Return error if the config file is invalid.

Refactor the root command to make it testable.

cmd/root.go

@@ -26,35 +26,34 @@ import (
 
 var (
 	cfgFile   string
+	err       error
 	configObj cfg.Config
 )
-var rootCmd = &cobra.Command{
-	Use:   "gcsfuse [flags] bucket mount_point",
-	Short: "Mount a specified GCS bucket or all accessible buckets locally",
-	Long: `Cloud Storage FUSE is an open source FUSE adapter that lets you mount 
+
+func NewRootCmd() *cobra.Command {
+	rootCmd := &cobra.Command{
+		Use:   "gcsfuse [flags] bucket mount_point",
+		Short: "Mount a specified GCS bucket or all accessible buckets locally",
+		Long: `Cloud Storage FUSE is an open source FUSE adapter that lets you mount 
 and access Cloud Storage buckets as local file systems. For a technical overview
 of Cloud Storage FUSE, see https://cloud.google.com/storage/docs/gcs-fuse.`,
-	Version: getVersion(),
-	RunE: func(cmd *cobra.Command, args []string) error {
-		// TODO: the following error will be removed once the command is implemented.
-		return fmt.Errorf("unsupported operation")
-	},
-}
-
-func Execute() {
-	if err := rootCmd.Execute(); err != nil {
-		panic(err)
+		Version: getVersion(),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if err != nil {
+				return err
+			}
+			// TODO: the following error will be removed once the command is implemented.
+			return fmt.Errorf("unsupported operation")
+		},
 	}
-}
-
-func init() {
 	cobra.OnInitialize(initConfig)
 	rootCmd.PersistentFlags().StringVar(&cfgFile, "config-file", "", "Absolute path to the config file.")
 
 	// Add all the other flags.
 	if err := cfg.BindFlags(rootCmd.PersistentFlags()); err != nil {
 		logger.Fatal("error while declaring/binding flags: %v", err)
 	}
+	return rootCmd
 }
 
 func initConfig() {
@@ -63,15 +62,14 @@ func initConfig() {
 	}
 	viper.SetConfigFile(cfgFile)
 	viper.SetConfigType("yaml")
-	if err := viper.ReadInConfig(); err != nil {
-		logger.Fatal("error while reading the config: %v", err)
+	if err = viper.ReadInConfig(); err != nil {
+		return
 	}
-	err := viper.Unmarshal(&configObj, viper.DecodeHook(cfg.DecodeHook()), func(decoderConfig *mapstructure.DecoderConfig) {
+	err = viper.Unmarshal(&configObj, viper.DecodeHook(cfg.DecodeHook()), func(decoderConfig *mapstructure.DecoderConfig) {
 		// By default, viper supports mapstructure tags for unmarshalling. Override that to support yaml tag.
 		decoderConfig.TagName = "yaml"
+		// Reject the config file if any of the fields in the YAML don't map to the struct.
+		decoderConfig.ErrorUnused = true
 	},
 	)
-	if err != nil {
-		logger.Fatal("error while unmarshalling the config: %v", err)
-	}
 }

cmd/root_test.go

@@ -0,0 +1,33 @@
+// Copyright 2024 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cmd
+
+import (
+	"testing"
+
+	"github.com/mitchellh/mapstructure"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestInvalidConfig(t *testing.T) {
+	cmd := NewRootCmd()
+	cmd.SetArgs([]string{"--config-file=testdata/invalid_config.yml", "abc", "pqr"})
+
+	err := cmd.Execute()
+
+	if assert.NotNil(t, err) {
+		assert.IsType(t, err, &mapstructure.Error{})
+	}
+}

cmd/testdata/invalid_config.yml

@@ -0,0 +1 @@
+a: abc

cmd/testdata/valid_config.yml

@@ -0,0 +1 @@
+app-name: hello

main.go

@@ -64,7 +64,7 @@ func main() {
 	log.SetFlags(log.Ldate | log.Ltime | log.Lmicroseconds)
 	if strings.ToLower(os.Getenv("ENABLE_GCSFUSE_VIPER_CONFIG")) == "true" {
 		os.Args = convertToPosixArgs(os.Args)
-		cmd.Execute()
+		cmd.NewRootCmd().Execute()
 		return
 	}
 	cmd.ExecuteLegacyMain()