Flask Server Sent Event Sample

sse-flask.py

import flask
from random import randint
app = flask.Flask(__name__)
box = ""


@app.route('/subscribe')
def subscribe():
    def get_subscribtion_message():
        global box
        while True:
            if box:
                data = box
                box = ""
                yield data

    return flask.Response(get_subscribtion_message(), content_type='text/event-stream')


@app.route('/notify')
def notify():
    global box

    r = randint(0, 999999)
    box = f"data: Random number = {r}\n\n"
    return f"Published {r}"


@app.route('/')
def root():
    return """
        <script>
        var es = new EventSource('/subscribe');
        es.onmessage = function(e) {
            console.log(e.data);
        }
        es.onerror = function(e) {
            console.error(e);
        }
        </script>
"""


app.run(debug=True, threaded=True)