Session does not get updated inside WebSocket even with `managed_session=False` #1868

limmatfun · 2022-08-28T08:42:44Z

limmatfun
Aug 28, 2022

I'm trying to make a simple game using Flask and SocketIO. It seems like I can't get the session to be updated via SocketIO, even after setting managed_session=False (I've read https://blog.miguelgrinberg.com/post/flask-socketio-and-the-user-session). The game right now is very simple, a user can only move left, up, down or right. The modifications do not seem to get saved when a button is clicked (e.g. clicking 'right' always returns 3).

This is my code:
__init__.py:

from flask import Flask
from flask_socketio import SocketIO
from flask_session import Session
from uuid import uuid4

app = Flask(__name__)
app.config['SECRET_KEY'] = uuid4().hex
app.config["SESSION_PERMANENT"] = False
app.config["SESSION_TYPE"] = "filesystem"
Session(app)

# manage_session needs to be set to False because of
# https://blog.miguelgrinberg.com/post/flask-socketio-and-the-user-session
socketio = SocketIO(app, manage_session=False, logger=True, engineio_logger=True)

__views__.py:

from datetime import datetime

from . import app, socketio

from flask import render_template
from flask_socketio import emit, join_room

from flask import session
from flask import request


@app.route("/", methods=['GET', 'POST'])
def home():
    if request.method == 'POST':
        if request.form["action"] == "create_game":
            session['game_id'] = "test_id1"
            session['curr_pos'] = [2, 2]
        elif request.form["action"] == "end_game":
            session.pop('game_id')
    return render_template("index.html", session=session, post_data=request.form)

@socketio.on('connect')
def connect():
    if session['game_id']:
        join_room(session['game_id'])
    pass

@socketio.on('next_pos')
def next_pos(message):
    if message['action'] == 'left':
        session['curr_pos'][0] -= 1
    elif message['action'] == 'right':
        session['curr_pos'][0] += 1
    elif message['action'] == 'up':
        session['curr_pos'][1] -= 1
    elif message['action'] == 'down':
        session['curr_pos'][1] += 1
    elif message['action'] == 'arrow':
        pass

    pos = session['curr_pos']
    
    emit('update_status', 
                {"x": pos[0],
                "y": pos[1]}, 
                room=session['game_id'])

../wsgi.py:

from app import app, socketio    # For application discovery by the 'flask' command.
from app import views  # For import side-effects of setting up routes.

if __name__ == "__main__":
    socketio.run(app, debug=True)

templates/index.html:

<!doctype html>
<html>
<head>
  <meta charset="utf-8">
  <title>Hello World</title>
  <script src="{{ url_for('static', filename='pixi/pixi.min.js')}}"></script>
  <script src="https://cdn.socket.io/4.5.0/socket.io.min.js" integrity="sha384-7EyYLQZgWBi67fBtVxw60/OWl1kjsfrPFcaU0pp0nAh+i8FD068QogUvg85Ewy1k" crossorigin="anonymous"></script>
  <script src="https://code.jquery.com/jquery-3.6.0.min.js" integrity="sha256-/xUj+3OJU5yExlq6GSYGSHk7tPXikynS7ogEvDej/m4=" crossorigin="anonymous"></script>
</head>
<body>
  <p>Debug Session: {{ session }}</p>
  <p>Debug POST: {{ post_data }}</p>
  <div class='setup'>
    <form method='POST'>
      {% if session.game_id %}
      <button class='play' name="action" value="end_game" type="submit">End Game</button>
      {% else %}
      <button class='play' name="action" value="create_game" type="submit">Start Game</button>
      {% endif %}
    </form>
</div>
{% if session.game_id %}
<div class="controls">
  <p>SocketIO Actions:</p>
  <div class="left"><button class='play'>Left</button></div>
  <div class="up"><button class='play'>Up</button></div>
  <div class="down"><button class='play'>Down</button></div>
  <div class="right"><button class='play'>Right</button></div>    
</div>
{% endif %}

  <script type="text/javascript">
playing = true
$(document).ready(function(){
    const socket = io();
    //actions
    $('.left').click(function(){
        if (playing) {
          socket.emit('next_pos', {'action':'left'})
        }
    })
    $('.right').click(function(){
        if (playing) socket.emit('next_pos', {'action':'right'})
    })
    $('.up').click(function(){
        if (playing) socket.emit('next_pos', {'action':'up'})
    })
    $('.down').click(function(){
        if (playing) socket.emit('next_pos', {'action':'down'})
    })
    socket.on('update_status', (data)=>{
        alert("New Pos X: " + data['x']);
    })
})
  </script>
</body>
</html>

limmatfun · 2022-08-28T08:46:27Z

limmatfun
Aug 28, 2022
Author

Oh wow, I was just the simplifying the code even a bit more and now it works. When I changed session['curr_pos'] to be a single number instead of an array of two numbers in views.py it worked:

@socketio.on('next_pos')
def next_pos(message):
    if message['action'] == 'left':
        session['curr_pos'] -= 1
    elif message['action'] == 'right':
        session['curr_pos'] += 1

    pos = session['curr_pos']
    
    emit('update_status', 
                {"x": pos}, 
                room=session['game_id'])

(plus on start_game setting session['curr_pos'] = 2.)

It started working properly. Is this WAI regarding arrays? Perhaps there's some python or flask session detail I'm missing?

2 replies

miguelgrinberg Aug 28, 2022
Maintainer

What you are missing is that lists are mutable. Flask detects that the session has been modified when the session dictionary changes. In this case you were just changing one of the lists that were already stored in the session, so from Flask's perspective the session had the same keys and the same values, so it did not save the session again.

You can force a session to be changed by setting the modified attribute to True.

limmatfun Aug 28, 2022
Author

Great, and thank you for the lightning fast support!

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Session does not get updated inside WebSocket even with `managed_session=False` #1868

limmatfun
Aug 28, 2022

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limmatfun
Aug 28, 2022
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miguelgrinberg Aug 28, 2022
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limmatfun Aug 28, 2022
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