[ragel-users] Work On Binary datagrams

[Joseph Stewart]

(whoops... the text should have read "Len is a big-endian length
designator")

On Thu, Dec 16, 2010 at 9:24 AM, Joseph Stewart <joseph.stewart at gmail.com>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> 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
>>>
>>> _______________________________________________
>>> ragel-users mailing list
>>> ragel-users at complang.org
>>> http://www.complang.org/mailman/listinfo/ragel-users
>>>
>>>
>> _______________________________________________
>> ragel-users mailing list
>> ragel-users at complang.org
>> http://www.complang.org/mailman/listinfo/ragel-users
>>
>
>
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