Implement dns-hijack

cmd/sing-box/cmd_tools.go

@@ -1,6 +1,9 @@
 package main
 
 import (
+	"errors"
+	"os"
+
 	"github.com/sagernet/sing-box"
 	E "github.com/sagernet/sing/common/exceptions"
 	N "github.com/sagernet/sing/common/network"
@@ -23,7 +26,9 @@ func init() {
 func createPreStartedClient() (*box.Box, error) {
 	options, err := readConfigAndMerge()
 	if err != nil {
-		return nil, err
+		if !(errors.Is(err, os.ErrNotExist) && len(configDirectories) == 0 && len(configPaths) == 1) || configPaths[0] != "config.json" {
+			return nil, err
+		}
 	}
 	instance, err := box.New(box.Options{Options: options})
 	if err != nil {