Uploading file is not working using Functions Frameworks

[Boardtale]

I'm trying to implement simple uploading file but it does not work for me anyway. Something is going on under function framework that is not happening when express is listening directly.

Created repo:

https://github.com/Boardtale/FunctionFrameworkAndUploadingFiles

Here: https://github.com/Boardtale/FunctionFrameworkAndUploadingFiles/blob/master/index.js
is simple app listen or export app. That I run via functions-framework --target=playground --port 3001

Then there are 4 implementations that are working perfectly fine when calling via port 3000 which is directly calling express.
But when I do the same when via functions-frameworks it does not work at all.

Used multer, formidable, busboy and even tried without
https://github.com/Boardtale/FunctionFrameworkAndUploadingFiles/blob/master/multerEndpoint.js
https://github.com/Boardtale/FunctionFrameworkAndUploadingFiles/blob/master/formidableEndpoint.js
https://github.com/Boardtale/FunctionFrameworkAndUploadingFiles/blob/master/busboyEndpoint.js

Any idea why? What is happening behind the scenes in functions framework?

[Boardtale]

Found out, that functions-framework put file into req.rawBody