draft-ietf-httpbis-p6-cache-19.txt		draft-ietf-httpbis-p6-cache-latest.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: November 20, 2012 M. Nottingham, Ed.
	Rackspace		Rackspace
	J. Reschke, Ed.		J. Reschke, Ed.
	greenbytes		greenbytes
	March 12, 2012		May 19, 2012
	HTTP/1.1, part 6: Caching		HTTP/1.1, part 6: Caching
	draft-ietf-httpbis-p6-cache-19		draft-ietf-httpbis-p6-cache-latest
	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. HTTP has been in use by the World Wide Web global
	information initiative since 1990. This document is Part 6 of the		information initiative since 1990. This document is Part 6 of the
	seven-part specification that defines the protocol referred to as		seven-part specification that defines the protocol referred to as
	"HTTP/1.1" and, taken together, obsoletes RFC 2616.		"HTTP/1.1" and, taken together, obsoletes RFC 2616.
	skipping to change at page 1, line 40		skipping to change at page 1, line 40
	Discussion of this draft should take place on the HTTPBIS working		Discussion of this draft should take place on the HTTPBIS working
	group mailing list (ietf-http-wg@w3.org), which is archived at		group 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 C.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 November 20, 2012.
	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 42
	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 . . . . . . . . . . . . . . . . . . . . . 6
	1.4.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 8		1.4.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 7
	1.4.2. ABNF Rules defined in other Parts of the		1.4.2. ABNF Rules defined in other Parts of the
	Specification . . . . . . . . . . . . . . . . . . . . 8		Specification . . . . . . . . . . . . . . . . . . . . 7
	1.5. Delta Seconds . . . . . . . . . . . . . . . . . . . . . . 8		1.5. Delta Seconds . . . . . . . . . . . . . . . . . . . . . . 7
	2. Cache Operation . . . . . . . . . . . . . . . . . . . . . . . 8		2. Cache Operation . . . . . . . . . . . . . . . . . . . . . . . 7
	2.1. Response Cacheability . . . . . . . . . . . . . . . . . . 9		2.1. Response Cacheability . . . . . . . . . . . . . . . . . . 8
	2.2. Constructing Responses from Caches . . . . . . . . . . . . 10		2.2. Constructing Responses from Caches . . . . . . . . . . . . 9
	2.3. Freshness Model . . . . . . . . . . . . . . . . . . . . . 12		2.3. Freshness Model . . . . . . . . . . . . . . . . . . . . . 11
	2.3.1. Calculating Freshness Lifetime . . . . . . . . . . . . 13		2.3.1. Calculating Freshness Lifetime . . . . . . . . . . . . 12
	2.3.2. Calculating Age . . . . . . . . . . . . . . . . . . . 14		2.3.2. Calculating Age . . . . . . . . . . . . . . . . . . . 13
	2.3.3. Serving Stale Responses . . . . . . . . . . . . . . . 16		2.3.3. Serving Stale Responses . . . . . . . . . . . . . . . 15
	2.4. Validation Model . . . . . . . . . . . . . . . . . . . . . 16		2.4. Validation Model . . . . . . . . . . . . . . . . . . . . . 15
	2.4.1. Freshening Responses with 304 Not Modified . . . . . . 17		2.4.1. Freshening Responses with 304 Not Modified . . . . . . 16
	2.5. Updating Caches with HEAD Responses . . . . . . . . . . . 18		2.5. Updating Caches with HEAD Responses . . . . . . . . . . . 17
	2.6. Request Methods that Invalidate . . . . . . . . . . . . . 18		2.6. Request Methods that Invalidate . . . . . . . . . . . . . 17
	2.7. Shared Caching of Authenticated Responses . . . . . . . . 19		2.7. Shared Caching of Authenticated Responses . . . . . . . . 18
	2.8. Caching Negotiated Responses . . . . . . . . . . . . . . . 19		2.8. Caching Negotiated Responses . . . . . . . . . . . . . . . 18
	2.9. Combining Partial Content . . . . . . . . . . . . . . . . 20		2.9. Combining Partial Content . . . . . . . . . . . . . . . . 19
	3. Header Field Definitions . . . . . . . . . . . . . . . . . . . 21		3. Header Field Definitions . . . . . . . . . . . . . . . . . . . 20
	3.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 21		3.1. Age . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
	3.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 21		3.2. Cache-Control . . . . . . . . . . . . . . . . . . . . . . 20
	3.2.1. Request Cache-Control Directives . . . . . . . . . . . 22		3.2.1. Request Cache-Control Directives . . . . . . . . . . . 21
	3.2.2. Response Cache-Control Directives . . . . . . . . . . 24		3.2.2. Response Cache-Control Directives . . . . . . . . . . 23
	3.2.3. Cache Control Extensions . . . . . . . . . . . . . . . 26		3.2.3. Cache Control Extensions . . . . . . . . . . . . . . . 25
	3.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 27		3.3. Expires . . . . . . . . . . . . . . . . . . . . . . . . . 26
	3.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 28		3.4. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . . 27
	3.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . . 29		3.5. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
	3.6. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 30		3.6. Warning . . . . . . . . . . . . . . . . . . . . . . . . . 29
	3.6.1. 110 Response is Stale . . . . . . . . . . . . . . . . 31		3.6.1. 110 Response is Stale . . . . . . . . . . . . . . . . 30
	3.6.2. 111 Revalidation Failed . . . . . . . . . . . . . . . 31		3.6.2. 111 Revalidation Failed . . . . . . . . . . . . . . . 30
	3.6.3. 112 Disconnected Operation . . . . . . . . . . . . . . 31		3.6.3. 112 Disconnected Operation . . . . . . . . . . . . . . 30
	3.6.4. 113 Heuristic Expiration . . . . . . . . . . . . . . . 32		3.6.4. 113 Heuristic Expiration . . . . . . . . . . . . . . . 31
	3.6.5. 199 Miscellaneous Warning . . . . . . . . . . . . . . 32		3.6.5. 199 Miscellaneous Warning . . . . . . . . . . . . . . 31
	3.6.6. 214 Transformation Applied . . . . . . . . . . . . . . 32		3.6.6. 214 Transformation Applied . . . . . . . . . . . . . . 31
	3.6.7. 299 Miscellaneous Persistent Warning . . . . . . . . . 32		3.6.7. 299 Miscellaneous Persistent Warning . . . . . . . . . 31
	3.6.8. Warn Code Extensions . . . . . . . . . . . . . . . . . 32		3.6.8. Warn Code Extensions . . . . . . . . . . . . . . . . . 31
	4. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 32		4. History Lists . . . . . . . . . . . . . . . . . . . . . . . . 31
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
	5.1. Cache Directive Registry . . . . . . . . . . . . . . . . . 33		5.1. Cache Directive Registry . . . . . . . . . . . . . . . . . 32
	5.2. Warn Code Registry . . . . . . . . . . . . . . . . . . . . 33		5.2. Warn Code Registry . . . . . . . . . . . . . . . . . . . . 32
	5.3. Header Field Registration . . . . . . . . . . . . . . . . 34		5.3. Header Field Registration . . . . . . . . . . . . . . . . 33
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 34		6. Security Considerations . . . . . . . . . . . . . . . . . . . 33
	7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 34		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35		8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 35		8.1. Normative References . . . . . . . . . . . . . . . . . . . 34
	8.2. Informative References . . . . . . . . . . . . . . . . . . 35		8.2. Informative References . . . . . . . . . . . . . . . . . . 34
	Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 36		Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 35
	Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 36		Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 35
	Appendix C. Change Log (to be removed by RFC Editor before		Appendix C. Change Log (to be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . 37		publication) . . . . . . . . . . . . . . . . . . . . 36
	C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 38		C.1. Since draft-ietf-httpbis-p6-cache-19 . . . . . . . . . . . 37
	C.2. Since draft-ietf-httpbis-p6-cache-00 . . . . . . . . . . . 38		Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
	C.3. Since draft-ietf-httpbis-p6-cache-01 . . . . . . . . . . . 38
	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
	skipping to change at page 8, line 21		skipping to change at page 7, line 21
	OWS = <OWS, defined in [Part1], Section 3.2.1>		OWS = <OWS, defined in [Part1], Section 3.2.1>
	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>
	1.4.2. ABNF Rules defined in other Parts of the Specification		1.4.2. ABNF Rules defined in other Parts of the Specification
	The ABNF rules below are defined in other parts:		The ABNF rules below are defined in other parts:
	field-name = <field-name, defined in [Part1], Section 3.2>		field-name = <field-name, defined in [Part1], Section 3.2>
	HTTP-date = <HTTP-date, defined in [Part2], Section 8>		HTTP-date = <HTTP-date, defined in [Part2], Section 5.1>
	port = <port, defined in [Part1], Section 2.7>		port = <port, defined in [Part1], Section 2.7>
	pseudonym = <pseudonym, defined in [Part1], Section 6.2>		pseudonym = <pseudonym, defined in [Part1], Section 6.2>
	uri-host = <uri-host, defined in [Part1], Section 2.7>		uri-host = <uri-host, defined in [Part1], Section 2.7>
	1.5. Delta Seconds		1.5. 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
	skipping to change at page 11, line 37		skipping to change at page 10, line 37
	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 3.2.3.
	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 3.1) 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 2.3.2.
	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 2.6.
	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
	skipping to change at page 13, line 30		skipping to change at page 12, line 30
	A heuristic freshness lifetime might be applicable; see		A heuristic freshness lifetime might be applicable; see
	Section 2.3.1.1.		Section 2.3.1.1.
	Note that this calculation is not vulnerable to clock skew, since all		Note that this calculation is not vulnerable to clock skew, since all
	of the information comes from the origin server.		of the information comes from the origin server.
	2.3.1.1. Calculating Heuristic Freshness		2.3.1.1. Calculating Heuristic Freshness
	If no explicit expiration time is present in a stored response that		If no explicit expiration time is present in a stored response that
	has a status code 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, 203, 206,
	300, 301 and 410), a cache MAY calculate a heuristic expiration time.		300, 301 and 410), a cache MAY calculate a heuristic expiration time.
	A cache MUST NOT use heuristics to determine freshness for responses		A cache MUST NOT use heuristics to determine freshness for responses
	with status codes that do not explicitly allow it.		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
	skipping to change at page 14, line 29		skipping to change at page 13, line 29
	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 3.1), 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 18, line 47		skipping to change at page 17, line 47
	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 response to replace all
	instances of the corresponding header fields in the stored		instances of the corresponding header fields in the stored
	response.		response.
	2.6. Request Methods that Invalidate		2.6. Request Methods that Invalidate
	Because unsafe request methods (Section 6.1.1 of [Part2]) such as		Because unsafe request methods (Section 2.1.1 of [Part2]) such as
	PUT, POST or DELETE have the potential for changing state on the		PUT, POST or DELETE have the potential for changing state on the
	origin server, intervening caches can use them to keep their contents		origin server, intervening caches can use them to keep their contents
	up-to-date.		up-to-date.
	A cache MUST invalidate the effective Request URI (Section 5.5 of		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		[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		response header fields (if present) when a non-error response to a
	request with an unsafe method is received.		request with an unsafe method is received.
	skipping to change at page 27, line 52		skipping to change at page 26, line 52
	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 2.3 for further discussion
	of the freshness model.		of the freshness model.
	The presence of an Expires field does not imply that the original		The presence of an Expires field does not imply that the original
	resource will change or cease to exist at, before, or after that		resource will change or cease to exist at, before, or after that
	time.		time.
	The field-value is an absolute date and time as defined by HTTP-date		The field-value is an absolute date and time as defined by HTTP-date
	in Section 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").
	skipping to change at page 35, line 8		skipping to change at page 34, line 8
	7. Acknowledgments		7. Acknowledgments
	See Section 9 of [Part1].		See Section 9 of [Part1].
	8. References		8. References
	8.1. Normative References		8.1. 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: URIs, Connections, and Message
	Parsing", draft-ietf-httpbis-p1-messaging-19 (work in		Parsing", draft-ietf-httpbis-p1-messaging-latest (work in
	progress), March 2012.		progress), May 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: Message Semantics",
	draft-ietf-httpbis-p2-semantics-19 (work in progress),		draft-ietf-httpbis-p2-semantics-latest (work in progress),
	March 2012.		May 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-latest (work in
	March 2012.		progress), May 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 and Partial Responses",
	draft-ietf-httpbis-p5-range-19 (work in progress),		draft-ietf-httpbis-p5-range-latest (work in progress),
	March 2012.		May 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-latest (work in progress),
	March 2012.		May 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		8.2. Informative References
	[RFC1305] Mills, D., "Network Time Protocol (Version 3)		[RFC1305] Mills, D., "Network Time Protocol (Version 3)
	skipping to change at page 36, line 37		skipping to change at page 35, line 37
	Appendix B. Collected ABNF		Appendix B. 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 6.1>
	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 ]
	skipping to change at page 38, line 4		skipping to change at page 36, line 48
	ABNF diagnostics:		ABNF diagnostics:
	; Age defined but not used		; Age defined but not used
	; Cache-Control defined but not used		; Cache-Control defined but not used
	; Expires defined but not used		; Expires defined but not used
	; Pragma defined but not used		; Pragma defined but not used
	; Vary defined but not used		; Vary defined but not used
	; Warning defined but not used		; Warning defined but not used
	Appendix C. Change Log (to be removed by RFC Editor before publication)		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:		Changes up to the first Working Group Last Call draft are summarized
			in <http://trac.tools.ietf.org/html/
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/147>: "serving		draft-ietf-httpbis-p6-cache-19#appendix-C>.
	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
	directive case sensitivity"
	C.19. Since draft-ietf-httpbis-p6-cache-17
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/293>: "Interaction
	of request and response Cache-Control"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/212>: "Refining age
	for 1.1 proxy chains"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/274>: "warn-code
	registry"
	C.20. Since draft-ietf-httpbis-p6-cache-18
	Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/227>: "Combining		C.1. Since draft-ietf-httpbis-p6-cache-19
	HEAD responses"
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/337>: "Field names		None yet.
	in cache-control header arguments"
	Index		Index
	1		1
	110 Response is Stale (warn code) 31		110 Response is Stale (warn code) 30
	111 Revalidation Failed (warn code) 31		111 Revalidation Failed (warn code) 30
	112 Disconnected Operation (warn code) 31		112 Disconnected Operation (warn code) 30
	113 Heuristic Expiration (warn code) 32		113 Heuristic Expiration (warn code) 31
	199 Miscellaneous Warning (warn code) 32		199 Miscellaneous Warning (warn code) 31
	2		2
	214 Transformation Applied (warn code) 32		214 Transformation Applied (warn code) 31
	299 Miscellaneous Persistent Warning (warn code) 32		299 Miscellaneous Persistent Warning (warn code) 31
	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 24
	no-cache 22, 24		no-cache 21, 23
	no-store 22, 25		no-store 21, 24
	no-transform 23, 26		no-transform 22, 25
	only-if-cached 23		only-if-cached 22
	private 24		private 23
	proxy-revalidate 26		proxy-revalidate 25
	public 24		public 23
	s-maxage 26		s-maxage 25
	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 26
	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-extension 21
	cache-request-directive 22		cache-request-directive 21
	cache-response-directive 24		cache-response-directive 23
	delta-seconds 8		delta-seconds 7
	Expires 28		Expires 27
	extension-pragma 28		extension-pragma 27
	Pragma 28		Pragma 27
	pragma-directive 28		pragma-directive 27
	Vary 29		Vary 28
	warn-agent 30		warn-agent 29
	warn-code 30		warn-code 29
	warn-date 30		warn-date 29
	warn-text 30		warn-text 29
	Warning 30		Warning 29
	warning-value 30		warning-value 29
	H		H
	Header Fields		Header Fields
	Age 21		Age 20
	Cache-Control 21		Cache-Control 20
	Expires 27		Expires 26
	Pragma 28		Pragma 27
	Vary 29		Vary 28
	Warning 30		Warning 29
	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 24
	N		N
	no-cache		no-cache
	Cache Directive 22, 24		Cache Directive 21, 23
	no-store		no-store
	Cache Directive 22, 25		Cache Directive 21, 24
	no-transform		no-transform
	Cache Directive 23, 26		Cache Directive 22, 25
	O		O
	only-if-cached		only-if-cached
	Cache Directive 23		Cache Directive 22
	P		P
	Pragma header field 28		Pragma header field 27
	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 25
	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 28
	W		W
	Warn Codes		Warn Codes
	110 Response is Stale 31		110 Response is Stale 30
	111 Revalidation Failed 31		111 Revalidation Failed 30
	112 Disconnected Operation 31		112 Disconnected Operation 30
	113 Heuristic Expiration 32		113 Heuristic Expiration 31
	199 Miscellaneous Warning 32		199 Miscellaneous Warning 31
	214 Transformation Applied 32		214 Transformation Applied 31
	299 Miscellaneous Persistent Warning 32		299 Miscellaneous Persistent Warning 31
	Warning header field 30		Warning header field 29
	Authors' Addresses		Authors' Addresses
	Roy T. Fielding (editor)		Roy T. Fielding (editor)
	Adobe Systems Incorporated		Adobe Systems Incorporated
	345 Park Ave		345 Park Ave
	San Jose, CA 95110		San Jose, CA 95110
	USA		USA
	EMail: fielding@gbiv.com		EMail: fielding@gbiv.com
End of changes. 48 change blocks.
	460 lines changed or deleted		167 lines changed or added
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