Re: Protocol: control specifications.

[John McMeeking <jmcmeek@us.ibm.com>]

See comments below.

John McMeeking

"Jim Sermersheim" <jimse@novell.com> wrote on 01/13/2004 10:12:36 AM:

> John,
>
> If there were such a control specification, only servers supporting
> the control would know to return protocolError when that control is
> marked FALSE. All other servers will allow the operation to
> progress, and the undesireable results to occur.
>

True, but assuming the application had been tested with a server that
supports such a control properly, the app would not be using
criticality=FALSE.  So the app should get unavailable critical extension.

The concern was going the other way -- an application was developed and
tested on a server that supported the extension, then used with a server
that does not support it.

>
> Also, a client implementation could receive either protocolError or
> success (or other) in the resultCode of an operation containing such
> a control by two compliant servers. It may even receive these
> different results from the same server, depending on configuration
> state and control architecture.

I don't follow this part.  If the control spec says the control critcality
MUST be TRUE, and the client follows this, how would it get protocolError?
I would hope that the current control architectures allow the "control
implementation" to access criticality, as controls now certainly can be
inappropriate (must be able to return unavailable critical extension if
criticality is TRUE), and implementations should be able to return protocol
error if the control value is in error.

>
> I'm not sure that this is worth the benefit of having servers that
> 'slap the hand' of clients that don't properly populate the
> criticality field. It does seem more straght forward for servers to
> keep doing what has historically been done. That is; examine the
> control type for support and applicability, if not supported or
> innapropriate, check the criticality field and act accordingly. When
> the contol is supported and appropriate, I believe most servers do
> not even bother making any decisions (and may not even read or
> store) the criticality field.
>

Folks disagree on this ;-)  I was casting my vote.

I would suggest, then, that if we do not choose to enforce criticality,
that
"always set to TRUE, ... FALSE, or sender's choice" does not add anything
and has been the source of questions that folks have received as to what it
means
when a control is "always critical".  If the server does not enforce
criticality,
a control is, by definition, critical at sender's choice.  X.511 just has a
table
with a column labeled "recommended criticality" (critical or not critical).
Limit
the control specification guidance in 4.1.11 to:

- a recommended control criticality,

> Jim
>
>
>
> >>> John McMeeking <jmcmeek@us.ibm.com> 1/13/04 8:22:19 AM >>>
>
>
>
>
> After further discussion here, I side with Hallvard. There are likely to
> be cases where the behavior of a control is such that it really ought to
be
> marked critical because the outcome when used with a server that doesn't
> support the control is clearly undesirable. To the end user, it is little
> consolation that the application they are using is at fault because it
> neglected to mark the control critical.
>
> I haven't come up with an argument that a control must have
> criticality=FALSE to prevent similar situations, so I suggest we get rid
of
> the "criticality always set to FALSE" part.
>
> To make it clear that "criticality MUST be TRUE" is a requirement to both
> the client and server and to avoid confusion (I hope) with previous
> guidance that criticality always be set to TRUE, I suggest a specific RFC
> "MUST" clause that can ! be used in future control specifications. I
don't
> believe current control specification have such language, so there should
> be no compatibility issue. Support for a new control generally requires
> some sort of server change; support for a new control could include a
> mandatory criticality check.
>
> That leaves control criticality options as:
> - critical at senders choice, with a recommended criticality in the
control
> specification, or
> - criticality MUST be TRUE
>
> I suggest that we update protocal 4.1.11 as follows.
>
> 1) add the following text somewhere in 4.1.11:
>
> A control specification MAY state that "the control criticality MUST be
> TRUE."
> If a control is defined in this way and the sender's control criticality
> is
> FALSE, the server MUST return protocolError. If a specification does not
> state that "the control criticality MUST be TRUE" the sender's control
> criticality is used.
>
> 2) update the guidance to control ! specification writers:
>
> The specification of a control consists of:
>
> ...
>
> - a recommended control criticality, or a requirement that the control
> criticality MUST be TRUE.
>
>
> John McMeeking
>
>
> "Kurt D. Zeilenga" < Kurt@OpenLDAP.org > wrote on 01/09/2004 10:11:02 PM:
>
> > At 12:55 PM 1/9/2004, John McMeeking wrote:
> > >X.511 has a similar notion of recommended criticality.
> >
> > Similar or same? Given that one of planned uses of LDAP
> > Controls was to provide a mechanism in which additional
> > X.511 semantics could be added to LDAP in a manner which
> > would facilitate implementation of LDAP<->X.511 gateways,
> > I think the intent was for the criticality semantics to
> > be the same.
>
> Yes, I could have used "the same".
>
> >
> > X.511:
> > The criticalExtensions component provides a mechanism
> > to list a set of extensions which are critical to the
> > performance of a Direc! tory operation. If the originator
> > of the extended operation wishes to indicate that the
> > operation shall be performed with one or more extensions
> > (i.e. that performing the operation without these
> > extensions is not acceptable), it does so by setting the
> > criticalExtensions bit(s) which corresponds to the
> > extension(s). If the Directory, or some part of it, is
> > unable to perform a critical extension it returns an
> > indication of unavailableCriticalExtension (as a
> > ServiceError or PartialOutcomeQualifier). If the Directory
> > is unable to perform an extension which is not critical,
> > it ignores the presence of the extension.
> >
> > Sounds the same to me.
> >