New static configuration loading system.

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>

pkg/config/flag/flag.go

@@ -0,0 +1,44 @@
+// Package flag implements encoding and decoding between flag arguments and a typed Configuration.
+package flag
+
+import (
+	"github.com/containous/traefik/pkg/config/parser"
+)
+
+// Decode decodes the given flag arguments into the given element.
+// The operation goes through four stages roughly summarized as:
+// flag arguments -> parsed map of flags
+// map -> tree of untyped nodes
+// untyped nodes -> nodes augmented with metadata such as kind (inferred from element)
+// "typed" nodes -> typed element
+func Decode(args []string, element interface{}) error {
+	ref, err := Parse(args, element)
+	if err != nil {
+		return err
+	}
+
+	return parser.Decode(ref, element)
+}
+
+// Encode encodes the configuration in element into the flags represented in the returned Flats.
+// The operation goes through three stages roughly summarized as:
+// typed configuration in element -> tree of untyped nodes
+// untyped nodes -> nodes augmented with metadata such as kind (inferred from element)
+// "typed" nodes -> flags with default values (determined by type/kind)
+func Encode(element interface{}) ([]parser.Flat, error) {
+	if element == nil {
+		return nil, nil
+	}
+
+	node, err := parser.EncodeToNode(element, false)
+	if err != nil {
+		return nil, err
+	}
+
+	err = parser.AddMetadata(element, node)
+	if err != nil {
+		return nil, err
+	}
+
+	return parser.EncodeToFlat(element, node, parser.FlatOpts{Separator: ".", SkipRoot: true})
+}