feat: add option to expose the stats by using metrics

proxy/lib/pt_event_metrics.go

@@ -0,0 +1,29 @@
+package snowflake_proxy
+
+import (
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/event"
+)
+
+type EventCollector interface {
+	TrackInBoundTraffic(value int64)
+	TrackOutBoundTraffic(value int64)
+	TrackNewConnection()
+}
+
+type EventMetrics struct {
+	collector EventCollector
+}
+
+func NewEventMetrics(collector EventCollector) *EventMetrics {
+	return &EventMetrics{collector: collector}
+}
+
+func (em *EventMetrics) OnNewSnowflakeEvent(e event.SnowflakeEvent) {
+	switch e.(type) {
+	case event.EventOnProxyConnectionOver:
+		e := e.(event.EventOnProxyConnectionOver)
+		em.collector.TrackInBoundTraffic(e.InboundTraffic)
+		em.collector.TrackOutBoundTraffic(e.OutboundTraffic)
+		em.collector.TrackNewConnection()
+	}
+}