func unzip(archive, target string) error {
    reader, err := zip.OpenReader(archive)
    if err != nil {
        return err
    }

    if err := os.MkdirAll(target, 0755); err != nil {
        return err
    }

    for _, file := range reader.File {
        path := filepath.Join(target, file.Name)
        if file.FileInfo().IsDir() {
            os.MkdirAll(path, file.Mode())
            continue
        }

        fileReader, err := file.Open()
        if err != nil {
            return err
        }
        defer fileReader.Close()

        targetFile, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, file.Mode())
        if err != nil {
            return err
        }
        defer targetFile.Close()

        if _, err := io.Copy(targetFile, fileReader); err != nil {
            return err
        }
    }

    return nil
}