Re: [netmod] ?= ?==?utf-8?q? mandatory choice with non-presence container cas

Martin Bjorklund <mbj@tail-f.com> Tue, 25 June 2019 11:59 UTC

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Subject: Re: [netmod] =?utf-8?b?Pz0gID89PT91dGYtOD9xPyBtYW5kYXRvcnkgY2hvaWNl?= =?utf-8?q?_with_non-presence_container_cas?=
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Michal Vaško <mvasko@cesnet.cz> wrote:
> Hi Rob,
> actually, I have used model with the container TOP just for
> simplification, I have encountered the issue while implementing
> ietf-ssh-server model from its current draft. I have created the
> container "users" [1] without any "user" list instances. Now, you may
> argue that this is still not a valid use-case because there are no
> users but I only tried to satisfy the condition.

Yes, I think that this list (user) should have a "min-elements 1".  I
think that matches the intent.


/martin



> There are some users
> on the system but they are generated into the configuration on-demand
> when operational data is requested.
> 
> Regards,
> Michal
> 
> [1]
> https://tools.ietf.org/html/draft-ietf-netconf-ssh-client-server-14#page-22
> 
> On Tuesday, June 25, 2019 11:08 CEST, "Rob Wilton (rwilton)"
> <rwilton@cisco.com> wrote:
>  
> > Hi Michal,
> > 
> > It is not the printing of the data that makes it valid/invalid.
> > 
> > I don't think that your input data was ever valid, because "container
> > C" doesn't satisfy the mandatory statement because it isn't a real
> > data node in the tree - it is instantiated when required and may be
> > deleted when it is no longer required.
> > 
> > I.e. your model has been designed such that it can never be satisfied.
> > 
> > 
> > If your model was instead:
> > 
> > container TOP {
> >   leaf L {
> >     type empty;
> >   }
> >   choice A {
> >     mandatory true;
> >     container C {
> >       leaf L2 {
> >         type empty;
> >       }
> >     }
> >   }
> > }
> > 
> > 
> > Then this data is valid:
> > 
> > <TOP>
> >   <L/>
> >   <C>
> >    <L2/>
> >   </C>
> > </TOP>
> > 
> > 
> > But this data is not:
> > 
> > <TOP>
> >   <L/>
> > </TOP>
> > 
> > 
> > Nor is this, which is directly equivalent to the one above, because
> > the <C/> container doesn't really exist if it doesn't have a child
> > node present.
> > 
> > <TOP>
> >   <L/>
> >   <C/>
> > </TOP>
> > 
> > Thanks,
> > Rob
> > 
> > 
> > > -----Original Message-----
> > > From: Michal Vaško <mvasko@cesnet.cz>
> > > Sent: 24 June 2019 18:15
> > > To: Andy Bierman <andy@yumaworks.com>
> > > Cc: Rob Wilton (rwilton) <rwilton@cisco.com>om>; netmod <netmod@ietf.org>
> > > Subject: Re: [netmod] ?= mandatory choice with non-presence container
> > > cas
> > > 
> > > Hi Andy,
> > > 
> > > On Monday, June 24, 2019 19:11 CEST, Andy Bierman <andy@yumaworks.com>
> > > wrote:
> > > 
> > > > On Mon, Jun 24, 2019 at 10:01 AM Michal Vaško <mvasko@cesnet.cz>
> > > > wrote:
> > > >
> > > > > Hi Rob,
> > > > > I think there is a problem in the RFC because using only allowed
> > > > > steps I got invalid data from initially valid data. That cannot be
> > > correct.
> > > > >
> > > > >
> > > > No.  See sec. 7.5.7
> > > >
> > > >    If a non-presence container does not have any child nodes, the
> > > >    container may or may not be present in the XML encoding.
> > > >
> > > >
> > > > Just because your retrieval does not contain the NP-container, that
> > > > does not mean the NP-container was not present in the server for the
> > > > mandatory-stmt validation.
> > > 
> > > I agree, but these valid data were correctly printed into invalid
> > > data. I
> > > do not think printing is allowed to change the validity of data.
> > > 
> > > Michal
> > > 
> > > >
> > > > Regards,
> > > > > Michal
> > > > >
> > > > >
> > > > Andy
> > > >
> > > >
> > > > > On Monday, June 24, 2019 18:52 CEST, "Rob Wilton (rwilton)" <
> > > > > rwilton@cisco.com> wrote:
> > > > >
> > > > > > Hi Michal,
> > > > > >
> > > > > > My thoughts:
> > > > > >
> > > > > > According to 7.5.1:
> > > > > >
> > > > > >    In the first style, the container has no meaning of its own,
> > > existing
> > > > > >    only to contain child nodes.  In particular, the presence of the
> > > > > >    container node with no child nodes is semantically equivalent to
> > > the
> > > > > >    absence of the container node.  YANG calls this style a "non-
> > > presence
> > > > > >    container".  This is the default style.
> > > > > >
> > > > > > Hence your request (because the NP container does not have any
> > > > > > children)
> > > > > is equivalent to:
> > > > > >
> > > > > >  <TOP>
> > > > > >    <L/>
> > > > > >  </TOP>
> > > > > >
> > > > > > which fails the "mandatory" check.
> > > > > >
> > > > > > Thanks,
> > > > > > Rob
> > > > > >
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: netmod <netmod-bounces@ietf.org> On Behalf Of Michal Vaško
> > > > > > > Sent: 24 June 2019 17:39
> > > > > > > To: netmod <netmod@ietf.org>
> > > > > > > Subject: [netmod] mandatory choice with non-presence container
> > > > > > > case
> > > > > > >
> > > > > > > Hi,
> > > > > > > I have encountered a situation that I think is not covered by
> > > > > > > RFC
> > > > > 7950. My
> > > > > > > specific use-case was as follows.
> > > > > > >
> > > > > > > model:
> > > > > > >
> > > > > > > container TOP {
> > > > > > >   leaf L {
> > > > > > >     type empty;
> > > > > > >   }
> > > > > > >   choice A {
> > > > > > >     mandatory true;
> > > > > > >     container C;
> > > > > > >   }
> > > > > > > }
> > > > > > >
> > > > > > > data:
> > > > > > >
> > > > > > > <TOP>
> > > > > > >   <L/>
> > > > > > >   <C/>
> > > > > > > </TOP>
> > > > > > >
> > > > > > > Parsing was successful, but printing these data back to XML
> > > produced:
> > > > > > >
> > > > > > > <TOP>
> > > > > > >   <L/>
> > > > > > > </TOP>
> > > > > > >
> > > > > > > and parsing this correctly failed with missing mandatory choice.
> > > > > According
> > > > > > > to section 7.5.7 [1], I think the C container could be omitted
> > > > > > > but the whole situation does not seem correct. Thank you for any
> > > input.
> > > > > > >
> > > > > > > Regards,
> > > > > > > Michal
> > > > > > >
> > > > > > > [1] https://tools.ietf.org/html/rfc7950#section-7.5.7
> > > > > > >
> > > > > > > _______________________________________________
> > > > > > > netmod mailing list
> > > > > > > netmod@ietf.org
> > > > > > > https://www.ietf.org/mailman/listinfo/netmod
> > > > >
> > > > >
> > > > >
> > > > > _______________________________________________
> > > > > netmod mailing list
> > > > > netmod@ietf.org
> > > > > https://www.ietf.org/mailman/listinfo/netmod
> > > > >
> > > 
> > > 
> > 
>  
>  
> 
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