Add encodeWithSize to Encode

src/FilePack/Encode.hs

@@ -7,43 +7,69 @@ import Data.ByteString.Char8 qualified as BC
 import Data.Text (Text)
 import Data.Text.Encoding (encodeUtf8)
 import Data.Word (Word32, Word8)
+import System.Posix (CMode (..), FileMode)
 
 class Encode a where
-    encode :: a -> ByteString
+  encode :: a -> ByteString
+  encode = BS.drop 4 . encodeWithSize
+
+  encodeWithSize :: a -> ByteString
+  encodeWithSize x =
+    let s = encode x
+        l = fromIntegral $ BS.length s
+     in word32ToByteString l <> s
+
+  {-# MINIMAL encode | encodeWithSize #-}
 
 instance Encode ByteString where
-    encode = id
+  encode = id
 
 instance Encode Text where
-    encode = encodeUtf8
+  encode = encodeUtf8
 
 instance Encode String where
-    encode = BC.pack
+  encode = BC.pack
 
 type Byte = Word8
 
-{- | @word32ToBytes@ splits a 32bit word into its 4 byte components.
-
- >>> word32ToBytes 0xdeadbeef
- (222,173,190,239)
--}
+-- | @word32ToBytes@ splits a 32bit word into its 4 byte components.
+--
+-- >>> word32ToBytes 0xdeadbeef
+-- (222,173,190,239)
+--
+-- >>> word32ToBytes 4
+-- (0,0,0,4)
 word32ToBytes :: Word32 -> (Byte, Byte, Byte, Byte)
 word32ToBytes word = (a, b, c, d)
-  where
-    !a = fromIntegral $ (word .&. 0xff000000) `shift` (-24)
-    !b = fromIntegral $ (word .&. 0x00ff0000) `shift` (-16)
-    !c = fromIntegral $ (word .&. 0x0000ff00) `shift` (-8)
-    !d = fromIntegral $ (word .&. 0x000000ff) `shift` (-0)
+ where
+  !a = fromIntegral $ (word .&. 0xff000000) `shift` (-24)
+  !b = fromIntegral $ (word .&. 0x00ff0000) `shift` (-16)
+  !c = fromIntegral $ (word .&. 0x0000ff00) `shift` (-8)
+  !d = fromIntegral $ (word .&. 0x000000ff) `shift` (-0)
 
-{- | @word32ToByteString@ encodes a 32-bit wide word into a bytestring.
-
- >>> word32ToByteString 0xdeadbeef
- "\222\173\190\239"
--}
+-- | @word32ToByteString@ encodes a 32-bit wide word into a bytestring.
+--
+-- >>> word32ToByteString 0xdeadbeef
+-- "\222\173\190\239"
 word32ToByteString :: Word32 -> ByteString
 word32ToByteString word =
-    let (a, b, c, d) = word32ToBytes word
-     in BS.pack [a, b, c, d]
+  let (a, b, c, d) = word32ToBytes word
+   in BS.pack [a, b, c, d]
 
 instance Encode Word32 where
-    encode = word32ToByteString
+  encode = word32ToByteString
+  encodeWithSize w =
+    let (a, b, c, d) = word32ToBytes w
+     in BS.pack
+          [ 0
+          , 0
+          , 0
+          , 4
+          , a
+          , b
+          , c
+          , d
+          ]
+
+instance Encode FileMode where
+  encode (CMode mode) = encode mode