Concurrent port scanner in Haskell

concurrent_port_scanner.hs

module Main (main) where

import Control.Concurrent
import Control.Exception
import Data.Maybe
import Network
import Network.BSD
import System.Environment
import System.Exit
import System.IO

main :: IO ()
main = do
    args <- getArgs
    case args of
        [host, from, to] -> withSocketsDo $
                            scanRange host [read from .. read to]
        _                -> usage

usage = do
    hPutStrLn stderr "Usage: Portscan host from_port to_port"
    exitFailure

scanRange host ports =
    mapM (threadWithChannel . scanPort host . fromIntegral) ports >>=
    mapM_ hitCheck
  where
    hitCheck mvar = takeMVar mvar >>= maybe (return ()) printHit
    printHit port = putStrLn =<< showService port

threadWithChannel action = do
    mvar <- newEmptyMVar
    forkIO (action >>= putMVar mvar)
    return mvar

scanPort host port =
    withDefault Nothing (tryPort >> return (Just port))
  where
    tryPort = connectTo host (PortNumber port) >>= hClose

showService port =
    withDefault (show port) $ do
        service <- getServiceByPort port "tcp" 
        return (show port ++ " " ++ serviceName service)

withDefault defaultVal action =
    handle (const $ return defaultVal) action

-- Local Variables:  ***
-- compile-command: "ghc -o Portscan --make Portscan.hs" ***
-- End: ***