draft-ietf-httpbis-p4-conditional-07.txt		draft-ietf-httpbis-p4-conditional-08.txt
	HTTPbis Working Group R. Fielding, Ed.		HTTPbis Working Group R. Fielding, Ed.
	Internet-Draft Day Software		Internet-Draft Day Software
	Obsoletes: 2616 (if approved) J. Gettys		Obsoletes: 2616 (if approved) J. Gettys
	Intended status: Standards Track One Laptop per Child		Intended status: Standards Track One Laptop per Child
	Expires: January 14, 2010 J. Mogul		Expires: April 29, 2010 J. Mogul
	HP		HP
	H. Frystyk		H. Frystyk
	Microsoft		Microsoft
	L. Masinter		L. Masinter
	Adobe Systems		Adobe Systems
	P. Leach		P. Leach
	Microsoft		Microsoft
	T. Berners-Lee		T. Berners-Lee
	W3C/MIT		W3C/MIT
	Y. Lafon, Ed.		Y. Lafon, Ed.
	W3C		W3C
	J. Reschke, Ed.		J. Reschke, Ed.
	greenbytes		greenbytes
	July 13, 2009		October 26, 2009
	HTTP/1.1, part 4: Conditional Requests		HTTP/1.1, part 4: Conditional Requests
	draft-ietf-httpbis-p4-conditional-07		draft-ietf-httpbis-p4-conditional-08
	Status of this Memo		Status of this Memo
	This Internet-Draft is submitted to IETF in full conformance with the		This Internet-Draft is submitted to IETF in full conformance with the
	provisions of BCP 78 and BCP 79. This document may contain material		provisions of BCP 78 and BCP 79. This document may contain material
	from IETF Documents or IETF Contributions published or made publicly		from IETF Documents or IETF Contributions published or made publicly
	available before November 10, 2008. The person(s) controlling the		available before November 10, 2008. The person(s) controlling the
	copyright in some of this material may not have granted the IETF		copyright in some of this material may not have granted the IETF
	Trust the right to allow modifications of such material outside the		Trust the right to allow modifications of such material outside the
	IETF Standards Process. Without obtaining an adequate license from		IETF Standards Process. Without obtaining an adequate license from
	skipping to change at page 2, line 10		skipping to change at page 2, line 10
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	The list of current Internet-Drafts can be accessed at		The list of current Internet-Drafts can be accessed at
	http://www.ietf.org/ietf/1id-abstracts.txt.		http://www.ietf.org/ietf/1id-abstracts.txt.
	The list of Internet-Draft Shadow Directories can be accessed at		The list of Internet-Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
	This Internet-Draft will expire on January 14, 2010.		This Internet-Draft will expire on April 29, 2010.
	Copyright Notice		Copyright Notice
	Copyright (c) 2009 IETF Trust and the persons identified as the		Copyright (c) 2009 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents in effect on the date of		Provisions Relating to IETF Documents in effect on the date of
	publication of this document (http://trustee.ietf.org/license-info).		publication of this document (http://trustee.ietf.org/license-info).
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	skipping to change at page 2, line 42		skipping to change at page 2, line 42
	rules for constructing responses to those requests.		rules for constructing responses to those requests.
	Editorial Note (To be removed by RFC Editor)		Editorial Note (To be removed by RFC Editor)
	Discussion of this draft should take place on the HTTPBIS working		Discussion of this draft should take place on the HTTPBIS working
	group mailing list (ietf-http-wg@w3.org). The current issues list is		group mailing list (ietf-http-wg@w3.org). The current issues list is
	at <http://tools.ietf.org/wg/httpbis/trac/report/11> and related		at <http://tools.ietf.org/wg/httpbis/trac/report/11> 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.8.		The changes in this draft are summarized in Appendix C.9.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
	1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4		1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4
	1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 4		1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 4
	1.2.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 5		1.2.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 5
	1.2.2. ABNF Rules defined in other Parts of the		1.2.2. ABNF Rules defined in other Parts of the
	Specification . . . . . . . . . . . . . . . . . . . . 5		Specification . . . . . . . . . . . . . . . . . . . . 5
	2. Entity Tags . . . . . . . . . . . . . . . . . . . . . . . . . 5		2. Entity Tags . . . . . . . . . . . . . . . . . . . . . . . . . 5
	skipping to change at page 3, line 27		skipping to change at page 3, line 27
	4. Weak and Strong Validators . . . . . . . . . . . . . . . . . . 7		4. Weak and Strong Validators . . . . . . . . . . . . . . . . . . 7
	5. Rules for When to Use Entity Tags and Last-Modified Dates . . 9		5. Rules for When to Use Entity Tags and Last-Modified Dates . . 9
	6. Header Field Definitions . . . . . . . . . . . . . . . . . . . 11		6. Header Field Definitions . . . . . . . . . . . . . . . . . . . 11
	6.1. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 11		6.1. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
	6.2. If-Match . . . . . . . . . . . . . . . . . . . . . . . . . 12		6.2. If-Match . . . . . . . . . . . . . . . . . . . . . . . . . 12
	6.3. If-Modified-Since . . . . . . . . . . . . . . . . . . . . 13		6.3. If-Modified-Since . . . . . . . . . . . . . . . . . . . . 13
	6.4. If-None-Match . . . . . . . . . . . . . . . . . . . . . . 15		6.4. If-None-Match . . . . . . . . . . . . . . . . . . . . . . 15
	6.5. If-Unmodified-Since . . . . . . . . . . . . . . . . . . . 16		6.5. If-Unmodified-Since . . . . . . . . . . . . . . . . . . . 16
	6.6. Last-Modified . . . . . . . . . . . . . . . . . . . . . . 17		6.6. Last-Modified . . . . . . . . . . . . . . . . . . . . . . 17
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
	7.1. Message Header Registration . . . . . . . . . . . . . . . 17		7.1. Status Code Registration . . . . . . . . . . . . . . . . . 17
			7.2. Message Header Registration . . . . . . . . . . . . . . . 18
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 18		8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
	9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18		9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18		10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
	10.1. Normative References . . . . . . . . . . . . . . . . . . . 18		10.1. Normative References . . . . . . . . . . . . . . . . . . . 18
	10.2. Informative References . . . . . . . . . . . . . . . . . . 19		10.2. Informative References . . . . . . . . . . . . . . . . . . 19
	Appendix A. Compatibility with Previous Versions . . . . . . . . 19		Appendix A. Compatibility with Previous Versions . . . . . . . . 19
	A.1. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 19		A.1. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 19
	Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 20		Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 20
	Appendix C. Change Log (to be removed by RFC Editor before		Appendix C. Change Log (to be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . 20		publication) . . . . . . . . . . . . . . . . . . . . 20
	C.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 20		C.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 20
	C.2. Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 21		C.2. Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 21
	C.3. Since draft-ietf-httpbis-p4-conditional-01 . . . . . . . . 21		C.3. Since draft-ietf-httpbis-p4-conditional-01 . . . . . . . . 21
	C.4. Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 21		C.4. Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 21
	C.5. Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 21		C.5. Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 21
	C.6. Since draft-ietf-httpbis-p4-conditional-04 . . . . . . . . 22		C.6. Since draft-ietf-httpbis-p4-conditional-04 . . . . . . . . 22
	C.7. Since draft-ietf-httpbis-p4-conditional-05 . . . . . . . . 22		C.7. Since draft-ietf-httpbis-p4-conditional-05 . . . . . . . . 22
	C.8. Since draft-ietf-httpbis-p4-conditional-06 . . . . . . . . 22		C.8. Since draft-ietf-httpbis-p4-conditional-06 . . . . . . . . 22
			C.9. Since draft-ietf-httpbis-p4-conditional-07 . . . . . . . . 22
	Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22		Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
	1. Introduction		1. Introduction
	This document defines HTTP/1.1 response metadata for indicating		This document defines HTTP/1.1 response metadata for indicating
	potential changes to payload content, including modification time		potential changes to payload content, including modification time
	stamps and opaque entity-tags, and the HTTP conditional request		stamps and opaque entity-tags, and the HTTP conditional request
	mechanisms that allow preconditions to be placed on a request method.		mechanisms that allow preconditions to be placed on a request method.
	Conditional GET requests allow for efficient cache updates. Other		Conditional GET requests allow for efficient cache updates. Other
	skipping to change at page 5, line 19		skipping to change at page 5, line 19
	The core rules below are defined in Section 1.2.2 of [Part1]:		The core rules below are defined in Section 1.2.2 of [Part1]:
	quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>		quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
	OWS = <OWS, defined in [Part1], Section 1.2.2>		OWS = <OWS, defined in [Part1], Section 1.2.2>
	1.2.2. ABNF Rules defined in other Parts of the Specification		1.2.2. 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:
	HTTP-date = <HTTP-date, defined in [Part1], Section 3.2>		HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
	2. Entity Tags		2. Entity Tags
	Entity tags are used for comparing two or more entities from the same		Entity tags are used for comparing two or more entities from the same
	requested resource. HTTP/1.1 uses entity tags in the ETag		requested resource. HTTP/1.1 uses entity tags in the ETag
	(Section 6.1), If-Match (Section 6.2), If-None-Match (Section 6.4),		(Section 6.1), If-Match (Section 6.2), If-None-Match (Section 6.4),
	and If-Range (Section 5.3 of [Part5]) header fields. The definition		and If-Range (Section 5.3 of [Part5]) header fields. The definition
	of how they are used and compared as cache validators is in		of how they are used and compared as cache validators is in
	Section 4. An entity tag consists of an opaque quoted string,		Section 4. An entity tag consists of an opaque quoted string,
	possibly prefixed by a weakness indicator.		possibly prefixed by a weakness indicator.
	skipping to change at page 6, line 17		skipping to change at page 6, line 17
	3.1. 304 Not Modified		3.1. 304 Not Modified
	If the client has performed a conditional GET request and access is		If the client has performed a conditional GET request and access is
	allowed, but the document has not been modified, the server SHOULD		allowed, but the document has not been modified, the server SHOULD
	respond with this status code. The 304 response MUST NOT contain a		respond with this status code. The 304 response MUST NOT contain a
	message-body, and thus is always terminated by the first empty line		message-body, and thus is always terminated by the first empty line
	after the header fields.		after the header fields.
	The response MUST include the following header fields:		The response MUST include the following header fields:
	o Date, unless its omission is required by Section 8.3.1 of [Part1].		o Date, unless its omission is required by Section 9.3.1 of [Part1].
	If a clockless origin server obeys these rules, and proxies and		If a clockless origin server obeys these rules, and proxies and
	clients add their own Date to any response received without one		clients add their own Date to any response received without one
	(as already specified by Section 8.3 of [Part1], caches will		(as already specified by Section 9.3 of [Part1], caches will
	operate correctly.		operate correctly.
	o ETag and/or Content-Location, if the header would have been sent		o ETag and/or Content-Location, if the header would have been sent
	in a 200 response to the same request.		in a 200 response to the same request.
	o Expires, Cache-Control, and/or Vary, if the field-value might		o Expires, Cache-Control, and/or Vary, if the field-value might
	differ from that sent in any previous response for the same		differ from that sent in any previous response for the same
	variant.		variant.
	If the conditional GET used a strong cache validator (see Section 4),		If the conditional GET used a strong cache validator (see Section 4),
	skipping to change at page 8, line 14		skipping to change at page 8, line 14
	The only function that HTTP/1.1 defines on validators is comparison.		The only function that HTTP/1.1 defines on validators is comparison.
	There are two validator comparison functions, depending on whether		There are two validator comparison functions, depending on whether
	the comparison context allows the use of weak validators or not:		the comparison context allows the use of weak validators or not:
	o The strong comparison function: in order to be considered equal,		o The strong comparison function: in order to be considered equal,
	both opaque-tags MUST be identical character-by-character, and		both opaque-tags MUST be identical character-by-character, and
	both MUST NOT be weak.		both MUST NOT be weak.
	o The weak comparison function: in order to be considered equal,		o The weak comparison function: in order to be considered equal,
	both opaque-tags MUST be identical character-by-character.		both opaque-tags MUST be identical character-by-character, but
			either or both of them MAY be tagged as "weak" without affecting
			the result.
	The example below shows the results for a set of entity tag pairs,		The example below shows the results for a set of entity tag pairs,
	and both the weak and strong comparison function results:		and both the weak and strong comparison function results:
	+--------+--------+-------------------+-----------------+		+--------+--------+-------------------+-----------------+
	| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |		| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
	+--------+--------+-------------------+-----------------+		+--------+--------+-------------------+-----------------+
	| W/"1" | W/"1" | no match | match |		| W/"1" | W/"1" | no match | match |
	| W/"1" | W/"2" | no match | no match |		| W/"1" | W/"2" | no match | no match |
	| W/"1" | "1" | no match | match |		| W/"1" | "1" | no match | match |
	skipping to change at page 11, line 39		skipping to change at page 11, line 41
	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 conditional requests.		fields related to conditional requests.
	For entity-header fields, both sender and recipient refer to either		For entity-header fields, both sender and recipient refer to either
	the client or the server, depending on who sends and who receives the		the client or the server, depending on who sends and who receives the
	entity.		entity.
	6.1. ETag		6.1. ETag
	The response-header field "ETag" provides the current value of the		The "ETag" response-header field provides the current value of the
	entity tag (see Section 2) for the requested variant. The headers		entity tag (see Section 2) for the requested variant, which may be
	used with entity tags are described in Sections 6.2 and 6.4 of this		used for comparison with other entities from the same resource (see
	document, and in Section 5.3 of [Part5]. The entity tag MAY be used
	for comparison with other entities from the same resource (see
	Section 4).		Section 4).
	ETag = "ETag" ":" OWS ETag-v		ETag = "ETag" ":" OWS ETag-v
	ETag-v = entity-tag		ETag-v = entity-tag
	Examples:		Examples:
	ETag: "xyzzy"		ETag: "xyzzy"
	ETag: W/"xyzzy"		ETag: W/"xyzzy"
	ETag: ""		ETag: ""
	skipping to change at page 12, line 27		skipping to change at page 12, line 27
	The principle behind entity tags is that only the service author		The principle behind entity tags is that only the service author
	knows the semantics of a resource well enough to select an		knows the semantics of a resource well enough to select an
	appropriate cache validation mechanism, and the specification of any		appropriate cache validation mechanism, and the specification of any
	validator comparison function more complex than byte-equality would		validator comparison function more complex than byte-equality would
	open up a can of worms. Thus, comparisons of any other headers		open up a can of worms. Thus, comparisons of any other headers
	(except Last-Modified, for compatibility with HTTP/1.0) are never		(except Last-Modified, for compatibility with HTTP/1.0) are never
	used for purposes of validating a cache entry.		used for purposes of validating a cache entry.
	6.2. If-Match		6.2. If-Match
	The request-header field "If-Match" is used with a method to make it		The "If-Match" request-header field is used to make a request method
	conditional. A client that has one or more entities previously		conditional. A client that has one or more entities previously
	obtained from the resource can verify that one of those entities is		obtained from the resource can verify that one of those entities is
	current by including a list of their associated entity tags in the		current by including a list of their associated entity tags in the
	If-Match header field. Entity tags are defined in Section 2. The		If-Match header field.
	purpose of this feature is to allow efficient updates of cached
	information with a minimum amount of transaction overhead. It is		This allows efficient updates of cached information with a minimum
	also used, on updating requests, to prevent inadvertent modification		amount of transaction overhead. It is also used when updating
	of the wrong version of a resource. As a special case, the value "*"		resources, to prevent inadvertent modification of the wrong version
	matches any current entity of the resource.		of a resource. As a special case, the value "*" matches any current
			entity of the resource.
	If-Match = "If-Match" ":" OWS If-Match-v		If-Match = "If-Match" ":" OWS If-Match-v
	If-Match-v = "*" / 1#entity-tag		If-Match-v = "*" / 1#entity-tag
	If any of the entity tags match the entity tag of the entity that		If any of the entity tags match the entity tag of the entity that
	would have been returned in the response to a similar GET request		would have been returned in the response to a similar GET request
	(without the If-Match header) on that resource, or if "*" is given		(without the If-Match header) on that resource, or if "*" is given
	and any current entity exists for that resource, then the server MAY		and any current entity exists for that resource, then the server MAY
	perform the requested method as if the If-Match header field did not		perform the requested method as if the If-Match header field did not
	exist.		exist.
	A server MUST use the strong comparison function (see Section 4) to
	compare the entity tags in If-Match.
	If none of the entity tags match, or if "*" is given and no current		If none of the entity tags match, or if "*" is given and no current
	entity exists, the server MUST NOT perform the requested method, and		entity exists, the server MUST NOT perform the requested method, and
	MUST return a 412 (Precondition Failed) response. This behavior is		MUST return a 412 (Precondition Failed) response. This behavior is
	most useful when the client wants to prevent an updating method, such		most useful when the client wants to prevent an updating method, such
	as PUT, from modifying a resource that has changed since the client		as PUT, from modifying a resource that has changed since the client
	last retrieved it.		last retrieved it.
	If the request would, without the If-Match header field, result in		If the request would, without the If-Match header field, result in
	anything other than a 2xx or 412 status, then the If-Match header		anything other than a 2xx or 412 status, then the If-Match header
	MUST be ignored.		MUST be ignored.
	skipping to change at page 13, line 38		skipping to change at page 13, line 36
	If-Match: "xyzzy"		If-Match: "xyzzy"
	If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"		If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
	If-Match: *		If-Match: *
	The result of a request having both an If-Match header field and		The result of a request having both an If-Match header field and
	either an If-None-Match or an If-Modified-Since header fields is		either an If-None-Match or an If-Modified-Since header fields is
	undefined by this specification.		undefined by this specification.
	6.3. If-Modified-Since		6.3. If-Modified-Since
	The request-header field "If-Modified-Since" is used with a method to		The "If-Modified-Since" request-header field is used to make a
	make it conditional: if the requested variant has not been modified		request method conditional: if the requested variant has not been
	since the time specified in this field, an entity will not be		modified since the time specified in this field, the server will not
	returned from the server; instead, a 304 (Not Modified) response will		return an entity; instead, a 304 (Not Modified) response will be
	be returned without any message-body.		returned.
	If-Modified-Since = "If-Modified-Since" ":" OWS		If-Modified-Since = "If-Modified-Since" ":" OWS
	If-Modified-Since-v		If-Modified-Since-v
	If-Modified-Since-v = HTTP-date		If-Modified-Since-v = HTTP-date
	An example of the field is:		An example of the field is:
	If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT		If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
	A GET method with an If-Modified-Since header and no Range header		A GET method with an If-Modified-Since header and no Range header
	requests that the identified entity be transferred only if it has		requests that the identified entity be transferred only if it has
	been modified since the date given by the If-Modified-Since header.		been modified since the date given by the If-Modified-Since header.
	The algorithm for determining this includes the following cases:		The algorithm for determining this includes the following cases:
	1. If the request would normally result in anything other than a 200		1. If the request would normally result in anything other than a 200
	(OK) status, or if the passed If-Modified-Since date is invalid,		(OK) status, or if the passed If-Modified-Since date is invalid,
	the response is exactly the same as for a normal GET. A date		the response is exactly the same as for a normal GET. A date
	which is later than the server's current time is invalid.		which is later than the server's current time is invalid.
	skipping to change at page 15, line 11		skipping to change at page 15, line 9
	to the server's clock. Corrections for different time bases		to the server's clock. Corrections for different time bases
	between client and server are at best approximate due to network		between client and server are at best approximate due to network
	latency.		latency.
	The result of a request having both an If-Modified-Since header field		The result of a request having both an If-Modified-Since header field
	and either an If-Match or an If-Unmodified-Since header fields is		and either an If-Match or an If-Unmodified-Since header fields is
	undefined by this specification.		undefined by this specification.
	6.4. If-None-Match		6.4. If-None-Match
	The request-header field "If-None-Match" is used with a method to		The "If-None-Match" request-header field is used to make a request
	make it conditional. A client that has one or more entities		method conditional. A client that has one or more entities
	previously obtained from the resource can verify that none of those		previously obtained from the resource can verify that none of those
	entities is current by including a list of their associated entity		entities is current by including a list of their associated entity
	tags in the If-None-Match header field. The purpose of this feature		tags in the If-None-Match header field.
	is to allow efficient updates of cached information with a minimum
			This allows efficient updates of cached information with a minimum
	amount of transaction overhead. It is also used to prevent a method		amount of transaction overhead. It is also used to prevent a method
	(e.g. PUT) from inadvertently modifying an existing resource when		(e.g. PUT) from inadvertently modifying an existing resource when
	the client believes that the resource does not exist.		the client believes that the resource does not exist.
	As a special case, the value "*" matches any current entity of the		As a special case, the value "*" matches any current entity of the
	resource.		resource.
	If-None-Match = "If-None-Match" ":" OWS If-None-Match-v		If-None-Match = "If-None-Match" ":" OWS If-None-Match-v
	If-None-Match-v = "*" / 1#entity-tag		If-None-Match-v = "*" / 1#entity-tag
	skipping to change at page 15, line 40		skipping to change at page 15, line 39
	given and any current entity exists for that resource, then the		given and any current entity exists for that resource, then the
	server MUST NOT perform the requested method, unless required to do		server MUST NOT perform the requested method, unless required to do
	so because the resource's modification date fails to match that		so because the resource's modification date fails to match that
	supplied in an If-Modified-Since header field in the request.		supplied in an If-Modified-Since header field in the request.
	Instead, if the request method was GET or HEAD, the server SHOULD		Instead, if the request method was GET or HEAD, the server SHOULD
	respond with a 304 (Not Modified) response, including the cache-		respond with a 304 (Not Modified) response, including the cache-
	related header fields (particularly ETag) of one of the entities that		related header fields (particularly ETag) of one of the entities that
	matched. For all other request methods, the server MUST respond with		matched. For all other request methods, the server MUST respond with
	a status of 412 (Precondition Failed).		a status of 412 (Precondition Failed).
	See Section 4 for rules on how to determine if two entity tags match.
	If none of the entity tags match, then the server MAY perform the		If none of the entity tags match, then the server MAY perform the
	requested method as if the If-None-Match header field did not exist,		requested method as if the If-None-Match header field did not exist,
	but MUST also ignore any If-Modified-Since header field(s) in the		but MUST also ignore any If-Modified-Since header field(s) in the
	request. That is, if no entity tags match, then the server MUST NOT		request. That is, if no entity tags match, then the server MUST NOT
	return a 304 (Not Modified) response.		return a 304 (Not Modified) response.
	If the request would, without the If-None-Match header field, result		If the request would, without the If-None-Match header field, result
	in anything other than a 2xx or 304 status, then the If-None-Match		in anything other than a 2xx or 304 status, then the If-None-Match
	header MUST be ignored. (See Section 5 for a discussion of server		header MUST be ignored. (See Section 5 for a discussion of server
	behavior when both If-Modified-Since and If-None-Match appear in the		behavior when both If-Modified-Since and If-None-Match appear in the
	skipping to change at page 16, line 25		skipping to change at page 16, line 24
	If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"		If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
	If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"		If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
	If-None-Match: *		If-None-Match: *
	The result of a request having both an If-None-Match header field and		The result of a request having both an If-None-Match header field and
	either an If-Match or an If-Unmodified-Since header fields is		either an If-Match or an If-Unmodified-Since header fields is
	undefined by this specification.		undefined by this specification.
	6.5. If-Unmodified-Since		6.5. If-Unmodified-Since
	The request-header field "If-Unmodified-Since" is used with a method		The "If-Unmodified-Since" request-header field is used to make a
	to make it conditional. If the requested resource has not been		request method conditional. If the requested resource has not been
	modified since the time specified in this field, the server SHOULD		modified since the time specified in this field, the server SHOULD
	perform the requested operation as if the If-Unmodified-Since header		perform the requested operation as if the If-Unmodified-Since header
	were not present.		were not present.
	If the requested variant has been modified since the specified time,		If the requested variant has been modified since the specified time,
	the server MUST NOT perform the requested operation, and MUST return		the server MUST NOT perform the requested operation, and MUST return
	a 412 (Precondition Failed).		a 412 (Precondition Failed).
	If-Unmodified-Since = "If-Unmodified-Since" ":" OWS		If-Unmodified-Since = "If-Unmodified-Since" ":" OWS
	If-Unmodified-Since-v		If-Unmodified-Since-v
	skipping to change at page 17, line 7		skipping to change at page 17, line 7
	If-Unmodified-Since header SHOULD be ignored.		If-Unmodified-Since header SHOULD be ignored.
	If the specified date is invalid, the header is ignored.		If the specified date is invalid, the header is ignored.
	The result of a request having both an If-Unmodified-Since header		The result of a request having both an If-Unmodified-Since header
	field and either an If-None-Match or an If-Modified-Since header		field and either an If-None-Match or an If-Modified-Since header
	fields is undefined by this specification.		fields is undefined by this specification.
	6.6. Last-Modified		6.6. Last-Modified
	The entity-header field "Last-Modified" indicates the date and time		The "Last-Modified" entity-header field indicates the date and time
	at which the origin server believes the variant was last modified.		at which the origin server believes the variant was last modified.
	Last-Modified = "Last-Modified" ":" OWS Last-Modified-v		Last-Modified = "Last-Modified" ":" OWS Last-Modified-v
	Last-Modified-v = HTTP-date		Last-Modified-v = HTTP-date
	An example of its use is		An example of its use is
	Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT		Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
	The exact meaning of this header field depends on the implementation		The exact meaning of this header field depends on the implementation
	skipping to change at page 17, line 46		skipping to change at page 17, line 46
	near the time that the response is generated.		near the time that the response is generated.
	HTTP/1.1 servers SHOULD send Last-Modified whenever feasible.		HTTP/1.1 servers SHOULD send Last-Modified whenever feasible.
	The Last-Modified entity-header field value is often used as a cache		The Last-Modified entity-header field value is often used as a cache
	validator. In simple terms, a cache entry is considered to be valid		validator. In simple terms, a cache entry is considered to be valid
	if the entity has not been modified since the Last-Modified value.		if the entity has not been modified since the Last-Modified value.
	7. IANA Considerations		7. IANA Considerations
	7.1. Message Header Registration		7.1. Status Code Registration
			The HTTP Status Code Registry located at
			<http://www.iana.org/assignments/http-status-codes> should be updated
			with the registrations below:
			+-------+---------------------+-------------+
			| Value | Description | Reference |
			+-------+---------------------+-------------+
			| 304 | Not Modified | Section 3.1 |
			| 412 | Precondition Failed | Section 3.2 |
			+-------+---------------------+-------------+
			7.2. Message Header Registration
	The Message Header Registry located at <http://www.iana.org/		The Message Header Registry located at <http://www.iana.org/
	assignments/message-headers/message-header-index.html> should be		assignments/message-headers/message-header-index.html> should be
	updated with the permanent registrations below (see [RFC3864]):		updated with the permanent registrations below (see [RFC3864]):
	+---------------------+----------+----------+-------------+		+---------------------+----------+----------+-------------+
	| Header Field Name | Protocol | Status | Reference |		| Header Field Name | Protocol | Status | Reference |
	+---------------------+----------+----------+-------------+		+---------------------+----------+----------+-------------+
	| ETag | http | standard | Section 6.1 |		| ETag | http | standard | Section 6.1 |
	| If-Match | http | standard | Section 6.2 |		| If-Match | http | standard | Section 6.2 |
	skipping to change at page 18, line 33		skipping to change at page 18, line 46
	9. Acknowledgments		9. Acknowledgments
	10. References		10. References
	10.1. Normative References		10.1. Normative References
	[Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,		[Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,		Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
	and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections,		and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections,
	and Message Parsing", draft-ietf-httpbis-p1-messaging-07		and Message Parsing", draft-ietf-httpbis-p1-messaging-08
	(work in progress), July 2009.		(work in progress), October 2009.
	[Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,		[Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,		Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
	and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and		and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and
	Partial Responses", draft-ietf-httpbis-p5-range-07 (work		Partial Responses", draft-ietf-httpbis-p5-range-08 (work
	in progress), July 2009.		in progress), October 2009.
	[Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,		[Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,		Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
	Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part		Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part
	6: Caching", draft-ietf-httpbis-p6-cache-07 (work in		6: Caching", draft-ietf-httpbis-p6-cache-08 (work in
	progress), July 2009.		progress), October 2009.
	[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.
	10.2. Informative References		10.2. Informative References
	[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,		[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
	skipping to change at page 20, line 10		skipping to change at page 20, line 10
	A.1. Changes from RFC 2616		A.1. Changes from RFC 2616
	Allow weak entity tags in all requests except range requests		Allow weak entity tags in all requests except range requests
	(Sections 4 and 6.4).		(Sections 4 and 6.4).
	Appendix B. Collected ABNF		Appendix B. Collected ABNF
	ETag = "ETag:" OWS ETag-v		ETag = "ETag:" OWS ETag-v
	ETag-v = entity-tag		ETag-v = entity-tag
	HTTP-date = <HTTP-date, defined in [Part1], Section 3.2>		HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
	If-Match = "If-Match:" OWS If-Match-v		If-Match = "If-Match:" OWS If-Match-v
	If-Match-v = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS		If-Match-v = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
	entity-tag ] ) )		entity-tag ] ) )
	If-Modified-Since = "If-Modified-Since:" OWS If-Modified-Since-v		If-Modified-Since = "If-Modified-Since:" OWS If-Modified-Since-v
	If-Modified-Since-v = HTTP-date		If-Modified-Since-v = HTTP-date
	If-None-Match = "If-None-Match:" OWS If-None-Match-v		If-None-Match = "If-None-Match:" OWS If-None-Match-v
	If-None-Match-v = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS		If-None-Match-v = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
	entity-tag ] ) )		entity-tag ] ) )
	If-Unmodified-Since = "If-Unmodified-Since:" OWS		If-Unmodified-Since = "If-Unmodified-Since:" OWS
	skipping to change at page 22, line 33		skipping to change at page 22, line 33
	o Add appendix containing collected and expanded ABNF, reorganize		o Add appendix containing collected and expanded ABNF, reorganize
	ABNF introduction.		ABNF introduction.
	C.8. Since draft-ietf-httpbis-p4-conditional-06		C.8. Since draft-ietf-httpbis-p4-conditional-06
	Closed issues:		Closed issues:
	o <http://tools.ietf.org/wg/httpbis/trac/ticket/153>: "case-		o <http://tools.ietf.org/wg/httpbis/trac/ticket/153>: "case-
	sensitivity of etag weakness indicator"		sensitivity of etag weakness indicator"
			C.9. Since draft-ietf-httpbis-p4-conditional-07
			Closed issues:
			o <http://tools.ietf.org/wg/httpbis/trac/ticket/116>: "Weak ETags on
			non-GET requests" (If-Match still was defined to require strong
			matching)
			o <http://tools.ietf.org/wg/httpbis/trac/ticket/198>: "move IANA
			registrations for optional status codes"
	Index		Index
	3		3
	304 Not Modified (status code) 6		304 Not Modified (status code) 6
	4		4
	412 Precondition Failed (status code) 6		412 Precondition Failed (status code) 6
	E		E
	ETag header 11		ETag header 11
	G		G
	Grammar		Grammar
	entity-tag 5		entity-tag 5
	ETag 11		ETag 11
	ETag-v 11		ETag-v 11
	If-Match 12		If-Match 12
	If-Match-v 12		If-Match-v 12
End of changes. 29 change blocks.
	48 lines changed or deleted		71 lines changed or added
This html diff was produced by rfcdiff 1.35. The latest version is available from http://tools.ietf.org/tools/rfcdiff/