From 4bc1c206e6e57a9ff2f75fcc8912b55c7b590b83 Mon Sep 17 00:00:00 2001
From: Alireza <a.atharifard1384@gmail.com>
Date: Sat, 31 Oct 2026 10:28:21 +0330
Subject: [PATCH] SOCKS inbound: Serialize concurrent mux responses

Reuse BufferedWriter with buffering disabled before DispatchLink. Add a concurrent-response regression over WebSocket.
---
 proxy/socks/server.go               |  4 +-
 testing/scenarios/proxy_mux_test.go | 86 +++++++++++++++++++++++++++++
 2 files changed, 89 insertions(+), 1 deletion(-)
 create mode 100644 testing/scenarios/proxy_mux_test.go

diff --git a/proxy/socks/server.go b/proxy/socks/server.go
index d68e5c4338db..527c2167104e 100644
--- a/proxy/socks/server.go
+++ b/proxy/socks/server.go
@@ -154,10 +154,12 @@ func (s *Server) processTCP(ctx context.Context, conn stat.Connection, dispatche
 		if inbound.CanSpliceCopy == 2 {
 			inbound.CanSpliceCopy = 1
 		}
+		writer := buf.NewBufferedWriter(buf.NewWriter(conn))
+		common.Must(writer.SetBuffered(false))
 		if err := dispatcher.DispatchLink(
 			ctx, dest, &transport.Link{
 				Reader: reader,
-				Writer: buf.NewWriter(conn),
+				Writer: writer,
 			},
 		); err != nil {
 			return errors.New("failed to dispatch request").Base(err)
diff --git a/testing/scenarios/proxy_mux_test.go b/testing/scenarios/proxy_mux_test.go
new file mode 100644
index 000000000000..609664b2d9c3
--- /dev/null
+++ b/testing/scenarios/proxy_mux_test.go
@@ -0,0 +1,86 @@
+package scenarios
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/xtls/xray-core/core"
+	"github.com/xtls/xray-core/infra/conf/serial"
+	"github.com/xtls/xray-core/testing/servers/tcp"
+)
+
+func TestSocksMuxConcurrentWrites(t *testing.T) {
+	testMuxConcurrentWrites(t, "socks")
+}
+
+func testMuxConcurrentWrites(t *testing.T, protocol string) {
+	t.Helper()
+	echo := &tcp.Server{MsgProcessor: xor}
+	dest, err := echo.Start()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = echo.Close() })
+	serverPort, clientPort := tcp.PickPort(), tcp.PickPort()
+	for _, config := range []string{
+		fmt.Sprintf(`{
+			"inbounds": [{"listen": "127.0.0.1", "port": %d, "protocol": "%s", "streamSettings": {"network": "ws"}}],
+			"outbounds": [{"protocol": "freedom", "settings": {"finalRules": [{"action": "allow"}]}}]
+		}`, serverPort, protocol),
+		fmt.Sprintf(`{
+			"inbounds": [{"listen": "127.0.0.1", "port": %d, "protocol": "dokodemo-door", "settings": {"address": "127.0.0.1", "port": %d, "network": "tcp"}}],
+			"outbounds": [{"protocol": "%s", "settings": {"servers": [{"address": "127.0.0.1", "port": %d}]}, "streamSettings": {"network": "ws"}, "mux": {"enabled": true, "concurrency": 8}}]
+		}`, clientPort, dest.Port, protocol, serverPort),
+	} {
+		cfg, err := serial.LoadJSONConfig(strings.NewReader(config))
+		if err != nil {
+			t.Fatal(err)
+		}
+		instance, err := core.New(cfg)
+		if err != nil {
+			t.Fatal(err)
+		}
+		t.Cleanup(func() { _ = instance.Close() })
+		if err := instance.Start(); err != nil {
+			t.Fatal(err)
+		}
+	}
+	var wg sync.WaitGroup
+	for id := range 8 {
+		wg.Go(func() {
+			conn, err := net.Dial("tcp", net.JoinHostPort("127.0.0.1", clientPort.String()))
+			if err != nil {
+				t.Error(err)
+				return
+			}
+			defer conn.Close()
+			if err := conn.SetDeadline(time.Now().Add(5 * time.Second)); err != nil {
+				t.Error(err)
+				return
+			}
+			payload := bytes.Repeat([]byte{byte(id)}, 32*1024)
+			response := make([]byte, len(payload))
+			for range 8 {
+				if _, err := conn.Write(payload); err != nil {
+					t.Error(err)
+					return
+				}
+				if _, err := io.ReadFull(conn, response); err != nil {
+					t.Error(err)
+					return
+				}
+				if !bytes.Equal(response, xor(payload)) {
+					t.Errorf("corrupted response for session %d", id)
+					return
+				}
+			}
+		})
+	}
+	wg.Wait()
+}