Adds a new MIME part containing body to multipart
Uses "Content-Disposition: form-data", as per the HTML forms specification.
the name of the control associated with this file
the name of the file, or null if not known
the MIME type of the file, or null if not known
the file data
Adds a new MIME part containing body to multipart
Uses "Content-Disposition: form-data", as per the HTML forms specification.