Mux client: Fix b.UDP being overwritten by the next frame (#6822)

https://github.com/XTLS/Xray-core/pull/6822#issuecomment-5993165787

common/mux/client_test.go

@@ -7,9 +7,11 @@ import (
 
 	"github.com/golang/mock/gomock"
 	"github.com/xtls/xray-core/common"
+	"github.com/xtls/xray-core/common/buf"
 	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/common/mux"
 	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/protocol"
 	"github.com/xtls/xray-core/common/session"
 	"github.com/xtls/xray-core/testing/mocks"
 	"github.com/xtls/xray-core/transport"
@@ -114,3 +116,48 @@ func TestClientWorkerClose(t *testing.T) {
 
 	common.Must(w2.Close())
 }
+
+func TestClientWorkerUDPSource(t *testing.T) {
+	downR, downW := pipe.New(pipe.WithoutSizeLimit())
+	upR, upW := pipe.New(pipe.WithoutSizeLimit())
+	worker, err := mux.NewClientWorker(transport.Link{Reader: downR, Writer: upW}, mux.ClientStrategy{})
+	common.Must(err)
+
+	inR, inW := pipe.New(pipe.WithoutSizeLimit())
+	outR, outW := pipe.New(pipe.WithoutSizeLimit())
+	ctx := session.ContextWithOutbounds(context.Background(), []*session.Outbound{{
+		Target: net.UDPDestination(net.ParseAddress("8.8.8.8"), 53),
+	}})
+	if !worker.Dispatch(ctx, &transport.Link{Reader: inR, Writer: outW}) {
+		t.Fatal("failed to dispatch")
+	}
+	b := buf.New()
+	b.WriteString("query")
+	common.Must(inW.WriteMultiBuffer(buf.MultiBuffer{b}))
+	mb, err := upR.ReadMultiBuffer() // New frame, the session is UDP from now on
+	common.Must(err)
+	buf.ReleaseMulti(mb)
+
+	srcs := []net.Destination{
+		net.UDPDestination(net.ParseAddress("1.1.1.1"), 1111),
+		net.UDPDestination(net.DomainAddress("example.com"), 2222),
+		net.UDPDestination(net.ParseAddress("3.3.3.3"), 3333),
+	}
+	w := mux.NewResponseWriter(1, downW, protocol.TransferTypePacket)
+	var got buf.MultiBuffer
+	for i := range srcs {
+		b := buf.New()
+		b.WriteString("reply")
+		b.UDP = &srcs[i]
+		common.Must(w.WriteMultiBuffer(buf.MultiBuffer{b}))
+		// keep earlier replies around while the next frame is parsed
+		mb, err := outR.ReadMultiBuffer()
+		common.Must(err)
+		got = append(got, mb...)
+	}
+	for i, b := range got {
+		if b.UDP == nil || *b.UDP != srcs[i] {
+			t.Errorf("reply %d: source = %v, want %v", i, b.UDP, srcs[i])
+		}
+	}
+}

common/mux/reader.go

@@ -14,15 +14,16 @@ import (
 type PacketReader struct {
 	reader io.Reader
 	eof    bool
-	dest   *net.Destination
+	dest   net.Destination
 }
 
 // NewPacketReader creates a new PacketReader.
+// dest is copied because the caller reuses it for the next frame.
 func NewPacketReader(reader io.Reader, dest *net.Destination) *PacketReader {
 	return &PacketReader{
 		reader: reader,
 		eof:    false,
-		dest:   dest,
+		dest:   *dest,
 	}
 }
 
@@ -47,8 +48,8 @@ func (r *PacketReader) ReadMultiBuffer() (buf.MultiBuffer, error) {
 		return nil, err
 	}
 	r.eof = true
-	if r.dest != nil && r.dest.Network == net.Network_UDP {
-		b.UDP = r.dest
+	if r.dest.Network == net.Network_UDP {
+		b.UDP = &r.dest // only one packet is read, so b owns r.dest
 	}
 	return buf.MultiBuffer{b}, nil
 }