Propagate error cause to middlewares (actix#2280)

src/response/response.rs

@@ -49,7 +49,10 @@ impl HttpResponse<AnyBody> {
     /// Create an error response.
     #[inline]
     pub fn from_error(error: impl Into<Error>) -> Self {
-        error.into().as_response_error().error_response()
+        let error = error.into();
+        let mut response = error.as_response_error().error_response();
+        response.error = Some(error);
+        response
     }
 }
 

tests/test_error_propagation.rs

@@ -0,0 +1,100 @@
+use actix_utils::future::{ok, Ready};
+use actix_web::dev::{Service, ServiceRequest, ServiceResponse, Transform};
+use actix_web::test::{call_service, init_service, TestRequest};
+use actix_web::{HttpResponse, ResponseError};
+use futures_util::lock::Mutex;
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::{Context, Poll};
+
+#[derive(Debug, Clone)]
+pub struct MyError;
+
+impl ResponseError for MyError {}
+
+impl std::fmt::Display for MyError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "A custom error")
+    }
+}
+
+#[actix_web::get("/test")]
+async fn test() -> Result<actix_web::HttpResponse, actix_web::error::Error> {
+    Err(MyError)?;
+    Ok(HttpResponse::NoContent().finish())
+}
+
+#[derive(Clone)]
+pub struct SpyMiddleware(Arc<Mutex<Option<bool>>>);
+
+impl<S, B> Transform<S, ServiceRequest> for SpyMiddleware
+where
+    S: Service<ServiceRequest, Response = ServiceResponse<B>, Error = actix_web::Error>,
+    S::Future: 'static,
+    B: 'static,
+{
+    type Response = ServiceResponse<B>;
+    type Error = actix_web::Error;
+    type Transform = Middleware<S>;
+    type InitError = ();
+    type Future = Ready<Result<Self::Transform, Self::InitError>>;
+
+    fn new_transform(&self, service: S) -> Self::Future {
+        ok(Middleware {
+            was_error: self.0.clone(),
+            service,
+        })
+    }
+}
+
+#[doc(hidden)]
+pub struct Middleware<S> {
+    was_error: Arc<Mutex<Option<bool>>>,
+    service: S,
+}
+
+impl<S, B> Service<ServiceRequest> for Middleware<S>
+where
+    S: Service<ServiceRequest, Response = ServiceResponse<B>, Error = actix_web::Error>,
+    S::Future: 'static,
+    B: 'static,
+{
+    type Response = ServiceResponse<B>;
+    type Error = actix_web::Error;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>>>>;
+
+    fn poll_ready(&self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        self.service.poll_ready(cx)
+    }
+
+    fn call(&self, req: ServiceRequest) -> Self::Future {
+        let lock = self.was_error.clone();
+        let response_future = self.service.call(req);
+        Box::pin(async move {
+            let response = response_future.await;
+            if let Ok(success) = &response {
+                *lock.lock().await = Some(success.response().error().is_some());
+            }
+            response
+        })
+    }
+}
+
+#[actix_rt::test]
+async fn error_cause_should_be_propagated_to_middlewares() {
+    let lock = Arc::new(Mutex::new(None));
+    let spy_middleware = SpyMiddleware(lock.clone());
+
+    let app = init_service(
+        actix_web::App::new()
+            .wrap(spy_middleware.clone())
+            .service(test),
+    )
+    .await;
+
+    call_service(&app, TestRequest::with_uri("/test").to_request()).await;
+
+    let was_error_captured = lock.lock().await.unwrap();
+    assert!(was_error_captured);
+}