Add KV store providers (dynamic configuration only)

Co-authored-by: Jean-Baptiste Doumenjou <jb.doumenjou@gmail.com>

pkg/config/kv/kv.go

@@ -0,0 +1,75 @@
+package kv
+
+import (
+	"path"
+	"reflect"
+
+	"github.com/abronan/valkeyrie/store"
+	"github.com/containous/traefik/v2/pkg/config/parser"
+)
+
+// Decode decodes the given KV pairs into the given element.
+// The operation goes through three stages roughly summarized as:
+// KV pairs -> tree of untyped nodes
+// untyped nodes -> nodes augmented with metadata such as kind (inferred from element)
+// "typed" nodes -> typed element
+func Decode(pairs []*store.KVPair, element interface{}, rootName string) error {
+	if element == nil {
+		return nil
+	}
+
+	filters := getRootFieldNames(rootName, element)
+
+	node, err := DecodeToNode(pairs, rootName, filters...)
+	if err != nil {
+		return err
+	}
+
+	metaOpts := parser.MetadataOpts{TagName: parser.TagLabel, AllowSliceAsStruct: false}
+	err = parser.AddMetadata(element, node, metaOpts)
+	if err != nil {
+		return err
+	}
+
+	return parser.Fill(element, node, parser.FillerOpts{AllowSliceAsStruct: false})
+}
+
+func getRootFieldNames(rootName string, element interface{}) []string {
+	if element == nil {
+		return nil
+	}
+
+	rootType := reflect.TypeOf(element)
+
+	return getFieldNames(rootName, rootType)
+}
+
+func getFieldNames(rootName string, rootType reflect.Type) []string {
+	var names []string
+
+	if rootType.Kind() == reflect.Ptr {
+		rootType = rootType.Elem()
+	}
+
+	if rootType.Kind() != reflect.Struct {
+		return nil
+	}
+
+	for i := 0; i < rootType.NumField(); i++ {
+		field := rootType.Field(i)
+
+		if !parser.IsExported(field) {
+			continue
+		}
+
+		if field.Anonymous &&
+			(field.Type.Kind() == reflect.Ptr && field.Type.Elem().Kind() == reflect.Struct || field.Type.Kind() == reflect.Struct) {
+			names = append(names, getFieldNames(rootName, field.Type)...)
+			continue
+		}
+
+		names = append(names, path.Join(rootName, field.Name))
+	}
+
+	return names
+}