[Errno 2] No usable temporary directory found in ['/tmp', '/var/tmp', '/usr/tmp', '/app'] There was an error parsing the body is too generic 400 status msg, wrong permissions to file system hide real problem

[IOR88]

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Example Code

router = APIRouter(
    prefix="/v1/xxx/",
    tags=['xxx'],
    responses={404: {'description': 'Not found'}},
)


@router.post("/upload", status_code=status.HTTP_200_OK)
async def upload(
    request: Request,
    file: UploadFile = File(...),
    dbsession: SessionLocal = Depends(create_session)
):
    pass

Description

My problem was related to this change of code

fastapi/fastapi/routing.py

Line 264 in 38929aa

status_code=400, detail="There was an error parsing the body"

I am using Kubernetes and I apply security context which enable readOnlyRootFilesystem

      securityContext:
        fsGroup: 1000
        runAsNonRoot: true
        runAsUser: 1000
      containers:
      - name: x-backend
        securityContext:
          readOnlyRootFilesystem: true 

I think this caused https://docs.python.org/3/library/tempfile.html#module-tempfile to fail as it was trying to create temp file in directory where it doesn't have permissions.

Problem was on my side with wrong configuration but fastapi in that case give only this error:

"There was an error parsing the body", the original error was "detail "[Errno 2] No usable temporary directory found in ['/tmp', '/var/tmp', '/usr/tmp', '/app']"" but it was never revealed to me, I only discovered that after I created custom route and remove this exception.

I think we should at least log this exception as it can be many different reasons behind, an Error log would really help here.

I haven;t found similar issue anywhere.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.100

Pydantic Version

1.10.1

Python Version

3.9

Additional Context

No response