Add basic OCPP support (#395)

util/cache.go

@@ -1,6 +1,7 @@
 package util
 
 import (
+	"errors"
 	"sync"
 )
 
@@ -91,3 +92,15 @@ func (c *Cache) Get(key string) Param {
 
 	return Param{}
 }
+
+// GetChecked returns checked value from cache
+func (c *Cache) GetChecked(id int, key string) (res Param, err error) {
+	pid := Param{LoadPoint: &id, Key: key}
+
+	res = c.Get(pid.UniqueID())
+	if res.Key == "" {
+		err = errors.New("not found")
+	}
+
+	return res, err
+}