draft-ietf-httpbis-retrofit-02.txt		draft-ietf-httpbis-retrofit-latest.txt
	Network Working Group M. Nottingham		Network Working Group M. Nottingham
	Internet-Draft May 11, 2021		Internet-Draft May 13, 2022
	Intended status: Standards Track		Intended status: Standards Track
	Expires: November 12, 2021		Expires: November 14, 2022
	Retrofit Structured Fields for HTTP		Retrofit Structured Fields for HTTP
	draft-ietf-httpbis-retrofit-02		draft-ietf-httpbis-retrofit-latest
	Abstract		Abstract
	This specification nominates a selection of existing HTTP fields as		This specification nominates a selection of existing HTTP fields as
	having syntax that is compatible with Structured Fields, so that they		having syntax that is compatible with Structured Fields, so that they
	can be handled as such (subject to certain caveats).		can be handled as such (subject to certain caveats).
	To accommodate some additional fields whose syntax is not compatible,		To accommodate some additional fields whose syntax is not compatible,
	it also defines mappings of their semantics into new Structured		it also defines mappings of their semantics into new Structured
	Fields. It does not specify how to negotiate their use.		Fields. It does not specify how to negotiate their use.
	skipping to change at page 2, line 4 ¶		skipping to change at page 2, line 4 ¶
	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 November 12, 2021.		This Internet-Draft will expire on November 14, 2022.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2022 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
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://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 5, line 33 ¶		skipping to change at page 5, line 33 ¶
	Table 1: Compatible Fields		Table 1: Compatible Fields
	Note the following caveats regarding compatibility:		Note the following caveats regarding compatibility:
	Parameter and Dictionary keys: HTTP parameter names are case-		Parameter and Dictionary keys: HTTP parameter names are case-
	insensitive (per Section 5.6.6 of [HTTP]), but Structured Fields		insensitive (per Section 5.6.6 of [HTTP]), but Structured Fields
	require them to be all-lowercase. Although the vast majority of		require them to be all-lowercase. Although the vast majority of
	parameters seen in typical traffic are all-lowercase,		parameters seen in typical traffic are all-lowercase,
	compatibility can be improved by force-lowercasing parameters when		compatibility can be improved by force-lowercasing parameters when
	encountered. Likewise, many Dictionary-based fields (e.g., Cache-		parsing. Likewise, many Dictionary-based fields (e.g., Cache-
	Control, Expect-CT, Pragma, Prefer, Preference-Applied, Surrogate-		Control, Expect-CT, Pragma, Prefer, Preference-Applied, Surrogate-
	Control) have case-insensitive keys, and compatibility can be		Control) have case-insensitive keys, and compatibility can be
	improved by force-lowercasing them.		improved by force-lowercasing them when parsing.
	Parameter delimitation: The parameters rule in HTTP (see		Parameter delimitation: The parameters rule in HTTP (see
	Section 5.6.6 of [HTTP]) allows whitespace before the ";"		Section 5.6.6 of [HTTP]) allows whitespace before the ";"
	delimiter, but Structured Fields does not. Compatibility can be		delimiter, but Structured Fields does not. Compatibility can be
	improved by allowing such whitespace.		improved by allowing such whitespace when parsing.
	String quoting: Section 5.6.4 of [HTTP] allows backslash-escaping		String quoting: Section 5.6.4 of [HTTP] allows backslash-escaping
	most characters in quoted strings, whereas Structured Field		most characters in quoted strings, whereas Structured Field
	Strings only escape "\" and DQUOTE. Compatibility can be improved		Strings only escape "\" and DQUOTE. Compatibility can be improved
	by unescaping other characters before processing as Strings.		by unescaping other characters before parsing.
	Token limitations: In Structured Fields, tokens are required to		Token limitations: In Structured Fields, tokens are required to
	begin with an alphabetic character or "*", whereas HTTP tokens		begin with an alphabetic character or "*", whereas HTTP tokens
	allow a wider range of characters. This prevents use of mapped		allow a wider range of characters. This prevents use of mapped
	values that begin with one of these characters. For example,		values that begin with one of these characters. For example,
	media types, field names, methods, range-units, character and		media types, field names, methods, range-units, character and
	transfer codings that begin with a number or special character		transfer codings that begin with a number or special character
	other than "*" might be valid HTTP protocol elements, but will not		other than "*" might be valid HTTP protocol elements, but will not
	be able to be parsed as Structured Field Tokens.		be able to be parsed as Structured Field Tokens.
	Integer limitations: Structured Fields Integers can have at most 15		Integer limitations: Structured Fields Integers can have at most 15
	digits; larger values will not be able to be represented in them.		digits; larger values will not be able to be represented in them.
	IPv6 Literals: Fields whose values can contain IPv6 literal		IPv6 Literals: Fields whose values contain IPv6 literal addresses
	addresses (such as CDN-Loop, Host, and Origin) are not compatible		(such as CDN-Loop, Host, and Origin) are not able to be
	when those values are parsed as Structured Fields Tokens, because		represented as Structured Fields Tokens, because the brackets used
	the brackets used to delimit them are not allowed in Tokens.		to delimit them are not allowed in Tokens.
	Empty Field Values: Empty and whitespace-only field values are		Empty Field Values: Empty and whitespace-only field values are
	considered errors in Structured Fields. For compatible fields, an		considered errors in Structured Fields. For compatible fields, an
	empty field indicates that the field should be silently ignored.		empty field indicates that the field should be silently ignored.
	Alt-Svc: Some ALPN tokens (e.g., "h3-Q43") do not conform to key's		Alt-Svc: Some ALPN tokens (e.g., "h3-Q43") do not conform to key's
	syntax. Since the final version of HTTP/3 uses the "h3" token,		syntax, and therefore cannot be represented as a Token. Since the
	this shouldn't be a long-term issue, although future tokens may		final version of HTTP/3 uses the "h3" token, this shouldn't be a
	again violate this assumption.		long-term issue, although future tokens may again violate this
			assumption.
	Content-Length: Content-Length is defined as a List because it is		Content-Length: Note that Content-Length is defined as a List
	not uncommon for implementations to mistakenly send multiple		because it is not uncommon for implementations to mistakenly send
	values. See Section 8.6 of [HTTP] for handling requirements.		multiple values. See Section 8.6 of [HTTP] for handling
			requirements.
	Retry-After: Only the delta-seconds form of Retry-After is		Retry-After: Only the delta-seconds form of Retry-After can be
	supported; a Retry-After value containing a http-date will need to		represented; a Retry-After value containing a http-date will need
	be either converted into delta-seconds or represented as a raw		to be either converted into delta-seconds to be conveyed as a
	value.		Structured Field Value.
	3. Mapped Fields		3. Mapped Fields
	Some HTTP field values have syntax that cannot be successfully parsed		Some HTTP field values have syntax that cannot be successfully parsed
	as Structured Fields. Instead, it is necessary to map them into a		as Structured Fields. Instead, it is necessary to map them into a
	separate Structured Field with an alternative name.		separate Structured Field with an alternative name.
	For example, the Date HTTP header field carries a date:		For example, the Date HTTP header field carries a date:
	Date: Sun, 06 Nov 1994 08:49:37 GMT		Date: Sun, 06 Nov 1994 08:49:37 GMT
End of changes. 13 change blocks.
	23 lines changed or deleted		25 lines changed or added
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