feat: add pre-config function

Allows using the in-database configuration without SUPERUSER

src/PostgREST/CLI.hs

@@ -136,6 +136,9 @@ exampleConfigFile =
       |## Enable in-database configuration
       |db-config = true
       |
+      |## Function for in-database configuration
+      |## db-pre-config = "postgrest.pre_config"
+      |
       |## Extra schemas to add to the search_path of every request
       |db-extra-search-path = "public"
       |

src/PostgREST/Config.hs

@@ -80,6 +80,7 @@ data AppConfig = AppConfig
   , configDbRootSpec               :: Maybe QualifiedIdentifier
   , configDbSchemas                :: NonEmpty Text
   , configDbConfig                 :: Bool
+  , configDbPreConfig              :: Maybe QualifiedIdentifier
   , configDbTxAllowOverride        :: Bool
   , configDbTxRollbackAll          :: Bool
   , configDbUri                    :: Text
@@ -144,6 +145,7 @@ toText conf =
       ,("db-root-spec",              q . maybe mempty dumpQi . configDbRootSpec)
       ,("db-schemas",                q . T.intercalate "," . toList . configDbSchemas)
       ,("db-config",                     T.toLower . show . configDbConfig)
+      ,("db-pre-config",             q . maybe mempty dumpQi . configDbPreConfig)
       ,("db-tx-end",                 q . showTxEnd)
       ,("db-uri",                    q . configDbUri)
       ,("db-use-legacy-gucs",            T.toLower . show . configDbUseLegacyGucs)
@@ -240,6 +242,7 @@ parser optPath env dbSettings roleSettings =
     <*> (fromList . maybe ["public"] splitOnCommas <$> optWithAlias (optValue "db-schemas")
                                                                     (optValue "db-schema"))
     <*> (fromMaybe True <$> optBool "db-config")
+    <*> (fmap toQi <$> optString "db-pre-config")
     <*> parseTxEnd "db-tx-end" snd
     <*> parseTxEnd "db-tx-end" fst
     <*> (fromMaybe "postgresql://" <$> optString "db-uri")

src/PostgREST/Config/Database.hs

@@ -35,6 +35,7 @@ dbSettingsNames :: [Text]
 dbSettingsNames =
   (prefix <>) <$>
   ["db_anon_role"
+  ,"db_pre_config"
   ,"db_extra_search_path"
   ,"db_max_rows"
   ,"db_plan_enabled"
@@ -64,21 +65,21 @@ pgVersionStatement = SQL.Statement sql HE.noParams versionRow
     sql = "SELECT current_setting('server_version_num')::integer, current_setting('server_version')"
     versionRow = HD.singleRow $ PgVersion <$> column HD.int4 <*> column HD.text
 
-queryDbSettings :: Bool -> Session [(Text, Text)]
-queryDbSettings prepared =
-  let transaction = if prepared then SQL.transaction else SQL.unpreparedTransaction in
-  transaction SQL.ReadCommitted SQL.Read $ SQL.statement dbSettingsNames $ dbSettingsStatement prepared
-
--- | Get db settings from the connection role. Global settings will be overridden by database specific settings.
--- i.e. Doing:
---  ALTER ROLE authenticator IN DATABASE postgres SET <prefix>jwt_aud = 'val';
---  ALTER ROLE authenticator SET <prefix>jwt_aud = 'overridden';
--- Will result in <prefix>jwt_aud = 'overridden'
+-- | Query the in-database configuration. The settings have the following priorities:
 --
--- A setting on the database only will have no effect
---  ALTER DATABASE postgres SET <prefix>jwt_aud = 'xx'
-dbSettingsStatement :: Bool -> SQL.Statement [Text] [(Text, Text)]
-dbSettingsStatement = SQL.Statement sql (arrayParam HE.text) decodeSettings
+-- 1. Role + with database-specific settings:
+--    ALTER ROLE authenticator IN DATABASE postgres SET <prefix>jwt_aud = 'val';
+-- 2. Role + with settings:
+--    ALTER ROLE authenticator SET <prefix>jwt_aud = 'overridden';
+-- 3. pre-config function:
+--    CREATE FUNCTION pre_config() .. PERFORM set_config(<prefix>jwt_aud, 'pre_config_aud'..)
+--
+-- The example above will result in <prefix>jwt_aud = 'val'
+-- A setting on the database only will have no effect: ALTER DATABASE postgres SET <prefix>jwt_aud = 'xx'
+queryDbSettings :: Maybe Text -> Bool -> Session [(Text, Text)]
+queryDbSettings preConfFunc prepared =
+  let transaction = if prepared then SQL.transaction else SQL.unpreparedTransaction in
+  transaction SQL.ReadCommitted SQL.Read $ SQL.statement dbSettingsNames $ SQL.Statement sql (arrayParam HE.text) decodeSettings prepared
   where
     sql = [qc|
       WITH
@@ -94,14 +95,26 @@ dbSettingsStatement = SQL.Statement sql (arrayParam HE.text) decodeSettings
                substr(setting, 1, strpos(setting, '=') - 1) as k,
                substr(setting, strpos(setting, '=') + 1) as v
         FROM role_setting
+        {preConfigF}
       )
       SELECT DISTINCT ON (key)
              replace(k, '{prefix}', '') AS key,
              v AS value
       FROM kv_settings
-      WHERE k = ANY($1)
-      ORDER BY key, database DESC;
+      WHERE k = ANY($1) AND v IS NOT NULL
+      ORDER BY key, database DESC NULLS LAST;
     |]
+    preConfigF = case preConfFunc of
+      Nothing   -> mempty
+      Just func -> [qc|
+          UNION
+          SELECT
+            null as database,
+            x as k,
+            current_setting(x, true) as v
+          FROM unnest($1) x
+          JOIN {func}() _ ON TRUE
+      |]::Text
     decodeSettings = HD.rowList $ (,) <$> column HD.text <*> column HD.text
 
 queryRoleSettings :: Bool -> Session RoleSettings

src/PostgREST/Workers.hs

@@ -25,13 +25,17 @@ import Hasql.Connection (acquire)
 import Network.Socket
 import Network.Socket.ByteString
 
-import PostgREST.AppState         (AppState)
-import PostgREST.Config           (AppConfig (..), readAppConfig)
-import PostgREST.Config.Database  (queryDbSettings, queryPgVersion,
-                                   queryRoleSettings)
-import PostgREST.Config.PgVersion (PgVersion (..), minimumPgVersion)
-import PostgREST.Error            (checkIsFatal)
-import PostgREST.SchemaCache      (querySchemaCache)
+import PostgREST.AppState                (AppState)
+import PostgREST.Config                  (AppConfig (..),
+                                          readAppConfig)
+import PostgREST.Config.Database         (queryDbSettings,
+                                          queryPgVersion,
+                                          queryRoleSettings)
+import PostgREST.Config.PgVersion        (PgVersion (..),
+                                          minimumPgVersion)
+import PostgREST.Error                   (checkIsFatal)
+import PostgREST.SchemaCache             (querySchemaCache)
+import PostgREST.SchemaCache.Identifiers (dumpQi)
 
 import qualified PostgREST.AppState as AppState
 
@@ -89,8 +93,8 @@ connectionWorker appState = do
           when configDbChannelEnabled $
             AppState.signalListener appState
           AppState.logWithZTime appState "Connection successful"
-          -- this could be fail because the connection drops, but the
-          -- loadSchemaCache will pick the error and retry again
+          -- this could be fail because the connection drops, but the loadSchemaCache will pick the error and retry again
+          -- We cannot retry after it fails immediately, because db-pre-config could have user errors. We just log the error and continue.
           when configDbConfig $ reReadConfig False appState
           scStatus <- loadSchemaCache appState
           case scStatus of
@@ -237,7 +241,7 @@ reReadConfig startingUp appState = do
   AppConfig{..} <- AppState.getConfig appState
   dbSettings <-
     if configDbConfig then do
-      qDbSettings <- AppState.usePool appState $ queryDbSettings configDbPreparedStatements
+      qDbSettings <- AppState.usePool appState $ queryDbSettings (dumpQi <$> configDbPreConfig) configDbPreparedStatements
       case qDbSettings of
         Left e -> do
           AppState.logWithZTime appState