code: func (p *PackageReader) Open(path string) (io.ReadCloser, int64, error) {
  	for _, f := range p.zr.File {
  		if f.Name == path {
  			if f.UncompressedSize64 > math.MaxInt64 {
  				return nil, 0, errors.Reason("the file %q is unbelievably huge (%d bytes)", path, f.UncompressedSize64).Err()
  			}
  			rc, err := f.Open()
  			if err != nil {
  				return nil, 0, err
  			}
  			return rc, int64(f.UncompressedSize64), nil
  		}
  	}
  	return nil, 0, errors.Reason("no file %q inside the package", path).Err()
  }
docs: // Open opens some file inside the package for reading.
  //
  // Returns the ReadCloser and the uncompressed file size.