1 files changed, 48 insertions, 0 deletions
diff --git a/iserv/src/Remote/Message.hs b/iserv/src/Remote/Message.hs
new file mode 100644
index 0000000000..faef45dcab
--- /dev/null
+++ b/iserv/src/Remote/Message.hs
@@ -0,0 +1,48 @@
+{-# LANGUAGE GADTs, StandaloneDeriving, ExistentialQuantification #-}
+
+module Remote.Message
+  ( SlaveMessage(..)
+  , SlaveMsg(..)
+  , sha256sum
+  , putSlaveMessage
+  , getSlaveMessage )
+where
+
+import Data.Binary
+import Data.ByteString as BS (ByteString, readFile)
+
+import Crypto.Hash
+
+type Sha256Hash = String
+
+sha256 :: ByteString -> Digest SHA256
+sha256 = hash
+
+sha256sum :: FilePath -> IO Sha256Hash
+sha256sum path = (show . sha256) <$> BS.readFile path
+
+-- | A @SlaveMessage a@ is message from the iserv process on the
+-- target, requesting something from the Proxy of with result type @a@.
+data SlaveMessage a where
+  -- sends either a new file, or nothing if the file is acceptable.
+  Have     :: FilePath -> Sha256Hash -> SlaveMessage (Maybe ByteString)
+  Missing  :: FilePath -> SlaveMessage ByteString
+  Done     :: SlaveMessage ()
+
+deriving instance Show (SlaveMessage a)
+
+putSlaveMessage :: SlaveMessage a -> Put
+putSlaveMessage m = case m of
+  Have path sha  -> putWord8 0 >> put path >> put sha
+  Missing path   -> putWord8 1 >> put path
+  Done           -> putWord8 2
+
+data SlaveMsg = forall a . (Binary a, Show a) => SlaveMsg (SlaveMessage a)
+
+getSlaveMessage :: Get SlaveMsg
+getSlaveMessage = do
+  b <- getWord8
+  case b of
+    0 -> SlaveMsg <$> (Have   <$> get <*> get)
+    1 -> SlaveMsg <$> Missing <$> get
+    2 -> return (SlaveMsg Done)