Re: [art] Fwd: New Version Notification for draft-rivest-sexp-06.txt

[Marc Petit-Huguenin <[e-mail]>]

Hi Erik,

See inline my response to one of your comment related to the ABNF, as I wrote it.

On 4/17/24 4:20 AM, Erik Auerswald wrote:
> Hi,
> 
> On Wed, Apr 17, 2024 at 01:02:54AM -0400, Donald Eastlake wrote:
>>
>> An improved version has been posted responding to many of the comments
>> that have been made.
> 
> Thanks for the update!
> 
> I'd like to make a few comments from a quick glance:
> 
> 1. It seems to me as if the second example of an S-expression given in
>    section 6.1 does not match the ABNF given in section 7.1.

You are right.  I wrote the ABNF by looking exclusively at the text, ignoring both the BNF and the examples in -00, a common practice when reading a standard with too many discrepancies.

Section 4.1 does not talk about display-hints at all, which is why they do not appear in the ABNF.  But they do appear in the BNF.  Another issue that was bothering me is that the memory representation in section 8.2 is not isomorphic to both the canonical or the basic transport (converting from the memory representation would lose information).  That's reasons enough IMO to update the ABNF.

> 
> 2. It seems to me as if the "canonical" representation is not uniquely
>    defined, because -- according to the examples -- it may use "display
>    hints", but it is not specified if the "default" display hint
>    ("application/octet-stream" in the current draft) may be given or not.
> 
> 3. Since the "default" display hint may be application-specific, omitting
>    it from the "canonical" representation, as shown in two of the three
>    examples in section 6.1, seems to possibly change the "canonical"
>    S-expression value when changing applications.
> 
> 4. The value of the "default" display hint has changed over the versions
>    of this draft.  I'd expect this to cause interoperability problems
>    if any new implementation were to emerge, and if any existing
>    implementation would already implement the original default display
>    hint.
> 
> 5. I'd say that this S-expression format has no similarities to
>    Bernstein's "netstrings", i.e., the length of a general S-expression
>    is not given up front.  Giving the complete length up front is the
>    one special property provided by netstrings.  Thus I'd say that the
>    last sentence of the first paragraph of section 1.1 is misleading.
> 
> Best regards,
> Erik
> 
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-- 
Marc Petit-Huguenin
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