fix: allow subcommands with TRIVY_RUN_AS_PLUGIN (#2577)

cmd/trivy/main.go

@@ -1,8 +1,14 @@
 package main
 
 import (
+	"context"
+	"os"
+
+	"golang.org/x/xerrors"
+
 	"github.com/aquasecurity/trivy/pkg/commands"
 	"github.com/aquasecurity/trivy/pkg/log"
+	"github.com/aquasecurity/trivy/pkg/plugin"
 )
 
 var (
@@ -10,8 +16,26 @@ var (
 )
 
 func main() {
-	app := commands.NewApp(version)
-	if err := app.Execute(); err != nil {
+	if err := run(); err != nil {
 		log.Fatal(err)
 	}
 }
+
+func run() error {
+	// Trivy behaves as the specified plugin.
+	if runAsPlugin := os.Getenv("TRIVY_RUN_AS_PLUGIN"); runAsPlugin != "" {
+		if !plugin.IsPredefined(runAsPlugin) {
+			return xerrors.Errorf("unknown plugin: %s", runAsPlugin)
+		}
+		if err := plugin.RunWithArgs(context.Background(), runAsPlugin, os.Args); err != nil {
+			return xerrors.Errorf("plugin error: %w", err)
+		}
+		return nil
+	}
+
+	app := commands.NewApp(version)
+	if err := app.Execute(); err != nil {
+		return err
+	}
+	return nil
+}

pkg/commands/app.go

@@ -68,15 +68,6 @@ func SetOut(out io.Writer) {
 func NewApp(version string) *cobra.Command {
 	globalFlags := flag.NewGlobalFlagGroup()
 	rootCmd := NewRootCommand(version, globalFlags)
-
-	if runAsPlugin := os.Getenv("TRIVY_RUN_AS_PLUGIN"); runAsPlugin != "" {
-		rootCmd.RunE = func(cmd *cobra.Command, args []string) error {
-			return plugin.RunWithArgs(cmd.Context(), runAsPlugin, args)
-		}
-		rootCmd.DisableFlagParsing = true
-		return rootCmd
-	}
-
 	rootCmd.AddCommand(
 		NewImageCommand(globalFlags),
 		NewFilesystemCommand(globalFlags),

pkg/plugin/plugin.go

@@ -293,6 +293,11 @@ func RunWithArgs(ctx context.Context, url string, args []string) error {
 	return nil
 }
 
+func IsPredefined(name string) bool {
+	_, ok := officialPlugins[name]
+	return ok
+}
+
 func loadMetadata(dir string) (Plugin, error) {
 	filePath := filepath.Join(dir, configFile)
 	f, err := os.Open(filePath)