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

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. 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>; 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
> > > > > >
> > > > > > _______________________________________________
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> > > > > > netmod@ietf.org
> > > > > > https://www.ietf.org/mailman/listinfo/netmod
> > > >
> > > >
> > > >
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> > > >
> > 
> > 
> 