Add XML payload support

Fixes #238

vendor/github.com/clbanning/mxj/rename.go

@@ -0,0 +1,54 @@
+package mxj
+
+import (
+	"errors"
+	"strings"
+)
+
+// RenameKey renames a key in a Map.
+// It works only for nested maps. It doesn't work for cases when it buried in a list.
+func (mv Map) RenameKey(path string, newName string) error {
+	if !mv.Exists(path) {
+		return errors.New("RenameKey: path not found: " + path)
+	}
+	if mv.Exists(parentPath(path) + "." + newName) {
+		return errors.New("RenameKey: key already exists: " + newName)
+	}
+
+	m := map[string]interface{}(mv)
+	return renameKey(m, path, newName)
+}
+
+func renameKey(m interface{}, path string, newName string) error {
+	val, err := prevValueByPath(m, path)
+	if err != nil {
+		return err
+	}
+
+	oldName := lastKey(path)
+	val[newName] = val[oldName]
+	delete(val, oldName)
+
+	return nil
+}
+
+// returns a value which contains a last key in the path
+// For example: prevValueByPath("a.b.c", {a{b{c: 3}}}) returns {c: 3}
+func prevValueByPath(m interface{}, path string) (map[string]interface{}, error) {
+	keys := strings.Split(path, ".")
+
+	switch mValue := m.(type) {
+	case map[string]interface{}:
+		for key, value := range mValue {
+			if key == keys[0] {
+				if len(keys) == 1 {
+					return mValue, nil
+				} else {
+					// keep looking for the full path to the key
+					return prevValueByPath(value, strings.Join(keys[1:], "."))
+				}
+			}
+		}
+	}
+	return nil, errors.New("prevValueByPath: didn't find path – " + path)
+}