code: func GetFileSize(filename string) (fileSize int64) {
  	var (
  		fileInfo os.FileInfo
  		err      error
  		file     *os.File
  	)
  
  	if file, err = os.Open(filename); err == nil {
  		fileInfo, err = file.Stat()
  		fileSize = fileInfo.Size()
  
  	} else {
  		fileSize = -1
  	}
  	return
  }
docs: //GetFileSize - gets the filesize of a given path