Class Router

starlette/routing.py:579–765

class Router:
    def __init__(
        self,
        routes: Sequence[BaseRoute] | None = None,
        redirect_slashes: bool = True,
        default: ASGIApp | None = None,
        # the generic to Lifespan[AppType] is the type of the top level application
        # which the router cannot know statically, so we use Any
        lifespan: Lifespan[Any] | None = None,
        *,
        middleware: Sequence[Middleware] | None = None,
        max_body_size: int | None = None,
    ) -> None:
        self.routes = [] if routes is None else list(routes)
        self.redirect_slashes = redirect_slashes
        self.default = self.not_found if default is None else default

        if lifespan is None:
            self.lifespan_context: Lifespan[Any] = _DefaultLifespan(self)

        elif inspect.isasyncgenfunction(lifespan):
            warnings.warn(
                "async generator function lifespans are deprecated, "
                "use an @contextlib.asynccontextmanager function instead",
                StarletteDeprecationWarning,
            )
            self.lifespan_context = asynccontextmanager(lifespan)
        elif inspect.isgeneratorfunction(lifespan):
            warnings.warn(
                "generator function lifespans are deprecated, use an @contextlib.asynccontextmanager function instead",
                StarletteDeprecationWarning,
            )
            self.lifespan_context = _wrap_gen_lifespan_context(lifespan)
        else:
            self.lifespan_context = lifespan

        self.middleware_stack = self.app
        if middleware:
            for cls, args, kwargs in reversed(middleware):
                self.middleware_stack = cls(self.middleware_stack, *args, **kwargs)
        if max_body_size is not None:
            self.middleware_stack = RequestBodyLimitMiddleware(self.middleware_stack, max_body_size=max_body_size)

    async def not_found(self, scope: Scope, receive: Receive, send: Send) -> None:
        if scope["type"] == "websocket":
            websocket_close = WebSocketClose()
            await websocket_close(scope, receive, send)
            return

        # If we're running inside a starlette application then raise an
        # exception, so that the configurable exception handler can deal with
        # returning the response. For plain ASGI apps, just return the response.
        if "app" in scope:
            raise HTTPException(status_code=404)
        else:
            response = PlainTextResponse("Not Found", status_code=404)
        await response(scope, receive, send)