Method call_next

starlette/middleware/base.py:112–187

(request: Request)

        exception_already_raised = False

        async def call_next(request: Request) -> Response:
            async def receive_or_disconnect() -> Message:
                if response_sent.is_set():
                    return {"type": "http.disconnect"}

                async with anyio.create_task_group() as task_group:

                    async def wrap(func: Callable[[], Awaitable[T]]) -> T:
                        result = await func()
                        task_group.cancel_scope.cancel()
                        return result

                    task_group.start_soon(wrap, response_sent.wait)
                    message = await wrap(wrapped_receive)

                if response_sent.is_set():
                    return {"type": "http.disconnect"}

                return message

            async def send_no_error(message: Message) -> None:
                try:
                    await send_stream.send(message)
                except anyio.BrokenResourceError:
                    # recv_stream has been closed, i.e. response_sent has been set.
                    return

            async def coro() -> None:
                nonlocal app_exc

                with send_stream:
                    try:
                        await self.app(scope, receive_or_disconnect, send_no_error)
                    except Exception as exc:
                        app_exc = exc

            task_group.start_soon(coro)

            try:
                message = await recv_stream.receive()
                info = message.get("info", None)
                if message["type"] == "http.response.debug" and info is not None:
                    message = await recv_stream.receive()
            except anyio.EndOfStream:
                if app_exc is not None:
                    nonlocal exception_already_raised
                    exception_already_raised = True
                    # Prevent `anyio.EndOfStream` from polluting app exception context.
                    # If both cause and context are None then the context is suppressed
                    # and `anyio.EndOfStream` is not present in the exception traceback.
                    # If exception cause is not None then it is propagated with
                    # reraising here.
                    # If exception has no cause but has context set then the context is
                    # propagated as a cause with the reraise. This is necessary in order
                    # to prevent `anyio.EndOfStream` from polluting the exception
                    # context.
                    raise app_exc from app_exc.__cause__ or app_exc.__context__
                raise RuntimeError("No response returned.")