ietf-nntp Wildmats

Clive D.W. Feather clive at demon.net
Tue Mar 13 03:04:54 PST 2001


Charles Lindsey said:
>> If we do this, then I recommend that we ban backslash entirely in 
>> wildmats, including in [...] sets. This allows them to be used in the 
>> future if we ever need an escape mechanism and in the meantime 
>> eliminates some potential confusion.
> 
> If you ban backslash, then there are other candidates for banning too,
> such as comma which you mention later on. I think it would be simpler
> just to specify those characters which you DO allow, with a NOTE to the
> effect that wildmats are for matching newsgroup-names, and the allowed
> characters reflect that.

I disagree. We don't specify the valid characters in newsgroup names
either. We should leave wildmat as wide as possible. Basically comma and
backslash should be banned but nothing else.

>> Which reminds me: *somewhere* we need text along the lines of:
> 
>>     If a parameter that is specified as a wildmat does not meet the
>>     syntax of 5.1.1, the NNTP server MAY place some interpretation on it
>>     (not specified by this document) or otherwise MUST generate a 501
>>     response.
> 
> I think what you say is that extensions to this standard MAY extend the
> list of allowed characters or augment the syntax in a backward-compatible
> fashion so as to allow the use of wildmats in other contexts, in which
> case the extended syntax MAY be used even when matching newsgroups (though
> it would not cause anything new to be matched). The only extension likely
> to want to do this is XPAT, which is deligthfully silent on this issue so
> far.

Um, something like that.

>>>>  5.1.2 Formalised syntax

> I think it was a useful exercise to demonstrate that your original method
> was better.

Agreed.

>>>>  If the first char in a range has a higher code than the second one, the
>>>>  characters represented by the range are determined by the implementation.
>>>>  This must be done in a consistent manner, so that, for example,
>>>>  "[d-a],[^d-a]" will match every possible character.

>> We had this discussion previously. The consensus was that all ranges 
>> should match exactly one character, and that such ranges were allowed 
>> but had no definition of which characters matched. That is, the existing 
>> wording.
> 
>> The only question left is the one I asked: do we require consistency or 
>> not ?
> 
> Hmm! I would prefer disallowing it. But if the consensus was otherwise,
> then I suppose consistency is a good thing. Would it be possible to say
> that [d-a] was allowed syntactically, but would never match anything. In
> that case it would still happen that "[d-a],[^d-a]" would match
> everything.

I think you misunderstand me. The consensus from last time was that "[d-a]"
would match exactly one character. That is, there exists a legitimate set
that it's equivalent to.

I'd like opinions (not just yours) on the following choices:

(1) Within a set, "d-a" is ignored. This means that:
    * "[d-a]" never matches anything
    * "[^d-a]" is equivalent to "?"
    * "[d-ax-z]" is equivalent to "[x-z]"
    * "[^d-ax-z]" is equivalent to "[^x-z]"
(2) Within a set, "d-a" is converted by the implementation to some
    (legal) set (not necessarily a range), converting it the same way
    each time. This means that:
    * "[d-a]", "[d-ad-a]", and "[d-a],[d-a]" all match the same set
    * "[d-a],[^d-a]" matches every possible one-character string
    * nothing matches both "[d-a]" and "[^d-a]"
    * "[d-ax-z],[^d-ax-z]" also matches every possible one-character string
    * nothing matches both "[d-ax-z]" and "[^d-ax-z]"
    * "[d-ax-z]" definitely matches "x", "y", and "z"
(3) Within a set, "d-a" causes the entire set contents (including the "^")
    to be replaced by an arbitrary set of characters that may differ each
    time it occurs. This means that:
    * "[d-a]", "[d-ad-a]", and "[d-a],[d-a]" might all match different sets
    * "[d-a],[^d-a]" might not match some one-character strings
    * something could match both "[d-a]" and "[^d-a]"
    * "[d-ax-z]" might not match "x"

-- 
Clive D.W. Feather  | Work:  <clive at demon.net>   | Tel:  +44 20 8371 1138
Internet Expert     | Home:  <clive at davros.org>  | Fax:  +44 20 8371 1037
Demon Internet      | WWW: http://www.davros.org | DFax: +44 20 8371 4037
Thus plc            |                            | Mobile: +44 7973 377646 



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