Piwik\Plugins\CorePluginsAdmin\PluginInstaller::getNameOfFirstSubfolder PHP Method

    private function getNameOfFirstSubfolder($pluginDir)
    {
        if (!($dir = opendir($pluginDir))) {
            return false;
        }
        $firstSubFolder = '';
        while ($file = readdir($dir)) {
            if ($file[0] != '.' && is_dir($pluginDir . DIRECTORY_SEPARATOR . $file)) {
                $firstSubFolder = $file;
                break;
            }
        }
        if (empty($firstSubFolder)) {
            throw new PluginInstallerException('The plugin ZIP file does not contain a subfolder, but Piwik expects plugin files to be within a subfolder in the Zip archive.');
        }
        return $firstSubFolder;
    }