dyndns/service/dns.go

package service

import (
	"fmt"
	"log"
	"net"

	"github.com/miekg/dns"
)

var dnsClient dns.Client

func init() {
	dnsClient = dns.Client{
		Net: "tcp",
	}
}

func DNSUpdateEntry(domain string, hostname string, ip4 net.IP, ip6 net.IP) error {
	if ip4 == nil && ip6 == nil {
		return fmt.Errorf("at least one of --ipv4 and --ipv6 have to be set")
	}

	msg := new(dns.Msg)
	fqdn := fmt.Sprintf("%s.%s.", hostname, domain)
	zone := fmt.Sprintf("%s.", domain)

	msg.SetUpdate(zone)
	msg.RemoveName([]dns.RR{
		&dns.RR_Header{Name: fqdn},
	})

	var rrs []dns.RR

	if ip4 != nil {
		ip4bin := ip4.To4()
		if ip4bin == nil {
			return fmt.Errorf("ip4 (%v) is not a valid IPv4 address", ip4)
		}
		rrs = append(rrs, &dns.A{
			Hdr: dns.RR_Header{
				Name:   fqdn,
				Rrtype: dns.TypeA,
				Class:  dns.ClassINET,
				Ttl:    C.DNS.DefaultTTL,
			},
			A: ip4bin,
		})
	}

	if ip6 != nil {
		ip6bin := ip6.To16()
		if ip6bin == nil {
			return fmt.Errorf("ip6 (%v) is not a valid IPv6 address", ip4)
		}
		rrs = append(rrs, &dns.AAAA{
			Hdr: dns.RR_Header{
				Name:   fqdn,
				Rrtype: dns.TypeAAAA,
				Class:  dns.ClassINET,
				Ttl:    C.DNS.DefaultTTL,
			},
			AAAA: ip6bin,
		})
	}

	msg.Insert(rrs)

	log.Printf("Sending DNS Update: %v", msg)

	reply, _, err := dnsClient.Exchange(msg, C.DNS.Server)
	if err != nil {
		return fmt.Errorf("failed to execute DNS Udpate: %v", err)
	}

	log.Printf("Received DNS Update Reply: %v", reply)

	return nil
}