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2 HTTP Working Group J. Reschke
3 Internet-Draft greenbytes
4 Intended status: Standards Track May 30, 2015
5 Expires: December 1, 2015
7 Hypertext Transfer Protocol (HTTP) Client-Initiated Content-Encoding
8 draft-ietf-httpbis-cice-01
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 that content codings 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.4.
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 December 1, 2015.
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 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
75 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
76 8.2. Informative References . . . . . . . . . . . . . . . . . . 6
77 Appendix A. Change Log (to be removed by RFC Editor before
78 publication) . . . . . . . . . . . . . . . . . . . . . 6
79 A.1. Since draft-reschke-http-cice-00 . . . . . . . . . . . . . 6
80 A.2. Since draft-reschke-http-cice-01 . . . . . . . . . . . . . 6
81 A.3. Since draft-reschke-http-cice-02 . . . . . . . . . . . . . 6
82 A.4. Since draft-ietf-httpbis-cice-00 . . . . . . . . . . . . . 7
83 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . . 7
85 1. Introduction
87 In HTTP, content codings allow for payload encodings such as for
88 compression or integrity checks ([RFC7231], Section 3.1.2). In
89 particular, the "gzip" content coding is widely used for payload data
90 sent in response messages.
92 Content codings can be used in request messages as well, however
93 discoverability is not on par with response messages. This document
94 extends the HTTP "Accept-Encoding" header field ([RFC7231], Section
95 5.3.4) for use in responses, to indicate that content codings are
96 supported in requests.
98 2. Notational Conventions
100 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
101 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
102 document are to be interpreted as described in [RFC2119].
104 This document reuses terminology defined in the base HTTP
105 specifications, namely Section 2 of [RFC7230] and Section 3.1.2 of
106 [RFC7231].
108 3. Using the 'Accept-Encoding' Header Field in Responses
110 Section 5.3.4 of [RFC7231] defines "Accept-Encoding" as a request
111 header field only.
113 This specification expands that definition to allow "Accept-Encoding"
114 as a response header field as well. When present in a response, it
115 indicates what content codings the resource was willing to accept in
116 the associated request. A field value that only contains "identity"
117 implies that no content codings were supported.
119 Note that this information is specific to the associated request; the
120 set of supported encodings might be different for other resources on
121 the same server, and could change over time or depend on other
122 aspects of the request (such as the request method).
124 Section 6.5.13 of [RFC7231] defines status code 415 (Unsupported
125 Media Type) to apply to both media type and content coding related
126 problems.
128 Servers that fail a request due to an unsupported content coding
129 SHOULD respond with a 415 status and SHOULD include an "Accept-
130 Encoding" header field in that response, allowing clients to
131 distinguish between content coding related issues and media type
132 related issues. In order to avoid confusion with media type related
133 problems, servers that fail a request with a 415 status for reasons
134 unrelated to content codings SHOULD NOT include the "Accept-Encoding"
135 header field.
137 It is expected that the most common use of "Accept-Encoding" in
138 responses will have the 415 (Unsupported Media Type) status code, in
139 response to optimistic use of a content coding by clients. However,
140 the header field can also be used to indicate to clients that content
141 codings are supported, to optimize future interactions. For example,
142 a resource might include it in a 2xx response when the request
143 payload was big enough to justify use of a compression coding, but
144 the client failed do so.
146 4. Example
148 A client submits a POST request using the "compress" content coding
149 ([RFC7231], Section 3.1.2.1):
151 POST /edit/ HTTP/1.1
152 Host: example.org
153 Content-Type: application/atom+xml;type=entry
154 Content-Encoding: compress
156 ...compressed payload...
158 The server rejects request because it only allows the "gzip" content
159 coding:
161 HTTP/1.1 415 Unsupported Media Type
162 Date: Fri, 09 May 2014 11:43:53 GMT
163 Accept-Encoding: gzip
164 Content-Length: 68
165 Content-Type: text/plain
167 This resource only supports the "gzip" content coding in requests.
169 ...at which point the client can retry the request with the supported
170 "gzip" content coding.
172 Alternatively, a server that does not support any content codings in
173 requests could answer with:
175 HTTP/1.1 415 Unsupported Media Type
176 Date: Fri, 09 May 2014 11:43:53 GMT
177 Accept-Encoding: identity
178 Content-Length: 61
179 Content-Type: text/plain
180 This resource does not support content codings in requests.
182 5. Deployment Considerations
184 Servers that do not support content codings in requests already are
185 required to fail a request that does use a content coding. Section
186 6.5.13 of [RFC7231] recommends using the status code 415 (Unsupported
187 Media Type), so the only change needed is to include the "Accept-
188 Encoding" header field with value "identity" in that response.
190 Servers that do support some content codings are required to fail
191 requests with unsupported content codings as well. To be compliant
192 with this specification, servers will need to use the status code 415
193 (Unsupported Media Type) to signal the problem, and will have to
194 include an "Accept-Encoding" header field that enumerates the content
195 codings that are supported. As the set of supported content codings
196 is usually static and small, adding the header field ought to be
197 trivial.
199 6. Security Considerations
201 This specification does not introduce any new security considerations
202 beyond those discussed in Section 9 of [RFC7231].
204 7. IANA Considerations
206 HTTP header fields are registered within the "Message Headers"
207 registry located at
208 , as defined by
209 [BCP90].
211 This document updates the definition of the "Accept-Encoding" header
212 field, so the "Permanent Message Header Field Names" registry shall
213 be updated accordingly:
215 +-----------------+----------+----------+---------------------------+
216 | Header Field | Protocol | Status | Reference |
217 | Name | | | |
218 +-----------------+----------+----------+---------------------------+
219 | Accept-Encoding | http | standard | [RFC7231], Section 5.3.4, |
220 | | | | and Section 3 of this |
221 | | | | document |
222 +-----------------+----------+----------+---------------------------+
224 8. References
225 8.1. Normative References
227 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
228 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
229 RFC2119, March 1997,
230 .
232 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
233 Protocol (HTTP/1.1): Message Syntax and Routing",
234 RFC 7230, DOI 10.17487/RFC7230, June 2014,
235 .
237 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
238 Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
239 DOI 10.17487/RFC7231, June 2014,
240 .
242 8.2. Informative References
244 [BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
245 Procedures for Message Header Fields", BCP 90, RFC 3864,
246 September 2004, .
248 Appendix A. Change Log (to be removed by RFC Editor before publication)
250 A.1. Since draft-reschke-http-cice-00
252 Clarified that the information returned in Accept-Encoding is per
253 resource, not per server.
255 Added some deployment considerations.
257 Updated HTTP/1.1 references.
259 A.2. Since draft-reschke-http-cice-01
261 Restrict the scope of A-E from "future requests" to "at the time of
262 this request".
264 Mention use of A-E in responses other than 415.
266 Recommend not to include A-E in a 415 response unless there was
267 actually a problem related to content coding.
269 A.3. Since draft-reschke-http-cice-02
271 First Working Group draft; updated boilerplate accordingly.
273 A.4. Since draft-ietf-httpbis-cice-00
275 Apply editorial improvements suggested by Mark Nottingham.
277 Appendix B. Acknowledgements
279 Thanks go to the members of the and HTTPbis Working Group, namely
280 Amos Jeffries, Mark Nottingham, and Ted Hardie.
282 Author's Address
284 Julian F. Reschke
285 greenbytes GmbH
286 Hafenweg 16
287 Muenster, NW 48155
288 Germany
290 EMail: julian.reschke@greenbytes.de
291 URI: http://greenbytes.de/tech/webdav/