[Cbor] tag 24, CBOR sequence and non-CBOR sequence

[Laurence Lundblade <[e-mail]>]

Here’s some example of CBOR sequence (e.g., application/cbor-seq) and CBOR that is not a sequence (e.g., application/cbor)

0x00 
This is a legal sequence or non-sequence

0x00 0x00
This is a legal sequence, but not non-sequence. A non-sequence can contain only one data item, this contains two.

0x82 0x00 0x00
This is a legal sequence or non-sequence. It is how you encode two zeros as a non-sequence.

Looks to me that tag 24 cannot contain a CBOR sequence. It says “a data item”. The use of “a” implies one data item and thus not a sequence. That means a decoder should always consider a sequence in the contents of a tag 24 invalid.

This seems overly restrictive and unfortunate to me.  Would it be wrong for a generic decoder to allow this?

The wording for tag 55799 avoids the issue of sequence or not.


Technically, it seems that something labeled application/cbor or in a file named foo.cbor can’t contain the CBOR 0x00 0x00 because it is not a legal non-sequence. That might implies a generic decoder should have a sequence mode and a non-sequence mode. In practice this doesn’t seem like a very useful restriction. What is useful is whether the encoded CBOR is legal for the protocol being implemented.


From what I’ve experienced, it seems easier if everything is just a CBOR sequence and no distinction is made. Individual CBOR protocols can decide on their own structure either deciding to bind things together in an array or not. Am I missing something?

LL