Use 400 Bad Request for FailedToDeserializeQueryString rejections (#1387)

* Use `400 Bad Request` for `FailedToDeserializeQueryString` rejections

Fixes https://github.com/tokio-rs/axum/issues/1378

From [the spec] about `422 Unprocessable Entity`:

> For example, this error condition may occur if an XML request body
> contains well-formed (i.e., syntactically correct), but semantically
> erroneous, XML instructions.

I understand this to mean that query params shouldn't use 422 because
that is about the request body.

So this changes `FailedToDeserializeQueryString` from `422 Unprocessable
Entity` to `400 Bad Request`.

[the spec]: https://datatracker.ietf.org/doc/html/rfc4918#section-11.2

* changelog

axum/CHANGELOG.md

@@ -12,8 +12,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   `serde_json::Error` ([#1371])
 - **added**: `JsonRejection` now displays the path at which a deserialization
   error occurred too ([#1371])
+- **fixed:** Used `400 Bad Request` for `FailedToDeserializeQueryString`
+  rejections, instead of `422 Unprocessable Entity` ([#1387])
 
 [#1371]: https://github.com/tokio-rs/axum/pull/1371
+[#1387]: https://github.com/tokio-rs/axum/pull/1387
 
 # 0.6.0-rc.2 (10. September, 2022)
 

axum/src/extract/query.rs

@@ -75,9 +75,11 @@ impl<T> Deref for Query<T> {
 
 #[cfg(test)]
 mod tests {
+    use crate::{routing::get, test_helpers::TestClient, Router};
+
     use super::*;
     use axum_core::extract::FromRequest;
-    use http::Request;
+    use http::{Request, StatusCode};
     use serde::Deserialize;
     use std::fmt::Debug;
 
@@ -124,4 +126,21 @@ mod tests {
         )
         .await;
     }
+
+    #[tokio::test]
+    async fn correct_rejection_status_code() {
+        #[derive(Deserialize)]
+        #[allow(dead_code)]
+        struct Params {
+            n: i32,
+        }
+
+        async fn handler(_: Query<Params>) {}
+
+        let app = Router::new().route("/", get(handler));
+        let client = TestClient::new(app);
+
+        let res = client.get("/?n=hi").send().await;
+        assert_eq!(res.status(), StatusCode::BAD_REQUEST);
+    }
 }

axum/src/extract/rejection.rs

@@ -116,7 +116,7 @@ impl FailedToDeserializeQueryString {
 
 impl IntoResponse for FailedToDeserializeQueryString {
     fn into_response(self) -> Response {
-        (http::StatusCode::UNPROCESSABLE_ENTITY, self.to_string()).into_response()
+        (http::StatusCode::BAD_REQUEST, self.to_string()).into_response()
     }
 }