From f2dded5b90fba2083e00980c4a2c7d5801428950 Mon Sep 17 00:00:00 2001
From: Daniel Nelson <daniel.nelson@influxdb.com>
Date: Tue, 30 Jun 2020 11:30:34 -0700
Subject: [PATCH] Allow histograms with no buckets and summary without
 quantiles (#7740)

---
 .../prometheus_client_v2_test.go              | 59 +++++++++++++++++++
 plugins/serializers/prometheus/collection.go  |  8 ---
 .../serializers/prometheus/prometheus_test.go | 26 ++++++++
 3 files changed, 85 insertions(+), 8 deletions(-)

diff --git a/plugins/outputs/prometheus_client/prometheus_client_v2_test.go b/plugins/outputs/prometheus_client/prometheus_client_v2_test.go
index 3404ab2ed..27be9103b 100644
--- a/plugins/outputs/prometheus_client/prometheus_client_v2_test.go
+++ b/plugins/outputs/prometheus_client/prometheus_client_v2_test.go
@@ -48,6 +48,34 @@ func TestMetricVersion2(t *testing.T) {
 # HELP cpu_time_idle Telegraf collected metric
 # TYPE cpu_time_idle untyped
 cpu_time_idle{host="example.org"} 42
+`),
+		},
+		{
+			name: "summary no quantiles",
+			output: &PrometheusClient{
+				Listen:            ":0",
+				MetricVersion:     2,
+				CollectorsExclude: []string{"gocollector", "process"},
+				Path:              "/metrics",
+				Log:               Logger,
+			},
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{},
+					map[string]interface{}{
+						"rpc_duration_seconds_sum":   1.7560473e+07,
+						"rpc_duration_seconds_count": 2693,
+					},
+					time.Unix(0, 0),
+					telegraf.Summary,
+				),
+			},
+			expected: []byte(`
+# HELP rpc_duration_seconds Telegraf collected metric
+# TYPE rpc_duration_seconds summary
+rpc_duration_seconds_sum 1.7560473e+07
+rpc_duration_seconds_count 2693
 `),
 		},
 		{
@@ -239,6 +267,37 @@ cpu_usage_idle_bucket{cpu="cpu1",le="100"} 20
 cpu_usage_idle_bucket{cpu="cpu1",le="+Inf"} 20
 cpu_usage_idle_sum{cpu="cpu1"} 2000
 cpu_usage_idle_count{cpu="cpu1"} 20
+`),
+		},
+		{
+			name: "histogram no buckets",
+			output: &PrometheusClient{
+				Listen:            ":0",
+				MetricVersion:     2,
+				CollectorsExclude: []string{"gocollector", "process"},
+				Path:              "/metrics",
+				Log:               Logger,
+			},
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"cpu",
+					map[string]string{
+						"cpu": "cpu1",
+					},
+					map[string]interface{}{
+						"usage_idle_sum":   2000.0,
+						"usage_idle_count": 20.0,
+					},
+					time.Unix(0, 0),
+					telegraf.Histogram,
+				),
+			},
+			expected: []byte(`
+# HELP cpu_usage_idle Telegraf collected metric
+# TYPE cpu_usage_idle histogram
+cpu_usage_idle_bucket{cpu="cpu1",le="+Inf"} 20
+cpu_usage_idle_sum{cpu="cpu1"} 2000
+cpu_usage_idle_count{cpu="cpu1"} 20
 `),
 		},
 	}
diff --git a/plugins/serializers/prometheus/collection.go b/plugins/serializers/prometheus/collection.go
index 10e85de07..d37ecaaaf 100644
--- a/plugins/serializers/prometheus/collection.go
+++ b/plugins/serializers/prometheus/collection.go
@@ -446,10 +446,6 @@ func (c *Collection) GetProto() []*dto.MetricFamily {
 					})
 				}
 
-				if len(buckets) == 0 {
-					continue
-				}
-
 				m.Histogram = &dto.Histogram{
 					Bucket:      buckets,
 					SampleCount: proto.Uint64(metric.Histogram.Count),
@@ -464,10 +460,6 @@ func (c *Collection) GetProto() []*dto.MetricFamily {
 					})
 				}
 
-				if len(quantiles) == 0 {
-					continue
-				}
-
 				m.Summary = &dto.Summary{
 					Quantile:    quantiles,
 					SampleCount: proto.Uint64(metric.Summary.Count),
diff --git a/plugins/serializers/prometheus/prometheus_test.go b/plugins/serializers/prometheus/prometheus_test.go
index ff082f7b2..a2a95482d 100644
--- a/plugins/serializers/prometheus/prometheus_test.go
+++ b/plugins/serializers/prometheus/prometheus_test.go
@@ -108,6 +108,11 @@ http_requests_total{code="400",method="post"} 3
 				telegraf.Histogram,
 			),
 			expected: []byte(`
+# HELP http_request_duration_seconds Telegraf collected metric
+# TYPE http_request_duration_seconds histogram
+http_request_duration_seconds_bucket{le="+Inf"} 144320
+http_request_duration_seconds_sum 53423
+http_request_duration_seconds_count 144320
 `),
 		},
 		{
@@ -645,6 +650,27 @@ cpu_time_user{cpu="cpu0"} 92904.33
 cpu_time_user{cpu="cpu1"} 96912.57
 cpu_time_user{cpu="cpu2"} 96034.08
 cpu_time_user{cpu="cpu3"} 94148
+`),
+		},
+		{
+			name: "summary with no quantile",
+			metrics: []telegraf.Metric{
+				testutil.MustMetric(
+					"prometheus",
+					map[string]string{},
+					map[string]interface{}{
+						"rpc_duration_seconds_sum":   1.7560473e+07,
+						"rpc_duration_seconds_count": 2693,
+					},
+					time.Unix(0, 0),
+					telegraf.Summary,
+				),
+			},
+			expected: []byte(`
+# HELP rpc_duration_seconds Telegraf collected metric
+# TYPE rpc_duration_seconds summary
+rpc_duration_seconds_sum 1.7560473e+07
+rpc_duration_seconds_count 2693
 `),
 		},
 	}