the "type" attribute as name, 551 and element value included as a string value. The values of 552 properties with empty values (i.e. using the REQUIRED 553 "xsi:nil='true'" attribute) are included as "null". If more than 554 one "Property" element is present with the same "type" attribute, 555 only the last instance is included. 557 o "Link" elements are included as a single name/value pair with the 558 name 'links' and with each element included as an object. Each 559 attribute is included as name/value pair with the attribute name 560 as name, and value included as a string. 562 o "Link" child "Property" elements are included using the same 563 method as XRD-level "Property" elements using a name/value pair 564 inside the link object. 566 o "Link" child "Title" elements are included as a single object with 567 the name 'titles', and value an object with each element included 568 as a name/value pair with the value of the "xml:lang" attribute as 569 name, and element value included as a string value. The names of 570 elements without a "xml:lang" attribute are added with the name 571 'default'. If more than one "Title" element is present with the 572 same (or no) "xml:lang" attribute, only the last instance is 573 included. 575 o The conversion of any other element is left undefined. 577 For example, the following XRD document: 579 <?xml version='1.0' encoding='UTF-8'?> 580 <XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0' 581 xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'> 583 <Subject>http://blog.example.com/article/id/314</Subject> 584 <Expires>2010-01-30T09:30:00Z</Expires> 586 <Alias>http://blog.example.com/cool_new_thing</Alias> 587 <Alias>http://blog.example.com/steve/article/7</Alias> 589 <Property type='http://blgx.example.net/ns/version'>1.2</Property> 590 <Property type='http://blgx.example.net/ns/version'>1.3</Property> 591 <Property type='http://blgx.example.net/ns/ext' xsi:nil='true' /> 593 <Link rel='author' type='text/html' 594 href='http://blog.example.com/author/steve'> 595 <Title>About the Author 596 Author Information 597 editor 598 600 601 The other guy 602 The other author 603 605 607 609 Is represented by the following JRD document: 611 { 612 "subject":"http://blog.example.com/article/id/314", 613 "expires":"2010-01-30T09:30:00Z", 615 "aliases":[ 616 "http://blog.example.com/cool_new_thing", 617 "http://blog.example.com/steve/article/7"], 619 "properties":{ 620 "http://blgx.example.net/ns/version":"1.3", 621 "http://blgx.example.net/ns/ext":null 622 }, 624 "links":[ 625 { 626 "rel":"author", 627 "type":"text/html", 628 "href":"http://blog.example.com/author/steve", 629 "titles":{ 630 "default":"About the Author", 631 "en-us":"Author Information" 632 }, 633 "properties":{ 634 "http://example.com/role":"editor" 635 } 636 }, 637 { 638 "rel":"author", 639 "href":"http://example.com/author/john", 640 "titles":{ 641 "default":"The other author" 642 } 643 }, 644 { 645 "rel":"copyright", 646 "template":"http://example.com/copyright?id={uri}" 647 } 648 ] 649 } 651 Appendix B. Acknowledgments 653 The authors would like to acknowledge the contributions of everyone 654 who provided feedback and use cases for this specification; in 655 particular, Dirk Balfanz, DeWitt Clinton, Eve Maler, Breno de 656 Medeiros, Brad Fitzpatrick, James Manger, Will Norris, Mark 657 Nottingham, John Panzer, Drummond Reed, and Peter Saint-Andre. 659 7. Normative References 661 [OASIS.XRD-1.0] 662 Hammer-Lahav, E. and W. Norris, "Extensible Resource 663 Descriptor (XRD) Version 1.0", 664 . 666 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 667 Requirement Levels", BCP 14, RFC 2119, March 1997. 669 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 670 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 671 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 673 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 675 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 676 Resource Identifier (URI): Generic Syntax", STD 66, 677 RFC 3986, January 2005. 679 [RFC4627] Crockford, D., "The application/json Media Type for 680 JavaScript Object Notation (JSON)", RFC 4627, July 2006. 682 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 683 Specifications: ABNF", STD 68, RFC 5234, January 2008. 685 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known 686 Uniform Resource Identifiers (URIs)", RFC 5785, 687 April 2010. 689 [RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010. 691 [1] 693 Authors' Addresses 695 Eran Hammer-Lahav 696 Yahoo! 698 Email: eran@hueniverse.com 699 URI: http://hueniverse.com 701 Blaine Cook 703 Email: romeda@gmail.com 704 URI: http://romeda.org