chore: remove the redundant layer of udpnat in sing-tun to reduce resource usage when processing udp

go.mod

@@ -31,7 +31,7 @@ require (
 	github.com/metacubex/sing-shadowsocks v0.2.9
 	github.com/metacubex/sing-shadowsocks2 v0.2.3
 	github.com/metacubex/sing-shadowtls v0.0.0-20250503063515-5d9f966d17a2
-	github.com/metacubex/sing-tun v0.4.6-0.20250523121712-972bc1c2b1e7
+	github.com/metacubex/sing-tun v0.4.6-0.20250524070426-1a615b3de4c5
 	github.com/metacubex/sing-vmess v0.2.1
 	github.com/metacubex/sing-wireguard v0.0.0-20250503063753-2dc62acc626f
 	github.com/metacubex/smux v0.0.0-20250503055512-501391591dee

go.sum

@@ -128,8 +128,8 @@ github.com/metacubex/sing-shadowsocks2 v0.2.3 h1:v3rNS/5Ywh0NIZ6VU/NmdERQIN5RePz
 github.com/metacubex/sing-shadowsocks2 v0.2.3/go.mod h1:/WNy/Q8ahLCoPRriWuFZFD0Jy+JNp1MEQl28Zw6SaF8=
 github.com/metacubex/sing-shadowtls v0.0.0-20250503063515-5d9f966d17a2 h1:gXU+MYPm7Wme3/OAY2FFzVq9d9GxPHOqu5AQfg/ddhI=
 github.com/metacubex/sing-shadowtls v0.0.0-20250503063515-5d9f966d17a2/go.mod h1:mbfboaXauKJNIHJYxQRa+NJs4JU9NZfkA+I33dS2+9E=
-github.com/metacubex/sing-tun v0.4.6-0.20250523121712-972bc1c2b1e7 h1:vxkBCkZocH2de2tqeeCZxWvT1VjSJPFkE/8hGqvcLCQ=
+github.com/metacubex/sing-tun v0.4.6-0.20250524070426-1a615b3de4c5 h1:i+aNFgMMcGFl0vxh7xf4LwAWhc7OzOBdd9SKsWx6vdQ=
-github.com/metacubex/sing-tun v0.4.6-0.20250523121712-972bc1c2b1e7/go.mod h1:HDaHDL6onAX2ZGbAGUXKp++PohRdNb7Nzt6zxzhox+U=
+github.com/metacubex/sing-tun v0.4.6-0.20250524070426-1a615b3de4c5/go.mod h1:HDaHDL6onAX2ZGbAGUXKp++PohRdNb7Nzt6zxzhox+U=
 github.com/metacubex/sing-vmess v0.2.1 h1:I6gM3VUjtvJ15D805EUbNH+SRBuqzJeFnuIbKYUsWZ0=
 github.com/metacubex/sing-vmess v0.2.1/go.mod h1:DsODWItJtOMZNna8Qhheg8r3tUivrcO3vWgaTYKnfTo=
 github.com/metacubex/sing-wireguard v0.0.0-20250503063753-2dc62acc626f h1:Sr/DYKYofKHKc4GF3qkRGNuj6XA6c0eqPgEDN+VAsYU=

listener/sing/sing.go

@@ -146,11 +146,11 @@ func (h *ListenerHandler) NewConnection(ctx context.Context, conn net.Conn, meta
 func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.PacketConn, metadata M.Metadata) error {
 	defer func() { _ = conn.Close() }()
 	mutex := sync.Mutex{}
-	conn2 := bufio.NewNetPacketConn(conn) // a new interface to set nil in defer
+	writer := bufio.NewNetPacketWriter(conn) // a new interface to set nil in defer
 	defer func() {
 		mutex.Lock() // this goroutine must exit after all conn.WritePacket() is not running
 		defer mutex.Unlock()
-		conn2 = nil
+		writer = nil
 	}()
 	rwOptions := network.ReadWaitOptions{}
 	readWaiter, isReadWaiter := bufio.CreatePacketReadWaiter(conn)
@@ -180,30 +180,46 @@ func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.
 			return err
 		}
 		cPacket := &packet{
-			conn:  &conn2,
+			writer: &writer,
 			mutex:  &mutex,
 			rAddr:  metadata.Source.UDPAddr(),
 			lAddr:  conn.LocalAddr(),
 			buff:   buff,
 		}
+		h.handlePacket(ctx, cPacket, metadata.Source, dest)
+	}
+	return nil
+}
 
+func (h *ListenerHandler) NewPacket(ctx context.Context, key netip.AddrPort, buffer *buf.Buffer, metadata M.Metadata, init func(natConn network.PacketConn) network.PacketWriter) {
+	writer := bufio.NewNetPacketWriter(init(nil))
+	mutex := sync.Mutex{}
+	cPacket := &packet{
+		writer: &writer,
+		mutex:  &mutex,
+		rAddr:  metadata.Source.UDPAddr(),
+		lAddr:  metadata.Source.UDPAddr(), // tun does not have real inAddr
+		buff:   buffer,
+	}
+	h.handlePacket(ctx, cPacket, metadata.Source, metadata.Destination)
+}
+
+func (h *ListenerHandler) handlePacket(ctx context.Context, cPacket *packet, source M.Socksaddr, destination M.Socksaddr) {
 	cMetadata := &C.Metadata{
 		NetWork: C.UDP,
 		Type:    h.Type,
 	}
-		if metadata.Source.IsIP() && metadata.Source.Fqdn == "" {
+	if source.IsIP() && source.Fqdn == "" {
-			cMetadata.RawSrcAddr = metadata.Source.Unwrap().UDPAddr()
+		cMetadata.RawSrcAddr = source.Unwrap().UDPAddr()
 	}
-		if dest.IsIP() && dest.Fqdn == "" {
+	if destination.IsIP() && destination.Fqdn == "" {
-			cMetadata.RawDstAddr = dest.Unwrap().UDPAddr()
+		cMetadata.RawDstAddr = destination.Unwrap().UDPAddr()
 	}
-		inbound.ApplyAdditions(cMetadata, inbound.WithDstAddr(dest), inbound.WithSrcAddr(metadata.Source), inbound.WithInAddr(conn.LocalAddr()))
+	inbound.ApplyAdditions(cMetadata, inbound.WithDstAddr(destination), inbound.WithSrcAddr(source), inbound.WithInAddr(cPacket.InAddr()))
 	inbound.ApplyAdditions(cMetadata, h.Additions...)
 	inbound.ApplyAdditions(cMetadata, getAdditions(ctx)...)
 
 	h.Tunnel.HandleUDPPacket(cPacket, cMetadata)
-	}
-	return nil
 }
 
 func (h *ListenerHandler) NewError(ctx context.Context, err error) {
@@ -225,7 +241,7 @@ func ShouldIgnorePacketError(err error) bool {
 }
 
 type packet struct {
-	conn  *network.NetPacketConn
+	writer *network.NetPacketWriter
 	mutex  *sync.Mutex
 	rAddr  net.Addr
 	lAddr  net.Addr
@@ -245,7 +261,7 @@ func (c *packet) WriteBack(b []byte, addr net.Addr) (n int, err error) {
 
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
-	conn := *c.conn
+	conn := *c.writer
 	if conn == nil {
 		err = errors.New("writeBack to closed connection")
 		return

listener/sing_tun/dns.go

@@ -43,16 +43,31 @@ func (h *ListenerHandler) NewConnection(ctx context.Context, conn net.Conn, meta
 	return h.ListenerHandler.NewConnection(ctx, conn, metadata)
 }
 
+func (h *ListenerHandler) NewPacket(ctx context.Context, key netip.AddrPort, buffer *buf.Buffer, metadata M.Metadata, init func(natConn network.PacketConn) network.PacketWriter) {
+	if h.ShouldHijackDns(metadata.Destination.AddrPort()) {
+		log.Debugln("[DNS] hijack udp:%s from %s", metadata.Destination.String(), metadata.Source.String())
+		writer := init(nil)
+		rwOptions := network.ReadWaitOptions{
+			FrontHeadroom: network.CalculateFrontHeadroom(writer),
+			RearHeadroom:  network.CalculateRearHeadroom(writer),
+			MTU:           resolver.SafeDnsPacketSize,
+		}
+		go relayDnsPacket(ctx, buffer, rwOptions, metadata.Destination, nil, &writer)
+		return
+	}
+	h.ListenerHandler.NewPacket(ctx, key, buffer, metadata, init)
+}
+
 func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.PacketConn, metadata M.Metadata) error {
 	if h.ShouldHijackDns(metadata.Destination.AddrPort()) {
 		log.Debugln("[DNS] hijack udp:%s from %s", metadata.Destination.String(), metadata.Source.String())
 		defer func() { _ = conn.Close() }()
 		mutex := sync.Mutex{}
-		conn2 := conn // a new interface to set nil in defer
+		var writer network.PacketWriter = conn // a new interface to set nil in defer
 		defer func() {
 			mutex.Lock() // this goroutine must exit after all conn.WritePacket() is not running
 			defer mutex.Unlock()
-			conn2 = nil
+			writer = nil
 		}()
 		rwOptions := network.ReadWaitOptions{
 			FrontHeadroom: network.CalculateFrontHeadroom(conn),
@@ -89,7 +104,14 @@ func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.
 				}
 				return err
 			}
-			go func() {
+			go relayDnsPacket(ctx, readBuff, rwOptions, dest, &mutex, &writer)
+		}
+		return nil
+	}
+	return h.ListenerHandler.NewPacketConnection(ctx, conn, metadata)
+}
+
+func relayDnsPacket(ctx context.Context, readBuff *buf.Buffer, rwOptions network.ReadWaitOptions, dest M.Socksaddr, mutex *sync.Mutex, writer *network.PacketWriter) {
 	ctx, cancel := context.WithTimeout(ctx, resolver.DefaultDnsRelayTimeout)
 	defer cancel()
 	inData := readBuff.Bytes()
@@ -107,9 +129,11 @@ func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.
 		return
 	}
 	writeBuff.Truncate(len(msg))
+	if mutex != nil {
 		mutex.Lock()
 		defer mutex.Unlock()
-				conn := conn2
+	}
+	conn := *writer
 	if conn == nil {
 		writeBuff.Release()
 		return
@@ -119,11 +143,6 @@ func (h *ListenerHandler) NewPacketConnection(ctx context.Context, conn network.
 		writeBuff.Release()
 		return
 	}
-			}()
-		}
-		return nil
-	}
-	return h.ListenerHandler.NewPacketConnection(ctx, conn, metadata)
 }
 
 func (h *ListenerHandler) TypeMutation(typ C.Type) *ListenerHandler {