[Haskell-cafe] Reading pcap

[mukesh tiwari]

Hello everyone
I started writing this application but there is some thing missing. I
read this file http://www.viste.com/Linux/Server/WireShark/libpcapformat.pdf
and it say that first 24 bytes are global headers , after that every
packet  contains pcap local header . What i am trying to do is , first
trying to get the bytes of data in  each packet by reading the third
field incl_len in local header but my code is not behaving as it
suppose . My test libcap file is
http://wiki.wireshark.org/SampleCaptures?action=AttachFile&do=view&target=udp_lite_normal_coverage_8-20.pcap

--http://www.viste.com/Linux/Server/WireShark/libpcapformat.pdf
--http://hackage.haskell.org/packages/archive/bytestring/0.9.0.4/doc/
html/Data-ByteString-Lazy.html
import Data.List
import qualified Data.ByteString.Lazy as BS
import qualified Data.ByteString.Lazy.Char8 as B
import Control.Monad
import Text.Printf
import Data.Word
import Data.Char
import System.Time
import Numeric
import System.Environment

hexTodec :: BS.ByteString ->  Integer
hexTodec lst = read $   "0x" ++  (  concatMap ( \x -> showHex x "" )
$ BS.unpack lst  )


parseFile :: BS.ByteString -> Bool -> IO [ BS.ByteString ]
parseFile xs revflag
  | BS.null xs = return []
  | otherwise =   do
	let ind =if revflag then   hexTodec . BS.reverse . BS.take 4 .
BS.drop 8 $ xs
		  else hexTodec  . BS.take 4 . BS.drop 8 $ xs
	print ind
	let ( x , ys ) = BS.splitAt  ( fromIntegral ind  )  xs
	--BS.putStrLn $ x
	tmp <- parseFile ys revflag
	return $ x : tmp

main = do
	[ file ]  <- getArgs
	contents  <- BS.readFile file
	let ( a , rest ) =  BS.splitAt 24  contents  --strip global header

	let revflag = case BS.unpack $ BS.take 4  a of
	  		[ 0xd4 , 0xc3 , 0xb2 , 0xa1 ] -> True
	  		_ -> False
	p <-   parseFile  rest  revflag
	print $ p !! 0
	BS.putStr $  p !! 0

Regards
Mukesh Tiwari