diff --git a/examples/server.rs b/examples/server.rs
index 67ef971..96507f9 100644
--- a/examples/server.rs
+++ b/examples/server.rs
@@ -129,9 +129,10 @@ async fn proxy_pull_worker(source: &str, app: &str, stream: &str, cancel: Cancel
         .stream(stream)
         .add_option("rtp_type", "0")
         .build();
-    let (tx, rx) = tokio::sync::oneshot::channel::<String>();
+    let poll_cancel = CancellationToken::new();
+    let poll_cancel_clone = poll_cancel.clone();
     player.on_close(move |_, _, _| {
-        let _ = tx.send(String::from(""));
+        poll_cancel_clone.cancel();
     });
     player.play(&source);
 
@@ -140,7 +141,7 @@ async fn proxy_pull_worker(source: &str, app: &str, stream: &str, cancel: Cancel
             _ = cancel.cancelled() => {
                 break;
             },
-            _ = rx => {
+            _ = poll_cancel.cancelled() => {
                 // todo retry
                 break;
             }
diff --git a/src/lib.rs b/src/lib.rs
index 21851a8..b36a4c2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -40,4 +40,7 @@ macro_rules! box_to_mut_void_ptr {
     ($a:ident) => {
         Box::into_raw(Box::new($a)) as *mut _
     };
+    ($a:expr) => {
+        Box::into_raw(Box::new($a)) as *mut _
+    };
 }
diff --git a/src/player.rs b/src/player.rs
index 36fa56c..f0185ba 100644
--- a/src/player.rs
+++ b/src/player.rs
@@ -28,8 +28,14 @@ impl ProxyPlayer {
         unsafe { mk_proxy_player_total_reader_count(self.0) }
     }
 
-    pub fn on_close(&self, cb: impl FnOnce(i32, &str, i32) + 'static) {
-        let cb = Box::new(cb);
+    pub fn on_close<T>(&self, cb: T)
+    where
+        T: FnMut(i32, String, i32) + 'static,
+    {
+        self.on_close_inner(Box::new(cb))
+    }
+
+    fn on_close_inner(&self, cb: OnCloseCallbackFn) {
         unsafe {
             mk_proxy_player_set_on_close(
                 self.0,
@@ -130,7 +136,7 @@ impl ProxyPlayerBuilder {
     }
 }
 
-pub type OnCloseCallbackFn = Box<dyn FnMut(i32, &str, i32) + 'static>;
+pub type OnCloseCallbackFn = Box<dyn FnMut(i32, String, i32) + 'static>;
 extern "C" fn proxy_player_on_close(
     user_data: *mut ::std::os::raw::c_void,
     err: ::std::os::raw::c_int,
@@ -139,6 +145,6 @@ extern "C" fn proxy_player_on_close(
 ) {
     unsafe {
         let cb: &mut OnCloseCallbackFn = std::mem::transmute(user_data);
-        cb(err, const_ptr_to_string!(what).as_str(), sys_err);
+        cb(err, const_ptr_to_string!(what), sys_err);
     };
 }
diff --git a/src/pusher.rs b/src/pusher.rs
index 17b96af..0751bfa 100644
--- a/src/pusher.rs
+++ b/src/pusher.rs
@@ -28,11 +28,25 @@ impl Pusher {
         unsafe { mk_pusher_publish(self.0, url.as_ptr()) }
     }
 
-    pub fn on_result(&self, cb: OnEventCallbackFn) {
+    pub fn on_result<T>(&self, cb: T)
+    where
+        T: FnMut(i32, String) + 'static,
+    {
+        self.on_result_inner(Box::new(cb))
+    }
+
+    fn on_result_inner(&self, cb: OnEventCallbackFn) {
         unsafe { mk_pusher_set_on_result(self.0, Some(on_push_event), box_to_mut_void_ptr!(cb)) }
     }
 
-    pub fn on_shutdown(&self, cb: OnEventCallbackFn) {
+    pub fn on_shutdown<T>(&self, cb: T)
+    where
+        T: FnMut(i32, String) + 'static,
+    {
+        self.on_shutdown_inner(Box::new(cb))
+    }
+
+    pub fn on_shutdown_inner(&self, cb: OnEventCallbackFn) {
         unsafe { mk_pusher_set_on_result(self.0, Some(on_push_event), box_to_mut_void_ptr!(cb)) }
     }
 }
@@ -93,7 +107,7 @@ impl PusherBuilder {
     }
 }
 
-pub type OnEventCallbackFn = Box<dyn FnMut(i32, &str) + 'static>;
+pub type OnEventCallbackFn = Box<dyn FnMut(i32, String) + 'static>;
 extern "C" fn on_push_event(
     user_data: *mut ::std::os::raw::c_void,
     err_code: ::std::os::raw::c_int,
@@ -101,6 +115,6 @@ extern "C" fn on_push_event(
 ) {
     unsafe {
         let cb: &mut OnEventCallbackFn = std::mem::transmute(user_data);
-        cb(err_code, const_ptr_to_string!(err_msg).as_str());
+        cb(err_code, const_ptr_to_string!(err_msg));
     };
 }
diff --git a/src/server.rs b/src/server.rs
index 3483a25..613b018 100644
--- a/src/server.rs
+++ b/src/server.rs
@@ -50,8 +50,14 @@ impl RtpServer {
         unsafe { mk_rtp_server_port(self.0) }
     }
 
-    pub fn on_detach(&self, cb: impl FnOnce() + 'static) {
-        let cb = Box::new(cb);
+    pub fn on_detach<T>(&self, cb: T)
+    where
+        T: FnMut() + 'static,
+    {
+        self.on_detach_inner(Box::new(cb));
+    }
+
+    fn on_detach_inner(&self, cb: OnRtpServerDetachCallbackFn) {
         unsafe {
             mk_rtp_server_set_on_detach(
                 self.0,
@@ -61,8 +67,14 @@ impl RtpServer {
         }
     }
 
-    pub fn connect(&self, url: &str, dst_port: u16, cb: impl FnOnce(i32, &str, i32) + 'static) {
-        let cb = Box::new(cb);
+    pub fn connect<T>(&self, url: &str, dst_port: u16, cb: T)
+    where
+        T: FnMut(i32, String, i32) + 'static,
+    {
+        self.connect_inner(url, dst_port, Box::new(cb));
+    }
+
+    fn connect_inner(&self, url: &str, dst_port: u16, cb: OnRtpServerConnectedCallbackFn) {
         let url = const_str_to_ptr!(url);
         unsafe {
             mk_rtp_server_connect(
@@ -76,13 +88,15 @@ impl RtpServer {
     }
 }
 
+type OnRtpServerDetachCallbackFn = Box<dyn FnMut() + 'static>;
 extern "C" fn on_rtp_server_detach(user_data: *mut ::std::os::raw::c_void) {
     unsafe {
-        let cb: &mut Box<dyn FnMut() + 'static> = std::mem::transmute(user_data);
+        let cb: &mut OnRtpServerDetachCallbackFn = std::mem::transmute(user_data);
         cb();
     };
 }
 
+type OnRtpServerConnectedCallbackFn = Box<dyn FnMut(i32, String, i32) + 'static>;
 extern "C" fn on_rtp_server_connected(
     user_data: *mut ::std::os::raw::c_void,
     err: ::std::os::raw::c_int,
@@ -90,8 +104,8 @@ extern "C" fn on_rtp_server_connected(
     sys_err: ::std::os::raw::c_int,
 ) {
     unsafe {
-        let cb: &mut Box<dyn FnMut(i32, &str, i32) + 'static> = std::mem::transmute(user_data);
-        cb(err, const_ptr_to_string!(what).as_str(), sys_err);
+        let cb: &mut OnRtpServerConnectedCallbackFn = std::mem::transmute(user_data);
+        cb(err, const_ptr_to_string!(what), sys_err);
     };
 }