szurubooru/src/Views/layout-file.phtml

<?php
$lastModified = $this->context->transport->lastModified;
$eTag = $this->context->transport->fileHash;
$ttl = $this->context->transport->cacheDaysToLive * 24 * 3600;

$ifModifiedSince = isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])
	? $_SERVER['HTTP_IF_MODIFIED_SINCE']
	: false;

$eTagHeader = isset($_SERVER['HTTP_IF_NONE_MATCH'])
	? trim(trim($_SERVER['HTTP_IF_NONE_MATCH']), '"')
	: false;

\Chibi\Util\Headers::set('ETag', '"' . $eTag . '"');
\Chibi\Util\Headers::set('Last-Modified', gmdate('D, d M Y H:i:s \G\M\T', $lastModified));
\Chibi\Util\Headers::set('Pragma', 'public');
\Chibi\Util\Headers::set('Cache-Control', 'public, max-age=' . $ttl);
\Chibi\Util\Headers::set('Expires', gmdate('D, d M Y H:i:s \G\M\T', time() + $ttl));

if (isset($this->context->transport->customFileName))
{
	\Chibi\Util\Headers::set(
		'Content-Disposition',
		'inline; filename="' . $this->context->transport->customFileName . '"');
}

\Chibi\Util\Headers::set(
	'Content-Type',
	$this->context->transport->mimeType);

if (strtotime($ifModifiedSince) == $lastModified or $eTagHeader == $eTag)
{
	\Chibi\Util\Headers::setCode('304');
	exit;
}

echo $this->context->transport->fileContent;
flush();