Symfony\Component\HttpFoundation\Request::getHost PHP Method

    public function getHost()
    {
        if ($this->isFromTrustedProxy() && self::$trustedHeaders[self::HEADER_CLIENT_HOST] && $host = $this->headers->get(self::$trustedHeaders[self::HEADER_CLIENT_HOST])) {
            $elements = explode(',', $host);

            $host = $elements[count($elements) - 1];
        } elseif (!$host = $this->headers->get('HOST')) {
            if (!$host = $this->server->get('SERVER_NAME')) {
                $host = $this->server->get('SERVER_ADDR', '');
            }
        }

        // trim and remove port number from host
        // host is lowercase as per RFC 952/2181
        $host = strtolower(preg_replace('/:\d+$/', '', trim($host)));

        // as the host can come from the user (HTTP_HOST and depending on the configuration, SERVER_NAME too can come from the user)
        // check that it does not contain forbidden characters (see RFC 952 and RFC 2181)
        // use preg_replace() instead of preg_match() to prevent DoS attacks with long host names
        if ($host && '' !== preg_replace('/(?:^\[)?[a-zA-Z0-9-:\]_]+\.?/', '', $host)) {
            if (!$this->isHostValid) {
                return '';
            }
            $this->isHostValid = false;

            throw new SuspiciousOperationException(sprintf('Invalid Host "%s".', $host));
        }

        if (count(self::$trustedHostPatterns) > 0) {
            // to avoid host header injection attacks, you should provide a list of trusted host patterns

            if (in_array($host, self::$trustedHosts)) {
                return $host;
            }

            foreach (self::$trustedHostPatterns as $pattern) {
                if (preg_match($pattern, $host)) {
                    self::$trustedHosts[] = $host;

                    return $host;
                }
            }

            if (!$this->isHostValid) {
                return '';
            }
            $this->isHostValid = false;

            throw new SuspiciousOperationException(sprintf('Untrusted Host "%s".', $host));
        }

        return $host;
    }

 public function matches(Request $request)
 {
     if (!$this->language) {
         throw new \LogicException('Unable to match the request as the expression language is not available.');
     }
     return $this->language->evaluate($this->expression, array('request' => $request, 'method' => $request->getMethod(), 'path' => rawurldecode($request->getPathInfo()), 'host' => $request->getHost(), 'ip' => $request->getClientIp(), 'attributes' => $request->attributes->all())) && parent::matches($request);
 }