Extract utility functions

These are later going to be used by the client too

src/Forest/Util.hs

@@ -0,0 +1,36 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Forest.Util
+  ( withThread
+  , sendPacket
+  , receivePacket
+  , closeWithErrorMessage
+  ) where
+
+import           Control.Concurrent.Async
+import           Data.Aeson
+import qualified Data.Text                as T
+import qualified Network.WebSockets       as WS
+
+withThread :: IO () -> IO () -> IO ()
+withThread thread main = withAsync thread $ const main
+
+sendPacket :: ToJSON a => WS.Connection -> a -> IO ()
+sendPacket conn packet = WS.sendTextData conn $ encode packet
+
+closeWithErrorMessage :: WS.Connection -> T.Text -> IO ()
+closeWithErrorMessage conn = WS.sendCloseCode conn 1003
+
+receivePacket :: FromJSON a => WS.Connection -> IO (Maybe a)
+receivePacket conn = do
+  dataMessage <- WS.receiveDataMessage conn
+  closeOnErrorMessage $ case dataMessage of
+    WS.Binary _  -> Left "Invalid message format: Binary"
+    WS.Text bs _ -> case eitherDecode' bs of
+      Left errorMsg -> Left $ "Invalid packet: " <> T.pack errorMsg
+      Right packet  -> Right packet
+  where
+    closeOnErrorMessage :: Either T.Text a -> IO (Maybe a)
+    closeOnErrorMessage (Right a) = pure $ Just a
+    closeOnErrorMessage (Left errorMsg) =
+      Nothing <$ closeWithErrorMessage conn errorMsg