draft-reschke-http-jfv-12.txt		draft-reschke-http-jfv-latest.txt
	Network Working Group J. F. Reschke		Network Working Group J. F. Reschke
	Internet-Draft greenbytes		Internet-Draft greenbytes
	Intended status: Informational September 1, 2020		Intended status: Informational January 15, 2021
	Expires: March 5, 2021		Expires: July 19, 2021
	A JSON Encoding for HTTP Field Values		A JSON Encoding for HTTP Field Values
	draft-reschke-http-jfv-12		draft-reschke-http-jfv-latest
	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 fields.		values in HTTP fields.
	Editorial Note		Editorial Note
	This note is to be removed before publishing as an RFC.		This note is to be removed before publishing as an RFC.
	skipping to change at page 1, line 34 ¶		skipping to change at page 1, line 34 ¶
	sending a message with subject "subscribe" to ietf-http-wg-		sending a message with subject "subscribe" to ietf-http-wg-
	request@w3.org (mailto:ietf-http-wg-		request@w3.org (mailto:ietf-http-wg-
	request@w3.org?subject=subscribe).		request@w3.org?subject=subscribe).
	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 B.15.		The changes in this draft are summarized in Appendix B.16.
	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 https://datatracker.ietf.org/drafts/current/.		Drafts is at https://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 March 5, 2021.		This Internet-Draft will expire on July 19, 2021.
	Copyright Notice		Copyright Notice
	Copyright (c) 2020 IETF Trust and the persons identified as the		Copyright (c) 2021 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 (https://trustee.ietf.org/		Provisions Relating to IETF Documents (https://trustee.ietf.org/
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	and restrictions with respect to this document. Code Components		and restrictions with respect to this document. Code Components
	extracted from this document must include Simplified BSD License text		extracted from this document must include Simplified BSD License text
	as described in Section 4.e of the Trust Legal Provisions and are		as described in Section 4.e of the Trust Legal Provisions and are
	provided without warranty as described in the Simplified BSD License.		provided without warranty as described in the Simplified BSD License.
	skipping to change at page 3, line 11 ¶		skipping to change at page 3, line 11 ¶
	B.6. Since draft-ietf-httpbis-jfv-00 . . . . . . . . . . . . . 10		B.6. Since draft-ietf-httpbis-jfv-00 . . . . . . . . . . . . . 10
	B.7. Since draft-ietf-httpbis-jfv-01 . . . . . . . . . . . . . 11		B.7. Since draft-ietf-httpbis-jfv-01 . . . . . . . . . . . . . 11
	B.8. Since draft-ietf-httpbis-jfv-02 . . . . . . . . . . . . . 11		B.8. Since draft-ietf-httpbis-jfv-02 . . . . . . . . . . . . . 11
	B.9. Since draft-reschke-http-jfv-05 . . . . . . . . . . . . . 11		B.9. Since draft-reschke-http-jfv-05 . . . . . . . . . . . . . 11
	B.10. Since draft-reschke-http-jfv-06 . . . . . . . . . . . . . 11		B.10. Since draft-reschke-http-jfv-06 . . . . . . . . . . . . . 11
	B.11. Since draft-reschke-http-jfv-07 . . . . . . . . . . . . . 11		B.11. Since draft-reschke-http-jfv-07 . . . . . . . . . . . . . 11
	B.12. Since draft-reschke-http-jfv-08 . . . . . . . . . . . . . 11		B.12. Since draft-reschke-http-jfv-08 . . . . . . . . . . . . . 11
	B.13. Since draft-reschke-http-jfv-09 . . . . . . . . . . . . . 11		B.13. Since draft-reschke-http-jfv-09 . . . . . . . . . . . . . 11
	B.14. Since draft-reschke-http-jfv-10 . . . . . . . . . . . . . 12		B.14. Since draft-reschke-http-jfv-10 . . . . . . . . . . . . . 12
	B.15. Since draft-reschke-http-jfv-11 . . . . . . . . . . . . . 12		B.15. Since draft-reschke-http-jfv-11 . . . . . . . . . . . . . 12
			B.16. Since draft-reschke-http-jfv-12 . . . . . . . . . . . . . 12
	Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 12		Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 12
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
	1. Introduction		1. Introduction
	Defining syntax for new HTTP fields ([HTTP], Section 5) is non-		Defining syntax for new HTTP fields ([HTTP], Section 5) is non-
	trivial. Among the commonly encountered problems are:		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 fields do use a similarly looking syntax, but it is hard to		known fields do use a similarly looking syntax, but it is hard to
	write generic parsing code that will both correctly handle valid		write generic parsing code that will both correctly handle valid
	field values but also reject invalid ones.		field values but also reject invalid ones.
	o The HTTP message format allows fields to repeat, so field syntax		o The HTTP message format allows field lines to repeat, so field
	needs to be designed in a way that these cases are either		syntax needs to be designed in a way that these cases are either
	meaningful, or can be unambiguously detected and rejected.		meaningful, or can be unambiguously detected and rejected.
	o HTTP does not define a character encoding scheme ([RFC6365],		o HTTP does not define a character encoding scheme ([RFC6365],
	Section 2), so fields are either stuck with US-ASCII ([RFC0020]),		Section 2), so fields are either stuck with US-ASCII ([RFC0020]),
	or need out-of-band information to decide what encoding scheme is		or need out-of-band information to decide what encoding scheme is
	used. Furthermore, APIs usually assume a default encoding scheme		used. Furthermore, APIs usually assume a default encoding scheme
	in order to map from octet sequences to strings (for instance,		in order to map from octet sequences to strings (for instance,
	[XMLHttpRequest] uses the IDL type "ByteString", effectively		[XMLHttpRequest] uses the IDL type "ByteString", effectively
	resulting in the ISO-8859-1 character encoding scheme [ISO-8859-1]		resulting in the ISO-8859-1 character encoding scheme [ISO-8859-1]
	being used).		being used).
	(See Section 5.7 of [HTTP] for a summary of considerations for new		(See Section 16.3 of [HTTP] for a summary of considerations for new
	fields.)		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 ([RFC8259]) data model and a concrete wire		a generic JSON-based ([RFC8259]) data model and a concrete wire
	format that can be used in definitions of new fields, where the goals		format that can be used in definitions of new fields, where the goals
	were:		were:
	o to be compatible with field recombination when fields occur		o to be compatible with field recombination when field lines occur
	multiple times in a single message (Section 5.1 of [HTTP]), and		multiple times in a single message (Section 5.3 of [HTTP]), and
	o not to use any problematic characters in the field value (non-		o not to use any problematic characters in the field value (non-
	ASCII characters and certain whitespace characters).		ASCII characters and certain whitespace characters).
	| *Note:* [HSTRUCT], a work item of the IETF HTTP Working Group,		| *Note:* [HSTRUCT], a work item of the IETF HTTP Working Group,
	| is a different attempt to address this set of problems - it		| is a different attempt to address this set of problems - it
	| tries to identify and formalize common field structures in		| tries to identify and formalize common field structures in
	| existing fields; the syntax defined over there would usually		| existing fields; the syntax defined over there would usually
	| lead to a more compact notation.		| lead to a more compact notation.
	2. Data Model and Format		2. Data Model and Format
	In HTTP, fields with the same field name can occur multiple times		In HTTP, field lines with the same field name can occur multiple
	within a single message (Section 5.1 of [HTTP]). When this happens,		times within a single message (Section 5.3 of [HTTP]). When this
	recipients are allowed to combine the field values using commas as		happens, recipients are allowed to combine the field line values
	delimiter. This rule matches nicely JSON's array format (Section 5		using commas as delimiter, forming a combined "field value". This
	of [RFC8259]). Thus, the basic data model used here is the JSON		rule matches nicely JSON's array format (Section 5 of [RFC8259]).
	array.		Thus, the basic data model used here is the JSON array.
	Field definitions that need only a single value can restrict		Field definitions that need only a single value can restrict
	themselves to arrays of length 1, and are encouraged to define error		themselves to arrays of length 1, and are encouraged to define error
	handling in case more values are received (such as "first wins",		handling in case more values are received (such as "first wins",
	"last wins", or "abort with fatal error message").		"last wins", or "abort with fatal error message").
	JSON arrays are mapped to field values by creating a sequence of		JSON arrays are mapped to field values by creating a sequence of
	serialized member elements, separated by commas and optionally		serialized member elements, separated by commas and optionally
	whitespace. This is equivalent to using the full JSON array format,		whitespace. This is equivalent to using the full JSON array format,
	while leaving out the "begin-array" ('[') and "end-array" (']')		while leaving out the "begin-array" ('[') and "end-array" (']')
	skipping to change at page 4, line 51 ¶		skipping to change at page 4, line 51 ¶
	HTTP field values - that is, not in the "VCHAR" definition - need to		HTTP field values - that is, not in the "VCHAR" definition - need to
	be represented using JSON's "backslash" escaping mechanism		be represented using JSON's "backslash" escaping mechanism
	([RFC8259], Section 7).		([RFC8259], Section 7).
	The control characters CR, LF, and HTAB do not appear inside JSON		The control characters CR, LF, and HTAB do not appear inside JSON
	strings, but can be used outside (line breaks, indentation etc.).		strings, but can be used outside (line breaks, indentation etc.).
	These characters need to be either stripped or replaced by space		These characters need to be either stripped or replaced by space
	characters (ABNF "SP").		characters (ABNF "SP").
	Formally, using the HTTP specification's ABNF extensions defined in		Formally, using the HTTP specification's ABNF extensions defined in
	Section 5.5 of [HTTP]:		Section 5.6.1 of [HTTP]:
	json-field-value = #json-field-item		json-field-value = #json-field-item
	json-field-item = JSON-Text		json-field-item = JSON-Text
	; see [RFC8259], Section 2,		; see [RFC8259], Section 2,
	; post-processed so that only VCHAR characters		; post-processed so that only VCHAR characters
	; are used		; are used
	3. Sender Requirements		3. Sender Requirements
	To map a JSON array to an HTTP field value, process each array		To map a JSON array to an HTTP field value, process each array
	skipping to change at page 5, line 31 ¶		skipping to change at page 5, line 31 ¶
	3. replacing all remaining non-VSPACE characters by the equivalent		3. replacing all remaining non-VSPACE characters by the equivalent
	backslash-escape sequence ([RFC8259], Section 7).		backslash-escape sequence ([RFC8259], Section 7).
	The resulting list of strings is transformed into an HTTP field value		The resulting list of strings is transformed into an HTTP field value
	by combining them using comma (%x2C) plus optional SP as delimiter,		by combining them using comma (%x2C) plus optional SP as delimiter,
	and encoding the resulting string into an octet sequence using the		and encoding the resulting string into an octet sequence using the
	US-ASCII character encoding scheme ([RFC0020]).		US-ASCII character encoding scheme ([RFC0020]).
	4. Recipient Requirements		4. Recipient Requirements
	To map a set of HTTP field instances to a JSON array:		To map a set of HTTP field line values to a JSON array:
	1. combine all field instances into a single field as per		1. combine all field line values into a single field value as per
	Section 5.1 of [HTTP],		Section 5.3 of [HTTP],
	2. add a leading begin-array ("[") octet and a trailing end-array		2. add a leading begin-array ("[") octet and a trailing end-array
	("]") octet, then		("]") octet, then
	3. run the resulting octet sequence through a JSON parser.		3. run the resulting octet sequence through a JSON parser.
	The result of the parsing operation is either an error (in which case		The result of the parsing operation is either an error (in which case
	the field values needs to be considered invalid), or a JSON array.		the field values needs to be considered invalid), or a JSON array.
	5. Using this Format in Field Definitions		5. Using this Format in Field Definitions
	Specifications defining new HTTP fields need to take the		Specifications defining new HTTP fields need to take the
	considerations listed in Section 5.7 of [HTTP] into account. Many of		considerations listed in Section 16.3 of [HTTP] into account. Many
	these will already be accounted for by using the format defined in		of these will already be accounted for by using the format defined in
	this specification.		this specification.
	Readers of HTTP-related specifications frequently expect an ABNF		Readers of HTTP-related specifications frequently expect an ABNF
	definition of the field value syntax. This is not really needed		definition of the field value syntax. This is not really needed
	here, as the actual syntax is JSON text, as defined in Section 2 of		here, as the actual syntax is JSON text, as defined in Section 2 of
	[RFC8259].		[RFC8259].
	A very simple way to use this JSON encoding thus is just to cite this		A very simple way to use this JSON encoding thus is just to cite this
	specification - specifically the "json-field-value" ABNF production		specification - specifically the "json-field-value" ABNF production
	defined in Section 2 - and otherwise not to talk about the details of		defined in Section 2 - and otherwise not to talk about the details of
	skipping to change at page 6, line 31 ¶		skipping to change at page 6, line 31 ¶
	how recipients ought to treat unknown field names. In general, a		how recipients ought to treat unknown field names. In general, a
	"must ignore" approach will allow protocols to evolve without		"must ignore" approach will allow protocols to evolve without
	versioning or even using entire new field names.		versioning or even using entire new field names.
	6. Deployment Considerations		6. Deployment Considerations
	This JSON-based syntax will only apply to newly introduced fields,		This JSON-based syntax will only apply to newly introduced fields,
	thus backwards compatibility is not a problem. That being said, it		thus backwards compatibility is not a problem. That being said, it
	is conceivable that there is existing code that might trip over		is conceivable that there is existing code that might trip over
	double quotes not being used for HTTP's quoted-string syntax		double quotes not being used for HTTP's quoted-string syntax
	(Section 5.4.1 of [HTTP]).		(Section 5.6.4 of [HTTP]).
	7. Interoperability Considerations		7. Interoperability Considerations
	The "I-JSON Message Format" specification ([RFC7493]) addresses known		The "I-JSON Message Format" specification ([RFC7493]) addresses known
	JSON interoperability pain points. This specification borrows from		JSON interoperability pain points. This specification borrows from
	the requirements made over there:		the requirements made over there:
	7.1. Encoding and Characters		7.1. Encoding and Characters
	This specification requires that field values use only US-ASCII		This specification requires that field values use only US-ASCII
	skipping to change at page 7, line 23 ¶		skipping to change at page 7, line 23 ¶
	Furthermore, ordering of object members is not significant and can		Furthermore, ordering of object members is not significant and can
	not be relied upon.		not be relied upon.
	8. Internationalization Considerations		8. Internationalization Considerations
	In current versions of HTTP, field values are represented by octet		In current versions of HTTP, field values are represented by octet
	sequences, usually used to transmit ASCII characters, with		sequences, usually used to transmit ASCII characters, with
	restrictions on the use of certain control characters, and no		restrictions on the use of certain control characters, and no
	associated default character encoding, nor a way to describe it		associated default character encoding, nor a way to describe it
	([HTTP], Section 5). HTTP/2 does not change this.		([HTTP], Section 5).
	This specification maps all characters which can cause problems to		This specification maps all characters which can cause problems to
	JSON escape sequences, thereby solving the HTTP field		JSON escape sequences, thereby solving the HTTP field
	internationalization problem.		internationalization problem.
	Future specifications of HTTP might change to allow non-ASCII		Future specifications of HTTP might change to allow non-ASCII
	characters natively. In that case, fields using the syntax defined		characters natively. In that case, fields using the syntax defined
	by this specification would have a simple migration path (by just		by this specification would have a simple migration path (by just
	stopping to require escaping of non-ASCII characters).		stopping to require escaping of non-ASCII characters).
	skipping to change at page 8, line 5 ¶		skipping to change at page 8, line 5 ¶
	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
	in the form of name/value pairs.		in the form of name/value pairs.
	10. References		10. References
	10.1. Normative References		10.1. Normative References
	[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. F. Reschke,		[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
	Ed., "HTTP Semantics", Work in Progress, Internet-Draft,		Ed., "HTTP Semantics", Work in Progress, Internet-Draft,
	draft-ietf-httpbis-semantics-11, August 27, 2020,		draft-ietf-httpbis-semantics-13, December 14, 2020,
	<https://tools.ietf.org/html/draft-ietf-httpbis-semantics-		<https://tools.ietf.org/html/draft-ietf-httpbis-semantics-
	11>.		13>.
	[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,		[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
	RFC 20, DOI 10.17487/RFC0020, October 1969,		RFC 20, DOI 10.17487/RFC0020, October 1969,
	<https://www.rfc-editor.org/info/rfc20>.		<https://www.rfc-editor.org/info/rfc20>.
	[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax		[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", STD 68, RFC 5234,		Specifications: ABNF", STD 68, RFC 5234,
	DOI 10.17487/RFC5234, January 2008,		DOI 10.17487/RFC5234, January 2008,
	<https://www.rfc-editor.org/info/rfc5234>.		<https://www.rfc-editor.org/info/rfc5234>.
	skipping to change at page 12, line 26 ¶		skipping to change at page 12, line 26 ¶
	terminology accordingly.		terminology accordingly.
	Remove discussion about the relation to KEY (as that spec is dormant:		Remove discussion about the relation to KEY (as that spec is dormant:
	<https://datatracker.ietf.org/doc/draft-ietf-httpbis-key/>).		<https://datatracker.ietf.org/doc/draft-ietf-httpbis-key/>).
	Remove appendices "Examples" and "Discussion".		Remove appendices "Examples" and "Discussion".
	Mark "Use of JSON Field Value Encoding in the Wild" for removal in		Mark "Use of JSON Field Value Encoding in the Wild" for removal in
	RFC.		RFC.
			B.16. Since draft-reschke-http-jfv-12
			Update HTTP reference and update terminology some more.
	Acknowledgements		Acknowledgements
	Thanks go to the Hypertext Transfer Protocol Working Group		Thanks go to the Hypertext Transfer Protocol Working Group
	participants.		participants.
	Author's Address		Author's Address
	Julian F. Reschke		Julian F. Reschke
	greenbytes GmbH		greenbytes GmbH
	Hafenweg 16		Hafenweg 16
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