HTTP Cache Groups
draft-ietf-httpbis-cache-groups-02
| Document | Type | Active Internet-Draft (httpbis WG) | |
|---|---|---|---|
| Author | Mark Nottingham | ||
| Last updated | 2024-06-17 | ||
| Replaces | draft-nottingham-http-cache-groups | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
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| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
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| Send notices to | (None) |
draft-ietf-httpbis-cache-groups-02
Network Working Group M. Nottingham
Internet-Draft 17 June 2024
Intended status: Standards Track
Expires: 19 December 2024
HTTP Cache Groups
draft-ietf-httpbis-cache-groups-02
Abstract
This specification introduces a means of describing the relationships
between stored responses in HTTP caches, "grouping" them by
associating a stored response with one or more opaque strings.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-httpbis-cache-groups/.
Discussion of this document takes place on the HTTP Working Group
mailing list (mailto:ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/. Working Group
information can be found at https://httpwg.org/.
Source for this draft and an issue tracker can be found at
https://github.com/httpwg/http-extensions/labels/cache-groups.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 19 December 2024.
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Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. The Cache-Groups Response Header Field . . . . . . . . . . . 3
2.1. Identifying Grouped Responses . . . . . . . . . . . . . . 4
2.2. Cache Behaviour . . . . . . . . . . . . . . . . . . . . . 4
2.2.1. Invalidation . . . . . . . . . . . . . . . . . . . . 4
3. The Cache-Group-Invalidation Response Header Field . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4.1. HTTP Field Names . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
HTTP caching [HTTP-CACHING] operates at the granularity of a single
resource; the freshness of one stored response does not affect that
of others. This granularity can make caching more efficient -- for
example, when a page is composed of many assets that have different
requirements for caching.
However, there are also cases where the relationship between stored
responses could be used to improve cache efficiency.
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For example, it is often necessary to invalidate a set of related
resources. This might be because a state-changing request has side
effects on other resources, or it might be purely for administrative
convenience (e.g., "invalidate this part of the site"). Grouping
responses together provides a dedicated way to express these
relationships, instead of relying on things like URL structure.
In addition to sharing invalidation events, the relationships
indicated by grouping can also be used by caches to optimise their
operation; for example, it could be used to inform the operation of
cache eviction algorithms.
Section 2 introduces a means of describing the relationships between
a set of stored responses in HTTP caches by associating them with one
or more opaque strings. It also 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
header that allows a state-changing response to trigger a group
invalidation.
These mechanisms operate within a single cache, across the stored
responses associated with a single origin server. They do not
address this issues of synchronising state between multiple caches
(e.g., in a hierarchy or mesh), nor do they facilitate association of
stored responses from disparate origins.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This specification uses the following terminology from
[STRUCTURED-FIELDS]: List, String, Parameter.
2. The Cache-Groups Response Header Field
The Cache-Groups HTTP Response Header is a List of Strings
[STRUCTURED-FIELDS]. Each member of the list is an opaque value that
identifies a group that the response belongs to.
HTTP/1.1 200 OK
Content-Type: application/javascript
Cache-Control: max-age=3600
Cache-Groups: "scripts"
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The ordering of members is not significant. Unrecognised Parameters
MUST be ignored.
Implementations MUST support at least 128 groups in a field value,
with up to at least 128 characters in each member. Note that generic
limitations on HTTP field lengths may constrain the size of this
field value in practice.
2.1. Identifying Grouped Responses
Two responses stored in the same cache are considered to have the
same group when all of the following conditions are met:
1. They both contain a Cache-Groups response header field that
contains the same String (in any position in the List), when
compared character-by-character.
2. The both share the same URI origin (per Section 4.3.1 of [HTTP]).
2.2. Cache Behaviour
2.2.1. Invalidation
A cache that invalidates a stored response MAY invalidate any stored
responses that share groups (per Section 2.1) with that response.
Cache extensions can explicitly strengthen the requirement above.
For example, a targeted cache control header field [TARGETED] might
specify that caches processing it are required to invalidate such
responses.
3. The Cache-Group-Invalidation Response Header Field
The Cache-Group-Invalidation response header field is a List of
Strings [STRUCTURED-FIELDS]. Each member of the list is an opaque
value that identifies a group that the response invalidates, per
Section 2.2.1.
For example, a POST request that has side effects on two cache groups
could indicate that stored responses associated with either or both
of those groups should be invalidated with:
HTTP/1.1 200 OK
Content-Type: text/html
Cache-Group-Invalidation: "eurovision-results", "kylie-minogue"
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The Cache-Group-Invalidation header field MUST be ignored on
responses to requests that have a safe method (e.g., GET; see
Section 9.2.1 of [HTTP]).
A cache that receives a Cache-Group-Invalidation header field on a
response to an unsafe request MAY invalidate any stored responses
that share groups (per Section 2.1) with any of the listed groups.
Cache extensions can explicitly strengthen the requirement above.
For example, a targeted cache control header field [TARGETED] might
specify that caches processing it are required to respect the Cache-
Group-Invalidation signal.
The ordering of members is not significant. Unrecognised Parameters
MUST be ignored.
Implementations MUST support at least 128 groups in a field value,
with up to at least 128 characters in each member. Note that generic
limitations on HTTP field lengths may constrain the size of this
field value in practice.
4. IANA Considerations
IANA should perform the following tasks:
4.1. HTTP Field Names
Enter the following into the Hypertext Transfer Protocol (HTTP) Field
Name Registry:
* Field Name: Cache-Groups
* Status: permanent
* Reference: RFC nnnn
* Comments:
* Field Name: Cache-Group-Invalidation
* Status: permanent
* Reference: RFC nnnn
* Comments:
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5. Security Considerations
This mechanism allows resources that share an origin to invalidate
each other. Because of this, origins that represent multiple parties
(sometimes referred to as "shared hosting") might allow one party to
group its resources with those of others, or to send signals which
have side effects upon them.
Shared hosts that wish to mitigate these risks can control access to
the header fields defined in this specification.
6. References
6.1. Normative References
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[HTTP-CACHING]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Caching", STD 98, RFC 9111,
DOI 10.17487/RFC9111, June 2022,
<https://www.rfc-editor.org/rfc/rfc9111>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[STRUCTURED-FIELDS]
Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", Work in Progress, Internet-Draft, draft-ietf-
httpbis-sfbis-06, 21 April 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
sfbis-06>.
6.2. Informative References
[TARGETED] Ludin, S., Nottingham, M., and Y. Wu, "Targeted HTTP Cache
Control", RFC 9213, DOI 10.17487/RFC9213, June 2022,
<https://www.rfc-editor.org/rfc/rfc9213>.
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Appendix A. Acknowledgements
Thanks to Stephen Ludin for his review and suggestions.
Author's Address
Mark Nottingham
Prahran
Australia
Email: mnot@mnot.net
URI: https://www.mnot.net/
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