Re: draft-ietf-ldapbis-protocol - controls

Mark Ennis wrote:
> As indicated in the message Jim referenced, our server will ignore the 
> criticality flag of a control it recognises. However, this does not 
> entirely address the issue Howard raised.

> In a distributed environment, a server receiving a request may need to 
> chain this request to a number of other servers, where the support of 
> various controls in the different servers may be different. Where a 
> given server receiving a chained request does not support a control, it 
> will base its processing decision on the criticality of the control. So 
> even if the server which received the request from the client can 
> support a given control, the control will potentially be ignored for 
> some part of the result set. This results in the effective behaviour of 
> the server, which received the original request from the client, 
> ignoring the non-critical control for some contexts, even though it does 
> support the control. This is the way our server effectively behaves.

Yes, exactly. If we persist with this mandate that servers return errors 
for recognized, unusable non-critical controls, and tell client writers 
to prepare for these error cases, we will have clients relying on these 
error returns when the result is in fact unreliable. That is clearly a 
broken spec.

> The only way around this, at present, would seem to be to force all the 
> controls in a chained request to be critical, which would seem to be 
> counter to the client's request that the processing of a non-critical 
> control is optional.

Right.
> 
> Our policy is to handle controls, in general, in the way John McMeeking 
> described, which is to ignore unsupported and inapropriate non-critical 
> controls.

Please, we're all using the word "appropriate" in these responses but 
not all with same meaning. I believe your response and John's response 
are the more liberal interpretation, not "appropriate as defined by the 
control's specification", but it would be best to be clear and explicit.
> 
> - Mark.
> 
> Jim Sermersheim wrote:
> 
>>> From another vendor:
>>
>> http://www.openldap.org/lists/ietf-ldapbis/200403/msg00055.html
>>
>>
>>>>> "Jim Sermersheim" <[email protected]> 3/29/05 5:08:37 PM >>>
>>
>>
>>
>> Our implementations do this:
>>  
>> Is the control recognized and appropriate (as specified) for the 
>> operation?
>>    Yes, process the operation
>>    No, Is it marked critical?
>>       Yes, fail with unavailable critical extension
>>       No, Ignore the control and process the operation
>>  
>> This has been discussed at length in the past, and consensus was that 
>> this was the original intent and that this is what should be conveyed 
>> in the new document.
>>  
>> IIRC, there were interoperability side effects of allowing 
>> "appropriate" to mean anything the server wishes it to mean.
>>  
>> Jim
>>
>>
>>>>> "Kurt D. Zeilenga" <[email protected]> 3/29/05 12:14:07 PM >>>
>>
>>
>> At 10:01 AM 3/29/2005, Jim Sermersheim wrote:
>>
>>> Appropriate means that the control specification says it can be 
>>> applied to that operation. I can add that clarification.
>>
>>
>>
>> That seems what the WG has concluded, but I still for wonder
>> if that's best. It certainly seem counter to how many
>> implementor have interpreted the RFC 2251 language, as well
>> as quite counter-intuitive to me.
>>
>> To test the waters, I implemented code in OpenLDAP 2.3beta
>> which behaves as the WG concluded. If a client asks for
>> paged results (regardless of critical), the server returns
>> unwillingToPerform if it cannot honor this control for
>> the particular search operation requested. However, this
>> is not the behavior client developers seem to expect. They
>> assume that if the client says paging is not critical
>> to them, that the server should simply ignore the control
>> if it not willing to honor the control for that operation.
>>
>> It seems they expect this behavior, not only based on how
>> they RFC 2251, but how many current servers behave today.
>> I wonder how other servers which have different capabilities
>> in different contexts behave? I understand that many servers
>> support configuration and monitoring contexts, it is likely
>> that these contexts do not support all the same capabilities
>> of DIT contexts. So, are there cases in your server
>> (or other servers you are familiar with) ignores a
>> recognized non-critical control attached to an applicable
>> request? (applicable here meaning that the technical
>> specification indicated the control was appropriate to that
>> kind of request)
>>
>> Personally, I think the logic that RFC 2251 was intending
>> was that a server should not apply non-critical controls to
>> portions of the operation. It must up front (before
>> initiating the operation) make a determination whether
>> to make use of the control or to ignore it. Once
>> it does choose to make use of the control in the operation,
>> there is no going back. This implies, for instance, that
>> if a client asks for non-critical FOO and the server
>> involves other servers in the evaluation of the operation,
>> that all the servers involved must either all provide
>> paging or none provide FOO. If the first server decides
>> to provide FOO, then it must indicate to the other servers
>> that FOO is now critical. If the first server decides
>> not to provide FOO, then it must indicate to the other
>> servers that FOO is not to be provided (e.g., remove the
>> control).
>>
>> Kurt
>>
>>
>>
>>
>>
>>
> 


-- 
   -- Howard Chu
   Chief Architect, Symas Corp.       Director, Highland Sun
   http://www.symas.com               http://highlandsun.com/hyc
   Symas: Premier OpenSource Development and Support