draft-ietf-httpbis-p6-cache-19.txt   draft-ietf-httpbis-p6-cache-20.txt 
HTTPbis Working Group R. Fielding, Ed. HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Adobe Internet-Draft Adobe
Obsoletes: 2616 (if approved) Y. Lafon, Ed. Obsoletes: 2616 (if approved) Y. Lafon, Ed.
Intended status: Standards Track W3C Intended status: Standards Track W3C
Expires: September 13, 2012 M. Nottingham, Ed. Expires: January 17, 2013 M. Nottingham, Ed.
Rackspace Rackspace
J. Reschke, Ed. J. Reschke, Ed.
greenbytes greenbytes
March 12, 2012 July 16, 2012
HTTP/1.1, part 6: Caching HTTP/1.1, part 6: Caching
draft-ietf-httpbis-p6-cache-19 draft-ietf-httpbis-p6-cache-20
Abstract Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypertext information protocol for distributed, collaborative, hypertext information
systems. HTTP has been in use by the World Wide Web global systems. This document defines requirements on HTTP caches and the
information initiative since 1990. This document is Part 6 of the associated header fields that control cache behavior or indicate
seven-part specification that defines the protocol referred to as cacheable response messages.
"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) Editorial Note (To be removed by RFC Editor)
Discussion of this draft should take place on the HTTPBIS working Discussion of this draft takes place on the HTTPBIS working group
group mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>. <http://lists.w3.org/Archives/Public/ietf-http-wg/>.
The current issues list is at The current issues list is at
<http://tools.ietf.org/wg/httpbis/trac/report/3> and related <http://tools.ietf.org/wg/httpbis/trac/report/3> and related
documents (including fancy diffs) can be found at documents (including fancy diffs) can be found at
<http://tools.ietf.org/wg/httpbis/>. <http://tools.ietf.org/wg/httpbis/>.
The changes in this draft are summarized in Appendix C.20. The changes in this draft are summarized in Appendix D.1.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 13, 2012. This Internet-Draft will expire on January 17, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 42 skipping to change at page 2, line 37
modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Conformance and Error Handling . . . . . . . . . . . . . . 7 1.3. Conformance and Error Handling . . . . . . . . . . . . . . 6
1.4. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 7 1.4. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 7
1.4.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 8 1.4.1. Delta Seconds . . . . . . . . . . . . . . . . . . . . 7
1.4.2. ABNF Rules defined in other Parts of the 2. Overview of Cache Operation . . . . . . . . . . . . . . . . . 7
Specification . . . . . . . . . . . . . . . . . . . . 8 3. Storing Responses in Caches . . . . . . . . . . . . . . . . . 8
1.5. Delta Seconds . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Storing Incomplete Responses . . . . . . . . . . . . . . . 9
2. Cache Operation . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Storing Responses to Authenticated Requests . . . . . . . 9
2.1. Response Cacheability . . . . . . . . . . . . . . . . . . 9 4. Constructing Responses from Caches . . . . . . . . . . . . . . 10
2.2. Constructing Responses from Caches . . . . . . . . . . . . 10 4.1. Freshness Model . . . . . . . . . . . . . . . . . . . . . 11
2.3. Freshness Model . . . . . . . . . . . . . . . . . . . . . 12 4.1.1. Calculating Freshness Lifetime . . . . . . . . . . . . 12
2.3.1. Calculating Freshness Lifetime . . . . . . . . . . . . 13 4.1.2. Calculating Heuristic Freshness . . . . . . . . . . . 12
2.3.2. Calculating Age . . . . . . . . . . . . . . . . . . . 14 4.1.3. Calculating Age . . . . . . . . . . . . . . . . . . . 13
2.3.3. Serving Stale Responses . . . . . . . . . . . . . . . 16 4.1.4. Serving Stale Responses . . . . . . . . . . . . . . . 15
2.4. Validation Model . . . . . . . . . . . . . . . . . . . . . 16 4.2. Validation Model . . . . . . . . . . . . . . . . . . . . . 16
2.4.1. Freshening Responses with 304 Not Modified . . . . . . 17 4.2.1. Freshening Responses with 304 Not Modified . . . . . . 16
2.5. Updating Caches with HEAD Responses . . . . . . . . . . . 18 4.3. Using Negotiated Responses . . . . . . . . . . . . . . . . 17
2.6. Request Methods that Invalidate . . . . . . . . . . . . . 18 4.4. Combining Partial Content . . . . . . . . . . . . . . . . 18
2.7. Shared Caching of Authenticated Responses . . . . . . . . 19 5. Updating Caches with HEAD Responses . . . . . . . . . . . . . 19
2.8. Caching Negotiated Responses . . . . . . . . . . . . . . . 19 6. Request Methods that Invalidate . . . . . . . . . . . . . . . 19
2.9. Combining Partial Content . . . . . . . . . . . . . . . . 20 7. Header Field Definitions . . . . . . . . . . . . . . . . . . . 20
3. Header Field Definitions . . . . . . . . . . . . . . . . . . . 21 7.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 20
3.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 21 7.2.1. Request Cache-Control Directives . . . . . . . . . . . 21
3.2.1. Request Cache-Control Directives . . . . . . . . . . . 22 7.2.2. Response Cache-Control Directives . . . . . . . . . . 23
3.2.2. Response Cache-Control Directives . . . . . . . . . . 24 7.2.3. Cache Control Extensions . . . . . . . . . . . . . . . 26
3.2.3. Cache Control Extensions . . . . . . . . . . . . . . . 26 7.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 28 7.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 7.6. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.6. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 30 7.6.1. 110 Response is Stale . . . . . . . . . . . . . . . . 31
3.6.1. 110 Response is Stale . . . . . . . . . . . . . . . . 31 7.6.2. 111 Revalidation Failed . . . . . . . . . . . . . . . 32
3.6.2. 111 Revalidation Failed . . . . . . . . . . . . . . . 31 7.6.3. 112 Disconnected Operation . . . . . . . . . . . . . . 32
3.6.3. 112 Disconnected Operation . . . . . . . . . . . . . . 31 7.6.4. 113 Heuristic Expiration . . . . . . . . . . . . . . . 32
3.6.4. 113 Heuristic Expiration . . . . . . . . . . . . . . . 32 7.6.5. 199 Miscellaneous Warning . . . . . . . . . . . . . . 32
3.6.5. 199 Miscellaneous Warning . . . . . . . . . . . . . . 32 7.6.6. 214 Transformation Applied . . . . . . . . . . . . . . 32
3.6.6. 214 Transformation Applied . . . . . . . . . . . . . . 32 7.6.7. 299 Miscellaneous Persistent Warning . . . . . . . . . 32
3.6.7. 299 Miscellaneous Persistent Warning . . . . . . . . . 32 7.6.8. Warn Code Extensions . . . . . . . . . . . . . . . . . 32
3.6.8. Warn Code Extensions . . . . . . . . . . . . . . . . . 32 8. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 33
4. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 32 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 9.1. Cache Directive Registry . . . . . . . . . . . . . . . . . 33
5.1. Cache Directive Registry . . . . . . . . . . . . . . . . . 33 9.2. Warn Code Registry . . . . . . . . . . . . . . . . . . . . 34
5.2. Warn Code Registry . . . . . . . . . . . . . . . . . . . . 33 9.3. Header Field Registration . . . . . . . . . . . . . . . . 34
5.3. Header Field Registration . . . . . . . . . . . . . . . . 34 10. Security Considerations . . . . . . . . . . . . . . . . . . . 35
6. Security Considerations . . . . . . . . . . . . . . . . . . . 34 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 34 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35 12.1. Normative References . . . . . . . . . . . . . . . . . . . 35
8.1. Normative References . . . . . . . . . . . . . . . . . . . 35 12.2. Informative References . . . . . . . . . . . . . . . . . . 36
8.2. Informative References . . . . . . . . . . . . . . . . . . 35
Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 36 Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 36
Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 36 Appendix B. Imported ABNF . . . . . . . . . . . . . . . . . . . . 37
Appendix C. Change Log (to be removed by RFC Editor before Appendix C. Collected ABNF . . . . . . . . . . . . . . . . . . . 38
publication) . . . . . . . . . . . . . . . . . . . . 37 Appendix D. Change Log (to be removed by RFC Editor before
C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 38 publication) . . . . . . . . . . . . . . . . . . . . 39
C.2. Since draft-ietf-httpbis-p6-cache-00 . . . . . . . . . . . 38 D.1. Since draft-ietf-httpbis-p6-cache-19 . . . . . . . . . . . 39
C.3. Since draft-ietf-httpbis-p6-cache-01 . . . . . . . . . . . 38 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
C.4. Since draft-ietf-httpbis-p6-cache-02 . . . . . . . . . . . 39
C.5. Since draft-ietf-httpbis-p6-cache-03 . . . . . . . . . . . 39
C.6. Since draft-ietf-httpbis-p6-cache-04 . . . . . . . . . . . 39
C.7. Since draft-ietf-httpbis-p6-cache-05 . . . . . . . . . . . 39
C.8. Since draft-ietf-httpbis-p6-cache-06 . . . . . . . . . . . 40
C.9. Since draft-ietf-httpbis-p6-cache-07 . . . . . . . . . . . 40
C.10. Since draft-ietf-httpbis-p6-cache-08 . . . . . . . . . . . 40
C.11. Since draft-ietf-httpbis-p6-cache-09 . . . . . . . . . . . 41
C.12. Since draft-ietf-httpbis-p6-cache-10 . . . . . . . . . . . 41
C.13. Since draft-ietf-httpbis-p6-cache-11 . . . . . . . . . . . 42
C.14. Since draft-ietf-httpbis-p6-cache-12 . . . . . . . . . . . 42
C.15. Since draft-ietf-httpbis-p6-cache-13 . . . . . . . . . . . 42
C.16. Since draft-ietf-httpbis-p6-cache-14 . . . . . . . . . . . 42
C.17. Since draft-ietf-httpbis-p6-cache-15 . . . . . . . . . . . 43
C.18. Since draft-ietf-httpbis-p6-cache-16 . . . . . . . . . . . 43
C.19. Since draft-ietf-httpbis-p6-cache-17 . . . . . . . . . . . 43
C.20. Since draft-ietf-httpbis-p6-cache-18 . . . . . . . . . . . 43
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
1. Introduction 1. Introduction
HTTP is typically used for distributed information systems, where HTTP is typically used for distributed information systems, where
performance can be improved by the use of response caches. This performance can be improved by the use of response caches. This
document defines aspects of HTTP/1.1 related to caching and reusing document defines aspects of HTTP/1.1 related to caching and reusing
response messages. response messages.
1.1. Purpose 1.1. Purpose
An HTTP cache is a local store of response messages and the subsystem An HTTP cache is a local store of response messages and the subsystem
that controls its message storage, retrieval, and deletion. A cache that controls its message storage, retrieval, and deletion. A cache
stores cacheable responses in order to reduce the response time and stores cacheable responses in order to reduce the response time and
network bandwidth consumption on future, equivalent requests. Any network bandwidth consumption on future, equivalent requests. Any
client or server MAY employ a cache, though a cache cannot be used by client or server MAY employ a cache, though a cache cannot be used by
a server that is acting as a tunnel. a server that is acting as a tunnel.
The goal of caching in HTTP/1.1 is to significantly improve The goal of caching in HTTP/1.1 is to significantly improve
performance by reusing a prior response message to satisfy a current performance by reusing a prior response message to satisfy a current
request. A stored response is considered "fresh", as defined in request. A stored response is considered "fresh", as defined in
Section 2.3, if the response can be reused without "validation" Section 4.1, if the response can be reused without "validation"
(checking with the origin server to see if the cached response (checking with the origin server to see if the cached response
remains valid for this request). A fresh cache response can remains valid for this request). A fresh cache response can
therefore reduce both latency and network transfers each time it is therefore reduce both latency and network transfers each time it is
reused. When a cached response is not fresh, it might still be reused. When a cached response is not fresh, it might still be
reusable if it can be freshened by validation (Section 2.4) or if the reusable if it can be freshened by validation (Section 4.2) or if the
origin is unavailable. origin is unavailable.
1.2. Terminology 1.2. Terminology
This specification uses a number of terms to refer to the roles This specification uses a number of terms to refer to the roles
played by participants in, and objects of, HTTP caching. played by participants in, and objects of, HTTP caching.
cache cache
A conformant implementation of a HTTP cache. Note that this A conformant implementation of a HTTP cache. Note that this
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i.e., an entity-tag that is not marked as weak (Section 2.3 of i.e., an entity-tag that is not marked as weak (Section 2.3 of
[Part4]) or, if no entity-tag is provided, a Last-Modified value [Part4]) or, if no entity-tag is provided, a Last-Modified value
that is strong in the sense defined by Section 2.2.2 of [Part4]. that is strong in the sense defined by Section 2.2.2 of [Part4].
1.3. Conformance and Error Handling 1.3. Conformance and Error Handling
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
This document defines conformance criteria for several roles in HTTP This specification targets conformance criteria according to the role
communication, including Senders, Recipients, Clients, Servers, User- of a participant in HTTP communication. Hence, HTTP requirements are
Agents, Origin Servers, Intermediaries, Proxies and Gateways. See placed on senders, recipients, clients, servers, user agents,
Section 2 of [Part1] for definitions of these terms. intermediaries, origin servers, proxies, gateways, or caches,
depending on what behavior is being constrained by the requirement.
See Section 2 of [Part1] for definitions of these terms.
The verb "generate" is used instead of "send" where a requirement
differentiates between creating a protocol element and merely
forwarding a received element downstream.
An implementation is considered conformant if it complies with all of An implementation is considered conformant if it complies with all of
the requirements associated with its role(s). Note that SHOULD-level the requirements associated with the roles it partakes in HTTP. Note
requirements are relevant here, unless one of the documented that SHOULD-level requirements are relevant here, unless one of the
exceptions is applicable. documented exceptions is applicable.
This document also uses ABNF to define valid protocol elements This document also uses ABNF to define valid protocol elements
(Section 1.4). In addition to the prose requirements placed upon (Section 1.4). In addition to the prose requirements placed upon
them, Senders MUST NOT generate protocol elements that are invalid. them, senders MUST NOT generate protocol elements that do not match
the grammar defined by the ABNF rules for those protocol elements
that are applicable to the sender's role. If a received protocol
element is processed, the recipient MUST be able to parse any value
that would match the ABNF rules for that protocol element, excluding
only those rules not applicable to the recipient's role.
Unless noted otherwise, Recipients MAY take steps to recover a usable Unless noted otherwise, a recipient MAY attempt to recover a usable
protocol element from an invalid construct. However, HTTP does not protocol element from an invalid construct. HTTP does not define
define specific error handling mechanisms, except in cases where it specific error handling mechanisms except when they have a direct
has direct impact on security. This is because different uses of the impact on security, since different applications of the protocol
protocol require different error handling strategies; for example, a require different error handling strategies. For example, a Web
Web browser may wish to transparently recover from a response where browser might wish to transparently recover from a response where the
the Location header field doesn't parse according to the ABNF, Location header field doesn't parse according to the ABNF, whereas a
whereby in a systems control protocol using HTTP, this type of error systems control client might consider any form of error recovery to
recovery could lead to dangerous consequences. be dangerous.
1.4. Syntax Notation 1.4. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF) This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234] with the list rule extension defined in Section notation of [RFC5234] with the list rule extension defined in Section
1.2 of [Part1]. Appendix B shows the collected ABNF with the list 1.2 of [Part1]. Appendix B describes rules imported from other
rule expanded. documents. Appendix C shows the collected ABNF with the list rule
expanded.
The following core rules are included by reference, as defined in
[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit
sequence of data), SP (space), and VCHAR (any visible US-ASCII
character).
1.4.1. Core Rules
The core rules below are defined in [Part1]:
OWS = <OWS, defined in [Part1], Section 3.2.1>
quoted-string = <quoted-string, defined in [Part1], Section 3.2.4>
token = <token, defined in [Part1], Section 3.2.4>
1.4.2. ABNF Rules defined in other Parts of the Specification
The ABNF rules below are defined in other parts:
field-name = <field-name, defined in [Part1], Section 3.2>
HTTP-date = <HTTP-date, defined in [Part2], Section 8>
port = <port, defined in [Part1], Section 2.7>
pseudonym = <pseudonym, defined in [Part1], Section 6.2>
uri-host = <uri-host, defined in [Part1], Section 2.7>
1.5. Delta Seconds 1.4.1. Delta Seconds
The delta-seconds rule specifies a non-negative integer, representing The delta-seconds rule specifies a non-negative integer, representing
time in seconds. time in seconds.
delta-seconds = 1*DIGIT delta-seconds = 1*DIGIT
If an implementation receives a delta-seconds value larger than the If an implementation receives a delta-seconds value larger than the
largest positive integer it can represent, or if any of its largest positive integer it can represent, or if any of its
subsequent calculations overflows, it MUST consider the value to be subsequent calculations overflows, it MUST consider the value to be
2147483648 (2^31). Recipients parsing a delta-seconds value MUST use 2147483648 (2^31). Recipients parsing a delta-seconds value MUST use
an arithmetic type of at least 31 bits of range, and senders MUST NOT an arithmetic type of at least 31 bits of range, and senders MUST NOT
send delta-seconds with a value greater than 2147483648. send delta-seconds with a value greater than 2147483648.
2. Cache Operation 2. Overview of Cache Operation
Proper cache operation preserves the semantics of HTTP transfers Proper cache operation preserves the semantics of HTTP transfers
([Part2]) while eliminating the transfer of information already held ([Part2]) while eliminating the transfer of information already held
in the cache. Although caching is an entirely OPTIONAL feature of in the cache. Although caching is an entirely OPTIONAL feature of
HTTP, we assume that reusing the cached response is desirable and HTTP, we assume that reusing the cached response is desirable and
that such reuse is the default behavior when no requirement or that such reuse is the default behavior when no requirement or
locally-desired configuration prevents it. Therefore, HTTP cache locally-desired configuration prevents it. Therefore, HTTP cache
requirements are focused on preventing a cache from either storing a requirements are focused on preventing a cache from either storing a
non-reusable response or reusing a stored response inappropriately. non-reusable response or reusing a stored response inappropriately.
Each cache entry consists of a cache key and one or more HTTP Each cache entry consists of a cache key and one or more HTTP
responses corresponding to prior requests that used the same key. responses corresponding to prior requests that used the same key.
The most common form of cache entry is a successful result of a The most common form of cache entry is a successful result of a
retrieval request: i.e., a 200 (OK) response containing a retrieval request: i.e., a 200 (OK) response containing a
representation of the resource identified by the request target. representation of the resource identified by the request target.
However, it is also possible to cache negative results (e.g., 404 not However, it is also possible to cache negative results (e.g., 404
found), incomplete results (e.g., 206 partial content), and responses (Not Found), incomplete results (e.g., 206 (Partial Content)), and
to safe methods other than GET if the method's definition allows such responses to methods other than GET if the method's definition allows
caching and defines something suitable for use as a cache key. such caching and defines something suitable for use as a cache key.
The default cache key consists of the request method and target URI. The default cache key consists of the request method and target URI.
However, since HTTP caches in common use today are typically limited However, since HTTP caches in common use today are typically limited
to caching responses to GET, most implementations simply decline to caching responses to GET, many implementations simply decline
other methods and use only the URI as the key. other methods and use only the URI as the key.
If a request target is subject to content negotiation, its cache If a request target is subject to content negotiation, its cache
entry might consist of multiple stored responses, each differentiated entry might consist of multiple stored responses, each differentiated
by a secondary key for the values of the original request's selecting by a secondary key for the values of the original request's selecting
header fields (Section 2.8). header fields (Section 4.3).
2.1. Response Cacheability 3. Storing Responses in Caches
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 understood by the cache and defined as being o The request method is understood by the cache and defined as being
cacheable, and cacheable, and
o the response status code is understood by the cache, 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 7.2) does not appear
in request or response header fields, and in request or response header fields, and
o the "private" cache response directive (see Section 3.2.2) does o the "private" cache response directive (see Section 7.2.2.2) does
not appear in the response, if the cache is shared, and not appear in the response, if the cache is shared, and
o the "Authorization" header field (see Section 4.1 of [Part7]) does o the Authorization header field (see Section 4.1 of [Part7]) does
not appear in the request, if the cache is shared, unless the not appear in the request, if the cache is shared, unless the
response explicitly allows it (see Section 2.7), and response explicitly allows it (see Section 3.2), and
o the response either: o the response either:
* contains an Expires header field (see Section 3.3), or * contains an Expires header field (see Section 7.3), or
* contains a max-age response cache directive (see * contains a max-age response cache directive (see
Section 3.2.2), or Section 7.2.2.7), or
* contains a s-maxage response cache directive and the cache is * contains a s-maxage response cache directive and the cache is
shared, or shared, or
* contains a Cache Control Extension (see Section 3.2.3) that * contains a Cache Control Extension (see Section 7.2.3) that
allows it to be cached, or allows it to be cached, or
* has a status code that can be served with heuristic freshness * has a status code that can be served with heuristic freshness
(see Section 2.3.1.1). (see Section 4.1.2).
Note that any of the requirements listed above can be overridden by a Note that any of the requirements listed above can be overridden by a
cache-control extension; see Section 3.2.3. cache-control extension; see Section 7.2.3.
In this context, a cache has "understood" a request method or a In this context, a cache has "understood" a request method or a
response status code if it recognizes it and implements any cache- response status code if it recognizes it and implements any cache-
specific behavior. specific behavior.
Note that, in normal operation, most caches will not store a response Note that, in normal operation, many 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.
3.1. Storing Incomplete Responses
A response message is considered complete when all of the octets A response message is considered complete when all of the octets
indicated by the message framing ([Part1]) are received prior to the indicated by the message framing ([Part1]) are received prior to the
connection being closed. If the request is GET, the response status connection being closed. If the request is GET, the response status
is 200 (OK), and the entire response header block has been received, is 200 (OK), and the entire response header block has been received,
a cache MAY store an incomplete response message body if the cache a cache MAY store an incomplete response message body if the cache
entry is recorded as incomplete. Likewise, a 206 (Partial Content) entry is recorded as incomplete. Likewise, a 206 (Partial Content)
response MAY be stored as if it were an incomplete 200 (OK) cache response MAY be stored as if it were an incomplete 200 (OK) cache
entry. However, a cache MUST NOT store incomplete or partial content entry. However, a cache MUST NOT store incomplete or partial content
responses if it does not support the Range and Content-Range header responses if it does not support the Range and Content-Range header
fields or if it does not understand the range units used in those fields or if it does not understand the range units used in those
fields. fields.
A cache MAY complete a stored incomplete response by making a A cache MAY complete a stored incomplete response by making a
subsequent range request ([Part5]) and combining the successful subsequent range request ([Part5]) and combining the successful
response with the stored entry, as defined in Section 2.9. A cache response with the stored entry, as defined in Section 4.4. A cache
MUST NOT use an incomplete response to answer requests unless the MUST NOT use an incomplete response to answer requests unless the
response has been made complete or the request is partial and response has been made complete or the request is partial and
specifies a range that is wholly within the incomplete response. A specifies a range that is wholly within the incomplete response. A
cache MUST NOT send a partial response to a client without explicitly cache MUST NOT send a partial response to a client without explicitly
marking it as such using the 206 (Partial Content) status code. marking it as such using the 206 (Partial Content) status code.
2.2. Constructing Responses from Caches 3.2. Storing Responses to Authenticated Requests
A shared cache MUST NOT use a cached response to a request with an
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 7.2.2) 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 4.1.4) 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.
4. Constructing Responses from Caches
For a presented request, a cache MUST NOT return a stored response, For a presented request, a cache MUST NOT return a stored response,
unless: unless:
o The presented effective request URI (Section 5.5 of [Part1]) and o The presented effective request URI (Section 5.5 of [Part1]) and
that of the stored response match, and that of the stored response match, and
o the request method associated with the stored response allows it o the request method associated with the stored response allows it
to be used for the presented request, and to be used for the presented request, and
o selecting header fields nominated by the stored response (if any) o selecting header fields nominated by the stored response (if any)
match those presented (see Section 2.8), and match those presented (see Section 4.3), and
o the presented request does not contain the no-cache pragma o the presented request does not contain the no-cache pragma
(Section 3.4), nor the no-cache cache directive (Section 3.2.1), (Section 7.4), nor the no-cache cache directive (Section 7.2.1),
unless the stored response is successfully validated unless the stored response is successfully validated
(Section 2.4), and (Section 4.2), and
o the stored response does not contain the no-cache cache directive o the stored response does not contain the no-cache cache directive
(Section 3.2.2), unless it is successfully validated (Section 7.2.2.3), unless it is successfully validated
(Section 2.4), and (Section 4.2), and
o the stored response is either: o the stored response is either:
* fresh (see Section 2.3), or * fresh (see Section 4.1), or
* allowed to be served stale (see Section 2.3.3), or * allowed to be served stale (see Section 4.1.4), or
* successfully validated (see Section 2.4). * successfully validated (see Section 4.2).
Note that any of the requirements listed above can be overridden by a Note that any of the requirements listed above can be overridden by a
cache-control extension; see Section 3.2.3. cache-control extension; see Section 7.2.3.
When a stored response is used to satisfy a request without When a stored response is used to satisfy a request without
validation, a cache MUST include a single Age header field validation, a cache MUST include a single Age header field
(Section 3.1) in the response with a value equal to the stored (Section 7.1) in the response with a value equal to the stored
response's current_age; see Section 2.3.2. response's current_age; see Section 4.1.3.
A cache MUST write through requests with methods that are unsafe A cache MUST write through requests with methods that are unsafe
(Section 6.1.1 of [Part2]) to the origin server; i.e., a cache must (Section 2.1.1 of [Part2]) to the origin server; i.e., a cache is not
not generate a reply to such a request before having forwarded the allowed to generate a reply to such a request before having forwarded
request and having received a corresponding response. the request and having received a corresponding response.
Also, note that unsafe requests might invalidate already stored Also, note that unsafe requests might invalidate already stored
responses; see Section 2.6. responses; see Section 6.
When more than one suitable response is stored, a cache MUST use the When more than one suitable response is stored, a cache MUST use the
most recent response (as determined by the Date header field). It most recent response (as determined by the Date header field). It
can also forward a request with "Cache-Control: max-age=0" or "Cache- can 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.
A cache that does not have a clock available MUST NOT use stored A cache that does not have a clock available MUST NOT use stored
responses without revalidating them on every use. A cache, responses without revalidating them on every use. A cache,
especially a shared cache, SHOULD use a mechanism, such as NTP especially a shared cache, SHOULD use a mechanism, such as NTP
[RFC1305], to synchronize its clock with a reliable external [RFC1305], to synchronize its clock with a reliable external
standard. standard.
2.3. Freshness Model 4.1. Freshness Model
When a response is "fresh" in the cache, it can be used to satisfy When a response is "fresh" in the cache, it can be used to satisfy
subsequent requests without contacting the origin server, thereby subsequent requests without contacting the origin server, thereby
improving efficiency. improving efficiency.
The primary mechanism for determining freshness is for an origin The primary mechanism for determining freshness is for an origin
server to provide an explicit expiration time in the future, using server to provide an explicit expiration time in the future, using
either the Expires header field (Section 3.3) or the max-age response either the Expires header field (Section 7.3) or the max-age response
cache directive (Section 3.2.2). Generally, origin servers will cache directive (Section 7.2.2.7). Generally, origin servers will
assign future explicit expiration times to responses in the belief assign future explicit expiration times to responses in the belief
that the representation is not likely to change in a semantically that the representation is not likely to change in a semantically
significant way before the expiration time is reached. significant way before the expiration time is reached.
If an origin server wishes to force a cache to validate every If an origin server wishes to force a cache to validate every
request, it can assign an explicit expiration time in the past to request, it can assign an explicit expiration time in the past to
indicate that the response is already stale. Compliant caches will indicate that the response is already stale. Compliant caches will
normally validate the cached response before reusing it for normally validate the cached response before reusing it for
subsequent requests (see Section 2.3.3). subsequent requests (see Section 4.1.4).
Since origin servers do not always provide explicit expiration times, Since origin servers do not always provide explicit expiration times,
a cache MAY assign a heuristic expiration time when an explicit time a cache MAY assign a heuristic expiration time when an explicit time
is not specified, employing algorithms that use other header field is not specified, employing algorithms that use other header field
values (such as the Last-Modified time) to estimate a plausible values (such as the Last-Modified time) to estimate a plausible
expiration time. This specification does not provide specific expiration time. This 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 4.1.1; the current_age
is defined in Section 2.3.2. is defined in Section 4.1.3.
Additionally, clients can influence freshness calculation -- either Additionally, clients can influence freshness calculation -- either
constraining it relaxing it -- by using the max-age and min-fresh constraining it relaxing it -- by using the max-age and min-fresh
request cache directives. See Section 3.2.1 for details. request cache directives. See Section 7.2.1 for details.
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 8 for an explanation of the difference between
caches and history mechanisms. caches and history mechanisms.
2.3.1. Calculating Freshness Lifetime 4.1.1. Calculating Freshness Lifetime
A cache can calculate the freshness lifetime (denoted as A cache can calculate the freshness lifetime (denoted as
freshness_lifetime) of a response by using the first match of: freshness_lifetime) of a response by using the first match of:
o If the cache is shared and the s-maxage response cache directive o If the cache is shared and the s-maxage response cache directive
(Section 3.2.2) is present, use its value, or (Section 7.2.2.8) is present, use its value, or
o If the max-age response cache directive (Section 3.2.2) is o If the max-age response cache directive (Section 7.2.2.7) is
present, use its value, or present, use its value, or
o If the Expires response header field (Section 3.3) is present, use o If the Expires response header field (Section 7.3) is present, use
its value minus the value of the Date response header field, or its value minus the value of the Date response header field, or
o Otherwise, no explicit expiration time is present in the response. o Otherwise, no explicit expiration time is present in the response.
A heuristic freshness lifetime might be applicable; see A heuristic freshness lifetime might be applicable; see
Section 2.3.1.1. Section 4.1.2.
Note that this calculation is not vulnerable to clock skew, since all Note that this calculation is not vulnerable to clock skew, since all
of the information comes from the origin server. of the information comes from the origin server.
2.3.1.1. Calculating Heuristic Freshness When there is more than one value present for a given directive
(e.g., two Expires header fields, multiple Cache-Control: max-age
directives), it is considered invalid. Caches are encouraged to
consider responses that have invalid freshness information to be
stale.
4.1.2. Calculating Heuristic Freshness
If no explicit expiration time is present in a stored response that If no explicit expiration time is present in a stored response that
has a status code whose definition allows heuristic freshness to be has a status code whose definition allows heuristic freshness to be
used (including the following in Section 7 of [Part2]: 200, 203, 206, used (including the following in Section 4 of [Part2]: 200 (OK), 203
300, 301 and 410), a cache MAY calculate a heuristic expiration time. (Non-Authoritative Information), 206 (Partial Content), 300 (Multiple
A cache MUST NOT use heuristics to determine freshness for responses Choices), 301 (Moved Permanently) and 410 (Gone)), a cache MAY
with status codes that do not explicitly allow it. calculate a heuristic expiration time. A cache MUST NOT use
heuristics to determine freshness for responses with status codes
that do not explicitly allow it.
When a heuristic is used to calculate freshness lifetime, a cache When a heuristic is used to calculate freshness lifetime, a cache
SHOULD attach a Warning header field with a 113 warn-code to the 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 response if its current_age is more than 24 hours and such a warning
is not already present. is not already present.
Also, if the response has a Last-Modified header field (Section 2.2 Also, if the response has a Last-Modified header field (Section 2.2
of [Part4]), caches are encouraged to use a heuristic expiration of [Part4]), caches are encouraged to use a heuristic expiration
value that is no more than some fraction of the interval since that value that is no more than some fraction of the interval since that
time. A typical setting of this fraction might be 10%. time. A typical setting of this fraction might be 10%.
Note: RFC 2616 ([RFC2616], Section 13.9) required that caches do Note: Section 13.9 of [RFC2616] prohibited caches from calculating
not calculate heuristic freshness for URIs with query components heuristic freshness for URIs with query components (i.e., those
(i.e., those containing '?'). In practice, this has not been containing '?'). In practice, this has not been widely
widely implemented. Therefore, servers are encouraged to send implemented. Therefore, servers are encouraged to send explicit
explicit directives (e.g., Cache-Control: no-cache) if they wish directives (e.g., Cache-Control: no-cache) if they wish to
to preclude caching. preclude caching.
2.3.2. Calculating Age 4.1.3. Calculating Age
HTTP/1.1 uses the Age header field to convey the estimated age of the HTTP/1.1 uses the Age header field to convey the estimated age of the
response message when obtained from a cache. The Age field value is 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 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.
The following data is used for the age calculation: The following data is used for the age calculation:
age_value age_value
The term "age_value" denotes the value of the Age header field The term "age_value" denotes the value of the Age header field
(Section 3.1), in a form appropriate for arithmetic operation; or (Section 7.1), in a form appropriate for arithmetic operation; or
0, if not available. 0, if not available.
date_value date_value
HTTP/1.1 requires origin servers to send a Date header field, if HTTP/1.1 requires origin servers to send a Date header field, if
possible, with every response, giving the time at which the possible, with every response, giving the time at which the
response was generated. The term "date_value" denotes the value response was generated. The term "date_value" denotes the value
of the Date header field, in a form appropriate for arithmetic of the Date header field, in a form appropriate for arithmetic
operations. See Section 10.2 of [Part2] for the definition of the operations. See Section 9.10 of [Part2] for the definition of the
Date header field, and for requirements regarding responses Date header field, and for requirements regarding responses
without it. without it.
now now
The term "now" means "the current value of the clock at the host The term "now" means "the current value of the clock at the host
performing the calculation". A cache SHOULD use NTP ([RFC1305]) performing the calculation". A cache SHOULD use NTP ([RFC1305])
or some similar protocol to synchronize its clocks to a globally or some similar protocol to synchronize its clocks to a globally
accurate time standard. accurate time standard.
skipping to change at page 15, line 24 skipping to change at page 14, line 36
apparent_age = max(0, response_time - date_value); apparent_age = max(0, response_time - date_value);
response_delay = response_time - request_time; response_delay = response_time - request_time;
corrected_age_value = age_value + response_delay; corrected_age_value = age_value + response_delay;
These SHOULD be combined as These SHOULD be combined as
corrected_initial_age = max(apparent_age, corrected_age_value); corrected_initial_age = max(apparent_age, corrected_age_value);
unless the cache is confident in the value of the Age header (e.g., unless the cache is confident in the value of the Age header field
because there are no HTTP/1.0 hops in the Via header), in which case (e.g., because there are no HTTP/1.0 hops in the Via header field),
the corrected_age_value MAY be used as the corrected_initial_age. in which case the corrected_age_value MAY be used as the
corrected_initial_age.
The current_age of a stored response can then be calculated by adding The current_age of a stored response can then be calculated by adding
the amount of time (in seconds) since the stored response was last the amount of time (in seconds) since the stored response was last
validated by the origin server to the corrected_initial_age. validated by the origin server to the corrected_initial_age.
resident_time = now - response_time; resident_time = now - response_time;
current_age = corrected_initial_age + resident_time; current_age = corrected_initial_age + resident_time;
Additionally, to avoid common problems in date parsing: Additionally, to avoid common problems in date parsing:
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proper value. proper value.
o All expiration-related calculations MUST be done in GMT. The o All expiration-related calculations MUST be done in GMT. The
local time zone MUST NOT influence the calculation or comparison local time zone MUST NOT influence the calculation or comparison
of an age or expiration time. of an age or expiration time.
o If an HTTP header field incorrectly carries a date value with a o If an HTTP header field incorrectly carries a date value with a
time zone other than GMT, it MUST be converted into GMT using the time zone other than GMT, it MUST be converted into GMT using the
most conservative possible conversion. most conservative possible conversion.
2.3.3. Serving Stale Responses 4.1.4. Serving Stale Responses
A "stale" response is one that either has explicit expiry information A "stale" response is one that either has explicit expiry information
or is allowed to have heuristic expiry calculated, but is not fresh or is allowed to have heuristic expiry calculated, but is not fresh
according to the calculations in Section 2.3. according to the calculations in Section 4.1.
A cache MUST NOT return a stale response if it is prohibited by an A cache MUST NOT return a stale response if it is prohibited by an
explicit in-protocol directive (e.g., by a "no-store" or "no-cache" explicit in-protocol directive (e.g., by a "no-store" or "no-cache"
cache directive, a "must-revalidate" cache-response-directive, or an cache directive, a "must-revalidate" cache-response-directive, or an
applicable "s-maxage" or "proxy-revalidate" cache-response-directive; applicable "s-maxage" or "proxy-revalidate" cache-response-directive;
see Section 3.2.2). see Section 7.2.2).
A cache MUST NOT return stale responses unless it is disconnected A cache MUST NOT return stale responses unless it is disconnected
(i.e., it cannot contact the origin server or otherwise find a (i.e., it cannot contact the origin server or otherwise find a
forward path) or doing so is explicitly allowed (e.g., by the max- forward path) or doing so is explicitly allowed (e.g., by the max-
stale request directive; see Section 3.2.1). stale request directive; see Section 7.2.1).
A cache SHOULD append a Warning header field with the 110 warn-code A cache SHOULD append a Warning header field with the 110 warn-code
(see Section 3.6) to stale responses. Likewise, a cache SHOULD add (see Section 7.6) to stale responses. Likewise, a cache SHOULD add
the 112 warn-code to stale responses if the cache is disconnected. the 112 warn-code to stale responses if the cache is disconnected.
If a cache receives a first-hand response (either an entire response, If a cache receives a first-hand response (either an entire response,
or a 304 (Not Modified) response) that it would normally forward to or a 304 (Not Modified) response) that it would normally forward to
the requesting client, and the received response is no longer fresh, the requesting client, and the received response is no longer fresh,
the cache can forward it to the requesting client without adding a the cache can forward it to the requesting client without adding a
new Warning (but without removing any existing Warning header new Warning (but without removing any existing Warning header
fields). A cache shouldn't attempt to validate a response simply fields). A cache shouldn't attempt to validate a response simply
because that response became stale in transit. because that response became stale in transit.
2.4. Validation Model 4.2. Validation Model
When a cache has one or more stored responses for a requested URI, When a cache has one or more stored responses for a requested URI,
but cannot serve any of them (e.g., because they are not fresh, or but cannot serve any of them (e.g., because they are not fresh, or
one cannot be selected; see Section 2.8), it can use the conditional one cannot be selected; see Section 4.3), it can use the conditional
request mechanism [Part4] in the forwarded request to give the origin request mechanism [Part4] in the forwarded request to give the origin
server an opportunity to both select a valid stored response to be server an opportunity to both select a valid stored response to be
used, and to update it. This process is known as "validating" or used, and to update it. This process is known as "validating" or
"revalidating" the stored response. "revalidating" the stored response.
When sending such a conditional request, a cache adds an If-Modified- When sending such a conditional request, a cache adds an If-Modified-
Since header field whose value is that of the Last-Modified header Since header field whose value is that of the Last-Modified header
field from the selected (see Section 2.8) stored response, if field from the selected (see Section 4.3) stored response, if
available. available.
Additionally, a cache can add an If-None-Match header field whose Additionally, a cache can add an If-None-Match header field whose
value is that of the ETag header field(s) from all responses stored 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 for the requested URI, if present. However, if any of the stored
responses contains only partial content, the cache shouldn't include responses contains only partial content, the cache shouldn't include
its entity-tag in the If-None-Match header field unless the request its entity-tag in the If-None-Match header field unless the request
is for a range that would be fully satisfied by that stored response. is for a range that would be fully satisfied by that stored response.
Cache handling of a response to a conditional request is dependent Cache handling of a response to a conditional request is dependent
upon its status code: upon its status code:
o A 304 (Not Modified) response status code indicates that the o A 304 (Not Modified) response status code indicates that the
stored response can be updated and reused; see Section 2.4.1. stored response can be updated and reused; see Section 4.2.1.
o A full response (i.e., one with a response body) indicates that o A full response (i.e., one with a response body) indicates that
none of the stored responses nominated in the conditional request none of the stored responses nominated in the conditional request
is suitable. Instead, the cache can use the full response to is suitable. Instead, the cache can use the full response to
satisfy the request and MAY replace the stored response(s). satisfy the request and MAY replace the stored response(s).
o However, if a cache receives a 5xx response while attempting to o However, if a cache receives a 5xx (Server Error) response while
validate a response, it can either forward this response to the attempting to validate a response, it can either forward this
requesting client, or act as if the server failed to respond. In response to the requesting client, or act as if the server failed
the latter case, it can return a previously stored response (see to respond. In the latter case, it can return a previously stored
Section 2.3.3). response (see Section 4.1.4).
2.4.1. Freshening Responses with 304 Not Modified 4.2.1. Freshening Responses with 304 Not Modified
When a cache receives a 304 (Not Modified) response and already has When a cache receives a 304 (Not Modified) response and already has
one or more stored 200 (OK) responses for the same cache key, the one or more stored 200 (OK) responses for the same cache key, the
cache needs to identify which of the stored responses are updated by cache needs to identify which of the stored responses are updated by
this new response and then update the stored response(s) with the new this new response and then update the stored response(s) with the new
information provided in the 304 response. information provided in the 304 response.
o If the new response contains a strong validator, then that strong o If the new response contains a strong validator, then that strong
validator identifies the selected representation. All of the validator identifies the selected representation. All of the
stored responses with the same strong validator are selected. If stored responses with the same strong validator are selected. If
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corresponds to one of the cache's stored responses, then the most corresponds to one of the cache's stored responses, then the most
recent of those matching stored responses is selected. recent of those matching stored responses is selected.
o If the new response does not include any form of validator, there o If the new response does not include any form of validator, there
is only one stored response, and that stored response also lacks a is only one stored response, and that stored response also lacks a
validator, then that stored response is selected. validator, then that stored response is selected.
If a stored response is selected for update, the cache MUST: If a stored response is selected for update, the cache MUST:
o delete any Warning header fields in the stored response with warn- o delete any Warning header fields in the stored response with warn-
code 1xx (see Section 3.6); code 1xx (see Section 7.6);
o retain any Warning header fields in the stored response with warn-
code 2xx; and,
o use other header fields provided in the 304 response to replace
all instances of the corresponding header fields in the stored
response.
2.5. Updating Caches with HEAD Responses
A response to the HEAD method is identical to what an equivalent
request made with a GET would have been, except it lacks a body.
This property of HEAD responses is used to both invalidate and update
cached GET responses.
If one or more stored GET responses can be selected (as per
Section 2.8) for a HEAD request, and the Content-Length, ETag or
Last-Modified value of a HEAD response differs from that in a
selected GET response, the cache MUST consider that selected response
to be stale.
If the Content-Length, ETag and Last-Modified values of a HEAD
response (when present) are the same as that in a selected GET
response (as per Section 2.8), the cache SHOULD update the remaining
headers in the stored response using the following rules:
o delete any Warning header fields in the stored response with warn-
code 1xx (see Section 3.6);
o retain any Warning header fields in the stored response with warn- o retain any Warning header fields in the stored response with warn-
code 2xx; and, code 2xx; and,
o use other header fields provided in the response to replace all o use other header fields provided in the 304 (Not Modified)
instances of the corresponding header fields in the stored response to replace all instances of the corresponding header
response. fields in the stored response.
2.6. Request Methods that Invalidate
Because unsafe request methods (Section 6.1.1 of [Part2]) such as
PUT, POST or DELETE have the potential for changing state on the
origin server, intervening caches can use them to keep their contents
up-to-date.
A cache MUST invalidate the effective Request URI (Section 5.5 of
[Part1]) as well as the URI(s) in the Location and Content-Location
response header fields (if present) when a non-error response to a
request with an unsafe method is received.
However, a cache MUST NOT invalidate a URI from a Location or
Content-Location response header field if the host part of that URI
differs from the host part in the effective request URI (Section 5.5
of [Part1]). This helps prevent denial of service attacks.
A cache MUST invalidate the effective request URI (Section 5.5 of
[Part1]) when it receives a non-error response to a request with a
method whose safety is unknown.
Here, a "non-error response" is one with a 2xx or 3xx status code.
"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.
2.7. Shared Caching of Authenticated Responses
A shared cache MUST NOT use a cached response to a request with an
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.
2.8. Caching Negotiated Responses 4.3. Using 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 7.5), it MUST NOT use
that response unless all of the selecting header fields nominated by that response unless all of the selecting header fields nominated by
the Vary header field match in both the original request (i.e., that the Vary header field 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 header fields from two requests are defined to match if The selecting header fields from two requests are defined to match if
and only if those in the first request can be transformed to those in and only if those in the first request can be transformed to those in
the second request by applying any of the following: the second request by applying any of the following:
o adding or removing whitespace, where allowed in the header field's o adding or removing whitespace, where allowed in the header field's
syntax syntax
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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 header fields is known as The stored response with matching selecting header fields is known as
the selected response. the selected response.
If multiple selected responses are available, the most recent If multiple selected responses are available, the most recent
response (as determined by the Date header field) is used; see response (as determined by the Date header field) is used; see
Section 2.2. Section 4.
If no selected response is available, the cache can forward the If no selected response is available, the cache can forward the
presented request to the origin server in a conditional request; see presented request to the origin server in a conditional request; see
Section 2.4. Section 4.2.
2.9. Combining Partial Content 4.4. Combining Partial Content
A response might transfer only a partial representation if the A response might transfer only a partial representation if the
connection closed prematurely or if the request used one or more connection closed prematurely or if the request used one or more
Range specifiers ([Part5]). After several such transfers, a cache Range specifiers ([Part5]). After several such transfers, a cache
might have received several ranges of the same representation. A might have received several ranges of the same representation. A
cache MAY combine these ranges into a single stored response, and cache MAY combine these ranges into a single stored response, and
reuse that response to satisfy later requests, if they all share the reuse that response to satisfy later requests, if they all share the
same strong validator and the cache complies with the client same strong validator and the cache complies with the client
requirements in Section 4.2 of [Part5]. requirements in Section 4.2 of [Part5].
When combining the new response with one or more stored responses, a When combining the new response with one or more stored responses, a
cache MUST: cache MUST:
o delete any Warning header fields in the stored response with warn- o delete any Warning header fields in the stored response with warn-
code 1xx (see Section 3.6); code 1xx (see Section 7.6);
o retain any Warning header fields in the stored response with warn- o retain any Warning header fields in the stored response with warn-
code 2xx; and, code 2xx; and,
o use other header fields provided in the new response, aside from o use other header fields provided in the new response, aside from
Content-Range, to replace all instances of the corresponding Content-Range, to replace all instances of the corresponding
header fields in the stored response. header fields in the stored response.
3. Header Field Definitions 5. Updating Caches with HEAD Responses
A response to the HEAD method is identical to what an equivalent
request made with a GET would have been, except it lacks a body.
This property of HEAD responses is used to both invalidate and update
cached GET responses.
If one or more stored GET responses can be selected (as per
Section 4.3) for a HEAD request, and the Content-Length, ETag or
Last-Modified value of a HEAD response differs from that in a
selected GET response, the cache MUST consider that selected response
to be stale.
If the Content-Length, ETag and Last-Modified values of a HEAD
response (when present) are the same as that in a selected GET
response (as per Section 4.3), the cache SHOULD update the remaining
header fields in the stored response using the following rules:
o delete any Warning header fields in the stored response with warn-
code 1xx (see Section 7.6);
o retain any Warning header fields in the stored response with warn-
code 2xx; and,
o use other header fields provided in the response to replace all
instances of the corresponding header fields in the stored
response.
6. Request Methods that Invalidate
Because unsafe request methods (Section 2.1.1 of [Part2]) such as
PUT, POST or DELETE have the potential for changing state on the
origin server, intervening caches can use them to keep their contents
up-to-date.
A cache MUST invalidate the effective Request URI (Section 5.5 of
[Part1]) as well as the URI(s) in the Location and Content-Location
response header fields (if present) when a non-error response to a
request with an unsafe method is received.
However, a cache MUST NOT invalidate a URI from a Location or
Content-Location response header field if the host part of that URI
differs from the host part in the effective request URI (Section 5.5
of [Part1]). This helps prevent denial of service attacks.
A cache MUST invalidate the effective request URI (Section 5.5 of
[Part1]) when it receives a non-error response to a request with a
method whose safety is unknown.
Here, a "non-error response" is one with a 2xx (Successful) or 3xx
(Redirection) status code. "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.
7. 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.
3.1. Age 7.1. Age
The "Age" header field conveys the sender's estimate of the amount of The "Age" header field conveys the sender's estimate of the amount of
time since the response was generated or successfully validated at time since the response was generated or successfully validated at
the origin server. Age values are calculated as specified in the origin server. Age values are calculated as specified in
Section 2.3.2. Section 4.1.3.
Age = delta-seconds Age = delta-seconds
Age field-values are non-negative integers, representing time in Age field-values are non-negative integers, representing time in
seconds (see Section 1.5). seconds (see Section 1.4.1).
The presence of an Age header field in a response implies that a The presence of an Age header field in a response implies that a
response is not first-hand. However, the converse is not true, since response is not first-hand. However, the converse is not true, since
HTTP/1.0 caches might not implement the Age header field. HTTP/1.0 caches might not implement the Age header field.
3.2. Cache-Control 7.2. Cache-Control
The "Cache-Control" header field is used to specify directives for The "Cache-Control" header field is used to specify directives for
caches along the request/response chain. Such cache directives are caches along the request/response chain. Such cache directives are
unidirectional in that the presence of a directive in a request does unidirectional in that the presence of a directive in a request does
not imply that the same directive is to be given in the response. not imply that the same directive is to be given in the response.
A cache MUST obey the requirements of the Cache-Control directives A cache MUST obey the requirements of the Cache-Control directives
defined in this section. See Section 3.2.3 for information about how defined in this section. See Section 7.2.3 for information about how
Cache-Control directives defined elsewhere are handled. Cache-Control directives defined elsewhere are handled.
Note: HTTP/1.0 caches might not implement Cache-Control and might Note: HTTP/1.0 caches might not implement Cache-Control and might
only implement Pragma: no-cache (see Section 3.4). only implement Pragma: no-cache (see Section 7.4).
A proxy, whether or not it implements a cache, MUST pass cache A proxy, whether or not it implements a cache, MUST pass cache
directives through in forwarded messages, regardless of their directives through in forwarded messages, regardless of their
significance to that application, since the directives might be significance to that application, since the directives might be
applicable to all recipients along the request/response chain. It is applicable to all recipients along the request/response chain. It is
not possible to target a directive to a specific cache. not possible to target a directive to a specific cache.
Cache directives are identified by a token, to be compared case- Cache directives are identified by a token, to be compared case-
insensitively, and have an optional argument. insensitively, and have an optional argument, that can use both token
and quoted-string syntax. For the directives defined below that
define arguments, recipients ought to accept both forms, even if one
is documented to be preferred. For any directive not defined by this
specification, recipients MUST accept both forms.
Cache-Control = 1#cache-directive Cache-Control = 1#cache-directive
cache-directive = cache-request-directive cache-directive = token [ "=" ( token / quoted-string ) ]
/ cache-response-directive
cache-extension = token [ "=" ( token / quoted-string ) ] For the cache directives defined below, no argument is defined (nor
allowed) otherwise stated otherwise.
3.2.1. Request Cache-Control Directives 7.2.1. Request Cache-Control Directives
cache-request-directive = 7.2.1.1. no-cache
"no-cache"
/ "no-store"
/ "max-age" "=" delta-seconds
/ "max-stale" [ "=" delta-seconds ]
/ "min-fresh" "=" delta-seconds
/ "no-transform"
/ "only-if-cached"
/ cache-extension
no-cache The "no-cache" request directive indicates that a cache MUST NOT use
a stored response to satisfy the request without successful
validation on the origin server.
The no-cache request directive indicates that a cache MUST NOT use 7.2.1.2. no-store
a stored response to satisfy the request without successful
validation on the origin server.
no-store The "no-store" request directive indicates that a cache MUST NOT
store any part of either this request or any response to it. This
directive applies to both private and shared caches. "MUST NOT
store" in this context means that the cache MUST NOT intentionally
store the information in non-volatile storage, and MUST make a best-
effort attempt to remove the information from volatile storage as
promptly as possible after forwarding it.
The no-store request directive indicates that a cache MUST NOT This directive is NOT a reliable or sufficient mechanism for ensuring
store any part of either this request or any response to it. This privacy. In particular, malicious or compromised caches might not
directive applies to both private and shared caches. "MUST NOT recognize or obey this directive, and communications networks might
store" in this context means that the cache MUST NOT intentionally be vulnerable to eavesdropping.
store the information in non-volatile storage, and MUST make a
best-effort attempt to remove the information from volatile
storage as promptly as possible after forwarding it.
This directive is NOT a reliable or sufficient mechanism for Note that if a request containing this directive is satisfied from a
ensuring privacy. In particular, malicious or compromised caches cache, the no-store request directive does not apply to the already
might not recognize or obey this directive, and communications stored response.
networks might be vulnerable to eavesdropping.
Note that if a request containing this directive is satisfied from 7.2.1.3. max-age
a cache, the no-store request directive does not apply to the
already stored response.
max-age Argument syntax:
The max-age request directive indicates that the client is delta-seconds (see Section 1.4.1)
unwilling to accept a response whose age is greater than the
specified number of seconds. Unless the max-stale request
directive is also present, the client is not willing to accept a
stale response.
max-stale The "max-age" request directive indicates that the client is
unwilling to accept a response whose age is greater than the
specified number of seconds. Unless the max-stale request directive
is also present, the client is not willing to accept a stale
response.
The max-stale request directive indicates that the client is Note: This directive uses the token form of the argument syntax;
willing to accept a response that has exceeded its expiration e.g., 'max-age=5', not 'max-age="5"'. Senders SHOULD NOT use the
time. If max-stale is assigned a value, then the client is quoted-string form.
willing to accept a response that has exceeded its expiration time
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
stale response of any age.
min-fresh 7.2.1.4. max-stale
The min-fresh request directive indicates that the client is Argument syntax:
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 delta-seconds (see Section 1.4.1)
The no-transform request directive indicates that an intermediary The "max-stale" request directive indicates that the client is
(whether or not it implements a cache) MUST NOT change the willing to accept a response that has exceeded its expiration time.
Content-Encoding, Content-Range or Content-Type request header If max-stale is assigned a value, then the client is willing to
fields, nor the request representation. accept a response that has exceeded its expiration time 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 stale response of
any age.
only-if-cached Note: This directive uses the token form of the argument syntax;
e.g., 'max-stale=10', not 'max-stale="10"'. Senders SHOULD NOT use
the quoted-string form.
The only-if-cached request directive indicates that the client 7.2.1.5. min-fresh
only wishes to obtain 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, a member cache MAY forward such a request within
that group of caches.
3.2.2. Response Cache-Control Directives Argument syntax:
cache-response-directive = delta-seconds (see Section 1.4.1)
"public"
/ "private" [ "=" DQUOTE 1#field-name DQUOTE ]
/ "no-cache" [ "=" DQUOTE 1#field-name DQUOTE ]
/ "no-store"
/ "no-transform"
/ "must-revalidate"
/ "proxy-revalidate"
/ "max-age" "=" delta-seconds
/ "s-maxage" "=" delta-seconds
/ cache-extension
public 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.
The public response directive indicates that a response whose Note: This directive uses the token form of the argument syntax;
associated request contains an 'Authentication' header MAY be e.g., 'min-fresh=20', not 'min-fresh="20"'. Senders SHOULD NOT use
stored (see Section 2.7). the quoted-string form.
private 7.2.1.6. no-transform
The private response directive indicates that the response message The "no-transform" request directive indicates that an intermediary
is intended for a single user and MUST NOT be stored by a shared (whether or not it implements a cache) MUST NOT change the Content-
cache. A private cache MAY store the response. Encoding, Content-Range or Content-Type request header fields, nor
the request representation.
If the private response directive specifies one or more field- 7.2.1.7. only-if-cached
names, this requirement is limited to the field-values associated
with the listed response header fields. That is, a shared cache
MUST NOT store the specified field-names(s), whereas it MAY store
the remainder of the response message.
Note: This usage of the word "private" only controls where the The "only-if-cached" request directive indicates that the client only
response can be stored; it cannot ensure the privacy of the wishes to obtain a stored response. If it receives this directive, a
message content. Also, private response directives with field- cache SHOULD either respond using a stored response that is
names are often handled by implementations as if an unqualified consistent with the other constraints of the request, or respond with
private directive was received; i.e., the special handling for the a 504 (Gateway Timeout) status code. If a group of caches is being
qualified form is not widely implemented. operated as a unified system with good internal connectivity, a
member cache MAY forward such a request within that group of caches.
no-cache 7.2.2. Response Cache-Control Directives
The no-cache response directive indicates that the response MUST 7.2.2.1. public
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- The "public" response directive indicates that a response whose
names, then a cache MAY use the response to satisfy a subsequent associated request contains an 'Authentication' header MAY be stored
request, subject to any other restrictions on caching. However, (see Section 3.2).
any header fields in the response that have the field-name(s)
listed MUST NOT be sent in the response to a subsequent request
without successful revalidation with 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 7.2.2.2. private
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 Argument syntax:
The no-store response directive indicates that a cache MUST NOT #field-name
store any part of either the immediate request or response. This
directive applies to both private and shared caches. "MUST NOT
store" in this context means that the cache MUST NOT intentionally
store the information in non-volatile storage, and MUST make a
best-effort attempt to remove the information from volatile
storage as promptly as possible after forwarding it.
This directive is NOT a reliable or sufficient mechanism for The "private" response directive indicates that the response message
ensuring privacy. In particular, malicious or compromised caches is intended for a single user and MUST NOT be stored by a shared
might not recognize or obey this directive, and communications cache. A private cache MAY store the response.
networks might be vulnerable to eavesdropping.
must-revalidate If the private response directive specifies one or more field-names,
this requirement is limited to the field-values associated with the
listed response header fields. That is, a shared cache MUST NOT
store the specified field-names(s), whereas it MAY store the
remainder of the response message.
The must-revalidate response directive indicates that once it has The field-names given are not limited to the set of standard header
become stale, a cache MUST NOT use the response to satisfy fields defined by this specification. Field names are case-
subsequent requests without successful validation on the origin insensitive.
server.
The must-revalidate directive is necessary to support reliable Note: This usage of the word "private" only controls where the
operation for certain protocol features. In all circumstances a response can be stored; it cannot ensure the privacy of the message
cache MUST obey the must-revalidate directive; in particular, if a content. Also, private response directives with field-names are
cache cannot reach the origin server for any reason, it MUST often handled by implementations as if an unqualified private
generate a 504 (Gateway Timeout) response. directive was received; i.e., the special handling for the qualified
form is not widely implemented.
The must-revalidate directive ought to be used by servers if and Note: This directive uses the quoted-string form of the argument
only if failure to validate a request on the representation could syntax. Senders SHOULD NOT use the token form (even if quoting
result in incorrect operation, such as a silently unexecuted appears not to be needed for single-entry lists).
financial transaction.
proxy-revalidate 7.2.2.3. no-cache
The proxy-revalidate response directive has the same meaning as Argument syntax:
the must-revalidate response directive, except that it does not
apply to private caches.
max-age #field-name
The max-age response directive indicates that the response is to The "no-cache" response directive indicates that the response MUST
be considered stale after its age is greater than the specified NOT be used to satisfy a subsequent request without successful
number of seconds. 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.
s-maxage If the no-cache response directive specifies one or more field-names,
then a cache MAY use the response to satisfy a subsequent request,
subject to any other restrictions on caching. However, any header
fields in the response that have the field-name(s) listed MUST NOT be
sent in the response to a subsequent request without successful
revalidation with 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.
The s-maxage response directive indicates that, in shared caches, The field-names given are not limited to the set of standard header
the maximum age specified by this directive overrides the maximum fields defined by this specification. Field names are case-
age specified by either the max-age directive or the Expires insensitive.
header field. The s-maxage directive also implies the semantics
of the proxy-revalidate response directive.
no-transform Note: Many 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.
The no-transform response directive indicates that an intermediary Note: This directive uses the quoted-string form of the argument
(regardless of whether it implements a cache) MUST NOT change the syntax. Senders SHOULD NOT use the token form (even if quoting
Content-Encoding, Content-Range or Content-Type response header appears not to be needed for single-entry lists).
fields, nor the response representation.
3.2.3. Cache Control Extensions 7.2.2.4. no-store
The "no-store" response directive indicates that a cache MUST NOT
store any part of either the immediate request or response. This
directive applies to both private and shared caches. "MUST NOT
store" in this context means that the cache MUST NOT intentionally
store the information in non-volatile storage, and MUST make a best-
effort attempt to remove the information from volatile storage as
promptly as possible after forwarding it.
This directive is NOT a reliable or sufficient mechanism for ensuring
privacy. In particular, malicious or compromised caches might not
recognize or obey this directive, and communications networks might
be vulnerable to eavesdropping.
7.2.2.5. must-revalidate
The "must-revalidate" response directive indicates that once it has
become stale, a cache MUST NOT use the response to satisfy subsequent
requests without successful validation on the origin server.
The must-revalidate directive is necessary to support reliable
operation for certain protocol features. In all circumstances a
cache MUST obey the must-revalidate directive; in particular, if a
cache cannot reach the origin server for any reason, it MUST generate
a 504 (Gateway Timeout) response.
The must-revalidate directive ought to be used by servers if and only
if failure to validate a request on the representation could result
in incorrect operation, such as a silently unexecuted financial
transaction.
7.2.2.6. proxy-revalidate
The "proxy-revalidate" response directive has the same meaning as the
must-revalidate response directive, except that it does not apply to
private caches.
7.2.2.7. max-age
Argument syntax:
delta-seconds (see Section 1.4.1)
The "max-age" response directive indicates that the response is to be
considered stale after its age is greater than the specified number
of seconds.
Note: This directive uses the token form of the argument syntax;
e.g., 'max-age=5', not 'max-age="5"'. Senders SHOULD NOT use the
quoted-string form.
7.2.2.8. s-maxage
Argument syntax:
delta-seconds (see Section 1.4.1)
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
field. The s-maxage directive also implies the semantics of the
proxy-revalidate response directive.
Note: This directive uses the token form of the argument syntax;
e.g., 's-maxage=10', not 's-maxage="10"'. Senders SHOULD NOT use the
quoted-string form.
7.2.2.9. no-transform
The "no-transform" response directive indicates that an intermediary
(regardless of whether it implements a cache) MUST NOT change the
Content-Encoding, Content-Range or Content-Type response header
fields, nor the response representation.
7.2.3. Cache Control Extensions
The Cache-Control header field can be extended through the use of one The Cache-Control header field can be extended through the use of one
or more cache-extension tokens, each with an optional value. or more cache-extension tokens, each with an optional value.
Informational extensions (those that do not require a change in cache Informational extensions (those that do not require a change in cache
behavior) can be added without changing the semantics of other behavior) can be added without changing the semantics of other
directives. Behavioral extensions are designed to work by acting as directives. Behavioral extensions are designed to work by acting as
modifiers to the existing base of cache directives. Both the new modifiers to the existing base of cache directives. Both the new
directive and the standard directive are supplied, such that directive and the standard directive are supplied, such that
applications that do not understand the new directive will default to applications that do not understand the new directive will default to
the behavior specified by the standard directive, and those that the behavior specified by the standard directive, and those that
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This extension mechanism depends on an HTTP cache obeying all of the This extension mechanism depends on an HTTP cache obeying all of the
cache-control directives defined for its native HTTP-version, obeying cache-control directives defined for its native HTTP-version, obeying
certain extensions, and ignoring all directives that it does not certain extensions, and ignoring all directives that it does not
understand. understand.
For example, consider a hypothetical new response directive called For example, consider a hypothetical new response directive called
"community" that acts as a modifier to the private directive. We "community" that acts as a modifier to the private directive. We
define this new directive to mean that, in addition to any private define this new directive to mean that, in addition to any private
cache, any cache that is shared only by members of the community cache, any cache that is shared only by members of the community
named within its value may cache the response. An origin server named within its value is allowed to cache the response. An origin
wishing to allow the UCI community to use an otherwise private server wishing to allow the UCI community to use an otherwise private
response in their shared cache(s) could do so by including response in their shared cache(s) could do so by including
Cache-Control: private, community="UCI" Cache-Control: private, community="UCI"
A cache seeing this header field will act correctly even if the cache A cache seeing this header field will act correctly even if the cache
does not understand the community cache-extension, since it will also does not understand the community cache-extension, since it will also
see and understand the private directive and thus default to the safe see and understand the private directive and thus default to the safe
behavior. behavior.
A cache MUST ignore unrecognized cache directives; it is assumed that A cache MUST ignore unrecognized cache directives; it is assumed that
any cache directive likely to be unrecognized by an HTTP/1.1 cache any cache directive likely to be unrecognized by an HTTP/1.1 cache
will be combined with standard directives (or the response's default will be combined with standard directives (or the response's default
cacheability) such that the cache behavior will remain minimally cacheability) such that the cache behavior will remain minimally
correct even if the cache does not understand the extension(s). correct even if the cache does not understand the extension(s).
New extension directives ought to consider defining:
o What it means for a directive to be specified multiple times,
o When the directive does not take an argument, what it means when
an argument is present,
o When the directive requires an argument, what it means when it is
missing.
The HTTP Cache Directive Registry defines the name space for the The HTTP Cache Directive Registry defines the name space for the
cache directives. cache directives.
A registration MUST include the following fields: A registration MUST include the following fields:
o Cache Directive Name o Cache Directive Name
o Pointer to specification text o Pointer to specification text
Values to be added to this name space require IETF Review (see Values to be added to this name space require IETF Review (see
[RFC5226], Section 4.1). [RFC5226], Section 4.1).
The registry itself is maintained at The registry itself is maintained at
<http://www.iana.org/assignments/http-cache-directives>. <http://www.iana.org/assignments/http-cache-directives>.
3.3. Expires 7.3. Expires
The "Expires" header field gives the date/time after which the The "Expires" header field gives the date/time after which the
response is considered stale. See Section 2.3 for further discussion response is considered stale. See Section 4.1 for further discussion
of the freshness model. of the freshness model.
The presence of an Expires field does not imply that the original The presence of an Expires field does not imply that the original
resource will change or cease to exist at, before, or after that resource will change or cease to exist at, before, or after that
time. time.
The field-value is an absolute date and time as defined by HTTP-date The field-value is an absolute date and time as defined by HTTP-date
in Section 8 of [Part2]; a sender MUST use the rfc1123-date format. in Section 5.1 of [Part2]; a sender MUST use the rfc1123-date format.
Expires = HTTP-date Expires = HTTP-date
For example For example
Expires: Thu, 01 Dec 1994 16:00:00 GMT Expires: Thu, 01 Dec 1994 16:00:00 GMT
A cache MUST treat other invalid date formats, especially including A cache MUST treat other invalid date formats, especially including
the value "0", as in the past (i.e., "already expired"). the value "0", as in the past (i.e., "already expired").
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 7.2.2.7), that directive overrides the
Expires field. Likewise, the s-maxage directive overrides Expires Expires field. Likewise, the s-maxage directive (Section 7.2.2.8)
in shared caches. overrides the Expires header fieldin shared caches.
Historically, HTTP required the Expires field-value to be no more Historically, HTTP required the Expires field-value to be no more
than a year in the future. While longer freshness lifetimes are no than a year in the future. While longer freshness lifetimes are no
longer prohibited, extremely large values have been demonstrated to longer prohibited, extremely large values have been demonstrated to
cause problems (e.g., clock overflows due to use of 32-bit integers cause problems (e.g., clock overflows due to use of 32-bit integers
for time values), and most caches will evict a response far sooner for time values), and many caches will evict a response far sooner
than that. Therefore, senders ought not produce them. than that. Therefore, senders ought not produce them.
An origin server without a clock MUST NOT assign Expires values to a An origin server without a clock MUST NOT assign Expires values to a
response unless these values were associated with the resource by a response unless these values were associated with the resource by a
system or user with a reliable clock. It MAY assign an Expires value system or user with a reliable clock. It MAY assign an Expires value
that is known, at or before server configuration time, to be in the that is known, at or before server configuration time, to be in the
past (this allows "pre-expiration" of responses without storing past (this allows "pre-expiration" of responses without storing
separate Expires values for each resource). separate Expires values for each resource).
3.4. Pragma 7.4. Pragma
The "Pragma" header field allows backwards compatibility with The "Pragma" header field allows backwards compatibility with
HTTP/1.0 caches, so that clients can specify a "no-cache" request HTTP/1.0 caches, so that clients can specify a "no-cache" request
that they will understand (as Cache-Control was not defined until that they will understand (as Cache-Control was not defined until
HTTP/1.1). When the Cache-Control header is also present and HTTP/1.1). When the Cache-Control header field is also present and
understood in a request, Pragma is ignored. understood in a request, Pragma is ignored.
In HTTP/1.0, Pragma was defined as an extensible field for In HTTP/1.0, Pragma was defined as an extensible field for
implementation-specified directives for recipients. This implementation-specified directives for recipients. This
specification deprecates such extensions to improve interoperability. specification deprecates such extensions to improve interoperability.
Pragma = 1#pragma-directive Pragma = 1#pragma-directive
pragma-directive = "no-cache" / extension-pragma pragma-directive = "no-cache" / extension-pragma
extension-pragma = token [ "=" ( token / quoted-string ) ] extension-pragma = token [ "=" ( token / quoted-string ) ]
When the Cache-Control header is not present in a request, the no- When the Cache-Control header field is not present in a request, the
cache request pragma-directive MUST have the same effect on caches as no-cache request pragma-directive MUST have the same effect on caches
if "Cache-Control: no-cache" were present (see Section 3.2.1). as if "Cache-Control: no-cache" were present (see Section 7.2.1).
When sending a no-cache request, a client ought to include both the When sending a no-cache request, a client ought to include both the
pragma and cache-control directives, unless Cache-Control: no-cache pragma and cache-control directives, unless Cache-Control: no-cache
is purposefully omitted to target other Cache-Control response is purposefully omitted to target other Cache-Control response
directives at HTTP/1.1 caches. For example: directives at HTTP/1.1 caches. For example:
GET / HTTP/1.1 GET / HTTP/1.1
Host: www.example.com Host: www.example.com
Cache-Control: max-age=30 Cache-Control: max-age=30
Pragma: no-cache Pragma: no-cache
will constrain HTTP/1.1 caches to serve a response no older than 30 will constrain HTTP/1.1 caches to serve a response no older than 30
seconds, while precluding implementations that do not understand seconds, while precluding implementations that do not understand
Cache-Control from serving a cached response. Cache-Control from serving a cached response.
Note: Because the meaning of "Pragma: no-cache" in responses is Note: Because the meaning of "Pragma: no-cache" in responses is
not specified, it does not provide a reliable replacement for not specified, it does not provide a reliable replacement for
"Cache-Control: no-cache" in them. "Cache-Control: no-cache" in them.
3.5. Vary 7.5. Vary
The "Vary" header field conveys the set of header fields that were The "Vary" header field conveys the set of header fields that were
used to select the representation. 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 satisfy a given request; see Section 2.8. response can be used to satisfy a given request; see Section 4.3.
determines, while the response is fresh, whether a cache is permitted
to use the response to reply to a subsequent request without
validation; see Section 2.8.
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 = "*" / 1#field-name Vary = "*" / 1#field-name
The set of header fields named by the Vary field value is known as The set of header fields named by the Vary field value is known as
the selecting header fields. the selecting header fields.
skipping to change at page 30, line 15 skipping to change at page 30, line 25
A Vary field value of "*" signals that unspecified parameters not A Vary field value of "*" signals that unspecified parameters not
limited to the header fields (e.g., the network address of the limited to the header fields (e.g., the network address of the
client), play a role in the selection of the response representation; client), play a role in the selection of the response representation;
therefore, a cache cannot determine whether this response is therefore, a cache cannot determine whether this response is
appropriate. A proxy MUST NOT generate the "*" value. appropriate. A proxy MUST NOT generate the "*" value.
The field-names given are not limited to the set of standard header The field-names given are not limited to the set of standard header
fields defined by this specification. Field names are case- fields defined by this specification. Field names are case-
insensitive. insensitive.
3.6. Warning 7.6. Warning
The "Warning" header field is used to carry additional information The "Warning" header field is used to carry additional information
about the status or transformation of a message that might not be about the status or transformation of a message that might not be
reflected in the message. This information is typically used to warn reflected in the message. This information is typically used to warn
about possible incorrectness introduced by caching operations or about possible incorrectness introduced by caching operations or
transformations applied to the payload of the message. transformations applied to the payload of the message.
Warnings can be used for other purposes, both cache-related and Warnings can be used for other purposes, both cache-related and
otherwise. The use of a warning, rather than an error status code, otherwise. The use of a warning, rather than an error status code,
distinguishes these responses from true failures. distinguishes these responses from true failures.
skipping to change at page 30, line 52 skipping to change at page 31, line 14
Multiple warnings can be attached to a response (either by the origin Multiple warnings can be attached to a response (either by the origin
server or by a cache), including multiple warnings with the same code server or by a cache), including multiple warnings with the same code
number, only differing in warn-text. number, only differing in warn-text.
When this occurs, the user agent SHOULD inform the user of as many of 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. them as possible, in the order that they appear in the response.
Systems that generate multiple Warning header fields are encouraged Systems that generate multiple Warning header fields are encouraged
to order them with this user agent behavior in mind. New Warning to order them with this user agent behavior in mind. New Warning
header fields are added after any existing Warning headers fields. header fields are added after any existing Warning header fields.
Warnings are assigned three digit warn-codes. The first digit Warnings are assigned three digit warn-codes. The first digit
indicates whether the Warning is required to be deleted from a stored indicates whether the Warning is required to be deleted from a stored
response after validation: response after validation:
o 1xx Warnings describe the freshness or validation status of the o 1xx Warnings describe the freshness or validation status of the
response, and so MUST be deleted by a cache after validation. response, and so MUST be deleted by a cache after validation.
They can only be generated by a cache when validating a cached They can only be generated by a cache when validating a cached
entry, and MUST NOT be generated in any other situation. entry, and MUST NOT be generated in any other situation.
skipping to change at page 31, line 36 skipping to change at page 31, line 47
warn-date, and that warn-date is different from the Date value in the 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 response, then that warning-value MUST be deleted from the message
before storing, forwarding, or using it. (preventing the consequences before storing, forwarding, or using it. (preventing the consequences
of naive caching of Warning header fields.) If all of the warning- of naive caching of Warning header fields.) If all of the warning-
values are deleted for this reason, the Warning header field MUST be values are deleted for this reason, the Warning header field MUST be
deleted as well. deleted as well.
The following warn-codes are defined by this specification, each with The following warn-codes are defined by this specification, each with
a recommended warn-text in English, and a description of its meaning. a recommended warn-text in English, and a description of its meaning.
3.6.1. 110 Response is Stale 7.6.1. 110 Response is Stale
A cache SHOULD include this whenever the returned response is stale. A cache SHOULD include this whenever the returned response is stale.
3.6.2. 111 Revalidation Failed 7.6.2. 111 Revalidation Failed
A cache SHOULD include this when returning a stale response because A cache SHOULD include this when returning a stale response because
an attempt to validate the response failed, due to an inability to an attempt to validate the response failed, due to an inability to
reach the server. reach the server.
3.6.3. 112 Disconnected Operation 7.6.3. 112 Disconnected Operation
A cache SHOULD include this if it is intentionally disconnected from A cache SHOULD include this if it is intentionally disconnected from
the rest of the network for a period of time. the rest of the network for a period of time.
3.6.4. 113 Heuristic Expiration 7.6.4. 113 Heuristic Expiration
A cache SHOULD include this if it heuristically chose a freshness A cache SHOULD include this if it heuristically chose a freshness
lifetime greater than 24 hours and the response's age is greater than lifetime greater than 24 hours and the response's age is greater than
24 hours. 24 hours.
3.6.5. 199 Miscellaneous Warning 7.6.5. 199 Miscellaneous Warning
The warning text can include arbitrary information to be presented to The warning text can include arbitrary information to be presented to
a human user, or logged. A system receiving this warning MUST NOT a human user, or logged. A system receiving this warning MUST NOT
take any automated action, besides presenting the warning to the take any automated action, besides presenting the warning to the
user. user.
3.6.6. 214 Transformation Applied 7.6.6. 214 Transformation Applied
MUST be added by a proxy if it applies any transformation to the MUST be added by a proxy if it applies any transformation to the
representation, such as changing the content-coding, media-type, or representation, such as changing the content-coding, media-type, or
modifying the representation data, unless this Warning code already modifying the representation data, unless this Warning code already
appears in the response. appears in the response.
3.6.7. 299 Miscellaneous Persistent Warning 7.6.7. 299 Miscellaneous Persistent Warning
The warning text can include arbitrary information to be presented to The warning text can include arbitrary information to be presented to
a human user, or logged. A system receiving this warning MUST NOT a human user, or logged. A system receiving this warning MUST NOT
take any automated action. take any automated action.
3.6.8. Warn Code Extensions 7.6.8. Warn Code Extensions
The HTTP Warn Code Registry defines the name space for warn codes. The HTTP Warn Code Registry defines the name space for warn codes.
A registration MUST include the following fields: A registration MUST include the following fields:
o Warn Code (3 digits) o Warn Code (3 digits)
o Short Description o Short Description
o Pointer to specification text o Pointer to specification text
Values to be added to this name space require IETF Review (see Values to be added to this name space require IETF Review (see
[RFC5226], Section 4.1). [RFC5226], Section 4.1).
The registry itself is maintained at The registry itself is maintained at
<http://www.iana.org/assignments/http-warn-codes>. <http://www.iana.org/assignments/http-warn-codes>.
4. History Lists 8. 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 a representation history lists, that can be used to redisplay a representation
retrieved earlier in a session. retrieved earlier in a session.
The freshness model (Section 2.3) does not necessarily apply to The freshness model (Section 4.1) does not necessarily apply to
history mechanisms. I.e., a history mechanism can display a previous history mechanisms. I.e., a history mechanism can display a previous
representation even if it has expired. representation even if it has expired.
This does not prohibit the history mechanism from telling the user This does not prohibit the history mechanism from telling the user
that a view might be stale, or from honoring cache directives (e.g., that a view might be stale, or from honoring cache directives (e.g.,
Cache-Control: no-store). Cache-Control: no-store).
5. IANA Considerations 9. IANA Considerations
5.1. Cache Directive Registry 9.1. Cache Directive Registry
The registration procedure for HTTP Cache Directives is defined by The registration procedure for HTTP Cache Directives is defined by
Section 3.2.3 of this document. Section 7.2.3 of this document.
The HTTP Cache Directive Registry shall be created at The HTTP Cache Directive Registry shall be created at
<http://www.iana.org/assignments/http-cache-directives> and be <http://www.iana.org/assignments/http-cache-directives> and be
populated with the registrations below: populated with the registrations below:
+------------------------+------------------------------+ +------------------------+----------------------------------+
| Cache Directive | Reference | | Cache Directive | Reference |
+------------------------+------------------------------+ +------------------------+----------------------------------+
| max-age | Section 3.2.1, Section 3.2.2 | | max-age | Section 7.2.1.3, Section 7.2.2.7 |
| max-stale | Section 3.2.1 | | max-stale | Section 7.2.1.4 |
| min-fresh | Section 3.2.1 | | min-fresh | Section 7.2.1.5 |
| must-revalidate | Section 3.2.2 | | must-revalidate | Section 7.2.2.5 |
| no-cache | Section 3.2.1, Section 3.2.2 | | no-cache | Section 7.2.1.1, Section 7.2.2.3 |
| no-store | Section 3.2.1, Section 3.2.2 | | no-store | Section 7.2.1.2, Section 7.2.2.4 |
| no-transform | Section 3.2.1, Section 3.2.2 | | no-transform | Section 7.2.1.6, Section 7.2.2.9 |
| only-if-cached | Section 3.2.1 | | only-if-cached | Section 7.2.1.7 |
| private | Section 3.2.2 | | private | Section 7.2.2.2 |
| proxy-revalidate | Section 3.2.2 | | proxy-revalidate | Section 7.2.2.6 |
| public | Section 3.2.2 | | public | Section 7.2.2.1 |
| s-maxage | Section 3.2.2 | | s-maxage | Section 7.2.2.8 |
| stale-if-error | [RFC5861], Section 4 | | stale-if-error | [RFC5861], Section 4 |
| stale-while-revalidate | [RFC5861], Section 3 | | stale-while-revalidate | [RFC5861], Section 3 |
+------------------------+------------------------------+ +------------------------+----------------------------------+
5.2. Warn Code Registry 9.2. Warn Code Registry
The registration procedure for HTTP Warn Codes is defined by The registration procedure for HTTP Warn Codes is defined by
Section 3.6.8 of this document. Section 7.6.8 of this document.
The HTTP Warn Code Registry shall be created at The HTTP Warn Code Registry shall be created at
<http://www.iana.org/assignments/http-cache-directives> and be <http://www.iana.org/assignments/http-cache-directives> and be
populated with the registrations below: populated with the registrations below:
+-----------+----------------------------------+---------------+ +-----------+----------------------------------+---------------+
| Warn Code | Short Description | Reference | | Warn Code | Short Description | Reference |
+-----------+----------------------------------+---------------+ +-----------+----------------------------------+---------------+
| 110 | Response is Stale | Section 3.6.1 | | 110 | Response is Stale | Section 7.6.1 |
| 111 | Revalidation Failed | Section 3.6.2 | | 111 | Revalidation Failed | Section 7.6.2 |
| 112 | Disconnected Operation | Section 3.6.3 | | 112 | Disconnected Operation | Section 7.6.3 |
| 113 | Heuristic Expiration | Section 3.6.4 | | 113 | Heuristic Expiration | Section 7.6.4 |
| 199 | Miscellaneous Warning | Section 3.6.5 | | 199 | Miscellaneous Warning | Section 7.6.5 |
| 214 | Transformation Applied | Section 3.6.6 | | 214 | Transformation Applied | Section 7.6.6 |
| 299 | Miscellaneous Persistent Warning | Section 3.6.7 | | 299 | Miscellaneous Persistent Warning | Section 7.6.7 |
+-----------+----------------------------------+---------------+ +-----------+----------------------------------+---------------+
5.3. Header Field Registration 9.3. Header Field Registration
The Message Header Field Registry located at <http://www.iana.org/ The Message Header Field Registry located at <http://www.iana.org/
assignments/message-headers/message-header-index.html> shall be assignments/message-headers/message-header-index.html> shall be
updated with the permanent registrations below (see [RFC3864]): updated with the permanent registrations below (see [RFC3864]):
+-------------------+----------+----------+-------------+ +-------------------+----------+----------+-------------+
| Header Field Name | Protocol | Status | Reference | | Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-------------+ +-------------------+----------+----------+-------------+
| Age | http | standard | Section 3.1 | | Age | http | standard | Section 7.1 |
| Cache-Control | http | standard | Section 3.2 | | Cache-Control | http | standard | Section 7.2 |
| Expires | http | standard | Section 3.3 | | Expires | http | standard | Section 7.3 |
| Pragma | http | standard | Section 3.4 | | Pragma | http | standard | Section 7.4 |
| Vary | http | standard | Section 3.5 | | Vary | http | standard | Section 7.5 |
| Warning | http | standard | Section 3.6 | | Warning | http | standard | Section 7.6 |
+-------------------+----------+----------+-------------+ +-------------------+----------+----------+-------------+
The change controller is: "IETF (iesg@ietf.org) - Internet The change controller is: "IETF (iesg@ietf.org) - Internet
Engineering Task Force". Engineering Task Force".
6. Security Considerations 10. Security Considerations
Caches expose additional potential vulnerabilities, since the Caches expose additional potential vulnerabilities, since the
contents of the cache represent an attractive target for malicious contents of the cache represent an attractive target for malicious
exploitation. Because cache contents persist after an HTTP request exploitation. Because cache contents persist after an HTTP request
is complete, an attack on the cache can reveal information long after is complete, an attack on the cache can reveal information long after
a user believes that the information has been removed from the a user believes that the information has been removed from the
network. Therefore, cache contents need to be protected as sensitive network. Therefore, cache contents need to be protected as sensitive
information. information.
7. Acknowledgments 11. Acknowledgments
See Section 9 of [Part1]. See Section 9 of [Part1].
8. References 12. References
8.1. Normative References
12.1. Normative References
[Part1] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., [Part1] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"HTTP/1.1, part 1: URIs, Connections, and Message "HTTP/1.1, part 1: Message Routing and Syntax"",
Parsing", draft-ietf-httpbis-p1-messaging-19 (work in draft-ietf-httpbis-p1-messaging-20 (work in progress),
progress), March 2012. July 2012.
[Part2] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., [Part2] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"HTTP/1.1, part 2: Message Semantics", "HTTP/1.1, part 2: Semantics and Payloads",
draft-ietf-httpbis-p2-semantics-19 (work in progress), draft-ietf-httpbis-p2-semantics-20 (work in progress),
March 2012. July 2012.
[Part4] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., [Part4] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"HTTP/1.1, part 4: Conditional Requests", "HTTP/1.1, part 4: Conditional Requests",
draft-ietf-httpbis-p4-conditional-19 (work in progress), draft-ietf-httpbis-p4-conditional-20 (work in progress),
March 2012. July 2012.
[Part5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., [Part5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"HTTP/1.1, part 5: Range Requests and Partial Responses", "HTTP/1.1, part 5: Range Requests",
draft-ietf-httpbis-p5-range-19 (work in progress), draft-ietf-httpbis-p5-range-20 (work in progress),
March 2012. July 2012.
[Part7] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., [Part7] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"HTTP/1.1, part 7: Authentication", "HTTP/1.1, part 7: Authentication",
draft-ietf-httpbis-p7-auth-19 (work in progress), draft-ietf-httpbis-p7-auth-20 (work in progress),
March 2012. July 2012.
[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 12.2. Informative References
[RFC1305] Mills, D., "Network Time Protocol (Version 3) [RFC1305] Mills, D., "Network Time Protocol (Version 3)
Specification, Implementation", RFC 1305, March 1992. Specification, Implementation", RFC 1305, March 1992.
[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,
skipping to change at page 36, line 12 skipping to change at page 36, line 42
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008. May 2008.
[RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale [RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale
Content", RFC 5861, April 2010. Content", RFC 5861, April 2010.
Appendix A. Changes from RFC 2616 Appendix A. Changes from RFC 2616
Make the specified age calculation algorithm less conservative. Make the specified age calculation algorithm less conservative.
(Section 2.3.2) (Section 4.1.3)
Remove requirement to consider Content-Location in successful Remove requirement to consider Content-Location in successful
responses in order to determine the appropriate response to use. responses in order to determine the appropriate response to use.
(Section 2.4) (Section 4.2)
Clarify denial of service attack avoidance requirement. Clarify denial of service attack avoidance requirement. (Section 6)
(Section 2.6)
Change ABNF productions for header fields to only define the field Change ABNF productions for header fields to only define the field
value. (Section 3) value. (Section 7)
Do not mention RFC 2047 encoding and multiple languages in Warning Do not mention RFC 2047 encoding and multiple languages in Warning
header fields anymore, as these aspects never were implemented. header fields anymore, as these aspects never were implemented.
(Section 3.6) (Section 7.6)
Appendix B. Collected ABNF Introduce Cache Directive and Warn Code Registries. (Section 7.2.3
and Section 7.6.8)
Appendix B. Imported ABNF
The following core rules are included by reference, as defined in
Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return),
CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
quote), HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any
8-bit sequence of data), SP (space), and VCHAR (any visible US-ASCII
character).
The rules below are defined in [Part1]:
OWS = <OWS, defined in [Part1], Section 3.2.1>
field-name = <field-name, defined in [Part1], Section 3.2>
quoted-string = <quoted-string, defined in [Part1], Section 3.2.4>
token = <token, defined in [Part1], Section 3.2.4>
port = <port, defined in [Part1], Section 2.8>
pseudonym = <pseudonym, defined in [Part1], Section 6.2>
uri-host = <uri-host, defined in [Part1], Section 2.8>
The rules below are defined in other parts:
HTTP-date = <HTTP-date, defined in [Part2], Section 5.1>
Appendix C. Collected ABNF
Age = delta-seconds Age = delta-seconds
Cache-Control = *( "," OWS ) cache-directive *( OWS "," [ OWS Cache-Control = *( "," OWS ) cache-directive *( OWS "," [ OWS
cache-directive ] ) cache-directive ] )
Expires = HTTP-date Expires = HTTP-date
HTTP-date = <HTTP-date, defined in [Part2], Section 8> HTTP-date = <HTTP-date, defined in [Part2], Section 5.1>
OWS = <OWS, defined in [Part1], Section 3.2.1> OWS = <OWS, defined in [Part1], Section 3.2.1>
Pragma = *( "," OWS ) pragma-directive *( OWS "," [ OWS Pragma = *( "," OWS ) pragma-directive *( OWS "," [ OWS
pragma-directive ] ) pragma-directive ] )
Vary = "*" / ( *( "," OWS ) field-name *( OWS "," [ OWS field-name ] Vary = "*" / ( *( "," OWS ) field-name *( OWS "," [ OWS field-name ]
) ) ) )
Warning = *( "," OWS ) warning-value *( OWS "," [ OWS warning-value ] Warning = *( "," OWS ) warning-value *( OWS "," [ OWS warning-value ]
) )
cache-directive = cache-request-directive / cache-response-directive cache-directive = token [ "=" ( token / quoted-string ) ]
cache-extension = token [ "=" ( token / quoted-string ) ]
cache-request-directive = "no-cache" / "no-store" / ( "max-age="
delta-seconds ) / ( "max-stale" [ "=" delta-seconds ] ) / (
"min-fresh=" delta-seconds ) / "no-transform" / "only-if-cached" /
cache-extension
cache-response-directive = "public" / ( "private" [ "=" DQUOTE *( ","
OWS ) field-name *( OWS "," [ OWS field-name ] ) DQUOTE ] ) / (
"no-cache" [ "=" DQUOTE *( "," OWS ) field-name *( OWS "," [ OWS
field-name ] ) DQUOTE ] ) / "no-store" / "no-transform" /
"must-revalidate" / "proxy-revalidate" / ( "max-age=" delta-seconds
) / ( "s-maxage=" delta-seconds ) / cache-extension
delta-seconds = 1*DIGIT delta-seconds = 1*DIGIT
extension-pragma = token [ "=" ( token / quoted-string ) ] extension-pragma = token [ "=" ( token / quoted-string ) ]
field-name = <field-name, defined in [Part1], Section 3.2> field-name = <field-name, defined in [Part1], Section 3.2>
port = <port, defined in [Part1], Section 2.7> port = <port, defined in [Part1], Section 2.8>
pragma-directive = "no-cache" / extension-pragma pragma-directive = "no-cache" / extension-pragma
pseudonym = <pseudonym, defined in [Part1], Section 6.2> pseudonym = <pseudonym, defined in [Part1], Section 6.2>
quoted-string = <quoted-string, defined in [Part1], Section 3.2.4> quoted-string = <quoted-string, defined in [Part1], Section 3.2.4>
token = <token, defined in [Part1], Section 3.2.4> token = <token, defined in [Part1], Section 3.2.4>
uri-host = <uri-host, defined in [Part1], Section 2.7> uri-host = <uri-host, defined in [Part1], Section 2.8>
warn-agent = ( uri-host [ ":" port ] ) / pseudonym warn-agent = ( uri-host [ ":" port ] ) / pseudonym
warn-code = 3DIGIT warn-code = 3DIGIT
warn-date = DQUOTE HTTP-date DQUOTE warn-date = DQUOTE HTTP-date DQUOTE
warn-text = quoted-string warn-text = quoted-string
warning-value = warn-code SP warn-agent SP warn-text [ SP warn-date warning-value = warn-code SP warn-agent SP warn-text [ SP warn-date
] ]
ABNF diagnostics: Appendix D. Change Log (to be removed by RFC Editor before publication)
; Age defined but not used
; Cache-Control defined but not used
; Expires defined but not used
; Pragma defined but not used
; Vary defined but not used
; Warning defined but not used
Appendix C. Change Log (to be removed by RFC Editor before publication)
C.1. Since RFC 2616
Extracted relevant partitions from [RFC2616].
C.2. Since draft-ietf-httpbis-p6-cache-00
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/9>: "Trailer"
(<http://purl.org/NET/http-errata#trailer-hop>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/12>: "Invalidation
after Update or Delete"
(<http://purl.org/NET/http-errata#invalidupd>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative and
Informative references"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/48>: "Date reference
typo"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/49>: "Connection
header text"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/65>: "Informative
references"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/66>: "ISO-8859-1
Reference"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/86>: "Normative up-
to-date references"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/87>: "typo in
13.2.2"
Other changes:
o Use names of RFC4234 core rules DQUOTE and HTAB (work in progress
on <http://tools.ietf.org/wg/httpbis/trac/ticket/36>)
C.3. Since draft-ietf-httpbis-p6-cache-01
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/82>: "rel_path not
used"
Other changes:
o Get rid of duplicate BNF rule names ("host" -> "uri-host") (work
in progress on <http://tools.ietf.org/wg/httpbis/trac/ticket/36>)
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 Field Registration
(<http://tools.ietf.org/wg/httpbis/trac/ticket/40>):
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 <http://tools.ietf.org/wg/httpbis/trac/ticket/106>: "Vary header
classification"
C.6. Since draft-ietf-httpbis-p6-cache-04
Ongoing work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
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
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 <http://tools.ietf.org/wg/httpbis/trac/ticket/54>: "Definition of
1xx Warn-Codes"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/60>: "Placement of
13.5.1 and 13.5.2"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/138>: "The role of
Warning and Semantic Transparency in Caching"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/139>: "Methods and
Caching"
In addition: Final work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Add appendix containing collected and expanded ABNF, reorganize
ABNF introduction.
C.8. Since draft-ietf-httpbis-p6-cache-06
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/161>: "base for
numeric protocol elements"
Affected issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/37>: "Vary and non-
existant headers"
C.9. Since draft-ietf-httpbis-p6-cache-07
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/54>: "Definition of
1xx Warn-Codes"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/167>: "Content-
Location on 304 responses"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/169>: "private and
no-cache CC directives with headers"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/187>: "RFC2047 and
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"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/291>: "Cache
Extensions can override no-store, etc."
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"
C.11. Since draft-ietf-httpbis-p6-cache-09
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/29>: "Age
calculation"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/168>: "Clarify
differences between / requirements for request and response CC
directives"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/174>: "Caching
authenticated responses"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/208>: "IANA registry
for cache-control directives"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/211>: "Heuristic
caching of URLs with query components"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/196>: "Term for the
requested resource's URI"
C.12. Since draft-ietf-httpbis-p6-cache-10
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/109>: "Clarify
entity / representation / variant terminology"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/220>: "consider
removing the 'changes from 2068' sections"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/223>: "Allowing
heuristic caching for new status codes"
o Clean up TODOs and prose in "Combining Responses."
C.13. Since draft-ietf-httpbis-p6-cache-11
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/204>: "Text about
clock requirement for caches belongs in p6"
C.14. Since draft-ietf-httpbis-p6-cache-12
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/224>: "Header
Classification"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/268>: "Clarify
'public'"
C.15. Since draft-ietf-httpbis-p6-cache-13
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
ABNFs for header fields"
C.16. Since draft-ietf-httpbis-p6-cache-14
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/38>: "Mismatch Vary"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/235>: "Cache
Invalidation only happens upon successful responses"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/282>: "Recommend
minimum sizes for protocol elements"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/289>: "Proxies don't
'understand' methods"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/291>: "Cache
Extensions can override no-store, etc."
o <http://tools.ietf.org/wg/httpbis/trac/ticket/292>: "Pragma"
C.17. Since draft-ietf-httpbis-p6-cache-15
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/290>: "Motivate one-
year limit for Expires"
C.18. Since draft-ietf-httpbis-p6-cache-16
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/186>: "Document
HTTP's error-handling philosophy"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/317>: "Cache-Control Changes up to the first Working Group Last Call draft are summarized
directive case sensitivity" in <http://trac.tools.ietf.org/html/
draft-ietf-httpbis-p6-cache-19#appendix-C>.
C.19. Since draft-ietf-httpbis-p6-cache-17 D.1. Since draft-ietf-httpbis-p6-cache-19
Closed issues: Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/293>: "Interaction o <http://tools.ietf.org/wg/httpbis/trac/ticket/307>: "untangle
of request and response Cache-Control" Cache-Control ABNF"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/212>: "Refining age o <http://tools.ietf.org/wg/httpbis/trac/ticket/353>: "Multiple
for 1.1 proxy chains" values in Cache-Control header fields"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/274>: "warn-code o <http://tools.ietf.org/wg/httpbis/trac/ticket/355>: "Case
registry" sensitivity of header fields in CC values"
C.20. Since draft-ietf-httpbis-p6-cache-18 o <http://tools.ietf.org/wg/httpbis/trac/ticket/356>: "Spurious
'MAYs'"
Closed issues: o <http://tools.ietf.org/wg/httpbis/trac/ticket/360>: "enhance
considerations for new cache control directives"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/227>: "Combining o <http://tools.ietf.org/wg/httpbis/trac/ticket/361>: "ABNF
HEAD responses" requirements for recipients"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/337>: "Field names o <http://tools.ietf.org/wg/httpbis/trac/ticket/368>: "note
in cache-control header arguments" introduction of new IANA registries as normative changes"
Index Index
1 1
110 Response is Stale (warn code) 31 110 Response is Stale (warn code) 31
111 Revalidation Failed (warn code) 31 111 Revalidation Failed (warn code) 32
112 Disconnected Operation (warn code) 31 112 Disconnected Operation (warn code) 32
113 Heuristic Expiration (warn code) 32 113 Heuristic Expiration (warn code) 32
199 Miscellaneous Warning (warn code) 32 199 Miscellaneous Warning (warn code) 32
2 2
214 Transformation Applied (warn code) 32 214 Transformation Applied (warn code) 32
299 Miscellaneous Persistent Warning (warn code) 32 299 Miscellaneous Persistent Warning (warn code) 32
A A
age 6 age 5
Age header field 21 Age header field 20
C C
cache 5 cache 4
Cache Directives Cache Directives
max-age 23, 26 max-age 22, 25
max-stale 23 max-stale 22
min-fresh 23 min-fresh 22
must-revalidate 25 must-revalidate 25
no-cache 22, 24 no-cache 21, 24
no-store 22, 25 no-store 21, 25
no-transform 23, 26 no-transform 23, 26
only-if-cached 23 only-if-cached 23
private 24 private 23
proxy-revalidate 26 proxy-revalidate 25
public 24 public 23
s-maxage 26 s-maxage 26
cache entry 8 cache entry 7
cache key 8 cache key 7
Cache-Control header field 21 Cache-Control header field 20
cacheable 5 cacheable 4
E E
Expires header field 27 Expires header field 28
explicit expiration time 6 explicit expiration time 5
F F
first-hand 6 first-hand 5
fresh 6 fresh 5
freshness lifetime 6 freshness lifetime 5
G G
Grammar Grammar
Age 21 Age 20
Cache-Control 22 Cache-Control 21
cache-extension 22 cache-directive 21
cache-request-directive 22 delta-seconds 7
cache-response-directive 24
delta-seconds 8
Expires 28 Expires 28
extension-pragma 28 extension-pragma 29
Pragma 28 Pragma 29
pragma-directive 28 pragma-directive 29
Vary 29 Vary 29
warn-agent 30 warn-agent 30
warn-code 30 warn-code 30
warn-date 30 warn-date 30
warn-text 30 warn-text 30
Warning 30 Warning 30
warning-value 30 warning-value 30
H H
Header Fields Header Fields
Age 21 Age 20
Cache-Control 21 Cache-Control 20
Expires 27 Expires 28
Pragma 28 Pragma 28
Vary 29 Vary 29
Warning 30 Warning 30
heuristic expiration time 6 heuristic expiration time 5
M M
max-age max-age
Cache Directive 23, 26 Cache Directive 22, 25
max-stale max-stale
Cache Directive 23 Cache Directive 22
min-fresh min-fresh
Cache Directive 23 Cache Directive 22
must-revalidate must-revalidate
Cache Directive 25 Cache Directive 25
N N
no-cache no-cache
Cache Directive 22, 24 Cache Directive 21, 24
no-store no-store
Cache Directive 22, 25 Cache Directive 21, 25
no-transform no-transform
Cache Directive 23, 26 Cache Directive 23, 26
O O
only-if-cached only-if-cached
Cache Directive 23 Cache Directive 23
P P
Pragma header field 28 Pragma header field 28
private private
Cache Directive 24 Cache Directive 23
private cache 5 private cache 4
proxy-revalidate proxy-revalidate
Cache Directive 26 Cache Directive 25
public public
Cache Directive 24 Cache Directive 23
S S
s-maxage s-maxage
Cache Directive 26 Cache Directive 26
shared cache 5 shared cache 4
stale 6 stale 5
strong validator 7 strong validator 6
V V
validator 6 validator 5
strong 7 strong 6
Vary header field 29 Vary header field 29
W W
Warn Codes Warn Codes
110 Response is Stale 31 110 Response is Stale 31
111 Revalidation Failed 31 111 Revalidation Failed 32
112 Disconnected Operation 31 112 Disconnected Operation 32
113 Heuristic Expiration 32 113 Heuristic Expiration 32
199 Miscellaneous Warning 32 199 Miscellaneous Warning 32
214 Transformation Applied 32 214 Transformation Applied 32
299 Miscellaneous Persistent Warning 32 299 Miscellaneous Persistent Warning 32
Warning header field 30 Warning header field 30
Authors' Addresses Authors' Addresses
Roy T. Fielding (editor) Roy T. Fielding (editor)
Adobe Systems Incorporated Adobe Systems Incorporated
skipping to change at page 47, line 19 skipping to change at page 43, line 4
France France
EMail: ylafon@w3.org EMail: ylafon@w3.org
URI: http://www.raubacapeu.net/people/yves/ URI: http://www.raubacapeu.net/people/yves/
Mark Nottingham (editor) Mark Nottingham (editor)
Rackspace Rackspace
EMail: mnot@mnot.net EMail: mnot@mnot.net
URI: http://www.mnot.net/ URI: http://www.mnot.net/
Julian F. Reschke (editor) Julian F. Reschke (editor)
greenbytes GmbH greenbytes GmbH
Hafenweg 16 Hafenweg 16
Muenster, NW 48155 Muenster, NW 48155
Germany Germany
Phone: +49 251 2807760
Fax: +49 251 2807761
EMail: julian.reschke@greenbytes.de EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/ URI: http://greenbytes.de/tech/webdav/
 End of changes. 229 change blocks. 
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