Process.hs

-- | A module adapting the functions from "System.Process" to work with
-- @io-streams@.
module System.IO.Streams.Process
  ( module System.Process
  , runInteractiveCommand
  , runInteractiveProcess
  ) where

------------------------------------------------------------------------------
import           Data.ByteString.Char8         (ByteString)
import           System.IO                     (hClose)
import qualified System.IO.Streams.Combinators as Streams
import qualified System.IO.Streams.Handle      as Streams
import           System.IO.Streams.Internal    (InputStream, OutputStream)
import qualified System.IO.Streams.Internal    as Streams
import           System.Process                hiding (env,
                                                runInteractiveCommand,
                                                runInteractiveProcess,
                                                runProcess)
import qualified System.Process                as P
------------------------------------------------------------------------------


------------------------------------------------------------------------------
-- | Runs a command using the shell, and returns streams that may be used to
-- communicate with the process via its stdin, stdout, and stderr respectively.
--
-- The streams returned by this command are guarded by locks and are therefore
-- safe to use in multithreaded code.
--
-- /Since: 1.0.2.0/
--
runInteractiveCommand :: String
                      -> IO (OutputStream ByteString,
                             InputStream ByteString,
                             InputStream ByteString,
                             ProcessHandle)
runInteractiveCommand scmd = do
    (hin, hout, herr, ph) <- P.runInteractiveCommand scmd
    sIn  <- Streams.handleToOutputStream hin >>=
            Streams.atEndOfOutput (hClose hin) >>=
            Streams.lockingOutputStream
    sOut <- Streams.handleToInputStream hout >>=
            Streams.atEndOfInput (hClose hout) >>=
            Streams.lockingInputStream
    sErr <- Streams.handleToInputStream herr >>=
            Streams.atEndOfInput (hClose herr) >>=
            Streams.lockingInputStream
    return (sIn, sOut, sErr, ph)


------------------------------------------------------------------------------
-- | Runs a raw command, and returns streams that may be used to communicate
-- with the process via its @stdin@, @stdout@ and @stderr@ respectively.
--
-- For example, to start a process and feed a string to its stdin:
--
-- > (inp,out,err,pid) <- runInteractiveProcess "..."
-- > forkIO (Streams.write (Just str) inp)
--
-- The streams returned by this command are guarded by locks and are therefore
-- safe to use in multithreaded code.
--
-- /Since: 1.0.2.0/
--
runInteractiveProcess
    :: FilePath                 -- ^ Filename of the executable (see 'proc' for details)
    -> [String]                 -- ^ Arguments to pass to the executable
    -> Maybe FilePath           -- ^ Optional path to the working directory
    -> Maybe [(String,String)]  -- ^ Optional environment (otherwise inherit)
    -> IO (OutputStream ByteString,
           InputStream ByteString,
           InputStream ByteString,
           ProcessHandle)
runInteractiveProcess cmd args wd env = do
    (hin, hout, herr, ph) <- P.runInteractiveProcess cmd args wd env
    sIn  <- Streams.handleToOutputStream hin >>=
            Streams.atEndOfOutput (hClose hin) >>=
            Streams.lockingOutputStream
    sOut <- Streams.handleToInputStream hout >>=
            Streams.atEndOfInput (hClose hout) >>=
            Streams.lockingInputStream
    sErr <- Streams.handleToInputStream herr >>=
            Streams.atEndOfInput (hClose herr) >>=
            Streams.lockingInputStream
    return (sIn, sOut, sErr, ph)