Re: [Cbor] Simple values 24..31 (was Re: List of not-well-formed CBOR and test vectors)

Carsten Bormann <cabo@tzi.org> Thu, 01 August 2019 06:52 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Thu, 1 Aug 2019 08:52:52 +0200
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To: Laurence Lundblade <lgl@island-resort.com>
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Subject: Re: [Cbor] Simple values 24..31 (was Re: List of not-well-formed CBOR and test vectors)
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On Aug 1, 2019, at 05:01, Laurence Lundblade <lgl@island-resort.com>; wrote:
> 
> Why wouldn’t 24 through 255 be considered unassigned and encoded 0xf8 0x18 through 0xf8 0xff?

Because we considered those values confusing, and decided to give up on 8 potential values in exchange for reducing this confusion.  See Section 2.3 of RFC 7049 (parenthesis in first paragraph on page 13).

Whether that was a particularly wise decision can be discussed.  Since we already have to check for too-low values in the second byte of 7.24, checking for 32 is not more onerous than checking for 24 (see pseudocode).  Giving up 8 values seems to be of limited concern given the number of allocations of Simple values so far.  Changing this now, however, would be a backward compatibility issue that we need to avoid.

Grüße, Carsten