Add instrumentation with prometheus

lib/instrument/dummy.go

@@ -0,0 +1,14 @@
+// +build noprometheus
+
+package instrument
+
+import "time"
+
+type dummyInst struct{}
+
+func Init() Instrument {
+	return &dummyInst{}
+}
+
+func (i dummyInst) Visit(section string, id string, search string, fmt string) {}
+func (i dummyInst) Duration(section string, duration time.Duration)            {}

lib/instrument/instrument.go

@@ -0,0 +1,8 @@
+package instrument
+
+import "time"
+
+type Instrument interface {
+	Visit(section string, id string, search string, fmt string)
+	Duration(section string, duration time.Duration)
+}

lib/instrument/prometheus.go

@@ -0,0 +1,66 @@
+// +build !noprometheus
+
+package instrument
+
+import (
+	"time"
+
+	log "github.com/cihub/seelog"
+
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+const (
+	promAddr = ":9123"
+)
+
+type promInst struct {
+	visits *prometheus.CounterVec
+	reqDur *prometheus.HistogramVec
+}
+
+func Init() Instrument {
+	go promHandle()
+
+	visits := prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "trantor_visits_total",
+			Help: "Number of visits.",
+		},
+		[]string{"section", "id", "search", "fmt"},
+	)
+	reqDur := prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name: "trantor_request_duration_seconds",
+			Help: "Duration of the request in seconds.",
+		},
+		[]string{"section"},
+	)
+
+	prometheus.MustRegister(visits)
+	prometheus.MustRegister(reqDur)
+
+	return &promInst{
+		visits: visits,
+		reqDur: reqDur,
+	}
+}
+
+func promHandle() {
+	server := http.Server{
+		Addr:    promAddr,
+		Handler: promhttp.Handler(),
+	}
+	log.Error(server.ListenAndServe())
+}
+
+func (in promInst) Visit(section string, id string, search string, fmt string) {
+	in.visits.WithLabelValues(section, id, search, fmt).Inc()
+}
+
+func (in promInst) Duration(section string, duration time.Duration) {
+	in.reqDur.WithLabelValues(section).Observe(duration.Seconds())
+}