First take

lib/Streamly/ByteString.hs

@@ -0,0 +1,57 @@
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module Streamly.ByteString where
+
+import Control.Monad.IO.Class
+import Data.ByteString hiding (length)
+import qualified Data.ByteString as BS
+import Data.ByteString.Unsafe
+import Data.Word (Word8)
+import Foreign.ForeignPtr
+import Foreign.ForeignPtr.Unsafe
+import Foreign.Ptr (castPtr, minusPtr, plusPtr)
+import Prelude hiding (length)
+import Streamly
+import Streamly.Internal.Memory.Array.Types
+import Streamly.Memory.Array
+import qualified Streamly.Prelude as S
+
+toByteString ::
+     forall m. (MonadIO m, MonadAsync m)
+  => SerialT m (Array Word8)
+  -> m ByteString
+toByteString stream =
+  let xs = S.mapM arrayToByteString stream
+      ys = S.foldlM' (\a b -> pure $ a <> b) mempty xs
+   in ys
+
+arrayToByteString :: (MonadIO m) => Array Word8 -> m ByteString
+arrayToByteString arr
+  | length arr == 0 = return mempty
+arrayToByteString Array {..} =
+  liftIO $
+  withForeignPtr aStart $ \ptr ->
+    unsafePackCStringFinalizer ptr aLen (return ())
+  where
+    aLen =
+      let p = unsafeForeignPtrToPtr aStart
+       in aEnd `minusPtr` p
+
+byteStringToArray :: (MonadIO m) => ByteString -> m (Array Word8)
+byteStringToArray bs =
+  liftIO $
+  unsafeUseAsCStringLen
+    bs
+    (\(ptr, _) -> do
+       let endPtr pr = (castPtr pr `plusPtr` (BS.length bs))
+       fptr <- newForeignPtr_ (castPtr ptr)
+       return $ Array {aStart = fptr, aEnd = endPtr ptr, aBound = endPtr ptr})
+
+fromByteString ::
+     forall m. (MonadIO m)
+  => ByteString
+  -> m (Array Word8)
+fromByteString bs = byteStringToArray bs