package dns import ( "bytes" "context" "encoding/binary" "net/url" "sync" "sync/atomic" "time" "golang.org/x/net/dns/dnsmessage" "github.com/xtls/xray-core/common" "github.com/xtls/xray-core/common/buf" "github.com/xtls/xray-core/common/net" "github.com/xtls/xray-core/common/net/cnc" "github.com/xtls/xray-core/common/protocol/dns" "github.com/xtls/xray-core/common/session" "github.com/xtls/xray-core/common/signal/pubsub" "github.com/xtls/xray-core/common/task" dns_feature "github.com/xtls/xray-core/features/dns" "github.com/xtls/xray-core/features/routing" "github.com/xtls/xray-core/transport/internet" ) // TCPNameServer implemented DNS over TCP (RFC7766). type TCPNameServer struct { sync.RWMutex name string destination *net.Destination ips map[string]*record pub *pubsub.Service cleanup *task.Periodic reqID uint32 dial func(context.Context) (net.Conn, error) } // NewTCPNameServer creates DNS over TCP server object for remote resolving. func NewTCPNameServer(url *url.URL, dispatcher routing.Dispatcher) (*TCPNameServer, error) { s, err := baseTCPNameServer(url, "TCP") if err != nil { return nil, err } s.dial = func(ctx context.Context) (net.Conn, error) { link, err := dispatcher.Dispatch(ctx, *s.destination) if err != nil { return nil, err } return cnc.NewConnection( cnc.ConnectionInputMulti(link.Writer), cnc.ConnectionOutputMulti(link.Reader), ), nil } return s, nil } // NewTCPLocalNameServer creates DNS over TCP client object for local resolving func NewTCPLocalNameServer(url *url.URL) (*TCPNameServer, error) { s, err := baseTCPNameServer(url, "TCPL") if err != nil { return nil, err } s.dial = func(ctx context.Context) (net.Conn, error) { return internet.DialSystem(ctx, *s.destination, nil) } return s, nil } func baseTCPNameServer(url *url.URL, prefix string) (*TCPNameServer, error) { var err error port := net.Port(53) if url.Port() != "" { port, err = net.PortFromString(url.Port()) if err != nil { return nil, err } } dest := net.TCPDestination(net.ParseAddress(url.Hostname()), port) s := &TCPNameServer{ destination: &dest, ips: make(map[string]*record), pub: pubsub.NewService(), name: prefix + "//" + dest.NetAddr(), } s.cleanup = &task.Periodic{ Interval: time.Minute, Execute: s.Cleanup, } return s, nil } // Name implements Server. func (s *TCPNameServer) Name() string { return s.name } // Cleanup clears expired items from cache func (s *TCPNameServer) Cleanup() error { now := time.Now() s.Lock() defer s.Unlock() if len(s.ips) == 0 { return newError("nothing to do. stopping...") } for domain, record := range s.ips { if record.A != nil && record.A.Expire.Before(now) { record.A = nil } if record.AAAA != nil && record.AAAA.Expire.Before(now) { record.AAAA = nil } if record.A == nil && record.AAAA == nil { newError(s.name, " cleanup ", domain).AtDebug().WriteToLog() delete(s.ips, domain) } else { s.ips[domain] = record } } if len(s.ips) == 0 { s.ips = make(map[string]*record) } return nil } func (s *TCPNameServer) updateIP(req *dnsRequest, ipRec *IPRecord) { elapsed := time.Since(req.start) s.Lock() rec, found := s.ips[req.domain] if !found { rec = &record{} } updated := false switch req.reqType { case dnsmessage.TypeA: if isNewer(rec.A, ipRec) { rec.A = ipRec updated = true } case dnsmessage.TypeAAAA: addr := make([]net.Address, 0) for _, ip := range ipRec.IP { if len(ip.IP()) == net.IPv6len { addr = append(addr, ip) } } ipRec.IP = addr if isNewer(rec.AAAA, ipRec) { rec.AAAA = ipRec updated = true } } newError(s.name, " got answer: ", req.domain, " ", req.reqType, " -> ", ipRec.IP, " ", elapsed).AtInfo().WriteToLog() if updated { s.ips[req.domain] = rec } switch req.reqType { case dnsmessage.TypeA: s.pub.Publish(req.domain+"4", nil) case dnsmessage.TypeAAAA: s.pub.Publish(req.domain+"6", nil) } s.Unlock() common.Must(s.cleanup.Start()) } func (s *TCPNameServer) newReqID() uint16 { return uint16(atomic.AddUint32(&s.reqID, 1)) } func (s *TCPNameServer) sendQuery(ctx context.Context, domain string, clientIP net.IP, option dns_feature.IPOption) { newError(s.name, " querying DNS for: ", domain).AtDebug().WriteToLog(session.ExportIDToError(ctx)) reqs := buildReqMsgs(domain, option, s.newReqID, genEDNS0Options(clientIP)) var deadline time.Time if d, ok := ctx.Deadline(); ok { deadline = d } else { deadline = time.Now().Add(time.Second * 5) } for _, req := range reqs { go func(r *dnsRequest) { dnsCtx := ctx if inbound := session.InboundFromContext(ctx); inbound != nil { dnsCtx = session.ContextWithInbound(dnsCtx, inbound) } dnsCtx = session.ContextWithContent(dnsCtx, &session.Content{ Protocol: "dns", SkipDNSResolve: true, }) var cancel context.CancelFunc dnsCtx, cancel = context.WithDeadline(dnsCtx, deadline) defer cancel() b, err := dns.PackMessage(r.msg) if err != nil { newError("failed to pack dns query").Base(err).AtError().WriteToLog() return } conn, err := s.dial(dnsCtx) if err != nil { newError("failed to dial namesever").Base(err).AtError().WriteToLog() return } defer conn.Close() dnsReqBuf := buf.New() binary.Write(dnsReqBuf, binary.BigEndian, uint16(b.Len())) dnsReqBuf.Write(b.Bytes()) b.Release() _, err = conn.Write(dnsReqBuf.Bytes()) if err != nil { newError("failed to send query").Base(err).AtError().WriteToLog() return } dnsReqBuf.Release() respBuf := buf.New() defer respBuf.Release() n, err := respBuf.ReadFullFrom(conn, 2) if err != nil && n == 0 { newError("failed to read response length").Base(err).AtError().WriteToLog() return } var length int16 err = binary.Read(bytes.NewReader(respBuf.Bytes()), binary.BigEndian, &length) if err != nil { newError("failed to parse response length").Base(err).AtError().WriteToLog() return } respBuf.Clear() n, err = respBuf.ReadFullFrom(conn, int32(length)) if err != nil && n == 0 { newError("failed to read response length").Base(err).AtError().WriteToLog() return } rec, err := parseResponse(respBuf.Bytes()) if err != nil { newError("failed to parse DNS over TCP response").Base(err).AtError().WriteToLog() return } s.updateIP(r, rec) }(req) } } func (s *TCPNameServer) findIPsForDomain(domain string, option dns_feature.IPOption) ([]net.IP, error) { s.RLock() record, found := s.ips[domain] s.RUnlock() if !found { return nil, errRecordNotFound } var err4 error var err6 error var ips []net.Address var ip6 []net.Address if option.IPv4Enable { ips, err4 = record.A.getIPs() } if option.IPv6Enable { ip6, err6 = record.AAAA.getIPs() ips = append(ips, ip6...) } if len(ips) > 0 { return toNetIP(ips) } if err4 != nil { return nil, err4 } if err6 != nil { return nil, err6 } return nil, dns_feature.ErrEmptyResponse } // QueryIP implements Server. func (s *TCPNameServer) QueryIP(ctx context.Context, domain string, clientIP net.IP, option dns_feature.IPOption, disableCache bool) ([]net.IP, error) { fqdn := Fqdn(domain) if disableCache { newError("DNS cache is disabled. Querying IP for ", domain, " at ", s.name).AtDebug().WriteToLog() } else { ips, err := s.findIPsForDomain(fqdn, option) if err != errRecordNotFound { newError(s.name, " cache HIT ", domain, " -> ", ips).Base(err).AtDebug().WriteToLog() return ips, err } } // ipv4 and ipv6 belong to different subscription groups var sub4, sub6 *pubsub.Subscriber if option.IPv4Enable { sub4 = s.pub.Subscribe(fqdn + "4") defer sub4.Close() } if option.IPv6Enable { sub6 = s.pub.Subscribe(fqdn + "6") defer sub6.Close() } done := make(chan interface{}) go func() { if sub4 != nil { select { case <-sub4.Wait(): case <-ctx.Done(): } } if sub6 != nil { select { case <-sub6.Wait(): case <-ctx.Done(): } } close(done) }() s.sendQuery(ctx, fqdn, clientIP, option) for { ips, err := s.findIPsForDomain(fqdn, option) if err != errRecordNotFound { return ips, err } select { case <-ctx.Done(): return nil, ctx.Err() case <-done: } } }