Re: control combination was: Re: protocol-22 comments)

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

There is a subtle difference in the suggested text from the
current text that might be, well, a bit too subtle.

The current text talks about avoiding combinations whose
semantics are not SPECFIED while the suggested talks about
avoiding combinations which are not DEFINED.  While defined
and specified are synonyms of each other, the latter can
be viewed as implying there is a specification (e.g., document)
where the semantics are defined, the former only can be viewed
only as implying the semantics are defined (without regard
to where they are specified).

In the example of Sort+SignedOp, I think it can be argued that
the semantics are defined even though they are not explicitly
specified.  The intent of the text is not to prohibit such
combinations.

The text is intended to disallow use of combinations where the
semantics are undefined, such as a combination of PagedResults
[RFC2696] and VLV [draft-ietf-ldapext-ldapv3-vlv-08.txt].

If I reading everyone's comment well, I think we have consensus
on what we want to say but just haven't found the words that say
it well enough.  Specific suggestions welcomed.

Kurt

At 06:02 AM 5/7/2004, Hallvard B Furuseth wrote:
>Kurt D. Zeilenga writes:
>>At 08:55 PM 5/5/2004, Jim Sermersheim wrote:
>>
>>> "server MUST NOT make use of a combination of controls whose semantics
>>> are not defined (or not known to it). When such a combination of
>>> controls is encountered, it is RECOMMENDED that the server return
>>> protocolError. Otherwise behavior is undefined.
>> 
>> I dislike the wording as it could be taken as allowing the server
>> not to return an error (as opposed to suggesting which code to
>> return in this case). 
>
>I thought that was the intent, which looked reasonable to me.
>
>> How about?
>>   Controls are not to be combined (with other controls
>>   of same or different types) unless the semantics of the
>>   combination have been defined.  When an implementation
>>   (client or server) encounters a combination of controls
>>   whose semantics are not defined (or not known to that
>>   implementation), the implementation MUST treat the
>>   request as a protocol error.
>
>Sounds too strict to me.  Or at least, it can be interpreted too strict.
>For example, does that forbid the combination of the rfc2649 Operation
>Signature control with e.g. the rfc2891 Server Side Sorting control?
>Neither document explicitly states how the combination should work, but
>rfc2649 does say how to apply that control to LDAPMessages in general,
>and the combination seems to make sense to me.
>
>Also, I wonder about the combination of controls defined in different
>"standards repositories" or whatever one should call it.  If all
>controls were RFCs, one control spec could list all previously defined
>controls.  However, in the previous discussions of controls, people were
>referring to controls that I could not find RFCs for.
>
>Finally, one detail: If we stick to RFC controls, each control author
>will need to check all previous RFC controls.  It might be easy to miss
>one, and make a control combination with an obvious semantics invalid.
>We could fix that with a requirement that all LDAP control RFCs must
>have the phrase "LDAP control" in its title.  Or someone (IANA?)  could
>maintain an official list of published controls.  However, it seems
>simpler to me to allow controls that obviously do not interfere with
>each other, to be combined even if their specs do not say so.
>
>> (Note: I generalized this for both clients and servers,
>> and for requests which don't have responses.)
>
>-- 
>Hallvard