dialer: use KeepAliveConfig for TCP keepalive

common/dialer/default.go

@@ -142,8 +142,7 @@ func NewDefault(ctx context.Context, options option.DialerOptions) (*DefaultDial
 		dialer.Timeout = C.TCPConnectTimeout
 	}
 	// TODO: Add an option to customize the keep alive period
-	dialer.KeepAlive = C.TCPKeepAliveInitial
-	dialer.Control = control.Append(dialer.Control, control.SetKeepAlivePeriod(C.TCPKeepAliveInitial, C.TCPKeepAliveInterval))
+	setKeepAliveConfig(&dialer, C.TCPKeepAliveInitial, C.TCPKeepAliveInterval)
 	var udpFragment bool
 	if options.UDPFragment != nil {
 		udpFragment = *options.UDPFragment

common/dialer/default_go123.go

@@ -0,0 +1,16 @@
+//go:build go1.23
+
+package dialer
+
+import (
+	"net"
+	"time"
+)
+
+func setKeepAliveConfig(dialer *net.Dialer, idle time.Duration, interval time.Duration) {
+	dialer.KeepAliveConfig = net.KeepAliveConfig{
+		Enable:   true,
+		Idle:     idle,
+		Interval: interval,
+	}
+}

common/dialer/default_nongo123.go

@@ -0,0 +1,15 @@
+//go:build !go1.23
+
+package dialer
+
+import (
+	"net"
+	"time"
+
+	"github.com/sagernet/sing/common/control"
+)
+
+func setKeepAliveConfig(dialer *net.Dialer, idle time.Duration, interval time.Duration) {
+	dialer.KeepAlive = idle
+	dialer.Control = control.Append(dialer.Control, control.SetKeepAlivePeriod(idle, interval))
+}