From c43a2f742e1d764075723b6c04ed55338c5d52b4 Mon Sep 17 00:00:00 2001
From: Steven Normore <steven@xmtp.com>
Date: Thu, 28 Dec 2023 19:10:09 -0500
Subject: [PATCH] Emit subscribed topics metric

---
 go.sum                        |  8 --------
 pkg/api/message/v1/service.go |  4 ++++
 pkg/metrics/api.go            | 14 ++++++++++++++
 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/go.sum b/go.sum
index 165565fe..7f82e8f3 100644
--- a/go.sum
+++ b/go.sum
@@ -1140,14 +1140,6 @@ github.com/xdg/stringprep v1.0.0/go.mod h1:Jhud4/sHMO4oL310DaZAKk9ZaJ08SJfe+sJh0
 github.com/xlab/treeprint v0.0.0-20180616005107-d6fb6747feb6/go.mod h1:ce1O1j6UtZfjr22oyGxGLbauSBp2YVXpARAosm7dHBg=
 github.com/xmtp/go-msgio v0.2.1-0.20220510223757-25a701b79cd3 h1:wzUffJGCTBGXIDyNU+1UBu1fn2Nzo+OQzM1pLrheh58=
 github.com/xmtp/go-msgio v0.2.1-0.20220510223757-25a701b79cd3/go.mod h1:bJREWk+NDnZYjgLQdAi8SUWuq/5pkMme4GqiffEhUF4=
-github.com/xmtp/proto/v3 v3.27.0 h1:G70006UEffkCmWvp9G/7Dywosj1sLm9StR5HWEb891U=
-github.com/xmtp/proto/v3 v3.27.0/go.mod h1:NF2zAjtNpVIhS4tFG19g4L1tJcPZHm81oeDFXltmOiY=
-github.com/xmtp/proto/v3 v3.29.1-0.20231019020501-b49bc6ffb5eb h1:q2lR64lGFehm8m0FtcdRDMeH8MlkMyU4sz235+Ufq9E=
-github.com/xmtp/proto/v3 v3.29.1-0.20231019020501-b49bc6ffb5eb/go.mod h1:NF2zAjtNpVIhS4tFG19g4L1tJcPZHm81oeDFXltmOiY=
-github.com/xmtp/proto/v3 v3.29.1-0.20231019022514-1cc4b0d5a51a h1:kDEPyzhqQO9YdRAfvl21ysitvzWjdu4Ai8YCvHwqqbY=
-github.com/xmtp/proto/v3 v3.29.1-0.20231019022514-1cc4b0d5a51a/go.mod h1:NF2zAjtNpVIhS4tFG19g4L1tJcPZHm81oeDFXltmOiY=
-github.com/xmtp/proto/v3 v3.29.1-0.20231019163152-2a17d00f45f4 h1:Mxnc833msN9gX8DJyELd+E7oUJNHlhbIsZlTd88kg5M=
-github.com/xmtp/proto/v3 v3.29.1-0.20231019163152-2a17d00f45f4/go.mod h1:NF2zAjtNpVIhS4tFG19g4L1tJcPZHm81oeDFXltmOiY=
 github.com/xmtp/proto/v3 v3.30.0 h1:x6LGCWpO2HTQNhUiTXfE0l+u2HSL3Z35p41xhgy6hlw=
 github.com/xmtp/proto/v3 v3.30.0/go.mod h1:NF2zAjtNpVIhS4tFG19g4L1tJcPZHm81oeDFXltmOiY=
 github.com/xrash/smetrics v0.0.0-20201216005158-039620a65673 h1:bAn7/zixMGCfxrRTfdpNzjtPYqr8smhKouy9mxVdGPU=
diff --git a/pkg/api/message/v1/service.go b/pkg/api/message/v1/service.go
index 16797ba5..bb1b256a 100644
--- a/pkg/api/message/v1/service.go
+++ b/pkg/api/message/v1/service.go
@@ -178,6 +178,8 @@ 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))
+
 	var streamLock sync.Mutex
 	for _, topic := range req.ContentTopics {
 		subject := topic
@@ -278,6 +280,8 @@ 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))
+
 			topics := map[string]bool{}
 			for _, topic := range req.ContentTopics {
 				topics[topic] = true
diff --git a/pkg/metrics/api.go b/pkg/metrics/api.go
index 89a81a99..ca9907f0 100644
--- a/pkg/metrics/api.go
+++ b/pkg/metrics/api.go
@@ -57,6 +57,20 @@ func EmitAPIRequest(ctx context.Context, log *zap.Logger, fields []zapcore.Field
 	apiRequests.With(labels).Inc()
 }
 
+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",