Re: Empty IA5String

["Kurt D. Zeilenga" <Kurt@OpenLDAP.org>]

At 05:47 PM 11/10/2004, Steven Legg wrote:

>Kurt,
>
>Kurt D. Zeilenga wrote:
>>At 07:26 PM 11/9/2004, Steven Legg wrote:
>>
>>>For the record, I don't care whether IA5 String syntax is constrained to have
>>>at least one character. However, I increasingly believe that stringprep should
>>>be able to produce a zero-length string as input to a matching function. 
>>
>>I assume what you mean here is that you are increasing
>>believing that LDAPprep should be redesigned to accept
>>as input an zero-length string and output a zero-length
>>string for this input.
>
>No, I believe that LDAPprep should be able to output a zero-length
>string given a non-zero-length input string.

I disagree.  I believe it LDAPprep must be idempotent. That is,
        LDAPprep(LDAPprep(x)) = LDAPprep(x)
be true for all X.

>There are steps within
>LDAPPrep that remove various insignificant characters. It should be
>allowed to produce a zero-length string when it turns out that all the
>characters are insignificant.
>
>
>>This would require a major redesign of the algorithm.
>
>I don't see why.
>
>There are internal steps where an empty string is replaced by
>a single space. Just take those bits out.

Not enough to ensure idempotence.

>I think the current description of the matching semantics in [syntaxes] is
>compatible with zero-length strings being output by LDAPprep, but it would
>be worth me adding some text to point out that zero-length strings can be
>output by LDAPprep, and to formally state that two empty strings match.
>
>>If the designers of a particular matching rule desires
>>that zero-length input strings be matched as X strings
>>(where X is either a zero-length string or a particular
>>non-zero-length string, e.g. " "), the specification for
>>that rule should say something like:
>>        For non-zero-length input strings, the string
>>        is to prepared in accordance with LDAPprep.
>>        For zero-length input strings, no preparation
>>        is done.  The input string is used directly.
>>or:
>>        If the input string is zero-length, the string
>>        is matched as if X was inputted.  For input
>>        strings which are non-zero-length, the input
>>        string is prepared in accordance with LDAPprep
>>        before being compared.
>>I don't think we should undertake a redesign LDAPprep
>>to handle zero-length input string.
>
>Allowing it to produce a zero-length output string is enough.

Not enough to ensure idempotence.


>Regards,
>Steven