def _raster_layers(self):
        """Return a list of raster layers available.

        :return: List of raster layers available in the geopackage.
        :rtype: list

        .. versionadded:: 4.0
        """
        layers = []

        raster_datasource = gdal.Open(self.uri.absoluteFilePath())
        if raster_datasource:
            subdatasets = raster_datasource.GetSubDatasets()
            if len(subdatasets) == 0:
                metadata = raster_datasource.GetMetadata()
                layers.append(metadata['IDENTIFIER'])
            else:
                for subdataset in subdatasets:
                    layers.append(subdataset[0].split(':')[2])

        return layers
Return a list of raster layers available.

        :return: List of raster layers available in the geopackage.
        :rtype: list

        .. versionadded:: 4.0