Check whether connection succeeded and set encoding in connect

lib/Database/PostgreSQL/Opium/Connection.hs

@@ -1,8 +1,10 @@
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE OverloadedRecordDot #-}
+{-# LANGUAGE OverloadedStrings #-}
 
 module Database.PostgreSQL.Opium.Connection
   ( Connection
+  , ConnectionError
   , unsafeWithRawConnection
   , withRawConnection
   , connect
@@ -10,14 +12,20 @@ module Database.PostgreSQL.Opium.Connection
   ) where
 
 import Control.Concurrent.MVar (MVar, newMVar, modifyMVar_, withMVar)
-import Data.ByteString (ByteString)
+import Data.Maybe (fromMaybe)
+import Data.Text (Text)
+import Database.PostgreSQL.LibPQ (ConnStatus (..))
 import GHC.Stack (HasCallStack)
 
+import qualified Data.Text.Encoding as Encoding
 import qualified Database.PostgreSQL.LibPQ as LibPQ
 
 newtype Connection = Connection
   { rawConnection :: MVar (Maybe LibPQ.Connection)
-  } 
+  }
+
+newtype ConnectionError = ConnectionError Text
+  deriving (Show)
 
 withRawConnection
   :: HasCallStack
@@ -35,11 +43,18 @@ unsafeWithRawConnection f = withRawConnection $ \case
   Nothing -> error "raw connection is missing! perhaps the connection was already closed."
   Just rawConn -> f rawConn
 
-connect :: ByteString -> IO Connection
+connect :: Text -> IO (Either ConnectionError Connection)
 connect connectionString = do
-  rawConn <- LibPQ.connectdb connectionString
-
-  Connection <$> newMVar (Just rawConn)
+  -- Appending the client_encoding setting overrides any previous setting in the connection string.
+  -- We set the client encoding here to make sure we can use it below for decoding connection
+  -- error messages.
+  rawConn <- LibPQ.connectdb $ Encoding.encodeUtf8 $ connectionString <> " client_encoding=UTF8"
+  status <- LibPQ.status rawConn
+  if status == ConnectionOk then
+    Right . Connection <$> newMVar (Just rawConn)
+  else do
+    rawError <- fromMaybe "" <$> LibPQ.errorMessage rawConn
+    pure $ Left $ ConnectionError $ Encoding.decodeUtf8Lenient rawError
 
 close :: Connection -> IO ()
 close conn = modifyMVar_ conn.rawConnection $ \case