Expose external attributes on zipping only

For #6 -- based on patch by @utdemir

Codec/Archive/Zip/Conduit/Types.hs

@@ -10,7 +10,7 @@ import           Data.String (IsString(..))
 import qualified Data.Text as T
 import           Data.Time.LocalTime (LocalTime)
 import           Data.Typeable (Typeable)
-import           Data.Word (Word64)
+import           Data.Word (Word32, Word64)
 
 -- |Errors thrown during zip file processing
 newtype ZipError = ZipError String
@@ -33,6 +33,7 @@ data ZipEntry = ZipEntry
   { zipEntryName :: Either T.Text ByteString -- ^File name (in posix format, no leading slashes), either UTF-8 encoded text or raw bytes (CP437), with a trailing slash for directories
   , zipEntryTime :: LocalTime -- ^Modification time
   , zipEntrySize :: Maybe Word64 -- ^Size of file data (if known); checked on zipping and also used as hint to enable zip64
+  , zipEntryExternalAttributes :: Maybe Word32 -- ^Host-dependent attributes, often MS-DOS directory attribute byte (only supported when zipping)
   } deriving (Eq, Show)
 
 -- |The data contents for a 'ZipEntry'. For empty entries (e.g., directories), use 'mempty'.

Codec/Archive/Zip/Conduit/UnZip.hs

@@ -221,6 +221,7 @@ unZipStream = next where
         { zipEntryName = if testBit gpf 11 then Left (TE.decodeUtf8 name) else Right name
         , zipEntryTime = time
         , zipEntrySize = if testBit gpf 3 then Nothing else Just extZip64USize
+        , zipEntryExternalAttributes = Nothing
         }
       , fileDecompress = dcomp
       , fileCSize = extZip64CSize

Codec/Archive/Zip/Conduit/Zip.hs

@@ -192,7 +192,7 @@ zipStream ZipOptions{..} = execStateC 0 $ do
       P.putWord16le 0 -- comment length
       P.putWord16le 0 -- disk number
       P.putWord16le 0 -- internal file attributes
-      P.putWord32le 0 -- external file attributes
+      P.putWord32le $ fromMaybe 0 zipEntryExternalAttributes
       P.putWord32le $ if o64 then maxBound32 else fromIntegral off
       P.putByteString name
       when a64 $ do

cmd/zip.hs

@@ -48,6 +48,7 @@ generate (p:paths) = do
         { zipEntryName = Right $ BSC.pack $ dropWhile ('/' ==) p
         , zipEntryTime = utcToLocalTime utc t -- FIXME: timezone
         , zipEntrySize = Nothing
+        , zipEntryExternalAttributes = Nothing
         }
   isd <- liftIO $ doesDirectoryExist p
   if isd