Implement SSE for flask

api.py

from flask import Blueprint, jsonify
from sse import sse

# required line at the top of every blueprint file
api = Blueprint("api", __name__)  # match variable name and first arg to file name
# register more blueprints here to further split up the api
# e.g.
# api.register_blueprint(blueprint, url_prefix='/users')
# would cascade through /api/users

# api routes when hitting /api
@api.route("/")
def heartbeat():
    return jsonify({"status": "healthy"})
  
# if you wanted you could supply a unique id to the listen method to send messages to specific clients
@api.route("/listen")
def listen():
  client, stream = sse.listen()
  return stream

# this will ping all sse clients
@api.route('/ping')
def pingall():
    sse.announce('command', {'data': 'data'})
    return {}, 200
  

# this will ping all sse clients
@api.route('/ping/<int:client>')
def ping(client: int):
    sse.send(client, 'command', {'data': 'data'})
    return {}, 200

sse.py

from queue import Queue
from flask import Response
from json import dumps

class __Sse:
    def __init__(self):
        self.__listeners = {}

    def listen(self, client: int=None) -> Response:
        q = Queue(maxsize=5)
        if not client:
            client = id(q)
        self.__listeners[client] = q

        # generator for flask response
        def stream():
            while True:
                msg = q.get()
                if msg == 'stop':
                    break
                yield 'event: message\ndata: ' + dumps(msg) + '\n\n'

        response =  Response(stream(), content_type='text/event-stream')
        response.headers['Cache-Control'] = 'no-cache'
        response.headers['X-Accel-Buffering'] = 'no'
        return client, response

    def announce(self, event: str, data):
        for id in self.__listeners:
            self.send(id, event, data)

    def send(self, client: int, event: str, data):
        msg = 'event: ' + event + '\ndata: ' + dumps(data) + '\n\n'
        try:
            self.__listeners[client].put_nowait(msg)
        except queue.Full:
            del self.__listeners[client]
    
    def stop(self):
        for id in list(self.__listeners):
            self.__listeners[id].put_nowait('stop')

sse = __Sse()