of the data stream processed, or null if the header was not yet fully processed, is not present at all, or the compressor's #GZlibDecompressor:format property is not gio.types.ZlibCompressorFormat.Gzip.
ZlibDecompressor.fileInfo
gio.file_info.FileInfo fileInfo() @propertyGet fileInfo property.
Returns
A #GFileInfo containing the information found in the GZIP header