sio-test.js

const fs = require("fs");
const http = require("http");
const https = require("https");
const { Server } = require("socket.io");
const express = require("express");

const tlsEnabled = true;

const app = express();

let server;
if (tlsEnabled) {
  const key = fs.readFileSync("key.pem");
  const cert = fs.readFileSync("cert.pem");

  const options = {
    key,
    cert,
  };

  server = https.createServer(options, app);
} else {
  server = http.createServer(app);
}

const io = new Server(server);

const errorListener = (e) => {
  reject(e.message);
};

server.once("error", errorListener);

server.listen(3000, () => {
  server.removeListener("error", errorListener);
  console.log("listening");
  resolve();
});

io.on("connection", (socket) => {
  console.log("connection!");
  socket.on("disconnect", (reason) => {
    console.log("disconnected: " + reason);
  });
});

Reference documentation: https://nodejs.org/en/knowledge/HTTP/servers/how-to-create-a-HTTPS-server/

To generate a self-signed certificate:

openssl genrsa -out key.pem
openssl req -new -key key.pem -out csr.pem
openssl x509 -req -days 9999 -in csr.pem -signkey key.pem -out cert.pem
rm csr.pem