draft-ietf-httpbis-content-disp-09.txt		draft-ietf-httpbis-content-disp-latest.txt
	HTTPbis Working Group J. Reschke		HTTPbis Working Group J. Reschke
	Internet-Draft greenbytes		Internet-Draft greenbytes
	Updates: 2616 (if approved) March 28, 2011		Updates: 2616 (if approved) June 2011
	Intended status: Standards Track		Intended status: Standards Track
	Expires: September 29, 2011		Expires: December 3, 2011
	Use of the Content-Disposition Header Field in the		Use of the Content-Disposition Header Field in the
	Hypertext Transfer Protocol (HTTP)		Hypertext Transfer Protocol (HTTP)
	draft-ietf-httpbis-content-disp-09		draft-ietf-httpbis-content-disp-latest
	Abstract		Abstract
	RFC 2616 defines the Content-Disposition response header field, but		RFC 2616 defines the Content-Disposition response header field, but
	points out that it is not part of the HTTP/1.1 Standard. This		points out that it is not part of the HTTP/1.1 Standard. This
	specification takes over the definition and registration of Content-		specification takes over the definition and registration of Content-
	Disposition, as used in HTTP, and clarifies internationalization		Disposition, as used in HTTP, and clarifies internationalization
	aspects.		aspects.
	Editorial Note (To be removed by RFC Editor before publication)
	This specification is expected to replace the definition of Content-
	Disposition in the HTTP/1.1 specification, as currently revised by
	the IETF HTTPbis working group. See also
	<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/123>.
	Discussion of this draft should take place on the HTTPBIS working
	group mailing list (ietf-http-wg@w3.org). The current issues list is
	at <http://trac.tools.ietf.org/wg/httpbis/trac/
	query?component=content-disp> and related documents (including fancy
	diffs) can be found at <http://tools.ietf.org/wg/httpbis/>.
	The changes in this draft are summarized in Appendix E.13.
	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-
	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 September 29, 2011.
			This Internet-Draft will expire on December 3, 2011.
	Copyright Notice		Copyright Notice
	Copyright (c) 2011 IETF Trust and the persons identified as the		Copyright (c) 2011 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 Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4		2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
	3. Conformance and Error Handling . . . . . . . . . . . . . . . . 4		3. Conformance and Error Handling . . . . . . . . . . . . . . . . 3
	4. Header Field Definition . . . . . . . . . . . . . . . . . . . 5		4. Header Field Definition . . . . . . . . . . . . . . . . . . . 4
	4.1. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 5		4.1. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . 4
	4.2. Disposition Type . . . . . . . . . . . . . . . . . . . . . 6		4.2. Disposition Type . . . . . . . . . . . . . . . . . . . . . 5
	4.3. Disposition Parameter: 'Filename' . . . . . . . . . . . . 6		4.3. Disposition Parameter: 'Filename' . . . . . . . . . . . . 5
	4.4. Disposition Parameter: Extensions . . . . . . . . . . . . 7		4.4. Disposition Parameter: Extensions . . . . . . . . . . . . 6
	4.5. Extensibility . . . . . . . . . . . . . . . . . . . . . . 7		4.5. Extensibility . . . . . . . . . . . . . . . . . . . . . . 6
	5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8		5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
	6. Internationalization Considerations . . . . . . . . . . . . . 8		6. Internationalization Considerations . . . . . . . . . . . . . 7
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 9		7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	8.1. Registry for Disposition Values and Parameter . . . . . . 9		8.1. Registry for Disposition Values and Parameters . . . . . . 8
	8.2. Header Field Registration . . . . . . . . . . . . . . . . 9		8.2. Header Field Registration . . . . . . . . . . . . . . . . 8
	9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9		10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
	10.1. Normative References . . . . . . . . . . . . . . . . . . . 9		10.1. Normative References . . . . . . . . . . . . . . . . . . . 8
	10.2. Informative References . . . . . . . . . . . . . . . . . . 10		10.2. Informative References . . . . . . . . . . . . . . . . . . 9
	Appendix A. Changes from the RFC 2616 Definition . . . . . . . . 11		Appendix A. Changes from the RFC 2616 Definition . . . . . . . . 10
	Appendix B. Differences compared to RFC 2183 . . . . . . . . . . 11		Appendix B. Differences Compared to RFC 2183 . . . . . . . . . . 10
	Appendix C. Alternative Approaches to Internationalization . . . 11		Appendix C. Alternative Approaches to Internationalization . . . 10
	C.1. RFC 2047 Encoding . . . . . . . . . . . . . . . . . . . . 12		C.1. RFC 2047 Encoding . . . . . . . . . . . . . . . . . . . . 11
	C.2. Percent Encoding . . . . . . . . . . . . . . . . . . . . . 12		C.2. Percent Encoding . . . . . . . . . . . . . . . . . . . . . 11
	C.3. Encoding Sniffing . . . . . . . . . . . . . . . . . . . . 12		C.3. Encoding Sniffing . . . . . . . . . . . . . . . . . . . . 11
	C.4. Implementations (to be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . . . . 12
	Appendix D. Advice on Generating Content-Disposition Header		Appendix D. Advice on Generating Content-Disposition Header
	Fields . . . . . . . . . . . . . . . . . . . . . . . 13		Fields . . . . . . . . . . . . . . . . . . . . . . . 11
	Appendix E. Change Log (to be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . 14
	E.1. Since draft-reschke-rfc2183-in-http-00 . . . . . . . . . . 14
	E.2. Since draft-reschke-rfc2183-in-http-01 . . . . . . . . . . 14
	E.3. Since draft-reschke-rfc2183-in-http-02 . . . . . . . . . . 15
	E.4. Since draft-reschke-rfc2183-in-http-03 . . . . . . . . . . 15
	E.5. Since draft-ietf-httpbis-content-disp-00 . . . . . . . . . 15
	E.6. Since draft-ietf-httpbis-content-disp-01 . . . . . . . . . 15
	E.7. Since draft-ietf-httpbis-content-disp-02 . . . . . . . . . 15
	E.8. Since draft-ietf-httpbis-content-disp-03 . . . . . . . . . 15
	E.9. Since draft-ietf-httpbis-content-disp-04 . . . . . . . . . 16
	E.10. Since draft-ietf-httpbis-content-disp-05 . . . . . . . . . 16
	E.11. Since draft-ietf-httpbis-content-disp-06 . . . . . . . . . 16
	E.12. Since draft-ietf-httpbis-content-disp-07 . . . . . . . . . 17
	E.13. Since draft-ietf-httpbis-content-disp-08 . . . . . . . . . 17
	Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
	1. Introduction		1. Introduction
	RFC 2616 defines the Content-Disposition response header field in		RFC 2616 defines the Content-Disposition response header field
	Section 19.5.1 of [RFC2616], but points out that it is not part of		(Section 19.5.1 of [RFC2616]) but points out that it is not part of
	the HTTP/1.1 Standard (Section 15.5):		the HTTP/1.1 Standard (Section 15.5):
	Content-Disposition is not part of the HTTP standard, but since it		Content-Disposition is not part of the HTTP standard, but since it
	is widely implemented, we are documenting its use and risks for		is widely implemented, we are documenting its use and risks for
	implementers.		implementers.
	This specification takes over the definition and registration of		This specification takes over the definition and registration of
	Content-Disposition, as used in HTTP. Based on interoperability		Content-Disposition, as used in HTTP. Based on interoperability
	testing with existing User Agents, it fully defines a profile of the		testing with existing user agents (UAs), it fully defines a profile
	features defined in the Multipurpose Internet Mail Extensions (MIME)		of the features defined in the Multipurpose Internet Mail Extensions
	variant ([RFC2183]) of the header field, and also clarifies		(MIME) variant ([RFC2183]) of the header field, and also clarifies
	internationalization aspects.		internationalization aspects.
	Note: this document does not apply to Content-Disposition header		Note: This document does not apply to Content-Disposition header
	fields appearing in payload bodies transmitted over HTTP, such as		fields appearing in payload bodies transmitted over HTTP, such as
	when using the media type "multipart/form-data" ([RFC2388]).		when using the media type "multipart/form-data" ([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 augmented BNF (ABNF) notation defined in		This specification uses the augmented BNF (ABNF) notation defined in
	skipping to change at page 4, line 44 ¶		skipping to change at page 3, line 44 ¶
	whitespace (LWS).		whitespace (LWS).
	3. Conformance and Error Handling		3. Conformance and Error Handling
	This specification defines conformance criteria for both senders		This specification defines conformance criteria for both senders
	(usually, HTTP origin servers) and recipients (usually, HTTP user		(usually, HTTP origin servers) and recipients (usually, HTTP user
	agents) of the Content-Disposition header field. An implementation		agents) of the Content-Disposition header field. An implementation
	is considered conformant if it complies with all of the requirements		is considered conformant if it complies with all of the requirements
	associated with its role.		associated with its role.
	This specification also defines certain forms of the header field-		This specification also defines certain forms of the header field
	value to be invalid, using both ABNF and prose requirements		value to be invalid, using both ABNF and prose requirements
	(Section 4), but it does not define special handling of these invalid		(Section 4), but it does not define special handling of these invalid
	field-values.		field values.
	Senders MUST NOT generate Content-Disposition header fields that are		Senders MUST NOT generate Content-Disposition header fields that are
	invalid.		invalid.
	Recipients MAY take steps to recover a usable field-value from an		Recipients MAY take steps to recover a usable field value from an
	invalid header field, but SHOULD NOT reject the message outright,		invalid header field, but SHOULD NOT reject the message outright,
	unless this is explicitly desirable behaviour (e.g., the		unless this is explicitly desirable behavior (e.g., the
	implementation is a validator). As such, the default handling of		implementation is a validator). As such, the default handling of
	invalid fields is to ignore them.		invalid fields is to ignore them.
	4. Header Field Definition		4. Header Field Definition
	The Content-Disposition response header field is used to convey		The Content-Disposition response header field is used to convey
	additional information about how to process the response payload, and		additional information about how to process the response payload, and
	also can be used to attach additional metadata, such as the filename		also can be used to attach additional metadata, such as the filename
	to use when saving the response payload locally.		to use when saving the response payload locally.
	skipping to change at page 6, line 5 ¶		skipping to change at page 5, line 5 ¶
	ext-value = <ext-value, defined in [RFC5987], Section 3.2>		ext-value = <ext-value, defined in [RFC5987], Section 3.2>
	Content-Disposition header field values with multiple instances of		Content-Disposition header field values with multiple instances of
	the same parameter name are invalid.		the same parameter name are invalid.
	Note that due to the rules for implied linear whitespace (Section 2.1		Note that due to the rules for implied linear whitespace (Section 2.1
	of [RFC2616]), OPTIONAL whitespace can appear between words (token or		of [RFC2616]), OPTIONAL whitespace can appear between words (token or
	quoted-string) and separator characters.		quoted-string) and separator characters.
	Furthermore note that the format used for ext-value allows specifying		Furthermore, note that the format used for ext-value allows
	a natural language (e.g., "en"); this is of limited use for filenames		specifying a natural language (e.g., "en"); this is of limited use
	and is likely to be ignored by recipients.		for filenames and is likely to be ignored by recipients.
	4.2. Disposition Type		4.2. Disposition Type
	If the disposition type matches "attachment" (case-insensitively),		If the disposition type matches "attachment" (case-insensitively),
	this indicates that the recipient should prompt the user to save the		this indicates that the recipient should prompt the user to save the
	response locally, rather than process it normally (as per its media		response locally, rather than process it normally (as per its media
	type).		type).
	On the other hand, if it matches "inline" (case-insensitively), this		On the other hand, if it matches "inline" (case-insensitively), this
	implies default processing. Therefore, the disposition type "inline"		implies default processing. Therefore, the disposition type "inline"
	skipping to change at page 6, line 52 ¶		skipping to change at page 5, line 52 ¶
	Many user agent implementations predating this specification do not		Many user agent implementations predating this specification do not
	understand the "filename*" parameter. Therefore, when both		understand the "filename*" parameter. Therefore, when both
	"filename" and "filename*" are present in a single header field		"filename" and "filename*" are present in a single header field
	value, recipients SHOULD pick "filename*" and ignore "filename".		value, recipients SHOULD pick "filename*" and ignore "filename".
	This way, senders can avoid special-casing specific user agents by		This way, senders can avoid special-casing specific user agents by
	sending both the more expressive "filename*" parameter, and the		sending both the more expressive "filename*" parameter, and the
	"filename" parameter as fallback for legacy recipients (see Section 5		"filename" parameter as fallback for legacy recipients (see Section 5
	for an example).		for an example).
	It is essential that recipients treat the specified filename as		It is essential that recipients treat the specified filename as
	advisory only, thus be very careful in extracting the desired		advisory only, and thus be very careful in extracting the desired
	information. In particular:		information. In particular:
	o Recipients MUST NOT be able to write into any location other than		o Recipients MUST NOT be able to write into any location other than
	one to which they are specifically entitled. To illustrate the		one to which they are specifically entitled. To illustrate the
	problem consider the consequences of being able to overwrite well-		problem, consider the consequences of being able to overwrite
	known system locations (such as "/etc/passwd"). One strategy to		well-known system locations (such as "/etc/passwd"). One strategy
	achieve this is to never trust folder name information in the		to achieve this is to never trust folder name information in the
	filename parameter, for instance by stripping all but the last		filename parameter, for instance by stripping all but the last
	path segment and only consider the actual filename (where 'path		path segment and only considering the actual filename (where 'path
	segment' are the components of the field value delimited by the		segments' are the components of the field value delimited by the
	path separator characters "\" and "/").		path separator characters "\" and "/").
	o Many platforms do not use Internet Media Types ([RFC2046]) to hold		o Many platforms do not use Internet Media Types ([RFC2046]) to hold
	type information in the file system, but rely on filename		type information in the file system, but rely on filename
	extensions instead. Trusting the server-provided file extension		extensions instead. Trusting the server-provided file extension
	could introduce a privilege escalation when the saved file is		could introduce a privilege escalation when the saved file is
	later opened (consider ".exe"). Thus, recipients which make use		later opened (consider ".exe"). Thus, recipients that make use of
	of file extensions to determine the media type MUST ensure that a		file extensions to determine the media type MUST ensure that a
	file extension is used that is safe, optimally matching the media		file extension is used that is safe, optimally matching the media
	type of the received payload.		type of the received payload.
	o Recipients SHOULD strip or replace character sequences that are		o Recipients SHOULD strip or replace character sequences that are
	known to cause confusion both in user interfaces and in filenames,		known to cause confusion both in user interfaces and in filenames,
	such as control characters and leading and trailing whitespace.		such as control characters and leading and trailing whitespace.
	o Other aspects recipients need to be aware of are names that have a		o Other aspects recipients need to be aware of are names that have a
	special meaning in the file system or in shell commands, such as		special meaning in the file system or in shell commands, such as
	"." and "..", "~", "|", and also device names. Recipients SHOULD		"." and "..", "~", "|", and also device names. Recipients SHOULD
	skipping to change at page 8, line 7 ¶		skipping to change at page 7, line 7 ¶
	4.5. Extensibility		4.5. Extensibility
	Note that Section 9 of [RFC2183] defines IANA registries both for		Note that Section 9 of [RFC2183] defines IANA registries both for
	disposition types and disposition parameters. This registry is		disposition types and disposition parameters. This registry is
	shared by different protocols using Content-Disposition, such as MIME		shared by different protocols using Content-Disposition, such as MIME
	and HTTP. Therefore, not all registered values may make sense in the		and HTTP. Therefore, not all registered values may make sense in the
	context of HTTP.		context of HTTP.
	5. Examples		5. Examples
	Direct UA to show "save as" dialog, with a filename of		Direct the UA to show "save as" dialog, with a filename of
	"example.html":		"example.html":
	Content-Disposition: Attachment; filename=example.html		Content-Disposition: Attachment; filename=example.html
	Direct UA to behave as if the Content-Disposition header field wasn't		Direct the UA to behave as if the Content-Disposition header field
	present, but to remember the filename "an example.html" for a		wasn't present, but to remember the filename "an example.html" for a
	subsequent save operation:		subsequent save operation:
	Content-Disposition: INLINE; FILENAME= "an example.html"		Content-Disposition: INLINE; FILENAME= "an example.html"
	Note: this uses the quoted-string form so that the space character		Note: This uses the quoted-string form so that the space character
	can be included.		can be included.
	Direct UA to show "save as" dialog, with a filename containing the		Direct the UA to show "save as" dialog, with a filename containing
	Unicode character U+20AC (EURO SIGN):		the Unicode character U+20AC (EURO SIGN):
	Content-Disposition: attachment;		Content-Disposition: attachment;
	filename*= UTF-8''%e2%82%ac%20rates		filename*= UTF-8''%e2%82%ac%20rates
	Here, the encoding defined in [RFC5987] is also used to encode the		Here, the encoding defined in [RFC5987] is also used to encode the
	non-ISO-8859-1 character.		non-ISO-8859-1 character.
	Same as above, but adding the "filename" parameter for compatibility		This example is the same as the one above, but adding the "filename"
	with user agents not implementing RFC 5987:		parameter for compatibility with user agents not implementing
			RFC 5987:
	Content-Disposition: attachment;		Content-Disposition: attachment;
	filename="EURO rates";		filename="EURO rates";
	filename*=utf-8''%e2%82%ac%20rates		filename*=utf-8''%e2%82%ac%20rates
	Note: those user agents that do not support the RFC 5987 encoding		Note: Those user agents that do not support the RFC 5987 encoding
	ignore "filename*" when it occurs after "filename".		ignore "filename*" when it occurs after "filename".
	6. Internationalization Considerations		6. Internationalization Considerations
	The "filename*" parameter (Section 4.3), using the encoding defined		The "filename*" parameter (Section 4.3), using the encoding defined
	in [RFC5987], allows the server to transmit characters outside the		in [RFC5987], allows the server to transmit characters outside the
	ISO-8859-1 character set, and also to optionally specify the language		ISO-8859-1 character set, and also to optionally specify the language
	in use.		in use.
	Future parameters might also require internationalization, in which		Future parameters might also require internationalization, in which
	case the same encoding can be used.		case the same encoding can be used.
	7. Security Considerations		7. Security Considerations
	Using server-supplied information for constructing local filenames		Using server-supplied information for constructing local filenames
	introduces many risks. These are summarized in Section 4.3.		introduces many risks. These are summarized in Section 4.3.
	Furthermore, implementers also ought to be aware of the Security		Furthermore, implementers ought to be aware of the security
	Considerations applying to HTTP (see Section 15 of [RFC2616]), and		considerations applying to HTTP (see Section 15 of [RFC2616]), and
	also the parameter encoding defined in [RFC5987] (see Section 5).		also the parameter encoding defined in [RFC5987] (see Section 5).
	8. IANA Considerations		8. IANA Considerations
	8.1. Registry for Disposition Values and Parameter		8.1. Registry for Disposition Values and Parameters
	This specification does not introduce any changes to the registration		This specification does not introduce any changes to the registration
	procedures for disposition values and parameters that are defined in		procedures for disposition values and parameters that are defined in
	Section 9 of [RFC2183].		Section 9 of [RFC2183].
	8.2. Header Field Registration		8.2. Header Field Registration
	This document updates the definition of the Content-Disposition HTTP		This document updates the definition of the Content-Disposition HTTP
	header field in the permanent HTTP header field registry (see		header field in the permanent HTTP header field registry (see
	[RFC3864]).		[RFC3864]).
	skipping to change at page 9, line 52 ¶		skipping to change at page 8, line 52 ¶
	Thanks to Adam Barth, Rolf Eike Beer, Stewart Bryant, Bjoern		Thanks to Adam Barth, Rolf Eike Beer, Stewart Bryant, Bjoern
	Hoehrmann, Alfred Hoenes, Roar Lauritzsen, Alexey Melnikov, Henrik		Hoehrmann, Alfred Hoenes, Roar Lauritzsen, Alexey Melnikov, Henrik
	Nordstrom, and Mark Nottingham for their valuable feedback.		Nordstrom, and Mark Nottingham for their valuable feedback.
	10. References		10. References
	10.1. Normative References		10.1. Normative References
	[ISO-8859-1] International Organization for Standardization,		[ISO-8859-1] International Organization for Standardization,
	"Information technology -- 8-bit single-byte coded		"Information technology -- 8-bit single-byte coded
	graphic character sets -- Part 1: Latin alphabet No.		graphic character sets -- Part 1: Latin alphabet
			No. 1", ISO/IEC 8859-1:1998, 1998.
	1", ISO/IEC 8859-1:1998, 1998.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,		[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext		Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
	Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.		Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
	[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
	skipping to change at page 10, line 28 ¶		skipping to change at page 9, line 27 ¶
	10.2. Informative References		10.2. Informative References
	[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet		[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet
	Mail Extensions (MIME) Part Two: Media Types",		Mail Extensions (MIME) Part Two: Media Types",
	RFC 2046, November 1996.		RFC 2046, November 1996.
	[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail		[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail
	Extensions) Part Three: Message Header Extensions for		Extensions) Part Three: Message Header Extensions for
	Non-ASCII Text", RFC 2047, November 1996.		Non-ASCII Text", RFC 2047, November 1996.
	[RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating		[RFC2183] Troost, R., Dorner, S., and K. Moore, Ed.,
	Presentation Information in Internet Messages: The		"Communicating Presentation Information in Internet
	Content-Disposition Header Field", RFC 2183,		Messages: The Content-Disposition Header Field",
	August 1997.		RFC 2183, August 1997.
	[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and		[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and
	Encoded Word Extensions: Character Sets, Languages, and		Encoded Word Extensions: Character Sets, Languages, and
	Continuations", RFC 2231, November 1997.		Continuations", RFC 2231, November 1997.
	[RFC2388] Masinter, L., "Returning Values from Forms: multipart/		[RFC2388] Masinter, L., "Returning Values from Forms: multipart/
	form-data", RFC 2388, August 1998.		form-data", RFC 2388, August 1998.
	[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration		[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
	Procedures for Message Header Fields", BCP 90,		Procedures for Message Header Fields", BCP 90,
	skipping to change at page 11, line 27 ¶		skipping to change at page 10, line 27 ¶
	This would be an exceptional parameter syntax, and also doesn't		This would be an exceptional parameter syntax, and also doesn't
	reflect actual use.		reflect actual use.
	o The definition for the disposition type "inline" ([RFC2183],		o The definition for the disposition type "inline" ([RFC2183],
	Section 2.1) has been re-added with a suggestion for its		Section 2.1) has been re-added with a suggestion for its
	processing.		processing.
	o This specification requires support for the extended parameter		o This specification requires support for the extended parameter
	encoding defined in [RFC5987].		encoding defined in [RFC5987].
	Appendix B. Differences compared to RFC 2183		Appendix B. Differences Compared to RFC 2183
	Section 2 of [RFC2183] defines several additional disposition		Section 2 of [RFC2183] defines several additional disposition
	parameters: "creation-date", "modification-date", "quoted-date-time",		parameters: "creation-date", "modification-date", "quoted-date-time",
	and "size". The majority of user agents does not implement these,		and "size". The majority of user agents do not implement these;
	thus they have been omitted from this specification.		thus, they have been omitted from this specification.
	Appendix C. Alternative Approaches to Internationalization		Appendix C. Alternative Approaches to Internationalization
	By default, HTTP header field parameters cannot carry characters		By default, HTTP header field parameters cannot carry characters
	outside the ISO-8859-1 ([ISO-8859-1]) character encoding (see		outside the ISO-8859-1 ([ISO-8859-1]) character encoding (see
	[RFC2616], Section 2.2). For the "filename" parameter, this of		[RFC2616], Section 2.2). For the "filename" parameter, this of
	course is an unacceptable restriction.		course is an unacceptable restriction.
	Unfortunately, user agent implementers have not managed to come up		Unfortunately, user agent implementers have not managed to come up
	with an interoperable approach, although the IETF Standards Track		with an interoperable approach, although the IETF Standards Track
	specifies exactly one solution ([RFC2231], clarified and profiled for		specifies exactly one solution ([RFC2231], clarified and profiled for
	HTTP in [RFC5987]).		HTTP in [RFC5987]).
	For completeness, the sections below describe the various approaches		For completeness, the sections below describe the various approaches
	that have been tried, and explains how they are inferior to the RFC		that have been tried, and explain how they are inferior to the
	5987 encoding used in this specification.		RFC 5987 encoding used in this specification.
	C.1. RFC 2047 Encoding		C.1. RFC 2047 Encoding
	RFC 2047 defines an encoding mechanism for header fields, but this		RFC 2047 defines an encoding mechanism for header fields, but this
	encoding is not supposed to be used for header field parameters - see		encoding is not supposed to be used for header field parameters --
	Section 5 of [RFC2047]:		see Section 5 of [RFC2047]:
	An 'encoded-word' MUST NOT appear within a 'quoted-string'.		An 'encoded-word' MUST NOT appear within a 'quoted-string'.
	...		...
	An 'encoded-word' MUST NOT be used in parameter of a MIME Content-		An 'encoded-word' MUST NOT be used in parameter of a MIME Content-
	Type or Content-Disposition field, or in any structured field body		Type or Content-Disposition field, or in any structured field body
	except within a 'comment' or 'phrase'.		except within a 'comment' or 'phrase'.
	In practice, some user agents implement the encoding, some do not		In practice, some user agents implement the encoding, some do not
	(exposing the encoded string to the user), and some get confused by		(exposing the encoded string to the user), and some get confused by
	it.		it.
	C.2. Percent Encoding		C.2. Percent Encoding
	Some user agents accept percent encoded ([RFC3986], Section 2.1)		Some user agents accept percent-encoded ([RFC3986], Section 2.1)
	sequences of characters. The character encoding being used for		sequences of characters. The character encoding being used for
	decoding depends on various factors, including the encoding of the		decoding depends on various factors, including the encoding of the
	referring page, the user agent's locale, its configuration, and also		referring page, the user agent's locale, its configuration, and also
	the actual value of the parameter.		the actual value of the parameter.
	In practice, this is hard to use because those user agents that do		In practice, this is hard to use because those user agents that do
	not support it will display the escaped character sequence to the		not support it will display the escaped character sequence to the
	user. For those user agents that do implement this it is difficult		user. For those user agents that do implement this, it is difficult
	to predict what character encoding they actually expect.		to predict what character encoding they actually expect.
	C.3. Encoding Sniffing		C.3. Encoding Sniffing
	Some user agents inspect the value (which defaults to ISO-8859-1 for		Some user agents inspect the value (which defaults to ISO-8859-1 for
	the quoted-string form) and switch to UTF-8 when it seems to be more		the quoted-string form) and switch to UTF-8 when it seems to be more
	likely to be the correct interpretation.		likely to be the correct interpretation.
	As with the approaches above, this is not interoperable and		As with the approaches above, this is not interoperable and,
	furthermore risks misinterpreting the actual value.		furthermore, risks misinterpreting the actual value.
	C.4. Implementations (to be removed by RFC Editor before publication)
	Unfortunately, as of March 2011, neither the encoding defined in RFCs
	2231 and 5987, nor any of the alternate approaches discussed above
	was implemented interoperably. Thus, this specification recommends
	the approach defined in RFC 5987, which at least has the advantage of
	actually being specified properly.
	The table below shows the support for the various approaches in the
	current implementations:
	+---------------+------------+--------+--------------+--------------+
	| User Agent | RFC | RFC | Percent | Encoding |
	| | 2231/5987 | 2047 | Encoding | Sniffing |
	+---------------+------------+--------+--------------+--------------+
	| Chrome | yes | yes | yes | yes |
	| Firefox | yes (*) | yes | no | yes |
	| Internet | yes (**) | no | yes | no |
	| Explorer | | | | |
	| Konqueror | yes | no | no | no |
	| Opera | yes | no | no | no |
	| Safari | no | no | no | yes |
	+---------------+------------+--------+--------------+--------------+
	(*) Does not implement the fallback behavior to "filename" described
	in Section 4.3; a fix is planned for Firefox 5.
	(**) Starting with Internet Explorer 9, but only implements UTF-8.
	Appendix D. Advice on Generating Content-Disposition Header Fields		Appendix D. Advice on Generating Content-Disposition Header Fields
	To successfully interoperate with existing and future user agents,		To successfully interoperate with existing and future user agents,
	senders of the Content-Disposition header field are advised to:		senders of the Content-Disposition header field are advised to:
	o Include a "filename" parameter when US-ASCII ([US-ASCII]) is		o Include a "filename" parameter when US-ASCII ([US-ASCII]) is
	sufficiently expressive.		sufficiently expressive.
	o Use the 'token' form of the filename parameter only when it does		o Use the 'token' form of the filename parameter only when it does
	not contain disallowed characters (e.g., spaces); in such cases,		not contain disallowed characters (e.g., spaces); in such cases,
	the quoted-string form should be used.		the quoted-string form should be used.
	o Avoid including the percent character followed by two hexadecimal		o Avoid including the percent character followed by two hexadecimal
	characters (e.g., %A9) in the filename parameter, since some		characters (e.g., %A9) in the filename parameter, since some
	existing implementations consider it to be an escape character,		existing implementations consider it to be an escape character,
	while others will pass it through unchanged.		while others will pass it through unchanged.
	o Avoid including the "\" character in the quoted-string form of the		o Avoid including the "\" character in the quoted-string form of the
	filename parameter, as escaping is not implemented by some user		filename parameter, as escaping is not implemented by some user
	agents, and can be considered as an illegal path character.		agents, and "\" can be considered an illegal path character.
	o Avoid using non-ASCII characters in the filename parameter.		o Avoid using non-ASCII characters in the filename parameter.
	Although most existing implementations will decode them as ISO-		Although most existing implementations will decode them as
	8859-1, some will apply heuristics to detect UTF-8, and thus might		ISO-8859-1, some will apply heuristics to detect UTF-8, and thus
	fail on certain names.		might fail on certain names.
	o Include a "filename*" parameter where the desired filename cannot		o Include a "filename*" parameter where the desired filename cannot
	be expressed faithfully using the "filename" form. Note that		be expressed faithfully using the "filename" form. Note that
	legacy user agents will not process this, and will fall back to		legacy user agents will not process this, and will fall back to
	using the "filename" parameter's content.		using the "filename" parameter's content.
	o When a "filename*" parameter is sent, to also generate a		o When a "filename*" parameter is sent, to also generate a
	"filename" parameter as a fallback for user agents that do not		"filename" parameter as a fallback for user agents that do not
	support the "filename*" form, if possible. This can be done by		support the "filename*" form, if possible. This can be done by
	substituting characters with US-ASCII sequences (e.g., Unicode		substituting characters with US-ASCII sequences (e.g., Unicode
	character point U+00E4 (LATIN SMALL LETTER A WITH DIARESIS) by		character point U+00E4 (LATIN SMALL LETTER A WITH DIARESIS) by
	"ae"). Note that this may not be possible in some locales.		"ae"). Note that this may not be possible in some locales.
	o When a "filename" parameter is included as a fallback (as per		o When a "filename" parameter is included as a fallback (as per
	above), "filename" should occur first, due to parsing problems in		above), "filename" should occur first, due to parsing problems in
	some existing implementations. [[fallbackbug: Firefox is known to		some existing implementations.
	pick the wrong parameter; a bug fix is scheduled for Firefox 5.
	--jre]] [[NOTE-TO-RFC-EDITOR: PLEASE REMOVE THIS AND THE PRECEDING
	COMMENT BEFORE PUBLICATION AS RFC. --jre]]
	o Use UTF-8 as the encoding of the "filename*" parameter, when		o Use UTF-8 as the encoding of the "filename*" parameter, when
	present, because at least one existing implementation only		present, because at least one existing implementation only
	implements that encoding.		implements that encoding.
	Note that this advice is based upon UA behaviour at the time of		Note that this advice is based upon UA behavior at the time of
	writing, and might be superseded. At the time of publication of this		writing, and might be superseded. At the time of publication of this
	document, <http://purl.org/NET/http/content-disposition-tests>		document, <http://purl.org/NET/http/content-disposition-tests>
	provides an overview of current levels of support in various		provides an overview of current levels of support in various
	implementations.		implementations.
	Appendix E. Change Log (to be removed by RFC Editor before publication)
	Note: the issues names in the change log entries for
	draft-reschke-rfc2183-in-http refer to <http://greenbytes.de/tech/
	webdav/draft-reschke-rfc2183-in-http-issues.html>.
	E.1. Since draft-reschke-rfc2183-in-http-00
	Adjust terminology ("header" -> "header field"). Update rfc2231-in-
	http reference.
	E.2. Since draft-reschke-rfc2183-in-http-01
	Update rfc2231-in-http reference. Actually define the "filename"
	parameter. Add internationalization considerations. Add examples
	using the RFC 5987 encoding. Add overview over other approaches,
	plus a table reporting implementation status. Add and resolve issue
	"nodep2183". Add issues "asciivsiso", "deplboth", "quoted", and
	"registry".
	E.3. Since draft-reschke-rfc2183-in-http-02
	Add and close issue "docfallback". Close issues "asciivsiso",
	"deplboth", "quoted", and "registry".
	E.4. Since draft-reschke-rfc2183-in-http-03
	Updated to be a Working Draft of the IETF HTTPbis Working Group.
	E.5. Since draft-ietf-httpbis-content-disp-00
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/242>: "handling of
	unknown disposition types"
	Slightly updated the notes about the proposed fallback behavior.
	E.6. Since draft-ietf-httpbis-content-disp-01
	Various editorial improvements.
	E.7. Since draft-ietf-httpbis-content-disp-02
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/244>: "state that
	repeating parameters are invalid"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/245>: "warn about
	%xx in filenames being misinterpreted"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/246>: "mention
	control chars when talking about postprecessing the filename
	parameter"
	Update Appendix C.4; Opera 10.63 RC implements the recommended
	fallback behavior.
	E.8. Since draft-ietf-httpbis-content-disp-03
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/252>:
	"'modification-date' *is* implemented in Konq 4.5"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/253>: "clarify what
	LWS means for the Content-Disp grammar"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/258>: "Avoid passive
	voice in message requirements"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/263>: "text about
	historical percent-decoding unclear"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/264>: "add
	explanation of language tagging"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/265>: "Clarify that
	C-D spec does not apply to multipart upload"
	E.9. Since draft-ietf-httpbis-content-disp-04
	Updated implementation information (Chrome 9 implements RFC 5987, IE
	9 RC implements it for UTF-8 only).
	Clarify who requirements are on, add a section discussing conformance
	and handling of invalid field values in general.
	Closed issues:
	o <http://trac.tools.ietf.org/wg/httpbis/trac/ticket/243>: "avoid
	stating ISO-8859-1 default for header param" (the default is still
	mentioned, but it was clarified what it applies to).
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/272>: "Path
	Separator Characters"
	E.10. Since draft-ietf-httpbis-content-disp-05
	Editorial changes: Fixed two typos where the new Conformance section
	said "Content-Location" instead of "Content-Disposition". Cleaned up
	terminology ("user agent", "recipient", "sender", "message body",
	...). Stated what the escape character for quoted-string is.
	Explained a use case for "inline" disposition type. Updated
	implementation notes with respect to the fallback behavior.
	Added appendix "Advice on Generating Content-Disposition Header
	Fields".
	E.11. Since draft-ietf-httpbis-content-disp-06
	Closed issues:
	o <http://trac.tools.ietf.org/wg/httpbis/trac/ticket/278>:
	"conformance language"
	E.12. Since draft-ietf-httpbis-content-disp-07
	Rephrase the requirement about well-known file system locations, and
	also clarify that by "last path segment" we mean the actual filename.
	Added a forward reference from "invalid" to the section that defines
	a valid header field.
	E.13. Since draft-ietf-httpbis-content-disp-08
	Update: Internet Explorer 9 is released. Various editorial
	improvements. Add US-ASCII reference. Strengthen file extension
	handling requirement to MUST for those recipients that actually use
	file extensions to map media types.
	Index
	C
	Content-Disposition header field 5
	H
	Header Fields
	Content-Disposition 5
	Author's Address		Author's Address
	Julian F. Reschke		Julian F. Reschke
	greenbytes GmbH		greenbytes GmbH
	Hafenweg 16		Hafenweg 16
	Muenster, NW 48155		Muenster, NW 48155
	Germany		Germany
	EMail: julian.reschke@greenbytes.de		EMail: julian.reschke@greenbytes.de
	URI: http://greenbytes.de/tech/webdav/		URI: http://greenbytes.de/tech/webdav/
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