` tag
* which instructs the browser to start prefetching DNS
* records for every domain listed in the `domains` attribute
* of this ViewHelper. Prefetching starts as soon as the browser
* becomes aware of the tag - to optimise even further, you may
* wish to control the output buffer's size to deliver your site
* HTML in chunks, the first chunk being the one containing this
* ViewHelper.
*
* Note that the web server daemon may send headers which prevent
* this prefetching and that these headers can be added in many
* ways. If prefetching does not work, you will need to inspect
* the HTTP headers returned from the actual environment. Or you
* may prefer to simply add `force="TRUE"` to this tag - but
* beware that this will affect the entire document's behaviour,
* not just for this particular set of domain prefetches. Once
* force-enabled this setting cannot be disabled (unless done so
* by manually adding an additional meta header tag as examplified
* by the `build()` method.
*
* ### Example usage:
*
*
*
* See: https://developer.mozilla.org/en-US/docs/Controlling_DNS_prefetching
*
* @package Vhs
* @subpackage ViewHelpers\Asset
*/
class PrefetchViewHelper extends AbstractAssetViewHelper {
/**
* @var string
*/
protected $type = 'link';
/**
* @return void
*/
public function initializeArguments() {
parent::initializeArguments();
$this->registerArgument('domains', 'mixed', 'Domain DNS names to prefetch. By default will add all sys_domain record DNS names', TRUE);
$this->registerArgument('protocol', 'string', 'Optional value of protocol as inserted in the resulting HREF value. If you experience problems with a non-protocol link, try enforcing http/https here', FALSE, NULL);
$this->registerArgument('protocolSeparator', 'string', 'If you do not enforce a particular protocol and wish to remove the double slashes from the hostname (your browser may not understand this!), set this attribute to an empty value (not-zero)', FALSE, '//');
$this->registerArgument('force', 'boolean', 'If TRUE, adds an additional meta header tag which forces prefetching to be enabled even if otherwise requested by the http daemon', FALSE, FALSE);
}
/**
* @return void
*/
public function render() {
$this->arguments['standalone'] = TRUE;
$this->arguments['allowMoveToFooter'] = FALSE;
$this->tagBuilder->forceClosingTag(FALSE);
$this->tagBuilder->addAttribute('rel', 'dns-prefetch');
$this->tagBuilder->addAttribute('href', '');
$this->tagBuilder->setTagName('link');
$this->finalize();
}
/**
* @return string
*/
public function build() {
$domains = $this->arguments['domains'];
if (FALSE === is_array($domains)) {
$domains = GeneralUtility::trimExplode(',', $domains, TRUE);
}
$headerCode = '';
if (TRUE === (boolean) $this->arguments['force']) {
$headerCode .= '' . LF;
}
foreach ($domains as $domain) {
$this->tagBuilder->removeAttribute('href');
$this->tagBuilder->addAttribute('href', $this->arguments['protocol'] . $this->arguments['protocolSeparator'] . $domain);
$headerCode .= $this->tagBuilder->render() . LF;
}
return $headerCode;
}
}