Network Working Group J. Reschke
Internet-Draft greenbytes
Intended status: Standards Track March 30, 2010
Expires: October 1, 2010
Application of RFC 2231 Encoding to
Hypertext Transfer Protocol (HTTP) Header Fields
draft-reschke-rfc2231-in-http-11
Abstract
By default, message header field parameters in Hypertext Transfer
Protocol (HTTP) messages can not carry characters outside the ISO-
8859-1 character set. RFC 2231 defines an escaping mechanism for use
in Multipurpose Internet Mail Extensions (MIME) headers. This
document specifies a profile of that encoding suitable for use in
HTTP header fields.
Editorial Note (To be removed by RFC Editor before publication)
There are multiple HTTP header fields that already use RFC 2231
encoding in practice (Content-Disposition) or might use it in the
future (Link). The purpose of this document is to provide a single
place where the generic aspects of RFC 2231 encoding in HTTP header
fields are defined.
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 and the issues list for this document are
available from
<http://greenbytes.de/tech/webdav/#draft-reschke-rfc2231-in-http>. A
collection of test cases is available at
<http://greenbytes.de/tech/tc2231/>.
Note: as of February 2010, there were at least three independent
implementations of the encoding defined in Section 3.2: Konqueror
(starting with 4.4.1), Mozilla Firefox, and Opera.
Status of This Memo
Reschke Expires October 1, 2010 [Page 1]
Internet-Draft RFC2231 Encoding in HTTP March 2010
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 1, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
Reschke Expires October 1, 2010 [Page 2]
Internet-Draft RFC2231 Encoding in HTTP March 2010
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4
3. A Profile of RFC 2231 for Use in HTTP . . . . . . . . . . . . 4
3.1. Parameter Continuations . . . . . . . . . . . . . . . . . 5
3.2. Parameter Value Character Set and Language Information . . 5
3.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Language specification in Encoded Words . . . . . . . . . 8
4. Guidelines for Usage in HTTP Header Field Definitions . . . . 8
4.1. When to Use the Extension . . . . . . . . . . . . . . . . 9
4.2. Error Handling . . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Document History and Future Plans (to be removed
by RFC Editor before publication) . . . . . . . . . . 12
Appendix B. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 12
B.1. Since draft-reschke-rfc2231-in-http-00 . . . . . . . . . . 12
B.2. Since draft-reschke-rfc2231-in-http-01 . . . . . . . . . . 12
B.3. Since draft-reschke-rfc2231-in-http-02 . . . . . . . . . . 13
B.4. Since draft-reschke-rfc2231-in-http-03 . . . . . . . . . . 13
B.5. Since draft-reschke-rfc2231-in-http-04 . . . . . . . . . . 13
B.6. Since draft-reschke-rfc2231-in-http-05 . . . . . . . . . . 13
B.7. Since draft-reschke-rfc2231-in-http-06 . . . . . . . . . . 13
B.8. Since draft-reschke-rfc2231-in-http-07 . . . . . . . . . . 13
B.9. Since draft-reschke-rfc2231-in-http-08 . . . . . . . . . . 13
B.10. Since draft-reschke-rfc2231-in-http-09 . . . . . . . . . . 13
B.11. Since draft-reschke-rfc2231-in-http-10 . . . . . . . . . . 13
Appendix C. Resolved issues (to be removed by RFC Editor
before publication) . . . . . . . . . . . . . . . . . 14
C.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
C.2. charset-registered . . . . . . . . . . . . . . . . . . . . 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
Reschke Expires October 1, 2010 [Page 3]
Internet-Draft RFC2231 Encoding in HTTP March 2010
1. Introduction
By default, message header field parameters in HTTP ([RFC2616])
messages can not carry characters outside the ISO-8859-1 character
set ([ISO-8859-1]). RFC 2231 (Appendix of [RFC2231]) defines an
escaping mechanism for use in MIME headers. This document specifies
a profile of that encoding for use in HTTP header fields.
Note: this profile does not apply to message payloads transmitted
over HTTP, such as when using the media type "multipart/form-data"
([RFC2388]).
2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This specification uses the ABNF (Augmented Backus-Naur Form)
notation defined in [RFC5234]. The following core rules are included
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
(linear white space).
Note that this specification uses the term "character set" for
consistency with other IETF specifications such as RFC 2277 (see
[RFC2277], Section 3). A more accurate term would be "character
encoding" (a mapping of code points to octet sequences).
3. A Profile of RFC 2231 for Use in HTTP
RFC 2231 defines several extensions to MIME. The sections below
discuss if and how they apply to HTTP.
In short:
o Parameter Continuations aren't needed (Section 3.1),
o Character Set and Language Information are useful, therefore a
simple subset is specified (Section 3.2), and
o Language Specifications in Encoded Words aren't needed
(Section 3.3).
Reschke Expires October 1, 2010 [Page 4]
Internet-Draft RFC2231 Encoding in HTTP March 2010
3.1. Parameter Continuations
Section 3 of [RFC2231] defines a mechanism that deals with the length
limitations that apply to MIME headers. These limitations do not
apply to HTTP ([RFC2616], Section 19.4.7).
Thus in HTTP, senders MUST NOT use parameter continuations, and
therefore recipients do not need to support them.
3.2. Parameter Value Character Set and Language Information
Section 4 of [RFC2231] specifies how to embed language information
into parameter values, and also how to encode non-ASCII characters,
dealing with restrictions both in MIME and HTTP header parameters.
However, RFC 2231 does not specify a mandatory-to-implement character
set, making it hard for senders to decide which character set to use.
Thus, recipients implementing this specification MUST support the
character sets "ISO-8859-1" [ISO-8859-1] and "UTF-8" [RFC3629].
Furthermore, RFC 2231 allows leaving out the character set
information. The profile defined by this specification does not
allow that.
The syntax for parameters is defined in Section 3.6 of [RFC2616]
(with RFC 2616 implied LWS translated to RFC 5234 LWSP):
parameter = attribute LWSP "=" LWSP value
attribute = token
value = token / quoted-string
quoted-string = <quoted-string, defined in [RFC2616], Section 2.2>
token = <token, defined in [RFC2616], Section 2.2>
This specification modifies the grammar to:
Reschke Expires October 1, 2010 [Page 5]
Internet-Draft RFC2231 Encoding in HTTP March 2010
parameter = reg-parameter / ext-parameter
reg-parameter = parmname LWSP "=" LWSP value
ext-parameter = parmname "*" LWSP "=" LWSP ext-value
parmname = 1*attr-char
ext-value = charset "'" [ language ] "'" value-chars
; extended-initial-value,
; defined in [RFC2231], Section 7
charset = "UTF-8" / "ISO-8859-1" / mime-charset
mime-charset = 1*mime-charsetc
mime-charsetc = ALPHA / DIGIT
/ "!" / "#" / "$" / "%" / "&"
/ "+" / "-" / "^" / "_" / "`"
/ "{" / "}" / "~"
; as <mime-charset> in Section 2.3 of [RFC2978]
; except that the single quote is not included
; SHOULD be registered in the IANA charset registry
language = <Language-Tag, defined in [RFC5646], Section 2.1>
value-chars = *( pct-encoded / attr-char )
pct-encoded = "%" HEXDIG HEXDIG
; see [RFC3986], Section 2.1
attr-char = ALPHA / DIGIT
/ "!" / "#" / "$" / "&" / "+" / "-" / "."
/ "^" / "_" / "`" / "|" / "~"
; token except ( "*" / "'" / "%" )
Thus, a parameter is either regular parameter (reg-parameter), as
previously defined in Section 3.6 of [RFC2616], or an extended
parameter (ext-parameter).
Extended parameters are those where the left hand side of the
assignment ends with an asterisk character.
The value part of an extended parameter (ext-value) is a token that
consists of three parts: the REQUIRED character set name (charset),
the OPTIONAL language information (language), and a character
sequence representing the actual value (value-chars), separated by
single quote characters. Note that both character set names and
language tags are restricted to the US-ASCII character set, and are
Reschke Expires October 1, 2010 [Page 6]
Internet-Draft RFC2231 Encoding in HTTP March 2010
matched case-insensitively (see [RFC2978], Section 2.3 and [RFC5646],
Section 2.1.1).
Inside the value part, characters not contained in attr-char are
encoded into an octet sequence using the specified character set.
That octet sequence then is percent-encoded as specified in Section
2.1 of [RFC3986].
Producers MUST NOT use character sets other than "UTF-8" ([RFC3629])
or "ISO-8859-1" ([ISO-8859-1]). Extension character sets (ext-
charset) are reserved for future use.
Note: recipients should be prepared to handle encoding errors,
such as malformed or incomplete percent escape sequences, or non-
decodable octet sequences, in a robust manner. This specification
does not mandate any specific behavior, for instance the following
strategies are all acceptable:
* ignoring the parameter,
* stripping a non-decodable octet sequence,
* substituting a non-decodable octet sequence by a replacement
character, such as the Unicode character U+FFFD (Replacement
Character).
Note: the RFC 2616 token production ([RFC2616], Section 2.2)
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
Section 2.3 of [RFC2978] in that it does not allow the single
quote character (see also RFC Editor Errata ID 1912 [3]). In
practice, no character set names using that character have been
registered at the time of this writing.
3.2.1. Examples
Non-extended notation, using "token":
foo: bar; title=Economy
Non-extended notation, using "quoted-string":
foo: bar; title="US-$ rates"
Reschke Expires October 1, 2010 [Page 7]
Internet-Draft RFC2231 Encoding in HTTP March 2010
Extended notation, using the unicode character U+00A3 (POUND SIGN):
foo: bar; title*=iso-8859-1'en'%A3%20rates
Note: the Unicode pound sign character U+00A3 was encoded using ISO-
8859-1 into the single octet A3, then percent-encoded. Also note
that the space character was encoded as %20, as it is not contained
in attr-char.
Extended notation, using the unicode characters U+00A3 (POUND SIGN)
and U+20AC (EURO SIGN):
foo: bar; title*=UTF-8''%c2%a3%20and%20%e2%82%ac%20rates
Note: the unicode pound sign character U+00A3 was encoded using UTF-8
into the octet sequence C2 A3, then percent-encoded. Likewise, the
unicode euro sign character U+20AC was encoded into the octet
sequence E2 82 AC, then percent-encoded. Also note that HEXDIG
allows both lower-case and upper-case character, so recipients must
understand both, and that the language information is optional, while
the character set is not.
3.3. Language specification in Encoded Words
Section 5 of [RFC2231] extends the encoding defined in [RFC2047] to
also support language specification in encoded words. Although the
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
whether it is implemented in practice (see
<http://tools.ietf.org/wg/httpbis/trac/ticket/111> for details).
Thus, the RFC 2231 profile defined by this specification does not
include this feature.
4. Guidelines for Usage in HTTP Header Field Definitions
Specifications of HTTP header fields that use the extensions defined
in Section 3.2 should clearly state that. A simple way to achieve
this is to normatively reference this specification, and to include
the ext-value production into the ABNF for that header field.
For instance:
foo-header = "foo" LWSP ":" LWSP token ";" LWSP title-param
title-param = "title" LWSP "=" LWSP value
/ "title*" LWSP "=" LWSP ext-value
ext-value = <see RFCxxxx, Section 3.2>
Reschke Expires October 1, 2010 [Page 8]
Internet-Draft RFC2231 Encoding in HTTP March 2010
[[rfcno: Note to RFC Editor: in the figure above, please replace
"xxxx" by the RFC number assigned to this specification.]]
Note: The Parameter Value Continuation feature defined in Section
3 of [RFC2231] makes it impossible to have multiple instances of
extended parameters with identical parmname components, as the
processing of continuations would become ambiguous. Thus,
specifications using this extension are recommended to disallow
this case for compatibility with RFC 2231.
4.1. When to Use the Extension
Section 4.2 of [RFC2277] requires that protocol elements containing
text are able to carry language information. Thus, the ext-value
production should always be used when the parameter value is of
textual nature and its language is known.
Furthermore, the extension should also be used whenever the parameter
value needs to carry characters not present in the US-ASCII
([USASCII]) character set (note that it would be unacceptable to
define a new parameter that would be restricted to a subset of the
Unicode character set).
4.2. Error Handling
Header field specifications need to define whether multiple instances
of parameters with identical parmname components are allowed, and how
they should processed. It is recommended that a parameter using the
extended syntax takes precedence. This could be used by producers to
use both formats without breaking recipients that do not understand
the extended syntax yet.
Example:
foo: bar; title="EURO exchange rates";
title*=utf-8''%e2%82%ac%20exchange%20rates
In this case, the sender provides an ASCII version of the title for
legacy recipients, but also includes an internationalized version for
recipients understanding this specification -- the latter obviously
should prefer the new syntax over the old one.
Note: at the time of this writing, many implementations failed to
ignore the form they do not understand, or prioritize the ASCII
form although the extended syntax was present.
Reschke Expires October 1, 2010 [Page 9]
Internet-Draft RFC2231 Encoding in HTTP March 2010
5. Security Considerations
The format described in this document makes it possible to transport
non-ASCII characters, and thus enables character "spoofing"
scenarios, in which a displayed value appears to be something other
than it is.
Furthermore, there are known attack scenarios relating to decoding
UTF-8.
See Section 10 of [RFC3629] for more information on both topics.
In addition, the extension specified in this document makes it
possible to transport multiple language variants for a single
parameter, and such use might allow spoofing attacks, where different
language versions of the same parameter are not equivalent. Whether
this attack is useful as an attack depends on the parameter
specified.
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
ABNF details, to Graham Klyne and Alexey Melnikov for general review,
Chris Newman for pointing out an RFC 2231 incompatibility, and to
Benjamin Carlyle and Roar Lauritzsen for implementer's feedback.
8. References
8.1. Normative References
[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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2978] Freed, N. and J. Postel, "IANA Charset Registration
Procedures", BCP 19, RFC 2978, October 2000.
Reschke Expires October 1, 2010 [Page 10]
Internet-Draft RFC2231 Encoding in HTTP March 2010
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 3629, STD 63, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax",
RFC 3986, STD 66, January 2005.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234,
January 2008.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for
Identifying Languages", BCP 47, RFC 5646,
September 2009.
[USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
8.2. Informative References
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", RFC 2045, November 1996.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail
Extensions) Part Three: Message Header Extensions for
Non-ASCII Text", RFC 2047, November 1996.
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and
Encoded Word Extensions: Character Sets, Languages, and
Continuations", RFC 2231, November 1997.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[RFC2388] Masinter, L., "Returning Values from Forms: multipart/
form-data", RFC 2388, August 1998.
URIs
[1] <mailto:ietf-http-wg@w3.org>
[2] <mailto:ietf-http-wg-request@w3.org?subject=subscribe>
[3] <http://www.rfc-editor.org/errata_search.php?eid=1912>
Reschke Expires October 1, 2010 [Page 11]
Internet-Draft RFC2231 Encoding in HTTP March 2010
Appendix A. Document History and Future Plans (to be removed by RFC
Editor before publication)
Problems with the internationalization of the HTTP Content-
Disposition header field have been known for many years (see test
cases at <http://greenbytes.de/tech/tc2231/>).
During IETF 72
(<http://tools.ietf.org/wg/httpbis/minutes?item=minutes72.html>), the
HTTPbis Working Group shortly discussed how to deal with the
underspecification of (1) Content-Disposition, and its (2)
internationalization aspects. Back then, there was rough consensus
in the room to move the definition into a separate draft.
This specification addresses problem (2), by defining a simple subset
of the encoding format defined in RFC 2231. A separate
specification, draft-reschke-rfc2183-in-http, is planned to address
problem (1). Note that this approach was chosen because Content-
Disposition is just an example for an HTTP header field using this
kind of encoding. Another example is the currently proposed Link
header field (draft-nottingham-http-link-header).
This document is planned to be published on the IETF Standards Track,
so that other standards-track level documents can depend on it, such
as the new specification of Content-Disposition, or potentially
future revisions of the HTTP Link Header specification.
Also note that this document specifies a proper subset of the
extensions defined in RFC 2231, but does not normatively refer to it.
Thus, RFC 2231 can be revised separately, should the email community
decide to.
Appendix B. Change Log (to be removed by RFC Editor before publication)
B.1. Since draft-reschke-rfc2231-in-http-00
Use RFC5234-style ABNF, closer to the one used in RFC 2231.
Make RFC 2231 dependency informative, so this specification can
evolve independently.
Explain the ABNF in prose.
B.2. Since draft-reschke-rfc2231-in-http-01
Remove unneeded RFC5137 notation (code point vs character).
Reschke Expires October 1, 2010 [Page 12]
Internet-Draft RFC2231 Encoding in HTTP March 2010
B.3. Since draft-reschke-rfc2231-in-http-02
And and resolve issues "charset", "repeats" and "rfc4646".
B.4. Since draft-reschke-rfc2231-in-http-03
And and resolve issue "charsetmatch".
B.5. Since draft-reschke-rfc2231-in-http-04
Add and resolve issues "badseq" and "tokenquotcharset".
B.6. Since draft-reschke-rfc2231-in-http-05
Say "header field" instead of "header" in the context of HTTP.
B.7. Since draft-reschke-rfc2231-in-http-06
Add an appendix discussing document history and future plans, to be
removed before publication.
B.8. Since draft-reschke-rfc2231-in-http-07
Add and resolve issues "impl" and "rel-2388".
B.9. Since draft-reschke-rfc2231-in-http-08
Editorial improvements. Add and resolve issues "attrcharvstoken" and
"tokengrammar".
B.10. Since draft-reschke-rfc2231-in-http-09
Add issues "i18n-spoofing", "iso8859", "parameter-abnf", and "when-
ext-value". Add and resolve issues "rfc2978-normative", "rfc3986-
normative" and "usascii-normative".
B.11. Since draft-reschke-rfc2231-in-http-10
Resolve issues "i18n-spoofing", "iso8859", "parameter-abnf", and
"when-ext-value".
Add and resolve issue "charset-registered", "handling-multiple",
"multiple-inst-spoofing", "repeated-param" and "value-abnf".
Update the KDE implementation note.
Reschke Expires October 1, 2010 [Page 13]
Internet-Draft RFC2231 Encoding in HTTP March 2010
Appendix C. Resolved issues (to be removed by RFC Editor before
publication)
Issues that were either rejected or resolved in this version of this
document.
C.1. edit
Type: edit
julian.reschke@greenbytes.de (2009-04-17): Umbrella issue for
editorial fixes/enhancements.
C.2. charset-registered
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:
Reschke Expires October 1, 2010 [Page 14]
Internet-Draft RFC2231 Encoding in HTTP March 2010
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
Reschke Expires October 1, 2010 [Page 15]
Internet-Draft RFC2231 Encoding in HTTP March 2010
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
Reschke Expires October 1, 2010 [Page 16]
Internet-Draft RFC2231 Encoding in HTTP March 2010
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
kivinen@iki.fi (2010-03-01): Yes, but the impact of them is
different. For example it does not really matter if the filename
parameters having different languages differ, but there might be
parameters where this really matters.
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.
Reschke Expires October 1, 2010 [Page 17]
Internet-Draft RFC2231 Encoding in HTTP March 2010
Author's Address
Julian F. Reschke
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
Reschke Expires October 1, 2010 [Page 18]
