| draft-ietf-httpbis-p6-cache-08.txt |  | draft-ietf-httpbis-p6-cache-09.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 One Laptop per Child |  | Intended status: Standards Track One Laptop per Child |
| Expires: April 29, 2010 J. Mogul |  | Expires: September 9, 2010 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 |
| October 26, 2009 |  | March 8, 2010 |
| HTTP/1.1, part 6: Caching |  | HTTP/1.1, part 6: Caching |
| draft-ietf-httpbis-p6-cache-08 |  | draft-ietf-httpbis-p6-cache-09 |
| Status of this Memo |  | Abstract |
|  |  | The Hypertext Transfer Protocol (HTTP) is an application-level |
|  |  | protocol for distributed, collaborative, hypermedia information |
|  |  | systems. This document is Part 6 of the seven-part specification |
|  |  | that defines the protocol referred to as "HTTP/1.1" and, taken |
|  |  | together, obsoletes RFC 2616. Part 6 defines requirements on HTTP |
|  |  | caches and the associated header fields that control cache behavior |
|  |  | or indicate cacheable response messages. |
|  |  | Editorial Note (To be removed by RFC Editor) |
|  |  | Discussion of this draft should take place on the HTTPBIS working |
|  |  | group mailing list (ietf-http-wg@w3.org). The current issues list is |
|  |  | at <http://tools.ietf.org/wg/httpbis/trac/report/11> and related |
|  |  | documents (including fancy diffs) can be found at |
|  |  | <http://tools.ietf.org/wg/httpbis/>. |
|  |  | The changes in this draft are summarized in Appendix C.10. |
|  |  | Status of this Memo |
| This Internet-Draft is submitted to IETF in full conformance with the |  | This Internet-Draft is submitted to IETF in full conformance with the |
| provisions of BCP 78 and BCP 79. This document may contain material |  | provisions of BCP 78 and BCP 79. |
| from IETF Documents or IETF Contributions published or made publicly |  |  |
| available before November 10, 2008. The person(s) controlling the |  |  |
| copyright in some of this material may not have granted the IETF |  |  |
| Trust the right to allow modifications of such material outside the |  |  |
| IETF Standards Process. Without obtaining an adequate license from |  |  |
| the person(s) controlling the copyright in such materials, this |  |  |
| document may not be modified outside the IETF Standards Process, and |  |  |
| derivative works of it may not be created outside the IETF Standards |  |  |
| Process, except to format it for publication as an RFC or to |  |  |
| translate it into languages other than English. |  |  |
| Internet-Drafts are working documents of the Internet Engineering |  | Internet-Drafts are working documents of the Internet Engineering |
| Task Force (IETF), its areas, and its working groups. Note that |  | Task Force (IETF), its areas, and its working groups. Note that |
| other groups may also distribute working documents as Internet- |  | other groups may also distribute working documents as Internet- |
| Drafts. |  | Drafts. |
| 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." |
| The list of current Internet-Drafts can be accessed at |  | The list of current Internet-Drafts can be accessed at |
| http://www.ietf.org/ietf/1id-abstracts.txt. |  | http://www.ietf.org/ietf/1id-abstracts.txt. |
| The list of Internet-Draft Shadow Directories can be accessed at |  | The list of Internet-Draft Shadow Directories can be accessed at |
| http://www.ietf.org/shadow.html. |  | http://www.ietf.org/shadow.html. |
| This Internet-Draft will expire on April 29, 2010. |  | This Internet-Draft will expire on September 9, 2010. |
| Copyright Notice |  | Copyright Notice |
| Copyright (c) 2009 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 in effect on the date of |  | Provisions Relating to IETF Documents |
| publication of this document (http://trustee.ietf.org/license-info). |  | (http://trustee.ietf.org/license-info) in effect on the date of |
| Please review these documents carefully, as they describe your rights |  | publication of this document. Please review these documents |
| and restrictions with respect to this document. |  | carefully, as they describe your rights and restrictions with respect |
|  |  | to this document. Code Components extracted from this document must |
| Abstract |  | include Simplified BSD License text as described in Section 4.e of |
|  |  | the Trust Legal Provisions and are provided without warranty as |
| The Hypertext Transfer Protocol (HTTP) is an application-level |  | described in the BSD License. |
| protocol for distributed, collaborative, hypermedia information |  |  |
| systems. This document is Part 6 of the seven-part specification |  |  |
| that defines the protocol referred to as "HTTP/1.1" and, taken |  |  |
| together, obsoletes RFC 2616. Part 6 defines requirements on HTTP |  |  |
| caches and the associated header fields that control cache behavior |  |  |
| or indicate cacheable response messages. |  |  |
| Editorial Note (To be removed by RFC Editor) |  |  |
| Discussion of this draft should take place on the HTTPBIS working |  |  |
| group mailing list (ietf-http-wg@w3.org). The current issues list is |  |  |
| at <http://tools.ietf.org/wg/httpbis/trac/report/11> and related |  |  |
| documents (including fancy diffs) can be found at |  |  |
| <http://tools.ietf.org/wg/httpbis/>. |  |  |
| The changes in this draft are summarized in Appendix C.9. |  | This document may contain material from IETF Documents or IETF |
|  |  | Contributions published or made publicly available before November |
|  |  | 10, 2008. The person(s) controlling the copyright in some of this |
|  |  | material may not have granted the IETF Trust the right to allow |
|  |  | modifications of such material outside the IETF Standards Process. |
|  |  | Without obtaining an adequate license from the person(s) controlling |
|  |  | the copyright in such materials, this document may not be modified |
|  |  | outside the IETF Standards Process, and derivative works of it may |
|  |  | not be created outside the IETF Standards Process, except to format |
|  |  | it for publication as an RFC or to translate it into languages other |
|  |  | than English. |
| Table of Contents |  | Table of Contents |
| 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 |  | 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 |
| 1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 5 |  | 1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 5 |
| 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 |  | 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 |
| 1.3. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6 |  | 1.3. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6 |
| 1.4. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 7 |  | 1.4. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 7 |
| 1.4.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 7 |  | 1.4.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 7 |
| 1.4.2. ABNF Rules defined in other Parts of the |  | 1.4.2. ABNF Rules defined in other Parts of the |
| Specification . . . . . . . . . . . . . . . . . . . . 7 |  | Specification . . . . . . . . . . . . . . . . . . . . 7 |
| 2. Cache Operation . . . . . . . . . . . . . . . . . . . . . . . 7 |  | 2. Cache Operation . . . . . . . . . . . . . . . . . . . . . . . 7 |
| 2.1. Response Cacheability . . . . . . . . . . . . . . . . . . 7 |  | 2.1. Response Cacheability . . . . . . . . . . . . . . . . . . 7 |
| 2.1.1. Storing Partial and Incomplete Responses . . . . . . . 8 |  | 2.1.1. Storing Partial and Incomplete Responses . . . . . . . 8 |
| 2.2. Constructing Responses from Caches . . . . . . . . . . . . 8 |  | 2.2. Constructing Responses from Caches . . . . . . . . . . . . 9 |
| 2.3. Freshness Model . . . . . . . . . . . . . . . . . . . . . 9 |  | 2.3. Freshness Model . . . . . . . . . . . . . . . . . . . . . 10 |
| 2.3.1. Calculating Freshness Lifetime . . . . . . . . . . . . 10 |  | 2.3.1. Calculating Freshness Lifetime . . . . . . . . . . . . 11 |
| 2.3.2. Calculating Age . . . . . . . . . . . . . . . . . . . 11 |  | 2.3.2. Calculating Age . . . . . . . . . . . . . . . . . . . 12 |
| 2.3.3. Serving Stale Responses . . . . . . . . . . . . . . . 13 |  | 2.3.3. Serving Stale Responses . . . . . . . . . . . . . . . 13 |
| 2.4. Validation Model . . . . . . . . . . . . . . . . . . . . . 13 |  | 2.4. Validation Model . . . . . . . . . . . . . . . . . . . . . 14 |
| 2.5. Request Methods that Invalidate . . . . . . . . . . . . . 14 |  | 2.5. Request Methods that Invalidate . . . . . . . . . . . . . 14 |
| 2.6. Caching Negotiated Responses . . . . . . . . . . . . . . . 15 |  | 2.6. Caching Negotiated Responses . . . . . . . . . . . . . . . 15 |
| 2.7. Combining Responses . . . . . . . . . . . . . . . . . . . 16 |  | 2.7. Combining Responses . . . . . . . . . . . . . . . . . . . 16 |
| 3. Header Field Definitions . . . . . . . . . . . . . . . . . . . 16 |  | 3. Header Field Definitions . . . . . . . . . . . . . . . . . . . 17 |
| 3.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 |  | 3.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 |
| 3.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 17 |  | 3.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 18 |
| 3.2.1. Request Cache-Control Directives . . . . . . . . . . . 18 |  | 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 . . . . . . . . . . . . . . . 22 |  | 3.2.3. Cache Control Extensions . . . . . . . . . . . . . . . 22 |
| 3.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 23 |  | 3.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 23 |
| 3.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 24 |  | 3.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 24 |
| 3.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 |  | 3.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 |
| 3.6. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 25 |  | 3.6. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 25 |
| 4. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 28 |  | 4. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 28 |
| 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 |  | 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 |
| 5.1. Message Header Registration . . . . . . . . . . . . . . . 28 |  | 5.1. Message Header Registration . . . . . . . . . . . . . . . 28 |
| 6. Security Considerations . . . . . . . . . . . . . . . . . . . 29 |  | 6. Security Considerations . . . . . . . . . . . . . . . . . . . 28 |
| 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29 |  | 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29 |
| 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 |  | 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 |
| 8.1. Normative References . . . . . . . . . . . . . . . . . . . 29 |  | 8.1. Normative References . . . . . . . . . . . . . . . . . . . 29 |
| 8.2. Informative References . . . . . . . . . . . . . . . . . . 30 |  | 8.2. Informative References . . . . . . . . . . . . . . . . . . 30 |
| Appendix A. Compatibility with Previous Versions . . . . . . . . 30 |  | Appendix A. Compatibility with Previous Versions . . . . . . . . 30 |
| A.1. Changes from RFC 2068 . . . . . . . . . . . . . . . . . . 31 |  | A.1. Changes from RFC 2068 . . . . . . . . . . . . . . . . . . 30 |
| A.2. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 31 |  | A.2. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 30 |
| Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 31 |  | Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 31 |
| Appendix C. Change Log (to be removed by RFC Editor before |  | Appendix C. Change Log (to be removed by RFC Editor before |
| publication) . . . . . . . . . . . . . . . . . . . . 33 |  | publication) . . . . . . . . . . . . . . . . . . . . 32 |
| C.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 33 |  | C.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 32 |
| C.2. Since draft-ietf-httpbis-p6-cache-00 . . . . . . . . . . . 33 |  | C.2. Since draft-ietf-httpbis-p6-cache-00 . . . . . . . . . . . 32 |
| C.3. Since draft-ietf-httpbis-p6-cache-01 . . . . . . . . . . . 34 |  | C.3. Since draft-ietf-httpbis-p6-cache-01 . . . . . . . . . . . 33 |
| C.4. Since draft-ietf-httpbis-p6-cache-02 . . . . . . . . . . . 34 |  | C.4. Since draft-ietf-httpbis-p6-cache-02 . . . . . . . . . . . 33 |
| C.5. Since draft-ietf-httpbis-p6-cache-03 . . . . . . . . . . . 34 |  | 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 . . . . . . . . . . . 35 |  | C.7. Since draft-ietf-httpbis-p6-cache-05 . . . . . . . . . . . 34 |
| C.8. Since draft-ietf-httpbis-p6-cache-06 . . . . . . . . . . . 35 |  | 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 . . . . . . . . . . . 35 |
| Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 |  | Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 |
| Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38 |  | Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38 |
| 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. |
| skipping to change at page 8, line 5 |  | skipping to change at page 8, line 5 |
| port = <port, defined in [Part1], Section 2.6> |  | port = <port, defined in [Part1], Section 2.6> |
| pseudonym = <pseudonym, defined in [Part1], Section 9.9> |  | pseudonym = <pseudonym, defined in [Part1], Section 9.9> |
| uri-host = <uri-host, defined in [Part1], Section 2.6> |  | uri-host = <uri-host, defined in [Part1], Section 2.6> |
| 2. Cache Operation |  | 2. Cache Operation |
| 2.1. Response Cacheability |  | 2.1. Response Cacheability |
| A cache MUST NOT store a response to any request, unless: |  | A cache MUST NOT store a response to any request, unless: |
| o The request method is defined as being cacheable, and |  | o The request method is understood by the cache and defined as being |
|  |  | cacheable, and |
|  |  | o the response status code is understood by the cache, and |
| o the "no-store" cache directive (see Section 3.2) does not appear |  | o the "no-store" cache directive (see Section 3.2) does not appear |
| in request or response headers, and |  | in request or response headers, and |
| o the "private" cache response directive (see Section 3.2 does not |  | o the "private" cache response directive (see Section 3.2.2 does not |
| appear in the response, if the cache is shared, and |  | appear in the response, if the cache is shared, and |
| o the "Authorization" header (see Section 3.1 of [Part7]) does not |  | o the "Authorization" header (see Section 3.1 of [Part7]) does not |
| appear in the request, if the cache is shared (unless the "public" |  | appear in the request, if the cache is shared (unless the "public" |
| directive is present; see Section 3.2), and |  | directive is present; see Section 3.2), and |
| o the cache understands partial responses, if the response is |  | o the response either: |
| partial or incomplete (see Section 2.1.1). |  |  |
|  |  | * contains an Expires header (see Section 3.3), or |
|  |  | * contains a max-age response cache directive (see |
|  |  | Section 3.2.2), or |
|  |  | * contains a s-maxage response cache directive and the cache is |
|  |  | shared, or |
|  |  | * contains a Cache Control Extension (see Section 3.2.3) that |
|  |  | allows it to be cached, or |
|  |  | * has a status code that can be served with heuristic freshness |
|  |  | (see Section 2.3.1.1). |
|  |  | In this context, a cache has "understood" a request method or a |
|  |  | response status code if it recognises it and implements any cache- |
|  |  | specific behaviour. In particular, 206 Partial Content responses |
|  |  | cannot be cached by an implementation that does not handle partial |
|  |  | content (see Section 2.1.1). |
| Note that in normal operation, most caches will not store a response |  | Note that in normal operation, most caches will not store a response |
| that has neither a cache validator nor an explicit expiration time, |  | that has neither a cache validator nor an explicit expiration time, |
| as such responses are not usually useful to store. However, caches |  | as such responses are not usually useful to store. However, caches |
| are not prohibited from storing such responses. |  | are not prohibited from storing such responses. |
| 2.1.1. Storing Partial and Incomplete Responses |  | 2.1.1. Storing Partial and Incomplete Responses |
| A cache that receives an incomplete response (for example, with fewer |  | A cache that receives an incomplete response (for example, with fewer |
| bytes of data than specified in a Content-Length header) can store |  | bytes of data than specified in a Content-Length header) can store |
| skipping to change at page 9, line 25 |  | skipping to change at page 9, line 47 |
| * 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 |  | [[TODO-method-cacheability: define method cacheability for GET, HEAD |
| and POST in p2-semantics.]] |  | and POST in p2-semantics.]] |
| When a stored response is used to satisfy a request, caches MUST |  | When a stored response is used to satisfy a request, caches MUST |
| include a single Age header field (Section 3.1) in the response with |  | include a single Age header field (Section 3.1) in the response with |
| a value equal to the stored response's current_age; see |  | a value equal to the stored response's current_age; see |
| Section 2.3.2. [[anchor1: DISCUSS: this currently includes |  | Section 2.3.2. [[DISCUSS-includes-validated: this currently includes |
| successfully validated responses.]] |  | 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 |
| header) when more than one suitable response is stored. They can |  | header) when more than one suitable response is stored. They can |
| also forward a request with "Cache-Control: max-age=0" or "Cache- |  | also forward a 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. |
| skipping to change at page 10, line 12 |  | skipping to change at page 10, line 34 |
| 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 |  | entity is not likely to change in a semantically significant way |
| before the expiration time is reached. |  | 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. This |
| means that the response is always stale, so that caches should |  | means that the response is always stale, so that caches should |
| validate it before using it for subsequent requests. [[anchor2: This |  | validate it before using it for subsequent requests. [[TODO- |
| wording may cause confusion, because the response may still be served |  | response-stale: This wording may cause confusion, because the |
| stale.]] |  | 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 also assign heuristic expiration times when they are |
| not specified, employing algorithms that use other header values |  | 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 may 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. |
| [[anchor3: ISSUE: there are not requirements directly applying to |  | [[ISSUE-no-req-for-directives: there are not requirements directly |
| 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 |
| caches and history mechanisms. |  | caches and history mechanisms. |
| 2.3.1. Calculating Freshness Lifetime |  | 2.3.1. Calculating Freshness Lifetime |
| A cache can calculate the freshness lifetime (denoted as |  | A cache can calculate the freshness lifetime (denoted as |
| freshness_lifetime) of a response by using the first match of: |  | freshness_lifetime) of a response by using the first match of: |
| skipping to change at page 11, line 34 |  | skipping to change at page 12, line 6 |
| 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%. |
| [[anchor4: REVIEW: took away HTTP/1.0 query string heuristic |  | [[REVIEW-query-string-heuristics: took away HTTP/1.0 query string |
| uncacheability.]] |  | heuristic uncacheability.]] |
| 2.3.2. Calculating Age |  | 2.3.2. Calculating Age |
| HTTP/1.1 uses the Age response-header to convey the estimated age of |  | HTTP/1.1 uses the Age response-header to convey the estimated age of |
| the response message when obtained from a cache. The Age field value |  | the response message when obtained from a cache. The Age field value |
| is the cache's estimate of the amount of time since the response was |  | is the cache's estimate of the amount of time since the response was |
| generated or validated by the origin server. In essence, the Age |  | generated or validated by the origin server. In essence, the Age |
| value is the sum of the time that the response has been resident in |  | value is the sum of the time that the response has been resident in |
| each of the caches along the path from the origin server, plus the |  | each of the caches along the path from the origin server, plus the |
| amount of time it has been in transit along network paths. |  | amount of time it has been in transit along network paths. |
| skipping to change at page 14, line 26 |  | skipping to change at page 14, line 37 |
| 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 2.7. |  | response can be updated and reused; see Section 2.7. |
| 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 is used both to satisfy the |
| request and replace the stored response. [[anchor5: Should there be a |  | request and replace the stored response. [[TODO-req-missing: Should |
| requirement here?]] |  | 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 |
| skipping to change at page 15, line 7 |  | skipping to change at page 15, line 18 |
| 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 Request-URI. This helps prevent denial of |  | from the host part in the Request-URI. This helps prevent denial of |
| service attacks. |  | service attacks. |
| [[anchor6: TODO: "host part" needs to be specified better.]] |  | [[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 Request-URI. |  | understand SHOULD invalidate the Request-URI. |
| 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 Request-URI, or will mark these as "invalid" |  | responses related to the Request-URI, or will mark these as "invalid" |
| and in need of a mandatory validation before they can be returned in |  | and in need of a mandatory validation before they can be returned in |
| response to a subsequent request. |  | 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. |
| [[anchor7: TODO: specify that only successful (2xx, 3xx?) responses |  | [[TODO-spec-success-invalidate: specify that only successful (2xx, |
| invalidate.]] |  | 3xx?) responses invalidate.]] |
| 2.6. Caching Negotiated Responses |  | 2.6. Caching Negotiated Responses |
| 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 3.5), it MUST NOT use |  | response that has a Vary header field (Section 3.5), it MUST NOT use |
| that response unless all of the selecting request-headers nominated |  | that response unless all of the selecting request-headers nominated |
| by the Vary header match in both the original request (i.e., that |  | by the Vary header match in both the original request (i.e., that |
| associated with the stored response), and the presented request. |  | associated with the stored response), and the presented request. |
| The selecting request-headers from two requests are defined to match |  | The selecting request-headers from two requests are defined to match |
| if and only if the selecting request-headers in the first request can |  | if and only if those in the first request can be transformed to those |
| be transformed to the selecting request-headers in the second request |  | in the second request by applying any of the following: |
| by adding or removing linear white space [[anchor8: [ref]]] at places |  |  |
| where this is allowed by the corresponding ABNF, and/or combining |  |  |
| multiple message-header fields with the same field name following the |  |  |
| rules about header fields in Section 3.2 of [Part1]. |  |  |
| If a header field is absent from a request, it can only match another |  | o adding or removing whitespace, where allowed in the header's |
| request if it is also absent there. |  | syntax |
|  |  | o combining multiple message-header fields with the same field name |
|  |  | (see Section 3.2 of [Part1]) |
|  |  | o normalizing both header values in a way that is known to have |
|  |  | identical semantics, according to the header's specification |
|  |  | (e.g., re-ordering field values when order is not significant; |
|  |  | case-normalization, where values are defined to be case- |
|  |  | insensitive) |
|  |  | If (after any normalisation that may take place) a header field is |
|  |  | absent from a request, it can only match another request if it is |
|  |  | 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 |
| skipping to change at page 16, line 16 |  | skipping to change at page 16, line 38 |
| 2.7. Combining Responses |  | 2.7. 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. |
| 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. [[anchor9: may need language about Content-Location |  | response to use. [[TODO-mention-CL: may need language about Content- |
| here]][[anchor10: cover case where INM with multiple etags was sent]] |  | Location here]][[TODO-inm-mult-etags: cover case where INM with |
|  |  | multiple etags was sent]] |
| If the status code is 206 (partial content), both the stored and new |  | If the status code is 206 (partial content), both the stored and new |
| responses MUST have validators, and those validators MUST match using |  | responses MUST have validators, and those validators MUST match using |
| the strong comparison function (see Section 4 of [Part4]). |  | the strong comparison function (see Section 4 of [Part4]). |
| Otherwise, the responses MUST NOT be combined. |  | 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) |
| skipping to change at page 16, line 40 |  | skipping to change at page 17, line 15 |
| o any stored Warning headers with warn-code 2xx MUST be retained in |  | o any stored Warning headers with warn-code 2xx MUST be retained in |
| the stored response and the updated response. |  | the stored response and the updated response. |
| o any headers provided in the new response MUST replace the |  | o any headers provided in the new response MUST replace the |
| corresponding headers from the stored response. |  | corresponding headers from the stored response. |
| If a header field-name in the new response matches more than one |  | If a header field-name in the new response matches more than one |
| header in the stored response, all such stored headers MUST be |  | header in the stored response, all such stored headers MUST be |
| replaced. |  | replaced. |
| The updated response can [[[[anchor11: requirement?]]]] be used to |  | The updated response can [[TODO-is-req: requirement?]] be used to |
| replace the stored response in cache. In the case of a 206 response, |  | replace the stored response in cache. In the case of a 206 response, |
| the combined entity-body MAY be stored. |  | the combined entity-body MAY be stored. |
| [[anchor12: ISSUE: discuss how to handle HEAD updates]] |  | [[ISSUE-how-head: discuss how to handle HEAD updates]] |
| 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 |  | For entity-header fields, both sender and recipient refer to either |
| the client or the server, depending on who sends and who receives the |  | the client or the server, depending on who sends and who receives the |
| entity. |  | entity. |
| skipping to change at page 19, line 13 |  | skipping to change at page 19, line 32 |
| client is not willing to accept a stale response. |  | 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. [[anchor13: of any staleness? --mnot]] |  | stale response of any age. [[TODO-staleness: of any staleness? |
|  |  | --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 |
| skipping to change at page 20, line 42 |  | skipping to change at page 20, line 50 |
| 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 may be stored, and 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 recieved; 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 caching even by caches that have been configured to return |
| stale responses. |  | stale responses. |
| skipping to change at page 21, line 17 |  | skipping to change at page 21, line 25 |
| 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. |
| Note: Most HTTP/1.0 caches will not recognize or obey this |  | Note: Most HTTP/1.0 caches will not recognize or obey this |
| directive. Also, no-cache response directives with field-names |  | directive. Also, no-cache response directives with field-names |
| are often handled by implementations as if an unqualified no-cache |  | are often handled by implementations as if an unqualified no-cache |
| directive was recieved; i.e., the special handling for the |  | directive was received; i.e., the special handling for the |
| qualified form is not widely implemented. |  | qualified form is not widely implemented. |
| no-store |  | 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. 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 |
| skipping to change at page 23, line 41 |  | skipping to change at page 24, line 4 |
| 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. |
| Expires = "Expires" ":" OWS Expires-v |  | Expires = "Expires" ":" OWS Expires-v |
| Expires-v = HTTP-date |  | Expires-v = HTTP-date |
| For example |  | For example |
| Expires: Thu, 01 Dec 1994 16:00:00 GMT |  | Expires: Thu, 01 Dec 1994 16:00:00 GMT |
|  |  | Note: If a response includes a Cache-Control field with the max- |
| Note: if a response includes a Cache-Control field with the max- |  |  |
| age directive (see Section 3.2.2), that directive overrides the |  | age directive (see Section 3.2.2), that directive overrides the |
| Expires field. Likewise, the s-maxage directive overrides Expires |  | Expires field. Likewise, the s-maxage directive overrides Expires |
| in shared caches. |  | in shared caches. |
| HTTP/1.1 servers SHOULD NOT send Expires dates more than one year in |  | HTTP/1.1 servers SHOULD NOT send Expires dates more than one year in |
| the future. |  | the future. |
| HTTP/1.1 clients and caches MUST treat other invalid date formats, |  | HTTP/1.1 clients and caches MUST treat other invalid date formats, |
| especially including the value "0", as in the past (i.e., "already |  | especially including the value "0", as in the past (i.e., "already |
| expired"). |  | expired"). |
| skipping to change at page 24, line 29 |  | skipping to change at page 24, line 39 |
| When the no-cache directive is present in a request message, an |  | When the no-cache directive is present in a request message, an |
| application SHOULD forward the request toward the origin server even |  | application SHOULD forward the request toward the origin server even |
| if it has a cached copy of what is being requested. This pragma |  | if it has a cached copy of what is being requested. This pragma |
| directive has the same semantics as the no-cache response directive |  | directive has the same semantics as the no-cache response directive |
| (see Section 3.2.2) and is defined here for backward compatibility |  | (see Section 3.2.2) and is defined here for backward compatibility |
| with HTTP/1.0. Clients SHOULD include both header fields when a no- |  | with HTTP/1.0. Clients SHOULD include both header fields when a no- |
| cache request is sent to a server not known to be HTTP/1.1 compliant. |  | cache request is sent to a server not known to be HTTP/1.1 compliant. |
| HTTP/1.1 caches SHOULD treat "Pragma: no-cache" as if the client had |  | HTTP/1.1 caches SHOULD treat "Pragma: no-cache" as if the client had |
| sent "Cache-Control: no-cache". |  | sent "Cache-Control: no-cache". |
| Note: because the meaning of "Pragma: no-cache" as a response- |  | Note: Because the meaning of "Pragma: no-cache" as a response- |
| header field is not actually specified, it does not provide a |  | header field is not actually specified, it does not provide a |
| reliable replacement for "Cache-Control: no-cache" in a response. |  | reliable replacement for "Cache-Control: no-cache" in a response. |
| This mechanism is deprecated; no new Pragma directives will be |  | This mechanism is deprecated; no new Pragma directives will be |
| defined in HTTP. |  | defined in HTTP. |
| 3.5. Vary |  | 3.5. Vary |
| The "Vary" response-header field conveys the set of request-header |  | The "Vary" response-header field conveys the set of request-header |
| fields that were used to select the representation. |  | fields that were used to select the representation. |
| Caches use this information, in part, to determine whether a stored |  | Caches use this information, in part, to determine whether a stored |
| response can be used to satisdy a given request; see Section 2.6. |  | response can be used to satisfy a given request; see Section 2.6. |
| determines, while the response is fresh, whether a cache is permitted |  | determines, while the response is fresh, whether a cache is permitted |
| to use the response to reply to a subsequent request without |  | to use the response to reply to a subsequent request without |
| validation; see Section 2.6. |  | validation; see Section 2.6. |
| In uncacheable or stale responses, the Vary field value advises the |  | In uncacheable or stale responses, the Vary field value advises the |
| user agent about the criteria that were used to select the |  | user agent about the criteria that were used to select the |
| representation. |  | representation. |
| Vary = "Vary" ":" OWS Vary-v |  | Vary = "Vary" ":" OWS Vary-v |
| Vary-v = "*" / 1#field-name |  | Vary-v = "*" / 1#field-name |
| skipping to change at page 25, line 41 |  | skipping to change at page 25, line 51 |
| 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 entity body 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, |
| distinguish 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 |
| Warning-v = 1#warning-value |  | Warning-v = 1#warning-value |
| warning-value = warn-code SP warn-agent SP warn-text |  | warning-value = warn-code SP warn-agent SP warn-text |
| [SP warn-date] |  | [SP warn-date] |
| skipping to change at page 28, line 12 |  | skipping to change at page 28, line 17 |
| 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 an entity retrieved |
| earlier in a session. |  | earlier in a session. |
| History mechanisms and caches are different. In particular history |  | The freshness model (Section 2.3) does not necessarily apply to |
| mechanisms SHOULD NOT try to show a correct view of the current state |  | history mechanisms. I.e., a history mechanism can display a previous |
| of a resource. Rather, a history mechanism is meant to show exactly |  | representation even if it has expired. |
| what the user saw at the time when the resource was retrieved. |  |  |
| By default, an expiration time does not apply to history mechanisms. |  |  |
| If the entity is still in storage, a history mechanism SHOULD display |  |  |
| it even if the entity has expired, unless the user has specifically |  |  |
| configured the agent to refresh expired history documents. |  |  |
| This is not to be construed to prohibit the history mechanism from |  |  |
| telling the user that a view might be stale. |  |  |
| Note: if history list mechanisms unnecessarily prevent users from |  | This does not prohibit the history mechanism from telling the user |
| viewing stale resources, this will tend to force service authors |  | that a view might be stale, or from honoring cache directives (e.g., |
| to avoid using HTTP expiration controls and cache controls when |  | Cache-Control: no-store). |
| they would otherwise like to. Service authors may consider it |  |  |
| important that users not be presented with error messages or |  |  |
| warning messages when they use navigation controls (such as BACK) |  |  |
| to view previously fetched resources. Even though sometimes such |  |  |
| resources ought not be cached, or ought to expire quickly, user |  |  |
| interface considerations may force service authors to resort to |  |  |
| other means of preventing caching (e.g. "once-only" URLs) in order |  |  |
| not to suffer the effects of improperly functioning history |  |  |
| mechanisms. |  |  |
| 5. IANA Considerations |  | 5. IANA Considerations |
| 5.1. Message Header Registration |  | 5.1. Message Header Registration |
| The Message Header Registry located at <http://www.iana.org/ |  | The Message Header Registry located at <http://www.iana.org/ |
| assignments/message-headers/message-header-index.html> should be |  | assignments/message-headers/message-header-index.html> should be |
| updated with the permanent registrations below (see [RFC3864]): |  | updated with the permanent registrations below (see [RFC3864]): |
| +-------------------+----------+----------+-------------+ |  | +-------------------+----------+----------+-------------+ |
| skipping to change at page 29, line 42 |  | skipping to change at page 29, line 24 |
| 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-08 |  | and Message Parsing", draft-ietf-httpbis-p1-messaging-09 |
| (work in progress), October 2009. |  | (work in progress), March 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-08 (work in |  | Semantics", draft-ietf-httpbis-p2-semantics-09 (work in |
| progress), October 2009. |  | progress), March 2010. |
| [Part3] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., |  |  |
| Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., |  |  |
| and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload |  |  |
| and Content Negotiation", draft-ietf-httpbis-p3-payload-08 |  |  |
| (work in progress), October 2009. |  |  |
| [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-08 (work in |  | Requests", draft-ietf-httpbis-p4-conditional-09 (work in |
| progress), October 2009. |  | progress), March 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-08 (work |  | Partial Responses", draft-ietf-httpbis-p5-range-09 (work |
| in progress), October 2009. |  | in progress), March 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-08 (work in progress), |  | draft-ietf-httpbis-p7-auth-09 (work in progress), |
| October 2009. |  | March 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 31, line 4 |  | skipping to change at page 30, line 25 |
| [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, June 1999. |  | Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. |
| [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration |  | [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration |
| Procedures for Message Header Fields", BCP 90, RFC 3864, |  | Procedures for Message Header Fields", BCP 90, RFC 3864, |
| September 2004. |  | September 2004. |
| Appendix A. Compatibility with Previous Versions |  | Appendix A. Compatibility with Previous Versions |
| A.1. Changes from RFC 2068 |  | A.1. Changes from RFC 2068 |
| A case was missed in the Cache-Control model of HTTP/1.1; s-maxage |  | 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). |  | was introduced to add this missing case. (Sections 2.1, 3.2). |
| Transfer-coding and message lengths all interact in ways that |  |  |
| required fixing exactly when chunked encoding is used (to allow for |  |  |
| transfer encoding that may not be self delimiting); it was important |  |  |
| to straighten out exactly how message lengths are computed. (see also |  |  |
| [Part1], [Part3] and [Part5]) [[anchor16: This used to refer to the |  |  |
| text about non-modifiable headers, and will have to be updated later |  |  |
| on. --jre]] |  |  |
| Proxies should be able to add Content-Length when appropriate. |  |  |
| [[anchor17: This used to refer to the text about non-modifiable |  |  |
| headers, and will have to be updated later on. --jre]] |  |  |
| Range request responses would become very verbose if all meta-data |  | Range request responses would become very verbose if all meta-data |
| were always returned; by allowing the server to only send needed |  | were always returned; by allowing the server to only send needed |
| headers in a 206 response, this problem can be avoided. |  | headers in a 206 response, this problem can be avoided. |
| (Section 2.7) |  | (Section 2.7) |
| The Cache-Control: max-age directive was not properly defined for |  | The Cache-Control: max-age directive was not properly defined for |
| responses. (Section 3.2.2) |  | responses. (Section 3.2.2) |
| Warnings could be cached incorrectly, or not updated appropriately. |  | Warnings could be cached incorrectly, or not updated appropriately. |
| (Section 2.3, 2.7, 3.2, and 3.6) Warning also needed to be a general |  | (Section 2.3, 2.7, 3.2, and 3.6) Warning also needed to be a general |
| skipping to change at page 36, line 21 |  | skipping to change at page 35, line 33 |
| o <http://tools.ietf.org/wg/httpbis/trac/ticket/167>: "Content- |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/167>: "Content- |
| Location on 304 responses" |  | Location on 304 responses" |
| o <http://tools.ietf.org/wg/httpbis/trac/ticket/169>: "private and |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/169>: "private and |
| no-cache CC directives with headers" |  | no-cache CC directives with headers" |
| o <http://tools.ietf.org/wg/httpbis/trac/ticket/187>: "RFC2047 and |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/187>: "RFC2047 and |
| warn-text" |  | warn-text" |
|  |  | C.10. Since draft-ietf-httpbis-p6-cache-08 |
|  |  | Closed issues: |
|  |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/147>: "serving |
|  |  | negotiated responses from cache: header-specific canonicalization" |
|  |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/197>: "Effect of CC |
|  |  | directives on history lists" |
|  |  | Affected issues: |
|  |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/199>: Status codes |
|  |  | and caching |
|  |  | Partly resolved issues: |
|  |  | o <http://tools.ietf.org/wg/httpbis/trac/ticket/60>: "Placement of |
|  |  | 13.5.1 and 13.5.2" |
| 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 18, 22 |  | max-age 19, 22 |
| max-stale 19 |  | max-stale 19 |
| min-fresh 19 |  | min-fresh 19 |
| must-revalidate 21 |  | must-revalidate 21 |
| no-cache 18, 20 |  | no-cache 18, 21 |
| no-store 18, 21 |  | no-store 18, 21 |
| no-transform 19, 22 |  | no-transform 19, 22 |
| only-if-cached 19 |  | only-if-cached 19 |
| private 20 |  | private 20 |
| proxy-revalidate 21 |  | proxy-revalidate 22 |
| public 20 |  | public 20 |
| s-maxage 22 |  | s-maxage 22 |
| Cache-Control header 17 |  | Cache-Control header 18 |
| cacheable 5 |  | cacheable 5 |
| E |  | E |
| Expires header 23 |  | Expires header 23 |
| 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 |
| skipping to change at page 37, line 22 |  | skipping to change at page 37, line 5 |
| cache-extension 18 |  | cache-extension 18 |
| cache-request-directive 18 |  | cache-request-directive 18 |
| cache-response-directive 20 |  | cache-response-directive 20 |
| delta-seconds 17 |  | delta-seconds 17 |
| Expires 23 |  | Expires 23 |
| Expires-v 23 |  | Expires-v 23 |
| extension-pragma 24 |  | extension-pragma 24 |
| Pragma 24 |  | Pragma 24 |
| pragma-directive 24 |  | pragma-directive 24 |
| Pragma-v 24 |  | Pragma-v 24 |
| Vary 24 |  | Vary 25 |
| Vary-v 24 |  | Vary-v 25 |
| warn-agent 26 |  | warn-agent 26 |
| warn-code 26 |  | warn-code 26 |
| warn-date 26 |  | warn-date 26 |
| warn-text 26 |  | warn-text 26 |
| Warning 26 |  | Warning 26 |
| Warning-v 26 |  | Warning-v 26 |
| warning-value 26 |  | warning-value 26 |
| H |  | H |
| Headers |  | Headers |
| Age 17 |  | Age 17 |
| Cache-Control 17 |  | Cache-Control 18 |
| Expires 23 |  | Expires 23 |
| Pragma 24 |  | Pragma 24 |
| Vary 24 |  | Vary 24 |
| Warning 25 |  | Warning 25 |
| heuristic expiration time 5 |  | heuristic expiration time 5 |
| M |  | M |
| max-age |  | max-age |
| Cache Directive 18, 22 |  | Cache Directive 19, 22 |
| max-stale |  | max-stale |
| Cache Directive 19 |  | Cache Directive 19 |
| min-fresh |  | min-fresh |
| Cache Directive 19 |  | Cache Directive 19 |
| must-revalidate |  | must-revalidate |
| Cache Directive 21 |  | Cache Directive 21 |
| N |  | N |
| no-cache |  | no-cache |
| Cache Directive 18, 20 |  | Cache Directive 18, 21 |
| no-store |  | no-store |
| Cache Directive 18, 21 |  | Cache Directive 18, 21 |
| no-transform |  | no-transform |
| Cache Directive 19, 22 |  | Cache Directive 19, 22 |
| O |  | O |
| only-if-cached |  | only-if-cached |
| Cache Directive 19 |  | Cache Directive 19 |
| P |  | P |
| Pragma header 24 |  | Pragma header 24 |
| private |  | private |
| Cache Directive 20 |  | Cache Directive 20 |
| proxy-revalidate |  | proxy-revalidate |
| Cache Directive 21 |  | 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 |
| V |  | V |
| validator 6 |  | validator 6 |
End of changes. 61 change blocks.
| 158 lines changed or deleted |  | 181 lines changed or added |
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