I typically don't recommend Ragel for DNS due to it being a binary
protocol, but it can be done.
With Ragel there are two ways to count things. You can use conditions to
check for the counters getting down to zero. The advantage of conditions
is that you can more freely use machines with with embedded conditions
in the construction of other machines.
The other approach is the one you're taking, which is to count and
call/return in actions. This is generally easier to program, because it
more closely resembles standard programming practice. The downside is
that you lose the ability freely union and you have to be more careful
with the other operations. The call/return statements are best for high
level flow control and can get you into a bind when used for the inner
definitions of a grammar.
All in all, you may find that a hand-written parser for DNS is faster
and simpler due to all the counting.
-Adrian
Pete Gervais wrote:
I’m using ragel to decode protocols as a test of its capabilities.
One of the protocols is DNS.
This protocol has a fixed set of fields followed by one or more optional
fields. The count of these optional fields are encoded within the fixed
data field.
Would the code below be the best way to do this ?Initial the dnsAnswer
section called via fcall dnsAnswer. It then sequentially processes all
fields in the order given. In the last field,
dnsAnswerResourceDataField , it gets the count of the number of answer
fields included in the protocol, then perform a series of fgoto’s until
the dnsRecordCount is 0 at which time it returns.
dnsAnswer := (
dnsAnswerNameField .
dnsAnswerTypeField .
dnsAnswerClassField .
dnsAnswerTimeToLiveField .
dnsAnswerResourceDataLengthField .
dnsAnswerResourceDataField @{ cout <<
"In dnsAnswer processing" << endl; if (fsm->getdnsAnswerRecordCount() >
0 ) {
fsm->dnsAnswerRecordCount--;
fgoto dnsAnswer; } else {
fret; }
}
);
Regards,
Peter J. Gervais
President, Simtree Information Systems
17621 Island Rd,
RR#2 , Martintown,
Martintown,Ont
K0C 1S0
Business: 613-938-6549
Cell: 613-864-7370
E-mail: [email protected]
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