draft-ietf-httpbis-cache-14.txt		draft-ietf-httpbis-cache-latest.txt
	HTTP Working Group R. Fielding, Ed.		HTTP Working Group R. Fielding, Ed.
	Internet-Draft Adobe		Internet-Draft Adobe
	Obsoletes: 7234 (if approved) M. Nottingham, Ed.		Obsoletes: 7234 (if approved) M. Nottingham, Ed.
	Intended status: Standards Track Fastly		Intended status: Standards Track Fastly
	Expires: July 17, 2021 J. Reschke, Ed.		Expires: August 30, 2021 J. Reschke, Ed.
	greenbytes		greenbytes
	January 13, 2021		February 26, 2021
	HTTP Caching		HTTP Caching
	draft-ietf-httpbis-cache-14		draft-ietf-httpbis-cache-latest
	Abstract		Abstract
	The Hypertext Transfer Protocol (HTTP) is a stateless application-		The Hypertext Transfer Protocol (HTTP) is a stateless application-
	level protocol for distributed, collaborative, hypertext information		level protocol for distributed, collaborative, hypertext information
	systems. This document defines HTTP caches and the associated header		systems. This document defines HTTP caches and the associated header
	fields that control cache behavior or indicate cacheable response		fields that control cache behavior or indicate cacheable response
	messages.		messages.
	This document obsoletes RFC 7234.		This document obsoletes RFC 7234.
	skipping to change at page 1, line 36 ¶		skipping to change at page 1, line 36 ¶
	This note is to be removed before publishing as an RFC.		This note is to be removed before publishing as an RFC.
	Discussion of this draft takes place on the HTTP working group		Discussion of this draft takes place on the HTTP working group
	mailing list (ietf-http-wg@w3.org), which is archived at		mailing list (ietf-http-wg@w3.org), which is archived at
	<https://lists.w3.org/Archives/Public/ietf-http-wg/>.		<https://lists.w3.org/Archives/Public/ietf-http-wg/>.
	Working Group information can be found at <https://httpwg.org/>;		Working Group information can be found at <https://httpwg.org/>;
	source code and issues list for this draft can be found at		source code and issues list for this draft can be found at
	<https://github.com/httpwg/http-core>.		<https://github.com/httpwg/http-core>.
	The changes in this draft are summarized in Appendix C.15.		The changes in this draft are summarized in Appendix C.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 July 17, 2021.		This Internet-Draft will expire on August 30, 2021.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 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
	skipping to change at page 2, line 49 ¶		skipping to change at page 2, line 49 ¶
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
	1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5		1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
	1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 5		1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 5
	1.3. Delta Seconds . . . . . . . . . . . . . . . . . . . . . . 5		1.3. Delta Seconds . . . . . . . . . . . . . . . . . . . . . . 5
	2. Overview of Cache Operation . . . . . . . . . . . . . . . . . 6		2. Overview of Cache Operation . . . . . . . . . . . . . . . . . 6
	3. Storing Responses in Caches . . . . . . . . . . . . . . . . . 7		3. Storing Responses in Caches . . . . . . . . . . . . . . . . . 7
	3.1. Storing Header and Trailer Fields . . . . . . . . . . . . 8		3.1. Storing Header and Trailer Fields . . . . . . . . . . . . 8
	3.2. Updating Stored Header Fields . . . . . . . . . . . . . . 9		3.2. Updating Stored Header Fields . . . . . . . . . . . . . . 9
	3.3. Storing Incomplete Responses . . . . . . . . . . . . . . 10		3.3. Storing Incomplete Responses . . . . . . . . . . . . . . 10
	3.4. Combining Partial Content . . . . . . . . . . . . . . . . 10		3.4. Combining Partial Content . . . . . . . . . . . . . . . . 11
	3.5. Storing Responses to Authenticated Requests . . . . . . . 10		3.5. Storing Responses to Authenticated Requests . . . . . . . 11
	4. Constructing Responses from Caches . . . . . . . . . . . . . 11		4. Constructing Responses from Caches . . . . . . . . . . . . . 11
	4.1. Calculating Cache Keys with Vary . . . . . . . . . . . . 12		4.1. Calculating Cache Keys with Vary . . . . . . . . . . . . 12
	4.2. Freshness . . . . . . . . . . . . . . . . . . . . . . . . 13		4.2. Freshness . . . . . . . . . . . . . . . . . . . . . . . . 14
	4.2.1. Calculating Freshness Lifetime . . . . . . . . . . . 15		4.2.1. Calculating Freshness Lifetime . . . . . . . . . . . 15
	4.2.2. Calculating Heuristic Freshness . . . . . . . . . . . 15		4.2.2. Calculating Heuristic Freshness . . . . . . . . . . . 16
	4.2.3. Calculating Age . . . . . . . . . . . . . . . . . . . 16		4.2.3. Calculating Age . . . . . . . . . . . . . . . . . . . 17
	4.2.4. Serving Stale Responses . . . . . . . . . . . . . . . 17		4.2.4. Serving Stale Responses . . . . . . . . . . . . . . . 18
	4.3. Validation . . . . . . . . . . . . . . . . . . . . . . . 18		4.3. Validation . . . . . . . . . . . . . . . . . . . . . . . 18
	4.3.1. Sending a Validation Request . . . . . . . . . . . . 18		4.3.1. Sending a Validation Request . . . . . . . . . . . . 19
	4.3.2. Handling a Received Validation Request . . . . . . . 19		4.3.2. Handling a Received Validation Request . . . . . . . 19
	4.3.3. Handling a Validation Response . . . . . . . . . . . 20		4.3.3. Handling a Validation Response . . . . . . . . . . . 21
	4.3.4. Freshening Stored Responses upon Validation . . . . . 21		4.3.4. Freshening Stored Responses upon Validation . . . . . 21
	4.3.5. Freshening Responses with HEAD . . . . . . . . . . . 21		4.3.5. Freshening Responses with HEAD . . . . . . . . . . . 22
	4.4. Invalidating Stored Responses . . . . . . . . . . . . . . 22		4.4. Invalidating Stored Responses . . . . . . . . . . . . . . 22
	5. Field Definitions . . . . . . . . . . . . . . . . . . . . . . 23		5. Field Definitions . . . . . . . . . . . . . . . . . . . . . . 23
	5.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 23		5.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
	5.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 23		5.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 24
	5.2.1. Request Cache-Control Directives . . . . . . . . . . 24		5.2.1. Request Cache-Control Directives . . . . . . . . . . 24
	5.2.2. Response Cache-Control Directives . . . . . . . . . . 26		5.2.2. Response Cache-Control Directives . . . . . . . . . . 26
	5.2.3. Cache Control Extensions . . . . . . . . . . . . . . 30		5.2.3. Cache Control Extensions . . . . . . . . . . . . . . 31
	5.2.4. Cache Directive Registry . . . . . . . . . . . . . . 31		5.2.4. Cache Directive Registry . . . . . . . . . . . . . . 32
	5.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 31		5.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 32
	5.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . 32		5.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . 33
	5.5. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 33		5.5. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 33
	6. Relationship to Applications and Other Caches . . . . . . . . 33		6. Relationship to Applications and Other Caches . . . . . . . . 33
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 34		7. Security Considerations . . . . . . . . . . . . . . . . . . . 34
	7.1. Cache Poisoning . . . . . . . . . . . . . . . . . . . . . 34		7.1. Cache Poisoning . . . . . . . . . . . . . . . . . . . . . 35
	7.2. Timing Attacks . . . . . . . . . . . . . . . . . . . . . 34		7.2. Timing Attacks . . . . . . . . . . . . . . . . . . . . . 35
	7.3. Caching of Sensitive Information . . . . . . . . . . . . 35		7.3. Caching of Sensitive Information . . . . . . . . . . . . 35
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
	8.1. Field Name Registration . . . . . . . . . . . . . . . . . 35		8.1. Field Name Registration . . . . . . . . . . . . . . . . . 36
	8.2. Cache Directive Registration . . . . . . . . . . . . . . 35		8.2. Cache Directive Registration . . . . . . . . . . . . . . 36
	8.3. Warn Code Registry . . . . . . . . . . . . . . . . . . . 36		8.3. Warn Code Registry . . . . . . . . . . . . . . . . . . . 37
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 36		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 37
	9.1. Normative References . . . . . . . . . . . . . . . . . . 36		9.1. Normative References . . . . . . . . . . . . . . . . . . 37
	9.2. Informative References . . . . . . . . . . . . . . . . . 37		9.2. Informative References . . . . . . . . . . . . . . . . . 37
	Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 38		Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 38
	Appendix B. Changes from RFC 7234 . . . . . . . . . . . . . . . 38		Appendix B. Changes from RFC 7234 . . . . . . . . . . . . . . . 39
	Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 39		Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 40
	C.1. Between RFC7234 and draft 00 . . . . . . . . . . . . . . 39		C.1. Between RFC7234 and draft 00 . . . . . . . . . . . . . . 40
	C.2. Since draft-ietf-httpbis-cache-00 . . . . . . . . . . . . 39		C.2. Since draft-ietf-httpbis-cache-00 . . . . . . . . . . . . 40
	C.3. Since draft-ietf-httpbis-cache-01 . . . . . . . . . . . . 40		C.3. Since draft-ietf-httpbis-cache-01 . . . . . . . . . . . . 40
	C.4. Since draft-ietf-httpbis-cache-02 . . . . . . . . . . . . 40		C.4. Since draft-ietf-httpbis-cache-02 . . . . . . . . . . . . 41
	C.5. Since draft-ietf-httpbis-cache-03 . . . . . . . . . . . . 40		C.5. Since draft-ietf-httpbis-cache-03 . . . . . . . . . . . . 41
	C.6. Since draft-ietf-httpbis-cache-04 . . . . . . . . . . . . 41		C.6. Since draft-ietf-httpbis-cache-04 . . . . . . . . . . . . 41
	C.7. Since draft-ietf-httpbis-cache-05 . . . . . . . . . . . . 41		C.7. Since draft-ietf-httpbis-cache-05 . . . . . . . . . . . . 42
	C.8. Since draft-ietf-httpbis-cache-06 . . . . . . . . . . . . 41		C.8. Since draft-ietf-httpbis-cache-06 . . . . . . . . . . . . 42
	C.9. Since draft-ietf-httpbis-cache-07 . . . . . . . . . . . . 42		C.9. Since draft-ietf-httpbis-cache-07 . . . . . . . . . . . . 43
	C.10. Since draft-ietf-httpbis-cache-08 . . . . . . . . . . . . 42		C.10. Since draft-ietf-httpbis-cache-08 . . . . . . . . . . . . 43
	C.11. Since draft-ietf-httpbis-cache-09 . . . . . . . . . . . . 42		C.11. Since draft-ietf-httpbis-cache-09 . . . . . . . . . . . . 43
	C.12. Since draft-ietf-httpbis-cache-10 . . . . . . . . . . . . 42		C.12. Since draft-ietf-httpbis-cache-10 . . . . . . . . . . . . 43
	C.13. Since draft-ietf-httpbis-cache-11 . . . . . . . . . . . . 42		C.13. Since draft-ietf-httpbis-cache-11 . . . . . . . . . . . . 43
	C.14. Since draft-ietf-httpbis-cache-12 . . . . . . . . . . . . 42		C.14. Since draft-ietf-httpbis-cache-12 . . . . . . . . . . . . 43
	C.15. Since draft-ietf-httpbis-cache-13 . . . . . . . . . . . . 44		C.15. Since draft-ietf-httpbis-cache-13 . . . . . . . . . . . . 45
	Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 44		C.16. Since draft-ietf-httpbis-cache-14 . . . . . . . . . . . . 45
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44		Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 46
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
	1. Introduction		1. Introduction
	The Hypertext Transfer Protocol (HTTP) is a stateless application-		The Hypertext Transfer Protocol (HTTP) is a stateless application-
	level request/response protocol that uses extensible semantics and		level request/response protocol that uses extensible semantics and
	self-descriptive messages for flexible interaction with network-based		self-descriptive messages for flexible interaction with network-based
	hypertext information systems. It is typically used for distributed		hypertext information systems. It is typically used for distributed
	information systems, where the use of response caches can improve		information systems, where the use of response caches can improve
	performance. This document defines aspects of HTTP related to		performance. This document defines aspects of HTTP related to
	caching and reusing response messages.		caching and reusing response messages.
	skipping to change at page 6, line 27 ¶		skipping to change at page 6, line 27 ¶
	([Semantics]) while reducing the transmission of information already		([Semantics]) while reducing the transmission of information already
	held in the cache. Although caching is an entirely OPTIONAL feature		held in the cache. Although caching is an entirely OPTIONAL feature
	of HTTP, it can be assumed that reusing a cached response is		of HTTP, it can be assumed that reusing a cached response is
	desirable and that such reuse is the default behavior when no		desirable and that such reuse is the default behavior when no
	requirement or local configuration prevents it. Therefore, HTTP		requirement or local configuration prevents it. Therefore, HTTP
	cache requirements are focused on preventing a cache from either		cache requirements are focused on preventing a cache from either
	storing a non-reusable response or reusing a stored response		storing a non-reusable response or reusing a stored response
	inappropriately, rather than mandating that caches always store and		inappropriately, rather than mandating that caches always store and
	reuse particular responses.		reuse particular responses.
	The _cache key_ is comprised of, at a minimum, the request method and		The _cache key_ is the information a cache uses to select a response
	target URI used to retrieve the stored response; the method		and is comprised of, at a minimum, the request method and target URI
	determines under which circumstances that response can be used to		used to retrieve the stored response; the method determines under
	satisfy a subsequent request. However, many HTTP caches in common		which circumstances that response can be used to satisfy a subsequent
	use today only cache GET responses, and therefore only use the URI as		request. However, many HTTP caches in common use today only cache
	the cache key, forwarding other methods.		GET responses, and therefore only use the URI as the cache key,
			forwarding other methods.
	If a request target is subject to content negotiation, the cache		If a request target is subject to content negotiation, the cache
	might store multiple responses for it. Caches differentiate these		might store multiple responses for it. Caches differentiate these
	responses by incorporating values of the original request's selecting		responses by incorporating values of the original request's selecting
	header fields into the cache key as well, using information in the		header fields into the cache key as well, using information in the
	Vary response header field, as per Section 4.1.		Vary response header field, as per Section 4.1.
	Caches might incorporate additional material into the cache key. For		Caches might incorporate additional material into the cache key. For
	example, user agent caches might include the referring site's		example, user agent caches might include the referring site's
	identity, thereby "double keying" the cache to avoid some privacy		identity, thereby "double keying" the cache to avoid some privacy
	skipping to change at page 7, line 18 ¶		skipping to change at page 7, line 27 ¶
	3. Storing Responses in Caches		3. Storing Responses in Caches
	A cache MUST NOT store a response to a request unless:		A cache MUST NOT store a response to a request unless:
	o the request method is understood by the cache;		o the request method is understood by the cache;
	o the response status code is final (see Section 15 of [Semantics]);		o the response status code is final (see Section 15 of [Semantics]);
	o if the response status code is 206 or 304, or the "must-		o if the response status code is 206 or 304, or the "must-
	understand" cache directive (see Section 5.2.2.2) is present: the		understand" cache directive (see Section 5.2.2.3) is present: the
	cache understands the response status code;		cache understands the response status code;
	o the "no-store" cache directive is not present in the response (see		o the "no-store" cache directive is not present in the response (see
	Section 5.2.2.4);		Section 5.2.2.5);
	o if the cache is shared: the "private" response directive is either		o if the cache is shared: the "private" response directive is either
	not present or allows a shared cache to store a modified response;		not present or allows a shared cache to store a modified response;
	see Section 5.2.2.7);		see Section 5.2.2.7);
	o if the cache is shared: the Authorization header field is not		o if the cache is shared: the Authorization header field is not
	present in the request (see Section 11.6.2 of [Semantics]) or a		present in the request (see Section 11.6.2 of [Semantics]) or a
	response directive is present that explicitly allows shared		response directive is present that explicitly allows shared
	caching (see Section 3.5); and,		caching (see Section 3.5); and,
	o the response contains at least one of:		o the response contains at least one of:
	* a public response directive (see Section 5.2.2.6);		* a public response directive (see Section 5.2.2.9);
	* a private response directive, if the cache is not shared (see		* a private response directive, if the cache is not shared (see
	Section 5.2.2.7);		Section 5.2.2.7);
	* an Expires header field (see Section 5.3);		* an Expires header field (see Section 5.3);
	* a max-age response directive (see Section 5.2.2.9);		* a max-age response directive (see Section 5.2.2.1);
	* if the cache is shared: an s-maxage response directive (see		* if the cache is shared: an s-maxage response directive (see
	Section 5.2.2.10);		Section 5.2.2.10);
	* a Cache Control Extension that allows it to be cached (see		* a Cache Control Extension that allows it to be cached (see
	Section 5.2.3); or,		Section 5.2.3); or,
	* a status code that is defined as heuristically cacheable (see		* a status code that is defined as heuristically cacheable (see
	Section 4.2.2).		Section 4.2.2).
	Note that a cache-control extension can override any of the		Note that a cache-control extension can override any of the
	skipping to change at page 8, line 34 ¶		skipping to change at page 8, line 42 ¶
	o The Connection header field and fields whose names are listed in		o The Connection header field and fields whose names are listed in
	it are required by Section 7.6.1 of [Semantics] to be removed		it are required by Section 7.6.1 of [Semantics] to be removed
	before forwarding the message. This MAY be implemented by doing		before forwarding the message. This MAY be implemented by doing
	so before storage.		so before storage.
	o Likewise, some fields' semantics require them to be removed before		o Likewise, some fields' semantics require them to be removed before
	forwarding the message, and this MAY be implemented by doing so		forwarding the message, and this MAY be implemented by doing so
	before storage; see Section 7.6.1 of [Semantics] for some		before storage; see Section 7.6.1 of [Semantics] for some
	examples.		examples.
	o The no-cache (Section 5.2.2.3) and private (Section 5.2.2.7) cache		o The no-cache (Section 5.2.2.4) and private (Section 5.2.2.7) cache
	directives can have arguments that prevent storage of header		directives can have arguments that prevent storage of header
	fields by all caches and shared caches, respectively.		fields by all caches and shared caches, respectively.
	o Header fields that are specific to a client's proxy configuration		o Header fields that are specific to the proxy that a cache uses
	MUST NOT be stored, unless the cache incorporates the identity of		when forwarding a request MUST NOT be stored, unless the cache
	the proxy into the cache key. Effectively, this is limited to		incorporates the identity of the proxy into the cache key.
	Proxy-Authenticate (Section 11.7.1 of [Semantics]), Proxy-		Effectively, this is limited to Proxy-Authenticate (Section 11.7.1
	Authentication-Info (Section 11.7.3 of [Semantics]), and Proxy-		of [Semantics]), Proxy-Authentication-Info (Section 11.7.3 of
	Authorization (Section 11.7.2 of [Semantics]).		[Semantics]), and Proxy-Authorization (Section 11.7.2 of
			[Semantics]).
	Caches MAY either store trailer fields separate from header fields,		Caches MAY either store trailer fields separate from header fields,
	or discard them. Caches MUST NOT combine trailer fields with header		or discard them. Caches MUST NOT combine trailer fields with header
	fields.		fields.
	3.2. Updating Stored Header Fields		3.2. Updating Stored Header Fields
	Caches are required to update a stored response's header fields from		Caches are required to update a stored response's header fields from
	another (typically newer) response in several situations; for		another (typically newer) response in several situations; for
	example, see Section 3.4, Section 4.3.4 and Section 4.3.5.		example, see Section 3.4, Section 4.3.4 and Section 4.3.5.
	skipping to change at page 11, line 6 ¶		skipping to change at page 11, line 30 ¶
	3.5. Storing Responses to Authenticated Requests		3.5. Storing Responses to Authenticated Requests
	A shared cache MUST NOT use a cached response to a request with an		A shared cache MUST NOT use a cached response to a request with an
	Authorization header field (Section 11.6.2 of [Semantics]) to satisfy		Authorization header field (Section 11.6.2 of [Semantics]) to satisfy
	any subsequent request unless the response contains a Cache-Control		any subsequent request unless the response contains a Cache-Control
	field with a response directive (Section 5.2.2) that allows it to be		field with a response directive (Section 5.2.2) that allows it to be
	stored by a shared cache and the cache conforms to the requirements		stored by a shared cache and the cache conforms to the requirements
	of that directive for that response.		of that directive for that response.
	In this specification, the following response directives have such an		In this specification, the following response directives have such an
	effect: must-revalidate (Section 5.2.2.1), public (Section 5.2.2.6),		effect: must-revalidate (Section 5.2.2.2), public (Section 5.2.2.9),
	and s-maxage (Section 5.2.2.10).		and s-maxage (Section 5.2.2.10).
	4. Constructing Responses from Caches		4. Constructing Responses from Caches
	When presented with a request, a cache MUST NOT reuse a stored		When presented with a request, a cache MUST NOT reuse a stored
	response, unless:		response, unless:
	o The presented target URI (Section 7.1 of [Semantics]) and that of		o The presented target URI (Section 7.1 of [Semantics]) and that of
	the stored response match, and		the stored response match, and
	o the request method associated with the stored response allows it		o the request method associated with the stored response allows it
	to be used for the presented request, and		to be used for the presented request, and
	o selecting header fields nominated by the stored response (if any)		o selecting header fields nominated by the stored response (if any)
	match those presented (see Section 4.1), and		match those presented (see Section 4.1), and
	o the stored response does not contain the no-cache cache directive		o the stored response does not contain the no-cache cache directive
	(Section 5.2.2.3), unless it is successfully validated		(Section 5.2.2.4), unless it is successfully validated
	(Section 4.3), and		(Section 4.3), and
	o the stored response is either:		o the stored response is either:
	* fresh (see Section 4.2), or		* fresh (see Section 4.2), or
	* allowed to be served stale (see Section 4.2.4), or		* allowed to be served stale (see Section 4.2.4), or
	* successfully validated (see Section 4.3).		* successfully validated (see Section 4.3).
	skipping to change at page 14, line 8 ¶		skipping to change at page 14, line 28 ¶
	A response's _age_ is the time that has passed since it was generated		A response's _age_ is the time that has passed since it was generated
	by, or successfully validated with, the origin server.		by, or successfully validated with, the origin server.
	When a response is fresh, it can be used to satisfy subsequent		When a response is fresh, it can be used to satisfy subsequent
	requests without contacting the origin server, thereby improving		requests without contacting the origin server, thereby improving
	efficiency.		efficiency.
	The primary mechanism for determining freshness is for an origin		The primary mechanism for determining freshness is for an origin
	server to provide an explicit expiration time in the future, using		server to provide an explicit expiration time in the future, using
	either the Expires header field (Section 5.3) or the max-age response		either the Expires header field (Section 5.3) or the max-age response
	directive (Section 5.2.2.9). Generally, origin servers will assign		directive (Section 5.2.2.1). Generally, origin servers will assign
	future explicit expiration times to responses in the belief that the		future explicit expiration times to responses in the belief that the
	representation is not likely to change in a semantically significant		representation is not likely to change in a semantically significant
	way before the expiration time is reached.		way before the expiration time is reached.
	If an origin server wishes to force a cache to validate every		If an origin server wishes to force a cache to validate every
	request, it can assign an explicit expiration time in the past to		request, it can assign an explicit expiration time in the past to
	indicate that the response is already stale. Compliant caches will		indicate that the response is already stale. Compliant caches will
	normally validate a stale cached response before reusing it for		normally validate a stale cached response before reusing it for
	subsequent requests (see Section 4.2.4).		subsequent requests (see Section 4.2.4).
	skipping to change at page 15, line 18 ¶		skipping to change at page 15, line 39 ¶
	caches and history mechanisms.		caches and history mechanisms.
	4.2.1. Calculating Freshness Lifetime		4.2.1. Calculating Freshness Lifetime
	A cache can calculate the freshness lifetime (denoted as		A cache can calculate the freshness lifetime (denoted as
	freshness_lifetime) of a response by using the first match of:		freshness_lifetime) of a response by using the first match of:
	o If the cache is shared and the s-maxage response directive		o If the cache is shared and the s-maxage response directive
	(Section 5.2.2.10) is present, use its value, or		(Section 5.2.2.10) is present, use its value, or
	o If the max-age response directive (Section 5.2.2.9) is present,		o If the max-age response directive (Section 5.2.2.1) is present,
	use its value, or		use its value, or
	o If the Expires response header field (Section 5.3) is present, use		o If the Expires response header field (Section 5.3) is present, use
	its value minus the value of the Date response header field (using		its value minus the value of the Date response header field (using
	the time the message was received if it is not present, as per		the time the message was received if it is not present, as per
	Section 10.2.2 of [Semantics]), or		Section 10.2.2 of [Semantics]), or
	o Otherwise, no explicit expiration time is present in the response.		o Otherwise, no explicit expiration time is present in the response.
	A heuristic freshness lifetime might be applicable; see		A heuristic freshness lifetime might be applicable; see
	Section 4.2.2.		Section 4.2.2.
	skipping to change at page 23, line 23 ¶		skipping to change at page 23, line 46 ¶
	time since the response was generated or successfully validated at		time since the response was generated or successfully validated at
	the origin server. Age values are calculated as specified in		the origin server. Age values are calculated as specified in
	Section 4.2.3.		Section 4.2.3.
	Age = delta-seconds		Age = delta-seconds
	The Age field value is a non-negative integer, representing time in		The Age field value is a non-negative integer, representing time in
	seconds (see Section 1.3).		seconds (see Section 1.3).
	Although it is defined as a singleton header field, a cache		Although it is defined as a singleton header field, a cache
	encountering a message with multiple Age field lines SHOULD use the		encountering a message with a list-based Age field value SHOULD use
	first field line, discarding subsequent ones.		the first member of the field value, discarding subsequent ones.
	If the field value (after discarding additional lines, as per above)		If the field value (after discarding additional members, as per
	is invalid (e.g., it contains a list or something other than a non-		above) is invalid (e.g., it contains something other than a non-
	negative integer), a cache SHOULD consider the response to be stale.		negative integer), a cache SHOULD ignore the field.
	The presence of an Age header field implies that the response was not		The presence of an Age header field implies that the response was not
	generated or validated by the origin server for this request.		generated or validated by the origin server for this request.
	However, lack of an Age header field does not imply the origin was		However, lack of an Age header field does not imply the origin was
	contacted.		contacted.
	5.2. Cache-Control		5.2. Cache-Control
	The "Cache-Control" header field is used to list directives for		The "Cache-Control" header field is used to list directives for
	caches along the request/response chain. Such cache directives are		caches along the request/response chain. Such cache directives are
	skipping to change at page 26, line 24 ¶		skipping to change at page 26, line 43 ¶
	wishes to obtain a stored response. Caches that honor this request		wishes to obtain a stored response. Caches that honor this request
	directive SHOULD, upon receiving it, either respond using a stored		directive SHOULD, upon receiving it, either respond using a stored
	response consistent with the other constraints of the request, or		response consistent with the other constraints of the request, or
	respond with a 504 (Gateway Timeout) status code.		respond with a 504 (Gateway Timeout) status code.
	5.2.2. Response Cache-Control Directives		5.2.2. Response Cache-Control Directives
	This section defines cache response directives. A cache MUST obey		This section defines cache response directives. A cache MUST obey
	the Cache-Control directives defined in this section.		the Cache-Control directives defined in this section.
	5.2.2.1. must-revalidate		5.2.2.1. max-age
			Argument syntax:
			delta-seconds (see Section 1.3)
			The "max-age" response directive indicates that the response is to be
			considered stale after its age is greater than the specified number
			of seconds.
			This directive uses the token form of the argument syntax: e.g.,
			'max-age=5' not 'max-age="5"'. A sender MUST NOT generate the
			quoted-string form.
			5.2.2.2. must-revalidate
	The "must-revalidate" response directive indicates that once the		The "must-revalidate" response directive indicates that once the
	response has become stale, a cache MUST NOT reuse that response to		response has become stale, a cache MUST NOT reuse that response to
	satisfy another request until it has been successfully validated by		satisfy another request until it has been successfully validated by
	the origin, as defined by Section 4.3.		the origin, as defined by Section 4.3.
	The must-revalidate directive is necessary to support reliable		The must-revalidate directive is necessary to support reliable
	operation for certain protocol features. In all circumstances a		operation for certain protocol features. In all circumstances a
	cache MUST NOT ignore the must-revalidate directive; in particular,		cache MUST NOT ignore the must-revalidate directive; in particular,
	if a cache is disconnected, the cache MUST generate an error response		if a cache is disconnected, the cache MUST generate an error response
	skipping to change at page 26, line 48 ¶		skipping to change at page 27, line 33 ¶
	The must-revalidate directive ought to be used by servers if and only		The must-revalidate directive ought to be used by servers if and only
	if failure to validate a request could cause incorrect operation,		if failure to validate a request could cause incorrect operation,
	such as a silently unexecuted financial transaction.		such as a silently unexecuted financial transaction.
	The must-revalidate directive also permits a shared cache to reuse a		The must-revalidate directive also permits a shared cache to reuse a
	response to a request containing an Authorization header field		response to a request containing an Authorization header field
	(Section 11.6.2 of [Semantics]), subject to the above requirement on		(Section 11.6.2 of [Semantics]), subject to the above requirement on
	revalidation (Section 3.5).		revalidation (Section 3.5).
	5.2.2.2. must-understand		5.2.2.3. must-understand
	The "must-understand" response directive limits caching of the		The "must-understand" response directive limits caching of the
	response to a cache that understands and conforms to the requirements		response to a cache that understands and conforms to the requirements
	for that response's status code.		for that response's status code.
	Responses containing "must-understand" SHOULD also contain the "no-		Responses containing "must-understand" SHOULD also contain the "no-
	store" directive; caches that implement "must-understand" SHOULD		store" directive; caches that implement "must-understand" SHOULD
	ignore the "no-store" directive in responses that contain both		ignore the "no-store" directive in responses that contain both
	directives and a status code that the cache understands and conforms		directives and a status code that the cache understands and conforms
	to any related caching requirements.		to any related caching requirements.
	5.2.2.3. no-cache		5.2.2.4. no-cache
	Argument syntax:		Argument syntax:
	#field-name		#field-name
	The "no-cache" response directive, in its unqualified form (without		The "no-cache" response directive, in its unqualified form (without
	an argument), indicates that the response MUST NOT be used to satisfy		an argument), indicates that the response MUST NOT be used to satisfy
	any other request without forwarding it for validation and receiving		any other request without forwarding it for validation and receiving
	a successful response; see Section 4.3.		a successful response; see Section 4.3.
	skipping to change at page 27, line 48 ¶		skipping to change at page 28, line 36 ¶
	This directive uses the quoted-string form of the argument syntax. A		This directive uses the quoted-string form of the argument syntax. A
	sender SHOULD NOT generate the token form (even if quoting appears		sender SHOULD NOT generate the token form (even if quoting appears
	not to be needed for single-entry lists).		not to be needed for single-entry lists).
	| *Note:* The qualified form of the directive is often handled by		| *Note:* The qualified form of the directive is often handled by
	| caches as if an unqualified no-cache directive was received;		| caches as if an unqualified no-cache directive was received;
	| i.e., the special handling for the qualified form is not widely		| i.e., the special handling for the qualified form is not widely
	| implemented.		| implemented.
	5.2.2.4. no-store		5.2.2.5. no-store
	The "no-store" response directive indicates that a cache MUST NOT		The "no-store" response directive indicates that a cache MUST NOT
	store any part of either the immediate request or response, and MUST		store any part of either the immediate request or response, and MUST
	NOT use the response to satisfy any other request.		NOT use the response to satisfy any other request.
	This directive applies to both private and shared caches. "MUST NOT		This directive applies to both private and shared caches. "MUST NOT
	store" in this context means that the cache MUST NOT intentionally		store" in this context means that the cache MUST NOT intentionally
	store the information in non-volatile storage, and MUST make a best-		store the information in non-volatile storage, and MUST make a best-
	effort attempt to remove the information from volatile storage as		effort attempt to remove the information from volatile storage as
	promptly as possible after forwarding it.		promptly as possible after forwarding it.
	This directive is _not_ a reliable or sufficient mechanism for		This directive is _not_ a reliable or sufficient mechanism for
	ensuring privacy. In particular, malicious or compromised caches		ensuring privacy. In particular, malicious or compromised caches
	might not recognize or obey this directive, and communications		might not recognize or obey this directive, and communications
	networks might be vulnerable to eavesdropping.		networks might be vulnerable to eavesdropping.
	Note that the "must-understand" cache directive overrides "no-store"		Note that the "must-understand" cache directive overrides "no-store"
	in certain circumstances; see Section 5.2.2.2.		in certain circumstances; see Section 5.2.2.3.
	5.2.2.5. no-transform		5.2.2.6. no-transform
	The "no-transform" response directive indicates that an intermediary		The "no-transform" response directive indicates that an intermediary
	(regardless of whether it implements a cache) MUST NOT transform the		(regardless of whether it implements a cache) MUST NOT transform the
	content, as defined in Section 7.7 of [Semantics].		content, as defined in Section 7.7 of [Semantics].
	5.2.2.6. public
	The "public" response directive indicates that a cache MAY store the
	response even if it would otherwise be prohibited, subject to the
	constraints defined in Section 3. In other words, public explicitly
	marks the response as cacheable. For example, public permits a
	shared cache to reuse a response to a request containing an
	Authorization header field (Section 3.5).
	Note that it is unnecessary to add the public directive to a response
	that is already cacheable according to Section 3.
	If a response with the public directive has no explicit freshness
	information, it is heuristically cacheable (Section 4.2.2).
	5.2.2.7. private		5.2.2.7. private
	Argument syntax:		Argument syntax:
	#field-name		#field-name
	The unqualified "private" response directive indicates that a shared		The unqualified "private" response directive indicates that a shared
	cache MUST NOT store the response (i.e., the response is intended for		cache MUST NOT store the response (i.e., the response is intended for
	a single user). It also indicates that a private cache MAY store the		a single user). It also indicates that a private cache MAY store the
	response, subject the constraints defined in Section 3, even if the		response, subject the constraints defined in Section 3, even if the
	skipping to change at page 29, line 32 ¶		skipping to change at page 30, line 11 ¶
	| often handled by caches as if an unqualified private directive		| often handled by caches as if an unqualified private directive
	| was received; i.e., the special handling for the qualified form		| was received; i.e., the special handling for the qualified form
	| is not widely implemented.		| is not widely implemented.
	5.2.2.8. proxy-revalidate		5.2.2.8. proxy-revalidate
	The "proxy-revalidate" response directive indicates that once the		The "proxy-revalidate" response directive indicates that once the
	response has become stale, a shared cache MUST NOT reuse that		response has become stale, a shared cache MUST NOT reuse that
	response to satisfy another request until it has been successfully		response to satisfy another request until it has been successfully
	validated by the origin, as defined by Section 4.3. This is		validated by the origin, as defined by Section 4.3. This is
	analogous to must-revalidate (Section 5.2.2.1), except that proxy-		analogous to must-revalidate (Section 5.2.2.2), except that proxy-
	revalidate does not apply to private caches.		revalidate does not apply to private caches.
	Note that "proxy-revalidate" on its own does not imply that a		Note that "proxy-revalidate" on its own does not imply that a
	response is cacheable. For example, it might be combined with the		response is cacheable. For example, it might be combined with the
	public directive (Section 5.2.2.6), allowing the response to be		public directive (Section 5.2.2.9), allowing the response to be
	cached while requiring only a shared cache to revalidate when stale.		cached while requiring only a shared cache to revalidate when stale.
	5.2.2.9. max-age		5.2.2.9. public
	Argument syntax:
	delta-seconds (see Section 1.3)		The "public" response directive indicates that a cache MAY store the
			response even if it would otherwise be prohibited, subject to the
			constraints defined in Section 3. In other words, public explicitly
			marks the response as cacheable. For example, public permits a
			shared cache to reuse a response to a request containing an
			Authorization header field (Section 3.5).
	The "max-age" response directive indicates that the response is to be		Note that it is unnecessary to add the public directive to a response
	considered stale after its age is greater than the specified number		that is already cacheable according to Section 3.
	of seconds.
	This directive uses the token form of the argument syntax: e.g.,		If a response with the public directive has no explicit freshness
	'max-age=5' not 'max-age="5"'. A sender MUST NOT generate the		information, it is heuristically cacheable (Section 4.2.2).
	quoted-string form.
	5.2.2.10. s-maxage		5.2.2.10. s-maxage
	Argument syntax:		Argument syntax:
	delta-seconds (see Section 1.3)		delta-seconds (see Section 1.3)
	The "s-maxage" response directive indicates that, for a shared cache,		The "s-maxage" response directive indicates that, for a shared cache,
	the maximum age specified by this directive overrides the maximum age		the maximum age specified by this directive overrides the maximum age
	specified by either the max-age directive or the Expires header		specified by either the max-age directive or the Expires header
	skipping to change at page 32, line 10 ¶		skipping to change at page 32, line 35 ¶
	The "Expires" response header field gives the date/time after which		The "Expires" response header field gives the date/time after which
	the response is considered stale. See Section 4.2 for further		the response is considered stale. See Section 4.2 for further
	discussion of the freshness model.		discussion of the freshness model.
	The presence of an Expires header field does not imply that the		The presence of an Expires header field does not imply that the
	original resource will change or cease to exist at, before, or after		original resource will change or cease to exist at, before, or after
	that time.		that time.
	The Expires field value is an HTTP-date timestamp, as defined in		The Expires field value is an HTTP-date timestamp, as defined in
	Section 5.6.7 of [Semantics].		Section 5.6.7 of [Semantics]. See also Section 4.2 for parsing
			requirements specific to caches.
	Expires = HTTP-date		Expires = HTTP-date
	For example		For example
	Expires: Thu, 01 Dec 1994 16:00:00 GMT		Expires: Thu, 01 Dec 1994 16:00:00 GMT
	A cache recipient MUST interpret invalid date formats, especially the		A cache recipient MUST interpret invalid date formats, especially the
	value "0", as representing a time in the past (i.e., "already		value "0", as representing a time in the past (i.e., "already
	expired").		expired").
	If a response includes a Cache-Control header field with the max-age		If a response includes a Cache-Control header field with the max-age
	directive (Section 5.2.2.9), a recipient MUST ignore the Expires		directive (Section 5.2.2.1), a recipient MUST ignore the Expires
	header field. Likewise, if a response includes the s-maxage		header field. Likewise, if a response includes the s-maxage
	directive (Section 5.2.2.10), a shared cache recipient MUST ignore		directive (Section 5.2.2.10), a shared cache recipient MUST ignore
	the Expires header field. In both these cases, the value in Expires		the Expires header field. In both these cases, the value in Expires
	is only intended for recipients that have not yet implemented the		is only intended for recipients that have not yet implemented the
	Cache-Control header field.		Cache-Control header field.
	An origin server without a clock MUST NOT generate an Expires header		An origin server without a clock MUST NOT generate an Expires header
	field unless its value represents a fixed time in the past (always		field unless its value represents a fixed time in the past (always
	expired) or its value has been associated with the resource by a		expired) or its value has been associated with the resource by a
	system or user with a reliable clock.		system or user with a reliable clock.
	skipping to change at page 34, line 23 ¶		skipping to change at page 35, line 7 ¶
	Caches expose additional potential vulnerabilities, since the		Caches expose additional potential vulnerabilities, since the
	contents of the cache represent an attractive target for malicious		contents of the cache represent an attractive target for malicious
	exploitation. Because cache contents persist after an HTTP request		exploitation. Because cache contents persist after an HTTP request
	is complete, an attack on the cache can reveal information long after		is complete, an attack on the cache can reveal information long after
	a user believes that the information has been removed from the		a user believes that the information has been removed from the
	network. Therefore, cache contents need to be protected as sensitive		network. Therefore, cache contents need to be protected as sensitive
	information.		information.
	7.1. Cache Poisoning		7.1. Cache Poisoning
	Various attacks might be amplified by being stored in a shared cache.		Various attacks might be amplified by being stored in a cache. Such
	Such "cache poisoning" attacks use the cache to distribute malicious		"cache poisoning" attacks happen when an attacker uses implementation
	content to many clients, and are especially effective when an		flaws, elevated privileges, or other techniques to insert a response
	attacker can use implementation flaws, elevated privileges, or other		into a cache. This is especially effective when shared caches are
	techniques to insert such a response into a cache.		used to distribute malicious content to many clients.
	One common attack vector for cache poisoning is to exploit		One common attack vector for cache poisoning is to exploit
	differences in message parsing on proxies and in user agents; see		differences in message parsing on proxies and in user agents; see
	Section 6.3 of [Messaging] for the relevant requirements regarding		Section 6.3 of [Messaging] for the relevant requirements regarding
	HTTP/1.1.		HTTP/1.1.
	7.2. Timing Attacks		7.2. Timing Attacks
	Because one of the primary uses of a cache is to optimise		Because one of the primary uses of a cache is to optimise
	performance, its use can "leak" information about what resources have		performance, its use can "leak" information about what resources have
	skipping to change at page 36, line 8 ¶		skipping to change at page 36, line 36 ¶
	8.2. Cache Directive Registration		8.2. Cache Directive Registration
	Please update the "Hypertext Transfer Protocol (HTTP) Cache Directive		Please update the "Hypertext Transfer Protocol (HTTP) Cache Directive
	Registry" at <https://www.iana.org/assignments/http-cache-directives>		Registry" at <https://www.iana.org/assignments/http-cache-directives>
	with the registration procedure of Section 5.2.4 and the cache		with the registration procedure of Section 5.2.4 and the cache
	directive names summarized in the table below.		directive names summarized in the table below.
	+------------------+----------------------------------+		+------------------+----------------------------------+
	| Cache Directive | Reference |		| Cache Directive | Reference |
	+------------------+----------------------------------+		+------------------+----------------------------------+
	| max-age | Section 5.2.1.1, Section 5.2.2.9 |		| max-age | Section 5.2.1.1, Section 5.2.2.1 |
	| max-stale | Section 5.2.1.2 |		| max-stale | Section 5.2.1.2 |
	| min-fresh | Section 5.2.1.3 |		| min-fresh | Section 5.2.1.3 |
	| must-revalidate | Section 5.2.2.1 |		| must-revalidate | Section 5.2.2.2 |
	| must-understand | Section 5.2.2.2 |		| must-understand | Section 5.2.2.3 |
	| no-cache | Section 5.2.1.4, Section 5.2.2.3 |		| no-cache | Section 5.2.1.4, Section 5.2.2.4 |
	| no-store | Section 5.2.1.5, Section 5.2.2.4 |		| no-store | Section 5.2.1.5, Section 5.2.2.5 |
	| no-transform | Section 5.2.1.6, Section 5.2.2.5 |		| no-transform | Section 5.2.1.6, Section 5.2.2.6 |
	| only-if-cached | Section 5.2.1.7 |		| only-if-cached | Section 5.2.1.7 |
	| private | Section 5.2.2.7 |		| private | Section 5.2.2.7 |
	| proxy-revalidate | Section 5.2.2.8 |		| proxy-revalidate | Section 5.2.2.8 |
	| public | Section 5.2.2.6 |		| public | Section 5.2.2.9 |
	| s-maxage | Section 5.2.2.10 |		| s-maxage | Section 5.2.2.10 |
	+------------------+----------------------------------+		+------------------+----------------------------------+
	Table 2		Table 2
	8.3. Warn Code Registry		8.3. Warn Code Registry
	Please add a note to the "Hypertext Transfer Protocol (HTTP) Warn		Please add a note to the "Hypertext Transfer Protocol (HTTP) Warn
	Codes" registry at <https://www.iana.org/assignments/http-warn-codes>		Codes" registry at <https://www.iana.org/assignments/http-warn-codes>
	to the effect that Warning is obsoleted.		to the effect that Warning is obsoleted.
	9. References		9. References
	9.1. Normative References		9.1. Normative References
	[Messaging]		[Messaging]
	Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,		Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
	Ed., "HTTP/1.1", Work in Progress, Internet-Draft, draft-		Ed., "HTTP/1.1", Work in Progress, Internet-Draft, draft-
	ietf-httpbis-messaging-latest, January 2021,		ietf-httpbis-messaging-latest, February 2021,
	<https://tools.ietf.org/html/draft-ietf-httpbis-messaging-		<https://tools.ietf.org/html/draft-ietf-httpbis-messaging-
	latest>.		latest>.
	[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,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[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,
	skipping to change at page 37, line 16 ¶		skipping to change at page 37, line 43 ¶
	RFC 7405, DOI 10.17487/RFC7405, December 2014,		RFC 7405, DOI 10.17487/RFC7405, December 2014,
	<https://www.rfc-editor.org/info/rfc7405>.		<https://www.rfc-editor.org/info/rfc7405>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[Semantics]		[Semantics]
	Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,		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-latest, January 2021,		draft-ietf-httpbis-semantics-latest, February 2021,
	<https://tools.ietf.org/html/draft-ietf-httpbis-semantics-		<https://tools.ietf.org/html/draft-ietf-httpbis-semantics-
	latest>.		latest>.
	9.2. Informative References		9.2. Informative References
	[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,		Transfer Protocol -- HTTP/1.1", RFC 2616,
	DOI 10.17487/RFC2616, June 1999,		DOI 10.17487/RFC2616, June 1999,
	<https://www.rfc-editor.org/info/rfc2616>.		<https://www.rfc-editor.org/info/rfc2616>.
	skipping to change at page 39, line 4 ¶		skipping to change at page 39, line 47 ¶
	Handling invalid and multiple Age header field values has been		Handling invalid and multiple Age header field values has been
	clarified. (Section 5.1)		clarified. (Section 5.1)
	Some cache directives defined by this specification now have stronger		Some cache directives defined by this specification now have stronger
	prohibitions against generating the quoted form of their values,		prohibitions against generating the quoted form of their values,
	since this has been found to create interoperability problems.		since this has been found to create interoperability problems.
	Consumers of extension cache directives are no longer required to		Consumers of extension cache directives are no longer required to
	accept both token and quoted-string forms, but they still need to		accept both token and quoted-string forms, but they still need to
	parse them properly for unknown extensions. (Section 5.2)		parse them properly for unknown extensions. (Section 5.2)
	The "public" and "private" cache directives were clarified, so that		The "public" and "private" cache directives were clarified, so that
	they do not make responses reusable under any condition.		they do not make responses reusable under any condition.
	(Section 5.2.2)		(Section 5.2.2)
	The "must-understand" cache directive was introduced; caches are no		The "must-understand" cache directive was introduced; caches are no
	longer required to understand the semantics of new response status		longer required to understand the semantics of new response status
	codes unless it is present. (Section 5.2.2.2)		codes unless it is present. (Section 5.2.2.3)
	The Warning response header was obsoleted. Much of the information		The Warning response header was obsoleted. Much of the information
	supported by Warning could be gleaned by examining the response, and		supported by Warning could be gleaned by examining the response, and
	the remaining warn-codes - although potentially useful - were		the remaining warn-codes - although potentially useful - were
	entirely advisory. In practice, Warning was not added by caches or		entirely advisory. In practice, Warning was not added by caches or
	intermediaries. (Section 5.5)		intermediaries. (Section 5.5)
	Appendix C. Change Log		Appendix C. Change Log
	This section is to be removed before publishing as an RFC.		This section is to be removed before publishing as an RFC.
	skipping to change at page 41, line 36 ¶		skipping to change at page 42, line 29 ¶
	<https://www.rfc-editor.org/errata/eid5300>)		<https://www.rfc-editor.org/errata/eid5300>)
	o Refactored Section 7, and added a section on timing attacks		o Refactored Section 7, and added a section on timing attacks
	(<https://github.com/httpwg/http-core/issues/233>)		(<https://github.com/httpwg/http-core/issues/233>)
	o Changed "cacheable by default" to "heuristically cacheable"		o Changed "cacheable by default" to "heuristically cacheable"
	throughout (<https://github.com/httpwg/http-core/issues/242>)		throughout (<https://github.com/httpwg/http-core/issues/242>)
	C.8. Since draft-ietf-httpbis-cache-06		C.8. Since draft-ietf-httpbis-cache-06
	o In Section 3 and Section 5.2.2.2, change response cacheability to		o In Section 3 and Section 5.2.2.3, change response cacheability to
	only require understanding the response status code if the must-		only require understanding the response status code if the must-
	understand cache directive is present (<https://github.com/httpwg/		understand cache directive is present (<https://github.com/httpwg/
	http-core/issues/120>)		http-core/issues/120>)
	o Change requirements for handling different forms of cache		o Change requirements for handling different forms of cache
	directives in Section 5.2 (<https://github.com/httpwg/http-core/		directives in Section 5.2 (<https://github.com/httpwg/http-core/
	issues/128>)		issues/128>)
	o Fix typo in Section 5.2.2.10 (<https://github.com/httpwg/http-		o Fix typo in Section 5.2.2.10 (<https://github.com/httpwg/http-
	core/issues/264>)		core/issues/264>)
	o In Section 5.2.2.6 and Section 5.2.2.7, clarify "private" and		o In Section 5.2.2.9 and Section 5.2.2.7, clarify "private" and
	"public" so that they do not override all other cache directives		"public" so that they do not override all other cache directives
	(<https://github.com/httpwg/http-core/issues/268>)		(<https://github.com/httpwg/http-core/issues/268>)
	o In Section 3, distinguish between private with and without		o In Section 3, distinguish between private with and without
	qualifying headers (<https://github.com/httpwg/http-core/		qualifying headers (<https://github.com/httpwg/http-core/
	issues/270>)		issues/270>)
	o In Section 4.1, clarify that any "*" as a member of Vary will		o In Section 4.1, clarify that any "*" as a member of Vary will
	disable caching (<https://github.com/httpwg/http-core/issues/286>)		disable caching (<https://github.com/httpwg/http-core/issues/286>)
	o In Section 1.1, reference RFC 8174 as well		o In Section 1.1, reference RFC 8174 as well
	(<https://github.com/httpwg/http-core/issues/303>)		(<https://github.com/httpwg/http-core/issues/303>)
	C.9. Since draft-ietf-httpbis-cache-07		C.9. Since draft-ietf-httpbis-cache-07
	o Throughout, replace "effective request URI", "request-target" and		o Throughout, replace "effective request URI", "request-target" and
	similar with "target URI" (<https://github.com/httpwg/http-core/		similar with "target URI" (<https://github.com/httpwg/http-core/
	issues/259>)		issues/259>)
	o In Section 5.2.2.6 and Section 5.2.2.7, make it clear that these		o In Section 5.2.2.9 and Section 5.2.2.7, make it clear that these
	directives do not ignore other requirements for caching		directives do not ignore other requirements for caching
	(<https://github.com/httpwg/http-core/issues/320>)		(<https://github.com/httpwg/http-core/issues/320>)
	o In Section 3.3, move definition of "complete" into semantics		o In Section 3.3, move definition of "complete" into semantics
	(<https://github.com/httpwg/http-core/issues/334>)		(<https://github.com/httpwg/http-core/issues/334>)
	C.10. Since draft-ietf-httpbis-cache-08		C.10. Since draft-ietf-httpbis-cache-08
	o Appendix A now uses the sender variant of the "#" list expansion		o Appendix A now uses the sender variant of the "#" list expansion
	(<https://github.com/httpwg/http-core/issues/192>)		(<https://github.com/httpwg/http-core/issues/192>)
	skipping to change at page 44, line 14 ¶		skipping to change at page 45, line 14 ¶
	o Changed to using "payload data" when defining requirements about		o Changed to using "payload data" when defining requirements about
	the data being conveyed within a message, instead of the terms		the data being conveyed within a message, instead of the terms
	"payload body" or "response body" or "representation body", since		"payload body" or "response body" or "representation body", since
	they often get confused with the HTTP/1.1 message body (which		they often get confused with the HTTP/1.1 message body (which
	includes transfer coding) (<https://github.com/httpwg/http-core/		includes transfer coding) (<https://github.com/httpwg/http-core/
	issues/553>)		issues/553>)
	C.15. Since draft-ietf-httpbis-cache-13		C.15. Since draft-ietf-httpbis-cache-13
	o In Section 5.2.2.1, clarify requirements around generating an		o In Section 5.2.2.2, clarify requirements around generating an
	error response (<https://github.com/httpwg/http-core/issues/608>)		error response (<https://github.com/httpwg/http-core/issues/608>)
	o Changed to using "content" instead of "payload" or "payload data"		o Changed to using "content" instead of "payload" or "payload data"
	to avoid confusion with the payload of version-specific messaging		to avoid confusion with the payload of version-specific messaging
	frames (<https://github.com/httpwg/http-core/issues/654>)		frames (<https://github.com/httpwg/http-core/issues/654>)
	o In Section 4.3.4, clarify how multiple validators are handled		o In Section 4.3.4, clarify how multiple validators are handled
	(<https://github.com/httpwg/http-core/issues/659>)		(<https://github.com/httpwg/http-core/issues/659>)
	o In Section 4.2.3, Section 5.2, and Section 5.2.2.3, remove notes		o In Section 4.2.3, Section 5.2, and Section 5.2.2.4, remove notes
	about very old HTTP/1.0 behaviours (<https://github.com/httpwg/		about very old HTTP/1.0 behaviours (<https://github.com/httpwg/
	http-core/issues/660>)		http-core/issues/660>)
	o In Section 5.2.2.2, modify operation to be more backwards-		o In Section 5.2.2.3, modify operation to be more backwards-
	compatible with existing implementations		compatible with existing implementations
	(<https://github.com/httpwg/http-core/issues/661>)		(<https://github.com/httpwg/http-core/issues/661>)
			C.16. Since draft-ietf-httpbis-cache-14
			o Fix subsection ordering in Section 5.2.2
			(<https://github.com/httpwg/http-core/issues/674>)
			o In Section 2, define what a cache key is
			(<https://github.com/httpwg/http-core/issues/728>)
			o In Section 3.1, clarify what cache proxy headers apply to
			(<https://github.com/httpwg/http-core/issues/729>)
			o In Section 7.1, cache poisoning can affect private caches too
			(<https://github.com/httpwg/http-core/issues/730>)
			o In Section 5.1, adjust handling of invalid values to match most
			deployed caches (<https://github.com/httpwg/http-core/issues/778>)
			o In Section 5.3, mention parsing requirement relaxation
			(<https://github.com/httpwg/http-core/issues/779>)
	Acknowledgments		Acknowledgments
	See Appendix "Acknowledgments" of [Semantics].		See Appendix "Acknowledgments" of [Semantics].
	Authors' Addresses		Authors' Addresses
	Roy T. Fielding (editor)		Roy T. Fielding (editor)
	Adobe		Adobe
	345 Park Ave		345 Park Ave
	San Jose, CA 95110		San Jose, CA 95110
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