[ragel-users] Handling binary protocols with ragel

[Joseph Stewart]

Sure... I'll share a "working example" from what I was working on at the
time. Pleas keep in mind I wrote this over 8 months ago and never placed it
into production (I've moved to a new role since them).

Anyway beyond what's in the attached example, I had a terrible file format
that I'd written an equally terrible state machine to read. This sample
only deals with the wrapper part of the file. Essentially it looks like:

opening xml-like tag with parameters type and info... this looks like
<XRNDATA08192> the code
length... this is a 4-byte little endian length
binary blog of length bytes... binary data of the length from the previous
element
closing xml-like tag... this looks like </XRNDATA> in the code

Finally, here's the C-code pasted below

//----code start----
#include <stdio.h>

/*

chunks in file look like

<XRNDATA08192020001>LenData</XRNDATA>
where "08192" is an ASCII type designator (can expect other types)
where "020001" is an ASCII information field
where Len is a 4-byte little endian length designator
where Data is binary data of Len length

*/

#define XRN 'X', 'R', 'N', 'D', 'A', 'T', 'A'
#define T1  '0', '8', '1', '9', '2'
#define T2  '0', '0', '0', '1', '6'
#define T3  '0', '0', '0', '0', '8'
#define T4  '0', '0', '0', '0', '1'
#define I1  '0', '2', '0', '0', '0', '1'

%%{
machine tds;
write data;
}%%

int main() {
int len = 0;
unsigned char buf[] = {
'<', XRN, T1, I1, '>', 0, 0, 0, 5, 48,49,50,51,52, '<', '/', XRN, '>',
'<', XRN, T2, I1, '>', 0, 0, 0, 1, 10, '<', '/', XRN, '>',
'<', XRN, T3, I1, '>', 0, 0, 0, 1, 10, '<', '/', XRN, '>',
'<', XRN, T4, I1, '>', 0, 0, 0, 1, 10, '<', '/', XRN, '>',
'<', XRN, T1, I1, '>', 0, 0, 0, 0, '<', '/', XRN, '>',
'<', T1, I1, '>', 0, 0, 0, 0, '<', '/', XRN, '>',
};
int cs, r = 0;
unsigned char *p = (unsigned char *)&buf;
unsigned char *pe = p + sizeof(buf);
unsigned char *eof = NULL;
printf("len=%d\n", len);
%%{
t1 = '08192' @{ printf("t1\n"); };
t2 = '00016' @{ printf("t2\n"); };
t3 = '00008' @{ printf("t3\n"); };
t4 = '00001' @{ printf("t4\n"); };
type = (t1 | t2 | t3 | t4);
info = '020001';
open = '<XRNDATA' type info '>' @{ printf("begin XRNDATA\n"); len = 0; };
len = extend{4} @{ printf("len = %d\n", (int)*p); len = (len*256) + (*p); };
action check {len--}
action bad {printf("BAD\n");}
buffer = (any when check)* %when !check @{ printf("[%d]:%d\n", len, *p); };
close = '</XRNDATA>' @{ printf("end XRNDATA\n"); };
expr = (
open @lerr(bad)
len
buffer
close
);
main := expr* ;
write init;
write exec;
}%%
return 0;
}
//----code end----

On Wed, Mar 14, 2012 at 7:09 PM, <pyguest at fastmail.fm> wrote:

> Joesph Stewart,
>
> I think you were doing some work with binary protocols earlier. Any
> chance you can post some examples?
>
> Andrew,
>
> Reading some of your older posts, it seems that you were going to have
> stronger support for binary protocols in version 7. Is that still true?
> If so, any idea when we can expect to see this?
>
> --
> http://www.fastmail.fm - The way an email service should be
>
>
> _______________________________________________
> ragel-users mailing list
> ragel-users at complang.org
> http://www.complang.org/mailman/listinfo/ragel-users
>
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