draft-ietf-httpapi-link-template-02.unpg.txt		draft-ietf-httpapi-link-template-latest.txt
	Building Blocks for HTTP APIs M. Nottingham		Building Blocks for HTTP APIs M. Nottingham
	Internet-Draft February 1, 2023		Internet-Draft September 03, 2023
	Intended status: Standards Track		Intended status: Standards Track
	Expires: August 5, 2023		Expires: March 6, 2024
	The Link-Template HTTP Header Field		The Link-Template HTTP Header Field
	draft-ietf-httpapi-link-template-02		draft-ietf-httpapi-link-template-latest
	Abstract		Abstract
	This specification defines the Link-Template HTTP header field,		This specification defines the Link-Template HTTP header field,
	providing a means for describing the structure of a link between two		providing a means for describing the structure of a link between two
	resources, so that new links can be generated.		resources, so that new links can be generated.
	About This Document		About This Document
	This note is to be removed before publishing as an RFC.		This note is to be removed before publishing as an RFC.
	skipping to change at line 48 ¶		skipping to change at page 2, line 4 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
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	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
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			This Internet-Draft will expire on March 6, 2024.
	This Internet-Draft will expire on August 5, 2023.
	Copyright Notice		Copyright Notice
	Copyright (c) 2023 IETF Trust and the persons identified as the		Copyright (c) 2023 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/license-info) in effect on the date of		(https://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
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	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		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Notational Conventions		1.1. Notational Conventions . . . . . . . . . . . . . . . . . 2
	2. The Link-Template Header Field		2. The Link-Template Header Field . . . . . . . . . . . . . . . 3
	2.1. The 'var-base' parameter		2.1. The 'var-base' parameter . . . . . . . . . . . . . . . . 4
	3. Security Considerations		3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
	4. IANA Considerations		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	5. Normative References		5. Normative References . . . . . . . . . . . . . . . . . . . . 5
	Author's Address		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
	1. Introduction		1. Introduction
	[URI-TEMPLATE] defines a syntax for templates that, when expanded		[URI-TEMPLATE] defines a syntax for templates that, when expanded
	using a set of variables, results in a URI [URI].		using a set of variables, results in a URI [URI].
	This specification defines a HTTP header field [HTTP] for conveying		This specification defines a HTTP header field [HTTP] for conveying
	templates for links in the headers of a HTTP message. It is		templates for links in the headers of a HTTP message. It is
	complimentary to the Link header field defined in Section 3 of		complimentary to the Link header field defined in Section 3 of
	[WEB-LINKING], which carries links directly.		[WEB-LINKING], which carries links directly.
	skipping to change at line 111 ¶		skipping to change at page 3, line 18 ¶
	[STRUCTURED-FIELDS] that serializes one or more links into HTTP		[STRUCTURED-FIELDS] that serializes one or more links into HTTP
	message metadata. It is semantically equivalent to the Link header		message metadata. It is semantically equivalent to the Link header
	field defined in Section 3 of [WEB-LINKING], except that it uses URI		field defined in Section 3 of [WEB-LINKING], except that it uses URI
	Templates [URI-TEMPLATE] to convey the structure of links.		Templates [URI-TEMPLATE] to convey the structure of links.
	Its value is a List of Strings. Each String is a URI Template, and		Its value is a List of Strings. Each String is a URI Template, and
	Parameters on it carry associated metadata.		Parameters on it carry associated metadata.
	For example:		For example:
	Link-Template: "/{username}"; rel="https://example.org/rel/user"		Link-Template: "/{username}"; rel="item"
	indicates that a resource with the relation type
	"https://example.org/rel/user" can be found by expanding the
	"username" variable into the template given.
	The target for the link (as defined in Section 2 of [WEB-LINKING]) is
	the result of expanding the URI Template [URI-TEMPLATE] (being
	converted to an absolute URI after expansion, if necessary).
	The context, relation type and target attributes for the link are		indicates that a resource with the relation type "item" for a given
	determined as defined for the Link header field in Section 3 of		"username" can be found by expanding the "username" variable into the
	[WEB-LINKING].		template given.
	Parameters on a templated link have identical semantics to those of a		The link target (as defined in Section 2 of [WEB-LINKING]) is the
	Link header field. This includes (but is not limited to) the use of		result of expanding the URI Template [URI-TEMPLATE] (being converted
	the "rel" parameter to convey the relation type, the "anchor"		to an absolute URI after expansion, if necessary).
	parameter to modify the context IRI, and so on. Parameter values
	MUST be Strings.
	Likewise, the requirements for parameters on templated links are the		The link context and link relation type for the link (as defined in
	same as those for a Link header field.		Section 2 of [WEB-LINKING]) are conveyed using the "anchor" and "rel"
			Parameters, as they are for the Link header field in Section 3 of
			[WEB-LINKING]. Their values MUST be Strings.
	However, the "anchor" parameter MAY contain a URI Template. For		However, the "anchor" Parameter MAY contain a URI Template. For
	example:		example:
	Link-Template: </books/{book_id}/author>;		Link-Template: "/books/{book_id}/author";
	rel="author" anchor="#{book_id}"		rel="author"; anchor="#{book_id}"
	Here, the link to the author for a particular book in a list of books		Here, the link to the author for a particular book in a list of books
	can be found by following the link template.		can be found by following the link template.
	Implementations MUST support all levels of template defined by
	[URI-TEMPLATE] in both the rel and anchor parameters.
	This specification defines additional semantics for the "var-base"		This specification defines additional semantics for the "var-base"
	parameter on templated links; see below.		Parameter on templated links; see below.
			The link's target attributes (as defined in Section 2.2 of
			[WEB-LINKING]) are conveyed using other Parameters, in a manner
			similar to the Link header field. These Parameter values MUST be
			Strings. Note that some target attribute names will not serialise as
			Structure Field Parameter keys (see Section 3.1.2 of
			[STRUCTURED-FIELDS]).
			Implementations MUST support all levels of template defined by
			[URI-TEMPLATE] in the link String and the anchor Parameter.
	2.1. The 'var-base' parameter		2.1. The 'var-base' parameter
	When a templated link has a 'var-base' parameter, its value conveys a		When a templated link has a 'var-base' parameter, its value conveys a
	URI-reference that is used as a base URI for the variable names in		URI-reference that is used as a base URI for the variable names in
	the URI template. This allows template variables to be globally		the URI template. This allows template variables to be globally
	identified, rather than specific to the context of use.		identified, rather than specific to the context of use.
	Dereferencing the URI for a particular variable might lead to more		Dereferencing the URI for a particular variable might lead to more
	information about the syntax or semantics of that variable;		information about the syntax or semantics of that variable;
	specification of particular formats for this information is out of		specification of particular formats for this information is out of
	scope for this document.		scope for this document.
	To determine the URI for a given variable, the value given is used as		To determine the URI for a given variable, the value given is used as
	a base URI in reference resolution (as specified in [URI]). If the		a base URI in reference resolution (as specified in [URI]). If the
	resulting URI is still relative, the context of the link is used as		resulting URI is still relative, the context of the link is used as
	the base URI in a further resolution; see [WEB-LINKING].		the base URI in a further resolution; see [WEB-LINKING].
	For example:		For example:
	Link-Template: "/widgets/{widget_id}"		Link-Template: "/widgets/{widget_id}";
	rel="https://example.org/rel/widget";		rel="https://example.org/rel/widget";
	var-base="https://example.org/vars/"		var-base="https://example.org/vars/"
	indicates that a resource with the relation type		indicates that a resource with the relation type
	"https://example.org/rel/widget" can be found by expanding the		"https://example.org/rel/widget" can be found by expanding the
	"https://example.org/vars/widget_id" variable into the template		"https://example.org/vars/widget_id" variable into the template
	given.		given.
	If the current context of the message that the header appears within		If the current context of the message that the header appears within
	is "https://example.org/", the same information could be conveyed by		is "https://example.org/", the same information could be conveyed by
	skipping to change at line 195 ¶		skipping to change at page 5, line 10 ¶
	3. Security Considerations		3. Security Considerations
	The security consideration for the Link header field in [WEB-LINKING]		The security consideration for the Link header field in [WEB-LINKING]
	and those for URI Templates [URI-TEMPLATE] both apply.		and those for URI Templates [URI-TEMPLATE] both apply.
	4. IANA Considerations		4. IANA Considerations
	This specification enters the "Link-Template" into the Hypertext		This specification enters the "Link-Template" into the Hypertext
	Transfer Protocol (HTTP) Field Name Registry.		Transfer Protocol (HTTP) Field Name Registry.
	Field Name: Link-Template		o Field Name: Link-Template
	Status: permanent
	Specification document: [this document]		o Status: permanent
			o Specification document: [this document]
	5. Normative References		5. Normative References
	[HTTP] Fielding, R., Nottingham, M., and J. Reschke, "HTTP		[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
	Semantics", draft-ietf-httpbis-semantics-19 (work in		Ed., "HTTP Semantics", STD 97, RFC 9110,
	progress), September 2021.		DOI 10.17487/RFC9110, June 2022,
			<https://www.rfc-editor.org/info/rfc9110>.
	[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>.
	[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>.
	[STRUCTURED-FIELDS]		[STRUCTURED-FIELDS]
	Nottingham, M. and P-H. Kamp, "Structured Field Values for		Nottingham, M. and P. Kamp, "Structured Field Values for
	HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,		HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
	<https://www.rfc-editor.org/info/rfc8941>.		<https://www.rfc-editor.org/info/rfc8941>.
	[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform		[URI] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
	Resource Identifier (URI): Generic Syntax", STD 66,		Resource Identifier (URI): Generic Syntax", STD 66,
	RFC 3986, DOI 10.17487/RFC3986, January 2005,		RFC 3986, DOI 10.17487/RFC3986, January 2005,
	<https://www.rfc-editor.org/info/rfc3986>.		<https://www.rfc-editor.org/info/rfc3986>.
	[URI-TEMPLATE]		[URI-TEMPLATE]
	Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,		Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
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