refactor: cache the isolation level

src/PostgREST/Config.hs

@@ -51,7 +51,8 @@ import Numeric                 (readOct, showOct)
 import System.Environment      (getEnvironment)
 import System.Posix.Types      (FileMode)
 
-import PostgREST.Config.Database         (RoleSettings)
+import PostgREST.Config.Database         (RoleIsolationLvl,
+                                          RoleSettings)
 import PostgREST.Config.JSPath           (JSPath, JSPathExp (..),
                                           dumpJSPath, pRoleClaimKey)
 import PostgREST.Config.Proxy            (Proxy (..),
@@ -103,6 +104,7 @@ data AppConfig = AppConfig
   , configServerUnixSocketMode     :: FileMode
   , configAdminServerPort          :: Maybe Int
   , configRoleSettings             :: RoleSettings
+  , configRoleIsoLvl               :: RoleIsolationLvl
   , configInternalSCSleep          :: Maybe Int32
   }
 
@@ -198,13 +200,13 @@ instance JustIfMaybe a (Maybe a) where
 
 -- | Reads and parses the config and overrides its parameters from env vars,
 -- files or db settings.
-readAppConfig :: [(Text, Text)] -> Maybe FilePath -> Maybe Text -> RoleSettings -> IO (Either Text AppConfig)
-readAppConfig dbSettings optPath prevDbUri roleSettings = do
+readAppConfig :: [(Text, Text)] -> Maybe FilePath -> Maybe Text -> RoleSettings -> RoleIsolationLvl -> IO (Either Text AppConfig)
+readAppConfig dbSettings optPath prevDbUri roleSettings roleIsolationLvl = do
   env <- readPGRSTEnvironment
   -- if no filename provided, start with an empty map to read config from environment
   conf <- maybe (return $ Right M.empty) loadConfig optPath
 
-  case C.runParser (parser optPath env dbSettings roleSettings) =<< mapLeft show conf of
+  case C.runParser (parser optPath env dbSettings roleSettings roleIsolationLvl) =<< mapLeft show conf of
     Left err ->
       return . Left $ "Error in config " <> err
     Right parsedConfig ->
@@ -219,8 +221,8 @@ readAppConfig dbSettings optPath prevDbUri roleSettings = do
       decodeJWKS <$>
         (decodeSecret =<< readSecretFile =<< readDbUriFile prevDbUri parsedConfig)
 
-parser :: Maybe FilePath -> Environment -> [(Text, Text)] -> RoleSettings -> C.Parser C.Config AppConfig
-parser optPath env dbSettings roleSettings =
+parser :: Maybe FilePath -> Environment -> [(Text, Text)] -> RoleSettings -> RoleIsolationLvl -> C.Parser C.Config AppConfig
+parser optPath env dbSettings roleSettings roleIsolationLvl =
   AppConfig
     <$> parseAppSettings "app.settings"
     <*> (fmap encodeUtf8 <$> optString "db-anon-role")
@@ -268,6 +270,7 @@ parser optPath env dbSettings roleSettings =
     <*> parseSocketFileMode "server-unix-socket-mode"
     <*> optInt "admin-server-port"
     <*> pure roleSettings
+    <*> pure roleIsolationLvl
     <*> optInt "internal-schema-cache-sleep"
   where
     parseAppSettings :: C.Key -> C.Parser C.Config [(Text, Text)]