feat(event_handler): define exception_handler directly from the router (#3979)

Adding router.exception_handler

Author: leandrodamascena

aws_lambda_powertools/event_handler/api_gateway.py

@@ -2133,6 +2133,9 @@ def include_router(self, router: "Router", prefix: Optional[str] = None) -> None
         logger.debug("Appending Router middlewares into App middlewares.")
         self._router_middlewares = self._router_middlewares + router._router_middlewares
 
+        logger.debug("Appending Router exception_handler into App exception_handler.")
+        self._exception_handlers.update(router._exception_handlers)
+
         # use pointer to allow context clearance after event is processed e.g., resolve(evt, ctx)
         router.context = self.context
 
@@ -2198,6 +2201,7 @@ def __init__(self):
         self._routes_with_middleware: Dict[tuple, List[Callable]] = {}
         self.api_resolver: Optional[BaseRouter] = None
         self.context = {}  # early init as customers might add context before event resolution
+        self._exception_handlers: Dict[Type, Callable] = {}
 
     def route(
         self,
@@ -2252,6 +2256,17 @@ def register_route(func: Callable):
 
         return register_route
 
+    def exception_handler(self, exc_class: Union[Type[Exception], List[Type[Exception]]]):
+        def register_exception_handler(func: Callable):
+            if isinstance(exc_class, list):
+                for exp in exc_class:
+                    self._exception_handlers[exp] = func
+            else:
+                self._exception_handlers[exc_class] = func
+            return func
+
+        return register_exception_handler
+
 
 class APIGatewayRestResolver(ApiGatewayResolver):
     current_event: APIGatewayProxyEvent

tests/functional/event_handler/test_api_gateway.py

@@ -1504,6 +1504,36 @@ def get_lambda(param: int): ...
     assert result["body"] == '{"msg":"Invalid data. Number of errors: 1"}'
 
 
+def test_exception_handler_with_route():
+    app = ApiGatewayResolver()
+    # GIVEN a Router object with an exception handler defined for ValueError
+    router = Router()
+
+    @router.exception_handler(ValueError)
+    def handle_value_error(ex: ValueError):
+        print(f"request path is '{app.current_event.path}'")
+        return Response(
+            status_code=418,
+            content_type=content_types.TEXT_HTML,
+            body=str(ex),
+        )
+
+    @router.get("/my/path")
+    def get_lambda() -> Response:
+        raise ValueError("Foo!")
+
+    app.include_router(router)
+
+    # WHEN calling the event handler
+    # AND a ValueError is raised
+    result = app(LOAD_GW_EVENT, {})
+
+    # THEN call the exception_handler from Router
+    assert result["statusCode"] == 418
+    assert result["multiValueHeaders"]["Content-Type"] == [content_types.TEXT_HTML]
+    assert result["body"] == "Foo!"
+
+
 def test_data_validation_error():
     # GIVEN a resolver without an exception handler
     app = ApiGatewayResolver(enable_validation=True)