Flask Socketio not functioning after adjusting flask app init

[mphilip9]

We recently upgraded a number of dependencies to our Flask application. During this process, we also adjusted the way we initialize the map in local development.

Flask socketio is still functioning just fine on remote environments, as that is being launched through wsgi.py

But locally, nothing is working. There are no errors, but connection requests from SocketIO are timing out and returning 400 responses. Which made me think this might be a CORS issue. But on local, we are allowing all (*) origins

It seems the cause must be somewhere in the app configuration process. I've tried a number of different approaches, but nothing has worked. Perhaps someone has experienced a similar issue?

Here is how we are now running the dev server.

Note, socket_instance is defined as

from flask_socketio import SocketIO, emit
import os


# configure cors_allowed_origins
if os.environ.get('FLASK_ENV') == 'production':
    origins = [
        # app url here
    ]
else:
    # allow all origins for development
    origins = "*"

# initialize your socket instance
socketio = SocketIO(async_mode='gevent', cors_allowed_origins=origins)

def create_app(db_uri=None):
    # BEGIN SET UP APP
    app = Flask(__name__)
    """The core Flask Application

    .. note:: More info on Flask at http://flask.pocoo.org/docs/0.12/api/

    .. todo:: Upgrade to latest Flask

    We then update the Flask app with our custom configuration.

    APP_CONFIG reads from environment variables to create a configuration dictionary.

    .. code-block:: python

        APP_CONFIG = {
                ...
        }


    """



    

        """
       ...
    return app

app = create_app()

# configure CLI
cli = FlaskGroup(app)

# configure Flask-Migrate
migrate = Migrate(app, alchemist, compare_type=True)

socketio.init_app(app, message_queue='amqp://flasksocket:mysocket@127.0.0.1:5672//')

@socketio.on('disconnect')
def handle_disconnect():
    """Handles a client disconnect event"""
    session_id = request.sid
    # app.logger.info('Client disconnected: \n\n\n', session_id)
    # Delete any locks associated with this session ID
    handle_locks_on_disconnect(session_id)

@socketio.on('get_lock')
def get_lock(data):
    """Handles a client request for a lock"""
    # app.logger.info('getting lock:', data)
    return handle_get_lock(data)

@socketio.on('lock')
def on_lock(data):
    """Handles a client request to lock a resource"""
    # print('attempting to lock:', data)
    return handle_lock_event(data)

@socketio.on('unlock')
def on_unlock(data):
    """Handles a client request to unlock a resource"""
    print('attempting to unlock:', data)
    return handle_unlock_event(data)

@cli.command('create-dbs')
def create_dbs():
    # This method will create the Postgres database if not already created
    try:
        logging.error('creating!')
        # alchemist.drop_all(app=app) #this will drop all tables except for alembic_version table
        alchemist.create_all(app=app)  # 1st time run `python app.py -p -c`
        logging.error('done!')
    except Exception as e:
        logging.error(e)

@cli.command('run')
@click.option('--no_permissions', '-p', is_flag=True,
                    help='Disable Permissions. Use for Local Development ONLY.')
@click.option('--no_manifest', '-n', is_flag=True,
                    help='DO NOT register clients from manifest.')
@click.option('--spoof_user', '-U', type=str, help='Spoof a user by entering an email address from the user list here. Use for Local Development ONLY.')
@click.option('--url_map', is_flag=True, help='Logs app.url_map on startup')
def run(no_permissions, no_manifest, spoof_user, url_map):
    if spoof_user:
        logging.warning("WARNING! SPOOFING USER " + spoof_user)
        app.config.update({'SPOOF_USER': spoof_user})

    if no_permissions:
        logging.warning("WARNING! DISABLING LOGIN")
        app.config.update({'LOGIN_DISABLED': True})

    if not no_manifest:
        register_clients.register_all(app)
    """Register All Clients"""
    # END CLIENT AND TOOL DECLARATIONS

    CORS(app)

    if url_map:
        logging.info('\n\n########################################\n\n')
        logging.info(app.url_map)
        logging.info(
            '\n\n########################################\n^^^ App URL Map ^^^\n')

    socketio.run(app)


if __name__ != '__main__':
    gunicorn_logger = logging.getLogger('gunicorn.error')
    app.logger.handlers = gunicorn_logger.handlers
    app.logger.setLevel(gunicorn_logger.level)

if __name__ == "__main__":
    cli()

[mphilip9]

Here are some relevant logs as well. Flask Socketio is receiving the message, but the handlers are not being used

QfEbp3mqB3Pxkx6EAAAA: Received packet MESSAGE data 214["get_lock",{"resource":"buy","recordId":120}]
INFO:engineio.server:QfEbp3mqB3Pxkx6EAAAA: Received packet MESSAGE data 214["get_lock",{"resource":"buy","recordId":120}]
received event "get_lock" from jIP8rNzuwvnKhCcRAAAB [/]
INFO:socketio.server:received event "get_lock" from jIP8rNzuwvnKhCcRAAAB [/]
QfEbp3mqB3Pxkx6EAAAA: Received packet MESSAGE data 2["unsubscribe",{"topic":"lock/buy/120"}]
INFO:engineio.server:QfEbp3mqB3Pxkx6EAAAA: Received packet MESSAGE data 2["unsubscribe",{"topic":"lock/buy/120"}]
received event "unsubscribe" from jIP8rNzuwvnKhCcRAAAB [/]
INFO:socketio.server:received event "unsubscribe" from jIP8rNzuwvnKhCcRAAAB [/]
QfEbp3mqB3Pxkx6EAAAA: Received packet MESSAGE data 2["unsubscribe",{"topic":"lock/buy/120"}]
INFO:engineio.server:QfEbp3mqB3Pxkx6EAAAA: Received packet MESSAGE data 2["unsubscribe",{"topic":"lock/buy/120"}]
received event "unsubscribe" from jIP8rNzuwvnKhCcRAAAB [/]
INFO:socketio.server:received event "unsubscribe" from jIP8rNzuwvnKhCcRAAAB [/]
QfEbp3mqB3Pxkx6EAAAA: Received packet MESSAGE data 2["unsubscribe",{"topic":"lock/buy/120"}]
INFO:engineio.server:QfEbp3mqB3Pxkx6EAAAA: Received packet MESSAGE data 2["unsubscribe",{"topic":"lock/buy/120"}]
received event "unsubscribe" from jIP8rNzuwvnKhCcRAAAB [/]
INFO:socketio.server:received event "unsubscribe" from jIP8rNzuwvnKhCcRAAAB [/]
QfEbp3mqB3Pxkx6EAAAA: Sending packet MESSAGE data 314["",400]
INFO:engineio.server:QfEbp3mqB3Pxkx6EAAAA: Sending packet MESSAGE data 314["",400]

[miguelgrinberg]

This shows that events are being received. You said there were 400 errors. Where are they? To me this looks like a problem with the file structure of your application. Maybe your event handlers aren't being imported anywhere, which means that Flask-SocketIO does not know about them and will not call them when an event is received.

[mphilip9]

So I figured out the problem. For some reason, when I imported the socket instance from another file the event handlers were not being registered properly. After I declared the socket instance directly in app.py before defining the app setup in create_app it worked. I also moved the handler definitions into create_app

I'm not entirely sure why I couldn't import the socket instance from another file, but everything is working now. The setup looks like this

socketio = SocketIO(async_mode='gevent', engineio_logger=True, logger=True, cors_allowed_origins=socketio_origins, message_queue='...')

def create_app(db_uri=None):
    # BEGIN SET UP APP
    app = Flask(__name__)

...lots of unrelated configuration...

    socketio.init_app(app)
    @socketio.on('disconnect')
    def handle_disconnect():
        """Handles a client disconnect event"""
        session_id = request.sid
        # app.logger.info('Client disconnected: \n\n\n', session_id)
        # Delete any locks associated with this session ID
        handle_locks_on_disconnect(session_id)

    @socketio.on('get_lock')
    def get_lock(data):
        """Handles a client request for a lock"""
        # app.logger.info('getting lock:', data)
        return handle_get_lock(data)

    @socketio.on('lock')
    def on_lock(data):
        """Handles a client request to lock a resource"""
        return handle_lock_event(data)

    @socketio.on('unlock')
    def on_unlock(data):
        """Handles a client request to unlock a resource"""
        return handle_unlock_event(data)
    return app
    
def run(no_permissions, no_manifest, spoof_user, url_map):
...

    socketio.run(app)


if __name__ == "__main__":
    cli()