The solution given by @luzzodev can be a workaround for it.

You might need to modify max_file_size as well depending on your needs.

from starlette.formparsers import MultiPartParser

MultiPartParser.max_part_size = 10 * 1024 * 1024  # 10MB
MultiPartParser.max_file_size = 20 * 1024 * 1024   # 20MB

The value of MultiPartParser.max_file_size should be used for SpooledTemporaryFile(max_size=self.max_file_size), it seems that you don't need to set this parameter, if you set it to 20M, then anything up to 20M will be saved in memory.

This has stopped working since Starlette 0.44.0 with the change introduced in this commit.

Is there a new workaround for this now that this has stopped working since Starlette 0.44.0?

Hi @luzzodev I'm running into this issue right now and I'm sure I don't understand this but when I add this middleware:

from fastapi import Request
from starlette.middleware.base import BaseHTTPMiddleware

class PayloadSizeIncrease(BaseHTTPMiddleware):
    async def dispatch(self, request: Request, call_next):
        # do something with the request object, for example
        max_mb = 50
        max_bytes = max_mb * 1024 * 1024
        form = await request.form(
            max_part_size=max_bytes
		)
        
        # process the request and get the response    
        response = await call_next(request)
        
        return response

I lose all the form data, I don't understand this flow very well hoping you can shed some light on how to do this properly?

Hello @Nixxs, you are using BaseHttMiddleware and this is the reason why you are losing you form data. You can find more information here #13739.
Hope this helps 😁

Hi, @luzzodev !

It's now possible to intercept the request with a middleware and call request.form() with the desired options.

Could you elaborate more here? e.g. could you provide full example of the workaround based on your idea of calling Request.form inside a middleware?

Thoughts:

• We could not do this via starlette usual middleware (ASGI app interface), because there is no "shared" Request there, and if we create one, and call form() that we just drain the stream, and underlying apps recieve nothing.
• Using @app.middleware('http') is a bit discouraging for this too. The Request here is "shared", but not always, so again calling form() stores the form data in Request._form, but drains the stream, and so newly created Request inside api router gets nothing from the stream.

Hello @alex-700, I’m actually on mobile, so I’m unable to provide a full example, but I’ll try to give you some ideas.

I totally agree with you and with what you have pointed out.

Starting from the most important one:

That said, there’s no doubt we should have a way to control these parameters globally.

My opinion on this is that FastAPI must provide an easy way to control all limits and constraints related to forms at all levels (globally, per route, etc.).

Before the changes, you were able to control the limits globally with the first suggested workaround. After the changes, you now have a way to control those constraints without any workaround. On the other hand, FastAPI still does not offer a built-in way to control this, and you have to use different approaches depending on the case.

1 You can refer to https://fastapi.tiangolo.com/how-to/custom-request-and-route/#create-a-custom-gziprequest-class

And create a custom request with the proper handling of the form.

2 You can use only the Request dependency and access to form with custom constrains ( this one will not work in some cases and you should build the doc manually

3 you can create a custom middleware taking inspiration from the base http middleware and forward the stream or cache it.

All those approaches have their own pitfalls and there is not a way that will fit all use cases, especially if you need to have the the form constrains more relaxed.

As far as I know, there isn’t a two-line solution for that, and like I said at the beginning, we should have a way to control it.

Hope this helps