config forbid same server-port and admin-server-port

CHANGELOG.md

@@ -14,6 +14,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  - #2052, Dropped support for PostgreSQL 9.6 - @wolfgangwalther
  - #2052, Dropped support for PostgreSQL 10 - @wolfgangwalther
  - #2052, Dropped support for PostgreSQL 11 - @wolfgangwalther
+ - #3508, #3559, Server port and admin server port can end up with the same value - @develop7
+    + The app fails to start when the server port and admin server port are the same
 
 ## [12.2.0] - 2024-06-11
 

docs/references/configuration.rst

@@ -174,7 +174,7 @@ admin-server-port
   **In-Database** `n/a`
   =============== =======================
 
-  Specifies the port for the :ref:`admin_server`.
+  Specifies the port for the :ref:`admin_server`. Cannot be equal to :ref:`server-port`.
 
 .. _app.settings.*:
 

src/PostgREST/Config.hs

@@ -222,12 +222,21 @@
     Left err ->
       return . Left $ "Error in config " <> err
     Right parsedConfig ->
-      Right <$> decodeLoadFiles parsedConfig
+      case processForbiddenValues parsedConfig of
+        Left err' ->
+          return . Left $ "Error in config " <> err'
+        Right config ->
+          Right <$> decodeLoadFiles config
   where
     -- Both C.ParseError and IOError are shown here
     loadConfig :: FilePath -> IO (Either SomeException C.Config)
     loadConfig = try . C.load
 
+    processForbiddenValues :: AppConfig -> Either Text AppConfig
+    processForbiddenValues cfg@AppConfig{..}
+      | configAdminServerPort == Just configServerPort = Left "admin-server-port cannot be the same as server-port"
+      | otherwise = Right cfg
+
     decodeLoadFiles :: AppConfig -> IO AppConfig
     decodeLoadFiles parsedConfig =
       decodeJWKS <$>