Mailing List Archive

I found a solution, which I think is nice.

I used Ragel (http://www.cs.queensu.ca/~thurston/ragel/) to create a finite
state machine which implements the grammar from the RFC.

It's simple, and the syntax is even similar. Here's the relevant fragment from
the RFC:

name = ALPHA *( ALPHA / DIGIT / "-" / "_" / "." )
macro-letter = "s" / "l" / "o" / "d" / "i" / "p" / "h" /
"c" / "r" / "t"
transformers = *DIGIT [ "r" ]
delimiter = "." / "-" / "+" / "," / "/" / "_" / "="
macro-expand = ( "%{" macro-letter transformers *delimiter "}" )
/ "%%" / "%_" / "%-"
toplabel = ( *alphanum ALPHA *alphanum ) /
( 1*alphanum "-" *( alphanum / "-" ) alphanum )
domain-end = ( "." toplabel [ "." ] ) / macro-expand
macro-literal = %x21-24 / %x26-7E
macro-string = *( macro-expand / macro-literal )
domain-spec = macro-string domain-end


And here's the ragel code:

machine domain_spec;
name = ( alpha ( alpha | digit | '-' | '_' | '.' )* );
macro_letter = 's' | 'l' | 'o' | 'd' | 'i' | 'p' | 'h' | 'c' | 'r' | 't';
transformers = digit* 'r'?;
delimiter = '.' | '-' | '+' | ',' | '|' | '_' | '=';
macro_expand = ( '%{' macro_letter transformers delimiter* '}' ) |
'%%' | '%_' | '%-';
toplabel = ( alnum* alpha alnum* ) |
( alnum{1,} '-' ( alnum | '-' )* alnum );
domain_end = ( '.' toplabel '.'? ) | macro_expand;
macro_literal = 0x21 .. 0x24 | 0x26 .. 0x7E;
macro_string = ( macro_expand | macro_literal )*;
domain_spec := macro_string domain_end 0 @{ res = 1; };

And now raspf passes 137 of 145 tests from the suite :-)
 
--
 ("\''/").__..-''"`-. .         Roberto Alsina
 `9_ 9  )   `-. (    ).`-._.`)  ralsina@kde.org
 (_Y_.)' ._   ) `._`.  " -.-'   KDE Developer (MFCH)
  _..`-'_..-_/ /-'_.'
(l)-'' ((i).' ((!.'   Buenos Aires - Argentina

Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it. --Brian W. Kernighan

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