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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: Informational November 8, 2009 5 Expires: May 12, 2010 7 host-meta: Web Host Metadata 8 draft-hammer-hostmeta-03 10 Abstract 12 This memo describes a method for locating host metadata for Web-based 13 protocols. 15 Status of this Memo 17 This Internet-Draft is submitted to IETF in full conformance with the 18 provisions of BCP 78 and BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as Internet- 23 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 28 material 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 This Internet-Draft will expire on May 12, 2010. 38 Copyright Notice 40 Copyright (c) 2009 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 BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 1.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 1.2. Namespace and Version . . . . . . . . . . . . . . . . . . 4 58 1.3. Notational Conventions . . . . . . . . . . . . . . . . . . 4 59 2. Metadata Scope . . . . . . . . . . . . . . . . . . . . . . . . 5 60 3. The host-meta Document Format . . . . . . . . . . . . . . . . 5 61 3.1. The 'hm:Host' Element . . . . . . . . . . . . . . . . . . 5 62 3.2. The 'Link' Element . . . . . . . . . . . . . . . . . . . . 6 63 3.2.1. Template Syntax . . . . . . . . . . . . . . . . . . . 6 64 4. Obtaining host-meta Documents . . . . . . . . . . . . . . . . 7 65 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 66 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 67 6.1. The host-meta Well-Known URI . . . . . . . . . . . . . . . 8 68 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 9 69 Appendix B. Document History . . . . . . . . . . . . . . . . . . 9 70 7. Normative References . . . . . . . . . . . . . . . . . . . . . 9 71 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10 73 1. Introduction 75 Web-based protocols often require the discovery of host policy or 76 metadata, where host is not a single resource but the entity 77 controlling the collection of resources identified by URIs with a 78 common host as defined by [RFC3986]. While these protocols have a 79 wide range of metadata needs, they often define metadata that is 80 concise, has simple syntax requirements, and can benefit from storing 81 its metadata in a common location used by other related protocols. 83 Because there is no URI or a resource available to describe a host, 84 many of the methods used for associating per-resource metadata (such 85 as HTTP headers) are not available. This often leads to the 86 overloading of the root HTTP resource (e.g. 'http://example.com/') 87 with host metadata that is not specific to the root resource (e.g. a 88 home page or web application), and which often has nothing to do it. 90 This memo registers the "well-known" URI suffix 'host-meta' in the 91 Well-Known URI Registry established by [I-D.nottingham-site-meta], 92 and specifies a simple, general-purpose metadata document for hosts, 93 to be used by multiple Web-based protocols. 95 Please discuss this draft on the apps-discuss@ietf.org [1] mailing 96 list. 98 1.1. Example 100 A simple host-meta document for the 'example.com' and 101 'www.example.com' hosts with a link providing host-wide copyright 102 information and a link template providing a URI for obtaining 103 resource-specific metadata for each resource within the host-meta 104 document scope: 106 107 110 http://example.com 111 http://www.example.com 113 114 Site License Policy 115 license 116 http://example.com/license 117 118 119 Resource Descriptor 120 describedby 121 http://meta.example.com?uri={uri} 122 123 125 1.2. Namespace and Version 127 The host-meta document uses the XRD 1.0 XML namespace URI 128 [W3C.REC-xml-names-19990114]: 130 http://docs.oasis-open.org/ns/xri/xrd-1.0 132 The XML namespace URI for the host-meta specific extension elements 133 defined in this specification is: 135 http://host-meta.net/ns/1.0 137 1.3. Notational Conventions 139 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 140 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 141 document are to be interpreted as described in [RFC2119]. 143 This specification uses the namespace prefix "hm:" for the extension 144 Namespace URI identified in Section 1.2. Note that the choice of 145 namespace prefix is arbitrary and not semantically significant. 146 Element names without a namespace prefix belong to the XRD 1.0 XML 147 namespace identified in Section 1.2. 149 This document uses the Augmented Backus-Naur Form (ABNF) notation of 150 [RFC5234]. Additionally, the following rules are included from 151 [RFC3986]: reserved, unreserved, and host. 153 2. Metadata Scope 155 Each host-meta document describes one or more hosts. The scope MUST 156 be expressed explicitly within the document using the 'hm:Host' 157 elements (Section 3.1). The host-meta scope does not apply to any 158 other hostname (or sub-domain) not explicitly declared. For example, 159 'example.net', 'example.com', and 'www.example.com' all have 160 different and non-overlapping scopes. 162 3. The host-meta Document Format 164 The host-meta document uses the XRD 1.0 document format as defined by 165 [OASIS.XRD-1.0], which provides a simple and extensible XML-based 166 schema for describing resources. This memo defines additional 167 elements and processing rules needed to describe hosts. XRD elements 168 not explicitly mentioned in this memo are permitted and used as 169 defined in [OASIS.XRD-1.0]. 171 The host-meta document root MUST be an 'XRD' element. The document 172 SHOULD NOT include a 'Subject' element, as at this time no URI is 173 available to identify hosts. The use of the 'Alias' element in host- 174 meta is undefined and NOT RECOMMENDED. 176 This memo defines the 'hm:Host' element (Section 3.1) for declaring 177 document scope. The subject (or "context resource" as defined by 178 [I-D.nottingham-http-link-header]) of the XRD 'Type' and 'Link' 179 elements are the hosts included in the document scope, with the 180 exception of 'Link' elements with a 'URITemplate' child element for 181 which the subject are individual resources included in the document 182 scope as defined in Section 3.2. 184 3.1. The 'hm:Host' Element 186 The 'hm:Host" element is used to declare the scope of the host-meta 187 document and is defined as a child element of the root 'XRD' element. 188 The parent 'XRD' element MUST include one but MAY include more 'hm: 189 Host' elements (order does not matter). If a host-meta document 190 includes more than one 'hm:Host' element, it does not signify any 191 relationship between the individual hosts other than sharing the same 192 metadata. 194 The element value syntax ABNF: 196 Host-Element-Value = host 198 3.2. The 'Link' Element 200 The XRD 'Link' element, when used with the 'URI' child element, 201 conveys a link relation between the host (or hosts) described by the 202 document and a common target URI. 204 For example, the following link declares a common author for the 205 entire scope: 207 208 author 209 http://example.com/author 210 212 In addition, a 'Link' element with a 'URITemplate' child element 213 conveys relations whose context are individual resources within the 214 host-meta document scope, and whose target is constructed by applying 215 the context URI to a template. 217 For example, a blog with multiple authors can provide information 218 about each article's author by providing an endpoint with a parameter 219 set to the URI of each article. Each article has a unique author, 220 but all share the same pattern of where that information is located: 222 223 author 224 http://example.com?author={uri} 225 227 3.2.1. Template Syntax 229 This memo defines a simple template syntax for URI transformation. A 230 template is a string containing brace-enclosed ("{}") variable names 231 marking the parts of the string that are to be substituted by the 232 corresponding variable values. 234 Before substituting template variables, any value character other 235 than unreserved (as defined by [RFC3986]) MUST be percent-encoded per 236 [RFC3986]. 238 This memo defines a single variable, 'uri', as the entire context 239 URI. Protocols MAY define additional relation-specific variables and 240 syntax rules, but SHOULD only do so for protocol-specific relation 241 types, and MUST NOT change the meaning of the 'uri' variable. If a 242 client is unable to successfully process a template (due to unknown 243 variable names, or unknown or incompatible syntax) the parent 'Link' 244 element SHOULD be ignored. 246 The template syntax ABNF: 248 URI-Template = *( uri-char | variable ) 249 variable = "{" var-name "}" 250 uri-char = ( reserved | unreserved ) 251 var-name = "uri" | ( 1*var-char ) 252 var-char = ALPHA / DIGIT / "." / "_" 254 For example: 256 Input: http://example.com/r?f=1 257 Template: http://example.org?q={uri} 258 Output: http://example.org?q=http%3A%2F%2Fexample.com%2Fr%3Ff%3D1 260 4. Obtaining host-meta Documents 262 The host-meta document is obtained by making an HTTP [RFC2616] GET 263 request to the host's port 80, or an HTTPS [RFC2818] GET request to 264 the host's port 443 for the '/.well-known/host-meta' path. 266 Servers MUST support at least one but SHOULD support both ports 267 unless restricted by other considerations. If both ports are 268 supported, they MUST serve the same document. Clients MAY attempt to 269 obtain the host-meta document from either port, and SHOULD attempt 270 the other port if the first fails, unless restricted by other 271 considerations. 273 For example, the following request is used to obtain the host-meta 274 document for the 'example.com' host: 276 GET /.well-known/host-meta HTTP/1.1 277 Host: example.com 279 If the server response indicates that the host-meta resource is 280 located elsewhere (a 301, 302, or 307 response status codes), the 281 client SHOULD try to obtain the resource from the location provided 282 in the response. This means that the host-meta document for one host 283 MAY be retrieved from a different host. Likewise, if the resource is 284 not available or exists (the 404 or 410 response status codes), the 285 client SHOULD infer that metadata is not available via this 286 mechanism. 288 If a representation is successfully obtained, but is not in the 289 format described above, clients SHOULD infer that the path is being 290 used for other purposes, and not process it as a host-meta document. 291 To aid in this process, authorities using this mechanism SHOULD 292 correctly label host-meta responses with the "application/xrd+xml" 293 internet media type. 295 The scope declared within the host-meta document MUST match the 296 desired host. 298 5. Security Considerations 300 The metadata returned by the host-meta resource is presumed to be 301 under the control of the appropriate authority and representative of 302 all the resources described by it. If this resource is compromised 303 or otherwise under the control of another party, it may represent a 304 risk to the security of the server and data served by it, depending 305 on what protocols use it. 307 The host-meta scope is explicitly declared by the 'hm:Host' elements 308 listed in the document. Clients SHOULD evaluate the authority of a 309 host-meta document obtained from one host to describe any other host. 310 Protocols that change the scope from the one declared in the document 311 without careful consideration can incur security risks. 313 Protocols using host-meta templates SHOULD evaluate the construction 314 of their templates as well as any protocol-specific variables or 315 syntax to ensure that the templates cannot be abused by an attacker. 316 For example, a client can be tricked into following a malicious link 317 due to a poorly constructed template which produces unexpected 318 results when its variable values contain unexpected characters. 320 Protocols MAY restrict document retrieval to HTTPS based on their 321 security needs. Protocols utilizing host-meta documents obtained via 322 other methods not described in this memo SHOULD consider the security 323 and authority risks associated with such methods. 325 6. IANA Considerations 327 6.1. The host-meta Well-Known URI 329 This memo registers the 'host-meta' well-known URI in the Well-Known 330 URI Registry as defined by [I-D.nottingham-site-meta]. 331 URI suffix: host-meta 332 Change controller: IETF 333 Specification document(s): [[ this document ]] 334 Related information: None 336 Appendix A. Acknowledgments 338 This memo was initially based on [I-D.nottingham-site-meta]. 340 The author would like to acknowledge the contributions of everyone 341 who provided feedback and use cases for this memo; in particular, 342 Dirk Balfanz, DeWitt Clinton, Blaine Cook, Breno de Medeiros, Brad 343 Fitzpatrick, James Manger, Will Norris, Mark Nottingham, John Panzer, 344 and Drummond Reed. 346 Appendix B. Document History 348 [[ to be removed by the RFC editor before publication as an RFC ]] 350 -03 351 o Changed scope to an entire host (per RFC 3986). 352 o Simplified template syntax to always percent-encode values and 353 vocabulary to a single 'uri' variable. 354 o Changed document retrieval to always use HTTP(S). 355 o Added security consideration about the use of templates. 356 o Explicitly defined the root element to be 'XRD'. 358 -02 359 o Changed Scope element syntax from attributes to URI-like string 360 value. 362 -01 363 o Editorial rewrite. 364 o Redefined scope as a scheme-authority pair. 365 o Added document structure section. 367 -00 368 o Initial draft. 370 7. Normative References 372 [I-D.nottingham-http-link-header] 373 Nottingham, M., "Web Linking", 374 draft-nottingham-http-link-header-06 (work in progress), 375 July 2009. 377 [I-D.nottingham-site-meta] 378 Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known 379 URIs", draft-nottingham-site-meta-03 (work in progress), 380 September 2009. 382 [OASIS.XRD-1.0] 383 Hammer-Lahav, E. and W. Norris, "Extensible Resource 384 Descriptor (XRD) Version 1.0 (work in progress)", . 388 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 389 Requirement Levels", BCP 14, RFC 2119, March 1997. 391 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 392 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 393 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 395 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 397 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 398 Resource Identifier (URI): Generic Syntax", STD 66, 399 RFC 3986, January 2005. 401 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 402 Specifications: ABNF", STD 68, RFC 5234, January 2008. 404 [W3C.REC-P3P-20020416] 405 Marchiori, M., "The Platform for Privacy Preferences 1.0 406 (P3P1.0) Specification", World Wide Web Consortium 407 Recommendation REC-P3P-20020416, April 2002, 408 . 410 [W3C.REC-xml-names-19990114] 411 Hollander, D., Layman, A., and T. Bray, "Namespaces in 412 XML", World Wide Web Consortium FirstEdition REC-xml- 413 names-19990114, January 1999, 414 . 416 [1] 418 Author's Address 420 Eran Hammer-Lahav 421 Yahoo! 423 Email: eran@hueniverse.com 424 URI: http://hueniverse.com