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Re: Empty IA5String
At 08:47 AM 11/9/2004, John McMeeking wrote:
>On a personal note, I've always found the notion of an zero-length value
>hard to digest. I could really use a real world example (not in the
>drafts, just to help me accept the concept) where a zero-length value has a
>different meaning than no value.
I concur.
>Otherwise, from the perspective of not breaking existing implementations
>(or applications),
Which applications would we be breaking? Is there actually
interoperability between implementor of IA5 string?
I argue that allowing empty IA5 strings might actually break
more applications.
>since zero-length values are valid for several syntaxes
>(distinguished name, octet string, IA5 string),
The problem I have with empty IA5 strings is that the
matching semantics of them is not clear, both when
comparing IA5 strings to IA5 strings, but also when
comparing IA5 strings to Directory strings.
>unless someone can make a
>good argument for zero-length values being an error in the current RFC,
>I don't think we should change it.
I believe it was the intent of designers of RFC 1274 for the
IA5String syntax to disallow empty IA5 string values. I
believe it was their intent that IA5 string values behave
in a manner consistent with X.500 directory strings.
Note that in RFC 1274 any where that a max size limit was
stated for a value, it was listed as (1..N) not (0..N).
This implies that the when no constraint was stated, that
(1..) was intended. Note also for all of the attributes
(mail, domain names, etc.) introduced of this syntax, empty
values are nonsense.
That is, it can be reasonable argued that it would be a
change to REMOVE the restriction implied by RFC 1274
(and possible other ISDs).
>John McMeeking
>
>
>owner-ietf-ldapbis@OpenLDAP.org wrote on 11/09/2004 07:19:03 AM:
>
>> Steven Legg writes:
>> >Hallvard B Furuseth wrote:
>> >>[Syntaxes] section 3.3.15 says an IA5 String may be empty.
>> >>
>> >> Why is that, when Directory String and Printable String may not?
>> >
>> > The Directory String and Printable String syntaxes derive from syntaxes
>> > in X.520 that have been constrained to have at least one character.
>> > The IA5 String syntax does not have a counterpart in X.520 so it
>doesn't
>> > need to be constrained for interoperability reasons.
>> > (...)
>> > The working group needs to decide whether to restrict IA5 String to at
>> > least one character, or to allow empty strings to compare true.
>>
>> My vote from an LDAP viewpoint would be minimal change, i.e. do not
>> disallow empty IA5 Strings.
>>
>> OTOH, if an X.500 implementor wants to support IA5 String, maybe the
>> reason why X.500 requires 1+ characters in the other string syntaxes,
>> also would make the same restriction preferable in IA5 String?
>>
>> --
>> Hallvard