source: draft-ietf-httpbis-content-disp/latest/draft-ietf-httpbis-content-disp.xml @ 1020

Last change on this file since 1020 was 1020, checked in by julian.reschke@…, 9 years ago

fix subsection title

  • Property svn:executable set to *
File size: 30.8 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../../draft-ietf-httpbis/myxml2rfc.xslt' ?>
3<?rfc toc="yes"?>
4<?rfc symrefs="yes"?>
5<?rfc sortrefs="yes"?>
6<?rfc compact="yes"?>
7<?rfc comments="yes"?>
8<?rfc inline="yes"?>
9<?rfc subcompact="no"?>
10<?rfc rfcedstyle="yes"?>
11<?rfc-ext allow-markup-in-artwork="yes" ?>
12<?rfc-ext include-references-in-index="yes" ?>
13
14<!DOCTYPE rfc [
15  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
16  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
17  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
18  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
19  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
20  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
21  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
22  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
23  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
24  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
25]>
26
27<rfc xmlns:x="http://purl.org/net/xml2rfc/ext" xmlns:ed="http://greenbytes.de/2002/rfcedit" ipr="trust200902" docName="draft-ietf-httpbis-content-disp-latest" category="std" x:maturity-level="proposed" xml:lang="en" updates="2616">
28        <front>
29  <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition&#160;Header&#160;Field
30  in the Hypertext&#160;Transfer&#160;Protocol&#160;(HTTP)</title>
31  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
32    <organization abbrev="greenbytes">greenbytes GmbH</organization>
33    <address>
34      <postal>
35        <street>Hafenweg 16</street>
36        <city>Muenster</city><region>NW</region><code>48155</code>
37        <country>Germany</country>
38      </postal>
39      <email>julian.reschke@greenbytes.de</email>       
40      <uri>http://greenbytes.de/tech/webdav/</uri>     
41    </address>
42  </author>
43
44  <date month="October" year="2010"/>
45  <workgroup>HTTPbis Working Group</workgroup>
46 
47  <abstract>
48    <t>
49      HTTP/1.1 defines the Content-Disposition response header field,
50      but points out that it is not part of the HTTP/1.1 Standard.
51      This specification takes over the definition and registration of
52      Content-Disposition, as used in HTTP, and clarifies internationalization
53      aspects.
54    </t>
55  </abstract>
56 
57  <note title="Editorial Note (To be removed by RFC Editor before publication)">
58    <t>
59      This specification is expected to replace the definition of Content-Disposition
60      in the HTTP/1.1 specification, as currently revised by the IETF HTTPbis
61      working group. See also <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/123"/>.
62    </t>
63    <t>
64      Discussion of this draft should take place on the HTTPBIS working group
65      mailing list (ietf-http-wg@w3.org). The current issues list is
66      at <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/query?component=content-disp"/>
67      and related documents (including fancy diffs) can be found at
68      <eref target="http://tools.ietf.org/wg/httpbis/"/>.
69    </t>
70    <t>
71      The changes in this draft are summarized in <xref target="changes.since.02"/>.
72    </t>
73  </note>
74  </front>
75
76  <middle>
77
78<section title="Introduction" anchor="introduction">
79<t>
80  HTTP/1.1 defines the Content-Disposition response header field in <xref target="RFC2616" x:fmt="of" x:sec="19.5.1"/>,
81  but points out that it is not part of the HTTP/1.1 Standard (<xref target="RFC2616" x:fmt="sec" x:sec="15.5"/>):
82</t>
83<x:blockquote cite="http://tools.ietf.org/html/rfc2616#section-15.5">
84  <t>
85    Content-Disposition is not part of the HTTP standard, but since it is
86    widely implemented, we are documenting its use and risks for implementers.
87  </t>
88</x:blockquote>
89<t>
90  This specification takes over the definition and registration of
91  Content-Disposition, as used in HTTP.
92  Based on interoperability testing with existing User Agents,
93  it fully defines a profile of the
94  features defined in the Multipurpose Internet Mail Extensions (MIME) variant (<xref target="RFC2183"/>) of the
95  header field, and also clarifies internationalization
96  aspects.
97</t>
98</section> 
99
100<section title="Notational Conventions">
101<t>
102  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
103  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
104  are to be interpreted as described in <xref target="RFC2119"/>.
105</t>
106<t>
107  This specification uses the augmented BNF notation defined in
108  <xref target="RFC2616" x:fmt="of" x:sec="2.1"/>, including its rules for
109  linear whitespace (LWS).
110</t>
111</section> 
112
113<section title="Header Field Definition" anchor="header.field.definition">
114  <iref item="Headers" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
115  <iref item="Content-Disposition header" primary="true" x:for-anchor=""/>
116<t>
117  The Content-Disposition response header field is used to convey additional
118  information about how to process the response payload, and also can be used
119  to attach additional metadata, such as the filename to use when saving the
120  response payload locally.
121</t>
122
123<section title="Grammar">
124<figure><artwork type="abnf2616">
125  content-disposition = "Content-Disposition" ":"
126                         disposition-type *( ";" disposition-parm )
127
128  disposition-type    = "inline" | "attachment" | disp-ext-type
129                      ; case-insensitive
130  disp-ext-type       = token
131
132  disposition-parm    = filename-parm | disp-ext-parm
133
134  filename-parm       = "filename" "=" value
135                      | "filename*" "=" ext-value
136 
137  disp-ext-parm       = token "=" value
138                      | ext-token "=" ext-value
139  ext-token           = &lt;the characters in token, followed by "*"&gt;
140</artwork></figure>
141
142<figure>
143<preamble>Defined in <xref target="RFC2616"/>:</preamble>
144<artwork type="abnf2616">
145  token       = &lt;token, defined in <xref target="RFC2616" x:fmt="," x:sec="2.2"/>&gt;
146  value       = &lt;value, defined in <xref target="RFC2616" x:fmt="," x:sec="3.6"/>&gt;
147</artwork></figure>
148<figure>
149<preamble>Defined in <xref target="RFC5987"/>:</preamble>
150<artwork type="abnf2616">
151  ext-value   = &lt;ext-value, defined in <xref target="RFC5987" x:sec="3.2"/>&gt;
152</artwork></figure>
153</section>
154
155<section title="Disposition Type" anchor="disposition.type">
156<t>
157  If the disposition type matches "attachment" (case-insensitively), this
158  indicates that the user agent should prompt the user to save the response
159  locally, rather than process it normally (as per its media type).
160</t>
161<t>
162  On the other hand, if it matches "inline" (case-insensitively), this implies
163  default processing.
164</t>
165<t>
166  Unknown or unhandled disposition types &SHOULD; be handled the same way as
167  "attachment" (see also <xref target="RFC2183" x:fmt="," x:sec="2.8"/>).
168</t>
169</section>
170
171<section title="Disposition Parameter: 'Filename'" anchor="disposition.parameter.filename">
172<t>
173  The parameters "filename" and "filename*", to be matched case-insensitively,
174  provide information on how to construct a filename for storing the message
175  payload.
176</t>
177<t>
178  Depending on the disposition type, this information might be used right away
179  (in the "save as..." interaction caused for the "attachment" disposition type),
180  or later on (for instance, when the user decides to save the contents of the
181  current page being displayed).
182</t>
183<t>
184  The parameters "filename" and "filename*" differ only in that "filename*" uses
185  the encoding defined in <xref target="RFC5987"/>, allowing the use
186  of characters not present in the ISO-8859-1 character set (<xref target="ISO-8859-1"/>).
187</t>
188<t>
189  Many user agent implementations predating this specification
190  do not understand the "filename*" parameter. Therefore, when both "filename"
191  and "filename*" are present in a single header field value, recipients
192  &SHOULD; pick "filename*" and ignore "filename". This way, senders
193  can avoid special-casing specific user agents by sending both the
194  more expressive "filename*" parameter, and the "filename" parameter
195  as fallback for legacy recipients (see <xref target="examples"/> for
196  an example).
197</t>
198<t>
199  It is essential that user agents treat the specified filename as advisory
200  only, thus be very careful in extracting the desired information.
201  In particular:
202  <list style="symbols">
203    <x:lt><t>
204      When the value contains path separator characters, all but the last
205      segment &SHOULD; be ignored. This prevents unintentional overwriting
206      of well-known file system location (such as "/etc/passwd").
207    </t></x:lt>
208    <x:lt><t>
209      Many platforms do not use Internet Media Types (<xref target="RFC2046"/>)
210      to hold type information in the file system, but rely on filename
211      extensions instead. Trusting the server-provided file extension could
212      introduce a privilege escalation when the saved file is later opened
213      (consider ".exe"). Thus, recipients need to ensure that a file extension
214      is used that is safe, optimally matching the media type of the received
215      payload.
216    </t></x:lt>
217    <x:lt><t>
218      Other aspects recipients need to be aware of are names that have a
219      special meaning in the file system or in shell commands, such as "." and "..",
220      "~", "|", and also device names.
221    </t></x:lt>
222  </list>
223</t>
224</section>
225
226<section title="Disposition Parameter: Extensions" anchor="disposition.parameter.extensions">
227<t>
228  To enable future extensions, unknown parameters &SHOULD; be ignored (see also <xref target="RFC2183" x:fmt="," x:sec="2.8"/>).
229</t>
230</section>
231
232<section title="Extensibility" anchor="extensibility">
233<t>
234  Note that <xref target="RFC2183" x:fmt="of" x:sec="9"/> defines IANA registries both
235  for disposition types and disposition parameters. This registry is
236  shared by different protocols using Content-Disposition, such as MIME and HTTP.
237  Therefore, not all registered values may make sense in the context of HTTP.
238</t>
239</section>
240
241</section> 
242
243<section title="Examples" anchor="examples">
244
245<figure>
246<preamble>
247Direct UA to show "save as" dialog, with a filename of "example.html": 
248</preamble>
249<artwork type="example">
250Content-Disposition: Attachment; filename=example.html
251</artwork></figure>
252<figure>
253<preamble>
254Direct UA to behave as if the Content-Disposition header field wasn't present,
255but to remember the filename "example.html" for a subsequent save operation:
256</preamble>
257<artwork type="example" x:indent-with="  ">
258Content-Disposition: INLINE; FILENAME= "example.html"
259</artwork></figure>
260<figure>
261<preamble>
262Direct UA to show "save as" dialog, with a filename of "an example":
263</preamble>
264<artwork type="example">
265Content-Disposition: Attachment; Filename*=UTF-8'<x:highlight>en</x:highlight>'an<x:highlight>%20</x:highlight>example
266</artwork>
267<postamble>Note that this example uses the extended encoding defined in
268<xref target="RFC5987"/> to specify that the natural language of the filename
269is English, and also to encode the space character which is not allowed in the
270token production.
271</postamble>
272</figure>
273<figure>
274<preamble>
275Direct UA to show "save as" dialog, with a filename containing the Unicode character  U+20AC (EURO SIGN):
276</preamble>
277<artwork type="example" x:indent-with="  ">
278Content-Disposition: attachment;
279                     filename*= UTF-8''<x:highlight>%e2%82%ac</x:highlight>%20rates
280</artwork>
281<postamble>
282  Here, the encoding defined in <xref target="RFC5987"/> is also used to encode the
283  non-ISO-8859-1 character.
284</postamble>
285</figure>
286<figure>
287<preamble>
288Same as above, but adding the "filename" parameter for compatibility with
289user agents not implementing RFC 5987:
290</preamble>
291<artwork type="example" x:indent-with="  ">
292Content-Disposition: attachment;
293                     filename="EURO rates";
294                     filename*=utf-8''<x:highlight>%e2%82%ac</x:highlight>%20rates
295</artwork>
296<postamble>
297  Note: as of September 2010, those user agents that do not support the RFC 5987
298  encoding ignore "filename*" when it occurs after "filename". Unfortunately,
299  some user agents that do support RFC 5987 do pick the "filename" rather
300  than the "filename*" parameter when it occurs first; it is expected that
301  this situation is going to improve soon.
302</postamble>
303</figure>
304
305</section>
306
307<section title="Internationalization Considerations" anchor="i18n">
308<t>
309  The "filename*" parameter (<xref target="disposition.parameter.filename"/>),
310  using the encoding defined in <xref target="RFC5987"/>, allows the
311  server to transmit characters outside the ISO-8859-1 character set,
312  and also to optionally specify the language in use.
313</t>
314<t>
315  Future parameters might also require internationalization, in which case
316  the same encoding can be used.
317</t>
318</section>
319
320<section title="Security Considerations" anchor="security.considerations">
321<t>
322  Using server-supplied information for constructing local filenames introduces
323  many risks. These are summarized in <xref target="disposition.parameter.filename"/>.
324</t>
325<t>
326  Furthermore, implementers also ought to be aware of the Security
327  Considerations applying to HTTP (see <xref target="RFC2616" x:fmt="of" x:sec="15"/>), and also the parameter encoding defined in <xref target="RFC5987"/>
328  (see <xref target="RFC5987" x:fmt="sec" x:sec="5"/>).
329</t>
330</section> 
331
332<section title="IANA Considerations" anchor="iana.considerations">
333
334<section title="Registry for Disposition Values and Parameter" anchor="registry">
335<t>
336  This specification does not introduce any changes to the registration
337  procedures for disposition values and parameters that are defined in
338  <xref target="RFC2183" x:fmt="of" x:sec="9"/>.
339</t>
340</section>
341
342<section title="Header Field Registration" anchor="header.field.registration"> 
343<t>
344  This document updates the definition of the Content-Disposition HTTP header field
345  in the permanent HTTP header field registry (see <xref target="RFC3864"/>).
346</t>
347<t>
348<list style="hanging">
349  <t hangText="Header field name:">Content-Disposition</t>
350  <t hangText="Applicable protocol:">http</t>
351  <t hangText="Status:">standard</t>
352  <t hangText="Author/Change controller:">IETF</t>
353  <t hangText="Specification document:">this specification (<xref target="header.field.definition"/>)</t>
354</list>
355</t>
356</section>
357
358</section> 
359
360<section title="Acknowledgements">
361<t>
362  Thanks to Rolf Eike Beer, Bjoern Hoehrmann, Alfred Hoenes, Roar Lauritzsen,
363  Henrik Nordstrom, and Mark Nottingham for their valuable feedback.
364</t>
365</section> 
366
367  </middle>
368  <back>
369 
370<references title="Normative References">
371 
372  <reference anchor="RFC2119">
373    <front>
374      <title abbrev="RFC Key Words">Key words for use in RFCs to Indicate Requirement Levels</title>
375      <author initials="S." surname="Bradner" fullname="Scott Bradner">
376        <organization>Harvard University</organization>
377        <address><email>sob@harvard.edu</email></address>
378      </author>
379      <date month="March" year="1997"/>
380      <area>General</area>
381      <keyword>keyword</keyword>
382    </front>
383    <seriesInfo name="BCP" value="14"/>
384    <seriesInfo name="RFC" value="2119"/>
385  </reference>
386
387  <reference anchor="RFC2616">
388    <front>
389      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
390      <author initials="R." surname="Fielding" fullname="R. Fielding">
391        <organization>University of California, Irvine</organization>
392        <address><email>fielding@ics.uci.edu</email></address>
393      </author>
394      <author initials="J." surname="Gettys" fullname="J. Gettys">
395        <organization>W3C</organization>
396        <address><email>jg@w3.org</email></address>
397      </author>
398      <author initials="J." surname="Mogul" fullname="J. Mogul">
399        <organization>Compaq Computer Corporation</organization>
400        <address><email>mogul@wrl.dec.com</email></address>
401      </author>
402      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
403        <organization>MIT Laboratory for Computer Science</organization>
404        <address><email>frystyk@w3.org</email></address>
405      </author>
406      <author initials="L." surname="Masinter" fullname="L. Masinter">
407        <organization>Xerox Corporation</organization>
408        <address><email>masinter@parc.xerox.com</email></address>
409      </author>
410      <author initials="P." surname="Leach" fullname="P. Leach">
411        <organization>Microsoft Corporation</organization>
412        <address><email>paulle@microsoft.com</email></address>
413      </author>
414      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
415        <organization>W3C</organization>
416        <address><email>timbl@w3.org</email></address>
417      </author>
418      <date month="June" year="1999"/>
419    </front>
420    <seriesInfo name="RFC" value="2616"/>
421  </reference>
422
423  <reference anchor="RFC5987">
424        <front>
425      <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
426      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
427        <organization abbrev="greenbytes">greenbytes GmbH</organization>
428        <address>
429          <postal>
430            <street>Hafenweg 16</street>
431            <city>Muenster</city><region>NW</region><code>48155</code>
432            <country>Germany</country>
433          </postal>
434          <email>julian.reschke@greenbytes.de</email>   
435          <uri>http://greenbytes.de/tech/webdav/</uri> 
436        </address>
437      </author>
438      <date month="August" year="2010"/>
439    </front>
440    <seriesInfo name="RFC" value="5987"/>
441  </reference>
442
443  <reference anchor="ISO-8859-1">
444    <front>
445      <title>Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1</title>
446      <author>
447        <organization>International Organization for Standardization</organization>
448      </author>
449      <date year="1998"/>
450    </front>
451    <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
452  </reference>
453
454</references>
455 
456<references title="Informative References">
457
458  <reference anchor="RFC2046">
459    <front>
460      <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
461      <author initials="N." surname="Freed" fullname="Ned Freed">
462        <organization>Innosoft International, Inc.</organization>
463        <address><email>ned@innosoft.com</email></address>
464      </author>
465      <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
466        <organization>First Virtual Holdings</organization>
467        <address><email>nsb@nsb.fv.com</email></address>
468      </author>
469      <date month="November" year="1996"/>
470    </front>
471    <seriesInfo name="RFC" value="2046"/>
472  </reference>
473
474  <reference anchor="RFC2047">
475    <front>
476      <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
477      <author initials="K." surname="Moore" fullname="Keith Moore">
478        <organization>University of Tennessee</organization>
479        <address><email>moore@cs.utk.edu</email></address>
480      </author>
481      <date month="November" year="1996"/>
482    </front>
483    <seriesInfo name="RFC" value="2047"/>
484  </reference>
485
486  <reference anchor="RFC2183">
487    <front>
488      <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
489      <author initials="R." surname="Troost" fullname="Rens Troost">
490        <organization>New Century Systems</organization>
491        <address><email>rens@century.com</email></address>
492      </author>
493      <author initials="S." surname="Dorner" fullname="Steve Dorner">
494        <organization>QUALCOMM Incorporated</organization>
495        <address><email>sdorner@qualcomm.com</email></address>
496      </author>
497      <author initials="K." surname="Moore" fullname="Keith Moore">
498        <organization>Department of Computer Science</organization>
499        <address><email>moore@cs.utk.edu</email></address>
500      </author>
501      <date year="1997" month="August"/>
502    </front>
503    <seriesInfo name="RFC" value="2183"/>
504  </reference>
505
506  <reference anchor="RFC2231">
507    <front>
508      <title abbrev="MIME Value and Encoded Word Extensions">MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations</title>
509      <author initials="N." surname="Freed" fullname="Ned Freed">
510        <organization abbrev="Innosoft">Innosoft International, Inc.</organization>
511        <address><email>ned.freed@innosoft.com</email></address>
512      </author>
513      <author initials="K." surname="Moore" fullname="Keith Moore">
514        <organization>University of Tennessee</organization>
515        <address><email>moore@cs.utk.edu</email></address>
516      </author>
517      <date year="1997" month="November"/>
518    </front>
519    <seriesInfo name="RFC" value="2231"/>
520  </reference>
521
522  <reference anchor="RFC3629">
523    <front>
524      <title>UTF-8, a transformation format of ISO 10646</title>
525      <author initials="F." surname="Yergeau" fullname="F. Yergeau">
526        <organization>Alis Technologies</organization>
527        <address><email>fyergeau@alis.com</email></address>
528      </author>
529      <date month="November" year="2003"/>
530    </front>
531    <seriesInfo name="STD" value="63"/>
532    <seriesInfo name="RFC" value="3629"/>
533  </reference>
534
535  <reference anchor="RFC3864">
536    <front>
537      <title>Registration Procedures for Message Header Fields</title>
538      <author initials="G." surname="Klyne" fullname="G. Klyne">
539        <organization>Nine by Nine</organization>
540        <address><email>GK-IETF@ninebynine.org</email></address>
541      </author>
542      <author initials="M." surname="Nottingham" fullname="M. Nottingham">
543        <organization>BEA Systems</organization>
544        <address><email>mnot@pobox.com</email></address>
545      </author>
546      <author initials="J." surname="Mogul" fullname="J. Mogul">
547        <organization>HP Labs</organization>
548        <address><email>JeffMogul@acm.org</email></address>
549      </author>
550      <date year="2004" month="September"/>
551    </front>
552    <seriesInfo name="BCP" value="90"/>
553    <seriesInfo name="RFC" value="3864"/>
554  </reference>
555
556  <reference anchor="RFC3986">
557   <front>
558    <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
559    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
560      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
561      <address>
562         <email>timbl@w3.org</email>
563         <uri>http://www.w3.org/People/Berners-Lee/</uri>
564      </address>
565    </author>
566    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
567      <organization abbrev="Day Software">Day Software</organization>
568      <address>
569        <email>fielding@gbiv.com</email>
570        <uri>http://roy.gbiv.com/</uri>
571      </address>
572    </author>
573    <author initials="L." surname="Masinter" fullname="Larry Masinter">
574      <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
575      <address>
576        <email>LMM@acm.org</email>
577        <uri>http://larry.masinter.net/</uri>
578      </address>
579    </author>
580    <date month="January" year="2005"/>
581   </front>
582   <seriesInfo name="STD" value="66"/>
583   <seriesInfo name="RFC" value="3986"/>
584  </reference>
585
586</references>
587
588<section title="Changes from the RFC 2616 Definition" anchor="changes.from.rfc2616">
589<t>
590  Compared to <xref target="RFC2616" x:fmt="of" x:sec="19.5.1"/>, the following
591  normative changes reflecting actual implementations have been made:
592<list style="symbols">
593  <t>
594    According to RFC 2616, the disposition type "attachment" only applies to
595    content of type "application/octet-stream". This restriction has been
596    removed, because user agents in practice do not check the content type, and
597    it also discourages properly declaring the media type.
598  </t>
599  <t>
600    RFC 2616 only allows "quoted-string" for the filename parameter. This
601    would be an exceptional parameter syntax, and also doesn't reflect actual
602    use.
603  </t>
604  <t>
605    The definition for the disposition type "inline" (<xref target="RFC2183" x:fmt="," x:sec="2.1"/>)
606    has been re-added with a suggestion for its processing.
607  </t>
608  <t>
609    This specification requires support for the extended parameter encoding
610    defined in <xref target="RFC5987"/>.
611  </t>
612</list>
613</t>
614</section>
615
616<section title="Differences compared to RFC 2183" anchor="diffs.compared.to.rfc2183">
617<t>
618  <xref target="RFC2183" x:fmt="of" x:sec="2"/> defines several additional
619  disposition parameters: "creation-date", "modification-date",
620  "quoted-date-time", and "size". These do not appear to be implemented by
621  any user agent, thus have been omitted from this specification.
622</t>
623</section>
624
625<section title="Alternative Approaches to Internationalization" anchor="alternatives">
626<t>
627  By default, HTTP header field parameters cannot carry characters outside
628  the ISO-8859-1 (<xref target="ISO-8859-1"/>) character encoding (see
629  <xref target="RFC2616" x:fmt="," x:sec="2.2"/>). For the "filename"
630  parameter, this of course is an unacceptable restriction.
631</t>
632<t>
633  Unfortunately, user agent implementers have not managed to come up with
634  an interoperable approach, although the IETF Standards Track specifies
635  exactly one solution (<xref target="RFC2231"/>, clarified and profiled for
636  HTTP in <xref target="RFC5987"/>).
637</t>
638<t>
639  For completeness, the sections below describe the various approaches that
640  have been tried, and explains how they are inferior to the RFC 5987
641  encoding used in this specification.
642</t>
643
644<section title="RFC 2047 Encoding" anchor="alternatives.rfc2047">
645<t>
646  RFC 2047 defines an encoding mechanism for
647  header fields, but this encoding is not supposed to be used for
648  header field parameters - see <xref target="RFC2047" x:fmt="of" x:sec="5"/>
649</t>
650<x:blockquote cite="http://tools.ietf.org/html/rfc2047#section-5">
651  <t>
652    An 'encoded-word' MUST NOT appear within a 'quoted-string'.
653  </t>
654  <t>
655    ...
656  </t>
657  <t>
658    An 'encoded-word' MUST NOT be used in parameter of a MIME Content-Type or Content-Disposition field, or in any structured field body except within a 'comment' or 'phrase'.
659  </t>
660</x:blockquote>
661<t>
662  In practice, some user agents implement the encoding, some do not
663  (exposing the encoded string to the user), and some get confused by it.
664</t>
665</section>
666
667<section title="Percent Encoding" anchor="alternatives.percent">
668<t>
669  Some user agents accept percent encoded (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>)
670  sequences of characters encoded using the UTF-8 (<xref target="RFC3629"/>) character encoding.
671</t>
672<t>
673  In practice, this is hard to use because those user agents
674  that do not support it will display the escaped character sequence to the user.
675</t>
676<t>
677  Furthermore, the first user agent to implement this did choose the encoding
678  based on local settings; thus making it very hard to use in multi-lingual
679  environments.
680</t>
681</section>
682
683<section title="Encoding Sniffing" anchor="alternatives.sniff">
684<t>
685  Some user agents inspect the value (which defaults to ISO-8859-1) and
686  switch to UTF-8 when it seems to be more likely to be the correct
687  interpretation.
688</t>
689<t>
690  As with the approaches above, this is not interoperable and furthermore
691  risks misinterpreting the actual value.
692</t>
693</section>
694
695<section title="Implementations (to be removed by RFC Editor before publication)" anchor="alternatives.implementations">
696<t>
697  Unfortunately, as of September 2010, neither the encoding defined in RFCs 2231
698  and 5987, nor any of the alternate approaches discussed above was
699  implemented interoperably. Thus, this specification recommends the approach
700  defined in RFC 5987, which at least has the advantage of actually being
701  specified properly.
702</t>
703<t>
704  The table below shows the implementation support for the various approaches:
705</t>
706<texttable align="left">
707  <ttcol>User Agent</ttcol>
708  <ttcol>RFC 2231/5987</ttcol>
709  <ttcol>RFC 2047</ttcol>
710  <ttcol>Percent Encoding</ttcol>
711  <ttcol>Encoding Sniffing</ttcol>
712 
713  <c>Chrome</c>
714  <c>no</c>
715  <c>yes</c>
716  <c>yes</c>
717  <c>yes</c>
718
719  <c>Firefox</c>
720  <c>yes (*)</c>
721  <c>yes</c>
722  <c>no</c>
723  <c>yes</c>
724
725  <c>Internet Explorer</c>
726  <c>no</c>
727  <c>no</c>
728  <c>yes</c>
729  <c>no</c>
730
731  <c>Konqueror</c>
732  <c>yes</c>
733  <c>no</c>
734  <c>no</c>
735  <c>no</c>
736
737  <c>Opera</c>
738  <c>yes (*)</c>
739  <c>no</c>
740  <c>no</c>
741  <c>no</c>
742
743  <c>Safari</c>
744  <c>no</c>
745  <c>no</c>
746  <c>no</c>
747  <c>yes</c>
748 
749  <postamble>
750  (*) Does not implement the fallback behavior to "filename" described in
751  <xref target="disposition.parameter.filename"/>.
752  </postamble>
753
754</texttable>
755
756</section>
757
758</section>
759
760
761<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
762<section title="Since draft-reschke-rfc2183-in-http-00">
763<t> 
764  Adjust terminology ("header" -&gt; "header field").
765  Update rfc2231-in-http reference.
766</t>
767</section>
768
769
770<section title="Since draft-reschke-rfc2183-in-http-01">
771<t> 
772  Update rfc2231-in-http reference. Actually define the "filename"
773  parameter. Add internationalization considerations.
774  Add examples using the RFC 5987 encoding.
775  Add overview over other approaches, plus a table reporting
776  implementation status.
777  Add and resolve issue "nodep2183".
778  Add issues "asciivsiso",
779  "deplboth", "quoted", and "registry".
780</t>
781</section>
782
783<section title="Since draft-reschke-rfc2183-in-http-02">
784<t>
785  Add and close issue "docfallback".
786  Close issues "asciivsiso", "deplboth", "quoted", and
787  "registry".
788</t>
789</section>
790
791<section title="Since draft-reschke-rfc2183-in-http-03">
792<t>
793  Updated to be a Working Draft of the IETF HTTPbis Working Group.
794</t>
795</section>
796
797<section title="Since draft-ietf-httpbis-content-disp-00" anchor="changes.since.00">
798<t>
799  Closed issues:
800  <list style="symbols">
801    <t>
802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/242"/>:
803      "handling of unknown disposition types"
804    </t>
805  </list>
806</t>
807<t>
808  Slightly updated the notes about the proposed fallback behavior.
809</t>
810</section>
811
812<section title="Since draft-ietf-httpbis-content-disp-01" anchor="changes.since.01">
813<t>
814  Various editorial improvements.
815</t>
816</section>
817
818<section title="Since draft-ietf-httpbis-content-disp-02" anchor="changes.since.02">
819<t>
820  None yet.
821</t>
822</section>
823</section>
824
825
826  </back>
827
828</rfc>
Note: See TracBrowser for help on using the repository browser.