Re: [yang-doctors] YANG QUIC-LB model

[Ladislav Lhotka <[e-mail]>]

On 02. 02. 21 8:56, Martin Björklund wrote:
> Hi,
> 
> 
> Martin Duke <[e-mail]> wrote:
>> Hello yang-doctors,
>>
>> I don't know that this rises to the level of a full review, but the QUIC-LB
>> draft (currently adopted by the QUIC WG) is basically a standard for
>> configuration of QUIC Load Balancers and servers to work together. After
>> much reluctance to take on a format I don't understand, I took a shot at a
>> YANG model:
>>
>> https://github.com/quicwg/load-balancers/blob/yang/draft-ietf-quic-load-balancers.md
>>
>> (The YANG stuff is in an appendix near the end -- search for #yang-model).
>>
>> Before we talk about a full review where you labor to understand the data
>> items, I'd appreciate an informal quick sanity check that I am doing this
>> roughly correctly, as I have zero experience with YANG.
> 
> I downloaded the module and ran it through a YANG compiler, and
> started to fix several minor syntactical errors (such as missing ";"),
> but then I ran into other issues that made it difficult for me to
> guess what you meant.  I suggest you ensure that the model compiles
> (there are a bunch of compilers available, e.g., pyang, yanglint, ...)
> and post it again.
> 
> Some comments though:
> 
> You have:
> 
>        list cid-configs {
>          key "config-rotation-bits";
> 
>          leaf config-rotation-bits {
>            type uint8 {
>              range "0..2";
>            }
> 
> This means that there can only be max 3 entries in this list.  Is that
> what you meant?
> 
> 
> You also have:
> 
>        typedef quic-lb-key {
>          type yang:hex-string {
>            length 16;
>          }
>        }
> 
> The YANG statement "length", when given on a type "string", or derived
> from "string", operates on the number of characters in the string.  In
> this case, you probably what to limit the number of bytes represented
> by the hex-string.  Unfortunately, it is not possible in standard YANG
> 1.1 to do this.

An alternative then might be to use the "binary" type, its length
restriction is related to the number of octets.

Lada

> 
> However, in this particular case it sort-of works, since the length of
> the hex-string is 2 * N + 1, where N is the number of bytes.  Hence,
> the length would be 33.  If you do this I suggest you explain this in
> the description statement.
> 
> An alternative could be to drop the length statement and only explain
> it in the description statement.
> 
>> One other silly question: I have a field whose length depends on other
>> fields. Can you give me an example on how to express this correctly? e.g.
>>
>> leaf foo-length {
>>     type uint8
>> }
>>
>> leaf foo {
>>     type yang:hex-string {
>>         length foo-length;
>>     }
>> }
> 
> This is possible by using a "must" statement.  However, it has the
> same problem with the lexical value as above:
> 
>   leaf foo {
>     type yang:hex-string;
>     must 'string-length(.) = 2 * ../foo-length + 1';
>   }
> 
> 
> 
> /martin
> 
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-- 
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67