core: add state height to prometheus metrics

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/core/blockchain.go

@@ -1272,6 +1272,7 @@ func (bc *Blockchain) updateStateHeight(newHeight uint32) error {
 	if err != nil {
 		return errors.WithMessage(err, "can't get current state root height")
 	} else if newHeight == h+1 {
+		updateStateHeightMetric(newHeight)
 		return bc.dao.PutCurrentStateRootHeight(h + 1)
 	}
 	return nil

pkg/core/prometheus.go

@@ -30,6 +30,14 @@ var (
 			Namespace: "neogo",
 		},
 	)
+	//stateHeight prometheus metric.
+	stateHeight = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Help:      "Current verified state height",
+			Name:      "current_state_height",
+			Namespace: "neogo",
+		},
+	)
 )
 
 func init() {
@@ -51,3 +59,7 @@ func updateHeaderHeightMetric(hHeight int) {
 func updateBlockHeightMetric(bHeight uint32) {
 	blockHeight.Set(float64(bHeight))
 }
+
+func updateStateHeightMetric(sHeight uint32) {
+	stateHeight.Set(float64(sHeight))
+}