title: The WebSocket transport is not available, you must install a WebSocket server that is compatible with your async mode to enable it
body: <p>When I development some socket.io service in python environment by using python-socketio and gunicorn, I meet an issue here.</p>
  <p>I am using Mac OS X and I am using python 3.7.</p>
  <p><strong>Environment setting</strong><br />
  <code>$ pip install python-socketio</code><br />
  <code>$ pip install gunicorn</code></p>
  <p><strong>server-side code</strong><br />
  app.py</p>
  <pre class="lang-py prettyprint-override"><code>import socketio
  
  sio = socketio.Server()
  app = socketio.WSGIApp(sio, static_files = {
      '/': './socketio-client.html'
  })
  
  @sio.event
  def connect(sid, environ):
      print(sid, 'connected')
  
  @sio.event
  def disconnect(sid):
      print(sid, 'disconnected')
  
  </code></pre>
  <p><strong>client-side code</strong><br />
  socketio-client.html</p>
  <pre class="lang-html prettyprint-override"><code>&lt;html&gt;
    &lt;head&gt;
      &lt;title&gt;Socket.IO Demo&lt;/title&gt;
      &lt;script src=&quot;https://cdn.socket.io/3.1.3/socket.io.min.js&quot; integrity=&quot;sha384-cPwlPLvBTa3sKAgddT6krw0cJat7egBga3DJepJyrLl4Q9/5WLra3rrnMcyTyOnh&quot; crossorigin=&quot;anonymous&quot;&gt;&lt;/script&gt;
    &lt;/head&gt;
    &lt;body&gt;
      &lt;h1&gt;Socket.IO Demo&lt;/h1&gt;
      &lt;script&gt;
        const sio = io();
        sio.on('connect', () =&gt; {
          console.log('connected');
        });
  
        sio.on('disconnect', () =&gt; {
          console.log('disconnected');
        });
      &lt;/script&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  <p><strong>Start program</strong><br />
  I put the files in the same folder. And start it by following the command.<br />
  <strong>$ gunicorn --thread 50 app:app</strong><br />
  <a href="https://i.stack.imgur.com/5hgG1.png" rel="noreferrer"><img src="https://i.stack.imgur.com/5hgG1.png" alt="enter image description here" /></a></p>
  <p>I use the browser to open http://localhost:8000 and that works.
  <strong>Issue</strong>
  But there is an issue with the server</p>
  <blockquote>
  <p>The WebSocket transport is not available, you must install a WebSocket server that is compatible with your async mode to enable it. See the documentation for details. (further occurrences of this error will be logged with level INFO)</p>
  </blockquote>
  <p>I try to do<br />
  <code>$ gunicorn --log-level INFO --thread 50 app:app</code><br />
  But I still cannot get helpful information from INFO log-level.</p>
  <p>The code can keep going to run but the message shows me to install WebSocket server and I don't know which kind of package I need to install for this case of python-socketio or gunicorn.</p>
  <p>What kind of package I missed to install?
  It's my first time to use python-socketio and gunicorn.<br />
  What should I do next?</p>
  <p>Thanks for your help.</p>