Use +Inf label additionally for Histogram metrics (#18807)

cmd/metrics-v2.go

@@ -20,6 +20,7 @@ package cmd
 import (
 	"context"
 	"fmt"
+	"math"
 	"net/http"
 	"runtime"
 	"strconv"
@@ -1715,6 +1716,17 @@ func getHistogramMetrics(hist *prometheus.HistogramVec, desc MetricDescription)
 			}
 			metrics = append(metrics, metric)
 		}
+		// add metrics with +Inf label
+		labels1 := make(map[string]string)
+		for _, lp := range dtoMetric.GetLabel() {
+			labels1[*lp.Name] = *lp.Value
+		}
+		labels1["le"] = fmt.Sprintf("%.3f", math.Inf(+1))
+		metrics = append(metrics, Metric{
+			Description:    desc,
+			VariableLabels: labels1,
+			Value:          dtoMetric.Counter.GetValue(),
+		})
 	}
 	return metrics
 }

cmd/metrics-v2_test.go

@@ -81,7 +81,8 @@ func TestGetHistogramMetrics(t *testing.T) {
 	}
 
 	metrics := getHistogramMetrics(ttfbHist, getBucketTTFBDistributionMD())
-	if expPoints := len(labels) * len(histBuckets); expPoints != len(metrics) {
+	// additional labels for +Inf for all histogram metrics
+	if expPoints := len(labels) * (len(histBuckets) + 1); expPoints != len(metrics) {
 		t.Fatalf("Expected %v data points but got %v", expPoints, len(metrics))
 	}
 }