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REST API Media Types
draft-ietf-httpapi-rest-api-mediatypes-02

Document Type Active Internet-Draft (httpapi WG)
Author Roberto Polli
Last updated 2022-09-07
Replaces draft-polli-rest-api-mediatypes
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draft-ietf-httpapi-rest-api-mediatypes-02
HTTPAPI                                                         R. Polli
Internet-Draft     Digital Transformation Department, Italian Government
Intended status: Informational                          7 September 2022
Expires: 11 March 2023

                          REST API Media Types
               draft-ietf-httpapi-rest-api-mediatypes-02

Abstract

   This document registers the following media types used in APIs on the
   IANA Media Types registry: application/schema+json, application/
   schema-instance+json, application/openapi+json, and application/
   openapi+yaml.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-httpapi-rest-api-
   mediatypes/.

   Discussion of this document takes place on the HTTPAPI Working Group
   mailing list (mailto:httpapi@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/httpapi/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/httpapi/.  Working Group
   information can be found at https://datatracker.ietf.org/wg/httpapi/
   about/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ietf-wg-httpapi/mediatypes/labels/rest-api.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on 11 March 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Media Type registrations  . . . . . . . . . . . . . . . . . .   3
     2.1.  The OpenAPI Media Types . . . . . . . . . . . . . . . . .   3
       2.1.1.  Media Type application/openapi+json . . . . . . . . .   4
       2.1.2.  Media Type application/openapi+yaml . . . . . . . . .   5
     2.2.  JSON Schema Media Types . . . . . . . . . . . . . . . . .   6
       2.2.1.  The "$schema" Keyword . . . . . . . . . . . . . . . .   6
       2.2.2.  Identifying a Schema via a Media Type Parameter . . .   7
       2.2.3.  Linking to a Schema . . . . . . . . . . . . . . . . .   8
       2.2.4.  Fragment Identifiers  . . . . . . . . . . . . . . . .   8
       2.2.5.  Media Type application/schema+json  . . . . . . . . .   9
       2.2.6.  Media Type application/schema-instance+json . . . . .  10
   3.  Interoperability Considerations . . . . . . . . . . . . . . .  11
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .  12
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  14
   FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Change Log  . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
     Since -00 . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   OpenAPI Specification [oas] version 3 and above is a consolidated
   standard for describing HTTP APIs using the JSON [JSON] and YAML
   [YAML] data format.

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   YAML media type registration is addressed in [YAML-MEDIATYPES], which
   provides interoperability and security considerations.

   To increase interoperability when processing API specifications and
   leverage content negotiation mechanisms when exchanging OpenAPI
   Specification resources this specification register the following
   media-types: application/schema+json, application/schema-
   instance+json, application/openapi+json and application/openapi+yaml.

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.  These words may also appear in this
   document in lower case as plain English words, absent their normative
   meanings.

   This document uses the Augmented BNF defined in [RFC5234] and updated
   by [RFC7405].

   The terms "content", "content negotiation", "resource", and "user
   agent" in this document are to be interpreted as in [SEMANTICS].

2.  Media Type registrations

   This section describes the information required to register the above
   media types according to [MEDIATYPE]

2.1.  The OpenAPI Media Types

   The OpenAPI Specification Media Types convey OpenAPI document (OAS)
   files as defined in [oas] for version 3.0.0 and above.

   Those files can be serialized in [JSON] or [YAML].  Since there are
   multiple OpenAPI Specification versions, those media-types support
   the version parameter.

   The following examples conveys the desire of a client to receive an
   OpenAPI Specification resource preferably in the following order:

   1.  openapi 3.1 in YAML

   2.  openapi 3.0 in YAML

   3.  any openapi version in json

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   Accept: application/openapi+yaml;version=3.1,
           application/openapi+yaml;version=3.0;q=0.5,
           application/openapi+json;q=0.3

2.1.1.  Media Type application/openapi+json

   The following information serves as the registration form for the
   application/openapi+json media type.

   Type name:  application

   Subtype name:  openapi+json

   Required parameters:  None

   Optional parameters:  version; unrecognized parameters should be
      ignored

   Encoding considerations:  Same as [JSON]

   Security considerations:  see Section 4 of this document

   Interoperability considerations:  None

   Published specification:  this document

   Applications that use this media type:  HTTP

   Fragment identifier considerations:  Same as for application/json
      [JSON]

   Additional information:

   *  Deprecated alias names for this type: n/a

   *  Magic number(s): n/a

   *  File extension(s): json

   *  Macintosh file type code(s): n/a

   Person and email address to contact for further information:  See Aut
      hors' Addresses section.

   Intended usage:  COMMON

   Restrictions on usage:  None.

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   Author:  See Authors' Addresses section.

   Change controller:  n/a

2.1.2.  Media Type application/openapi+yaml

   The following information serves as the registration form for the
   application/openapi+yaml media type.

   Type name:  application

   Subtype name:  openapi+yaml

   Required parameters:  None

   Optional parameters:  version; unrecognized parameters should be
      ignored

   Encoding considerations:  See [YAML-MEDIATYPES]

   Security considerations:  see Section 4 of [YAML-MEDIATYPES]

   Interoperability considerations:  see Section 3 of [YAML-MEDIATYPES]

   Published specification:  this document

   Applications that use this media type:  HTTP

   Fragment identifier considerations:  Same as for application/json
      [JSON]

   Additional information:

   *  Deprecated alias names for this type: n/a

   *  Magic number(s): n/a

   *  File extension(s): yaml, yml

   *  Macintosh file type code(s): n/a

   Person and email address to contact for further information:  See Aut
      hors' Addresses section

   Intended usage:  COMMON

   Restrictions on usage:  None.

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   Author:  See Authors' Addresses section

   Change controller:  n/a

2.2.  JSON Schema Media Types

   JSON Schema is a declarative domain-specific language for validating
   and annotating JSON documents (see [jsonschema]).

   This document registers the media types associated with JSON Schema.

   There are many dialects of JSON Schema in wide use today.  The JSON
   Schema maintainers have released several dialects including draft-04,
   draft-07, and draft 2020-12.  There are also several third-party JSON
   Schema dialects in wide use including the ones defined for use in
   OpenAPI and MongoDB.

   This specification defines little more than how to identify the
   dialect while leaving most of the semantics of the schema up to the
   dialect to define.  Clients MUST use the following order of
   precedence for determining the dialect of a schema.

   *  The $schema keyword (Section 2.2.1)

   *  The "schema" media type parameter (Section 2.2.2)

   *  The context of the enclosing document.  This applies only when a
      schema is embedded within a document.  The enclosing document
      could be another schema in the case of a bundled schema or it
      could be another type of document that includes schemas such as an
      OpenAPI document.

   *  If none of the above result in identifying the dialect, client
      behavior is undefined.

2.2.1.  The "$schema" Keyword

   The $schema keyword is used as a JSON Schema dialect identifier.  The
   value of this keyword MUST be a URI [RFC3986].  This URI SHOULD
   identify a meta-schema that can be used to validate that the schema
   is syntactically correct according to the dialect the URI identifies.

   The dialect SHOULD define where the $schema keyword is allowed and/or
   recognized in a schema, but it is RECOMMENDED that dialects do not
   allow the schema to change within the same Schema Resource.

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2.2.2.  Identifying a Schema via a Media Type Parameter

   Media types MAY allow for a schema media type parameter, to support
   content negotiation based on schema identifier (see Section 12 of
   [SEMANTICS]).  The schema media type parameter MUST be a URI-
   reference [RFC3986].

   The schema parameter identifies a schema that provides semantic
   information about the resource the media type represents.  When using
   the application/schema+json media type, the schema parameter
   identifies the dialect of the schema the media type represents.

   The schema URI is opaque and SHOULD NOT automatically be
   dereferenced.  Since schema doesn't necessarily point to a network
   location, the "describedby" relation is used for linking to a
   downloadable schema.

   The following is an example of content negotiation where a user agent
   can accept two different versions of a "pet" resource.  Each resource
   version is identified by a unique JSON Schema.

   Request:

   NOTE: '\' line wrapping per RFC 8792

   GET /pet/1234 HTTP/1.1
   Host: foo.example
   Accept: \
     application/schema-instance+json; schema="/schemas/v2/pet"; q=0.2, \
     application/schema-instance+json; schema="/schemas/v1/pet"; q=0.1

   Response:

   NOTE: '\' line wrapping per RFC 8792

   HTTP/1.1 200 Ok
   Content-Type: \
     application/schema-instance+json; schema="/schemas/v2/pet"

   {
     "petId": "1234",
     "name": "Pluto",
     ...
   }

   In the following example, the user agent is able to accept two
   possible dialects of JSON Schema and the server replies with the
   latest one.

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   Request:

   NOTE: '\' line wrapping per RFC 8792

   GET /schemas/v2/pet HTTP/1.1
   Host: foo.example
   Accept: application/schema+json; \
               schema="https://json-schema.org/draft/2020-12/schema", \
           application/schema+json; \
               schema="http://json-schema.org/draft-07/schema#"

   Response:

   NOTE: '\' line wrapping per RFC 8792

   HTTP/1.1 200 OK
   Content-Type: \
     application/schema+json; \
         schema="https://json-schema.org/draft/2020-12/schema"

   {
     "$id": "https://json-schema.org/draft/2020-12/schema",
     "$schema": "https://json-schema.org/draft/2020-12/schema",
     ...
   }

2.2.3.  Linking to a Schema

   It is RECOMMENDED that instances described by a schema provide a link
   to a downloadable JSON Schema using the link relation describedby, as
   defined by Linked Data Protocol 1.0, section 8.1
   [W3C.REC-ldp-20150226].

   In HTTP, such links can be attached to any response using the Link
   header [LINK].

   Link: <https://example.com/my-hyper-schema#>; rel="describedby"

2.2.4.  Fragment Identifiers

   Two fragment identifier structures are supported: JSON Pointers and
   plain-names.

   The use of JSON Pointers as URI fragment identifiers is described in
   [JSON-POINTER].  Fragment identifiers that are empty or start with a
   /, MUST be interpreted as JSON Pointer fragment identifiers.

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   Plain-name fragment identifiers reference locally named locations in
   the document.  The dialect determines how plain-name identifiers map
   to locations within the document.  All fragment identifiers that do
   not match the JSON Pointer syntax MUST be interpreted as plain name
   fragment identifiers.

2.2.5.  Media Type application/schema+json

   The application/schema+json media type represents JSON Schema.  This
   schema can be an official dialect or a third-party dialect.  The
   following information serves as the registration form for the
   application/schema+json media type.

   Type name:  application

   Subtype name:  schema+json

   Required parameters:  N/A

   Optional parameters:

   *  schema: A URI identifying the JSON Schema dialect the schema was
      written for.  If this value conflicts with the value of the
      $schema keyword in the schema, the $schema keyword takes
      precedence.

   Encoding considerations:  Same as [JSON]

   Security considerations:  See the "Security Considerations" section
      of [jsonschema]

   Interoperability considerations:  See the "General Considerations"
      section of [jsonschema]

   Published specification:  this document

   Applications that use this media type:  JSON Schema is used in a
      variety of applications including API servers and clients that
      validate JSON requests and responses, IDEs that valid
      configuration files, databases that store JSON, and more.

   Fragment identifier considerations:  See Section 2.2.4

   Additional information:

   *  Deprecated alias names for this type: N/A

   *  Magic number(s): N/A

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   *  File extension(s): json, schema.json

   *  Macintosh file type code(s): N/A

   Person and email address to contact for further information:  See Aut
      hors' Addresses section.

   Intended usage:  COMMON

   Restrictions on usage:  N/A.

   Author:  See Authors' Addresses section.

   Change controller:  N/A

2.2.6.  Media Type application/schema-instance+json

   The application/schema-instance+json media type is an extension of
   the [JSON] media type that just adds the schema media type parameter
   and fragment identification.  The following information serves as the
   registration form for the application/schema-instance+json media
   type.

   Type name:  application

   Subtype name:  schema-instance+json

   Required parameters:  N/A

   Optional parameters:

   *  schema:  A URI identifying a JSON Schema that provides semantic
         information about this JSON representation.

   Encoding considerations:  Same as [JSON]

   Security considerations:  Same as [JSON]

   Interoperability considerations:  Same as [JSON]

   Published specification:  this document

   Applications that use this media type:  JSON Schema is used in a
      variety of applications including API servers and clients that
      validate JSON requests and responses, IDEs that valid
      configuration files, databases that store JSON, and more.

   Fragment identifier considerations:  See Section 2.2.4

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   Additional information:

   *  Deprecated alias names for this type: N/A

   *  Magic number(s): N/A

   *  File extension(s): json

   *  Macintosh file type code(s): N/A

   Person and email address to contact for further information:  See Aut
      hors' Addresses section.

   Intended usage:  COMMON

   Restrictions on usage:  N/A

   Author:  See Authors' Addresses section.

   Change controller:  N/A

3.  Interoperability Considerations

   Interoperability requirements for media type registrations are
   discussed in Section 4.6 of [MEDIATYPE]. and Section 3 of
   [YAML-MEDIATYPES].

4.  Security Considerations

   Security requirements for media type registrations are discussed in
   Section 4.6 of [MEDIATYPE]. and Section 4 of [YAML-MEDIATYPES].

5.  IANA Considerations

   This specification defines the following new Internet media types
   [MEDIATYPE].

   IANA has updated the "Media Types" registry at
   https://www.iana.org/assignments/media-types
   (https://www.iana.org/assignments/media-types) with the registration
   information provided below.

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   +==================================+================================+
   | Media Type                       | Section                        |
   +==================================+================================+
   | application/openapi+yaml         | Section 2.1.2 of this document |
   +----------------------------------+--------------------------------+
   | application/openapi+json         | Section 2.1.1 of this document |
   +----------------------------------+--------------------------------+
   | application/schema+json          | Section 2.2.5 of this document |
   +----------------------------------+--------------------------------+
   | application/schema-              | Section 2.2.6 of this document |
   | instance+json                    |                                |
   +----------------------------------+--------------------------------+

                                  Table 1

6.  Normative References

   [JSON]     Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/rfc/rfc8259>.

   [JSON-POINTER]
              Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/rfc/rfc6901>.

   [jsonschema]
              Wright, A., Andrews, H., Hutton, B., and G. Dennis, "JSON
              Schema Core", 28 January 2020,
              <https://json-schema.org/specification.html>.

   [LINK]     Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,
              <https://www.rfc-editor.org/rfc/rfc8288>.

   [MEDIATYPE]
              Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/rfc/rfc6838>.

   [oas]      Darrel Miller, Jeremy Whitlock, Marsh Gardiner, Mike
              Ralphson, Ron Ratovsky, and Uri Sarid, "OpenAPI
              Specification 3.0.0", 26 July 2017.

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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3986>.

   [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/rfc/rfc5234>.

   [RFC7405]  Kyzivat, P., "Case-Sensitive String Support in ABNF",
              RFC 7405, DOI 10.17487/RFC7405, December 2014,
              <https://www.rfc-editor.org/rfc/rfc7405>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [SEMANTICS]
              Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
              Semantics", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-semantics-19, 12 September 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              semantics-19>.

   [W3C.REC-ldp-20150226]
              Malhotra, A., Ed., Arwe, J., Ed., and S. Speicher, Ed.,
              "Linked Data Platform 1.0", W3C REC REC-ldp-20150226, W3C 
              REC-ldp-20150226, 26 February 2015,
              <https://www.w3.org/TR/2015/REC-ldp-20150226/>.

   [YAML]     Oren Ben-Kiki, Clark Evans, and Ingy dot Net, "YAML Ain't
              Markup Language Version 1.2", 1 October 2021,
              <https://yaml.org/spec/1.2/spec.html>.

   [YAML-MEDIATYPES]
              Polli, R., Wilde, E., and E. Aro, "YAML Media Type", Work
              in Progress, Internet-Draft, draft-ietf-httpapi-yaml-
              mediatypes-03, 5 August 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpapi-
              yaml-mediatypes-03>.

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Appendix A.  Acknowledgements

   Thanks to Erik Wilde and David Biesack for being the initial
   contributors of this specification, and to Darrel Miller and Rich
   Salz for their support during the adoption phase.

   In addition to the people above, this document owes a lot to the
   extensive discussion inside and outside the HTTPAPI workgroup.  The
   following contributors have helped improve this specification by
   opening pull requests, reporting bugs, asking smart questions,
   drafting or reviewing text, and evaluating open issues:

   Eemeli Aro, Tina (tinita) Mueller, Ben Hutton and Jason Desrosiers.

FAQ

   Q: Why this document?  After all these years, we still lack a proper
      media-type for REST related document types.  This has some
      security implications too (eg. wrt on identifying parsers or treat
      downloads)

Change Log

   RFC EDITOR PLEASE DELETE THIS SECTION.

Since -00

   *  Split YAML registrations in a separate I-D.

Author's Address

   Roberto Polli
   Digital Transformation Department, Italian Government
   Italy
   Email: robipolli@gmail.com

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