app.py

#!/usr/bin/env python
from threading import Lock
from flask import Flask, render_template, session, request
from flask_socketio import SocketIO, emit, disconnect
from random import random

# Set this variable to "threading", "eventlet" or "gevent" to test the
# different async modes, or leave it set to None for the application to choose
# the best option based on installed packages.
# Personally, I install and use eventlet
async_mode = None

app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app, async_mode=async_mode)
thread = None
thread_lock = Lock()

# The websocket is maintained in the background, and this
# function outputs a random number every 5 seconds
def background_thread():
    """Example of how to send server generated events to clients."""
    count = 0
    while True:
        socketio.sleep(5)
        count += 1
        number = round(random()*10, 3)
        socketio.emit('my_response',
                      {'data': number, 'count': count},
                      namespace='/test')

# Route for serving up the index page
@app.route('/')
def index():
    return render_template('index.html', async_mode=socketio.async_mode)

# This function is called when a web browser connects
@socketio.on('connect', namespace='/test')
def test_connect():
    global thread
    with thread_lock:
        if thread is None:
            thread = socketio.start_background_task(target=background_thread)
    emit('my_response', {'data': 'Connected', 'count': 0})

# Ping-pong allows Javascript in the web page to calculate the
# connection latency, averaging over time
@socketio.on('my_ping', namespace='/test')
def ping_pong():
    emit('my_pong')

# Notification that a client has disconnected
@socketio.on('disconnect', namespace='/test')
def test_disconnect():
    print('Client disconnected', request.sid)

# Run the web app
if __name__ == '__main__':
    socketio.run(app, debug=True, host='0.0.0.0')