Clearly document applying DefaultBodyLimit to individual routes (#2157)

axum-core/src/extract/default_body_limit.rs

@@ -64,6 +64,28 @@ use tower_layer::Layer;
 /// extractors and want to sure a limit is also applied there then [`RequestBodyLimit`] should be
 /// used.
 ///
+/// # Different limits for different routes
+///
+/// `DefaultBodyLimit` can also be selectively applied to have different limits for different
+/// routes:
+///
+/// ```
+/// use axum::{
+///     Router,
+///     routing::post,
+///     body::Body,
+///     http::Request,
+///     extract::DefaultBodyLimit,
+/// };
+///
+/// let app = Router::new()
+///     // this route has a different limit
+///     .route("/", post(|request: Request<_>| async {}).layer(DefaultBodyLimit::max(1024)))
+///     // this route still has the default limit
+///     .route("/foo", post(|request: Request<_>| async {}));
+/// # let _: Router = app;
+/// ```
+///
 /// [`Body::data`]: http_body::Body::data
 /// [`Bytes`]: bytes::Bytes
 /// [`Json`]: https://docs.rs/axum/0.6.0/axum/struct.Json.html

axum/src/routing/tests/mod.rs

@@ -743,6 +743,75 @@ async fn changing_the_default_limit() {
     assert_eq!(res.status(), StatusCode::PAYLOAD_TOO_LARGE);
 }
 
+#[crate::test]
+async fn changing_the_default_limit_differently_on_different_routes() {
+    let limit1 = 2;
+    let limit2 = 10;
+
+    let app = Router::new()
+        .route(
+            "/limit1",
+            post(|_: Bytes| async {}).layer(DefaultBodyLimit::max(limit1)),
+        )
+        .route(
+            "/limit2",
+            post(|_: Bytes| async {}).layer(DefaultBodyLimit::max(limit2)),
+        )
+        .route("/default", post(|_: Bytes| async {}));
+
+    let client = TestClient::new(app);
+
+    let res = client
+        .post("/limit1")
+        .body(reqwest::Body::from("a".repeat(limit1)))
+        .send()
+        .await;
+    assert_eq!(res.status(), StatusCode::OK);
+
+    let res = client
+        .post("/limit1")
+        .body(reqwest::Body::from("a".repeat(limit2)))
+        .send()
+        .await;
+    assert_eq!(res.status(), StatusCode::PAYLOAD_TOO_LARGE);
+
+    let res = client
+        .post("/limit2")
+        .body(reqwest::Body::from("a".repeat(limit1)))
+        .send()
+        .await;
+    assert_eq!(res.status(), StatusCode::OK);
+
+    let res = client
+        .post("/limit2")
+        .body(reqwest::Body::from("a".repeat(limit2)))
+        .send()
+        .await;
+    assert_eq!(res.status(), StatusCode::OK);
+
+    let res = client
+        .post("/limit2")
+        .body(reqwest::Body::from("a".repeat(limit1 + limit2)))
+        .send()
+        .await;
+    assert_eq!(res.status(), StatusCode::PAYLOAD_TOO_LARGE);
+
+    let res = client
+        .post("/default")
+        .body(reqwest::Body::from("a".repeat(limit1 + limit2)))
+        .send()
+        .await;
+    assert_eq!(res.status(), StatusCode::OK);
+
+    let res = client
+        .post("/default")
+        // `DEFAULT_LIMIT` is 2mb so make a body larger than that
+        .body(reqwest::Body::from("a".repeat(3_000_000)))
+        .send()
+        .await;
+    assert_eq!(res.status(), StatusCode::PAYLOAD_TOO_LARGE);
+}
+
 #[crate::test]
 async fn limited_body_with_streaming_body() {
     const LIMIT: usize = 3;