A RuntimeError: Stream consumed error is raised when request.body() is read in the custom middleware

[theredfoxlee]

Hi,

I encountered the following issue while using Starlette today :)

Issue description

A RuntimeError: Stream consumed error is raised when request.body() is read in the custom middleware (1) after call_next, given that a route uses request.body().

How to reproduce the issue?

Code

from starlette.applications import Starlette
from starlette.responses import JSONResponse
from starlette.routing import Route
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.middleware import Middleware

async def testpage(request):
    await request.body()
    return JSONResponse({'hello': 'world'})


class CustomMiddleware(BaseHTTPMiddleware):

    async def dispatch(self, request, call_next):
        response = await call_next(request)
        await request.body()  # THIS WILL RAISE -> RuntimeError: Stream consumed
        return response


app = Starlette(
    debug=True,
    routes=[Route('/', testpage, methods=["PUT"])],
    middleware=[Middleware(CustomMiddleware)]
)

Dependencies

starlette==0.37.2
uvicorn==0.29.0

Commands

• 1st terminal: uvicorn example:app
• 2nd terminal: curl -XPUT http://127.0.0.1:8000 -d '123'

Known workarounds

1. Use request.body() at least once before call_next to ensure that the _body is cached.

I prefer not to use a workaround, as I only want to read the body in the middleware conditionally, based on the response, rather than always.

---

This is my first time using starlette. Is this usage incorrect, or is it a bug?

[theredfoxlee]

I believe it's a bug. May I move it to the issues?

[Kludex]

No.

[theredfoxlee]

Oh... what does it take to state that this is an issue, then? 🤔

[Kludex]

A maintainer to label this as an issue.

This is probably not an issue, you didn't check the discussions, and issues about the topic.