< draft-ietf-httpbis-targeted-cache-control-02.txt		draft-ietf-httpbis-targeted-cache-control-03.txt >
	HTTP S. Ludin		HTTP S. Ludin
	Internet-Draft Akamai		Internet-Draft Akamai
	Intended status: Standards Track M. Nottingham		Intended status: Standards Track M. Nottingham
	Expires: 17 April 2022 Fastly		Expires: 8 July 2022 Fastly
	Y. Wu		Y. Wu
	Cloudflare		Cloudflare
	14 October 2021		4 January 2022
	Targeted HTTP Cache Control		Targeted HTTP Cache Control
	draft-ietf-httpbis-targeted-cache-control-02		draft-ietf-httpbis-targeted-cache-control-03
	Abstract		Abstract
	This specification defines a convention for HTTP response header		This specification defines a convention for HTTP response header
	fields that allow cache directives to be targeted at specific caches		fields that allow cache directives to be targeted at specific caches
	or classes of caches. It also defines one such header field,		or classes of caches. It also defines one such header field,
	targeted at Content Delivery Network (CDN) caches.		targeted at Content Delivery Network (CDN) caches.
	Note to Readers		About This Document
	_RFC EDITOR: please remove this section before publication_		This note is to be removed before publishing as an RFC.
	The issues list for this draft can be found at		Status information for this document may be found at
	https://github.com/httpwg/http-extensions/labels/targeted-cc		https://datatracker.ietf.org/doc/draft-ietf-httpbis-targeted-cache-
	(https://github.com/httpwg/http-extensions/labels/targeted-cc).		control/.
	The most recent (often, unpublished) draft is at https://httpwg.org/		Discussion of this document takes place on the HTTP Working Group
	http-extensions/draft-ietf-httpbis-targeted-cache-control.html		mailing list (mailto:ietf-http-wg@w3.org), which is archived at
	(https://httpwg.org/http-extensions/draft-ietf-httpbis-targeted-		https://lists.w3.org/Archives/Public/ietf-http-wg/. Working Group
	cache-control.html).		information can be found at https://httpwg.org/.
	See also the draft's current status in the IETF datatracker, at		Source for this draft and an issue tracker can be found at
	https://datatracker.ietf.org/doc/draft-ietf-httpbis-targeted-cache-		https://github.com/httpwg/http-extensions/labels/targeted-cc.
	control/ (https://datatracker.ietf.org/doc/draft-ietf-httpbis-
	targeted-cache-control/).
	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 17 April 2022.		This Internet-Draft will expire on 8 July 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 (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 Revised BSD License text as
	as described in Section 4.e of the Trust Legal Provisions and are		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 Revised BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3		1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
	2. Targeted Cache-Control Header Fields . . . . . . . . . . . . 3		2. Targeted Cache-Control Header Fields . . . . . . . . . . . . 3
	2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 3		2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 4
	2.2. Cache Behavior . . . . . . . . . . . . . . . . . . . . . 4		2.2. Cache Behavior . . . . . . . . . . . . . . . . . . . . . 5
	2.3. Interaction with HTTP Freshness . . . . . . . . . . . . . 6		2.3. Interaction with HTTP Freshness . . . . . . . . . . . . . 6
	2.4. Defining Targeted Fields . . . . . . . . . . . . . . . . 6		2.4. Defining Targeted Fields . . . . . . . . . . . . . . . . 7
	3. The CDN-Cache-Control Targeted Field . . . . . . . . . . . . 7		3. The CDN-Cache-Control Targeted Field . . . . . . . . . . . . 7
	3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 7		3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 7
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 8		5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
	6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8		6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
	6.1. Normative References . . . . . . . . . . . . . . . . . . 8		6.1. Normative References . . . . . . . . . . . . . . . . . . 8
	6.2. Informative References . . . . . . . . . . . . . . . . . 9		6.2. Informative References . . . . . . . . . . . . . . . . . 9
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
	1. Introduction		1. Introduction
	skipping to change at page 3, line 52 ¶		skipping to change at page 4, line 10 ¶
	CDN-Cache-Control: max-age=60		CDN-Cache-Control: max-age=60
	is a targeted field that applies to Content Delivery Networks (CDNs),		is a targeted field that applies to Content Delivery Networks (CDNs),
	as defined in Section 3.		as defined in Section 3.
	2.1. Syntax		2.1. Syntax
	Targeted fields are Dictionary Structured Fields (Section 3.2 of		Targeted fields are Dictionary Structured Fields (Section 3.2 of
	[STRUCTURED-FIELDS]). Each member of the dictionary is a cache		[STRUCTURED-FIELDS]). Each member of the dictionary is a cache
	response directive from the Hypertext Transfer Protocol (HTTP) Cache		response directive from the Hypertext Transfer Protocol (HTTP) Cache
	Directive Registry.		Directive Registry (https://www.iana.org/assignments/http-cache-
			directives/). Note that while targeted fields often have the same
			syntax as Cache-Control fields, differences in error handling mean
			that using a Cache-Control parser rather than a Structured Fields
			parser can introduce interoperability issues.
	Because cache directives are not defined in terms of structured data		Because cache directives are not defined in terms of structured data
	types, it is necessary to map their values into the appropriate		types, it is necessary to map their values into the appropriate
	types. Section 5.2 of [HTTP-CACHING] defines cache directive values		types. Section 5.2 of [HTTP-CACHING] defines cache directive values
	to be either absent, a quoted-string, or a token.		to be either absent, a quoted-string, or a token.
	This means that cache directives that have no value will be mapped to		This means that cache directives that have no value will be mapped to
	a Boolean (Section 3.3.6 of [STRUCTURED-FIELDS]). When the value is		a Boolean (Section 3.3.6 of [STRUCTURED-FIELDS]). When the value is
	a quoted-string, it will be mapped to a String (Section 3.3.3 of		a quoted-string, it will be mapped to a String (Section 3.3.3 of
	[STRUCTURED-FIELDS]), and when it is a token, it will map to a Token		[STRUCTURED-FIELDS]), and when it is a token, it will map to a Token
	skipping to change at page 4, line 46 ¶		skipping to change at page 5, line 12 ¶
	Parameters received on directives are to be ignored, unless other		Parameters received on directives are to be ignored, unless other
	handling is explicitly specified.		handling is explicitly specified.
	If a targeted field in a given response is empty, or a parsing error		If a targeted field in a given response is empty, or a parsing error
	is encountered, that field MUST be ignored by the cache (i.e., it		is encountered, that field MUST be ignored by the cache (i.e., it
	behaves as if the field were not present, likely falling back to		behaves as if the field were not present, likely falling back to
	other cache control mechanisms present).		other cache control mechanisms present).
	2.2. Cache Behavior		2.2. Cache Behavior
	A cache that implement this specification maintains a _target list_ -		A cache that implements this specification maintains a _target list_
	an ordered list of the targeted field names that it uses for caching		- an ordered list of the targeted field names that it uses for
	policy, with the order reflecting priority from most applicable to		caching policy, with the order reflecting priority from most
	least. The target list might be fixed, user-configurable, or		applicable to least. The target list might be fixed, user-
	generated per request, depending upon the implementation.		configurable, or generated per request, depending upon the
			implementation.
	For example, a CDN cache might support both CDN-Cache-Control and a		For example, a CDN cache might support both CDN-Cache-Control and a
	header specific to that CDN, ExampleCDN-Cache-Control, with the		header specific to that CDN, ExampleCDN-Cache-Control, with the
	latter overriding the former. Its target list would be:		latter overriding the former. Its target list would be:
	[ExampleCDN-Cache-Control, CDN-Cache-Control]		[ExampleCDN-Cache-Control, CDN-Cache-Control]
	When a cache that implements this specification receives a response		When a cache that implements this specification receives a response
	with one or more of of the header field names on its target list, the		with one or more of of the header field names on its target list, the
	cache MUST select the first (in target list order) field with a		cache MUST select the first (in target list order) field with a
	skipping to change at page 6, line 47 ¶		skipping to change at page 7, line 9 ¶
	any Cache-Control: max-age value		any Cache-Control: max-age value
	This specification does not place any specific requirements on		This specification does not place any specific requirements on
	implementations to mitigate these effects, but definitions of		implementations to mitigate these effects, but definitions of
	targeted fields can do so.		targeted fields can do so.
	2.4. Defining Targeted Fields		2.4. Defining Targeted Fields
	A targeted field for a particular class of cache can be defined by		A targeted field for a particular class of cache can be defined by
	requesting registration in the Hypertext Transfer Protocol (HTTP)		requesting registration in the Hypertext Transfer Protocol (HTTP)
	Field Name Registry https://www.iana.org/assignments/http-fields/		Field Name Registry (https://www.iana.org/assignments/http-fields/).
	(https://www.iana.org/assignments/http-fields/), listing this
	specification as the specification document. The Comments field of		Registration requests can use this document as the specification
	the registration should clearly define the class of caches that the		document, in which case the Comments field should clearly define the
	targeted field applies to.		class of caches that the targeted field applies to. Alternatively,
			if other documentation for the field has been created, it can be used
			as the specification document.
	By convention, targeted fields have the suffix "-Cache-Control":		By convention, targeted fields have the suffix "-Cache-Control":
	e.g., "ExampleCDN-Cache-Control". However, this suffix MUST NOT be		e.g., "ExampleCDN-Cache-Control". However, this suffix MUST NOT be
	used on its own to identify targeted fields; it is only a convention.		used on its own to identify targeted fields; it is only a convention.
	3. The CDN-Cache-Control Targeted Field		3. The CDN-Cache-Control Targeted Field
	The CDN-Cache-Control response header field is a targeted field		The CDN-Cache-Control response header field is a targeted field
	(Section 2) that allows origin servers to control the behaviour of		(Section 2) that allows origin servers to control the behaviour of
	CDN caches interposed between them and clients, separately from other		CDN caches interposed between them and clients, separately from other
	skipping to change at page 7, line 28 ¶		skipping to change at page 7, line 40 ¶
	Delivery Network or CDN).		Delivery Network or CDN).
	CDN caches that use CDN-Cache-Control will typically forward this		CDN caches that use CDN-Cache-Control will typically forward this
	header so that downstream CDN caches can use it as well. However,		header so that downstream CDN caches can use it as well. However,
	they MAY remove it when this is undesirable (for example, when		they MAY remove it when this is undesirable (for example, when
	configured to do so because it is known not to be used downstream).		configured to do so because it is known not to be used downstream).
	3.1. Examples		3.1. Examples
	For example, the following header fields would instruct a CDN cache		For example, the following header fields would instruct a CDN cache
	to consider the response fresh for 600 seconds, other shared caches		(i.e., a cache with a target list of \[CDN-Cache-Control]]) to
	for 120 seconds and any remaining caches for 60 seconds:		consider the response fresh for 600 seconds, other shared caches for
			120 seconds and any remaining caches for 60 seconds:
	Cache-Control: max-age=60, s-maxage=120		Cache-Control: max-age=60, s-maxage=120
	CDN-Cache-Control: max-age=600		CDN-Cache-Control: max-age=600
	These header fields would instruct a CDN cache to consider the		These header fields would instruct a CDN cache to consider the
	response fresh for 600 seconds, while all other caches would be		response fresh for 600 seconds, while all other caches would be
	prevented from storing it:		prevented from storing it:
	CDN-Cache-Control: max-age=600		CDN-Cache-Control: max-age=600
	Cache-Control: no-store		Cache-Control: no-store
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