diff --git a/common/bufio/copy.go b/common/bufio/copy.go
index ebb03fe..506eab1 100644
--- a/common/bufio/copy.go
+++ b/common/bufio/copy.go
@@ -30,27 +30,38 @@ func Copy(destination io.Writer, source io.Reader) (n int64, err error) {
 			cachedBuffer := cachedSrc.ReadCached()
 			if cachedBuffer != nil {
 				if !cachedBuffer.IsEmpty() {
+					dataLen := cachedBuffer.Len()
+					for _, counter := range readCounters {
+						counter(int64(dataLen))
+					}
 					_, err = destination.Write(cachedBuffer.Bytes())
 					if err != nil {
 						cachedBuffer.Release()
 						return
 					}
+					for _, counter := range writeCounters {
+						counter(int64(dataLen))
+					}
 				}
 				cachedBuffer.Release()
 				continue
 			}
 		}
-		srcSyscallConn, srcIsSyscall := source.(syscall.Conn)
-		dstSyscallConn, dstIsSyscall := destination.(syscall.Conn)
-		if srcIsSyscall && dstIsSyscall {
-			var handled bool
-			handled, n, err = copyDirect(srcSyscallConn, dstSyscallConn, readCounters, writeCounters)
-			if handled {
-				return
-			}
-		}
 		break
 	}
+	return CopyWithCounters(destination, source, originSource, readCounters, writeCounters)
+}
+
+func CopyWithCounters(destination io.Writer, source io.Reader, originSource io.Reader, readCounters []N.CountFunc, writeCounters []N.CountFunc) (n int64, err error) {
+	srcSyscallConn, srcIsSyscall := source.(syscall.Conn)
+	dstSyscallConn, dstIsSyscall := destination.(syscall.Conn)
+	if srcIsSyscall && dstIsSyscall {
+		var handled bool
+		handled, n, err = copyDirect(srcSyscallConn, dstSyscallConn, readCounters, writeCounters)
+		if handled {
+			return
+		}
+	}
 	return CopyExtended(originSource, NewExtendedWriter(destination), NewExtendedReader(source), readCounters, writeCounters)
 }
 
@@ -75,6 +86,7 @@ func CopyExtended(originSource io.Reader, destination N.ExtendedWriter, source N
 	return CopyExtendedWithPool(originSource, destination, source, readCounters, writeCounters)
 }
 
+// Deprecated: not used
 func CopyExtendedBuffer(originSource io.Writer, destination N.ExtendedWriter, source N.ExtendedReader, buffer *buf.Buffer, readCounters []N.CountFunc, writeCounters []N.CountFunc) (n int64, err error) {
 	buffer.IncRef()
 	defer buffer.DecRef()
@@ -113,19 +125,10 @@ func CopyExtendedBuffer(originSource io.Writer, destination N.ExtendedWriter, so
 }
 
 func CopyExtendedWithPool(originSource io.Reader, destination N.ExtendedWriter, source N.ExtendedReader, readCounters []N.CountFunc, writeCounters []N.CountFunc) (n int64, err error) {
-	frontHeadroom := N.CalculateFrontHeadroom(destination)
-	rearHeadroom := N.CalculateRearHeadroom(destination)
-	bufferSize := N.CalculateMTU(source, destination)
-	if bufferSize > 0 {
-		bufferSize += frontHeadroom + rearHeadroom
-	} else {
-		bufferSize = buf.BufferSize
-	}
+	options := N.NewReadWaitOptions(source, destination)
 	var notFirstTime bool
 	for {
-		buffer := buf.NewSize(bufferSize)
-		buffer.Resize(frontHeadroom, 0)
-		buffer.Reserve(rearHeadroom)
+		buffer := options.NewBuffer()
 		err = source.ReadBuffer(buffer)
 		if err != nil {
 			buffer.Release()
@@ -136,7 +139,10 @@ func CopyExtendedWithPool(originSource io.Reader, destination N.ExtendedWriter,
 			return
 		}
 		dataLen := buffer.Len()
-		buffer.OverCap(rearHeadroom)
+		for _, counter := range readCounters {
+			counter(int64(dataLen))
+		}
+		options.PostReturn(buffer)
 		err = destination.WriteBuffer(buffer)
 		if err != nil {
 			buffer.Leak()
@@ -146,9 +152,6 @@ func CopyExtendedWithPool(originSource io.Reader, destination N.ExtendedWriter,
 			return
 		}
 		n += int64(dataLen)
-		for _, counter := range readCounters {
-			counter(int64(dataLen))
-		}
 		for _, counter := range writeCounters {
 			counter(int64(dataLen))
 		}
@@ -196,18 +199,6 @@ func CopyConn(ctx context.Context, source net.Conn, destination net.Conn) error
 	return group.Run(ctx)
 }
 
-// Deprecated: not used
-func CopyConnContextList(contextList []context.Context, source net.Conn, destination net.Conn) error {
-	switch len(contextList) {
-	case 0:
-		return CopyConn(context.Background(), source, destination)
-	case 1:
-		return CopyConn(contextList[0], source, destination)
-	default:
-		panic("invalid context list")
-	}
-}
-
 func CopyPacket(destinationConn N.PacketWriter, source N.PacketReader) (n int64, err error) {
 	var readCounters, writeCounters []N.CountFunc
 	var cachedPackets []*N.PacketBuffer
@@ -225,24 +216,24 @@ func CopyPacket(destinationConn N.PacketWriter, source N.PacketReader) (n int64,
 		break
 	}
 	if cachedPackets != nil {
-		n, err = WritePacketWithPool(originSource, destinationConn, cachedPackets)
+		n, err = WritePacketWithPool(originSource, destinationConn, cachedPackets, readCounters, writeCounters)
 		if err != nil {
 			return
 		}
 	}
-	frontHeadroom := N.CalculateFrontHeadroom(destinationConn)
-	rearHeadroom := N.CalculateRearHeadroom(destinationConn)
+	copeN, err := CopyPacketWithCounters(destinationConn, source, originSource, readCounters, writeCounters)
+	n += copeN
+	return
+}
+
+func CopyPacketWithCounters(destinationConn N.PacketWriter, source N.PacketReader, originSource N.PacketReader, readCounters []N.CountFunc, writeCounters []N.CountFunc) (n int64, err error) {
 	var (
 		handled bool
 		copeN   int64
 	)
 	readWaiter, isReadWaiter := CreatePacketReadWaiter(source)
 	if isReadWaiter {
-		needCopy := readWaiter.InitializeReadWaiter(N.ReadWaitOptions{
-			FrontHeadroom: frontHeadroom,
-			RearHeadroom:  rearHeadroom,
-			MTU:           N.CalculateMTU(source, destinationConn),
-		})
+		needCopy := readWaiter.InitializeReadWaiter(N.NewReadWaitOptions(source, destinationConn))
 		if !needCopy || common.LowMemory {
 			handled, copeN, err = copyPacketWaitWithPool(originSource, destinationConn, readWaiter, readCounters, writeCounters, n > 0)
 			if handled {
@@ -256,28 +247,22 @@ func CopyPacket(destinationConn N.PacketWriter, source N.PacketReader) (n int64,
 	return
 }
 
-func CopyPacketWithPool(originSource N.PacketReader, destinationConn N.PacketWriter, source N.PacketReader, readCounters []N.CountFunc, writeCounters []N.CountFunc, notFirstTime bool) (n int64, err error) {
-	frontHeadroom := N.CalculateFrontHeadroom(destinationConn)
-	rearHeadroom := N.CalculateRearHeadroom(destinationConn)
-	bufferSize := N.CalculateMTU(source, destinationConn)
-	if bufferSize > 0 {
-		bufferSize += frontHeadroom + rearHeadroom
-	} else {
-		bufferSize = buf.UDPBufferSize
-	}
-	var destination M.Socksaddr
+func CopyPacketWithPool(originSource N.PacketReader, destination N.PacketWriter, source N.PacketReader, readCounters []N.CountFunc, writeCounters []N.CountFunc, notFirstTime bool) (n int64, err error) {
+	options := N.NewReadWaitOptions(source, destination)
+	var destinationAddress M.Socksaddr
 	for {
-		buffer := buf.NewSize(bufferSize)
-		buffer.Resize(frontHeadroom, 0)
-		buffer.Reserve(rearHeadroom)
-		destination, err = source.ReadPacket(buffer)
+		buffer := options.NewPacketBuffer()
+		destinationAddress, err = source.ReadPacket(buffer)
 		if err != nil {
 			buffer.Release()
 			return
 		}
 		dataLen := buffer.Len()
-		buffer.OverCap(rearHeadroom)
-		err = destinationConn.WritePacket(buffer, destination)
+		for _, counter := range readCounters {
+			counter(int64(dataLen))
+		}
+		options.PostReturn(buffer)
+		err = destination.WritePacket(buffer, destinationAddress)
 		if err != nil {
 			buffer.Leak()
 			if !notFirstTime {
@@ -285,34 +270,25 @@ func CopyPacketWithPool(originSource N.PacketReader, destinationConn N.PacketWri
 			}
 			return
 		}
-		n += int64(dataLen)
-		for _, counter := range readCounters {
-			counter(int64(dataLen))
-		}
 		for _, counter := range writeCounters {
 			counter(int64(dataLen))
 		}
+		n += int64(dataLen)
 		notFirstTime = true
 	}
 }
 
-func WritePacketWithPool(originSource N.PacketReader, destinationConn N.PacketWriter, packetBuffers []*N.PacketBuffer) (n int64, err error) {
-	frontHeadroom := N.CalculateFrontHeadroom(destinationConn)
-	rearHeadroom := N.CalculateRearHeadroom(destinationConn)
+func WritePacketWithPool(originSource N.PacketReader, destination N.PacketWriter, packetBuffers []*N.PacketBuffer, readCounters []N.CountFunc, writeCounters []N.CountFunc) (n int64, err error) {
+	options := N.NewReadWaitOptions(nil, destination)
 	var notFirstTime bool
 	for _, packetBuffer := range packetBuffers {
-		buffer := buf.NewPacket()
-		buffer.Resize(frontHeadroom, 0)
-		buffer.Reserve(rearHeadroom)
-		_, err = buffer.Write(packetBuffer.Buffer.Bytes())
-		packetBuffer.Buffer.Release()
-		if err != nil {
-			buffer.Release()
-			continue
+		for _, counter := range readCounters {
+			counter(int64(packetBuffer.Buffer.Len()))
 		}
+		buffer := options.Copy(packetBuffer.Buffer)
 		dataLen := buffer.Len()
-		buffer.OverCap(rearHeadroom)
-		err = destinationConn.WritePacket(buffer, packetBuffer.Destination)
+		err = destination.WritePacket(buffer, packetBuffer.Destination)
+		N.PutPacketBuffer(packetBuffer)
 		if err != nil {
 			buffer.Leak()
 			if !notFirstTime {
@@ -320,7 +296,11 @@ func WritePacketWithPool(originSource N.PacketReader, destinationConn N.PacketWr
 			}
 			return
 		}
+		for _, counter := range writeCounters {
+			counter(int64(dataLen))
+		}
 		n += int64(dataLen)
+		notFirstTime = true
 	}
 	return
 }
@@ -339,15 +319,3 @@ func CopyPacketConn(ctx context.Context, source N.PacketConn, destination N.Pack
 	group.FastFail()
 	return group.Run(ctx)
 }
-
-// Deprecated: not used
-func CopyPacketConnContextList(contextList []context.Context, source N.PacketConn, destination N.PacketConn) error {
-	switch len(contextList) {
-	case 0:
-		return CopyPacketConn(context.Background(), source, destination)
-	case 1:
-		return CopyPacketConn(contextList[0], source, destination)
-	default:
-		panic("invalid context list")
-	}
-}
diff --git a/common/network/direct.go b/common/network/direct.go
index 1122d70..f587cd6 100644
--- a/common/network/direct.go
+++ b/common/network/direct.go
@@ -15,6 +15,14 @@ type ReadWaitOptions struct {
 	MTU           int
 }
 
+func NewReadWaitOptions(source any, destination any) ReadWaitOptions {
+	return ReadWaitOptions{
+		FrontHeadroom: CalculateFrontHeadroom(destination),
+		RearHeadroom:  CalculateRearHeadroom(destination),
+		MTU:           CalculateMTU(source, destination),
+	}
+}
+
 func (o ReadWaitOptions) NeedHeadroom() bool {
 	return o.FrontHeadroom > 0 || o.RearHeadroom > 0
 }
diff --git a/common/udpnat2/conn.go b/common/udpnat2/conn.go
index 5d474e6..9d5bfa9 100644
--- a/common/udpnat2/conn.go
+++ b/common/udpnat2/conn.go
@@ -12,7 +12,14 @@ import (
 	"github.com/sagernet/sing/common/pipe"
 )
 
-type Conn struct {
+type Conn interface {
+	N.PacketConn
+	SetHandler(handler N.UDPHandlerEx)
+}
+
+var _ Conn = (*natConn)(nil)
+
+type natConn struct {
 	writer          N.PacketWriter
 	localAddr       M.Socksaddr
 	handler         N.UDPHandlerEx
@@ -22,7 +29,7 @@ type Conn struct {
 	readWaitOptions N.ReadWaitOptions
 }
 
-func (c *Conn) ReadPacket(buffer *buf.Buffer) (addr M.Socksaddr, err error) {
+func (c *natConn) ReadPacket(buffer *buf.Buffer) (addr M.Socksaddr, err error) {
 	select {
 	case p := <-c.packetChan:
 		_, err = buffer.ReadOnceFrom(p.Buffer)
@@ -37,12 +44,17 @@ func (c *Conn) ReadPacket(buffer *buf.Buffer) (addr M.Socksaddr, err error) {
 	}
 }
 
-func (c *Conn) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
+func (c *natConn) WritePacket(buffer *buf.Buffer, destination M.Socksaddr) error {
 	return c.writer.WritePacket(buffer, destination)
 }
 
-func (c *Conn) SetHandler(handler N.UDPHandlerEx) {
+func (c *natConn) SetHandler(handler N.UDPHandlerEx) {
+	select {
+	case <-c.doneChan:
+	default:
+	}
 	c.handler = handler
+	c.readWaitOptions = N.NewReadWaitOptions(c.writer, handler)
 fetch:
 	for {
 		select {
@@ -56,12 +68,12 @@ fetch:
 	}
 }
 
-func (c *Conn) InitializeReadWaiter(options N.ReadWaitOptions) (needCopy bool) {
+func (c *natConn) InitializeReadWaiter(options N.ReadWaitOptions) (needCopy bool) {
 	c.readWaitOptions = options
 	return false
 }
 
-func (c *Conn) WaitReadPacket() (buffer *buf.Buffer, destination M.Socksaddr, err error) {
+func (c *natConn) WaitReadPacket() (buffer *buf.Buffer, destination M.Socksaddr, err error) {
 	select {
 	case packet := <-c.packetChan:
 		buffer = c.readWaitOptions.Copy(packet.Buffer)
@@ -75,7 +87,7 @@ func (c *Conn) WaitReadPacket() (buffer *buf.Buffer, destination M.Socksaddr, er
 	}
 }
 
-func (c *Conn) Close() error {
+func (c *natConn) Close() error {
 	select {
 	case <-c.doneChan:
 	default:
@@ -84,27 +96,27 @@ func (c *Conn) Close() error {
 	return nil
 }
 
-func (c *Conn) LocalAddr() net.Addr {
+func (c *natConn) LocalAddr() net.Addr {
 	return c.localAddr
 }
 
-func (c *Conn) RemoteAddr() net.Addr {
+func (c *natConn) RemoteAddr() net.Addr {
 	return M.Socksaddr{}
 }
 
-func (c *Conn) SetDeadline(t time.Time) error {
+func (c *natConn) SetDeadline(t time.Time) error {
 	return os.ErrInvalid
 }
 
-func (c *Conn) SetReadDeadline(t time.Time) error {
+func (c *natConn) SetReadDeadline(t time.Time) error {
 	c.readDeadline.Set(t)
 	return nil
 }
 
-func (c *Conn) SetWriteDeadline(t time.Time) error {
+func (c *natConn) SetWriteDeadline(t time.Time) error {
 	return os.ErrInvalid
 }
 
-func (c *Conn) Upstream() any {
+func (c *natConn) Upstream() any {
 	return c.writer
 }
diff --git a/common/udpnat2/service.go b/common/udpnat2/service.go
index 4bbef75..ac5da1d 100644
--- a/common/udpnat2/service.go
+++ b/common/udpnat2/service.go
@@ -14,7 +14,7 @@ import (
 )
 
 type Service struct {
-	cache   freelru.Cache[netip.AddrPort, *Conn]
+	cache   freelru.Cache[netip.AddrPort, *natConn]
 	handler N.UDPConnectionHandlerEx
 	prepare PrepareFunc
 	metrics Metrics
@@ -30,15 +30,15 @@ type Metrics struct {
 }
 
 func New(handler N.UDPConnectionHandlerEx, prepare PrepareFunc, timeout time.Duration, shared bool) *Service {
-	var cache freelru.Cache[netip.AddrPort, *Conn]
+	var cache freelru.Cache[netip.AddrPort, *natConn]
 	if !shared {
-		cache = common.Must1(freelru.New[netip.AddrPort, *Conn](1024, maphash.NewHasher[netip.AddrPort]().Hash32))
+		cache = common.Must1(freelru.New[netip.AddrPort, *natConn](1024, maphash.NewHasher[netip.AddrPort]().Hash32))
 	} else {
-		cache = common.Must1(freelru.NewSharded[netip.AddrPort, *Conn](1024, maphash.NewHasher[netip.AddrPort]().Hash32))
+		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 *Conn) bool {
+	cache.SetHealthCheck(func(port netip.AddrPort, conn *natConn) bool {
 		select {
 		case <-conn.doneChan:
 			return false
@@ -46,7 +46,7 @@ func New(handler N.UDPConnectionHandlerEx, prepare PrepareFunc, timeout time.Dur
 			return true
 		}
 	})
-	cache.SetOnEvict(func(_ netip.AddrPort, conn *Conn) {
+	cache.SetOnEvict(func(_ netip.AddrPort, conn *natConn) {
 		conn.Close()
 	})
 	return &Service{
@@ -64,7 +64,7 @@ func (s *Service) NewPacket(bufferSlices [][]byte, source M.Socksaddr, destinati
 			s.metrics.Rejects++
 			return
 		}
-		conn = &Conn{
+		conn = &natConn{
 			writer:       writer,
 			localAddr:    source,
 			packetChan:   make(chan *N.PacketBuffer, 64),