101 lines
2.4 KiB
Go
101 lines
2.4 KiB
Go
package weavedns
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import (
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"github.com/miekg/dns"
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"net"
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)
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type MDNSServer struct {
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localAddrs []net.Addr
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sendconn *net.UDPConn
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zone Zone
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}
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func NewMDNSServer(zone Zone) (*MDNSServer, error) {
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// This is a bit of a kludge - per the RFC we should send responses from 5353, but that doesn't seem to work
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sendconn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
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if err != nil {
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return nil, err
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}
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retval := &MDNSServer{sendconn: sendconn, zone: zone}
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return retval, nil
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}
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func makeDNSReply(r *dns.Msg, name string, qtype uint16, addrs []net.IP) *dns.Msg {
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m := new(dns.Msg)
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m.SetReply(r)
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m.RecursionAvailable = true
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hdr := dns.RR_Header{Name: name, Rrtype: qtype, Class: dns.ClassINET, Ttl: 3600}
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for _, addr := range addrs {
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if qtype == dns.TypeA {
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if ip4 := addr.To4(); ip4 != nil {
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m.Answer = append(m.Answer, &dns.A{hdr, addr})
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}
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} else if qtype == dns.TypeAAAA {
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if ip4 := addr.To4(); ip4 == nil {
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m.Answer = append(m.Answer, &dns.AAAA{hdr, addr})
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}
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}
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}
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return m
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}
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// Return true if testaddr is a UDP address with IP matching my local i/f
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func (s *MDNSServer) addrIsLocal(testaddr net.Addr) bool {
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if udpaddr, ok := testaddr.(*net.UDPAddr); ok {
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for _, localaddr := range s.localAddrs {
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if ipnetlocal, ok := localaddr.(*net.IPNet); ok {
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if ipnetlocal.IP.Equal(udpaddr.IP) {
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return true
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}
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}
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}
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}
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return false
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}
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func (s *MDNSServer) Start(ifi *net.Interface) error {
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handleMDNS := func(w dns.ResponseWriter, r *dns.Msg) {
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// Ignore answers to other questions
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if len(r.Answer) == 0 && len(r.Question) > 0 {
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q := r.Question[0]
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ip, err := s.zone.MatchLocal(q.Name)
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if err == nil {
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m := makeDNSReply(r, q.Name, dns.TypeA, []net.IP{ip})
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s.SendResponse(m)
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} else if s.addrIsLocal(w.RemoteAddr()) {
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// ignore this - it's our own query received via multicast
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} else {
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Debug.Printf("Failed MDNS lookup for %s", q.Name)
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}
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}
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}
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conn, err := LinkLocalMulticastListener(ifi)
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if err != nil {
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return err
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}
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if ifi == nil {
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s.localAddrs, err = net.InterfaceAddrs()
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} else {
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s.localAddrs, err = ifi.Addrs()
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}
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if err != nil {
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return err
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}
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go dns.ActivateAndServe(nil, conn, dns.HandlerFunc(handleMDNS))
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return err
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}
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func (s *MDNSServer) SendResponse(m *dns.Msg) error {
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buf, err := m.Pack()
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if err != nil {
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return err
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}
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_, err = s.sendconn.WriteTo(buf, ipv4Addr)
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return err
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}
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