feat: allow reloading config with NOTIFY

Enables reloading the config by doing:
NOTIFY pgrst, 'reload config'

Adds an alias for reloading the schema cache:
NOTIFY pgrst, 'reload schema'

main/Main.hs

@@ -1,4 +1,5 @@
-{-# LANGUAGE CPP #-}
+{-# LANGUAGE CPP        #-}
+{-# LANGUAGE MultiWayIf #-}
 
 module Main (main) where
 
@@ -13,10 +14,6 @@ import qualified Hasql.Transaction.Sessions as HT
 
 import Control.AutoUpdate       (defaultUpdateSettings, mkAutoUpdate,
                                  updateAction)
-import Control.Debounce         (debounceAction, debounceEdge,
-                                 debounceFreq,
-                                 defaultDebounceSettings, mkDebounce,
-                                 trailingEdge)
 import Control.Retry            (RetryStatus, capDelay,
                                  exponentialBackoff, retrying,
                                  rsPreviousDelay)
@@ -64,11 +61,11 @@ main = do
   -- read PGRST_ env variables
   env <- readEnvironment
 
-  -- read path from commad line
-  opts <- readCLIShowHelp env
+  -- read command/path from commad line
+  (command, confPath) <- ((,) <$> cliCommand <*> cliPath) <$> readCLIShowHelp env
 
   -- build the 'AppConfig' from the config file path
-  conf <- readValidateConfig mempty env $ cliPath opts
+  conf <- readValidateConfig mempty env confPath
 
   -- These are config values that can't be reloaded at runtime. Reloading some of them would imply restarting the web server.
   let
@@ -105,11 +102,12 @@ main = do
   -- Config that can change at runtime
   refConf <- newIORef conf
 
+  let configRereader = reReadConfig pool gucConfigEnabled env confPath refConf
+
   -- re-read and override the config if db-load-guc-config is true
-  when gucConfigEnabled $
-    reReadConfig pool gucConfigEnabled env (cliPath opts) refConf
+  when gucConfigEnabled configRereader
 
-  case cliCommand opts of
+  case command of
     CmdDumpConfig ->
       do
         dumpedConfig <- dumpAppConfig <$> readIORef refConf
@@ -149,13 +147,13 @@ main = do
 
   -- Re-read the config on SIGUSR2
   void $ installHandler sigUSR2 (
-    Catch $ reReadConfig pool gucConfigEnabled env (cliPath opts) refConf >> putStrLn ("Config reloaded" :: Text)
+    Catch $ configRereader >> putStrLn ("Config reloaded" :: Text)
     ) Nothing
 #endif
 
-  -- reload schema cache on NOTIFY
+  -- reload schema cache + config on NOTIFY
   when dbChannelEnabled $
-    listener dbUri dbChannel pool refConf refDbStructure mvarConnectionStatus connWorker
+    listener dbUri dbChannel pool refConf refDbStructure mvarConnectionStatus connWorker configRereader
 
   -- ask for the OS time at most once per second
   getTime <- mkAutoUpdate defaultUpdateSettings {updateAction = getCurrentTime}
@@ -310,32 +308,27 @@ loadSchemaCache pool actualPgVersion refConf refDbStructure = do
   When a NOTIFY <db-channel> - with an empty payload - is done, it refills the schema cache.
   It uses the connectionWorker in case the LISTEN connection dies.
 -}
-listener :: ByteString -> Text -> P.Pool -> IORef AppConfig -> IORef (Maybe DbStructure) -> MVar ConnectionStatus -> IO () -> IO ()
-listener dbUri dbChannel pool refConf refDbStructure mvarConnectionStatus connWorker = start
+listener :: ByteString -> Text -> P.Pool -> IORef AppConfig -> IORef (Maybe DbStructure) -> MVar ConnectionStatus -> IO () -> IO () -> IO ()
+listener dbUri dbChannel pool refConf refDbStructure mvarConnectionStatus connWorker configRereader = start
   where
     start = do
       connStatus <- takeMVar mvarConnectionStatus -- takeMVar makes the thread wait if the MVar is empty(until there's a connection).
       case connStatus of
         Connected actualPgVersion -> void $ forkFinally (do -- forkFinally allows to detect if the thread dies
           dbOrError <- C.acquire dbUri
-          -- Debounce in case too many NOTIFYs arrive. Could happen on a migration(assuming a pg EVENT TRIGGER is set up).
-          -- This might not be needed according to pg docs https://www.postgresql.org/docs/12/sql-notify.html:
-          -- "If the same channel name is signaled multiple times from the same transaction with identical payload strings, the database server can decide to deliver a single notification only."
-          -- But we do it to be extra safe.
-          scFiller <- mkDebounce (defaultDebounceSettings {
-                        -- It's not necessary to check the loadSchemaCache success here. If the connection drops, the thread will die and proceed to recover below.
-                        debounceAction = void $ loadSchemaCache pool actualPgVersion refConf refDbStructure,
-                        debounceEdge = trailingEdge, -- wait until the function hasn’t been called in _1s
-                        debounceFreq = _1s })
           case dbOrError of
             Right db -> do
               putStrLn $ "Listening for notifications on the " <> dbChannel <> " channel"
               let channelToListen = N.toPgIdentifier dbChannel
+                  cfLoader = configRereader >> putStrLn ("Config reloaded" :: Text)
+                  scLoader = void $ loadSchemaCache pool actualPgVersion refConf refDbStructure -- It's not necessary to check the loadSchemaCache success here. If the connection drops, the thread will die and proceed to recover below.
               N.listen db channelToListen
               N.waitForNotifications (\_ msg ->
-                if BS.null msg
-                  then scFiller    -- reload the schema cache
-                  else pure ()) db -- Do nothing if anything else than an empty message is sent
+                if | BS.null msg            -> scLoader -- reload the schema cache
+                   | msg == "reload schema" -> scLoader -- reload the schema cache
+                   | msg == "reload config" -> cfLoader -- reload the config
+                   | otherwise              -> pure ()  -- Do nothing if anything else than an empty message is sent
+                ) db
             _ -> die errorMessage)
           (\_ -> do -- if the thread dies, we try to recover
             putStrLn retryMessage

test/fixtures/roles.sql

@@ -17,7 +17,7 @@ ALTER ROLE postgrest_test_authenticator SET pgrst."db-tx-end" = 'commit-allow-ov
 ALTER ROLE postgrest_test_authenticator SET pgrst."db-schemas" = 'test, tenant1, tenant2';
 ALTER ROLE postgrest_test_authenticator SET pgrst."db-root-spec" = 'root';
 ALTER ROLE postgrest_test_authenticator SET pgrst."db-prepared-statements" = 'false';
-ALTER ROLE postgrest_test_authenticator SET pgrst."db-pre-request" = 'custom_headers';
+ALTER ROLE postgrest_test_authenticator SET pgrst."db-pre-request" = 'test.custom_headers';
 ALTER ROLE postgrest_test_authenticator SET pgrst."db-max-rows" = '1000';
 ALTER ROLE postgrest_test_authenticator SET pgrst."db-extra-search-path" = 'public, extensions';
 

test/fixtures/schema.sql

@@ -1925,9 +1925,33 @@ $$ language sql;
 create view prepared_statements as
 select * from pg_catalog.pg_prepared_statements;
 
-create or replace function change_max_rows_config(val int) returns void as $_$
+create or replace function change_max_rows_config(val int, notify bool default false) returns void as $_$
 begin
   execute format($$
     alter role postgrest_test_authenticator set pgrst."db-max-rows" = %L;
   $$, val);
+  if notify then
+    perform pg_notify('pgrst', 'reload config');
+  end if;
+end $_$ volatile security definer language plpgsql ;
+
+create or replace function reset_max_rows_config() returns void as $_$
+begin
+  alter role postgrest_test_authenticator set pgrst."db-max-rows" = '1000';
+end $_$ volatile security definer language plpgsql ;
+
+create or replace function change_db_schema_and_full_reload(schemas text) returns void as $_$
+begin
+  execute format($$
+    alter role postgrest_test_authenticator set pgrst."db-schemas" = %L;
+  $$, schemas);
+  perform pg_notify('pgrst', 'reload config');
+  perform pg_notify('pgrst', 'reload schema');
+end $_$ volatile security definer language plpgsql ;
+
+create or replace function v1.reset_db_schema_config() returns void as $_$
+begin
+  alter role postgrest_test_authenticator set pgrst."db-schemas" = 'test';
+  perform pg_notify('pgrst', 'reload config');
+  perform pg_notify('pgrst', 'reload schema');
 end $_$ volatile security definer language plpgsql ;

test/io-tests/configs/expected/no-defaults-with-db.config

@@ -5,7 +5,7 @@ db-extra-search-path = "public,extensions"
 db-max-rows = 1000
 db-pool = 1
 db-pool-timeout = 100
-db-pre-request = "custom_headers"
+db-pre-request = "test.custom_headers"
 db-prepared-statements = false
 db-root-spec = "root"
 db-schemas = "test,tenant1,tenant2"

test/io-tests/test_io.py

@@ -87,7 +87,7 @@ def defaultenv():
         "PGRST_DB_URI": os.environ["PGRST_DB_URI"],
         "PGRST_DB_SCHEMAS": os.environ["PGRST_DB_SCHEMAS"],
         "PGRST_DB_ANON_ROLE": os.environ["PGRST_DB_ANON_ROLE"],
-        "PGRST_DB_LOAD_GUC_CONFIG": "false"
+        "PGRST_DB_LOAD_GUC_CONFIG": "false",
     }
 
 
@@ -187,7 +187,6 @@ def wait_until_ready(url):
     for _ in range(10):
         try:
             response = session.get(url, timeout=1)
-
             if response.status_code == 200:
                 return
         except (requests.ConnectionError, requests.ReadTimeout):
@@ -508,6 +507,34 @@ def test_db_schema_reload(tmp_path, defaultenv):
         assert response.status_code == 200
 
 
+def test_db_schema_notify_reload(defaultenv):
+    "DB schema and config should be reloaded when PostgREST is sent a NOTIFY"
+
+    env = {
+        **defaultenv,
+        "PGRST_DB_LOAD_GUC_CONFIG": "true",
+        "PGRST_DB_CHANNEL_ENABLED": "true",
+        "PGRST_DB_SCHEMAS": "test",
+    }
+
+    with run(env=env) as postgrest:
+        response = postgrest.session.get("/parents")
+        assert response.status_code == 404
+
+        # change db-schemas config on the db and reload config and cache with notify
+        postgrest.session.post(
+            "/rpc/change_db_schema_and_full_reload", data={"schemas": "v1"}
+        )
+
+        time.sleep(0.5)
+
+        response = postgrest.session.get("/parents?select=*,children(*)")
+        assert response.status_code == 200
+
+        # reset db-schemas config on the db
+        postgrest.session.post("/rpc/reset_db_schema_config")
+
+
 def test_max_rows_reload(defaultenv):
     "max-rows should be reloaded from role settings when PostgREST receives a SIGUSR2."
     config = CONFIGSDIR / "sigusr2-settings.config"
@@ -530,4 +557,36 @@ def test_max_rows_reload(defaultenv):
         time.sleep(0.1)
 
         response = postgrest.session.head("/projects")
+
         assert response.headers["Content-Range"] == "0-0/*"
+
+        # reset max-rows config on the db
+        postgrest.session.post("/rpc/reset_max_rows_config")
+
+
+def test_max_rows_notify_reload(defaultenv):
+    "max-rows should be reloaded from role settings when PostgREST receives a NOTIFY"
+
+    env = {
+        **defaultenv,
+        "PGRST_DB_LOAD_GUC_CONFIG": "true",
+        "PGRST_DB_CHANNEL_ENABLED": "true",
+    }
+
+    with run(env=env) as postgrest:
+        response = postgrest.session.head("/projects")
+        assert response.headers["Content-Range"] == "0-4/*"
+
+        # change max-rows config on the db and reload with notify
+        postgrest.session.post(
+            "/rpc/change_max_rows_config", data={"val": 1, "notify": True}
+        )
+
+        time.sleep(0.1)
+
+        response = postgrest.session.head("/projects")
+
+        assert response.headers["Content-Range"] == "0-0/*"
+
+        # reset max-rows config on the db
+        postgrest.session.post("/rpc/reset_max_rows_config")