add a simple abstraction for bytearray allocation+fill

Crypto/Internal/ByteArray.hs

@@ -0,0 +1,46 @@
+-- |
+-- Module      : Crypto.Internal.ByteArray
+-- License     : BSD-style
+-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
+-- Stability   : stable
+-- Portability : Good
+--
+-- Simple and efficient byte array types
+--
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE MagicHash #-}
+{-# LANGUAGE UnboxedTuples #-}
+module Crypto.Internal.ByteArray
+    ( ByteArray(..)
+    , byteArrayAllocAndFreeze
+    ) where
+
+import Data.SecureMem
+import Crypto.Internal.Memory
+import Crypto.Internal.Compat
+import Foreign.Ptr
+import Foreign.ForeignPtr
+
+import Data.ByteString (ByteString)
+import qualified Data.ByteString.Internal as B
+
+class ByteArray ba where
+    byteArrayAlloc :: Int -> (Ptr p -> IO ()) -> IO ba
+
+instance ByteArray Bytes where
+    byteArrayAlloc = bytesAlloc
+
+instance ByteArray ByteString where
+    byteArrayAlloc sz f = do
+        fptr <- B.mallocByteString sz
+        withForeignPtr fptr (f . castPtr)
+        return $! B.PS fptr 0 sz
+
+instance ByteArray SecureMem where
+    byteArrayAlloc sz f = do
+        out <- allocateSecureMem sz
+        withSecureMemPtr out (f . castPtr)
+        return out
+
+byteArrayAllocAndFreeze :: ByteArray a => Int -> (Ptr p -> IO ()) -> a
+byteArrayAllocAndFreeze sz f = unsafeDoIO (byteArrayAlloc sz f)