fix: ensure BaseRouteHandler.on_registration is only called once per handler

litestar/app.py

@@ -657,7 +657,7 @@ def _create_route_handler_method_map(
 
         return route_map
 
-    def _build_routes(self, route_handlers: Iterable[BaseRouteHandler]) -> list[HTTPRoute | ASGIRoute | WebSocketRoute]:
+    def _build_routes(self, route_handlers: Iterable[BaseRouteHandler]) -> list[HTTPRoute | ASGIRoute | WebSocketRoute]:  # noqa: C901
         """Create routes for all the handlers"""
         routes: list[HTTPRoute | ASGIRoute | WebSocketRoute] = []
 
@@ -683,11 +683,19 @@ def _build_routes(self, route_handlers: Iterable[BaseRouteHandler]) -> list[HTTP
                 HTTPRoute(path=path, route_handlers=_maybe_add_options_handler(path, http_handlers, root=self))
             )
 
+        registered_route_handlers = set()
+
         for finalized_route in routes:
             route_handlers = get_route_handlers(finalized_route)
 
             for route_handler in route_handlers:
-                route_handler.on_registration(route=finalized_route, app=self)
+                # handlers can be registered multiple times, if they define multiple
+                # paths. in these cases, we don't want to call 'on_registration' more
+                # than once, so we keep track of the handlers we've already called this
+                # hook
+                if route_handler not in registered_route_handlers:
+                    route_handler.on_registration(route=finalized_route, app=self)
+                    registered_route_handlers.add(route_handler)
 
             for plugin in self.plugins.receive_route:
                 plugin.receive_route(finalized_route)

tests/unit/test_app.py

@@ -10,6 +10,7 @@
 import pytest
 from click import Group
 from pytest import MonkeyPatch
+from pytest_mock import MockerFixture
 
 from litestar import Litestar, MediaType, Request, Response, get
 from litestar.config.app import AppConfig, ExperimentalFeatures
@@ -22,6 +23,7 @@
     LitestarWarning,
     NotFoundException,
 )
+from litestar.handlers import BaseRouteHandler
 from litestar.plugins import CLIPlugin
 from litestar.status_codes import HTTP_200_OK, HTTP_400_BAD_REQUEST, HTTP_500_INTERNAL_SERVER_ERROR
 from litestar.testing import TestClient, create_test_client
@@ -424,3 +426,24 @@ def handler(scope: Scope) -> None:
         client.get("/")
 
     mock.assert_called_once_with(app)
+
+
+def test_handler_registration_on_registration_called_only_once(mocker: MockerFixture) -> None:
+    mock_on_registration = mocker.spy(BaseRouteHandler, "on_registration")
+
+    @get(["/a", "/b"], name="hello_this_is_a_test")
+    async def handler() -> None:
+        pass
+
+    Litestar([handler], openapi_config=None)
+
+    assert (
+        len(
+            [
+                c
+                for c in mock_on_registration.call_args_list
+                if isinstance(c.args[0], BaseRouteHandler) and c.args[0].name == "hello_this_is_a_test"
+            ]
+        )
+        == 1
+    )