libmagic-1.2: Magic/Utils.hsc

{- -*- Mode: haskell; -*-
Haskell magic Interface
Copyright (C) 2005 John Goerzen <jgoerzen@complete.org>

This code is under a 3-clause BSD license; see COPYING for details.
-}

{- |
   Module     : Magic.Utils
   Copyright  : Copyright (C) 2005 John Goerzen
   License    : BSD

   Maintainer : Joey Hess,
   Maintainer : id\@joeyh.name
   Stability  : provisional
   Portability: portable

Utils

Written by John Goerzen, jgoerzen\@complete.org
-}

module Magic.Utils (flaglist2int, fromMagicPtr, withMagicPtr, checkIntError,
                    throwErrorIfNull)
where

import Foreign
import Foreign.C.Error
import Foreign.C.String
import Magic.TypesLL
import Magic.Types
import Foreign.C.Types
import Control.Concurrent.MVar

flaglist2int :: [MagicFlag] -> CInt
flaglist2int mfl =
    foldl (\c f -> c .|. (fromIntegral . fromEnum $ f)) 0 mfl

fromMagicPtr :: String -> IO (Ptr CMagic) -> IO Magic
fromMagicPtr caller action =
    do ptr <- throwErrnoIfNull caller action
       m <- newForeignPtr magic_close ptr
       mvar <- newMVar m
       return (Magic mvar)

throwErrorIfNull :: String -> Ptr CMagic -> IO (Ptr a) -> IO (Ptr a)
throwErrorIfNull caller m action =
    do res <- action
       if res == nullPtr
          then throwError caller m
          else return res

withMagicPtr :: Magic -> (Ptr CMagic -> IO a) -> IO a
withMagicPtr (Magic mvar) a = withMVar mvar $ \m -> withForeignPtr m a

throwError :: String -> Ptr CMagic -> IO a
throwError caller cmagic =
               do errormsg <- magic_error cmagic
                  if errormsg /= nullPtr
                     then do em <- peekCString errormsg
                             fail $ caller ++ ": " ++ em
                     else fail $ caller ++ ": got error code but no error message"

checkIntError :: String -> Ptr CMagic -> IO CInt -> IO ()
checkIntError caller cmagic action = 
    do res <- action
       if res == 0
          then return ()
          else throwError caller cmagic


foreign import ccall unsafe "magic.h &magic_close"
  magic_close :: FunPtr (Ptr CMagic -> IO ())

foreign import ccall unsafe "magic.h magic_error"
  magic_error :: Ptr CMagic -> IO CString