code: func SaveMultipartFile(fh *multipart.FileHeader, path string) error {
  	f, err := fh.Open()
  	if err != nil {
  		return err
  	}
  
  	if ff, ok := f.(*os.File); ok {
  		// Windows can't rename files that are opened.
  		if err := f.Close(); err != nil {
  			return err
  		}
  
  		// If renaming fails we try the normal copying method.
  		// Renaming could fail if the files are on different devices.
  		if os.Rename(ff.Name(), path) == nil {
  			return nil
  		}
  
  		// Reopen f for the code below.
  		f, err = fh.Open()
  		if err != nil {
  			return err
  		}
  	}
  
  	defer f.Close()
  
  	ff, err := os.Create(path)
  	if err != nil {
  		return err
  	}
  	defer ff.Close()
  	_, err = copyZeroAlloc(ff, f)
  	return err
  }
docs: // SaveMultipartFile saves multipart file fh under the given filename path.