Check whether connection succeeded and set encoding in connect

lib/Database/PostgreSQL/Opium.hs

@@ -5,6 +5,7 @@
 module Database.PostgreSQL.Opium
     -- * Connection Management
   ( Connection
+  , ConnectionError
   , connect
   , close
     -- * Queries
@@ -40,7 +41,7 @@ import Database.PostgreSQL.LibPQ (Result)
 import qualified Data.Text.Encoding as Encoding
 import qualified Database.PostgreSQL.LibPQ as LibPQ
 
-import Database.PostgreSQL.Opium.Connection (Connection, connect, close, withRawConnection)
+import Database.PostgreSQL.Opium.Connection (Connection, ConnectionError, connect, close, withRawConnection)
 import Database.PostgreSQL.Opium.Error (Error (..), ErrorPosition (..))
 import Database.PostgreSQL.Opium.FromField (FromField (..), RawField (..))
 import Database.PostgreSQL.Opium.FromRow (FromRow (..), ColumnTable)

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
@@ -10,15 +12,21 @@ 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
   => (Maybe LibPQ.Connection -> IO a)
@@ -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

opium.cabal

@@ -126,6 +126,7 @@ test-suite opium-test
         base,
         opium,
         bytestring,
+        containers,
         hspec,
         postgresql-libpq,
         time,

test/SpecHook.hs

@@ -8,7 +8,6 @@ import Test.Hspec (Spec, SpecWith, around)
 import Text.Printf (printf)
 
 import qualified Data.Text as Text
-import qualified Data.Text.Encoding as Encoding
 
 import qualified Database.PostgreSQL.Opium as Opium
 
@@ -20,7 +19,7 @@ setupConnection = do
   Just dbPort <- lookupEnv "DB_PORT"
 
   let dsn = printf "host=localhost user=%s password=%s dbname=%s port=%s" dbUser dbPass dbName dbPort
-  conn <- Opium.connect $ Encoding.encodeUtf8 $ Text.pack dsn
+  Right conn <- Opium.connect $ Text.pack dsn
 
   Right _ <- Opium.execute_ "DROP TABLE IF EXISTS person" conn
   Right _ <- Opium.execute_ "CREATE TABLE person (name TEXT NOT NULL, age INT NOT NULL, score DOUBLE PRECISION NOT NULL, motto TEXT)" conn