feat(dns): add parallel query (#5239)

app/dns/cache_controller.go

@@ -194,7 +194,7 @@ func (c *CacheController) migrate() {
 		return
 	}
 
-	errors.LogDebug(context.Background(), c.name, " starting background cache migration for ", len(dirtyips), " items.")
+	errors.LogDebug(context.Background(), c.name, " starting background cache migration for ", len(dirtyips), " items")
 
 	batch := make([]migrationEntry, 0, migrationBatchSize)
 	for domain, recD := range dirtyips {
@@ -214,7 +214,7 @@ func (c *CacheController) migrate() {
 	c.dirtyips = nil
 	c.Unlock()
 
-	errors.LogDebug(context.Background(), c.name, " cache migration completed.")
+	errors.LogDebug(context.Background(), c.name, " cache migration completed")
 }
 
 func (c *CacheController) flush(batch []migrationEntry) {

app/dns/config.pb.go

@@ -147,6 +147,7 @@ type NameServer struct {
 	FinalQuery        bool                         `protobuf:"varint,12,opt,name=finalQuery,proto3" json:"finalQuery,omitempty"`
 	UnexpectedGeoip   []*router.GeoIP              `protobuf:"bytes,13,rep,name=unexpected_geoip,json=unexpectedGeoip,proto3" json:"unexpected_geoip,omitempty"`
 	ActUnprior        bool                         `protobuf:"varint,14,opt,name=actUnprior,proto3" json:"actUnprior,omitempty"`
+	PolicyID          uint32                       `protobuf:"varint,17,opt,name=policyID,proto3" json:"policyID,omitempty"`
 }
 
 func (x *NameServer) Reset() {
@@ -291,6 +292,13 @@ func (x *NameServer) GetActUnprior() bool {
 	return false
 }
 
+func (x *NameServer) GetPolicyID() uint32 {
+	if x != nil {
+		return x.PolicyID
+	}
+	return 0
+}
+
 type Config struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -312,6 +320,7 @@ type Config struct {
 	QueryStrategy          QueryStrategy `protobuf:"varint,9,opt,name=query_strategy,json=queryStrategy,proto3,enum=xray.app.dns.QueryStrategy" json:"query_strategy,omitempty"`
 	DisableFallback        bool          `protobuf:"varint,10,opt,name=disableFallback,proto3" json:"disableFallback,omitempty"`
 	DisableFallbackIfMatch bool          `protobuf:"varint,11,opt,name=disableFallbackIfMatch,proto3" json:"disableFallbackIfMatch,omitempty"`
+	EnableParallelQuery    bool          `protobuf:"varint,14,opt,name=enableParallelQuery,proto3" json:"enableParallelQuery,omitempty"`
 }
 
 func (x *Config) Reset() {
@@ -414,6 +423,13 @@ func (x *Config) GetDisableFallbackIfMatch() bool {
 	return false
 }
 
+func (x *Config) GetEnableParallelQuery() bool {
+	if x != nil {
+		return x.EnableParallelQuery
+	}
+	return false
+}
+
 type NameServer_PriorityDomain struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -599,7 +615,7 @@ var file_app_dns_config_proto_rawDesc = []byte{
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@@ -646,70 +662,75 @@ var file_app_dns_config_proto_rawDesc = []byte{
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+	0x0c, 0x64, 0x69, 0x73, 0x61, 0x62, 0x6c, 0x65, 0x43, 0x61, 0x63, 0x68, 0x65, 0x18, 0x08, 0x20,
+	0x01, 0x28, 0x08, 0x52, 0x0c, 0x64, 0x69, 0x73, 0x61, 0x62, 0x6c, 0x65, 0x43, 0x61, 0x63, 0x68,
+	0x65, 0x12, 0x1e, 0x0a, 0x0a, 0x73, 0x65, 0x72, 0x76, 0x65, 0x53, 0x74, 0x61, 0x6c, 0x65, 0x18,
+	0x0c, 0x20, 0x01, 0x28, 0x08, 0x52, 0x0a, 0x73, 0x65, 0x72, 0x76, 0x65, 0x53, 0x74, 0x61, 0x6c,
+	0x65, 0x12, 0x28, 0x0a, 0x0f, 0x73, 0x65, 0x72, 0x76, 0x65, 0x45, 0x78, 0x70, 0x69, 0x72, 0x65,
+	0x64, 0x54, 0x54, 0x4c, 0x18, 0x0d, 0x20, 0x01, 0x28, 0x0d, 0x52, 0x0f, 0x73, 0x65, 0x72, 0x76,
+	0x65, 0x45, 0x78, 0x70, 0x69, 0x72, 0x65, 0x64, 0x54, 0x54, 0x4c, 0x12, 0x42, 0x0a, 0x0e, 0x71,
+	0x75, 0x65, 0x72, 0x79, 0x5f, 0x73, 0x74, 0x72, 0x61, 0x74, 0x65, 0x67, 0x79, 0x18, 0x09, 0x20,
+	0x01, 0x28, 0x0e, 0x32, 0x1b, 0x2e, 0x78, 0x72, 0x61, 0x79, 0x2e, 0x61, 0x70, 0x70, 0x2e, 0x64,
+	0x6e, 0x73, 0x2e, 0x51, 0x75, 0x65, 0x72, 0x79, 0x53, 0x74, 0x72, 0x61, 0x74, 0x65, 0x67, 0x79,
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+	0x28, 0x0a, 0x0f, 0x64, 0x69, 0x73, 0x61, 0x62, 0x6c, 0x65, 0x46, 0x61, 0x6c, 0x6c, 0x62, 0x61,
+	0x63, 0x6b, 0x18, 0x0a, 0x20, 0x01, 0x28, 0x08, 0x52, 0x0f, 0x64, 0x69, 0x73, 0x61, 0x62, 0x6c,
+	0x65, 0x46, 0x61, 0x6c, 0x6c, 0x62, 0x61, 0x63, 0x6b, 0x12, 0x36, 0x0a, 0x16, 0x64, 0x69, 0x73,
+	0x61, 0x62, 0x6c, 0x65, 0x46, 0x61, 0x6c, 0x6c, 0x62, 0x61, 0x63, 0x6b, 0x49, 0x66, 0x4d, 0x61,
+	0x74, 0x63, 0x68, 0x18, 0x0b, 0x20, 0x01, 0x28, 0x08, 0x52, 0x16, 0x64, 0x69, 0x73, 0x61, 0x62,
+	0x6c, 0x65, 0x46, 0x61, 0x6c, 0x6c, 0x62, 0x61, 0x63, 0x6b, 0x49, 0x66, 0x4d, 0x61, 0x74, 0x63,
+	0x68, 0x12, 0x30, 0x0a, 0x13, 0x65, 0x6e, 0x61, 0x62, 0x6c, 0x65, 0x50, 0x61, 0x72, 0x61, 0x6c,
+	0x6c, 0x65, 0x6c, 0x51, 0x75, 0x65, 0x72, 0x79, 0x18, 0x0e, 0x20, 0x01, 0x28, 0x08, 0x52, 0x13,
+	0x65, 0x6e, 0x61, 0x62, 0x6c, 0x65, 0x50, 0x61, 0x72, 0x61, 0x6c, 0x6c, 0x65, 0x6c, 0x51, 0x75,
+	0x65, 0x72, 0x79, 0x1a, 0x92, 0x01, 0x0a, 0x0b, 0x48, 0x6f, 0x73, 0x74, 0x4d, 0x61, 0x70, 0x70,
+	0x69, 0x6e, 0x67, 0x12, 0x34, 0x0a, 0x04, 0x74, 0x79, 0x70, 0x65, 0x18, 0x01, 0x20, 0x01, 0x28,
+	0x0e, 0x32, 0x20, 0x2e, 0x78, 0x72, 0x61, 0x79, 0x2e, 0x61, 0x70, 0x70, 0x2e, 0x64, 0x6e, 0x73,
+	0x2e, 0x44, 0x6f, 0x6d, 0x61, 0x69, 0x6e, 0x4d, 0x61, 0x74, 0x63, 0x68, 0x69, 0x6e, 0x67, 0x54,
+	0x79, 0x70, 0x65, 0x52, 0x04, 0x74, 0x79, 0x70, 0x65, 0x12, 0x16, 0x0a, 0x06, 0x64, 0x6f, 0x6d,
+	0x61, 0x69, 0x6e, 0x18, 0x02, 0x20, 0x01, 0x28, 0x09, 0x52, 0x06, 0x64, 0x6f, 0x6d, 0x61, 0x69,
+	0x6e, 0x12, 0x0e, 0x0a, 0x02, 0x69, 0x70, 0x18, 0x03, 0x20, 0x03, 0x28, 0x0c, 0x52, 0x02, 0x69,
+	0x70, 0x12, 0x25, 0x0a, 0x0e, 0x70, 0x72, 0x6f, 0x78, 0x69, 0x65, 0x64, 0x5f, 0x64, 0x6f, 0x6d,
+	0x61, 0x69, 0x6e, 0x18, 0x04, 0x20, 0x01, 0x28, 0x09, 0x52, 0x0d, 0x70, 0x72, 0x6f, 0x78, 0x69,
+	0x65, 0x64, 0x44, 0x6f, 0x6d, 0x61, 0x69, 0x6e, 0x4a, 0x04, 0x08, 0x07, 0x10, 0x08, 0x2a, 0x45,
+	0x0a, 0x12, 0x44, 0x6f, 0x6d, 0x61, 0x69, 0x6e, 0x4d, 0x61, 0x74, 0x63, 0x68, 0x69, 0x6e, 0x67,
+	0x54, 0x79, 0x70, 0x65, 0x12, 0x08, 0x0a, 0x04, 0x46, 0x75, 0x6c, 0x6c, 0x10, 0x00, 0x12, 0x0d,
+	0x0a, 0x09, 0x53, 0x75, 0x62, 0x64, 0x6f, 0x6d, 0x61, 0x69, 0x6e, 0x10, 0x01, 0x12, 0x0b, 0x0a,
+	0x07, 0x4b, 0x65, 0x79, 0x77, 0x6f, 0x72, 0x64, 0x10, 0x02, 0x12, 0x09, 0x0a, 0x05, 0x52, 0x65,
+	0x67, 0x65, 0x78, 0x10, 0x03, 0x2a, 0x42, 0x0a, 0x0d, 0x51, 0x75, 0x65, 0x72, 0x79, 0x53, 0x74,
+	0x72, 0x61, 0x74, 0x65, 0x67, 0x79, 0x12, 0x0a, 0x0a, 0x06, 0x55, 0x53, 0x45, 0x5f, 0x49, 0x50,
+	0x10, 0x00, 0x12, 0x0b, 0x0a, 0x07, 0x55, 0x53, 0x45, 0x5f, 0x49, 0x50, 0x34, 0x10, 0x01, 0x12,
+	0x0b, 0x0a, 0x07, 0x55, 0x53, 0x45, 0x5f, 0x49, 0x50, 0x36, 0x10, 0x02, 0x12, 0x0b, 0x0a, 0x07,
+	0x55, 0x53, 0x45, 0x5f, 0x53, 0x59, 0x53, 0x10, 0x03, 0x42, 0x46, 0x0a, 0x10, 0x63, 0x6f, 0x6d,
+	0x2e, 0x78, 0x72, 0x61, 0x79, 0x2e, 0x61, 0x70, 0x70, 0x2e, 0x64, 0x6e, 0x73, 0x50, 0x01, 0x5a,
+	0x21, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x78, 0x74, 0x6c, 0x73,
+	0x2f, 0x78, 0x72, 0x61, 0x79, 0x2d, 0x63, 0x6f, 0x72, 0x65, 0x2f, 0x61, 0x70, 0x70, 0x2f, 0x64,
+	0x6e, 0x73, 0xaa, 0x02, 0x0c, 0x58, 0x72, 0x61, 0x79, 0x2e, 0x41, 0x70, 0x70, 0x2e, 0x44, 0x6e,
+	0x73, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (

app/dns/config.proto

@@ -37,6 +37,7 @@ message NameServer {
   bool finalQuery = 12;
   repeated xray.app.router.GeoIP unexpected_geoip = 13;
   bool actUnprior = 14;
+  uint32 policyID = 17;
 }
 
 enum DomainMatchingType {
@@ -89,4 +90,6 @@ message Config {
 
   bool disableFallback = 10;
   bool disableFallbackIfMatch = 11;
+
+  bool enableParallelQuery = 14;
 }

app/dns/dns.go

@@ -25,6 +25,7 @@ type DNS struct {
 	sync.Mutex
 	disableFallback        bool
 	disableFallbackIfMatch bool
+	enableParallelQuery    bool
 	ipOption               *dns.IPOption
 	hosts                  *StaticHosts
 	clients                []*Client
@@ -157,6 +158,7 @@ func New(ctx context.Context, config *Config) (*DNS, error) {
 		matcherInfos:           matcherInfos,
 		disableFallback:        config.DisableFallback,
 		disableFallbackIfMatch: config.DisableFallbackIfMatch,
+		enableParallelQuery:    config.EnableParallelQuery,
 		checkSystem:            checkSystem,
 	}, nil
 }
@@ -235,45 +237,11 @@ func (s *DNS) LookupIP(domain string, option dns.IPOption) ([]net.IP, uint32, er
 	}
 
 	// Name servers lookup
-	var errs []error
-	for _, client := range s.sortClients(domain) {
-		if !option.FakeEnable && strings.EqualFold(client.Name(), "FakeDNS") {
-			errors.LogDebug(s.ctx, "skip DNS resolution for domain ", domain, " at server ", client.Name())
-			continue
-		}
-
-		ips, ttl, err := client.QueryIP(s.ctx, domain, option)
-
-		if len(ips) > 0 {
-			if ttl == 0 {
-				ttl = 1
-			}
-			return ips, ttl, nil
-		}
-
-		errors.LogInfoInner(s.ctx, err, "failed to lookup ip for domain ", domain, " at server ", client.Name())
-		if err == nil {
-			err = dns.ErrEmptyResponse
-		}
-		errs = append(errs, err)
-
-		if client.IsFinalQuery() {
-			break
-		}
-	}
-
-	if len(errs) > 0 {
-		allErrs := errors.Combine(errs...)
-		err0 := errs[0]
-		if errors.AllEqual(err0, allErrs) {
-			if go_errors.Is(err0, dns.ErrEmptyResponse) {
-				return nil, 0, dns.ErrEmptyResponse
-			}
-			return nil, 0, errors.New("returning nil for domain ", domain).Base(err0)
-		}
-		return nil, 0, errors.New("returning nil for domain ", domain).Base(allErrs)
+	if s.enableParallelQuery {
+		return s.parallelQuery(domain, option)
+	} else {
+		return s.serialQuery(domain, option)
 	}
-	return nil, 0, dns.ErrEmptyResponse
 }
 
 func (s *DNS) sortClients(domain string) []*Client {
@@ -300,6 +268,9 @@ func (s *DNS) sortClients(domain string) []*Client {
 		clients = append(clients, client)
 		clientNames = append(clientNames, client.Name())
 		hasMatch = true
+		if client.finalQuery {
+			return clients
+		}
 	}
 
 	if !(s.disableFallback || s.disableFallbackIfMatch && hasMatch) {
@@ -311,6 +282,9 @@ func (s *DNS) sortClients(domain string) []*Client {
 			clientUsed[idx] = true
 			clients = append(clients, client)
 			clientNames = append(clientNames, client.Name())
+			if client.finalQuery {
+				return clients
+			}
 		}
 	}
 
@@ -322,14 +296,214 @@ func (s *DNS) sortClients(domain string) []*Client {
 	}
 
 	if len(clients) == 0 {
-		clients = append(clients, s.clients[0])
-		clientNames = append(clientNames, s.clients[0].Name())
-		errors.LogDebug(s.ctx, "domain ", domain, " will use the first DNS: ", clientNames)
+		if len(s.clients) > 0 {
+			clients = append(clients, s.clients[0])
+			clientNames = append(clientNames, s.clients[0].Name())
+			errors.LogWarning(s.ctx, "domain ", domain, " will use the first DNS: ", clientNames)
+		} else {
+			errors.LogError(s.ctx, "no DNS clients available for domain ", domain, " and no default clients configured")
+		}
 	}
 
 	return clients
 }
 
+func mergeQueryErrors(domain string, errs []error) error {
+	if len(errs) == 0 {
+		return dns.ErrEmptyResponse
+	}
+
+	var noRNF error
+	for _, err := range errs {
+		if go_errors.Is(err, errRecordNotFound) {
+			continue // server no response, ignore
+		} else if noRNF == nil {
+			noRNF = err
+		} else if !go_errors.Is(err, noRNF) {
+			return errors.New("returning nil for domain ", domain).Base(errors.Combine(errs...))
+		}
+	}
+	if go_errors.Is(noRNF, dns.ErrEmptyResponse) {
+		return dns.ErrEmptyResponse
+	}
+	if noRNF == nil {
+		noRNF = errRecordNotFound
+	}
+	return errors.New("returning nil for domain ", domain).Base(noRNF)
+}
+
+func (s *DNS) serialQuery(domain string, option dns.IPOption) ([]net.IP, uint32, error) {
+	var errs []error
+	for _, client := range s.sortClients(domain) {
+		if !option.FakeEnable && strings.EqualFold(client.Name(), "FakeDNS") {
+			errors.LogDebug(s.ctx, "skip DNS resolution for domain ", domain, " at server ", client.Name())
+			continue
+		}
+
+		ips, ttl, err := client.QueryIP(s.ctx, domain, option)
+
+		if len(ips) > 0 {
+			return ips, ttl, nil
+		}
+
+		errors.LogInfoInner(s.ctx, err, "failed to lookup ip for domain ", domain, " at server ", client.Name(), " in serial query mode")
+		if err == nil {
+			err = dns.ErrEmptyResponse
+		}
+		errs = append(errs, err)
+	}
+	return nil, 0, mergeQueryErrors(domain, errs)
+}
+
+func (s *DNS) parallelQuery(domain string, option dns.IPOption) ([]net.IP, uint32, error) {
+	var errs []error
+	clients := s.sortClients(domain)
+
+	resultsChan := asyncQueryAll(domain, option, clients, s.ctx)
+
+	groups, groupOf := makeGroups( /*s.ctx,*/ clients)
+	results := make([]*queryResult, len(clients))
+	pending := make([]int, len(groups))
+	for gi, g := range groups {
+		pending[gi] = g.end - g.start + 1
+	}
+
+	nextGroup := 0
+	for range clients {
+		result := <-resultsChan
+		results[result.index] = &result
+
+		gi := groupOf[result.index]
+		pending[gi]--
+
+		for nextGroup < len(groups) {
+			g := groups[nextGroup]
+
+			// group race, minimum rtt -> return
+			for j := g.start; j <= g.end; j++ {
+				r := results[j]
+				if r != nil && r.err == nil && len(r.ips) > 0 {
+					return r.ips, r.ttl, nil
+				}
+			}
+
+			// current group is incomplete and no one success -> continue pending
+			if pending[nextGroup] > 0 {
+				break
+			}
+
+			// all failed -> log and continue next group
+			for j := g.start; j <= g.end; j++ {
+				r := results[j]
+				e := r.err
+				if e == nil {
+					e = dns.ErrEmptyResponse
+				}
+				errors.LogInfoInner(s.ctx, e, "failed to lookup ip for domain ", domain, " at server ", clients[j].Name(), " in parallel query mode")
+				errs = append(errs, e)
+			}
+			nextGroup++
+		}
+	}
+
+	return nil, 0, mergeQueryErrors(domain, errs)
+}
+
+type queryResult struct {
+	ips   []net.IP
+	ttl   uint32
+	err   error
+	index int
+}
+
+func asyncQueryAll(domain string, option dns.IPOption, clients []*Client, ctx context.Context) chan queryResult {
+	if len(clients) == 0 {
+		ch := make(chan queryResult)
+		close(ch)
+		return ch
+	}
+
+	ch := make(chan queryResult, len(clients))
+	for i, client := range clients {
+		if !option.FakeEnable && strings.EqualFold(client.Name(), "FakeDNS") {
+			errors.LogDebug(ctx, "skip DNS resolution for domain ", domain, " at server ", client.Name())
+			ch <- queryResult{err: dns.ErrEmptyResponse, index: i}
+			continue
+		}
+
+		go func(i int, c *Client) {
+			qctx := ctx
+			if !c.server.IsDisableCache() {
+				nctx, cancel := context.WithTimeout(context.WithoutCancel(ctx), c.timeoutMs*2)
+				qctx = nctx
+				defer cancel()
+			}
+			ips, ttl, err := c.QueryIP(qctx, domain, option)
+			ch <- queryResult{ips: ips, ttl: ttl, err: err, index: i}
+		}(i, client)
+	}
+	return ch
+}
+
+type group struct{ start, end int }
+
+// merge only adjacent and rule-equivalent Client into a single group
+func makeGroups( /*ctx context.Context,*/ clients []*Client) ([]group, []int) {
+	n := len(clients)
+	if n == 0 {
+		return nil, nil
+	}
+	groups := make([]group, 0, n)
+	groupOf := make([]int, n)
+
+	s, e := 0, 0
+	for i := 1; i < n; i++ {
+		if clients[i-1].policyID == clients[i].policyID {
+			e = i
+		} else {
+			for k := s; k <= e; k++ {
+				groupOf[k] = len(groups)
+			}
+			groups = append(groups, group{start: s, end: e})
+			s, e = i, i
+		}
+	}
+	for k := s; k <= e; k++ {
+		groupOf[k] = len(groups)
+	}
+	groups = append(groups, group{start: s, end: e})
+
+	// var b strings.Builder
+	// b.WriteString("dns grouping: total clients=")
+	// b.WriteString(strconv.Itoa(n))
+	// b.WriteString(", groups=")
+	// b.WriteString(strconv.Itoa(len(groups)))
+
+	// for gi, g := range groups {
+	// 	b.WriteString("\n  [")
+	// 	b.WriteString(strconv.Itoa(g.start))
+	// 	b.WriteString("..")
+	// 	b.WriteString(strconv.Itoa(g.end))
+	// 	b.WriteString("] gid=")
+	// 	b.WriteString(strconv.Itoa(gi))
+	// 	b.WriteString(" pid=")
+	// 	b.WriteString(strconv.FormatUint(uint64(clients[g.start].policyID), 10))
+	// 	b.WriteString(" members: ")
+
+	// 	for i := g.start; i <= g.end; i++ {
+	// 		if i > g.start {
+	// 			b.WriteString(", ")
+	// 		}
+	// 		b.WriteString(strconv.Itoa(i))
+	// 		b.WriteByte(':')
+	// 		b.WriteString(clients[i].Name())
+	// 	}
+	// }
+	// errors.LogDebug(ctx, b.String())
+
+	return groups, groupOf
+}
+
 func init() {
 	common.Must(common.RegisterConfig((*Config)(nil), func(ctx context.Context, config interface{}) (interface{}, error) {
 		return New(ctx, config.(*Config))

app/dns/nameserver.go

@@ -20,6 +20,9 @@ import (
 type Server interface {
 	// Name of the Client.
 	Name() string
+
+	IsDisableCache() bool
+
 	// QueryIP sends IP queries to its configured server.
 	QueryIP(ctx context.Context, domain string, option dns.IPOption) ([]net.IP, uint32, error)
 }
@@ -38,6 +41,7 @@ type Client struct {
 	finalQuery    bool
 	ipOption      *dns.IPOption
 	checkSystem   bool
+	policyID      uint32
 }
 
 // NewServer creates a name server object according to the network destination url.
@@ -199,6 +203,7 @@ func NewClient(
 		client.finalQuery = ns.FinalQuery
 		client.ipOption = &ipOption
 		client.checkSystem = checkSystem
+		client.policyID = ns.PolicyID
 		return nil
 	})
 	return client, err
@@ -209,10 +214,6 @@ func (c *Client) Name() string {
 	return c.server.Name()
 }
 
-func (c *Client) IsFinalQuery() bool {
-	return c.finalQuery
-}
-
 // QueryIP sends DNS query to the name server with the client's IP.
 func (c *Client) QueryIP(ctx context.Context, domain string, option dns.IPOption) ([]net.IP, uint32, error) {
 	if c.checkSystem {

app/dns/nameserver_cached.go

@@ -28,12 +28,12 @@ func queryIP(ctx context.Context, s CachedNameserver, domain string, option dns.
 			ips, ttl, err := merge(option, rec.A, rec.AAAA)
 			if !go_errors.Is(err, errRecordNotFound) {
 				if ttl > 0 {
-					// errors.LogDebugInner(ctx, err, cache.name, " cache HIT ", fqdn, " -> ", ips)
+					errors.LogDebugInner(ctx, err, cache.name, " cache HIT ", fqdn, " -> ", ips)
 					log.Record(&log.DNSLog{Server: cache.name, Domain: fqdn, Result: ips, Status: log.DNSCacheHit, Elapsed: 0, Error: err})
 					return ips, uint32(ttl), err
 				}
 				if cache.serveStale && (cache.serveExpiredTTL == 0 || cache.serveExpiredTTL < ttl) {
-					// errors.LogDebugInner(ctx, err, cache.name, " cache OPTIMISTE ", fqdn, " -> ", ips)
+					errors.LogDebugInner(ctx, err, cache.name, " cache OPTIMISTE ", fqdn, " -> ", ips)
 					log.Record(&log.DNSLog{Server: cache.name, Domain: fqdn, Result: ips, Status: log.DNSCacheOptimiste, Elapsed: 0, Error: err})
 					go pull(ctx, s, fqdn, option)
 					return ips, 1, err

app/dns/nameserver_doh.go

@@ -116,6 +116,11 @@ func (s *DoHNameServer) Name() string {
 	return s.cacheController.name
 }
 
+// IsDisableCache implements Server.
+func (s *DoHNameServer) IsDisableCache() bool {
+	return s.cacheController.disableCache
+}
+
 func (s *DoHNameServer) newReqID() uint16 {
 	return 0
 }
@@ -130,7 +135,7 @@ func (s *DoHNameServer) sendQuery(ctx context.Context, noResponseErrCh chan<- er
 	errors.LogInfo(ctx, s.Name(), " querying: ", fqdn)
 
 	if s.Name()+"." == "DOH//"+fqdn {
-		errors.LogError(ctx, s.Name(), " tries to resolve itself! Use IP or set \"hosts\" instead.")
+		errors.LogError(ctx, s.Name(), " tries to resolve itself! Use IP or set \"hosts\" instead")
 		if noResponseErrCh != nil {
 			noResponseErrCh <- errors.New("tries to resolve itself!", s.Name())
 		}

app/dns/nameserver_fakedns.go

@@ -20,6 +20,11 @@ func (FakeDNSServer) Name() string {
 	return "FakeDNS"
 }
 
+// IsDisableCache implements Server.
+func (s *FakeDNSServer) IsDisableCache() bool {
+	return true
+}
+
 func (f *FakeDNSServer) QueryIP(ctx context.Context, domain string, opt dns.IPOption) ([]net.IP, uint32, error) {
 	if f.fakeDNSEngine == nil {
 		return nil, 0, errors.New("Unable to locate a fake DNS Engine").AtError()

app/dns/nameserver_local.go

@@ -35,6 +35,11 @@ func (s *LocalNameServer) Name() string {
 	return "localhost"
 }
 
+// IsDisableCache implements Server.
+func (s *LocalNameServer) IsDisableCache() bool {
+	return true
+}
+
 // NewLocalNameServer creates localdns server object for directly lookup in system DNS.
 func NewLocalNameServer() *LocalNameServer {
 	errors.LogInfo(context.Background(), "DNS: created localhost client")

app/dns/nameserver_quic.go

@@ -37,8 +37,6 @@ type QUICNameServer struct {
 
 // NewQUICNameServer creates DNS-over-QUIC client object for local resolving
 func NewQUICNameServer(url *url.URL, disableCache bool, serveStale bool, serveExpiredTTL uint32, clientIP net.IP) (*QUICNameServer, error) {
-	errors.LogInfo(context.Background(), "DNS: created Local DNS-over-QUIC client for ", url.String())
-
 	var err error
 	port := net.Port(853)
 	if url.Port() != "" {
@@ -55,6 +53,7 @@ func NewQUICNameServer(url *url.URL, disableCache bool, serveStale bool, serveEx
 		clientIP:        clientIP,
 	}
 
+	errors.LogInfo(context.Background(), "DNS: created Local DNS-over-QUIC client for ", url.String())
 	return s, nil
 }
 
@@ -63,6 +62,11 @@ func (s *QUICNameServer) Name() string {
 	return s.cacheController.name
 }
 
+// IsDisableCache implements Server.
+func (s *QUICNameServer) IsDisableCache() bool {
+	return s.cacheController.disableCache
+}
+
 func (s *QUICNameServer) newReqID() uint16 {
 	return 0
 }

app/dns/nameserver_tcp.go

@@ -52,6 +52,7 @@ func NewTCPNameServer(
 		), nil
 	}
 
+	errors.LogInfo(context.Background(), "DNS: created TCP client initialized for ", url.String())
 	return s, nil
 }
 
@@ -66,6 +67,7 @@ func NewTCPLocalNameServer(url *url.URL, disableCache bool, serveStale bool, ser
 		return internet.DialSystem(ctx, *s.destination, nil)
 	}
 
+	errors.LogInfo(context.Background(), "DNS: created Local TCP client initialized for ", url.String())
 	return s, nil
 }
 
@@ -93,6 +95,11 @@ func (s *TCPNameServer) Name() string {
 	return s.cacheController.name
 }
 
+// IsDisableCache implements Server.
+func (s *TCPNameServer) IsDisableCache() bool {
+	return s.cacheController.disableCache
+}
+
 func (s *TCPNameServer) newReqID() uint16 {
 	return uint16(atomic.AddUint32(&s.reqID, 1))
 }
@@ -104,7 +111,7 @@ func (s *TCPNameServer) getCacheController() *CacheController {
 
 // sendQuery implements CachedNameserver.
 func (s *TCPNameServer) sendQuery(ctx context.Context, noResponseErrCh chan<- error, fqdn string, option dns_feature.IPOption) {
-	errors.LogDebug(ctx, s.Name(), " querying DNS for: ", fqdn)
+	errors.LogInfo(ctx, s.Name(), " querying DNS for: ", fqdn)
 
 	reqs := buildReqMsgs(fqdn, option, s.newReqID, genEDNS0Options(s.clientIP, 0))
 

app/dns/nameserver_udp.go

@@ -54,6 +54,7 @@ func NewClassicNameServer(address net.Destination, dispatcher routing.Dispatcher
 		Execute:  s.RequestsCleanup,
 	}
 	s.udpServer = udp.NewDispatcher(dispatcher, s.HandleResponse)
+
 	errors.LogInfo(context.Background(), "DNS: created UDP client initialized for ", address.NetAddr())
 	return s
 }
@@ -63,6 +64,11 @@ func (s *ClassicNameServer) Name() string {
 	return s.cacheController.name
 }
 
+// IsDisableCache implements Server.
+func (s *ClassicNameServer) IsDisableCache() bool {
+	return s.cacheController.disableCache
+}
+
 // RequestsCleanup clears expired items from cache
 func (s *ClassicNameServer) RequestsCleanup() error {
 	now := time.Now()
@@ -92,7 +98,7 @@ func (s *ClassicNameServer) HandleResponse(ctx context.Context, packet *udp_prot
 	ipRec, err := parseResponse(payload.Bytes())
 	payload.Release()
 	if err != nil {
-		errors.LogError(ctx, s.Name(), " fail to parse responded DNS udp")
+		errors.LogErrorInner(ctx, err, s.Name(), " fail to parse responded DNS udp")
 		return
 	}
 
@@ -105,7 +111,7 @@ func (s *ClassicNameServer) HandleResponse(ctx context.Context, packet *udp_prot
 	}
 	s.Unlock()
 	if !ok {
-		errors.LogError(ctx, s.Name(), " cannot find the pending request")
+		errors.LogErrorInner(ctx, err, s.Name(), " cannot find the pending request")
 		return
 	}
 
@@ -155,7 +161,7 @@ func (s *ClassicNameServer) getCacheController() *CacheController {
 
 // sendQuery implements CachedNameserver.
 func (s *ClassicNameServer) sendQuery(ctx context.Context, _ chan<- error, fqdn string, option dns_feature.IPOption) {
-	errors.LogDebug(ctx, s.Name(), " querying DNS for: ", fqdn)
+	errors.LogInfo(ctx, s.Name(), " querying DNS for: ", fqdn)
 
 	reqs := buildReqMsgs(fqdn, option, s.newReqID, genEDNS0Options(s.clientIP, 0))
 

infra/conf/dns.go

@@ -206,6 +206,7 @@ type DNSConfig struct {
 	ServeExpiredTTL        uint32              `json:"serveExpiredTTL"`
 	DisableFallback        bool                `json:"disableFallback"`
 	DisableFallbackIfMatch bool                `json:"disableFallbackIfMatch"`
+	EnableParallelQuery    bool                `json:"enableParallelQuery"`
 	UseSystemHosts         bool                `json:"useSystemHosts"`
 }
 
@@ -405,6 +406,7 @@ func (c *DNSConfig) Build() (*dns.Config, error) {
 		ServeExpiredTTL:        c.ServeExpiredTTL,
 		DisableFallback:        c.DisableFallback,
 		DisableFallbackIfMatch: c.DisableFallbackIfMatch,
+		EnableParallelQuery:    c.EnableParallelQuery,
 		QueryStrategy:          resolveQueryStrategy(c.QueryStrategy),
 	}
 
@@ -415,11 +417,78 @@ func (c *DNSConfig) Build() (*dns.Config, error) {
 		config.ClientIp = []byte(c.ClientIP.IP())
 	}
 
+	// Build PolicyID
+	policyMap := map[string]uint32{}
+	nextPolicyID := uint32(1)
+	buildPolicyID := func(nsc *NameServerConfig) uint32 {
+		var sb strings.Builder
+
+		// ClientIP
+		if nsc.ClientIP != nil {
+			sb.WriteString("client=")
+			sb.WriteString(nsc.ClientIP.String())
+			sb.WriteByte('|')
+		} else {
+			sb.WriteString("client=none|")
+		}
+
+		// SkipFallback
+		if nsc.SkipFallback {
+			sb.WriteString("skip=1|")
+		} else {
+			sb.WriteString("skip=0|")
+		}
+
+		// QueryStrategy
+		sb.WriteString("qs=")
+		sb.WriteString(strings.ToLower(strings.TrimSpace(nsc.QueryStrategy)))
+		sb.WriteByte('|')
+
+		// Tag
+		sb.WriteString("tag=")
+		sb.WriteString(strings.ToLower(strings.TrimSpace(nsc.Tag)))
+		sb.WriteByte('|')
+
+		// []string helper
+		writeList := func(tag string, lst []string) {
+			if len(lst) == 0 {
+				sb.WriteString(tag)
+				sb.WriteString("=[]|")
+				return
+			}
+			cp := make([]string, len(lst))
+			for i, s := range lst {
+				cp[i] = strings.TrimSpace(strings.ToLower(s))
+			}
+			sort.Strings(cp)
+			sb.WriteString(tag)
+			sb.WriteByte('=')
+			sb.WriteString(strings.Join(cp, ","))
+			sb.WriteByte('|')
+		}
+
+		writeList("domains", nsc.Domains)
+		writeList("expected", nsc.ExpectedIPs)
+		writeList("expect", nsc.ExpectIPs)
+		writeList("unexpected", nsc.UnexpectedIPs)
+
+		key := sb.String()
+
+		if id, ok := policyMap[key]; ok {
+			return id
+		}
+		id := nextPolicyID
+		nextPolicyID++
+		policyMap[key] = id
+		return id
+	}
+
 	for _, server := range c.Servers {
 		ns, err := server.Build()
 		if err != nil {
 			return nil, errors.New("failed to build nameserver").Base(err)
 		}
+		ns.PolicyID = buildPolicyID(server)
 		config.NameServer = append(config.NameServer, ns)
 	}
 

infra/conf/dns_test.go

@@ -74,6 +74,7 @@ func TestDNSConfigParsing(t *testing.T) {
 						},
 						ServeStale:      true,
 						ServeExpiredTTL: &expectedServeExpiredTTL,
+						PolicyID:        1, // Servers with certain identical fields share this ID, incrementing starting from 1. See: Build PolicyID
 					},
 				},
 				StaticHosts: []*dns.Config_HostMapping{