code: func setupEdns0Opt(r *dns.Msg) *dns.OPT {
  	o := r.IsEdns0()
  	if o == nil {
  		r.SetEdns0(4096, true)
  		o = r.IsEdns0()
  	}
  	return o
  }
docs: // setupEdns0Opt will retrieve the EDNS0 OPT or create it if it does not exist