FastAPI does not allow to send a "None" UploadFile

[phuchm]

Privileged issue

• I'm @tiangolo or he asked me directly to create an issue here.

Issue Content

I have a POST method with FastAPI which has 2 params with UploadFile type. But one of them is required and one of them is Optional. When I send required param with None value, I got 422 error relating to "Field required". But if I send Optional param with None value, it's acceptable.
When I use:
from fastapi import Request
And add:
request: Request as extra param, then log request.form(), I don't see Optional param.
It seems to FastAPI ignored it?

My code is below:

from fastapi import File, Request, UploadFile

from typing import Annatoted

app: FastAPI = FastAPI()

@app.post(/test)
async def test(
    request: Request,
    firstFile: Annatoted[UploadFile, File(...)],
    secondFile: Annatoted[UploadFile | None, File(...)] = None):
    logger.debug(await request.form())

[YuriiMotov]

You don't need to use ellipsis with File when you use Annotated.

To fix your code you should remove ellipsis and use SkipJsonSchema to fix openapi documentation:

from fastapi import FastAPI, File, Request, UploadFile
from typing import Annotated
from pydantic.json_schema import SkipJsonSchema

app: FastAPI = FastAPI()

@app.post("/test")
async def test(
    request: Request,
    firstFile: Annotated[UploadFile, File()],
    secondFile: Annotated[UploadFile | SkipJsonSchema[None], File()] = None
):
    logger.debug(await request.form())

[phuchm]

Here is my client code:

from requests import post

with open("a.txt", "rb") as f:
    response = post(
        url="http://localhost:8080/test",
        files=(
            ("firstFile", ("a.txt", f, "application/octet-stream")),
            ("secondFile", None)
        ),

        timeout=None
    )

And with server code as above, you will get a FormData object from logger.debug(await request.form()). This object only contains firstFile without secondFile while I expected secondFile will be inside this object with None value

[YuriiMotov]

You should use triple ``` symbol to format multi-line code

[phuchm]

I'm sorry. I corrected it. My mistake when using mobile :)

[YuriiMotov]

I think the problem is that requests just ignores the file parameter that is None and sends the request without it.
You can use the code below to see the raw request, that is sent:

import requests

def pretty_print_POST(req):
    print('{}\n{}\r\n{}\r\n\r\n{}'.format(
        '-----------START-----------',
        req.method + ' ' + req.url,
        '\r\n'.join('{}: {}'.format(k, v) for k, v in req.headers.items()),
        req.body,
    ))

with open("a.txt", "rb") as f:
    req = requests.Request(
        'POST',
        "http://localhost:8080/test",
        files=(
            ("firstFile", ("a.txt", f, "application/octet-stream")),
            ("secondFile", None)
        ),

    )
    prepared = req.prepare()
    pretty_print_POST(prepared)

The output shows that only firstFile is sent:

-----------START-----------
POST http://localhost:8080/test
Content-Length: 1985
Content-Type: multipart/form-data; boundary=7b19875569a580e9c5efa930a9c8e060


--7b19875569a580e9c5efa930a9c8e060
Content-Disposition: form-data;
name="firstFile";
filename="a.txt"
Content-Type: application/octet-stream

...file content goes here...
--7b19875569a580e9c5efa930a9c8e060--

[phuchm]

Yes, I saw. So, it seems to be problem of requests library, not FastAPI. I will investigate more about requests. Thank you so much for your support!