[Python] How do I return a FileResponse (or StreamingResponse) in flet-fastapi?

I'm actually trying to create a web-app that would ask a person some info, then edit \*.docx with jinja and return this \*.docx to the person as a download.

I'm having trouble making flet-fastapi return a FileResponse. My workdir looks like this:

__pycache__/
.venv/
output/
output/test.docx
main.py
requirements.txt


requirements.txt:

flet-fastapi
flet
uvicorn
pydantic
fastapi


main.py:

from contextlib import asynccontextmanager
import flet as ft
import flet_fastapi
from fastapi import FastAPI
from fastapi.responses import FileResponse

@asynccontextmanager
async def lifespan(app=FastAPI):
await flet_fastapi.app_manager.start()
yield
await flet_fastapi.app_manager.shutdown()

app = FastAPI(lifespan=lifespan)

# I believe that it doesn't matter which endpoint we choose here, since later we mount
# our flet on the root-path. Decorator is here because without it "return FileResponse()"
# does nothing at all.
@app.get("/")
async def dl_test(page: ft.Page):
async def download(e):
return FileResponse(f"output/test.docx", media_type="application/vnd.openxmlformats-officedocument.wordprocessingml.document", filename="test.docx")
await page.add_async(ft.OutlinedButton(text="Get file", on_click=download))
await page.update_async()

app.mount("/", flet_fastapi.app(dl_test))


This code is the minimal reproducible example. To reproduce it, we can prepare our virtual environment:

python -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt


And then run it:

uvicorn --reload main:app


As we run it, we can see an exception:

fastapi.exceptions.FastAPIError: Invalid args for response field! Hint: check that <class 'flet_core.page.Page'> is a valid Pydantic field type. If you are using a return type annotation that is not a valid Pydantic field (e.g. Union[Response, dict, None]) you can disable generating the response model from the type annotation with the path operation decorator parameter response_model=None.
​

How can we make return FileResponse() working?

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