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2 Network Working Group J. Reschke
3 Internet-Draft greenbytes
4 Intended status: Standards Track March 30, 2010
5 Expires: October 1, 2010
7 Application of RFC 2231 Encoding to
8 Hypertext Transfer Protocol (HTTP) Header Fields
9 draft-reschke-rfc2231-in-http-11
11 Abstract
13 By default, message header field parameters in Hypertext Transfer
14 Protocol (HTTP) messages can not carry characters outside the ISO-
15 8859-1 character set. RFC 2231 defines an escaping mechanism for use
16 in Multipurpose Internet Mail Extensions (MIME) headers. This
17 document specifies a profile of that encoding suitable for use in
18 HTTP header fields.
20 Editorial Note (To be removed by RFC Editor before publication)
22 There are multiple HTTP header fields that already use RFC 2231
23 encoding in practice (Content-Disposition) or might use it in the
24 future (Link). The purpose of this document is to provide a single
25 place where the generic aspects of RFC 2231 encoding in HTTP header
26 fields are defined.
28 Distribution of this document is unlimited. Although this is not a
29 work item of the HTTPbis Working Group, comments should be sent to
30 the Hypertext Transfer Protocol (HTTP) mailing list at
31 ietf-http-wg@w3.org [1], which may be joined by sending a message
32 with subject "subscribe" to ietf-http-wg-request@w3.org [2].
34 Discussions of the HTTPbis Working Group are archived at
35 .
37 XML versions, latest edits and the issues list for this document are
38 available from
39 . A
40 collection of test cases is available at
41 .
43 Note: as of February 2010, there were at least three independent
44 implementations of the encoding defined in Section 3.2: Konqueror
45 (starting with 4.4.1), Mozilla Firefox, and Opera.
47 Status of This Memo
48 This Internet-Draft is submitted to IETF in full conformance with the
49 provisions of BCP 78 and BCP 79.
51 Internet-Drafts are working documents of the Internet Engineering
52 Task Force (IETF), its areas, and its working groups. Note that
53 other groups may also distribute working documents as Internet-
54 Drafts.
56 Internet-Drafts are draft documents valid for a maximum of six months
57 and may be updated, replaced, or obsoleted by other documents at any
58 time. It is inappropriate to use Internet-Drafts as reference
59 material or to cite them other than as "work in progress."
61 The list of current Internet-Drafts can be accessed at
62 http://www.ietf.org/ietf/1id-abstracts.txt.
64 The list of Internet-Draft Shadow Directories can be accessed at
65 http://www.ietf.org/shadow.html.
67 This Internet-Draft will expire on October 1, 2010.
69 Copyright Notice
71 Copyright (c) 2010 IETF Trust and the persons identified as the
72 document authors. All rights reserved.
74 This document is subject to BCP 78 and the IETF Trust's Legal
75 Provisions Relating to IETF Documents
76 (http://trustee.ietf.org/license-info) in effect on the date of
77 publication of this document. Please review these documents
78 carefully, as they describe your rights and restrictions with respect
79 to this document. Code Components extracted from this document must
80 include Simplified BSD License text as described in Section 4.e of
81 the Trust Legal Provisions and are provided without warranty as
82 described in the BSD License.
84 Table of Contents
86 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
87 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4
88 3. A Profile of RFC 2231 for Use in HTTP . . . . . . . . . . . . 4
89 3.1. Parameter Continuations . . . . . . . . . . . . . . . . . 5
90 3.2. Parameter Value Character Set and Language Information . . 5
91 3.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 7
92 3.3. Language specification in Encoded Words . . . . . . . . . 8
93 4. Guidelines for Usage in HTTP Header Field Definitions . . . . 8
94 4.1. When to Use the Extension . . . . . . . . . . . . . . . . 9
95 4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . . 9
96 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
97 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
98 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
99 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
100 8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
101 8.2. Informative References . . . . . . . . . . . . . . . . . . 11
102 Appendix A. Document History and Future Plans (to be removed
103 by RFC Editor before publication) . . . . . . . . . . 12
104 Appendix B. Change Log (to be removed by RFC Editor before
105 publication) . . . . . . . . . . . . . . . . . . . . 12
106 B.1. Since draft-reschke-rfc2231-in-http-00 . . . . . . . . . . 12
107 B.2. Since draft-reschke-rfc2231-in-http-01 . . . . . . . . . . 12
108 B.3. Since draft-reschke-rfc2231-in-http-02 . . . . . . . . . . 13
109 B.4. Since draft-reschke-rfc2231-in-http-03 . . . . . . . . . . 13
110 B.5. Since draft-reschke-rfc2231-in-http-04 . . . . . . . . . . 13
111 B.6. Since draft-reschke-rfc2231-in-http-05 . . . . . . . . . . 13
112 B.7. Since draft-reschke-rfc2231-in-http-06 . . . . . . . . . . 13
113 B.8. Since draft-reschke-rfc2231-in-http-07 . . . . . . . . . . 13
114 B.9. Since draft-reschke-rfc2231-in-http-08 . . . . . . . . . . 13
115 B.10. Since draft-reschke-rfc2231-in-http-09 . . . . . . . . . . 13
116 B.11. Since draft-reschke-rfc2231-in-http-10 . . . . . . . . . . 13
117 Appendix C. Resolved issues (to be removed by RFC Editor
118 before publication) . . . . . . . . . . . . . . . . . 14
119 C.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
120 C.2. charset-registered . . . . . . . . . . . . . . . . . . . . 14
121 C.3. parameter-abnf . . . . . . . . . . . . . . . . . . . . . . 14
122 C.4. value-abnf . . . . . . . . . . . . . . . . . . . . . . . . 14
123 C.5. iso8859 . . . . . . . . . . . . . . . . . . . . . . . . . 15
124 C.6. when-ext-value . . . . . . . . . . . . . . . . . . . . . . 15
125 C.7. repeated-param . . . . . . . . . . . . . . . . . . . . . . 15
126 C.8. handling-multiple . . . . . . . . . . . . . . . . . . . . 16
127 C.9. i18n-spoofing . . . . . . . . . . . . . . . . . . . . . . 17
128 C.10. multiple-inst-spoofing . . . . . . . . . . . . . . . . . . 17
130 1. Introduction
132 By default, message header field parameters in HTTP ([RFC2616])
133 messages can not carry characters outside the ISO-8859-1 character
134 set ([ISO-8859-1]). RFC 2231 (Appendix of [RFC2231]) defines an
135 escaping mechanism for use in MIME headers. This document specifies
136 a profile of that encoding for use in HTTP header fields.
138 Note: this profile does not apply to message payloads transmitted
139 over HTTP, such as when using the media type "multipart/form-data"
140 ([RFC2388]).
142 2. Notational Conventions
144 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
145 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
146 document are to be interpreted as described in [RFC2119].
148 This specification uses the ABNF (Augmented Backus-Naur Form)
149 notation defined in [RFC5234]. The following core rules are included
150 by reference, as defined in [RFC5234], Appendix B.1: ALPHA (letters),
151 DIGIT (decimal 0-9), HEXDIG (hexadecimal 0-9/A-F/a-f) and LWSP
152 (linear white space).
154 Note that this specification uses the term "character set" for
155 consistency with other IETF specifications such as RFC 2277 (see
156 [RFC2277], Section 3). A more accurate term would be "character
157 encoding" (a mapping of code points to octet sequences).
159 3. A Profile of RFC 2231 for Use in HTTP
161 RFC 2231 defines several extensions to MIME. The sections below
162 discuss if and how they apply to HTTP.
164 In short:
166 o Parameter Continuations aren't needed (Section 3.1),
168 o Character Set and Language Information are useful, therefore a
169 simple subset is specified (Section 3.2), and
171 o Language Specifications in Encoded Words aren't needed
172 (Section 3.3).
174 3.1. Parameter Continuations
176 Section 3 of [RFC2231] defines a mechanism that deals with the length
177 limitations that apply to MIME headers. These limitations do not
178 apply to HTTP ([RFC2616], Section 19.4.7).
180 Thus in HTTP, senders MUST NOT use parameter continuations, and
181 therefore recipients do not need to support them.
183 3.2. Parameter Value Character Set and Language Information
185 Section 4 of [RFC2231] specifies how to embed language information
186 into parameter values, and also how to encode non-ASCII characters,
187 dealing with restrictions both in MIME and HTTP header parameters.
189 However, RFC 2231 does not specify a mandatory-to-implement character
190 set, making it hard for senders to decide which character set to use.
191 Thus, recipients implementing this specification MUST support the
192 character sets "ISO-8859-1" [ISO-8859-1] and "UTF-8" [RFC3629].
194 Furthermore, RFC 2231 allows leaving out the character set
195 information. The profile defined by this specification does not
196 allow that.
198 The syntax for parameters is defined in Section 3.6 of [RFC2616]
199 (with RFC 2616 implied LWS translated to RFC 5234 LWSP):
201 parameter = attribute LWSP "=" LWSP value
203 attribute = token
204 value = token / quoted-string
206 quoted-string =
207 token =
209 This specification modifies the grammar to:
211 parameter = reg-parameter / ext-parameter
213 reg-parameter = parmname LWSP "=" LWSP value
215 ext-parameter = parmname "*" LWSP "=" LWSP ext-value
217 parmname = 1*attr-char
219 ext-value = charset "'" [ language ] "'" value-chars
220 ; extended-initial-value,
221 ; defined in [RFC2231], Section 7
223 charset = "UTF-8" / "ISO-8859-1" / mime-charset
225 mime-charset = 1*mime-charsetc
226 mime-charsetc = ALPHA / DIGIT
227 / "!" / "#" / "$" / "%" / "&"
228 / "+" / "-" / "^" / "_" / "`"
229 / "{" / "}" / "~"
230 ; as in Section 2.3 of [RFC2978]
231 ; except that the single quote is not included
232 ; SHOULD be registered in the IANA charset registry
234 language =
236 value-chars = *( pct-encoded / attr-char )
238 pct-encoded = "%" HEXDIG HEXDIG
239 ; see [RFC3986], Section 2.1
241 attr-char = ALPHA / DIGIT
242 / "!" / "#" / "$" / "&" / "+" / "-" / "."
243 / "^" / "_" / "`" / "|" / "~"
244 ; token except ( "*" / "'" / "%" )
246 Thus, a parameter is either regular parameter (reg-parameter), as
247 previously defined in Section 3.6 of [RFC2616], or an extended
248 parameter (ext-parameter).
250 Extended parameters are those where the left hand side of the
251 assignment ends with an asterisk character.
253 The value part of an extended parameter (ext-value) is a token that
254 consists of three parts: the REQUIRED character set name (charset),
255 the OPTIONAL language information (language), and a character
256 sequence representing the actual value (value-chars), separated by
257 single quote characters. Note that both character set names and
258 language tags are restricted to the US-ASCII character set, and are
259 matched case-insensitively (see [RFC2978], Section 2.3 and [RFC5646],
260 Section 2.1.1).
262 Inside the value part, characters not contained in attr-char are
263 encoded into an octet sequence using the specified character set.
264 That octet sequence then is percent-encoded as specified in Section
265 2.1 of [RFC3986].
267 Producers MUST NOT use character sets other than "UTF-8" ([RFC3629])
268 or "ISO-8859-1" ([ISO-8859-1]). Extension character sets (ext-
269 charset) are reserved for future use.
271 Note: recipients should be prepared to handle encoding errors,
272 such as malformed or incomplete percent escape sequences, or non-
273 decodable octet sequences, in a robust manner. This specification
274 does not mandate any specific behavior, for instance the following
275 strategies are all acceptable:
277 * ignoring the parameter,
279 * stripping a non-decodable octet sequence,
281 * substituting a non-decodable octet sequence by a replacement
282 character, such as the Unicode character U+FFFD (Replacement
283 Character).
285 Note: the RFC 2616 token production ([RFC2616], Section 2.2)
286 differs from the production used in RFC 2231 (imported from
287 Section 5.1 of [RFC2045]) in that curly braces ("{" and "}") are
288 excluded. Thus, these two characters are excluded from the attr-
289 char production as well.
291 Note: the ABNF defined here differs from the one in
292 Section 2.3 of [RFC2978] in that it does not allow the single
293 quote character (see also RFC Editor Errata ID 1912 [3]). In
294 practice, no character set names using that character have been
295 registered at the time of this writing.
297 3.2.1. Examples
299 Non-extended notation, using "token":
301 foo: bar; title=Economy
303 Non-extended notation, using "quoted-string":
305 foo: bar; title="US-$ rates"
307 Extended notation, using the unicode character U+00A3 (POUND SIGN):
309 foo: bar; title*=iso-8859-1'en'%A3%20rates
311 Note: the Unicode pound sign character U+00A3 was encoded using ISO-
312 8859-1 into the single octet A3, then percent-encoded. Also note
313 that the space character was encoded as %20, as it is not contained
314 in attr-char.
316 Extended notation, using the unicode characters U+00A3 (POUND SIGN)
317 and U+20AC (EURO SIGN):
319 foo: bar; title*=UTF-8''%c2%a3%20and%20%e2%82%ac%20rates
321 Note: the unicode pound sign character U+00A3 was encoded using UTF-8
322 into the octet sequence C2 A3, then percent-encoded. Likewise, the
323 unicode euro sign character U+20AC was encoded into the octet
324 sequence E2 82 AC, then percent-encoded. Also note that HEXDIG
325 allows both lower-case and upper-case character, so recipients must
326 understand both, and that the language information is optional, while
327 the character set is not.
329 3.3. Language specification in Encoded Words
331 Section 5 of [RFC2231] extends the encoding defined in [RFC2047] to
332 also support language specification in encoded words. Although the
333 HTTP/1.1 specification does refer to RFC 2047 ([RFC2616], Section
334 2.2), it's not clear to which header field exactly it applies, and
335 whether it is implemented in practice (see
336 for details).
338 Thus, the RFC 2231 profile defined by this specification does not
339 include this feature.
341 4. Guidelines for Usage in HTTP Header Field Definitions
343 Specifications of HTTP header fields that use the extensions defined
344 in Section 3.2 should clearly state that. A simple way to achieve
345 this is to normatively reference this specification, and to include
346 the ext-value production into the ABNF for that header field.
348 For instance:
350 foo-header = "foo" LWSP ":" LWSP token ";" LWSP title-param
351 title-param = "title" LWSP "=" LWSP value
352 / "title*" LWSP "=" LWSP ext-value
353 ext-value =
355 [[rfcno: Note to RFC Editor: in the figure above, please replace
356 "xxxx" by the RFC number assigned to this specification.]]
358 Note: The Parameter Value Continuation feature defined in Section
359 3 of [RFC2231] makes it impossible to have multiple instances of
360 extended parameters with identical parmname components, as the
361 processing of continuations would become ambiguous. Thus,
362 specifications using this extension are recommended to disallow
363 this case for compatibility with RFC 2231.
365 4.1. When to Use the Extension
367 Section 4.2 of [RFC2277] requires that protocol elements containing
368 text are able to carry language information. Thus, the ext-value
369 production should always be used when the parameter value is of
370 textual nature and its language is known.
372 Furthermore, the extension should also be used whenever the parameter
373 value needs to carry characters not present in the US-ASCII
374 ([USASCII]) character set (note that it would be unacceptable to
375 define a new parameter that would be restricted to a subset of the
376 Unicode character set).
378 4.2. Error Handling
380 Header field specifications need to define whether multiple instances
381 of parameters with identical parmname components are allowed, and how
382 they should processed. It is recommended that a parameter using the
383 extended syntax takes precedence. This could be used by producers to
384 use both formats without breaking recipients that do not understand
385 the extended syntax yet.
387 Example:
389 foo: bar; title="EURO exchange rates";
390 title*=utf-8''%e2%82%ac%20exchange%20rates
392 In this case, the sender provides an ASCII version of the title for
393 legacy recipients, but also includes an internationalized version for
394 recipients understanding this specification -- the latter obviously
395 should prefer the new syntax over the old one.
397 Note: at the time of this writing, many implementations failed to
398 ignore the form they do not understand, or prioritize the ASCII
399 form although the extended syntax was present.
401 5. Security Considerations
403 The format described in this document makes it possible to transport
404 non-ASCII characters, and thus enables character "spoofing"
405 scenarios, in which a displayed value appears to be something other
406 than it is.
408 Furthermore, there are known attack scenarios relating to decoding
409 UTF-8.
411 See Section 10 of [RFC3629] for more information on both topics.
413 In addition, the extension specified in this document makes it
414 possible to transport multiple language variants for a single
415 parameter, and such use might allow spoofing attacks, where different
416 language versions of the same parameter are not equivalent. Whether
417 this attack is useful as an attack depends on the parameter
418 specified.
420 6. IANA Considerations
422 There are no IANA Considerations related to this specification.
424 7. Acknowledgements
426 Thanks to Martin Duerst and Frank Ellermann for help figuring out
427 ABNF details, to Graham Klyne and Alexey Melnikov for general review,
428 Chris Newman for pointing out an RFC 2231 incompatibility, and to
429 Benjamin Carlyle and Roar Lauritzsen for implementer's feedback.
431 8. References
433 8.1. Normative References
435 [ISO-8859-1] International Organization for Standardization,
436 "Information technology -- 8-bit single-byte coded
437 graphic character sets -- Part 1: Latin alphabet No.
438 1", ISO/IEC 8859-1:1998, 1998.
440 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
441 Requirement Levels", BCP 14, RFC 2119, March 1997.
443 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
444 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
445 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
447 [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration
448 Procedures", BCP 19, RFC 2978, October 2000.
450 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
451 10646", RFC 3629, STD 63, November 2003.
453 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
454 "Uniform Resource Identifier (URI): Generic Syntax",
455 RFC 3986, STD 66, January 2005.
457 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
458 Syntax Specifications: ABNF", STD 68, RFC 5234,
459 January 2008.
461 [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for
462 Identifying Languages", BCP 47, RFC 5646,
463 September 2009.
465 [USASCII] American National Standards Institute, "Coded Character
466 Set -- 7-bit American Standard Code for Information
467 Interchange", ANSI X3.4, 1986.
469 8.2. Informative References
471 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
472 Mail Extensions (MIME) Part One: Format of Internet
473 Message Bodies", RFC 2045, November 1996.
475 [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail
476 Extensions) Part Three: Message Header Extensions for
477 Non-ASCII Text", RFC 2047, November 1996.
479 [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and
480 Encoded Word Extensions: Character Sets, Languages, and
481 Continuations", RFC 2231, November 1997.
483 [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
484 Languages", BCP 18, RFC 2277, January 1998.
486 [RFC2388] Masinter, L., "Returning Values from Forms: multipart/
487 form-data", RFC 2388, August 1998.
489 URIs
491 [1]
493 [2]
495 [3]
497 Appendix A. Document History and Future Plans (to be removed by RFC
498 Editor before publication)
500 Problems with the internationalization of the HTTP Content-
501 Disposition header field have been known for many years (see test
502 cases at ).
504 During IETF 72
505 (), the
506 HTTPbis Working Group shortly discussed how to deal with the
507 underspecification of (1) Content-Disposition, and its (2)
508 internationalization aspects. Back then, there was rough consensus
509 in the room to move the definition into a separate draft.
511 This specification addresses problem (2), by defining a simple subset
512 of the encoding format defined in RFC 2231. A separate
513 specification, draft-reschke-rfc2183-in-http, is planned to address
514 problem (1). Note that this approach was chosen because Content-
515 Disposition is just an example for an HTTP header field using this
516 kind of encoding. Another example is the currently proposed Link
517 header field (draft-nottingham-http-link-header).
519 This document is planned to be published on the IETF Standards Track,
520 so that other standards-track level documents can depend on it, such
521 as the new specification of Content-Disposition, or potentially
522 future revisions of the HTTP Link Header specification.
524 Also note that this document specifies a proper subset of the
525 extensions defined in RFC 2231, but does not normatively refer to it.
526 Thus, RFC 2231 can be revised separately, should the email community
527 decide to.
529 Appendix B. Change Log (to be removed by RFC Editor before publication)
531 B.1. Since draft-reschke-rfc2231-in-http-00
533 Use RFC5234-style ABNF, closer to the one used in RFC 2231.
535 Make RFC 2231 dependency informative, so this specification can
536 evolve independently.
538 Explain the ABNF in prose.
540 B.2. Since draft-reschke-rfc2231-in-http-01
542 Remove unneeded RFC5137 notation (code point vs character).
544 B.3. Since draft-reschke-rfc2231-in-http-02
546 And and resolve issues "charset", "repeats" and "rfc4646".
548 B.4. Since draft-reschke-rfc2231-in-http-03
550 And and resolve issue "charsetmatch".
552 B.5. Since draft-reschke-rfc2231-in-http-04
554 Add and resolve issues "badseq" and "tokenquotcharset".
556 B.6. Since draft-reschke-rfc2231-in-http-05
558 Say "header field" instead of "header" in the context of HTTP.
560 B.7. Since draft-reschke-rfc2231-in-http-06
562 Add an appendix discussing document history and future plans, to be
563 removed before publication.
565 B.8. Since draft-reschke-rfc2231-in-http-07
567 Add and resolve issues "impl" and "rel-2388".
569 B.9. Since draft-reschke-rfc2231-in-http-08
571 Editorial improvements. Add and resolve issues "attrcharvstoken" and
572 "tokengrammar".
574 B.10. Since draft-reschke-rfc2231-in-http-09
576 Add issues "i18n-spoofing", "iso8859", "parameter-abnf", and "when-
577 ext-value". Add and resolve issues "rfc2978-normative", "rfc3986-
578 normative" and "usascii-normative".
580 B.11. Since draft-reschke-rfc2231-in-http-10
582 Resolve issues "i18n-spoofing", "iso8859", "parameter-abnf", and
583 "when-ext-value".
585 Add and resolve issue "charset-registered", "handling-multiple",
586 "multiple-inst-spoofing", "repeated-param" and "value-abnf".
588 Update the KDE implementation note.
590 Appendix C. Resolved issues (to be removed by RFC Editor before
591 publication)
593 Issues that were either rejected or resolved in this version of this
594 document.
596 C.1. edit
598 Type: edit
600 julian.reschke@greenbytes.de (2009-04-17): Umbrella issue for
601 editorial fixes/enhancements.
603 C.2. charset-registered
605 In Section 3.2:
607 Type: change
609 julian.reschke@greenbytes.de (2010-02-20): Mention to use only
610 registered charset names? (reported by Alexey Melnikov).
612 Resolution (2010-03-29): State this in the ABNF.
614 C.3. parameter-abnf
616 In Section 3.2:
618 Type: change
620 julian.reschke@greenbytes.de (2010-02-20): The ABNF for reg-parameter
621 and ext-parameter is ambiguous, as "*" is a valid token character;
622 furthermore, RFC 2616's "attribute" production allows "*" while RFC
623 2231's does not. (reported by Alexey Melnikov).
625 julian.reschke@greenbytes.de (2010-02-21): Proposal: restrict the
626 allowable character set in parameter names to exclude "*" (and maybe
627 even more non-name characters?). Also, consider extending the set of
628 value characters (for the right hand side) to allow more characters
629 that can be unambiguously parsed outside quoted strings, such as "/".
631 Resolution: Introduced parmname, disallowing "*" / "'" / "%". Moving
632 the value ABNF discussion into a separate issue ("value-abnf").
634 C.4. value-abnf
636 In Section 3.2:
638 Type: change
640 julian.reschke@greenbytes.de (2010-02-26): Consider extending the
641 right-hand side ABNF - both for regular and extended parameters - to
642 include more characters that can be unambiguously parsed outside
643 quoted strings, such as "/".
645 Resolution (2010-03-29): No change due to lack of feedback.
646 Potentially defer to future versions of HTTP/1.1 (defining guidelines
647 for header definitions), or a revision of this spec.
649 C.5. iso8859
651 In Section 3.2:
653 Type: change
655 julian.reschke@greenbytes.de (2010-02-20): The protocol could be
656 further simplified by mandating UTF-8 only (reported by Alexey
657 Melnikov). On the other hand and not surprinsingly, testing shows
658 that ISO-8859-1 support is widely implemented. The author is looking
659 for community feedback on this choice.
661 Resolution (2010-03-29): Further feedback was requested during IETF
662 LC; but none was received. Thus defaulting to no change; keeping the
663 support for ISO-8859-1.
665 C.6. when-ext-value
667 In Section 4.1:
669 Type: change
671 julian.reschke@greenbytes.de (2010-02-18): There's no point in using
672 ext-value when the language is unknown and no "special" characters
673 are present.
675 Resolution (2010-02-23): Fixed.
677 C.7. repeated-param
679 In Section 4:
681 Type: change
683 Chris.Newman@Sun.COM (2010-03-22): RFC 2231 did not allow two
684 parameters with the same name but different languages, at least in
685 the context of continuations that was impossible. Absent
686 continuations, RFC 2231 was otherwise silent on that topic.
687 So section 4.3 adds a new feature over and above what RFC 2231 did.
688 It's a feature that will make implementations significantly more
689 complex and is likely to cause interoperability problems.
690 Much of the experience with deployment of both language tagging and
691 language variants in the IETF seems to result in unnecessary
692 complexity. While there are good abstract arguments for language
693 tagging in theory, it seems more often than not that the parties in
694 the exchange are unable to put anything useful in the field in which
695 case it falls into the realm of unnecessary complexity. In addition,
696 we have experience where we attempted to allow language variants
697 (multipart/alternative) and not only did that usage not deploy, it is
698 actively broken despite being an explicit example in RFC 1766.
699 The one place where I've seen language variants mostly work is when
700 the language tag is actually included in the attribute name (LDAP
701 does this) and the "search" mechanism allows wildcarding of
702 languages. But having two attributes with the same name seems
703 dangerous.
704 My recommendation is to remove this feature as I believe it will not
705 be used in practice and will add unnecessary complexity that is
706 likely to create interoperability problems.
708 Resolution (2010-03-29): State the issue. Remove section 4.3.
709 Rephrase 4.2 accordingly.
711 C.8. handling-multiple
713 In Section 4.2:
715 Type: change
717
720 roessler@gmail.com (2010-02-24): Leaving the choice of precedence to
721 the header specification implies that parsers need to special-case.
722 It would seem reasonable to make a choice in this specification that
723 for properties which can only occur once, the traditional syntax
724 takes precedence.
726 julian.reschke@greenbytes.de (2010-02-26): That would rule out the
727 use case where the traditional syntax is used as a fallback for
728 clients that do not support the new syntax, as discussed in that
729 section: ... http://greenbytes.de/tech/tc2231/#attfnboth2 is a test
730 case that shows that using this technique, both variants can be
731 served to clients, and those that understand the ext-parameter
732 encoding will indeed pick the "better" parameter. Unfortunately,
733 this appears to depend on parameter ordering, which I didn't want to
734 mention in this spec. Maybe I should?
736 Resolution (2010-03-29): Just state that when repetitions are not
737 allowed, the extended form should take precedence.
739 C.9. i18n-spoofing
741 In Section 5:
743 Type: change
745
748 GK@ninebynine.org (2010-02-20): I note that the security
749 considerations section says nothing about possible character
750 "spoofing" - i.e. making a displayed prompt or value appear to be
751 something other than it is. E.g. Non-ASCII characters have been
752 used to set up exploits involving dodgy URIs that may appear to a
753 user to be legitimate.
755 Resolution (2010-02-23): Mention the problem, and point to RFC 3629's
756 security considerations which mention this as well. While at it,
757 also mention the other UTF-8 related attack scenario.
759 C.10. multiple-inst-spoofing
761 In Section 5:
763 Type: change
765 kivinen@iki.fi (2010-03-01): Yes, but the impact of them is
766 different. For example it does not really matter if the filename
767 parameters having different languages differ, but there might be
768 parameters where this really matters.
769 As this document does not define any exact parameters, it might be
770 enough to comment something like that "This document specifies way to
771 transport multiple language variants for parameters, and such use
772 might allow spoofing attacks, where different language versions of
773 the same parameters do not match. Whether this attack is useful as
774 an attack depends on the parameter specified."
776 Resolution (2010-03-01): Add text based on the recommendation.
778 Author's Address
780 Julian F. Reschke
781 greenbytes GmbH
782 Hafenweg 16
783 Muenster, NW 48155
784 Germany
786 EMail: julian.reschke@greenbytes.de
787 URI: http://greenbytes.de/tech/webdav/