fix: sing-based listener panic

listener/sing/sing.go

@@ -58,6 +58,14 @@ func (c *waitCloseConn) Upstream() any {
 	return c.ExtendedConn
 }
 
+func (c *waitCloseConn) ReaderReplaceable() bool {
+	return true
+}
+
+func (c *waitCloseConn) WriterReplaceable() bool {
+	return true
+}
+
 func UpstreamMetadata(metadata M.Metadata) M.Metadata {
 	return M.Metadata{
 		Source:      metadata.Source,
@@ -116,7 +124,7 @@ func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.
 		defer mutex.Unlock()
 		conn2 = nil
 	}()
-	readWaiter, isReadWaiter := bufio.CreatePacketReadWaiter(conn)
+	connReader := network.UnwrapPacketReader(conn) // decrease runtime cost for bufio.CreatePacketReadWaiter
 	for {
 		var (
 			buff *buf.Buffer
@@ -127,7 +135,9 @@ func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.
 			buff = buf.NewPacket() // do not use stack buffer
 			return buff
 		}
-		if isReadWaiter {
+		// syscallPacketReadWaiter.WaitReadPacket will cache newBuffer function
+		// so create new PacketReadWaiter in each loop
+		if readWaiter, isReadWaiter := bufio.CreatePacketReadWaiter(connReader); isReadWaiter {
 			dest, err = readWaiter.WaitReadPacket(newBuffer)
 		} else {
 			dest, err = conn.ReadPacket(newBuffer())

listener/sing_shadowsocks/server.go

@@ -22,6 +22,7 @@ import (
 	"github.com/sagernet/sing/common/buf"
 	"github.com/sagernet/sing/common/bufio"
 	M "github.com/sagernet/sing/common/metadata"
+	"github.com/sagernet/sing/common/network"
 )
 
 type Listener struct {
@@ -92,7 +93,7 @@ func New(config LC.ShadowsocksServer, tcpIn chan<- C.ConnContext, udpIn chan<- C
 
 			go func() {
 				conn := bufio.NewPacketConn(ul)
-				readWaiter, isReadWaiter := bufio.CreatePacketReadWaiter(conn)
+				connReader := network.UnwrapPacketReader(conn) // decrease runtime cost for bufio.CreatePacketReadWaiter
 				for {
 					var (
 						buff *buf.Buffer
@@ -103,7 +104,9 @@ func New(config LC.ShadowsocksServer, tcpIn chan<- C.ConnContext, udpIn chan<- C
 						buff = buf.NewPacket() // do not use stack buffer
 						return buff
 					}
-					if isReadWaiter {
+					// syscallPacketReadWaiter.WaitReadPacket will cache newBuffer function
+					// so create new PacketReadWaiter in each loop
+					if readWaiter, isReadWaiter := bufio.CreatePacketReadWaiter(connReader); isReadWaiter {
 						dest, err = readWaiter.WaitReadPacket(newBuffer)
 					} else {
 						dest, err = conn.ReadPacket(newBuffer())

listener/sing_tun/dns.go

@@ -109,7 +109,8 @@ func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.
 			defer mutex.Unlock()
 			conn2 = nil
 		}()
-		readWaiter, isReadWaiter := bufio.CreatePacketReadWaiter(conn)
+
+		connReader := network.UnwrapPacketReader(conn) // decrease runtime cost for bufio.CreatePacketReadWaiter
 		for {
 			var (
 				buff *buf.Buffer
@@ -123,7 +124,9 @@ func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.
 				return buff
 			}
 			_ = conn.SetReadDeadline(time.Now().Add(DefaultDnsReadTimeout))
-			if isReadWaiter {
+			// syscallPacketReadWaiter.WaitReadPacket will cache newBuffer function
+			// so create new PacketReadWaiter in each loop
+			if readWaiter, isReadWaiter := bufio.CreatePacketReadWaiter(connReader); isReadWaiter {
 				dest, err = readWaiter.WaitReadPacket(newBuffer)
 			} else {
 				dest, err = conn.ReadPacket(newBuffer())