A Django + Starlette or FastAPI connection handling example (ASGI, with WSGIMiddleware).

asgi.py

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import functools
import importlib
import os

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "myproject.settings")  # noqa
import anyio
from asgiref.sync import sync_to_async
from django.conf import settings
from django.core.wsgi import get_wsgi_application
from django.db import (
    InterfaceError,
    OperationalError,
    close_old_connections,
    connections,
)
from fastapi import FastAPI
from starlette.applications import Starlette
from starlette.concurrency import run_in_threadpool
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.middleware.wsgi import WSGIMiddleware

FILES_TO_IMPORT = {
    "api.py",
    "views.py",
    "urls.py",
}


def run_once(func):
    def wrapper(*args, **kwargs):
        if not wrapper.has_run:
            wrapper.has_run = True
            return func(*args, **kwargs)

    wrapper.has_run = False
    return wrapper


@run_once
def find_and_load_select_modules():
    """
    Use os.walk and importlib.import_module to find all views.py files
    in settings.BASE_DIR and "import" them such that any @app.get()
    decorators are found and executed properly, before any traffic is
    served.
    """
    for root, dirs, files in os.walk(settings.BASE_DIR):
        files = [f for f in files if not f[0] == "."]
        dirs[:] = [d for d in dirs if not d[0] == "."]
        for file in files:
            if any(file.endswith(file_to_import) for file_to_import in FILES_TO_IMPORT):
                module_path = os.path.join(root, file)
                module_dir = os.path.dirname(module_path)
                module_rel_path = os.path.relpath(module_dir, settings.BASE_DIR)
                module_rel_path = module_rel_path.replace(os.sep, ".")
                module_name = module_rel_path + "." + file.replace(".py", "")
                importlib.import_module(module_name)


def close_connections_for_func(func):
    """
    A decorator that will close all connections after calling the function,
    if it throws an appropriate error.
    """

    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        try:
            return func(*args, **kwargs)
        except (OperationalError, InterfaceError):
            close_old_connections()
            raise

    return wrapper


async def smart_sync_to_async(func, *args, **kwargs):
    """
    A Starlette/FastAPI compatible replacement for Django's, with slightly
    different __call__ semantics (drop currying pattern for immediate invoke).
    """
    wrapped_func = close_connections_for_func(func)
    is_starlette = anyio.get_current_task().name.startswith("starlette.")
    if is_starlette:
        return await run_in_threadpool(wrapped_func, *args, **kwargs)
    else:
        return await sync_to_async(wrapped_func)(*args, **kwargs)


class AsyncCloseConnectionsMiddleware(BaseHTTPMiddleware):
    """
    Using this middleware to call close_old_connections() twice is a pretty yucky hack,
    as it appears that run_in_threadpool (used by Starlette/FastAPI) and sync_to_async
    (used by Django) have divergent behavior, ultimately acquiring the incorrect thread
    in mixed sync/async which has the effect of duplicating connections.

    We could fix the duplicate connections too if we normalized the thread behavior,
    but at minimum we need to clean up connections in each case to prevent persistent
    "InterfaceError: connection already closed" errors when the database connection is
    reset via a database restart or something -- so here we are!

    If we always use smart_sync_to_async(), this double calling isn't necessary, but
    depending on what levels of abstraction we introduce, we might silently break the
    assumptions. Better to be safe than sorry!
    """

    async def dispatch(self, request, call_next):
        await run_in_threadpool(close_old_connections)
        await sync_to_async(close_old_connections)()
        try:
            response = await call_next(request)
        finally:
            # in tests, use @override_settings(CLOSE_CONNECTIONS_AFTER_REQUEST=True)
            if getattr(settings, 'CLOSE_CONNECTIONS_AFTER_REQUEST', False):
                await run_in_threadpool(connections.close_all)
                await sync_to_async(connections.close_all)()
        return response


@functools.cache
def register_fast_api_application(root_path: str, **kwargs) -> FastAPI:
    """
    In your views.py, etc. files, you can do this:

        app = register_fast_api_application("/api/v1/")

        @app.get("/hello")
        def hello():
            return {"hello": "world"}

    """
    application = get_starlette_application()
    fast_api_application = FastAPI(root_path=root_path, debug=settings.DEBUG, **kwargs)
    application.mount(root_path, fast_api_application)
    return fast_api_application


@functools.cache
def get_starlette_application() -> Starlette:
    return Starlette(debug=settings.DEBUG)


@functools.cache
def get_application() -> Starlette:
    django_application = get_wsgi_application()
    application = get_starlette_application()
    application.add_middleware(AsyncCloseConnectionsMiddleware)
    find_and_load_select_modules()  # this must happen before the django mount
    application.mount("/", WSGIMiddleware(django_application))
    return application


# run me with `uvicorn myproject.asgi:application`
application = get_application()

license.txt

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@bryanhelmig I slightly improved the file by fixing RuntimeError with custom middleware when client drops connection before the request is finished.

https://gist.github.com/xshapira/653b8d7dbd4757e183132c3c82f232b0