WebSocket connection to 'ws://localhost:3000/' failed: Connection closed before receiving a handshake response

Question

I took a game that my friend made and wanted to make it playable across browsers by sending keypress data between peers with WebRTC and websockets. However, I get this error in the console:

WebSocket connection to 'ws://localhost:3000/' failed: Connection closed before receiving a handshake response

My server file has the following few lines:

'use strict';

const express = require('express');
const SocketServer = require('ws').Server;
const path = require('path');

const PORT = process.env.PORT || 3000;
const INDEX = path.join(__dirname, 'index.html');

const server = express();

server.use(express.static(path.join(__dirname, 'lib')));
server.use('/assets', express.static(path.join(__dirname, 'assets')));
server.listen(PORT, () => console.log(`Listening on ${ PORT }`));

const wss = new SocketServer({ server });
var users = {};
let usernames = [];


wss.on('connection', function(connection) {

   connection.on('message', function(message) {

      var data;
      try {
         data = JSON.parse(message);
      } catch (e) {
         console.log("Invalid JSON");
         data = {};
      }

      switch (data.type) {
         case "login":
            console.log("User logged", data.name);
            if(users[data.name]) {
               sendTo(connection, {
                  type: "login",
                  success: false
               });
            } else {
               users[data.name] = connection;
               connection.name = data.name;
               usernames.push(data.name);

               sendTo(connection, {
                  type: "login",
                  success: true,
                  users: usernames
               });
            }

            break;

         case "offer":
            console.log("Sending offer to: ", data.name);
            var conn = users[data.name];

            if(conn != null) {
               connection.otherName = data.name;

               sendTo(conn, {
                  type: "offer",
                  offer: data.offer,
                  name: connection.name
               });
            }

            break;

         case "answer":
            console.log("Sending answer to: ", data.name);
            var conn = users[data.name];

            if(conn != null) {
               connection.otherName = data.name;
               sendTo(conn, {
                  type: "answer",
                  answer: data.answer
               });
            }

            break;

         case "candidate":
            console.log("Sending candidate to:",data.name);
            var conn = users[data.name];

            if(conn != null) {
               sendTo(conn, {
                  type: "candidate",
                  candidate: data.candidate
               });
            }

            break;

         case "leave":
            console.log("Disconnecting from", data.name);
            var conn = users[data.name];
            conn.otherName = null;

            if(conn != null) {
               sendTo(conn, {
                  type: "leave"
               });
            }

            break;

         default:
            sendTo(connection, {
               type: "error",
               message: "Command not found: " + data.type
            });

            break;
      }
   });

And the client side of the connection looks as follows:

const Game = require("./game");
const GameView = require("./game_view");
var HOST = location.origin.replace(/^http/, 'ws');
console.log('host: ', HOST);
console.log(process.env.PORT);

document.addEventListener("DOMContentLoaded", function() {
  const connection = new WebSocket(HOST);

.....

This is the point that the error occurs and this is the caught error that I get:

bubbles
:
false
cancelBubble
:
false
cancelable
:
false
composed
:
false
currentTarget
:
WebSocket
defaultPrevented
:
false
eventPhase
:
0
isTrusted
:
true
path
:
Array(0)
returnValue
:
true
srcElement
:
WebSocket
target
:
WebSocket
timeStamp
:
213.01500000000001
type
:
"error"
__proto__
:
Event

I am not too familiar with server side programming and was trying to understand. I tried looking up this issue, but it seems like a variety of different things can cause this. If you want to see the repository you can see and try it yourself (uses webpack): SlidingWarfare Repo

Answer 1

The confusion starts here:

const server = express();

The express function doesn't really return a server, it returns an application. Commonly, the variable used for this is app, but that's of course nothing more than convention (i.e. not a requirement).

However, it becomes an issue when you pass the app to the WS server:

const wss = new SocketServer({ server });

That's because SocketServer requires an HTTP server instance, which server is not.

Here's a fix, without renaming your variables:

let httpServer = server.listen(PORT, () => console.log(`Listening on ${ PORT }`));
...
const wss = new SocketServer({ server : httpServer });

(because when you call .listen() on the Express instance, it will return an HTTP server instance)

Using the variable naming convention it would be this:

const app = express();

app.use(express.static(path.join(__dirname, 'lib')));
app.use('/assets', express.static(path.join(__dirname, 'assets')));

let server = app.listen(PORT, () => console.log(`Listening on ${ PORT }`));

const wss = new SocketServer({ server });