draft-ietf-httpbis-cache-14.txt   draft-ietf-httpbis-cache-15.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: 1 October 2021 J. Reschke, Ed.
greenbytes greenbytes
January 13, 2021 30 March 2021
HTTP Caching HTTP Caching
draft-ietf-httpbis-cache-14 draft-ietf-httpbis-cache-15
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.
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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 1 October 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
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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 . . . . . . . . . . . . . . . . . 38
Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 38 Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 39
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 . . . . . . . . . . . . 41
C.3. Since draft-ietf-httpbis-cache-01 . . . . . . . . . . . . 40 C.3. Since draft-ietf-httpbis-cache-01 . . . . . . . . . . . . 41
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 . . . . . . . . . . . . 42
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 . . . . . . . . . . . . 44
C.14. Since draft-ietf-httpbis-cache-12 . . . . . . . . . . . . 42 C.14. Since draft-ietf-httpbis-cache-12 . . . . . . . . . . . . 44
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.
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([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
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as a cache key. as a cache key.
A cache is _disconnected_ when it cannot contact the origin server or A cache is _disconnected_ when it cannot contact the origin server or
otherwise find a forward path for a request. A disconnected cache otherwise find a forward path for a request. A disconnected cache
can serve stale responses in some circumstances (Section 4.2.4). can serve stale responses in some circumstances (Section 4.2.4).
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; * the request method is understood by the cache;
o the response status code is final (see Section 15 of [Semantics]); * the response status code is final (see Section 15 of [Semantics]);
o if the response status code is 206 or 304, or the "must- * 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 * 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 * 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 * 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: * 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);
* if the cache is shared: an s-maxage response directive (see - a max-age response directive (see Section 5.2.2.1);
- 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
requirements listed; see Section 5.2.3. requirements listed; see Section 5.2.3.
In this context, a cache has "understood" a request method or a In this context, a cache has "understood" a request method or a
response status code if it recognizes it and implements all specified response status code if it recognizes it and implements all specified
caching-related behavior. caching-related behavior.
Note that, in normal operation, some caches will not store a response Note that, in normal operation, some caches will not store a response
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as such responses are not usually useful to store. However, caches as such responses are not usually useful to store. However, caches
are not prohibited from storing such responses. are not prohibited from storing such responses.
3.1. Storing Header and Trailer Fields 3.1. Storing Header and Trailer Fields
Caches MUST include all received response header fields - including Caches MUST include all received response header fields - including
unrecognised ones - when storing a response; this assures that new unrecognised ones - when storing a response; this assures that new
HTTP header fields can be successfully deployed. However, the HTTP header fields can be successfully deployed. However, the
following exceptions are made: following exceptions are made:
o The Connection header field and fields whose names are listed in * 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 * 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 * 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 * 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.
When doing so, the cache MUST add each header field in the provided When doing so, the cache MUST add each header field in the provided
response to the stored response, replacing field values that are response to the stored response, replacing field values that are
already present, with the following exceptions: already present, with the following exceptions:
o Header fields excepted from storage in Section 3.1, * Header fields excepted from storage in Section 3.1,
o Header fields that the cache's stored response depends upon, as * Header fields that the cache's stored response depends upon, as
described below, described below,
o Header fields that are automatically processed and removed by the * Header fields that are automatically processed and removed by the
recipient, as described below, and recipient, as described below, and
o The Content-Length header field. * The Content-Length header field.
In some cases, caches (especially in user agents) store the results In some cases, caches (especially in user agents) store the results
of processing the received response, rather than the response itself, of processing the received response, rather than the response itself,
and updating header fields that affect that processing can result in and updating header fields that affect that processing can result in
inconsistent behavior and security issues. Caches in this situation inconsistent behavior and security issues. Caches in this situation
MAY omit these header fields from updating stored responses on an MAY omit these header fields from updating stored responses on an
exceptional basis, but SHOULD limit such omission to those fields exceptional basis, but SHOULD limit such omission to those fields
necessary to assure integrity of the stored response. necessary to assure integrity of the stored response.
For example, a browser might decode the content coding of a response For example, a browser might decode the content coding of a response
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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 * 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 * 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) * 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 * 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: * 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).
Note that a cache-control extension can override any of the Note that a cache-control extension can override any of the
requirements listed; see Section 5.2.3. requirements listed; see Section 5.2.3.
When a stored response is used to satisfy a request without When a stored response is used to satisfy a request without
validation, a cache MUST generate an Age header field (Section 5.1), validation, a cache MUST generate an Age header field (Section 5.1),
replacing any present in the response with a value equal to the replacing any present in the response with a value equal to the
stored response's current_age; see Section 4.2.3. stored response's current_age; see Section 4.2.3.
A cache MUST write through requests with methods that are unsafe A cache MUST write through requests with methods that are unsafe
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response that has a Vary header field (Section 12.5.5 of response that has a Vary header field (Section 12.5.5 of
[Semantics]), it MUST NOT use that response unless all the selecting [Semantics]), it MUST NOT use that response unless all the selecting
header fields nominated by the Vary header field match in both the header fields nominated by the Vary header field match in both the
original request (i.e., that associated with the stored response), original request (i.e., that associated with the stored response),
and the presented request. and the presented request.
The selecting header fields from two requests are defined to match if The selecting header fields from two requests are defined to match if
and only if those in the first request can be transformed to those in and only if those in the first request can be transformed to those in
the second request by applying any of: the second request by applying any of:
o adding or removing whitespace, where allowed in the header field's * adding or removing whitespace, where allowed in the header field's
syntax syntax
o combining multiple header field lines with the same field name * combining multiple header field lines with the same field name
(see Section 5.2 of [Semantics]) (see Section 5.2 of [Semantics])
o normalizing both header field values in a way that is known to * normalizing both header field values in a way that is known to
have identical semantics, according to the header field's have identical semantics, according to the header field's
specification (e.g., reordering field values when order is not specification (e.g., reordering field values when order is not
significant; case-normalization, where values are defined to be significant; case-normalization, where values are defined to be
case-insensitive) case-insensitive)
If (after any normalization that might take place) a header field is If (after any normalization that might take place) a header field is
absent from a request, it can only match another request if it is absent from a request, it can only match another request if it is
also absent there. also absent there.
A Vary header field value containing a member "*" always fails to A Vary header field value containing a member "*" always fails to
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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).
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freshness_lifetime is defined in Section 4.2.1; current_age is freshness_lifetime is defined in Section 4.2.1; current_age is
defined in Section 4.2.3. defined in Section 4.2.3.
Clients can send the max-age or min-fresh request directives Clients can send the max-age or min-fresh request directives
(Section 5.2.1) to constrain or relax freshness calculations for the (Section 5.2.1) to constrain or relax freshness calculations for the
corresponding response. However, caches are not required to honor corresponding response. However, caches are not required to honor
them. them.
When calculating freshness, to avoid common problems in date parsing: When calculating freshness, to avoid common problems in date parsing:
o Although all date formats are specified to be case-sensitive, a * Although all date formats are specified to be case-sensitive, a
cache recipient SHOULD match the field value case-insensitively. cache recipient SHOULD match the field value case-insensitively.
o If a cache recipient's internal implementation of time has less * If a cache recipient's internal implementation of time has less
resolution than the value of an HTTP-date, the recipient MUST resolution than the value of an HTTP-date, the recipient MUST
internally represent a parsed Expires date as the nearest time internally represent a parsed Expires date as the nearest time
equal to or earlier than the received value. equal to or earlier than the received value.
o A cache recipient MUST NOT allow local time zones to influence the * A cache recipient MUST NOT allow local time zones to influence the
calculation or comparison of an age or expiration time. calculation or comparison of an age or expiration time.
o A cache recipient SHOULD consider a date with a zone abbreviation * A cache recipient SHOULD consider a date with a zone abbreviation
other than "GMT" to be invalid for calculating expiration. other than "GMT" to be invalid for calculating expiration.
Note that freshness applies only to cache operation; it cannot be Note that freshness applies only to cache operation; it cannot be
used to force a user agent to refresh its display or reload a used to force a user agent to refresh its display or reload a
resource. See Section 6 for an explanation of the difference between resource. See Section 6 for an explanation of the difference between
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 * 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, * 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 * 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. * 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.
Note that this calculation is not vulnerable to clock skew, since all Note that this calculation is not vulnerable to clock skew, since all
of the information comes from the origin server. of the information comes from the origin server.
When there is more than one value present for a given directive When there is more than one value present for a given directive
(e.g., two Expires header field lines or multiple Cache-Control: max- (e.g., two Expires header field lines or multiple Cache-Control: max-
age directives), either the first occurrence should be used, or the age directives), either the first occurrence should be used, or the
response should be considered stale. If directives conflict (e.g., response should be considered stale. If directives conflict (e.g.,
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A cache that implements partial responses to range requests, as A cache that implements partial responses to range requests, as
defined in Section 14.2 of [Semantics], also needs to evaluate a defined in Section 14.2 of [Semantics], also needs to evaluate a
received If-Range header field (Section 13.1.5 of [Semantics]) received If-Range header field (Section 13.1.5 of [Semantics])
regarding its selected stored response. regarding its selected stored response.
4.3.3. Handling a Validation Response 4.3.3. Handling a Validation Response
Cache handling of a response to a conditional request depends upon Cache handling of a response to a conditional request depends upon
its status code: its status code:
o A 304 (Not Modified) response status code indicates that the * A 304 (Not Modified) response status code indicates that the
stored response can be updated and reused; see Section 4.3.4. stored response can be updated and reused; see Section 4.3.4.
o A full response (i.e., one containing content) indicates that none * A full response (i.e., one containing content) indicates that none
of the stored responses nominated in the conditional request is of the stored responses nominated in the conditional request is
suitable. Instead, the cache MUST use the full response to suitable. Instead, the cache MUST use the full response to
satisfy the request. The cache MAY store such a full response, satisfy the request. The cache MAY store such a full response,
subject to its constraints (see Section 3). subject to its constraints (see Section 3).
o However, if a cache receives a 5xx (Server Error) response while * However, if a cache receives a 5xx (Server Error) response while
attempting to validate a response, it can either forward this attempting to validate a response, it can either forward this
response to the requesting client, or act as if the server failed response to the requesting client, or act as if the server failed
to respond. In the latter case, the cache can send a previously to respond. In the latter case, the cache can send a previously
stored response, subject to its constraints on doing so (see stored response, subject to its constraints on doing so (see
Section 4.2.4), or retry the validation request. Section 4.2.4), or retry the validation request.
4.3.4. Freshening Stored Responses upon Validation 4.3.4. Freshening Stored Responses upon Validation
When a cache receives a 304 (Not Modified) response and already has When a cache receives a 304 (Not Modified) response and already has
one or more stored 200 (OK) responses for the applicable cache key, one or more stored 200 (OK) responses for the applicable cache key,
the cache needs to identify which (if any) are to be updated by the the cache needs to identify which (if any) are to be updated by the
new information provided, and then do so. new information provided, and then do so.
The stored response(s) to update are identified by using the first The stored response(s) to update are identified by using the first
match (if any) of: match (if any) of:
o If the new response contains one or more _strong validators_ (see * If the new response contains one or more _strong validators_ (see
Section 8.8.1 of [Semantics]), then each of those strong Section 8.8.1 of [Semantics]), then each of those strong
validators identify the selected representation for update. All validators identify the selected representation for update. All
the stored responses with one of those same strong validators are the stored responses with one of those same strong validators are
identified for update. If none of the stored responses contain at identified for update. If none of the stored responses contain at
least one of the same strong validators, then the cache MUST NOT least one of the same strong validators, then the cache MUST NOT
use the new response to update any stored responses. use the new response to update any stored responses.
o If the new response contains no strong validators but does contain * If the new response contains no strong validators but does contain
one or more _weak validators_, and those validators correspond to one or more _weak validators_, and those validators correspond to
one of the cache's stored responses, then the most recent of those one of the cache's stored responses, then the most recent of those
matching stored responses is identified for update. matching stored responses is identified for update.
o If the new response does not include any form of validator (such * If the new response does not include any form of validator (such
as where a client generates an If-Modified-Since request from a as where a client generates an If-Modified-Since request from a
source other than the Last-Modified response header field), and source other than the Last-Modified response header field), and
there is only one stored response, and that stored response also there is only one stored response, and that stored response also
lacks a validator, then that stored response is identified for lacks a validator, then that stored response is identified for
update. update.
For each stored response identified, the cache MUST update its header For each stored response identified, the cache MUST update its header
fields with the header fields provided in the 304 (Not Modified) fields with the header fields provided in the 304 (Not Modified)
response, as per Section 3.2. response, as per Section 3.2.
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HEAD response to update the stored response (see Section 3.2). HEAD response to update the stored response (see Section 3.2).
4.4. Invalidating Stored Responses 4.4. Invalidating Stored Responses
Because unsafe request methods (Section 9.2.1 of [Semantics]) such as Because unsafe request methods (Section 9.2.1 of [Semantics]) such as
PUT, POST or DELETE have the potential for changing state on the PUT, POST or DELETE have the potential for changing state on the
origin server, intervening caches are required to invalidate stored origin server, intervening caches are required to invalidate stored
responses to keep their contents up to date. responses to keep their contents up to date.
A cache MUST invalidate the target URI (Section 7.1 of [Semantics]) A cache MUST invalidate the target URI (Section 7.1 of [Semantics])
when a non-error status code is received in response to an unsafe when it receives a non-error status code in response to an unsafe
request method (including methods whose safety is unknown). request method (including methods whose safety is unknown).
A cache MAY invalidate other URIs when a non-error status code is A cache MAY invalidate other URIs when it receives a non-error status
received in response to an unsafe request method (including methods code in response to an unsafe request method (including methods whose
whose safety is unknown). In particular, the URI(s) in the Location safety is unknown). In particular, the URI(s) in the Location and
and Content-Location response header fields (if present) are Content-Location response header fields (if present) are candidates
candidates for invalidation; other URIs might be discovered through for invalidation; other URIs might be discovered through mechanisms
mechanisms not specified in this document. However, a cache MUST NOT not specified in this document. However, a cache MUST NOT trigger an
trigger an invalidation under these conditions if the origin invalidation under these conditions if the origin (Section 4.3.1 of
(Section 4.3.1 of [Semantics]) of the URI to be invalidated differs [Semantics]) of the URI to be invalidated differs from that of the
from that of the target URI (Section 7.1 of [Semantics]). This helps target URI (Section 7.1 of [Semantics]). This helps prevent denial-
prevent denial-of-service attacks. of-service attacks.
_Invalidate_ means that the cache will either remove all stored _Invalidate_ means that the cache will either remove all stored
responses whose target URI matches the given URI, or will mark them responses whose target URI matches the given URI, or will mark them
as "invalid" and in need of a mandatory validation before they can be as "invalid" and in need of a mandatory validation before they can be
sent in response to a subsequent request. sent in response to a subsequent request.
A "non-error response" is one with a 2xx (Successful) or 3xx A "non-error response" is one with a 2xx (Successful) or 3xx
(Redirection) status code. (Redirection) status code.
Note that this does not guarantee that all appropriate responses are Note that this does not guarantee that all appropriate responses are
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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
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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
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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.
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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
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| 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 31, line 12 skipping to change at page 31, line 35
old directive. In this way, extensions to the existing cache-control old directive. In this way, extensions to the existing cache-control
directives can be made without breaking deployed caches. directives can be made without breaking deployed caches.
For example, consider a hypothetical new response directive called For example, consider a hypothetical new response directive called
"community" that acts as a modifier to the private directive: in "community" that acts as a modifier to the private directive: in
addition to private caches, any cache that is shared only by members addition to private caches, any cache that is shared only by members
of the named community is allowed to cache the response. An origin of the named community is allowed to cache the response. An origin
server wishing to allow the UCI community to use an otherwise private server wishing to allow the UCI community to use an otherwise private
response in their shared cache(s) could do so by including response in their shared cache(s) could do so by including
Cache-Control: private, community="UCI" Cache-Control: private, community="UCI"
A cache that recognizes such a community cache-extension could A cache that recognizes such a community cache-extension could
broaden its behavior in accordance with that extension. A cache that broaden its behavior in accordance with that extension. A cache that
does not recognize the community cache-extension would ignore it and does not recognize the community cache-extension would ignore it and
adhere to the private directive. adhere to the private directive.
New extension directives ought to consider defining: New extension directives ought to consider defining:
o What it means for a directive to be specified multiple times, * What it means for a directive to be specified multiple times,
o When the directive does not take an argument, what it means when * When the directive does not take an argument, what it means when
an argument is present, an argument is present,
o When the directive requires an argument, what it means when it is * When the directive requires an argument, what it means when it is
missing, missing,
o Whether the directive is specific to requests, responses, or able * Whether the directive is specific to requests, responses, or able
to be used in either. to be used in either.
5.2.4. Cache Directive Registry 5.2.4. Cache Directive Registry
The "Hypertext Transfer Protocol (HTTP) Cache Directive Registry" The "Hypertext Transfer Protocol (HTTP) Cache Directive Registry"
defines the namespace for the cache directives. It has been created defines the namespace for the cache directives. It has been created
and is now maintained at <https://www.iana.org/assignments/http- and is now maintained at <https://www.iana.org/assignments/http-
cache-directives>. cache-directives>.
A registration MUST include the following fields: A registration MUST include the following fields:
o Cache Directive Name * Cache Directive Name
o Pointer to specification text * Pointer to specification text
Values to be added to this namespace require IETF Review (see Values to be added to this namespace require IETF Review (see
[RFC8126], Section 4.8). [RFC8126], Section 4.8).
5.3. Expires 5.3. Expires
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 33, line 30 skipping to change at page 34, line 10
Applications using HTTP often specify additional forms of caching. Applications using HTTP often specify additional forms of caching.
For example, Web browsers often have history mechanisms such as For example, Web browsers often have history mechanisms such as
"Back" buttons that can be used to redisplay a representation "Back" buttons that can be used to redisplay a representation
retrieved earlier in a session. retrieved earlier in a session.
Likewise, some Web browsers implement caching of images and other Likewise, some Web browsers implement caching of images and other
assets within a page view; they may or may not honor HTTP caching assets within a page view; they may or may not honor HTTP caching
semantics. semantics.
The requirements in this specification do not necessarily apply to The requirements in this specification do not necessarily apply to
how applications use data after it is retrieved from a HTTP cache. how applications use data after it is retrieved from an HTTP cache.
For example, a history mechanism can display a previous For example, a history mechanism can display a previous
representation even if it has expired, and an application can use representation even if it has expired, and an application can use
cached data in other ways beyond its freshness lifetime. cached data in other ways beyond its freshness lifetime.
This specification does not prohibit the application from taking HTTP This specification does not prohibit the application from taking HTTP
caching into account; for example, a history mechanism might tell the caching into account; for example, a history mechanism might tell the
user that a view is stale, or it might honor cache directives (e.g., user that a view is stale, or it might honor cache directives (e.g.,
Cache-Control: no-store). Cache-Control: no-store).
However, when an application caches data and does not make this However, when an application caches data and does not make this
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 35, line 32 skipping to change at page 36, line 14
8.1. Field Name Registration 8.1. Field Name Registration
First, introduce the new "Hypertext Transfer Protocol (HTTP) Field First, introduce the new "Hypertext Transfer Protocol (HTTP) Field
Name Registry" at <https://www.iana.org/assignments/http-fields> as Name Registry" at <https://www.iana.org/assignments/http-fields> as
described in Section 18.4 of [Semantics]. described in Section 18.4 of [Semantics].
Then, please update the registry with the field names listed in the Then, please update the registry with the field names listed in the
table below: table below:
--------------- ----------- ------ ---------- +===============+===========+======+==========+
Field Name Status Ref. Comments | Field Name | Status | Ref. | Comments |
--------------- ----------- ------ ---------- +===============+===========+======+==========+
Age standard 5.1 | Age | standard | 5.1 | |
Cache-Control standard 5.2 +---------------+-----------+------+----------+
Expires standard 5.3 | Cache-Control | standard | 5.2 | |
Pragma standard 5.4 +---------------+-----------+------+----------+
Warning obsoleted 5.5 | Expires | standard | 5.3 | |
--------------- ----------- ------ ---------- +---------------+-----------+------+----------+
| Pragma | standard | 5.4 | |
+---------------+-----------+------+----------+
| Warning | obsoleted | 5.5 | |
+---------------+-----------+------+----------+
Table 1 Table 1
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 +------------------+----------------------------------+
min-fresh Section 5.2.1.3 | max-stale | Section 5.2.1.2 |
must-revalidate Section 5.2.2.1 +------------------+----------------------------------+
must-understand Section 5.2.2.2 | min-fresh | Section 5.2.1.3 |
no-cache Section 5.2.1.4, Section 5.2.2.3 +------------------+----------------------------------+
no-store Section 5.2.1.5, Section 5.2.2.4 | must-revalidate | Section 5.2.2.2 |
no-transform Section 5.2.1.6, Section 5.2.2.5 +------------------+----------------------------------+
only-if-cached Section 5.2.1.7 | must-understand | Section 5.2.2.3 |
private Section 5.2.2.7 +------------------+----------------------------------+
proxy-revalidate Section 5.2.2.8 | no-cache | Section 5.2.1.4, Section 5.2.2.4 |
public Section 5.2.2.6 +------------------+----------------------------------+
s-maxage Section 5.2.2.10 | no-store | Section 5.2.1.5, 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 |
+------------------+----------------------------------+
| private | Section 5.2.2.7 |
+------------------+----------------------------------+
| proxy-revalidate | Section 5.2.2.8 |
+------------------+----------------------------------+
| public | Section 5.2.2.9 |
+------------------+----------------------------------+
| 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-14, January 13, 2021, ietf-httpbis-messaging-15, 30 March 2021,
<https://tools.ietf.org/html/draft-ietf-httpbis-messaging- <https://tools.ietf.org/html/draft-ietf-httpbis-messaging-
14>. 15>.
[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,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
skipping to change at page 37, line 16 skipping to change at page 38, line 26
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-14, January 13, 2021, draft-ietf-httpbis-semantics-15, 30 March 2021,
<https://tools.ietf.org/html/draft-ietf-httpbis-semantics- <https://tools.ietf.org/html/draft-ietf-httpbis-semantics-
14>. 15>.
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>.
[RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale [RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale
skipping to change at page 38, line 42 skipping to change at page 40, line 4
Handling of duplicate and conflicting cache directives has been Handling of duplicate and conflicting cache directives has been
clarified. (Section 4.2.1) clarified. (Section 4.2.1)
Cache invalidation of the URIs in the Location and Content-Location Cache invalidation of the URIs in the Location and Content-Location
header fields is no longer required, but still allowed. header fields is no longer required, but still allowed.
(Section 4.4) (Section 4.4)
Cache invalidation of the URIs in the Location and Content-Location Cache invalidation of the URIs in the Location and Content-Location
header fields is disallowed when the origin is different; previously, header fields is disallowed when the origin is different; previously,
it was the host. (Section 4.4) it was the host. (Section 4.4)
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.
C.1. Between RFC7234 and draft 00 C.1. Between RFC7234 and draft 00
The changes were purely editorial: The changes were purely editorial:
o Change boilerplate and abstract to indicate the "draft" status, * Change boilerplate and abstract to indicate the "draft" status,
and update references to ancestor specifications. and update references to ancestor specifications.
o Remove version "1.1" from document title, indicating that this * Remove version "1.1" from document title, indicating that this
specification applies to all HTTP versions. specification applies to all HTTP versions.
o Adjust historical notes. * Adjust historical notes.
o Update links to sibling specifications. * Update links to sibling specifications.
o Replace sections listing changes from RFC 2616 by new empty * Replace sections listing changes from RFC 2616 by new empty
sections referring to RFC 723x. sections referring to RFC 723x.
o Remove acknowledgements specific to RFC 723x. * Remove acknowledgements specific to RFC 723x.
o Move "Acknowledgements" to the very end and make them unnumbered. * Move "Acknowledgements" to the very end and make them unnumbered.
C.2. Since draft-ietf-httpbis-cache-00 C.2. Since draft-ietf-httpbis-cache-00
The changes are purely editorial: The changes are purely editorial:
o Moved all extensibility tips, registration procedures, and * Moved all extensibility tips, registration procedures, and
registry tables from the IANA considerations to normative registry tables from the IANA considerations to normative
sections, reducing the IANA considerations to just instructions sections, reducing the IANA considerations to just instructions
that will be removed prior to publication as an RFC. that will be removed prior to publication as an RFC.
C.3. Since draft-ietf-httpbis-cache-01 C.3. Since draft-ietf-httpbis-cache-01
o Cite RFC 8126 instead of RFC 5226 (<https://github.com/httpwg/ * Cite RFC 8126 instead of RFC 5226 (<https://github.com/httpwg/
http-core/issues/75>) http-core/issues/75>)
o In Section 5.4, misleading statement about the relation between * In Section 5.4, misleading statement about the relation between
Pragma and Cache-Control (<https://github.com/httpwg/http-core/ Pragma and Cache-Control (<https://github.com/httpwg/http-core/
issues/92>, <https://www.rfc-editor.org/errata/eid4674>) issues/92>, <https://www.rfc-editor.org/errata/eid4674>)
C.4. Since draft-ietf-httpbis-cache-02 C.4. Since draft-ietf-httpbis-cache-02
o In Section 3, explain that only final responses are cacheable * In Section 3, explain that only final responses are cacheable
(<https://github.com/httpwg/http-core/issues/29>) (<https://github.com/httpwg/http-core/issues/29>)
o In Section 5.2.2, clarify what responses various directives apply * In Section 5.2.2, clarify what responses various directives apply
to (<https://github.com/httpwg/http-core/issues/52>) to (<https://github.com/httpwg/http-core/issues/52>)
o In Section 4.3.1, clarify the source of validators in conditional * In Section 4.3.1, clarify the source of validators in conditional
requests (<https://github.com/httpwg/http-core/issues/110>) requests (<https://github.com/httpwg/http-core/issues/110>)
o Revise Section 6 to apply to more than just History Lists * Revise Section 6 to apply to more than just History Lists
(<https://github.com/httpwg/http-core/issues/126>) (<https://github.com/httpwg/http-core/issues/126>)
o In Section 5.5, deprecated "Warning" header field * In Section 5.5, deprecated "Warning" header field
(<https://github.com/httpwg/http-core/issues/139>) (<https://github.com/httpwg/http-core/issues/139>)
o In Section 3.5, remove a spurious note * In Section 3.5, remove a spurious note
(<https://github.com/httpwg/http-core/issues/141>) (<https://github.com/httpwg/http-core/issues/141>)
C.5. Since draft-ietf-httpbis-cache-03 C.5. Since draft-ietf-httpbis-cache-03
o In Section 2, define what a disconnected cache is * In Section 2, define what a disconnected cache is
(<https://github.com/httpwg/http-core/issues/5>) (<https://github.com/httpwg/http-core/issues/5>)
o In Section 4, clarify language around how to select a response * In Section 4, clarify language around how to select a response
when more than one matches (<https://github.com/httpwg/http-core/ when more than one matches (<https://github.com/httpwg/http-core/
issues/23>) issues/23>)
o in Section 4.2.4, mention stale-while-revalidate and stale-if- * in Section 4.2.4, mention stale-while-revalidate and stale-if-
error (<https://github.com/httpwg/http-core/issues/122>) error (<https://github.com/httpwg/http-core/issues/122>)
o Remove requirements around cache request directives * Remove requirements around cache request directives
(<https://github.com/httpwg/http-core/issues/129>) (<https://github.com/httpwg/http-core/issues/129>)
o Deprecate Pragma (<https://github.com/httpwg/http-core/ * Deprecate Pragma (<https://github.com/httpwg/http-core/
issues/140>) issues/140>)
o In Section 3.5 and Section 5.2.2, note effect of some directives * In Section 3.5 and Section 5.2.2, note effect of some directives
on authenticated requests (<https://github.com/httpwg/http-core/ on authenticated requests (<https://github.com/httpwg/http-core/
issues/161>) issues/161>)
C.6. Since draft-ietf-httpbis-cache-04 C.6. Since draft-ietf-httpbis-cache-04
o In Section 5.2, remove the registrations for stale-if-error and * In Section 5.2, remove the registrations for stale-if-error and
stale-while-revalidate which happened in RFC 7234 stale-while-revalidate which happened in RFC 7234
(<https://github.com/httpwg/http-core/issues/207>) (<https://github.com/httpwg/http-core/issues/207>)
C.7. Since draft-ietf-httpbis-cache-05 C.7. Since draft-ietf-httpbis-cache-05
o In Section 3.3, clarify how weakly framed content is considered * In Section 3.3, clarify how weakly framed content is considered
for purposes of completeness (<https://github.com/httpwg/http- for purposes of completeness (<https://github.com/httpwg/http-
core/issues/25>) core/issues/25>)
o Throughout, describe Vary and cache key operations more clearly * Throughout, describe Vary and cache key operations more clearly
(<https://github.com/httpwg/http-core/issues/28>) (<https://github.com/httpwg/http-core/issues/28>)
o In Section 3, remove concept of "cacheable methods" in favor of * In Section 3, remove concept of "cacheable methods" in favor of
prose (<https://github.com/httpwg/http-core/issues/54>, prose (<https://github.com/httpwg/http-core/issues/54>,
<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 * 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" * 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 * 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 * 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- * 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 * 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 * 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 * 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 * 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 * 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 * 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 * 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 * 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>)
C.11. Since draft-ietf-httpbis-cache-09 C.11. Since draft-ietf-httpbis-cache-09
o In Section 5.1, discuss handling of invalid and multiple Age * In Section 5.1, discuss handling of invalid and multiple Age
header field values (<https://github.com/httpwg/http-core/ header field values (<https://github.com/httpwg/http-core/
issues/193>) issues/193>)
o Switch to xml2rfc v3 mode for draft generation * Switch to xml2rfc v3 mode for draft generation
(<https://github.com/httpwg/http-core/issues/394>) (<https://github.com/httpwg/http-core/issues/394>)
C.12. Since draft-ietf-httpbis-cache-10 C.12. Since draft-ietf-httpbis-cache-10
o In Section 5.2 (Cache-Control), adjust ABNF to allow empty lists * In Section 5.2 (Cache-Control), adjust ABNF to allow empty lists
(<https://github.com/httpwg/http-core/issues/210>) (<https://github.com/httpwg/http-core/issues/210>)
C.13. Since draft-ietf-httpbis-cache-11 C.13. Since draft-ietf-httpbis-cache-11
o None. * None.
C.14. Since draft-ietf-httpbis-cache-12 C.14. Since draft-ietf-httpbis-cache-12
o In Section 4.2.4, remove 'no-store', as it won't be in cache in
* In Section 4.2.4, remove 'no-store', as it won't be in cache in
the first place (<https://github.com/httpwg/http-core/issues/447>) the first place (<https://github.com/httpwg/http-core/issues/447>)
o In Section 3.1, make it clear that only response headers need be * In Section 3.1, make it clear that only response headers need be
stored (<https://github.com/httpwg/http-core/issues/457>) stored (<https://github.com/httpwg/http-core/issues/457>)
o Rewrote "Updating Stored Header Fields" Section 3.2 * Rewrote "Updating Stored Header Fields" Section 3.2
(<https://github.com/httpwg/http-core/issues/458>) (<https://github.com/httpwg/http-core/issues/458>)
o In Section 4.2.1 clarify how to handle invalid and conflicting * In Section 4.2.1 clarify how to handle invalid and conflicting
directives (<https://github.com/httpwg/http-core/issues/460>) directives (<https://github.com/httpwg/http-core/issues/460>)
o In Section 4.3.3, mention retry of failed validation requests * In Section 4.3.3, mention retry of failed validation requests
(<https://github.com/httpwg/http-core/issues/462>) (<https://github.com/httpwg/http-core/issues/462>)
o In Section 4.3.3, clarify requirement on storing a full response * In Section 4.3.3, clarify requirement on storing a full response
to a conditional request (<https://github.com/httpwg/http-core/ to a conditional request (<https://github.com/httpwg/http-core/
issues/463>) issues/463>)
o In Section 5.1, clarify error handling * In Section 5.1, clarify error handling
(<https://github.com/httpwg/http-core/issues/471>) (<https://github.com/httpwg/http-core/issues/471>)
o In Section 4.2, remove spurious "UTC" (<https://github.com/httpwg/ * In Section 4.2, remove spurious "UTC" (<https://github.com/httpwg/
http-core/issues/472>) http-core/issues/472>)
o In Section 4.2, correct the date-related rule names to consider * In Section 4.2, correct the date-related rule names to consider
case-insensitive (<https://github.com/httpwg/http-core/ case-insensitive (<https://github.com/httpwg/http-core/
issues/473>) issues/473>)
o In Section 6, strengthen recommendation for application caches to * In Section 6, strengthen recommendation for application caches to
pay attention to cache directives (<https://github.com/httpwg/ pay attention to cache directives (<https://github.com/httpwg/
http-core/issues/474>) http-core/issues/474>)
o In Section 4, mention collapsed requests * In Section 4, mention collapsed requests
(<https://github.com/httpwg/http-core/issues/475>) (<https://github.com/httpwg/http-core/issues/475>)
o In Section 4.4, relax requirements on Content-Location and * In Section 4.4, relax requirements on Content-Location and
Location invalidation (<https://github.com/httpwg/http-core/ Location invalidation (<https://github.com/httpwg/http-core/
issues/478>) issues/478>)
o In Section 4.3.4, refine the exceptions to update on a 304 * In Section 4.3.4, refine the exceptions to update on a 304
(<https://github.com/httpwg/http-core/issues/488>) (<https://github.com/httpwg/http-core/issues/488>)
o Moved table of Cache-Control directives into Section 8.2 * Moved table of Cache-Control directives into Section 8.2
(<https://github.com/httpwg/http-core/issues/506>) (<https://github.com/httpwg/http-core/issues/506>)
o In Section 1.2, remove unused core ABNF rules * In Section 1.2, remove unused core ABNF rules
(<https://github.com/httpwg/http-core/issues/529>) (<https://github.com/httpwg/http-core/issues/529>)
o Changed to using "payload data" when defining requirements about * 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 * 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" * 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 * 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 * 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- * 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
* Fix subsection ordering in Section 5.2.2
(<https://github.com/httpwg/http-core/issues/674>)
* In Section 2, define what a cache key is
(<https://github.com/httpwg/http-core/issues/728>)
* In Section 3.1, clarify what cache proxy headers apply to
(<https://github.com/httpwg/http-core/issues/729>)
* In Section 7.1, cache poisoning can affect private caches too
(<https://github.com/httpwg/http-core/issues/730>)
* In Section 5.1, adjust handling of invalid values to match most
deployed caches (<https://github.com/httpwg/http-core/issues/778>)
* 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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