source: draft-ietf-httpbis-content-disp/latest/draft-ietf-httpbis-content-disp.xml @ 1073

Last change on this file since 1073 was 1073, checked in by julian.reschke@…, 11 years ago

avoid passive voice in requirement (resolves #258)

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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="November" 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.03"/>.
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  implied 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  quoted-string = &lt;quoted-string, defined in <xref target="RFC2616" x:fmt="," x:sec="2.2"/>&gt;
147  value         = &lt;value, defined in <xref target="RFC2616" x:fmt="," x:sec="3.6"/>&gt;
148                ; token | quoted-string
149             
150</artwork></figure>
151<figure>
152<preamble>Defined in <xref target="RFC5987"/>:</preamble>
153<artwork type="abnf2616">
154  ext-value   = &lt;ext-value, defined in <xref target="RFC5987" x:sec="3.2"/>&gt;
155</artwork></figure>
156
157<t>
158  Senders &MUST-NOT; generate header field values with multiple instances of
159  the same parameter name. Recipients &SHOULD; treat these values
160  as invalid.
161</t>
162<t>
163  Note that due to the rules for implied linear whitespace
164  (<xref target="RFC2616" x:fmt="of" x:sec="2.1"/>), OPTIONAL whitespace can
165  appear between words (token or quoted-string) and separator characters.
166</t>
167
168</section>
169
170<section title="Disposition Type" anchor="disposition.type">
171<t>
172  If the disposition type matches "attachment" (case-insensitively), this
173  indicates that the user agent should prompt the user to save the response
174  locally, rather than process it normally (as per its media type).
175</t>
176<t>
177  On the other hand, if it matches "inline" (case-insensitively), this implies
178  default processing.
179</t>
180<t>
181  Unknown or unhandled disposition types &SHOULD; be handled the same way as
182  "attachment" (see also <xref target="RFC2183" x:fmt="," x:sec="2.8"/>).
183</t>
184</section>
185
186<section title="Disposition Parameter: 'Filename'" anchor="disposition.parameter.filename">
187<t>
188  The parameters "filename" and "filename*", to be matched case-insensitively,
189  provide information on how to construct a filename for storing the message
190  payload.
191</t>
192<t>
193  Depending on the disposition type, this information might be used right away
194  (in the "save as..." interaction caused for the "attachment" disposition type),
195  or later on (for instance, when the user decides to save the contents of the
196  current page being displayed).
197</t>
198<t>
199  The parameters "filename" and "filename*" differ only in that "filename*" uses
200  the encoding defined in <xref target="RFC5987"/>, allowing the use
201  of characters not present in the ISO-8859-1 character set (<xref target="ISO-8859-1"/>).
202</t>
203<t>
204  Many user agent implementations predating this specification
205  do not understand the "filename*" parameter. Therefore, when both "filename"
206  and "filename*" are present in a single header field value, recipients
207  &SHOULD; pick "filename*" and ignore "filename". This way, senders
208  can avoid special-casing specific user agents by sending both the
209  more expressive "filename*" parameter, and the "filename" parameter
210  as fallback for legacy recipients (see <xref target="examples"/> for
211  an example).
212</t>
213<t>
214  It is essential that user agents treat the specified filename as advisory
215  only, thus be very careful in extracting the desired information.
216  In particular:
217  <list style="symbols">
218    <x:lt><t>
219      When the value contains path separator characters, all but the last
220      segment &SHOULD; be ignored. This prevents unintentional overwriting
221      of well-known file system location (such as "/etc/passwd").
222    </t></x:lt>
223    <x:lt><t>
224      Many platforms do not use Internet Media Types (<xref target="RFC2046"/>)
225      to hold type information in the file system, but rely on filename
226      extensions instead. Trusting the server-provided file extension could
227      introduce a privilege escalation when the saved file is later opened
228      (consider ".exe"). Thus, recipients need to ensure that a file extension
229      is used that is safe, optimally matching the media type of the received
230      payload.
231    </t></x:lt>
232    <x:lt><t>
233      Recipients are advised to strip or replace character sequences that are
234      known to cause confusion both in user interfaces and in filenames, such as
235      control characters and leading and trailing whitespace.
236    </t></x:lt>
237    <x:lt><t>
238      Other aspects recipients need to be aware of are names that have a
239      special meaning in the file system or in shell commands, such as "." and "..",
240      "~", "|", and also device names.
241    </t></x:lt>
242  </list>
243</t>
244<x:note>
245  <t>
246    <x:h>Note:</x:h> Many user agents do not properly handle escape characters
247    when using the quoted-string form. Furthermore, some user agents
248    erroneously try to perform unescaping of "percent" escapes (see
249    <xref target="alternatives.percent"/>), and thus might misinterpret
250    filenames containing the percent character followed by two hex digits.
251  </t>
252</x:note>
253</section>
254
255<section title="Disposition Parameter: Extensions" anchor="disposition.parameter.extensions">
256<t>
257  To enable future extensions, unknown parameters &SHOULD; be ignored (see also <xref target="RFC2183" x:fmt="," x:sec="2.8"/>).
258</t>
259</section>
260
261<section title="Extensibility" anchor="extensibility">
262<t>
263  Note that <xref target="RFC2183" x:fmt="of" x:sec="9"/> defines IANA registries both
264  for disposition types and disposition parameters. This registry is
265  shared by different protocols using Content-Disposition, such as MIME and HTTP.
266  Therefore, not all registered values may make sense in the context of HTTP.
267</t>
268</section>
269
270</section> 
271
272<section title="Examples" anchor="examples">
273
274<figure>
275<preamble>
276Direct UA to show "save as" dialog, with a filename of "example.html": 
277</preamble>
278<artwork type="example">
279Content-Disposition: Attachment; filename=example.html
280</artwork></figure>
281<figure>
282<preamble>
283Direct UA to behave as if the Content-Disposition header field wasn't present,
284but to remember the filename "example.html" for a subsequent save operation:
285</preamble>
286<artwork type="example" x:indent-with="  ">
287Content-Disposition: INLINE; FILENAME= "example.html"
288</artwork></figure>
289<figure>
290<preamble>
291Direct UA to show "save as" dialog, with a filename of "an example":
292</preamble>
293<artwork type="example">
294Content-Disposition: Attachment; Filename*=UTF-8'<x:highlight>en</x:highlight>'an<x:highlight>%20</x:highlight>example
295</artwork>
296<postamble>Note that this example uses the extended encoding defined in
297<xref target="RFC5987"/> to specify that the natural language of the filename
298is English, and also to encode the space character which is not allowed in the
299token production.
300</postamble>
301</figure>
302<figure>
303<preamble>
304Direct UA to show "save as" dialog, with a filename containing the Unicode character  U+20AC (EURO SIGN):
305</preamble>
306<artwork type="example" x:indent-with="  ">
307Content-Disposition: attachment;
308                     filename*= UTF-8''<x:highlight>%e2%82%ac</x:highlight>%20rates
309</artwork>
310<postamble>
311  Here, the encoding defined in <xref target="RFC5987"/> is also used to encode the
312  non-ISO-8859-1 character.
313</postamble>
314</figure>
315<figure>
316<preamble>
317Same as above, but adding the "filename" parameter for compatibility with
318user agents not implementing RFC 5987:
319</preamble>
320<artwork type="example" x:indent-with="  ">
321Content-Disposition: attachment;
322                     filename="EURO rates";
323                     filename*=utf-8''<x:highlight>%e2%82%ac</x:highlight>%20rates
324</artwork>
325<postamble>
326  Note: as of November 2010, those user agents that do not support the RFC 5987
327  encoding ignore "filename*" when it occurs after "filename". Unfortunately,
328  some user agents that do support RFC 5987 do pick the "filename" rather
329  than the "filename*" parameter when it occurs first; it is expected that
330  this situation is going to improve soon.
331</postamble>
332</figure>
333
334</section>
335
336<section title="Internationalization Considerations" anchor="i18n">
337<t>
338  The "filename*" parameter (<xref target="disposition.parameter.filename"/>),
339  using the encoding defined in <xref target="RFC5987"/>, allows the
340  server to transmit characters outside the ISO-8859-1 character set,
341  and also to optionally specify the language in use.
342</t>
343<t>
344  Future parameters might also require internationalization, in which case
345  the same encoding can be used.
346</t>
347</section>
348
349<section title="Security Considerations" anchor="security.considerations">
350<t>
351  Using server-supplied information for constructing local filenames introduces
352  many risks. These are summarized in <xref target="disposition.parameter.filename"/>.
353</t>
354<t>
355  Furthermore, implementers also ought to be aware of the Security
356  Considerations applying to HTTP (see <xref target="RFC2616" x:fmt="of" x:sec="15"/>), and also the parameter encoding defined in <xref target="RFC5987"/>
357  (see <xref target="RFC5987" x:fmt="sec" x:sec="5"/>).
358</t>
359</section> 
360
361<section title="IANA Considerations" anchor="iana.considerations">
362
363<section title="Registry for Disposition Values and Parameter" anchor="registry">
364<t>
365  This specification does not introduce any changes to the registration
366  procedures for disposition values and parameters that are defined in
367  <xref target="RFC2183" x:fmt="of" x:sec="9"/>.
368</t>
369</section>
370
371<section title="Header Field Registration" anchor="header.field.registration"> 
372<t>
373  This document updates the definition of the Content-Disposition HTTP header field
374  in the permanent HTTP header field registry (see <xref target="RFC3864"/>).
375</t>
376<t>
377<list style="hanging">
378  <t hangText="Header field name:">Content-Disposition</t>
379  <t hangText="Applicable protocol:">http</t>
380  <t hangText="Status:">standard</t>
381  <t hangText="Author/Change controller:">IETF</t>
382  <t hangText="Specification document:">this specification (<xref target="header.field.definition"/>)</t>
383</list>
384</t>
385</section>
386
387</section> 
388
389<section title="Acknowledgements">
390<t>
391  Thanks to Adam Barth, Rolf Eike Beer, Bjoern Hoehrmann, Alfred Hoenes, Roar Lauritzsen,
392  Henrik Nordstrom, and Mark Nottingham for their valuable feedback.
393</t>
394</section> 
395
396  </middle>
397  <back>
398 
399<references title="Normative References">
400 
401  <reference anchor="RFC2119">
402    <front>
403      <title abbrev="RFC Key Words">Key words for use in RFCs to Indicate Requirement Levels</title>
404      <author initials="S." surname="Bradner" fullname="Scott Bradner">
405        <organization>Harvard University</organization>
406        <address><email>sob@harvard.edu</email></address>
407      </author>
408      <date month="March" year="1997"/>
409      <area>General</area>
410      <keyword>keyword</keyword>
411    </front>
412    <seriesInfo name="BCP" value="14"/>
413    <seriesInfo name="RFC" value="2119"/>
414  </reference>
415
416  <reference anchor="RFC2616">
417    <front>
418      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
419      <author initials="R." surname="Fielding" fullname="R. Fielding">
420        <organization>University of California, Irvine</organization>
421        <address><email>fielding@ics.uci.edu</email></address>
422      </author>
423      <author initials="J." surname="Gettys" fullname="J. Gettys">
424        <organization>W3C</organization>
425        <address><email>jg@w3.org</email></address>
426      </author>
427      <author initials="J." surname="Mogul" fullname="J. Mogul">
428        <organization>Compaq Computer Corporation</organization>
429        <address><email>mogul@wrl.dec.com</email></address>
430      </author>
431      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
432        <organization>MIT Laboratory for Computer Science</organization>
433        <address><email>frystyk@w3.org</email></address>
434      </author>
435      <author initials="L." surname="Masinter" fullname="L. Masinter">
436        <organization>Xerox Corporation</organization>
437        <address><email>masinter@parc.xerox.com</email></address>
438      </author>
439      <author initials="P." surname="Leach" fullname="P. Leach">
440        <organization>Microsoft Corporation</organization>
441        <address><email>paulle@microsoft.com</email></address>
442      </author>
443      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
444        <organization>W3C</organization>
445        <address><email>timbl@w3.org</email></address>
446      </author>
447      <date month="June" year="1999"/>
448    </front>
449    <seriesInfo name="RFC" value="2616"/>
450  </reference>
451
452  <reference anchor="RFC5987">
453        <front>
454      <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
455      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
456        <organization abbrev="greenbytes">greenbytes GmbH</organization>
457        <address>
458          <postal>
459            <street>Hafenweg 16</street>
460            <city>Muenster</city><region>NW</region><code>48155</code>
461            <country>Germany</country>
462          </postal>
463          <email>julian.reschke@greenbytes.de</email>   
464          <uri>http://greenbytes.de/tech/webdav/</uri> 
465        </address>
466      </author>
467      <date month="August" year="2010"/>
468    </front>
469    <seriesInfo name="RFC" value="5987"/>
470  </reference>
471
472  <reference anchor="ISO-8859-1">
473    <front>
474      <title>Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1</title>
475      <author>
476        <organization>International Organization for Standardization</organization>
477      </author>
478      <date year="1998"/>
479    </front>
480    <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
481  </reference>
482
483</references>
484 
485<references title="Informative References">
486
487  <reference anchor="RFC2046">
488    <front>
489      <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
490      <author initials="N." surname="Freed" fullname="Ned Freed">
491        <organization>Innosoft International, Inc.</organization>
492        <address><email>ned@innosoft.com</email></address>
493      </author>
494      <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
495        <organization>First Virtual Holdings</organization>
496        <address><email>nsb@nsb.fv.com</email></address>
497      </author>
498      <date month="November" year="1996"/>
499    </front>
500    <seriesInfo name="RFC" value="2046"/>
501  </reference>
502
503  <reference anchor="RFC2047">
504    <front>
505      <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
506      <author initials="K." surname="Moore" fullname="Keith Moore">
507        <organization>University of Tennessee</organization>
508        <address><email>moore@cs.utk.edu</email></address>
509      </author>
510      <date month="November" year="1996"/>
511    </front>
512    <seriesInfo name="RFC" value="2047"/>
513  </reference>
514
515  <reference anchor="RFC2183">
516    <front>
517      <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
518      <author initials="R." surname="Troost" fullname="Rens Troost">
519        <organization>New Century Systems</organization>
520        <address><email>rens@century.com</email></address>
521      </author>
522      <author initials="S." surname="Dorner" fullname="Steve Dorner">
523        <organization>QUALCOMM Incorporated</organization>
524        <address><email>sdorner@qualcomm.com</email></address>
525      </author>
526      <author initials="K." surname="Moore" fullname="Keith Moore">
527        <organization>Department of Computer Science</organization>
528        <address><email>moore@cs.utk.edu</email></address>
529      </author>
530      <date year="1997" month="August"/>
531    </front>
532    <seriesInfo name="RFC" value="2183"/>
533  </reference>
534
535  <reference anchor="RFC2231">
536    <front>
537      <title abbrev="MIME Value and Encoded Word Extensions">MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations</title>
538      <author initials="N." surname="Freed" fullname="Ned Freed">
539        <organization abbrev="Innosoft">Innosoft International, Inc.</organization>
540        <address><email>ned.freed@innosoft.com</email></address>
541      </author>
542      <author initials="K." surname="Moore" fullname="Keith Moore">
543        <organization>University of Tennessee</organization>
544        <address><email>moore@cs.utk.edu</email></address>
545      </author>
546      <date year="1997" month="November"/>
547    </front>
548    <seriesInfo name="RFC" value="2231"/>
549  </reference>
550
551  <reference anchor="RFC3629">
552    <front>
553      <title>UTF-8, a transformation format of ISO 10646</title>
554      <author initials="F." surname="Yergeau" fullname="F. Yergeau">
555        <organization>Alis Technologies</organization>
556        <address><email>fyergeau@alis.com</email></address>
557      </author>
558      <date month="November" year="2003"/>
559    </front>
560    <seriesInfo name="STD" value="63"/>
561    <seriesInfo name="RFC" value="3629"/>
562  </reference>
563
564  <reference anchor="RFC3864">
565    <front>
566      <title>Registration Procedures for Message Header Fields</title>
567      <author initials="G." surname="Klyne" fullname="G. Klyne">
568        <organization>Nine by Nine</organization>
569        <address><email>GK-IETF@ninebynine.org</email></address>
570      </author>
571      <author initials="M." surname="Nottingham" fullname="M. Nottingham">
572        <organization>BEA Systems</organization>
573        <address><email>mnot@pobox.com</email></address>
574      </author>
575      <author initials="J." surname="Mogul" fullname="J. Mogul">
576        <organization>HP Labs</organization>
577        <address><email>JeffMogul@acm.org</email></address>
578      </author>
579      <date year="2004" month="September"/>
580    </front>
581    <seriesInfo name="BCP" value="90"/>
582    <seriesInfo name="RFC" value="3864"/>
583  </reference>
584
585  <reference anchor="RFC3986">
586   <front>
587    <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
588    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
589      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
590      <address>
591         <email>timbl@w3.org</email>
592         <uri>http://www.w3.org/People/Berners-Lee/</uri>
593      </address>
594    </author>
595    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
596      <organization abbrev="Day Software">Day Software</organization>
597      <address>
598        <email>fielding@gbiv.com</email>
599        <uri>http://roy.gbiv.com/</uri>
600      </address>
601    </author>
602    <author initials="L." surname="Masinter" fullname="Larry Masinter">
603      <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
604      <address>
605        <email>LMM@acm.org</email>
606        <uri>http://larry.masinter.net/</uri>
607      </address>
608    </author>
609    <date month="January" year="2005"/>
610   </front>
611   <seriesInfo name="STD" value="66"/>
612   <seriesInfo name="RFC" value="3986"/>
613  </reference>
614
615</references>
616
617<section title="Changes from the RFC 2616 Definition" anchor="changes.from.rfc2616">
618<t>
619  Compared to <xref target="RFC2616" x:fmt="of" x:sec="19.5.1"/>, the following
620  normative changes reflecting actual implementations have been made:
621<list style="symbols">
622  <t>
623    According to RFC 2616, the disposition type "attachment" only applies to
624    content of type "application/octet-stream". This restriction has been
625    removed, because user agents in practice do not check the content type, and
626    it also discourages properly declaring the media type.
627  </t>
628  <t>
629    RFC 2616 only allows "quoted-string" for the filename parameter. This
630    would be an exceptional parameter syntax, and also doesn't reflect actual
631    use.
632  </t>
633  <t>
634    The definition for the disposition type "inline" (<xref target="RFC2183" x:fmt="," x:sec="2.1"/>)
635    has been re-added with a suggestion for its processing.
636  </t>
637  <t>
638    This specification requires support for the extended parameter encoding
639    defined in <xref target="RFC5987"/>.
640  </t>
641</list>
642</t>
643</section>
644
645<section title="Differences compared to RFC 2183" anchor="diffs.compared.to.rfc2183">
646<t>
647  <xref target="RFC2183" x:fmt="of" x:sec="2"/> defines several additional
648  disposition parameters: "creation-date", "modification-date",
649  "quoted-date-time", and "size". The majority of user agents does not implement
650  these, thus they have been omitted from this specification.
651</t>
652</section>
653
654<section title="Alternative Approaches to Internationalization" anchor="alternatives">
655<t>
656  By default, HTTP header field parameters cannot carry characters outside
657  the ISO-8859-1 (<xref target="ISO-8859-1"/>) character encoding (see
658  <xref target="RFC2616" x:fmt="," x:sec="2.2"/>). For the "filename"
659  parameter, this of course is an unacceptable restriction.
660</t>
661<t>
662  Unfortunately, user agent implementers have not managed to come up with
663  an interoperable approach, although the IETF Standards Track specifies
664  exactly one solution (<xref target="RFC2231"/>, clarified and profiled for
665  HTTP in <xref target="RFC5987"/>).
666</t>
667<t>
668  For completeness, the sections below describe the various approaches that
669  have been tried, and explains how they are inferior to the RFC 5987
670  encoding used in this specification.
671</t>
672
673<section title="RFC 2047 Encoding" anchor="alternatives.rfc2047">
674<t>
675  RFC 2047 defines an encoding mechanism for
676  header fields, but this encoding is not supposed to be used for
677  header field parameters - see <xref target="RFC2047" x:fmt="of" x:sec="5"/>: 
678</t>
679<x:blockquote cite="http://tools.ietf.org/html/rfc2047#section-5">
680  <t>
681    An 'encoded-word' MUST NOT appear within a 'quoted-string'.
682  </t>
683  <t>
684    ...
685  </t>
686  <t>
687    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'.
688  </t>
689</x:blockquote>
690<t>
691  In practice, some user agents implement the encoding, some do not
692  (exposing the encoded string to the user), and some get confused by it.
693</t>
694</section>
695
696<section title="Percent Encoding" anchor="alternatives.percent">
697<t>
698  Some user agents accept percent encoded (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>)
699  sequences of characters encoded using the UTF-8 (<xref target="RFC3629"/>) character encoding.
700</t>
701<t>
702  In practice, this is hard to use because those user agents
703  that do not support it will display the escaped character sequence to the user.
704</t>
705<t>
706  Furthermore, the first user agent to implement this did choose the encoding
707  based on local settings; thus making it very hard to use in multi-lingual
708  environments.
709</t>
710</section>
711
712<section title="Encoding Sniffing" anchor="alternatives.sniff">
713<t>
714  Some user agents inspect the value (which defaults to ISO-8859-1) and
715  switch to UTF-8 when it seems to be more likely to be the correct
716  interpretation.
717</t>
718<t>
719  As with the approaches above, this is not interoperable and furthermore
720  risks misinterpreting the actual value.
721</t>
722</section>
723
724<section title="Implementations (to be removed by RFC Editor before publication)" anchor="alternatives.implementations">
725<t>
726  Unfortunately, as of October 2010, neither the encoding defined in RFCs 2231
727  and 5987, nor any of the alternate approaches discussed above was
728  implemented interoperably. Thus, this specification recommends the approach
729  defined in RFC 5987, which at least has the advantage of actually being
730  specified properly.
731</t>
732<t>
733  The table below shows the implementation support for the various approaches:
734</t>
735<texttable align="left">
736  <ttcol>User Agent</ttcol>
737  <ttcol>RFC 2231/5987</ttcol>
738  <ttcol>RFC 2047</ttcol>
739  <ttcol>Percent Encoding</ttcol>
740  <ttcol>Encoding Sniffing</ttcol>
741 
742  <c>Chrome</c>
743  <c>no</c>
744  <c>yes</c>
745  <c>yes</c>
746  <c>yes</c>
747
748  <c>Firefox</c>
749  <c>yes (*)</c>
750  <c>yes</c>
751  <c>no</c>
752  <c>yes</c>
753
754  <c>Internet Explorer</c>
755  <c>no</c>
756  <c>no</c>
757  <c>yes</c>
758  <c>no</c>
759
760  <c>Konqueror</c>
761  <c>yes</c>
762  <c>no</c>
763  <c>no</c>
764  <c>no</c>
765
766  <c>Opera</c>
767  <c>yes</c>
768  <c>no</c>
769  <c>no</c>
770  <c>no</c>
771
772  <c>Safari</c>
773  <c>no</c>
774  <c>no</c>
775  <c>no</c>
776  <c>yes</c>
777 
778  <postamble>
779  (*) Does not implement the fallback behavior to "filename" described in
780  <xref target="disposition.parameter.filename"/>.
781  </postamble>
782
783</texttable>
784
785</section>
786
787</section>
788
789
790<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
791<t>
792  Note: the issues names in the change log entries for draft-reschke-rfc2183-in-http
793  refer to <eref target="http://greenbytes.de/tech/webdav/draft-reschke-rfc2183-in-http-issues.html"/>.
794</t>
795
796<section title="Since draft-reschke-rfc2183-in-http-00">
797<t> 
798  Adjust terminology ("header" -&gt; "header field").
799  Update rfc2231-in-http reference.
800</t>
801</section>
802
803<section title="Since draft-reschke-rfc2183-in-http-01">
804<t> 
805  Update rfc2231-in-http reference. Actually define the "filename"
806  parameter. Add internationalization considerations.
807  Add examples using the RFC 5987 encoding.
808  Add overview over other approaches, plus a table reporting
809  implementation status.
810  Add and resolve issue "nodep2183".
811  Add issues "asciivsiso",
812  "deplboth", "quoted", and "registry".
813</t>
814</section>
815
816<section title="Since draft-reschke-rfc2183-in-http-02">
817<t>
818  Add and close issue "docfallback".
819  Close issues "asciivsiso", "deplboth", "quoted", and
820  "registry".
821</t>
822</section>
823
824<section title="Since draft-reschke-rfc2183-in-http-03">
825<t>
826  Updated to be a Working Draft of the IETF HTTPbis Working Group.
827</t>
828</section>
829
830<section title="Since draft-ietf-httpbis-content-disp-00" anchor="changes.since.00">
831<t>
832  Closed issues:
833  <list style="symbols">
834    <t>
835      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/242"/>:
836      "handling of unknown disposition types"
837    </t>
838  </list>
839</t>
840<t>
841  Slightly updated the notes about the proposed fallback behavior.
842</t>
843</section>
844
845<section title="Since draft-ietf-httpbis-content-disp-01" anchor="changes.since.01">
846<t>
847  Various editorial improvements.
848</t>
849</section>
850
851<section title="Since draft-ietf-httpbis-content-disp-02" anchor="changes.since.02">
852<t>
853  Closed issues:
854  <list style="symbols">
855    <t>
856      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/244"/>:
857      "state that repeating parameters are invalid"
858    </t>
859    <t>
860      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/245"/>:
861      "warn about %xx in filenames being misinterpreted"
862    </t>
863    <t>
864      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/246"/>:
865      "mention control chars when talking about postprecessing the filename parameter"
866    </t>
867  </list>
868</t>
869<t>
870  Update <xref target="alternatives.implementations"/>; Opera 10.63 RC
871  implements the recommended fallback behavior.
872</t>
873</section>
874
875<section title="Since draft-ietf-httpbis-content-disp-03" anchor="changes.since.03">
876<t>
877  Closed issues:
878  <list style="symbols">
879    <t>
880      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/252"/>:
881      "'modification-date' *is* implemented in Konq 4.5"
882    </t>
883    <t>
884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/253"/>:
885      "clarify what LWS means for the Content-Disp grammar"
886    </t>
887    <t>
888      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/258"/>:
889      "Avoid passive voice in message requirements"
890    </t>
891  </list>
892</t>
893</section>
894
895</section>
896
897
898  </back>
899
900</rfc>
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