metrics: pull library and introduce ResettingTimer and InfluxDB reporter (#15910)

* go-metrics: fork library and introduce ResettingTimer and InfluxDB reporter.

* vendor: change nonsense/go-metrics to ethersphere/go-metrics

* go-metrics: add tests. move ResettingTimer logic from reporter to type.

* all, metrics: pull in metrics package in go-ethereum

* metrics/test: make sure metrics are enabled for tests

* metrics: apply gosimple rules

* metrics/exp, internal/debug: init expvar endpoint when starting pprof server

* internal/debug: tiny comment formatting fix

metrics/resetting_timer_test.go

@@ -0,0 +1,106 @@
+package metrics
+
+import (
+	"testing"
+	"time"
+)
+
+func TestResettingTimer(t *testing.T) {
+	tests := []struct {
+		values   []int64
+		start    int
+		end      int
+		wantP50  int64
+		wantP95  int64
+		wantP99  int64
+		wantMean float64
+		wantMin  int64
+		wantMax  int64
+	}{
+		{
+			values:  []int64{},
+			start:   1,
+			end:     11,
+			wantP50: 5, wantP95: 10, wantP99: 10,
+			wantMin: 1, wantMax: 10, wantMean: 5.5,
+		},
+		{
+			values:  []int64{},
+			start:   1,
+			end:     101,
+			wantP50: 50, wantP95: 95, wantP99: 99,
+			wantMin: 1, wantMax: 100, wantMean: 50.5,
+		},
+		{
+			values:  []int64{1},
+			start:   0,
+			end:     0,
+			wantP50: 1, wantP95: 1, wantP99: 1,
+			wantMin: 1, wantMax: 1, wantMean: 1,
+		},
+		{
+			values:  []int64{0},
+			start:   0,
+			end:     0,
+			wantP50: 0, wantP95: 0, wantP99: 0,
+			wantMin: 0, wantMax: 0, wantMean: 0,
+		},
+		{
+			values:  []int64{},
+			start:   0,
+			end:     0,
+			wantP50: 0, wantP95: 0, wantP99: 0,
+			wantMin: 0, wantMax: 0, wantMean: 0,
+		},
+		{
+			values:  []int64{1, 10},
+			start:   0,
+			end:     0,
+			wantP50: 1, wantP95: 10, wantP99: 10,
+			wantMin: 1, wantMax: 10, wantMean: 5.5,
+		},
+	}
+	for ind, tt := range tests {
+		timer := NewResettingTimer()
+
+		for i := tt.start; i < tt.end; i++ {
+			tt.values = append(tt.values, int64(i))
+		}
+
+		for _, v := range tt.values {
+			timer.Update(time.Duration(v))
+		}
+
+		snap := timer.Snapshot()
+
+		ps := snap.Percentiles([]float64{50, 95, 99})
+
+		val := snap.Values()
+
+		if len(val) > 0 {
+			if tt.wantMin != val[0] {
+				t.Fatalf("%d: min: got %d, want %d", ind, val[0], tt.wantMin)
+			}
+
+			if tt.wantMax != val[len(val)-1] {
+				t.Fatalf("%d: max: got %d, want %d", ind, val[len(val)-1], tt.wantMax)
+			}
+		}
+
+		if tt.wantMean != snap.Mean() {
+			t.Fatalf("%d: mean: got %.2f, want %.2f", ind, snap.Mean(), tt.wantMean)
+		}
+
+		if tt.wantP50 != ps[0] {
+			t.Fatalf("%d: p50: got %d, want %d", ind, ps[0], tt.wantP50)
+		}
+
+		if tt.wantP95 != ps[1] {
+			t.Fatalf("%d: p95: got %d, want %d", ind, ps[1], tt.wantP95)
+		}
+
+		if tt.wantP99 != ps[2] {
+			t.Fatalf("%d: p99: got %d, want %d", ind, ps[2], tt.wantP99)
+		}
+	}
+}