peterrus/flask-websocket-log-stream.py

## flask-websocket-log-stream.py
# Runs a scheduled job in a background thread using APScheduler and streams
# it's output to a web client using websockets. Communication between the Flask
# thread and APScheduler thread is being done through (blinker) signals.
#
# Install dependencies (preferably in your virtualenv)
#   pip install flask apscheduler sqlalchemy blinker flask-socketio simple-websocket
# and then run with:
#   python this_script.py

from time import sleep

from apscheduler.jobstores.sqlalchemy import SQLAlchemyJobStore
from apscheduler.schedulers.background import BackgroundScheduler
from blinker import signal
from flask import Flask
from flask_socketio import SocketIO
from pytz import utc

# initialize Flask+SocketIO
app = Flask(__name__)
socketio = SocketIO(app)

# signal to communicate between background thread and Flask
logsignal = signal('log')


# handle signals coming from background thread and emit them
# over the websocket
@logsignal.connect
def send_log_update(log_line):
    socketio.emit('logUpdate', log_line)


# Background job that will run in the scheduler thread
def background_job():
    logsignal.send('starting job')
    sleep(3)
    logsignal.send('job done')


# configure APScheduler
jobstores = {
    'default': SQLAlchemyJobStore(url='sqlite:///scheduler.sqlite')
}
job_defaults = {
    'coalesce': False,
    'max_instances': 1
}

# create and start scheduler
scheduler = BackgroundScheduler(
    job_defaults=job_defaults, jobstores=jobstores, timezone=utc)


# simple websocket client for testing purposes
@app.route("/")
def info():
    return """
    <html>
    <head>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/4.0.1/socket.io.js" integrity="sha512-q/dWJ3kcmjBLU4Qc47E4A9kTB4m3wuTY7vkFJDTZKjTs8jhyGQnaUrxa0Ytd0ssMZhbNua9hE+E7Qv1j+DyZwA==" crossorigin="anonymous"></script>
    </head>
    <body>
    <h1>Streaming log</h1>
    <pre id="log"></pre>
    <script type="text/javascript" charset="utf-8">
        var socket = io();

        socket.on('logUpdate', function(msg) {
            let log = document.getElementById('log');
            log.append(msg + '\\n');
        });
    </script>
    </body>
    </html>
"""


if __name__ == '__main__':
    scheduler.add_job(background_job, 'interval', seconds=5,
                      replace_existing=True, id='sample_job',
                      args=[])

    scheduler.start()
    socketio.run(app)
	# Runs a scheduled job in a background thread using APScheduler and streams
	# it's output to a web client using websockets. Communication between the Flask
	# thread and APScheduler thread is being done through (blinker) signals.
	#
	# Install dependencies (preferably in your virtualenv)
	# pip install flask apscheduler sqlalchemy blinker flask-socketio simple-websocket
	# and then run with:
	# python this_script.py

	from time import sleep

	from apscheduler.jobstores.sqlalchemy import SQLAlchemyJobStore
	from apscheduler.schedulers.background import BackgroundScheduler
	from blinker import signal
	from flask import Flask
	from flask_socketio import SocketIO
	from pytz import utc

	# initialize Flask+SocketIO
	app = Flask(__name__)
	socketio = SocketIO(app)

	# signal to communicate between background thread and Flask
	logsignal = signal('log')


	# handle signals coming from background thread and emit them
	# over the websocket
	@logsignal.connect
	def send_log_update(log_line):
	socketio.emit('logUpdate', log_line)


	# Background job that will run in the scheduler thread
	def background_job():
	logsignal.send('starting job')
	sleep(3)
	logsignal.send('job done')


	# configure APScheduler
	jobstores = {
	'default': SQLAlchemyJobStore(url='sqlite:///scheduler.sqlite')
	}
	job_defaults = {
	'coalesce': False,
	'max_instances': 1
	}

	# create and start scheduler
	scheduler = BackgroundScheduler(
	job_defaults=job_defaults, jobstores=jobstores, timezone=utc)


	# simple websocket client for testing purposes
	@app.route("/")
	def info():
	return """
	<html>
	<head>
	<script src="https://cdnjs.cloudflare.com/ajax/libs/socket.io/4.0.1/socket.io.js" integrity="sha512-q/dWJ3kcmjBLU4Qc47E4A9kTB4m3wuTY7vkFJDTZKjTs8jhyGQnaUrxa0Ytd0ssMZhbNua9hE+E7Qv1j+DyZwA==" crossorigin="anonymous"></script>
	</head>
	<body>
	<h1>Streaming log</h1>
	<pre id="log"></pre>
	<script type="text/javascript" charset="utf-8">
	var socket = io();

	socket.on('logUpdate', function(msg) {
	let log = document.getElementById('log');
	log.append(msg + '\\n');
	});
	</script>
	</body>
	</html>
	"""


	if __name__ == '__main__':
	scheduler.add_job(background_job, 'interval', seconds=5,
	replace_existing=True, id='sample_job',
	args=[])

	scheduler.start()
	socketio.run(app)