draft-reschke-http-jfv-02.txt		draft-reschke-http-jfv-03.txt
	Network Working Group J. Reschke		Network Working Group J. Reschke
	Internet-Draft greenbytes		Internet-Draft greenbytes
	Intended status: Standards Track October 5, 2015		Intended status: Standards Track March 15, 2016
	Expires: April 7, 2016		Expires: September 16, 2016
	A JSON Encoding for HTTP Header Field Values		A JSON Encoding for HTTP Header Field Values
	draft-reschke-http-jfv-02		draft-reschke-http-jfv-03
	Abstract		Abstract
	This document establishes a convention for use of JSON-encoded field		This document establishes a convention for use of JSON-encoded field
	values in HTTP header fields.		values in HTTP header fields.
	Editorial Note (To be removed by RFC Editor before publication)		Editorial Note (To be removed by RFC Editor before publication)
	Distribution of this document is unlimited. Although this is not a		Distribution of this document is unlimited. Although this is not a
	work item of the HTTPbis Working Group, comments should be sent to		work item of the HTTPbis Working Group, comments should be sent to
	the Hypertext Transfer Protocol (HTTP) mailing list at		the Hypertext Transfer Protocol (HTTP) mailing list at
	ietf-http-wg@w3.org [1], which may be joined by sending a message		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].		with subject "subscribe" to ietf-http-wg-request@w3.org [2].
	Discussions of the HTTPbis Working Group are archived at		Discussions of the HTTPbis Working Group are archived at
	<http://lists.w3.org/Archives/Public/ietf-http-wg/>.		<http://lists.w3.org/Archives/Public/ietf-http-wg/>.
	XML versions and latest edits for this document are available from		XML versions and latest edits for this document are available from
	<http://greenbytes.de/tech/webdav/#draft-reschke-http-jfv>.		<http://greenbytes.de/tech/webdav/#draft-reschke-http-jfv>.
	The changes in this draft are summarized in Appendix A.2.		The changes in this draft are summarized in Appendix A.3.
	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/.
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	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
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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."
	This Internet-Draft will expire on April 7, 2016.		This Internet-Draft will expire on September 16, 2016.
	Copyright Notice		Copyright Notice
	Copyright (c) 2015 IETF Trust and the persons identified as the		Copyright (c) 2016 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
	skipping to change at page 2, line 28 ¶		skipping to change at page 2, line 28 ¶
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Data Model and Format . . . . . . . . . . . . . . . . . . . . 3		2. Data Model and Format . . . . . . . . . . . . . . . . . . . . 3
	3. Sender Requirements . . . . . . . . . . . . . . . . . . . . . 4		3. Sender Requirements . . . . . . . . . . . . . . . . . . . . . 4
	4. Recipient Requirements . . . . . . . . . . . . . . . . . . . . 5		4. Recipient Requirements . . . . . . . . . . . . . . . . . . . . 5
	5. Using this Format in Header Field Definitions . . . . . . . . 5		5. Using this Format in Header Field Definitions . . . . . . . . 5
	6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5		6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	6.1. Content-Length . . . . . . . . . . . . . . . . . . . . . . 5		6.1. Content-Length . . . . . . . . . . . . . . . . . . . . . . 5
	6.2. Content-Disposition . . . . . . . . . . . . . . . . . . . 6		6.2. Content-Disposition . . . . . . . . . . . . . . . . . . . 6
	6.3. WWW-Authenticate . . . . . . . . . . . . . . . . . . . . . 7		6.3. WWW-Authenticate . . . . . . . . . . . . . . . . . . . . . 7
	7. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 7		7. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 8
	8. Deployment Considerations . . . . . . . . . . . . . . . . . . 8		8. Deployment Considerations . . . . . . . . . . . . . . . . . . 8
	9. Internationalization Considerations . . . . . . . . . . . . . 8		9. Internationalization Considerations . . . . . . . . . . . . . 8
	10. Security Considerations . . . . . . . . . . . . . . . . . . . 8		10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8		11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
	11.1. Normative References . . . . . . . . . . . . . . . . . . . 8		11.1. Normative References . . . . . . . . . . . . . . . . . . . 9
	11.2. Informative References . . . . . . . . . . . . . . . . . . 9		11.2. Informative References . . . . . . . . . . . . . . . . . . 9
	Appendix A. Change Log (to be removed by RFC Editor before		Appendix A. Change Log (to be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . 10		publication) . . . . . . . . . . . . . . . . . . . . 10
	A.1. Since draft-reschke-http-jfv-00 . . . . . . . . . . . . . 10		A.1. Since draft-reschke-http-jfv-00 . . . . . . . . . . . . . 10
	A.2. Since draft-reschke-http-jfv-01 . . . . . . . . . . . . . 10		A.2. Since draft-reschke-http-jfv-01 . . . . . . . . . . . . . 10
			A.3. Since draft-reschke-http-jfv-02 . . . . . . . . . . . . . 10
			Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 11
	1. Introduction		1. Introduction
	Defining syntax for new HTTP header fields ([RFC7230], Section 3.2)		Defining syntax for new HTTP header fields ([RFC7230], Section 3.2)
	is non-trivial. Among the commonly encountered problems are:		is non-trivial. Among the commonly encountered problems are:
	o There is no common syntax for complex field values. Several well-		o There is no common syntax for complex field values. Several well-
	known header fields do use a similarly looking syntax, but it is		known header fields do use a similarly looking syntax, but it is
	hard to write generic parsing code that will both correctly handle		hard to write generic parsing code that will both correctly handle
	valid field values but also reject invalid ones.		valid field values but also reject invalid ones.
	skipping to change at page 3, line 33 ¶		skipping to change at page 3, line 33 ¶
	default encoding scheme in order to map from octet sequences to		default encoding scheme in order to map from octet sequences to
	strings (for instance, [XMLHttpRequest] uses the IDL type		strings (for instance, [XMLHttpRequest] uses the IDL type
	"ByteString", effectively resulting in the ISO-8859-1 character		"ByteString", effectively resulting in the ISO-8859-1 character
	encoding scheme [ISO-8859-1] being used).		encoding scheme [ISO-8859-1] being used).
	(See Section 8.3.1 of [RFC7231] for a summary of considerations for		(See Section 8.3.1 of [RFC7231] for a summary of considerations for
	new header fields.)		new header fields.)
	This specification addresses the issues listed above by defining both		This specification addresses the issues listed above by defining both
	a generic JSON-based ([RFC7159]) data model and a concrete wire		a generic JSON-based ([RFC7159]) data model and a concrete wire
	format that can be used in definitions of new header fields.		format that can be used in definitions of new header fields, where
			the goals were:
			o to be compatible with header field recombination when fields occur
			multiple times in a single message (Section 3.2.2 of [RFC7230]),
			and
			o not to use any problematic characters in the field value (non-
			ASCII characters and certain whitespace characters).
	2. Data Model and Format		2. Data Model and Format
	In HTTP, header fields with the same field name can occur multiple		In HTTP, header fields with the same field name can occur multiple
	times within a single message (Section 3.2.2 of [RFC7230]). When		times within a single message (Section 3.2.2 of [RFC7230]). When
	this happens, recipients are allowed to combine the field values		this happens, recipients are allowed to combine the field values
	using commas as delimiter. This rule matches nicely JSON's array		using commas as delimiter. This rule matches nicely JSON's array
	format (Section 5 of [RFC7159]). Thus, the basic data model used		format (Section 5 of [RFC7159]). Thus, the basic data model used
	here is the JSON array.		here is the JSON array.
	skipping to change at page 5, line 38 ¶		skipping to change at page 5, line 46 ¶
	This section shows how some of the existing HTTP header fields would		This section shows how some of the existing HTTP header fields would
	look like if they would use the format defined by this specification.		look like if they would use the format defined by this specification.
	6.1. Content-Length		6.1. Content-Length
	"Content-Length" is defined in Section 3.3.2 of [RFC7230], with the		"Content-Length" is defined in Section 3.3.2 of [RFC7230], with the
	field value's ABNF being:		field value's ABNF being:
	Content-Length = 1*DIGIT		Content-Length = 1*DIGIT
	So the field value is similar to a JSON number ([RFC7230], Section		So the field value is similar to a JSON number ([RFC7159], Section
	6).		6).
	Content-Length is restricted to a single field instance, as it		Content-Length is restricted to a single field instance, as it
	doesn't use the list production (as per Section 3.2.2 of [RFC7230]).		doesn't use the list production (as per Section 3.2.2 of [RFC7230]).
	However, in practice multiple instances do occur, and the definition		However, in practice multiple instances do occur, and the definition
	of the header field does indeed discuss how to handle these cases.		of the header field does indeed discuss how to handle these cases.
	If Content-Length was defined using the JSON format discussed here,		If Content-Length was defined using the JSON format discussed here,
	the ABNF would be something like:		the ABNF would be something like:
	skipping to change at page 8, line 8 ¶		skipping to change at page 8, line 14 ¶
	7. Discussion		7. Discussion
	This approach uses a default of "JSON array", using implicit array		This approach uses a default of "JSON array", using implicit array
	markers. An alternative would be a default of "JSON object". This		markers. An alternative would be a default of "JSON object". This
	would simplify the syntax for non-list-typed header fields, but all		would simplify the syntax for non-list-typed header fields, but all
	the benefits of having the same data model for both types of header		the benefits of having the same data model for both types of header
	fields would be gone. A hybrid approach might make sense, as long as		fields would be gone. A hybrid approach might make sense, as long as
	it doesn't require any heuristics on the recipient's side.		it doesn't require any heuristics on the recipient's side.
			Note: a concrete proposal was made by Kazuho Oku in <https://
			lists.w3.org/Archives/Public/ietf-http-wg/2016JanMar/0155.html>.
	[[anchor7: Use of generic libs vs compactness of field values..]]		[[anchor7: Use of generic libs vs compactness of field values..]]
	8. Deployment Considerations		8. Deployment Considerations
	This JSON-based syntax will only apply to newly introduced header		This JSON-based syntax will only apply to newly introduced header
	fields, thus backwards compatibility is not a problem. That being		fields, thus backwards compatibility is not a problem. That being
	said, it is conceivable that there is existing code that might trip		said, it is conceivable that there is existing code that might trip
	over double quotes not being used for HTTP's quoted-string syntax		over double quotes not being used for HTTP's quoted-string syntax
	(Section 3.2.6 of [RFC7230]).		(Section 3.2.6 of [RFC7230]).
	9. Internationalization Considerations		9. Internationalization Considerations
	[[anchor10: TBD, mention migration path to message format that is		In HTTP/1.1, header field values are represented by octet sequences,
	robust wrt UTF-8, or other binary encodings of JSON]]		usually used to transmit ASCII characters, with restrictions on the
			use of certain control characters, and no associated default
			character encoding, nor a way to describe it ([RFC7230], Section
			3.2). HTTP/2 does not change this.
			This specification maps all characters which can cause problems to
			JSON escape sequences, thereby solving the HTTP header field
			internationalization problem.
			Future specifications of HTTP might change to allow non-ASCII
			characters natively. In that case, header fields using the syntax
			defined by this specification would have a simple migration path (by
			just stopping to require escaping of non-ASCII characters).
	10. Security Considerations		10. Security Considerations
	Using JSON-shaped field values is believed to not introduce any new		Using JSON-shaped field values is believed to not introduce any new
	threads beyond those described in Section 12 of [RFC7159], namely the		threads beyond those described in Section 12 of [RFC7159], namely the
	risk of recipients using the wrong tools to parse them.		risk of recipients using the wrong tools to parse them.
	Other than that, any syntax that makes extensions easy can be used to		Other than that, any syntax that makes extensions easy can be used to
	smuggle information through field values; however, this concern is		smuggle information through field values; however, this concern is
	shared with other widely used formats, such as those using parameters		shared with other widely used formats, such as those using parameters
	skipping to change at page 10, line 22 ¶		skipping to change at page 10, line 42 ¶
	A.1. Since draft-reschke-http-jfv-00		A.1. Since draft-reschke-http-jfv-00
	Editorial fixes + working on the TODOs.		Editorial fixes + working on the TODOs.
	A.2. Since draft-reschke-http-jfv-01		A.2. Since draft-reschke-http-jfv-01
	Mention slightly increased risk of smuggling information in header		Mention slightly increased risk of smuggling information in header
	field values.		field values.
			A.3. Since draft-reschke-http-jfv-02
			Mention Kazuho Oku's proposal for abbreviated forms.
			Added a bit of text about the motivation for a concrete JSON subset
			(ack Cory Benfield).
			Expand I18N section.
			Appendix B. Acknowledgements
			Thanks go to the Hypertext Transfer Protocol Working Group
			participants.
	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/
End of changes. 13 change blocks.
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