reorganize code

README.md

@@ -10,6 +10,10 @@ It was inspired by [local-ip.co](http://local-ip.co) and
 ```sh
 $ dig 10-0-1-29.my.local-ip.dev +short
 10.0.1.29
+$ dig app.10-0-1-29.my.local-ip.dev +short
+10.0.1.29
+$ dig foo.bar.10.0.1.29.my.local-ip.dev +short
+10.0.1.29
 $ dig 127.0.0.1.my.local-ip.dev +short
 127.0.0.1
 ```

main.go

@@ -1,104 +1,21 @@
 package main
 
 import (
-	"fmt"
+	"flag"
-	"log"
-	"net"
-	"os"
-	"regexp"
-	"strconv"
 	"strings"
 
-	"github.com/miekg/dns"
+	xip "local-ip.dev/xip"
 )
 
-const zone = "my.local-ip.dev."
+const (
+	zone        = "my.local-ip.dev."
+	nameservers = "ns.local-ip.dev."
+)
 
 func main() {
-	dns.HandleFunc(zone, handleDnsRequest)
+	var port = flag.Int("port", 53, "port the DNS server should bind to")
+	flag.Parse()
 
-	port, err := strconv.Atoi(os.Getenv("PORT"))
+	n := xip.NewXip(zone, strings.Split(nameservers, ","), *port)
-	if err != nil {
+	n.StartServer()
-		port = 9053
-	}
-	server := &dns.Server{
-		Addr: ":" + strconv.Itoa(port),
-		Net:  "udp",
-	}
-	log.Printf("Starting at %d\n", port)
-	err = server.ListenAndServe()
-	defer server.Shutdown()
-	if err != nil {
-		log.Fatalf("Failed to start server: %s\n ", err.Error())
-	}
-}
-
-func handleDnsRequest(response dns.ResponseWriter, request *dns.Msg) {
-	go func() {
-		message := new(dns.Msg)
-		message.SetReply(request)
-		message.Compress = true
-
-		switch request.Opcode {
-		case dns.OpcodeQuery:
-			handleQuery(message)
-		default:
-			refuseMessage(message)
-		}
-
-		response.WriteMsg(message)
-	}()
-}
-
-func handleQuery(message *dns.Msg) {
-	for _, question := range message.Question {
-		switch question.Qtype {
-		case dns.TypeA:
-			ip := extractIp(question.Name)
-			log.Printf("%s => %s\n", question.Name, ip)
-			if ip == nil {
-				refuseMessage(message)
-				break
-			}
-
-			resource := new(dns.A)
-			resource.Hdr = dns.RR_Header{Ttl: 10, Name: question.Name, Rrtype: dns.TypeA, Class: dns.ClassINET}
-			resource.A = ip
-			message.Answer = append(message.Answer, resource)
-		}
-	}
-}
-
-func extractIp(fqdn string) net.IP {
-	var ip string
-	dashedIpRegex := regexp.MustCompile(fmt.Sprintf(`^(((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\-?\b){4}).%s$`, zone))
-	matches := dashedIpRegex.FindStringSubmatch(fqdn)
-	if len(matches) < 2 {
-		return nil
-	}
-
-	ip = strings.ReplaceAll(matches[1], "-", ".")
-
-	return net.ParseIP(ip)
-}
-
-func refuseMessage(message *dns.Msg) {
-	message.MsgHdr.Rcode = dns.RcodeRefused
-
-	soa := new(dns.SOA)
-	soa.Hdr = dns.RR_Header{
-		Name:     "my.local-ip.dev.",
-		Rrtype:   dns.TypeSOA,
-		Class:    dns.ClassINET,
-		Ttl:      10,
-		Rdlength: 0,
-	}
-	soa.Ns = "ns-1.local-ip.dev."
-	soa.Mbox = "admin.local-ip.dev."
-	soa.Serial = 2022102400
-	soa.Refresh = 10
-	soa.Retry = 10
-	soa.Expire = 10
-	soa.Minttl = 10
-	message.Ns = append(message.Ns, soa)
 }

xip/xip.go

@@ -0,0 +1,130 @@
+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()),
+					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) handleQuery(message *dns.Msg) {
+	for _, question := range message.Question {
+		switch question.Qtype {
+		case dns.TypeA:
+			record := xip.handleA(question, message)
+			message.Answer = append(message.Answer, record)
+		}
+	}
+}
+
+func (xip *Xip) refuseMessage(message *dns.Msg) {
+	message.MsgHdr.Rcode = dns.RcodeRefused
+
+	soa := new(dns.SOA)
+	soa.Hdr = dns.RR_Header{
+		Name:     "my.local-ip.dev.",
+		Rrtype:   dns.TypeSOA,
+		Class:    dns.ClassINET,
+		Ttl:      uint32((time.Hour * 24 * 7).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.Retry = uint32((time.Minute * 15).Seconds())
+	soa.Expire = uint32((time.Minute * 30).Seconds())
+	soa.Minttl = uint32((time.Minute * 5).Seconds())
+	message.Ns = append(message.Ns, soa)
+}
+
+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:
+			xip.refuseMessage(message)
+		}
+
+		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
+}