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Re: [Cbor] CDDL parsing questions

Derek Atkins <derek@ihtfp.com> Thu, 18 August 2022 23:27 UTC

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Date: Thu, 18 Aug 2022 19:26:54 -0400
From: Derek Atkins <derek@ihtfp.com>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
Cc: cbor@ietf.org, Toerless Eckert <tte@cs.fau.de>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/cbor/5Uvy62X-owrnMH4ucpFbKZYwSkM>
Subject: Re: [Cbor] CDDL parsing questions
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Brian,

On Thu, August 18, 2022 7:15 pm, Brian E Carpenter wrote:
> On 18-Aug-22 23:32, Derek Atkins wrote:
>>
>>
>> On the other hand, if you see a CBOR object that decodes to:
>>
>> {
>>    1:  "foo",
>>    2:  "bar",
>>    3:  "baz"
>> }
>>
>> --- what does this mean?   You need to know what '1', '2', and '3',
>> mean.
>> Yes, the CDDL can tell you, but that assumes you're being sent the
>> object
>> you expect.
>
> And if you don't know what '3' means, should you ignore it (Postel
> principle)
> or throw an error (draft-iab-protocol-maintenance)?

Well, it depends on the underlying protocol.  You could have a map
defined as:
{
  1 : tstr,
  2 : tstr,
  ?int : tstr
}

Which means the 3: "baz" is allowed...  So yes, what do you do if you
don't know what '3' means?

Even with CDDL, however, if defined like it is above, you still don't have
an answer to that question.

-derek

-- 
       Derek Atkins                 617-623-3745
       derek@ihtfp.com             www.ihtfp.com
       Computer and Internet Security Consultant

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