Add ability to set default error handlers to the ErrorHandler middleware

actix-web/CHANGES.md

@@ -1,12 +1,16 @@
 # Changelog
 
 ## Unreleased - 2022-xx-xx
+### Changed
 - Minimum supported Rust version (MSRV) is now 1.57 due to transitive `time` dependency.
 ### Added
 - Add `ServiceRequest::{parts, request}()` getter methods. [#2786]
+- Add `ErrorHandlers::default_handler()` (as well as `default_handler_{server, client}()`) to make registering handlers with the `ErrorHandlers` middleware easier. [#2784]
 
+[#2784]: https://github.com/actix/actix-web/pull/2784
 [#2786]: https://github.com/actix/actix-web/pull/2786
 
+
 ## 4.1.0 - 2022-06-11
 ### Added
 - Add `ServiceRequest::extract()` to make it easier to use extractors when writing middlewares. [#2647]

actix-web/src/middleware/err_handlers.rs

@@ -30,11 +30,25 @@ pub enum ErrorHandlerResponse<B> {
 
 type ErrorHandler<B> = dyn Fn(ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>>;
 
+type DefaultHandler<B> = Option<Rc<ErrorHandler<B>>>;
+
 /// Middleware for registering custom status code based error handlers.
 ///
-/// Register handlers with the `ErrorHandlers::handler()` method to register a custom error handler
+/// Register handlers with the [`ErrorHandlers::handler()`] method to register a custom error handler
 /// for a given status code. Handlers can modify existing responses or create completely new ones.
 ///
+/// To register a default handler, use the [`ErrorHandlers::default_handler()`] method. This
+/// handler will be used only if a response has an error status code (400-599) that isn't covered by
+/// a more specific handler (set with the [`handler()`][ErrorHandlers::handler] method). See examples
+/// below.
+///
+/// To register a default for only client errors (400-499) or only server errors (500-599), use the
+/// [`ErrorHandlers::default_handler_client()`] and [`ErrorHandlers::default_handler_server()`]
+/// methods, respectively.
+///
+/// Any response with a status code that isn't covered by a specific handler or a default handler
+/// will pass by unchanged by this middleware.
+///
 /// # Examples
 /// ```
 /// use actix_web::http::{header, StatusCode};
@@ -53,7 +67,70 @@ type ErrorHandler<B> = dyn Fn(ServiceResponse<B>) -> Result<ErrorHandlerResponse
 ///     .wrap(ErrorHandlers::new().handler(StatusCode::INTERNAL_SERVER_ERROR, add_error_header))
 ///     .service(web::resource("/").route(web::get().to(HttpResponse::InternalServerError)));
 /// ```
+/// ## Registering default handler
+/// ```
+/// # use actix_web::http::{header, StatusCode};
+/// # use actix_web::middleware::{ErrorHandlerResponse, ErrorHandlers};
+/// # use actix_web::{dev, web, App, HttpResponse, Result};
+/// fn add_error_header<B>(mut res: dev::ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>> {
+///     res.response_mut().headers_mut().insert(
+///         header::CONTENT_TYPE,
+///         header::HeaderValue::from_static("Error"),
+///     );
+///     Ok(ErrorHandlerResponse::Response(res.map_into_left_body()))
+/// }
+///
+/// fn handle_bad_request<B>(mut res: dev::ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>> {
+///     res.response_mut().headers_mut().insert(
+///         header::CONTENT_TYPE,
+///         header::HeaderValue::from_static("Bad Request Error"),
+///     );
+///     Ok(ErrorHandlerResponse::Response(res.map_into_left_body()))
+/// }
+///
+/// // Bad Request errors will hit `handle_bad_request()`, while all other errors will hit
+/// // `add_error_header()`. The order in which the methods are called is not meaningful.
+/// let app = App::new()
+///     .wrap(
+///         ErrorHandlers::new()
+///             .default_handler(add_error_header)
+///             .handler(StatusCode::BAD_REQUEST, handle_bad_request)
+///     )
+///     .service(web::resource("/").route(web::get().to(HttpResponse::InternalServerError)));
+/// ```
+/// Alternatively, you can set default handlers for only client or only server errors:
+///
+/// ```rust
+/// # use actix_web::http::{header, StatusCode};
+/// # use actix_web::middleware::{ErrorHandlerResponse, ErrorHandlers};
+/// # use actix_web::{dev, web, App, HttpResponse, Result};
+/// # fn add_error_header<B>(mut res: dev::ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>> {
+/// #     res.response_mut().headers_mut().insert(
+/// #         header::CONTENT_TYPE,
+/// #         header::HeaderValue::from_static("Error"),
+/// #     );
+/// #     Ok(ErrorHandlerResponse::Response(res.map_into_left_body()))
+/// # }
+/// # fn handle_bad_request<B>(mut res: dev::ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>> {
+/// #     res.response_mut().headers_mut().insert(
+/// #         header::CONTENT_TYPE,
+/// #         header::HeaderValue::from_static("Bad Request Error"),
+/// #     );
+/// #     Ok(ErrorHandlerResponse::Response(res.map_into_left_body()))
+/// # }
+/// // Bad request errors will hit `handle_bad_request()`, other client errors will hit
+/// // `add_error_header()`, and server errors will pass through unchanged
+/// let app = App::new()
+///     .wrap(
+///         ErrorHandlers::new()
+///             .default_handler_client(add_error_header) // or .default_handler_server
+///             .handler(StatusCode::BAD_REQUEST, handle_bad_request)
+///     )
+///     .service(web::resource("/").route(web::get().to(HttpResponse::InternalServerError)));
+/// ```
 pub struct ErrorHandlers<B> {
+    default_client: DefaultHandler<B>,
+    default_server: DefaultHandler<B>,
     handlers: Handlers<B>,
 }
 
@@ -62,6 +139,8 @@ type Handlers<B> = Rc<AHashMap<StatusCode, Box<ErrorHandler<B>>>>;
 impl<B> Default for ErrorHandlers<B> {
     fn default() -> Self {
         ErrorHandlers {
+            default_client: Default::default(),
+            default_server: Default::default(),
             handlers: Default::default(),
         }
     }
@@ -83,6 +162,66 @@ impl<B> ErrorHandlers<B> {
             .insert(status, Box::new(handler));
         self
     }
+
+    /// Register a default error handler.
+    ///
+    /// Any request with a status code that hasn't been given a specific other handler (by calling
+    /// [`.handler()`][ErrorHandlers::handler]) will fall back on this.
+    ///
+    /// Note that this will overwrite any default handlers previously set by calling
+    /// [`.default_handler_client()`][ErrorHandlers::default_handler_client] or
+    /// [`.default_handler_server()`][ErrorHandlers::default_handler_server], but not any set by
+    /// calling [`.handler()`][ErrorHandlers::handler].
+    pub fn default_handler<F>(self, handler: F) -> Self
+    where
+        F: Fn(ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>> + 'static,
+    {
+        let handler = Rc::new(handler);
+        Self {
+            default_server: Some(handler.clone()),
+            default_client: Some(handler),
+            ..self
+        }
+    }
+
+    /// Register a handler on which to fall back for client error status codes (400-499).
+    pub fn default_handler_client<F>(self, handler: F) -> Self
+    where
+        F: Fn(ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>> + 'static,
+    {
+        Self {
+            default_client: Some(Rc::new(handler)),
+            ..self
+        }
+    }
+
+    /// Register a handler on which to fall back for server error status codes (500-599).
+    pub fn default_handler_server<F>(self, handler: F) -> Self
+    where
+        F: Fn(ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>> + 'static,
+    {
+        Self {
+            default_server: Some(Rc::new(handler)),
+            ..self
+        }
+    }
+
+    /// Selects the most appropriate handler for the given status code.
+    ///
+    /// If the `handlers` map has an entry for that status code, that handler is returned.
+    /// Otherwise, fall back on the appropriate default handler.
+    fn get_handler<'a>(
+        status: &StatusCode,
+        default_client: Option<&'a ErrorHandler<B>>,
+        default_server: Option<&'a ErrorHandler<B>>,
+        handlers: &'a Handlers<B>,
+    ) -> Option<&'a ErrorHandler<B>> {
+        handlers
+            .get(status)
+            .map(|h| h.as_ref())
+            .or_else(|| status.is_client_error().then(|| default_client).flatten())
+            .or_else(|| status.is_server_error().then(|| default_server).flatten())
+    }
 }
 
 impl<S, B> Transform<S, ServiceRequest> for ErrorHandlers<B>
@@ -99,13 +238,24 @@ where
 
     fn new_transform(&self, service: S) -> Self::Future {
         let handlers = self.handlers.clone();
-        Box::pin(async move { Ok(ErrorHandlersMiddleware { service, handlers }) })
+        let default_client = self.default_client.clone();
+        let default_server = self.default_server.clone();
+        Box::pin(async move {
+            Ok(ErrorHandlersMiddleware {
+                service,
+                default_client,
+                default_server,
+                handlers,
+            })
+        })
     }
 }
 
 #[doc(hidden)]
 pub struct ErrorHandlersMiddleware<S, B> {
     service: S,
+    default_client: DefaultHandler<B>,
+    default_server: DefaultHandler<B>,
     handlers: Handlers<B>,
 }
 
@@ -123,8 +273,15 @@ where
 
     fn call(&self, req: ServiceRequest) -> Self::Future {
         let handlers = self.handlers.clone();
+        let default_client = self.default_client.clone();
+        let default_server = self.default_server.clone();
         let fut = self.service.call(req);
-        ErrorHandlersFuture::ServiceFuture { fut, handlers }
+        ErrorHandlersFuture::ServiceFuture {
+            fut,
+            default_client,
+            default_server,
+            handlers,
+        }
     }
 }
 
@@ -137,6 +294,8 @@ pin_project! {
         ServiceFuture {
             #[pin]
             fut: Fut,
+            default_client: DefaultHandler<B>,
+            default_server: DefaultHandler<B>,
             handlers: Handlers<B>,
         },
         ErrorHandlerFuture {
@@ -153,10 +312,22 @@ where
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
         match self.as_mut().project() {
-            ErrorHandlersProj::ServiceFuture { fut, handlers } => {
+            ErrorHandlersProj::ServiceFuture {
+                fut,
+                default_client,
+                default_server,
+                handlers,
+            } => {
                 let res = ready!(fut.poll(cx))?;
-
-                match handlers.get(&res.status()) {
+                let status = res.status();
+
+                let handler = ErrorHandlers::get_handler(
+                    &status,
+                    default_client.as_mut().map(|f| Rc::as_ref(f)),
+                    default_server.as_mut().map(|f| Rc::as_ref(f)),
+                    handlers,
+                );
+                match handler {
                     Some(handler) => match handler(res)? {
                         ErrorHandlerResponse::Response(res) => Poll::Ready(Ok(res)),
                         ErrorHandlerResponse::Future(fut) => {
@@ -166,7 +337,6 @@ where
                             self.poll(cx)
                         }
                     },
-
                     None => Poll::Ready(Ok(res.map_into_left_body())),
                 }
             }
@@ -298,4 +468,117 @@ mod tests {
             "error in error handler"
         );
     }
+
+    #[actix_rt::test]
+    async fn default_error_handler() {
+        #[allow(clippy::unnecessary_wraps)]
+        fn error_handler<B>(mut res: ServiceResponse<B>) -> Result<ErrorHandlerResponse<B>> {
+            res.response_mut()
+                .headers_mut()
+                .insert(CONTENT_TYPE, HeaderValue::from_static("0001"));
+            Ok(ErrorHandlerResponse::Response(res.map_into_left_body()))
+        }
+
+        let make_mw = |status| async move {
+            ErrorHandlers::new()
+                .default_handler(error_handler)
+                .new_transform(test::status_service(status).into_service())
+                .await
+                .unwrap()
+        };
+        let mw_server = make_mw(StatusCode::INTERNAL_SERVER_ERROR).await;
+        let mw_client = make_mw(StatusCode::BAD_REQUEST).await;
+
+        let resp =
+            test::call_service(&mw_client, TestRequest::default().to_srv_request()).await;
+        assert_eq!(resp.headers().get(CONTENT_TYPE).unwrap(), "0001");
+
+        let resp =
+            test::call_service(&mw_server, TestRequest::default().to_srv_request()).await;
+        assert_eq!(resp.headers().get(CONTENT_TYPE).unwrap(), "0001");
+    }
+
+    #[actix_rt::test]
+    async fn default_handlers_separate_client_server() {
+        #[allow(clippy::unnecessary_wraps)]
+        fn error_handler_client<B>(
+            mut res: ServiceResponse<B>,
+        ) -> Result<ErrorHandlerResponse<B>> {
+            res.response_mut()
+                .headers_mut()
+                .insert(CONTENT_TYPE, HeaderValue::from_static("0001"));
+            Ok(ErrorHandlerResponse::Response(res.map_into_left_body()))
+        }
+
+        #[allow(clippy::unnecessary_wraps)]
+        fn error_handler_server<B>(
+            mut res: ServiceResponse<B>,
+        ) -> Result<ErrorHandlerResponse<B>> {
+            res.response_mut()
+                .headers_mut()
+                .insert(CONTENT_TYPE, HeaderValue::from_static("0002"));
+            Ok(ErrorHandlerResponse::Response(res.map_into_left_body()))
+        }
+
+        let make_mw = |status| async move {
+            ErrorHandlers::new()
+                .default_handler_server(error_handler_server)
+                .default_handler_client(error_handler_client)
+                .new_transform(test::status_service(status).into_service())
+                .await
+                .unwrap()
+        };
+        let mw_server = make_mw(StatusCode::INTERNAL_SERVER_ERROR).await;
+        let mw_client = make_mw(StatusCode::BAD_REQUEST).await;
+
+        let resp =
+            test::call_service(&mw_client, TestRequest::default().to_srv_request()).await;
+        assert_eq!(resp.headers().get(CONTENT_TYPE).unwrap(), "0001");
+
+        let resp =
+            test::call_service(&mw_server, TestRequest::default().to_srv_request()).await;
+        assert_eq!(resp.headers().get(CONTENT_TYPE).unwrap(), "0002");
+    }
+
+    #[actix_rt::test]
+    async fn default_handlers_specialization() {
+        #[allow(clippy::unnecessary_wraps)]
+        fn error_handler_client<B>(
+            mut res: ServiceResponse<B>,
+        ) -> Result<ErrorHandlerResponse<B>> {
+            res.response_mut()
+                .headers_mut()
+                .insert(CONTENT_TYPE, HeaderValue::from_static("0001"));
+            Ok(ErrorHandlerResponse::Response(res.map_into_left_body()))
+        }
+
+        #[allow(clippy::unnecessary_wraps)]
+        fn error_handler_specific<B>(
+            mut res: ServiceResponse<B>,
+        ) -> Result<ErrorHandlerResponse<B>> {
+            res.response_mut()
+                .headers_mut()
+                .insert(CONTENT_TYPE, HeaderValue::from_static("0003"));
+            Ok(ErrorHandlerResponse::Response(res.map_into_left_body()))
+        }
+
+        let make_mw = |status| async move {
+            ErrorHandlers::new()
+                .default_handler_client(error_handler_client)
+                .handler(StatusCode::UNPROCESSABLE_ENTITY, error_handler_specific)
+                .new_transform(test::status_service(status).into_service())
+                .await
+                .unwrap()
+        };
+        let mw_client = make_mw(StatusCode::BAD_REQUEST).await;
+        let mw_specific = make_mw(StatusCode::UNPROCESSABLE_ENTITY).await;
+
+        let resp =
+            test::call_service(&mw_client, TestRequest::default().to_srv_request()).await;
+        assert_eq!(resp.headers().get(CONTENT_TYPE).unwrap(), "0001");
+
+        let resp =
+            test::call_service(&mw_specific, TestRequest::default().to_srv_request()).await;
+        assert_eq!(resp.headers().get(CONTENT_TYPE).unwrap(), "0003");
+    }
 }