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
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