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Re: (ITS#4860) Sets' enhancement


Le Sam 10 novembre 2007 16:37, ando@sys-net.it a écrit :
>> Below I represent sets in {element1, element2} notation, to describe the
>> current behaviour (in HEAD) for slap_set_join on the '+' operation:
>> - {"One", "Two"} + {"Three", "Four"} ==> {"OneThree", "OneFour",
>> "TwoThree", "TwoFour"}
>> - {"One", "Two"} + {""} ==> {"One", "Two"}
>> - {"One", "Two"} + {NULL} ==> {"One", "Two"}
> Although sets lack a specification, I think this behavior is desirable
> in many cases: adding NULL is equivalent to adding EMPTY ("").

The problem is that {NULL} is equivalent to NULL, ie the empty set.

>> Consider the following set:
>> set="[ldap:///] + [ldap:///<searchbase>??<scope>?<filter1>] +
>> [??<scope>?<filter2>]"
>> Assuming [ldap:///<searchbase>??<scope>?<filter1>] returns a DN, this
>> works. However, if [ldap:///<searchbase>??<scope>?<filter1>] returns no
>> entries, this value is NULL. Therefore, the rest of the set becomes:
>> "[ldap:///] + {NULL} + [??<scope>?<filter2>]"
>> ...which is handed to the '+' operation in slap_set_join, to become:
>> [ldap:///??<scope>?<filter2>]
>> ...which obviously isn't valid.
> Well, it is valid: it's an URI with an EMPTY DN.

In terms of LDAP, yes, but it can cause security issues here, as the EMPTY
DN is at a higher level that any one which would have been returned by a
normal result.

>> The attached patch changes the last case of the current behaviour for
>> slap_set_join on the '+' operation. This was already the behaviour
>> before version Thu Sep 13 20:43:29 2007 UTC:
>> - {"One", "Two"} + {NULL} ==> {NULL}
> This is different from the above behavior, although it makes sense on
> its own.  Probably we need two different addition operators: one
> inclusive (NULL is equivalent to "") and one exclusive (NULL nullifies
> the concatenation).
> Comments?

No problem in having the two operators.  I just think the normal behavior
is to return NULL, has in term of sets the cartesian product A x NULL
returns NULL, not A.

Raphael Ouazana.