fix: periodicProxyStats.connectionCount race

And `failedConnectionCount`.
Convert the `int` / `uint` to `atomic.Int32` / `atomic.Uint32`.
The race was discovered by running a proxy with the `-race` flag.

proxy/lib/pt_event_logger.go

@@ -3,6 +3,7 @@ package snowflake_proxy
 import (
 	"io"
 	"log"
+	"sync/atomic"
 	"time"
 
 	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/event"
@@ -44,9 +45,9 @@ func (p *proxyEventLogger) OnNewSnowflakeEvent(e event.SnowflakeEvent) {
 type periodicProxyStats struct {
 	bytesLogger bytesLogger
 	// Completed successful connections.
-	connectionCount int
+	connectionCount atomic.Int32
 	// Connections that failed to establish.
-	failedConnectionCount uint
+	failedConnectionCount atomic.Uint32
 	logPeriod             time.Duration
 	task                  *task.Periodic
 	dispatcher            event.SnowflakeEventDispatcher
@@ -62,9 +63,9 @@ func newPeriodicProxyStats(logPeriod time.Duration, dispatcher event.SnowflakeEv
 func (p *periodicProxyStats) OnNewSnowflakeEvent(e event.SnowflakeEvent) {
 	switch e.(type) {
 	case event.EventOnProxyConnectionOver:
-		p.connectionCount += 1
+		p.connectionCount.Add(1)
 	case event.EventOnProxyConnectionFailed:
-		p.failedConnectionCount += 1
+		p.failedConnectionCount.Add(1)
 	}
 }
 
@@ -72,14 +73,12 @@ func (p *periodicProxyStats) logTick() error {
 	inboundSum, outboundSum := p.bytesLogger.GetStat()
 	e := event.EventOnProxyStats{
 		SummaryInterval:       p.logPeriod,
-		ConnectionCount:       p.connectionCount,
-		FailedConnectionCount: p.failedConnectionCount,
+		ConnectionCount:       int(p.connectionCount.Swap(0)),
+		FailedConnectionCount: uint(p.failedConnectionCount.Swap(0)),
 	}
 	e.InboundBytes, e.InboundUnit = formatTraffic(inboundSum)
 	e.OutboundBytes, e.OutboundUnit = formatTraffic(outboundSum)
 	p.dispatcher.OnNewSnowflakeEvent(e)
-	p.connectionCount = 0
-	p.failedConnectionCount = 0
 	return nil
 }