From 56bababcdfce097a4e08cc3d1de8d798e7999ce7 Mon Sep 17 00:00:00 2001
From: Loic Blot <loic.blot@unix-experience.fr>
Date: Mon, 27 Apr 2020 08:31:37 +0200
Subject: Add MetricsBackend with prometheus counter support

---
 src/util/metricsbackend.cpp | 140 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 140 insertions(+)
 create mode 100644 src/util/metricsbackend.cpp

(limited to 'src/util/metricsbackend.cpp')

diff --git a/src/util/metricsbackend.cpp b/src/util/metricsbackend.cpp
new file mode 100644
index 000000000..4454557a3
--- /dev/null
+++ b/src/util/metricsbackend.cpp
@@ -0,0 +1,140 @@
+/*
+Minetest
+Copyright (C) 2013-2020 Minetest core developers team
+
+This program 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 2.1 of the License, or
+(at your option) any later version.
+
+This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#include "metricsbackend.h"
+#if USE_PROMETHEUS
+#include <prometheus/exposer.h>
+#include <prometheus/registry.h>
+#include <prometheus/counter.h>
+#include <prometheus/gauge.h>
+#include "log.h"
+#include "settings.h"
+#endif
+
+MetricCounterPtr MetricsBackend::addCounter(
+		const std::string &name, const std::string &help_str)
+{
+	return std::make_shared<SimpleMetricCounter>(name, help_str);
+}
+
+MetricGaugePtr MetricsBackend::addGauge(
+		const std::string &name, const std::string &help_str)
+{
+	return std::make_shared<SimpleMetricGauge>(name, help_str);
+}
+
+#if USE_PROMETHEUS
+
+class PrometheusMetricCounter : public MetricCounter
+{
+public:
+	PrometheusMetricCounter() = delete;
+
+	PrometheusMetricCounter(const std::string &name, const std::string &help_str,
+			std::shared_ptr<prometheus::Registry> registry) :
+			MetricCounter(),
+			m_family(prometheus::BuildCounter()
+							.Name(name)
+							.Help(help_str)
+							.Register(*registry)),
+			m_counter(m_family.Add({}))
+	{
+	}
+
+	virtual ~PrometheusMetricCounter() {}
+
+	virtual void increment(double number) { m_counter.Increment(number); }
+	virtual double get() const { return m_counter.Value(); }
+
+private:
+	prometheus::Family<prometheus::Counter> &m_family;
+	prometheus::Counter &m_counter;
+};
+
+class PrometheusMetricGauge : public MetricGauge
+{
+public:
+	PrometheusMetricGauge() = delete;
+
+	PrometheusMetricGauge(const std::string &name, const std::string &help_str,
+			std::shared_ptr<prometheus::Registry> registry) :
+			MetricGauge(),
+			m_family(prometheus::BuildGauge()
+							.Name(name)
+							.Help(help_str)
+							.Register(*registry)),
+			m_gauge(m_family.Add({}))
+	{
+	}
+
+	virtual ~PrometheusMetricGauge() {}
+
+	virtual void increment(double number) { m_gauge.Increment(number); }
+	virtual void decrement(double number) { m_gauge.Decrement(number); }
+	virtual void set(double number) { m_gauge.Set(number); }
+	virtual double get() const { return m_gauge.Value(); }
+
+private:
+	prometheus::Family<prometheus::Gauge> &m_family;
+	prometheus::Gauge &m_gauge;
+};
+
+class PrometheusMetricsBackend : public MetricsBackend
+{
+public:
+	PrometheusMetricsBackend(const std::string &addr) :
+			MetricsBackend(), m_exposer(std::unique_ptr<prometheus::Exposer>(
+							  new prometheus::Exposer(addr))),
+			m_registry(std::make_shared<prometheus::Registry>())
+	{
+		m_exposer->RegisterCollectable(m_registry);
+	}
+
+	virtual ~PrometheusMetricsBackend() {}
+
+	virtual MetricCounterPtr addCounter(
+			const std::string &name, const std::string &help_str);
+	virtual MetricGaugePtr addGauge(
+			const std::string &name, const std::string &help_str);
+
+private:
+	std::unique_ptr<prometheus::Exposer> m_exposer;
+	std::shared_ptr<prometheus::Registry> m_registry;
+};
+
+MetricCounterPtr PrometheusMetricsBackend::addCounter(
+		const std::string &name, const std::string &help_str)
+{
+	return std::make_shared<PrometheusMetricCounter>(name, help_str, m_registry);
+}
+
+MetricGaugePtr PrometheusMetricsBackend::addGauge(
+		const std::string &name, const std::string &help_str)
+{
+	return std::make_shared<PrometheusMetricGauge>(name, help_str, m_registry);
+}
+
+MetricsBackend *createPrometheusMetricsBackend()
+{
+	std::string addr;
+	g_settings->getNoEx("prometheus_listener_address", addr);
+	return new PrometheusMetricsBackend(addr);
+}
+
+#endif
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