feat(application): inital commit

main.go

@@ -0,0 +1,111 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"time"
+
+	"github.com/kelseyhightower/envconfig"
+	"github.com/miekg/dns"
+)
+
+type App struct {
+	DNSRecord    string `envconfig:"DNS_RECORD" required:"true"`          // must have trailing dot
+	DNSServer    string `envconfig:"DNS_SERVER" required:"true"`          // must have :53
+	DNSZone      string `envconfig:"DNS_ZONE" required:"true"`            // must have trailing dot
+	DNSKeyName   string `envconfig:"DNS_KEY_NAME" required:"true"`        // must have trailing dot
+	DNSKeySecret string `envconfig:"DNS_KEY_Secret" required:"true"`      // no trailing dot :)
+	DNSKeyAlgo   string `envconfig:"DNS_KEY_ALGO" default:"hmac-sha512."` // must have trailing dot
+
+	Listen string `envconfig:"LISTEN" default:":8080"`
+	Token  string `envconfig:"TOKEN" required:"true"`
+}
+
+func main() {
+	app := &App{}
+	err := envconfig.Process("", app)
+	if err != nil {
+		log.Fatalf("unable to parse config: %s", err)
+	}
+
+	http.HandleFunc("/update", app.handler)
+
+	err = http.ListenAndServe(app.Listen, nil)
+	if err != nil {
+		log.Fatalf("unable to listen: %s", err)
+	}
+}
+
+func (a *App) handler (w http.ResponseWriter, r *http.Request) {
+	query := r.URL.Query()
+
+	token := query.Get("token")
+	v4 := net.ParseIP(query.Get("v4"))
+	v6 := net.ParseIP(query.Get("v6"))
+
+	if token != a.Token {
+		w.WriteHeader(http.StatusForbidden)
+		fmt.Fprintf(w, "no :(")
+		return
+	}
+	if v4 == nil || v6 == nil {
+		w.WriteHeader(http.StatusBadRequest)
+		fmt.Fprintf(w, "no :(")
+		return
+	}
+
+	err := a.dnsUpdate(v4, v6)
+	if err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		log.Printf("unable to update: %s", err)
+		fmt.Fprintf(w, "error")
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+	fmt.Fprintf(w, "updated")
+
+}
+
+func (a *App) dnsUpdate(v4, v6 net.IP) error {
+	// dns key name as fqdn
+	key := dns.Fqdn(a.DNSKeyName)
+
+	// create records
+	rra := &dns.A{
+		Hdr: dns.RR_Header{Name: a.DNSRecord, Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 300},
+		A:   v4,
+	}
+	rraaaa := &dns.AAAA{
+		Hdr:  dns.RR_Header{Name: a.DNSRecord, Rrtype: dns.TypeAAAA, Class: dns.ClassINET, Ttl: 300},
+		AAAA: v6,
+	}
+	rrs := []dns.RR{rra, rraaaa}
+
+	// create message
+	m := new(dns.Msg)
+	m.SetUpdate(a.DNSZone)
+	m.RemoveRRset(rrs)
+	m.Insert(rrs)
+	m.SetTsig(key, a.DNSKeyAlgo, 300, time.Now().Unix())
+
+	// client
+	c := &dns.Client{
+		SingleInflight: true,
+		TsigSecret:     map[string]string{key: a.DNSKeySecret},
+	}
+
+	// send and handle message
+	reply, _, err := c.Exchange(m, a.DNSServer)
+	if err != nil {
+		return fmt.Errorf("update failed: %w", err)
+	}
+
+	if reply != nil && reply.Rcode != dns.RcodeSuccess {
+		return fmt.Errorf("dns update failed: %w", err)
+	}
+
+	return nil
+}