Application-Oriented Literals in CBOR Extended Diagnostic Notation

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Table of Contents

1. Introduction

For the Concise Binary Object Representation, CBOR, Section 8 of [RFC8949] in conjunction with Appendix G of [RFC8610] 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 [I-D.ietf-core-coral] [I-D.ietf-core-href].¶

2. 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 Section 8 of [RFC8949], the diagnostic notation can notate byte strings in a number of [RFC4648] 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 (Section 5). 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.¶

3. The "cri" Extension

The application-extension identifier "cri" is used to notate a Constrained Resource Identifier literal as per [I-D.ietf-core-href].¶

The text of the literal is a URI Reference as per [RFC3986] or an IRI Reference as per [RFC3987].¶

The value of the literal is a CRI that can be converted to the text of the literal using the procedure of Section 6.1 of [I-D.ietf-core-href]. 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¶

cri'https://example.com/bottarga/shaved'

is equivalent to¶

[-4, ["example", "com"], ["bottarga", "shaved"]]

4. 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 Section 3.4.2 of [RFC8949].¶

The text of the literal is a Standard Date/Time String as per Section 3.4.1 of [RFC8949].¶

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 Appendix A of [RFC3339]), the value is a floating-point number; the value is an integer number otherwise.¶

As an example, the CBOR diagnostic notation¶

dt'1969-07-21T02:56:16Z'

is equivalent to¶

-14159024

5. IANA Considerations

IANA is requested to create a registry [[where?]] for application-extension identifiers, with the initial content shown in Table 1.¶

(Define policy; detailed template)¶

6. Security considerations

The security considerations of [RFC8949] and [RFC8610] apply.¶

Anything else meaningful to say here?¶

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.¶

Author's Address