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How to create a Websocket server

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Lloyd Brookes edited this page Jun 17, 2019 · 4 revisions

The easiest way to handle Websocket requests is to use the websockets/ws module in a middleware plugin.

  1. Install the websocket/ws module.
$ npm install --save-dev ws
  1. Create a middleware plugin. Save the following example code as websocket.js. This plugin delegates Websocket request handling to the websocket module by passing in lws.server. If a Websocket request comes in, it will be handled by this plugin else passed to the next middleware plugin in the stack.
class Websocket {
  middleware (config, lws) {
    const WebSocket = require('ws')
    const wss = new WebSocket.Server({ server: lws.server })

    wss.on('connection', socket => {
      socket.on('message', message => {
        console.log(`Received: ${message}`)
        const reply = "Wow, that's great"
        console.log(`Sending: ${reply}`)
        socket.send(reply)
      })
    })
  }
}

module.exports = Websocket
  1. Now we need a client to test our server. Save this as index.html.
<!DOCTYPE html>
<html>
<head>
  <title>Websocket example</title>
</head>
<body>
  <h1>Websocket example</h1>
  <p><button>Send message</button></p>
  <pre><code></code></pre>
  <script>
    const socket = new WebSocket('ws://localhost:8000')
    const $ = document.querySelector.bind(document)

    function sendMessage (msg) {
      $('code').innerHTML += `Sending: ${msg}\n`
      socket.send(msg)
    }
    socket.addEventListener('open', () => {
      sendMessage('Hello from the client')
    })

    socket.addEventListener('message', event => {
      $('code').innerHTML += `Received: ${event.data}\n`
    })

    $('button').addEventListener('click', e => {
      sendMessage('Client clicked the button')
    })
  </script>
</body>
</html>
  1. Launch the server using our Websocket plugin plus lws-static to handle requests for static assets (e.g. index.html).
$ ws --stack websocket.js lws-static
Listening on http://mba4.local:8000, http://127.0.0.1:8000, http://192.168.0.200:8000
  1. Finally, open your browser and navigate to http://127.0.0.1:8000 and click the button. On the client, you should see this output:
Sending: Hello from the client
Received: Wow, that's great
Sending: Client clicked the button
Received: Wow, that's great

And the output from the server should look like this:

Received: Hello from the client
Sending: Wow, that's great
Received: Client clicked the button
Sending: Wow, that's great

See also

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