Resubmit a stored event as a new undelivered event (closes #250)

internal/metrics/metrics.go

@@ -83,6 +83,7 @@ type Set struct {
 	deliveriesFailed    *prometheus.CounterVec
 	deliveryRetries     *prometheus.CounterVec
 	deliveryReplays     *prometheus.CounterVec
+	eventsResubmitted   prometheus.Counter
 	deliveryDuration    *prometheus.HistogramVec
 	deliveriesPending   *prometheus.GaugeVec
 	deliveriesRetrying  *prometheus.GaugeVec
@@ -166,6 +167,23 @@ func (s *Set) DeliveryReplayed(t database.TargetType) {
 		Inc()
 }
 
+// EventResubmitted counts one stored event an operator re-injected
+// from the event log.
+//
+// It counts the operator action once, not the deliveries it fans out
+// to: those already move the attempt, outcome and duration series, and
+// the new event moves events_received_total, since it is a stored
+// event that the delivery side will be compared against. This counter
+// is what separates a resubmitted event from a received one.
+//
+// It carries no labels. The only label available at the call site
+// would be the route pattern, which has exactly one value and so would
+// distinguish nothing; the target types the event fans out to belong
+// to the delivery series, not to this one.
+func (s *Set) EventResubmitted() {
+	s.eventsResubmitted.Inc()
+}
+
 // DeliveryStatusChanged counts a delivery's transition into a new
 // status. The mapping from status to counter lives here, next to the
 // collectors, so the engine has a single call for every transition it
@@ -298,6 +316,15 @@ func (s *Set) registerCounters(factory promauto.Factory) {
 		},
 		[]string{targetTypeLabel},
 	)
+
+	s.eventsResubmitted = factory.NewCounter(
+		prometheus.CounterOpts{
+			Namespace: namespace,
+			Name:      "events_resubmitted_total",
+			Help: "Stored events an operator re-injected from " +
+				"the event log as new events.",
+		},
+	)
 }
 
 func (s *Set) registerGauges(factory promauto.Factory) {