code: func (r *Response) File(path string) error {
  	abspath, err := filepath.Abs(path)
  
  	if err != nil {
  		return err
  	}
  
  	if !r.fileExists(abspath) {
  		return err
  	}
  
  	r.file = abspath
  	return nil
  }
docs: // Find file, and send it to client.