Re: [Cbor] hildjj/cbor-map-entries: Explicit Map datatype for CBOR, in array format

Carsten Bormann <cabo@tzi.org> Thu, 18 February 2021 17:52 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Thu, 18 Feb 2021 18:52:33 +0100
Cc: Kio Smallwood <kio@mothers-arms.co.uk>, Joe Hildebrand <hildjj@cursive.net>, cbor@ietf.org, "Dale R. Worley" <worley@ariadne.com>
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To: Laurence Lundblade <lgl@island-resort.com>
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Subject: Re: [Cbor] hildjj/cbor-map-entries: Explicit Map datatype for CBOR, in array format
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> On 2021-02-18, at 17:48, Laurence Lundblade <lgl@island-resort.com> wrote:
> 
> This is semi-related and maybe something I’m a little confused about.
> 
> My understanding is that map keys/labels can be anything in CBOR including a map or array.

Yes.  

Or a Tag!

> What to do?
> 
> - Don’t standardize any IETF protocols that use exotic map keys?

Yes.

(I don’t know what’s exotic, but on the implementation side generally any data structure that is mutable is a bit ugly as a map key.  E.g., languages where strings are mutable already need to jump through extra hoops here.  But, e.g., C++ handles maps with non-trivial keys just fine; these are certainly not exotic at all to a C++ programmer.)

> - Add text to Kio’s proposal to restrict map keys to text string, byte string and integer?

No.

(E.g., think what https://tools.ietf.org/id/draft-ietf-cbor-tags-oid-02.html#name-distinguished-name-in-cbor- would look like without tag factoring.)

> - Write some warning against this somewhere?

Should be obvious to anyone skilled in the art :-)

(The reason CBOR can do this is that many platforms can do it — so not supporting it in the format would have made CBOR less useful for native code/protocols for specific platforms.)

Grüße, Carsten