Build multipart form data elements. The form_file function uploads a file. The form_data function allows for posting a string or raw vector with a custom content-type.
form_file(path, type =NULL, name =NULL)form_data(value, type =NULL)
Arguments
path: a string with a path to an existing file on disk
type: MIME content-type of the file.
name: a string with the file name to use for the upload