udpnat2: Fix concurrency

common/udpnat2/conn.go

@@ -3,6 +3,7 @@ package udpnat
 import (
 	"io"
 	"net"
+	"net/netip"
 	"os"
 	"sync"
 	"time"
@@ -12,6 +13,7 @@ import (
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
 	"github.com/sagernet/sing/common/pipe"
+	"github.com/sagernet/sing/contrab/freelru"
 )
 
 type Conn interface {
@@ -23,7 +25,7 @@ type Conn interface {
 var _ Conn = (*natConn)(nil)
 
 type natConn struct {
-	service         *Service
+	cache           freelru.Cache[netip.AddrPort, *natConn]
 	writer          N.PacketWriter
 	localAddr       M.Socksaddr
 	handler         N.UDPHandlerEx
@@ -93,7 +95,7 @@ fetch:
 }
 
 func (c *natConn) Timeout() time.Duration {
-	rawConn, lifetime, loaded := c.service.cache.PeekWithLifetime(c.localAddr.AddrPort())
+	rawConn, lifetime, loaded := c.cache.PeekWithLifetime(c.localAddr.AddrPort())
 	if !loaded || rawConn != c {
 		return 0
 	}
@@ -101,7 +103,7 @@ func (c *natConn) Timeout() time.Duration {
 }
 
 func (c *natConn) SetTimeout(timeout time.Duration) bool {
-	return c.service.cache.UpdateLifetime(c.localAddr.AddrPort(), c, timeout)
+	return c.cache.UpdateLifetime(c.localAddr.AddrPort(), c, timeout)
 }
 
 func (c *natConn) Close() error {

common/udpnat2/service.go

@@ -17,18 +17,10 @@ type Service struct {
 	cache   freelru.Cache[netip.AddrPort, *natConn]
 	handler N.UDPConnectionHandlerEx
 	prepare PrepareFunc
-	metrics Metrics
 }
 
 type PrepareFunc func(source M.Socksaddr, destination M.Socksaddr, userData any) (bool, context.Context, N.PacketWriter, N.CloseHandlerFunc)
 
-type Metrics struct {
-	Creates uint64
-	Rejects uint64
-	Inputs  uint64
-	Drops   uint64
-}
-
 func New(handler N.UDPConnectionHandlerEx, prepare PrepareFunc, timeout time.Duration, shared bool) *Service {
 	if timeout == 0 {
 		panic("invalid timeout")
@@ -40,7 +32,6 @@ func New(handler N.UDPConnectionHandlerEx, prepare PrepareFunc, timeout time.Dur
 		cache = common.Must1(freelru.NewSharded[netip.AddrPort, *natConn](1024, maphash.NewHasher[netip.AddrPort]().Hash32))
 	}
 	cache.SetLifetime(timeout)
-	cache.SetUpdateLifetimeOnGet(true)
 	cache.SetHealthCheck(func(port netip.AddrPort, conn *natConn) bool {
 		select {
 		case <-conn.doneChan:
@@ -60,25 +51,26 @@ func New(handler N.UDPConnectionHandlerEx, prepare PrepareFunc, timeout time.Dur
 }
 
 func (s *Service) NewPacket(bufferSlices [][]byte, source M.Socksaddr, destination M.Socksaddr, userData any) {
-	conn, loaded := s.cache.Get(source.AddrPort())
-	if !loaded {
+	conn, loaded := s.cache.GetAndRefreshOrAdd(source.AddrPort(), func() (*natConn, bool) {
 		ok, ctx, writer, onClose := s.prepare(source, destination, userData)
 		if !ok {
-			s.metrics.Rejects++
-			return
+			return nil, false
 		}
-		conn = &natConn{
-			service:      s,
+		newConn := &natConn{
+			cache:        s.cache,
 			writer:       writer,
 			localAddr:    source,
 			packetChan:   make(chan *N.PacketBuffer, 64),
 			doneChan:     make(chan struct{}),
 			readDeadline: pipe.MakeDeadline(),
 		}
-		s.PurgeExpired()
-		s.cache.Add(source.AddrPort(), conn)
-		go s.handler.NewPacketConnectionEx(ctx, conn, source, destination, onClose)
-		s.metrics.Creates++
+		go s.handler.NewPacketConnectionEx(ctx, newConn, source, destination, onClose)
+		return newConn, true
+	})
+	if !loaded {
+		if conn == nil {
+			return
+		}
 	}
 	buffer := conn.readWaitOptions.NewPacketBuffer()
 	for _, bufferSlice := range bufferSlices {
@@ -95,11 +87,9 @@ func (s *Service) NewPacket(bufferSlices [][]byte, source M.Socksaddr, destinati
 	}
 	select {
 	case conn.packetChan <- packet:
-		s.metrics.Inputs++
 	default:
 		packet.Buffer.Release()
 		N.PutPacketBuffer(packet)
-		s.metrics.Drops++
 	}
 }
 
@@ -110,13 +100,3 @@ func (s *Service) Purge() {
 func (s *Service) PurgeExpired() {
 	s.cache.PurgeExpired()
 }
-
-func (s *Service) Metrics() Metrics {
-	return s.metrics
-}
-
-func (s *Service) ResetMetrics() Metrics {
-	metrics := s.metrics
-	s.metrics = Metrics{}
-	return metrics
-}