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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