| draft-ietf-httpbis-p6-cache-10.txt |  | draft-ietf-httpbis-p6-cache-11.txt |
--- | --- | --- | --- | ---
| HTTPbis Working Group R. Fielding, Ed. |  | HTTPbis Working Group R. Fielding, Ed. |
| Internet-Draft Day Software |  | Internet-Draft Day Software |
| Obsoletes: 2616 (if approved) J. Gettys |  | Obsoletes: 2616 (if approved) J. Gettys |
| Intended status: Standards Track Alcatel-Lucent |  | Intended status: Standards Track Alcatel-Lucent |
| Expires: January 13, 2011 J. Mogul |  | Expires: February 5, 2011 J. Mogul |
| HP |  | HP |
| H. Frystyk |  | H. Frystyk |
| Microsoft |  | Microsoft |
| L. Masinter |  | L. Masinter |
| Adobe Systems |  | Adobe Systems |
| P. Leach |  | P. Leach |
| Microsoft |  | Microsoft |
| T. Berners-Lee |  | T. Berners-Lee |
| W3C/MIT |  | W3C/MIT |
| Y. Lafon, Ed. |  | Y. Lafon, Ed. |
| W3C |  | W3C |
| M. Nottingham, Ed. |  | M. Nottingham, Ed. |
| J. Reschke, Ed. |  | J. Reschke, Ed. |
| greenbytes |  | greenbytes |
| July 12, 2010 |  | August 4, 2010 |
| HTTP/1.1, part 6: Caching |  | HTTP/1.1, part 6: Caching |
| draft-ietf-httpbis-p6-cache-10 |  | draft-ietf-httpbis-p6-cache-11 |
| Abstract |  | Abstract |
| The Hypertext Transfer Protocol (HTTP) is an application-level |  | The Hypertext Transfer Protocol (HTTP) is an application-level |
| protocol for distributed, collaborative, hypermedia information |  | protocol for distributed, collaborative, hypermedia information |
| systems. This document is Part 6 of the seven-part specification |  | systems. This document is Part 6 of the seven-part specification |
| that defines the protocol referred to as "HTTP/1.1" and, taken |  | that defines the protocol referred to as "HTTP/1.1" and, taken |
| together, obsoletes RFC 2616. Part 6 defines requirements on HTTP |  | together, obsoletes RFC 2616. Part 6 defines requirements on HTTP |
| caches and the associated header fields that control cache behavior |  | caches and the associated header fields that control cache behavior |
| or indicate cacheable response messages. |  | or indicate cacheable response messages. |
| Editorial Note (To be removed by RFC Editor) |  | Editorial Note (To be removed by RFC Editor) |
| Discussion of this draft should take place on the HTTPBIS working |  | Discussion of this draft should take place on the HTTPBIS working |
| group mailing list (ietf-http-wg@w3.org). The current issues list is |  | group mailing list (ietf-http-wg@w3.org). The current issues list is |
| at <http://tools.ietf.org/wg/httpbis/trac/report/3> and related |  | at <http://tools.ietf.org/wg/httpbis/trac/report/3> and related |
| documents (including fancy diffs) can be found at |  | documents (including fancy diffs) can be found at |
| <http://tools.ietf.org/wg/httpbis/>. |  | <http://tools.ietf.org/wg/httpbis/>. |
| The changes in this draft are summarized in Appendix C.11. |  | The changes in this draft are summarized in Appendix C.12. |
| 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 http://datatracker.ietf.org/drafts/current/. |  | Drafts is at http://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 January 13, 2011. |  | This Internet-Draft will expire on February 5, 2011. |
| Copyright Notice |  | Copyright Notice |
| Copyright (c) 2010 IETF Trust and the persons identified as the |  | Copyright (c) 2010 IETF Trust and the persons identified as the |
| document authors. All rights reserved. |  | document authors. All rights reserved. |
| This document is subject to BCP 78 and the IETF Trust's Legal |  | This document is subject to BCP 78 and the IETF Trust's Legal |
| Provisions Relating to IETF Documents |  | Provisions Relating to IETF Documents |
| (http://trustee.ietf.org/license-info) in effect on the date of |  | (http://trustee.ietf.org/license-info) in effect on the date of |
| publication of this document. Please review these documents |  | publication of this document. Please review these documents |
| skipping to change at page 3, line 24 |  | skipping to change at page 3, line 24 |
| 2.3.2. Calculating Age . . . . . . . . . . . . . . . . . . . 12 |  | 2.3.2. Calculating Age . . . . . . . . . . . . . . . . . . . 12 |
| 2.3.3. Serving Stale Responses . . . . . . . . . . . . . . . 13 |  | 2.3.3. Serving Stale Responses . . . . . . . . . . . . . . . 13 |
| 2.4. Validation Model . . . . . . . . . . . . . . . . . . . . . 14 |  | 2.4. Validation Model . . . . . . . . . . . . . . . . . . . . . 14 |
| 2.5. Request Methods that Invalidate . . . . . . . . . . . . . 14 |  | 2.5. Request Methods that Invalidate . . . . . . . . . . . . . 14 |
| 2.6. Shared Caching of Authenticated Responses . . . . . . . . 15 |  | 2.6. Shared Caching of Authenticated Responses . . . . . . . . 15 |
| 2.7. Caching Negotiated Responses . . . . . . . . . . . . . . . 16 |  | 2.7. Caching Negotiated Responses . . . . . . . . . . . . . . . 16 |
| 2.8. Combining Responses . . . . . . . . . . . . . . . . . . . 16 |  | 2.8. Combining Responses . . . . . . . . . . . . . . . . . . . 16 |
| 3. Header Field Definitions . . . . . . . . . . . . . . . . . . . 17 |  | 3. Header Field Definitions . . . . . . . . . . . . . . . . . . . 17 |
| 3.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 |  | 3.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 |
| 3.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 18 |  | 3.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 18 |
| 3.2.1. Request Cache-Control Directives . . . . . . . . . . . 19 |  | 3.2.1. Request Cache-Control Directives . . . . . . . . . . . 18 |
| 3.2.2. Response Cache-Control Directives . . . . . . . . . . 20 |  | 3.2.2. Response Cache-Control Directives . . . . . . . . . . 20 |
| 3.2.3. Cache Control Extensions . . . . . . . . . . . . . . . 23 |  | 3.2.3. Cache Control Extensions . . . . . . . . . . . . . . . 22 |
| 3.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 24 |  | 3.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 24 |
| 3.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 25 |  | 3.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 24 |
| 3.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 |  | 3.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 |
| 3.6. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 26 |  | 3.6. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 26 |
| 4. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 29 |  | 4. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 28 |
| 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 |  | 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 |
| 5.1. Cache Directive Registry . . . . . . . . . . . . . . . . . 29 |  | 5.1. Cache Directive Registry . . . . . . . . . . . . . . . . . 28 |
| 5.2. Message Header Registration . . . . . . . . . . . . . . . 30 |  | 5.2. Header Field Registration . . . . . . . . . . . . . . . . 29 |
| 6. Security Considerations . . . . . . . . . . . . . . . . . . . 30 |  | 6. Security Considerations . . . . . . . . . . . . . . . . . . . 29 |
| 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30 |  | 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30 |
| 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30 |  | 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30 |
| 8.1. Normative References . . . . . . . . . . . . . . . . . . . 30 |  | 8.1. Normative References . . . . . . . . . . . . . . . . . . . 30 |
| 8.2. Informative References . . . . . . . . . . . . . . . . . . 31 |  | 8.2. Informative References . . . . . . . . . . . . . . . . . . 31 |
| Appendix A. Compatibility with Previous Versions . . . . . . . . 32 |  | Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 31 |
| A.1. Changes from RFC 2068 . . . . . . . . . . . . . . . . . . 32 |  | Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 31 |
| A.2. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 32 |  |  |
| Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 32 |  |  |
| Appendix C. Change Log (to be removed by RFC Editor before |  | Appendix C. Change Log (to be removed by RFC Editor before |
| publication) . . . . . . . . . . . . . . . . . . . . 34 |  | publication) . . . . . . . . . . . . . . . . . . . . 33 |
| C.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 34 |  | C.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 33 |
| C.2. Since draft-ietf-httpbis-p6-cache-00 . . . . . . . . . . . 34 |  | C.2. Since draft-ietf-httpbis-p6-cache-00 . . . . . . . . . . . 33 |
| C.3. Since draft-ietf-httpbis-p6-cache-01 . . . . . . . . . . . 35 |  | C.3. Since draft-ietf-httpbis-p6-cache-01 . . . . . . . . . . . 34 |
| C.4. Since draft-ietf-httpbis-p6-cache-02 . . . . . . . . . . . 35 |  | C.4. Since draft-ietf-httpbis-p6-cache-02 . . . . . . . . . . . 34 |
| C.5. Since draft-ietf-httpbis-p6-cache-03 . . . . . . . . . . . 35 |  | C.5. Since draft-ietf-httpbis-p6-cache-03 . . . . . . . . . . . 34 |
| C.6. Since draft-ietf-httpbis-p6-cache-04 . . . . . . . . . . . 35 |  | C.6. Since draft-ietf-httpbis-p6-cache-04 . . . . . . . . . . . 34 |
| C.7. Since draft-ietf-httpbis-p6-cache-05 . . . . . . . . . . . 36 |  | C.7. Since draft-ietf-httpbis-p6-cache-05 . . . . . . . . . . . 35 |
| C.8. Since draft-ietf-httpbis-p6-cache-06 . . . . . . . . . . . 36 |  | C.8. Since draft-ietf-httpbis-p6-cache-06 . . . . . . . . . . . 35 |
| C.9. Since draft-ietf-httpbis-p6-cache-07 . . . . . . . . . . . 36 |  | C.9. Since draft-ietf-httpbis-p6-cache-07 . . . . . . . . . . . 35 |
| C.10. Since draft-ietf-httpbis-p6-cache-08 . . . . . . . . . . . 37 |  | C.10. Since draft-ietf-httpbis-p6-cache-08 . . . . . . . . . . . 36 |
| C.11. Since draft-ietf-httpbis-p6-cache-09 . . . . . . . . . . . 37 |  | C.11. Since draft-ietf-httpbis-p6-cache-09 . . . . . . . . . . . 36 |
| Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 |  | C.12. Since draft-ietf-httpbis-p6-cache-10 . . . . . . . . . . . 37 |
|  |  | Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 |
| 1. Introduction |  | 1. Introduction |
| HTTP is typically used for distributed information systems, where |  | HTTP is typically used for distributed information systems, where |
| performance can be improved by the use of response caches. This |  | performance can be improved by the use of response caches. This |
| document defines aspects of HTTP/1.1 related to caching and reusing |  | document defines aspects of HTTP/1.1 related to caching and reusing |
| response messages. |  | response messages. |
| 1.1. Purpose |  | 1.1. Purpose |
| An HTTP cache is a local store of response messages and the subsystem |  | An HTTP cache is a local store of response messages and the subsystem |
| that controls its message storage, retrieval, and deletion. A cache |  | that controls its message storage, retrieval, and deletion. A cache |
| stores cacheable responses in order to reduce the response time and |  | stores cacheable responses in order to reduce the response time and |
| network bandwidth consumption on future, equivalent requests. Any |  | network bandwidth consumption on future, equivalent requests. Any |
| client or server may include a cache, though a cache cannot be used |  | client or server MAY employ a cache, though a cache cannot be used by |
| by a server that is acting as a tunnel. |  | a server that is acting as a tunnel. |
| Caching would be useless if it did not significantly improve |  | Caching would be useless if it did not significantly improve |
| performance. The goal of caching in HTTP/1.1 is to reuse a prior |  | performance. The goal of caching in HTTP/1.1 is to reuse a prior |
| response message to satisfy a current request. In some cases, a |  | response message to satisfy a current request. In some cases, a |
| stored response can be reused without the need for a network request, |  | stored response can be reused without the need for a network request, |
| reducing latency and network round-trips; a "freshness" mechanism is |  | reducing latency and network round-trips; a "freshness" mechanism is |
| used for this purpose (see Section 2.3). Even when a new request is |  | used for this purpose (see Section 2.3). Even when a new request is |
| required, it is often possible to reuse all or parts of the payload |  | required, it is often possible to reuse all or parts of the payload |
| of a prior response to satisfy the request, thereby reducing network |  | of a prior response to satisfy the request, thereby reducing network |
| bandwidth usage; a "validation" mechanism is used for this purpose |  | bandwidth usage; a "validation" mechanism is used for this purpose |
| skipping to change at page 5, line 41 |  | skipping to change at page 5, line 41 |
| 1.2. Terminology |  | 1.2. Terminology |
| This specification uses a number of terms to refer to the roles |  | This specification uses a number of terms to refer to the roles |
| played by participants in, and objects of, HTTP caching. |  | played by participants in, and objects of, HTTP caching. |
| cacheable |  | cacheable |
| A response is cacheable if a cache is allowed to store a copy of |  | A response is cacheable if a cache is allowed to store a copy of |
| the response message for use in answering subsequent requests. |  | the response message for use in answering subsequent requests. |
| Even when a response is cacheable, there may be additional |  | Even when a response is cacheable, there might be additional |
| constraints on whether a cache can use the cached copy to satisfy |  | constraints on whether a cache can use the cached copy to satisfy |
| a particular request. |  | a particular request. |
| explicit expiration time |  | explicit expiration time |
| The time at which the origin server intends that an entity should |  | The time at which the origin server intends that a representation |
| no longer be returned by a cache without further validation. |  | no longer be returned by a cache without further validation. |
| heuristic expiration time |  | heuristic expiration time |
| An expiration time assigned by a cache when no explicit expiration |  | An expiration time assigned by a cache when no explicit expiration |
| time is available. |  | time is available. |
| age |  | age |
| The age of a response is the time since it was sent by, or |  | The age of a response is the time since it was sent by, or |
| skipping to change at page 6, line 37 |  | skipping to change at page 6, line 37 |
| A response is fresh if its age has not yet exceeded its freshness |  | A response is fresh if its age has not yet exceeded its freshness |
| lifetime. |  | lifetime. |
| stale |  | stale |
| A response is stale if its age has passed its freshness lifetime |  | A response is stale if its age has passed its freshness lifetime |
| (either explicit or heuristic). |  | (either explicit or heuristic). |
| validator |  | validator |
| A protocol element (e.g., an entity tag or a Last-Modified time) |  | A protocol element (e.g., an entity-tag or a Last-Modified time) |
| that is used to find out whether a stored response is an |  | that is used to find out whether a stored response has an |
| equivalent copy of an entity. |  | equivalent copy of a representation. |
| shared cache |  | shared cache |
| A cache that is accessible to more than one user. A non-shared |  | A cache that is accessible to more than one user. A non-shared |
| cache is dedicated to a single user. |  | cache is dedicated to a single user. |
| 1.3. Requirements |  | 1.3. Requirements |
| The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", |  | The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", |
| "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this |  | "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this |
| skipping to change at page 9, line 14 |  | skipping to change at page 9, line 14 |
| status code. |  | status code. |
| A cache that does not support the Range and Content-Range headers |  | A cache that does not support the Range and Content-Range headers |
| MUST NOT store incomplete or partial responses. |  | MUST NOT store incomplete or partial responses. |
| 2.2. Constructing Responses from Caches |  | 2.2. Constructing Responses from Caches |
| For a presented request, a cache MUST NOT return a stored response, |  | For a presented request, a cache MUST NOT return a stored response, |
| unless: |  | unless: |
| o The presented Effective Request URI (Section 4.3 of [Part1]) and |  | o The presented effective request URI (Section 4.3 of [Part1]) and |
| that of the stored response match, and |  | that of 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 |
| o selecting request-headers nominated by the stored response (if |  | o selecting request-headers nominated by the stored response (if |
| any) match those presented (see Section 2.7), and |  | any) match those presented (see Section 2.7), and |
| o the presented request and stored response are free from directives |  | o the presented request and stored response are free from directives |
| that would prevent its use (see Section 3.2 and Section 3.4), and |  | that would prevent its use (see Section 3.2 and Section 3.4), and |
| o the stored response is either: |  | o the stored response is either: |
| * fresh (see Section 2.3), or |  | * fresh (see Section 2.3), or |
| * allowed to be served stale (see Section 2.3.3), or |  | * allowed to be served stale (see Section 2.3.3), or |
| * successfully validated (see Section 2.4). |  | * successfully validated (see Section 2.4). |
| [[TODO-method-cacheability: define method cacheability for GET, HEAD |  | When a stored response is used to satisfy a request without |
| and POST in p2-semantics.]] |  | validation, caches MUST include a single Age header field |
|  |  | (Section 3.1) in the response with a value equal to the stored |
| When a stored response is used to satisfy a request, caches MUST |  | response's current_age; see Section 2.3.2. |
| include a single Age header field (Section 3.1) in the response with |  |  |
| a value equal to the stored response's current_age; see |  |  |
| Section 2.3.2. [[DISCUSS-includes-validated: this currently includes |  |  |
| successfully validated responses.]] |  |  |
| Requests with methods that are unsafe (Section 7.1.1 of [Part2]) MUST |  | Requests with methods that are unsafe (Section 7.1.1 of [Part2]) MUST |
| be written through the cache to the origin server; i.e., a cache must |  | be written through the cache to the origin server; i.e., a cache must |
| not reply to such a request before having forwarded the request and |  | not reply to such a request before having forwarded the request and |
| having received a corresponding response. |  | 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 2.5. |  | responses; see Section 2.5. |
| Caches MUST use the most recent response (as determined by the Date |  | Caches MUST use the most recent response (as determined by the Date |
| skipping to change at page 10, line 19 |  | skipping to change at page 10, line 16 |
| When a response is "fresh" in the cache, it can be used to satisfy |  | When a response is "fresh" in the cache, it can be used to satisfy |
| subsequent requests without contacting the origin server, thereby |  | subsequent requests without contacting the origin server, thereby |
| improving efficiency. |  | improving 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 (Section 3.3) or the max-age response cache |  | either the Expires header (Section 3.3) or the max-age response cache |
| directive (Section 3.2.2). Generally, origin servers will assign |  | directive (Section 3.2.2). 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 |
| entity is not likely to change in a semantically significant way |  | representation is not likely to change in a semantically significant |
| before the expiration time is reached. |  | way before the expiration time is reached. |
| If an origin server wishes to force a cache to validate every |  | If an origin server wishes to force a cache to validate every |
| request, it can assign an explicit expiration time in the past. This |  | request, it can assign an explicit expiration time in the past to |
| means that the response is always stale, so that caches should |  | indicate that the response is already stale. Compliant caches will |
| validate it before using it for subsequent requests. [[TODO- |  | validate the cached response before reusing it for subsequent |
| response-stale: This wording may cause confusion, because the |  | requests. |
| response may still be served stale.]] |  |  |
| Since origin servers do not always provide explicit expiration times, |  | Since origin servers do not always provide explicit expiration times, |
| HTTP caches may also assign heuristic expiration times when they are |  | HTTP caches MAY assign heuristic expiration times when explicit times |
| not specified, employing algorithms that use other header values |  | are not specified, employing algorithms that use other header values |
| (such as the Last-Modified time) to estimate a plausible expiration |  | (such as the Last-Modified time) to estimate a plausible expiration |
| time. The HTTP/1.1 specification does not provide specific |  | time. The HTTP/1.1 specification does not provide specific |
| algorithms, but does impose worst-case constraints on their results. |  | algorithms, but does impose worst-case constraints on their results. |
| The calculation to determine if a response is fresh is: |  | The calculation to determine if a response is fresh is: |
| response_is_fresh = (freshness_lifetime > current_age) |  | response_is_fresh = (freshness_lifetime > current_age) |
| The freshness_lifetime is defined in Section 2.3.1; the current_age |  | The freshness_lifetime is defined in Section 2.3.1; the current_age |
| is defined in Section 2.3.2. |  | is defined in Section 2.3.2. |
| Additionally, clients may need to influence freshness calculation. |  | Additionally, clients might need to influence freshness calculation. |
| They can do this using several request cache directives, with the |  | They can do this using several request cache directives, with the |
| effect of either increasing or loosening constraints on freshness. |  | effect of either increasing or loosening constraints on freshness. |
| See Section 3.2.1. |  | See Section 3.2.1. |
| [[ISSUE-no-req-for-directives: there are not requirements directly |  | [[ISSUE-no-req-for-directives: there are not requirements directly |
| applying to cache-request-directives and freshness.]] |  | applying to cache-request-directives and freshness.]] |
| Note that freshness applies only to cache operation; it cannot be |  | Note that freshness applies only to cache operation; it cannot be |
| used to force a user agent to refresh its display or reload a |  | used to force a user agent to refresh its display or reload a |
| resource. See Section 4 for an explanation of the difference between |  | resource. See Section 4 for an explanation of the difference between |
| skipping to change at page 11, line 32 |  | skipping to change at page 11, line 29 |
| 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 2.3.1.1. |  | Section 2.3.1.1. |
| 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. |
| 2.3.1.1. Calculating Heuristic Freshness |  | 2.3.1.1. Calculating Heuristic Freshness |
| If no explicit expiration time is present in a stored response that |  | If no explicit expiration time is present in a stored response that |
| has a status code of 200, 203, 206, 300, 301 or 410, a heuristic |  | has a status code whose definition allows heuristic freshness to be |
| expiration time can be calculated. Heuristics MUST NOT be used for |  | used (including the following in Section 8 of [Part2]: 200, 203, 206, |
| other response status codes. |  | 300, 301 and 410), a heuristic expiration time MAY be calculated. |
|  |  | Heuristics MUST NOT be used for response status codes that do not |
|  |  | explicitly allow it. |
| When a heuristic is used to calculate freshness lifetime, the cache |  | When a heuristic is used to calculate freshness lifetime, the cache |
| SHOULD attach a Warning header with a 113 warn-code to the response |  | SHOULD attach a Warning header with a 113 warn-code to the response |
| if its current_age is more than 24 hours and such a warning is not |  | if its current_age is more than 24 hours and such a warning is not |
| already present. |  | already present. |
| Also, if the response has a Last-Modified header (Section 6.6 of |  | Also, if the response has a Last-Modified header (Section 6.6 of |
| [Part4]), the heuristic expiration value SHOULD be no more than some |  | [Part4]), the heuristic expiration value SHOULD be no more than some |
| fraction of the interval since that time. A typical setting of this |  | fraction of the interval since that time. A typical setting of this |
| fraction might be 10%. |  | fraction might be 10%. |
| skipping to change at page 14, line 39 |  | skipping to change at page 14, line 39 |
| requested URI, if present. However, if any of the stored responses |  | requested URI, if present. However, if any of the stored responses |
| contains only partial content, its entity-tag SHOULD NOT be included |  | contains only partial content, its entity-tag SHOULD NOT be included |
| in the If-None-Match header field unless the request is for a range |  | in the If-None-Match header field unless the request is for a range |
| that would be fully satisfied by that stored response. |  | that would be fully satisfied by that stored response. |
| A 304 (Not Modified) response status code indicates that the stored |  | A 304 (Not Modified) response status code indicates that the stored |
| response can be updated and reused; see Section 2.8. |  | response can be updated and reused; see Section 2.8. |
| A full response (i.e., one with a response body) indicates that none |  | A full response (i.e., one with a response body) indicates that none |
| of the stored responses nominated in the conditional request is |  | of the stored responses nominated in the conditional request is |
| suitable. Instead, the full response is used both to satisfy the |  | suitable. Instead, the full response SHOULD be used to satisfy the |
| request and replace the stored response. [[TODO-req-missing: Should |  | request and MAY replace the stored response. |
| there be a requirement here?]] |  |  |
| If a cache receives a 5xx response while attempting to validate a |  | If a cache receives a 5xx response while attempting to validate a |
| response, it MAY either forward this response to the requesting |  | response, it MAY either forward this response to the requesting |
| client, or act as if the server failed to respond. In the latter |  | client, or act as if the server failed to respond. In the latter |
| case, it MAY return a previously stored response (see Section 2.3.3). |  | case, it MAY return a previously stored response (see Section 2.3.3). |
| 2.5. Request Methods that Invalidate |  | 2.5. Request Methods that Invalidate |
| Because unsafe methods (Section 7.1.1 of [Part2]) have the potential |  | Because unsafe methods (Section 7.1.1 of [Part2]) have the potential |
| for changing state on the origin server, intervening caches can use |  | for changing state on the origin server, intervening caches can use |
| them to keep their contents up-to-date. |  | them to keep their contents up-to-date. |
| The following HTTP methods MUST cause a cache to invalidate the |  | The following HTTP methods MUST cause a cache to invalidate the |
| Effective Request URI (Section 4.3 of [Part1]) as well as the URI(s) |  | effective Request URI (Section 4.3 of [Part1]) as well as the URI(s) |
| in the Location and Content-Location headers (if present): |  | in the Location and Content-Location headers (if present): |
| o PUT |  | o PUT |
| o DELETE |  | o DELETE |
| o POST |  | o POST |
| An invalidation based on a URI from a Location or Content-Location |  | An invalidation based on a URI from a Location or Content-Location |
| header MUST NOT be performed if the host part of that URI differs |  | header MUST NOT be performed if the host part of that URI differs |
| from the host part in the Effective Request URI (Section 4.3 of |  | from the host part in the effective request URI (Section 4.3 of |
| [Part1]). This helps prevent denial of service attacks. |  | [Part1]). This helps prevent denial of service attacks. |
| [[TODO-def-host-part: "host part" needs to be specified better.]] |  |  |
| A cache that passes through requests for methods it does not |  | A cache that passes through requests for methods it does not |
| understand SHOULD invalidate the Effective Request URI (Section 4.3 |  | understand SHOULD invalidate the effective request URI (Section 4.3 |
| of [Part1]). |  | of [Part1]). |
| Here, "invalidate" means that the cache will either remove all stored |  | Here, "invalidate" means that the cache will either remove all stored |
| responses related to the Effective Request URI, or will mark these as |  | responses related to the effective request URI, or will mark these as |
| "invalid" and in need of a mandatory validation before they can be |  | "invalid" and in need of a mandatory validation before they can be |
| returned in response to a subsequent request. |  | returned in response to a subsequent request. |
| Note that this does not guarantee that all appropriate responses are |  | Note that this does not guarantee that all appropriate responses are |
| invalidated. For example, the request that caused the change at the |  | invalidated. For example, the request that caused the change at the |
| origin server might not have gone through the cache where a response |  | origin server might not have gone through the cache where a response |
| is stored. |  | is stored. |
| [[TODO-spec-success-invalidate: specify that only successful (2xx, |  |  |
| 3xx?) responses invalidate.]] |  |  |
| 2.6. Shared Caching of Authenticated Responses |  | 2.6. Shared Caching of Authenticated Responses |
| Shared caches MUST NOT use a cached response to a request with an |  | Shared caches MUST NOT use a cached response to a request with an |
| Authorization header (Section 3.1 of [Part7]) to satisfy any |  | Authorization header (Section 3.1 of [Part7]) to satisfy any |
| subsequent request unless a cache directive that allows such |  | subsequent request unless a cache directive that allows such |
| responses to be stored is present in the response. |  | responses to be stored is present in the response. |
| In this specification, the following Cache-Control response |  | In this specification, the following Cache-Control response |
| directives (Section 3.2.2) have such an effect: must-revalidate, |  | directives (Section 3.2.2) have such an effect: must-revalidate, |
| public, s-maxage. |  | public, s-maxage. |
| skipping to change at page 16, line 32 |  | skipping to change at page 16, line 29 |
| o combining multiple message-header fields with the same field name |  | o combining multiple message-header fields with the same field name |
| (see Section 3.2 of [Part1]) |  | (see Section 3.2 of [Part1]) |
| o normalizing both header values in a way that is known to have |  | o normalizing both header values in a way that is known to have |
| identical semantics, according to the header's specification |  | identical semantics, according to the header's specification |
| (e.g., re-ordering field values when order is not significant; |  | (e.g., re-ordering field values when order is not significant; |
| case-normalization, where values are defined to be case- |  | case-normalization, where values are defined to be case- |
| insensitive) |  | insensitive) |
| If (after any normalisation that may 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 of "*" always fails to match, and |  | A Vary header field-value of "*" always fails to match, and |
| subsequent requests to that resource can only be properly interpreted |  | subsequent requests to that resource can only be properly interpreted |
| by the origin server. |  | by the origin server. |
| The stored response with matching selecting request-headers is known |  | The stored response with matching selecting request-headers is known |
| as the selected response. |  | as the selected response. |
| If no selected response is available, the cache MAY forward the |  | If no selected response is available, the cache MAY forward the |
| presented request to the origin server in a conditional request; see |  | presented request to the origin server in a conditional request; see |
| Section 2.4. |  | Section 2.4. |
| 2.8. Combining Responses |  | 2.8. Combining Responses |
| When a cache receives a 304 (Not Modified) response or a 206 (Partial |  | When a cache receives a 304 (Not Modified) response or a 206 (Partial |
| Content) response (in this section, the "new" response"), it needs to |  | Content) response (in this section, the "new" response"), it needs to |
| created an updated response by combining the stored response with the |  | created an updated response by combining the stored response with the |
| new one, so that the updated response can be used to satisfy the |  | new one, so that the updated response can be used to satisfy the |
| request. |  | request, and potentially update the cached response. |
| If the new response contains an ETag, it identifies the stored |  | If the new response contains an ETag, it identifies the stored |
| response to use. [[TODO-mention-CL: may need language about Content- |  | response to use. [[TODO-mention-CL: might need language about |
| Location here]][[TODO-inm-mult-etags: cover case where INM with |  | Content-Location here]][[TODO-select-for-combine: Shouldn't this be |
| multiple etags was sent]] |  | the selected response?]] |
| If the status code is 206 (partial content), both the stored and new |  | If the new response's status code is 206 (partial content), both the |
| responses MUST have validators, and those validators MUST match using |  | stored and new responses MUST have validators, and those validators |
| the strong comparison function (see Section 4 of [Part4]). |  | MUST match using the strong comparison function (see Section 4 of |
| Otherwise, the responses MUST NOT be combined. |  | [Part4]). Otherwise, the responses MUST NOT be combined. |
| The stored response headers are used as those of the updated |  | The stored response headers are used as those of the updated |
| response, except that |  | response, except that |
| o any stored Warning headers with warn-code 1xx (see Section 3.6) |  | o any stored Warning headers with warn-code 1xx (see Section 3.6) |
| MUST be deleted from the stored response and the updated response. |  | MUST be deleted. |
| o any stored Warning headers with warn-code 2xx MUST be retained in |  |  |
| the stored response and the updated response. |  |  |
| o any headers provided in the new response MUST replace the |  |  |
| corresponding headers from the stored response. |  |  |
| If a header field-name in the new response matches more than one |  | o any stored Warning headers with warn-code 2xx MUST be retained. |
| header in the stored response, all such stored headers MUST be |  |  |
| replaced. |  |  |
| The updated response can [[TODO-is-req: requirement?]] be used to |  | o any other headers provided in the new response MUST replace all |
| replace the stored response in cache. In the case of a 206 response, |  | instances of the corresponding headers from the stored response. |
| the combined entity-body MAY be stored. |  |  |
| [[ISSUE-how-head: discuss how to handle HEAD updates]] |  | The updated response headers MUST be used to replace those of the |
|  |  | stored response in cache (unless the stored response is removed from |
|  |  | cache). In the case of a 206 response, the combined representation |
|  |  | MAY be stored. |
| 3. Header Field Definitions |  | 3. Header Field Definitions |
| This section defines the syntax and semantics of HTTP/1.1 header |  | This section defines the syntax and semantics of HTTP/1.1 header |
| fields related to caching. |  | fields related to caching. |
| For entity-header fields, both sender and recipient refer to either |  |  |
| the client or the server, depending on who sends and who receives the |  |  |
| entity. |  |  |
| 3.1. Age |  | 3.1. Age |
| The "Age" response-header field conveys the sender's estimate of the |  | The "Age" response-header field conveys the sender's estimate of the |
| amount of time since the response was generated or successfully |  | amount of time since the response was generated or successfully |
| validated at the origin server. Age values are calculated as |  | validated at the origin server. Age values are calculated as |
| specified in Section 2.3.2. |  | specified in Section 2.3.2. |
| Age = "Age" ":" OWS Age-v |  | Age = "Age" ":" OWS Age-v |
| Age-v = delta-seconds |  | Age-v = delta-seconds |
| skipping to change at page 18, line 18 |  | skipping to change at page 18, line 4 |
| Age-v = delta-seconds |  | Age-v = delta-seconds |
| Age field-values are non-negative integers, representing time in |  | Age field-values are non-negative integers, representing time in |
| seconds. |  | seconds. |
| delta-seconds = 1*DIGIT |  | delta-seconds = 1*DIGIT |
| If a cache receives a value larger than the largest positive integer |  | If a cache receives a value larger than the largest positive integer |
| it can represent, or if any of its age calculations overflows, it |  | it can represent, or if any of its age calculations overflows, it |
| MUST transmit an Age header with a field-value of 2147483648 (2^31). |  | MUST transmit an Age header with a field-value of 2147483648 (2^31). |
| Caches SHOULD use an arithmetic type of at least 31 bits of range. |  | Caches SHOULD use an arithmetic type of at least 31 bits of range. |
| The presence of an Age header field in a response implies that a |  | The presence of an Age header field in a response implies that a |
| response is not first-hand. However, the converse is not true, since |  | response is not first-hand. However, the converse is not true, since |
| HTTP/1.0 caches may not implement the Age header field. |  | HTTP/1.0 caches might not implement the Age header field. |
| 3.2. Cache-Control |  | 3.2. Cache-Control |
| The "Cache-Control" general-header field is used to specify |  | The "Cache-Control" general-header field is used to specify |
| directives for caches along the request/response chain. Such cache |  | directives for caches along the request/response chain. Such cache |
| directives are unidirectional in that the presence of a directive in |  | directives are unidirectional in that the presence of a directive in |
| a request does not imply that the same directive is to be given in |  | a request does not imply that the same directive is to be given in |
| the response. |  | the response. |
| HTTP/1.1 caches MUST obey the requirements of the Cache-Control |  | HTTP/1.1 caches MUST obey the requirements of the Cache-Control |
| skipping to change at page 19, line 38 |  | skipping to change at page 19, line 24 |
| 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 non-shared and shared caches. "MUST NOT |  | directive applies to both non-shared 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 |  | store the information in non-volatile storage, and MUST make a |
| best-effort attempt to remove the information from volatile |  | best-effort attempt to remove the information from volatile |
| storage as promptly as possible after forwarding it. |  | storage as promptly as possible after forwarding it. |
| This directive is NOT a reliable or sufficient mechanism for |  | This directive is NOT a reliable or sufficient mechanism for |
| ensuring privacy. In particular, malicious or compromised caches |  | ensuring privacy. In particular, malicious or compromised caches |
| might not recognize or obey this directive, and communications |  | might not recognize or obey this directive, and communications |
| networks may be vulnerable to eavesdropping. |  | networks might be vulnerable to eavesdropping. |
| max-age |  | max-age |
| The max-age request directive indicates that the client is willing |  | The max-age request directive indicates that the client is willing |
| to accept a response whose age is no greater than the specified |  | to accept a response whose age is no greater than the specified |
| time in seconds. Unless the max-stale request directive is also |  | time in seconds. Unless the max-stale request directive is also |
| present, the client is not willing to accept a stale response. |  | present, the client is not willing to accept a stale response. |
| max-stale |  | max-stale |
| The max-stale request directive indicates that the client is |  | The max-stale request directive indicates that the client is |
| willing to accept a response that has exceeded its expiration |  | willing to accept a response that has exceeded its expiration |
| time. If max-stale is assigned a value, then the client is |  | time. If max-stale is assigned a value, then the client is |
| willing to accept a response that has exceeded its expiration time |  | willing to accept a response that has exceeded its expiration time |
| by no more than the specified number of seconds. If no value is |  | by no more than the specified number of seconds. If no value is |
| assigned to max-stale, then the client is willing to accept a |  | assigned to max-stale, then the client is willing to accept a |
| stale response of any age. [[TODO-staleness: of any staleness? |  | stale response of any age. |
| --mnot]] |  |  |
| min-fresh |  | min-fresh |
| The min-fresh request directive indicates that the client is |  | The min-fresh request directive indicates that the client is |
| willing to accept a response whose freshness lifetime is no less |  | willing to accept a response whose freshness lifetime is no less |
| than its current age plus the specified time in seconds. That is, |  | than its current age plus the specified time in seconds. That is, |
| the client wants a response that will still be fresh for at least |  | the client wants a response that will still be fresh for at least |
| the specified number of seconds. |  | the specified number of seconds. |
| no-transform |  | no-transform |
| The no-transform request directive indicates that an intermediate |  | The no-transform request directive indicates that an intermediate |
| cache or proxy MUST NOT change the Content-Encoding, Content-Range |  | cache or proxy MUST NOT change the Content-Encoding, Content-Range |
| or Content-Type request headers, nor the request entity-body. |  | or Content-Type request headers, nor the request representation. |
| only-if-cached |  | only-if-cached |
| The only-if-cached request directive indicates that the client |  | The only-if-cached request directive indicates that the client |
| only wishes to return a stored response. If it receives this |  | only wishes to return a stored response. If it receives this |
| directive, a cache SHOULD either respond using a stored response |  | directive, a cache SHOULD either respond using a stored response |
| that is consistent with the other constraints of the request, or |  | that is consistent with the other constraints of the request, or |
| respond with a 504 (Gateway Timeout) status. If a group of caches |  | respond with a 504 (Gateway Timeout) status code. If a group of |
| is being operated as a unified system with good internal |  | caches is being operated as a unified system with good internal |
| connectivity, such a request MAY be forwarded within that group of |  | connectivity, such a request MAY be forwarded within that group of |
| caches. |  | caches. |
| 3.2.2. Response Cache-Control Directives |  | 3.2.2. Response Cache-Control Directives |
| cache-response-directive = |  | cache-response-directive = |
| "public" |  | "public" |
| / "private" [ "=" DQUOTE 1#field-name DQUOTE ] |  | / "private" [ "=" DQUOTE 1#field-name DQUOTE ] |
| / "no-cache" [ "=" DQUOTE 1#field-name DQUOTE ] |  | / "no-cache" [ "=" DQUOTE 1#field-name DQUOTE ] |
| / "no-store" |  | / "no-store" |
| skipping to change at page 21, line 20 |  | skipping to change at page 21, line 7 |
| is intended for a single user and MUST NOT be stored by a shared |  | is intended for a single user and MUST NOT be stored by a shared |
| cache. A private (non-shared) cache MAY store the response. |  | cache. A private (non-shared) cache MAY store the response. |
| If the private response directive specifies one or more field- |  | If the private response directive specifies one or more field- |
| names, this requirement is limited to the field-values associated |  | names, this requirement is limited to the field-values associated |
| with the listed response headers. That is, the specified field- |  | with the listed response headers. That is, the specified field- |
| names(s) MUST NOT be stored by a shared cache, whereas the |  | names(s) MUST NOT be stored by a shared cache, whereas the |
| remainder of the response message MAY be. |  | remainder of the response message MAY be. |
| Note: This usage of the word private only controls where the |  | Note: This usage of the word private only controls where the |
| response may be stored, and cannot ensure the privacy of the |  | response can be stored; it cannot ensure the privacy of the |
| message content. Also, private response directives with field- |  | message content. Also, private response directives with field- |
| names are often handled by implementations as if an unqualified |  | names are often handled by implementations as if an unqualified |
| private directive was received; i.e., the special handling for the |  | private directive was received; i.e., the special handling for the |
| qualified form is not widely implemented. |  | qualified form is not widely implemented. |
| no-cache |  | no-cache |
| The no-cache response directive indicates that the response MUST |  | The no-cache response directive indicates that the response MUST |
| NOT be used to satisfy a subsequent request without successful |  | NOT be used to satisfy a subsequent request without successful |
| validation on the origin server. This allows an origin server to |  | validation on the origin server. This allows an origin server to |
| prevent caching even by caches that have been configured to return |  | prevent a cache from using it to satisfy a request without |
|  |  | contacting it, even by caches that have been configured to return |
| stale responses. |  | stale responses. |
| If the no-cache response directive specifies one or more field- |  | If the no-cache response directive specifies one or more field- |
| names, this requirement is limited to the field-values associated |  | names, this requirement is limited to the field-values associated |
| with the listed response headers. That is, the specified field- |  | with the listed response headers. That is, the specified field- |
| name(s) MUST NOT be sent in the response to a subsequent request |  | name(s) MUST NOT be sent in the response to a subsequent request |
| without successful validation on the origin server. This allows |  | without successful validation on the origin server. This allows |
| an origin server to prevent the re-use of certain header fields in |  | an origin server to prevent the re-use of certain header fields in |
| a response, while still allowing caching of the rest of the |  | a response, while still allowing caching of the rest of the |
| response. |  | response. |
| skipping to change at page 22, line 18 |  | skipping to change at page 21, line 50 |
| store any part of either the immediate request or response. This |  | store any part of either the immediate request or response. This |
| directive applies to both non-shared and shared caches. "MUST NOT |  | directive applies to both non-shared 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 |  | store the information in non-volatile storage, and MUST make a |
| best-effort attempt to remove the information from volatile |  | best-effort attempt to remove the information from volatile |
| storage as promptly as possible after forwarding it. |  | storage as promptly as possible after forwarding it. |
| This directive is NOT a reliable or sufficient mechanism for |  | This directive is NOT a reliable or sufficient mechanism for |
| ensuring privacy. In particular, malicious or compromised caches |  | ensuring privacy. In particular, malicious or compromised caches |
| might not recognize or obey this directive, and communications |  | might not recognize or obey this directive, and communications |
| networks may be vulnerable to eavesdropping. |  | networks might be vulnerable to eavesdropping. |
| must-revalidate |  | must-revalidate |
| The must-revalidate response directive indicates that once it has |  | The must-revalidate response directive indicates that once it has |
| become stale, the response MUST NOT be used to satisfy subsequent |  | become stale, the response MUST NOT be used to satisfy subsequent |
| requests without successful validation on the origin server. |  | requests without successful validation on the origin server. |
| 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 an |  | operation for certain protocol features. In all circumstances an |
| HTTP/1.1 cache MUST obey the must-revalidate directive; in |  | HTTP/1.1 cache MUST obey the must-revalidate directive; in |
| particular, if the cache cannot reach the origin server for any |  | particular, if the cache cannot reach the origin server for any |
| reason, it MUST generate a 504 (Gateway Timeout) response. |  | reason, it MUST generate a 504 (Gateway Timeout) response. |
| Servers SHOULD send the must-revalidate directive if and only if |  | Servers SHOULD send the must-revalidate directive if and only if |
| failure to validate a request on the entity could result in |  | failure to validate a request on the representation could result |
| incorrect operation, such as a silently unexecuted financial |  | in incorrect operation, such as a silently unexecuted financial |
| transaction. |  | transaction. |
| proxy-revalidate |  | proxy-revalidate |
| The proxy-revalidate response directive has the same meaning as |  | The proxy-revalidate response directive has the same meaning as |
| the must-revalidate response directive, except that it does not |  | the must-revalidate response directive, except that it does not |
| apply to non-shared caches. |  | apply to non-shared caches. |
| max-age |  | max-age |
| skipping to change at page 23, line 12 |  | skipping to change at page 22, line 46 |
| The s-maxage response directive indicates that, in shared caches, |  | The s-maxage response directive indicates that, in shared caches, |
| the maximum age specified by this directive overrides the maximum |  | the maximum age specified by this directive overrides the maximum |
| age specified by either the max-age directive or the Expires |  | age specified by either the max-age directive or the Expires |
| header. The s-maxage directive also implies the semantics of the |  | header. The s-maxage directive also implies the semantics of the |
| proxy-revalidate response directive. |  | proxy-revalidate response directive. |
| no-transform |  | no-transform |
| The no-transform response directive indicates that an intermediate |  | The no-transform response directive indicates that an intermediate |
| cache or proxy MUST NOT change the Content-Encoding, Content-Range |  | cache or proxy MUST NOT change the Content-Encoding, Content-Range |
| or Content-Type response headers, nor the response entity-body. |  | or Content-Type response headers, nor the response representation. |
| 3.2.3. Cache Control Extensions |  | 3.2.3. 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. |  | or more cache-extension tokens, each with an optional value. |
| Informational extensions (those that do not require a change in cache |  | Informational extensions (those that do not require a change in cache |
| behavior) can be added without changing the semantics of other |  | behavior) can be added without changing the semantics of other |
| directives. Behavioral extensions are designed to work by acting as |  | directives. Behavioral extensions are designed to work by acting as |
| modifiers to the existing base of cache directives. Both the new |  | modifiers to the existing base of cache directives. Both the new |
| directive and the standard directive are supplied, such that |  | directive and the standard directive are supplied, such that |
| skipping to change at page 24, line 25 |  | skipping to change at page 24, line 10 |
| o Pointer to specification text |  | o Pointer to specification text |
| Values to be added to this name space are subject to IETF review |  | Values to be added to this name space are subject to IETF review |
| ([RFC5226], Section 4.1). |  | ([RFC5226], Section 4.1). |
| The registry itself is maintained at |  | The registry itself is maintained at |
| <http://www.iana.org/assignments/http-cache-directives>. |  | <http://www.iana.org/assignments/http-cache-directives>. |
| 3.3. Expires |  | 3.3. Expires |
| The "Expires" entity-header field gives the date/time after which the |  | The "Expires" header field gives the date/time after which the |
| response is considered stale. See Section 2.3 for further discussion |  | response is considered stale. See Section 2.3 for further discussion |
| of the freshness model. |  | of the freshness model. |
| The presence of an Expires field does not imply that the original |  | The presence of an Expires field does not imply that the original |
| resource will change or cease to exist at, before, or after that |  | resource will change or cease to exist at, before, or after that |
| time. |  | time. |
| The field-value is an absolute date and time as defined by HTTP-date |  | The field-value is an absolute date and time as defined by HTTP-date |
| in Section 6.1 of [Part1]; it MUST be sent in rfc1123-date format. |  | in Section 6.1 of [Part1]; it MUST be sent in rfc1123-date format. |
| skipping to change at page 26, line 25 |  | skipping to change at page 26, line 9 |
| resource. A server MAY include a Vary header field with a non- |  | resource. A server MAY include a Vary header field with a non- |
| cacheable response that is subject to server-driven negotiation, |  | cacheable response that is subject to server-driven negotiation, |
| since this might provide the user agent with useful information about |  | since this might provide the user agent with useful information about |
| the dimensions over which the response varies at the time of the |  | the dimensions over which the response varies at the time of the |
| response. |  | response. |
| A Vary field value of "*" signals that unspecified parameters not |  | A Vary field value of "*" signals that unspecified parameters not |
| limited to the request-headers (e.g., the network address of the |  | limited to the request-headers (e.g., the network address of the |
| client), play a role in the selection of the response representation; |  | client), play a role in the selection of the response representation; |
| therefore, a cache cannot determine whether this response is |  | therefore, a cache cannot determine whether this response is |
| appropriate. The "*" value MUST NOT be generated by a proxy server; |  | appropriate. The "*" value MUST NOT be generated by a proxy server. |
| it may only be generated by an origin server. |  |  |
| The field-names given are not limited to the set of standard request- |  | The field-names given are not limited to the set of standard request- |
| header fields defined by this specification. Field names are case- |  | header fields defined by this specification. Field names are case- |
| insensitive. |  | insensitive. |
| 3.6. Warning |  | 3.6. Warning |
| The "Warning" general-header field is used to carry additional |  | The "Warning" general-header field is used to carry additional |
| information about the status or transformation of a message that |  | information about the status or transformation of a message that |
| might not be reflected in the message. This information is typically |  | might not be reflected in the message. This information is typically |
| used to warn about possible incorrectness introduced by caching |  | used to warn about possible incorrectness introduced by caching |
| operations or transformations applied to the entity body of the |  | operations or transformations applied to the payload of the message. |
| message. |  |  |
| Warnings can be used for other purposes, both cache-related and |  | Warnings can be used for other purposes, both cache-related and |
| otherwise. The use of a warning, rather than an error status code, |  | otherwise. The use of a warning, rather than an error status code, |
| distinguishes these responses from true failures. |  | distinguishes these responses from true failures. |
| Warning headers can in general be applied to any message, however |  | Warning headers can in general be applied to any message, however |
| some warn-codes are specific to caches and can only be applied to |  | some warn-codes are specific to caches and can only be applied to |
| response messages. |  | response messages. |
| Warning = "Warning" ":" OWS Warning-v |  | Warning = "Warning" ":" OWS Warning-v |
| skipping to change at page 27, line 38 |  | skipping to change at page 27, line 15 |
| Warnings are assigned three digit warn-codes. The first digit |  | Warnings are assigned three digit warn-codes. The first digit |
| indicates whether the Warning is required to be deleted from a stored |  | indicates whether the Warning is required to be deleted from a stored |
| response after validation: |  | response after validation: |
| o 1xx Warnings describe the freshness or validation status of the |  | o 1xx Warnings describe the freshness or validation status of the |
| response, and so MUST be deleted by caches after validation. They |  | response, and so MUST be deleted by caches after validation. They |
| can only be generated by a cache when validating a cached entry, |  | can only be generated by a cache when validating a cached entry, |
| and MUST NOT be generated in any other situation. |  | and MUST NOT be generated in any other situation. |
| o 2xx Warnings describe some aspect of the entity body or entity |  | o 2xx Warnings describe some aspect of the representation that is |
| headers that is not rectified by a validation (for example, a |  | not rectified by a validation (for example, a lossy compression of |
| lossy compression of the entity bodies) and MUST NOT be deleted by |  | the representation) and MUST NOT be deleted by caches after |
| caches after validation, unless a full response is returned, in |  | validation, unless a full response is returned, in which case they |
| which case they MUST be. |  | MUST be. |
| If an implementation sends a message with one or more Warning headers |  | If an implementation sends a message with one or more Warning headers |
| to a receiver whose version is HTTP/1.0 or lower, then the sender |  | to a receiver whose version is HTTP/1.0 or lower, then the sender |
| MUST include in each warning-value a warn-date that matches the Date |  | MUST include in each warning-value a warn-date that matches the Date |
| header in the message. |  | header in the message. |
| If an implementation receives a message with a warning-value that |  | If an implementation receives a message with a warning-value that |
| includes a warn-date, and that warn-date is different from the Date |  | includes a warn-date, and that warn-date is different from the Date |
| value in the response, then that warning-value MUST be deleted from |  | value in the response, then that warning-value MUST be deleted from |
| the message before storing, forwarding, or using it. (preventing the |  | the message before storing, forwarding, or using it. (preventing the |
| skipping to change at page 28, line 41 |  | skipping to change at page 28, line 20 |
| 199 Miscellaneous warning |  | 199 Miscellaneous warning |
| The warning text can include arbitrary information to be presented |  | The warning text can include arbitrary information to be presented |
| to a human user, or logged. A system receiving this warning MUST |  | to a human user, or logged. A system receiving this warning MUST |
| NOT take any automated action, besides presenting the warning to |  | NOT take any automated action, besides presenting the warning to |
| the user. |  | the user. |
| 214 Transformation applied |  | 214 Transformation applied |
| MUST be added by an intermediate cache or proxy if it applies any |  | MUST be added by an intermediate proxy if it applies any |
| transformation changing the content-coding (as specified in the |  | transformation to the representation, such as changing the |
| Content-Encoding header) or media-type (as specified in the |  | content-coding, media-type, or modifying the representation data, |
| Content-Type header) of the response, or the entity-body of the |  | unless this Warning code already appears in the response. |
| response, unless this Warning code already appears in the |  |  |
| response. |  |  |
| 299 Miscellaneous persistent warning |  | 299 Miscellaneous persistent warning |
| The warning text can include arbitrary information to be presented |  | The warning text can include arbitrary information to be presented |
| to a human user, or logged. A system receiving this warning MUST |  | to a human user, or logged. A system receiving this warning MUST |
| NOT take any automated action. |  | NOT take any automated action. |
| 4. History Lists |  | 4. History Lists |
| User agents often have history mechanisms, such as "Back" buttons and |  | User agents often have history mechanisms, such as "Back" buttons and |
| history lists, that can be used to redisplay an entity retrieved |  | history lists, that can be used to redisplay a representation |
| earlier in a session. |  | retrieved earlier in a session. |
| The freshness model (Section 2.3) does not necessarily apply to |  | The freshness model (Section 2.3) does not necessarily apply to |
| history mechanisms. I.e., a history mechanism can display a previous |  | history mechanisms. I.e., a history mechanism can display a previous |
| representation even if it has expired. |  | representation even if it has expired. |
| This does not prohibit the history mechanism from telling the user |  | This does not prohibit the history mechanism from telling the user |
| that a view might be stale, or from honoring cache directives (e.g., |  | that a view might be stale, or from honoring cache directives (e.g., |
| Cache-Control: no-store). |  | Cache-Control: no-store). |
| 5. IANA Considerations |  | 5. IANA Considerations |
| 5.1. Cache Directive Registry |  | 5.1. Cache Directive Registry |
| The registration procedure for HTTP Cache Directives is defined by |  | The registration procedure for HTTP Cache Directives is defined by |
| Section 3.2.3 of this document. |  | Section 3.2.3 of this document. |
| The HTTP Cache Directive Registry should be created at |  | The HTTP Cache Directive Registry shall be created at |
| <http://www.iana.org/assignments/http-cache-directives> and be |  | <http://www.iana.org/assignments/http-cache-directives> and be |
| populated with the registrations below: |  | populated with the registrations below: |
| +------------------------+------------------------------+ |  | +------------------------+------------------------------+ |
| | Cache Directive | Reference | |  | | Cache Directive | Reference | |
| +------------------------+------------------------------+ |  | +------------------------+------------------------------+ |
| | max-age | Section 3.2.1, Section 3.2.2 | |  | | max-age | Section 3.2.1, Section 3.2.2 | |
| | max-stale | Section 3.2.1 | |  | | max-stale | Section 3.2.1 | |
| | min-fresh | Section 3.2.1 | |  | | min-fresh | Section 3.2.1 | |
| | must-revalidate | Section 3.2.2 | |  | | must-revalidate | Section 3.2.2 | |
| skipping to change at page 30, line 5 |  | skipping to change at page 29, line 26 |
| | no-transform | Section 3.2.1, Section 3.2.2 | |  | | no-transform | Section 3.2.1, Section 3.2.2 | |
| | only-if-cached | Section 3.2.1 | |  | | only-if-cached | Section 3.2.1 | |
| | private | Section 3.2.2 | |  | | private | Section 3.2.2 | |
| | proxy-revalidate | Section 3.2.2 | |  | | proxy-revalidate | Section 3.2.2 | |
| | public | Section 3.2.2 | |  | | public | Section 3.2.2 | |
| | s-maxage | Section 3.2.2 | |  | | s-maxage | Section 3.2.2 | |
| | stale-if-error | [RFC5861], Section 4 | |  | | stale-if-error | [RFC5861], Section 4 | |
| | stale-while-revalidate | [RFC5861], Section 3 | |  | | stale-while-revalidate | [RFC5861], Section 3 | |
| +------------------------+------------------------------+ |  | +------------------------+------------------------------+ |
| 5.2. Message Header Registration |  | 5.2. Header Field Registration |
| The Message Header Registry located at <http://www.iana.org/ |  | The Message Header Field Registry located at <http://www.iana.org/ |
| assignments/message-headers/message-header-index.html> should be |  | assignments/message-headers/message-header-index.html> shall be |
| updated with the permanent registrations below (see [RFC3864]): |  | updated with the permanent registrations below (see [RFC3864]): |
| +-------------------+----------+----------+-------------+ |  | +-------------------+----------+----------+-------------+ |
| | Header Field Name | Protocol | Status | Reference | |  | | Header Field Name | Protocol | Status | Reference | |
| +-------------------+----------+----------+-------------+ |  | +-------------------+----------+----------+-------------+ |
| | Age | http | standard | Section 3.1 | |  | | Age | http | standard | Section 3.1 | |
| | Cache-Control | http | standard | Section 3.2 | |  | | Cache-Control | http | standard | Section 3.2 | |
| | Expires | http | standard | Section 3.3 | |  | | Expires | http | standard | Section 3.3 | |
| | Pragma | http | standard | Section 3.4 | |  | | Pragma | http | standard | Section 3.4 | |
| | Vary | http | standard | Section 3.5 | |  | | Vary | http | standard | Section 3.5 | |
| skipping to change at page 30, line 32 |  | skipping to change at page 30, line 5 |
| The change controller is: "IETF (iesg@ietf.org) - Internet |  | The change controller is: "IETF (iesg@ietf.org) - Internet |
| Engineering Task Force". |  | Engineering Task Force". |
| 6. Security Considerations |  | 6. Security Considerations |
| Caches expose additional potential vulnerabilities, since the |  | Caches expose additional potential vulnerabilities, since the |
| contents of the cache represent an attractive target for malicious |  | contents of the cache represent an attractive target for malicious |
| exploitation. Because cache contents persist after an HTTP request |  | exploitation. Because cache contents persist after an HTTP request |
| is complete, an attack on the cache can reveal information long after |  | is complete, an attack on the cache can reveal information long after |
| a user believes that the information has been removed from the |  | a user believes that the information has been removed from the |
| network. Therefore, cache contents should be protected as sensitive |  | network. Therefore, cache contents need to be protected as sensitive |
| information. |  | information. |
| 7. Acknowledgments |  | 7. Acknowledgments |
| Much of the content and presentation of the caching design is due to |  | Much of the content and presentation of the caching design is due to |
| suggestions and comments from individuals including: Shel Kaphan, |  | suggestions and comments from individuals including: Shel Kaphan, |
| Paul Leach, Koen Holtman, David Morris, and Larry Masinter. |  | Paul Leach, Koen Holtman, David Morris, and Larry Masinter. |
| 8. References |  | 8. References |
| 8.1. Normative References |  | 8.1. Normative References |
| [Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |  | [Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |
| Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |  | Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |
| and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections, |  | and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections, |
| and Message Parsing", draft-ietf-httpbis-p1-messaging-10 |  | and Message Parsing", draft-ietf-httpbis-p1-messaging-11 |
| (work in progress), July 2010. |  | (work in progress), August 2010. |
| [Part2] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |  | [Part2] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |
| Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |  | Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |
| and J. Reschke, Ed., "HTTP/1.1, part 2: Message |  | and J. Reschke, Ed., "HTTP/1.1, part 2: Message |
| Semantics", draft-ietf-httpbis-p2-semantics-10 (work in |  | Semantics", draft-ietf-httpbis-p2-semantics-11 (work in |
| progress), July 2010. |  | progress), August 2010. |
| [Part4] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |  | [Part4] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |
| Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |  | Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |
| and J. Reschke, Ed., "HTTP/1.1, part 4: Conditional |  | and J. Reschke, Ed., "HTTP/1.1, part 4: Conditional |
| Requests", draft-ietf-httpbis-p4-conditional-10 (work in |  | Requests", draft-ietf-httpbis-p4-conditional-11 (work in |
| progress), July 2010. |  | progress), August 2010. |
| [Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |  | [Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |
| Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |  | Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |
| and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and |  | and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and |
| Partial Responses", draft-ietf-httpbis-p5-range-10 (work |  | Partial Responses", draft-ietf-httpbis-p5-range-11 (work |
| in progress), July 2010. |  | in progress), August 2010. |
| [Part7] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |  | [Part7] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |
| Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |  | Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |
| and J. Reschke, Ed., "HTTP/1.1, part 7: Authentication", |  | and J. Reschke, Ed., "HTTP/1.1, part 7: Authentication", |
| draft-ietf-httpbis-p7-auth-10 (work in progress), |  | draft-ietf-httpbis-p7-auth-11 (work in progress), |
| July 2010. |  | August 2010. |
| [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, March 1997. |  | Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [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, January 2008. |  | Specifications: ABNF", STD 68, RFC 5234, January 2008. |
| 8.2. Informative References |  | 8.2. Informative References |
| [RFC1305] Mills, D., "Network Time Protocol (Version 3) |  | [RFC1305] Mills, D., "Network Time Protocol (Version 3) |
| skipping to change at page 32, line 5 |  | skipping to change at page 31, line 26 |
| Procedures for Message Header Fields", BCP 90, RFC 3864, |  | Procedures for Message Header Fields", BCP 90, RFC 3864, |
| September 2004. |  | September 2004. |
| [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an |  | [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an |
| IANA Considerations Section in RFCs", BCP 26, RFC 5226, |  | IANA Considerations Section in RFCs", BCP 26, RFC 5226, |
| May 2008. |  | May 2008. |
| [RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale |  | [RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale |
| Content", RFC 5861, April 2010. |  | Content", RFC 5861, April 2010. |
| Appendix A. Compatibility with Previous Versions |  | Appendix A. Changes from RFC 2616 |
| A.1. Changes from RFC 2068 |  |  |
| A case was missed in the Cache-Control model of HTTP/1.1; s-maxage |  |  |
| was introduced to add this missing case. (Sections 2.1, 3.2). |  |  |
| Range request responses would become very verbose if all meta-data |  |  |
| were always returned; by allowing the server to only send needed |  |  |
| headers in a 206 response, this problem can be avoided. |  |  |
| (Section 2.8) |  |  |
| The Cache-Control: max-age directive was not properly defined for |  |  |
| responses. (Section 3.2.2) |  |  |
| Warnings could be cached incorrectly, or not updated appropriately. |  |  |
| (Section 2.3, 2.8, 3.2, and 3.6) Warning also needed to be a general |  |  |
| header, as PUT or other methods may have need for it in requests. |  |  |
| A.2. Changes from RFC 2616 |  |  |
| Make the specified age calculation algorithm less conservative. |  | Make the specified age calculation algorithm less conservative. |
| (Section 2.3.2) |  | (Section 2.3.2) |
| Remove requirement to consider Content-Location in successful |  | Remove requirement to consider Content-Location in successful |
| responses in order to determine the appropriate response to use. |  | responses in order to determine the appropriate response to use. |
| (Section 2.4) |  | (Section 2.4) |
| Clarify denial of service attack avoidance requirement. |  | Clarify denial of service attack avoidance requirement. |
| (Section 2.5) |  | (Section 2.5) |
| skipping to change at page 38, line 8 |  | skipping to change at page 37, line 10 |
| for cache-control directives" |  | for cache-control directives" |
| o <http://tools.ietf.org/wg/httpbis/trac/ticket/211>: "Heuristic |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/211>: "Heuristic |
| caching of URLs with query components" |  | caching of URLs with query components" |
| Partly resolved issues: |  | Partly resolved issues: |
| o <http://tools.ietf.org/wg/httpbis/trac/ticket/196>: "Term for the |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/196>: "Term for the |
| requested resource's URI" |  | requested resource's URI" |
|  |  | C.12. Since draft-ietf-httpbis-p6-cache-10 |
|  |  | Closed issues: |
|  |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/109>: "Clarify |
|  |  | entity / representation / variant terminology" |
|  |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/220>: "consider |
|  |  | removing the 'changes from 2068' sections" |
|  |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/223>: "Allowing |
|  |  | heuristic caching for new status codes" |
|  |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/223>: "Allowing |
|  |  | heuristic caching for new status codes" |
|  |  | o Clean up TODOs and prose in "Combining Responses." |
| Index |  | Index |
| A |  | A |
| age 6 |  | age 6 |
| Age header 17 |  | Age header 17 |
| C |  | C |
| cache 5 |  | cache 5 |
| Cache Directives |  | Cache Directives |
| max-age 19, 22 |  | max-age 19, 22 |
| max-stale 19 |  | max-stale 19 |
| min-fresh 20 |  | min-fresh 19 |
| must-revalidate 22 |  | must-revalidate 22 |
| no-cache 19, 21 |  | no-cache 19, 21 |
| no-store 19, 22 |  | no-store 19, 21 |
| no-transform 20, 23 |  | no-transform 20, 22 |
| only-if-cached 20 |  | only-if-cached 20 |
| private 21 |  | private 20 |
| proxy-revalidate 22 |  | proxy-revalidate 22 |
| public 20 |  | public 20 |
| s-maxage 22 |  | s-maxage 22 |
| Cache-Control header 18 |  | Cache-Control header 18 |
| cacheable 5 |  | cacheable 5 |
| E |  | E |
| Expires header 24 |  | Expires header 24 |
| explicit expiration time 5 |  | explicit expiration time 5 |
| F |  | F |
| first-hand 6 |  | first-hand 6 |
| fresh 6 |  | fresh 6 |
| freshness lifetime 6 |  | freshness lifetime 6 |
| G |  | G |
| Grammar |  | Grammar |
| Age 18 |  | Age 17 |
| Age-v 18 |  | Age-v 17 |
| Cache-Control 18 |  | Cache-Control 18 |
| Cache-Control-v 18 |  | Cache-Control-v 18 |
| cache-extension 18 |  | cache-extension 18 |
| cache-request-directive 19 |  | cache-request-directive 18 |
| cache-response-directive 20 |  | cache-response-directive 20 |
| delta-seconds 18 |  | delta-seconds 17 |
| Expires 24 |  | Expires 24 |
| Expires-v 24 |  | Expires-v 24 |
| extension-pragma 25 |  | extension-pragma 24 |
| Pragma 25 |  | Pragma 24 |
| pragma-directive 25 |  | pragma-directive 24 |
| Pragma-v 25 |  | Pragma-v 24 |
| Vary 26 |  | Vary 25 |
| Vary-v 26 |  | Vary-v 25 |
| warn-agent 27 |  | warn-agent 26 |
| warn-code 27 |  | warn-code 26 |
| warn-date 27 |  | warn-date 26 |
| warn-text 27 |  | warn-text 26 |
| Warning 27 |  | Warning 26 |
| Warning-v 27 |  | Warning-v 26 |
| warning-value 27 |  | warning-value 26 |
| H |  | H |
| Headers |  | Headers |
| Age 17 |  | Age 17 |
| Cache-Control 18 |  | Cache-Control 18 |
| Expires 24 |  | Expires 24 |
| Pragma 25 |  | Pragma 24 |
| Vary 25 |  | Vary 25 |
| Warning 26 |  | Warning 26 |
| heuristic expiration time 5 |  | heuristic expiration time 5 |
| M |  | M |
| max-age |  | max-age |
| Cache Directive 19, 22 |  | Cache Directive 19, 22 |
| max-stale |  | max-stale |
| Cache Directive 19 |  | Cache Directive 19 |
| min-fresh |  | min-fresh |
| Cache Directive 20 |  | Cache Directive 19 |
| must-revalidate |  | must-revalidate |
| Cache Directive 22 |  | Cache Directive 22 |
| N |  | N |
| no-cache |  | no-cache |
| Cache Directive 19, 21 |  | Cache Directive 19, 21 |
| no-store |  | no-store |
| Cache Directive 19, 22 |  | Cache Directive 19, 21 |
| no-transform |  | no-transform |
| Cache Directive 20, 23 |  | Cache Directive 20, 22 |
| O |  | O |
| only-if-cached |  | only-if-cached |
| Cache Directive 20 |  | Cache Directive 20 |
| P |  | P |
| Pragma header 25 |  | Pragma header 24 |
| private |  | private |
| Cache Directive 21 |  | Cache Directive 20 |
| proxy-revalidate |  | proxy-revalidate |
| Cache Directive 22 |  | Cache Directive 22 |
| public |  | public |
| Cache Directive 20 |  | Cache Directive 20 |
| S |  | S |
| s-maxage |  | s-maxage |
| Cache Directive 22 |  | Cache Directive 22 |
| stale 6 |  | stale 6 |
End of changes. 79 change blocks.
| 191 lines changed or deleted |  | 167 lines changed or added |
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