draft-ietf-httpbis-cache-13.txt   draft-ietf-httpbis-cache-14.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: June 17, 2021 J. Reschke, Ed. Expires: July 17, 2021 J. Reschke, Ed.
greenbytes greenbytes
December 14, 2020 January 13, 2021
HTTP Caching HTTP Caching
draft-ietf-httpbis-cache-13 draft-ietf-httpbis-cache-14
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.14. The changes in this draft are summarized in Appendix C.15.
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 June 17, 2021. This Internet-Draft will expire on July 17, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 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
and restrictions with respect to this document. Code Components and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License. provided without warranty as described in the Simplified BSD License.
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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. Storing Responses to Authenticated Requests . . . . . . . 10 3.4. Combining Partial Content . . . . . . . . . . . . . . . . 10
3.5. Combining Partial Content . . . . . . . . . . . . . . . . 10 3.5. Storing Responses to Authenticated Requests . . . . . . . 10
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 . . . . . . . . . . . . . . . . . . . . . . . . 13
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 . . . . . . . . . . . 15
4.2.3. Calculating Age . . . . . . . . . . . . . . . . . . . 16 4.2.3. Calculating Age . . . . . . . . . . . . . . . . . . . 16
4.2.4. Serving Stale Responses . . . . . . . . . . . . . . . 17 4.2.4. Serving Stale Responses . . . . . . . . . . . . . . . 17
4.3. Validation . . . . . . . . . . . . . . . . . . . . . . . 18 4.3. Validation . . . . . . . . . . . . . . . . . . . . . . . 18
4.3.1. Sending a Validation Request . . . . . . . . . . . . 18 4.3.1. Sending a Validation Request . . . . . . . . . . . . 18
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 . . . . . . . . . . . 20
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 . . . . . . . . . . . 22 4.3.5. Freshening Responses with HEAD . . . . . . . . . . . 21
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 . . . . . . . . . . . . . . . . . . . . . . 24 5.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 23
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 . . . . . . . . . . . . . . 30
5.2.4. Cache Directive Registry . . . . . . . . . . . . . . 31 5.2.4. Cache Directive Registry . . . . . . . . . . . . . . 31
5.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 32 5.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . 33 5.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . 32
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 . . . . . . . . . . . . . . . . . . . . . 34
7.2. Timing Attacks . . . . . . . . . . . . . . . . . . . . . 35 7.2. Timing Attacks . . . . . . . . . . . . . . . . . . . . . 34
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 . . . . . . . . . . . . . . . . . 35
8.2. Cache Directive Registration . . . . . . . . . . . . . . 36 8.2. Cache Directive Registration . . . . . . . . . . . . . . 35
8.3. Warn Code Registry . . . . . . . . . . . . . . . . . . . 36 8.3. Warn Code Registry . . . . . . . . . . . . . . . . . . . 36
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 36 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.1. Normative References . . . . . . . . . . . . . . . . . . 36 9.1. Normative References . . . . . . . . . . . . . . . . . . 36
9.2. Informative References . . . . . . . . . . . . . . . . . 37 9.2. Informative References . . . . . . . . . . . . . . . . . 37
Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 38 Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 38
Appendix B. Changes from RFC 7234 . . . . . . . . . . . . . . . 38 Appendix B. Changes from RFC 7234 . . . . . . . . . . . . . . . 38
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 39 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 39
C.1. Between RFC7234 and draft 00 . . . . . . . . . . . . . . 39 C.1. Between RFC7234 and draft 00 . . . . . . . . . . . . . . 39
C.2. Since draft-ietf-httpbis-cache-00 . . . . . . . . . . . . 40 C.2. Since draft-ietf-httpbis-cache-00 . . . . . . . . . . . . 39
C.3. Since draft-ietf-httpbis-cache-01 . . . . . . . . . . . . 40 C.3. Since draft-ietf-httpbis-cache-01 . . . . . . . . . . . . 40
C.4. Since draft-ietf-httpbis-cache-02 . . . . . . . . . . . . 40 C.4. Since draft-ietf-httpbis-cache-02 . . . . . . . . . . . . 40
C.5. Since draft-ietf-httpbis-cache-03 . . . . . . . . . . . . 40 C.5. Since draft-ietf-httpbis-cache-03 . . . . . . . . . . . . 40
C.6. Since draft-ietf-httpbis-cache-04 . . . . . . . . . . . . 41 C.6. Since draft-ietf-httpbis-cache-04 . . . . . . . . . . . . 41
C.7. Since draft-ietf-httpbis-cache-05 . . . . . . . . . . . . 41 C.7. Since draft-ietf-httpbis-cache-05 . . . . . . . . . . . . 41
C.8. Since draft-ietf-httpbis-cache-06 . . . . . . . . . . . . 41 C.8. Since draft-ietf-httpbis-cache-06 . . . . . . . . . . . . 41
C.9. Since draft-ietf-httpbis-cache-07 . . . . . . . . . . . . 42 C.9. Since draft-ietf-httpbis-cache-07 . . . . . . . . . . . . 42
C.10. Since draft-ietf-httpbis-cache-08 . . . . . . . . . . . . 42 C.10. Since draft-ietf-httpbis-cache-08 . . . . . . . . . . . . 42
C.11. Since draft-ietf-httpbis-cache-09 . . . . . . . . . . . . 42 C.11. Since draft-ietf-httpbis-cache-09 . . . . . . . . . . . . 42
C.12. Since draft-ietf-httpbis-cache-10 . . . . . . . . . . . . 43 C.12. Since draft-ietf-httpbis-cache-10 . . . . . . . . . . . . 42
C.13. Since draft-ietf-httpbis-cache-11 . . . . . . . . . . . . 43 C.13. Since draft-ietf-httpbis-cache-11 . . . . . . . . . . . . 42
C.14. Since draft-ietf-httpbis-cache-12 . . . . . . . . . . . . 43 C.14. Since draft-ietf-httpbis-cache-12 . . . . . . . . . . . . 42
C.15. Since draft-ietf-httpbis-cache-13 . . . . . . . . . . . . 44
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 44 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44
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.
An HTTP _cache_ is a local store of response messages and the An HTTP _cache_ is a local store of response messages and the
subsystem that controls storage, retrieval, and deletion of messages subsystem that controls storage, retrieval, and deletion of messages
in it. A cache stores cacheable responses to reduce the response in it. A cache stores cacheable responses to reduce the response
time and network bandwidth consumption on future equivalent requests. time and network bandwidth consumption on future equivalent requests.
Any client or server MAY use a cache, though a server that is acting Any client or server MAY use a cache, though not when acting as a
as a tunnel cannot. tunnel.
A _shared cache_ is a cache that stores responses for reuse by more A _shared cache_ is a cache that stores responses for reuse by more
than one user; shared caches are usually (but not always) deployed as than one user; shared caches are usually (but not always) deployed as
a part of an intermediary. A _private cache_, in contrast, is a part of an intermediary. A _private cache_, in contrast, is
dedicated to a single user; often, they are deployed as a component dedicated to a single user; often, they are deployed as a component
of a user agent. of a user agent.
HTTP caching's goal is significantly improving performance by reusing HTTP caching's goal is significantly improving performance by reusing
a prior response message to satisfy a current request. A cache a prior response message to satisfy a current request. A cache
considers a stored response "fresh", as defined in Section 4.2, if it considers a stored response "fresh", as defined in Section 4.2, if it
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| stored in binary form; an implementation could produce it as a | stored in binary form; an implementation could produce it as a
| canned string if any overflow occurs, even if the calculations | canned string if any overflow occurs, even if the calculations
| are performed with an arithmetic type incapable of directly | are performed with an arithmetic type incapable of directly
| representing that number. What matters here is that an | representing that number. What matters here is that an
| overflow be detected and not treated as a negative value in | overflow be detected and not treated as a negative value in
| later calculations. | later calculations.
2. Overview of Cache Operation 2. Overview of Cache Operation
Proper cache operation preserves the semantics of HTTP transfers Proper cache operation preserves the semantics of HTTP transfers
([Semantics]) while reducing the transfer of information already held ([Semantics]) while reducing the transmission of information already
in the cache. Although caching is an entirely OPTIONAL feature of held in the cache. Although caching is an entirely OPTIONAL feature
HTTP, it can be assumed that reusing a cached response is desirable of HTTP, it can be assumed that reusing a cached response is
and that such reuse is the default behavior when no requirement or desirable and that such reuse is the default behavior when no
local configuration prevents it. Therefore, HTTP cache requirements requirement or local configuration prevents it. Therefore, HTTP
are focused on preventing a cache from either storing a non-reusable cache requirements are focused on preventing a cache from either
response or reusing a stored response inappropriately, rather than storing a non-reusable response or reusing a stored response
mandating that caches always store and reuse particular responses. inappropriately, rather than mandating that caches always store and
reuse particular responses.
The base _cache key_ comprises the request method and target URI used The _cache key_ is comprised of, at a minimum, the request method and
to retrieve the stored response; the method determines under which target URI used to retrieve the stored response; the method
circumstances that response can be used to satisfy a request. determines under which circumstances that response can be used to
However, many HTTP caches in common use today only cache GET satisfy a subsequent request. However, many HTTP caches in common
responses, and therefore only use the URI as the cache key, use today only cache GET responses, and therefore only use the URI as
forwarding other methods. 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, as per Section 4.1. header fields into the cache key as well, using information in the
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
risks (see Section 7.2). risks (see Section 7.2).
Most commonly, caches store the successful result of a retrieval Most commonly, caches store the successful result of a retrieval
request: i.e., a 200 (OK) response to a GET request, which contains a request: i.e., a 200 (OK) response to a GET request, which contains a
representation of the target resource (Section 9.3.1 of [Semantics]). representation of the target resource (Section 9.3.1 of [Semantics]).
However, it is also possible to store redirects, negative results However, it is also possible to store redirects, negative results
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3. Storing Responses in Caches 3. Storing Responses in Caches
A cache MUST NOT store a response to a request unless: A cache MUST NOT store a response to a request unless:
o the request method is understood by the cache; o the request method is understood by the cache;
o the response status code is final (see Section 15 of [Semantics]); o the response status code is final (see Section 15 of [Semantics]);
o if the response status code is 206 or 304, or the "must- o if the response status code is 206 or 304, or the "must-
understand" cache directive (see Section 5.2) is present: the understand" cache directive (see Section 5.2.2.2) is present: the
cache understands the response status code; cache understands the response status code;
o the "no-store" cache directive is not present in the response (see o the "no-store" cache directive is not present in the response (see
Section 5.2); Section 5.2.2.4);
o if the cache is shared: the "private" response directive is either o if the cache is shared: the "private" response directive is either
not present or allows a shared cache to store a modified response; not present or allows a shared cache to store a modified response;
see Section 5.2.2.7); see Section 5.2.2.7);
o if the cache is shared: the Authorization header field is not o if the cache is shared: the Authorization header field is not
present in the request (see Section 11.6.2 of [Semantics]) or a present in the request (see Section 11.6.2 of [Semantics]) or a
response directive is present that explicitly allows shared response directive is present that explicitly allows shared
caching (see Section 3.4); and, caching (see Section 3.5); and,
o the response contains at least one of: o the response contains at least one of:
* a public response directive (see Section 5.2.2.6); * a public response directive (see Section 5.2.2.6);
* a private response directive, if the cache is not shared (see * a private response directive, if the cache is not shared (see
Section 5.2.2.7); Section 5.2.2.7);
* an Expires header field (see Section 5.3); * an Expires header field (see Section 5.3);
* a max-age response directive (see Section 5.2.2.9); * a max-age response directive (see Section 5.2.2.9);
* if the cache is shared, an s-maxage response directive (see * if the cache is shared: an s-maxage response directive (see
Section 5.2.2.10); Section 5.2.2.10);
* a Cache Control Extension that allows it to be cached (see * a Cache Control Extension that allows it to be cached (see
Section 5.2.3); or, Section 5.2.3); or,
* a status code that is defined as heuristically cacheable (see * a status code that is defined as heuristically cacheable (see
Section 4.2.2). Section 4.2.2).
Note that a cache-control extension can override any of the Note that a cache-control extension can override any of the
requirements listed; see Section 5.2.3. requirements listed; see Section 5.2.3.
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Authorization (Section 11.7.2 of [Semantics]). 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 3.5, 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, o Header fields excepted from storage in Section 3.1,
o Header fields that the cache's stored representation of the o Header fields that the cache's stored response depends upon, as
response depends upon, as described below, described below,
o Header fields that are automatically processed and removed by the o 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. o The Content-Length header field.
In some cases, caches (especially in user agents) store processed In some cases, caches (especially in user agents) store the results
representations of the received response, rather than the response of processing the received response, rather than the response itself,
itself, and updating header fields that affect that processing can and updating header fields that affect that processing can result in
result in inconsistent behavior and security issues. Caches in this inconsistent behavior and security issues. Caches in this situation
situation MAY omit these header fields from updating stored MAY omit these header fields from updating stored responses on an
representations on an exceptional basis, but SHOULD limit such exceptional basis, but SHOULD limit such omission to those fields
omission to those fields necessary to assure integrity of the stored necessary to assure integrity of the stored response.
representation.
For example, a browser might decode the content coding of a response For example, a browser might decode the content coding of a response
payload while it is being received, creating a disconnect between the while it is being received, creating a disconnect between the data it
data it has stored and the response payload's original metadata. has stored and the response's original metadata. Updating that
Updating that stored metadata with a different Content-Encoding stored metadata with a different Content-Encoding header field would
header field would be problematic. Likewise, a browser might store a be problematic. Likewise, a browser might store a post-parse HTML
post-parse tree representation of HTML, rather than the payload tree, rather than the content received in the response; updating the
received in the response; updating the Content-Type header field Content-Type header field would not be workable in this case, because
would not be workable in this case, because any assumptions about the any assumptions about the format made in parsing would now be
format made in parsing would now be invalid. invalid.
Furthermore, some fields are automatically processed and removed by Furthermore, some fields are automatically processed and removed by
the HTTP implementation; for example, the Content-Range header field. the HTTP implementation; for example, the Content-Range header field.
Implementations MAY automatically omit such header fields from Implementations MAY automatically omit such header fields from
updates, even when the processing does not actually occur. updates, even when the processing does not actually occur.
Note that the Content-* prefix is not a signal that a header field is Note that the Content-* prefix is not a signal that a header field is
omitted from update; it is a convention for MIME header fields, not omitted from update; it is a convention for MIME header fields, not
HTTP. HTTP.
3.3. Storing Incomplete Responses 3.3. Storing Incomplete Responses
If the request method is GET, the response status code is 200 (OK), If the request method is GET, the response status code is 200 (OK),
and the entire response header section has been received, a cache MAY and the entire response header section has been received, a cache MAY
store a response body that is not complete (Section 3.3 of store a response body that is not complete (Section 3.4 of
[Semantics]) if the stored response is recorded as being incomplete. [Semantics]) if the stored response is recorded as being incomplete.
Likewise, a 206 (Partial Content) response MAY be stored as if it Likewise, a 206 (Partial Content) response MAY be stored as if it
were an incomplete 200 (OK) response. However, a cache MUST NOT were an incomplete 200 (OK) response. However, a cache MUST NOT
store incomplete or partial-content responses if it does not support store incomplete or partial-content responses if it does not support
the Range and Content-Range header fields or if it does not the Range and Content-Range header fields or if it does not
understand the range units used in those fields. understand the range units used in those fields.
A cache MAY complete a stored incomplete response by making a A cache MAY complete a stored incomplete response by making a
subsequent range request (Section 14.2 of [Semantics]) and combining subsequent range request (Section 14.2 of [Semantics]) and combining
the successful response with the stored response, as defined in the successful response with the stored response, as defined in
Section 3.5. A cache MUST NOT use an incomplete response to answer Section 3.4. A cache MUST NOT use an incomplete response to answer
requests unless the response has been made complete, or the request requests unless the response has been made complete, or the request
is partial and specifies a range wholly within the incomplete is partial and specifies a range wholly within the incomplete
response. A cache MUST NOT send a partial response to a client response. A cache MUST NOT send a partial response to a client
without explicitly marking it using the 206 (Partial Content) status without explicitly marking it using the 206 (Partial Content) status
code. code.
3.4. Storing Responses to Authenticated Requests 3.4. Combining Partial Content
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
any subsequent request unless the response contains a Cache-Control
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
of that directive for that response.
In this specification, the following response directives have such an
effect: must-revalidate (Section 5.2.2.1), public (Section 5.2.2.6),
and s-maxage (Section 5.2.2.10).
3.5. Combining Partial Content
A response might transfer only a partial representation if the A response might transfer only a partial representation if the
connection closed prematurely or if the request used one or more connection closed prematurely or if the request used one or more
Range specifiers (Section 14.2 of [Semantics]). After several such Range specifiers (Section 14.2 of [Semantics]). After several such
transfers, a cache might have received several ranges of the same transfers, a cache might have received several ranges of the same
representation. A cache MAY combine these ranges into a single representation. A cache MAY combine these ranges into a single
stored response, and reuse that response to satisfy later requests, stored response, and reuse that response to satisfy later requests,
if they all share the same strong validator and the cache complies if they all share the same strong validator and the cache complies
with the client requirements in Section 15.3.7.3 of [Semantics]. with the client requirements in Section 15.3.7.3 of [Semantics].
When combining the new response with one or more stored responses, a When combining the new response with one or more stored responses, a
cache MUST update the stored response header fields using the header cache MUST update the stored response header fields using the header
fields provided in the new response, as per Section 3.2. fields provided in the new response, as per Section 3.2.
3.5. Storing Responses to Authenticated Requests
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
any subsequent request unless the response contains a Cache-Control
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
of that directive for that response.
In this specification, the following response directives have such an
effect: must-revalidate (Section 5.2.2.1), public (Section 5.2.2.6),
and s-maxage (Section 5.2.2.10).
4. Constructing Responses from Caches 4. Constructing Responses from Caches
When presented with a request, a cache MUST NOT reuse a stored When presented with a request, a cache MUST NOT reuse a stored
response, unless: response, unless:
o The presented target URI (Section 7.1 of [Semantics]) and that of o The presented target URI (Section 7.1 of [Semantics]) and that of
the stored response match, and the stored response match, and
o the request method associated with the stored response allows it o the request method associated with the stored response allows it
to be used for the presented request, and to be used for the presented request, and
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A cache MUST write through requests with methods that are unsafe A cache MUST write through requests with methods that are unsafe
(Section 9.2.1 of [Semantics]) to the origin server; i.e., a cache is (Section 9.2.1 of [Semantics]) to the origin server; i.e., a cache is
not allowed to generate a reply to such a request before having not allowed to generate a reply to such a request before having
forwarded the request and having received a corresponding response. forwarded the request and having received a corresponding response.
Also, note that unsafe requests might invalidate already-stored Also, note that unsafe requests might invalidate already-stored
responses; see Section 4.4. responses; see Section 4.4.
A response that is stored or storable can be used to satisfy multiple A response that is stored or storable can be used to satisfy multiple
requests, provided that it is allowed to reuse that response for the requests, provided that it is allowed to reuse that response for the
requests in question. This enables caches to "collapse" multiple requests in question. This enables caches to _collapse requests_ -
incoming requests into a single forward request upon a cache miss, or combine multiple incoming requests into a single forward one upon
thereby reducing load on the origin server and network. However, a cache miss - thereby reducing load on the origin server and
note that if the response returned is not able to be used for some or network. However, note that if the response returned is not able to
all of the collapsed requests, additional latency might be be used for some or all of the collapsed requests, additional latency
introduced, because they will need to be forwarded to be satisfied. might be introduced, because they will need to be forwarded to be
satisfied.
When more than one suitable response is stored, a cache MUST use the When more than one suitable response is stored, a cache MUST use the
most recent one (as determined by the Date header field). It can most recent one (as determined by the Date header field). It can
also forward the request with "Cache-Control: max-age=0" or "Cache- also forward the request with "Cache-Control: max-age=0" or "Cache-
Control: no-cache" to disambiguate which response to use. Control: no-cache" to disambiguate which response to use.
A cache that does not have a clock available MUST NOT use stored A cache that does not have a clock available MUST NOT use stored
responses without revalidating them upon every use. responses without revalidating them upon every use.
4.1. Calculating Cache Keys with Vary 4.1. Calculating Cache Keys with Vary
When a cache receives a request that can be satisfied by a stored When a cache receives a request that can be satisfied by a stored
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 field values from two requests are defined to The selecting header fields from two requests are defined to match if
match if and only if those in the first request can be transformed to and only if those in the first request can be transformed to those in
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 o adding or removing whitespace, where allowed in the header field's
syntax syntax
o combining multiple header field lines with the same field name o 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 o 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
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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
match. match.
The stored response with matching selecting header fields is known as The stored response with matching selecting header fields is known as
the selected response. the _selected response_.
If multiple selected responses are available (potentially including If multiple selected responses are available (potentially including
responses without a Vary header field), the cache will need to choose responses without a Vary header field), the cache will need to choose
one to use. When a selecting header field has a known mechanism for one to use. When a selecting header field has a known mechanism for
doing so (e.g., qvalues on Accept and similar request header fields), doing so (e.g., qvalues on Accept and similar request header fields),
that mechanism MAY be used to select a preferred response. If such a that mechanism MAY be used to select a preferred response. If such a
mechanism is not available, or leads to equally preferred responses, mechanism is not available, or leads to equally preferred responses,
the most recent response (as determined by the Date header field) is the most recent response (as determined by the Date header field) is
used, as per Section 4. used, as per Section 4.
Some resources mistakenly omit the Vary header field from their Some resources mistakenly omit the Vary header field from their
default response (i.e., the one sent when no more preferable response default response (i.e., the one sent when no more preferable response
is available), selecting it for requests to that resource even when is available), with the effect of selecting it for requests to that
more preferable responses are available. When a cache has multiple resource even when more preferable responses are available. When a
responses for a target URI and one or more omits the Vary header cache has multiple responses for a target URI and one or more omits
field, it SHOULD use the most recent (see Section 4.2.3) valid Vary the Vary header field, it SHOULD use the most recent (see
field value available to select an appropriate response for the Section 4.2.3) valid Vary field value available to select an
request. appropriate response for the request.
If no selected response is available, the cache cannot satisfy the If no selected response is available, the cache cannot satisfy the
presented request. Typically, it is forwarded to the origin server presented request. Typically, it is forwarded to the origin server
in a (possibly conditional; see Section 4.3) request. in a (possibly conditional; see Section 4.3) request.
4.2. Freshness 4.2. Freshness
A _fresh_ response is one whose age has not yet exceeded its A _fresh_ response is one whose age has not yet exceeded its
freshness lifetime. Conversely, a _stale_ response is one where it freshness lifetime. Conversely, a _stale_ response is one where it
has. has.
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A response's _freshness lifetime_ is the length of time between its A response's _freshness lifetime_ is the length of time between its
generation by the origin server and its expiration time. An generation by the origin server and its expiration time. An
_explicit expiration time_ is the time at which the origin server _explicit expiration time_ is the time at which the origin server
intends that a stored response can no longer be used by a cache intends that a stored response can no longer be used by a cache
without further validation, whereas a _heuristic expiration time_ is without further validation, whereas a _heuristic expiration time_ is
assigned by a cache when no explicit expiration time is available. assigned by a cache when no explicit expiration time is available.
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" in the cache, it can be used to satisfy When a response is fresh, it can be used to satisfy subsequent
subsequent requests without contacting the origin server, thereby requests without contacting the origin server, thereby improving
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 5.2.2.9). 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
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A cache can calculate the freshness lifetime (denoted as A cache can calculate the freshness lifetime (denoted as
freshness_lifetime) of a response by using the first match of: freshness_lifetime) of a response by using the first match of:
o If the cache is shared and the s-maxage response directive o If the cache is shared and the s-maxage response directive
(Section 5.2.2.10) is present, use its value, or (Section 5.2.2.10) is present, use its value, or
o If the max-age response directive (Section 5.2.2.9) is present, o If the max-age response directive (Section 5.2.2.9) is present,
use its value, or use its value, or
o If the Expires response header field (Section 5.3) is present, use o If the Expires response header field (Section 5.3) is present, use
its value minus the value of the Date response header field, or 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
Section 10.2.2 of [Semantics]), or
o Otherwise, no explicit expiration time is present in the response. o Otherwise, no explicit expiration time is present in the response.
A heuristic freshness lifetime might be applicable; see A heuristic freshness lifetime might be applicable; see
Section 4.2.2. Section 4.2.2.
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-
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a cache MAY assign a heuristic expiration time when an explicit time a cache MAY assign a heuristic expiration time when an explicit time
is not specified, employing algorithms that use other field values is not specified, employing algorithms that use other field values
(such as the Last-Modified time) to estimate a plausible expiration (such as the Last-Modified time) to estimate a plausible expiration
time. This specification does not provide specific algorithms, but time. This specification does not provide specific algorithms, but
does impose worst-case constraints on their results. does impose worst-case constraints on their results.
A cache MUST NOT use heuristics to determine freshness when an A cache MUST NOT use heuristics to determine freshness when an
explicit expiration time is present in the stored response. Because explicit expiration time is present in the stored response. Because
of the requirements in Section 3, this means that heuristics can only of the requirements in Section 3, this means that heuristics can only
be used on responses without explicit freshness whose status codes be used on responses without explicit freshness whose status codes
are defined as "_heuristically cacheable_" (e.g., see Section 15.1 of are defined as _heuristically cacheable_ (e.g., see Section 15.1 of
[Semantics]), and those responses without explicit freshness that [Semantics]), and those responses without explicit freshness that
have been marked as explicitly cacheable (e.g., with a "public" have been marked as explicitly cacheable (e.g., with a "public"
response directive). response directive).
Note that in previous specifications heuristically cacheable response Note that in previous specifications heuristically cacheable response
status codes were called "cacheable by default." status codes were called "cacheable by default."
If the response has a Last-Modified header field (Section 8.9.2 of If the response has a Last-Modified header field (Section 8.8.2 of
[Semantics]), caches are encouraged to use a heuristic expiration [Semantics]), caches are encouraged to use a heuristic expiration
value that is no more than some fraction of the interval since that value that is no more than some fraction of the interval since that
time. A typical setting of this fraction might be 10%. time. A typical setting of this fraction might be 10%.
| *Note:* Section 13.9 of [RFC2616] prohibited caches from | *Note:* Section 13.9 of [RFC2616] prohibited caches from
| calculating heuristic freshness for URIs with query components | calculating heuristic freshness for URIs with query components
| (i.e., those containing '?'). In practice, this has not been | (i.e., those containing '?'). In practice, this has not been
| widely implemented. Therefore, origin servers are encouraged | widely implemented. Therefore, origin servers are encouraged
| to send explicit directives (e.g., Cache-Control: no-cache) if | to send explicit directives (e.g., Cache-Control: no-cache) if
| they wish to prevent caching. | they wish to prevent caching.
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2. the "corrected_age_value", if all of the caches along the 2. the "corrected_age_value", if all of the caches along the
response path implement HTTP/1.1 or greater. A cache MUST response path implement HTTP/1.1 or greater. A cache MUST
interpret this value relative to the time the request was interpret this value relative to the time the request was
initiated, not the time that the response was received. initiated, not the time that the response was received.
apparent_age = max(0, response_time - date_value); apparent_age = max(0, response_time - date_value);
response_delay = response_time - request_time; response_delay = response_time - request_time;
corrected_age_value = age_value + response_delay; corrected_age_value = age_value + response_delay;
These are combined as The corrected_age_value MAY be used as the corrected_initial_age. In
circumstances where very old cache implementations that might not
correctly insert Age are present, corrected_initial_age can be
calculated more conservatively as
corrected_initial_age = max(apparent_age, corrected_age_value); corrected_initial_age = max(apparent_age, corrected_age_value);
unless the cache is confident in the value of the Age header field
(e.g., because there are no HTTP/1.0 hops in the Via header field),
in which case the corrected_age_value MAY be used as the
corrected_initial_age.
The current_age of a stored response can then be calculated by adding The current_age of a stored response can then be calculated by adding
the time (in seconds) since the stored response was last validated by the time (in seconds) since the stored response was last validated by
the origin server to the corrected_initial_age. the origin server to the corrected_initial_age.
resident_time = now - response_time; resident_time = now - response_time;
current_age = corrected_initial_age + resident_time; current_age = corrected_initial_age + resident_time;
4.2.4. Serving Stale Responses 4.2.4. Serving Stale Responses
A "stale" response is one that either has explicit expiry information A "stale" response is one that either has explicit expiry information
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4.3. Validation 4.3. Validation
When a cache has one or more stored responses for a requested URI, When a cache has one or more stored responses for a requested URI,
but cannot serve any of them (e.g., because they are not fresh, or but cannot serve any of them (e.g., because they are not fresh, or
one cannot be selected; see Section 4.1), it can use the conditional one cannot be selected; see Section 4.1), it can use the conditional
request mechanism (Section 13.1 of [Semantics]) in the forwarded request mechanism (Section 13.1 of [Semantics]) in the forwarded
request to give the next inbound server an opportunity to select a request to give the next inbound server an opportunity to select a
valid stored response to use, updating the stored metadata in the valid stored response to use, updating the stored metadata in the
process, or to replace the stored response(s) with a new response. process, or to replace the stored response(s) with a new response.
This process is known as "_validating_" or "_revalidating_" the This process is known as _validating_ or _revalidating_ the stored
stored response. response.
4.3.1. Sending a Validation Request 4.3.1. Sending a Validation Request
When generating a conditional request for validation, a cache starts When generating a conditional request for validation, a cache starts
with either a request it is attempting to satisfy, or - if it is with either a request it is attempting to satisfy, or - if it is
initiating the request independently - it synthesises a request using initiating the request independently - it synthesises a request using
a stored response by copying the method, target URI, and request a stored response by copying the method, target URI, and request
header fields identified by the Vary header field (Section 4.1). header fields identified by the Vary header field (Section 4.1).
It then updates that request with one or more precondition header It then updates that request with one or more precondition header
fields. These contain validator metadata sourced from stored fields. These contain validator metadata sourced from stored
response(s) that have the same cache key. response(s) that have the same cache key.
The precondition header fields are then compared by recipients to The precondition header fields are then compared by recipients to
determine whether any stored response is equivalent to a current determine whether any stored response is equivalent to a current
representation of the resource. representation of the resource.
One such validator is the timestamp given in a Last-Modified header One such validator is the timestamp given in a Last-Modified header
field (Section 8.9.2 of [Semantics]), which can be used in an If- field (Section 8.8.2 of [Semantics]), which can be used in an If-
Modified-Since header field for response validation, or in an If- Modified-Since header field for response validation, or in an If-
Unmodified-Since or If-Range header field for representation Unmodified-Since or If-Range header field for representation
selection (i.e., the client is referring specifically to a previously selection (i.e., the client is referring specifically to a previously
obtained representation with that timestamp). obtained representation with that timestamp).
Another validator is the entity-tag given in an ETag field Another validator is the entity-tag given in an ETag field
(Section 8.9.3 of [Semantics]). One or more entity-tags, indicating (Section 8.8.3 of [Semantics]). One or more entity-tags, indicating
one or more stored responses, can be used in an If-None-Match header one or more stored responses, can be used in an If-None-Match header
field for response validation, or in an If-Match or If-Range header field for response validation, or in an If-Match or If-Range header
field for representation selection (i.e., the client is referring field for representation selection (i.e., the client is referring
specifically to one or more previously obtained representations with specifically to one or more previously obtained representations with
the listed entity-tags). the listed entity-tags).
4.3.2. Handling a Received Validation Request 4.3.2. Handling a Received Validation Request
Each client in the request chain may have its own cache, so it is Each client in the request chain may have its own cache, so it is
common for a cache at an intermediary to receive conditional requests common for a cache at an intermediary to receive conditional requests
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SHOULD evaluate any applicable conditional header field preconditions SHOULD evaluate any applicable conditional header field preconditions
received in that request with respect to the corresponding validators received in that request with respect to the corresponding validators
contained within the selected response. A cache MUST NOT evaluate contained within the selected response. A cache MUST NOT evaluate
conditional header fields that only apply to an origin server, occur conditional header fields that only apply to an origin server, occur
in a request with semantics that cannot be satisfied with a cached in a request with semantics that cannot be satisfied with a cached
response, or occur in a request with a target resource for which it response, or occur in a request with a target resource for which it
has no stored responses; such preconditions are likely intended for has no stored responses; such preconditions are likely intended for
some other (inbound) server. some other (inbound) server.
The proper evaluation of conditional requests by a cache depends on The proper evaluation of conditional requests by a cache depends on
the received precondition header fields and their precedence, as the received precondition header fields and their precedence. In
defined in Section 13.3 of [Semantics]. The If-Match and If- summary, the If-Match and If-Unmodified-Since conditional header
Unmodified-Since conditional header fields are not applicable to a fields are not applicable to a cache, and If-None-Match takes
cache. precedence over If-Modified-Since. See Section 13.2.2 of [Semantics]
for a complete specification of precondition precedence.
A request containing an If-None-Match header field (Section 13.1.2 of A request containing an If-None-Match header field (Section 13.1.2 of
[Semantics]) indicates that the client wants to validate one or more [Semantics]) indicates that the client wants to validate one or more
of its own stored responses in comparison to whichever stored of its own stored responses in comparison to whichever stored
response is selected by the cache. If the field value is "*", or if response is selected by the cache.
the field value is a list of entity-tags and at least one of them
matches the entity-tag of the selected stored response, a cache
recipient SHOULD generate a 304 (Not Modified) response (using the
metadata of the selected stored response) instead of sending that
stored response.
When a cache decides to revalidate its own stored responses for a When a cache decides to revalidate its own stored responses for a
request that contains an If-None-Match list of entity-tags, the cache request that contains an If-None-Match list of entity-tags, the cache
MAY combine the received list with a list of entity-tags from its own MAY combine the received list with a list of entity-tags from its own
stored set of responses (fresh or stale) and send the union of the stored set of responses (fresh or stale) and send the union of the
two lists as a replacement If-None-Match header field value in the two lists as a replacement If-None-Match header field value in the
forwarded request. If a stored response contains only partial forwarded request. If a stored response contains only partial
content, the cache MUST NOT include its entity-tag in the union content, the cache MUST NOT include its entity-tag in the union
unless the request is for a range that would be fully satisfied by unless the request is for a range that would be fully satisfied by
that partial stored response. If the response to the forwarded that partial stored response. If the response to the forwarded
request is 304 (Not Modified) and has an ETag field value with an request is 304 (Not Modified) and has an ETag field value with an
entity-tag that is not in the client's list, the cache MUST generate entity-tag that is not in the client's list, the cache MUST generate
a 200 (OK) response for the client by reusing its corresponding a 200 (OK) response for the client by reusing its corresponding
stored response, as updated by the 304 response metadata stored response, as updated by the 304 response metadata
(Section 4.3.4). (Section 4.3.4).
If an If-None-Match header field is not present, a request containing If an If-None-Match header field is not present, a request containing
an If-Modified-Since header field (Section 13.1.3 of [Semantics]) an If-Modified-Since header field (Section 13.1.3 of [Semantics])
indicates that the client wants to validate one or more of its own indicates that the client wants to validate one or more of its own
stored responses by modification date. A cache recipient SHOULD stored responses by modification date.
generate a 304 (Not Modified) response (using the metadata of the
selected stored response) if one of the following cases is true:
1. the selected stored response has a Last-Modified field value that
is earlier than or equal to the conditional timestamp;
2. no Last-Modified header field is present in the selected stored
response, but it has a Date field value that is earlier than or
equal to the conditional timestamp; or,
3. neither Last-Modified nor Date is present in the selected stored If a request contains an If-Modified-Since header field and the Last-
response, but the cache recorded it as having been received at a Modified header field is not present in a selected stored response, a
time earlier than or equal to the conditional timestamp. cache SHOULD use the stored response's Date field value (or, if no
Date field is present, the time that the stored response was
received) to evaluate the conditional.
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 o 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 with a payload body) indicates that o A full response (i.e., one containing content) indicates that none
none of the stored responses nominated in the conditional request of the stored responses nominated in the conditional request is
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 o 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 a _strong validator_ (see o If the new response contains one or more _strong validators_ (see
Section 8.9.1 of [Semantics]), then that strong validator Section 8.8.1 of [Semantics]), then each of those strong
identifies the selected representation for update. All the stored validators identify the selected representation for update. All
responses with the same strong validator are identified for the stored responses with one of those same strong validators are
update. If none of the stored responses contain the same strong identified for update. If none of the stored responses contain at
validator, then the cache MUST NOT use the new response to update least one of the same strong validators, then the cache MUST NOT
any stored responses. use the new response to update any stored responses.
o If the new response contains a _weak validator_ and that validator o If the new response contains no strong validators but does contain
corresponds to one of the cache's stored responses, then the most one or more _weak validators_, and those validators correspond to
recent of those matching stored responses is identified for one of the cache's stored responses, then the most recent of those
update. matching stored responses is identified for update.
o If the new response does not include any form of validator (such o 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.
4.3.5. Freshening Responses with HEAD 4.3.5. Freshening Responses with HEAD
A response to the HEAD method is identical to what an equivalent A response to the HEAD method is identical to what an equivalent
request made with a GET would have been, except it lacks payload request made with a GET would have been, without sending the content.
data. This property of HEAD responses can be used to invalidate or This property of HEAD responses can be used to invalidate or update a
update a cached GET response if the more efficient conditional GET cached GET response if the more efficient conditional GET request
request mechanism is not available (due to no validators being mechanism is not available (due to no validators being present in the
present in the stored response) or if transmission of the payload stored response) or if transmission of the content is not desired
data is not desired even if it has changed. even if it has changed.
When a cache makes an inbound HEAD request for a target URI and When a cache makes an inbound HEAD request for a target URI and
receives a 200 (OK) response, the cache SHOULD update or invalidate receives a 200 (OK) response, the cache SHOULD update or invalidate
each of its stored GET responses that could have been selected for each of its stored GET responses that could have been selected for
that request (see Section 4.1). that request (see Section 4.1).
For each of the stored responses that could have been selected, if For each of the stored responses that could have been selected, if
the stored response and HEAD response have matching values for any the stored response and HEAD response have matching values for any
received validator fields (ETag and Last-Modified) and, if the HEAD received validator fields (ETag and Last-Modified) and, if the HEAD
response has a Content-Length header field, the value of Content- response has a Content-Length header field, the value of Content-
skipping to change at page 23, line 45 skipping to change at page 23, line 33
encountering a message with multiple Age field lines SHOULD use the encountering a message with multiple Age field lines SHOULD use the
first field line, discarding subsequent ones. first field line, discarding subsequent ones.
If the field value (after discarding additional lines, as per above) If the field value (after discarding additional lines, as per above)
is invalid (e.g., it contains a list or something other than a non- is invalid (e.g., it contains a list or something other than a non-
negative integer), a cache SHOULD consider the response to be stale. negative integer), a cache SHOULD consider the response to be stale.
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, since the response might have been received from an contacted.
HTTP/1.0 cache that does not implement Age.
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
unidirectional in that the presence of a directive in a request does unidirectional in that the presence of a directive in a request does
not imply that the same directive is present in the response, or to not imply that the same directive is present in the response, or to
be repeated in it. be repeated in it.
See Section 5.2.3 for information about how Cache-Control directives See Section 5.2.3 for information about how Cache-Control directives
defined elsewhere are handled. defined elsewhere are handled.
| *Note:* Some HTTP/1.0 caches might not implement Cache-Control.
A proxy, whether or not it implements a cache, MUST pass cache A proxy, whether or not it implements a cache, MUST pass cache
directives through in forwarded messages, regardless of their directives through in forwarded messages, regardless of their
significance to that application, since the directives might apply to significance to that application, since the directives might apply to
all recipients along the request/response chain. It is not possible all recipients along the request/response chain. It is not possible
to target a directive to a specific cache. to target a directive to a specific cache.
Cache directives are identified by a token, to be compared case- Cache directives are identified by a token, to be compared case-
insensitively, and have an optional argument that can use both token insensitively, and have an optional argument that can use both token
and quoted-string syntax. For the directives defined below that and quoted-string syntax. For the directives defined below that
define arguments, recipients ought to accept both forms, even if a define arguments, recipients ought to accept both forms, even if a
skipping to change at page 26, line 15 skipping to change at page 25, line 41
5.2.1.5. no-store 5.2.1.5. no-store
The "no-store" request directive indicates that a cache MUST NOT The "no-store" request directive indicates that a cache MUST NOT
store any part of either this request or any response to it. This store any part of either this request or any response to it. This
directive applies to both private and shared caches. "MUST NOT 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 ensuring This directive is _not_ a reliable or sufficient mechanism for
privacy. In particular, malicious or compromised caches might not ensuring privacy. In particular, malicious or compromised caches
recognize or obey this directive, and communications networks might might not recognize or obey this directive, and communications
be vulnerable to eavesdropping. networks might be vulnerable to eavesdropping.
Note that if a request containing this directive is satisfied from a Note that if a request containing this directive is satisfied from a
cache, the no-store request directive does not apply to the already cache, the no-store request directive does not apply to the already
stored response. stored response.
5.2.1.6. no-transform 5.2.1.6. no-transform
The "no-transform" request directive indicates that the client is The "no-transform" request directive indicates that the client is
asking for intermediaries to avoid transforming the payload, as asking for intermediaries to avoid transforming the content, as
defined in Section 7.7 of [Semantics]. defined in Section 7.7 of [Semantics].
5.2.1.7. only-if-cached 5.2.1.7. only-if-cached
The "only-if-cached" request directive indicates that the client only The "only-if-cached" request directive indicates that the client only
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.
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5.2.2.1. must-revalidate 5.2.2.1. 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 obey the must-revalidate directive; in particular, if a cache MUST NOT ignore the must-revalidate directive; in particular,
cache is disconnected, the cache MUST generate a 504 (Gateway if a cache is disconnected, the cache MUST generate an error response
Timeout) response rather than reuse the stale response. rather than reuse the stale response. The generated status code
SHOULD be 504 (Gateway Timeout) unless another error status code is
more applicable.
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 on the representation could cause if failure to validate a request could cause incorrect operation,
incorrect operation, such as a silently unexecuted financial such as a silently unexecuted financial transaction.
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 3.4). revalidation (Section 3.5).
5.2.2.2. must-understand 5.2.2.2. 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. A cache MUST NOT store a response for that response's status code.
containing the must-understand directive if the cache does not
understand the response status code. Responses containing "must-understand" SHOULD also contain the "no-
store" directive; caches that implement "must-understand" SHOULD
ignore the "no-store" directive in responses that contain both
directives and a status code that the cache understands and conforms
to any related caching requirements.
5.2.2.3. no-cache 5.2.2.3. 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
skipping to change at page 28, line 12 skipping to change at page 27, line 43
certain header fields in a response, while still allowing caching of certain header fields in a response, while still allowing caching of
the rest of the response. the rest of the response.
The field names given are not limited to the set of header fields The field names given are not limited to the set of header fields
defined by this specification. Field names are case-insensitive. defined by this specification. Field names are case-insensitive.
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:* Although it has been back-ported to many | *Note:* The qualified form of the directive is often handled by
| implementations, some HTTP/1.0 caches will not recognize or | caches as if an unqualified no-cache directive was received;
| obey this directive. Also, the qualified form of the directive | i.e., the special handling for the qualified form is not widely
| is often handled by caches as if an unqualified no-cache | implemented.
| directive was received; i.e., the special handling for the
| qualified form is not widely implemented.
5.2.2.4. no-store 5.2.2.4. 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 ensuring This directive is _not_ a reliable or sufficient mechanism for
privacy. In particular, malicious or compromised caches might not ensuring privacy. In particular, malicious or compromised caches
recognize or obey this directive, and communications networks might might not recognize or obey this directive, and communications
be vulnerable to eavesdropping. networks might be vulnerable to eavesdropping.
Note that the "must-understand" cache directive overrides "no-store"
in certain circumstances; see Section 5.2.2.2.
5.2.2.5. no-transform 5.2.2.5. 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
payload, as defined in Section 7.7 of [Semantics]. content, as defined in Section 7.7 of [Semantics].
5.2.2.6. public 5.2.2.6. public
The "public" response directive indicates that a cache MAY store the The "public" response directive indicates that a cache MAY store the
response even if it would otherwise be prohibited, subject to the response even if it would otherwise be prohibited, subject to the
constraints defined in Section 3. In other words, public explicitly constraints defined in Section 3. In other words, public explicitly
marks the response as cacheable. For example, public permits a marks the response as cacheable. For example, public permits a
shared cache to reuse a response to a request containing an shared cache to reuse a response to a request containing an
Authorization header field (Section 3.4). Authorization header field (Section 3.5).
Note that it is unnecessary to add the public directive to a response Note that it is unnecessary to add the public directive to a response
that is already cacheable according to Section 3. that is already cacheable according to Section 3.
If a response with the public directive has no explicit freshness If a response with the public directive has no explicit freshness
information, it is heuristically cacheable (Section 4.2.2). information, it is heuristically cacheable (Section 4.2.2).
5.2.2.7. private 5.2.2.7. private
Argument syntax: Argument syntax:
skipping to change at page 30, line 42 skipping to change at page 30, line 23
specified by either the max-age directive or the Expires header specified by either the max-age directive or the Expires header
field. field.
The s-maxage directive incorporates the proxy-revalidate The s-maxage directive incorporates the proxy-revalidate
(Section 5.2.2.8) response directive's semantics for a shared cache. (Section 5.2.2.8) response directive's semantics for a shared cache.
A shared cache MUST NOT reuse a stale response with s-maxage to A shared cache MUST NOT reuse a stale response with s-maxage 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. This directive also permits a the origin, as defined by Section 4.3. This directive also permits a
shared cache to reuse a response to a request containing an shared cache to reuse a response to a request containing an
Authorization header field, subject to the above requirements on Authorization header field, subject to the above requirements on
maximum age and revalidation (Section 3.4). maximum age and revalidation (Section 3.5).
This directive uses the token form of the argument syntax: e.g., This directive uses the token form of the argument syntax: e.g.,
's-maxage=10' not 's-maxage="10"'. A sender MUST NOT generate the 's-maxage=10' not 's-maxage="10"'. A sender MUST NOT generate the
quoted-string form. quoted-string form.
5.2.3. Cache Control Extensions 5.2.3. Cache Control Extensions
The Cache-Control header field can be extended through the use of one The Cache-Control header field can be extended through the use of one
or more cache-extension tokens, each with an optional value. A cache or more cache-extension tokens, each with an optional value. A cache
MUST ignore unrecognized cache directives. MUST ignore unrecognized cache directives.
skipping to change at page 34, line 41 skipping to change at page 34, line 24
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 shared cache.
Such "cache poisoning" attacks use the cache to distribute a Such "cache poisoning" attacks use the cache to distribute malicious
malicious payload to many clients, and are especially effective when content to many clients, and are especially effective when an
an attacker can use implementation flaws, elevated privileges, or attacker can use implementation flaws, elevated privileges, or other
other techniques to insert such a response into a cache. techniques to insert such a response into a cache.
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 37, line 8 skipping to change at page 36, line 38
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-13, December 14, 2020, ietf-httpbis-messaging-14, January 13, 2021,
<https://tools.ietf.org/html/draft-ietf-httpbis-messaging- <https://tools.ietf.org/html/draft-ietf-httpbis-messaging-
13>. 14>.
[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 33 skipping to change at page 37, line 16
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-13, December 14, 2020, draft-ietf-httpbis-semantics-14, January 13, 2021,
<https://tools.ietf.org/html/draft-ietf-httpbis-semantics- <https://tools.ietf.org/html/draft-ietf-httpbis-semantics-
13>. 14>.
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 40, line 44 skipping to change at page 40, line 31
o In Section 4.3.1, clarify the source of validators in conditional o 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 o 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 o 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 3.4, remove a spurious note o 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 o 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 o 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- o 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 o 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/ o Deprecate Pragma (<https://github.com/httpwg/http-core/
issues/140>) issues/140>)
o In Section 3.4 and Section 5.2.2, note effect of some directives o 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 o 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
skipping to change at page 44, line 25 skipping to change at page 44, line 12
o In Section 1.2, remove unused core ABNF rules o 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 o Changed to using "payload data" when defining requirements about
the data being conveyed within a message, instead of the terms the data being conveyed within a message, instead of the terms
"payload body" or "response body" or "representation body", since "payload body" or "response body" or "representation body", since
they often get confused with the HTTP/1.1 message body (which they often get confused with the HTTP/1.1 message body (which
includes transfer coding) (<https://github.com/httpwg/http-core/ includes transfer coding) (<https://github.com/httpwg/http-core/
issues/553>) issues/553>)
C.15. Since draft-ietf-httpbis-cache-13
o In Section 5.2.2.1, clarify requirements around generating an
error response (<https://github.com/httpwg/http-core/issues/608>)
o Changed to using "content" instead of "payload" or "payload data"
to avoid confusion with the payload of version-specific messaging
frames (<https://github.com/httpwg/http-core/issues/654>)
o In Section 4.3.4, clarify how multiple validators are handled
(<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
about very old HTTP/1.0 behaviours (<https://github.com/httpwg/
http-core/issues/660>)
o In Section 5.2.2.2, modify operation to be more backwards-
compatible with existing implementations
(<https://github.com/httpwg/http-core/issues/661>)
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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