Add check/format command

cmd/sing-box/cmd_check.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"context"
+	"os"
+
+	"github.com/goccy/go-json"
+	"github.com/sagernet/sing-box"
+	"github.com/sagernet/sing-box/option"
+	"github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+)
+
+var commandCheck = &cobra.Command{
+	Use:   "check",
+	Short: "check configuration",
+	Run:   checkConfiguration,
+}
+
+func checkConfiguration(cmd *cobra.Command, args []string) {
+	configContent, err := os.ReadFile(configPath)
+	if err != nil {
+		logrus.Fatal("read config: ", err)
+	}
+	var options option.Options
+	err = json.Unmarshal(configContent, &options)
+	if err != nil {
+		logrus.Fatal("decode config: ", err)
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	_, err = box.NewService(ctx, options)
+	if err != nil {
+		logrus.Fatal("create service: ", err)
+	}
+	cancel()
+}