Add engine.Config to encapsulate writing

This change adds an engine.Config type to encapsulate the writing
of config files for container engines.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

pkg/config/engine/containerd/config_v2.go

@@ -18,8 +18,8 @@ package containerd
 
 import (
 	"fmt"
-	"os"
 
+	"github.com/NVIDIA/nvidia-container-toolkit/pkg/config/engine"
 	"github.com/pelletier/go-toml"
 )
 
@@ -133,34 +133,11 @@ func (c *Config) RemoveRuntime(name string) error {
 // Save writes the config to the specified path
 func (c Config) Save(path string) (int64, error) {
 	config := c.Tree
-	output, err := config.ToTomlString()
+	output, err := config.Marshal()
 	if err != nil {
 		return 0, fmt.Errorf("unable to convert to TOML: %v", err)
 	}
 
-	if path == "" {
-		os.Stdout.WriteString(fmt.Sprintf("%s\n", output))
-		return int64(len(output)), nil
-	}
-
-	if len(output) == 0 {
-		err := os.Remove(path)
-		if err != nil {
-			return 0, fmt.Errorf("unable to remove empty file: %v", err)
-		}
-		return 0, nil
-	}
-
-	f, err := os.Create(path)
-	if err != nil {
-		return 0, fmt.Errorf("unable to open '%v' for writing: %v", path, err)
-	}
-	defer f.Close()
-
-	n, err := f.WriteString(output)
-	if err != nil {
-		return 0, fmt.Errorf("unable to write output: %v", err)
-	}
-
+	n, err := engine.Config(path).Write(output)
 	return int64(n), err
 }

pkg/config/engine/containerd/option.go

@@ -108,26 +108,23 @@ func (b *builder) build() (engine.Interface, error) {
 
 // loadConfig loads the containerd config from disk
 func (b *builder) loadConfig(config string) (*Config, error) {
-	b.logger.Infof("Loading config: %v", config)
-
 	info, err := os.Stat(config)
 	if os.IsExist(err) && info.IsDir() {
 		return nil, fmt.Errorf("config file is a directory")
 	}
 
-	configFile := config
 	if os.IsNotExist(err) {
-		configFile = "/dev/null"
-		b.logger.Infof("Config file does not exist, creating new one")
+		b.logger.Infof("Config file does not exist; using empty config")
+		config = "/dev/null"
+	} else {
+		b.logger.Infof("Loading config from %v", config)
 	}
 
-	tomlConfig, err := toml.LoadFile(configFile)
+	tomlConfig, err := toml.LoadFile(config)
 	if err != nil {
 		return nil, err
 	}
 
-	b.logger.Infof("Successfully loaded config")
-
 	cfg := Config{
 		Tree: tomlConfig,
 	}