Re: [netmod] type equivalence

[tom petch <[e-mail]>]

From: netmod <[e-mail]> on behalf of Martin Björklund <[e-mail]>
Sent: 22 February 2021 10:13

Juergen Schoenwaelder <[e-mail]> wrote:
> Thanks Martin,
>
> so you are saying that
>
>   int8 { range "1..10"; }
>
> is indeed different from
>
>   uint8 { range "1..10"; }
>
> and
>
>   int32 { range "1..10"; }

Yes.

> The use of the word "syntax" in the text you quote may be a left-over
> from SMIv2 times

[That's what I thought as well, but I couldn't find it in the SMIv2
RFCs.  Perhaps it was from some sming text?]

<tp>
When asked about SNMP/SMI, I always say to start with RFC1155/1156/1157.  Either of the first two gives, for me, a clear exposition of the meaning of 'syntax' which I have always taken as read in YANG.

Going back, well, ASN.1, ISO etc etc

Tom Petch

> , it does not really seem to be aligned with how the
> term 'syntax' is used elsewhere in RFC 7950. Anyway, if the agreement
> back then was that you can't change base types (regardless of type
> restrictions), it would have been nice if the text would say this more
> clearly.

Agreed.


/martin



>
> /js
>
> On Mon, Feb 22, 2021 at 10:49:38AM +0100, Martin Björklund wrote:
> > Hi,
> >
> > Section 11 of RFC 7950 says:
> >
> >    o  A "type" statement may be replaced with another "type" statement
> >       that does not change the syntax or semantics of the type.  For
> >       example, an inline type definition may be replaced with a typedef,
> >       but an int8 type cannot be replaced by an int16, since the syntax
> >       would change.
> >
> > If we're just considering XML, then the syntax or encoding wouldn't
> > change if we went from
> >
> >   type int64 { range "2..4"; }
> >
> > to
> >
> >   type string { pattern "2|3|4"; }
> >
> > or
> >
> >   type enumeration {
> >     enum 2;
> >     enum 3;
> >     enum 4;
> >   }
> >
> > or
> >
> >   type union {
> >     type uint8 { range "2"; }
> >     type string { pattern "3"; }
> >     type enumeration { enum 4; }
> >   }
> >
> >
> > But I don't think this is reasonable, and not the intention.  I think
> > that changing the base built-in type always should be considered
> > non-backwards compatible (which the quoted text above seems to imply).
> >
> >
> > /martin
> >
> >
> >
> >
> > Juergen Schoenwaelder <[e-mail]> wrote:
> > > On Fri, Feb 19, 2021 at 10:32:34PM +0100, Carsten Bormann wrote:
> > > >
> > > >
> > > > > On 2021-02-19, at 19:18, Juergen Schoenwaelder <[e-mail]> wrote:
> > > > >
> > > > > I think the CBOR encoding picks different tags depending on the
> > > > > signedness of the base type and this is why things are not that simple
> > > > > anymore.
> > > >
> > > > (This is not the CBOR encoding, but the COMI encoding of keys in URIs.)
> > >
> > > OK. The CBOR document indeed says:
> > >
> > > 6.1.  The unsigned integer Types
> > >
> > >    Leafs of type uint8, uint16, uint32 and uint64 MUST be encoded using
> > >    a CBOR unsigned integer data item (major type 0).
> > >
> > > 6.2.  The integer Types
> > >
> > >    Leafs of type int8, int16, int32 and int64 MUST be encoded using
> > >    either CBOR unsigned integer (major type 0) or CBOR negative integer
> > >    (major type 1), depending on the actual value.
> > >
> > > This means the type 'int8 { range 0..10; }' leads to the same
> > > encodings as the type 'uint8 { range 0..10; }'.
> > >
> > > > > For the XML and JSON encodings, all definitions lead to the
> > > > > same on-the-wire representation, hence the difference is more an
> > > > > implementation detail. I have no clue what the gnmi people do. The
> > > > > more diverse encodings we add, the more complex things get.
> > > >
> > > > Well, if the equivalence expectation that I was trying to describe actually is ingrained, then whoever designs an encoding (COMI for its URI encoding included) needs to respect it.  That would be important to know.
> > > >
> > >
> > > Exactly. I think we never defined this. And of course, this can get
> > > even more fun if you consider string based encodings. The type
> > >
> > >    type string { pattern "1|2|3|4"; }
> > >
> > > yields the same _XML encoded_ value space as
> > >
> > >    type int32 { range "1..4"; }
> > >
> > > but as far as I recall the JSON/CBOR encodings will treat these two
> > > differently. So yes, ideally the YANG language would have clear rules
> > > what YANG's type equivalences are.
> > >
> > > /js
> > >
> > > --
> > > Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> > > Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
> > > Fax:   [phone]         <https://www.jacobs-university.de/>
> > >
> > > _______________________________________________
> > > netmod mailing list
> > > [e-mail]
> > > https://www.ietf.org/mailman/listinfo/netmod
>
> --
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   [phone]         <https://www.jacobs-university.de/>

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