Use config package to handle all controller configurations

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

cmd/root.go

@@ -34,6 +34,7 @@ package cmd
 import (
 	"context"
 	"os"
+	"path/filepath"
 
 	"code.fbi.h-da.de/danet/gosdn"
 
@@ -80,16 +81,22 @@ func init() {
 	rootCmd.Flags().StringVar(&csbiOrchestrstor, "csbi-orchestrator", "localhost:55056", "csbi orchestrator address")
 }
 
+const (
+	configHome string = "./configs"
+	configName string = "gosdn"
+	configType string = "toml"
+)
+
 // initConfig reads in config file and ENV variables if set.
 func initConfig() {
 	if cfgFile != "" {
 		// Use config file from the flag.
 		viper.SetConfigFile(cfgFile)
 	} else {
-		viper.AddConfigPath("./configs")
+		viper.AddConfigPath(configHome)
 		viper.AddConfigPath("/usr/local/etc/gosdn/")
-		viper.SetConfigType("toml")
-		viper.SetConfigName("gosdn")
+		viper.SetConfigType(configType)
+		viper.SetConfigName(configName)
 	}
 
 	viper.AutomaticEnv() // read in environment variables that match
@@ -97,6 +104,8 @@ func initConfig() {
 	// If a config file is found, read it in.
 	if err := viper.ReadInConfig(); err == nil {
 		log.Debug("Using config file:", viper.ConfigFileUsed())
+	} else {
+		ensureViperConfigFileExists()
 	}
 
 	viper.SetDefault("socket", ":55055")
@@ -118,3 +127,28 @@ func initConfig() {
 		log.SetReportCaller(false)
 	}
 }
+
+func ensureFileSystemStoreExists(pathToStore string) error {
+	emptyString := []byte("")
+	err := os.WriteFile(pathToStore, emptyString, 0600)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func ensureViperConfigFileExists() {
+	// Viper will crash if you call 'WriteConfig()' and the file does
+	// not exists yet.
+	// Therefore we handle this case here.
+	// Inspired by //https://github.com/spf13/viper/issues/430#issuecomment-661945101
+	configPath := filepath.Join(configHome, configName+"."+configType)
+
+	if _, err := os.Stat(configPath); os.IsNotExist(err) {
+		err := ensureFileSystemStoreExists(configPath)
+		if err != nil {
+			panic(err)
+		}
+	}
+}