Re: (ITS#4860) Sets' enhancement

[ando@sys-net.it]

Jonathan Clarke wrote:
> Pierangelo Masarati a écrit :
>>> The patch attached corrects this problem on RE23 and HEAD for me
>>> and doesn't have any side effects on our test set. However, it
>>> may not be the "right" way - please correct if necessary!
>> It seems to work correctly, but there seems to be an easier fix: just
>> NULL out the pointer to lset/rset, respectively.  I'm patching the
>> code this way, please test if you get a chance.
> 
> Whoops - looks like I spoke too soon. After more testing, I've
> realized that the same commit this patch applied to actually changed the
> behaviour of the "+" operation in the slap_set_join() function when
> operating on empty sets, and can cause errors.
> 
> The attached proposed patch restores the original design. The difference
> is minor, but can cause slapd to hang indefinitely on some sets, like
> the one in the generic example below.
> 
> I understand an element in a set can have 3 possible states:
> 1) non-empty string (example: "cn=user,ou=people,dc=example,dc=com")
> 2) empty string (example: "", BER_BVISEMPTY)
> 3) NULL (BER_BVISNULL)
> 
> 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 ("").

> 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.

> 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 1.24.2.6 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?

p.



Ing. Pierangelo Masarati
OpenLDAP Core Team

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