Example (incomplete) web socket testing with k6

ws_test.js

import http from 'k6/http';
import ws from 'k6/ws';
import { check, fail, sleep } from 'k6';

// App specific settings, whatever your app needs 
let app = {
  apiBase: "http://localhost:8080",
  ws1: "ws://localhost:8080/api/foo/subscribe",
  ws2: "ws://localhost:8080/api/baz/",
  sessionCookieName: "sessionToken",
  userPassword: __ENV.USER_PASSWORD,
  viewSeconds: 10, // how long is a user on the page for?
};

export let options = {
  stages: [
    { duration: "1m", target: 60 }, // Stage 1 lasts 1 minute and builds up to 60 users
    { duration: "2m", target: 600 }, // Build up to 600 users
    { duration: "10m", target: 600 }, // Soak test for 10 minutes
    { duration: "2m", target: 0 }, // Ramp down
  ],
  thresholds: {
    http_req_failed: ['rate<0.01'], // http errors should be less than 1%
    http_req_duration: ['p(95)<200'], // 95% of requests should be below 200ms
  },
};

// Pre-flight custom validation
export function setup() {
  if (!app.userPassword) {
    fail("Password for login not set. Run with -e USER_PASSWORD=??? to set the password");
  }
}


export default function() {

  // __VU is a "virtual user ID" provided by k6
  const username = `user${__VU}`;

  // This example is grabbing a cookie post-login for authentication:
  const loginResponse = login(username, app.userPassword);
  const cookies = loginResponse.cookies;
  const sessionCookie = cookies[app.sessionCookieName];

  if (!sessionCookie) {
    console.error("No session cookie", username, loginResponse);
    fail("Session cookie not found");
  }

  if (sessionCookie.length !== 1) {
    fail("Expected single cookie value");
  }

  // We will connect to both WS endpoints, then disconnect at the end ("leave the page")

  // We're using a cookie-based authentication scheme
  // The options are limited:
  // https://ably.com/blog/websocket-authentication
  const wsParams = {
    headers: {
      "Cookie": `${sessionCookie[0].name}=${sessionCookie[0].value}`
    }
  };

  // Connect to two web sockets and sit on them for a bit
  const ws1Response = connect(app.ws1, wsParams, function(ws1Socket) {
    const ws2Response = connect(app.ws2, wsParams, function(ws2Socket) {

      sleep(app.viewSeconds);

      ws1Socket ? ws1Socket.close() : fail("ws1 failed");
      ws2Socket ? ws2Socket.close() : fail("ws2 failed");

    });
    check(ws2Response, { '101 ws2 status': (res) => res.status === 101 });
  });

  check(ws1Response, { '101 ws1 status': (res) => res.status === 101 });

}

function login(_username, _password) {
  // Exactly how you login is for you to fill in
  // Here we're making a post with some form data and headers
  return http.post(url, formData, { redirects: 0, headers: headers });
}

function connect(wsUrl, wsParams, fn) {
  return ws.connect(wsUrl, wsParams, function(socket) {
    socket.on("open", function() {
      fn(socket)
    });
  });
}