code: func (handler *UnroutedHandler) absFileURL(r *http.Request, id string) string {
  	if handler.isBasePathAbs {
  		return handler.basePath + id
  	}
  
  	// Read origin and protocol from request
  	host, proto := getHostAndProtocol(r, handler.config.RespectForwardedHeaders)
  
  	url := proto + "://" + host + handler.basePath + id
  
  	return url
  }
docs: // Make an absolute URLs to the given upload id. If the base path is absolute
  // it will be prepended else the host and protocol from the request is used.