Socket.IO with uWebSockets: "initial_headers" event not being emitted

[AKibMg]

Describe the bug Seems like the "initial_headers" (and also "headers") event is never emitted when using Socket.IO with uWebSockets. Need a way to attach headers to the http handshake response.

To Reproduce socket.io v4.8.1 uWebSockets.js v20.51.0

Server

server.mjs 

import { App } from "uWebSockets.js";
import { Server } from "socket.io";

const app = new App();
const io = new Server({
  serveClient: false,
  transports: ["websocket"],
});

io.attachApp(app);

io.engine.on("initial_headers", (headers, req) => {
  console.log("initial headers event emitted");
});

io.on("connection", (socket) => {
  console.log("connected");
});

app.listen(3000, (token) => {
  if (token) {
    console.log("Server listening on port 3000");
  } else {
    console.log("Failed to listen on port 3000");
  }
});

Client

const socket = io("http://localhost:3000", {
  transports: ["websocket"],
  reconnection: true,
});

Expected behavior Expecting console to log "initial headers event emitted", but only getting "connected" and "Server listening on port 3000".