[QUESTION] Customizing UploadFile

Description I found issue with Starlette’s UploadFile where it actually always buffers file to RAM fully and never switches to disk.

To overcome this until new version lands, I want to use my own version of UploadFile. This is what I tried:

import logging
from fastapi import FastAPI, File, UploadFile

logging.basicConfig(level=logging.INFO)
logger = logging.getLogger()
app = FastAPI()

class FixedUploadFile(UploadFile):
    def __init__(self, *args, **kwargs):
        logger.info("FixedUploadFile is initializing...")
        super().__init__(self, *args, **kwargs)
        self.file.rollover()

@app.post("/uploadfile/")
async def create_upload_file(file: FixedUploadFile = File(...)):
    logger.info("Upload file handler")
    return {"filename": file.filename}

Running this I see that “FixedUploadFile is initializing…” is not called. How can I supply a custom class for UploadFile? (Either FastAPI’s or Starlette’s)

[haizaar]

Yeah… gross… Thanks though. Here is another one. We can start code-ugly competition 😃

from starlette.datastructures import UploadFile as StarletteUploadFile

def fix_starlette_upload_file():
    if hasattr(StarletteUploadFile, "_fixed"):
        return  # Occational double-call will chain initialization

    _init = StarletteUploadFile.__init__

    def new_init(self, *args, **kwargs):
        _init(self, *args, **kwargs)
        logger.info("Forcing rollover")
        self.file.rollover()

    StarletteUploadFile.__init__ = new_init
    StarletteUploadFile._fixed = True


fix_starlette_upload_file()

[haizaar]

@tiangolo this ticket was about customizing UploadFile in FastAPI, but the use case was a bug in then current UploadFile implementation. The bug was fixed at https://github.com/encode/starlette/issues/579 long time ago, but this ticket was left open since it was about customizing UploadFile which is still not possible without monkey patching.

I think it’s indeed resolved for now, because the only reason to customize was to work around a Starlette bug, hence the original use case became irrelevant and with it the whole reason to customize 😃