How to ensure files are uploaded before processing them?

I'm trying to set up a Web server that, when I upload some PDF files, parses and returns the text of that file.

Before I process a file, I need to be sure that multiparty has fiinished saving the file to my uploads folder.

Can I guarantee that this is true when multiparty.Form.parse's callback function parameter is called? Or do I need to use some other thing?