How do I periodically send data over a websocket with uWebSockets and C++?

Question

uWS::App::WebSocketBehavior<data> WebSocketBehavior;
    WebSocketBehavior.open = [](uWS::WebSocket<false, true, data> *ws)
    {
       

       
    };

After opening a websocket, I want to perdiodically send a changing value via ws->send(). Is there some way to set a timer with a callback that can do this?

I have managed to implement this by opening another thread in .open and executing it from there, but I want to do it on the same thread as the rest of the program. I have also done it by polling for it from the client side, but I want it to be automatic.

Answer 1

This uses a timer and only one thread:

#include "App.h"
   
using namespace std;

struct PerSocketData {};

uWS::WebSocket<false, true, PerSocketData> *gws=nullptr;
    
int main() {
   auto loop = uWS::Loop::get();

   struct us_timer_t *delayTimer = us_create_timer((struct us_loop_t *) loop, 0, 0);

   us_timer_set(delayTimer, [](struct us_timer_t *) {
                               if (gws) {
                                  cout << "calling send" << endl;
                                  gws->send("from server", uWS::OpCode::TEXT);
                               }
                            }, 1000, 1000);
   
   uWS::App app;

   app.ws<PerSocketData>("/*", {
         .idleTimeout = 0,
         .sendPingsAutomatically = false,
         .open = [](auto *ws) {
                    gws = ws;
                 },
         .close = [](auto */*ws*/, int /*code*/, std::string_view /*message*/) {
                     gws = nullptr;
                  }
      }).listen(9001, [](auto *) {
                      });

   app.run();
}