SSE events

app.py

import sys
import queue
from concurrent.futures import ThreadPoolExecutor

import flask

app = flask.Flask(__name__)
executor = ThreadPoolExecutor(max_workers=3)

def format_sse(data, event=None):
    if event is not None:
        msg = 'event: %s\ndata: %s\n\n' % (event, data)
    else:
        msg = 'data: %s\n\n' % data
    return msg


@app.route("/", methods=["GET"])
def method():
    q = queue.Queue(10)

    def job():
        #print('started', file=sys.stderr)
        q.put_nowait('started')
        #print('sleeping for 2 seconds', file=sys.stderr)
        #time.sleep(2)

        #print('almost done (50%)', file=sys.stderr)
        q.put_nowait('almost done (50%)')
        time.sleep(2)

        #print('99%', file=sys.stderr)
        q.put_nowait('99%')
        time.sleep(2)

        #print('100% - done!', file=sys.stderr)
        q.put_nowait('100% - done!')
        q.put_nowait(None)
        q.join()
        #print('consumer done')

    def stream():
        while True:
            print('fetching item from q', file=sys.stderr)
            item = q.get()
            print('got item: %s' % item, file=sys.stderr)
            if item is None:
                q.task_done()
                break
            yield format_sse(item)
            q.task_done()

    executor.submit(job)
    return flask.Response(stream(), mimetype='text/event-stream')