Re: [netmod] Pattern statements [was Re: Query about augmenting module from submodule in YANG 1.0]

[Vladimir Vassilev <[e-mail]>]

On 08/21/2017 05:14 PM, Robert Wilton wrote:

> Hi Acee,
>
> That makes sense.
>
> The other thing that I think that we have got wrong is modelling regex 
> pattern statements.  I think that it would be much better if these 
> were written to be less exhaustive and much simpler.
>
> E.g. the "route distinguisher" pattern in 
> draft-ietf-rtgwg-routing-types-09 is defined as this:
>
>           pattern
>             '(0:(6553[0-5]|655[0-2][0-9]|65[0-4][0-9]{2}|'
>           +     '6[0-4][0-9]{3}|'
>           +     '[0-5]?[0-9]{0,3}[0-9]):(429496729[0-5]|'
>           +     '42949672[0-8][0-9]|'
>           +     '4294967[01][0-9]{2}|429496[0-6][0-9]{3}|'
>           +     '42949[0-5][0-9]{4}|'
>           +     '4294[0-8][0-9]{5}|429[0-3][0-9]{6}|'
>           +     '42[0-8][0-9]{7}|4[01][0-9]{8}|'
>           +     '[0-3]?[0-9]{0,8}[0-9]))|'
>           + '(1:((([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|'
>           +     '25[0-5])\.){3}([0-9]|[1-9][0-9]|'
>           +     '1[0-9]{2}|2[0-4][0-9]|25[0-5])):(6553[0-5]|'
>           +     '655[0-2][0-9]|'
>           +     '65[0-4][0-9]{2}|6[0-4][0-9]{3}|'
>           +     '[0-5]?[0-9]{0,3}[0-9]))|'
>           + '(2:(429496729[0-5]|42949672[0-8][0-9]|'
>           +     '4294967[01][0-9]{2}|'
>           +     '429496[0-6][0-9]{3}|42949[0-5][0-9]{4}|'
>           +     '4294[0-8][0-9]{5}|'
>           +     '429[0-3][0-9]{6}|42[0-8][0-9]{7}|4[01][0-9]{8}|'
>           +     '[0-3]?[0-9]{0,8}[0-9]):'
>           +     '(6553[0-5]|655[0-2][0-9]|65[0-4][0-9]{2}|'
>           +     '6[0-4][0-9]{3}|'
>           +     '[0-5]?[0-9]{0,3}[0-9]))|'
>           + '(6(:[a-fA-F0-9]{2}){6})|'
>           + '(([3-57-9a-fA-F]|[1-9a-fA-F][0-9a-fA-F]{1,3}):'
>           +     '[0-9a-fA-F]{1,12})';
>         }
>
> But I think that it would be much easier to read, and quite possibly 
> more performant to execute, if the pattern regex was written something 
> like the following:
>
>  pattern:
>     '(0:[0-9]{1,5}:[0-9]{1,10})|
>      (1:([0-9]{1,3}\.){4}:[0-9]{1,5})|
>      (2:[0-9]{1,10}:0:[0-9]{1,5})|
>      (6(:[a-fA-F0-9]{2}){6})';
>
> Of course, this would allow more invalid values, but most servers 
> would be expected to reject those when it converts them into an 
> internal binary format any way.
>
> What do you, and others, think?
You still need the 
|(([3-57-9a-fA-F]|[1-9a-fA-F][0-9a-fA-F]{1,3}):[0-9a-fA-F]{1,12}) in the 
end to not reject valid values though.

IMO a pattern statement has value if it absolutely defines the set of 
valid strings. In general I do not see the benefit of pattern statements 
that do not reject all invalid string instances. I prefer the original 
pattern or none at all.

Vladimir

> Thanks,
> Rob