db session middleware with custom exception middleware raises AnyIO EndOfSteam when client closes early

[s-quinn]

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Example Code

import time
from typing import Callable, Awaitable

import uvicorn
from fastapi import FastAPI
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, declarative_base
from starlette.requests import Request
from starlette.responses import Response



SQLALCHEMY_DATABASE_URL = "postgresql://user:password@postgresserver/db"
engine = create_engine(
    SQLALCHEMY_DATABASE_URL
)
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
Base = declarative_base(bind=engine)

app = FastAPI()

class ExceptionHandlerMiddleware:
    async def __call__(
        self,
        request: Request,
        call_next: Callable[[Request], Awaitable[Response]],
    ) -> Response:
        try:
            return await call_next(request)
        except Exception as exc:
            print(exc)


app.middleware('http')(ExceptionHandlerMiddleware())


@app.middleware("http")
async def db_session_middleware(request: Request, call_next):
    response = Response("Internal server error", status_code=500)
    try:
        request.state.db = SessionLocal()
        response = await call_next(request)
    finally:
        request.state.db.close()
    return response


@app.get('/')
def test():
    time.sleep(2)
    return {'message': 'hello'}


if __name__ == '__main__':
    uvicorn.run(
        'example:app',
        reload=True,
    )

Description

We are using the db session middleware exactly as described here in combination with a custom http exception middleware. When a client is disconnecting from us early we get spammed with a bunch of No response returned errors from starlette.

How to reproduce:

Open browser and call the endpoint /
Close the window before the request completes.
You will see that AnyIO raises a EndOfStream error which ends up being propogated as a Runtime Error with the message as No response returned

Operating System

Linux, macOS

Operating System Details

No response

FastAPI Version

0.73.0

Python Version

Python 3.9.6

Additional Context

SQLAlchemy==1.4.31

[teamhide]

+1

[wwarne]

+1 too.

[guya-pecan]

+1 as well

[leydenberg]

+1 :(

[robotadam]

I did some tests on this after Starlette merged encode/starlette#1715, which contains further fixes for this. It resolved the issues in my fastapi app with early disconnection, so I'm feeling positive that the pending update will be the solution for this bug. #5471