Re: [Cbor] correctness of implied top level array?

[Carsten Bormann <[e-mail]>]

Hi Laurence,

the construction you describe is different from a CBOR data item:
It is a CBOR Sequence.  You piqued me to finally write it up, see below.

More generally speaking, an encoded CBOR data item followed by residual data is a very valid construction, for instance for a piece of metadata tacked on as a header to a binary blob.  CBOR’s self-delimiting is all you need here.
The metadata part doesn’t stop to be well-formed by being followed by that binary blob.
But of course the whole thing *is* not, but still *has* a well-formed encoded CBOR data item.

Unfortunately, not very many CBOR libraries have an API that allows isolating that metadata header from its residual data.  Maybe it’s worth writing a draft about suggested API functionality as well.  (One other thing that recently came up and is supported by too few CBOR library APIs is using an already encoded CBOR data item during encoding an array, map, or Tag.)

Grüße, Carsten


Name:		draft-bormann-cbor-sequence
Revision:	00
Title:		Concise Binary Object Representation (CBOR) Sequences
Document date:	2019-02-24
Group:		Individual Submission
Pages:		8
URL:            https://www.ietf.org/internet-drafts/draft-bormann-cbor-sequence-00.txt
Status:         https://datatracker.ietf.org/doc/draft-bormann-cbor-sequence/
Htmlized:       https://tools.ietf.org/html/draft-bormann-cbor-sequence-00
Htmlized:       https://datatracker.ietf.org/doc/html/draft-bormann-cbor-sequence


Abstract:
  This document describes the Concise Binary Object Representation
  (CBOR) Sequence format and associated media type "application/cbor-
  seq".  A CBOR Sequence consists of any number of encoded CBOR data
  items, simply concatenated in sequence.

  Structured syntax suffixes for media types allow other media types to
  build on them and make it explicit that they are built on an existing
  media type as their foundation.  This specification defines and
  registers "+cbor-seq" as a structured syntax suffix for CBOR
  Sequences.