Return 415 rather than 400 on Urlencoded Content-Type mismatch (#3334)

Co-authored-by: Rob Ede <robjtede@icloud.com>

actix-web/CHANGES.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - `ConnectionInfo::realip_remote_addr()` now handles IPv6 addresses from `Forwarded` header correctly. Previously, it sometimes returned the forwarded port as well.
+- The `UrlencodedError::ContentType` variant (relevant to the `Form` extractor) now uses the 415 (Media Type Unsupported) status code in it's `ResponseError` implementation.
 
 ## 4.7.0
 

actix-web/src/error/mod.rs

@@ -100,6 +100,7 @@ impl ResponseError for UrlencodedError {
         match self {
             Self::Overflow { .. } => StatusCode::PAYLOAD_TOO_LARGE,
             Self::UnknownLength => StatusCode::LENGTH_REQUIRED,
+            Self::ContentType => StatusCode::UNSUPPORTED_MEDIA_TYPE,
             Self::Payload(err) => err.status_code(),
             _ => StatusCode::BAD_REQUEST,
         }
@@ -232,7 +233,7 @@ mod tests {
         let resp = UrlencodedError::UnknownLength.error_response();
         assert_eq!(resp.status(), StatusCode::LENGTH_REQUIRED);
         let resp = UrlencodedError::ContentType.error_response();
-        assert_eq!(resp.status(), StatusCode::BAD_REQUEST);
+        assert_eq!(resp.status(), StatusCode::UNSUPPORTED_MEDIA_TYPE);
     }
 
     #[test]