rfc5987.txt   draft-reschke-rfc5987bis-latest.txt 
Internet Engineering Task Force (IETF) J. Reschke Network Working Group J. Reschke
Request for Comments: 5987 greenbytes Internet-Draft greenbytes
Category: Standards Track August 2010 Obsoletes: 5987 (if approved) October 29, 2014
ISSN: 2070-1721 Intended status: Standards Track
Expires: May 2, 2015
Character Set and Language Encoding for Indicating Character Encoding and Language for HTTP Header Field
Hypertext Transfer Protocol (HTTP) Header Field Parameters Parameters
draft-reschke-rfc5987bis-latest
Abstract Abstract
By default, message header field parameters in Hypertext Transfer By default, message header field parameters in Hypertext Transfer
Protocol (HTTP) messages cannot carry characters outside the ISO- Protocol (HTTP) messages cannot carry characters outside the ISO-
8859-1 character set. RFC 2231 defines an encoding mechanism for use 8859-1 character set. RFC 2231 defines an encoding mechanism for use
in Multipurpose Internet Mail Extensions (MIME) headers. This in Multipurpose Internet Mail Extensions (MIME) headers. This
document specifies an encoding suitable for use in HTTP header fields document specifies an encoding suitable for use in HTTP header fields
that is compatible with a profile of the encoding defined in RFC that is compatible with a profile of the encoding defined in RFC
2231. 2231.
Editorial Note (To be removed by RFC Editor before publication)
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
ietf-http-wg@w3.org [1], which may be joined by sending a message
with subject "subscribe" to ietf-http-wg-request@w3.org [2].
Discussions of the HTTPbis Working Group are archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>.
XML versions, latest edits, diffs, and the issues list for this
document are available from
<http://greenbytes.de/tech/webdav/#draft-reschke-rfc5987bis>. A
collection of test cases is available at
<http://greenbytes.de/tech/tc2231/>.
Status of This Memo Status of This Memo
This is an Internet Standards Track document. This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
This document is a product of the Internet Engineering Task Force Internet-Drafts are working documents of the Internet Engineering
(IETF). It represents the consensus of the IETF community. It has Task Force (IETF). Note that other groups may also distribute
received public review and has been approved for publication by the working documents as Internet-Drafts. The list of current Internet-
Internet Engineering Steering Group (IESG). Further information on Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, Internet-Drafts are draft documents valid for a maximum of six months
and how to provide feedback on it may be obtained at and may be updated, replaced, or obsoleted by other documents at any
http://www.rfc-editor.org/info/rfc5987. time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 2, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4
3. Comparison to RFC 2231 and Definition of the Encoding . . . . 3 3. Comparison to RFC 2231 and Definition of the Encoding . . . . 4
3.1. Parameter Continuations . . . . . . . . . . . . . . . . . 4 3.1. Parameter Continuations . . . . . . . . . . . . . . . . . 5
3.2. Parameter Value Character Set and Language Information . . 4 3.2. Parameter Value Character Encoding and Language
3.2.1. Definition . . . . . . . . . . . . . . . . . . . . . . 4 Information . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.2. Examples . . . . . . . . . . . . . . . . . . . . . . . 6 3.2.1. Definition . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Language Specification in Encoded Words . . . . . . . . . 7 3.2.2. Historical Notes . . . . . . . . . . . . . . . . . . . 7
4. Guidelines for Usage in HTTP Header Field Definitions . . . . 7 3.2.3. Examples . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. When to Use the Extension . . . . . . . . . . . . . . . . 8 3.3. Language Specification in Encoded Words . . . . . . . . . 8
4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . . 8 4. Guidelines for Usage in HTTP Header Field Definitions . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 4.1. When to Use the Extension . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . . 10 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Changes from RFC 5987 . . . . . . . . . . . . . . . . 12
Appendix B. Implementation Report . . . . . . . . . . . . . . . . 13
Appendix C. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 13
C.1. Since RFC5987 . . . . . . . . . . . . . . . . . . . . . . 13
C.2. Since draft-reschke-rfc5987bis-00 . . . . . . . . . . . . 13
C.3. Since draft-reschke-rfc5987bis-01 . . . . . . . . . . . . 14
C.4. Since draft-reschke-rfc5987bis-02 . . . . . . . . . . . . 14
C.5. Since draft-reschke-rfc5987bis-03 . . . . . . . . . . . . 14
C.6. Since draft-reschke-rfc5987bis-04 . . . . . . . . . . . . 14
C.7. Since draft-reschke-rfc5987bis-05 . . . . . . . . . . . . 14
C.8. Since draft-reschke-rfc5987bis-06 . . . . . . . . . . . . 14
Appendix D. Open issues (to be removed by RFC Editor prior to
publication) . . . . . . . . . . . . . . . . . . . . 14
D.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
D.2. httpbis . . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
By default, message header field parameters in HTTP ([RFC2616]) By default, message header field parameters in HTTP ([RFC2616])
messages cannot carry characters outside the ISO-8859-1 character set messages cannot carry characters outside the ISO-8859-1 coded
([ISO-8859-1]). RFC 2231 ([RFC2231]) defines an encoding mechanism character set ([ISO-8859-1]). RFC 2231 ([RFC2231]) defines an
for use in MIME headers. This document specifies an encoding encoding mechanism for use in MIME headers. This document specifies
suitable for use in HTTP header fields that is compatible with a an encoding suitable for use in HTTP header fields that is compatible
profile of the encoding defined in RFC 2231. with a profile of the encoding defined in RFC 2231.
This document obsoletes [RFC5987] and moves it to "historic" status;
the changes are summarized in Appendix A.
Note: in the remainder of this document, RFC 2231 is only Note: in the remainder of this document, RFC 2231 is only
referenced for the purpose of explaining the choice of features referenced for the purpose of explaining the choice of features
that were adopted; they are therefore purely informative. that were adopted; they are therefore purely informative.
Note: this encoding does not apply to message payloads transmitted Note: this encoding does not apply to message payloads transmitted
over HTTP, such as when using the media type "multipart/form-data" over HTTP, such as when using the media type "multipart/form-data"
([RFC2388]). ([RFC2388]).
2. Notational Conventions 2. Notational Conventions
skipping to change at page 3, line 34 skipping to change at page 4, line 37
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
This specification uses the ABNF (Augmented Backus-Naur Form) This specification uses the ABNF (Augmented Backus-Naur Form)
notation defined in [RFC5234]. The following core rules are included notation defined in [RFC5234]. The following core rules are included
by reference, as defined in [RFC5234], Appendix B.1: ALPHA (letters), by reference, as defined in [RFC5234], Appendix B.1: ALPHA (letters),
DIGIT (decimal 0-9), HEXDIG (hexadecimal 0-9/A-F/a-f), and LWSP DIGIT (decimal 0-9), HEXDIG (hexadecimal 0-9/A-F/a-f), and LWSP
(linear whitespace). (linear whitespace).
Note that this specification uses the term "character set" for This specification uses terminology defined in [RFC6365], namely:
consistency with other IETF specifications such as RFC 2277 (see "character encoding scheme" (below abbreviated to "character
[RFC2277], Section 3). A more accurate term would be "character encoding"), "charset" and "coded character set".
encoding" (a mapping of code points to octet sequences).
Note that this differs from RFC 2231, which uses the term "character
set" for "character encoding scheme".
3. Comparison to RFC 2231 and Definition of the Encoding 3. Comparison to RFC 2231 and Definition of the Encoding
RFC 2231 defines several extensions to MIME. The sections below RFC 2231 defines several extensions to MIME. The sections below
discuss if and how they apply to HTTP header fields. discuss if and how they apply to HTTP header fields.
In short: In short:
o Parameter Continuations aren't needed (Section 3.1), o Parameter Continuations aren't needed (Section 3.1),
o Character Encoding and Language Information are useful, therefore
o Character Set and Language Information are useful, therefore a a simple subset is specified (Section 3.2), and
simple subset is specified (Section 3.2), and
o Language Specifications in Encoded Words aren't needed o Language Specifications in Encoded Words aren't needed
(Section 3.3). (Section 3.3).
3.1. Parameter Continuations 3.1. Parameter Continuations
Section 3 of [RFC2231] defines a mechanism that deals with the length Section 3 of [RFC2231] defines a mechanism that deals with the length
limitations that apply to MIME headers. These limitations do not limitations that apply to MIME headers. These limitations do not
apply to HTTP ([RFC2616], Section 19.4.7). apply to HTTP ([RFC7231], Appendix A.6).
Thus, parameter continuations are not part of the encoding defined by Thus, parameter continuations are not part of the encoding defined by
this specification. this specification.
3.2. Parameter Value Character Set and Language Information 3.2. Parameter Value Character Encoding and Language Information
Section 4 of [RFC2231] specifies how to embed language information Section 4 of [RFC2231] specifies how to embed language information
into parameter values, and also how to encode non-ASCII characters, into parameter values, and also how to encode non-ASCII characters,
dealing with restrictions both in MIME and HTTP header parameters. dealing with restrictions both in MIME and HTTP header field
parameters.
However, RFC 2231 does not specify a mandatory-to-implement character However, RFC 2231 does not specify a mandatory-to-implement character
set, making it hard for senders to decide which character set to use. encoding, making it hard for senders to decide which encoding to use.
Thus, recipients implementing this specification MUST support the Thus, recipients implementing this specification MUST support the
character sets "ISO-8859-1" [ISO-8859-1] and "UTF-8" [RFC3629]. "UTF-8" character encoding [RFC3629].
Furthermore, RFC 2231 allows the character set information to be left Furthermore, RFC 2231 allows the character encoding information to be
out. The encoding defined by this specification does not allow that. left out. The encoding defined by this specification does not allow
that.
3.2.1. Definition 3.2.1. Definition
The syntax for parameters is defined in Section 3.6 of [RFC2616] The syntax for parameters is defined in Section 3.6 of [RFC2616]
(with RFC 2616 implied LWS translated to RFC 5234 LWSP): (with RFC 2616 implied LWS translated to RFC 5234 LWSP):
parameter = attribute LWSP "=" LWSP value parameter = attribute LWSP "=" LWSP value
attribute = token attribute = token
value = token / quoted-string value = token / quoted-string
quoted-string = <quoted-string, defined in [RFC2616], Section 2.2> quoted-string = <quoted-string, defined in [RFC7230], Section 3.2.6>
token = <token, defined in [RFC2616], Section 2.2> token = <token, defined in [RFC7230], Section 3.2.6>
In order to include character set and language information, this In order to include character encoding and language information, this
specification modifies the RFC 2616 grammar to be: specification modifies the RFC 2616 grammar to be:
parameter = reg-parameter / ext-parameter parameter = reg-parameter / ext-parameter
reg-parameter = parmname LWSP "=" LWSP value reg-parameter = parmname LWSP "=" LWSP value
ext-parameter = parmname "*" LWSP "=" LWSP ext-value ext-parameter = parmname "*" LWSP "=" LWSP ext-value
parmname = 1*attr-char parmname = 1*attr-char
ext-value = charset "'" [ language ] "'" value-chars ext-value = charset "'" [ language ] "'" value-chars
; like RFC 2231's <extended-initial-value> ; like RFC 2231's <extended-initial-value>
; (see [RFC2231], Section 7) ; (see [RFC2231], Section 7)
charset = "UTF-8" / "ISO-8859-1" / mime-charset charset = "UTF-8" / mime-charset
mime-charset = 1*mime-charsetc mime-charset = 1*mime-charsetc
mime-charsetc = ALPHA / DIGIT mime-charsetc = ALPHA / DIGIT
/ "!" / "#" / "$" / "%" / "&" / "!" / "#" / "$" / "%" / "&"
/ "+" / "-" / "^" / "_" / "`" / "+" / "-" / "^" / "_" / "`"
/ "{" / "}" / "~" / "{" / "}" / "~"
; as <mime-charset> in Section 2.3 of [RFC2978] ; as <mime-charset> in Section 2.3 of [RFC2978]
; except that the single quote is not included ; except that the single quote is not included
; SHOULD be registered in the IANA charset registry ; SHOULD be registered in the IANA charset registry
skipping to change at page 5, line 48 skipping to change at page 6, line 48
; token except ( "*" / "'" / "%" ) ; token except ( "*" / "'" / "%" )
Thus, a parameter is either a regular parameter (reg-parameter), as Thus, a parameter is either a regular parameter (reg-parameter), as
previously defined in Section 3.6 of [RFC2616], or an extended previously defined in Section 3.6 of [RFC2616], or an extended
parameter (ext-parameter). parameter (ext-parameter).
Extended parameters are those where the left-hand side of the Extended parameters are those where the left-hand side of the
assignment ends with an asterisk character. assignment ends with an asterisk character.
The value part of an extended parameter (ext-value) is a token that The value part of an extended parameter (ext-value) is a token that
consists of three parts: the REQUIRED character set name (charset), consists of three parts: the REQUIRED character encoding name
the OPTIONAL language information (language), and a character (charset), the OPTIONAL language information (language), and a
sequence representing the actual value (value-chars), separated by character sequence representing the actual value (value-chars),
single quote characters. Note that both character set names and separated by single quote characters. Note that both character
language tags are restricted to the US-ASCII character set, and are encoding names and language tags are restricted to the US-ASCII coded
matched case-insensitively (see [RFC2978], Section 2.3 and [RFC5646], character set, and are matched case-insensitively (see [RFC2978],
Section 2.1.1). Section 2.3 and [RFC5646], Section 2.1.1).
Inside the value part, characters not contained in attr-char are Inside the value part, characters not contained in attr-char are
encoded into an octet sequence using the specified character set. encoded into an octet sequence using the specified character
That octet sequence is then percent-encoded as specified in Section encoding. That octet sequence is then percent-encoded as specified
2.1 of [RFC3986]. in Section 2.1 of [RFC3986].
Producers MUST use either the "UTF-8" ([RFC3629]) or the "ISO-8859-1" Producers MUST use the "UTF-8" ([RFC3629]) character encoding.
([ISO-8859-1]) character set. Extension character sets (mime- Extension character encodings (mime-charset) are reserved for future
charset) are reserved for future use. use.
Note: recipients should be prepared to handle encoding errors, Note: recipients should be prepared to handle encoding errors,
such as malformed or incomplete percent escape sequences, or non- such as malformed or incomplete percent escape sequences, or non-
decodable octet sequences, in a robust manner. This specification decodable octet sequences, in a robust manner. This specification
does not mandate any specific behavior, for instance, the does not mandate any specific behavior, for instance, the
following strategies are all acceptable: following strategies are all acceptable:
* ignoring the parameter, * ignoring the parameter,
* stripping a non-decodable octet sequence, * stripping a non-decodable octet sequence,
* substituting a non-decodable octet sequence by a replacement * substituting a non-decodable octet sequence by a replacement
character, such as the Unicode character U+FFFD (Replacement character, such as the Unicode character U+FFFD (Replacement
Character). Character).
Note: the RFC 2616 token production ([RFC2616], Section 2.2) 3.2.2. Historical Notes
differs from the production used in RFC 2231 (imported from
Section 5.1 of [RFC2045]) in that curly braces ("{" and "}") are
excluded. Thus, these two characters are excluded from the attr-
char production as well.
Note: the <mime-charset> ABNF defined here differs from the one in The RFC 7230 token production ([RFC7230], Section 3.2.6) differs from
Section 2.3 of [RFC2978] in that it does not allow the single the production used in RFC 2231 (imported from Section 5.1 of
quote character (see also RFC Errata ID 1912 [Err1912]). In [RFC2045]) in that curly braces ("{" and "}") are excluded. Thus,
practice, no character set names using that character have been these two characters are excluded from the attr-char production as
registered at the time of this writing. well.
3.2.2. Examples The <mime-charset> ABNF defined here differs from the one in Section
2.3 of [RFC2978] in that it does not allow the single quote character
(see also RFC Errata ID 1912 [Err1912]). In practice, no character
encoding names using that character have been registered at the time
of this writing.
For backwards compatibility with RFC 2231, the encoding defined by
this specification deviates from common parameter syntax in that the
quoted-string notation is not allowed. Implementations using generic
parser components might not be able to detect the use of quoted-
string notation and thus might accept that format, although invalid,
as well.
[RFC5987] did require support for ISO-8859-1, too; for compatibility
with legacy code, recipients are encouraged to support this encoding
as well.
3.2.3. Examples
Non-extended notation, using "token": Non-extended notation, using "token":
foo: bar; title=Economy foo: bar; title=Economy
Non-extended notation, using "quoted-string": Non-extended notation, using "quoted-string":
foo: bar; title="US-$ rates" foo: bar; title="US-$ rates"
Extended notation, using the Unicode character U+00A3 (POUND SIGN): Extended notation, using the Unicode character U+00A3 (POUND SIGN):
foo: bar; title*=iso-8859-1'en'%A3%20rates foo: bar; title*=utf-8'en'%C2%A3%20rates
Note: the Unicode pound sign character U+00A3 was encoded into the Note: the Unicode pound sign character U+00A3 was encoded into the
single octet A3 using the ISO-8859-1 character encoding, then octet sequence C2 A3 using the UTF-8 character encoding, then
percent-encoded. Also, note that the space character was encoded as percent-encoded. Also, note that the space character was encoded as
%20, as it is not contained in attr-char. %20, as it is not contained in attr-char.
Extended notation, using the Unicode characters U+00A3 (POUND SIGN) Extended notation, using the Unicode characters U+00A3 (POUND SIGN)
and U+20AC (EURO SIGN): and U+20AC (EURO SIGN):
foo: bar; title*=UTF-8''%c2%a3%20and%20%e2%82%ac%20rates foo: bar; title*=UTF-8''%c2%a3%20and%20%e2%82%ac%20rates
Note: the Unicode pound sign character U+00A3 was encoded into the Note: the Unicode pound sign character U+00A3 was encoded into the
octet sequence C2 A3 using the UTF-8 character encoding, then octet sequence C2 A3 using the UTF-8 character encoding, then
percent-encoded. Likewise, the Unicode euro sign character U+20AC percent-encoded. Likewise, the Unicode euro sign character U+20AC
was encoded into the octet sequence E2 82 AC, then percent-encoded. was encoded into the octet sequence E2 82 AC, then percent-encoded.
Also note that HEXDIG allows both lowercase and uppercase characters, Also note that HEXDIG allows both lowercase and uppercase characters,
so recipients must understand both, and that the language information so recipients must understand both, and that the language information
is optional, while the character set is not. is optional, while the character encoding is not.
3.3. Language Specification in Encoded Words 3.3. Language Specification in Encoded Words
Section 5 of [RFC2231] extends the encoding defined in [RFC2047] to Section 5 of [RFC2231] extends the encoding defined in [RFC2047] to
also support language specification in encoded words. Although the also support language specification in encoded words. RFC 2616, the
HTTP/1.1 specification does refer to RFC 2047 ([RFC2616], Section now-obsolete HTTP/1.1 specification, did refer to RFC 2047
2.2), it's not clear to which header field exactly it applies, and ([RFC2616], Section 2.2). However, it wasn't clear to which header
whether it is implemented in practice (see field it applied. Consequently, the current revision of the HTTP/1.1
<http://tools.ietf.org/wg/httpbis/trac/ticket/111> for details). specification has deprecated use of the encoding forms defined in RFC
2047 (see Section 3.2.4 of [RFC7230]).
Thus, this specification does not include this feature. Thus, this specification does not include this feature.
4. Guidelines for Usage in HTTP Header Field Definitions 4. Guidelines for Usage in HTTP Header Field Definitions
Specifications of HTTP header fields that use the extensions defined Specifications of HTTP header fields that use the extensions defined
in Section 3.2 ought to clearly state that. A simple way to achieve in Section 3.2 ought to clearly state that. A simple way to achieve
this is to normatively reference this specification, and to include this is to normatively reference this specification, and to include
the ext-value production into the ABNF for that header field. the ext-value production into the ABNF for that header field.
skipping to change at page 8, line 4 skipping to change at page 9, line 18
in Section 3.2 ought to clearly state that. A simple way to achieve in Section 3.2 ought to clearly state that. A simple way to achieve
this is to normatively reference this specification, and to include this is to normatively reference this specification, and to include
the ext-value production into the ABNF for that header field. the ext-value production into the ABNF for that header field.
For instance: For instance:
foo-header = "foo" LWSP ":" LWSP token ";" LWSP title-param foo-header = "foo" LWSP ":" LWSP token ";" LWSP title-param
title-param = "title" LWSP "=" LWSP value title-param = "title" LWSP "=" LWSP value
/ "title*" LWSP "=" LWSP ext-value / "title*" LWSP "=" LWSP ext-value
ext-value = <see RFC 5987, Section 3.2> ext-value = <see RFC 5987, Section 3.2>
Note: The Parameter Value Continuation feature defined in Section Note: The Parameter Value Continuation feature defined in Section
3 of [RFC2231] makes it impossible to have multiple instances of 3 of [RFC2231] makes it impossible to have multiple instances of
extended parameters with identical parmname components, as the extended parameters with identical parmname components, as the
processing of continuations would become ambiguous. Thus, processing of continuations would become ambiguous. Thus,
specifications using this extension are advised to disallow this specifications using this extension are advised to disallow this
case for compatibility with RFC 2231. case for compatibility with RFC 2231.
Note: This specification does not automatically assign a new
interpretration to parameter names ending in an asterisk. As
pointed out above, it's up to the specification for the non-
extended parameter to "opt in" to the syntax defined here. That
being said, some existing implementations are known to
automatically switch to the use of this notation when a parameter
name ends with an asterisk, thus using parameter names ending in
an asterisk for something else is likely to cause interoperability
problems.
4.1. When to Use the Extension 4.1. When to Use the Extension
Section 4.2 of [RFC2277] requires that protocol elements containing Section 4.2 of [RFC2277] requires that protocol elements containing
human-readable text are able to carry language information. Thus, human-readable text are able to carry language information. Thus,
the ext-value production ought to be always used when the parameter the ext-value production ought to be always used when the parameter
value is of textual nature and its language is known. value is of textual nature and its language is known.
Furthermore, the extension ought to also be used whenever the Furthermore, the extension ought to also be used whenever the
parameter value needs to carry characters not present in the US-ASCII parameter value needs to carry characters not present in the US-ASCII
([USASCII]) character set (note that it would be unacceptable to ([USASCII]) coded character set (note that it would be unacceptable
define a new parameter that would be restricted to a subset of the to define a new parameter that would be restricted to a subset of the
Unicode character set). Unicode character set).
4.2. Error Handling 4.2. Error Handling
Header field specifications need to define whether multiple instances Header field specifications need to define whether multiple instances
of parameters with identical parmname components are allowed, and how of parameters with identical parmname components are allowed, and how
they should be processed. This specification suggests that a they should be processed. This specification suggests that a
parameter using the extended syntax takes precedence. This would parameter using the extended syntax takes precedence. This would
allow producers to use both formats without breaking recipients that allow producers to use both formats without breaking recipients that
do not understand the extended syntax yet. do not understand the extended syntax yet.
skipping to change at page 9, line 18 skipping to change at page 10, line 42
See Section 10 of [RFC3629] for more information on both topics. See Section 10 of [RFC3629] for more information on both topics.
In addition, the extension specified in this document makes it In addition, the extension specified in this document makes it
possible to transport multiple language variants for a single possible to transport multiple language variants for a single
parameter, and such use might allow spoofing attacks, where different parameter, and such use might allow spoofing attacks, where different
language versions of the same parameter are not equivalent. Whether language versions of the same parameter are not equivalent. Whether
this attack is useful as an attack depends on the parameter this attack is useful as an attack depends on the parameter
specified. specified.
6. Acknowledgements 6. IANA Considerations
There are no IANA Considerations related to this specification.
7. Acknowledgements
Thanks to Martin Duerst and Frank Ellermann for help figuring out Thanks to Martin Duerst and Frank Ellermann for help figuring out
ABNF details, to Graham Klyne and Alexey Melnikov for general review, ABNF details, to Graham Klyne and Alexey Melnikov for general review,
to Chris Newman for pointing out an RFC 2231 incompatibility, and to to Chris Newman for pointing out an RFC 2231 incompatibility, and to
Benjamin Carlyle and Roar Lauritzsen for implementer's feedback. Benjamin Carlyle, Roar Lauritzsen, Eric Lawrence, and James Manger
for implementer's feedback.
7. References
7.1. Normative References 8. References
[ISO-8859-1] International Organization for Standardization, 8.1. Normative References
"Information technology -- 8-bit single-byte coded
graphic character sets -- Part 1: Latin alphabet No.
1", ISO/IEC 8859-1:1998, 1998.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2978] Freed, N. and J. Postel, "IANA Charset Registration [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration
Procedures", BCP 19, RFC 2978, October 2000. Procedures", BCP 19, RFC 2978, October 2000.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 3629, STD 63, November 2003. 10646", STD 63, RFC 3629, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax", "Uniform Resource Identifier (URI): Generic Syntax",
RFC 3986, STD 66, January 2005. STD 66, RFC 3986, January 2005.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234, Syntax Specifications: ABNF", STD 68, RFC 5234,
January 2008. January 2008.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for
Identifying Languages", BCP 47, RFC 5646, Identifying Languages", BCP 47, RFC 5646,
September 2009. September 2009.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and
Routing", RFC 7230, June 2014.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Semantics and Content",
RFC 7231, June 2014.
[USASCII] American National Standards Institute, "Coded Character [USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986. Interchange", ANSI X3.4, 1986.
7.2. Informative References 8.2. Informative References
[Err1912] RFC Errata, "Errata ID 1912, RFC 2978", [Err1912] RFC Errata, "Errata ID 1912, RFC 2978",
<http://www.rfc-editor.org>. <http://www.rfc-editor.org>.
[ISO-8859-1] International Organization for Standardization,
"Information technology -- 8-bit single-byte coded
graphic character sets -- Part 1: Latin alphabet No.
1", ISO/IEC 8859-1:1998, 1998.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", RFC 2045, November 1996. Message Bodies", RFC 2045, November 1996.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail
Extensions) Part Three: Message Header Extensions for Extensions) Part Three: Message Header Extensions for
Non-ASCII Text", RFC 2047, November 1996. Non-ASCII Text", RFC 2047, November 1996.
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and
Encoded Word Extensions: Character Sets, Languages, and Encoded Word Extensions: Character Sets, Languages, and
Continuations", RFC 2231, November 1997. Continuations", RFC 2231, November 1997.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998. Languages", BCP 18, RFC 2277, January 1998.
[RFC2388] Masinter, L., "Returning Values from Forms: multipart/ [RFC2388] Masinter, L., "Returning Values from Forms: multipart/
form-data", RFC 2388, August 1998. form-data", RFC 2388, August 1998.
[RFC5987] Reschke, J., "Character Set and Language Encoding for
Hypertext Transfer Protocol (HTTP) Header Field
Parameters", RFC 5987, August 2010.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
[RFC6266] Reschke, J., "Use of the Content-Disposition Header
Field in the Hypertext Transfer Protocol (HTTP)",
RFC 6266, June 2011.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF", BCP 166, RFC 6365,
September 2011.
URIs
[1] <mailto:ietf-http-wg@w3.org>
[2] <mailto:ietf-http-wg-request@w3.org?subject=subscribe>
Appendix A. Changes from RFC 5987
This section summarizes the changes compared to [RFC5987]:
o The document title was changed to "Indicating Character Encoding
and Language for HTTP Header Field Parameters".
o The requirement to support the "ISO-8859-1" encoding was removed.
Appendix B. Implementation Report
The encoding defined in this document currently is used for two
different HTTP header fields:
o "Content-Disposition", defined in [RFC6266], and
o "Link", defined in [RFC5988].
As the encoding is a profile/clarification of the one defined in
[RFC2231] in 1997, many user agents already supported it for use in
"Content-Disposition" when [RFC5987] got published.
Since the publication of [RFC5987], three more popular desktop user
agents have added support for this encoding; see <http://purl.org/
NET/http/content-disposition-tests#encoding-2231-char> for details.
At this time, the current versions of all major desktop user agents
support it.
Note that the implementation in Internet Explorer 9 does not support
the ISO-8859-1 character encoding; this document revision
acknowledges that UTF-8 is sufficient for expressing all code points,
and removes the requirement to support ISO-8859-1.
The "Link" header field, on the other hand, was only recently
specified in [RFC5988]. At the time of this writing, no shipping
User Agent except Firefox supported the "title*" parameter (starting
with release 15).
Appendix C. Change Log (to be removed by RFC Editor before publication)
C.1. Since RFC5987
Only editorial changes for the purpose of starting the revision
process (obs5987).
C.2. Since draft-reschke-rfc5987bis-00
Resolved issues "iso-8859-1" and "title" (title simplified). Added
and resolved issue "historic5987".
C.3. Since draft-reschke-rfc5987bis-01
Added issues "httpbis", "parmsyntax", "terminology" and
"valuesyntax". Closed issue "impls".
C.4. Since draft-reschke-rfc5987bis-02
Resolved issue "terminology".
C.5. Since draft-reschke-rfc5987bis-03
In Section 3.2, pull historical notes into a separate subsection.
Resolved issues "valuesyntax" and "parmsyntax".
C.6. Since draft-reschke-rfc5987bis-04
Update status of Firefox support in HTTP Link Header field.
C.7. Since draft-reschke-rfc5987bis-05
Update status of Firefox support in HTTP Link Header field.
C.8. Since draft-reschke-rfc5987bis-06
Update status with respect to Safari 6.
Started work on update with respect to RFC 723x.
Appendix D. Open issues (to be removed by RFC Editor prior to
publication)
D.1. edit
Type: edit
julian.reschke@greenbytes.de (2011-04-15): Umbrella issue for
editorial fixes/enhancements.
D.2. httpbis
Type: edit
julian.reschke@greenbytes.de (2011-09-17): The document refers
normatively to RFC 2616. Should it continue to do so, or should we
wait for HTTPbis? This may affect edge case in the ABNF, such as the
definition of linear white space or the characters allowed in
"token".
Author's Address Author's Address
Julian F. Reschke Julian F. Reschke
greenbytes GmbH greenbytes GmbH
Hafenweg 16 Hafenweg 16
Muenster, NW 48155 Muenster, NW 48155
Germany Germany
EMail: julian.reschke@greenbytes.de EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/ URI: http://greenbytes.de/tech/webdav/
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