Add RawField utility type

test/Database/PostgreSQL/Opium/FromFieldSpec.hs

@@ -11,6 +11,8 @@ import Database.PostgreSQL.Opium (FromRow)
 import GHC.Generics (Generic)
 import Test.Hspec (SpecWith, describe, it, shouldBe, shouldSatisfy)
 
+import qualified Data.ByteString as BS
+
 import qualified Database.PostgreSQL.Opium as Opium
 
 newtype AnInt = AnInt
@@ -79,7 +81,13 @@ newtype ADay = ADay
 
 instance FromRow ADay where
 
-shouldFetch :: (Eq a, FromRow a, Show a) => Connection -> ByteString -> [a] -> IO ()
+newtype ARawField = ARawField
+  { raw :: Opium.RawField
+  } deriving (Eq, Generic, Show)
+
+instance FromRow ARawField where
+
+shouldFetch :: (Eq a, FromRow a, Show a) => Connection -> Text -> [a] -> IO ()
 shouldFetch conn query expectedRows = do
   actualRows <- Opium.fetch_ conn query
   actualRows `shouldBe` Right expectedRows
@@ -214,3 +222,12 @@ spec = do
       shouldFetch conn "SELECT date '2023-09-23' AS day" [ADay $ fromGregorian 2023 9 23]
       -- Example from postgres doc page
       shouldFetch conn "SELECT date 'J2451187' AS day" [ADay $ fromGregorian 1999 1 8]
+
+  describe "FromField RawField" $ do
+    it "Simply returns the bytestring without decoding it" $ \conn -> do
+      shouldFetch conn "SELECT 'Hello, World!'::bytea AS raw" [ARawField $ Opium.RawField "Hello, World!"]
+      shouldFetch conn "SELECT 42::int AS raw" [ARawField $ Opium.RawField "\0\0\0\42"]
+      shouldFetch conn "SELECT 42::bigint AS raw" [ARawField $ Opium.RawField "\0\0\0\0\0\0\0\42"]
+      -- Opium assumes that the connection always uses UTF-8.
+      -- The query string is encoded using UTF-8 before passing it to @libpq@.
+      shouldFetch conn "SELECT 'Ära'::text AS raw" [ARawField $ Opium.RawField $ BS.pack [0xC3, 0x84, 0x72, 0x61]]