draft-ietf-httpbis-rfc5987bis-05.txt   draft-ietf-httpbis-rfc5987bis-latest.txt 
HTTP Working Group J. Reschke HTTP Working Group J. Reschke
Internet-Draft greenbytes Internet-Draft greenbytes
Obsoletes: 5987 (if approved) March 2, 2017 Obsoletes: 5987 (if approved) October 13, 2025
Intended status: Standards Track Intended status: Standards Track
Expires: September 3, 2017 Expires: April 16, 2026
Indicating Character Encoding and Language for HTTP Header Field Indicating Character Encoding and Language for HTTP Header Field
Parameters Parameters
draft-ietf-httpbis-rfc5987bis-05 draft-ietf-httpbis-rfc5987bis-latest
Abstract Abstract
By default, header field values in Hypertext Transfer Protocol (HTTP) By default, header field values in Hypertext Transfer Protocol (HTTP)
messages cannot easily carry characters outside the US-ASCII coded messages cannot easily carry characters outside the US-ASCII coded
character set. RFC 2231 defines an encoding mechanism for use in character set. RFC 2231 defines an encoding mechanism for use in
parameters inside Multipurpose Internet Mail Extensions (MIME) header parameters inside Multipurpose Internet Mail Extensions (MIME) header
field values. This document specifies an encoding suitable for use field values. This document specifies an encoding suitable for use
in HTTP header fields that is compatible with a simplified profile of in HTTP header fields that is compatible with a simplified profile of
the encoding defined in RFC 2231. the encoding defined in RFC 2231.
This document obsoletes RFC 5987. This document obsoletes RFC 5987.
Editorial Note (To be removed by RFC Editor before publication)
Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at
<https://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information can be found at <http://httpwg.github.io/>;
source code and issues list for this draft can be found at
<https://github.com/httpwg/http-extensions>.
The changes in this draft are summarized in Appendix C.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 3, 2017. This Internet-Draft will expire on April 16, 2026.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 4 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3
3. Comparison to RFC 2231 and Definition of the Encoding . . . . 4 3. Comparison to RFC 2231 and Definition of the Encoding . . . . 3
3.1. Parameter Continuations . . . . . . . . . . . . . . . . . 4 3.1. Parameter Continuations . . . . . . . . . . . . . . . . . 4
3.2. Parameter Value Character Encoding and Language 3.2. Parameter Value Character Encoding and Language
Information . . . . . . . . . . . . . . . . . . . . . . . 5 Information . . . . . . . . . . . . . . . . . . . . . . . 4
3.2.1. Definition . . . . . . . . . . . . . . . . . . . . . 5 3.2.1. Definition . . . . . . . . . . . . . . . . . . . . . 4
3.2.2. Historical Notes . . . . . . . . . . . . . . . . . . 7 3.2.2. Historical Notes . . . . . . . . . . . . . . . . . . 6
3.2.3. Examples . . . . . . . . . . . . . . . . . . . . . . 7 3.2.3. Examples . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Language Specification in Encoded Words . . . . . . . . . 8 3.3. Language Specification in Encoded Words . . . . . . . . . 7
4. Guidelines for Usage in HTTP Header Field Definitions . . . . 8 4. Guidelines for Usage in HTTP Header Field Definitions . . . . 7
4.1. When to Use the Extension . . . . . . . . . . . . . . . . 9 4.1. When to Use the Extension . . . . . . . . . . . . . . . . 8
4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . 9 4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 11 7.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Changes from RFC 5987 . . . . . . . . . . . . . . . 14 Appendix A. Changes from RFC 5987 . . . . . . . . . . . . . . . 12
Appendix B. Implementation Report . . . . . . . . . . . . . . . 14 Appendix B. Implementation Report . . . . . . . . . . . . . . . 12
Appendix C. Change Log (to be removed by RFC Editor before Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 13
publication) . . . . . . . . . . . . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
C.1. Since RFC5987 . . . . . . . . . . . . . . . . . . . . . . 15
C.2. Since draft-reschke-rfc5987bis-00 . . . . . . . . . . . . 15
C.3. Since draft-reschke-rfc5987bis-01 . . . . . . . . . . . . 15
C.4. Since draft-reschke-rfc5987bis-02 . . . . . . . . . . . . 15
C.5. Since draft-reschke-rfc5987bis-03 . . . . . . . . . . . . 15
C.6. Since draft-reschke-rfc5987bis-04 . . . . . . . . . . . . 15
C.7. Since draft-reschke-rfc5987bis-05 . . . . . . . . . . . . 15
C.8. Since draft-reschke-rfc5987bis-06 . . . . . . . . . . . . 15
C.9. Since draft-ietf-httpbis-rfc5987bis-00 . . . . . . . . . 16
C.10. Since draft-ietf-httpbis-rfc5987bis-01 . . . . . . . . . 16
C.11. Since draft-ietf-httpbis-rfc5987bis-02 . . . . . . . . . 16
C.12. Since draft-ietf-httpbis-rfc5987bis-03 . . . . . . . . . 16
C.13. Since draft-ietf-httpbis-rfc5987bis-04 . . . . . . . . . 16
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
Use of characters outside the US-ASCII coded character set Use of characters outside the US-ASCII coded character set
([RFC0020]) in HTTP header fields ([RFC7230]) is non-trivial: ([RFC0020]) in HTTP header fields ([RFC7230]) is non-trivial:
o The HTTP specification discourages use of non-US-ASCII characters o The HTTP specification discourages use of non-US-ASCII characters
in field values, placing them into the "obs-text" ABNF production in field values, placing them into the "obs-text" Augmented
([RFC7230], Section 3.2). Backus-Naur Form (ABNF) production ([RFC7230], Section 3.2).
o Furthermore, it stays silent about default character encoding o Furthermore, it stays silent about default character encoding
schemes for field values, so any use of non-US-ASCII characters schemes for field values, so any use of non-US-ASCII characters
would need to be specific to the field definition, or would would need to be specific to the field definition or would require
require some other kind of out-of-band information. some other kind of out-of-band information.
o Finally, some APIs assume a default character encoding scheme in o Finally, some APIs assume a default character encoding scheme in
order to map from the octet sequences (obtained from the HTTP order to map from the octet sequences (obtained from the HTTP
message) to character sequences: for instance, the XMLHttpRequest message) to character sequences: for instance, the XMLHttpRequest
API ([XMLHttpRequest]) uses the Interface Definition Language type API ([XMLHttpRequest]) uses the Interface Definition Language type
"ByteString", effectively resulting in the ISO-8859-1 character "ByteString", effectively resulting in the ISO-8859-1 character
encoding scheme [ISO-8859-1] being used. encoding scheme ([ISO-8859-1]) being used.
On the other hand, RFC 2231 defines an encoding mechanism for On the other hand, RFC 2231 defines an encoding mechanism for
parameters inside MIME header fields ([RFC2231]), which, as opposed parameters inside MIME header fields ([RFC2231]), which, as opposed
to HTTP messages, do need to be sent over non-binary transports. to HTTP messages, do need to be sent over non-binary transports.
This document specifies an encoding suitable for use in HTTP header This document specifies an encoding suitable for use in HTTP header
fields that is compatible with a simplified profile of the encoding fields that is compatible with a simplified profile of the encoding
defined in RFC 2231. It can be applied to any HTTP header field that defined in RFC 2231. It can be applied to any HTTP header field that
uses the common "parameter" ("name=value") syntax. uses the common "parameter" ("name=value") syntax.
This document obsoletes [RFC5987] and moves it to "historic" status; This document obsoletes [RFC5987] and moves it to "Historic" status;
the changes are summarized in Appendix A. 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; therefore, they are 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"
([RFC7578]). ([RFC7578]).
2. Notational Conventions 2. Notational Conventions
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", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
This specification uses the ABNF (Augmented Backus-Naur Form) This specification uses the ABNF notation defined in [RFC5234]. The
notation defined in [RFC5234]. The following core rules are included following core rules are included by reference, as defined in
by reference, as defined in [RFC5234], Appendix B.1: ALPHA (letters), [RFC5234], Appendix B.1: ALPHA (letters), DIGIT (decimal 0-9), HEXDIG
DIGIT (decimal 0-9), HEXDIG (hexadecimal 0-9/A-F/a-f), and LWSP (hexadecimal 0-9/A-F/a-f), and LWSP (linear whitespace).
(linear whitespace).
This specification uses terminology defined in [RFC6365], namely: This specification uses terminology defined in [RFC6365], namely:
""character encoding scheme"" (below abbreviated to ""character ""character encoding scheme"" (abbreviated to ""character encoding""
encoding""), ""charset"" and ""coded character set"". below), ""charset"", and ""coded character set"".
Note that this differs from RFC 2231, which uses the term "character Note that this differs from RFC 2231, which uses the term "character
set" for "character encoding scheme". 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:
skipping to change at page 5, line 8 skipping to change at page 4, line 27
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 ([RFC7231], Appendix A.6). 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 Encoding 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 field dealing with restrictions both in MIME and HTTP header field
parameters. parameters.
However, RFC 2231 does not specify a mandatory-to-implement character However, RFC 2231 does not specify a mandatory-to-implement character
encoding, making it hard for senders to decide which encoding 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
"UTF-8" character encoding [RFC3629]. "UTF-8" character encoding [RFC3629].
Furthermore, RFC 2231 allows the character encoding information to be Furthermore, RFC 2231 allows the character encoding information to be
left out. The encoding defined by this specification does not allow left out. The encoding defined by this specification does not allow
that. that.
3.2.1. Definition 3.2.1. Definition
The presence of extended parameter values usually is indicated by a The presence of extended parameter values is usually indicated by a
parameter name ending in an asterisk character. Note however that parameter name ending in an asterisk character. However, note that
this is just a convention, and that it needs to be explicitly this is just a convention, and that the extended parameter values
specified in the definition of the header field using this extension need to be explicitly specified in the definition of the header field
(see Section 4). using this extension (see Section 4).
The ABNF for extended parameter values is specified below: The ABNF for extended parameter values is specified below:
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" / mime-charset charset = "UTF-8" / mime-charset
mime-charset = 1*mime-charsetc mime-charset = 1*mime-charsetc
skipping to change at page 6, line 43 skipping to change at page 5, line 43
consists of three parts: consists of three parts:
1. the REQUIRED character encoding name (charset), 1. the REQUIRED character encoding name (charset),
2. the OPTIONAL language information (language), and 2. the OPTIONAL language information (language), and
3. a character sequence representing the actual value (value-chars), 3. a character sequence representing the actual value (value-chars),
separated by single quote characters. separated by single quote characters.
Note that both character encoding names and language tags are Note that both character encoding names and language tags are
restricted to the US-ASCII coded character set, and are matched case- restricted to the US-ASCII coded character set and are matched case-
insensitively (see [RFC2978], Section 2.3 and [RFC5646], insensitively (see Section 2.3 of [RFC2978] and Section 2.1.1 of
Section 2.1.1). [RFC5646]).
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 encoded into an octet sequence using the specified character
encoding. That octet sequence is then percent-encoded as specified encoding. That octet sequence is then percent-encoded as specified
in Section 2.1 of [RFC3986]. in Section 2.1 of [RFC3986].
Producers MUST use the "UTF-8" ([RFC3629]) character encoding. Producers MUST use the "UTF-8" ([RFC3629]) character encoding.
Extension character encodings (mime-charset) are reserved for future Extension character encodings (mime-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, and
* 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).
3.2.2. Historical Notes 3.2.2. Historical Notes
The RFC 7230 token production ([RFC7230], Section 3.2.6) differs from The RFC 7230 token production ([RFC7230], Section 3.2.6) differs from
the production used in RFC 2231 (imported from Section 5.1 of the production used in RFC 2231 (imported from Section 5.1 of
[RFC2045]) in that curly braces ("{" and "}") are excluded. Thus, [RFC2045]) in that curly braces (i.e., "{" and "}") are excluded.
these two characters are excluded from the attr-char production as Thus, these two characters are excluded from the attr-char production
well. as well.
The <mime-charset> ABNF defined here differs from the one in 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 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 (see also RFC Errata ID 1912 [Err1912]). In practice, no
character encoding names using that character have been registered at character encoding names using that character have been registered at
the time of this writing. the time of this writing.
For backwards compatibility with RFC 2231, the encoding defined by For backwards compatibility with RFC 2231, the encoding defined by
this specification deviates from common parameter syntax in that the this specification deviates from common parameter syntax in that the
quoted-string notation is not allowed. Implementations using generic quoted-string notation is not allowed. Implementations using generic
skipping to change at page 8, line 14 skipping to change at page 7, line 14
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 Extended notation, using the Unicode character U+00A3 ("£", POUND
SIGN): SIGN):
foo: bar; title*=utf-8'en'%C2%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
octet sequence C2 A3 using the UTF-8 character encoding, then octet sequence C2 A3 using the UTF-8 character encoding, and 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 Extended notation, using the Unicode characters U+00A3 ("£", POUND
SIGN) and U+20AC ("€", EURO SIGN): 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, and 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, and then percent-
Also note that HEXDIG allows both lowercase and uppercase characters, encoded. Also note that HEXDIG allows both lowercase and uppercase
so recipients must understand both, and that the language information characters, so recipients must understand both, and that the language
is optional, while the character encoding is not. information 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. RFC 2616, the also support language specification in encoded words. RFC 2616, the
now-obsolete HTTP/1.1 specification, did refer to RFC 2047 now-obsolete HTTP/1.1 specification, did refer to RFC 2047
([RFC2616], Section 2.2). However, it wasn't clear to which header ([RFC2616], Section 2.2). However, it wasn't clear to which header
field it applied. Consequently, the current revision of the HTTP/1.1 field it applied. Consequently, the current revision of the HTTP/1.1
specification has deprecated use of the encoding forms defined in RFC specification has deprecated use of the encoding forms defined in RFC
2047 (see Section 3.2.4 of [RFC7230]). 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 specific header field the ext-value production into the ABNF for specific header field
parameters. parameters.
For instance: For instance:
foo = token ";" LWSP title-param foo = 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 draft-ietf-httpbis-rfc5987bis, Section 3.2> ext-value = <see RFC 8187, Section 3.2>
[[pub: Upon publication as RFC, the string "draft-ietf-httpbis-
rfc5987bis" needs to be replaced with the RFC name, and this comment
needs to be removed.]]
Note: The Parameter Value Continuation feature defined in Note: The Parameter Value Continuation feature defined in
Section 3 of [RFC2231] makes it impossible to have multiple Section 3 of [RFC2231] makes it impossible to have multiple
instances of extended parameters with identical names, as the instances of extended parameters with identical names, 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 Note: This specification does not automatically assign a new
interpretation to parameter names ending in an asterisk. As interpretation to parameter names ending in an asterisk. As
pointed out above, it's up to the specification for the non- pointed out above, it's up to the specification for the non-
extended parameter to "opt in" to the syntax defined here. That extended parameter to "opt in" to the syntax defined here. That
being said, some existing implementations are known to being said, some existing implementations are known to
automatically switch to the use of this notation when a parameter automatically switch to using this notation when a parameter name
name ends with an asterisk, thus using parameter names ending in ends with an asterisk; thus, using parameter names ending in an
an asterisk for something else is likely to cause interoperability asterisk for something else is likely to cause interoperability
problems. 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 be able to carry language information. Thus, the
the ext-value production ought to be always used when the parameter ext-value production ought to always be used when the parameter value
value is of textual nature and its language is known. is of a 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
([RFC0020]) coded character set (note that it would be unacceptable coded character set ([RFC0020]); note that it would be unacceptable
to 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 names are allowed, and how they should of parameters with identical names are allowed and how they should be
be processed. This specification suggests that a parameter using the processed. This specification suggests that a parameter using the
extended syntax takes precedence. This would allow producers to use extended syntax takes precedence. This would allow producers to use
both formats without breaking recipients that do not understand the both formats without breaking recipients that do not understand the
extended syntax yet. extended syntax yet.
Example: Example:
foo: bar; title="EURO exchange rates"; foo: bar; title="EURO exchange rates";
title*=utf-8''%e2%82%ac%20exchange%20rates title*=utf-8''%e2%82%ac%20exchange%20rates
In this case, the sender provides an ASCII version of the title for In this case, the sender provides an ASCII version of the title for
legacy recipients, but also includes an internationalized version for legacy recipients, but also includes an internationalized version for
recipients understanding this specification -- the latter obviously recipients understanding this specification -- the latter obviously
ought to prefer the new syntax over the old one. ought to prefer the new syntax over the old one.
5. Security Considerations 5. Security Considerations
The format described in this document makes it possible to transport The format described in this document makes it possible to transport
non-ASCII characters, and thus enables character "spoofing" non-ASCII characters, and thus enables character "spoofing" scenarios
scenarios, in which a displayed value appears to be something other in which a displayed value appears to be something other than it is.
than it is.
Furthermore, there are known attack scenarios relating to decoding Furthermore, there are known attack scenarios related to decoding
UTF-8. UTF-8.
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 effective as an attack depends on the parameter
specified. specified.
6. IANA Considerations 6. IANA Considerations
There are no IANA Considerations related to this specification. This document does not require any IANA actions.
7. References 7. References
7.1. Normative References 7.1. Normative References
[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80, [RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969, RFC 20, DOI 10.17487/RFC0020, October 1969,
<http://www.rfc-editor.org/info/rfc20>. <https://www.rfc-editor.org/info/rfc20>.
[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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2978] Freed, N. and J. Postel, "IANA Charset Registration [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration
Procedures", BCP 19, RFC 2978, DOI 10.17487/RFC2978, Procedures", BCP 19, RFC 2978, DOI 10.17487/RFC2978,
October 2000, <http://www.rfc-editor.org/info/rfc2978>. October 2000, <https://www.rfc-editor.org/info/rfc2978>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <http://www.rfc-editor.org/info/rfc3629>. 2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <http://www.rfc-editor.org/info/rfc5646>. September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014, RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>. <https://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
7.2. Informative References 7.2. Informative References
[Err1912] RFC Errata, "Errata ID 1912, RFC 2978", October 2009, [Err1912] RFC Errata, "Erratum ID 1912, RFC 2978",
<http://www.rfc-editor.org>. <https://www.rfc-editor.org/errata/eid1912>.
[ISO-8859-1] [ISO-8859-1]
International Organization for Standardization, International Organization for Standardization,
"Information technology -- 8-bit single-byte coded graphic "Information technology -- 8-bit single-byte coded graphic
character sets -- Part 1: Latin alphabet No. 1", ISO/ character sets -- Part 1: Latin alphabet No. 1", ISO/
IEC 8859-1:1998, 1998. IEC 8859-1:1998, 1998.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996, Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<http://www.rfc-editor.org/info/rfc2045>. <https://www.rfc-editor.org/info/rfc2045>.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions) [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text", Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, DOI 10.17487/RFC2047, November 1996, RFC 2047, DOI 10.17487/RFC2047, November 1996,
<http://www.rfc-editor.org/info/rfc2047>. <https://www.rfc-editor.org/info/rfc2047>.
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
Word Extensions: Character Sets, Languages, and Word Extensions: Character Sets, Languages, and
Continuations", RFC 2231, DOI 10.17487/RFC2231, November Continuations", RFC 2231, DOI 10.17487/RFC2231, November
1997, <http://www.rfc-editor.org/info/rfc2231>. 1997, <https://www.rfc-editor.org/info/rfc2231>.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, DOI 10.17487/RFC2277, Languages", BCP 18, RFC 2277, DOI 10.17487/RFC2277,
January 1998, <http://www.rfc-editor.org/info/rfc2277>. January 1998, <https://www.rfc-editor.org/info/rfc2277>.
[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, Transfer Protocol -- HTTP/1.1", RFC 2616,
DOI 10.17487/RFC2616, June 1999, DOI 10.17487/RFC2616, June 1999,
<http://www.rfc-editor.org/info/rfc2616>. <https://www.rfc-editor.org/info/rfc2616>.
[RFC5987] Reschke, J., "Character Set and Language Encoding for [RFC5987] Reschke, J., "Character Set and Language Encoding for
Hypertext Transfer Protocol (HTTP) Header Field Hypertext Transfer Protocol (HTTP) Header Field
Parameters", RFC 5987, DOI 10.17487/RFC5987, August 2010, Parameters", RFC 5987, DOI 10.17487/RFC5987, August 2010,
<http://www.rfc-editor.org/info/rfc5987>. <https://www.rfc-editor.org/info/rfc5987>.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, [RFC5988] Nottingham, M., "Web Linking", RFC 5988,
DOI 10.17487/RFC5988, October 2010, DOI 10.17487/RFC5988, October 2010,
<http://www.rfc-editor.org/info/rfc5988>. <https://www.rfc-editor.org/info/rfc5988>.
[RFC6266] Reschke, J., "Use of the Content-Disposition Header Field [RFC6266] Reschke, J., "Use of the Content-Disposition Header Field
in the Hypertext Transfer Protocol (HTTP)", RFC 6266, in the Hypertext Transfer Protocol (HTTP)", RFC 6266,
DOI 10.17487/RFC6266, June 2011, DOI 10.17487/RFC6266, June 2011,
<http://www.rfc-editor.org/info/rfc6266>. <https://www.rfc-editor.org/info/rfc6266>.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF", BCP 166, RFC 6365, Internationalization in the IETF", BCP 166, RFC 6365,
DOI 10.17487/RFC6365, September 2011, DOI 10.17487/RFC6365, September 2011,
<http://www.rfc-editor.org/info/rfc6365>. <https://www.rfc-editor.org/info/rfc6365>.
[RFC7578] Masinter, L., "Returning Values from Forms: multipart/ [RFC7578] Masinter, L., "Returning Values from Forms: multipart/
form-data", RFC 7578, DOI 10.17487/RFC7578, July 2015, form-data", RFC 7578, DOI 10.17487/RFC7578, July 2015,
<http://www.rfc-editor.org/info/rfc7578>. <https://www.rfc-editor.org/info/rfc7578>.
[RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP [RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP
Digest Access Authentication", RFC 7616, Digest Access Authentication", RFC 7616,
DOI 10.17487/RFC7616, September 2015, DOI 10.17487/RFC7616, September 2015,
<http://www.rfc-editor.org/info/rfc7616>. <https://www.rfc-editor.org/info/rfc7616>.
[RFC8053] Oiwa, Y., Watanabe, H., Takagi, H., Maeda, K., Hayashi, [RFC8053] Oiwa, Y., Watanabe, H., Takagi, H., Maeda, K., Hayashi,
T., and Y. Ioku, "HTTP Authentication Extensions for T., and Y. Ioku, "HTTP Authentication Extensions for
Interactive Clients", RFC 8053, DOI 10.17487/RFC8053, Interactive Clients", RFC 8053, DOI 10.17487/RFC8053,
January 2017, <http://www.rfc-editor.org/info/rfc8053>. January 2017, <https://www.rfc-editor.org/info/rfc8053>.
[XMLHttpRequest] [XMLHttpRequest]
WhatWG, "XMLHttpRequest", <https://xhr.spec.whatwg.org/>. WhatWG, "XMLHttpRequest", <https://xhr.spec.whatwg.org/>.
Appendix A. Changes from RFC 5987 Appendix A. Changes from RFC 5987
This section summarizes the changes compared to [RFC5987]: This section summarizes the changes compared to [RFC5987]:
o The document title was changed to "Indicating Character Encoding o The document title was changed to "Indicating Character Encoding
and Language for HTTP Header Field Parameters". and Language for HTTP Header Field Parameters".
o The introduction was rewritten to better explain the issues around o The introduction was rewritten to better explain the issues around
non-ASCII characters in field values. non-ASCII characters in field values.
o The requirement to support the "ISO-8859-1" encoding was removed. o The requirement to support the "ISO-8859-1" encoding was removed.
o The document does not attempt to re-define a generic "parameter" o This document no longer attempts to redefine a generic "parameter"
ABNF anymore (it turned out that there really isn't a generic ABNF (it turned out that there really isn't a generic definition
definition of parameters in HTTP; for instance, there are subtle of parameters in HTTP; for instance, there are subtle differences
differences with respect to whitespace handling). with respect to whitespace handling).
o A note about defects in error handling in current implementations o A note about defects in error handling in current implementations
was removed, as it wasn't accurate anymore. was removed, as it was no longer accurate.
Appendix B. Implementation Report Appendix B. Implementation Report
The encoding defined in this document currently is used in four The encoding defined in this document is currently used in four
different HTTP header fields: different HTTP header fields:
o "Authentication-Control", defined in [RFC8053], o "Authentication-Control", defined in [RFC8053],
o "Authorization" (as used in HTTP Digest Authentication, defined in o "Authorization" (as used in HTTP Digest Authentication, defined in
[RFC7616]), [RFC7616]),
o "Content-Disposition", defined in [RFC6266], and o "Content-Disposition", defined in [RFC6266], and
o "Link", defined in [RFC5988]. o "Link", defined in [RFC5988].
As the encoding is a profile/clarification of the one defined in As the encoding is a profile/clarification of the one defined in
[RFC2231] in 1997, many user agents already supported it for use in [RFC2231] in 1997, many user agents already supported it for use in
"Content-Disposition" when [RFC5987] got published. "Content-Disposition" when [RFC5987] was published.
Since the publication of [RFC5987], three more popular desktop user Since the publication of [RFC5987], three more popular desktop user
agents have added support for this encoding; see agents have added support for this encoding; see
<http://purl.org/NET/http/content-disposition-tests#encoding- <http://purl.org/NET/http/content-disposition-tests#encoding-
2231-char> for details. At this time, the current versions of all 2231-char> for details. At this time, the current versions of all
major desktop user agents support it. major desktop user agents support it.
Note that the implementation in Internet Explorer 9 does not support Note that the implementation in Internet Explorer 9 does not support
the ISO-8859-1 character encoding; this document revision the ISO-8859-1 character encoding; this document revision
acknowledges that UTF-8 is sufficient for expressing all code points, acknowledges that UTF-8 is sufficient for expressing all code points
and removes the requirement to support ISO-8859-1. and removes the requirement to support ISO-8859-1.
The "Link" header field, on the other hand, was more recently The "Link" header field, on the other hand, was more recently
specified in [RFC5988]. At the time of this writing, no User Agent specified in [RFC5988]. At the time of this writing, no user agent
except Firefox supported the "title*" parameter (starting with except Firefox supported the "title*" parameter (starting with
release 15). release 15).
Section 3.4 of [RFC7616] defines the "username*" parameter for use in Section 3.4 of [RFC7616] defines the "username*" parameter for use in
HTTP Digest Authentication. At the time of writing, no User Agent HTTP Digest Authentication. At the time of writing, no user agent
implemented this extension. implemented this extension.
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.
C.9. Since draft-ietf-httpbis-rfc5987bis-00
Editorial changes; introducing non-ASCII characters into author's
address, acknowledgements, and examples.
C.10. Since draft-ietf-httpbis-rfc5987bis-01
Removed mention of RFC 2616 from Abstract and Introduction.
Reference RFC 20 for US-ASCII.
Do not attempt to define a generic parameter ABNF; just concentrate
on the parameter value syntax.
C.11. Since draft-ietf-httpbis-rfc5987bis-02
RFC 2388 -> RFC 7578.
Expand on the motivation (see <https://github.com/httpwg/http-
extensions/issues/213>).
Mention RFC 7616 in implementation report.
C.12. Since draft-ietf-httpbis-rfc5987bis-03
Fixed one editorial issue. Updated XHR reference.
Fixed <https://github.com/httpwg/http-extensions/issues/266>: use of
now undefined term "parmname".
Include WG into Acknowledgements for this revision.
Mention RFC 5987 in the abstract (<https://github.com/httpwg/http-
extensions/issues/271>).
C.13. Since draft-ietf-httpbis-rfc5987bis-04
Mention RFC8053 in Implementation Report.
Acknowledgements Acknowledgements
Thanks to Martin Dürst and Frank Ellermann for help figuring out Thanks to Martin Dürst 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, Roar Lauritzsen, Eric Lawrence, and James Manger Benjamin Carlyle, Roar Lauritzsen, Eric Lawrence, and James Manger
for implementer's feedback. for implementers feedback.
Furthermore thanks to the members of the IETF HTTP Working Group for Furthermore, thanks to the members of the IETF HTTP Working Group for
the feedback specific to this update of RFC 5987. the feedback specific to this update of RFC 5987.
Author's Address Author's Address
Julian F. Reschke Julian F. Reschke
greenbytes GmbH greenbytes GmbH
Hafenweg 16 Hafenweg 16
Münster, NW 48155 Münster, 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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