How to save large files using BackgroundTasks or equivalent?

[ArturFortunato]

First Check

• I added a very descriptive title here.
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Example Code

@staticmethod
def upload_video(
    background_tasks: BackgroundTasks,
    video: UploadFile = File(...),
):
    background_tasks.add_task(ProjectService.upload_video, video)
    return {}

Description

My endpoints receives a very large video (2h with 1080p resolution). My function ProjectService.upload_video saves that video into a file. If I try to move ProjectService.upload_video(video) to backgroud_tasks, I get

Traceback (most recent call last):
  File "/app/./app/services/entities/Project.py", line 34, in upload_video
    video_location = upload_video_service.upload_video(video, project_id)
  File "/app/./app/services/Video.py", line 74, in upload_video
    file.write(video.file.read())
  File "/usr/local/lib/python3.10/tempfile.py", line 743, in read
    return self._file.read(*args)
ValueError: read of closed file

I found a similar request here, but there was no explicit answer on how to actually use BackgroundTasks for this.

So questions are:

1. How can prevent the file description from being closed
2. Is there a better way to force it directly into a file path that I choose (or get the path of the temporary file the FastApi creates? (This would be awesome!)

Thanks!

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.109.2

Pydantic Version

1.10.2

Python Version

3.9.6

Additional Context

No response

Edit: related thread here, possibly related to a breaking change release on 0.106.0

[ArturFortunato]

Can confirm that downgrading to 0.105.0 fixed the issue

[YuriiMotov]

That's because in 0.106.0 the braking change was introduced. Since then the background tasks are executed after the response is sent and browser can close the connection. So, at this point you can not longer read the request.

Can you describe why you need to move it to background tasks?

[4c0n]

I don't think it makes sense what you seem to be trying to do. As long as data is coming in, you would want to stay in the path operation context, as that is where the data is coming in. You could however read the input data in chunks and write the chunks to save your precious memory. At least I suspect that is what you're trying to achieve?