draft-ietf-httpbis-cache-groups-02.txt		draft-ietf-httpbis-cache-groups-latest.txt
	Network Working Group M. Nottingham		HTTP Working Group M. Nottingham
	Internet-Draft June 17, 2024		Internet-Draft Cloudflare
	Intended status: Standards Track		Intended status: Standards Track October 23, 2025
	Expires: December 19, 2024		Expires: April 26, 2026
	HTTP Cache Groups		HTTP Cache Groups
	draft-ietf-httpbis-cache-groups-02		draft-ietf-httpbis-cache-groups-latest
	Abstract		Abstract
	This specification introduces a means of describing the relationships		This specification introduces a means of describing the relationships
	between stored responses in HTTP caches, "grouping" them by		between stored responses in HTTP caches, grouping them by associating
	associating a stored response with one or more opaque strings.		a stored response with one or more strings.
	About This Document		About This Document
	This note is to be removed before publishing as an RFC.		This note is to be removed before publishing as an RFC.
	Status information for this document may be found at		Status information for this document may be found at
	<https://datatracker.ietf.org/doc/draft-ietf-httpbis-cache-groups/>.		<https://datatracker.ietf.org/doc/draft-ietf-httpbis-cache-groups/>.
	Discussion of this document takes place on the HTTP Working Group		Discussion of this document takes place on the HTTP Working Group
	mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at		mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at
	skipping to change at page 1, line 47 ¶		skipping to change at page 1, line 47 ¶
	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 December 19, 2024.		This Internet-Draft will expire on April 26, 2026.
	Copyright Notice		Copyright Notice
	Copyright (c) 2024 IETF Trust and the persons identified as the		Copyright (c) 2025 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 2, line 31 ¶		skipping to change at page 2, line 31 ¶
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3		1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
	2. The Cache-Groups Response Header Field . . . . . . . . . . . 3		2. The Cache-Groups Response Header Field . . . . . . . . . . . 3
	2.1. Identifying Grouped Responses . . . . . . . . . . . . . . 4		2.1. Identifying Grouped Responses . . . . . . . . . . . . . . 4
	2.2. Cache Behaviour . . . . . . . . . . . . . . . . . . . . . 4		2.2. Cache Behaviour . . . . . . . . . . . . . . . . . . . . . 4
	2.2.1. Invalidation . . . . . . . . . . . . . . . . . . . . 4		2.2.1. Invalidation . . . . . . . . . . . . . . . . . . . . 4
	3. The Cache-Group-Invalidation Response Header Field . . . . . 4		3. The Cache-Group-Invalidation Response Header Field . . . . . 4
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	4.1. HTTP Field Names . . . . . . . . . . . . . . . . . . . . 5		4.1. HTTP Field Names . . . . . . . . . . . . . . . . . . . . 5
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 5		5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
	6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6		6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
	6.1. Normative References . . . . . . . . . . . . . . . . . . 6		6.1. Normative References . . . . . . . . . . . . . . . . . . 6
	6.2. Informative References . . . . . . . . . . . . . . . . . 6		6.2. Informative References . . . . . . . . . . . . . . . . . 6
	Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 6		Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
	1. Introduction		1. Introduction
	HTTP caching [HTTP-CACHING] operates at the granularity of a single		HTTP caching [HTTP-CACHING] operates at the granularity of a single
	resource; the freshness of one stored response does not affect that		resource; the freshness of one stored response does not affect that
	of others. This granularity can make caching more efficient -- for		of others. This granularity can make caching more efficient -- for
	example, when a page is composed of many assets that have different		example, when a page is composed of many assets that have different
	requirements for caching.		requirements for caching.
	skipping to change at page 3, line 9 ¶		skipping to change at page 3, line 9 ¶
	For example, it is often necessary to invalidate a set of related		For example, it is often necessary to invalidate a set of related
	resources. This might be because a state-changing request has side		resources. This might be because a state-changing request has side
	effects on other resources, or it might be purely for administrative		effects on other resources, or it might be purely for administrative
	convenience (e.g., "invalidate this part of the site"). Grouping		convenience (e.g., "invalidate this part of the site"). Grouping
	responses together provides a dedicated way to express these		responses together provides a dedicated way to express these
	relationships, instead of relying on things like URL structure.		relationships, instead of relying on things like URL structure.
	In addition to sharing invalidation events, the relationships		In addition to sharing invalidation events, the relationships
	indicated by grouping can also be used by caches to optimise their		indicated by grouping can also be used by caches to optimise their
	operation; for example, it could be used to inform the operation of		operation (e.g., to inform the operation of cache eviction
	cache eviction algorithms.		algorithms).
	Section 2 introduces a means of describing the relationships between		Section 2 introduces a means of describing the relationships between
	a set of stored responses in HTTP caches by associating them with one		stored responses in HTTP caches, by associating those responses with
	or more opaque strings. It also describes how caches can use that		one or more groups that reflect those relationships. It also
	information to apply invalidation events to members of a group.		describes how caches can use that information to apply invalidation
			events to members of a group.
	Section 3 introduces one new source of such events: a HTTP response		Section 3 introduces one new source of such events: a HTTP response
	header that allows a state-changing response to trigger a group		header field that allows a state-changing response to trigger a group
	invalidation.		invalidation.
	These mechanisms operate within a single cache, across the stored		These mechanisms operate within a single cache, across the stored
	responses associated with a single origin server. They do not		responses associated with a single origin server (see Section 2.1).
	address this issues of synchronising state between multiple caches		They do not address the issues of synchronising state between
	(e.g., in a hierarchy or mesh), nor do they facilitate association of		multiple caches (e.g., in a hierarchy or mesh), nor do they
	stored responses from disparate origins.		facilitate association of stored responses from disparate origins.
	1.1. Notational Conventions		1.1. Notational Conventions
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in		"OPTIONAL" in this document are to be interpreted as described in
	BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all		BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	This specification uses the following terminology from		This specification uses the following terminology from
	[STRUCTURED-FIELDS]: List, String, Parameter.		[STRUCTURED-FIELDS]: List, String, Parameter.
	2. The Cache-Groups Response Header Field		2. The Cache-Groups Response Header Field
	The Cache-Groups HTTP Response Header is a List of Strings		The Cache-Groups HTTP response header field is a List of Strings
	[STRUCTURED-FIELDS]. Each member of the list is an opaque value that		(Sections 3.1 and 3.3.3 of [STRUCTURED-FIELDS]). Each member of the
	identifies a group that the response belongs to.		List is a value that identifies a group that the response belongs to.
			These Strings are opaque -- while they might have some meaning to the
			server that creates them, the cache does not have any insight into
			their structure or content (beyond uniquely identifying a group).
	HTTP/1.1 200 OK		HTTP/1.1 200 OK
	Content-Type: application/javascript		Content-Type: application/javascript
	Cache-Control: max-age=3600		Cache-Control: max-age=3600
	Cache-Groups: "scripts"		Cache-Groups: "scripts"
	The ordering of members is not significant. Unrecognised Parameters		The ordering of members is not significant. Unrecognised Parameters
	MUST be ignored.		are to be ignored.
	Implementations MUST support at least 128 groups in a field value,		Implementations MUST support at least 32 groups in a field value,
	with up to at least 128 characters in each member. Note that generic		with up to at least 32 characters in each member. Note that generic
	limitations on HTTP field lengths may constrain the size of this		limitations on HTTP field lengths may constrain the size of this
	field value in practice.		field value in practice.
	2.1. Identifying Grouped Responses		2.1. Identifying Grouped Responses
	Two responses stored in the same cache are considered to have the		Two responses stored in the same cache are considered to belong to
	same group when all of the following conditions are met:		the same group when all of the following conditions are met:
	1. They both contain a Cache-Groups response header field that		1. They both contain a Cache-Groups response header field that
	contains the same String (in any position in the List), when		contains the same String (in any position in the List), when
	compared character-by-character.		compared character-by-character (case sensitive).
	2. The both share the same URI origin (per Section 4.3.1 of [HTTP]).		2. They both share the same URI origin (per Section 4.3.1 of
			[HTTP]).
	2.2. Cache Behaviour		2.2. Cache Behaviour
	2.2.1. Invalidation		2.2.1. Invalidation
	A cache that invalidates a stored response MAY invalidate any stored		A cache that invalidates a stored response MAY invalidate any stored
	responses that share groups (per Section 2.1) with that response.		responses that share groups (per Section 2.1) with that response.
			Note that further grouped invalidations are not triggered by a
			grouped invalidation; i.e., this mechanism does not cascade.
	Cache extensions can explicitly strengthen the requirement above.		Cache extensions can explicitly strengthen the requirement above.
	For example, a targeted cache control header field [TARGETED] might		For example, a targeted cache control header field [TARGETED] might
	specify that caches processing it are required to invalidate such		specify that caches processing it are required to invalidate such
	responses.		responses.
	3. The Cache-Group-Invalidation Response Header Field		3. The Cache-Group-Invalidation Response Header Field
	The Cache-Group-Invalidation response header field is a List of		The Cache-Group-Invalidation response header field is a List of
	Strings [STRUCTURED-FIELDS]. Each member of the list is an opaque		Strings (Sections 3.1 and 3.3.3 of [STRUCTURED-FIELDS]). Each member
	value that identifies a group that the response invalidates, per		of the List is a value that identifies a group that the response
	Section 2.2.1.		invalidates, per Section 2.2.1.
	For example, a POST request that has side effects on two cache groups		For example, following a POST request that has side effects on two
	could indicate that stored responses associated with either or both		cache groups, the corresponding response could indicate that stored
	of those groups should be invalidated with:		responses associated with either or both of those groups should be
			invalidated with:
	HTTP/1.1 200 OK		HTTP/1.1 200 OK
	Content-Type: text/html		Content-Type: text/html
	Cache-Group-Invalidation: "eurovision-results", "kylie-minogue"		Cache-Group-Invalidation: "eurovision-results", "australia"
	The Cache-Group-Invalidation header field MUST be ignored on		The Cache-Group-Invalidation header field MUST be ignored on
	responses to requests that have a safe method (e.g., GET; see		responses to requests that have a safe method (e.g., GET; see
	Section 9.2.1 of [HTTP]).		Section 9.2.1 of [HTTP]).
	A cache that receives a Cache-Group-Invalidation header field on a		A cache that receives a Cache-Group-Invalidation header field on a
	response to an unsafe request MAY invalidate any stored responses		response to an unsafe request MAY invalidate any stored responses
	that share groups (per Section 2.1) with any of the listed groups.		that share groups (per Section 2.1) with any of the listed groups.
	Cache extensions can explicitly strengthen the requirement above.		Cache extensions can explicitly strengthen the requirement above.
	For example, a targeted cache control header field [TARGETED] might		For example, a targeted cache control header field [TARGETED] might
	specify that caches processing it are required to respect the Cache-		specify that caches processing it are required to respect the Cache-
	Group-Invalidation signal.		Group-Invalidation signal.
	The ordering of members is not significant. Unrecognised Parameters		The ordering of members is not significant. Unrecognised Parameters
	MUST be ignored.		are to be ignored.
	Implementations MUST support at least 128 groups in a field value,		Implementations MUST support at least 32 groups in a field value,
	with up to at least 128 characters in each member. Note that generic		with up to at least 32 characters in each member. Note that generic
	limitations on HTTP field lengths may constrain the size of this		limitations on HTTP field lengths may constrain the size of this
	field value in practice.		field value in practice.
	4. IANA Considerations		4. IANA Considerations
	IANA should perform the following tasks:		IANA should perform the following tasks:
	4.1. HTTP Field Names		4.1. HTTP Field Names
	Enter the following into the Hypertext Transfer Protocol (HTTP) Field		Enter the following into the Hypertext Transfer Protocol (HTTP) Field
	skipping to change at page 6, line 36 ¶		skipping to change at page 6, line 43 ¶
	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>.
	[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>.
	[STRUCTURED-FIELDS]		[STRUCTURED-FIELDS]
	Nottingham, M. and P. Kamp, "Structured Field Values for		Nottingham, M. and P. Kamp, "Structured Field Values for
	HTTP", draft-ietf-httpbis-sfbis-06 (work in progress),		HTTP", RFC 9651, DOI 10.17487/RFC9651, September 2024,
	April 2024.		<https://www.rfc-editor.org/info/rfc9651>.
	6.2. Informative References		6.2. Informative References
	[TARGETED]		[TARGETED]
	Ludin, S., Nottingham, M., and Y. Wu, "Targeted HTTP Cache		Ludin, S., Nottingham, M., and Y. Wu, "Targeted HTTP Cache
	Control", RFC 9213, DOI 10.17487/RFC9213, June 2022,		Control", RFC 9213, DOI 10.17487/RFC9213, June 2022,
	<https://www.rfc-editor.org/info/rfc9213>.		<https://www.rfc-editor.org/info/rfc9213>.
	Appendix A. Acknowledgements		Appendix A. Acknowledgements
	Thanks to Stephen Ludin for his review and suggestions.		Thanks to Stephen Ludin for his review and suggestions.
	Author's Address		Author's Address
	Mark Nottingham		Mark Nottingham
	Prahran		Cloudflare
			Melbourne
	Australia		Australia
	Email: mnot@mnot.net		Email: mnot@mnot.net
	URI: https://www.mnot.net/		URI: https://www.mnot.net/
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