update request modifier fn type to impl send and sync

rumqttc/CHANGELOG.md

@@ -25,6 +25,7 @@ To update your code simply remove `Key::ECC()` or `Key::RSA()` from the initiali
 
 ### Fixed
 - Lowered the MSRV to 1.64.0
+- Request modifier function should be Send and Sync and removed unnecessary Box
 
 ### Security
 

rumqttc/src/v5/mod.rs

@@ -50,8 +50,11 @@ pub enum Request {
 }
 
 #[cfg(feature = "websocket")]
-type RequestModifierFn =
-    dyn Fn(http::Request<()>) -> Pin<Box<dyn Future<Output = http::Request<()>>>>;
+type RequestModifierFn = Arc<
+    dyn Fn(http::Request<()>) -> Pin<Box<dyn Future<Output = http::Request<()>> + Send>>
+        + Send
+        + Sync,
+>;
 
 // TODO: Should all the options be exposed as public? Drawback
 // would be loosing the ability to panic when the user options
@@ -100,7 +103,7 @@ pub struct MqttOptions {
     /// The server may set its own maximum inflight limit, the smaller of the two will be used.
     outgoing_inflight_upper_limit: Option<u16>,
     #[cfg(feature = "websocket")]
-    request_modifier: Option<Arc<Box<RequestModifierFn>>>,
+    request_modifier: Option<RequestModifierFn>,
 }
 
 impl MqttOptions {
@@ -201,21 +204,20 @@ impl MqttOptions {
     #[cfg(feature = "websocket")]
     pub fn set_request_modifier<F, O>(&mut self, request_modifier: F) -> &mut Self
     where
-        F: Fn(http::Request<()>) -> O + 'static,
-        O: IntoFuture<Output = http::Request<()>>,
+        F: Fn(http::Request<()>) -> O + Send + Sync + 'static,
+        O: IntoFuture<Output = http::Request<()>> + 'static,
+        O::IntoFuture: Send,
     {
-        let request_modifier = Arc::new(Box::new(request_modifier));
-        self.request_modifier = Some(Arc::new(Box::new(move |request| {
-            Box::pin({
-                let request_modifier = Arc::clone(&request_modifier);
-                async move { request_modifier(request).into_future().await }
-            })
-        })));
+        self.request_modifier = Some(Arc::new(move |request| {
+            let request_modifier = request_modifier(request).into_future();
+            Box::pin(request_modifier)
+        }));
+
         self
     }
 
     #[cfg(feature = "websocket")]
-    pub fn request_modifier(&self) -> Option<Arc<Box<RequestModifierFn>>> {
+    pub fn request_modifier(&self) -> Option<RequestModifierFn> {
         self.request_modifier.clone()
     }