[ragel-users] Work On Binary datagrams

[Adrian Thurston]

Right now there is no 'right' way. There are actually are many different 
ways each with their own ups and downs. There is some work I want to do 
on conditions to ease length processing (comes up at work a lot) and I'm 
hoping to soon be able to prescribe a recommended way of dealing with 
lengths that is general enough to apply to the majority of cases that I see.

On 10-12-16 06:24 AM, Joseph Stewart wrote:
> Adrian,
>
> Do you have any tips or small examples for dealing with lengths? While I
> have something that works, it doesn't feel right and I don't have the
> experience with Ragel to know if I'm doing this right.
>
> Below is a shell I've started to parse/validate binary chunks out of
> XML-like tags (BTW, I did not create the format... I'm just the victim).
> Eventually I need to parse data inside the Bin chunks.
>
> The graphviz output for this is so gigantic that I think I'm doing
> something fundamentally wrong.
>
> Suggestions are greatly appreciated!
>
> -joe
>
> --- code follows ---
>
> #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, '>',
> };
> int cs, r = 0;
> unsigned char *p = (unsigned char *)&buf;
> unsigned char *pe = p + sizeof(buf);
> 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); };
> buffer = (extend when {len--})* @{ printf("[%d]:%d\n", len, *p); };
> close = '</XRNDATA>' @{ printf("end XRNDATA\n"); };
> expr = open len buffer close;
> main := expr*;
> write init;
> write exec;
> }%%
> return 0;
> }
>
>
>
> On Mon, Dec 6, 2010 at 1:16 PM, Adrian Thurston
> <adrian.thurston at esentire.com <mailto:adrian.thurston at esentire.com>> wrote:
>
>     I use ragel to parse binary protocols at work. Often, the most
>     difficult part is dealing with lengths, or counts of things. A good
>     example is the DNS protocol. There are several sections of N blocks
>     of questions and resource records items. Inside the blocks you must
>     also deal with lengths in names.
>
>     Unfortunately, there are not many open examples of parsing this way.
>     Start by looking in the manual. I would like to improve Ragel's
>     support for this kind of parsing.
>
>     -Adrian
>
>
>     On 10-12-03 02:53 AM, Vitaly V. Ch wrote:
>
>         Hi!
>
>         I'm interested in any tips or examples of using ragel on binary
>         datagrams.
>
>         \\wbr Vitaly Chernooky
>
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