Initial delivery of metrics code (#81)

* Initial delivery of metrics code

* Fix build issues

* Fix build issue with go vet

internal/metrics/exporter.go

@@ -0,0 +1,107 @@
+/*
+© Copyright IBM Corporation 2018
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package metrics contains code to provide metrics for the queue manager
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	namespace    = "ibmmq"
+	qmgrPrefix   = "qmgr"
+	qmgrLabel    = "qmgr"
+	objectPrefix = "object"
+	objectLabel  = "object"
+)
+
+type exporter struct {
+	qmName   string
+	gaugeMap map[string]*prometheus.GaugeVec
+}
+
+func newExporter(qmName string) *exporter {
+	return &exporter{
+		qmName:   qmName,
+		gaugeMap: make(map[string]*prometheus.GaugeVec),
+	}
+}
+
+// Describe provides details of all available metrics
+func (e *exporter) Describe(ch chan<- *prometheus.Desc) {
+
+	requestChannel <- false
+	response := <-responseChannel
+
+	for key, metric := range response {
+
+		// Allocate a Prometheus Gauge for each available metric
+		gaugeVec := createGaugeVec(metric.name, metric.description, metric.objectType)
+		e.gaugeMap[key] = gaugeVec
+
+		// Describe metric
+		gaugeVec.Describe(ch)
+	}
+}
+
+// Collect is called at regular intervals to provide the current metric data
+func (e *exporter) Collect(ch chan<- prometheus.Metric) {
+
+	requestChannel <- true
+	response := <-responseChannel
+
+	for key, metric := range response {
+
+		// Reset Prometheus Gauge
+		gaugeVec := e.gaugeMap[key]
+		gaugeVec.Reset()
+
+		// Populate Prometheus Gauge with metric values
+		for label, value := range metric.values {
+			if label == qmgrLabelValue {
+				gaugeVec.WithLabelValues(e.qmName).Set(value)
+			} else {
+				gaugeVec.WithLabelValues(label, e.qmName).Set(value)
+			}
+		}
+
+		// Collect metric
+		gaugeVec.Collect(ch)
+	}
+}
+
+// createGaugeVec returns a Prometheus GaugeVec populated with metric details
+func createGaugeVec(name, description string, objectType bool) *prometheus.GaugeVec {
+
+	prefix := qmgrPrefix
+	labels := []string{qmgrLabel}
+
+	if objectType {
+		prefix = objectPrefix
+		labels = []string{objectLabel, qmgrLabel}
+	}
+
+	gaugeVec := prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Namespace: namespace,
+			Name:      prefix + "_" + name,
+			Help:      description,
+		},
+		labels,
+	)
+	return gaugeVec
+}