CIntranetUtils::getHostName

static function getHostName()
{
	static $host;

	if (is_null($host))
	{
		$ttl = (CACHED_b_lang !== false ? CACHED_b_lang : 0);

		$site = BitrixMainSiteTable::getList(array(
			'filter' => defined('SITE_ID') ? array('=LID' => SITE_ID) : array(),
			'order'  => array('ACTIVE' => 'DESC', 'DEF' => 'DESC', 'SORT' => 'ASC'),
			'select' => array('SERVER_NAME'),
			'cache' => [ 'ttl' => $ttl ],
		))->fetch();

		$host = isModuleInstalled('bitrix24') && defined('BX24_HOST_NAME') ? BX24_HOST_NAME
			: ($site['SERVER_NAME'] ?: COption::getOptionString('main', 'server_name', ''));
	}

	return $host;
}