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Re: Getting 2822 to Draft

2004-01-03 23:47:42

Keith Moore wrote:

The one possible big thing has to do with the ABNF in 2822. Out of either altruism or insanity, some time ago Bruce Lilly had written up changes to the ABNF in 2822 to do some cool things. On the plus side, it seems to get rid of all of the [C]FWS shift-reduce conflicts, and it is already done. On the minus side, I don't know anyone (myself included) who has gone over it with a fine tooth comb, it is a significant number of ABNF changes, and it therefore might recycle us at Proposed. I am open to suggestions on this.

I can't comment on insanity (catch-22). I decided to build a grammar-based parser because I was tired of writing (and rewriting) application-specific 822 parsers. I started a couple of months after 2822 was published, which was a big help primarily because of the formal
and explicit use of FWS and CFWS vs. 822's rather vague text.

if the new grammar accepted the same language as the old one, I'd consider it nothing more than a clarification of the spec, and a reset to Proposed would be unnecessary.

or if the only differences could be seen as minor bug fixes to the old grammar, I'd consider it a minor bug fix to the spec.

The intent is to accept the same message text as the existing 2822 grammar, modulo some minor
glitches in 2822.

IMHO simplifying the grammar and getting rid of parsing conflicts would both be highly desirable improvements. if it then becomes possible to feed the ABNF to a parser generator and generate a verifier for 2822 messages, that's a huge win.

Whether it's "simpler" is perhaps debatable. Shift/reduce conflicts are eliminated. Generating a verifier for 2822 [822/733/724/561/MIME/etc.] isn't quite as easy as feeding the ABNF to a parser generator, but it is possible to feed something quite close to the ABNF to a parser generator ( And that parser generator can be used to build a message verifier. The complete grammar (2822/822/MIME/various extensions/most of 733, 724, 561) has no unresolved shift/reduce conflicts and a single reduce/reduce conflict (due to changing grammar of the MIXER Supersedes (formerly Obsoletes) field, resolved in favor of
the current (RFC 2156) definition).

why not post the revised ABNF as an I-D so that others can go over it with a fine tooth comb? or has this already been done, and I missed it?

An earlier version of the revised ABNF has been posted to ietf-822 and the full version (with encoded-word grammar) is available at the above URI. Let the combing begin.

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