RSV1.js

const defer = require('p-defer');
const getPort = require('get-port');
const Koa = require('koa');
const router = require('koa-route');
const WebSocket = require('ws');

const socketServer = new WebSocket.Server({ noServer: true });

/* eslint-disable no-param-reassign */
const middleware = async (ctx, next) => {
  const deferred = defer();
  const { upgrade = '' } = ctx.request.headers;
  const upgradable = upgrade
    .split(',')
    .map((header) => header.trim())
    .includes('websocket');

  if (upgradable) {
    ctx.ws = async () => {
      socketServer.handleUpgrade(ctx.req, ctx.request.socket, Buffer.alloc(0), deferred.resolve);
      ctx.respond = false;

      return deferred.promise;
    };
  }

  await next();
};

const run = async (t) => {
  const app = new Koa();
  const port = await getPort();
  const uri = `ws://localhost:${port}/test`;
  const routeDeferred = defer();
  const resultDeferred = defer();

  app.use(middleware);
  app.use(
    router.get('/test', async (ctx) => {
      const socket = await ctx.ws();
      routeDeferred.resolve();
    })
  );

  const server = app.listen(port);

  await {
    then(r, f) {
      server.on('listening', r);
      server.on('error', f);
    }
  };

  const socket = new WebSocket(uri);

  socket.on('open', async () => {
    await routeDeferred.promise;
    socket.close();
    resultDeferred.resolve();
  });

  await resultDeferred.promise;
}

run();