Parse NaN values from summary types in prometheus input (#6997)

(cherry picked from commit 0710cc7)

plugins/inputs/prometheus/parser.go

@@ -15,7 +15,6 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/metric"
-
 	"github.com/matttproud/golang_protobuf_extensions/pbutil"
 	dto "github.com/prometheus/client_model/go"
 	"github.com/prometheus/common/expfmt"
@@ -115,14 +114,13 @@ func makeQuantilesV2(m *dto.Metric, tags map[string]string, metricName string, m
 	for _, q := range m.GetSummary().Quantile {
 		newTags := tags
 		fields = make(map[string]interface{})
-		if !math.IsNaN(q.GetValue()) {
-			newTags["quantile"] = fmt.Sprint(q.GetQuantile())
-			fields[metricName] = float64(q.GetValue())
 
-			quantileMetric, err := metric.New("prometheus", newTags, fields, t, valueType(metricType))
-			if err == nil {
-				metrics = append(metrics, quantileMetric)
-			}
+		newTags["quantile"] = fmt.Sprint(q.GetQuantile())
+		fields[metricName] = float64(q.GetValue())
+
+		quantileMetric, err := metric.New("prometheus", newTags, fields, t, valueType(metricType))
+		if err == nil {
+			metrics = append(metrics, quantileMetric)
 		}
 	}
 	return metrics

plugins/inputs/prometheus/prometheus_test.go

@@ -2,12 +2,14 @@ package prometheus
 
 import (
 	"fmt"
+	"math"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
 	"testing"
 	"time"
 
+	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/testutil"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -148,6 +150,69 @@ func TestPrometheusGeneratesSummaryMetricsV2(t *testing.T) {
 
 }
 
+func TestSummaryMayContainNaN(t *testing.T) {
+	const data = `# HELP go_gc_duration_seconds A summary of the GC invocation durations.
+# TYPE go_gc_duration_seconds summary
+go_gc_duration_seconds{quantile="0"} NaN
+go_gc_duration_seconds{quantile="1"} NaN
+go_gc_duration_seconds_sum 42.0
+go_gc_duration_seconds_count 42
+`
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintln(w, data)
+	}))
+	defer ts.Close()
+
+	p := &Prometheus{
+		URLs:          []string{ts.URL},
+		URLTag:        "",
+		MetricVersion: 2,
+	}
+
+	var acc testutil.Accumulator
+
+	err := p.Gather(&acc)
+	require.NoError(t, err)
+
+	expected := []telegraf.Metric{
+		testutil.MustMetric(
+			"prometheus",
+			map[string]string{
+				"quantile": "0",
+			},
+			map[string]interface{}{
+				"go_gc_duration_seconds": math.NaN(),
+			},
+			time.Unix(0, 0),
+			telegraf.Summary,
+		),
+		testutil.MustMetric(
+			"prometheus",
+			map[string]string{
+				"quantile": "1",
+			},
+			map[string]interface{}{
+				"go_gc_duration_seconds": math.NaN(),
+			},
+			time.Unix(0, 0),
+			telegraf.Summary,
+		),
+		testutil.MustMetric(
+			"prometheus",
+			map[string]string{},
+			map[string]interface{}{
+				"go_gc_duration_seconds_sum":   42.0,
+				"go_gc_duration_seconds_count": 42.0,
+			},
+			time.Unix(0, 0),
+			telegraf.Summary,
+		),
+	}
+
+	testutil.RequireMetricsEqual(t, expected, acc.GetTelegrafMetrics(),
+		testutil.IgnoreTime(), testutil.SortMetrics())
+}
+
 func TestPrometheusGeneratesGaugeMetricsV2(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprintln(w, sampleGaugeTextFormat)