draft-ietf-httpbis-cache-digest-00.txt		draft-ietf-httpbis-cache-digest-01.txt
	Network Working Group K. Oku		Network Working Group K. Oku
	Internet-Draft DeNA Co, Ltd.		Internet-Draft DeNA Co, Ltd.
	Intended status: Standards Track M. Nottingham		Intended status: Standards Track M. Nottingham
	Expires: January 10, 2017 July 9, 2016		Expires: May 5, 2017 November 1, 2016
	Cache Digests for HTTP/2		Cache Digests for HTTP/2
	draft-ietf-httpbis-cache-digest-00		draft-ietf-httpbis-cache-digest-01
	Abstract		Abstract
	This specification defines a HTTP/2 frame type to allow clients to		This specification defines a HTTP/2 frame type to allow clients to
	inform the server of their cache's contents. Servers can then use		inform the server of their cache's contents. Servers can then use
	this to inform their choices of what to push to clients.		this to inform their choices of what to push to clients.
	Note to Readers		Note to Readers
	Discussion of this draft takes place on the HTTP working group		Discussion of this draft takes place on the HTTP working group
	skipping to change at page 1, line 42 ¶		skipping to change at page 1, line 42 ¶
	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 January 10, 2017.		This Internet-Draft will expire on May 5, 2017.
	Copyright Notice		Copyright Notice
	Copyright (c) 2016 IETF Trust and the persons identified as the		Copyright (c) 2016 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 20 ¶		skipping to change at page 2, line 20 ¶
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3		1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
	2. The CACHE_DIGEST Frame . . . . . . . . . . . . . . . . . . . 3		2. The CACHE_DIGEST Frame . . . . . . . . . . . . . . . . . . . 3
	2.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 3		2.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 4
	2.1.1. Computing the Digest-Value . . . . . . . . . . . . . 4		2.1.1. Computing the Digest-Value . . . . . . . . . . . . . 5
	2.1.2. Computing a Hash Value . . . . . . . . . . . . . . . 6		2.1.2. Computing a Hash Value . . . . . . . . . . . . . . . 6
	2.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 6		2.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 6
	2.2.1. Querying the Digest for a Value . . . . . . . . . . . 7		2.2.1. Querying the Digest for a Value . . . . . . . . . . . 7
	3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8		3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	4. Security Considerations . . . . . . . . . . . . . . . . . . . 8		4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
	5. References . . . . . . . . . . . . . . . . . . . . . . . . . 8		5. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
	5.1. Normative References . . . . . . . . . . . . . . . . . . 8		5.1. Normative References . . . . . . . . . . . . . . . . . . 9
	5.2. Informative References . . . . . . . . . . . . . . . . . 9		5.2. Informative References . . . . . . . . . . . . . . . . . 9
	Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9		Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
	1. Introduction		1. Introduction
	HTTP/2 [RFC7540] allows a server to "push" synthetic request/response		HTTP/2 [RFC7540] allows a server to "push" synthetic request/response
	pairs into a client's cache optimistically. While there is strong		pairs into a client's cache optimistically. While there is strong
	interest in using this facility to improve perceived Web browsing		interest in using this facility to improve perceived Web browsing
	performance, it is sometimes counterproductive because the client		performance, it is sometimes counterproductive because the client
	might already have cached the "pushed" response.		might already have cached the "pushed" response.
	When this is the case, the bandwidth used to "push" the response is		When this is the case, the bandwidth used to "push" the response is
	effectively wasted, and represents opportunity cost, because it could		effectively wasted, and represents opportunity cost, because it could
	be used by other, more relevant responses. HTTP/2 allows a stream to		be used by other, more relevant responses. HTTP/2 allows a stream to
	be cancelled by a client using a RST_STREAM frame in this situation,		be cancelled by a client using a RST_STREAM frame in this situation,
	but there is still at least one round trip of potentially wasted		but there is still at least one round trip of potentially wasted
	capacity even then.		capacity even then.
	This specification defines a HTTP/2 frame type to allow clients to		This specification defines a HTTP/2 frame type to allow clients to
	inform the server of their cache's contents using a Golumb-Rice Coded		inform the server of their cache's contents using a Golumb-Rice Coded
	Set. Servers can then use this to inform their choices of what to		Set [Rice]. Servers can then use this to inform their choices of
	push to clients.		what to push to clients.
	1.1. Notational Conventions		1.1. Notational Conventions
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC2119].		document are to be interpreted as described in [RFC2119].
	2. The CACHE_DIGEST Frame		2. The CACHE_DIGEST Frame
	The CACHE_DIGEST frame type is 0xf1. NOTE: This is an experimental		The CACHE_DIGEST frame type is 0xf1. NOTE: This is an experimental
	value; if standardised, a permanent value will be assigned.		value; if standardised, a permanent value will be assigned.
	+-----------------------------------------------+		+-------------------------------+-------------------------------+
	| Digest-Value? (\*) ...		| Origin-Len (16) | Origin? (\*) ...
	+-----------------------------------------------+		+-------------------------------+-------------------------------+
			| Digest-Value? (\*) ...
			+---------------------------------------------------------------+
	The CACHE_DIGEST frame payload has the following fields:		The CACHE_DIGEST frame payload has the following fields:
	o *Digest-Value*: A sequence of octets containing the digest as		Origin-Len: An unsigned, 16-bit integer indicating the length, in
	computed in Section 2.1.1.		octets, of the Origin field.
			Origin: A sequence of characters containing the ASCII serialization
			of an origin ([RFC6454], Section 6.2) that the Digest-Value
			applies to.
			Digest-Value: A sequence of octets containing the digest as computed
			in Section 2.1.1.
	The CACHE_DIGEST frame defines the following flags:		The CACHE_DIGEST frame defines the following flags:
	o *RESET* (0x1): When set, indicates that any and all cache digests		o *RESET* (0x1): When set, indicates that any and all cache digests
	for the applicable origin held by the recipient MUST be considered		for the applicable origin held by the recipient MUST be considered
	invalid.		invalid.
	o *COMPLETE* (0x2): When set, indicates that the currently valid set		o *COMPLETE* (0x2): When set, indicates that the currently valid set
	of cache digests held by the server constitutes a complete		of cache digests held by the server constitutes a complete
	representation of the cache's state regarding that origin, for the		representation of the cache's state regarding that origin, for the
	skipping to change at page 3, line 45 ¶		skipping to change at page 4, line 7 ¶
	o *VALIDATORS* (0x4): When set, indicates that the "validators"		o *VALIDATORS* (0x4): When set, indicates that the "validators"
	boolean in Section 2.1.1 is true.		boolean in Section 2.1.1 is true.
	o *STALE* (0x8): When set, indicates that all cached responses		o *STALE* (0x8): When set, indicates that all cached responses
	represented in the digest-value are stale [RFC7234] at the point		represented in the digest-value are stale [RFC7234] at the point
	in them that the digest was generated; otherwise, all are fresh.		in them that the digest was generated; otherwise, all are fresh.
	2.1. Client Behavior		2.1. Client Behavior
	A CACHE_DIGEST frame can be sent from a client to a server on any		A CACHE_DIGEST frame MUST be sent from a client to a server on stream
	stream in the "open" state, and conveys a digest of the contents of		0, and conveys a digest of the contents of the client's cache for the
	the client's cache for associated stream.		indicated origin.
	In typical use, a client will send one or more CACHE_DIGESTs		In typical use, a client will send one or more CACHE_DIGESTs
	immediately after the first request on a connection for a given		immediately after the first request on a connection for a given
	origin, on the same stream, because there is usually a short period		origin, on the same stream, because there is usually a short period
	of inactivity then, and servers can benefit most when they understand		of inactivity then, and servers can benefit most when they understand
	the state of the cache before they begin pushing associated assets		the state of the cache before they begin pushing associated assets
	(e.g., CSS, JavaScript and images). Clients MAY send CACHE_DIGEST at		(e.g., CSS, JavaScript and images). Clients MAY send CACHE_DIGEST at
	other times.		other times.
	If the cache's state is cleared, lost, or the client otherwise wishes		If the cache's state is cleared, lost, or the client otherwise wishes
	the server to stop using previously sent CACHE_DIGESTs, it can send a		the server to stop using previously sent CACHE_DIGESTs, it can send a
	CACHE_DIGEST with the RESET flag set.		CACHE_DIGEST with the RESET flag set.
	When generating CACHE_DIGEST, a client MUST NOT include cached		When generating CACHE_DIGEST, a client MUST NOT include cached
	responses whose URLs do not share origins [RFC6454] with the request		responses whose URLs do not share origins [RFC6454] with the
	of the stream that the frame is sent upon.		indicated origin. Clients MUST NOT send CACHE_DIGEST frames on
			connections that are not authoritative (as defined in [RFC7540],
			10.1) for the indicated origin.
	CACHE_DIGEST allows the client to indicate whether the set of URLs		CACHE_DIGEST allows the client to indicate whether the set of URLs
	used to compute the digest represent fresh or stale stored responses,		used to compute the digest represent fresh or stale stored responses,
	using the STALE flag. Clients MAY decide whether to only sent		using the STALE flag. Clients MAY decide whether to only sent
	CACHE_DIGEST frames representing their fresh stored responses, their		CACHE_DIGEST frames representing their fresh stored responses, their
	stale stored responses, or both.		stale stored responses, or both.
	Clients can choose to only send a subset of the suitable stored		Clients can choose to only send a subset of the suitable stored
	responses of each type (fresh or stale). However, when the		responses of each type (fresh or stale). However, when the
	CACHE_DIGEST frames sent represent the complete set of stored		CACHE_DIGEST frames sent represent the complete set of stored
	skipping to change at page 7, line 18 ¶		skipping to change at page 7, line 29 ¶
	stored CACHE_DIGESTs for its origin. Servers MUST treat an empty		stored CACHE_DIGESTs for its origin. Servers MUST treat an empty
	Digest-Value with a RESET flag set as effectively clearing all stored		Digest-Value with a RESET flag set as effectively clearing all stored
	digests for that origin.		digests for that origin.
	Clients are not likely to send updates to CACHE_DIGEST over the		Clients are not likely to send updates to CACHE_DIGEST over the
	lifetime of a connection; it is expected that servers will separately		lifetime of a connection; it is expected that servers will separately
	track what cacheable responses have been sent previously on the same		track what cacheable responses have been sent previously on the same
	connection, using that knowledge in conjunction with that provided by		connection, using that knowledge in conjunction with that provided by
	CACHE_DIGEST.		CACHE_DIGEST.
			Servers MUST ignore CACHE_DIGEST frames sent on a stream other than
			0.
	2.2.1. Querying the Digest for a Value		2.2.1. Querying the Digest for a Value
	Given:		Given:
	o "digest-value", an array of bits		o "digest-value", an array of bits
	o "URL", an array of characters		o "URL", an array of characters
	o "ETag", an array of characters		o "ETag", an array of characters
	skipping to change at page 8, line 43 ¶		skipping to change at page 9, line 10 ¶
	be.		be.
	Additionally, User Agents SHOULD NOT send CACHE_DIGEST when in		Additionally, User Agents SHOULD NOT send CACHE_DIGEST when in
	"privacy mode."		"privacy mode."
	5. References		5. References
	5.1. Normative References		5.1. Normative References
	[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, DOI 10.17487/		Requirement Levels", BCP 14, RFC 2119,
	RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<http://www.rfc-editor.org/info/rfc2119>.		<http://www.rfc-editor.org/info/rfc2119>.
	[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform		[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
	Resource Identifier (URI): Generic Syntax", STD 66, RFC		Resource Identifier (URI): Generic Syntax", STD 66,
	3986, DOI 10.17487/RFC3986, January 2005,		RFC 3986, DOI 10.17487/RFC3986, January 2005,
	<http://www.rfc-editor.org/info/rfc3986>.		<http://www.rfc-editor.org/info/rfc3986>.
	[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms		[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
	(SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI		(SHA and SHA-based HMAC and HKDF)", RFC 6234,
	10.17487/RFC6234, May 2011,		DOI 10.17487/RFC6234, May 2011,
	<http://www.rfc-editor.org/info/rfc6234>.		<http://www.rfc-editor.org/info/rfc6234>.
	[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, DOI		[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
	10.17487/RFC6454, December 2011,		DOI 10.17487/RFC6454, December 2011,
	<http://www.rfc-editor.org/info/rfc6454>.		<http://www.rfc-editor.org/info/rfc6454>.
	[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer		[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
	Protocol (HTTP/1.1): Message Syntax and Routing", RFC		Protocol (HTTP/1.1): Message Syntax and Routing",
	7230, DOI 10.17487/RFC7230, June 2014,		RFC 7230, DOI 10.17487/RFC7230, June 2014,
	<http://www.rfc-editor.org/info/rfc7230>.		<http://www.rfc-editor.org/info/rfc7230>.
	[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer		[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
	Protocol (HTTP/1.1): Conditional Requests", RFC 7232, DOI		Protocol (HTTP/1.1): Conditional Requests", RFC 7232,
	10.17487/RFC7232, June 2014,		DOI 10.17487/RFC7232, June 2014,
	<http://www.rfc-editor.org/info/rfc7232>.		<http://www.rfc-editor.org/info/rfc7232>.
	[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,		[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
	Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",		Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
	RFC 7234, DOI 10.17487/RFC7234, June 2014,		RFC 7234, DOI 10.17487/RFC7234, June 2014,
	<http://www.rfc-editor.org/info/rfc7234>.		<http://www.rfc-editor.org/info/rfc7234>.
	[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext		[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
	Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI		Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
	10.17487/RFC7540, May 2015,		DOI 10.17487/RFC7540, May 2015,
	<http://www.rfc-editor.org/info/rfc7540>.		<http://www.rfc-editor.org/info/rfc7540>.
	5.2. Informative References		5.2. Informative References
	[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,		[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
	DOI 10.17487/RFC6265, April 2011,		DOI 10.17487/RFC6265, April 2011,
	<http://www.rfc-editor.org/info/rfc6265>.		<http://www.rfc-editor.org/info/rfc6265>.
			[Rice] Rice, R. and J. Plaunt, "Adaptive variable-length coding
			for efficient compression of spacecraft television data",
			IEEE Transactions on Communication Technology 19.6 , 1971.
	Appendix A. Acknowledgements		Appendix A. Acknowledgements
	Thanks to Adam Langley and Giovanni Bajo for their explorations of		Thanks to Adam Langley and Giovanni Bajo for their explorations of
	Golumb-coded sets. In particular, see		Golumb-coded sets. In particular, see
	http://giovanni.bajo.it/post/47119962313/golomb-coded-sets-smaller-		http://giovanni.bajo.it/post/47119962313/golomb-coded-sets-smaller-
	than-bloom-filters , which refers to sample code.		than-bloom-filters , which refers to sample code.
	Thanks to Stefan Eissing for his suggestions.		Thanks to Stefan Eissing for his suggestions.
	Authors' Addresses		Authors' Addresses
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