add "chain_id" label for all metrics (#3123)

* add "chain_id" label for all metrics

Refs #3082

* fix labels extraction

state/metrics.go

@@ -7,14 +7,26 @@ import (
 	stdprometheus "github.com/prometheus/client_golang/prometheus"
 )
 
-const MetricsSubsystem = "state"
+const (
+	// MetricsSubsystem is a subsystem shared by all metrics exposed by this
+	// package.
+	MetricsSubsystem = "state"
+)
 
+// Metrics contains metrics exposed by this package.
 type Metrics struct {
 	// Time between BeginBlock and EndBlock.
 	BlockProcessingTime metrics.Histogram
 }
 
-func PrometheusMetrics(namespace string) *Metrics {
+// PrometheusMetrics returns Metrics build using Prometheus client library.
+// Optionally, labels can be provided along with their values ("foo",
+// "fooValue").
+func PrometheusMetrics(namespace string, labelsAndValues ...string) *Metrics {
+	labels := []string{}
+	for i := 0; i < len(labelsAndValues); i += 2 {
+		labels = append(labels, labelsAndValues[i])
+	}
 	return &Metrics{
 		BlockProcessingTime: prometheus.NewHistogramFrom(stdprometheus.HistogramOpts{
 			Namespace: namespace,
@@ -22,10 +34,11 @@ func PrometheusMetrics(namespace string) *Metrics {
 			Name:      "block_processing_time",
 			Help:      "Time between BeginBlock and EndBlock in ms.",
 			Buckets:   stdprometheus.LinearBuckets(1, 10, 10),
-		}, []string{}),
+		}, labels).With(labelsAndValues...),
 	}
 }
 
+// NopMetrics returns no-op Metrics.
 func NopMetrics() *Metrics {
 	return &Metrics{
 		BlockProcessingTime: discard.NewHistogram(),