source: draft-ietf-httpbis-content-disp/01/draft-ietf-httpbis-content-disp-01.xml @ 1338

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Prepare publication of draft-ietf-httpbis-content-disp-01

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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../../draft-ietf-httpbis/myxml2rfc.xslt' ?>
7<?rfc toc="yes"?>
8<?rfc symrefs="yes"?>
9<?rfc sortrefs="yes"?>
10<?rfc compact="yes"?>
11<?rfc comments="yes"?>
12<?rfc inline="yes"?>
13<?rfc subcompact="no"?>
14<?rfc rfcedstyle="yes"?>
15<!DOCTYPE rfc
16  PUBLIC "" "rfc2629.dtd">
17<rfc ipr="trust200902" docName="draft-ietf-httpbis-content-disp-01" category="std" updates="2616">
18        <front>
19  <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
20  in the Hypertext Transfer Protocol (HTTP)</title>
21  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
22    <organization abbrev="greenbytes">greenbytes GmbH</organization>
23    <address>
24      <postal>
25        <street>Hafenweg 16</street>
26        <city>Muenster</city><region>NW</region><code>48155</code>
27        <country>Germany</country>
28      </postal>
29      <email>julian.reschke@greenbytes.de</email>       
30      <uri>http://greenbytes.de/tech/webdav/</uri>     
31    </address>
32  </author>
33
34  <date month="September" year="2010" day="16"/>
35  <workgroup>HTTPbis Working Group</workgroup>
36 
37  <abstract>
38    <t>
39      HTTP/1.1 defines the Content-Disposition response header field,
40      but points out that it is not part of the HTTP/1.1 Standard.
41      This specification takes over the definition and registration of
42      Content-Disposition, as used in HTTP, and clarifies internationalization
43      aspects.
44    </t>
45  </abstract>
46 
47  <note title="Editorial Note (To be removed by RFC Editor before publication)">
48    <t>
49      This specification is expected to replace the definition of Content-Disposition
50      in the HTTP/1.1 specification, as currently revised by the IETF HTTPbis
51      working group. See also <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/123"/>.
52    </t>
53    <t>
54      Discussion of this draft should take place on the HTTPBIS working group
55      mailing list (ietf-http-wg@w3.org). The current issues list is
56      at <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/query?component=content-disp"/>
57      and related documents (including fancy diffs) can be found at
58      <eref target="http://tools.ietf.org/wg/httpbis/"/>.
59    </t>
60    <t>
61      The changes in this draft are summarized in <xref target="changes.since.00"/>.
62    </t>
63  </note>
64  </front>
65
66  <middle>
67
68<section title="Introduction" anchor="introduction">
69<t>
70  HTTP/1.1 defines the Content-Disposition response header field in Section 19.5.1 of <xref target="RFC2616"/>,
71  but points out that it is not part of the HTTP/1.1 Standard (Section 15.5):
72</t>
73<t><list>
74  <t>
75    Content-Disposition is not part of the HTTP standard, but since it is
76    widely implemented, we are documenting its use and risks for implementers.
77  </t>
78</list></t>
79<t>
80  This specification takes over the definition and registration of
81  Content-Disposition, as used in HTTP.
82  Based on interoperability testing with existing User Agents,
83  it fully defines a profile of the
84  features defined in the Multipurpose Internet Mail Extensions (MIME) variant (<xref target="RFC2183"/>) of the
85  header field, and also clarifies internationalization
86  aspects.
87</t>
88</section> 
89
90<section title="Notational Conventions">
91<t>
92  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
93  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
94  are to be interpreted as described in <xref target="RFC2119"/>.
95</t>
96<t>
97  This specification uses the augmented BNF notation defined in
98  Section 2.1 of <xref target="RFC2616"/>, including its rules for
99  linear whitespace (LWS).
100</t>
101</section> 
102
103<section title="Header Field Definition" anchor="header.field.definition">
104  <iref item="Headers" subitem="Content-Disposition" primary="true"/>
105  <iref item="Content-Disposition header" primary="true"/>
106<t>
107  The Content-Disposition response header field is used to convey additional
108  information about how to process the response payload, and also can be used
109  to attach additional metadata, such as the filename.
110</t>
111
112<section title="Grammar">
113<figure><artwork type="abnf2616"><![CDATA[
114  content-disposition = "Content-Disposition" ":"
115                         disposition-type *( ";" disposition-parm )
116
117  disposition-type    = "inline" | "attachment" | disp-ext-type
118                      ; case-insensitive
119  disp-ext-type       = token
120
121  disposition-parm    = filename-parm | disp-ext-parm
122
123  filename-parm       = "filename" "=" value
124                      | "filename*" "=" ext-value
125 
126  disp-ext-parm       = token "=" value
127                      | ext-token "=" ext-value
128  ext-token           = <the characters in token, followed by "*">
129]]></artwork></figure>
130
131<figure><preamble>Defined in <xref target="RFC2616"/>:</preamble><artwork type="abnf2616"><![CDATA[
132  token       = <token, defined in [RFC2616], Section 2.2>
133  value       = <value, defined in [RFC2616], Section 3.6>
134]]></artwork></figure>
135<figure><preamble>Defined in <xref target="RFC5987"/>:</preamble><artwork type="abnf2616"><![CDATA[
136  ext-value   = <ext-value, defined in [RFC5987], Section 3.2>
137]]></artwork></figure>
138</section>
139
140<section title="Disposition Type" anchor="disposition.type">
141<t>
142  If the disposition type matches "attachment" (case-insensitively), this indicates that the user agent should not display the response,
143  but directly enter a "save as..." dialog.
144</t>
145<t>
146  On the other hand, if it matches "inline" (case-insensitively), this implies default processing.
147</t>
148<t>
149  Unknown or unhandled disposition types SHOULD be handled the same way as "attachment"
150  (see also <xref target="RFC2183"/>, Section 2.8).
151</t>
152</section>
153
154<section title="Disposition Parameter: 'Filename'" anchor="disposition.parameter.filename">
155<t>
156  The parameters "filename" and "filename*", to be matched case-insensitively,
157  provide information on how to construct a filename for storing the message
158  payload.
159</t>
160<t>
161  Depending on the disposition type, this information might be used right away
162  (in the "save as..." interaction caused for the "attachment" disposition type),
163  or later on (for instance, when the user decides to save the contents of the
164  current page being displayed).
165</t>
166<t>
167  The parameters "filename" and "filename*" differ only in that "filename*" uses
168  the encoding defined in <xref target="RFC5987"/>, allowing the use
169  of characters not present in the ISO-8859-1 character set (<xref target="ISO-8859-1"/>).
170</t>
171<t>
172  Many user agent implementations predating this specification
173  do not understand the "filename*" parameter. Therefore, when both "filename"
174  and "filename*" are present in a single header field value, recipients
175  SHOULD pick "filename*" and ignore "filename". This way, senders
176  can avoid special-casing specific user agents by sending both the
177  more expressive "filename*" parameter, and the "filename" parameter
178  as fallback for legacy recipients (see <xref target="examples"/> for
179  an example).
180</t>
181<t>
182  It is essential that user agents treat the specified filename as advisory
183  only, thus be very careful in extracting the desired information.
184  In particular:
185  <list style="symbols">
186    <t>
187      When the value contains path separator characters, all but the last
188      segment SHOULD be ignored. This prevents unintentional overwriting
189      of well-known file system location (such as "/etc/passwd").
190    </t>
191    <t>
192      Many platforms do not use Internet Media Types (<xref target="RFC2046"/>)
193      to hold type information in the file system, but rely on filename
194      extensions instead. Trusting the server-provided file extension could
195      introduce a privilege escalation when later on the file is opened locally
196      (consider ".exe"). Thus, recipients need to ensure that a file extension
197      is used that is safe, optimally matching the media type of the received
198      payload.
199    </t>
200    <t>
201      Other aspects recipients need to be aware of are names that have a
202      special meaning in the file system or in shell commands, such as "." and "..",
203      "~", "|", and also device names.
204    </t>
205  </list>
206</t>
207</section>
208
209<section title="Disposition Parameter: Extensions" anchor="disposition.parameter.extensions">
210<t>
211  To enable future extensions, unknown parameters SHOULD be ignored (see also <xref target="RFC2183"/>, Section 2.8).
212</t>
213</section>
214
215<section title="Extensibility" anchor="extensibility">
216<t>
217  Note that Section 9 of <xref target="RFC2183"/> defines IANA registries both
218  for disposition types and disposition parameters. This registry is
219  shared by different protocols using Content-Disposition, such as MIME and HTTP.
220  Therefore, not all registered values may make sense in the context of HTTP.
221</t>
222</section>
223
224</section> 
225
226<section title="Examples" anchor="examples">
227
228<figure>
229<preamble>
230Direct UA to show "save as" dialog, with a filename of "example.html": 
231</preamble>
232<artwork type="example"><![CDATA[
233Content-Disposition: Attachment; filename=example.html
234]]></artwork></figure>
235<figure>
236<preamble>
237Direct UA to behave as if the Content-Disposition header field wasn't present,
238but to remember the filename "example.html" for a subsequent save operation:
239</preamble>
240<artwork type="example"><![CDATA[
241  Content-Disposition: INLINE; FILENAME= "example.html"
242  ]]></artwork></figure>
243<figure>
244<preamble>
245Direct UA to show "save as" dialog, with a filename of "an example":
246</preamble>
247<artwork type="example"><![CDATA[
248Content-Disposition: Attachment; Filename*=UTF-8'en'an%20example
249]]></artwork>
250<postamble>Note that this example uses the extended encoding defined in
251<xref target="RFC5987"/> to specify that the natural language of the filename
252is English, and also to encode the space character which is not allowed in the
253token production.
254</postamble>
255</figure>
256<figure>
257<preamble>
258Direct UA to show "save as" dialog, with a filename containing the Unicode character  U+20AC (EURO SIGN):
259</preamble>
260<artwork type="example"><![CDATA[
261  Content-Disposition: attachment;
262                       filename*= UTF-8''%e2%82%ac%20rates
263  ]]></artwork>
264<postamble>
265  Here, the encoding defined in <xref target="RFC5987"/> is also used to encode the
266  non-ISO-8859-1 character.
267</postamble>
268</figure>
269<figure>
270<preamble>
271Same as above, but adding the "filename" parameter for compatibility with
272user agents not implementing RFC 5987:
273</preamble>
274<artwork type="example"><![CDATA[
275  Content-Disposition: attachment;
276                       filename="EURO rates";
277                       filename*=utf-8''%e2%82%ac%20rates
278  ]]></artwork>
279<postamble>
280  Note: as of September 2010, those user agents that do not support the RFC 5987
281  encoding ignore "filename*" when it occurs after "filename". Unfortunately,
282  some user agents that do support RFC 5987 do pick the "filename" rather
283  than the "filename*" parameter when it occurs first; it is expected that
284  this situation is going to improve soon.
285</postamble>
286</figure>
287
288</section>
289
290<section title="Internationalization Considerations" anchor="i18n">
291<t>
292  The "filename*" parameter (<xref target="disposition.parameter.filename"/>),
293  using the encoding defined in <xref target="RFC5987"/>, allows the
294  server to transmit characters outside the ISO-8859-1 character set,
295  and also to optionally specify the language in use.
296</t>
297<t>
298  Future parameters might also require internationalization, in which case
299  the same encoding can be used.
300</t>
301</section>
302
303<section title="Security Considerations" anchor="security.considerations">
304<t>
305  Using server-supplied information for constructing local filenames introduces
306  many risks. These are summarized in <xref target="disposition.parameter.filename"/>.
307</t>
308<t>
309  Furthermore, implementers also ought to be aware of the Security
310  Considerations applying to HTTP (see Section 15 of <xref target="RFC2616"/>), and also the parameter encoding defined in <xref target="RFC5987"/>
311  (see Section 5).
312</t>
313</section> 
314
315<section title="IANA Considerations" anchor="iana.considerations">
316
317<section title="Registry for Disposition Values and Parameter" anchor="registry">
318<t>
319  This specification does not introduce any changes to the registration
320  procedures for disposition values and parameters that are defined in
321  Section 9 of <xref target="RFC2183"/>.
322</t>
323</section>
324
325<section title="Header Field Registration" anchor="header.field.registration"> 
326<t>
327  This document updates the definition of the Content-Disposition HTTP header field
328  in the permanent HTTP header field registry (see <xref target="RFC3864"/>).
329</t>
330<t>
331<list style="hanging">
332  <t hangText="Header field name:">Content-Disposition</t>
333  <t hangText="Applicable protocol:">http</t>
334  <t hangText="Status:">standard</t>
335  <t hangText="Author/Change controller:">IETF</t>
336  <t hangText="Specification document:">this specification (<xref target="header.field.definition"/>)</t>
337</list>
338</t>
339</section>
340
341</section> 
342
343<section title="Acknowledgements">
344<t>
345  Thanks to Rolf Eike Beer, Bjoern Hoehrmann, Alfred Hoenes, Roar Lauritzsen,
346  and Henrik Nordstrom for their valuable feedback.
347</t>
348</section> 
349
350  </middle>
351  <back>
352 
353<references title="Normative References">
354 
355  <reference anchor="RFC2119">
356    <front>
357      <title abbrev="RFC Key Words">Key words for use in RFCs to Indicate Requirement Levels</title>
358      <author initials="S." surname="Bradner" fullname="Scott Bradner">
359        <organization>Harvard University</organization>
360        <address><email>sob@harvard.edu</email></address>
361      </author>
362      <date month="March" year="1997"/>
363      <area>General</area>
364      <keyword>keyword</keyword>
365    </front>
366    <seriesInfo name="BCP" value="14"/>
367    <seriesInfo name="RFC" value="2119"/>
368  </reference>
369
370  <reference anchor="RFC2616">
371    <front>
372      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
373      <author initials="R." surname="Fielding" fullname="R. Fielding">
374        <organization>University of California, Irvine</organization>
375        <address><email>fielding@ics.uci.edu</email></address>
376      </author>
377      <author initials="J." surname="Gettys" fullname="J. Gettys">
378        <organization>W3C</organization>
379        <address><email>jg@w3.org</email></address>
380      </author>
381      <author initials="J." surname="Mogul" fullname="J. Mogul">
382        <organization>Compaq Computer Corporation</organization>
383        <address><email>mogul@wrl.dec.com</email></address>
384      </author>
385      <author initials="H." surname="Frystyk" fullname="H. Frystyk">
386        <organization>MIT Laboratory for Computer Science</organization>
387        <address><email>frystyk@w3.org</email></address>
388      </author>
389      <author initials="L." surname="Masinter" fullname="L. Masinter">
390        <organization>Xerox Corporation</organization>
391        <address><email>masinter@parc.xerox.com</email></address>
392      </author>
393      <author initials="P." surname="Leach" fullname="P. Leach">
394        <organization>Microsoft Corporation</organization>
395        <address><email>paulle@microsoft.com</email></address>
396      </author>
397      <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
398        <organization>W3C</organization>
399        <address><email>timbl@w3.org</email></address>
400      </author>
401      <date month="June" year="1999"/>
402    </front>
403    <seriesInfo name="RFC" value="2616"/>
404  </reference>
405
406  <reference anchor="RFC5987">
407        <front>
408      <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
409      <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
410        <organization abbrev="greenbytes">greenbytes GmbH</organization>
411        <address>
412          <postal>
413            <street>Hafenweg 16</street>
414            <city>Muenster</city><region>NW</region><code>48155</code>
415            <country>Germany</country>
416          </postal>
417          <email>julian.reschke@greenbytes.de</email>   
418          <uri>http://greenbytes.de/tech/webdav/</uri> 
419        </address>
420      </author>
421      <date month="August" year="2010"/>
422    </front>
423    <seriesInfo name="RFC" value="5987"/>
424  </reference>
425
426  <reference anchor="ISO-8859-1">
427    <front>
428      <title>Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1</title>
429      <author>
430        <organization>International Organization for Standardization</organization>
431      </author>
432      <date year="1998"/>
433    </front>
434    <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
435  </reference>
436
437</references>
438 
439<references title="Informative References">
440
441  <reference anchor="RFC2046">
442    <front>
443      <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
444      <author initials="N." surname="Freed" fullname="Ned Freed">
445        <organization>Innosoft International, Inc.</organization>
446        <address><email>ned@innosoft.com</email></address>
447      </author>
448      <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
449        <organization>First Virtual Holdings</organization>
450        <address><email>nsb@nsb.fv.com</email></address>
451      </author>
452      <date month="November" year="1996"/>
453    </front>
454    <seriesInfo name="RFC" value="2046"/>
455  </reference>
456
457  <reference anchor="RFC2047">
458    <front>
459      <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
460      <author initials="K." surname="Moore" fullname="Keith Moore">
461        <organization>University of Tennessee</organization>
462        <address><email>moore@cs.utk.edu</email></address>
463      </author>
464      <date month="November" year="1996"/>
465    </front>
466    <seriesInfo name="RFC" value="2047"/>
467  </reference>
468
469  <reference anchor="RFC2183">
470    <front>
471      <title abbrev="Content-Disposition">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</title>
472      <author initials="R." surname="Troost" fullname="Rens Troost">
473        <organization>New Century Systems</organization>
474        <address><email>rens@century.com</email></address>
475      </author>
476      <author initials="S." surname="Dorner" fullname="Steve Dorner">
477        <organization>QUALCOMM Incorporated</organization>
478        <address><email>sdorner@qualcomm.com</email></address>
479      </author>
480      <author initials="K." surname="Moore" fullname="Keith Moore">
481        <organization>Department of Computer Science</organization>
482        <address><email>moore@cs.utk.edu</email></address>
483      </author>
484      <date year="1997" month="August"/>
485    </front>
486    <seriesInfo name="RFC" value="2183"/>
487  </reference>
488
489  <reference anchor="RFC2231">
490    <front>
491      <title abbrev="MIME Value and Encoded Word Extensions">MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations</title>
492      <author initials="N." surname="Freed" fullname="Ned Freed">
493        <organization abbrev="Innosoft">Innosoft International, Inc.</organization>
494        <address><email>ned.freed@innosoft.com</email></address>
495      </author>
496      <author initials="K." surname="Moore" fullname="Keith Moore">
497        <organization>University of Tennessee</organization>
498        <address><email>moore@cs.utk.edu</email></address>
499      </author>
500      <date year="1997" month="November"/>
501    </front>
502    <seriesInfo name="RFC" value="2231"/>
503  </reference>
504
505  <reference anchor="RFC3629">
506    <front>
507      <title>UTF-8, a transformation format of ISO 10646</title>
508      <author initials="F." surname="Yergeau" fullname="F. Yergeau">
509        <organization>Alis Technologies</organization>
510        <address><email>fyergeau@alis.com</email></address>
511      </author>
512      <date month="November" year="2003"/>
513    </front>
514    <seriesInfo name="STD" value="63"/>
515    <seriesInfo name="RFC" value="3629"/>
516  </reference>
517
518  <reference anchor="RFC3864">
519    <front>
520      <title>Registration Procedures for Message Header Fields</title>
521      <author initials="G." surname="Klyne" fullname="G. Klyne">
522        <organization>Nine by Nine</organization>
523        <address><email>GK-IETF@ninebynine.org</email></address>
524      </author>
525      <author initials="M." surname="Nottingham" fullname="M. Nottingham">
526        <organization>BEA Systems</organization>
527        <address><email>mnot@pobox.com</email></address>
528      </author>
529      <author initials="J." surname="Mogul" fullname="J. Mogul">
530        <organization>HP Labs</organization>
531        <address><email>JeffMogul@acm.org</email></address>
532      </author>
533      <date year="2004" month="September"/>
534    </front>
535    <seriesInfo name="BCP" value="90"/>
536    <seriesInfo name="RFC" value="3864"/>
537  </reference>
538
539  <reference anchor="RFC3986">
540   <front>
541    <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
542    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
543      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
544      <address>
545         <email>timbl@w3.org</email>
546         <uri>http://www.w3.org/People/Berners-Lee/</uri>
547      </address>
548    </author>
549    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
550      <organization abbrev="Day Software">Day Software</organization>
551      <address>
552        <email>fielding@gbiv.com</email>
553        <uri>http://roy.gbiv.com/</uri>
554      </address>
555    </author>
556    <author initials="L." surname="Masinter" fullname="Larry Masinter">
557      <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
558      <address>
559        <email>LMM@acm.org</email>
560        <uri>http://larry.masinter.net/</uri>
561      </address>
562    </author>
563    <date month="January" year="2005"/>
564   </front>
565   <seriesInfo name="STD" value="66"/>
566   <seriesInfo name="RFC" value="3986"/>
567  </reference>
568
569</references>
570
571<section title="Changes from the RFC 2616 Definition" anchor="changes.from.rfc2616">
572<t>
573  Compared to Section 19.5.1 of <xref target="RFC2616"/>, the following
574  normative changes reflecting actual implementations have been made:
575<list style="symbols">
576  <t>
577    According to RFC 2616, the disposition type "attachment" only applies to
578    content of type "application/octet-stream". This restriction has been
579    removed, because user agents in practice do not check the content type, and
580    it also discourages properly declaring the media type.
581  </t>
582  <t>
583    RFC 2616 only allows "quoted-string" for the filename parameter. This
584    would be an exceptional parameter syntax, and also doesn't reflect actual
585    use.
586  </t>
587  <t>
588    The definition for the disposition type "inline" (<xref target="RFC2183"/>, Section 2.1)
589    has been re-added with a suggestion for its processing.
590  </t>
591  <t>
592    This specification requires support for the extended parameter encoding
593    defined in <xref target="RFC5987"/>.
594  </t>
595</list>
596</t>
597</section>
598
599<section title="Differences compared to RFC 2183" anchor="diffs.compared.to.rfc2183">
600<t>
601  Section 2 of <xref target="RFC2183"/> defines several additional
602  disposition parameters: "creation-date", "modification-date",
603  "quoted-date-time", and "size". These do not appear to be implemented by
604  any user agent, thus have been omitted from this specification.
605</t>
606</section>
607
608<section title="Alternative Approaches to Internationalization" anchor="alternatives">
609<t>
610  By default, HTTP header field parameters cannot carry characters outside
611  the ISO-8859-1 (<xref target="ISO-8859-1"/>) character encoding (see
612  <xref target="RFC2616"/>, Section 2.2). For the "filename"
613  parameter, this of course is an unacceptable restriction.
614</t>
615<t>
616  Unfortunately, user agent implementers have not managed to come up with
617  an interoperable approach, although the IETF Standards Track specifies
618  exactly one solution (<xref target="RFC2231"/>, clarified and profiled for
619  HTTP in <xref target="RFC5987"/>).
620</t>
621<t>
622  For completeness, the sections below describe the various approaches that
623  have been tried, and explains how they are inferior to the RFC 5987
624  encoding used in this specification.
625</t>
626
627<section title="RFC 2047 Encoding" anchor="alternatives.rfc2047">
628<t>
629  RFC 2047 defines an encoding mechanism for
630  header fields, but this encoding is not supposed to be used for
631  header field parameters - see Section 5 of <xref target="RFC2047"/>: 
632</t>
633<t><list>
634  <t>
635    An 'encoded-word' MUST NOT appear within a 'quoted-string'.
636  </t>
637  <t>
638    ...
639  </t>
640  <t>
641    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'.
642  </t>
643</list></t>
644<t>
645  In practice, some user agents implement the encoding, some do not
646  (exposing the encoded string to the user), and some get confused by it.
647</t>
648</section>
649
650<section title="Percent Encoding" anchor="alternatives.percent">
651<t>
652  Some user agents accept percent encoded (<xref target="RFC3986"/>, Section 2.1)
653  sequences of characters encoded using the UTF-8 (<xref target="RFC3629"/>) character encoding.
654</t>
655<t>
656  In practice, this is hard to use because those user agents
657  that do not support it will display the escaped character sequence to the user.
658</t>
659<t>
660  Furthermore, the first user agent to implement this did choose the encoding
661  based on local settings; thus making it very hard to use in multi-lingual
662  environments.
663</t>
664</section>
665
666<section title="Encoding Sniffing" anchor="alternatives.sniff">
667<t>
668  Some user agents inspect the value (which defaults to ISO-8859-1) and
669  switch to UTF-8 when it seems to be more likely to be the correct
670  interpretation.
671</t>
672<t>
673  As with the approaches above, this is not interoperable and furthermore
674  risks misinterpreting the actual value.
675</t>
676</section>
677
678<section title="Implementations (to be removed by RFC Editor before publication)" anchor="alternatives.implementations">
679<t>
680  Unfortunately, as of September 2010, neither the encoding defined in RFCs 2231
681  and 5987, nor any of the alternate approaches discussed above was
682  implemented interoperably. Thus, this specification recommends the approach
683  defined in RFC 5987, which at least has the advantage of actually being
684  specified properly.
685</t>
686<t>
687  The table below shows the implementation support for the various approaches:
688</t>
689<texttable align="left">
690  <ttcol>User Agent</ttcol>
691  <ttcol>RFC 2231/5987</ttcol>
692  <ttcol>RFC 2047</ttcol>
693  <ttcol>Percent Encoding</ttcol>
694  <ttcol>Encoding Sniffing</ttcol>
695 
696  <c>Chrome</c>
697  <c>no</c>
698  <c>yes</c>
699  <c>yes</c>
700  <c>yes</c>
701
702  <c>Firefox</c>
703  <c>yes (*)</c>
704  <c>yes</c>
705  <c>no</c>
706  <c>yes</c>
707
708  <c>Internet Explorer</c>
709  <c>no</c>
710  <c>no</c>
711  <c>yes</c>
712  <c>no</c>
713
714  <c>Konqueror</c>
715  <c>yes</c>
716  <c>no</c>
717  <c>no</c>
718  <c>no</c>
719
720  <c>Opera</c>
721  <c>yes (*)</c>
722  <c>no</c>
723  <c>no</c>
724  <c>no</c>
725
726  <c>Safari</c>
727  <c>no</c>
728  <c>no</c>
729  <c>no</c>
730  <c>yes</c>
731 
732  <postamble>
733  (*) Does not implement the fallback behavior to "filename" described in
734  <xref target="disposition.parameter.filename"/>.
735  </postamble>
736
737</texttable>
738
739</section>
740
741</section>
742
743
744<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
745<section title="Since draft-reschke-rfc2183-in-http-00">
746<t> 
747  Adjust terminology ("header" -&gt; "header field").
748  Update rfc2231-in-http reference.
749</t>
750</section>
751
752
753<section title="Since draft-reschke-rfc2183-in-http-01">
754<t> 
755  Update rfc2231-in-http reference. Actually define the "filename"
756  parameter. Add internationalization considerations.
757  Add examples using the RFC 5987 encoding.
758  Add overview over other approaches, plus a table reporting
759  implementation status.
760  Add and resolve issue "nodep2183".
761  Add issues "asciivsiso",
762  "deplboth", "quoted", and "registry".
763</t>
764</section>
765
766<section title="Since draft-reschke-rfc2183-in-http-02">
767<t>
768  Add and close issue "docfallback".
769  Close issues "asciivsiso", "deplboth", "quoted", and
770  "registry".
771</t>
772</section>
773
774<section title="Since draft-reschke-rfc2183-in-http-03">
775<t>
776  Updated to be a Working Draft of the IETF HTTPbis Working Group.
777</t>
778</section>
779
780<section title="Since draft-ietf-httpbis-content-disp-00" anchor="changes.since.00">
781<t>
782  Closed issues:
783  <list style="symbols">
784    <t>
785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/242"/>:
786      "handling of unknown disposition types"
787    </t>
788  </list>
789</t>
790<t>
791  Slightly updated the notes about the proposed fallback behavior.
792</t>
793</section>
794</section>
795
796
797  </back>
798
799</rfc>
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