test: add basic otlp histogram test case

Author: clementnuss

otlp_histogram.go

@@ -7,7 +7,7 @@ import (
 	"sync"
 )
 
-var defaultBuckets = []float64{.005, .01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10}
+var defaultUpperBounds = []float64{.005, .01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10}
 
 // OTLP Histogram is a histogram for non-negative values with pre-defined buckets
 //
@@ -70,8 +70,9 @@ func (h *OTLPHistogram) Update(v float64) {
 	}
 	h.mu.Lock()
 	h.sum += v
+	h.count++
 	if bucketIdx == -1 {
-		// +Inf, nothing to do
+		// +Inf, nothing to do, already accounted for in the total count
 	}
 	h.buckets[bucketIdx]++
 	h.mu.Unlock()
@@ -125,18 +126,39 @@ func GetOrCreateOTLPHistogram(name string) *OTLPHistogram {
 	return defaultSet.GetOrCreateOTLPHistogram(name)
 }
 
+func newOTLPHistogram(upperBounds []float64) *OTLPHistogram {
+	validateBuckets(&upperBounds)
+	oh := OTLPHistogram{
+		upperBounds: upperBounds,
+		buckets:     make([]uint64, len(upperBounds)),
+	}
+
+	return &oh
+}
+
+func validateBuckets(upperBounds *[]float64) {
+	// TODO
+	if len(*upperBounds) == 0 {
+		panic("not good")
+	}
+}
+
 func (h *OTLPHistogram) marshalTo(prefix string, w io.Writer) {
 	cumulativeSum := uint64(0)
 	h.mu.Lock()
+	count := h.count
+	sum := h.sum
+	if count == 0 {
+		h.mu.Unlock()
+		return
+	}
 	for i, ub := range h.upperBounds {
 		cumulativeSum += h.buckets[i]
 		tag := fmt.Sprintf(`le="%v"`, ub)
 		metricName := addTag(prefix, tag)
 		name, labels := splitMetricName(metricName)
 		fmt.Fprintf(w, "%s_bucket%s %d\n", name, labels, cumulativeSum)
 	}
-	count := h.count
-	sum := h.sum
 	h.mu.Unlock()
 
 	tag := fmt.Sprintf("le=%q", "+Inf")

otlp_histogram_test.go

@@ -0,0 +1,42 @@
+package metrics
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestOTLPHistogramSerial(t *testing.T) {
+	name := "TestOTLPHistogramSerial"
+	h := NewOTLPHistogram(name)
+
+	// Verify that the histogram is invisible in the output of WritePrometheus when it has no data.
+	var bb bytes.Buffer
+	WritePrometheus(&bb, false)
+	result := bb.String()
+	if strings.Contains(result, name) {
+		t.Fatalf("histogram %s shouldn't be visible in the WritePrometheus output; got\n%s", name, result)
+	}
+
+	// Write data to histogram
+	for i := 98; i < 218; i++ {
+		h.Update(float64(i)*1e-4)
+	}
+
+	// Make sure the histogram prints <prefix>_bucket on marshalTo call
+	testMarshalTo(t, h, "prefix", `prefix_bucket{le="0.005"} 0
+prefix_bucket{le="0.01"} 3
+prefix_bucket{le="0.025"} 120
+prefix_bucket{le="0.05"} 120
+prefix_bucket{le="0.1"} 120
+prefix_bucket{le="0.25"} 120
+prefix_bucket{le="0.5"} 120
+prefix_bucket{le="1"} 120
+prefix_bucket{le="2.5"} 120
+prefix_bucket{le="5"} 120
+prefix_bucket{le="10"} 120
+prefix_bucket{le="+Inf"} 120
+prefix_sum 1.8900000000000003
+prefix_count 120
+`)
+}

set.go

@@ -139,7 +139,7 @@ func (s *Set) GetOrCreateHistogram(name string) *Histogram {
 //
 // The returned histogram is safe to use from concurrent goroutines.
 func (s *Set) NewOTLPHistogram(name string) *OTLPHistogram {
-	h := &OTLPHistogram{}
+	h := newOTLPHistogram(defaultUpperBounds)
 	s.registerMetric(name, h)
 	return h
 }
@@ -168,7 +168,7 @@ func (s *Set) GetOrCreateOTLPHistogram(name string) *OTLPHistogram {
 		}
 		nmNew := &namedMetric{
 			name:   name,
-			metric: &OTLPHistogram{},
+			metric: newOTLPHistogram(defaultUpperBounds),
 		}
 		s.mu.Lock()
 		nm = s.m[name]