Re: [netmod] type equivalence

["Rob Wilton (rwilton)" <[e-mail]>]

> -----Original Message-----
> From: netmod <[e-mail]> On Behalf Of Martin Björklund
> Sent: 22 February 2021 10:14
> To: [e-mail]
> Cc: [e-mail]
> Subject: Re: [netmod] type equivalence
> 
> 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?]
> 
> > , 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.
[RW] 

Since the YANG module versioning draft clarifies the BC/NBC rules, perhaps we could add text to clarify this in that draft?

I.e., perhaps something for section 3.1.3 of https://datatracker.ietf.org/doc/draft-ietf-netmod-yang-module-versioning/

Regards,
Rob

// As a contributor.


> 
> 
> /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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