draft-ietf-httpbis-p4-conditional-03.txt		draft-ietf-httpbis-p4-conditional-04.txt
	Network Working Group R. Fielding, Ed.		Network 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: December 19, 2008 J. Mogul		Expires: March 2, 2009 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
	June 17, 2008		August 29, 2008
	HTTP/1.1, part 4: Conditional Requests		HTTP/1.1, part 4: Conditional Requests
	draft-ietf-httpbis-p4-conditional-03		draft-ietf-httpbis-p4-conditional-04
	Status of this Memo		Status of this Memo
	By submitting this Internet-Draft, each author represents that any		By submitting this Internet-Draft, each author represents that any
	applicable patent or other IPR claims of which he or she is aware		applicable patent or other IPR claims of which he or she is aware
	have been or will be disclosed, and any of which he or she becomes		have been or will be disclosed, and any of which he or she becomes
	aware will be disclosed, in accordance with Section 6 of BCP 79.		aware will be disclosed, in accordance with Section 6 of BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	skipping to change at page 1, line 49		skipping to change at page 1, line 49
	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 December 19, 2008.		This Internet-Draft will expire on March 2, 2009.
	Abstract		Abstract
	The Hypertext Transfer Protocol (HTTP) is an application-level		The Hypertext Transfer Protocol (HTTP) is an application-level
	protocol for distributed, collaborative, hypermedia information		protocol for distributed, collaborative, hypermedia 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 4 of the		information initiative since 1990. This document is Part 4 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. Part 4 defines		"HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 4 defines
	request header fields for indicating conditional requests and the		request header fields for indicating conditional requests and the
	skipping to change at page 3, line 18		skipping to change at page 3, line 18
	1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4		1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4
	2. Notational Conventions and Generic Grammar . . . . . . . . . . 4		2. Notational Conventions and Generic Grammar . . . . . . . . . . 4
	3. Entity Tags . . . . . . . . . . . . . . . . . . . . . . . . . 5		3. Entity Tags . . . . . . . . . . . . . . . . . . . . . . . . . 5
	4. Status Code Definitions . . . . . . . . . . . . . . . . . . . 5		4. Status Code Definitions . . . . . . . . . . . . . . . . . . . 5
	4.1. 304 Not Modified . . . . . . . . . . . . . . . . . . . . . 5		4.1. 304 Not Modified . . . . . . . . . . . . . . . . . . . . . 5
	4.2. 412 Precondition Failed . . . . . . . . . . . . . . . . . 6		4.2. 412 Precondition Failed . . . . . . . . . . . . . . . . . 6
	5. Weak and Strong Validators . . . . . . . . . . . . . . . . . . 6		5. Weak and Strong Validators . . . . . . . . . . . . . . . . . . 6
	6. Rules for When to Use Entity Tags and Last-Modified Dates . . 9		6. Rules for When to Use Entity Tags and Last-Modified Dates . . 9
	7. Header Field Definitions . . . . . . . . . . . . . . . . . . . 11		7. Header Field Definitions . . . . . . . . . . . . . . . . . . . 11
	7.1. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 11		7.1. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
	7.2. If-Match . . . . . . . . . . . . . . . . . . . . . . . . . 11		7.2. If-Match . . . . . . . . . . . . . . . . . . . . . . . . . 12
	7.3. If-Modified-Since . . . . . . . . . . . . . . . . . . . . 13		7.3. If-Modified-Since . . . . . . . . . . . . . . . . . . . . 13
	7.4. If-None-Match . . . . . . . . . . . . . . . . . . . . . . 14		7.4. If-None-Match . . . . . . . . . . . . . . . . . . . . . . 14
	7.5. If-Unmodified-Since . . . . . . . . . . . . . . . . . . . 15		7.5. If-Unmodified-Since . . . . . . . . . . . . . . . . . . . 16
	7.6. Last-Modified . . . . . . . . . . . . . . . . . . . . . . 16		7.6. Last-Modified . . . . . . . . . . . . . . . . . . . . . . 16
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
	8.1. Message Header Registration . . . . . . . . . . . . . . . 17		8.1. Message Header Registration . . . . . . . . . . . . . . . 17
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 17		9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
	10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17		10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18		11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
	11.1. Normative References . . . . . . . . . . . . . . . . . . . 18		11.1. Normative References . . . . . . . . . . . . . . . . . . . 18
	11.2. Informative References . . . . . . . . . . . . . . . . . . 18		11.2. Informative References . . . . . . . . . . . . . . . . . . 18
	Appendix A. Compatibility with Previous Versions . . . . . . . . 18		Appendix A. Compatibility with Previous Versions . . . . . . . . 18
	A.1. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 18		A.1. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 18
	Appendix B. Change Log (to be removed by RFC Editor before		Appendix B. Change Log (to be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . 19		publication) . . . . . . . . . . . . . . . . . . . . 19
	B.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 19		B.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 19
	B.2. Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 19		B.2. Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 19
	B.3. Since draft-ietf-httpbis-p4-conditional-01 . . . . . . . . 19		B.3. Since draft-ietf-httpbis-p4-conditional-01 . . . . . . . . 19
	B.4. Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 19		B.4. Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 19
	Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19		B.5. Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 19
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20		Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
	Intellectual Property and Copyright Statements . . . . . . . . . . 24		Intellectual Property and Copyright Statements . . . . . . . . . . 24
	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
	conditional request methods are used to protect against overwriting		conditional request methods are used to protect against overwriting
	skipping to change at page 6, line 5		skipping to change at page 6, line 5
	4.1. 304 Not Modified		4.1. 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 8.3.1 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 (as		clients add their own Date to any response received without one
	already specified by [RFC2068], Section 14.19), caches will operate		(as already specified by Section 8.3 of [Part1], caches will
	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 5),		If the conditional GET used a strong cache validator (see Section 5),
	the response SHOULD NOT include other entity-headers. Otherwise		the response SHOULD NOT include other entity-headers. Otherwise
	(i.e., the conditional GET used a weak validator), the response MUST		(i.e., the conditional GET used a weak validator), the response MUST
	NOT include other entity-headers; this prevents inconsistencies		NOT include other entity-headers; this prevents inconsistencies
	between cached entity-bodies and updated headers.		between cached entity-bodies and updated headers.
	If a 304 response indicates an entity not currently cached, then the		If a 304 response indicates an entity not currently cached, then the
	cache MUST disregard the response and repeat the request without the		cache MUST disregard the response and repeat the request without the
	conditional.		conditional.
	skipping to change at page 7, line 47		skipping to change at page 7, line 47
	range retrieval, since otherwise the client might end up with an		range retrieval, since otherwise the client might end up with an
	internally inconsistent entity.		internally inconsistent entity.
	Clients MUST NOT use weak validators in range requests ([Part5]).		Clients MUST NOT use weak validators in range requests ([Part5]).
	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 validators MUST be identical in every way, and both MUST NOT		both opaque-tags MUST be identical character-by-character, and
	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 validators MUST be identical in every way, but either or both		both opaque-tags MUST be identical character-by-character.
	of them MAY be tagged as "weak" without affecting the result.
			The example below shows the results for a set of entity tag pairs,
			and both the weak and strong comparison function results:
			+--------+--------+-------------------+-----------------+
			| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
			+--------+--------+-------------------+-----------------+
			| W/"1" | W/"1" | no match | match |
			| W/"1" | W/"2" | no match | no match |
			| W/"1" | "1" | no match | match |
			| "1" | "1" | match | match |
			+--------+--------+-------------------+-----------------+
	An entity tag is strong unless it is explicitly tagged as weak.		An entity tag is strong unless it is explicitly tagged as weak.
	Section 3 gives the syntax for entity tags.		Section 3 gives the syntax for entity tags.
	A Last-Modified time, when used as a validator in a request, is		A Last-Modified time, when used as a validator in a request, is
	implicitly weak unless it is possible to deduce that it is strong,		implicitly weak unless it is possible to deduce that it is strong,
	using the following rules:		using the following rules:
	o The validator is being compared by an origin server to the actual		o The validator is being compared by an origin server to the actual
	current validator for the entity and,		current validator for the entity and,
	skipping to change at page 9, line 42		skipping to change at page 10, line 4
	o SHOULD send a Last-Modified value if it is feasible to send one,		o SHOULD send a Last-Modified value if it is feasible to send one,
	unless the risk of a breakdown in semantic transparency that could		unless the risk of a breakdown in semantic transparency that could
	result from using this date in an If-Modified-Since header would		result from using this date in an If-Modified-Since header would
	lead to serious problems.		lead to serious problems.
	In other words, the preferred behavior for an HTTP/1.1 origin server		In other words, the preferred behavior for an HTTP/1.1 origin server
	is to send both a strong entity tag and a Last-Modified value.		is to send both a strong entity tag and a Last-Modified value.
	In order to be legal, a strong entity tag MUST change whenever the		In order to be legal, a strong entity tag MUST change whenever the
	associated entity value changes in any way. A weak entity tag SHOULD		associated entity changes in any way. A weak entity tag SHOULD
	change whenever the associated entity changes in a semantically		change whenever the associated entity changes in a semantically
	significant way.		significant way.
	Note: in order to provide semantically transparent caching, an		Note: in order to provide semantically transparent caching, an
	origin server must avoid reusing a specific strong entity tag		origin server must avoid reusing a specific strong entity tag
	value for two different entities, or reusing a specific weak		value for two different entities, or reusing a specific weak
	entity tag value for two semantically different entities. Cache		entity tag value for two semantically different entities. Cache
	entries might persist for arbitrarily long periods, regardless of		entries might persist for arbitrarily long periods, regardless of
	expiration times, so it might be inappropriate to expect that a		expiration times, so it might be inappropriate to expect that a
	cache will never again attempt to validate an entry using a		cache will never again attempt to validate an entry using a
	skipping to change at page 18, line 10		skipping to change at page 18, line 14
	10. Acknowledgments		10. Acknowledgments
	11. References		11. References
	11.1. Normative References		11.1. 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-03		and Message Parsing", draft-ietf-httpbis-p1-messaging-04
	(work in progress), June 2008.		(work in progress), August 2008.
	[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-03 (work		Partial Responses", draft-ietf-httpbis-p5-range-04 (work
	in progress), June 2008.		in progress), August 2008.
	[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.,
	and J. Reschke, Ed., "HTTP/1.1, part 6: Caching",		and J. Reschke, Ed., "HTTP/1.1, part 6: Caching",
	draft-ietf-httpbis-p6-cache-03 (work in progress),		draft-ietf-httpbis-p6-cache-04 (work in progress),
	June 2008.		August 2008.
	[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.
	11.2. Informative References		11.2. Informative References
	[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
	Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
	RFC 2068, January 1997.
	[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,		[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext		Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
	Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.		Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
	[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration		[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
	Procedures for Message Header Fields", BCP 90, RFC 3864,		Procedures for Message Header Fields", BCP 90, RFC 3864,
	September 2004.		September 2004.
	Appendix A. Compatibility with Previous Versions		Appendix A. Compatibility with Previous Versions
	skipping to change at page 19, line 43		skipping to change at page 19, line 43
	o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/116>: "Weak		o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/116>: "Weak
	ETags on non-GET requests"		ETags on non-GET requests"
	Ongoing work on IANA Message Header Registration		Ongoing work on IANA Message Header Registration
	(<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/40>):		(<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/40>):
	o Reference RFC 3984, and update header registrations for headers		o Reference RFC 3984, and update header registrations for headers
	defined in this document.		defined in this document.
			B.5. Since draft-ietf-httpbis-p4-conditional-03
			Closed issues:
			o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/71>: "Examples
			for ETag matching"
			o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/124>: "'entity
			value' undefined"
			o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/126>: "bogus
			2068 Date header reference"
	Index		Index
	3		3
	304 Not Modified (status code) 5		304 Not Modified (status code) 5
	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
	If-Match 12		If-Match 12
	If-Modified-Since 13		If-Modified-Since 13
	If-None-Match 14		If-None-Match 15
	If-Unmodified-Since 16		If-Unmodified-Since 16
	Last-Modified 16		Last-Modified 16
	opaque-tag 5		opaque-tag 5
	weak 5		weak 5
	H		H
	Headers		Headers
	ETag 11		ETag 11
	If-Match 11		If-Match 12
	If-Modified-Since 13		If-Modified-Since 13
	If-None-Match 14		If-None-Match 14
	If-Unmodified-Since 15		If-Unmodified-Since 16
	Last-Modified 16		Last-Modified 16
	I		I
	If-Match header 11		If-Match header 12
	If-Modified-Since header 13		If-Modified-Since header 13
	If-None-Match header 14		If-None-Match header 14
	If-Unmodified-Since header 15		If-Unmodified-Since header 16
	L		L
	Last-Modified header 16		Last-Modified header 16
	S		S
	Status Codes		Status Codes
	304 Not Modified 5		304 Not Modified 5
	412 Precondition Failed 6		412 Precondition Failed 6
	Authors' Addresses		Authors' Addresses
End of changes. 25 change blocks.
	35 lines changed or deleted		55 lines changed or added
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