How should I run flask server with socketio?

Question

I've built simple webserver in flask according to this tutorial: https://blog.miguelgrinberg.com/post/the-flask-mega-tutorial-part-i-hello-world Then I realized that I need websockets, because I need real-time communication between client and server. So I installed in my venv flask-socketio library. Then I modified my __init__.py file so it looks like that:

from flask import Flask
from flask_socketio import SocketIO
from config import Config
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
import logging
from logging.handlers import RotatingFileHandler
import os


app = Flask(__name__)
app.config.from_object(Config)
db = SQLAlchemy(app)
migrate = Migrate(app, db)
socketio = SocketIO(app)

if not app.debug:
    if not os.path.exists('logs'):
        os.mkdir('logs')
    file_handler = RotatingFileHandler('logs/webserver.log', maxBytes=10240,
                                       backupCount=10)
    file_handler.setFormatter(logging.Formatter(
        '%(asctime)s %(levelname)s: %(message)s [in %(pathname)s:%(lineno)d]'))
    file_handler.setLevel(logging.INFO)
    app.logger.addHandler(file_handler)

    app.logger.setLevel(logging.INFO)
    app.logger.info('Reaction test startup')

from app import routes, models, errors

if __name__ == '__main__':
    socketio.run(app)

The problem is that now when I try to run my server using flask run, I get warning:

WARNING in __init__: Flask-SocketIO is Running under Werkzeug, WebSocket is not available.

I saw other people had this problem too (https://github.com/miguelgrinberg/Flask-SocketIO/issues/894), and that I should run my __init__.py script instead of flask run. However, when I try to start my server with "python app/__init__.py", my imports are failing, feels like all dependencies are lost. At first I received message:

Traceback (most recent call last): File "app/init.py", line 3, in from config import Config

So I decided to basically rewrite whole config file into __init__.py script. This didn't help though, as after doing it i received message:

File "app/init.py", line 37, in from app import routes, models, errors ModuleNotFoundError: No module named 'app'

So I guess rewriting contents of Config.py file wasn't the problem solver. My question is, how should I run my app so that it supports websockets properly without rewriting it from scratch?

Are you using Gevent or eventlet? For developmet the docs mention you need to start your application with flask run instead of python app.py flask-socketio.readthedocs.io/en/latest — Lucas Scott
I use eventlet, but I actually solved my problem already, I just should have added socketio.run(app) line into my python script which was assigned to FLASK_APP (server.py) enviromental variable instead of "init.py" file. Then i should have ran python server.py and everything works just fine. — Mentos1105

Mentos1105 Mentos1105 · Accepted Answer · 2020-01-02T21:25:02

I solved my problem already. The problem was I tried to edit my __init__.py file instead of the one which was bound to FLASK_APP environmental variable. When I added:

if __name__ == '__main__':
    socketio.run(app)

to my FLASK_APP script and then ran this other script from console with python server.py (this is the name of my script bound to FLASK_APP variable) everything worked just fine.

How should I run flask server with socketio?

1 Answers