GHC/Serialized.hs

    {-# LANGUAGE CPP #-}
    {-# LANGUAGE GADTs #-}
    {-# LANGUAGE RankNTypes, ScopedTypeVariables #-}
    {-# OPTIONS_GHC -fno-warn-name-shadowing #-}

    --
    -- (c) The University of Glasgow 2002-2006
    --
    -- Serialized values

    module GHC.Serialized (
        -- * Main Serialized data type
        Serialized(..),

        -- * Going into and out of 'Serialized'
        toSerialized, fromSerialized,

        -- * Handy serialization functions
        serializeWithData, deserializeWithData,
      ) where

    import Data.Bits
    import Data.Word        ( Word8 )
    import Data.Data

    -- | Represents a serialized value of a particular type. Attempts can be made to deserialize it at certain types
    data Serialized = Serialized TypeRep [Word8]

    -- | Put a Typeable value that we are able to actually turn into bytes into a 'Serialized' value ready for deserialization later
    toSerialized :: forall a. Typeable a => (a -> [Word8]) -> a -> Serialized
    toSerialized serialize what = Serialized (typeOf what) (serialize what)

    -- | If the 'Serialized' value contains something of the given type, then use the specified deserializer to return @Just@ that.
    -- Otherwise return @Nothing@.
    fromSerialized :: forall a. Typeable a => ([Word8] -> a) -> Serialized -> Maybe a
    #if MIN_VERSION_base(4,10,0)
    fromSerialized deserialize (Serialized the_type bytes)
      | the_type == rep = Just (deserialize bytes)
      | otherwise       = Nothing
      where rep = typeRep (Proxy :: Proxy a)
    #else
    fromSerialized deserialize (Serialized the_type bytes)
      | the_type == typeOf (undefined :: a) = Just (deserialize bytes)
      | otherwise                           = Nothing
    #endif

    -- | Use a 'Data' instance to implement a serialization scheme dual to that of 'deserializeWithData'
    serializeWithData :: Data a => a -> [Word8]
    serializeWithData what = serializeWithData' what []

    serializeWithData' :: Data a => a -> [Word8] -> [Word8]
    serializeWithData' what = fst $ gfoldl (\(before, a_to_b) a -> (before . serializeWithData' a, a_to_b a))
                                           (\x -> (serializeConstr (constrRep (toConstr what)), x))
                                           what

    -- | Use a 'Data' instance to implement a deserialization scheme dual to that of 'serializeWithData'
    deserializeWithData :: Data a => [Word8] -> a
    deserializeWithData = snd . deserializeWithData'

    deserializeWithData' :: forall a. Data a => [Word8] -> ([Word8], a)
    deserializeWithData' bytes = deserializeConstr bytes $ \constr_rep bytes ->
                                 gunfold (\(bytes, b_to_r) -> let (bytes', b) = deserializeWithData' bytes in (bytes', b_to_r b))
                                         (\x -> (bytes, x))
                                         (repConstr (dataTypeOf (undefined :: a)) constr_rep)

    serializeConstr :: ConstrRep -> [Word8] -> [Word8]
    serializeConstr (AlgConstr ix)   = serializeWord8 1 . serializeInt ix
    serializeConstr (IntConstr i)    = serializeWord8 2 . serializeInteger i
    serializeConstr (FloatConstr r)  = serializeWord8 3 . serializeRational r
    serializeConstr (CharConstr c)   = serializeWord8 4 . serializeChar c

    deserializeConstr :: [Word8] -> (ConstrRep -> [Word8] -> a) -> a
    deserializeConstr bytes k = deserializeWord8 bytes $ \constr_ix bytes ->
                                case constr_ix of
                                    1 -> deserializeInt      bytes $ \ix -> k (AlgConstr ix)
                                    2 -> deserializeInteger  bytes $ \i  -> k (IntConstr i)
                                    3 -> deserializeRational bytes $ \r  -> k (FloatConstr r)
                                    4 -> deserializeChar     bytes $ \c  -> k (CharConstr c)
                                    x -> error $ "deserializeConstr: unrecognised serialized constructor type " ++ show x ++ " in context " ++ show bytes

    serializeFixedWidthNum :: forall a. (Integral a, FiniteBits a) => a -> [Word8] -> [Word8]
    serializeFixedWidthNum what = go (finiteBitSize what) what
      where
        go :: Int -> a -> [Word8] -> [Word8]
        go size current rest
          | size <= 0 = rest
          | otherwise = fromIntegral (current .&. 255) : go (size - 8) (current `shiftR` 8) rest

    deserializeFixedWidthNum :: forall a b. (Integral a, FiniteBits a) => [Word8] -> (a -> [Word8] -> b) -> b
    deserializeFixedWidthNum bytes k = go (finiteBitSize (undefined :: a)) bytes k
      where
        go :: Int -> [Word8] -> (a -> [Word8] -> b) -> b
        go size bytes k
          | size <= 0 = k 0 bytes
          | otherwise = case bytes of
                            (byte:bytes) -> go (size - 8) bytes (\x -> k ((x `shiftL` 8) .|. fromIntegral byte))
                            []           -> error "deserializeFixedWidthNum: unexpected end of stream"

    serializeEnum :: (Enum a) => a -> [Word8] -> [Word8]
    serializeEnum = serializeInt . fromEnum

    deserializeEnum :: Enum a => [Word8] -> (a -> [Word8] -> b) -> b
    deserializeEnum bytes k = deserializeInt bytes (k . toEnum)

    serializeWord8 :: Word8 -> [Word8] -> [Word8]
    serializeWord8 x = (x:)

    deserializeWord8 :: [Word8] -> (Word8 -> [Word8] -> a) -> a
    deserializeWord8 (byte:bytes) k = k byte bytes
    deserializeWord8 []           _ = error "deserializeWord8: unexpected end of stream"

    serializeInt :: Int -> [Word8] -> [Word8]
    serializeInt = serializeFixedWidthNum

    deserializeInt :: [Word8] -> (Int -> [Word8] -> a) -> a
    deserializeInt = deserializeFixedWidthNum

    serializeRational :: (Real a) => a -> [Word8] -> [Word8]
    serializeRational = serializeString . show . toRational

    deserializeRational :: (Fractional a) => [Word8] -> (a -> [Word8] -> b) -> b
    deserializeRational bytes k = deserializeString bytes (k . fromRational . read)

    serializeInteger :: Integer -> [Word8] -> [Word8]
    serializeInteger = serializeString . show

    deserializeInteger :: [Word8] -> (Integer -> [Word8] -> a) -> a
    deserializeInteger bytes k = deserializeString bytes (k . read)

    serializeChar :: Char -> [Word8] -> [Word8]
    serializeChar = serializeString . show

    deserializeChar :: [Word8] -> (Char -> [Word8] -> a) -> a
    deserializeChar bytes k = deserializeString bytes (k . read)

    serializeString :: String -> [Word8] -> [Word8]
    serializeString = serializeList serializeEnum

    deserializeString :: [Word8] -> (String -> [Word8] -> a) -> a
    deserializeString = deserializeList deserializeEnum

    serializeList :: (a -> [Word8] -> [Word8]) -> [a] -> [Word8] -> [Word8]
    serializeList serialize_element xs = serializeInt (length xs) . foldr (.) id (map serialize_element xs)

    deserializeList :: forall a b. (forall c. [Word8] -> (a -> [Word8] -> c) -> c)
                    -> [Word8] -> ([a] -> [Word8] -> b) -> b
    deserializeList deserialize_element bytes k = deserializeInt bytes $ \len bytes -> go len bytes k
      where
        go :: Int -> [Word8] -> ([a] -> [Word8] -> b) -> b
        go len bytes k
          | len <= 0  = k [] bytes
          | otherwise = deserialize_element bytes (\elt bytes -> go (len - 1) bytes (k . (elt:)))