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2 Network Working Group E. Hammer-Lahav
3 Internet-Draft Yahoo!
4 Intended status: Informational May 24, 2010
5 Expires: November 25, 2010
7 host-meta: Web Host Metadata
8 draft-hammer-hostmeta-09
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 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). Note that other groups may also distribute
22 working documents as Internet-Drafts. The list of current Internet-
23 Drafts is at http://datatracker.ietf.org/drafts/current/.
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 This Internet-Draft will expire on November 25, 2010.
32 Copyright Notice
34 Copyright (c) 2010 IETF Trust and the persons identified as the
35 document authors. All rights reserved.
37 This document is subject to BCP 78 and the IETF Trust's Legal
38 Provisions Relating to IETF Documents
39 (http://trustee.ietf.org/license-info) in effect on the date of
40 publication of this document. Please review these documents
41 carefully, as they describe your rights and restrictions with respect
42 to this document. Code Components extracted from this document must
43 include Simplified BSD License text as described in Section 4.e of
44 the Trust Legal Provisions and are provided without warranty as
45 described in the Simplified BSD License.
47 Table of Contents
49 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
50 1.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 3
51 1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 4
52 2. The host-meta Document Format . . . . . . . . . . . . . . . . . 4
53 2.1. The 'Link' Element . . . . . . . . . . . . . . . . . . . . 4
54 2.1.1. Template Syntax . . . . . . . . . . . . . . . . . . . . 5
55 3. Obtaining host-meta Documents . . . . . . . . . . . . . . . . . 5
56 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
57 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
58 5.1. The host-meta Well-Known URI . . . . . . . . . . . . . . . 7
59 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 7
60 Appendix B. Document History . . . . . . . . . . . . . . . . . . . 7
61 6. Normative References . . . . . . . . . . . . . . . . . . . . . 8
62 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
64 1. Introduction
66 Web-based protocols often require the discovery of host policy or
67 metadata, where host is not a single resource but the entity
68 controlling the collection of resources identified by Uniform
69 Resource Identifiers (URI) with a common URI host as defined by
70 [RFC3986]. While these protocols have a wide range of metadata
71 needs, they often define metadata that is concise, has simple syntax
72 requirements, and can benefit from storing its metadata in a common
73 location used by other related protocols.
75 Because there is no URI or resource available to describe a host,
76 many of the methods used for associating per-resource metadata (such
77 as HTTP headers) are not available. This often leads to the
78 overloading of the root HTTP resource (e.g. 'http://example.com/')
79 with host metadata that is not specific to the root resource, and
80 often has nothing to do it.
82 This memo registers the "well-known" URI suffix "host-meta" in the
83 Well-Known URI Registry established by [RFC5785], and specifies a
84 simple, general-purpose metadata document for hosts, to be used by
85 multiple Web-based protocols.
87 [[ Please discuss this draft on the apps-discuss@ietf.org [1] mailing
88 list. ]]
90 1.1. Example
92 The following is a simple host-meta document with a link providing
93 host-wide copyright information and a link template providing a URI
94 for obtaining resource-specific author information for each resource
95 within the host-meta document scope:
97
98
100
102 Site License Policy
103
104
106 Author Profile
107
108
110 1.2. Notational Conventions
112 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
113 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
114 document are to be interpreted as described in [RFC2119].
116 This document uses the Augmented Backus-Naur Form (ABNF) notation of
117 [RFC5234]. Additionally, the following rules are included from
118 [RFC3986]: reserved, unreserved, and pct-encoded.
120 2. The host-meta Document Format
122 The host-meta document uses the XRD 1.0 document format as defined by
123 [OASIS.XRD-1.0], which provides a simple and extensible XML-based
124 schema for describing resources. This memo defines additional
125 processing rules needed to describe hosts. Documents MAY include any
126 XRD element not explicitly excluded.
128 The host-meta document root MUST be an "XRD" element. The document
129 SHOULD NOT include a "Subject" element, as at this time no URI is
130 available to identify hosts. The use of the "Alias" element in host-
131 meta is undefined and NOT RECOMMENDED.
133 The subject (or "context resource" as defined by
134 [I-D.nottingham-http-link-header]) of the XRD "Property" and "Link"
135 elements is the host described by the host-meta document. However,
136 the subject of "Link" elements with a "template" attribute is the
137 individual resource whose URI is applied to the link template as
138 described in Section 2.1.
140 2.1. The 'Link' Element
142 The XRD "Link" element, when used with the "href" attribute, conveys
143 a link relation between the host described by the document and a
144 common target URI.
146 For example, the following link declares a common author for the
147 entire scope:
149
151 However, a "Link" element with a "template" attribute conveys a
152 relation whose context is an individual resource within the host-meta
153 document scope, and whose target is constructed by applying the
154 context resource URI to the template. The template string MAY
155 contain a URI string without any variables to represent a resource-
156 level relation that is identical for every individual resource.
158 For example, a blog with multiple authors can provide information
159 about each article's author by providing an endpoint with a parameter
160 set to the URI of each article. Each article has a unique author,
161 but all share the same pattern of where that information is located:
163
166 2.1.1. Template Syntax
168 This memo defines a simple template syntax for URI transformation. A
169 template is a string containing brace-enclosed ("{}") variable names
170 marking the parts of the string that are to be substituted by the
171 corresponding variable values.
173 Before substituting template variables, any value character other
174 than unreserved (as defined by [RFC3986]) MUST be percent-encoded per
175 [RFC3986].
177 This memo defines a single variable - "uri" - as the entire context
178 resource URI. Protocols MAY define additional relation-specific
179 variables and syntax rules, but SHOULD only do so for protocol-
180 specific relation types, and MUST NOT change the meaning of the "uri"
181 variable. If a client is unable to successfully process a template
182 (e.g. unknown variable names, unknown or incompatible syntax) the
183 parent "Link" element SHOULD be ignored.
185 The template syntax ABNF:
187 URI-Template = *( uri-char / variable )
188 variable = "{" var-name "}"
189 uri-char = ( reserved / unreserved / pct-encoded )
190 var-name = %x75.72.69 / ( 1*var-char ) ; "uri" or other names
191 var-char = ALPHA / DIGIT / "." / "_"
193 For example:
195 Input: http://example.com/r?f=1
196 Template: http://example.org/?q={uri}
197 Output: http://example.org/?q=http%3A%2F%2Fexample.com%2Fr%3Ff%3D1
199 3. Obtaining host-meta Documents
201 Clients obtain the host-meta document for a given host by making an
202 HTTPS [RFC2818] GET request to the host's port 443 for the
203 "/.well-known/host-meta" path. If the request fails to produce a
204 valid host-meta document, clients make an HTTP [RFC2616] GET request
205 to the host's port 80 for the "/.well-known/host-meta" path.
207 Servers MUST support at least one but SHOULD support both ports. If
208 both ports are supported, they MUST serve the same document. Clients
209 MAY attempt to obtain the host-meta document from either port, SHOULD
210 attempt using port 443 first, and SHOULD attempt the other port if
211 the first fails.
213 For example, the following request is used to obtain the host-meta
214 document for the 'example.com' host:
216 GET /.well-known/host-meta HTTP/1.1
217 Host: example.com
219 If a representation is successfully obtained, but is not in the
220 format described above, clients should infer that the path is being
221 used for other purposes, and not process the response as a host-meta
222 document. To aid in this process, authorities using this mechanism
223 SHOULD correctly label host-meta responses with the
224 "application/xrd+xml" internet media type.
226 If the server response indicates that the host-meta resource is
227 located elsewhere (a 301, 302, or 307 response status code), the
228 client MUST try to obtain the resource from the location provided in
229 the response. This means that the host-meta document for one host
230 MAY be retrieved from a another host. Likewise, if the resource is
231 not available or does not exist (e.g. a 404 or 410 response status
232 codes) at both ports, the client should infer that metadata is not
233 available via this mechanism.
235 4. Security Considerations
237 The metadata returned by the host-meta resource is presumed to be
238 under the control of the appropriate authority and representative of
239 all the resources described by it. If this resource is compromised
240 or otherwise under the control of another party, it may represent a
241 risk to the security of the server and data served by it, depending
242 on what protocols use it.
244 Protocols using host-meta templates SHOULD evaluate the construction
245 of their templates as well as any protocol-specific variables or
246 syntax to ensure that the templates cannot be abused by an attacker.
247 For example, a client can be tricked into following a malicious link
248 due to a poorly constructed template which produces unexpected
249 results when its variable values contain unexpected characters.
251 Protocols MAY restrict document retrieval to HTTPS based on their
252 security needs. Protocols utilizing host-meta documents obtained via
253 other methods not described in this memo SHOULD consider the security
254 and authority risks associated with such methods.
256 5. IANA Considerations
258 5.1. The host-meta Well-Known URI
260 This memo registers the 'host-meta' well-known URI in the Well-Known
261 URI Registry as defined by [RFC5785].
262 URI suffix: host-meta
263 Change controller: IETF
264 Specification document(s): [[ this document ]]
265 Related information: None
267 Appendix A. Acknowledgments
269 The author would like to acknowledge the contributions of everyone
270 who provided feedback and use cases for this memo; in particular,
271 Dirk Balfanz, DeWitt Clinton, Blaine Cook, Eve Maler, Breno de
272 Medeiros, Brad Fitzpatrick, James Manger, Will Norris, Mark
273 Nottingham, John Panzer, Drummond Reed, and Peter Saint-Andre.
275 Appendix B. Document History
277 [[ to be removed by the RFC editor before publication as an RFC ]]
279 -09
280 o Removed the element due to lack of use cases (protocols
281 with signature requirements can define their own way of declaring
282 the document's subject for this purpose).
283 o Minor editorial changes.
284 o Changed following redirections to MUST.
285 o Updated references.
287 -08
288 o Fixed typo.
290 -07
291 o Minor editorial clarifications.
292 o Added XML schema for host-meta extension.
293 o Updated XRD reference to the latest draft (no normative changes).
295 -06
296 o Updated well-known reference to RFC 5785.
297 o Minor editorial changes.
298 o Made HTTPS a higher priority (SHOULD) over HTTP.
300 -05
301 o Adjusted syntax to the latest XRD schema.
302 o Added note about using a link template without variables.
304 -04
305 o Corrected the example.
307 -03
308 o Changed scope to an entire host (per RFC 3986).
309 o Simplified template syntax to always percent-encode values and
310 vocabulary to a single 'uri' variable.
311 o Changed document retrieval to always use HTTP(S).
312 o Added security consideration about the use of templates.
313 o Explicitly defined the root element to be 'XRD'.
315 -02
316 o Changed Scope element syntax from attributes to URI-like string
317 value.
319 -01
320 o Editorial rewrite.
321 o Redefined scope as a scheme-authority pair.
322 o Added document structure section.
324 -00
325 o Initial draft.
327 6. Normative References
329 [I-D.nottingham-http-link-header]
330 Nottingham, M., "Web Linking",
331 draft-nottingham-http-link-header-10 (work in progress),
332 May 2010.
334 [OASIS.XRD-1.0]
335 Hammer-Lahav, E. and W. Norris, "Extensible Resource
336 Descriptor (XRD) Version 1.0 (work in progress)", .
340 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
341 Requirement Levels", BCP 14, RFC 2119, March 1997.
343 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
344 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
345 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
347 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
349 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
350 Resource Identifier (URI): Generic Syntax", STD 66,
351 RFC 3986, January 2005.
353 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
354 Specifications: ABNF", STD 68, RFC 5234, January 2008.
356 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
357 Uniform Resource Identifiers (URIs)", RFC 5785,
358 April 2010.
360 [1]
362 Author's Address
364 Eran Hammer-Lahav
365 Yahoo!
367 Email: eran@hueniverse.com
368 URI: http://hueniverse.com