[WIP]: broker ErrorHandler option (#1296)

* broker ErrorHandler option

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* rewrite Event interface, add error

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* implement new interface

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* change ErrorHandler func to broker.Handler

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* fix

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

broker/service/subscriber.go

@@ -17,6 +17,7 @@ type serviceSub struct {
 
 type serviceEvent struct {
 	topic   string
+	err     error
 	message *broker.Message
 }
 
@@ -32,6 +33,10 @@ func (s *serviceEvent) Ack() error {
 	return nil
 }
 
+func (s *serviceEvent) Error() error {
+	return s.err
+}
+
 func (s *serviceSub) isClosed() bool {
 	select {
 	case <-s.closed:
@@ -71,14 +76,14 @@ func (s *serviceSub) run() error {
 			return err
 		}
 
-		// TODO: handle error
-		s.handler(&serviceEvent{
+		p := &serviceEvent{
 			topic: s.topic,
 			message: &broker.Message{
 				Header: msg.Header,
 				Body:   msg.Body,
 			},
-		})
+		}
+		p.err = s.handler(p)
 	}
 }