metrics/prometheus: expose metrics in prometheus format too (#17077)

* metrics/prometheus: added prometheus http server and metrics collector

* metrics/prometheus: minor cleanups

* metrics/prometheus: named keys instead name in tag

* metrics/prometheus: minor typo cleanups, sorted report

2 files changed, 183 insertions, 0 deletions

diff --git a/metrics/prometheus/collector.go b/metrics/prometheus/collector.go
new file mode 100644
index 000000000..8350fa2aa
--- /dev/null
+++ b/metrics/prometheus/collector.go
@@ -0,0 +1,115 @@
+// Copyright 2019 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package prometheus
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/ethereum/go-ethereum/metrics"
+)
+
+var (
+	typeGaugeTpl           = "# TYPE %s gauge\n"
+	typeCounterTpl         = "# TYPE %s counter\n"
+	typeSummaryTpl         = "# TYPE %s summary\n"
+	keyValueTpl            = "%s %v\n\n"
+	keyQuantileTagValueTpl = "%s {quantile=\"%s\"} %v\n\n"
+)
+
+// collector is a collection of byte buffers that aggregate Prometheus reports
+// for different metric types.
+type collector struct {
+	buff *bytes.Buffer
+}
+
+// newCollector createa a new Prometheus metric aggregator.
+func newCollector() *collector {
+	return &collector{
+		buff: &bytes.Buffer{},
+	}
+}
+
+func (c *collector) addCounter(name string, m metrics.Counter) {
+	c.writeGaugeCounter(name, m.Count())
+}
+
+func (c *collector) addGauge(name string, m metrics.Gauge) {
+	c.writeGaugeCounter(name, m.Value())
+}
+
+func (c *collector) addGaugeFloat64(name string, m metrics.GaugeFloat64) {
+	c.writeGaugeCounter(name, m.Value())
+}
+
+func (c *collector) addHistogram(name string, m metrics.Histogram) {
+	pv := []float64{0.5, 0.75, 0.95, 0.99, 0.999, 0.9999}
+	ps := m.Percentiles(pv)
+	c.writeSummaryCounter(name, m.Count())
+	for i := range pv {
+		c.writeSummaryPercentile(name, strconv.FormatFloat(pv[i], 'f', -1, 64), ps[i])
+	}
+}
+
+func (c *collector) addMeter(name string, m metrics.Meter) {
+	c.writeGaugeCounter(name, m.Count())
+}
+
+func (c *collector) addTimer(name string, m metrics.Timer) {
+	pv := []float64{0.5, 0.75, 0.95, 0.99, 0.999, 0.9999}
+	ps := m.Percentiles(pv)
+	c.writeSummaryCounter(name, m.Count())
+	for i := range pv {
+		c.writeSummaryPercentile(name, strconv.FormatFloat(pv[i], 'f', -1, 64), ps[i])
+	}
+}
+
+func (c *collector) addResettingTimer(name string, m metrics.ResettingTimer) {
+	if len(m.Values()) <= 0 {
+		return
+	}
+	ps := m.Percentiles([]float64{50, 95, 99})
+	val := m.Values()
+	c.writeSummaryCounter(name, len(val))
+	c.writeSummaryPercentile(name, "0.50", ps[0])
+	c.writeSummaryPercentile(name, "0.95", ps[1])
+	c.writeSummaryPercentile(name, "0.99", ps[2])
+}
+
+func (c *collector) writeGaugeCounter(name string, value interface{}) {
+	name = mutateKey(name)
+	c.buff.WriteString(fmt.Sprintf(typeGaugeTpl, name))
+	c.buff.WriteString(fmt.Sprintf(keyValueTpl, name, value))
+}
+
+func (c *collector) writeSummaryCounter(name string, value interface{}) {
+	name = mutateKey(name + "_count")
+	c.buff.WriteString(fmt.Sprintf(typeCounterTpl, name))
+	c.buff.WriteString(fmt.Sprintf(keyValueTpl, name, value))
+}
+
+func (c *collector) writeSummaryPercentile(name, p string, value interface{}) {
+	name = mutateKey(name)
+	c.buff.WriteString(fmt.Sprintf(typeSummaryTpl, name))
+	c.buff.WriteString(fmt.Sprintf(keyQuantileTagValueTpl, name, p, value))
+}
+
+func mutateKey(key string) string {
+	return strings.Replace(key, "/", "_", -1)
+}
diff --git a/metrics/prometheus/prometheus.go b/metrics/prometheus/prometheus.go
new file mode 100644
index 000000000..9ad5ec7e9
--- /dev/null
+++ b/metrics/prometheus/prometheus.go
@@ -0,0 +1,68 @@
+// Copyright 2019 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+// Package prometheus exposes go-metrics into a Prometheus format.
+package prometheus
+
+import (
+	"fmt"
+	"net/http"
+	"sort"
+
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/metrics"
+)
+
+// Handler returns an HTTP handler which dump metrics in Prometheus format.
+func Handler(reg metrics.Registry) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Gather and pre-sort the metrics to avoid random listings
+		var names []string
+		reg.Each(func(name string, i interface{}) {
+			names = append(names, name)
+		})
+		sort.Strings(names)
+
+		// Aggregate all the metris into a Prometheus collector
+		c := newCollector()
+
+		for _, name := range names {
+			i := reg.Get(name)
+
+			switch m := i.(type) {
+			case metrics.Counter:
+				c.addCounter(name, m.Snapshot())
+			case metrics.Gauge:
+				c.addGauge(name, m.Snapshot())
+			case metrics.GaugeFloat64:
+				c.addGaugeFloat64(name, m.Snapshot())
+			case metrics.Histogram:
+				c.addHistogram(name, m.Snapshot())
+			case metrics.Meter:
+				c.addMeter(name, m.Snapshot())
+			case metrics.Timer:
+				c.addTimer(name, m.Snapshot())
+			case metrics.ResettingTimer:
+				c.addResettingTimer(name, m.Snapshot())
+			default:
+				log.Warn("Unknown Prometheus metric type", "type", fmt.Sprintf("%T", i))
+			}
+		}
+		w.Header().Add("Content-Type", "text/plain")
+		w.Header().Add("Content-Length", fmt.Sprint(c.buff.Len()))
+		w.Write(c.buff.Bytes())
+	})
+}