Refactor Toml config handling

This change refactors the toml config file handlig for runtimes
such as containerd or crio. A toml.Loader is introduced that
encapsulates loading the required file.

This can be extended to allow other mechanisms for loading
loading the current config.

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

pkg/config/engine/containerd/option.go

@@ -17,13 +17,8 @@
 package containerd
 
 import (
-	"fmt"
-	"os"
-
-	"github.com/pelletier/go-toml"
-
 	"github.com/NVIDIA/nvidia-container-toolkit/internal/logger"
-	"github.com/NVIDIA/nvidia-container-toolkit/pkg/config/engine"
+	"github.com/NVIDIA/nvidia-container-toolkit/pkg/config/toml"
 )
 
 const (
@@ -32,6 +27,7 @@ const (
 
 type builder struct {
 	logger               logger.Interface
+	configSource         toml.Loader
 	path                 string
 	runtimeType          string
 	useLegacyConfig      bool
@@ -55,6 +51,13 @@ func WithPath(path string) Option {
 	}
 }
 
+// WithConfigSource sets the source for the config.
+func WithConfigSource(configSource toml.Loader) Option {
+	return func(b *builder) {
+		b.configSource = configSource
+	}
+}
+
 // WithRuntimeType sets the runtime type for the config builder
 func WithRuntimeType(runtimeType string) Option {
 	return func(b *builder) {
@@ -75,82 +78,3 @@ func WithContainerAnnotations(containerAnnotations ...string) Option {
 		b.containerAnnotations = containerAnnotations
 	}
 }
-
-func (b *builder) build() (engine.Interface, error) {
-	if b.path == "" {
-		return nil, fmt.Errorf("config path is empty")
-	}
-
-	if b.runtimeType == "" {
-		b.runtimeType = defaultRuntimeType
-	}
-
-	config, err := b.loadConfig(b.path)
-	if err != nil {
-		return nil, fmt.Errorf("failed to load config: %v", err)
-	}
-	config.Logger = b.logger
-	config.RuntimeType = b.runtimeType
-	config.UseDefaultRuntimeName = !b.useLegacyConfig
-	config.ContainerAnnotations = b.containerAnnotations
-
-	version, err := config.parseVersion(b.useLegacyConfig)
-	if err != nil {
-		return nil, fmt.Errorf("failed to parse config version: %v", err)
-	}
-	switch version {
-	case 1:
-		return (*ConfigV1)(config), nil
-	case 2:
-		return config, nil
-	}
-
-	return nil, fmt.Errorf("unsupported config version: %v", version)
-}
-
-// loadConfig loads the containerd config from disk
-func (b *builder) loadConfig(config string) (*Config, error) {
-	info, err := os.Stat(config)
-	if os.IsExist(err) && info.IsDir() {
-		return nil, fmt.Errorf("config file is a directory")
-	}
-
-	if os.IsNotExist(err) {
-		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(config)
-	if err != nil {
-		return nil, err
-	}
-
-	cfg := Config{
-		Tree: tomlConfig,
-	}
-	return &cfg, nil
-}
-
-// parseVersion returns the version of the config
-func (c *Config) parseVersion(useLegacyConfig bool) (int, error) {
-	defaultVersion := 2
-	if useLegacyConfig {
-		defaultVersion = 1
-	}
-
-	switch v := c.Get("version").(type) {
-	case nil:
-		switch len(c.Keys()) {
-		case 0: // No config exists, or the config file is empty, use version inferred from containerd
-			return defaultVersion, nil
-		default: // A config file exists, has content, and no version is set
-			return 1, nil
-		}
-	case int64:
-		return int(v), nil
-	default:
-		return -1, fmt.Errorf("unsupported type for version field: %v", v)
-	}
-}