feat(proxy): add failed connection count stats

For the summary log and for Prometheus metrics.

Log output example:

> In the last 1h0m0s, there were 7 completed successful connections. 2 connections failed. Traffic Relayed ↓ 321 KB (0.10 KB/s), ↑ 123 KB (0.05 KB/s).

proxy/lib/metrics.go

@@ -13,9 +13,10 @@ const (
 )
 
 type Metrics struct {
-	totalInBoundTraffic  prometheus.Counter
-	totalOutBoundTraffic prometheus.Counter
-	totalConnections     *prometheus.CounterVec
+	totalInBoundTraffic    prometheus.Counter
+	totalOutBoundTraffic   prometheus.Counter
+	totalConnections       *prometheus.CounterVec
+	totalFailedConnections prometheus.Counter
 }
 
 func NewMetrics() *Metrics {
@@ -23,10 +24,15 @@ func NewMetrics() *Metrics {
 		totalConnections: prometheus.NewCounterVec(prometheus.CounterOpts{
 			Namespace: metricNamespace,
 			Name:      "connections_total",
-			Help:      "The total number of connections handled by the snowflake proxy",
+			Help:      "The total number of successful connections handled by the snowflake proxy",
 		},
 			[]string{"country"},
 		),
+		totalFailedConnections: prometheus.NewCounter(prometheus.CounterOpts{
+			Namespace: metricNamespace,
+			Name:      "failed_connections_total",
+			Help:      "The total number of client connection attempts that failed after successful rendezvous",
+		}),
 		totalInBoundTraffic: prometheus.NewCounter(prometheus.CounterOpts{
 			Namespace: metricNamespace,
 			Name:      "traffic_inbound_bytes_total",
@@ -54,6 +60,7 @@ func (m *Metrics) Start(addr string) error {
 
 func (m *Metrics) Collect(ch chan<- prometheus.Metric) {
 	m.totalConnections.Collect(ch)
+	m.totalFailedConnections.Collect(ch)
 	m.totalInBoundTraffic.Collect(ch)
 	m.totalOutBoundTraffic.Collect(ch)
 }
@@ -78,3 +85,8 @@ func (m *Metrics) TrackNewConnection(country string) {
 		With(prometheus.Labels{"country": country}).
 		Inc()
 }
+
+// TrackFailedConnection counts failed connection attempts
+func (m *Metrics) TrackFailedConnection() {
+	m.totalFailedConnections.Inc()
+}

proxy/lib/pt_event_logger.go

@@ -42,11 +42,14 @@ func (p *proxyEventLogger) OnNewSnowflakeEvent(e event.SnowflakeEvent) {
 }
 
 type periodicProxyStats struct {
-	bytesLogger     bytesLogger
+	bytesLogger bytesLogger
+	// Completed successful connections.
 	connectionCount int
-	logPeriod       time.Duration
-	task            *task.Periodic
-	dispatcher      event.SnowflakeEventDispatcher
+	// Connections that failed to establish.
+	failedConnectionCount uint
+	logPeriod             time.Duration
+	task                  *task.Periodic
+	dispatcher            event.SnowflakeEventDispatcher
 }
 
 func newPeriodicProxyStats(logPeriod time.Duration, dispatcher event.SnowflakeEventDispatcher, bytesLogger bytesLogger) *periodicProxyStats {
@@ -60,19 +63,23 @@ func (p *periodicProxyStats) OnNewSnowflakeEvent(e event.SnowflakeEvent) {
 	switch e.(type) {
 	case event.EventOnProxyConnectionOver:
 		p.connectionCount += 1
+	case event.EventOnProxyConnectionFailed:
+		p.failedConnectionCount += 1
 	}
 }
 
 func (p *periodicProxyStats) logTick() error {
 	inboundSum, outboundSum := p.bytesLogger.GetStat()
 	e := event.EventOnProxyStats{
-		SummaryInterval: p.logPeriod,
-		ConnectionCount: p.connectionCount,
+		SummaryInterval:       p.logPeriod,
+		ConnectionCount:       p.connectionCount,
+		FailedConnectionCount: p.failedConnectionCount,
 	}
 	e.InboundBytes, e.InboundUnit = formatTraffic(inboundSum)
 	e.OutboundBytes, e.OutboundUnit = formatTraffic(outboundSum)
 	p.dispatcher.OnNewSnowflakeEvent(e)
 	p.connectionCount = 0
+	p.failedConnectionCount = 0
 	return nil
 }
 

proxy/lib/pt_event_metrics.go

@@ -8,6 +8,7 @@ type EventCollector interface {
 	TrackInBoundTraffic(value int64)
 	TrackOutBoundTraffic(value int64)
 	TrackNewConnection(country string)
+	TrackFailedConnection()
 }
 
 type EventMetrics struct {
@@ -27,5 +28,7 @@ func (em *EventMetrics) OnNewSnowflakeEvent(e event.SnowflakeEvent) {
 	case event.EventOnProxyConnectionOver:
 		e := e.(event.EventOnProxyConnectionOver)
 		em.collector.TrackNewConnection(e.Country)
+	case event.EventOnProxyConnectionFailed:
+		em.collector.TrackFailedConnection()
 	}
 }

proxy/lib/snowflake.go

@@ -682,6 +682,9 @@ func (sf *SnowflakeProxy) runSession(sid string) {
 		connectedToClient = true
 	case <-time.After(dataChannelTimeout):
 		log.Println("Timed out waiting for client to open data channel.")
+		sf.EventDispatcher.OnNewSnowflakeEvent(
+			event.EventOnProxyConnectionFailed{},
+		)
 		if err := pc.Close(); err != nil {
 			log.Printf("error calling pc.Close: %v", err)
 		}