# dependencies' AsyncExitStack
def request_response(
    func: Callable[[Request], Union[Awaitable[Response], Response]],
) -> ASGIApp:
    """
    Takes a function or coroutine `func(request) -> response`,
    and returns an ASGI application.
    """
    f: Callable[[Request], Awaitable[Response]] = (
        func if is_async_callable(func) else functools.partial(run_in_threadpool, func)  # type:ignore
    )

        ```python
        import time
        from typing import Awaitable, Callable

        from fastapi import FastAPI, Request, Response

        app = FastAPI()


        @app.middleware("http")
        async def add_process_time_header(
            request: Request, call_next: Callable[[Request], Awaitable[Response]]
        ) -> Response:
            start_time = time.time()