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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO-8859-1' ** Obsolete normative reference: RFC 2616 (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235) ** Obsolete normative reference: RFC 5987 (Obsoleted by RFC 8187) Summary: 3 errors (**), 0 flaws (~~), 1 warning (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Reschke 3 Internet-Draft greenbytes 4 Updates: 2616 (if approved) August 30, 2010 5 Intended status: Standards Track 6 Expires: March 3, 2011 8 Use of the Content-Disposition Header Field in the 9 Hypertext Transfer Protocol (HTTP) 10 draft-reschke-rfc2183-in-http-03 12 Abstract 14 HTTP/1.1 defines the Content-Disposition response header field, but 15 points out that it is not part of the HTTP/1.1 Standard. This 16 specification takes over the definition and registration of Content- 17 Disposition, as used in HTTP, and clarifies internationalization 18 aspects. 20 Editorial Note (To be removed by RFC Editor before publication) 22 This specification is expected to replace the definition of Content- 23 Disposition in the HTTP/1.1 specification, as currently revised by 24 the IETF HTTPbis working group. See also 25 . 27 Distribution of this document is unlimited. Although this is not a 28 work item of the HTTPbis Working Group, comments should be sent to 29 the Hypertext Transfer Protocol (HTTP) mailing list at 30 ietf-http-wg@w3.org [1], which may be joined by sending a message 31 with subject "subscribe" to ietf-http-wg-request@w3.org [2]. 33 Discussions of the HTTPbis Working Group are archived at 34 . 36 XML versions, latest edits and the issues list for this document are 37 available from 38 . A 39 collection of test cases is available at 40 . 42 Status of This Memo 44 This Internet-Draft is submitted in full conformance with the 45 provisions of BCP 78 and BCP 79. 47 Internet-Drafts are working documents of the Internet Engineering 48 Task Force (IETF). Note that other groups may also distribute 49 working documents as Internet-Drafts. The list of current Internet- 50 Drafts is at http://datatracker.ietf.org/drafts/current/. 52 Internet-Drafts are draft documents valid for a maximum of six months 53 and may be updated, replaced, or obsoleted by other documents at any 54 time. It is inappropriate to use Internet-Drafts as reference 55 material or to cite them other than as "work in progress." 57 This Internet-Draft will expire on March 3, 2011. 59 Copyright Notice 61 Copyright (c) 2010 IETF Trust and the persons identified as the 62 document authors. All rights reserved. 64 This document is subject to BCP 78 and the IETF Trust's Legal 65 Provisions Relating to IETF Documents 66 (http://trustee.ietf.org/license-info) in effect on the date of 67 publication of this document. Please review these documents 68 carefully, as they describe your rights and restrictions with respect 69 to this document. Code Components extracted from this document must 70 include Simplified BSD License text as described in Section 4.e of 71 the Trust Legal Provisions and are provided without warranty as 72 described in the Simplified BSD License. 74 Table of Contents 76 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 77 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4 78 3. Header Field Definition . . . . . . . . . . . . . . . . . . . 4 79 3.1. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 5 80 3.2. Disposition Type . . . . . . . . . . . . . . . . . . . . . 5 81 3.3. Disposition Parameter: 'Filename' . . . . . . . . . . . . 5 82 3.4. Disposition Parameter: Extensions . . . . . . . . . . . . 6 83 3.5. Extensibility . . . . . . . . . . . . . . . . . . . . . . 6 84 4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 85 5. Internationalization Considerations . . . . . . . . . . . . . 7 86 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 87 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 88 7.1. Registry for Disposition Values and Parameter . . . . . . 8 89 7.2. Header Field Registration . . . . . . . . . . . . . . . . 8 90 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 91 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 92 9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 93 9.2. Informative References . . . . . . . . . . . . . . . . . . 9 94 Appendix A. Changes from the RFC 2616 Definition . . . . . . . . 10 95 Appendix B. Differences compared to RFC 2183 . . . . . . . . . . 10 96 Appendix C. Alternative Approaches to Internationalization . . . 10 97 C.1. RFC 2047 Encoding . . . . . . . . . . . . . . . . . . . . 11 98 C.2. Percent Encoding . . . . . . . . . . . . . . . . . . . . . 11 99 C.3. Encoding Sniffing . . . . . . . . . . . . . . . . . . . . 11 100 C.4. Implementations . . . . . . . . . . . . . . . . . . . . . 11 101 Appendix D. Change Log (to be removed by RFC Editor before 102 publication) . . . . . . . . . . . . . . . . . . . . 12 103 D.1. Since draft-reschke-rfc2183-in-http-00 . . . . . . . . . . 12 104 D.2. Since draft-reschke-rfc2183-in-http-01 . . . . . . . . . . 12 105 D.3. Since draft-reschke-rfc2183-in-http-02 . . . . . . . . . . 12 106 Appendix E. Resolved issues (to be removed by RFC Editor 107 before publication) . . . . . . . . . . . . . . . . . 12 108 E.1. quoted . . . . . . . . . . . . . . . . . . . . . . . . . . 13 109 E.2. asciivsiso . . . . . . . . . . . . . . . . . . . . . . . . 13 110 E.3. deplboth . . . . . . . . . . . . . . . . . . . . . . . . . 13 111 E.4. registry . . . . . . . . . . . . . . . . . . . . . . . . . 13 112 E.5. docfallback . . . . . . . . . . . . . . . . . . . . . . . 14 113 Appendix F. Open issues (to be removed by RFC Editor prior to 114 publication) . . . . . . . . . . . . . . . . . . . . 14 115 F.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 116 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 118 1. Introduction 120 HTTP/1.1 defines the Content-Disposition response header field in 121 Section 19.5.1 of [RFC2616], but points out that it is not part of 122 the HTTP/1.1 Standard (Section 15.5): 124 Content-Disposition is not part of the HTTP standard, but since it 125 is widely implemented, we are documenting its use and risks for 126 implementors. 128 This specification takes over the definition and registration of 129 Content-Disposition, as used in HTTP. Based on interoperability 130 testing with existing User Agents, it fully defines a profile of the 131 features defined in the Multipurpose Internet Mail Extensions (MIME) 132 variant ([RFC2183]) of the header field, and also clarifies 133 internationalization aspects. 135 2. Notational Conventions 137 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 138 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 139 document are to be interpreted as described in [RFC2119]. 141 This specification uses the augmented BNF notation defined in Section 142 2.1 of [RFC2616], including its rules for linear whitespace (LWS). 144 3. Header Field Definition 146 The Content-Disposition response header field is used to convey 147 additional information about how to process the response payload, and 148 also can be used to attach additional metadata, such as the filename. 150 3.1. Grammar 152 content-disposition = "Content-Disposition" ":" 153 disposition-type *( ";" disposition-parm ) 155 disposition-type = "inline" | "attachment" | disp-ext-type 156 ; case-insensitive 157 disp-ext-type = token 159 disposition-parm = filename-parm | disp-ext-parm 161 filename-parm = "filename" "=" value 162 | "filename*" "=" ext-value 164 disp-ext-parm = token "=" value 165 | ext-token "=" ext-value 166 ext-token = 168 Defined in [RFC2616]: 170 token = 171 value = 173 Defined in [RFC5987]: 175 ext-value = 177 3.2. Disposition Type 179 If the disposition type matches "attachment" (case-insensitively), 180 this indicates that the user agent should not display the response, 181 but directly enter a "save as..." dialog. 183 On the other hand, if it matches "inline" (case-insensitively), this 184 implies default processing. 186 Other disposition types SHOULD be handled the same way as 187 "attachment" (see also [RFC2183], Section 2.8). 189 3.3. Disposition Parameter: 'Filename' 191 The parameters "filename" and "filename*", to be matched case- 192 insensitively, provide information on how to construct a filename for 193 storing the message payload. 195 Depending on the disposition type, this information might be used 196 right away (in the "save as..." interaction caused for the 197 "attachment" disposition type), or later on (for instance, when the 198 user decides to save the contents of the current page being 199 displayed). 201 "filename" and "filename*" behave the same, except that "filename*" 202 uses the encoding defined in [RFC5987], allowing the use of 203 characters not present in the ISO-8859-1 character set 204 ([ISO-8859-1]). When both "filename" and "filename*" are present, a 205 recipient SHOULD pick "filename*" and ignore "filename" - this will 206 make it possible to send the same header value to clients that do not 207 support "filename*". 209 It is essential that user agents treat the specified filename as 210 advisory only, thus be very careful in extracting the desired 211 information. In particular: 213 o When the value contains path separator characters, all but the 214 last segment SHOULD be ignored. This prevents unintentional 215 overwriting of well-known file system location (such as "/etc/ 216 passwd"). 218 o Many platforms do not use Internet Media Types ([RFC2046]) to hold 219 type information in the file system, but rely on filename 220 extensions instead. Trusting the server-provided file extension 221 could introduce a privilege escalation when later on the file is 222 opened locally (consider ".exe"). Thus, recipients need to ensure 223 that a file extension is used that is safe, optimally matching the 224 media type of the received payload. 226 o Other aspects recipients need to be aware of are names that have a 227 special meaning in the filesystem or in shell commands, such as 228 "." and "..", "~", "|", and also device names. 230 3.4. Disposition Parameter: Extensions 232 To enable future extensions, unknown parameters SHOULD be ignored 233 (see also [RFC2183], Section 2.8). 235 3.5. Extensibility 237 Note that Section 9 of [RFC2183] defines IANA registries both for 238 disposition types and disposition parameters. This registry is 239 shared by different protocols using Content-Disposition, such as MIME 240 and HTTP. Therefore, not all registered values may make sense in the 241 context of HTTP. 243 4. Examples 245 Direct UA to show "save as" dialog, with a filename of "foo.html": 247 Content-Disposition: Attachment; filename=foo.html 249 Direct UA to behave as if the Content-Disposition header field wasn't 250 present, but to remember the filename "foo.html" for a subsequent 251 save operation: 253 Content-Disposition: INLINE; FILENAME= "foo.html" 255 Direct UA to show "save as" dialog, with a filename of "an example": 257 Content-Disposition: Attachment; Filename*=UTF-8'en'an%20example 259 Note that this example uses the extended encoding defined in 260 [RFC5987] to specify that the natural language of the filename is 261 English, and also to encode the space character which is not allowed 262 in the token production. 264 Direct UA to show "save as" dialog, with a filename containing the 265 Unicode character U+20AC (EURO SIGN): 267 Content-Disposition: attachment; filename*= UTF-8''%e2%82%ac%20rates 269 Here, the encoding defined in [RFC5987] is also used to encode the 270 non-ISO-8859-1 character. 272 Same as above, but adding the "filename" parameter for compatibility 273 with user agents not implementing RFC 5987: 275 Content-Disposition: attachment; filename="EURO rates"; 276 filename*=utf-8''%e2%82%ac%20rates 278 Note: as of August 2010, many user agents unfortunately did not 279 properly handle unexpected parameters, and some that implement RFC 280 5987 did not pick the extended parameter when both were present. 282 5. Internationalization Considerations 284 The "filename*" parameter (Section 3.3), using the encoding defined 285 in [RFC5987], allows the server to transmit characters outside the 286 ISO-8859-1 character set, and also to optionally specify the language 287 in use. 289 Future parameters might also require internationalization, in which 290 case the same encoding can be used. 292 6. Security Considerations 294 Using server-supplied information for constructing local filenames 295 introduces many risks. These are summarized in Section 3.3. 297 Furthermore, implementers also ought to be aware of the Security 298 Considerations applying to HTTP (see Section 15 of [RFC2616]), and 299 also the parameter encoding defined in [RFC5987] (see Section 5). 301 7. IANA Considerations 303 7.1. Registry for Disposition Values and Parameter 305 This specification does not introduce any changes to the registration 306 procedures for disposition values and parameters that are defined in 307 Section 9 of [RFC2183]. 309 7.2. Header Field Registration 311 This document updates the definition of the Content-Disposition HTTP 312 header field in the permanent HTTP header field registry (see 313 [RFC3864]). 315 Header field name: Content-Disposition 317 Applicable protocol: http 319 Status: standard 321 Author/Change controller: IETF 323 Specification document: this specification (Section 3) 325 8. Acknowledgements 327 Thanks to Rolf Eike Beer, Alfred Hoenes, and Roar Lauritzsen for 328 their valuable feedback. 330 9. References 332 9.1. Normative References 334 [ISO-8859-1] International Organization for Standardization, 335 "Information technology -- 8-bit single-byte coded 336 graphic character sets -- Part 1: Latin alphabet No. 337 1", ISO/IEC 8859-1:1998, 1998. 339 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 340 Requirement Levels", BCP 14, RFC 2119, March 1997. 342 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 343 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 344 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 346 [RFC5987] Reschke, J., "Applicability of RFC 2231 Encoding to 347 Hypertext Transfer Protocol (HTTP) Headers", RFC 5987, 348 August 2010. 350 9.2. Informative References 352 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet 353 Mail Extensions (MIME) Part Two: Media Types", 354 RFC 2046, November 1996. 356 [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail 357 Extensions) Part Three: Message Header Extensions for 358 Non-ASCII Text", RFC 2047, November 1996. 360 [RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating 361 Presentation Information in Internet Messages: The 362 Content-Disposition Header Field", RFC 2183, 363 August 1997. 365 [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and 366 Encoded Word Extensions: Character Sets, Languages, and 367 Continuations", RFC 2231, November 1997. 369 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 370 10646", RFC 3629, STD 63, November 2003. 372 [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration 373 Procedures for Message Header Fields", BCP 90, 374 RFC 3864, September 2004. 376 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, 377 "Uniform Resource Identifier (URI): Generic Syntax", 378 RFC 3986, STD 66, January 2005. 380 URIs 382 [1] 384 [2] 386 Appendix A. Changes from the RFC 2616 Definition 388 Compared to Section 19.5.1 of [RFC2616], the following normative 389 changes reflecting actual implementations have been made: 391 o According to RFC 2616, the disposition type "attachment" only 392 applies to content of type "application/octet-stream". This 393 restriction has been removed, because user agents in practice do 394 not check the content type, and it also discourages properly 395 declaring the media type. 397 o RFC 2616 only allows "quoted-string" for the filename parameter. 398 This would be an exceptional parameter syntax, and also doesn't 399 reflect actual use. 401 o The definition for the disposition type "inline" ([RFC2183], 402 Section 2.1) has been re-added with a suggestion for its 403 processing. 405 o This specification requires support for the extended parameter 406 encoding defined in [RFC5987]. 408 Appendix B. Differences compared to RFC 2183 410 Section 2 of [RFC2183] defines several additional disposition 411 parameters: "creation-date", "modification-date", "quoted-date-time", 412 and "size". These do not appear to be implemented by any user agent, 413 thus have been omitted from this specification. 415 Appendix C. Alternative Approaches to Internationalization 417 By default, HTTP header field parameters cannot carry characters 418 outside the ISO-8859-1 ([ISO-8859-1]) character encoding (see 419 [RFC2616], Section 2.2). For the "filename" parameter, this of 420 course is an unacceptable restriction. 422 Unfortunately, user agent implementers have not managed to come up 423 with an interoperable approach, although the IETF Standards Track 424 specifies exactly one solution ([RFC2231], clarified and profiled for 425 HTTP in [RFC5987]). 427 For completeness, the sections below describe the various approaches 428 that have been tried, and explains how they are inferior to the RFC 429 5987 encoding used in this specification. 431 C.1. RFC 2047 Encoding 433 RFC 2047 defines an encoding mechanism for header fields, but this 434 encoding is not supposed to be used for header field parameters - see 435 Section 5 of [RFC2047]: 437 An 'encoded-word' MUST NOT appear within a 'quoted-string'. 439 ... 441 An 'encoded-word' MUST NOT be used in parameter of a MIME Content- 442 Type or Content-Disposition field, or in any structured field body 443 except within a 'comment' or 'phrase'. 445 In practice, some user agents implement the encoding, some do not 446 (exposing the encoded string to the user), and some get confused by 447 it. 449 C.2. Percent Encoding 451 Some user agents accept percent encoded ([RFC3986], Section 2.1) 452 sequences of characters encoded using the UTF-8 ([RFC3629]) character 453 encoding. 455 In practice, this is hard to use because those user agents that do 456 not support it will display the escaped character sequence to the 457 user. 459 Furthermore, the first user agent to implement this did choose the 460 encoding based on local settings; thus making it very hard to use in 461 multi-lingual environments. 463 C.3. Encoding Sniffing 465 Some user agents inspect the value (which defaults to ISO-8859-1) and 466 switch to UTF-8 when it seems to be more likely to be the correct 467 interpretation. 469 As with the approaches above, this is not interoperable and 470 furthermore risks misinterpreting the actual value. 472 C.4. Implementations 474 Unfortunately, as of August 2010, neither the encoding defined in 475 RFCs 2231 and 5789, nor any of the alternate approaches discussed 476 above was implemented interoperably. Thus, this specification 477 recommends the approach defined in RFC 5987, which at least has the 478 advantage of actually being specified properly. 480 The table below shows the implementation support for the various 481 approaches: [[impls: Discuss: should we mention the implementation 482 status of actual UAs in a RFC? Up to the IESG to decide...]] 484 +---------------+------------+--------+--------------+--------------+ 485 | User Agent | RFC | RFC | Percent | Encoding | 486 | | 2231/5987 | 2047 | Encoding | Sniffing | 487 +---------------+------------+--------+--------------+--------------+ 488 | Chrome | no | yes | yes | yes | 489 | Firefox | yes (*) | yes | no | yes | 490 | Internet | no | no | yes | no | 491 | Explorer | | | | | 492 | Konqueror | yes | no | no | no | 493 | Opera | yes (*) | no | no | no | 494 | Safari | no | no | no | yes | 495 +---------------+------------+--------+--------------+--------------+ 497 (*) Does not implement the fallback behavior to "filename" described 498 in Section 3.3. 500 Appendix D. Change Log (to be removed by RFC Editor before publication) 502 D.1. Since draft-reschke-rfc2183-in-http-00 504 Adjust terminology ("header" -> "header field"). Update rfc2231-in- 505 http reference. 507 D.2. Since draft-reschke-rfc2183-in-http-01 509 Update rfc2231-in-http reference. Actually define the "filename" 510 parameter. Add internationalization considerations. Add examples 511 using the RFC 5987 encoding. Add overview over other approaches, 512 plus a table reporting implementation status. Add and resolve issue 513 "nodep2183". Add issues "asciivsiso", "deplboth", "quoted", and 514 "registry". 516 D.3. Since draft-reschke-rfc2183-in-http-02 518 Add and close issue "docfallback". Close issues "asciivsiso", 519 "deplboth", "quoted", and "registry". 521 Appendix E. Resolved issues (to be removed by RFC Editor before 522 publication) 524 Issues that were either rejected or resolved in this version of this 525 document. 527 E.1. quoted 529 In Section 3.1: 531 Type: change 533 julian.reschke@greenbytes.de (2010-08-23): Can value be quoted-pair 534 as well? It is "value" only in RFC 2183, but "quoted-string" only in 535 2616. UAs seem to handle quoted-strings, although some have trouble 536 unescaping backslashes. 538 julian.reschke@greenbytes.de (2010-08-24): Actually, "value" is 539 "token" or "quoted-string", both in RFC 2616 and RFC 2183 (by 540 reference to RFC 2045). The only problem is that RFC 2616 uses 541 quoted-string instead of value in the definition for the filename 542 parameter. This is a bug in 2616. 544 Resolution (2010-08-24): Note the change in "Changes from the RFC 545 2616 Definition". 547 E.2. asciivsiso 549 In Section 3.3: 551 Type: change 553 julian.reschke@greenbytes.de (2010-08-24): We should be consistent 554 about what RFC 2616 defaults to (ASCII vs ISO-8859-1). 556 Resolution (2010-08-30): Say "ISO-8859-1", and also make the ISO- 557 8859-1 ref normative. 559 E.3. deplboth 561 In Section 4: 563 Type: change 565 julian.reschke@greenbytes.de (2010-08-24): Add an example that uses 566 both "filename" and "filename*" and mention current UA behavior. 568 Resolution (2010-08-27): Add the example, and mention the issues with 569 it. 571 E.4. registry 573 In Section 7.1: 575 Type: change 577 julian.reschke@greenbytes.de (2010-08-23): The registry technically 578 is for the MIME header, but has been used for C-D in other protocols 579 already. What's missing are instructions that new registrations 580 should state which protocol they're for. Do we want to attempt to 581 modify the registry? 583 Resolution (2010-08-30): Add a section about extensibility explaining 584 the existing registries. 586 E.5. docfallback 588 In Section C.4: 590 Type: edit 592 julian.reschke@greenbytes.de (2010-08-30): Describe the 593 implementation quality of the fallback behavior. 595 Resolution (2010-08-30): Done. 597 Appendix F. Open issues (to be removed by RFC Editor prior to 598 publication) 600 F.1. edit 602 Type: edit 604 julian.reschke@greenbytes.de (2009-10-16): Umbrella issue for 605 editorial fixes/enhancements. 607 Index 609 C 610 Content-Disposition header 4 612 H 613 Headers 614 Content-Disposition 4 616 Author's Address 618 Julian F. Reschke 619 greenbytes GmbH 620 Hafenweg 16 621 Muenster, NW 48155 622 Germany 624 EMail: julian.reschke@greenbytes.de 625 URI: http://greenbytes.de/tech/webdav/