Backport changes from main to v0.6.x (#2141)

Co-authored-by: David Pedersen <[email protected]>

axum/CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **added:** `WebSocketUpgrade::write_buffer_size` and `WebSocketUpgrade::max_write_buffer_size`
 - **changed:** Deprecate `WebSocketUpgrade::max_send_queue`
 - **change:** Update tokio-tungstenite to 0.20
+- **added:** Implement `Handler` for `T: IntoResponse` ([#2140])
+
+[#2140]: https://github.com/tokio-rs/axum/pull/2140
 
 # 0.6.19 (17. July, 2023)
 

axum/src/handler/mod.rs

@@ -103,6 +103,31 @@ pub use self::service::HandlerService;
 /// {}
 /// ```
 #[doc = include_str!("../docs/debugging_handler_type_errors.md")]
+///
+/// # Handlers that aren't functions
+///
+/// The `Handler` trait is also implemented for `T: IntoResponse`. That allows easily returning
+/// fixed data for routes:
+///
+/// ```
+/// use axum::{
+///     Router,
+///     routing::{get, post},
+///     Json,
+///     http::StatusCode,
+/// };
+/// use serde_json::json;
+///
+/// let app = Router::new()
+///     // respond with a fixed string
+///     .route("/", get("Hello, World!"))
+///     // or return some mock data
+///     .route("/users", post((
+///         StatusCode::CREATED,
+///         Json(json!({ "id": 1, "username": "alice" })),
+///     )));
+/// # let _: Router = app;
+/// ```
 #[cfg_attr(
     nightly_error_messages,
     rustc_on_unimplemented(
@@ -231,6 +256,24 @@ macro_rules! impl_handler {
 
 all_the_tuples!(impl_handler);
 
+mod private {
+    // Marker type for `impl<T: IntoResponse> Handler for T`
+    #[allow(missing_debug_implementations)]
+    pub enum IntoResponseHandler {}
+}
+
+impl<T, S, B> Handler<private::IntoResponseHandler, S, B> for T
+where
+    T: IntoResponse + Clone + Send + 'static,
+    B: Send + 'static,
+{
+    type Future = std::future::Ready<Response>;
+
+    fn call(self, _req: Request<B>, _state: S) -> Self::Future {
+        std::future::ready(self.into_response())
+    }
+}
+
 /// A [`Service`] created from a [`Handler`] by applying a Tower middleware.
 ///
 /// Created with [`Handler::layer`]. See that method for more details.

axum/src/routing/tests/mod.rs

@@ -1026,3 +1026,14 @@ async fn connect_going_to_default_fallback() {
     let body = hyper::body::to_bytes(res).await.unwrap();
     assert!(body.is_empty());
 }
+
+#[crate::test]
+async fn impl_handler_for_into_response() {
+    let app = Router::new().route("/things", post((StatusCode::CREATED, "thing created")));
+
+    let client = TestClient::new(app);
+
+    let res = client.post("/things").send().await;
+    assert_eq!(res.status(), StatusCode::CREATED);
+    assert_eq!(res.text().await, "thing created");
+}