Use resolved in local DNS server if available

dns/transport/local/local.go

@@ -16,6 +16,7 @@ import (
 	"github.com/sagernet/sing-box/option"
 	"github.com/sagernet/sing/common/buf"
 	E "github.com/sagernet/sing/common/exceptions"
+	"github.com/sagernet/sing/common/logger"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
 
@@ -26,9 +27,11 @@ var _ adapter.DNSTransport = (*Transport)(nil)
 
 type Transport struct {
 	dns.TransportAdapter
-	ctx    context.Context
-	hosts  *hosts.File
-	dialer N.Dialer
+	ctx      context.Context
+	logger   logger.ContextLogger
+	hosts    *hosts.File
+	dialer   N.Dialer
+	resolved ResolvedResolver
 }
 
 func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, options option.LocalDNSServerOptions) (adapter.DNSTransport, error) {
@@ -39,20 +42,42 @@ func NewTransport(ctx context.Context, logger log.ContextLogger, tag string, opt
 	return &Transport{
 		TransportAdapter: dns.NewTransportAdapterWithLocalOptions(C.DNSTypeLocal, tag, options),
 		ctx:              ctx,
+		logger:           logger,
 		hosts:            hosts.NewFile(hosts.DefaultPath),
 		dialer:           transportDialer,
 	}, nil
 }
 
 func (t *Transport) Start(stage adapter.StartStage) error {
+	switch stage {
+	case adapter.StartStateInitialize:
+		resolvedResolver, err := NewResolvedResolver(t.ctx, t.logger)
+		if err == nil {
+			err = resolvedResolver.Start()
+			if err == nil {
+				t.resolved = resolvedResolver
+			} else {
+				t.logger.Warn(E.Cause(err, "initialize resolved resolver"))
+			}
+		}
+	}
 	return nil
 }
 
 func (t *Transport) Close() error {
+	if t.resolved != nil {
+		return t.resolved.Close()
+	}
 	return nil
 }
 
 func (t *Transport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
+	if t.resolved != nil {
+		resolverObject := t.resolved.Object()
+		if resolverObject != nil {
+			return t.resolved.Exchange(resolverObject, ctx, message)
+		}
+	}
 	question := message.Question[0]
 	if question.Qtype == mDNS.TypeA || question.Qtype == mDNS.TypeAAAA {
 		addresses := t.hosts.Lookup(dns.FqdnToDomain(question.Name))