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[Json] Fwd: Inconsistency between RFC 8259 and RFC 5234

Tim Bray <tbray@textuality.com> Tue, 12 December 2017 23:55 UTC

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From: Tim Bray <tbray@textuality.com>
Date: Tue, 12 Dec 2017 23:55:54 +0000
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Subject: [Json] Fwd: Inconsistency between RFC 8259 and RFC 5234
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Ouch, I think he's right.
---------- Forwarded message ----------
From: "Dale Schumacher" <dale.schumacher@gmail.com>
Date: Dec 12, 2017 12:42 PM
Subject: Inconsistency between RFC 8259 and RFC 5234
To: "Tim Bray" <tbray@textuality.com>
Cc: "Douglas Crockford" <douglas@crockford.com>

I'm attempted to reach out to you directly, since https://www.rfc-editor.
org/info/rfc8259 (the recommended feedback channel) currently returns "RFC
8259 does not exist".

It appears that the JSON grammar makes use of two "Core" ABNF rules:

         DIGIT          =  %x30-39
                                ; 0-9

         HEXDIG         =  DIGIT / "A" / "B" / "C" / "D" / "E" / "F"


However, JSON allows both upper and lower case in Unicode escapes within a
string. In which case, the grammar for such escapes:

      char = unescaped /
          escape (
              %x22 /          ; "    quotation mark  U+0022
              %x5C /          ; \    reverse solidus U+005C
              %x2F /          ; /    solidus         U+002F
              %x62 /          ; b    backspace       U+0008
              %x66 /          ; f    form feed       U+000C
              %x6E /          ; n    line feed       U+000A
              %x72 /          ; r    carriage return U+000D
              %x74 /          ; t    tab             U+0009
              %x75 4HEXDIG )  ; uXXXX                U+XXXX


is incorrect.

If I may be permitted a recommendation, I would suggest that the JSON
grammar _not_ use the "Core" ABNF rules. Instead it could provide local
definitions such as:

      digit0-9 = %x30-39         ; 0-9

      hexdigit = digit0-9 / %x41-x46 / %x61-66


The use of "Core" ABNF rules doesn't seem to save much, in this case, and
the indirection makes it easy to overlook this inconsistency.

Thanks for your consideration,
Dale Schumacher

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