[Haskell-beginners] please critique my first stab at systems programming
shaleh at speakeasy.net
Thu Apr 14 12:14:59 CEST 2011
The idea is to walk the disk looking for a signature, say NTFS or EXT. Since we do not know where the block containing this identifier is, we read the blocks in one at a time.
Long term I would like to support command line arguments for the name of the file and the offset to start looking.
Comments on style, idioms, etc. welcomed. I am particularly interested in the hIsEOF check and if there is a better way to handle that.
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as BC
chunkSize = 512
searchForPattern handle pat = searchForPattern' 0 handle pat
searchForPattern' index handle pat = do
eof <- hIsEOF handle
if eof then return Nothing
bytes <- B.hGet handle chunkSize
case BC.breakSubstring pat bytes of
(x, y) | BC.null y -> searchForPattern' (index + 1) handle pat
| otherwise -> return (Just index)
main = do
fromHandle <- openBinaryFile "blocks" ReadMode
result <- searchForPattern fromHandle (BC.pack "PART")
case result of
Nothing -> putStr "Not Found.\n"
Just n -> putStr $ "Found at " ++ show n ++ ".\n"
More information about the Beginners