Add subscribed topics gauge metric (#339)

* Add subscribe/unsubscribe gauge metric

* Emit unsubscribe in defer

pkg/api/message/v1/service.go

@@ -178,7 +178,7 @@ func (s *Service) Subscribe(req *proto.SubscribeRequest, stream proto.MessageApi
 	// See: https://github.com/xmtp/libxmtp/pull/58
 	_ = stream.SendHeader(metadata.Pairs("subscribed", "true"))
 
-	metrics.EmitSubscribeTopicsLength(stream.Context(), log, len(req.ContentTopics))
+	metrics.EmitSubscribeTopics(stream.Context(), log, len(req.ContentTopics))
 
 	var streamLock sync.Mutex
 	for _, topic := range req.ContentTopics {
@@ -211,17 +211,20 @@ func (s *Service) Subscribe(req *proto.SubscribeRequest, stream proto.MessageApi
 		}
 		defer func() {
 			_ = sub.Unsubscribe()
+			metrics.EmitUnsubscribeTopics(stream.Context(), log, 1)
 		}()
 	}
 
 	select {
 	case <-stream.Context().Done():
 		log.Debug("stream closed")
-		return nil
+		break
 	case <-s.ctx.Done():
 		log.Info("service closed")
-		return nil
+		break
 	}
+
+	return nil
 }
 
 func (s *Service) Subscribe2(stream proto.MessageApi_Subscribe2Server) error {
@@ -264,6 +267,7 @@ func (s *Service) Subscribe2(stream proto.MessageApi_Subscribe2Server) error {
 		for _, sub := range subs {
 			_ = sub.Unsubscribe()
 		}
+		metrics.EmitUnsubscribeTopics(stream.Context(), log, len(subs))
 	}()
 	var streamLock sync.Mutex
 	for {
@@ -280,7 +284,7 @@ func (s *Service) Subscribe2(stream proto.MessageApi_Subscribe2Server) error {
 			}
 			log.Info("updating subscription", zap.Int("num_content_topics", len(req.ContentTopics)))
 
-			metrics.EmitSubscribeTopicsLength(stream.Context(), log, len(req.ContentTopics))
+			metrics.EmitSubscribeTopics(stream.Context(), log, len(req.ContentTopics))
 
 			topics := map[string]bool{}
 			for _, topic := range req.ContentTopics {
@@ -313,13 +317,16 @@ func (s *Service) Subscribe2(stream proto.MessageApi_Subscribe2Server) error {
 			}
 
 			// If subscription not in topic, then unsubscribe.
+			var count int
 			for topic, sub := range subs {
 				if topics[topic] {
 					continue
 				}
 				_ = sub.Unsubscribe()
 				delete(subs, topic)
+				count++
 			}
+			metrics.EmitUnsubscribeTopics(stream.Context(), log, count)
 		}
 	}
 }

pkg/metrics/api-subscribe.go

@@ -0,0 +1,36 @@
+package metrics
+
+import (
+	"context"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"go.uber.org/zap"
+)
+
+var subscribedTopics = prometheus.NewGaugeVec(
+	prometheus.GaugeOpts{
+		Name: "xmtp_subscribed_topics",
+		Help: "Number of subscribed topics",
+	},
+	appClientVersionTagKeys,
+)
+
+var subscribeTopicsLength = prometheus.NewHistogramVec(
+	prometheus.HistogramOpts{
+		Name:    "xmtp_subscribe_topics_length",
+		Help:    "Number of subscribed topics per request",
+		Buckets: []float64{1, 2, 4, 8, 16, 50, 100, 10000, 100000},
+	},
+	appClientVersionTagKeys,
+)
+
+func EmitSubscribeTopics(ctx context.Context, log *zap.Logger, topics int) {
+	labels := contextLabels(ctx)
+	subscribeTopicsLength.With(labels).Observe(float64(topics))
+	subscribedTopics.With(labels).Add(float64(topics))
+}
+
+func EmitUnsubscribeTopics(ctx context.Context, log *zap.Logger, topics int) {
+	labels := contextLabels(ctx)
+	subscribedTopics.With(labels).Add(-float64(topics))
+}

pkg/metrics/api.go

@@ -67,20 +67,6 @@ func EmitAPIRequest(ctx context.Context, log *zap.Logger, fields []zapcore.Field
 	apiRequestsDuration.With(labels).Observe(float64(duration / time.Millisecond))
 }
 
-var subscribeTopicsLength = prometheus.NewHistogramVec(
-	prometheus.HistogramOpts{
-		Name:    "xmtp_subscribe_topics_length",
-		Help:    "Number of subscribed topics per request",
-		Buckets: []float64{1, 2, 4, 8, 16, 50, 100, 10000, 100000},
-	},
-	appClientVersionTagKeys,
-)
-
-func EmitSubscribeTopicsLength(ctx context.Context, log *zap.Logger, topics int) {
-	labels := contextLabels(ctx)
-	subscribeTopicsLength.With(labels).Observe(float64(topics))
-}
-
 var publishedEnvelopeSize = prometheus.NewHistogramVec(
 	prometheus.HistogramOpts{
 		Name:    "xmtp_published_envelope",

pkg/metrics/metrics.go

@@ -59,6 +59,7 @@ func registerCollectors(reg prometheus.Registerer) {
 		apiRequests,
 		apiRequestsDuration,
 		subscribeTopicsLength,
+		subscribedTopics,
 		publishedEnvelopeSize,
 		publishedEnvelopeCount,
 		queryDuration,