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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/