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EDITING: background_tasks.py

#!/usr/bin/env python3
"""Example of aiohttp.web.Application.on_startup signal handler"""
import asyncio
from typing import List

import aioredis

from aiohttp import web

redis_listener = web.AppKey("redis_listener", asyncio.Task[None])
websockets = web.AppKey("websockets", List[web.WebSocketResponse])

async def websocket_handler(request):
    ws = web.WebSocketResponse()
    await ws.prepare(request)
    request.app[websockets].append(ws)
    try:
        async for msg in ws:
            print(msg)
            await asyncio.sleep(1)
    finally:
        request.app[websockets].remove(ws)
    return ws

async def on_shutdown(app: web.Application) -> None:
    for ws in app[websockets]:
        await ws.close(code=999, message=b"Server shutdown")

async def listen_to_redis(app):
    try:
        sub = await aioredis.Redis(host="localhost", port=6379)
        ch, *_ = await sub.subscribe("news")
        async for msg in ch.iter(encoding="utf-8"):
            # Forward message to all connected websockets:
            for ws in app[websockets]:
                await ws.send_str(f"{ch.name}: {msg}")
            print(f"message in {ch.name}: {msg}")
    except asyncio.CancelledError:
        pass
    finally:
        print("Cancel Redis listener: close connection...")
        await sub.unsubscribe(ch.name)
        await sub.quit()
        print("Redis connection closed.")

async def start_background_tasks(app: web.Application) -> None:
    app[redis_listener] = asyncio.create_task(listen_to_redis(app))

async def cleanup_background_tasks(app):
    print("cleanup background tasks...")
    app[redis_listener].cancel()
    await app[redis_listener]

def init():
    app = web.Application()
    l: List[web.WebSocketResponse] = []
    app[websockets] = l
    app.router.add_get("/news", websocket_handler)
    app.on_startup.append(start_background_tasks)
    app.on_cleanup.append(cleanup_background_tasks)
    app.on_shutdown.append(on_shutdown)
    return app

web.run_app(init())

CANCEL

Name	Type	Size	Modified	Actions
↩ ..	DIR	—	—
📄 __init__.py	PY	0 B	2023-11-26 16:52	EDIT
📄 background_tasks.py	PY	2 KB	2023-11-26 16:52	EDIT
📄 cli_app.py	PY	1.5 KB	2023-11-26 16:52	EDIT
📄 client_auth.py	PY	551 B	2023-11-26 16:52	EDIT
📄 client_json.py	PY	489 B	2023-11-26 16:52	EDIT
📄 client_ws.py	PY	2.1 KB	2023-11-26 16:52	EDIT
📄 curl.py	PY	1 KB	2023-11-26 16:52	EDIT
📄 fake_server.py	PY	3.8 KB	2023-11-26 16:52	EDIT
📄 lowlevel_srv.py	PY	573 B	2024-08-21 16:28	EDIT
📄 server.crt	CRT	1.1 KB	2023-11-26 16:52	EDIT
📄 server.csr	CSR	952 B	2023-11-26 16:52	EDIT
📄 server.key	KEY	1.6 KB	2023-11-26 16:52	EDIT
📄 server_simple.py	PY	741 B	2024-08-21 16:28	EDIT
📄 static_files.py	PY	181 B	2023-11-26 16:52	EDIT
📄 web_classview.py	PY	1.5 KB	2023-11-26 16:52	EDIT
📄 web_cookies.py	PY	936 B	2023-11-26 16:52	EDIT
📄 web_rewrite_headers_middleware.py	PY	687 B	2023-11-26 16:52	EDIT
📄 web_srv.py	PY	1.4 KB	2023-11-26 16:52	EDIT
📄 web_srv_route_deco.py	PY	1.3 KB	2023-11-26 16:52	EDIT
📄 web_srv_route_table.py	PY	1.4 KB	2023-11-26 16:52	EDIT
📄 web_ws.py	PY	1.9 KB	2023-11-26 16:52	EDIT
📄 websocket.html	HTML	3 KB	2023-11-26 16:52	EDIT