Adding new metric to relay

Signed-off-by: Pedro Tanaka <pedro.tanaka@shopify.com>

pkg/relay/relay.go

@@ -35,8 +35,9 @@ type Relay struct {
 	logger        log.Logger
 	packetLength  uint
 
-	packetsTotal   prometheus.Counter
-	longLinesTotal prometheus.Counter
+	packetsTotal      prometheus.Counter
+	longLinesTotal    prometheus.Counter
+	relayedLinesTotal prometheus.Counter
 }
 
 var (
@@ -54,6 +55,13 @@ var (
 		},
 		[]string{"target"},
 	)
+	relayLinesRelayedTotal = promauto.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "statsd_exporter_relay_lines_relayed_total",
+			Help: "The number of lines that were buffered to be relayed.",
+		},
+		[]string{"target"},
+	)
 )
 
 // NewRelay creates a statsd UDP relay. It can be used to send copies of statsd raw
@@ -77,8 +85,9 @@ func NewRelay(l log.Logger, target string, packetLength uint) (*Relay, error) {
 		logger:        l,
 		packetLength:  packetLength,
 
-		packetsTotal:   relayPacketsTotal.WithLabelValues(target),
-		longLinesTotal: relayLongLinesTotal.WithLabelValues(target),
+		packetsTotal:      relayPacketsTotal.WithLabelValues(target),
+		longLinesTotal:    relayLongLinesTotal.WithLabelValues(target),
+		relayedLinesTotal: relayLinesRelayedTotal.WithLabelValues(target),
 	}
 
 	// Startup the UDP sender.
@@ -152,5 +161,6 @@ func (r *Relay) RelayLine(l string) {
 	if !strings.HasSuffix(l, "\n") {
 		l = l + "\n"
 	}
+	r.relayedLinesTotal.Inc()
 	r.bufferChannel <- []byte(l)
 }