FriendsOfSymfony / FOSHttpCacheBundle

            // Determine the default tags header for the varnish client, depending on whether we use BAN or xkey

            ->validate()

                ->ifTrue(

                    function ($v) {

                        return

                            array_key_exists('proxy_client', $v)

                            && array_key_exists('varnish', $v['proxy_client'])

                            && empty($v['proxy_client']['varnish']['tags_header'])

                        ;

                    }

                )

                ->then(function ($v) {

                    $v['proxy_client']['varnish']['tags_header'] =

        return $treeBuilder;

    }

    private function isVarnishXkey(array $v): bool

    {

        return array_key_exists('proxy_client', $v)

            && array_key_exists('varnish', $v['proxy_client'])

            && Varnish::TAG_XKEY === $v['proxy_client']['varnish']['tag_mode']

        ;

    }

    private function addCacheableResponseSection(ArrayNodeDefinition $rootNode)

    {