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2 HTTP Working Group J. Reschke
3 Internet-Draft greenbytes
4 Intended status: Standards Track September 8, 2015
5 Expires: March 11, 2016
7 Hypertext Transfer Protocol (HTTP) Client-Initiated Content-Encoding
8 draft-ietf-httpbis-cice-03
10 Abstract
12 In HTTP, content codings allow for payload encodings such as for
13 compression or integrity checks. In particular, the "gzip" content
14 coding is widely used for payload data sent in response messages.
16 Content codings can be used in request messages as well, however
17 discoverability is not on par with response messages. This document
18 extends the HTTP "Accept-Encoding" header field for use in responses,
19 to indicate the content codings that are supported in requests.
21 Editorial Note (To be removed by RFC Editor before publication)
23 Discussion of this draft takes place on the HTTPBIS working group
24 mailing list (ietf-http-wg@w3.org), which is archived at
25 .
27 Working Group information can be found at
28 and ;
29 source code and issues list for this draft can be found at
30 .
32 The changes in this draft are summarized in Appendix A.6.
34 Status of This Memo
36 This Internet-Draft is submitted in full conformance with the
37 provisions of BCP 78 and BCP 79.
39 Internet-Drafts are working documents of the Internet Engineering
40 Task Force (IETF). Note that other groups may also distribute
41 working documents as Internet-Drafts. The list of current Internet-
42 Drafts is at http://datatracker.ietf.org/drafts/current/.
44 Internet-Drafts are draft documents valid for a maximum of six months
45 and may be updated, replaced, or obsoleted by other documents at any
46 time. It is inappropriate to use Internet-Drafts as reference
47 material or to cite them other than as "work in progress."
48 This Internet-Draft will expire on March 11, 2016.
50 Copyright Notice
52 Copyright (c) 2015 IETF Trust and the persons identified as the
53 document authors. All rights reserved.
55 This document is subject to BCP 78 and the IETF Trust's Legal
56 Provisions Relating to IETF Documents
57 (http://trustee.ietf.org/license-info) in effect on the date of
58 publication of this document. Please review these documents
59 carefully, as they describe your rights and restrictions with respect
60 to this document. Code Components extracted from this document must
61 include Simplified BSD License text as described in Section 4.e of
62 the Trust Legal Provisions and are provided without warranty as
63 described in the Simplified BSD License.
65 Table of Contents
67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
68 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
69 3. Using the 'Accept-Encoding' Header Field in Responses . . . . . 3
70 4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
71 5. Deployment Considerations . . . . . . . . . . . . . . . . . . . 5
72 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
73 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
74 7.1. Header Field Registry . . . . . . . . . . . . . . . . . . . 5
75 7.2. Status Code Registry . . . . . . . . . . . . . . . . . . . 6
76 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
77 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
78 8.2. Informative References . . . . . . . . . . . . . . . . . . 7
79 Appendix A. Change Log (to be removed by RFC Editor before
80 publication) . . . . . . . . . . . . . . . . . . . . . 7
81 A.1. Since draft-reschke-http-cice-00 . . . . . . . . . . . . . 7
82 A.2. Since draft-reschke-http-cice-01 . . . . . . . . . . . . . 7
83 A.3. Since draft-reschke-http-cice-02 . . . . . . . . . . . . . 7
84 A.4. Since draft-ietf-httpbis-cice-00 . . . . . . . . . . . . . 7
85 A.5. Since draft-ietf-httpbis-cice-01 . . . . . . . . . . . . . 8
86 A.6. Since draft-ietf-httpbis-cice-02 . . . . . . . . . . . . . 8
87 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . . 8
89 1. Introduction
91 In HTTP, content codings allow for payload encodings such as for
92 compression or integrity checks ([RFC7231], Section 3.1.2). In
93 particular, the "gzip" content coding ([RFC7230], Section 4.2) is
94 widely used for payload data sent in response messages.
96 Content codings can be used in request messages as well, however
97 discoverability is not on par with response messages. This document
98 extends the HTTP "Accept-Encoding" header field ([RFC7231], Section
99 5.3.4) for use in responses, to indicate the content codings that are
100 supported in requests. It furthermore updates the definition of
101 status code 415 (Unsupported Media Type) ([RFC7231], Section 6.5.13),
102 recommending to include the "Accept-Encoding" header field when
103 appropriate.
105 2. Notational Conventions
107 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
108 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
109 document are to be interpreted as described in [RFC2119].
111 This document reuses terminology defined in the base HTTP
112 specifications, namely Section 2 of [RFC7230] and Section 3.1.2 of
113 [RFC7231].
115 3. Using the 'Accept-Encoding' Header Field in Responses
117 Section 5.3.4 of [RFC7231] defines "Accept-Encoding" as a request
118 header field only.
120 This specification expands that definition to allow "Accept-Encoding"
121 as a response header field as well. When present in a response, it
122 indicates what content codings the resource was willing to accept in
123 the associated request. A field value that only contains "identity"
124 implies that no content codings were supported.
126 Note that this information is specific to the associated request; the
127 set of supported encodings might be different for other resources on
128 the same server, and could change over time or depend on other
129 aspects of the request (such as the request method).
131 Section 6.5.13 of [RFC7231] defines status code 415 (Unsupported
132 Media Type) to apply to both media type and content coding related
133 problems.
135 Servers that fail a request due to an unsupported content coding
136 ought to respond with a 415 status and ought to include an "Accept-
137 Encoding" header field in that response, allowing clients to
138 distinguish between content coding related issues and media type
139 related issues. In order to avoid confusion with media type related
140 problems, servers that fail a request with a 415 status for reasons
141 unrelated to content codings MUST NOT include the "Accept-Encoding"
142 header field.
144 It is expected that the most common use of "Accept-Encoding" in
145 responses will have the 415 (Unsupported Media Type) status code, in
146 response to optimistic use of a content coding by clients. However,
147 the header field can also be used to indicate to clients that content
148 codings are supported, to optimize future interactions. For example,
149 a resource might include it in a 2xx response when the request
150 payload was big enough to justify use of a compression coding, but
151 the client failed do so.
153 4. Example
155 A client submits a POST request using the "compress" content coding
156 ([RFC7231], Section 3.1.2.1):
158 POST /edit/ HTTP/1.1
159 Host: example.org
160 Content-Type: application/atom+xml;type=entry
161 Content-Encoding: compress
163 ...compressed payload...
165 The server rejects request because it only allows the "gzip" content
166 coding:
168 HTTP/1.1 415 Unsupported Media Type
169 Date: Fri, 09 May 2014 11:43:53 GMT
170 Accept-Encoding: gzip
171 Content-Length: 68
172 Content-Type: text/plain
174 This resource only supports the "gzip" content coding in requests.
176 ...at which point the client can retry the request with the supported
177 "gzip" content coding.
179 Alternatively, a server that does not support any content codings in
180 requests could answer with:
182 HTTP/1.1 415 Unsupported Media Type
183 Date: Fri, 09 May 2014 11:43:53 GMT
184 Accept-Encoding: identity
185 Content-Length: 61
186 Content-Type: text/plain
188 This resource does not support content codings in requests.
190 5. Deployment Considerations
192 Servers that do not support content codings in requests already are
193 required to fail a request that uses a content coding. Section
194 6.5.13 of [RFC7231] defines the status code 415 (Unsupported Media
195 Type) for this purpose, so the only change needed is to include the
196 "Accept-Encoding" header field with value "identity" in that
197 response.
199 Servers that do support some content codings are required to fail
200 requests with unsupported content codings as well. To be compliant
201 with this specification, servers will need to use the status code 415
202 (Unsupported Media Type) to signal the problem, and will have to
203 include an "Accept-Encoding" header field that enumerates the content
204 codings that are supported. As the set of supported content codings
205 is usually static and small, adding the header field ought to be
206 trivial.
208 6. Security Considerations
210 This specification only adds discovery of supported content codings
211 and diagnostics for requests failing due to unsupported content
212 codings. As such, it doesn't introduce any new security
213 considerations over those already present in HTTP/1.1 (Section 9 of
214 [RFC7231]) and HTTP/2 (Section 10 of [RFC7540]).
216 However, the point of better discoverability and diagnostics is to
217 make it easier to use content codings in requests. This might lead
218 to increased usage of compression codings such as gzip (Section 4.2
219 of [RFC7230]), which, when used over a secure channel, can enable
220 side-channel attacks such as BREACH (see Section 10.6 of [RFC7540]
221 and [BREACH]). At the time of publication, it was unclear how
222 BREACH-like attacks can be applied to compression in HTTP requests.
224 7. IANA Considerations
226 7.1. Header Field Registry
228 HTTP header fields are registered within the "Message Headers"
229 registry located at
230 , as defined by
231 [BCP90].
233 This document updates the definition of the "Accept-Encoding" header
234 field, so the "Permanent Message Header Field Names" registry ought
235 to be updated accordingly:
237 +-----------------+----------+----------+---------------------------+
238 | Header Field | Protocol | Status | Reference |
239 | Name | | | |
240 +-----------------+----------+----------+---------------------------+
241 | Accept-Encoding | http | standard | [RFC7231], Section 5.3.4, |
242 | | | | and Section 3 of this |
243 | | | | document |
244 +-----------------+----------+----------+---------------------------+
246 7.2. Status Code Registry
248 HTTP status codes are registered within the "Status Code" registry
249 located at .
251 This document updates the definition of the status code 415
252 (Unsupported Media Type), so the "Status Code" registry ought to be
253 updated accordingly:
255 +-------+------------------+----------------------------------------+
256 | Value | Description | Reference |
257 +-------+------------------+----------------------------------------+
258 | 415 | Unsupported | [RFC7231], Section 6.5.13, and |
259 | | Media Type | Section 3 of this document |
260 +-------+------------------+----------------------------------------+
262 8. References
264 8.1. Normative References
266 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
267 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
268 RFC2119, March 1997,
269 .
271 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
272 Protocol (HTTP/1.1): Message Syntax and Routing",
273 RFC 7230, DOI 10.17487/RFC7230, June 2014,
274 .
276 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
277 Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
278 DOI 10.17487/RFC7231, June 2014,
279 .
281 8.2. Informative References
283 [BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
284 Procedures for Message Header Fields", BCP 90, RFC 3864,
285 September 2004, .
287 [BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the
288 CRIME Attack", July 2013, .
292 [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
293 Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
294 DOI 10.17487/RFC7540, May 2015,
295 .
297 Appendix A. Change Log (to be removed by RFC Editor before publication)
299 A.1. Since draft-reschke-http-cice-00
301 Clarified that the information returned in Accept-Encoding is per
302 resource, not per server.
304 Added some deployment considerations.
306 Updated HTTP/1.1 references.
308 A.2. Since draft-reschke-http-cice-01
310 Restrict the scope of A-E from "future requests" to "at the time of
311 this request".
313 Mention use of A-E in responses other than 415.
315 Recommend not to include A-E in a 415 response unless there was
316 actually a problem related to content coding.
318 A.3. Since draft-reschke-http-cice-02
320 First Working Group draft; updated boilerplate accordingly.
322 A.4. Since draft-ietf-httpbis-cice-00
324 Apply editorial improvements suggested by Mark Nottingham.
326 A.5. Since draft-ietf-httpbis-cice-01
328 Clarify that we're also extending the definition of status code 415
329 (so update that IANA registry entry as well).
331 A.6. Since draft-ietf-httpbis-cice-02
333 Removed normative language that required used of Accept-Encoding in
334 responses (which would have made existing servers non-compliant).
336 Add BREACH like attacks to security considerations
337 ().
339 Appendix B. Acknowledgements
341 Thanks go to the members of the and HTTPbis Working Group, namely
342 Amos Jeffries, Ben Campbell, Mark Nottingham, Pete Resnick, Stephen
343 Farrell, and Ted Hardie.
345 Author's Address
347 Julian F. Reschke
348 greenbytes GmbH
349 Hafenweg 16
350 Muenster, NW 48155
351 Germany
353 EMail: julian.reschke@greenbytes.de
354 URI: http://greenbytes.de/tech/webdav/