package xip import ( "log" "net" "os" "regexp" "strconv" "strings" "time" "github.com/miekg/dns" ) type Xip struct { Server dns.Server NameServers []*dns.NS Zone string } var ( flyRegion = os.Getenv("FLY_REGION") dottedIpV4Regex = regexp.MustCompile(`(?:^|(?:[\w\d])+\.)(((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\.?\b){4})($|[.-])`) dashedIpV4Regex = regexp.MustCompile(`(?:^|(?:[\w\d])+\.)(((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\-?\b){4})($|[.-])`) ) func (xip *Xip) handleA(question dns.Question, response *dns.Msg) *dns.A { fqdn := question.Name for _, ipV4RE := range []*regexp.Regexp{dashedIpV4Regex, dottedIpV4Regex} { if ipV4RE.MatchString(fqdn) { match := ipV4RE.FindStringSubmatch(fqdn)[1] match = strings.ReplaceAll(match, "-", ".") ipV4Address := net.ParseIP(match).To4() if ipV4Address == nil { return nil } resource := &dns.A{ Hdr: dns.RR_Header{ // Ttl: uint32((time.Hour * 24 * 7).Seconds()), Ttl: uint32((time.Second * 10).Seconds()), Name: fqdn, Rrtype: dns.TypeA, Class: dns.ClassINET, }, A: ipV4Address, } log.Printf("(%s) %s => %s\n", flyRegion, fqdn, ipV4Address) return resource } } return nil } func (xip *Xip) SOARecord(question dns.Question) *dns.SOA { soa := new(dns.SOA) soa.Hdr = dns.RR_Header{ Name: question.Name, Rrtype: dns.TypeSOA, Class: dns.ClassINET, // Ttl: uint32((time.Hour * 24 * 7).Seconds()), Ttl: uint32((time.Second * 10).Seconds()), Rdlength: 0, } soa.Ns = "ns.local-ip.dev." soa.Mbox = "admin.local-ip.dev." soa.Serial = 2022102800 // soa.Refresh = uint32((time.Minute * 15).Seconds()) soa.Refresh = uint32((time.Second * 10).Seconds()) // soa.Retry = uint32((time.Minute * 15).Seconds()) soa.Retry = uint32((time.Second * 10).Seconds()) // soa.Expire = uint32((time.Minute * 30).Seconds()) soa.Expire = uint32((time.Second * 10).Seconds()) // soa.Minttl = uint32((time.Minute * 5).Seconds()) soa.Minttl = uint32((time.Second * 10).Seconds()) return soa } func (xip *Xip) handleQuery(message *dns.Msg) { for _, question := range message.Question { switch question.Qtype { case dns.TypeA: record := xip.handleA(question, message) if record != nil { message.Answer = append(message.Answer, record) } else { message.Ns = append(message.Ns, xip.SOARecord(question)) } } } } func (xip *Xip) handleDnsRequest(response dns.ResponseWriter, request *dns.Msg) { go func() { message := new(dns.Msg) message.SetReply(request) message.Compress = true message.Authoritative = true message.RecursionAvailable = false switch request.Opcode { case dns.OpcodeQuery: xip.handleQuery(message) default: message.MsgHdr.Rcode = dns.RcodeRefused } response.WriteMsg(message) }() } func (xip *Xip) StartServer() { log.Printf("Listening on %s\n", xip.Server.Addr) err := xip.Server.ListenAndServe() defer xip.Server.Shutdown() if err != nil { log.Fatalf("Failed to start server: %s\n ", err.Error()) } } func NewXip(zone string, nameservers []string, port int) (xip *Xip) { xip = &Xip{} for _, ns := range nameservers { xip.NameServers = append(xip.NameServers, &dns.NS{Ns: ns}) } xip.Server = dns.Server{ Addr: ":" + strconv.Itoa(port), Net: "udp", } dns.HandleFunc(zone, xip.handleDnsRequest) return xip }