]> Digital Transformation Department, Italian Government

Italy robipolli@gmail.com

Applications and Real-Time HTTPAPI Internet-Draft 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 Status information for this document may be found at . Discussion of this document takes place on the HTTPAPI Working Group mailing list (), which is archived at . Subscribe at . Working Group information can be found at . Source for this draft and an issue tracker can be found at .

Introduction OpenAPI Specification version 3 and above is a consolidated standard for describing HTTP APIs using the JSON and YAML data format. YAML media type registration is addressed in , 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.

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 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 and updated by . The terms "content", "content negotiation", "resource", and "user agent" in this document are to be interpreted as in .

Media Type registrations This section describes the information required to register the above media types according to .

The OpenAPI Media Types The OpenAPI Specification Media Types convey OpenAPI document (OAS) files as defined in for version 3.0 and above. Those files can be serialized in or . Since there are multiple OpenAPI Specification versions, those media types support the version parameter. The following example 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

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 "application/json"

Security considerations:

See of this document, "application/json" and

Interoperability considerations:

See "application/json" and

Published specification:

this document,

Applications that use this media type:

HTTP

Fragment identifier considerations:

or the specific version of the OpenAPI document.

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 Authors' Addresses section.

Intended usage:

COMMON

Restrictions on usage:

None.

Author:

See Authors' Addresses section.

Change controller:

n/a

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:

Same as "+yaml" Structured Syntax Suffix

Security considerations:

See of this document, "+yaml" Structured Syntax Suffix and

Interoperability considerations:

See "+yaml" Structured Syntax Suffix and

Published specification:

Applications that use this media type:

HTTP

Fragment identifier considerations:

or the specific version of the OpenAPI document.

Additional information:

• Deprecated alias names for this type: n/a
• Magic number(s): n/a
• File extension(s): Same as "application/yaml"
• Macintosh file type code(s): n/a

Person and email address to contact for further information:

See Authors' Addresses section

Intended usage:

COMMON

Restrictions on usage:

None.

Author:

See Authors' Addresses section

Change controller:

n/a

JSON Schema Media Types JSON Schema is a declarative domain-specific language for validating and annotating JSON documents (see ). 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 ()
• The "schema" media type parameter ()
• 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.

The "$schema" Keyword The $schema keyword is used as a JSON Schema dialect identifier. The value of this keyword MUST be a URI . 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.

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 ). The schema media type parameter MUST be a URI-reference . 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: Response: 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. Request: Response:

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 . In HTTP, such links can be attached to any response using the Link header . ; rel="describedby" ]]>

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 . Fragment identifiers that are empty or start with a /, MUST be interpreted as JSON Pointer fragment identifiers. 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.

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 "application/json"

Security considerations:

See the "Security Considerations" section of

Interoperability considerations:

See the "General Considerations" section of

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

Additional information:

• Deprecated alias names for this type: N/A
• Magic number(s): N/A
• File extension(s): json, schema.json
• Macintosh file type code(s): N/A

Person and email address to contact for further information:

See Authors' Addresses section.

Intended usage:

COMMON

Restrictions on usage:

N/A.

Author:

See Authors' Addresses section.

Change controller:

N/A

Media Type application/schema-instance+json The application/schema-instance+json media type is an extension of the 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

Security considerations:

Same as

Interoperability considerations:

Same as

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

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 Authors' Addresses section.

Intended usage:

COMMON

Restrictions on usage:

N/A

Author:

See Authors' Addresses section.

Change controller:

N/A

Interoperability Considerations Interoperability requirements for media type registrations are discussed in Section 4.6 of . and .

Security Considerations Security requirements for media type registrations are discussed in Section 4.6 of . and .

General Considerations All REST API Media Types might reference nested or external resources, as well as processable information like HTML. Implementations that try to dereference or process those resource automatically might be subject to various security risks, from resource exhaustion (e.g. caused by cyclic references) to retrieval and processing of malicious code (e.g. embedded as markup language).

IANA Considerations This specification defines the following new Internet media types . IANA is asked to update the "Media Types" registry at https://www.iana.org/assignments/media-types with the registration information provided in the sections below.

Media Type	Registration Information Section
application/openapi+yaml	of this document
application/openapi+json	of this document
application/schema+json	of this document
application/schema-instance+json	of this document

Normative References JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance. Digital Transformation Department, Italian Government Axway Mozilla This document registers the application/yaml media type and the +yaml structured syntax suffix on the IANA Media Types registry, intended to be used to identify document components serialized according to the YAML specification. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] This document extends the base definition of ABNF (Augmented Backus-Naur Form) to include a way to specify US-ASCII string literals that are matched in a case-sensitive manner. Adobe Fastly greenbytes GmbH The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. This memo documents an Internet Best Current Practice. A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] This specification defines a model for the relationships between resources on the Web ("links") and the type of those relationships ("link relation types"). It also defines the serialisation of such links in HTTP headers with the Link header field. JSON Pointer defines a string syntax for identifying a specific value within a JavaScript Object Notation (JSON) document.

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) Müller, 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.