foo.hs

{-# LANGUAGE CPP #-}
{-# LANGUAGE ForeignFunctionInterface #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}


import           Prelude hiding (FilePath)
import qualified Data.ByteString
import           Data.ByteString (ByteString)
import           Foreign
import           Foreign.C

import           Filesystem
import           Filesystem.Path
import qualified Filesystem.Path.Rules as Rules


decode :: ByteString -> FilePath
decode = Rules.decode Rules.posix

encode :: FilePath -> ByteString
encode = Rules.encode Rules.posix


oldName = decode "old_\xA1\xA2\xA3.txt"
newName = decode "new_\xA1\xA2\xA3.txt"


withPathCString :: FilePath -> (CString -> IO a) -> IO a
withPathCString p = Data.ByteString.useAsCString (encode p)


foreign import ccall unsafe "fopen"
	c_fopen :: CString -> CString -> IO (Ptr ())

foreign import ccall unsafe "fclose"
	c_fclose :: Ptr () -> IO CInt

foreign import ccall unsafe "fwrite"
	c_fwrite :: CString -> CSize -> CSize -> Ptr () -> IO CSize



touch_ffi :: FilePath -> Data.ByteString.ByteString -> IO ()
touch_ffi path contents = do
  fp <- withPathCString path $ \path_cstr ->
                                Foreign.C.withCString "wb" $ \mode_cstr ->
                                                              c_fopen path_cstr mode_cstr

  _ <- Data.ByteString.useAsCStringLen contents $ \(buf, len) ->
		c_fwrite buf 1 (fromIntegral len) fp

  _ <- c_fclose fp
  return ()


main = do
  touch_ffi oldName ""
  Filesystem.copyFile oldName newName