Re: [Cbor] [Technical Errata Reported] RFC8610 (6527)

Barry Leiba <barryleiba@computer.org> Tue, 13 April 2021 13:07 UTC

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From: Barry Leiba <barryleiba@computer.org>
Date: Tue, 13 Apr 2021 09:07:18 -0400
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To: Carsten Bormann <cabo@tzi.org>
Cc: cbor@ietf.org, smbarte2@illinois.edu, Henk Birkholz <henk.birkholz@sit.fraunhofer.de>, christoph.vigano@uni-bremen.de, "Murray S. Kucherawy" <superuser@gmail.com>, Francesca Palombini <francesca.palombini@ericsson.com>, =?UTF-8?Q?Christian_Ams=C3=BCss?= <christian@amsuess.com>
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Subject: Re: [Cbor] [Technical Errata Reported] RFC8610 (6527)
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Indeed, this one screams "Hold for Document Update" to me, as it's
something that rather more complex.  It's clear that this isn't just
an "oops" when we published, but, rather a (valid) rethinking that
needs broader review and consensus on the solution.

Barry

On Tue, Apr 13, 2021 at 8:13 AM Carsten Bormann <cabo@tzi.org> wrote:
>
> On 2021-04-11, at 18:51, Carsten Bormann <cabo@tzi.org> wrote:
> >
> > However, there is one omission in the ABNF: the \u syntax, which is somewhat complicated in JSON because it is followed either by 4 hex digits that are not in the range d800 to dfff or by 4 hex digits in the range d800 to dbff, another \u, and four more hex digits dc00 to dfff.
> > Someone needs to sit down and write up the ABNF for that (or find some ABNF that already has done the work).
>
> I was too lazy to find some ABNF so I wrote my own.
>
> 76c76,84
> < SESC = "\" (%x20-7E / %x80-10FFFD)
> ---
> >
> > SESC = "\" ( %x22 / %x2F / %x5C / %x62 / %x66 / %x6E / %x72 / %x74 /
> >              (%x75 hexchar) )
> >
> > hexchar = ((DIGIT / "A"/"B"/"C" / "E"/"F") 3HEXDIG) /
> >            ("D"
> >             (( %x30-37 2HEXDIG ) /
> >              (("8"/"9"/"A"/"B") 2HEXDIG "\" %x75 "D"
> >               ("C"/"D"/"E"/"F") 2HEXDIG )))
> 79c87
> < BCHAR = %x20-26 / %x28-5B / %x5D-10FFFD / SESC / CRLF
> ---
> > BCHAR = %x20-26 / %x28-5B / %x5D-10FFFD / SESC / "\'" / CRLF
>
>
> The second change is necessary as SESC is now narrowly restricted to the escape combinations that JSON allows in text strings, and \' is not among those.
>
> You can play with this changed grammar in cddlc version 0.0.3 (`gem update` if needed).
>
> > I’m not sure this update should all be put into an errata item; maybe we should pursue writing this up in a document that updates RFC 8610 that could then also add a less unwieldy syntax for non-BMP code points such as the ubiquitous \u{…}.
>
> I’m still not entirely sure we want to handle this as a bog-standard errata item.
> Opinions welcome.
>
> Grüße, Carsten
>