import Control.Exception import Control.Monad.ST import Control.Monad.ST.Unsafe import Data.Word import Foreign.C.String import Foreign.C.String import Foreign.C.Types import Foreign.Marshal import Foreign.Ptr import Foreign.Storable foreign import ccall unsafe "strerror_r_portalbe.c strerror_r_portable" c_strerror_r :: CInt -> Ptr CChar -> CSize -> IO CInt memSet :: Ptr a -> Word8 -> Word32 -> IO (Ptr a) memSet ptr _ 0 = return ptr memSet ptr byte size = do let voidptr = castPtr ptr :: Ptr Word8 acts = map (\i -> pokeByteOff voidptr i byte) [0 .. fromIntegral (size - 1)] mapM_ id acts return ptr strError :: Int -> String strError errnum = runST $ unsafeIOToST ioString where baseSize :: CSize baseSize = 50 ioString = run baseSize run :: CSize -> IO String run size | size > 100000 = return $ "!!! INTERNAL strError memory leak detected, " ++ "you can not recover !!!" | otherwise = do may <- tryIOString size case may of Just str -> return str Nothing -> run (size + baseSize) tryIOString :: CSize -> IO (Maybe String) tryIOString size = allocaBytes (fromIntegral size) $ \ptr -> do zeroptr <- memSet ptr 0 (fromIntegral size) st <- c_strerror_r (fromIntegral errnum) ptr size -- heuristic case st of 22 -> return . return $ "Unknown error " ++ show errnum 34 -> return Nothing _ -> peekCAString ptr >>= return . return main = mapM_ (putStrLn) $ map strError [1 .. 1000] On Fri, 12 Apr 2024 15:27:57 -0000 Folsk Pratima wrote:

Also see [Haskell-beginners] FFI to POSIX libc; strerror (errnum); unfreed memory

Exactly how unsafe this code is? What do I do about it? It is so very stupid to have a pure function strerror_r in the IO monad!

StrError.hs

import Control.Exception import Control.Monad.ST import Control.Monad.ST.Unsafe import Data.Word import Foreign.C.String import Foreign.C.String import Foreign.C.Types import Foreign.Marshal import Foreign.Ptr import Foreign.Storable

foreign import ccall unsafe "strerror_r_portalbe.c strerror_r_portable" c_strerror_r :: CInt -> Ptr CChar -> CSize -> IO CInt

memSet :: Ptr a -> Word8 -> Word32 -> IO (Ptr a) memSet ptr _ 0 = return ptr memSet ptr byte size = do let voidptr = castPtr ptr :: Ptr Word8 acts = map (\i -> pokeByteOff voidptr i byte) [0 .. fromIntegral (size - 1)] mapM_ id acts return ptr

strError :: Int -> String strError errnum = runST $ unsafeIOToST ioString where buflen = 512 :: CSize ioString = allocaBytes (fromIntegral buflen) $ \ptr -> do zeroptr <- memSet ptr 0 (fromIntegral buflen) code <- c_strerror_r (fromIntegral errnum) ptr buflen -- heuristic! case code of 22 -> return $ "Unknown error " ++ show errnum -- this is very dangerous, as far as I understand, and nobody in -- his right might should not do it if he later intends to -- unsafely escape IO 34 -> throwIO $ userError $ "strError: " ++ show code ++ ": ERANGE: " ++ "Numerical result out of range: " ++ "this is internal an error, which means not enough space " ++ "was allocated to store the error. You can not recover" _ -> peekCAString ptr

main = mapM_ (putStrLn) $ map strError [1 .. 1000]

strerror_portable.c

#define _POSIX_C_SOURCE 200112L #include

int strerror_r_portable (int e, char *c, size_t s) { return strerror_r (e, c, s); }

The C code is needed because GHC uses _GNU_SOURCE, which I personally do not want to use. Besides, I do not know how to predict whether GHC will define _GNU_SOURCE or not, so this also feels more reliable.

To compile, do $ mkdir lib $ gcc -c -o lib/portable.o strerror_portable.c $ ar -csr lib/portable.a lib/portable.o $ ghc StrError.hs lib/portable.a

No leaks, of course. _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners