dns: implement per-DHCP-lease dyndns
The HTTP API is easy to use from the command line or from Go: % curl --data "host=sub&ip=192.168.33.44" -4 http://router7:8053/dyndns ok % host sub.$(hostname) sub.midna has address 192.168.33.44 This can be used in combination with https://github.com/gokrazy/gdns
This commit is contained in:
Michael Stapelberg
parent
92d995bf79
commit
bd8fc63b0e
@ -96,6 +96,7 @@ func logic() error {
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log.Printf("cannot resolve DHCP hostnames: %v", err)
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}
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http.Handle("/metrics", srv.PrometheusHandler())
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http.HandleFunc("/dyndns", srv.DyndnsHandler)
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if err := updateListeners(srv.Mux); err != nil {
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return err
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}
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@ -17,6 +17,7 @@ package dns
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import (
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"errors"
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"fmt"
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"log"
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"net"
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"net/http"
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@ -51,6 +52,7 @@ type Server struct {
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hostname, ip string
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hostsByName map[string]string
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hostsByIP map[string]string
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subnames map[string]map[string]net.IP // hostname → subname → ip
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}
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func NewServer(addr, domain string) *Server {
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@ -64,6 +66,7 @@ func NewServer(addr, domain string) *Server {
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sometimes: rate.NewLimiter(rate.Every(1*time.Second), 1), // at most once per second
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hostname: hostname,
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ip: ip,
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subnames: make(map[string]map[string]net.IP),
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}
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server.prom.registry = prometheus.NewRegistry()
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@ -105,6 +108,8 @@ func (s *Server) initHostsLocked() {
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if rev, err := dns.ReverseAddr(s.ip); err == nil {
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s.hostsByIP[rev] = s.hostname
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}
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s.Mux.HandleFunc(s.hostname+".", s.subnameHandler(s.hostname))
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s.Mux.HandleFunc(s.hostname+"."+s.domain+".", s.subnameHandler(s.hostname))
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}
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}
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@ -122,10 +127,52 @@ func (s *Server) hostByIP(n string) (string, bool) {
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return r, ok
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}
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func (s *Server) subname(hostname, host string) (net.IP, bool) {
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s.mu.Lock()
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defer s.mu.Unlock()
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r, ok := s.subnames[hostname][host]
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return r, ok
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}
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func (s *Server) PrometheusHandler() http.Handler {
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return promhttp.HandlerFor(s.prom.registry, promhttp.HandlerOpts{})
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}
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func (s *Server) DyndnsHandler(w http.ResponseWriter, r *http.Request) {
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host := r.FormValue("host")
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ip := net.ParseIP(r.FormValue("ip"))
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if ip == nil {
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http.Error(w, "invalid ip", http.StatusBadRequest)
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return
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}
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s.mu.Lock()
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defer s.mu.Unlock()
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remote, _, err := net.SplitHostPort(r.RemoteAddr)
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if err != nil {
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http.Error(w, fmt.Sprintf("net.SplitHostPort(%q): %v", r.RemoteAddr, err), http.StatusBadRequest)
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return
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}
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rev, err := dns.ReverseAddr(remote)
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if err != nil {
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http.Error(w, fmt.Sprintf("dns.ReverseAddr(%v): %v", remote, err), http.StatusBadRequest)
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return
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}
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hostname, ok := s.hostsByIP[rev]
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if !ok {
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err := fmt.Sprintf("connection without corresponding DHCP lease: %v", rev)
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http.Error(w, err, http.StatusForbidden)
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return
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}
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subnames, ok := s.subnames[hostname]
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if !ok {
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subnames = make(map[string]net.IP)
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s.subnames[hostname] = subnames
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}
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subnames[host] = ip
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w.Write([]byte("ok\n"))
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}
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func (s *Server) SetLeases(leases []dhcp4d.Lease) {
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s.mu.Lock()
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defer s.mu.Unlock()
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@ -135,6 +182,9 @@ func (s *Server) SetLeases(leases []dhcp4d.Lease) {
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if l.Expired(now) {
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continue
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}
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if l.Hostname == "" {
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continue
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}
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if _, ok := s.hostsByName[l.Hostname]; ok {
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continue // don’t overwrite e.g. the hostname entry
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}
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@ -142,6 +192,8 @@ func (s *Server) SetLeases(leases []dhcp4d.Lease) {
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if rev, err := dns.ReverseAddr(l.Addr.String()); err == nil {
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s.hostsByIP[rev] = l.Hostname
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}
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s.Mux.HandleFunc(l.Hostname+".", s.subnameHandler(l.Hostname))
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s.Mux.HandleFunc(l.Hostname+"."+s.domain+".", s.subnameHandler(l.Hostname))
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}
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}
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@ -284,3 +336,66 @@ func (s *Server) handleRequest(w dns.ResponseWriter, r *dns.Msg) {
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}
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w.WriteMsg(in)
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}
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func (s *Server) resolveSubname(hostname string, q dns.Question) (dns.RR, error) {
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if q.Qclass != dns.ClassINET {
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return nil, nil
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}
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if q.Qtype == dns.TypeA ||
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q.Qtype == dns.TypeAAAA ||
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q.Qtype == dns.TypeMX {
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name := strings.TrimSuffix(q.Name, "."+hostname+".")
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name = strings.TrimSuffix(name, "."+hostname+"."+s.domain+".")
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if q.Name == hostname+"." ||
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q.Name == hostname+"."+s.domain+"." {
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host, _ := s.hostByName(hostname)
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if q.Qtype == dns.TypeA {
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return dns.NewRR(q.Name + " 3600 IN A " + host)
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}
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return nil, sentinelEmpty
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}
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if ip, ok := s.subname(hostname, name); ok {
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if q.Qtype == dns.TypeA && ip.To4() != nil {
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return dns.NewRR(q.Name + " 3600 IN A " + ip.String())
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}
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if q.Qtype == dns.TypeAAAA && ip.To4() == nil {
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return dns.NewRR(q.Name + " 3600 IN AAAA " + ip.String())
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}
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return nil, sentinelEmpty
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}
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}
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return nil, nil
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}
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func (s *Server) subnameHandler(hostname string) func(w dns.ResponseWriter, r *dns.Msg) {
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return func(w dns.ResponseWriter, r *dns.Msg) {
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if len(r.Question) != 1 { // TODO: answer all questions we can answer
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return
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}
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rr, err := s.resolveSubname(hostname, r.Question[0])
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if err != nil {
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if err == sentinelEmpty {
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m := new(dns.Msg)
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m.SetReply(r)
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w.WriteMsg(m)
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return
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}
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log.Fatal(err)
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}
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if rr != nil {
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m := new(dns.Msg)
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m.SetReply(r)
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m.Answer = append(m.Answer, rr)
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w.WriteMsg(m)
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return
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}
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// Send an authoritative NXDOMAIN for local names:
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m := new(dns.Msg)
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m.SetReply(r)
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m.SetRcode(r, dns.RcodeNameError)
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w.WriteMsg(m)
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}
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}
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@ -16,8 +16,13 @@ package dns
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import (
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"bytes"
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"io/ioutil"
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"net"
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"net/http"
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"net/http/httptest"
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"net/url"
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"os"
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"strings"
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"testing"
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"time"
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@ -339,3 +344,97 @@ func TestDHCPReverse(t *testing.T) {
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}
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// TODO: multiple questions
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func TestSubname(t *testing.T) {
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r := &recorder{}
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s := NewServer("127.0.0.2:0", "lan")
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s.SetLeases([]dhcp4d.Lease{
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{
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Hostname: "testtarget",
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Addr: net.IP{192, 168, 42, 23},
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},
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})
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resolveTestTarget := func(t *testing.T, name string, want net.IP) {
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m := new(dns.Msg)
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typ := dns.TypeA
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if want.To4() == nil {
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typ = dns.TypeAAAA
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}
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m.SetQuestion(name, typ)
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s.Mux.ServeDNS(r, m)
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if r.response == nil {
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t.Fatalf("nil response")
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}
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if got, want := len(r.response.Answer), 1; got != want {
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t.Fatalf("unexpected number of answers: got %d, want %d", got, want)
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}
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a := r.response.Answer[0]
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if typ == dns.TypeA {
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if _, ok := a.(*dns.A); !ok {
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t.Fatalf("unexpected response type: got %T, want dns.A", a)
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}
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if got := a.(*dns.A).A; !got.Equal(want) {
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t.Fatalf("unexpected response IP: got %v, want %v", got, want)
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}
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} else {
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if _, ok := a.(*dns.AAAA); !ok {
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t.Fatalf("unexpected response type: got %T, want dns.A", a)
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}
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if got := a.(*dns.AAAA).AAAA; !got.Equal(want) {
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t.Fatalf("unexpected response IP: got %v, want %v", got, want)
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}
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}
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}
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t.Run("testtarget.lan.", func(t *testing.T) {
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resolveTestTarget(t, "testtarget.lan.", net.ParseIP("192.168.42.23"))
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})
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t.Run("sub.testtarget.lan.", func(t *testing.T) {
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m := new(dns.Msg)
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m.SetQuestion("notfound.lan.", dns.TypeA)
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s.Mux.ServeDNS(r, m)
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if got, want := r.response.Rcode, dns.RcodeNameError; got != want {
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t.Fatalf("unexpected rcode: got %v, want %v", got, want)
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}
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})
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setSubname := func(ip, remoteAddr string) {
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val := url.Values{
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"host": []string{"sub"},
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"ip": []string{ip},
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}
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req := httptest.NewRequest("POST", "/dyndns", strings.NewReader(val.Encode()))
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req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
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req.RemoteAddr = remoteAddr
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rec := httptest.NewRecorder()
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s.DyndnsHandler(rec, req)
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resp := rec.Result()
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if got, want := resp.StatusCode, http.StatusOK; got != want {
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body, _ := ioutil.ReadAll(resp.Body)
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t.Fatalf("POST /dyndns: unexpected HTTP status: got %v, want %v (%q)", resp.Status, want, string(body))
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}
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}
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const ip = "fdf5:3606:2a21:1341:b26e:bfff:fe30:504b"
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setSubname(ip, "192.168.42.23:1234")
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for _, name := range []string{
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"sub.testtarget.lan.",
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"sub.testtarget.",
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} {
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t.Run(name+" (after dyndns)", func(t *testing.T) {
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resolveTestTarget(t, name, net.ParseIP(ip))
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})
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}
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t.Run("Hostname", func(t *testing.T) {
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hostname, err := os.Hostname()
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if err != nil {
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t.Skipf("os.Hostname: %v", err)
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}
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resolveTestTarget(t, hostname+".lan.", net.ParseIP("127.0.0.2"))
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setSubname(ip, "127.0.0.2:1234")
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resolveTestTarget(t, "sub."+hostname+".lan.", net.ParseIP(ip))
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})
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}
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