One document matched: draft-reschke-rfc2231-in-http-11.xml
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<rfc ipr="trust200902" docName="draft-reschke-rfc2231-in-http-11" category="std">
<front>
<title abbrev="RFC2231 Encoding in HTTP">Application of RFC 2231
Encoding to Hypertext Transfer Protocol (HTTP) Header Fields</title>
<author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
<organization abbrev="greenbytes">greenbytes GmbH</organization>
<address>
<postal>
<street>Hafenweg 16</street>
<city>Muenster</city><region>NW</region><code>48155</code>
<country>Germany</country>
</postal>
<email>julian.reschke@greenbytes.de</email>
<uri>http://greenbytes.de/tech/webdav/</uri>
</address>
</author>
<date month="March" year="2010"/>
<abstract>
<t>
By default, message header field parameters in Hypertext Transfer Protocol (HTTP) messages
can not carry characters outside the ISO-8859-1 character set. RFC 2231
defines an escaping mechanism for use in Multipurpose Internet Mail Extensions
(MIME) headers. This document specifies a profile of that encoding
suitable for use in HTTP header fields.
</t>
</abstract>
<note title="Editorial Note (To be removed by RFC Editor before publication)">
<t>
There are multiple HTTP header fields that already use RFC 2231 encoding
in practice (Content-Disposition) or might use it in the future
(Link). The purpose of this document is to provide a single place where
the generic aspects of RFC 2231 encoding in HTTP header fields are defined.
</t>
<t>
Distribution of this document is unlimited. Although this is not a work
item of the HTTPbis Working Group, comments should be sent to the
Hypertext Transfer Protocol (HTTP) mailing list at <eref target="mailto:ietf-http-wg@w3.org">ietf-http-wg@w3.org</eref>,
which may be joined by sending a message with subject
"subscribe" to <eref target="mailto:ietf-http-wg-request@w3.org?subject=subscribe">ietf-http-wg-request@w3.org</eref>.
</t>
<t>
Discussions of the HTTPbis Working Group are archived at
<eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
</t>
<t>
XML versions, latest edits and the issues list for this document
are available from <eref target="http://greenbytes.de/tech/webdav/#draft-reschke-rfc2231-in-http"/>.
A collection of test cases is available at <eref target="http://greenbytes.de/tech/tc2231/"/>.
</t>
<t><list>
<t>
Note: as of February 2010, there were at least three independent
implementations of the encoding defined in <xref target="character.set.and.language.information"/>:
Konqueror (starting with 4.4.1), Mozilla Firefox, and Opera.
</t>
</list></t>
</note>
</front>
<middle>
<section title="Introduction" anchor="introduction">
<t>
By default, message header field parameters in HTTP (<xref target="RFC2616"/>) messages
can not carry characters outside the ISO-8859-1 character set (<xref target="ISO-8859-1"/>). RFC 2231
(Appendix of <xref target="RFC2231"/>) defines an escaping mechanism for use in MIME headers.
This document specifies a profile of that encoding for use in HTTP header fields.
</t>
<t><list>
<t>
Note: this profile does not apply to message payloads
transmitted over HTTP, such as when using the media type "multipart/form-data"
(<xref target="RFC2388"/>).
</t>
</list></t>
</section>
<section title="Notational Conventions">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
are to be interpreted as described in <xref target="RFC2119"/>.
</t>
<t>
This specification uses the ABNF (Augmented Backus-Naur Form) notation defined in
<xref target="RFC5234"/>. The following core rules are included by
reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
ALPHA (letters), DIGIT (decimal 0-9), HEXDIG (hexadecimal 0-9/A-F/a-f) and
LWSP (linear white space).
</t>
<t>
Note that this specification uses the term "character set" for consistency
with other IETF specifications such as RFC 2277 (see <xref target="RFC2277"/>, Section 3). A more accurate term would be "character
encoding" (a mapping of code points to octet sequences).
</t>
</section>
<section title="A Profile of RFC 2231 for Use in HTTP">
<t>
RFC 2231 defines several extensions to MIME. The sections below discuss
if and how they apply to HTTP.
</t>
<t>
In short:
<list style="symbols">
<t>Parameter Continuations aren't needed (<xref target="parameter.continuations"/>),</t>
<t>Character Set and Language Information are useful, therefore a simple subset
is specified (<xref target="character.set.and.language.information"/>), and</t>
<t>Language Specifications in Encoded Words aren't needed (<xref target="language.specification.in.encoded.words"/>).</t>
</list>
</t>
<section title="Parameter Continuations" anchor="parameter.continuations">
<t>
Section 3 of <xref target="RFC2231"/> defines a mechanism that
deals with the length limitations that apply to MIME headers. These
limitations do not apply to HTTP (<xref target="RFC2616"/>, Section 19.4.7).
</t>
<t>
Thus in HTTP, senders MUST NOT use parameter continuations, and
therefore recipients do not need to support them.
</t>
</section>
<section title="Parameter Value Character Set and Language Information" anchor="character.set.and.language.information">
<t>
Section 4 of <xref target="RFC2231"/> specifies how to embed
language information into parameter values, and also how to encode
non-ASCII characters, dealing with restrictions both in MIME and HTTP
header parameters.
</t>
<t>
However, RFC 2231 does not specify a mandatory-to-implement character set,
making it hard for senders to decide which character set to use.
Thus, recipients implementing this specification MUST support the
character sets "ISO-8859-1" <xref target="ISO-8859-1"/> and "UTF-8"
<xref target="RFC3629"/>.
</t>
<t>
Furthermore, RFC 2231 allows leaving out the character set information.
The profile defined by this specification does not allow that.
</t>
<t>
The syntax for parameters is defined in Section 3.6 of <xref target="RFC2616"/>
(with RFC 2616 implied LWS translated to RFC 5234 LWSP):
</t>
<figure><artwork type="inline"><![CDATA[
parameter = attribute LWSP "=" LWSP value
]]></artwork></figure>
<figure><artwork type="abnf"><![CDATA[ attribute = token
value = token / quoted-string
quoted-string = <quoted-string, defined in [RFC2616], Section 2.2>
token = <token, defined in [RFC2616], Section 2.2>
]]></artwork></figure>
<t anchor="bnf">
This specification modifies the grammar to:
</t>
<figure><artwork type="abnf"><![CDATA[
parameter = reg-parameter / ext-parameter
reg-parameter = parmname LWSP "=" LWSP value
ext-parameter = parmname "*" LWSP "=" LWSP ext-value
parmname = 1*attr-char
ext-value = charset "'" [ language ] "'" value-chars
; extended-initial-value,
; defined in [RFC2231], Section 7
charset = "UTF-8" / "ISO-8859-1" / mime-charset
mime-charset = 1*mime-charsetc
mime-charsetc = ALPHA / DIGIT
/ "!" / "#" / "$" / "%" / "&"
/ "+" / "-" / "^" / "_" / "`"
/ "{" / "}" / "~"
; as <mime-charset> in Section 2.3 of [RFC2978]
; except that the single quote is not included
; SHOULD be registered in the IANA charset registry
language = <Language-Tag, defined in [RFC5646], Section 2.1>
value-chars = *( pct-encoded / attr-char )
pct-encoded = "%" HEXDIG HEXDIG
; see [RFC3986], Section 2.1
attr-char = ALPHA / DIGIT
/ "!" / "#" / "$" / "&" / "+" / "-" / "."
/ "^" / "_" / "`" / "|" / "~"
; token except ( "*" / "'" / "%" )
]]></artwork></figure>
<t>
Thus, a parameter is either regular parameter (reg-parameter), as previously
defined in Section 3.6 of <xref target="RFC2616"/>, or an extended
parameter (ext-parameter).
</t>
<t>
Extended parameters are those where the left hand side of the assignment
ends with an asterisk character.
</t>
<t>
The value part of an extended parameter (ext-value) is a token that consists
of three parts: the REQUIRED character set name (charset), the OPTIONAL
language information (language), and a character sequence representing the
actual value (value-chars), separated by single quote
characters. Note that both character set names and
language tags are restricted to the US-ASCII character set, and are matched
case-insensitively (see <xref target="RFC2978"/>, Section 2.3 and
<xref target="RFC5646"/>, Section 2.1.1).
</t>
<t>
Inside the value part, characters not contained in attr-char are
encoded into an octet sequence using the specified character set. That octet
sequence then is percent-encoded as specified in Section 2.1 of <xref target="RFC3986"/>.
</t>
<t>
Producers MUST NOT use character sets other than "UTF-8" (<xref target="RFC3629"/>)
or "ISO-8859-1" (<xref target="ISO-8859-1"/>).
Extension character sets (ext-charset) are reserved for future use.
</t>
<t><list>
<t>
Note: recipients should be prepared to handle encoding
errors, such as malformed or incomplete percent escape sequences, or
non-decodable octet sequences, in a robust manner. This specification
does not mandate any specific behavior, for instance the following
strategies are all acceptable:
<list style="symbols">
<t>ignoring the parameter,</t>
<t>stripping a non-decodable octet sequence,</t>
<t>substituting a non-decodable octet sequence by a replacement
character, such as the Unicode character U+FFFD (Replacement Character).</t>
</list>
</t>
</list></t>
<t><list>
<t>
Note: the RFC 2616 token production (<xref target="RFC2616"/>, Section 2.2)
differs from the production used in RFC 2231 (imported from Section 5.1 of <xref target="RFC2045"/>)
in that curly braces ("{" and "}") are excluded. Thus, these two
characters are excluded from the attr-char production as well.
</t>
</list></t>
<t><list>
<t>
Note: the <mime-charset> ABNF defined here differs from
the one in Section 2.3 of <xref target="RFC2978"/> in that it does
not allow the single quote character (see also <eref target="http://www.rfc-editor.org/errata_search.php?eid=1912">RFC Editor Errata ID 1912</eref>). In practice, no character set names
using that character have been registered at the time of this writing.
</t>
</list></t>
<section title="Examples" anchor="examples">
<figure>
<preamble>
Non-extended notation, using "token":
</preamble>
<artwork type="example"><![CDATA[
foo: bar; title=Economy
]]></artwork></figure>
<figure>
<preamble>
Non-extended notation, using "quoted-string":
</preamble>
<artwork type="example"><![CDATA[
foo: bar; title="US-$ rates"
]]></artwork></figure>
<figure>
<preamble>
Extended notation, using the unicode character U+00A3 (POUND SIGN):
</preamble>
<artwork type="example"><![CDATA[
foo: bar; title*=iso-8859-1'en'%A3%20rates
]]></artwork>
<postamble>
Note: the Unicode pound sign character U+00A3 was encoded using
ISO-8859-1 into the single octet A3, then percent-encoded. Also note
that the space character was encoded as %20, as it is not contained in
attr-char.
</postamble>
</figure>
<figure>
<preamble>
Extended notation, using the unicode characters U+00A3 (POUND SIGN)
and U+20AC (EURO SIGN):
</preamble>
<artwork type="example"><![CDATA[
foo: bar; title*=UTF-8''%c2%a3%20and%20%e2%82%ac%20rates
]]></artwork>
<postamble>
Note: the unicode pound sign character U+00A3 was encoded using
UTF-8 into the octet sequence C2 A3, then percent-encoded. Likewise,
the unicode euro sign character U+20AC was encoded into the octet
sequence E2 82 AC, then percent-encoded. Also note that HEXDIG allows
both lower-case and upper-case character, so recipients must understand
both, and that the language information is optional, while the character
set is not.
</postamble>
</figure>
</section>
</section>
<section title="Language specification in Encoded Words" anchor="language.specification.in.encoded.words">
<t>
Section 5 of <xref target="RFC2231"/> extends the encoding
defined in <xref target="RFC2047"/> to also support language specification
in encoded words. Although the HTTP/1.1 specification does refer to RFC 2047
(<xref target="RFC2616"/>, Section 2.2),
it's not clear to which header field exactly it applies, and whether it is
implemented in practice (see <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>
for details).
</t>
<t>
Thus, the RFC 2231 profile defined by this specification does not include
this feature.
</t>
</section>
</section>
<section title="Guidelines for Usage in HTTP Header Field Definitions" anchor="usage.guidelines">
<t>
Specifications of HTTP header fields that use the extensions defined
in <xref target="character.set.and.language.information"/> should clearly
state that. A simple way to achieve this is to normatively reference
this specification, and to include the <xref target="bnf" format="none">ext-value</xref>
production into the ABNF for that header field.
</t>
<figure><preamble>For instance:</preamble><artwork type="example"><![CDATA[
foo-header = "foo" LWSP ":" LWSP token ";" LWSP title-param
title-param = "title" LWSP "=" LWSP value
/ "title*" LWSP "=" LWSP ext-value
ext-value = <see RFCxxxx, Section 3.2>
]]></artwork></figure>
<t>
<cref anchor="rfcno">Note to RFC Editor: in the figure above, please replace "xxxx" by the
RFC number assigned to this specification.</cref>
</t>
<t><list>
<t>
Note: The Parameter Value Continuation feature defined in
Section 3 of <xref target="RFC2231"/> makes it impossible to
have multiple instances of extended parameters with identical parmname components,
as the processing of continuations would become ambiguous. Thus, specifications
using this extension are recommended to disallow this case for compatibility
with RFC 2231.
</t>
</list></t>
<section title="When to Use the Extension">
<t>
Section 4.2 of <xref target="RFC2277"/> requires that protocol
elements containing text are able to carry language information. Thus, the <xref target="bnf" format="none">ext-value</xref>
production should always be used when the parameter value is of textual
nature and its language is known.
</t>
<t>
Furthermore, the extension should also be used whenever the parameter value
needs to carry characters not present in the US-ASCII (<xref target="USASCII"/>)
character set (note that it would be unacceptable to define a new parameter that
would be restricted to a subset of the Unicode character set).
</t>
</section>
<section title="Error Handling">
<t>
Header field specifications need to define whether multiple
instances of parameters with identical parmname components are allowed, and
how they should processed. It is recommended that a parameter using the
extended syntax takes precedence. This could be used by producers to use both
formats without breaking recipients that do not understand the extended syntax
yet.
</t>
<figure><preamble>Example:</preamble>
<artwork type="example"><![CDATA[
foo: bar; title="EURO exchange rates";
title*=utf-8''%e2%82%ac%20exchange%20rates
]]></artwork>
<postamble>In this case, the sender provides an ASCII version of the title
for legacy recipients, but also includes an internationalized version for
recipients understanding this specification -- the latter obviously
should prefer the new syntax over the old one.</postamble>
</figure>
<t><list>
<t>
Note: at the time of this writing, many implementations failed
to ignore the form they do not understand, or prioritize the ASCII form
although the extended syntax was present.
</t>
</list></t>
</section>
</section>
<section title="Security Considerations" anchor="security.considerations">
<t>
The format described in this document makes it possible to transport
non-ASCII characters, and thus enables character "spoofing" scenarios,
in which a displayed value appears to be something other than it is.
</t>
<t>
Furthermore, there are known attack scenarios relating to decoding UTF-8.
</t>
<t>
See Section 10 of <xref target="RFC3629"/> for more information on
both topics.
</t>
<t>
In addition, the extension specified in this document makes it possible
to transport multiple language variants for a single parameter, and such use might allow spoofing attacks, where
different language versions of the same parameter are not equivalent.
Whether this attack is useful as an attack depends on the parameter
specified.
</t>
</section>
<section title="IANA Considerations" anchor="iana.considerations">
<t>
There are no IANA Considerations related to this specification.
</t>
</section>
<section title="Acknowledgements">
<t>
Thanks to Martin Duerst and Frank Ellermann for help figuring out ABNF details,
to Graham Klyne and Alexey Melnikov for general review,
Chris Newman for pointing out an RFC 2231 incompatibility, and to
Benjamin Carlyle and Roar Lauritzsen for implementer's feedback.
</t>
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor="RFC2119">
<front>
<title abbrev="RFC Key Words">Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials="S." surname="Bradner" fullname="Scott Bradner">
<organization>Harvard University</organization>
<address><email>sob@harvard.edu</email></address>
</author>
<date month="March" year="1997"/>
</front>
<seriesInfo name="BCP" value="14"/>
<seriesInfo name="RFC" value="2119"/>
</reference>
<reference anchor="RFC2616">
<front>
<title>Hypertext Transfer Protocol -- HTTP/1.1</title>
<author initials="R." surname="Fielding" fullname="R. Fielding">
<organization>University of California, Irvine</organization>
<address><email>fielding@ics.uci.edu</email></address>
</author>
<author initials="J." surname="Gettys" fullname="J. Gettys">
<organization>W3C</organization>
<address><email>jg@w3.org</email></address>
</author>
<author initials="J." surname="Mogul" fullname="J. Mogul">
<organization>Compaq Computer Corporation</organization>
<address><email>mogul@wrl.dec.com</email></address>
</author>
<author initials="H." surname="Frystyk" fullname="H. Frystyk">
<organization>MIT Laboratory for Computer Science</organization>
<address><email>frystyk@w3.org</email></address>
</author>
<author initials="L." surname="Masinter" fullname="L. Masinter">
<organization>Xerox Corporation</organization>
<address><email>masinter@parc.xerox.com</email></address>
</author>
<author initials="P." surname="Leach" fullname="P. Leach">
<organization>Microsoft Corporation</organization>
<address><email>paulle@microsoft.com</email></address>
</author>
<author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
<organization>W3C</organization>
<address><email>timbl@w3.org</email></address>
</author>
<date month="June" year="1999"/>
</front>
<seriesInfo name="RFC" value="2616"/>
</reference>
<reference anchor="RFC2978">
<front>
<title>IANA Charset Registration Procedures</title>
<author initials="N." surname="Freed" fullname="N. Freed"/>
<author initials="J." surname="Postel" fullname="J. Postel"/>
<date year="2000" month="October"/>
</front>
<seriesInfo name="BCP" value="19"/>
<seriesInfo name="RFC" value="2978"/>
</reference>
<reference anchor="RFC3629">
<front>
<title>UTF-8, a transformation format of ISO 10646</title>
<author initials="F." surname="Yergeau" fullname="F. Yergeau">
<organization>Alis Technologies</organization>
<address><email>fyergeau@alis.com</email></address>
</author>
<date month="November" year="2003"/>
</front>
<seriesInfo name="RFC" value="3629"/>
<seriesInfo name="STD" value="63"/>
</reference>
<reference anchor="RFC3986">
<front>
<title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
<organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
<address>
<email>timbl@w3.org</email>
<uri>http://www.w3.org/People/Berners-Lee/</uri>
</address>
</author>
<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
<organization abbrev="Day Software">Day Software</organization>
<address>
<email>fielding@gbiv.com</email>
<uri>http://roy.gbiv.com/</uri>
</address>
</author>
<author initials="L." surname="Masinter" fullname="Larry Masinter">
<organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
<address>
<email>LMM@acm.org</email>
<uri>http://larry.masinter.net/</uri>
</address>
</author>
<date month="January" year="2005"/>
</front>
<seriesInfo name="RFC" value="3986"/>
<seriesInfo name="STD" value="66"/>
</reference>
<reference anchor="RFC5646">
<front>
<title>Tags for Identifying Languages</title>
<author initials="A." surname="Phillips" fullname="Addison Phillips" role="editor">
<organization>Lab126</organization>
<address><email>addison@inter-locale.com</email></address>
</author>
<author initials="M." surname="Davis" fullname="Mark Davis" role="editor">
<organization>Google</organization>
<address><email>mark.davis@google.com</email></address>
</author>
<date month="September" year="2009"/>
</front>
<seriesInfo name="BCP" value="47"/>
<seriesInfo name="RFC" value="5646"/>
</reference>
<reference anchor="RFC5234">
<front>
<title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
<author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
<organization>Brandenburg InternetWorking</organization>
<address>
<phone>+1.408.246.8253</phone>
<email>dcrocker@bbiw.net</email>
</address>
</author>
<author initials="P." surname="Overell" fullname="Paul Overell">
<organization>THUS plc.</organization>
<address>
<email>paul.overell@thus.net</email>
</address>
</author>
<date month="January" year="2008"/>
</front>
<seriesInfo name="STD" value="68"/>
<seriesInfo name="RFC" value="5234"/>
</reference>
<reference anchor="ISO-8859-1">
<front>
<title>Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1</title>
<author>
<organization>International Organization for Standardization</organization>
</author>
<date year="1998"/>
</front>
<seriesInfo name="ISO/IEC" value="8859-1:1998"/>
</reference>
<reference anchor="USASCII">
<front>
<title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
<author>
<organization>American National Standards Institute</organization>
</author>
<date year="1986"/>
</front>
<seriesInfo name="ANSI" value="X3.4"/>
</reference>
</references>
<references title="Informative References">
<reference anchor="RFC2045">
<front>
<title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
<author initials="N." surname="Freed" fullname="Ned Freed">
<organization>Innosoft International, Inc.</organization>
<address><email>ned@innosoft.com</email></address>
</author>
<author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
<organization>First Virtual Holdings</organization>
<address><email>nsb@nsb.fv.com</email></address>
</author>
<date month="November" year="1996"/>
</front>
<seriesInfo name="RFC" value="2045"/>
</reference>
<reference anchor="RFC2047">
<front>
<title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
<author initials="K." surname="Moore" fullname="Keith Moore">
<organization>University of Tennessee</organization>
<address><email>moore@cs.utk.edu</email></address>
</author>
<date month="November" year="1996"/>
</front>
<seriesInfo name="RFC" value="2047"/>
</reference>
<reference anchor="RFC2231">
<front>
<title abbrev="MIME Value and Encoded Word Extensions">MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations</title>
<author initials="N." surname="Freed" fullname="Ned Freed">
<organization abbrev="Innosoft">Innosoft International, Inc.</organization>
<address><email>ned.freed@innosoft.com</email></address>
</author>
<author initials="K." surname="Moore" fullname="Keith Moore">
<organization>University of Tennessee</organization>
<address><email>moore@cs.utk.edu</email></address>
</author>
<date year="1997" month="November"/>
</front>
<seriesInfo name="RFC" value="2231"/>
</reference>
<reference anchor="RFC2277">
<front>
<title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
<author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
<organization>UNINETT</organization>
<address><email>Harald.T.Alvestrand@uninett.no</email></address>
</author>
<date year="1998" month="January"/>
</front>
<seriesInfo name="BCP" value="18"/>
<seriesInfo name="RFC" value="2277"/>
</reference>
<reference anchor="RFC2388">
<front>
<title abbrev="multipart/form-data">Returning Values from Forms: multipart/form-data</title>
<author initials="L." surname="Masinter" fullname="Larry Masinter">
<organization>Xerox Palo Alto Research Center</organization>
<address>
<email>masinter@parc.xerox.com</email>
</address>
</author>
<date year="1998" month="August"/>
</front>
<seriesInfo name="RFC" value="2388"/>
</reference>
</references>
<section title="Document History and Future Plans (to be removed by RFC Editor before publication)" anchor="history">
<t>
Problems with the internationalization of the HTTP Content-Disposition header
field have been known for many years (see test cases at
<eref target="http://greenbytes.de/tech/tc2231/"/>).
</t>
<t>
During IETF 72 (<eref target="http://tools.ietf.org/wg/httpbis/minutes?item=minutes72.html"/>),
the HTTPbis Working Group shortly discussed how to deal with the underspecification
of (1) Content-Disposition, and its (2) internationalization aspects.
Back then, there was rough consensus in the room to move the definition
into a separate draft.
</t>
<t>
This specification addresses problem (2), by defining a simple subset of
the encoding format defined in RFC 2231. A separate specification,
draft-reschke-rfc2183-in-http, is planned to address problem (1). Note that
this approach was chosen because Content-Disposition is just an example for
an HTTP header field using this kind of encoding. Another example
is the currently proposed Link header field (draft-nottingham-http-link-header).
</t>
<t>
This document is planned to be published on the IETF Standards Track, so that
other standards-track level documents can depend on it, such as the new
specification of Content-Disposition, or potentially future revisions of
the HTTP Link Header specification.
</t>
<t>
Also note that this document specifies a proper subset of the extensions
defined in RFC 2231, but does not normatively refer to it. Thus, RFC 2231
can be revised separately, should the email community decide to.
</t>
</section>
<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
<section title="Since draft-reschke-rfc2231-in-http-00">
<t>
Use RFC5234-style ABNF, closer to the one used in RFC 2231.
</t>
<t>
Make RFC 2231 dependency informative, so this specification can evolve
independently.
</t>
<t>
Explain the ABNF in prose.
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-01">
<t>
Remove unneeded RFC5137 notation (code point vs character).
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-02">
<t>
And and resolve issues "charset", "repeats"
and "rfc4646".
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-03">
<t>
And and resolve issue "charsetmatch".
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-04">
<t>
Add and resolve issues "badseq" and
"tokenquotcharset".
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-05">
<t>
Say "header field" instead of "header" in the context of HTTP.
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-06">
<t>
Add an appendix discussing document history and future plans, to be removed before publication.
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-07">
<t>
Add and resolve issues "impl" and "rel-2388".
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-08">
<t>
Editorial improvements.
Add and resolve issues "attrcharvstoken" and
"tokengrammar".
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-09">
<t>
Add issues "i18n-spoofing",
"iso8859",
"parameter-abnf",
and
"when-ext-value".
Add and resolve issues
"rfc2978-normative",
"rfc3986-normative" and
"usascii-normative".
</t>
</section>
<section title="Since draft-reschke-rfc2231-in-http-10">
<t>
Resolve issues "i18n-spoofing",
"iso8859",
"parameter-abnf", and
"when-ext-value".
</t>
<t>
Add and resolve issue
"charset-registered",
"handling-multiple",
"multiple-inst-spoofing",
"repeated-param" and
"value-abnf".
</t>
<t>
Update the KDE implementation note.
</t>
</section>
</section>
<section title="Resolved issues (to be removed by RFC Editor before publication)"><t>
Issues that were either rejected or resolved in this version of this
document.
</t><section title="edit"><t>
Type: edit</t><t>julian.reschke@greenbytes.de (2009-04-17):
Umbrella issue for editorial fixes/enhancements.
</t></section><section title="charset-registered"><t>
In Section 3.2:
</t><t>
Type: change</t><t>julian.reschke@greenbytes.de (2010-02-20):
Mention to use only registered charset names?
(reported by Alexey Melnikov).
</t><t>Resolution (2010-03-29):
State this in the ABNF.
</t></section><section title="parameter-abnf"><t>
In Section 3.2:
</t><t>
Type: change</t><t>julian.reschke@greenbytes.de (2010-02-20):
The ABNF for reg-parameter and ext-parameter is ambiguous, as "*" is a valid
token character; furthermore, RFC 2616's "attribute" production allows "*"
while RFC 2231's does not.
(reported by Alexey Melnikov).
</t><t>julian.reschke@greenbytes.de (2010-02-21):
Proposal: restrict the allowable character set in parameter names to
exclude "*" (and maybe even more non-name characters?). Also, consider
extending the set of value characters (for the right hand side) to allow
more characters that can be unambiguously parsed outside quoted strings,
such as "/".
</t><t>Resolution:
Introduced parmname, disallowing "*" / "'" / "%". Moving the value
ABNF discussion into a separate issue ("value-abnf").
</t></section><section title="value-abnf"><t>
In Section 3.2:
</t><t>
Type: change</t><t>julian.reschke@greenbytes.de (2010-02-26):
Consider extending the right-hand side ABNF - both for regular and
extended parameters - to include more characters that can be
unambiguously parsed outside quoted strings, such as "/".
</t><t>Resolution (2010-03-29):
No change due to lack of feedback. Potentially defer to future versions
of HTTP/1.1 (defining guidelines for header definitions), or a revision
of this spec.
</t></section><section title="iso8859"><t>
In Section 3.2:
</t><t>
Type: change</t><t>julian.reschke@greenbytes.de (2010-02-20):
The protocol could be further simplified by mandating UTF-8 only
(reported by Alexey Melnikov).
On the other hand and not surprinsingly, testing shows that ISO-8859-1
support is widely implemented. The author is looking for community
feedback on this choice.
</t><t>Resolution (2010-03-29):
Further feedback was requested during IETF LC; but none was received.
Thus defaulting to no change; keeping the support for ISO-8859-1.
</t></section><section title="when-ext-value"><t>
In Section 4.1:
</t><t>
Type: change</t><t>julian.reschke@greenbytes.de (2010-02-18):
There's no point in using ext-value when the language is unknown and no
"special" characters are present.
</t><t>Resolution (2010-02-23):
Fixed.
</t></section><section title="repeated-param"><t>
In Section 4:
</t><t>
Type: change</t><t>Chris.Newman@Sun.COM (2010-03-22):
RFC 2231 did not allow two parameters with the same name but different
languages, at least in the context of continuations that was impossible.
Absent continuations, RFC 2231 was otherwise silent on that topic.
<vspace/>
So section 4.3 adds a new feature over and above what RFC 2231 did. It's a
feature that will make implementations significantly more complex and is
likely to cause interoperability problems.
<vspace/>
Much of the experience with deployment of both language tagging and
language variants in the IETF seems to result in unnecessary complexity.
While there are good abstract arguments for language tagging in theory, it
seems more often than not that the parties in the exchange are unable to
put anything useful in the field in which case it falls into the realm of
unnecessary complexity. In addition, we have experience where we attempted
to allow language variants (multipart/alternative) and not only did that
usage not deploy, it is actively broken despite being an explicit example
in RFC 1766.
<vspace/>
The one place where I've seen language variants mostly work is when the
language tag is actually included in the attribute name (LDAP does this)
and the "search" mechanism allows wildcarding of languages. But having two
attributes with the same name seems dangerous.
<vspace/>
My recommendation is to remove this feature as I believe it will not be
used in practice and will add unnecessary complexity that is likely to
create interoperability problems.
</t><t>Resolution (2010-03-29):
State the issue. Remove section 4.3. Rephrase 4.2 accordingly.
</t></section><section title="handling-multiple"><t>
In Section 4.2:
</t><t>
Type: change</t><t><http://www.ietf.org/mail-archive/web/apps-discuss/current/msg01344.html></t><t>roessler@gmail.com (2010-02-24):
Leaving the choice of precedence to the header specification implies
that parsers need to special-case. It would seem reasonable to make a
choice in this specification that for properties which can only occur
once, the traditional syntax takes precedence.
</t><t>julian.reschke@greenbytes.de (2010-02-26):
That would rule out the use case where the traditional syntax is used as a fallback for clients that do not support the new syntax, as discussed in that section:
...
http://greenbytes.de/tech/tc2231/#attfnboth2 is a test case
that shows that using this technique, both variants can be served to clients,
and those that understand the ext-parameter encoding will indeed pick the
"better" parameter. Unfortunately, this appears to depend on parameter ordering,
which I didn't want to mention in this spec. Maybe I should?</t><t>Resolution (2010-03-29):
Just state that when repetitions are not allowed, the extended form should
take precedence.
</t></section><section title="i18n-spoofing"><t>
In Section 5:
</t><t>
Type: change</t><t><http://www.ietf.org/mail-archive/web/apps-discuss/current/msg01329.html></t><t>GK@ninebynine.org (2010-02-20):
I note that the security considerations section says nothing about possible
character "spoofing" - i.e. making a displayed prompt or value appear to be
something other than it is. E.g. Non-ASCII characters have been used to set
up exploits involving dodgy URIs that may appear to a user to be legitimate.
</t><t>Resolution (2010-02-23):
Mention the problem, and point to RFC 3629's security considerations which
mention this as well. While at it, also mention the other UTF-8 related
attack scenario.
</t></section><section title="multiple-inst-spoofing"><t>
In Section 5:
</t><t>
Type: change</t><t>kivinen@iki.fi (2010-03-01):
Yes, but the impact of them is different. For example it does not
really matter if the filename parameters having different languages
differ, but there might be parameters where this really matters.
<vspace/>
As this document does not define any exact parameters, it might be
enough to comment something like that "This document specifies way to
transport multiple language variants for parameters, and such use
might allow spoofing attacks, where different language versions of the
same parameters do not match. Whether this attack is useful as an
attack depends on the parameter specified."
</t><t>Resolution (2010-03-01):
Add text based on the recommendation.
</t></section></section></back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-23 19:58:52 |