[Issue #22] Add EventBroadcaster metrics (#49)

metrics_prometheus.go

@@ -0,0 +1,123 @@
+package aether
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// PrometheusMetricsAdapter exposes BroadcasterMetrics as Prometheus metrics.
+// It implements prometheus.Collector and can be registered with a Prometheus registry.
+type PrometheusMetricsAdapter struct {
+	metrics BroadcasterMetrics
+
+	eventsPublishedDesc     *prometheus.Desc
+	eventsReceivedDesc      *prometheus.Desc
+	activeSubscriptionsDesc *prometheus.Desc
+	publishErrorsDesc       *prometheus.Desc
+	subscribeErrorsDesc     *prometheus.Desc
+	droppedEventsDesc       *prometheus.Desc
+}
+
+// NewPrometheusMetricsAdapter creates a new PrometheusMetricsAdapter that wraps
+// a BroadcasterMetrics implementation and exposes it as Prometheus metrics.
+//
+// The adapter implements prometheus.Collector and should be registered with
+// a Prometheus registry:
+//
+//	eb := aether.NewEventBus()
+//	adapter := aether.NewPrometheusMetricsAdapter(eb.Metrics())
+//	prometheus.MustRegister(adapter)
+func NewPrometheusMetricsAdapter(metrics BroadcasterMetrics) *PrometheusMetricsAdapter {
+	return &PrometheusMetricsAdapter{
+		metrics: metrics,
+		eventsPublishedDesc: prometheus.NewDesc(
+			"aether_events_published_total",
+			"Total number of events published per namespace",
+			[]string{"namespace"},
+			nil,
+		),
+		eventsReceivedDesc: prometheus.NewDesc(
+			"aether_events_received_total",
+			"Total number of events received per namespace",
+			[]string{"namespace"},
+			nil,
+		),
+		activeSubscriptionsDesc: prometheus.NewDesc(
+			"aether_active_subscriptions",
+			"Number of active subscriptions per namespace",
+			[]string{"namespace"},
+			nil,
+		),
+		publishErrorsDesc: prometheus.NewDesc(
+			"aether_publish_errors_total",
+			"Total number of publish errors per namespace",
+			[]string{"namespace"},
+			nil,
+		),
+		subscribeErrorsDesc: prometheus.NewDesc(
+			"aether_subscribe_errors_total",
+			"Total number of subscribe errors per namespace",
+			[]string{"namespace"},
+			nil,
+		),
+		droppedEventsDesc: prometheus.NewDesc(
+			"aether_dropped_events_total",
+			"Total number of dropped events per namespace",
+			[]string{"namespace"},
+			nil,
+		),
+	}
+}
+
+// Describe implements prometheus.Collector.
+func (a *PrometheusMetricsAdapter) Describe(ch chan<- *prometheus.Desc) {
+	ch <- a.eventsPublishedDesc
+	ch <- a.eventsReceivedDesc
+	ch <- a.activeSubscriptionsDesc
+	ch <- a.publishErrorsDesc
+	ch <- a.subscribeErrorsDesc
+	ch <- a.droppedEventsDesc
+}
+
+// Collect implements prometheus.Collector.
+func (a *PrometheusMetricsAdapter) Collect(ch chan<- prometheus.Metric) {
+	namespaces := a.metrics.Namespaces()
+
+	for _, ns := range namespaces {
+		ch <- prometheus.MustNewConstMetric(
+			a.eventsPublishedDesc,
+			prometheus.CounterValue,
+			float64(a.metrics.EventsPublished(ns)),
+			ns,
+		)
+		ch <- prometheus.MustNewConstMetric(
+			a.eventsReceivedDesc,
+			prometheus.CounterValue,
+			float64(a.metrics.EventsReceived(ns)),
+			ns,
+		)
+		ch <- prometheus.MustNewConstMetric(
+			a.activeSubscriptionsDesc,
+			prometheus.GaugeValue,
+			float64(a.metrics.ActiveSubscriptions(ns)),
+			ns,
+		)
+		ch <- prometheus.MustNewConstMetric(
+			a.publishErrorsDesc,
+			prometheus.CounterValue,
+			float64(a.metrics.PublishErrors(ns)),
+			ns,
+		)
+		ch <- prometheus.MustNewConstMetric(
+			a.subscribeErrorsDesc,
+			prometheus.CounterValue,
+			float64(a.metrics.SubscribeErrors(ns)),
+			ns,
+		)
+		ch <- prometheus.MustNewConstMetric(
+			a.droppedEventsDesc,
+			prometheus.CounterValue,
+			float64(a.metrics.DroppedEvents(ns)),
+			ns,
+		)
+	}
+}