Serving conent of a temporary file which is an injected dependency stopped working in v 0.106.0

[mezhaka]

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Example Code

import tempfile
from typing import Annotated

import fastapi
from fastapi import status, responses, testclient


def tmp_file() -> tempfile.NamedTemporaryFile():
    with tempfile.NamedTemporaryFile() as tmp:
        yield tmp


app = fastapi.FastAPI()


@app.get("/test", response_class=responses.FileResponse, status_code=status.HTTP_200_OK)
def serve(
    tmp_file: Annotated[tempfile.NamedTemporaryFile, fastapi.Depends(tmp_file)],
):
    tmp_file.write(b"test")
    tmp_file.seek(0)
    return responses.FileResponse(tmp_file.name)


@app.get("/test-no-inject", response_class=responses.FileResponse, status_code=status.HTTP_200_OK)
def serve_no_inject():
    def stream():
        with tempfile.NamedTemporaryFile() as tmp_file:
            tmp_file.write(b"test")
            tmp_file.seek(0)
            yield from tmp_file
    return responses.StreamingResponse(stream())


def test_serve():
    with testclient.TestClient(app) as client_:
        r = client_.get("/test")
    assert r.content == b"test"


def test_serve_no_inject():
    with testclient.TestClient(app) as client_:
        r = client_.get("/test-no-inject")
    assert r.content == b"test"

Description

test_serve used to work fine in v 0.105.0, but gives an exception in 0.106.0:

    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
        if self.stat_result is None:
            try:
                stat_result = await anyio.to_thread.run_sync(os.stat, self.path)
                self.set_stat_headers(stat_result)
            except FileNotFoundError:
>               raise RuntimeError(f"File at path {self.path} does not exist.")
E               RuntimeError: File at path /var/folders/gs/bdkyw8_x60sc_f1zss1gc30c0000gp/T/tmpv1x9vqb0 does not exist.

I suspect it has to do with the breaking change in 0.106.0 and would like to get a suggestion what is the idiomatic way of serving a temporary file.

The technique I used is also suggested in this SO discussion: https://stackoverflow.com/a/72535413/18775, but it seems this way is broken now.

There is a discussion here #8633 where a StreamingResponse is used--in my example test-no-inject endpoint works fine and test_serve_no_inject demonstrates it, however it is prone to an file descriptor leak in case response is broken halfway.

And here #2152 a background task is used to delete a temporary file.

I am in search for an idiomatic way, which is going to decrease the chances I have to rework this bit again.

Operating System

macOS

Operating System Details

I also tried it on Linux

FastAPI Version

0.106.0

Pydantic Version

1.10.13

Python Version

Python 3.10.13

Additional Context

No response

[rushilsrivastava]

The only viable solution I can think of at the moment is using BackgroundTasks, as suggested in #2512. This feels like a downgrade to the behavior of dependencies, but I understand there are other advantages of having dependencies resolve before the response is returned to the client.

Related issue: #10857

[etienne-monier]

Hi ! I've got the same issue ! I need to stay below 0.106.0