Inbounds & Outbounds: TCP KeepAlive better default value (#4931)

From https://github.com/XTLS/Xray-core/pull/4927

transport/internet/system_dialer.go

@@ -3,6 +3,7 @@ package internet
 import (
 	"context"
 	"math/rand"
+	gonet "net"
 	"syscall"
 	"time"
 
@@ -87,14 +88,34 @@ func (d *DefaultSystemDialer) Dial(ctx context.Context, src net.Address, dest ne
 			Dest: destAddr,
 		}, nil
 	}
-	goStdKeepAlive := time.Duration(0)
-	if sockopt != nil && (sockopt.TcpKeepAliveInterval != 0 || sockopt.TcpKeepAliveIdle != 0) {
-		goStdKeepAlive = time.Duration(-1)
+	// Chrome defaults
+	keepAliveConfig := gonet.KeepAliveConfig{
+		Enable:   true,
+		Idle:     45 * time.Second,
+		Interval: 45 * time.Second,
+		Count:    -1,
+	}
+	keepAlive := time.Duration(0)
+	if sockopt != nil {
+		if sockopt.TcpKeepAliveIdle*sockopt.TcpKeepAliveInterval < 0 {
+			return nil, errors.New("invalid TcpKeepAliveIdle or TcpKeepAliveInterval value: ", sockopt.TcpKeepAliveIdle, " ", sockopt.TcpKeepAliveInterval)
+		}
+		if sockopt.TcpKeepAliveIdle < 0 || sockopt.TcpKeepAliveInterval < 0 {
+			keepAlive = -1
+			keepAliveConfig.Enable = false
+		}
+		if sockopt.TcpKeepAliveIdle > 0 {
+			keepAliveConfig.Idle = time.Duration(sockopt.TcpKeepAliveIdle) * time.Second
+		}
+		if sockopt.TcpKeepAliveInterval > 0 {
+			keepAliveConfig.Interval = time.Duration(sockopt.TcpKeepAliveInterval) * time.Second
+		}
 	}
 	dialer := &net.Dialer{
-		Timeout:   time.Second * 16,
-		LocalAddr: resolveSrcAddr(dest.Network, src),
-		KeepAlive: goStdKeepAlive,
+		Timeout:         time.Second * 16,
+		LocalAddr:       resolveSrcAddr(dest.Network, src),
+		KeepAlive:       keepAlive,
+		KeepAliveConfig: keepAliveConfig,
 	}
 
 	if sockopt != nil || len(d.controllers) > 0 {