prometheus: Implement basic Prometheus support

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

prometheus/prometheus.go

@@ -0,0 +1,59 @@
+// Mgmt
+// Copyright (C) 2013-2016+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+// Package prometheus provides functions that are useful to control and manage
+// the build-in prometheus instance.
+package prometheus
+
+import (
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+// DefaultPrometheusListen is registered in
+// https://github.com/prometheus/prometheus/wiki/Default-port-allocation
+const DefaultPrometheusListen = "127.0.0.1:9233"
+
+// Prometheus is the struct that contains information about the
+// prometheus instance. Run Init() on it.
+type Prometheus struct {
+	Listen string // the listen specification for the net/http server
+}
+
+// Init some parameters - currently the Listen address.
+func (obj *Prometheus) Init() error {
+	if len(obj.Listen) == 0 {
+		obj.Listen = DefaultPrometheusListen
+	}
+	return nil
+}
+
+// Start runs a http server in a go routine, that responds to /metrics
+// as prometheus would expect.
+func (obj *Prometheus) Start() error {
+	http.Handle("/metrics", promhttp.Handler())
+	go http.ListenAndServe(obj.Listen, nil)
+	return nil
+}
+
+// Stop the http server.
+func (obj *Prometheus) Stop() error {
+	// TODO: There is no way in go < 1.8 to stop a http server.
+	// https://stackoverflow.com/questions/39320025/go-how-to-stop-http-listenandserve/41433555#41433555
+	return nil
+}