code: func hasStubEdns0(m *dns.Msg) bool {
  	option := m.IsEdns0()
  	if option == nil {
  		return false
  	}
  	for _, o := range option.Option {
  		if o.Option() == ednsStubCode && len(o.(*dns.EDNS0_LOCAL).Data) == 1 &&
  			o.(*dns.EDNS0_LOCAL).Data[0] == 1 {
  			return true
  		}
  	}
  	return false
  }
docs: // hasStubEdns0 checks if the message is carrying our special edns0 zero option.