105 lines
2.0 KiB
Go
105 lines
2.0 KiB
Go
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package main
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import (
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"fmt"
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"log"
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"net"
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"os"
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"regexp"
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"strconv"
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"strings"
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"github.com/miekg/dns"
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)
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const zone = "my.local-ip.dev."
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func main() {
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dns.HandleFunc(zone, handleDnsRequest)
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port, err := strconv.Atoi(os.Getenv("PORT"))
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if err != nil {
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port = 9053
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}
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server := &dns.Server{
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Addr: ":" + strconv.Itoa(port),
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Net: "udp",
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}
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log.Printf("Starting at %d\n", port)
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err = server.ListenAndServe()
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defer server.Shutdown()
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if err != nil {
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log.Fatalf("Failed to start server: %s\n ", err.Error())
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}
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}
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func handleDnsRequest(response dns.ResponseWriter, request *dns.Msg) {
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go func() {
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message := new(dns.Msg)
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message.SetReply(request)
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message.Compress = true
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switch request.Opcode {
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case dns.OpcodeQuery:
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handleQuery(message)
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default:
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refuseMessage(message)
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}
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response.WriteMsg(message)
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}()
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}
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func handleQuery(message *dns.Msg) {
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for _, question := range message.Question {
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switch question.Qtype {
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case dns.TypeA:
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ip := extractIp(question.Name)
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log.Printf("%s => %s\n", question.Name, ip)
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if ip == nil {
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refuseMessage(message)
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break
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}
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resource := new(dns.A)
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resource.Hdr = dns.RR_Header{Ttl: 10, Name: question.Name, Rrtype: dns.TypeA, Class: dns.ClassINET}
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resource.A = ip
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message.Answer = append(message.Answer, resource)
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}
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}
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}
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func extractIp(fqdn string) net.IP {
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var ip string
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dashedIpRegex := regexp.MustCompile(fmt.Sprintf(`^(((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\-?\b){4}).%s$`, zone))
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matches := dashedIpRegex.FindStringSubmatch(fqdn)
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if len(matches) < 2 {
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return nil
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}
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ip = strings.ReplaceAll(matches[1], "-", ".")
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return net.ParseIP(ip)
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}
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func refuseMessage(message *dns.Msg) {
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message.MsgHdr.Rcode = dns.RcodeRefused
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soa := new(dns.SOA)
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soa.Hdr = dns.RR_Header{
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Name: "my.local-ip.dev.",
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Rrtype: dns.TypeSOA,
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Class: dns.ClassINET,
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Ttl: 10,
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Rdlength: 0,
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}
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soa.Ns = "ns-1.local-ip.dev."
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soa.Mbox = "admin.local-ip.dev."
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soa.Serial = 2022102400
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soa.Refresh = 10
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soa.Retry = 10
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soa.Expire = 10
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soa.Minttl = 10
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message.Ns = append(message.Ns, soa)
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}
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