in writer.go [251:262]
func (w *Writer) prepare(fh *FileHeader) error {
if w.last != nil && !w.last.closed {
if err := w.last.close(); err != nil {
return err
}
}
if len(w.dir) > 0 && w.dir[len(w.dir)-1].FileHeader == fh {
// See https://golang.org/issue/11144 confusion.
return errors.New("archive/zip: invalid duplicate FileHeader")
}
return nil
}