"request.json()" hangs indefinitely in middleware

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Example Code

from fastapi import FastAPI, Request, Response
from starlette.middleware.base import BaseHTTPMiddleware, RequestResponseEndpoint


class Middleware(BaseHTTPMiddleware):

    async def dispatch(self, request: Request, call_next: RequestResponseEndpoint) -> Response:
        await request.json()
        response = await call_next(request)
        return response


app = FastAPI()
app.add_middleware(Middleware)


@app.post("/test")
async def test(test: dict) -> dict:
    return {"data": "test"}

Description

• Run script with: uvicorn main:app --reload
• Run CURL with POST request: curl -X 'POST' 'http://localhost:8000/test' -H 'accept: application/json' -H 'Content-Type: application/json' -d '{"test": "test"}'

The application keeps hanging indefinitely and don’t send a response to the request. I tested the equivalent code using app = Starlette() and it answers correctly.

Operating System

Linux

Operating System Details

Ubuntu 22.04

FastAPI Version

0.79.0

Python Version

Python 3.10.4

Additional Context

No response

[XingDongZhe]

@araujo88 It can’t be using self.stream(), for per request, only one time can use self.stream().
Or you will hang forever because of await self.event_message.wait()
You can see here: uvicorn/protocols/http/h11_impl.py#L543
This is because that when self.stream() done, there are no action to notify self.event_message This asyncio.Event will be notified of four actions:

• when Connection Lost
• when body_data received
• when body_data readed done
• when write reponse data done

And you can try this:

async for chunk in request.stream():
    print(chunk)
await request.json()

[csrgxtu]

@araujo88 you can ref this issue: https://github.com/tiangolo/fastapi/issues/394

in summary it is a bug or design issue from starlette, and there is work around:

from typing import Mapping

from starlette.requests import Request

from fastapi import FastAPI, APIRouter, Depends

app = FastAPI()
api_router = APIRouter()

@api_router.post("/")
def read_root(arg: Mapping[str, str]):
    return {"Hello": "World"}

async def auth_middleware(request: Request):
    # you can implement your auth here
    print(await request.json())

# the trick here is including auth_middleware in the dependencies:
app.include_router(api_router, dependencies=[Depends(auth_middleware)])

thus this middleware logic will work on every requests, we use it same way in our production env, works fine.

note: Dependencies will inject your auth logic into each request, for more detail ref: https://fastapi.tiangolo.com/tutorial/dependencies/