zero/telemetry: collect limited core metrics (#5142)

internal/zero/telemetry/opencensus/opencensus.go

@@ -0,0 +1,56 @@
+// Package opencensus is a provider of opencensus based telemetry metrics to the zero telemetry system.
+package opencensus
+
+import (
+	"context"
+	"sync/atomic"
+
+	"go.opentelemetry.io/otel/bridge/opencensus"
+	"go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/metric/metricdata"
+
+	"github.com/pomerium/pomerium/internal/sets"
+)
+
+type Producer struct {
+	producer metric.Producer
+	filter   atomic.Pointer[sets.Hash[string]]
+}
+
+var _ metric.Producer = (*Producer)(nil)
+
+func New() *Producer {
+	p := &Producer{
+		producer: opencensus.NewMetricProducer(),
+	}
+	p.SetFilter(nil)
+	return p
+}
+
+func (p *Producer) Produce(ctx context.Context) ([]metricdata.ScopeMetrics, error) {
+	filter := p.filter.Load()
+	metrics, err := p.producer.Produce(ctx)
+	if err != nil {
+		return nil, err
+	}
+	var out []metricdata.ScopeMetrics
+	for _, sm := range metrics {
+		var m []metricdata.Metrics
+		for _, metric := range sm.Metrics {
+			if filter.Has(metric.Name) {
+				m = append(m, metric)
+			}
+		}
+		if len(m) > 0 {
+			out = append(out, metricdata.ScopeMetrics{
+				Scope:   sm.Scope,
+				Metrics: m,
+			})
+		}
+	}
+	return out, nil
+}
+
+func (p *Producer) SetFilter(names []string) {
+	p.filter.Store(sets.NewHash(names...))
+}