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Internet-Draft The Concise Binary Object Representation, CBOR (RFC 8949), defines a "diagnostic notation" in order to be able to converse about CBOR data items without having to resort to binary data. ​This document specifies how to add application-oriented extensions to the diagnostic notation. It then defines two such extensions for the use of CBOR diagnostic notation with CoRAL and Constrained Resource Identifiers (draft-ietf-core-coral, draft-ietf-core-href). About This Document Status information for this document may be found at . Discussion of this document takes place on the cbor Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at . The content of this draft may preferably be distributed to a number of different documents. This is to be decided.

Introduction For the Concise Binary Object Representation, CBOR, in conjunction with defines a "diagnostic notation" in order to be able to converse about CBOR data items without having to resort to binary data. Diagnostic notation is based on JSON, with extensions for representing CBOR constructs such as binary data and tags. (Standardizing this together with the actual interchange format does not serve to create another interchange format, but enables the use of a shared diagnostic notation in tools for and documents about CBOR.) This document specifies how to add application-oriented extensions to the diagnostic notation. It then defines two such extensions for the use of CBOR diagnostic notation with CoRAL and Constrained Resource Identifiers .

Application-Oriented Extension Literals This document extends the syntax used in diagnostic notation for byte string literals to also be available for application-oriented extensions. As per , the diagnostic notation can notate byte strings in a number of base encodings, where the encoded text is enclosed in single quotes, prefixed by an identifier (>h< for base16, >b32< for base32, >h32< for base32hex, >b64< for base64 or base64url). This syntax can be thought to establish a name space, with the names "h", "b32", "h32", and "b64" taken, but other names being unallocated. The present specification defines additional names for this namespace, which we call application-extension identifiers. For the quoted string, the same rules apply as for byte strings. In particular, the escaping rules of JSON strings are applied equivalently for application-oriented extensions, e.g., \\ stands for a single backslash and \' stands for a single quote. An application-extension identifier is a name consisting of a lower-case ASCII letter (a-z) and zero or more additional ASCII characters that are either lower-case letters or digits (a-z0-9). Application-extension identifiers are registered in a registry (). Prefixing a single-quoted string, an application-extension identifier is used to build an application-oriented extension literal, which stands for a CBOR data item the value of which is derived from the text given in the single-quoted string using a procedure defined in the specification for an application-extension identifier. Examples for application-oriented extensions to CBOR diagnostic notation can be found in the following sections.

The "cri" Extension The application-extension identifier "cri" is used to notate a Constrained Resource Identifier literal as per . The text of the literal is a URI Reference as per or an IRI Reference as per . The value of the literal is a CRI that can be converted to the text of the literal using the procedure of . Note that there may be more than one CRI that can be converted to the URI/IRI given; implementations are expected to favor the simplest variant available and make non-surprising choices otherwise. As an example, the CBOR diagnostic notation is equivalent to

The "dt" Extension The application-extension identifier "dt" is used to notate a date/time literal that can be used as an Epoch-Based Date/Time as per . The text of the literal is a Standard Date/Time String as per . The value of the literal is a number representing the result of a conversion of the given Standard Date/Time String to an Epoch-Based Date/Time. If fractional seconds are given in the text (production time-fraction in ), the value is a floating-point number; the value is an integer number otherwise. As an example, the CBOR diagnostic notation is equivalent to

IANA Considerations IANA is requested to create a registry [[where?]] for application-extension identifiers, with the initial content shown in . Initial Content of application extension identifier registry

application-extension identifier	description	reference
h	Reserved	RFC8949
b32	Reserved	RFC8949
h32	Reserved	RFC8949
b64	Reserved	RFC8949
cri	Constrained Resource Identifier	RFCthis
dt	Date/Time	RFCthis

(Define policy; detailed template)

Security considerations The security considerations of and apply. Anything else meaningful to say here?

References Normative References This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. Universität Bremen TZI Fraunhofer SIT The Constrained Resource Identifier (CRI) is a complement to the Uniform Resource Identifier (URI) that serializes the URI components in Concise Binary Object Representation (CBOR) instead of a sequence of characters. This simplifies parsing, comparison and reference resolution in environments with severe limitations on processing power, code size, and memory size. The present revision -10 of this draft contains an experimental addition that allows representing user information (https://alice@chains.example) in the URI authority component. This feature lacks test vectors and implementation experience at the time of writing and requires discussion. This document defines a date and time format for use in Internet protocols that is a profile of the ISO 8601 standard for representation of dates and times using the Gregorian calendar. 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 document defines a new protocol element, the Internationalized Resource Identifier (IRI), as a complement of the Uniform Resource Identifier (URI). An IRI is a sequence of characters from the Universal Character Set (Unicode/ISO 10646). A mapping from IRIs to URIs is defined, which means that IRIs can be used instead of URIs, where appropriate, to identify resources. The approach of defining a new protocol element was chosen instead of extending or changing the definition of URIs. This was done in order to allow a clear distinction and to avoid incompatibilities with existing software. Guidelines are provided for the use and deployment of IRIs in various protocols, formats, and software components that currently deal with URIs. Informative References This document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK] ARM The Constrained RESTful Application Language (CoRAL) defines a data model and interaction model as well as a compact serialization formats for the description of typed connections between resources on the Web ("links"), possible operations on such resources ("forms"), and simple resource metadata.

Acknowledgements The concept of application-oriented extensions to diagnostic notation, as well as the definition for the "dt" extension were inspired by the CoRAL work by Klaus Hartke.