refactor: Split main/Main.hs into library modules

src/PostgREST/Config/Database.hs

@@ -0,0 +1,55 @@
+{-# LANGUAGE QuasiQuotes #-}
+
+module PostgREST.Config.Database
+  ( loadDbSettings
+  ) where
+
+import qualified Hasql.Decoders             as HD
+import qualified Hasql.Encoders             as HE
+import qualified Hasql.Pool                 as P
+import qualified Hasql.Statement            as H
+import qualified Hasql.Transaction          as HT
+import qualified Hasql.Transaction.Sessions as HT
+
+import Data.Text.IO                  (hPutStrLn)
+import Text.InterpolatedString.Perl6 (q)
+
+import Protolude hiding (hPutStrLn)
+
+
+loadDbSettings :: P.Pool -> IO [(Text, Text)]
+loadDbSettings pool = do
+  result <-
+    P.use pool . HT.transaction HT.ReadCommitted HT.Read $
+      HT.statement mempty dbSettingsStatement
+  case result of
+    Left  e -> do
+      hPutStrLn stderr $
+        "An error ocurred when trying to query database settings for the config parameters:\n"
+        <> show e
+      pure []
+    Right x -> pure x
+
+-- | Get db settings from the connection role. Global settings will be overridden by database specific settings.
+dbSettingsStatement :: H.Statement () [(Text, Text)]
+dbSettingsStatement = H.Statement sql HE.noParams decodeSettings False
+  where
+    sql = [q|
+      with
+      role_setting as (
+        select setdatabase, unnest(setconfig) as setting from pg_catalog.pg_db_role_setting
+        where setrole = current_user::regrole::oid
+          and setdatabase in (0, (select oid from pg_catalog.pg_database where datname = current_catalog))
+      ),
+      kv_settings as (
+        select setdatabase, split_part(setting, '=', 1) as k, split_part(setting, '=', 2) as value from role_setting
+        where setting like 'pgrst.%'
+      )
+      select distinct on (key) replace(k, 'pgrst.', '') as key, value
+      from kv_settings
+      order by key, setdatabase desc;
+    |]
+    decodeSettings = HD.rowList $ (,) <$> column HD.text <*> column HD.text
+
+column :: HD.Value a -> HD.Row a
+column = HD.column . HD.nonNullable