New static configuration loading system.

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

pkg/config/file/file.go

@@ -0,0 +1,31 @@
+// Package file implements decoding between configuration in a file and a typed Configuration.
+package file
+
+import (
+	"github.com/containous/traefik/pkg/config/parser"
+)
+
+// Decode decodes the given configuration file 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 Decode(filePath string, element interface{}) error {
+	if element == nil {
+		return nil
+	}
+
+	filters := getRootFieldNames(element)
+
+	root, err := decodeFileToNode(filePath, filters...)
+	if err != nil {
+		return err
+	}
+
+	err = parser.AddMetadata(element, root)
+	if err != nil {
+		return err
+	}
+
+	return parser.Fill(element, root)
+}