110 lines
2.8 KiB
Go
110 lines
2.8 KiB
Go
package nameserver
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import (
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"github.com/miekg/dns"
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. "github.com/zettio/weave/common"
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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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return &MDNSServer{sendconn: sendconn, zone: zone}, nil
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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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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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handler := func(qtype uint16, lookup func(*dns.Msg, *dns.Question) *dns.Msg) dns.HandlerFunc {
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return func(w dns.ResponseWriter, r *dns.Msg) {
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// Handle only questions, ignore answers. We might also
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// ignore questions that arise locally (i.e., that come
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// from an IP we think is local), but in the interest of
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// avoiding complication, and easier testing, this is
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// elided on the assumption that the client wouldn't ask
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// if it already knew the answer, and if it does ask,
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// it'll be happy to get an answer.
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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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if q.Qtype == qtype {
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if m := lookup(r, q); m != nil {
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Debug.Printf("Found local answer to mDNS query %s", q.Name)
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if err = s.sendResponse(m); err != nil {
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Warning.Printf("Error writing to %s", w)
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}
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} else {
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Debug.Printf("No local answer for mDNS query %s", q.Name)
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}
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}
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}
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}
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}
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handleLocal := handler(dns.TypeA, func(r *dns.Msg, q *dns.Question) *dns.Msg {
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if ip, err := s.zone.LookupLocal(q.Name); err == nil {
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return makeAddressReply(r, q, []net.IP{ip})
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} else {
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return nil
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}
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})
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handleReverse := handler(dns.TypePTR, func(r *dns.Msg, q *dns.Question) *dns.Msg {
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if name, err := s.zone.ReverseLookupLocal(q.Name); err == nil {
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return makePTRReply(r, q, []string{name})
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} else {
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return nil
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}
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})
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mux := dns.NewServeMux()
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mux.HandleFunc(LOCAL_DOMAIN, handleLocal)
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mux.HandleFunc(RDNS_DOMAIN, handleReverse)
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go dns.ActivateAndServe(nil, conn, mux)
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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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