TUN-2506: Expose active streams metrics

h2mux/muxmetrics.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/golang-collections/collections/queue"
+	"github.com/prometheus/client_golang/prometheus"
 
 	log "github.com/sirupsen/logrus"
 )
@@ -299,3 +300,14 @@ func (r *rate) get() (curr, min, max uint64) {
 	defer r.lock.RUnlock()
 	return r.curr, r.min, r.max
 }
+
+func NewActiveStreamsMetrics(namespace, subsystem string) prometheus.Gauge {
+	activeStreams := prometheus.NewGauge(prometheus.GaugeOpts{
+		Namespace: namespace,
+		Subsystem: subsystem,
+		Name:      "active_streams",
+		Help:      "Number of active streams created by all muxers.",
+	})
+	prometheus.MustRegister(activeStreams)
+	return activeStreams
+}