--- 1/draft-ietf-httpbis-p6-cache-11.txt 2010-10-25 15:16:33.000000000 +0200 +++ 2/draft-ietf-httpbis-p6-cache-12.txt 2010-10-25 15:16:33.000000000 +0200 @@ -1,71 +1,71 @@ HTTPbis Working Group R. Fielding, Ed. Internet-Draft Day Software Obsoletes: 2616 (if approved) J. Gettys Intended status: Standards Track Alcatel-Lucent -Expires: February 5, 2011 J. Mogul +Expires: April 28, 2011 J. Mogul HP H. Frystyk Microsoft L. Masinter Adobe Systems P. Leach Microsoft T. Berners-Lee W3C/MIT Y. Lafon, Ed. W3C M. Nottingham, Ed. J. Reschke, Ed. greenbytes - August 4, 2010 + October 25, 2010 HTTP/1.1, part 6: Caching - draft-ietf-httpbis-p6-cache-11 + draft-ietf-httpbis-p6-cache-12 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 and related documents (including fancy diffs) can be found at . - The changes in this draft are summarized in Appendix C.12. + The changes in this draft are summarized in Appendix C.13. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on February 5, 2011. + This Internet-Draft will expire on April 28, 2011. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -99,60 +99,61 @@ Specification . . . . . . . . . . . . . . . . . . . . 7 2. Cache Operation . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Response Cacheability . . . . . . . . . . . . . . . . . . 7 2.1.1. Storing Partial and Incomplete Responses . . . . . . . 8 2.2. Constructing Responses from Caches . . . . . . . . . . . . 9 2.3. Freshness Model . . . . . . . . . . . . . . . . . . . . . 10 2.3.1. Calculating Freshness Lifetime . . . . . . . . . . . . 11 2.3.2. Calculating Age . . . . . . . . . . . . . . . . . . . 12 2.3.3. Serving Stale Responses . . . . . . . . . . . . . . . 13 2.4. Validation Model . . . . . . . . . . . . . . . . . . . . . 14 - 2.5. Request Methods that Invalidate . . . . . . . . . . . . . 14 + 2.5. Request Methods that Invalidate . . . . . . . . . . . . . 15 2.6. Shared Caching of Authenticated Responses . . . . . . . . 15 2.7. Caching Negotiated Responses . . . . . . . . . . . . . . . 16 - 2.8. Combining Responses . . . . . . . . . . . . . . . . . . . 16 + 2.8. Combining Responses . . . . . . . . . . . . . . . . . . . 17 3. Header Field Definitions . . . . . . . . . . . . . . . . . . . 17 3.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 18 - 3.2.1. Request Cache-Control Directives . . . . . . . . . . . 18 + 3.2.1. Request Cache-Control Directives . . . . . . . . . . . 19 3.2.2. Response Cache-Control Directives . . . . . . . . . . 20 - 3.2.3. Cache Control Extensions . . . . . . . . . . . . . . . 22 + 3.2.3. Cache Control Extensions . . . . . . . . . . . . . . . 23 3.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 24 - 3.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 24 + 3.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.6. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 26 - 4. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 28 - 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 - 5.1. Cache Directive Registry . . . . . . . . . . . . . . . . . 28 - 5.2. Header Field Registration . . . . . . . . . . . . . . . . 29 - 6. Security Considerations . . . . . . . . . . . . . . . . . . . 29 + 4. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 29 + 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 + 5.1. Cache Directive Registry . . . . . . . . . . . . . . . . . 29 + 5.2. Header Field Registration . . . . . . . . . . . . . . . . 30 + 6. Security Considerations . . . . . . . . . . . . . . . . . . . 30 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30 8.1. Normative References . . . . . . . . . . . . . . . . . . . 30 8.2. Informative References . . . . . . . . . . . . . . . . . . 31 - Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 31 - Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 31 + Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 32 + Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 32 Appendix C. Change Log (to be removed by RFC Editor before publication) . . . . . . . . . . . . . . . . . . . . 33 - C.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 33 - C.2. Since draft-ietf-httpbis-p6-cache-00 . . . . . . . . . . . 33 + C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 34 + C.2. Since draft-ietf-httpbis-p6-cache-00 . . . . . . . . . . . 34 C.3. Since draft-ietf-httpbis-p6-cache-01 . . . . . . . . . . . 34 - C.4. Since draft-ietf-httpbis-p6-cache-02 . . . . . . . . . . . 34 - C.5. Since draft-ietf-httpbis-p6-cache-03 . . . . . . . . . . . 34 - C.6. Since draft-ietf-httpbis-p6-cache-04 . . . . . . . . . . . 34 + C.4. Since draft-ietf-httpbis-p6-cache-02 . . . . . . . . . . . 35 + C.5. Since draft-ietf-httpbis-p6-cache-03 . . . . . . . . . . . 35 + C.6. Since draft-ietf-httpbis-p6-cache-04 . . . . . . . . . . . 35 C.7. Since draft-ietf-httpbis-p6-cache-05 . . . . . . . . . . . 35 - C.8. Since draft-ietf-httpbis-p6-cache-06 . . . . . . . . . . . 35 - C.9. Since draft-ietf-httpbis-p6-cache-07 . . . . . . . . . . . 35 + C.8. Since draft-ietf-httpbis-p6-cache-06 . . . . . . . . . . . 36 + C.9. Since draft-ietf-httpbis-p6-cache-07 . . . . . . . . . . . 36 C.10. Since draft-ietf-httpbis-p6-cache-08 . . . . . . . . . . . 36 - C.11. Since draft-ietf-httpbis-p6-cache-09 . . . . . . . . . . . 36 + C.11. Since draft-ietf-httpbis-p6-cache-09 . . . . . . . . . . . 37 C.12. Since draft-ietf-httpbis-p6-cache-10 . . . . . . . . . . . 37 - Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 + C.13. Since draft-ietf-httpbis-p6-cache-11 . . . . . . . . . . . 38 + Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 1. Introduction HTTP is typically used for distributed information systems, where performance can be improved by the use of response caches. This document defines aspects of HTTP/1.1 related to caching and reusing response messages. 1.1. Purpose @@ -285,32 +286,32 @@ 2.1. Response Cacheability A cache MUST NOT store a response to any request, unless: 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 - in request or response headers, and + in request or response header fields, and o the "private" cache response directive (see Section 3.2.2 does not appear in the response, if the cache is shared, and - o the "Authorization" header (see Section 3.1 of [Part7]) does not - appear in the request, if the cache is shared, unless the response - explicitly allows it (see Section 2.6), and + o the "Authorization" header field (see Section 4.1 of [Part7]) does + not appear in the request, if the cache is shared, unless the + response explicitly allows it (see Section 2.6), and o the response either: - * contains an Expires header (see Section 3.3), or + * contains an Expires header field (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 @@ -324,44 +325,44 @@ content (see Section 2.1.1). Note that in normal operation, most caches will not store a response that has neither a cache validator nor an explicit expiration time, as such responses are not usually useful to store. However, caches are not prohibited from storing such responses. 2.1.1. Storing Partial and Incomplete Responses A cache that receives an incomplete response (for example, with fewer - bytes of data than specified in a Content-Length header) can store - the response, but MUST treat it as a partial response [Part5]. + bytes of data than specified in a Content-Length header field) can + store the response, but MUST treat it as a partial response [Part5]. Partial responses can be combined as described in Section 4 of [Part5]; the result might be a full response or might still be partial. A cache MUST NOT return a partial response to a client without explicitly marking it as such using the 206 (Partial Content) status code. - A cache that does not support the Range and Content-Range headers - MUST NOT store incomplete or partial responses. + A cache that does not support the Range and Content-Range header + fields MUST NOT store incomplete or partial responses. 2.2. Constructing Responses from Caches For a presented request, a cache MUST NOT return a stored response, unless: o The presented effective request URI (Section 4.3 of [Part1]) and that of the stored response match, and o the request method associated with the stored response allows it to be used for the presented request, and - o selecting request-headers nominated by the stored response (if - any) match those presented (see Section 2.7), and + o selecting request-header fields nominated by the stored response + (if any) match those presented (see Section 2.7), and 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 o the stored response is either: * fresh (see Section 2.3), or * allowed to be served stale (see Section 2.3.3), or @@ -374,50 +375,56 @@ 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 not reply to such a request before having forwarded the request and having received a corresponding response. Also, note that unsafe requests might invalidate already stored responses; see Section 2.5. Caches MUST use the most recent response (as determined by the Date - header) when more than one suitable response is stored. They can - also forward a request with "Cache-Control: max-age=0" or "Cache- + header field) when more than one suitable response is stored. They + can also forward a request with "Cache-Control: max-age=0" or "Cache- Control: no-cache" to disambiguate which response to use. + An HTTP implementation without a clock MUST NOT used stored responses + without revalidating them on every use. An HTTP cache, especially a + shared cache, SHOULD use a mechanism, such as NTP [RFC1305], to + synchronize its clock with a reliable external standard. + 2.3. Freshness Model When a response is "fresh" in the cache, it can be used to satisfy subsequent requests without contacting the origin server, thereby improving efficiency. The primary mechanism for determining freshness is for an origin server to provide an explicit expiration time in the future, using - either the Expires header (Section 3.3) or the max-age response cache - directive (Section 3.2.2). Generally, origin servers will assign - future explicit expiration times to responses in the belief that the - representation is not likely to change in a semantically significant - way before the expiration time is reached. + either the Expires header field (Section 3.3) or the max-age response + cache directive (Section 3.2.2). Generally, origin servers will + assign future explicit expiration times to responses in the belief + that the representation is not likely to change in a semantically + significant way before the expiration time is reached. If an origin server wishes to force a cache to validate every request, it can assign an explicit expiration time in the past to indicate that the response is already stale. Compliant caches will validate the cached response before reusing it for subsequent requests. Since origin servers do not always provide explicit expiration times, HTTP caches MAY assign heuristic expiration times when explicit times - are not specified, employing algorithms that use other header values - (such as the Last-Modified time) to estimate a plausible expiration - time. The HTTP/1.1 specification does not provide specific - algorithms, but does impose worst-case constraints on their results. + are not specified, employing algorithms that use other heade field + values (such as the Last-Modified time) to estimate a plausible + expiration time. The HTTP/1.1 specification does not provide + specific algorithms, but does impose worst-case constraints on their + results. The calculation to determine if a response is fresh is: response_is_fresh = (freshness_lifetime > current_age) The freshness_lifetime is defined in Section 2.3.1; the current_age is defined in Section 2.3.2. Additionally, clients might need to influence freshness calculation. They can do this using several request cache directives, with the @@ -436,83 +442,84 @@ A cache can calculate the freshness lifetime (denoted as freshness_lifetime) of a response by using the first match of: o If the cache is shared and the s-maxage response cache directive (Section 3.2.2) is present, use its value, or o If the max-age response cache directive (Section 3.2.2) is present, use its value, or - o If the Expires response header (Section 3.3) is present, use its - value minus the value of the Date response header, or + o If the Expires response header field (Section 3.3) is present, use + its value minus the value of the Date response header field, or o Otherwise, no explicit expiration time is present in the response. A heuristic freshness lifetime might be applicable; see Section 2.3.1.1. Note that this calculation is not vulnerable to clock skew, since all of the information comes from the origin server. 2.3.1.1. Calculating Heuristic Freshness If no explicit expiration time is present in a stored response that has a status code whose definition allows heuristic freshness to be used (including the following in Section 8 of [Part2]: 200, 203, 206, 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 - 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 - already present. + SHOULD attach a Warning header field with a 113 warn-code to the + response if its current_age is more than 24 hours and such a warning + is not already present. - Also, if the response has a Last-Modified header (Section 6.6 of - [Part4]), the heuristic expiration value SHOULD be no more than some - fraction of the interval since that time. A typical setting of this - fraction might be 10%. + Also, if the response has a Last-Modified header field (Section 6.6 + of [Part4]), the heuristic expiration value SHOULD be no more than + some fraction of the interval since that time. A typical setting of + this fraction might be 10%. Note: RFC 2616 ([RFC2616], Section 13.9) required that caches do not calculate heuristic freshness for URLs with query components (i.e., those containing '?'). In practice, this has not been widely implemented. Therefore, servers are encouraged to send explicit directives (e.g., Cache-Control: no-cache) if they wish to preclude caching. 2.3.2. Calculating Age - 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 - 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 - 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 - amount of time it has been in transit along network paths. + HTTP/1.1 uses the Age response-header field to convey the estimated + age of 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 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 each of the caches along the path from the origin + server, plus the amount of time it has been in transit along network + paths. The following data is used for the age calculation: age_value - The term "age_value" denotes the value of the Age header + The term "age_value" denotes the value of the Age header field (Section 3.1), in a form appropriate for arithmetic operation; or 0, if not available. date_value - HTTP/1.1 requires origin servers to send a Date header, if + HTTP/1.1 requires origin servers to send a Date header field, if possible, with every response, giving the time at which the response was generated. The term "date_value" denotes the value - of the Date header, in a form appropriate for arithmetic + of the Date header field, in a form appropriate for arithmetic operations. See Section 9.3 of [Part1] for the definition of the - Date header, and for requirements regarding responses without a - Date response header. + Date header field, and for requirements regarding responses + without it. now The term "now" means "the current value of the clock at the host performing the calculation". Hosts that use HTTP, but especially hosts running origin servers and caches, SHOULD use NTP ([RFC1305]) or some similar protocol to synchronize their clocks to a globally accurate time standard. request_time @@ -563,52 +570,53 @@ explicit in-protocol directive (e.g., by a "no-store" or "no-cache" cache directive, a "must-revalidate" cache-response-directive, or an applicable "s-maxage" or "proxy-revalidate" cache-response-directive; see Section 3.2.2). Caches SHOULD NOT return stale responses unless they are disconnected (i.e., it cannot contact the origin server or otherwise find a forward path) or otherwise explicitly allowed (e.g., the max-stale request directive; see Section 3.2.1). - Stale responses SHOULD have a Warning header with the 110 warn-code - (see Section 3.6). Likewise, the 112 warn-code SHOULD be sent on - stale responses if the cache is disconnected. + Stale responses SHOULD have a Warning header field with the 110 warn- + code (see Section 3.6). Likewise, the 112 warn-code SHOULD be sent + on stale responses if the cache is disconnected. If a cache receives a first-hand response (either an entire response, or a 304 (Not Modified) response) that it would normally forward to the requesting client, and the received response is no longer fresh, the cache SHOULD forward it to the requesting client without adding a - new Warning (but without removing any existing Warning headers). A - cache SHOULD NOT attempt to validate a response simply because that - response became stale in transit. + new Warning (but without removing any existing Warning header + fields). A cache SHOULD NOT attempt to validate a response simply + because that response became stale in transit. 2.4. Validation Model When a cache has one or more stored responses for a requested URI, but cannot serve any of them (e.g., because they are not fresh, or one cannot be selected; see Section 2.7), it can use the conditional request mechanism [Part4] in the forwarded request to give the origin server an opportunity to both select a valid stored response to be used, and to update it. This process is known as "validating" or "revalidating" the stored response. When sending such a conditional request, the cache SHOULD add an If- - Modified-Since header whose value is that of the Last-Modified header - from the selected (see Section 2.7) stored response, if available. + Modified-Since header field whose value is that of the Last-Modified + header field from the selected (see Section 2.7) stored response, if + available. - Additionally, the cache SHOULD add an If-None-Match header whose - value is that of the ETag header(s) from all responses stored for the - requested URI, if present. However, if any of the stored responses - 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 - that would be fully satisfied by that stored response. + Additionally, the cache SHOULD add an If-None-Match header field + whose value is that of the ETag header field(s) from all responses + stored for the requested URI, if present. However, if any of the + stored responses 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 that would be fully satisfied by that stored response. A 304 (Not Modified) response status code indicates that the stored response can be updated and reused; see Section 2.8. A full response (i.e., one with a response body) indicates that none of the stored responses nominated in the conditional request is suitable. Instead, the full response SHOULD be used to satisfy the request and MAY replace the stored response. If a cache receives a 5xx response while attempting to validate a @@ -617,99 +625,100 @@ case, it MAY return a previously stored response (see Section 2.3.3). 2.5. Request Methods that Invalidate Because unsafe methods (Section 7.1.1 of [Part2]) have the potential for changing state on the origin server, intervening caches can use them to keep their contents up-to-date. 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) - in the Location and Content-Location headers (if present): + in the Location and Content-Location header fields (if present): o PUT o DELETE o POST 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 - from the host part in the effective request URI (Section 4.3 of - [Part1]). This helps prevent denial of service attacks. + header field 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 [Part1]). This helps prevent denial of service attacks. A cache that passes through requests for methods it does not understand SHOULD invalidate the effective request URI (Section 4.3 of [Part1]). Here, "invalidate" means that the cache will either remove all stored responses related to the effective request URI, or will mark these as "invalid" and in need of a mandatory validation before they can be returned in response to a subsequent request. Note that this does not guarantee that all appropriate responses are invalidated. For example, the request that caused the change at the origin server might not have gone through the cache where a response is stored. 2.6. Shared Caching of Authenticated Responses 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 field (Section 4.1 of [Part7]) to satisfy any subsequent request unless a cache directive that allows such responses to be stored is present in the response. In this specification, the following Cache-Control response directives (Section 3.2.2) have such an effect: must-revalidate, public, s-maxage. Note that cached responses that contain the "must-revalidate" and/or "s-maxage" response directives are not allowed to be served stale (Section 2.3.3) by shared caches. In particular, a response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be used to satisfy a subsequent request without revalidating it on the origin server. 2.7. Caching Negotiated Responses 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 - that response unless all of the selecting request-headers nominated - by the Vary header match in both the original request (i.e., that - associated with the stored response), and the presented request. + that response unless all of the selecting request-header fields + nominated by the Vary header field match in both the original request + (i.e., that associated with the stored response), and the presented + request. - The selecting request-headers from two requests are defined to match - if and only if those in the first request can be transformed to those - in the second request by applying any of the following: + The selecting request-header fields from two requests are defined to + match if and only if those in the first request can be transformed to + those in the second request by applying any of the following: - o adding or removing whitespace, where allowed in the header's + o adding or removing whitespace, where allowed in the header field's 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) + o normalizing both header field values in a way that is known to + have identical semantics, according to the header field'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 normalization that might 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 subsequent requests to that resource can only be properly interpreted by the origin server. - The stored response with matching selecting request-headers is known - as the selected response. + The stored response with matching selecting request-header fields is + known as the selected response. If no selected response is available, the cache MAY forward the presented request to the origin server in a conditional request; see Section 2.4. 2.8. Combining Responses When a cache receives a 304 (Not Modified) response or a 206 (Partial Content) response (in this section, the "new" response"), it needs to created an updated response by combining the stored response with the @@ -719,35 +728,37 @@ If the new response contains an ETag, it identifies the stored response to use. [[TODO-mention-CL: might need language about Content-Location here]][[TODO-select-for-combine: Shouldn't this be the selected response?]] If the new response's status code is 206 (partial content), both the stored and new responses MUST have validators, and those validators MUST match using the strong comparison function (see Section 4 of [Part4]). Otherwise, the responses MUST NOT be combined. - The stored response headers are used as those of the updated + The stored response header fields are used as those of the updated response, except that - o any stored Warning headers with warn-code 1xx (see Section 3.6) - MUST be deleted. + o any stored Warning header fields with warn-code 1xx (see + Section 3.6) MUST be deleted. - o any stored Warning headers with warn-code 2xx MUST be retained. + o any stored Warning header fields with warn-code 2xx MUST be + retained. - o any other headers provided in the new response MUST replace all - instances of the corresponding headers from the stored response. + o any other header fields provided in the new response MUST replace + all instances of the corresponding header fields from the stored + response. - 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. + The updated response header fields 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 This section defines the syntax and semantics of HTTP/1.1 header fields related to caching. 3.1. Age The "Age" response-header field conveys the sender's estimate of the amount of time since the response was generated or successfully @@ -757,23 +768,23 @@ Age = "Age" ":" OWS Age-v Age-v = delta-seconds Age field-values are non-negative integers, representing time in seconds. delta-seconds = 1*DIGIT If a cache receives a value larger than the largest positive integer 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). - - Caches SHOULD use an arithmetic type of at least 31 bits of range. + MUST transmit an Age header field with a field-value of 2147483648 + (2^31). 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 response is not first-hand. However, the converse is not true, since HTTP/1.0 caches might not implement the Age header field. 3.2. Cache-Control The "Cache-Control" general-header field is used to specify directives for caches along the request/response chain. Such cache directives are unidirectional in that the presence of a directive in @@ -857,21 +868,22 @@ The min-fresh request directive indicates that the client is willing to accept a response whose freshness lifetime is no less 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 specified number of seconds. no-transform The no-transform request directive indicates that an intermediate cache or proxy MUST NOT change the Content-Encoding, Content-Range - or Content-Type request headers, nor the request representation. + or Content-Type request header fields, nor the request + representation. only-if-cached The only-if-cached request directive indicates that the client only wishes to return a stored response. If it receives this directive, a cache SHOULD either respond using a stored response that is consistent with the other constraints of the request, or respond with a 504 (Gateway Timeout) status code. If a group of caches is being operated as a unified system with good internal connectivity, such a request MAY be forwarded within that group of @@ -889,58 +901,58 @@ / "proxy-revalidate" / "max-age" "=" delta-seconds / "s-maxage" "=" delta-seconds / cache-extension public The public response directive indicates that the response MAY be cached, even if it would normally be non-cacheable or cacheable only within a non-shared cache. (See also Authorization, Section - 3.1 of [Part7], for additional details.) + 4.1 of [Part7], for additional details.) private The private response directive indicates that the response message is intended for a single user and MUST NOT be stored by a shared cache. A private (non-shared) cache MAY store the response. If the private response directive specifies one or more field- names, this requirement is limited to the field-values associated - with the listed response headers. That is, the specified field- - names(s) MUST NOT be stored by a shared cache, whereas the + with the listed response header fields. That is, the specified + field-names(s) MUST NOT be stored by a shared cache, whereas the remainder of the response message MAY be. Note: This usage of the word private only controls where the response can be stored; it cannot ensure the privacy of the message content. Also, private response directives with field- names are often handled by implementations as if an unqualified private directive was received; i.e., the special handling for the qualified form is not widely implemented. no-cache The no-cache response directive indicates that the response MUST NOT be used to satisfy a subsequent request without successful validation on the origin server. This allows an origin server to prevent a cache from using it to satisfy a request without contacting it, even by caches that have been configured to return stale responses. If the no-cache response directive specifies one or more field- names, this requirement is limited to the field-values associated - with the listed response headers. That is, the specified field- - name(s) MUST NOT be sent in the response to a subsequent request - without successful validation on the origin server. This allows - an origin server to prevent the re-use of certain header fields in - a response, while still allowing caching of the rest of the - response. + with the listed response header fields. That is, the specified + field-name(s) MUST NOT be sent in the response to a subsequent + request without successful validation on the origin server. This + allows an origin server to prevent the re-use of certain header + fields in a response, while still allowing caching of the rest of + the response. Note: Most HTTP/1.0 caches will not recognize or obey this directive. Also, no-cache response directives with field-names are often handled by implementations as if an unqualified no-cache directive was received; i.e., the special handling for the qualified form is not widely implemented. no-store The no-store response directive indicates that a cache MUST NOT @@ -983,28 +995,29 @@ The max-age response directive indicates that response is to be considered stale after its age is greater than the specified number of seconds. s-maxage The s-maxage response directive indicates that, in shared caches, the maximum age specified by this directive overrides the maximum age specified by either the max-age directive or the Expires - header. The s-maxage directive also implies the semantics of the - proxy-revalidate response directive. + header field. The s-maxage directive also implies the semantics + of the proxy-revalidate response directive. no-transform The no-transform response directive indicates that an intermediate cache or proxy MUST NOT change the Content-Encoding, Content-Range - or Content-Type response headers, nor the response representation. + or Content-Type response header fields, nor the response + representation. 3.2.3. Cache Control Extensions The Cache-Control header field can be extended through the use of one or more cache-extension tokens, each with an optional value. Informational extensions (those that do not require a change in cache behavior) can be added without changing the semantics of other directives. Behavioral extensions are designed to work by acting as modifiers to the existing base of cache directives. Both the new directive and the standard directive are supplied, such that @@ -1130,109 +1143,110 @@ validation; see Section 2.7. In uncacheable or stale responses, the Vary field value advises the user agent about the criteria that were used to select the representation. Vary = "Vary" ":" OWS Vary-v Vary-v = "*" / 1#field-name The set of header fields named by the Vary field value is known as - the selecting request-headers. + the selecting request-header fields. Servers SHOULD include a Vary header field with any cacheable response that is subject to server-driven negotiation. Doing so allows a cache to properly interpret future requests on that resource and informs the user agent about the presence of negotiation on that resource. A server MAY include a Vary header field with a non- cacheable response that is subject to server-driven negotiation, since this might provide the user agent with useful information about the dimensions over which the response varies at the time of the response. A Vary field value of "*" signals that unspecified parameters not - limited to the request-headers (e.g., the network address of the - client), play a role in the selection of the response representation; - therefore, a cache cannot determine whether this response is - appropriate. The "*" value MUST NOT be generated by a proxy server. + limited to the request-header fields (e.g., the network address of + the client), play a role in the selection of the response + representation; therefore, a cache cannot determine whether this + response is appropriate. The "*" value MUST NOT be generated by a + proxy server. The field-names given are not limited to the set of standard request- header fields defined by this specification. Field names are case- insensitive. 3.6. Warning The "Warning" general-header field is used to carry additional information about the status or transformation of a message that might not be reflected in the message. This information is typically used to warn about possible incorrectness introduced by caching operations or transformations applied to the payload of the message. Warnings can be used for other purposes, both cache-related and otherwise. The use of a warning, rather than an error status code, distinguishes these responses from true failures. - Warning headers can in general be applied to any message, however - some warn-codes are specific to caches and can only be applied to - response messages. + Warning header fields can in general be applied to any message, + however some warn-codes are specific to caches and can only be + applied to response messages. Warning = "Warning" ":" OWS Warning-v Warning-v = 1#warning-value warning-value = warn-code SP warn-agent SP warn-text [SP warn-date] warn-code = 3DIGIT warn-agent = ( uri-host [ ":" port ] ) / pseudonym ; the name or pseudonym of the server adding - ; the Warning header, for use in debugging + ; the Warning header field, for use in debugging warn-text = quoted-string warn-date = DQUOTE HTTP-date DQUOTE Multiple warnings can be attached to a response (either by the origin server or by a cache), including multiple warnings with the same code number, only differing in warn-text. When this occurs, the user agent SHOULD inform the user of as many of them as possible, in the order that they appear in the response. - Systems that generate multiple Warning headers SHOULD order them with - this user agent behavior in mind. New Warning headers SHOULD be - added after any existing Warning headers. + Systems that generate multiple Warning header fields SHOULD order + them with this user agent behavior in mind. New Warning header + fields SHOULD be added after any existing Warning headers fields. Warnings are assigned three digit warn-codes. The first digit indicates whether the Warning is required to be deleted from a stored response after validation: o 1xx Warnings describe the freshness or validation status of the response, and so MUST be deleted by caches after validation. They can only be generated by a cache when validating a cached entry, and MUST NOT be generated in any other situation. o 2xx Warnings describe some aspect of the representation that is not rectified by a validation (for example, a lossy compression of the representation) and MUST NOT be deleted by caches after validation, unless a full response is returned, in which case they MUST be. - 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 - MUST include in each warning-value a warn-date that matches the Date - header in the message. + If an implementation sends a message with one or more Warning header + fields 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 header field in the message. If an implementation receives a message with a warning-value that 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 the message before storing, forwarding, or using it. (preventing the consequences of naive caching of Warning header fields.) If all of the warning-values are deleted for this reason, the Warning header - MUST be deleted as well. + field MUST be deleted as well. The following warn-codes are defined by this specification, each with a recommended warn-text in English, and a description of its meaning. 110 Response is stale SHOULD be included whenever the returned response is stale. 111 Revalidation failed @@ -1351,46 +1365,46 @@ suggestions and comments from individuals including: Shel Kaphan, Paul Leach, Koen Holtman, David Morris, and Larry Masinter. 8. References 8.1. Normative References [Part1] 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 1: URIs, Connections, - and Message Parsing", draft-ietf-httpbis-p1-messaging-11 - (work in progress), August 2010. + and Message Parsing", draft-ietf-httpbis-p1-messaging-12 + (work in progress), October 2010. [Part2] 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 2: Message - Semantics", draft-ietf-httpbis-p2-semantics-11 (work in - progress), August 2010. + Semantics", draft-ietf-httpbis-p2-semantics-12 (work in + progress), October 2010. [Part4] 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 4: Conditional - Requests", draft-ietf-httpbis-p4-conditional-11 (work in - progress), August 2010. + Requests", draft-ietf-httpbis-p4-conditional-12 (work in + progress), October 2010. [Part5] 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 5: Range Requests and - Partial Responses", draft-ietf-httpbis-p5-range-11 (work - in progress), August 2010. + Partial Responses", draft-ietf-httpbis-p5-range-12 (work + in progress), October 2010. [Part7] 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 7: Authentication", - draft-ietf-httpbis-p7-auth-11 (work in progress), - August 2010. + draft-ietf-httpbis-p7-auth-12 (work in progress), + October 2010. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. 8.2. Informative References [RFC1305] Mills, D., "Network Time Protocol (Version 3) @@ -1417,21 +1431,21 @@ (Section 2.3.2) Remove requirement to consider Content-Location in successful responses in order to determine the appropriate response to use. (Section 2.4) Clarify denial of service attack avoidance requirement. (Section 2.5) Do not mention RFC 2047 encoding and multiple languages in Warning - headers anymore, as these aspects never were implemented. + header fields anymore, as these aspects never were implemented. (Section 3.6) Appendix B. Collected ABNF Age = "Age:" OWS Age-v Age-v = delta-seconds Cache-Control = "Cache-Control:" OWS Cache-Control-v Cache-Control-v = *( "," OWS ) cache-directive *( OWS "," [ OWS cache-directive ] ) @@ -1553,45 +1566,45 @@ Other changes: o Get rid of duplicate BNF rule names ("host" -> "uri-host") (work in progress on ) o Add explicit references to BNF syntax and rules imported from other parts of the specification. C.4. Since draft-ietf-httpbis-p6-cache-02 - Ongoing work on IANA Message Header Registration + Ongoing work on IANA Message Header Field Registration (): - o Reference RFC 3984, and update header registrations for headers - defined in this document. + o Reference RFC 3984, and update header field registrations for + header fields defined in this document. C.5. Since draft-ietf-httpbis-p6-cache-03 Closed issues: o : "Vary header classification" C.6. Since draft-ietf-httpbis-p6-cache-04 Ongoing work on ABNF conversion (): o Use "/" instead of "|" for alternatives. o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional whitespace ("OWS") and required whitespace ("RWS"). o Rewrite ABNFs to spell out whitespace rules, factor out header - value format definitions. + field value format definitions. C.7. Since draft-ietf-httpbis-p6-cache-05 This is a total rewrite of this part of the specification. Affected issues: o : "Definition of 1xx Warn-Codes" @@ -1612,22 +1625,22 @@ C.8. Since draft-ietf-httpbis-p6-cache-06 Closed issues: o : "base for numeric protocol elements" Affected issues: - o : Vary and non- - existant headers + o : WVary and non- + existant headers" C.9. Since draft-ietf-httpbis-p6-cache-07 Closed issues: o : "Definition of 1xx Warn-Codes" o : "Content- Location on 304 responses" @@ -1694,115 +1707,122 @@ removing the 'changes from 2068' sections" o : "Allowing heuristic caching for new status codes" o : "Allowing heuristic caching for new status codes" o Clean up TODOs and prose in "Combining Responses." +C.13. Since draft-ietf-httpbis-p6-cache-11 + + Closed issues: + + o : "Text about + clock requirement for caches belongs in p6" + Index A age 6 Age header 17 C cache 5 Cache Directives max-age 19, 22 max-stale 19 - min-fresh 19 + min-fresh 20 must-revalidate 22 no-cache 19, 21 no-store 19, 21 - no-transform 20, 22 + no-transform 20, 23 only-if-cached 20 - private 20 + private 21 proxy-revalidate 22 public 20 s-maxage 22 Cache-Control header 18 cacheable 5 E Expires header 24 explicit expiration time 5 F first-hand 6 fresh 6 freshness lifetime 6 G Grammar - Age 17 - Age-v 17 + Age 18 + Age-v 18 Cache-Control 18 Cache-Control-v 18 cache-extension 18 - cache-request-directive 18 + cache-request-directive 19 cache-response-directive 20 - delta-seconds 17 + delta-seconds 18 Expires 24 Expires-v 24 - extension-pragma 24 - Pragma 24 - pragma-directive 24 - Pragma-v 24 + extension-pragma 25 + Pragma 25 + pragma-directive 25 + Pragma-v 25 Vary 25 Vary-v 25 - warn-agent 26 - warn-code 26 - warn-date 26 - warn-text 26 - Warning 26 - Warning-v 26 - warning-value 26 + warn-agent 27 + warn-code 27 + warn-date 27 + warn-text 27 + Warning 27 + Warning-v 27 + warning-value 27 H Headers Age 17 Cache-Control 18 Expires 24 - Pragma 24 + Pragma 25 Vary 25 Warning 26 heuristic expiration time 5 M max-age Cache Directive 19, 22 max-stale Cache Directive 19 min-fresh - Cache Directive 19 + Cache Directive 20 must-revalidate Cache Directive 22 N no-cache Cache Directive 19, 21 no-store Cache Directive 19, 21 no-transform - Cache Directive 20, 22 + Cache Directive 20, 23 O only-if-cached Cache Directive 20 P - Pragma header 24 + Pragma header 25 private - Cache Directive 20 + Cache Directive 21 proxy-revalidate Cache Directive 22 public Cache Directive 20 S s-maxage Cache Directive 22 stale 6