// set response code msg := new(dns.Msg) msg.SetRcode(req, dns.RcodeRefused)In the above code, `new(dns.Msg)` creates a new DNS message. The `SetRcode` method sets the response code to `dns.RcodeRefused`, indicating that the request was refused by the server. This is a useful method for customizing DNS server behavior, and it's available in the `github.com/miekg/dns` package library.