code: func getLayerDetails(folder string) (*layerDetails, error) {
  	var fileInfo os.FileInfo
  	ld := &layerDetails{
  		isSandbox: false,
  		filename:  filepath.Join(folder, layerFilename),
  	}
  
  	fileInfo, err := os.Stat(ld.filename)
  	if err != nil {
  		ld.filename = filepath.Join(folder, sandboxFilename)
  		if fileInfo, err = os.Stat(ld.filename); err != nil {
  			return nil, fmt.Errorf("failed to locate layer or sandbox in %s", folder)
  		}
  		ld.isSandbox = true
  	}
  	ld.size = fileInfo.Size()
  
  	return ld, nil
  }
docs: // getLayerDetails is a utility for getting a file name, size and indication of
  // sandbox for a VHD(x) in a folder. A read-only layer will be layer.vhd. A
  // read-write layer will be sandbox.vhdx.