New static configuration loading system.

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

pkg/config/generator/generator.go

@@ -0,0 +1,97 @@
+// Package generator implements the custom initialization of all the fields of an empty interface.
+package generator
+
+import (
+	"reflect"
+
+	"github.com/containous/traefik/pkg/config/parser"
+)
+
+type initializer interface {
+	SetDefaults()
+}
+
+// Generate recursively initializes an empty structure, calling SetDefaults on each field, when it applies.
+func Generate(element interface{}) {
+	if element == nil {
+		return
+	}
+
+	generate(element)
+}
+
+func generate(element interface{}) {
+	field := reflect.ValueOf(element)
+
+	fill(field)
+}
+
+func fill(field reflect.Value) {
+	switch field.Kind() {
+	case reflect.Ptr:
+		setPtr(field)
+	case reflect.Struct:
+		setStruct(field)
+	case reflect.Map:
+		setMap(field)
+	case reflect.Slice:
+		if field.Type().Elem().Kind() == reflect.Struct ||
+			field.Type().Elem().Kind() == reflect.Ptr && field.Type().Elem().Elem().Kind() == reflect.Struct {
+			slice := reflect.MakeSlice(field.Type(), 1, 1)
+			field.Set(slice)
+
+			// use Ptr to allow "SetDefaults"
+			value := reflect.New(reflect.PtrTo(field.Type().Elem()))
+			setPtr(value)
+
+			elem := value.Elem().Elem()
+			field.Index(0).Set(elem)
+		} else if field.Len() == 0 {
+			slice := reflect.MakeSlice(field.Type(), 0, 0)
+			field.Set(slice)
+		}
+	}
+}
+
+func setPtr(field reflect.Value) {
+	if field.IsNil() {
+		field.Set(reflect.New(field.Type().Elem()))
+	}
+
+	if field.Type().Implements(reflect.TypeOf((*initializer)(nil)).Elem()) {
+		method := field.MethodByName("SetDefaults")
+		if method.IsValid() {
+			method.Call([]reflect.Value{})
+		}
+	}
+
+	fill(field.Elem())
+}
+
+func setStruct(field reflect.Value) {
+	for i := 0; i < field.NumField(); i++ {
+		fd := field.Field(i)
+		structField := field.Type().Field(i)
+
+		if structField.Tag.Get(parser.TagLabel) == "-" {
+			continue
+		}
+
+		if parser.IsExported(structField) {
+			fill(fd)
+		}
+	}
+}
+
+func setMap(field reflect.Value) {
+	if field.IsNil() {
+		field.Set(reflect.MakeMap(field.Type()))
+	}
+
+	ptrValue := reflect.New(reflect.PtrTo(field.Type().Elem()))
+	fill(ptrValue)
+
+	value := ptrValue.Elem().Elem()
+	key := reflect.ValueOf(parser.MapNamePlaceholder)
+	field.SetMapIndex(key, value)
+}