< draft-ietf-httpbis-cache-header-05.txt		draft-ietf-httpbis-cache-header-06.txt >
	HTTP M. Nottingham		HTTP M. Nottingham
	Internet-Draft Fastly		Internet-Draft Fastly
	Intended status: Standards Track August 11, 2020		Intended status: Standards Track 13 January 2021
	Expires: February 12, 2021		Expires: 17 July 2021
	The Cache-Status HTTP Response Header Field		The Cache-Status HTTP Response Header Field
	draft-ietf-httpbis-cache-header-05		draft-ietf-httpbis-cache-header-06
	Abstract		Abstract
	To aid debugging, HTTP caches often append header fields to a		To aid debugging, HTTP caches often append header fields to a
	response explaining how they handled the request. This specification		response explaining how they handled the request. This specification
	codifies that practice and updates it to align with HTTP's current		codifies that practice and updates it to align with HTTP's current
	caching model.		caching model.
	Note to Readers		Note to Readers
	_RFC EDITOR: please remove this section before publication_		_RFC EDITOR: please remove this section before publication_
	Discussion of this draft takes place on the HTTP working group		Discussion of this draft takes place on the HTTP working group
	mailing list (ietf-http-wg@w3.org), which is archived at		mailing list (ietf-http-wg@w3.org), which is archived at
	https://lists.w3.org/Archives/Public/ietf-http-wg/ [1].		https://lists.w3.org/Archives/Public/ietf-http-wg/
			(https://lists.w3.org/Archives/Public/ietf-http-wg/).
	Working Group information can be found at https://httpwg.org/ [2];		Working Group information can be found at https://httpwg.org/
	source code and issues list for this draft can be found at		(https://httpwg.org/); source code and issues list for this draft can
	https://github.com/httpwg/http-extensions/labels/cache-header [3].		be found at https://github.com/httpwg/http-extensions/labels/cache-
			header (https://github.com/httpwg/http-extensions/labels/cache-
			header).
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://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 February 12, 2021.		This Internet-Draft will expire on 17 July 2021.
	Copyright Notice		Copyright Notice
	Copyright (c) 2020 IETF Trust and the persons identified as the		Copyright (c) 2021 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 (https://trustee.ietf.org/
	(https://trustee.ietf.org/license-info) in effect on the date of		license-info) in effect on the date of publication of this document.
	publication of this document. Please review these documents		Please review these documents carefully, as they describe your rights
	carefully, as they describe your rights and restrictions with respect		and restrictions with respect to this document. Code Components
	to this document. Code Components extracted from this document must		extracted from this document must include Simplified BSD License text
	include Simplified BSD License text as described in Section 4.e of		as described in Section 4.e of the Trust Legal Provisions and are
	the Trust Legal Provisions and are provided without warranty as		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-Status HTTP Response Header Field . . . . . . . . . 3		2. The Cache-Status HTTP Response Header Field . . . . . . . . . 3
	2.1. The hit parameter . . . . . . . . . . . . . . . . . . . . 4		2.1. The hit parameter . . . . . . . . . . . . . . . . . . . . 4
	2.2. The fwd parameter . . . . . . . . . . . . . . . . . . . . 4		2.2. The fwd parameter . . . . . . . . . . . . . . . . . . . . 4
	2.3. The fwd-status parameter . . . . . . . . . . . . . . . . 5		2.3. The fwd-status parameter . . . . . . . . . . . . . . . . 5
	2.4. The ttl parameter . . . . . . . . . . . . . . . . . . . . 5		2.4. The ttl parameter . . . . . . . . . . . . . . . . . . . . 5
	2.5. The stored parameter . . . . . . . . . . . . . . . . . . 5		2.5. The stored parameter . . . . . . . . . . . . . . . . . . 5
	2.6. The collapsed parameter . . . . . . . . . . . . . . . . . 5		2.6. The collapsed parameter . . . . . . . . . . . . . . . . . 5
	2.7. The key parameter . . . . . . . . . . . . . . . . . . . . 5		2.7. The key parameter . . . . . . . . . . . . . . . . . . . . 5
	2.8. The detail parameter . . . . . . . . . . . . . . . . . . 5		2.8. The detail parameter . . . . . . . . . . . . . . . . . . 6
	3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6		3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	4. Defining New Proxy-Status Parameters . . . . . . . . . . . . 7		4. Defining New Proxy-Status Parameters . . . . . . . . . . . . 7
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 7		6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
	7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8		7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
	7.1. Normative References . . . . . . . . . . . . . . . . . . 8		7.1. Normative References . . . . . . . . . . . . . . . . . . 8
	7.2. Informative References . . . . . . . . . . . . . . . . . 9		7.2. Informative References . . . . . . . . . . . . . . . . . 9
	7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 9
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
	1. Introduction		1. Introduction
	To aid debugging, HTTP caches often append header fields to a		To aid debugging, HTTP caches often append header fields to a
	response explaining how they handled the request. Unfortunately, the		response explaining how they handled the request. Unfortunately, the
	semantics of these headers are often unclear, and both the semantics		semantics of these headers are often unclear, and both the semantics
	and syntax used vary greatly between implementations.		and syntax used vary between implementations.
	This specification defines a single, new HTTP response header field,		This specification defines a new HTTP response header field, "Cache-
	"Cache-Status" for this purpose.		Status" for this purpose.
	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", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	This document uses ABNF as defined in [RFC5234], along with the "%s"		This document uses ABNF as defined in [RFC5234], along with the "%s"
	extension for case sensitivity defined in [RFC7405].		extension for case sensitivity defined in [RFC7405].
	2. The Cache-Status HTTP Response Header Field		2. The Cache-Status HTTP Response Header Field
	The Cache-Status HTTP response header indicates caches' handling of		The Cache-Status HTTP response header field indicates caches'
	the request corresponding to the response it occurs within.		handling of the request corresponding to the response it occurs
			within.
	Its value is a List [I-D.ietf-httpbis-header-structure]:		Its value is a List [I-D.ietf-httpbis-header-structure], Section 3.1:
	Cache-Status = sf-list		Cache-Status = sf-list
	Each member of the list represents a cache that has handled the		Each member of the list represents a cache that has handled the
	request. The first member of the list represents the cache closest		request. The first member of the list represents the cache closest
	to the origin server, and the last member of the list represents the		to the origin server, and the last member of the list represents the
	cache closest to the client (possibly including the user agent's		cache closest to the user (possibly including the user agent's cache
	cache itself, if it chooses to append a value).		itself, if it appends a value).
	Caches determine when it is appropriate to add the Cache-Status		Caches determine when it is appropriate to add the Cache-Status
	header field to a response. Some might add it to all responses,		header field to a response. Some might add it to all responses,
	whereas others might only do so when specifically configured to, or		whereas others might only do so when specifically configured to, or
	when the request contains a header that activates a debugging mode.		when the request contains a header field that activates a debugging
			mode.
	When adding a value to the Cache-Status header field, caches SHOULD		When adding a value to the Cache-Status header field, caches SHOULD
	preserve the existing contents of the header field, to allow		preserve the existing field value, to allow debugging of the entire
	debugging of the entire chain of caches handling the request.		chain of caches handling the request.
	Each list member identifies the cache that inserted that value, and		Each list member identifies the cache that inserted it and MUST be a
	MUST be a String or Token. Depending on the deployment, this might		String or Token. Depending on the deployment, this might be a
	be a product or service name (e.g., ExampleCache or "Example CDN"), a		product or service name (e.g., ExampleCache or "Example CDN"), a
	hostname ("cache-3.example.com"), and IP address, or a generated		hostname ("cache-3.example.com"), an IP address, or a generated
	string.		string.
	Each member of the list can also have parameters that describe that		Each member of the list can have parameters that describe that
	cache's handling of the request. While all of these parameters are		cache's handling of the request. While these parameters are
	OPTIONAL, caches are encouraged to provide as much information as		OPTIONAL, caches are encouraged to provide as much information as
	possible.		possible.
	This specification defines these parameters:		This specification defines the following parameters:
	hit = sf-boolean		hit = sf-boolean
	fwd = sf-token		fwd = sf-token
	fwd-status = sf-integer		fwd-status = sf-integer
	ttl = sf-integer		ttl = sf-integer
	stored = sf-boolean		stored = sf-boolean
	collapsed = sf-boolean		collapsed = sf-boolean
	key = sf-string		key = sf-string
	detail = sf-token / sf-string		detail = sf-token / sf-string
	2.1. The hit parameter		2.1. The hit parameter
	"hit", when true, indicates that the request was satisfied by the		"hit", when true, indicates that the request was satisfied by the
	cache; i.e., it did not go forward, and the response was obtained		cache; i.e., it was not forwarded, and the response was obtained from
	from the cache. A response that originally was produced by the		the cache. A response that was originally produced by the origin but
	origin but was modified by the cache (for example, a 304 or 206		was modified by the cache (for example, a 304 or 206 status code) is
	status code) is still considered a hit.		still considered a hit, as long as it did not go forward (e.g., for
			validation).
	"hit" and "fwd" are exclusive; only one of them should appear on each		"hit" and "fwd" are exclusive; only one of them should appear on each
	list member.		list member.
	2.2. The fwd parameter		2.2. The fwd parameter
	"fwd" indicates that the request went forward towards the origin, and		"fwd" indicates that the request went forward towards the origin, and
	why.		why.
	The following values are defined to explain why the request went		The following parameter values are defined to explain why the request
	forward:		went forward, from most specific to least:
	o uri-miss - The cache did not contain any responses that matched		* bypass - The cache was configured to not handle this request
			* method - The request method's semantics require the request to be
			forwarded
			* request - The cache was able to select a fresh response for the
			request, but the request's semantics (e.g., Cache-Control request
			directives) did not allow its use
			* stale - The cache was able to select a response for the request,
			but it was stale
			* uri-miss - The cache did not contain any responses that matched
	the request URI		the request URI
	o vary-miss - The cache contained a response that matched the		* vary-miss - The cache contained a response that matched the
	request URI, but could not select a response based upon this		request URI, but could not select a response based upon this
	request's headers and stored Vary headers.		request's headers and stored Vary headers.
	o miss - The cache did not contain any responses that could be used		* miss - The cache did not contain any responses that could be used
	to satisfy this request (to be used when an implementation cannot		to satisfy this request (to be used when an implementation cannot
	distinguish between uri-miss and vary-miss)		distinguish between uri-miss and vary-miss)
	o stale - The cache was able to select a response for the request,		The most specific reason that the cache is aware of SHOULD be used.
	but it was stale
	o request - The cache was able to select a fresh response for the
	request, but client request headers (e.g., Cache-Control request
	directives) did not allow its use
	o bypass - The cache was configured to not handle this request
	2.3. The fwd-status parameter		2.3. The fwd-status parameter
	"fwd-status" indicates what status code the next hop server returned		"fwd-status" indicates what status code the next hop server returned
	in response to the request. Only meaningful when "fwd" is present;		in response to the request. Only meaningful when "fwd" is present;
	if "fwd-status" is not present but "fwd" is, it defaults to the		if "fwd-status" is not present but "fwd" is, it defaults to the
	status code sent in the response.		status code sent in the response.
	This parameter is useful to distinguish cases when the next hop		This parameter is useful to distinguish cases when the next hop
	server sends a 304 Not Modified response to a conditional request, or		server sends a 304 Not Modified response to a conditional request, or
	a 206 Partial Response because of a range request.		a 206 Partial Response because of a range request.
	2.4. The ttl parameter		2.4. The ttl parameter
	"ttl" indicates the response's remaining freshness lifetime as		"ttl" indicates the response's remaining freshness lifetime as
	calculated by the cache, as an integer number of seconds, measured		calculated by the cache, as an integer number of seconds, measured
	when the response is sent by the cache. This includes freshness		when the response header section is sent by the cache. This includes
	assigned by the cache; e.g., through heuristics, local configuration,		freshness assigned by the cache; e.g., through heuristics, local
	or other factors. May be negative, to indicate staleness.		configuration, or other factors. May be negative, to indicate
			staleness.
	2.5. The stored parameter		2.5. The stored parameter
	"stored" indicates whether the cache stored the response; a true		"stored" indicates whether the cache stored the response; a true
	value indicates that it did. Only meaningful when fwd is present.		value indicates that it did. Only meaningful when fwd is present.
	2.6. The collapsed parameter		2.6. The collapsed parameter
	"collapsed" indicates whether this request was collapsed together		"collapsed" indicates whether this request was collapsed together
	with one or more other forward requests; if true, the response was		with one or more other forward requests; if true, the response was
	skipping to change at page 6, line 4 ¶		skipping to change at page 6, line 14 ¶
	2.8. The detail parameter		2.8. The detail parameter
	"detail" allows implementations to convey additional information not		"detail" allows implementations to convey additional information not
	captured in other parameters; for example, implementation-specific		captured in other parameters; for example, implementation-specific
	states, or other caching-related metrics.		states, or other caching-related metrics.
	For example:		For example:
	Cache-Status: ExampleCache; hit; detail=MEMORY		Cache-Status: ExampleCache; hit; detail=MEMORY
	The semantics of a detail parameter are always specific to the cache		The semantics of a detail parameter are always specific to the cache
	that sent it; even if a member of details from another cache shares		that sent it; even if a member of details from another cache shares
	the same name, it might not mean the same thing.		the same name, it might not mean the same thing.
	This parameter is intentionally limited. If an implementation needs		This parameter is intentionally limited. If an implementation's
	to convey additional information, they are encouraged to register		developer or operator needs to convey additional information in an
	extension parameters (see Section 4) or define another header field.		interoperable fashion, they are encouraged to register extension
			parameters (see Section 4) or define another header field.
	3. Examples		3. Examples
	The most minimal cache hit:		The most minimal cache hit:
	Cache-Status: ExampleCache; hit		Cache-Status: ExampleCache; hit
	... but a polite cache will give some more information, e.g.:		... but a polite cache will give some more information, e.g.:
	Cache-Status: ExampleCache; hit; ttl=376		Cache-Status: ExampleCache; hit; ttl=376
	skipping to change at page 6, line 41 ¶		skipping to change at page 7, line 4 ¶
	Cache-Status: ExampleCache; fwd=stale; fwd-status=304		Cache-Status: ExampleCache; fwd=stale; fwd-status=304
	A miss that was collapsed with another request:		A miss that was collapsed with another request:
	Cache-Status: ExampleCache; fwd=uri-miss; collapsed		Cache-Status: ExampleCache; fwd=uri-miss; collapsed
	A miss that the cache attempted to collapse, but couldn't:		A miss that the cache attempted to collapse, but couldn't:
	Cache-Status: ExampleCache; fwd=uri-miss; collapsed=?0		Cache-Status: ExampleCache; fwd=uri-miss; collapsed=?0
	Going through two layers of caching, both of which were hits, and the		Going through two layers of caching, both of which were hits, and the
	second collapsed with other requests:		second collapsed with other requests:
	Cache-Status: OriginCache; hit; ttl=1100; collapsed,		Cache-Status: OriginCache; hit; ttl=1100; collapsed,
	"CDN Company Here"; hit; ttl=545		"CDN Company Here"; hit; ttl=545
	4. Defining New Proxy-Status Parameters		4. Defining New Proxy-Status Parameters
	New Cache-Status Parameters can be defined by registering them in the		New Cache-Status Parameters can be defined by registering them in the
	HTTP Cache-Status Parameters registry.		HTTP Cache-Status Parameters registry.
	Registration requests are reviewed and approved by a Designated		Registration requests are reviewed and approved by a Designated
	Expert, as per [RFC8126], Section 4.5. A specification document is		Expert, as per [RFC8126], Section 4.5. A specification document is
	appreciated, but not required.		appreciated, but not required.
	The Expert(s) should consider the following factors when evaluating		The Expert(s) should consider the following factors when evaluating
	requests:		requests:
	o Community feedback		* Community feedback
	o If the value is sufficiently well-defined		* If the value is sufficiently well-defined
	o Generic parameters are preferred over vendor-specific,		* Generic parameters are preferred over vendor-specific,
	application-specific or deployment-specific values. If a generic		application-specific, or deployment-specific values. If a generic
	value cannot be agreed upon in the community, the parameter's name		value cannot be agreed upon in the community, the parameter's name
	should be correspondingly specific (e.g., with a prefix that		should be correspondingly specific (e.g., with a prefix that
	identifies the vendor, application or deployment).		identifies the vendor, application or deployment).
	Registration requests should use the following template:		Registration requests should use the following template:
	o Name: [a name for the Cache-Status Parameter that matches key]		* Name: [a name for the Cache-Status Parameter that matches key]
	o Description: [a description of the parameter semantics and value]		* Description: [a description of the parameter semantics and value]
	o Reference: [to a specification defining this parameter]		* Reference: [to a specification defining this parameter]
	See the registry at https://iana.org/assignments/http-cache-status		See the registry at https://iana.org/assignments/http-cache-status
	[4] for details on where to send registration requests.		(https://iana.org/assignments/http-cache-status) for details on where
			to send registration requests.
	5. IANA Considerations		5. IANA Considerations
	Upon publication, please create the HTTP Cache-Status Parameters		Upon publication, please create the HTTP Cache-Status Parameters
	registry at https://iana.org/assignments/http-cache-status [5] and		registry at https://iana.org/assignments/http-cache-status
	populate it with the types defined in Section 2; see Section 4 for		(https://iana.org/assignments/http-cache-status) and populate it with
	its associated procedures.		the types defined in Section 2; see Section 4 for its associated
			procedures.
	6. Security Considerations		6. Security Considerations
	Attackers can use the information in Cache-Status to probe the		Attackers can use the information in Cache-Status to probe the
	behaviour of the cache (and other components), and infer the activity		behaviour of the cache (and other components), and infer the activity
	of those using the cache. The Cache-Status header field may not		of those using the cache. The Cache-Status header field may not
	create these risks on its own, but can assist attackers in exploiting		create these risks on its own, but can assist attackers in exploiting
	them.		them.
	For example, knowing if a cache has stored a response can help an		For example, knowing if a cache has stored a response can help an
	skipping to change at page 8, line 25 ¶		skipping to change at page 8, line 33 ¶
	To avoid assisting such attacks, the Cache-Status header field can be		To avoid assisting such attacks, the Cache-Status header field can be
	omitted, only sent when the client is authorized to receive it, or		omitted, only sent when the client is authorized to receive it, or
	only send sensitive information (e.g., the key parameter) when the		only send sensitive information (e.g., the key parameter) when the
	client is authorized.		client is authorized.
	7. References		7. References
	7.1. Normative References		7.1. Normative References
	[I-D.ietf-httpbis-header-structure]
	Nottingham, M. and P. Kamp, "Structured Field Values for
	HTTP", draft-ietf-httpbis-header-structure-19 (work in
	progress), June 2020.
	[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,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", STD 68, RFC 5234,
	DOI 10.17487/RFC5234, January 2008,
	<https://www.rfc-editor.org/info/rfc5234>.
	[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
	RFC 7405, DOI 10.17487/RFC7405, December 2014,
	<https://www.rfc-editor.org/info/rfc7405>.
	[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for		[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
	Writing an IANA Considerations Section in RFCs", BCP 26,		Writing an IANA Considerations Section in RFCs", BCP 26,
	RFC 8126, DOI 10.17487/RFC8126, June 2017,		RFC 8126, DOI 10.17487/RFC8126, June 2017,
	<https://www.rfc-editor.org/info/rfc8126>.		<https://www.rfc-editor.org/info/rfc8126>.
			[I-D.ietf-httpbis-header-structure]
			Nottingham, M. and P. Kamp, "Structured Field Values for
			HTTP", Work in Progress, Internet-Draft, draft-ietf-
			httpbis-header-structure-19, 3 June 2020,
			<http://www.ietf.org/internet-drafts/draft-ietf-httpbis-
			header-structure-19.txt>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
			[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
			Specifications: ABNF", STD 68, RFC 5234,
			DOI 10.17487/RFC5234, January 2008,
			<https://www.rfc-editor.org/info/rfc5234>.
			[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
			RFC 7405, DOI 10.17487/RFC7405, December 2014,
			<https://www.rfc-editor.org/info/rfc7405>.
	7.2. Informative References		7.2. Informative References
	[ENTANGLE]		[ENTANGLE] Kettle, J., "Web Cache Entanglement: Novel Pathways to
	Kettle, J., "Web Cache Entanglement: Novel Pathways to
	Poisoning", n.d., <https://i.blackhat.com/USA-		Poisoning", n.d., <https://i.blackhat.com/USA-
	20/Wednesday/us-20-Kettle-Web-Cache-Entanglement-Novel-		20/Wednesday/us-20-Kettle-Web-Cache-Entanglement-Novel-
	Pathways-To-Poisoning-wp.pdf>.		Pathways-To-Poisoning-wp.pdf>.
	7.3. URIs
	[1] https://lists.w3.org/Archives/Public/ietf-http-wg/
	[2] https://httpwg.org/
	[3] https://github.com/httpwg/http-extensions/labels/cache-header
	[4] https://iana.org/assignments/http-cache-status
	[5] https://iana.org/assignments/http-cache-status
	Author's Address		Author's Address
	Mark Nottingham		Mark Nottingham
	Fastly		Fastly
	made in		Prahran VIC
	Prahran, VIC
	Australia		Australia
	Email: mnot@mnot.net		Email: mnot@mnot.net
	URI: https://www.mnot.net/		URI: https://www.mnot.net/
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