cmd: add policy check command (#2553)

cmd/headscale/cli/policy.go

@@ -6,6 +6,7 @@ import (
 	"os"
 
 	v1 "github.com/juanfont/headscale/gen/go/headscale/v1"
+	"github.com/juanfont/headscale/hscontrol/policy"
 	"github.com/rs/zerolog/log"
 	"github.com/spf13/cobra"
 )
@@ -19,6 +20,12 @@ func init() {
 		log.Fatal().Err(err).Msg("")
 	}
 	policyCmd.AddCommand(setPolicy)
+
+	checkPolicy.Flags().StringP("file", "f", "", "Path to a policy file in HuJSON format")
+	if err := checkPolicy.MarkFlagRequired("file"); err != nil {
+		log.Fatal().Err(err).Msg("")
+	}
+	policyCmd.AddCommand(checkPolicy)
 }
 
 var policyCmd = &cobra.Command{
@@ -85,3 +92,30 @@ var setPolicy = &cobra.Command{
 		SuccessOutput(nil, "Policy updated.", "")
 	},
 }
+
+var checkPolicy = &cobra.Command{
+	Use:   "check",
+	Short: "Check the Policy file for errors",
+	Run: func(cmd *cobra.Command, args []string) {
+		output, _ := cmd.Flags().GetString("output")
+		policyPath, _ := cmd.Flags().GetString("file")
+
+		f, err := os.Open(policyPath)
+		if err != nil {
+			ErrorOutput(err, fmt.Sprintf("Error opening the policy file: %s", err), output)
+		}
+		defer f.Close()
+
+		policyBytes, err := io.ReadAll(f)
+		if err != nil {
+			ErrorOutput(err, fmt.Sprintf("Error reading the policy file: %s", err), output)
+		}
+
+		_, err = policy.NewPolicyManager(policyBytes, nil, nil)
+		if err != nil {
+			ErrorOutput(err, fmt.Sprintf("Error parsing the policy file: %s", err), output)
+		}
+
+		SuccessOutput(nil, "Policy is valid", "")
+	},
+}