[libmicrohttpd] File imperative for MHD_post_process() and MHD_PostDataIterator()?

[Bob Furber]

Is there any way I can access a MHD_PostDataIterator when it is called 
in a special situation where xhr data (not a file upload) is to be saved 
to a file, instead of being a file upload? That is, data is uploaded 
inside a xhr POST message, along with its destination path/filename.

It seems that MHD_PostDataIterator parameters such as filename must 
pre-exist in order for the MHD_PostDataIterator to be called. Is there 
any way around this?