Apply default buckets in Prometheus Factory (#90)

Signed-off-by: Konstantinos Moraitis <[email protected]>

Co-authored-by: Yuri Shkuro <[email protected]>

metrics/prometheus/factory.go

@@ -197,12 +197,13 @@ func (f *Factory) Histogram(options metrics.HistogramOptions) metrics.Histogram
 		help = options.Name
 	}
 	name := f.subScope(options.Name)
+	buckets := f.selectBuckets(options.Buckets)
 	tags := f.mergeTags(options.Tags)
 	labelNames := f.tagNames(tags)
 	opts := prometheus.HistogramOpts{
 		Name:    name,
 		Help:    help,
-		Buckets: options.Buckets,
+		Buckets: buckets,
 	}
 	hv := f.cache.getOrMakeHistogramVec(opts, labelNames)
 	return &histogram{
@@ -293,6 +294,13 @@ func (f *Factory) tagsAsLabelValues(labels []string, tags map[string]string) []s
 	return ret
 }
 
+func (f *Factory) selectBuckets(buckets []float64) []float64 {
+	if len(buckets) > 0 {
+		return buckets
+	}
+	return f.buckets
+}
+
 func counterNamingConvention(name string) string {
 	if !strings.HasSuffix(name, "_total") {
 		name += "_total"

metrics/prometheus/factory_test.go

@@ -361,6 +361,27 @@ func TestHistogramCustomBuckets(t *testing.T) {
 	assert.Len(t, m1.GetHistogram().GetBucket(), 1)
 }
 
+func TestHistogramDefaultBuckets(t *testing.T) {
+	registry := prometheus.NewPedanticRegistry()
+	f1 := New(WithRegisterer(registry), WithBuckets([]float64{1.5}))
+	// dot and dash in the metric name will be replaced with underscore
+	t1 := f1.Histogram(metrics.HistogramOptions{
+		Name:    "bender.bending-rodriguez",
+		Tags:    map[string]string{"x": "y"},
+		Buckets: nil,
+	})
+	t1.Record(1)
+	t1.Record(2)
+
+	snapshot, err := registry.Gather()
+	require.NoError(t, err)
+
+	m1 := findMetric(t, snapshot, "bender_bending_rodriguez", map[string]string{"x": "y"})
+	assert.EqualValues(t, 2, m1.GetHistogram().GetSampleCount(), "%+v", m1)
+	assert.EqualValues(t, 3, m1.GetHistogram().GetSampleSum(), "%+v", m1)
+	assert.Len(t, m1.GetHistogram().GetBucket(), 1)
+}
+
 func findMetric(t *testing.T, snapshot []*promModel.MetricFamily, name string, tags map[string]string) *promModel.Metric {
 	for _, mf := range snapshot {
 		if mf.GetName() != name {