feat: use parser to load dynamic config from file.

pkg/config/file/file.go

@@ -2,7 +2,11 @@
 package file
 
 import (
+	"fmt"
+
+	"github.com/BurntSushi/toml"
 	"github.com/containous/traefik/v2/pkg/config/parser"
+	"gopkg.in/yaml.v2"
 )
 
 // Decode decodes the given configuration file into the given element.
@@ -22,11 +26,57 @@ func Decode(filePath string, element interface{}) error {
 		return err
 	}
 
-	metaOpts := parser.MetadataOpts{TagName: parser.TagLabel, AllowSliceAsStruct: true}
+	metaOpts := parser.MetadataOpts{TagName: parser.TagFile, AllowSliceAsStruct: false}
 	err = parser.AddMetadata(element, root, metaOpts)
 	if err != nil {
 		return err
 	}
 
-	return parser.Fill(element, root, parser.FillerOpts{AllowSliceAsStruct: true})
+	return parser.Fill(element, root, parser.FillerOpts{AllowSliceAsStruct: false})
+}
+
+// DecodeContent decodes the given configuration file content into the given element.
+// The operation goes through three stages roughly summarized as:
+// file contents -> tree of untyped nodes
+// untyped nodes -> nodes augmented with metadata such as kind (inferred from element)
+// "typed" nodes -> typed element.
+func DecodeContent(content string, extension string, element interface{}) error {
+	data := make(map[string]interface{})
+
+	switch extension {
+	case ".toml":
+		_, err := toml.Decode(content, &data)
+		if err != nil {
+			return err
+		}
+
+	case ".yml", ".yaml":
+		var err error
+		err = yaml.Unmarshal([]byte(content), &data)
+		if err != nil {
+			return err
+		}
+
+	default:
+		return fmt.Errorf("unsupported file extension: %s", extension)
+	}
+
+	filters := getRootFieldNames(element)
+
+	node, err := decodeRawToNode(data, parser.DefaultRootName, filters...)
+	if err != nil {
+		return err
+	}
+
+	if len(node.Children) == 0 {
+		return nil
+	}
+
+	metaOpts := parser.MetadataOpts{TagName: parser.TagFile, AllowSliceAsStruct: false}
+	err = parser.AddMetadata(element, node, metaOpts)
+	if err != nil {
+		return err
+	}
+
+	return parser.Fill(element, node, parser.FillerOpts{AllowSliceAsStruct: false})
 }