[Django]-How to share (initialize and close) aiohttp.ClientSession between Django async views to use connection pooling

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Django doesn’t implement the ASGI Lifespan protocol.
Ref: https://github.com/django/django/pull/13636

Starlette does. FastAPI directly uses Starlette’s implementation of event handlers.

Here’s how you can achieve that with Django:

  1. Implement the ASGI Lifespan protocol in a subclass of Django’s ASGIHandler.
import django
from django.core.asgi import ASGIHandler


class MyASGIHandler(ASGIHandler):
    def __init__(self):
        super().__init__()
        self.on_shutdown = []

    async def __call__(self, scope, receive, send):
        if scope['type'] == 'lifespan':
            while True:
                message = await receive()
                if message['type'] == 'lifespan.startup':
                    # Do some startup here!
                    await send({'type': 'lifespan.startup.complete'})
                elif message['type'] == 'lifespan.shutdown':
                    # Do some shutdown here!
                    await self.shutdown()
                    await send({'type': 'lifespan.shutdown.complete'})
                    return
        await super().__call__(scope, receive, send)

    async def shutdown(self):
        for handler in self.on_shutdown:
            if asyncio.iscoroutinefunction(handler):
                await handler()
            else:
                handler()


def my_get_asgi_application():
    django.setup(set_prefix=False)
    return MyASGIHandler()
  1. Replace the application in asgi.py.
# application = get_asgi_application()
application = my_get_asgi_application()
  1. Implement a helper get_client_session to share the instance:
import asyncio
import aiohttp
from .asgi import application

CLIENT_SESSSION = None

_lock = asyncio.Lock()


async def get_client_session():
    global CLIENT_SESSSION

    async with _lock:
        if not CLIENT_SESSSION:
            CLIENT_SESSSION = aiohttp.ClientSession()
            application.on_shutdown.append(CLIENT_SESSSION.close)

    return CLIENT_SESSSION

Usage:

async def view(request: HttpRequest):
    session = await get_client_session()
    
    example_response = await session.get("https://example.com/")
    response_text = await example_response.text()

    return HttpResponse(response_text[:42], content_type="text/plain")
👤aaron

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