Add subscription event (placeholder)

Author: uNetworkingAB

src/App.h

@@ -241,6 +241,7 @@ struct TemplatedApp {
         MoveOnlyFunction<void(WebSocket<SSL, true, UserData> *)> drain = nullptr;
         MoveOnlyFunction<void(WebSocket<SSL, true, UserData> *, std::string_view)> ping = nullptr;
         MoveOnlyFunction<void(WebSocket<SSL, true, UserData> *, std::string_view)> pong = nullptr;
+        MoveOnlyFunction<void(WebSocket<SSL, true, UserData> *, std::string_view, int, int)> subscription = nullptr;
         MoveOnlyFunction<void(WebSocket<SSL, true, UserData> *, int, std::string_view)> close = nullptr;
     };
 
@@ -347,6 +348,7 @@ struct TemplatedApp {
         webSocketContext->getExt()->openHandler = std::move(behavior.open);
         webSocketContext->getExt()->messageHandler = std::move(behavior.message);
         webSocketContext->getExt()->drainHandler = std::move(behavior.drain);
+        webSocketContext->getExt()->subscriptionHandler = std::move(behavior.subscription);
         webSocketContext->getExt()->closeHandler = std::move([closeHandler = std::move(behavior.close)](WebSocket<SSL, true, UserData> *ws, int code, std::string_view message) mutable {
             if (closeHandler) {
                 closeHandler(ws, code, message);

src/WebSocketContextData.h

@@ -60,8 +60,8 @@ struct WebSocketContextData {
     MoveOnlyFunction<void(WebSocket<SSL, true, USERDATA> *)> openHandler = nullptr;
     MoveOnlyFunction<void(WebSocket<SSL, true, USERDATA> *, std::string_view, OpCode)> messageHandler = nullptr;
     MoveOnlyFunction<void(WebSocket<SSL, true, USERDATA> *)> drainHandler = nullptr;
+    MoveOnlyFunction<void(WebSocket<SSL, true, USERDATA> *, std::string_view, int, int)> subscriptionHandler = nullptr;
     MoveOnlyFunction<void(WebSocket<SSL, true, USERDATA> *, int, std::string_view)> closeHandler = nullptr;
-    /* Todo: these should take message also; breaking change for v0.18 */
     MoveOnlyFunction<void(WebSocket<SSL, true, USERDATA> *, std::string_view)> pingHandler = nullptr;
     MoveOnlyFunction<void(WebSocket<SSL, true, USERDATA> *, std::string_view)> pongHandler = nullptr;