WP_Upgrader::unpack_package( string $package, bool $delete_package = true )

	public function unpack_package( $package, $delete_package = true ) {
		global $wp_filesystem;

		$this->skin->feedback('unpack_package');

		$upgrade_folder = $wp_filesystem->wp_content_dir() . 'upgrade/';

		//Clean up contents of upgrade directory beforehand.
		$upgrade_files = $wp_filesystem->dirlist($upgrade_folder);
		if ( !empty($upgrade_files) ) {
			foreach ( $upgrade_files as $file )
				$wp_filesystem->delete($upgrade_folder . $file['name'], true);
		}

		// We need a working directory - Strip off any .tmp or .zip suffixes
		$working_dir = $upgrade_folder . basename( basename( $package, '.tmp' ), '.zip' );

		// Clean up working directory
		if ( $wp_filesystem->is_dir($working_dir) )
			$wp_filesystem->delete($working_dir, true);

		// Unzip package to working directory
		$result = unzip_file( $package, $working_dir );

		// Once extracted, delete the package if required.
		if ( $delete_package )
			unlink($package);

		if ( is_wp_error($result) ) {
			$wp_filesystem->delete($working_dir, true);
			if ( 'incompatible_archive' == $result->get_error_code() ) {
				return new WP_Error( 'incompatible_archive', $this->strings['incompatible_archive'], $result->get_error_data() );
			}
			return $result;
		}

		return $working_dir;
	}