TypeError: object str can't be used in 'await' expression in FastAPI Middleware

Question

from starlette.middleware import Middleware
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.routing import Mount
from fastapi import FastAPI, HTTPException

class CustomHeaderMiddleware(BaseHTTPMiddleware):

    async def dispatch(self, request: Request, call_next):
         customer =stripe.Customer.retrieve(request.session.get("user"))
         r= stripe.Subscription.list(customer=customer.id,limit=3)
         if r.data[0].status =="incomplete":
            raise HTTPException(401)
        #  response= RedirectResponse(url='/gradio')
         
         response = await call_next(request)
        
         return response  
 
io = gr.Interface(lambda x: "Hello, " + x + "!", "textbox", "textbox")

middleware = [
    Middleware(CustomHeaderMiddleware)
]

routes = [
    Mount('/gradio', app=io, middleware=middleware),
]
app = FastAPI(routes=routes)

File "C:\Users\Shivam 112\AppData\Roaming\Python\Python310\site-packages\starlette\middleware\base.py", line 69, in coro await self.app(scope, receive_or_disconnect, send_no_error)

TypeError: object str can't be used in 'await' expression

The traceback is incomplete and your question exhibits no debugging effort. Please review the [help] and in particular [How to ask](/help/how-to-ask) as well as the guidance for providing a [mre]. — tripleee, Jan 04 '23 at 10:14

score 0 · Answer 1 · answered Jan 04 '23 at 10:38

The issue here is that the routes argument in the FastAPI constructor does not accept plain Starlette routes. There is probably a way to work around that, but there is an even easier solution. Looking into gradio a bit, it turns out that their web app is a FastAPI application, meaning we can add the middleware in the normal way, and then mount the gradio app as a sub application:

import gradio
import gradio.routes
import stripe
from fastapi import FastAPI, Request, Response, status
from starlette.middleware.base import BaseHTTPMiddleware


class CustomHeaderMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request: Request, call_next):
        customer = stripe.Customer.retrieve(request.session.get("user"))
        r= stripe.Subscription.list(customer=customer.id,limit=3)
        if r.data[0].status =="incomplete":
            return Response(status_code=status.HTTP_401_UNAUTHORIZED)

        response = await call_next(request)
        return response

io = gradio.Interface(lambda x: "Hello, " + x + "!", "textbox", "textbox")

# Create gradio FastAPI application
gradio_app = gradio.routes.App.create_app(io)
gradio_app.add_middleware(CustomHeaderMiddleware)

app = FastAPI()

app.mount("/gradio", gradio_app)

Also, raising an HTTPException only works in a FastAPI route, not in a middleware, which is why I'm returning a plain response instead.

TypeError: object str can't be used in 'await' expression in FastAPI Middleware

1 Answers1