< draft-reschke-rfc2231-in-http-11.txt   draft-reschke-rfc2231-in-http-12.txt >
Network Working Group J. Reschke Network Working Group J. Reschke
Internet-Draft greenbytes Internet-Draft greenbytes
Intended status: Standards Track March 30, 2010 Intended status: Standards Track April 30, 2010
Expires: October 1, 2010 Expires: November 1, 2010
Application of RFC 2231 Encoding to Character Set and Language Encoding for Hypertext Transfer Protocol
Hypertext Transfer Protocol (HTTP) Header Fields (HTTP) Header Field Parameters
draft-reschke-rfc2231-in-http-11 draft-reschke-rfc2231-in-http-12
Abstract Abstract
By default, message header field parameters in Hypertext Transfer By default, message header field parameters in Hypertext Transfer
Protocol (HTTP) messages can not carry characters outside the ISO- Protocol (HTTP) messages can not carry characters outside the ISO-
8859-1 character set. RFC 2231 defines an escaping 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 a profile of that encoding suitable for use in document specifies an encoding suitable for use in HTTP header fields
HTTP header fields. which is compatible to a profile of the encoding defined in RFC 2231.
Editorial Note (To be removed by RFC Editor before publication) Editorial Note (To be removed by RFC Editor before publication)
There are multiple HTTP header fields that already use RFC 2231 There are multiple HTTP header fields that already use RFC 2231
encoding in practice (Content-Disposition) or might use it in the encoding in practice (Content-Disposition) or might use it in the
future (Link). The purpose of this document is to provide a single future (Link). The purpose of this document is to provide a single
place where the generic aspects of RFC 2231 encoding in HTTP header place where the generic aspects of RFC 2231 encoding in HTTP header
fields are defined. fields are defined.
Distribution of this document is unlimited. Although this is not a Distribution of this document is unlimited. Although this is not a
skipping to change at page 2, line 4 skipping to change at page 2, line 4
available from available from
<http://greenbytes.de/tech/webdav/#draft-reschke-rfc2231-in-http>. A <http://greenbytes.de/tech/webdav/#draft-reschke-rfc2231-in-http>. A
collection of test cases is available at collection of test cases is available at
<http://greenbytes.de/tech/tc2231/>. <http://greenbytes.de/tech/tc2231/>.
Note: as of February 2010, there were at least three independent Note: as of February 2010, there were at least three independent
implementations of the encoding defined in Section 3.2: Konqueror implementations of the encoding defined in Section 3.2: Konqueror
(starting with 4.4.1), Mozilla Firefox, and Opera. (starting with 4.4.1), Mozilla Firefox, and Opera.
Status of This Memo Status of This Memo
This Internet-Draft is submitted to IETF 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), its areas, and its working groups. Note that Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at This Internet-Draft will expire on November 1, 2010.
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on October 1, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4
3. A Profile of RFC 2231 for Use in HTTP . . . . . . . . . . . . 4 3. Comparison to RFC 2231 and Definition of the Encoding . . . . 4
3.1. Parameter Continuations . . . . . . . . . . . . . . . . . 5 3.1. Parameter Continuations . . . . . . . . . . . . . . . . . 5
3.2. Parameter Value Character Set and Language Information . . 5 3.2. Parameter Value Character Set and Language Information . . 5
3.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.1. Definition . . . . . . . . . . . . . . . . . . . . . . 5
3.2.2. Examples . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Language specification in Encoded Words . . . . . . . . . 8 3.3. Language specification in Encoded Words . . . . . . . . . 8
4. Guidelines for Usage in HTTP Header Field Definitions . . . . 8 4. Guidelines for Usage in HTTP Header Field Definitions . . . . 8
4.1. When to Use the Extension . . . . . . . . . . . . . . . . 9 4.1. When to Use the Extension . . . . . . . . . . . . . . . . 9
4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . . 9 4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10 8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 11 8.2. Informative References . . . . . . . . . . . . . . . . . . 11
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B.2. Since draft-reschke-rfc2231-in-http-01 . . . . . . . . . . 12 B.2. Since draft-reschke-rfc2231-in-http-01 . . . . . . . . . . 12
B.3. Since draft-reschke-rfc2231-in-http-02 . . . . . . . . . . 13 B.3. Since draft-reschke-rfc2231-in-http-02 . . . . . . . . . . 13
B.4. Since draft-reschke-rfc2231-in-http-03 . . . . . . . . . . 13 B.4. Since draft-reschke-rfc2231-in-http-03 . . . . . . . . . . 13
B.5. Since draft-reschke-rfc2231-in-http-04 . . . . . . . . . . 13 B.5. Since draft-reschke-rfc2231-in-http-04 . . . . . . . . . . 13
B.6. Since draft-reschke-rfc2231-in-http-05 . . . . . . . . . . 13 B.6. Since draft-reschke-rfc2231-in-http-05 . . . . . . . . . . 13
B.7. Since draft-reschke-rfc2231-in-http-06 . . . . . . . . . . 13 B.7. Since draft-reschke-rfc2231-in-http-06 . . . . . . . . . . 13
B.8. Since draft-reschke-rfc2231-in-http-07 . . . . . . . . . . 13 B.8. Since draft-reschke-rfc2231-in-http-07 . . . . . . . . . . 13
B.9. Since draft-reschke-rfc2231-in-http-08 . . . . . . . . . . 13 B.9. Since draft-reschke-rfc2231-in-http-08 . . . . . . . . . . 13
B.10. Since draft-reschke-rfc2231-in-http-09 . . . . . . . . . . 13 B.10. Since draft-reschke-rfc2231-in-http-09 . . . . . . . . . . 13
B.11. Since draft-reschke-rfc2231-in-http-10 . . . . . . . . . . 13 B.11. Since draft-reschke-rfc2231-in-http-10 . . . . . . . . . . 13
B.12. Since draft-reschke-rfc2231-in-http-11 . . . . . . . . . . 14
Appendix C. Resolved issues (to be removed by RFC Editor Appendix C. Resolved issues (to be removed by RFC Editor
before publication) . . . . . . . . . . . . . . . . . 14 before publication) . . . . . . . . . . . . . . . . . 14
C.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 C.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
C.2. charset-registered . . . . . . . . . . . . . . . . . . . . 14 C.2. nonorm2231 . . . . . . . . . . . . . . . . . . . . . . . . 14
C.3. parameter-abnf . . . . . . . . . . . . . . . . . . . . . . 14
C.4. value-abnf . . . . . . . . . . . . . . . . . . . . . . . . 14
C.5. iso8859 . . . . . . . . . . . . . . . . . . . . . . . . . 15
C.6. when-ext-value . . . . . . . . . . . . . . . . . . . . . . 15
C.7. repeated-param . . . . . . . . . . . . . . . . . . . . . . 15
C.8. handling-multiple . . . . . . . . . . . . . . . . . . . . 16
C.9. i18n-spoofing . . . . . . . . . . . . . . . . . . . . . . 17
C.10. multiple-inst-spoofing . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
By default, message header field parameters in HTTP ([RFC2616]) By default, message header field parameters in HTTP ([RFC2616])
messages can not carry characters outside the ISO-8859-1 character messages can not carry characters outside the ISO-8859-1 character
set ([ISO-8859-1]). RFC 2231 (Appendix of [RFC2231]) defines an set ([ISO-8859-1]). RFC 2231 ([RFC2231]) defines an encoding
escaping mechanism for use in MIME headers. This document specifies mechanism for use in MIME headers. This document specifies an
a profile of that encoding for use in HTTP header fields. encoding suitable for use in HTTP header fields which is compatible
to a profile of the encoding defined in RFC 2231.
Note: this profile does not apply to message payloads transmitted Note: in the remainder of this document, RFC 2231 is only
referenced for the purpose of explaining the choice of features
that were adopted; they are therefore purely informative.
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
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 white space). (linear white space).
Note that this specification uses the term "character set" for Note that this specification uses the term "character set" for
consistency with other IETF specifications such as RFC 2277 (see consistency with other IETF specifications such as RFC 2277 (see
[RFC2277], Section 3). A more accurate term would be "character [RFC2277], Section 3). A more accurate term would be "character
encoding" (a mapping of code points to octet sequences). encoding" (a mapping of code points to octet sequences).
3. A Profile of RFC 2231 for Use in HTTP 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. 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 Set and Language Information are useful, therefore a o Character Set and Language Information are useful, therefore 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 ([RFC2616], Section 19.4.7).
Thus in HTTP, senders MUST NOT use parameter continuations, and Thus, parameter continuations are not part of the encoding defined by
therefore recipients do not need to support them. this specification.
3.2. Parameter Value Character Set and Language Information 3.2. Parameter Value Character Set 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 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. set, making it hard for senders to decide which character set 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]. character sets "ISO-8859-1" [ISO-8859-1] and "UTF-8" [RFC3629].
Furthermore, RFC 2231 allows leaving out the character set Furthermore, RFC 2231 allows leaving out the character set
information. The profile defined by this specification does not information. The encoding defined by this specification does not
allow that. allow that.
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 [RFC2616], Section 2.2>
token = <token, defined in [RFC2616], Section 2.2> token = <token, defined in [RFC2616], Section 2.2>
This specification modifies the grammar to: In order to include character set and language information, this
specification modifies the RFC 2616 grammar to:
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
; extended-initial-value, ; like RFC 2231's <extended-initial-value>
; defined in [RFC2231], Section 7 ; (see [RFC2231], Section 7)
charset = "UTF-8" / "ISO-8859-1" / mime-charset charset = "UTF-8" / "ISO-8859-1" / 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
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single quote characters. Note that both character set names and single quote characters. Note that both character set names and
language tags are restricted to the US-ASCII character set, and are language tags are restricted to the US-ASCII character set, and are
matched case-insensitively (see [RFC2978], Section 2.3 and [RFC5646], matched case-insensitively (see [RFC2978], Section 2.3 and [RFC5646],
Section 2.1.1). 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 set.
That octet sequence then is percent-encoded as specified in Section That octet sequence then is percent-encoded as specified in Section
2.1 of [RFC3986]. 2.1 of [RFC3986].
Producers MUST NOT use character sets other than "UTF-8" ([RFC3629]) Producers MUST use either the "UTF-8" ([RFC3629]) or the "ISO-8859-1"
or "ISO-8859-1" ([ISO-8859-1]). Extension character sets (ext- ([ISO-8859-1]) character set. Extension character sets (mime-
charset) are reserved for future use. charset) are reserved for future 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 following does not mandate any specific behavior, for instance the following
strategies are all acceptable: strategies are all acceptable:
* ignoring the parameter, * ignoring the parameter,
skipping to change at page 7, line 42 skipping to change at page 7, line 42
Section 5.1 of [RFC2045]) in that curly braces ("{" and "}") are Section 5.1 of [RFC2045]) in that curly braces ("{" and "}") are
excluded. Thus, these two characters are excluded from the attr- excluded. Thus, these two characters are excluded from the attr-
char production as well. char production as well.
Note: the <mime-charset> ABNF defined here differs from the one in Note: the <mime-charset> ABNF defined here differs from the one in
Section 2.3 of [RFC2978] in that it does not allow the single Section 2.3 of [RFC2978] in that it does not allow the single
quote character (see also RFC Editor Errata ID 1912 [3]). In quote character (see also RFC Editor Errata ID 1912 [3]). In
practice, no character set names using that character have been practice, no character set names using that character have been
registered at the time of this writing. registered at the time of this writing.
3.2.1. Examples 3.2.2. 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):
skipping to change at page 8, line 36 skipping to change at page 8, line 36
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. Although the
HTTP/1.1 specification does refer to RFC 2047 ([RFC2616], Section HTTP/1.1 specification does refer to RFC 2047 ([RFC2616], Section
2.2), it's not clear to which header field exactly it applies, and 2.2), it's not clear to which header field exactly it applies, and
whether it is implemented in practice (see whether it is implemented in practice (see
<http://tools.ietf.org/wg/httpbis/trac/ticket/111> for details). <http://tools.ietf.org/wg/httpbis/trac/ticket/111> for details).
Thus, the RFC 2231 profile defined by this specification does not Thus, this specification does not include this feature.
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 should 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 RFCxxxx, Section 3.2> ext-value = <see RFCxxxx, Section 3.2>
[[rfcno: Note to RFC Editor: in the figure above, please replace [[rfcno: Note to RFC Editor: in the figure above, please replace
"xxxx" by the RFC number assigned to this specification.]] "xxxx" by the RFC number assigned to this specification.]]
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 recommended to disallow specifications using this extension are advised to disallow this
this case for compatibility with RFC 2231. case for compatibility with RFC 2231.
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
text are able to carry language information. Thus, the ext-value human-readable text are able to carry language information. Thus,
production should always be used when the parameter value is of the ext-value production ought to be always used when the parameter
textual nature and its language is known. value is of textual nature and its language is known.
Furthermore, the extension should also be used whenever the parameter Furthermore, the extension ought to also be used whenever the
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]) character set (note that it would be unacceptable to
define a new parameter that would be restricted to a subset of the 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 processed. It is recommended that a parameter using the they should processed. This specification suggests that a parameter
extended syntax takes precedence. This could be used by producers to using the extended syntax takes precedence. This could be used by
use both formats without breaking recipients that do not understand producers to use both formats without breaking recipients that do not
the extended syntax yet. understand the 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
should prefer the new syntax over the old one. ought to prefer the new syntax over the old one.
Note: at the time of this writing, many implementations failed to Note: at the time of this writing, many implementations failed to
ignore the form they do not understand, or prioritize the ASCII ignore the form they do not understand, or prioritize the ASCII
form although the extended syntax was present. form although the extended syntax was present.
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, in which a displayed value appears to be something other scenarios, in which a displayed value appears to be something other
skipping to change at page 14, line 5 skipping to change at page 14, line 5
B.11. Since draft-reschke-rfc2231-in-http-10 B.11. Since draft-reschke-rfc2231-in-http-10
Resolve issues "i18n-spoofing", "iso8859", "parameter-abnf", and Resolve issues "i18n-spoofing", "iso8859", "parameter-abnf", and
"when-ext-value". "when-ext-value".
Add and resolve issue "charset-registered", "handling-multiple", Add and resolve issue "charset-registered", "handling-multiple",
"multiple-inst-spoofing", "repeated-param" and "value-abnf". "multiple-inst-spoofing", "repeated-param" and "value-abnf".
Update the KDE implementation note. Update the KDE implementation note.
B.12. Since draft-reschke-rfc2231-in-http-11
In the prose in Section 3.2, "ext-charset" -> "mime-charset". In
Section 4, avoid the use of "should" and "recommended". In
Section 4.1 clarify that the RFC 2277 requirement is about human-
readable text. Clarify parts that made it look as if this spec has a
normative dependency on RFC 2231 (new issue "nonorm2231").
Appendix C. Resolved issues (to be removed by RFC Editor before Appendix C. Resolved issues (to be removed by RFC Editor before
publication) publication)
Issues that were either rejected or resolved in this version of this Issues that were either rejected or resolved in this version of this
document. document.
C.1. edit C.1. edit
Type: edit Type: edit
julian.reschke@greenbytes.de (2009-04-17): Umbrella issue for julian.reschke@greenbytes.de (2009-04-17): Umbrella issue for
editorial fixes/enhancements. editorial fixes/enhancements.
C.2. charset-registered C.2. nonorm2231
In Section 3.2:
Type: change
julian.reschke@greenbytes.de (2010-02-20): Mention to use only
registered charset names? (reported by Alexey Melnikov).
Resolution (2010-03-29): State this in the ABNF.
C.3. parameter-abnf
In Section 3.2:
Type: change
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).
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 "/".
Resolution: Introduced parmname, disallowing "*" / "'" / "%". Moving
the value ABNF discussion into a separate issue ("value-abnf").
C.4. value-abnf
In Section 3.2:
Type: change
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 "/".
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.
C.5. iso8859
In Section 3.2:
Type: change
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.
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.
C.6. when-ext-value
In Section 4.1:
Type: change
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.
Resolution (2010-02-23): Fixed.
C.7. repeated-param
In Section 4:
Type: change
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.
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.
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.
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.
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.
Resolution (2010-03-29): State the issue. Remove section 4.3.
Rephrase 4.2 accordingly.
C.8. handling-multiple
In Section 4.2:
Type: change
<http://www.ietf.org/mail-archive/web/apps-discuss/current/
msg01344.html>
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.
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?
Resolution (2010-03-29): Just state that when repetitions are not
allowed, the extended form should take precedence.
C.9. i18n-spoofing
In Section 5:
Type: change
<http://www.ietf.org/mail-archive/web/apps-discuss/current/
msg01329.html>
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.
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.
C.10. multiple-inst-spoofing
In Section 5:
Type: change Type: edit
kivinen@iki.fi (2010-03-01): Yes, but the impact of them is julian.reschke@greenbytes.de (2010-04-23): It's not totally clear
different. For example it does not really matter if the filename that the mentions of RFC 2231 really are all informative.
parameters having different languages differ, but there might be
parameters where this really matters.
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."
Resolution (2010-03-01): Add text based on the recommendation. Resolution (2010-04-28): Clarify title of the spec, plus text talking
about RFC 2231. Avoid saying "profile" in general.
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
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