code: func (resp *Response) SendFile(path string) error {
  	f, err := os.Open(path)
  	if err != nil {
  		return err
  	}
  	fileInfo, err := f.Stat()
  	if err != nil {
  		f.Close()
  		return err
  	}
  	size64 := fileInfo.Size()
  	size := int(size64)
  	if int64(size) != size64 {
  		size = -1
  	}
  
  	resp.Header.SetLastModified(fileInfo.ModTime())
  	resp.SetBodyStream(f, size)
  	return nil
  }
docs: // SendFile registers file on the given path to be used as response body
  // when Write is called.
  //
  // Note that SendFile doesn't set Content-Type, so set it yourself
  // with Header.SetContentType.