code: func (i *Image) LayerReader(id string) (io.ReadCloser, error) {
  	resp, err := i.getResponse(fmt.Sprintf("v1/images/%s/layer", id))
  	if err != nil {
  		return nil, err
  	}
  	return resp.Body, nil
  }
docs: // LayerReader returns io.ReadCloser that can be used to read Docker layer data.