source: draft-ietf-httpbis-content-disp/latest/draft-ietf-httpbis-content-disp.xml @ 1203

Last change on this file since 1203 was 1203, checked in by julian.reschke@…, 9 years ago

clarify that we talk about C-D only when making a statement about repeating params

  • Property svn:eol-style set to native
  • Property svn:executable set to *
File size: 40.8 KB
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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="March" year="2011"/>
45  <workgroup>HTTPbis Working Group</workgroup>
46 
47  <abstract>
48    <t>
49      RFC 2616 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.08"/>.
72    </t>
73  </note>
74  </front>
75
76  <middle>
77
78<section title="Introduction" anchor="introduction">
79<t>
80  RFC 2616 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<x:note>
99  <t>
100    <x:h>Note:</x:h> this document does not apply to Content-Disposition
101    header fields appearing in payload bodies transmitted over HTTP, such as
102    when using the media type "multipart/form-data" (<xref target="RFC2388"/>).
103  </t>
104</x:note>
105</section> 
106
107<section title="Notational Conventions" anchor="notational.conventions">
108<t>
109  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
110  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
111  are to be interpreted as described in <xref target="RFC2119"/>.
112</t>
113<t>
114  This specification uses the augmented BNF (ABNF) notation defined in
115  <xref target="RFC2616" x:fmt="of" x:sec="2.1"/>, including its rules for
116  implied linear whitespace (LWS).
117</t>
118</section>
119
120<section title="Conformance and Error Handling" anchor="conformance.and.error.handling">
121<t>
122  This specification defines conformance criteria for both senders (usually,
123  HTTP origin servers) and recipients (usually, HTTP user agents) of the
124  Content-Disposition header field. An implementation is considered conformant if
125  it complies with all of the requirements associated with its role.
126</t>
127<t>
128  This specification also defines certain forms of the header field-value to be
129  invalid, using both ABNF and prose requirements (<xref target="header.field.definition"/>),
130  but it does not define special handling of these invalid field-values.
131</t>
132<t>
133  Senders &MUST-NOT; generate Content-Disposition header fields that are
134  invalid.
135</t>
136<t>
137  Recipients &MAY; take steps to recover a usable field-value
138  from an invalid header field, but &SHOULD-NOT; reject the message outright,
139  unless this is explicitly desirable behaviour (e.g., the implementation is a
140  validator). As such, the default handling of invalid fields is to ignore them.
141</t>
142</section>
143
144<section title="Header Field Definition" anchor="header.field.definition">
145  <iref item="Header Fields" subitem="Content-Disposition" primary="true" x:for-anchor=""/>
146  <iref item="Content-Disposition header field" primary="true" x:for-anchor=""/>
147<t>
148  The Content-Disposition response header field is used to convey additional
149  information about how to process the response payload, and also can be used
150  to attach additional metadata, such as the filename to use when saving the
151  response payload locally.
152</t>
153
154<section title="Grammar">
155<figure><artwork type="abnf2616">
156  content-disposition = "Content-Disposition" ":"
157                         disposition-type *( ";" disposition-parm )
158
159  disposition-type    = "inline" | "attachment" | disp-ext-type
160                      ; case-insensitive
161  disp-ext-type       = token
162
163  disposition-parm    = filename-parm | disp-ext-parm
164
165  filename-parm       = "filename" "=" value
166                      | "filename*" "=" ext-value
167 
168  disp-ext-parm       = token "=" value
169                      | ext-token "=" ext-value
170  ext-token           = &lt;the characters in token, followed by "*"&gt;
171</artwork></figure>
172
173<figure>
174<preamble>Defined in <xref target="RFC2616"/>:</preamble>
175<artwork type="abnf2616">
176  token         = &lt;token, defined in <xref target="RFC2616" x:fmt="," x:sec="2.2"/>&gt;
177  quoted-string = &lt;quoted-string, defined in <xref target="RFC2616" x:fmt="," x:sec="2.2"/>&gt;
178  value         = &lt;value, defined in <xref target="RFC2616" x:fmt="," x:sec="3.6"/>&gt;
179                ; token | quoted-string
180             
181</artwork></figure>
182<figure>
183<preamble>Defined in <xref target="RFC5987"/>:</preamble>
184<artwork type="abnf2616">
185  ext-value   = &lt;ext-value, defined in <xref target="RFC5987" x:sec="3.2"/>&gt;
186</artwork></figure>
187<t>
188  Content-Disposition header field values with multiple instances of the same
189  parameter name are invalid.
190</t>
191<t>
192  Note that due to the rules for implied linear whitespace
193  (<xref target="RFC2616" x:fmt="of" x:sec="2.1"/>), &OPTIONAL; whitespace can
194  appear between words (token or quoted-string) and separator characters.
195</t>
196<t>
197  Furthermore note that the format used for ext-value allows specifying a
198  natural language (e.g., "en"); this is of limited use for filenames and is
199  likely to be ignored by recipients.
200</t>
201</section>
202
203<section title="Disposition Type" anchor="disposition.type">
204<t>
205  If the disposition type matches "attachment" (case-insensitively), this
206  indicates that the recipient should prompt the user to save the response
207  locally, rather than process it normally (as per its media type).
208</t>
209<t>
210  On the other hand, if it matches "inline" (case-insensitively), this implies
211  default processing. Therefore, the disposition type "inline" is only useful
212  when it is augmented with additional parameters, such as the filename (see
213  below).
214</t>
215<t>
216  Unknown or unhandled disposition types &SHOULD; be handled by recipients the
217  same way as "attachment" (see also <xref target="RFC2183" x:fmt="," x:sec="2.8"/>).
218</t>
219</section>
220
221<section title="Disposition Parameter: 'Filename'" anchor="disposition.parameter.filename">
222<t>
223  The parameters "filename" and "filename*", to be matched case-insensitively,
224  provide information on how to construct a filename for storing the message
225  payload.
226</t>
227<t>
228  Depending on the disposition type, this information might be used right away
229  (in the "save as..." interaction caused for the "attachment" disposition type),
230  or later on (for instance, when the user decides to save the contents of the
231  current page being displayed).
232</t>
233<t>
234  The parameters "filename" and "filename*" differ only in that "filename*" uses
235  the encoding defined in <xref target="RFC5987"/>, allowing the use
236  of characters not present in the ISO-8859-1 character set (<xref target="ISO-8859-1"/>).
237</t>
238<t>
239  Many user agent implementations predating this specification
240  do not understand the "filename*" parameter. Therefore, when both "filename"
241  and "filename*" are present in a single header field value, recipients
242  &SHOULD; pick "filename*" and ignore "filename". This way, senders
243  can avoid special-casing specific user agents by sending both the
244  more expressive "filename*" parameter, and the "filename" parameter
245  as fallback for legacy recipients (see <xref target="examples"/> for
246  an example).
247</t>
248<t>
249  It is essential that recipients treat the specified filename as advisory
250  only, thus be very careful in extracting the desired information.
251  In particular:
252  <list style="symbols">
253    <x:lt><t>
254      Recipients &MUST-NOT; be able to write into any location other than one
255      to which they are specifically entitled. To illustrate the problem
256      consider the consequences of being able to overwrite well-known system
257      locations (such as "/etc/passwd"). One strategy to achieve this is to
258      never trust folder name information in the filename parameter, for
259      instance by stripping all but the last path segment and only consider the
260      actual filename (where 'path segment' are the components of the field
261      value delimited by the path separator characters "\" and "/").
262    </t></x:lt>
263    <x:lt><t>
264      Many platforms do not use Internet Media Types (<xref target="RFC2046"/>)
265      to hold type information in the file system, but rely on filename
266      extensions instead. Trusting the server-provided file extension could
267      introduce a privilege escalation when the saved file is later opened
268      (consider ".exe"). Thus, recipients which make use of file extensions
269      to determine the media type &MUST; ensure that a file extension
270      is used that is safe, optimally matching the media type of the received
271      payload.
272    </t></x:lt>
273    <x:lt><t>
274      Recipients &SHOULD; strip or replace character sequences that are
275      known to cause confusion both in user interfaces and in filenames, such as
276      control characters and leading and trailing whitespace.
277    </t></x:lt>
278    <x:lt><t>
279      Other aspects recipients need to be aware of are names that have a
280      special meaning in the file system or in shell commands, such as "." and "..",
281      "~", "|", and also device names. Recipients &SHOULD; ignore or substitute
282      names like these.
283    </t></x:lt>
284  </list>
285</t>
286<x:note>
287  <t>
288    <x:h>Note:</x:h> Many user agents do not properly handle the escape
289    character "\" when using the quoted-string form. Furthermore, some user agents
290    erroneously try to perform unescaping of "percent" escapes (see
291    <xref target="alternatives.percent"/>), and thus might misinterpret
292    filenames containing the percent character followed by two hex digits.
293  </t>
294</x:note>
295</section>
296
297<section title="Disposition Parameter: Extensions" anchor="disposition.parameter.extensions">
298<t>
299  To enable future extensions, recipients &SHOULD; ignore unrecognized
300  parameters (see also <xref target="RFC2183" x:fmt="," x:sec="2.8"/>).
301</t>
302</section>
303
304<section title="Extensibility" anchor="extensibility">
305<t>
306  Note that <xref target="RFC2183" x:fmt="of" x:sec="9"/> defines IANA registries both
307  for disposition types and disposition parameters. This registry is
308  shared by different protocols using Content-Disposition, such as MIME and HTTP.
309  Therefore, not all registered values may make sense in the context of HTTP.
310</t>
311</section>
312
313</section> 
314
315<section title="Examples" anchor="examples">
316
317<figure>
318<preamble>
319Direct UA to show "save as" dialog, with a filename of "example.html": 
320</preamble>
321<artwork type="example">
322Content-Disposition: Attachment; filename=example.html
323</artwork></figure>
324<figure>
325<preamble>
326Direct UA to behave as if the Content-Disposition header field wasn't present,
327but to remember the filename "an example.html" for a subsequent save operation:
328</preamble>
329<artwork type="example" x:indent-with="  ">
330Content-Disposition: INLINE; FILENAME= "an example.html"
331</artwork>
332<postamble>
333  Note: this uses the quoted-string form so that the space character
334  can be included.
335</postamble>
336</figure>
337<figure>
338<preamble>
339Direct UA to show "save as" dialog, with a filename containing the Unicode character  U+20AC (EURO SIGN):
340</preamble>
341<artwork type="example" x:indent-with="  ">
342Content-Disposition: attachment;
343                     filename*= UTF-8''<x:highlight>%e2%82%ac</x:highlight>%20rates
344</artwork>
345<postamble>
346  Here, the encoding defined in <xref target="RFC5987"/> is also used to encode the
347  non-ISO-8859-1 character.
348</postamble>
349</figure>
350<figure>
351<preamble>
352Same as above, but adding the "filename" parameter for compatibility with
353user agents not implementing RFC 5987:
354</preamble>
355<artwork type="example" x:indent-with="  ">
356Content-Disposition: attachment;
357                     filename="EURO rates";
358                     filename*=utf-8''<x:highlight>%e2%82%ac</x:highlight>%20rates
359</artwork>
360<postamble>
361  Note: those user agents that do not support the RFC 5987 encoding ignore
362  "filename*" when it occurs after "filename".
363</postamble>
364</figure>
365
366</section>
367
368<section title="Internationalization Considerations" anchor="i18n">
369<t>
370  The "filename*" parameter (<xref target="disposition.parameter.filename"/>),
371  using the encoding defined in <xref target="RFC5987"/>, allows the
372  server to transmit characters outside the ISO-8859-1 character set,
373  and also to optionally specify the language in use.
374</t>
375<t>
376  Future parameters might also require internationalization, in which case
377  the same encoding can be used.
378</t>
379</section>
380
381<section title="Security Considerations" anchor="security.considerations">
382<t>
383  Using server-supplied information for constructing local filenames introduces
384  many risks. These are summarized in <xref target="disposition.parameter.filename"/>.
385</t>
386<t>
387  Furthermore, implementers also ought to be aware of the Security
388  Considerations applying to HTTP (see <xref target="RFC2616" x:fmt="of" x:sec="15"/>), and also the parameter encoding defined in <xref target="RFC5987"/>
389  (see <xref target="RFC5987" x:fmt="sec" x:sec="5"/>).
390</t>
391</section> 
392
393<section title="IANA Considerations" anchor="iana.considerations">
394
395<section title="Registry for Disposition Values and Parameter" anchor="registry">
396<t>
397  This specification does not introduce any changes to the registration
398  procedures for disposition values and parameters that are defined in
399  <xref target="RFC2183" x:fmt="of" x:sec="9"/>.
400</t>
401</section>
402
403<section title="Header Field Registration" anchor="header.field.registration"> 
404<t>
405  This document updates the definition of the Content-Disposition HTTP header field
406  in the permanent HTTP header field registry (see <xref target="RFC3864"/>).
407</t>
408<t>
409<list style="hanging">
410  <t hangText="Header field name:">Content-Disposition</t>
411  <t hangText="Applicable protocol:">http</t>
412  <t hangText="Status:">standard</t>
413  <t hangText="Author/Change controller:">IETF</t>
414  <t hangText="Specification document:">this specification (<xref target="header.field.definition"/>)</t>
415  <t hangText="Related information:">none</t>
416</list>
417</t>
418</section>
419
420</section> 
421
422<section title="Acknowledgements">
423<t>
424  Thanks to
425  Adam Barth,
426  Rolf Eike Beer,
427  Stewart Bryant,
428  Bjoern Hoehrmann,
429  Alfred Hoenes,
430  Roar Lauritzsen,
431  Alexey Melnikov,
432  Henrik Nordstrom, and
433  Mark Nottingham for
434  their valuable feedback.
435</t>
436</section> 
437
438  </middle>
439  <back>
440 
441<references title="Normative References">
442 
443  <reference anchor="RFC2119">
444    <front>
445      <title abbrev="RFC Key Words">Key words for use in RFCs to Indicate Requirement Levels</title>
446      <author initials="S." surname="Bradner" fullname="Scott Bradner">
447        <organization>Harvard University</organization>
448        <address><email>sob@harvard.edu</email></address>
449      </author>
450      <date month="March" year="1997"/>
451      <area>General</area>
452      <keyword>keyword</keyword>
453    </front>
454    <seriesInfo name="BCP" value="14"/>
455    <seriesInfo name="RFC" value="2119"/>
456  </reference>
457
458  <reference anchor="RFC2616">
459    <front>
460      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
461      <author initials="R." surname="Fielding" fullname="R. Fielding">
462        <organization>University of California, Irvine</organization>
463        <address><email>fielding@ics.uci.edu</email></address>
464      </author>
465      <author initials="J." surname="Gettys" fullname="J. Gettys">
466        <organization>W3C</organization>
467        <address><email>jg@w3.org</email></address>
468      </author>
469      <author initials="J." surname="Mogul" fullname="J. Mogul">
470        <organization>Compaq Computer Corporation</organization>
471        <address><email>mogul@wrl.dec.com</email></address>
472      </author>
473      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
474        <organization>MIT Laboratory for Computer Science</organization>
475        <address><email>frystyk@w3.org</email></address>
476      </author>
477      <author initials="L." surname="Masinter" fullname="L. Masinter">
478        <organization>Xerox Corporation</organization>
479        <address><email>masinter@parc.xerox.com</email></address>
480      </author>
481      <author initials="P." surname="Leach" fullname="P. Leach">
482        <organization>Microsoft Corporation</organization>
483        <address><email>paulle@microsoft.com</email></address>
484      </author>
485      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
486        <organization>W3C</organization>
487        <address><email>timbl@w3.org</email></address>
488      </author>
489      <date month="June" year="1999"/>
490    </front>
491    <seriesInfo name="RFC" value="2616"/>
492  </reference>
493
494  <reference anchor="RFC5987">
495        <front>
496      <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
497      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
498        <organization abbrev="greenbytes">greenbytes GmbH</organization>
499        <address>
500          <postal>
501            <street>Hafenweg 16</street>
502            <city>Muenster</city><region>NW</region><code>48155</code>
503            <country>Germany</country>
504          </postal>
505          <email>julian.reschke@greenbytes.de</email>   
506          <uri>http://greenbytes.de/tech/webdav/</uri> 
507        </address>
508      </author>
509      <date month="August" year="2010"/>
510    </front>
511    <seriesInfo name="RFC" value="5987"/>
512  </reference>
513
514  <reference anchor="ISO-8859-1">
515    <front>
516      <title>Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1</title>
517      <author>
518        <organization>International Organization for Standardization</organization>
519      </author>
520      <date year="1998"/>
521    </front>
522    <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
523  </reference>
524
525</references>
526 
527<references title="Informative References">
528
529  <reference anchor="RFC2046">
530    <front>
531      <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
532      <author initials="N." surname="Freed" fullname="Ned Freed">
533        <organization>Innosoft International, Inc.</organization>
534        <address><email>ned@innosoft.com</email></address>
535      </author>
536      <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
537        <organization>First Virtual Holdings</organization>
538        <address><email>nsb@nsb.fv.com</email></address>
539      </author>
540      <date month="November" year="1996"/>
541    </front>
542    <seriesInfo name="RFC" value="2046"/>
543  </reference>
544
545  <reference anchor="RFC2047">
546    <front>
547      <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
548      <author initials="K." surname="Moore" fullname="Keith Moore">
549        <organization>University of Tennessee</organization>
550        <address><email>moore@cs.utk.edu</email></address>
551      </author>
552      <date month="November" year="1996"/>
553    </front>
554    <seriesInfo name="RFC" value="2047"/>
555  </reference>
556
557  <reference anchor="RFC2183">
558    <front>
559      <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
560      <author initials="R." surname="Troost" fullname="Rens Troost">
561        <organization>New Century Systems</organization>
562        <address><email>rens@century.com</email></address>
563      </author>
564      <author initials="S." surname="Dorner" fullname="Steve Dorner">
565        <organization>QUALCOMM Incorporated</organization>
566        <address><email>sdorner@qualcomm.com</email></address>
567      </author>
568      <author initials="K." surname="Moore" fullname="Keith Moore">
569        <organization>Department of Computer Science</organization>
570        <address><email>moore@cs.utk.edu</email></address>
571      </author>
572      <date year="1997" month="August"/>
573    </front>
574    <seriesInfo name="RFC" value="2183"/>
575  </reference>
576
577  <reference anchor="RFC2231">
578    <front>
579      <title abbrev="MIME Value and Encoded Word Extensions">MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations</title>
580      <author initials="N." surname="Freed" fullname="Ned Freed">
581        <organization abbrev="Innosoft">Innosoft International, Inc.</organization>
582        <address><email>ned.freed@innosoft.com</email></address>
583      </author>
584      <author initials="K." surname="Moore" fullname="Keith Moore">
585        <organization>University of Tennessee</organization>
586        <address><email>moore@cs.utk.edu</email></address>
587      </author>
588      <date year="1997" month="November"/>
589    </front>
590    <seriesInfo name="RFC" value="2231"/>
591  </reference>
592
593  <reference anchor="RFC2388">
594    <front>
595      <title abbrev="multipart/form-data">Returning Values from Forms: multipart/form-data</title>
596      <author initials="L." surname="Masinter" fullname="Larry Masinter">
597        <organization>Xerox Palo Alto Research Center</organization>
598        <address>
599          <email>masinter@parc.xerox.com</email>
600        </address>
601      </author>
602      <date year="1998" month="August"/>
603    </front>
604    <seriesInfo name="RFC" value="2388"/>
605  </reference>
606<!--
607  <reference anchor="RFC3629">
608    <front>
609      <title>UTF-8, a transformation format of ISO 10646</title>
610      <author initials="F." surname="Yergeau" fullname="F. Yergeau">
611        <organization>Alis Technologies</organization>
612        <address><email>fyergeau@alis.com</email></address>
613      </author>
614      <date month="November" year="2003"/>
615    </front>
616    <seriesInfo name="STD" value="63"/>
617    <seriesInfo name="RFC" value="3629"/>
618  </reference>-->
619
620  <reference anchor="RFC3864">
621    <front>
622      <title>Registration Procedures for Message Header Fields</title>
623      <author initials="G." surname="Klyne" fullname="G. Klyne">
624        <organization>Nine by Nine</organization>
625        <address><email>GK-IETF@ninebynine.org</email></address>
626      </author>
627      <author initials="M." surname="Nottingham" fullname="M. Nottingham">
628        <organization>BEA Systems</organization>
629        <address><email>mnot@pobox.com</email></address>
630      </author>
631      <author initials="J." surname="Mogul" fullname="J. Mogul">
632        <organization>HP Labs</organization>
633        <address><email>JeffMogul@acm.org</email></address>
634      </author>
635      <date year="2004" month="September"/>
636    </front>
637    <seriesInfo name="BCP" value="90"/>
638    <seriesInfo name="RFC" value="3864"/>
639  </reference>
640
641  <reference anchor="RFC3986">
642   <front>
643    <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
644    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
645      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
646      <address>
647         <email>timbl@w3.org</email>
648         <uri>http://www.w3.org/People/Berners-Lee/</uri>
649      </address>
650    </author>
651    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
652      <organization abbrev="Day Software">Day Software</organization>
653      <address>
654        <email>fielding@gbiv.com</email>
655        <uri>http://roy.gbiv.com/</uri>
656      </address>
657    </author>
658    <author initials="L." surname="Masinter" fullname="Larry Masinter">
659      <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
660      <address>
661        <email>LMM@acm.org</email>
662        <uri>http://larry.masinter.net/</uri>
663      </address>
664    </author>
665    <date month="January" year="2005"/>
666   </front>
667   <seriesInfo name="STD" value="66"/>
668   <seriesInfo name="RFC" value="3986"/>
669  </reference>
670
671   <reference anchor="US-ASCII">
672    <front>
673      <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
674      <author>
675        <organization>American National Standards Institute</organization>
676      </author>
677      <date year="1986"/>
678    </front>
679    <seriesInfo name="ANSI" value="X3.4"/>
680   </reference>
681
682</references>
683
684<section title="Changes from the RFC 2616 Definition" anchor="changes.from.rfc2616">
685<t>
686  Compared to <xref target="RFC2616" x:fmt="of" x:sec="19.5.1"/>, the following
687  normative changes reflecting actual implementations have been made:
688<list style="symbols">
689  <t>
690    According to RFC 2616, the disposition type "attachment" only applies to
691    content of type "application/octet-stream". This restriction has been
692    removed, because recipients in practice do not check the content type, and
693    it also discourages properly declaring the media type.
694  </t>
695  <t>
696    RFC 2616 only allows "quoted-string" for the filename parameter. This
697    would be an exceptional parameter syntax, and also doesn't reflect actual
698    use.
699  </t>
700  <t>
701    The definition for the disposition type "inline" (<xref target="RFC2183" x:fmt="," x:sec="2.1"/>)
702    has been re-added with a suggestion for its processing.
703  </t>
704  <t>
705    This specification requires support for the extended parameter encoding
706    defined in <xref target="RFC5987"/>.
707  </t>
708</list>
709</t>
710</section>
711
712<section title="Differences compared to RFC 2183" anchor="diffs.compared.to.rfc2183">
713<t>
714  <xref target="RFC2183" x:fmt="of" x:sec="2"/> defines several additional
715  disposition parameters: "creation-date", "modification-date",
716  "quoted-date-time", and "size". The majority of user agents does not implement
717  these, thus they have been omitted from this specification.
718</t>
719</section>
720
721<section title="Alternative Approaches to Internationalization" anchor="alternatives">
722<t>
723  By default, HTTP header field parameters cannot carry characters outside
724  the ISO-8859-1 (<xref target="ISO-8859-1"/>) character encoding (see
725  <xref target="RFC2616" x:fmt="," x:sec="2.2"/>). For the "filename"
726  parameter, this of course is an unacceptable restriction.
727</t>
728<t>
729  Unfortunately, user agent implementers have not managed to come up with
730  an interoperable approach, although the IETF Standards Track specifies
731  exactly one solution (<xref target="RFC2231"/>, clarified and profiled for
732  HTTP in <xref target="RFC5987"/>).
733</t>
734<t>
735  For completeness, the sections below describe the various approaches that
736  have been tried, and explains how they are inferior to the RFC 5987
737  encoding used in this specification.
738</t>
739
740<section title="RFC 2047 Encoding" anchor="alternatives.rfc2047">
741<t>
742  RFC 2047 defines an encoding mechanism for
743  header fields, but this encoding is not supposed to be used for
744  header field parameters - see <xref target="RFC2047" x:fmt="of" x:sec="5"/>
745</t>
746<x:blockquote cite="http://tools.ietf.org/html/rfc2047#section-5">
747  <t>
748    An 'encoded-word' MUST NOT appear within a 'quoted-string'.
749  </t>
750  <t>
751    ...
752  </t>
753  <t>
754    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'.
755  </t>
756</x:blockquote>
757<t>
758  In practice, some user agents implement the encoding, some do not
759  (exposing the encoded string to the user), and some get confused by it.
760</t>
761</section>
762
763<section title="Percent Encoding" anchor="alternatives.percent">
764<t>
765  Some user agents accept percent encoded (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>)
766  sequences of characters. The character encoding being used for decoding
767  depends on various factors, including the encoding of the referring page,
768  the user agent's locale, its configuration, and also the actual value of
769  the parameter.
770</t>
771<t>
772  In practice, this is hard to use because those user agents that do not
773  support it will display the escaped character sequence to the user. For those
774  user agents that do implement this it is difficult to predict what character
775  encoding they actually expect.
776</t>
777</section>
778
779<section title="Encoding Sniffing" anchor="alternatives.sniff">
780<t>
781  Some user agents inspect the value (which defaults to ISO-8859-1 for the
782  quoted-string form) and switch to UTF-8 when it seems to be more likely to be
783  the correct interpretation.
784</t>
785<t>
786  As with the approaches above, this is not interoperable and furthermore
787  risks misinterpreting the actual value.
788</t>
789</section>
790
791<section title="Implementations (to be removed by RFC Editor before publication)" anchor="alternatives.implementations">
792<t>
793  Unfortunately, as of March 2011, neither the encoding defined in RFCs 2231
794  and 5987, nor any of the alternate approaches discussed above was
795  implemented interoperably. Thus, this specification recommends the approach
796  defined in RFC 5987, which at least has the advantage of actually being
797  specified properly.
798</t>
799<t>
800  The table below shows the support for the various approaches in the current
801  implementations:
802</t>
803<texttable align="left">
804  <ttcol>User Agent</ttcol>
805  <ttcol>RFC 2231/5987</ttcol>
806  <ttcol>RFC 2047</ttcol>
807  <ttcol>Percent Encoding</ttcol>
808  <ttcol>Encoding Sniffing</ttcol>
809 
810  <c>Chrome</c>
811  <c>yes</c>
812  <c>yes</c>
813  <c>yes</c>
814  <c>yes</c>
815
816  <c>Firefox</c>
817  <c>yes (*)</c>
818  <c>yes</c>
819  <c>no</c>
820  <c>yes</c>
821
822  <c>Internet Explorer</c>
823  <c>yes (**)</c>
824  <c>no</c>
825  <c>yes</c>
826  <c>no</c>
827
828  <c>Konqueror</c>
829  <c>yes</c>
830  <c>no</c>
831  <c>no</c>
832  <c>no</c>
833
834  <c>Opera</c>
835  <c>yes</c>
836  <c>no</c>
837  <c>no</c>
838  <c>no</c>
839
840  <c>Safari</c>
841  <c>no</c>
842  <c>no</c>
843  <c>no</c>
844  <c>yes</c>
845</texttable>
846
847<t>
848  (*) Does not implement the fallback behavior to "filename" described in
849  <xref target="disposition.parameter.filename"/>; a fix is planned for Firefox 5.
850</t>
851<t>
852  (**) Starting with Internet Explorer 9, but only implements UTF-8.
853</t>
854
855</section>
856
857</section>
858
859<section title="Advice on Generating Content-Disposition Header Fields" anchor="advice.generating">
860<t>
861  To successfully interoperate with existing and future user agents, senders of
862  the Content-Disposition header field are advised to:
863</t>
864<t>
865  <list style="symbols">
866    <t>Include a "filename" parameter when US-ASCII (<xref target="US-ASCII"/>) is sufficiently
867    expressive.</t>
868    <t>Use the 'token' form of the filename parameter only when it does not
869    contain disallowed characters (e.g., spaces); in such cases, the
870    quoted-string form should be used.</t>
871    <t>Avoid including the percent character followed by two hexadecimal
872    characters (e.g., %A9) in the filename parameter, since some existing
873    implementations consider it to be an escape character, while others will
874    pass it through unchanged.</t>
875    <t>Avoid including the "\" character in the quoted-string form of the
876    filename parameter, as escaping is not implemented by some user agents,
877    and can be considered as an illegal path character.</t> 
878    <t>Avoid using non-ASCII characters in the filename parameter. Although
879    most existing implementations will decode them as ISO-8859-1, some
880    will apply heuristics to detect UTF-8, and thus might fail on certain names.</t>
881    <t>Include a "filename*" parameter where the desired filename cannot be
882    expressed faithfully using the "filename" form. Note that legacy user
883    agents will not process this, and will fall back to using the "filename"
884    parameter's content.
885    </t>
886    <t>When a "filename*" parameter is sent, to also generate a "filename"
887    parameter as a fallback for user agents that do not support the "filename*"
888    form, if possible. This can be done by substituting characters with
889    US-ASCII sequences (e.g., Unicode character point U+00E4 (LATIN SMALL
890    LETTER A WITH DIARESIS) by "ae"). Note that this may not be possible in
891    some locales.
892    </t>
893    <t>When a "filename" parameter is included as a fallback (as per above),
894    "filename" should occur first, due to parsing problems in some existing
895    implementations.
896    <cref anchor="fallbackbug" source="jre">
897    Firefox is known to pick the wrong parameter; a bug fix is scheduled for
898    Firefox 5.</cref>
899    <cref anchor="NOTE-TO-RFC-EDITOR" source="jre">
900    PLEASE REMOVE THIS AND THE PRECEDING COMMENT BEFORE PUBLICATION AS RFC.</cref>
901    </t>
902    <t>Use UTF-8 as the encoding of the "filename*" parameter, when present,
903    because at least one existing implementation only implements that encoding.</t>
904  </list>
905</t>
906<t>
907  Note that this advice is based upon UA behaviour at the time of writing, and
908  might be superseded. At the time of publication of this document,
909  <eref target="http://purl.org/NET/http/content-disposition-tests"/> provides
910  an overview of current levels of support in various implementations.
911</t>
912</section>
913
914<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
915<t>
916  Note: the issues names in the change log entries for draft-reschke-rfc2183-in-http
917  refer to <eref target="http://greenbytes.de/tech/webdav/draft-reschke-rfc2183-in-http-issues.html"/>.
918</t>
919
920<section title="Since draft-reschke-rfc2183-in-http-00">
921<t> 
922  Adjust terminology ("header" -&gt; "header field").
923  Update rfc2231-in-http reference.
924</t>
925</section>
926
927<section title="Since draft-reschke-rfc2183-in-http-01">
928<t> 
929  Update rfc2231-in-http reference. Actually define the "filename"
930  parameter. Add internationalization considerations.
931  Add examples using the RFC 5987 encoding.
932  Add overview over other approaches, plus a table reporting
933  implementation status.
934  Add and resolve issue "nodep2183".
935  Add issues "asciivsiso",
936  "deplboth", "quoted", and "registry".
937</t>
938</section>
939
940<section title="Since draft-reschke-rfc2183-in-http-02">
941<t>
942  Add and close issue "docfallback".
943  Close issues "asciivsiso", "deplboth", "quoted", and
944  "registry".
945</t>
946</section>
947
948<section title="Since draft-reschke-rfc2183-in-http-03">
949<t>
950  Updated to be a Working Draft of the IETF HTTPbis Working Group.
951</t>
952</section>
953
954<section title="Since draft-ietf-httpbis-content-disp-00" anchor="changes.since.00">
955<t>
956  Closed issues:
957  <list style="symbols">
958    <t>
959      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/242"/>:
960      "handling of unknown disposition types"
961    </t>
962  </list>
963</t>
964<t>
965  Slightly updated the notes about the proposed fallback behavior.
966</t>
967</section>
968
969<section title="Since draft-ietf-httpbis-content-disp-01" anchor="changes.since.01">
970<t>
971  Various editorial improvements.
972</t>
973</section>
974
975<section title="Since draft-ietf-httpbis-content-disp-02" anchor="changes.since.02">
976<t>
977  Closed issues:
978  <list style="symbols">
979    <t>
980      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/244"/>:
981      "state that repeating parameters are invalid"
982    </t>
983    <t>
984      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/245"/>:
985      "warn about %xx in filenames being misinterpreted"
986    </t>
987    <t>
988      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/246"/>:
989      "mention control chars when talking about postprecessing the filename parameter"
990    </t>
991  </list>
992</t>
993<t>
994  Update <xref target="alternatives.implementations"/>; Opera 10.63 RC
995  implements the recommended fallback behavior.
996</t>
997</section>
998
999<section title="Since draft-ietf-httpbis-content-disp-03" anchor="changes.since.03">
1000<t>
1001  Closed issues:
1002  <list style="symbols">
1003    <t>
1004      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/252"/>:
1005      "'modification-date' *is* implemented in Konq 4.5"
1006    </t>
1007    <t>
1008      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/253"/>:
1009      "clarify what LWS means for the Content-Disp grammar"
1010    </t>
1011    <t>
1012      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/258"/>:
1013      "Avoid passive voice in message requirements"
1014    </t>
1015    <t>
1016      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/263"/>:
1017      "text about historical percent-decoding unclear"
1018    </t>
1019    <t>
1020      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/264"/>:
1021      "add explanation of language tagging"
1022    </t>
1023    <t>
1024      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/265"/>:
1025      "Clarify that C-D spec does not apply to multipart upload"
1026    </t>
1027  </list>
1028</t>
1029</section>
1030
1031<section title="Since draft-ietf-httpbis-content-disp-04" anchor="changes.since.04">
1032<t>
1033  Updated implementation information (Chrome 9 implements RFC 5987, IE 9 RC implements
1034  it for UTF-8 only).
1035</t>
1036<t>
1037  Clarify who requirements are on, add a section discussing conformance
1038  and handling of invalid field values in general.
1039</t>
1040<t>
1041  Closed issues:
1042  <list style="symbols">
1043     <t>
1044      <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/243"/>:
1045      "avoid stating ISO-8859-1 default for header param" (the default
1046      is still mentioned, but it was clarified what it applies to).
1047    </t>
1048   <t>
1049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/272"/>:
1050      "Path Separator Characters"
1051    </t>
1052  </list>
1053</t>
1054</section>
1055
1056<section title="Since draft-ietf-httpbis-content-disp-05" anchor="changes.since.05">
1057<t>
1058  Editorial changes:
1059  Fixed two typos where the new Conformance section said "Content-Location" instead
1060  of "Content-Disposition". Cleaned up terminology ("user agent", "recipient",
1061  "sender", "message body", ...). Stated what the escape character for quoted-string
1062  is. Explained a use case for "inline" disposition type. Updated implementation
1063  notes with respect to the fallback behavior.
1064</t>
1065<t>
1066  Added appendix "Advice on Generating Content-Disposition Header Fields".
1067</t>
1068</section>
1069
1070<section title="Since draft-ietf-httpbis-content-disp-06" anchor="changes.since.06">
1071<t>
1072  Closed issues:
1073  <list style="symbols">
1074     <t>
1075      <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/278"/>:
1076      "conformance language"
1077    </t>
1078  </list>
1079</t>
1080</section>
1081
1082<section title="Since draft-ietf-httpbis-content-disp-07" anchor="changes.since.07">
1083<t>
1084  Rephrase the requirement about well-known file system locations, and also
1085  clarify that by "last path segment" we mean the actual filename.
1086  Added a forward reference from "invalid" to the section that defines a valid
1087  header field.
1088</t>
1089</section>
1090
1091<section title="Since draft-ietf-httpbis-content-disp-08" anchor="changes.since.08">
1092<t>
1093  Update: Internet Explorer 9 is released.
1094  Various editorial improvements.
1095  Add US-ASCII reference.
1096  Strengthen file extension handling requirement to MUST for those recipients
1097  that actually use file extensions to map media types.
1098</t>
1099</section>
1100
1101</section>
1102
1103
1104  </back>
1105
1106</rfc>
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