draft-ietf-appsawg-mime-default-charset-01.txt		draft-ietf-appsawg-mime-default-charset-02.txt
	Applications Area Working Group A. Melnikov		Applications Area Working Group A. Melnikov
	Internet-Draft Isode Limited		Internet-Draft Isode Limited
	Updates: 2046 (if approved) J. Reschke		Updates: 2046 (if approved) J. Reschke
	Intended status: Standards Track greenbytes		Intended status: Standards Track greenbytes
	Expires: October 1, 2012 March 30, 2012		Expires: October 23, 2012 April 21, 2012
	Update to MIME regarding Charset Parameter Handling in		Update to MIME regarding Charset Parameter Handling in
	Textual Media Types		Textual Media Types
	draft-ietf-appsawg-mime-default-charset-01		draft-ietf-appsawg-mime-default-charset-02
	Abstract		Abstract
	This document changes RFC 2046 rules regarding default charset		This document changes RFC 2046 rules regarding default charset
	parameter values for text/* media types to better align with common		parameter values for text/* media types to better align with common
	usage by existing clients and servers.		usage by existing clients and servers.
	Editorial Note (To be removed by RFC Editor)		Editorial Note (To be removed by RFC Editor)
	Discussion of this draft should take place on the Apps Area Working		Discussion of this draft should take place on the Apps Area Working
	skipping to change at page 1, line 40		skipping to change at page 1, line 40
	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-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	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 October 1, 2012.		This Internet-Draft will expire on October 23, 2012.
	Copyright Notice		Copyright Notice
	Copyright (c) 2012 IETF Trust and the persons identified as the		Copyright (c) 2012 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
	skipping to change at page 2, line 20		skipping to change at page 2, line 20
	Table of Contents		Table of Contents
	1. Introduction and Overview . . . . . . . . . . . . . . . 3		1. Introduction and Overview . . . . . . . . . . . . . . . 3
	2. Conventions Used in This Document . . . . . . . . . . . 3		2. Conventions Used in This Document . . . . . . . . . . . 3
	3. New rules for default charset parameter values for		3. New rules for default charset parameter values for
	text/* media types . . . . . . . . . . . . . . . . . . 3		text/* media types . . . . . . . . . . . . . . . . . . 3
	4. Default charset parameter value for text/plain		4. Default charset parameter value for text/plain
	media type . . . . . . . . . . . . . . . . . . . . . . 4		media type . . . . . . . . . . . . . . . . . . . . . . 4
	5. Security Considerations . . . . . . . . . . . . . . . . 4		5. Security Considerations . . . . . . . . . . . . . . . . 4
	6. IANA Considerations . . . . . . . . . . . . . . . . . . 5		6. IANA Considerations . . . . . . . . . . . . . . . . . . 4
	7. References . . . . . . . . . . . . . . . . . . . . . . 5		7. References . . . . . . . . . . . . . . . . . . . . . . 5
	7.1. Normative References . . . . . . . . . . . . . . . . . 5		7.1. Normative References . . . . . . . . . . . . . . . . . 5
	7.2. Informative References . . . . . . . . . . . . . . . . 5		7.2. Informative References . . . . . . . . . . . . . . . . 5
	Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 5		Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 5
	Authors' Addresses . . . . . . . . . . . . . . . . . . 5		Authors' Addresses . . . . . . . . . . . . . . . . . . 5
	1. Introduction and Overview		1. Introduction and Overview
	[RFC2046] specified that the default charset parameter (i.e. the		[RFC2046] specified that the default charset parameter (i.e. the
	value used when it is not specified) is "US-ASCII". [RFC2616]		value used when it is not specified) is "US-ASCII". [RFC2616]
	changed the default for use by HTTP to be "ISO-8859-1". This		changed the default for use by HTTP to be "ISO-8859-1". This
	encoding is not very common for new text/* media types and a special		encoding is not very common for new text/* media types and a special
	rule in HTTP adds confusion about which specification ([RFC2046] or		rule in HTTP adds confusion about which specification ([RFC2046] or
	[RFC2616]) is authoritative in regards to the default charset for		[RFC2616]) is authoritative in regards to the default charset for
	text/* media types. [[anchor2: At the time of writing of this		text/* media types.
	document the IETF HTTPBIS WG is working on an update to RFC 2616
	which removes the default charset of "ISO-8859-1" for "text/*" media
	types. It is expected that the set of HTTPBIs documents will
	reference this document in order to use the updated rules of default
	charset in "text/*" media types.]]
	Many complex text subtypes such as text/html [RFC2854] and text/xml		Many complex text subtypes such as text/html [RFC2854] and text/xml
	[RFC3023] have internal (to their format) means of describing the		[RFC3023] have internal (to their format) means of describing the
	charset. Many existing User Agents ignore the default of "US-ASCII"		charset. Many existing User Agents ignore the default of "US-ASCII"
	rule for at least text/html and text/xml.		rule for at least text/html and text/xml.
	This document changes RFC 2046 rules regarding default charset		This document changes RFC 2046 rules regarding default charset
	parameter values for text/* media types to better align with common		parameter values for text/* media types to better align with common
	usage by existing clients and servers. It does not change the		usage by existing clients and servers. It does not change the
	defaults for any currently registered media type.		defaults for any currently registered media type.
	skipping to change at page 3, line 50		skipping to change at page 3, line 45
	The default character set, which must be assumed in the absence of		The default character set, which must be assumed in the absence of
	a charset parameter, is US-ASCII.		a charset parameter, is US-ASCII.
	As explained in the Introduction section this rule is considered to		As explained in the Introduction section this rule is considered to
	be outdated, so this document replaces it with the following set of		be outdated, so this document replaces it with the following set of
	rules:		rules:
	Each subtype of the "text" media type which uses the "charset"		Each subtype of the "text" media type which uses the "charset"
	parameter can define its own default value for the "charset"		parameter can define its own default value for the "charset"
	parameter, including absence of any default.		parameter, including the absence of any default.
	In order to improve interoperability with deployed agents, "text/*"		In order to improve interoperability with deployed agents, "text/*"
	media type registrations SHOULD either		media type registrations SHOULD either
	a. specify that the "charset" parameter is not used for the defined		a. specify that the "charset" parameter is not used for the defined
	subtype, because the charset information is transported inside		subtype, because the charset information is transported inside
	the payload (such as in "text/xml"), or		the payload (such as in "text/xml"), or
	b. require explicit unconditional inclusion of the "charset"		b. require explicit unconditional inclusion of the "charset"
	parameter eliminating the need for a default value.		parameter eliminating the need for a default value.
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	corresponding payloads (such as "text/html" and "text/xml") SHOULD		corresponding payloads (such as "text/html" and "text/xml") SHOULD
	NOT specify the use of a "charset" parameter, nor any default value,		NOT specify the use of a "charset" parameter, nor any default value,
	in order to avoid conflicting interpretations should the charset		in order to avoid conflicting interpretations should the charset
	parameter value and the value specified in the payload disagree.		parameter value and the value specified in the payload disagree.
	New subtypes of the "text" media type, thus, SHOULD NOT define a		New subtypes of the "text" media type, thus, SHOULD NOT define a
	default "charset" value. If there is a strong reason to do so		default "charset" value. If there is a strong reason to do so
	despite this advice, they SHOULD use the "UTF-8" [RFC3629] charset as		despite this advice, they SHOULD use the "UTF-8" [RFC3629] charset as
	the default.		the default.
	Specifications of how to specify the "charset" parameter, and what		Specifications covering the "charset" parameter, and what default
	default value, if any, is used, are subtype-specific, NOT protocol-		value, if any, is used, are subtype-specific, NOT protocol-specific.
	specific. Protocols that use MIME, therefore, MUST NOT override		Protocols that use MIME, therefore, MUST NOT override default charset
	default charset values for "text/*" media types to be different for		values for "text/*" media types to be different for their specific
	their specific protocol. The protocol definitions MUST leave that to		protocol. The protocol definitions MUST leave that to the subtype
	the subtype definitions.		definitions.
	4. Default charset parameter value for text/plain media type		4. Default charset parameter value for text/plain media type
	The default charset parameter value for text/plain is unchanged from		The default charset parameter value for text/plain is unchanged from
	[RFC2046] and remains as "US-ASCII".		[RFC2046] and remains as "US-ASCII".
	5. Security Considerations		5. Security Considerations
	Guessing of the charset parameter can lead to security issues such as		Guessing of the charset parameter can lead to security issues such as
	content buffer overflows, denial of services or bypass of filtering		content buffer overflows, denial of services or bypass of filtering
	skipping to change at page 5, line 39		skipping to change at page 5, line 35
	[RFC2854] Connolly, D. and L. Masinter, "The 'text/html' Media		[RFC2854] Connolly, D. and L. Masinter, "The 'text/html' Media
	Type", RFC 2854, June 2000.		Type", RFC 2854, June 2000.
	[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media		[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
	Types", RFC 3023, January 2001.		Types", RFC 3023, January 2001.
	Appendix A. Acknowledgements		Appendix A. Acknowledgements
	Many thanks to Ned Freed and John Klensin for comments and ideas that		Many thanks to Ned Freed and John Klensin for comments and ideas that
	motivated creation of this document, and to Barry Leiba for suggested		motivated creation of this document, and to Carsten Bormann, Murray
	text.		S. Kucherawy, Barry Leiba, and Henri Sivonen for feedback and text
			suggestions.
	Authors' Addresses		Authors' Addresses
	Alexey Melnikov		Alexey Melnikov
	Isode Limited		Isode Limited
	5 Castle Business Village		5 Castle Business Village
	36 Station Road		36 Station Road
	Hampton, Middlesex TW12 2BX		Hampton, Middlesex TW12 2BX
	UK		UK
	Email: Alexey.Melnikov@isode.com
			Email: Alexey.Melnikov@isode.com
	Julian F. Reschke		Julian F. Reschke
	greenbytes GmbH		greenbytes GmbH
	Hafenweg 16		Hafenweg 16
	Muenster, NW 48155		Muenster, NW 48155
	Germany		Germany
	Email: julian.reschke@greenbytes.de		Email: julian.reschke@greenbytes.de
	URI: http://greenbytes.de/tech/webdav/		URI: http://greenbytes.de/tech/webdav/
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