code: func NewDownloader(proxyConfig *api.ProxyConfig) Downloader {
  	httpReader := NewHTTPURLReader(proxyConfig)
  	return &downloader{
  		schemeReaders: map[string]schemeReader{
  			"http":  httpReader,
  			"https": httpReader,
  			"file":  &FileURLReader{},
  			"image": &ImageReader{},
  		},
  	}
  }
docs: // NewDownloader creates an instance of the default Downloader implementation