Initial delivery of metrics code (#81)

* Initial delivery of metrics code

* Fix build issues

* Fix build issue with go vet

internal/metrics/metrics.go

@@ -0,0 +1,97 @@
+/*
+© 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 (
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/ibm-messaging/mq-container/internal/logger"
+	"github.com/ibm-messaging/mq-golang/mqmetric"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	defaultPort = "9157"
+	retryCount  = 3
+	retryWait   = 5
+)
+
+// GatherMetrics gathers metrics for the queue manager
+func GatherMetrics(qmName string, log *logger.Logger) {
+
+	for i := 0; i <= retryCount; i++ {
+		err := startMetricsGathering(qmName, log)
+		if err != nil {
+			log.Errorf("Metrics Error: %s", err.Error())
+		}
+		if i != retryCount {
+			log.Printf("Waiting %d seconds before retrying metrics gathering", retryWait)
+			time.Sleep(retryWait * time.Second)
+		} else {
+			log.Println("Unable to gather metrics - metrics are now disabled")
+		}
+	}
+}
+
+// startMetricsGathering starts gathering metrics for the queue manager
+func startMetricsGathering(qmName string, log *logger.Logger) error {
+
+	defer func() {
+		if r := recover(); r != nil {
+			log.Errorf("Metrics Error: %v", r)
+		}
+	}()
+
+	log.Println("Starting metrics gathering")
+
+	// Set connection configuration
+	var connConfig mqmetric.ConnectionConfig
+	connConfig.ClientMode = false
+	connConfig.UserId = ""
+	connConfig.Password = ""
+
+	// Connect to the queue manager - open the command and dynamic reply queues
+	err := mqmetric.InitConnectionStats(qmName, "SYSTEM.DEFAULT.MODEL.QUEUE", "", &connConfig)
+	if err != nil {
+		return fmt.Errorf("Failed to connect to queue manager %s: %v", qmName, err)
+	}
+	defer mqmetric.EndConnection()
+
+	// Discover available metrics for the queue manager and subscribe to them
+	err = mqmetric.DiscoverAndSubscribe("", true, "")
+	if err != nil {
+		return fmt.Errorf("Failed to discover and subscribe to metrics: %v", err)
+	}
+
+	// Start processing metrics
+	go processMetrics(log)
+
+	// Register metrics
+	prometheus.MustRegister(newExporter(qmName))
+
+	// Setup HTTP server to handle requests from Prometheus
+	http.Handle("/metrics", prometheus.Handler())
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(200)
+		w.Write([]byte("Status: METRICS ACTIVE"))
+	})
+	err = http.ListenAndServe(":"+defaultPort, nil)
+	return fmt.Errorf("Failed to handle metrics request: %v", err)
+}