some logic to panic if a proper event callback hasn't been set

examples/tic-tac-toe-gui/src/main.rs

@@ -85,7 +85,7 @@ impl TicTacToeApp {
         // Establish a closure that handles the incoming messages
         self.waku.ctx.waku_set_event_callback(my_closure).expect("set event call back working");
 
-        // Subscribe to desired topic
+        // Subscribe to desired topic using the relay protocol
         // self.waku.relay_subscribe(&self.game_topic.to_string()).expect("waku should subscribe");
 
         let content_topic = WakuContentTopic::new("waku", "2", "tictactoegame", Encoding::Proto);

waku-bindings/src/node/context.rs

@@ -10,12 +10,21 @@ pub struct WakuNodeContext {
 
 impl WakuNodeContext {
     pub fn new(obj_ptr: *mut c_void) -> Self {
-        Self {
+        let me = Self {
             obj_ptr: obj_ptr,
-            msg_observer: Arc::new(Mutex::new(Box::new(|_response| {
-                println!("msg observer not set")
-            }))),
-        }
+            msg_observer: Arc::new(Mutex::new(Box::new(|_| {}))),
+        };
+
+        // By default we set a callback that will panic if the user didn't specify a valid callback.
+        // And by valid callback we mean a callback that can properly handle the waku events.
+        me.waku_set_event_callback(WakuNodeContext::panic_callback)
+            .expect("correctly set default callback");
+        me
+    }
+
+    // default callback that does nothing. A valid callback should be set
+    fn panic_callback(_response: LibwakuResponse) {
+        panic!("callback not set. Please use waku_set_event_callback to set a valid callback")
     }
 
     pub fn get_ptr(&self) -> *mut c_void {

waku-bindings/tests/node.rs

@@ -32,7 +32,7 @@ async fn test_echo_messages(
     content_topic: WakuContentTopic,
 ) -> Result<(), String> {
     // setting a naïve event handler to avoid appearing ERR messages in logs
-    node1.ctx.waku_set_event_callback(&|_| {});
+    let _ = node1.ctx.waku_set_event_callback(&|_| {});
 
     let rx_waku_message: Arc<Mutex<WakuMessage>> = Arc::new(Mutex::new(WakuMessage::default()));