draft-ietf-httpbis-early-hints-03.txt		draft-ietf-httpbis-early-hints-04.txt
	HTTP Working Group K. Oku		HTTP Working Group K. Oku
	Internet-Draft Fastly		Internet-Draft Fastly
	Intended status: Experimental June 20, 2017		Intended status: Experimental July 11, 2017
	Expires: December 22, 2017		Expires: January 12, 2018
	An HTTP Status Code for Indicating Hints		An HTTP Status Code for Indicating Hints
	draft-ietf-httpbis-early-hints-03		draft-ietf-httpbis-early-hints-04
	Abstract		Abstract
	This memo introduces an informational HTTP status code that can be		This memo introduces an informational HTTP status code that can be
	used to convey hints that help a client make preparations for		used to convey hints that help a client make preparations for
	processing the final response.		processing the final response.
	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 December 22, 2017.		This Internet-Draft will expire on January 12, 2018.
	Copyright Notice		Copyright Notice
	Copyright (c) 2017 IETF Trust and the persons identified as the		Copyright (c) 2017 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 22 ¶		skipping to change at page 2, line 22 ¶
	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. 103 Early Hints . . . . . . . . . . . . . . . . . . . . . . . 3		2. 103 Early Hints . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Security Considerations . . . . . . . . . . . . . . . . . . . 4		3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5		5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
	6. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 5		5.1. Normative References . . . . . . . . . . . . . . . . . . 5
	6.1. Since draft-ietf-httpbis-early-hints-02 . . . . . . . . . 5		5.2. Informative References . . . . . . . . . . . . . . . . . 5
	6.2. Since draft-ietf-httpbis-early-hints-01 . . . . . . . . . 5		Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . 6
	6.3. Since draft-ietf-httpbis-early-hints-00 . . . . . . . . . 5		A.1. Since draft-ietf-httpbis-early-hints-03 . . . . . . . . . 6
	7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5		A.2. Since draft-ietf-httpbis-early-hints-02 . . . . . . . . . 6
	7.1. Normative References . . . . . . . . . . . . . . . . . . 5		A.3. Since draft-ietf-httpbis-early-hints-01 . . . . . . . . . 6
	7.2. Informative References . . . . . . . . . . . . . . . . . 6		A.4. Since draft-ietf-httpbis-early-hints-00 . . . . . . . . . 6
			Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 6
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
	1. Introduction		1. Introduction
	It is common for HTTP responses to contain links to external		It is common for HTTP responses to contain links to external
	resources that need to be fetched prior to their use; for example,		resources that need to be fetched prior to their use; for example,
	rendering HTML by a Web browser. Having such links available to the		rendering HTML by a Web browser. Having such links available to the
	client as early as possible helps to minimize perceived latency.		client as early as possible helps to minimize perceived latency.
	The "preload" ([Preload]) link relation can be used to convey such		The "preload" ([Preload]) link relation can be used to convey such
	skipping to change at page 3, line 35 ¶		skipping to change at page 3, line 35 ¶
	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. 103 Early Hints		2. 103 Early Hints
	The 103 (Early Hints) informational status code indicates to the		The 103 (Early Hints) informational status code indicates to the
	client that the server is likely to send a final response with the		client that the server is likely to send a final response with the
	header fields included in the informational response.		header fields included in the informational response.
	A server MUST NOT include Content-Length, Transfer-Encoding, or any		Typically, a server will include the header fields sent in a 103
	hop-by-hop header fields ([RFC7230], Section 6.1) in a 103 (Early		(Early Hints) response in the final response as well. However, there
	Hints) response.		might be cases when this is not desirable, such as when the server
			learns that they are not correct before the final response is sent.
	A client can speculatively evaluate the header fields included in a		A client can speculatively evaluate the header fields included in a
	103 (Early Hints) response while waiting for the final response. For		103 (Early Hints) response while waiting for the final response. For
	example, a client might recognize a Link header field value		example, a client might recognize a Link header field value
	containing the relation type "preload" and start fetching the target		containing the relation type "preload" and start fetching the target
	resource.		resource. However, these header fields only provide hints to the
			client; they do not replace the header fields on the final response.
	However, these header fields only provide hints to the client; they		Aside from performance optimizations, such evaluation of the 103
	do not replace the header fields on the final response. Aside from		(Early Hints) response's header fields MUST NOT affect how the final
	performance optimizations, such evaluation of the 103 (Early Hints)		response is processed. A client MUST NOT interpret the 103 (Early
	response's header fields MUST NOT affect how the final response is		Hints) response header fields as if they applied to the informational
	processed. A client MUST NOT interpret the 103 (Early Hints)
	response header fields as if they applied to the informational
	response itself (e.g., as metadata about the 103 (Early Hints)		response itself (e.g., as metadata about the 103 (Early Hints)
	response).		response).
	An intermediary MAY drop the informational response. It MAY send
	HTTP/2 ([RFC7540]) server pushes using the information found in the
	103 (Early Hints) response.
	The following example illustrates a typical message exchange that		The following example illustrates a typical message exchange that
	involves a 103 (Early Hints) response.		involves a 103 (Early Hints) response.
	Client request:		Client request:
	GET / HTTP/1.1		GET / HTTP/1.1
	Host: example.com		Host: example.com
	Server response:		Server response:
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	HTTP/1.1 200 OK		HTTP/1.1 200 OK
	Date: Fri, 26 May 2017 10:02:11 GMT		Date: Fri, 26 May 2017 10:02:11 GMT
	Content-Length: 1234		Content-Length: 1234
	Content-Type: text/html; charset=utf-8		Content-Type: text/html; charset=utf-8
	Link: </style.css>; rel=preload; as=style		Link: </style.css>; rel=preload; as=style
	Link: </script.js>; rel=preload; as=script		Link: </script.js>; rel=preload; as=script
	<!doctype html>		<!doctype html>
	[... rest of the response body is ommitted from the example ...]		[... rest of the response body is ommitted from the example ...]
			As is the case with any informational response, a server might emit
			more than one 103 (Early Hints) response prior to sending a final
			response. This can happen for example when a caching intermediary
			generates a 103 (Early Hints) response based on the header fields of
			a stale-cached response, then forwards a 103 (Early Hints) response
			and a final response that were sent from the origin server in
			response to a revalidation request.
	3. Security Considerations		3. Security Considerations
	Some clients might have issues handling 103 (Early Hints), since		Some clients might have issues handling 103 (Early Hints), since
	informational responses are rarely used in reply to requests not		informational responses are rarely used in reply to requests not
	including an Expect header ([RFC7231], Section 5.1.1).		including an Expect header field ([RFC7231], Section 5.1.1).
	In particular, an HTTP/1.1 client that mishandles an informational		In particular, an HTTP/1.1 client that mishandles an informational
	response as a final response is likely to consider all responses to		response as a final response is likely to consider all responses to
	the succeeding requests sent over the same connection to be part of		the succeeding requests sent over the same connection to be part of
	the final response. Such behavior may constitute a cross-origin		the final response. Such behavior might constitute a cross-origin
	information disclosure vulnerability in case the client multiplexes		information disclosure vulnerability in case the client multiplexes
	requests to different origins onto a single persistent connection.		requests to different origins onto a single persistent connection.
	Therefore, a server might refrain from sending Early Hints over		Therefore, a server might refrain from sending Early Hints over
	HTTP/1.1 unless when the client is known to handle informational		HTTP/1.1 unless the client is known to handle informational responses
	responses correctly.		correctly.
	HTTP/2 clients are less likely to suffer from incorrect framing since		HTTP/2 clients are less likely to suffer from incorrect framing since
	handling of the response header fields does not affect how the end of		handling of the response header fields does not affect how the end of
	the response body is determined.		the response body is determined.
	4. IANA Considerations		4. IANA Considerations
	The HTTP Status Codes Registry will be updated with the following		The HTTP Status Codes Registry will be updated with the following
	entry:		entry:
	o Code: 103		o Code: 103
	o Description: Early Hints		o Description: Early Hints
	o Specification: [this document]		o Specification: [this document]
	5. Acknowledgements		5. References
	Thanks to Tatsuhiro Tsujikawa for coming up with the idea of sending
	the Link header fields using an informational response.
	6. Changes
	6.1. Since draft-ietf-httpbis-early-hints-02
	o Editorial changes.
	o Added an example.
	6.2. Since draft-ietf-httpbis-early-hints-01
	o Editorial changes.
	6.3. Since draft-ietf-httpbis-early-hints-00
	o Forbid processing the headers of a 103 response as part of the
	informational response.
	7. References
	7.1. 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,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<http://www.rfc-editor.org/info/rfc2119>.		<http://www.rfc-editor.org/info/rfc2119>.
	[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",		Protocol (HTTP/1.1): Message Syntax and Routing",
	RFC 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>.
	skipping to change at page 6, line 15 ¶		skipping to change at page 5, line 48 ¶
	[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer		[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
	Protocol (HTTP/1.1): Semantics and Content", RFC 7231,		Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
	DOI 10.17487/RFC7231, June 2014,		DOI 10.17487/RFC7231, June 2014,
	<http://www.rfc-editor.org/info/rfc7231>.		<http://www.rfc-editor.org/info/rfc7231>.
	[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,		Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
	DOI 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>.
	7.2. Informative References		5.2. Informative References
	[Preload] Grigorik, I., "Preload", n.d., <https://w3c.github.io/		[Preload] Grigorik, I., "Preload", n.d., <https://w3c.github.io/
	preload/>.		preload/>.
			Appendix A. Changes
			A.1. Since draft-ietf-httpbis-early-hints-03
			o Removed statements that were either redundant or contradictory to
			RFC7230-7234.
			o Clarified what the server's expected behavior is.
			o Explain that a server might want to send more than one 103
			response.
			o Editorial Changes.
			A.2. Since draft-ietf-httpbis-early-hints-02
			o Editorial changes.
			o Added an example.
			A.3. Since draft-ietf-httpbis-early-hints-01
			o Editorial changes.
			A.4. Since draft-ietf-httpbis-early-hints-00
			o Forbid processing the headers of a 103 response as part of the
			informational response.
			Appendix B. Acknowledgements
			Thanks to Tatsuhiro Tsujikawa for coming up with the idea of sending
			the Link header fields using an informational response.
	Author's Address		Author's Address
	Kazuho Oku		Kazuho Oku
	Fastly		Fastly
	Email: kazuhooku@gmail.com		Email: kazuhooku@gmail.com
End of changes. 16 change blocks.
	55 lines changed or deleted		72 lines changed or added
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