From 34ef24e14be560df477b43b51f15866c655d97ca Mon Sep 17 00:00:00 2001
From: Andrew Wilkins <axwalk@gmail.com>
Date: Wed, 28 Mar 2018 17:36:58 +0800
Subject: [PATCH] module/apmgometrics: go-metrics gatherer

---
 module/apmgometrics/gatherer.go      | 40 +++++++++++++++++++++
 module/apmgometrics/gatherer_test.go | 54 ++++++++++++++++++++++++++++
 2 files changed, 94 insertions(+)
 create mode 100644 module/apmgometrics/gatherer.go
 create mode 100644 module/apmgometrics/gatherer_test.go

diff --git a/module/apmgometrics/gatherer.go b/module/apmgometrics/gatherer.go
new file mode 100644
index 000000000..257233936
--- /dev/null
+++ b/module/apmgometrics/gatherer.go
@@ -0,0 +1,40 @@
+package apmgometrics
+
+import (
+	"context"
+
+	"github.com/rcrowley/go-metrics"
+
+	"github.com/elastic/apm-agent-go"
+)
+
+// Wrap wraps r, a go-metrics Registry, so that it can be used
+// as an elasticapm.MetricsGatherer.
+func Wrap(r metrics.Registry) elasticapm.MetricsGatherer {
+	return gatherer{r}
+}
+
+type gatherer struct {
+	r metrics.Registry
+}
+
+// GatherMEtrics gathers metrics into m.
+func (g gatherer) GatherMetrics(ctx context.Context, m *elasticapm.Metrics) error {
+	g.r.Each(func(name string, v interface{}) {
+		switch v := v.(type) {
+		case metrics.Counter:
+			// NOTE(axw) in go-metrics, counters can go up and down,
+			// hence we use a gauge here. Should we provide config
+			// to allow a user to specify that a counter is always
+			// increasing, hence represent it as a counter type?
+			m.AddGauge(name, nil, float64(v.Count()))
+		case metrics.Gauge:
+			m.AddGauge(name, nil, float64(v.Value()))
+		case metrics.GaugeFloat64:
+			m.AddGauge(name, nil, v.Value())
+		default:
+			// TODO(axw) Meter, Timer, Histogram, EWMA
+		}
+	})
+	return nil
+}
diff --git a/module/apmgometrics/gatherer_test.go b/module/apmgometrics/gatherer_test.go
new file mode 100644
index 000000000..9c002bfc1
--- /dev/null
+++ b/module/apmgometrics/gatherer_test.go
@@ -0,0 +1,54 @@
+package apmgometrics_test
+
+import (
+	"testing"
+
+	"github.com/rcrowley/go-metrics"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/elastic/apm-agent-go"
+	"github.com/elastic/apm-agent-go/model"
+	"github.com/elastic/apm-agent-go/module/apmgometrics"
+	"github.com/elastic/apm-agent-go/transport/transporttest"
+)
+
+func TestGatherer(t *testing.T) {
+	r := metrics.NewRegistry()
+	httpReqsTotal := metrics.GetOrRegisterCounter("http.requests_total", r)
+	httpReqsInflight := metrics.GetOrRegisterGauge("http.requests_inflight", r)
+	httpReqsTotal.Inc(123)
+	httpReqsInflight.Update(10)
+
+	g := apmgometrics.Wrap(r)
+	metrics := gatherMetrics(g)
+
+	assert.Equal(t, []*model.Metrics{{
+		Samples: map[string]model.Metric{
+			"http.requests_total": {
+				// go-metrics's counters are gauges
+				// by our definition, hence the Value
+				// field is set and Count is not.
+				Value: newFloat64(123),
+			},
+			"http.requests_inflight": {
+				Value: newFloat64(10),
+			},
+		},
+	}}, metrics)
+}
+
+func gatherMetrics(g elasticapm.MetricsGatherer) []*model.Metrics {
+	tracer, transport := transporttest.NewRecorderTracer()
+	defer tracer.Close()
+	tracer.AddMetricsGatherer(g)
+	tracer.SendMetrics(nil)
+	metrics := transport.Payloads()[0].Metrics()
+	for _, m := range metrics {
+		m.Timestamp = model.Time{}
+	}
+	return metrics
+}
+
+func newFloat64(v float64) *float64 {
+	return &v
+}