feat(event_handler): allow customers to catch request validation errors (#3396)

Author: rubenfonseca

aws_lambda_powertools/event_handler/api_gateway.py

@@ -32,6 +32,7 @@
 from aws_lambda_powertools.event_handler import content_types
 from aws_lambda_powertools.event_handler.exceptions import NotFoundError, ServiceError
 from aws_lambda_powertools.event_handler.openapi.constants import DEFAULT_API_VERSION, DEFAULT_OPENAPI_VERSION
+from aws_lambda_powertools.event_handler.openapi.exceptions import RequestValidationError
 from aws_lambda_powertools.event_handler.openapi.swagger_ui.html import generate_swagger_html
 from aws_lambda_powertools.event_handler.openapi.types import (
     COMPONENT_REF_PREFIX,
@@ -1972,6 +1973,17 @@ def _call_exception_handler(self, exp: Exception, route: Route) -> Optional[Resp
             except ServiceError as service_error:
                 exp = service_error
 
+        if isinstance(exp, RequestValidationError):
+            return self._response_builder_class(
+                response=Response(
+                    status_code=HTTPStatus.UNPROCESSABLE_ENTITY,
+                    content_type=content_types.APPLICATION_JSON,
+                    body={"statusCode": HTTPStatus.UNPROCESSABLE_ENTITY, "message": exp.errors()},
+                ),
+                serializer=self._serializer,
+                route=route,
+            )
+
         if isinstance(exp, ServiceError):
             return self._response_builder_class(
                 response=Response(

aws_lambda_powertools/event_handler/middlewares/openapi_validation.py

@@ -62,50 +62,43 @@ def handler(self, app: EventHandlerInstance, next_middleware: NextMiddleware) ->
         values: Dict[str, Any] = {}
         errors: List[Any] = []
 
-        try:
-            # Process path values, which can be found on the route_args
-            path_values, path_errors = _request_params_to_args(
-                route.dependant.path_params,
-                app.context["_route_args"],
+        # Process path values, which can be found on the route_args
+        path_values, path_errors = _request_params_to_args(
+            route.dependant.path_params,
+            app.context["_route_args"],
+        )
+
+        # Process query values
+        query_values, query_errors = _request_params_to_args(
+            route.dependant.query_params,
+            app.current_event.query_string_parameters or {},
+        )
+
+        values.update(path_values)
+        values.update(query_values)
+        errors += path_errors + query_errors
+
+        # Process the request body, if it exists
+        if route.dependant.body_params:
+            (body_values, body_errors) = _request_body_to_args(
+                required_params=route.dependant.body_params,
+                received_body=self._get_body(app),
             )
+            values.update(body_values)
+            errors.extend(body_errors)
 
-            # Process query values
-            query_values, query_errors = _request_params_to_args(
-                route.dependant.query_params,
-                app.current_event.query_string_parameters or {},
-            )
-
-            values.update(path_values)
-            values.update(query_values)
-            errors += path_errors + query_errors
+        if errors:
+            # Raise the validation errors
+            raise RequestValidationError(_normalize_errors(errors))
+        else:
+            # Re-write the route_args with the validated values, and call the next middleware
+            app.context["_route_args"] = values
 
-            # Process the request body, if it exists
-            if route.dependant.body_params:
-                (body_values, body_errors) = _request_body_to_args(
-                    required_params=route.dependant.body_params,
-                    received_body=self._get_body(app),
-                )
-                values.update(body_values)
-                errors.extend(body_errors)
+            # Call the handler by calling the next middleware
+            response = next_middleware(app)
 
-            if errors:
-                # Raise the validation errors
-                raise RequestValidationError(_normalize_errors(errors))
-            else:
-                # Re-write the route_args with the validated values, and call the next middleware
-                app.context["_route_args"] = values
-
-                # Call the handler by calling the next middleware
-                response = next_middleware(app)
-
-                # Process the response
-                return self._handle_response(route=route, response=response)
-        except RequestValidationError as e:
-            return Response(
-                status_code=422,
-                content_type="application/json",
-                body=json.dumps({"detail": e.errors()}),
-            )
+            # Process the response
+            return self._handle_response(route=route, response=response)
 
     def _handle_response(self, *, route: Route, response: Response):
         # Process the response body if it exists

tests/functional/event_handler/test_api_gateway.py

@@ -30,6 +30,7 @@
     ServiceError,
     UnauthorizedError,
 )
+from aws_lambda_powertools.event_handler.openapi.exceptions import RequestValidationError
 from aws_lambda_powertools.shared import constants
 from aws_lambda_powertools.shared.cookies import Cookie
 from aws_lambda_powertools.shared.json_encoder import Encoder
@@ -1458,6 +1459,51 @@ def get_lambda() -> Response:
     assert result["body"] == "Foo!"
 
 
+def test_exception_handler_with_data_validation():
+    # GIVEN a resolver with an exception handler defined for RequestValidationError
+    app = ApiGatewayResolver(enable_validation=True)
+
+    @app.exception_handler(RequestValidationError)
+    def handle_validation_error(ex: RequestValidationError):
+        print(f"request path is '{app.current_event.path}'")
+        return Response(
+            status_code=422,
+            content_type=content_types.TEXT_PLAIN,
+            body=f"Invalid data. Number of errors: {len(ex.errors())}",
+        )
+
+    @app.get("/my/path")
+    def get_lambda(param: int):
+        ...
+
+    # WHEN calling the event handler
+    # AND a RequestValidationError is raised
+    result = app(LOAD_GW_EVENT, {})
+
+    # THEN call the exception_handler
+    assert result["statusCode"] == 422
+    assert result["multiValueHeaders"]["Content-Type"] == [content_types.TEXT_PLAIN]
+    assert result["body"] == "Invalid data. Number of errors: 1"
+
+
+def test_data_validation_error():
+    # GIVEN a resolver without an exception handler
+    app = ApiGatewayResolver(enable_validation=True)
+
+    @app.get("/my/path")
+    def get_lambda(param: int):
+        ...
+
+    # WHEN calling the event handler
+    # AND a RequestValidationError is raised
+    result = app(LOAD_GW_EVENT, {})
+
+    # THEN call the exception_handler
+    assert result["statusCode"] == 422
+    assert result["multiValueHeaders"]["Content-Type"] == [content_types.APPLICATION_JSON]
+    assert "missing" in result["body"]
+
+
 def test_exception_handler_service_error():
     # GIVEN
     app = ApiGatewayResolver()

tests/functional/event_handler/test_openapi_validation_middleware.py

@@ -343,7 +343,7 @@ class Model(BaseModel):
     # WHEN a handler is defined with a body parameter
     @app.post("/")
     def handler(user: Model) -> Response[Model]:
-        return Response(body=user, status_code=200)
+        return Response(body=user, status_code=200, content_type="application/json")
 
     LOAD_GW_EVENT["httpMethod"] = "POST"
     LOAD_GW_EVENT["path"] = "/"
@@ -353,7 +353,7 @@ def handler(user: Model) -> Response[Model]:
     # THEN the body must be a dict
     result = app(LOAD_GW_EVENT, {})
     assert result["statusCode"] == 200
-    assert result["body"] == {"name": "John", "age": 30}
+    assert json.loads(result["body"]) == {"name": "John", "age": 30}
 
 
 def test_validate_response_invalid_return():