Add RawField utility type

lib/Database/PostgreSQL/Opium/FromField.hs

@@ -3,8 +3,11 @@
 {-# LANGUAGE TypeApplications #-}
 
 module Database.PostgreSQL.Opium.FromField
-  ( FromField (..)
+  ( -- * Decoding data from @libpq@
+    FromField (..)
   , fromField
+    -- * Utility types
+  , RawField (..)
   ) where
 
 import Data.Attoparsec.ByteString (Parser)
@@ -37,15 +40,19 @@ class FromField a where
   validOid :: Proxy a -> Oid -> Bool
   parseField :: Parser a
 
+-- | See https://www.postgresql.org/docs/current/datatype-binary.html.
+-- Accepts @bytea@.
 instance FromField ByteString where
   validOid Proxy = Oid.bytea
   parseField = AP.takeByteString
 
 -- | See https://www.postgresql.org/docs/current/datatype-character.html.
+-- Accepts @text@, @character@ and @character varying@.
 instance FromField Text where
   validOid Proxy = Oid.text \/ Oid.character \/ Oid.characterVarying
   parseField = Encoding.decodeUtf8 <$> AP.takeByteString
 
+-- Accepts @text@, @character@ and @character varying@.
 -- | See https://www.postgresql.org/docs/current/datatype-character.html.
 instance FromField String where
   validOid Proxy = validOid @Text Proxy
@@ -117,3 +124,10 @@ instance FromField Day where
   parseField = fromJulianDay . fromIntegral <$> intParser @Int32
     where
       fromJulianDay x = ModifiedJulianDay $ x + 51544
+
+newtype RawField = RawField ByteString
+  deriving (Eq, Show)
+
+instance FromField RawField where
+  validOid Proxy = const True
+  parseField = RawField <$> AP.takeByteString