package dns import ( "context" "strings" "sync" "sync/atomic" "time" "github.com/xtls/xray-core/common" "github.com/xtls/xray-core/common/log" "github.com/xtls/xray-core/common/net" "github.com/xtls/xray-core/common/protocol/dns" udp_proto "github.com/xtls/xray-core/common/protocol/udp" "github.com/xtls/xray-core/common/session" "github.com/xtls/xray-core/common/signal/pubsub" "github.com/xtls/xray-core/common/task" "github.com/xtls/xray-core/core" dns_feature "github.com/xtls/xray-core/features/dns" "github.com/xtls/xray-core/features/routing" "github.com/xtls/xray-core/transport/internet/udp" "golang.org/x/net/dns/dnsmessage" ) // ClassicNameServer implemented traditional UDP DNS. type ClassicNameServer struct { sync.RWMutex name string address *net.Destination ips map[string]*record requests map[uint16]*dnsRequest pub *pubsub.Service udpServer *udp.Dispatcher cleanup *task.Periodic reqID uint32 } // NewClassicNameServer creates udp server object for remote resolving. func NewClassicNameServer(address net.Destination, dispatcher routing.Dispatcher) *ClassicNameServer { // default to 53 if unspecific if address.Port == 0 { address.Port = net.Port(53) } s := &ClassicNameServer{ address: &address, ips: make(map[string]*record), requests: make(map[uint16]*dnsRequest), pub: pubsub.NewService(), name: strings.ToUpper(address.String()), } s.cleanup = &task.Periodic{ Interval: time.Minute, Execute: s.Cleanup, } s.udpServer = udp.NewDispatcher(dispatcher, s.HandleResponse) newError("DNS: created UDP client initialized for ", address.NetAddr()).AtInfo().WriteToLog() return s } // Name implements Server. func (s *ClassicNameServer) Name() string { return s.name } // Cleanup clears expired items from cache func (s *ClassicNameServer) Cleanup() error { now := time.Now() s.Lock() defer s.Unlock() if len(s.ips) == 0 && len(s.requests) == 0 { return newError(s.name, " 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) } for id, req := range s.requests { if req.expire.Before(now) { delete(s.requests, id) } } if len(s.requests) == 0 { s.requests = make(map[uint16]*dnsRequest) } return nil } // HandleResponse handles udp response packet from remote DNS server. func (s *ClassicNameServer) HandleResponse(ctx context.Context, packet *udp_proto.Packet) { ipRec, err := parseResponse(packet.Payload.Bytes()) if err != nil { newError(s.name, " fail to parse responded DNS udp").AtError().WriteToLog() return } s.Lock() id := ipRec.ReqID req, ok := s.requests[id] if ok { // remove the pending request delete(s.requests, id) } s.Unlock() if !ok { newError(s.name, " cannot find the pending request").AtError().WriteToLog() return } var rec record switch req.reqType { case dnsmessage.TypeA: rec.A = ipRec case dnsmessage.TypeAAAA: rec.AAAA = ipRec } elapsed := time.Since(req.start) newError(s.name, " got answer: ", req.domain, " ", req.reqType, " -> ", ipRec.IP, " ", elapsed).AtInfo().WriteToLog() if len(req.domain) > 0 && (rec.A != nil || rec.AAAA != nil) { s.updateIP(req.domain, &rec) } } func (s *ClassicNameServer) updateIP(domain string, newRec *record) { s.Lock() rec, found := s.ips[domain] if !found { rec = &record{} } updated := false if isNewer(rec.A, newRec.A) { rec.A = newRec.A updated = true } if isNewer(rec.AAAA, newRec.AAAA) { rec.AAAA = newRec.AAAA updated = true } if updated { newError(s.name, " updating IP records for domain:", domain).AtDebug().WriteToLog() s.ips[domain] = rec } if newRec.A != nil { s.pub.Publish(domain+"4", nil) } if newRec.AAAA != nil { s.pub.Publish(domain+"6", nil) } s.Unlock() common.Must(s.cleanup.Start()) } func (s *ClassicNameServer) newReqID() uint16 { return uint16(atomic.AddUint32(&s.reqID, 1)) } func (s *ClassicNameServer) addPendingRequest(req *dnsRequest) { s.Lock() defer s.Unlock() id := req.msg.ID req.expire = time.Now().Add(time.Second * 8) s.requests[id] = req } func (s *ClassicNameServer) 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)) for _, req := range reqs { s.addPendingRequest(req) b, _ := dns.PackMessage(req.msg) udpCtx := core.ToBackgroundDetachedContext(ctx) if inbound := session.InboundFromContext(ctx); inbound != nil { udpCtx = session.ContextWithInbound(udpCtx, inbound) } udpCtx = session.ContextWithContent(udpCtx, &session.Content{ Protocol: "dns", }) udpCtx = log.ContextWithAccessMessage(udpCtx, &log.AccessMessage{ From: "DNS", To: s.address, Status: log.AccessAccepted, Reason: "", }) s.udpServer.Dispatch(udpCtx, *s.address, b) } } func (s *ClassicNameServer) 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 *ClassicNameServer) 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() log.Record(&log.DNSLog{Server: s.name, Domain: domain, Result: ips, Status: log.DNSCacheHit, Elapsed: 0, Error: err}) 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) start := time.Now() for { ips, err := s.findIPsForDomain(fqdn, option) if err != errRecordNotFound { log.Record(&log.DNSLog{Server: s.name, Domain: domain, Result: ips, Status: log.DNSQueried, Elapsed: time.Since(start), Error: err}) return ips, err } select { case <-ctx.Done(): return nil, ctx.Err() case <-done: } } }