How to Enable WebSocket Support for a Python/Flask Application

steviejackson

Title: How to Enable WebSocket Support for a Python/Flask Application?

Body:

Hello,

I have been following your official documentation and successfully deployed a basic Flask application on my account. Thank you for the clear instructions!

Now, I am trying to run a WebSocket application using Python with the Flask-Sockets library. I am using the standard demo code for this.

The standard HTTP part of the Flask app works, but when the browser tries to connect to the WebSocket endpoint (/echo), the connection fails. When I check the application logs, I see the following error:

Traceback (most recent call last):
...
File "/usr/home/steviejackson/.venv/ssn/lib/python3.11/site-packages/werkzeug/routing/map.py", line 627, in match
    raise WebsocketMismatch() from None
werkzeug.routing.exceptions.WebsocketMismatch: 400 Bad Request: The browser (or proxy) sent a request that this server could not understand.

I believe this error is happening because Phusion Passenger is running my application in the default WSGI mode, which doesn't support the WebSocket Upgrade protocol.

Could you please tell me what is the correct way to configure my Python application on Serv00.com to enable WebSocket support?

Is there a setting in the control panel I need to change?
Do I need to create a Passengerfile.json in my application's root directory? If so, what should its content be?

Here is my setup information:

Domain: [Your Domain Name]
Application Path: [e.g., /usr/home/your_username/domains/your_domain.com/public_python]

passenger_wsgi.py:

    import sys, os
    sys.path.append(os.getcwd())
    from application import app as application

Main Application Code (application.py):

    from flask import Flask, render_template
    from flask_sockets import Sockets

    app = Flask(__name__)
    sockets = Sockets(app)

    @app.route('/')
    def index():
        return render_template('index.html')

    @sockets.route('/echo')
    def echo_socket(ws):
        while not ws.closed:
            try:
                message = ws.receive()
                if message is not None:
                    ws.send(f"Echo: {message}")
            except Exception as e:
                print(f"An error occurred: {e}")
                break

Thank you very much for your help

admin

steviejackson Websocket is fully supported in our Passenger (Python, Node.js and Ruby WWW types). Check your code again because there is a problem.

And please don't use AI here.

steviejackson

admin i am sorry about that i not good at english; i check my code again.
thx for ur reply.

steviejackson

admin here are my new code: i use new lib: flask-sock
example from flask-sock doc

from flask import Flask
from flask_sock import Sock

app = Flask(__name__)
app.config['SOCK_SERVER_OPTIONS'] = {'ping_interval': 25}
sock = Sock(app)
@sock.route('/echo')
def echo(ws):
    while True:
        data = ws.receive()
        ws.send(data)

passenger_wsgi.py from docs

a very simple html

<!DOCTYPE html>
<html lang="en">
<body>
    <div class="container">
        <h1>echo:</h1>
        <div class="time-display" id="time"></div>
    </div>

    <script>
        let socket = new WebSocket("wss://steviejackson.serv00.net/echo")
        console.log(socket.readyState)
    </script>
</body>
</html>

the error.log

[2025-08-25 16:09:52,825] ERROR in app: Exception on /echo [GET]
Traceback (most recent call last):
  File "/usr/home/steviejackson/.venv/ssn/lib/python3.11/site-packages/flask/app.py", line 1511, in wsgi_app
    response = self.full_dispatch_request()
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/home/steviejackson/.venv/ssn/lib/python3.11/site-packages/flask/app.py", line 919, in full_dispatch_request
    rv = self.handle_user_exception(e)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/home/steviejackson/.venv/ssn/lib/python3.11/site-packages/flask/app.py", line 917, in full_dispatch_request
    rv = self.dispatch_request()
         ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/home/steviejackson/.venv/ssn/lib/python3.11/site-packages/flask/app.py", line 902, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)  # type: ignore[no-any-return]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/home/steviejackson/.venv/ssn/lib/python3.11/site-packages/flask_sock/__init__.py", line 59, in websocket_route
    ws = Server(request.environ, **current_app.config.get(
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/home/steviejackson/.venv/ssn/lib/python3.11/site-packages/simple_websocket/ws.py", line 290, in __init__
    raise RuntimeError('Cannot obtain socket from WSGI environment.')
RuntimeError: Cannot obtain socket from WSGI environment.

Thank you for confirming that WebSockets are supported.but i try again and again,i used flask-sockets before ,i does not work,
now I am using the flask_sock library, and it seems unable to interface with the Passenger environment correctly, leading to the 'Cannot obtain socket' error. Could you please provide a minimal working passenger_wsgi.py and application example for a Python WebSocket setup code? This would help me align my code with your server's specific requirements.
thank again