class BaseMiddleware:
    """
    Base class for implementing ASGI middleware. Inherit from this and
    override the setup() method if you want to do things before you
    get to.

    Note that subclasses of this are not self-safe; don't store state on
    the instance, as it serves multiple application instances. Instead, use
    scope.
    """

    def __init__(self, inner):
        """
        Middleware constructor - just takes inner application.
        """
        self.inner = inner

    async def __call__(self, scope, receive, send):
        """
        ASGI application; can insert things into the scope and run asynchronous
        code.
        """
        # Copy scope to stop changes going upstream
        scope = dict(scope)
        # Run the inner application along with the scope
        return await self.inner(scope, receive, send)