feat: add tcp_user_timeout

```json
{"streamSettings":{"sockopt": {"tcpUserTimeout": 10000}}}
```

run `gofmt -w -s .` as well

Author: yichya

common/xudp/xudp_test.go

@@ -11,7 +11,7 @@ import (
 func TestXudpReadWrite(t *testing.T) {
 	addr, _ := net.ParseDestination("tcp:127.0.0.1:1345")
 	mb := make(buf.MultiBuffer, 0, 16)
-	m := buf.MultiBufferContainer {
+	m := buf.MultiBufferContainer{
 		MultiBuffer: mb,
 	}
 	var arr [8]byte
@@ -33,4 +33,4 @@ func TestXudpReadWrite(t *testing.T) {
 	if dest[0].UDP.Port != 1345 {
 		t.Error("failed to parse xudp buffer")
 	}
-}
+}

infra/conf/transport_internet.go

@@ -617,6 +617,7 @@ type SocketConfig struct {
 	TCPKeepAliveIdle     int32       `json:"tcpKeepAliveIdle"`
 	TCPCongestion        string      `json:"tcpCongestion"`
 	TCPWindowClamp       int32       `json:"tcpWindowClamp"`
+	TCPUserTimeout       int32       `json:"tcpUserTimeout"`
 	V6only               bool        `json:"v6only"`
 	Interface            string      `json:"interface"`
 }
@@ -669,6 +670,7 @@ func (c *SocketConfig) Build() (*internet.SocketConfig, error) {
 		TcpKeepAliveIdle:     c.TCPKeepAliveIdle,
 		TcpCongestion:        c.TCPCongestion,
 		TcpWindowClamp:       c.TCPWindowClamp,
+		TcpUserTimeout:       c.TCPUserTimeout,
 		V6Only:               c.V6only,
 		Interface:            c.Interface,
 	}, nil

transport/internet/config.pb.go

@@ -104,4 +104,6 @@ message SocketConfig {
   bool   v6only = 14;
 
   int32 tcp_window_clamp = 15;
+
+  int32 tcp_user_timeout = 16;
 }

transport/internet/config.proto

@@ -7,13 +7,6 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-const (
-	// For incoming connections.
-	TCP_FASTOPEN = 23
-	// For out-going connections.
-	TCP_FASTOPEN_CONNECT = 30
-)
-
 func bindAddr(fd uintptr, ip []byte, port uint32) error {
 	setReuseAddr(fd)
 	setReusePort(fd)
@@ -59,8 +52,8 @@ func applyOutboundSocketOptions(network string, address string, fd uintptr, conf
 			tfo = 1
 		}
 		if tfo >= 0 {
-			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, TCP_FASTOPEN_CONNECT, tfo); err != nil {
-				return newError("failed to set TCP_FASTOPEN_CONNECT=", tfo).Base(err)
+			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, unix.TCP_FASTOPEN_CONNECT, tfo); err != nil {
+				return newError("failed to set TCP_FASTOPEN_CONNECT", tfo).Base(err)
 			}
 		}
 
@@ -95,6 +88,12 @@ func applyOutboundSocketOptions(network string, address string, fd uintptr, conf
 				return newError("failed to set TCP_WINDOW_CLAMP", err)
 			}
 		}
+
+		if config.TcpUserTimeout > 0 {
+			if err := syscall.SetsockoptInt(int(fd), syscall.IPPROTO_TCP, unix.TCP_USER_TIMEOUT, int(config.TcpUserTimeout)); err != nil {
+				return newError("failed to set TCP_USER_TIMEOUT", err)
+			}
+		}
 	}
 
 	if config.Tproxy.IsEnabled() {
@@ -115,8 +114,8 @@ func applyInboundSocketOptions(network string, fd uintptr, config *SocketConfig)
 	if isTCPSocket(network) {
 		tfo := config.ParseTFOValue()
 		if tfo >= 0 {
-			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, TCP_FASTOPEN, tfo); err != nil {
-				return newError("failed to set TCP_FASTOPEN=", tfo).Base(err)
+			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_TCP, unix.TCP_FASTOPEN, tfo); err != nil {
+				return newError("failed to set TCP_FASTOPEN", tfo).Base(err)
 			}
 		}
 
@@ -151,6 +150,12 @@ func applyInboundSocketOptions(network string, fd uintptr, config *SocketConfig)
 				return newError("failed to set TCP_WINDOW_CLAMP", err)
 			}
 		}
+
+		if config.TcpUserTimeout > 0 {
+			if err := syscall.SetsockoptInt(int(fd), syscall.IPPROTO_TCP, unix.TCP_USER_TIMEOUT, int(config.TcpUserTimeout)); err != nil {
+				return newError("failed to set TCP_USER_TIMEOUT", err)
+			}
+		}
 	}
 
 	if config.Tproxy.IsEnabled() {