[Haskell-cafe] Zlib bindings

[Joel Reymont]

Well, I just coded this. Feedback is welcome!

One thing that I found interesting is that I actually have to  
allocate 4 bytes to pass the long into compress/uncompress. I thought  
that I could somehow obtain the address of the Haskell variable but  
this does not seem to be possible.

     Thanks, Joel

--
{-# INCLUDE <zlib.h> #-}
{-# OPTIONS -fffi -fglasgow-exts #-}

module ZLib
(
compress,
uncompress
)
where

import Foreign
import Foreign.C
import Data.FastPackedString
import Prelude hiding (length)

compress :: FastString -> IO FastString
compress src = do
                let src_size :: CULong = fromIntegral $ length src
                    dest_size :: CULong = compressBound src_size
                allocaBytes (sizeOf dest_size) $ \dest_size' ->
                    unsafeUseAsCString src $ \src' ->
                        do poke dest_size' dest_size
                           generate (fromIntegral dest_size) $ \dest ->
                               do err <- compress_
                                         dest dest_size'
                                         (castPtr src') src_size
                                  dest_size <- peek dest_size'
                                  return $ fromIntegral dest_size

uncompress :: FastString -> Int -> IO FastString
uncompress src orig_size = do
                let src_size :: CULong = fromIntegral $ length src
                    dest_size :: CULong = fromIntegral orig_size
                allocaBytes (sizeOf dest_size) $ \dest_size' ->
                    unsafeUseAsCString src $ \src' ->
                        do poke dest_size' dest_size
                           generate (fromIntegral dest_size) $ \dest ->
                               do err <- uncompress_
                                         dest dest_size'
                                         (castPtr src') src_size
                                  dest_size <- peek dest_size'
                                  return $ fromIntegral dest_size

foreign import ccall unsafe "compressBound" compressBound ::
     CULong -> CULong

foreign import ccall unsafe "compress" compress_ ::
     Ptr Word8 -> Ptr CULong -> Ptr Word8 -> CULong -> IO CInt

foreign import ccall unsafe "uncompress" uncompress_ ::
     Ptr Word8 -> Ptr CULong -> Ptr Word8 -> CULong -> IO CInt

--
http://wagerlabs.com/