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/containerd.go

@@ -17,10 +17,11 @@
 package containerd
 
 import (
-	"github.com/pelletier/go-toml"
+	"fmt"
 
 	"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"
 )
 
 // Config represents the containerd config
@@ -36,14 +37,64 @@ var _ engine.Interface = (*Config)(nil)
 
 // New creates a containerd config with the specified options
 func New(opts ...Option) (engine.Interface, error) {
-	b := &builder{}
+	b := &builder{
+		runtimeType: defaultRuntimeType,
+	}
 	for _, opt := range opts {
 		opt(b)
 	}
-
 	if b.logger == nil {
 		b.logger = logger.New()
 	}
+	if b.configSource == nil {
+		b.configSource = toml.FromFile(b.path)
+	}
 
-	return b.build()
+	tomlConfig, err := b.configSource.Load()
+	if err != nil {
+		return nil, fmt.Errorf("failed to load config: %v", err)
+	}
+
+	cfg := &Config{
+		Tree:                  tomlConfig,
+		Logger:                b.logger,
+		RuntimeType:           b.runtimeType,
+		UseDefaultRuntimeName: b.useLegacyConfig,
+		ContainerAnnotations:  b.containerAnnotations,
+	}
+
+	version, err := cfg.parseVersion(b.useLegacyConfig)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse config version: %v", err)
+	}
+	switch version {
+	case 1:
+		return (*ConfigV1)(cfg), nil
+	case 2:
+		return cfg, nil
+	}
+
+	return nil, fmt.Errorf("unsupported config version: %v", version)
+}
+
+// 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)
+	}
 }