no need for mut ref

src/json.rs

@@ -86,7 +86,7 @@ pub struct JsonBody<S, T: DeserializeOwned>{
 impl<S, T: DeserializeOwned> JsonBody<S, T> {
 
     /// Create `JsonBody` for request.
-    pub fn from_request(req: &mut HttpRequest<S>) -> Self {
+    pub fn from_request(req: &HttpRequest<S>) -> Self {
         JsonBody{
             limit: 262_144,
             req: Some(req.clone()),