Add metric to track unique metric names the exporter is tracking

Signed-off-by: Brian Akins <brian@akins.org>

exporter.go

@@ -102,6 +102,7 @@ func (c *CounterContainer) Get(metricName string, labels prometheus.Labels, help
 
 	counterVec, ok := c.Elements[mapKey]
 	if !ok {
+		metricsCount.Inc()
 		counterVec = prometheus.NewCounterVec(prometheus.CounterOpts{
 			Name: metricName,
 			Help: help,
@@ -138,6 +139,7 @@ func (c *GaugeContainer) Get(metricName string, labels prometheus.Labels, help s
 
 	gaugeVec, ok := c.Elements[mapKey]
 	if !ok {
+		metricsCount.Inc()
 		gaugeVec = prometheus.NewGaugeVec(prometheus.GaugeOpts{
 			Name: metricName,
 			Help: help,
@@ -176,6 +178,7 @@ func (c *SummaryContainer) Get(metricName string, labels prometheus.Labels, help
 
 	summaryVec, ok := c.Elements[mapKey]
 	if !ok {
+		metricsCount.Inc()
 		quantiles := c.mapper.Defaults.Quantiles
 		if mapping != nil && mapping.Quantiles != nil && len(mapping.Quantiles) > 0 {
 			quantiles = mapping.Quantiles
@@ -224,6 +227,7 @@ func (c *HistogramContainer) Get(metricName string, labels prometheus.Labels, he
 
 	histogramVec, ok := c.Elements[mapKey]
 	if !ok {
+		metricsCount.Inc()
 		buckets := c.mapper.Defaults.Buckets
 		if mapping != nil && mapping.Buckets != nil && len(mapping.Buckets) > 0 {
 			buckets = mapping.Buckets

telemetry.go

@@ -116,6 +116,12 @@ var (
 		},
 		[]string{"action"},
 	)
+	metricsCount = prometheus.NewCounter(
+		prometheus.CounterOpts{
+			Name: "statsd_exporter_metrics_total",
+			Help: "The total number of metrics.",
+		},
+	)
 )
 
 func init() {
@@ -135,4 +141,5 @@ func init() {
 	prometheus.MustRegister(conflictingEventStats)
 	prometheus.MustRegister(errorEventStats)
 	prometheus.MustRegister(eventsActions)
+	prometheus.MustRegister(metricsCount)
 }