Clarify comment about switchToDirectCopy flag remaining true

Co-authored-by: RPRX <63339210+RPRX@users.noreply.github.com>

app/dns/nameserver_udp.go

@@ -160,7 +160,7 @@ func (s *ClassicNameServer) getCacheController() *CacheController {
 }
 
 // sendQuery implements CachedNameserver.
-func (s *ClassicNameServer) sendQuery(ctx context.Context, _ chan<- error, fqdn string, option dns_feature.IPOption) {
+func (s *ClassicNameServer) sendQuery(ctx context.Context, noResponseErrCh chan<- error, fqdn string, option dns_feature.IPOption) {
 	errors.LogInfo(ctx, s.Name(), " querying DNS for: ", fqdn)
 
 	reqs := buildReqMsgs(fqdn, option, s.newReqID, genEDNS0Options(s.clientIP, 0))
@@ -171,7 +171,14 @@ func (s *ClassicNameServer) sendQuery(ctx context.Context, _ chan<- error, fqdn
 			ctx:        ctx,
 		}
 		s.addPendingRequest(udpReq)
-		b, _ := dns.PackMessage(req.msg)
+		b, err := dns.PackMessage(req.msg)
+		if err != nil {
+			errors.LogErrorInner(ctx, err, "failed to pack dns query")
+			if noResponseErrCh != nil {
+				noResponseErrCh <- err
+			}
+			return
+		}
 		copyDest := net.UDPDestination(s.address.Address, s.address.Port)
 		b.UDP = &copyDest
 		s.udpServer.Dispatch(toDnsContext(ctx, s.address.String()), *s.address, b)

go.mod

@@ -25,6 +25,7 @@ require (
 	golang.org/x/net v0.48.0
 	golang.org/x/sync v0.19.0
 	golang.org/x/sys v0.39.0
+	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2
 	golang.zx2c4.com/wireguard v0.0.0-20231211153847-12269c276173
 	google.golang.org/grpc v1.78.0
 	google.golang.org/protobuf v1.36.11
@@ -50,7 +51,6 @@ require (
 	golang.org/x/text v0.32.0 // indirect
 	golang.org/x/time v0.12.0 // indirect
 	golang.org/x/tools v0.39.0 // indirect
-	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20251029180050-ab9386a59fda // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect

proxy/proxy.go

@@ -224,7 +224,8 @@ func (w *VisionReader) ReadMultiBuffer() (buf.MultiBuffer, error) {
 		switchToDirectCopy = &w.trafficState.Outbound.DownlinkReaderDirectCopy
 	}
 
-	if *switchToDirectCopy {
+	if *switchToDirectCopy && w.input == nil {
+		// Already switched to direct copy mode
 		if w.directReadCounter != nil {
 			w.directReadCounter.Add(int64(buffer.Len()))
 		}
@@ -257,11 +258,18 @@ func (w *VisionReader) ReadMultiBuffer() (buf.MultiBuffer, error) {
 
 	if *switchToDirectCopy {
 		// XTLS Vision processes TLS-like conn's input and rawInput
+		// input contains decrypted application data - safe to merge
 		if inputBuffer, err := buf.ReadFrom(w.input); err == nil && !inputBuffer.IsEmpty() {
 			buffer, _ = buf.MergeMulti(buffer, inputBuffer)
 		}
-		if rawInputBuffer, err := buf.ReadFrom(w.rawInput); err == nil && !rawInputBuffer.IsEmpty() {
-			buffer, _ = buf.MergeMulti(buffer, rawInputBuffer)
+		// rawInput may contain encrypted bytes for the next TLS record
+		// If rawInput is not empty, we should NOT switch to direct mode yet
+		// because those bytes need to be processed by the TLS layer first
+		if w.rawInput != nil && w.rawInput.Len() > 0 {
+			// rawInput has pending data - defer direct copy to next read
+			// *switchToDirectCopy remains true (unchanged), so we will retry on the next ReadMultiBuffer call
+			// This ensures we don't mix encrypted bytes with application data
+			return buffer, err
 		}
 		*w.input = bytes.Reader{} // release memory
 		w.input = nil