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    <h3>Editing: SubRequestHandler.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier &lt;fabien@symfony.com&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\HttpKernel\HttpCache;

use Symfony\Component\HttpFoundation\IpUtils;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\HttpKernelInterface;

/**
 * @author Nicolas Grekas &lt;p@tchwork.com&gt;
 *
 * @internal
 */
class SubRequestHandler
{
    public static function handle(HttpKernelInterface $kernel, Request $request, int $type, bool $catch): Response
    {
        // save global state related to trusted headers and proxies
        $trustedProxies = Request::getTrustedProxies();
        $trustedHeaderSet = Request::getTrustedHeaderSet();

        // remove untrusted values
        $remoteAddr = $request-&gt;server-&gt;get('REMOTE_ADDR');
        if (!$remoteAddr || !IpUtils::checkIp($remoteAddr, $trustedProxies)) {
            $trustedHeaders = [
                'FORWARDED' =&gt; $trustedHeaderSet &amp; Request::HEADER_FORWARDED,
                'X_FORWARDED_FOR' =&gt; $trustedHeaderSet &amp; Request::HEADER_X_FORWARDED_FOR,
                'X_FORWARDED_HOST' =&gt; $trustedHeaderSet &amp; Request::HEADER_X_FORWARDED_HOST,
                'X_FORWARDED_PROTO' =&gt; $trustedHeaderSet &amp; Request::HEADER_X_FORWARDED_PROTO,
                'X_FORWARDED_PORT' =&gt; $trustedHeaderSet &amp; Request::HEADER_X_FORWARDED_PORT,
                'X_FORWARDED_PREFIX' =&gt; $trustedHeaderSet &amp; Request::HEADER_X_FORWARDED_PREFIX,
            ];
            foreach (array_filter($trustedHeaders) as $name =&gt; $key) {
                $request-&gt;headers-&gt;remove($name);
                $request-&gt;server-&gt;remove('HTTP_'.$name);
            }
        }

        // compute trusted values, taking any trusted proxies into account
        $trustedIps = [];
        $trustedValues = [];
        foreach (array_reverse($request-&gt;getClientIps()) as $ip) {
            $trustedIps[] = $ip;
            $trustedValues[] = sprintf('for=&quot;%s&quot;', $ip);
        }
        if ($ip !== $remoteAddr) {
            $trustedIps[] = $remoteAddr;
            $trustedValues[] = sprintf('for=&quot;%s&quot;', $remoteAddr);
        }

        // set trusted values, reusing as much as possible the global trusted settings
        if (Request::HEADER_FORWARDED &amp; $trustedHeaderSet) {
            $trustedValues[0] .= sprintf(';host=&quot;%s&quot;;proto=%s', $request-&gt;getHttpHost(), $request-&gt;getScheme());
            $request-&gt;headers-&gt;set('Forwarded', $v = implode(', ', $trustedValues));
            $request-&gt;server-&gt;set('HTTP_FORWARDED', $v);
        }
        if (Request::HEADER_X_FORWARDED_FOR &amp; $trustedHeaderSet) {
            $request-&gt;headers-&gt;set('X-Forwarded-For', $v = implode(', ', $trustedIps));
            $request-&gt;server-&gt;set('HTTP_X_FORWARDED_FOR', $v);
        } elseif (!(Request::HEADER_FORWARDED &amp; $trustedHeaderSet)) {
            Request::setTrustedProxies($trustedProxies, $trustedHeaderSet | Request::HEADER_X_FORWARDED_FOR);
            $request-&gt;headers-&gt;set('X-Forwarded-For', $v = implode(', ', $trustedIps));
            $request-&gt;server-&gt;set('HTTP_X_FORWARDED_FOR', $v);
        }

        // fix the client IP address by setting it to 127.0.0.1,
        // which is the core responsibility of this method
        $request-&gt;server-&gt;set('REMOTE_ADDR', '127.0.0.1');

        // ensure 127.0.0.1 is set as trusted proxy
        if (!IpUtils::checkIp('127.0.0.1', $trustedProxies)) {
            Request::setTrustedProxies(array_merge($trustedProxies, ['127.0.0.1']), Request::getTrustedHeaderSet());
        }

        try {
            return $kernel-&gt;handle($request, $type, $catch);
        } finally {
            // restore global state
            Request::setTrustedProxies($trustedProxies, $trustedHeaderSet);
        }
    }
}
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