begin adding udp conn (#69)

* begin adding udp conn * udp tests passing * bugfixes for udp Send,Abort,Encapsulate methods * document UDP methods
2026-08-15 04:13:44 +00:00 · 2026-04-10 00:34:37 -03:00
parent 568ef2854f
commit 0382410f02
6 changed files with 731 additions and 6 deletions
@@ -0,0 +1,231 @@
+package udp
+
+import (
+	"net"
+	"os"
+	"sync"
+	"time"
+
+	"github.com/soypat/lneto"
+	"github.com/soypat/lneto/internal"
+)
+
+var _ lneto.StackNode = (*Conn)(nil)
+
+// Conn implements a UDP datagram socket with SOCK_DGRAM semantics.
+// Each [Conn.Write] enqueues one datagram and each [Conn.Read] dequeues one complete datagram.
+type Conn struct {
+	mu sync.Mutex
+	h  Handler
+
+	remoteAddr []byte
+
+	rdead time.Time
+	wdead time.Time
+
+	ipID uint16
+}
+
+// ConnConfig configures a [Conn] or [Handler] with pre-allocated buffers and queue sizes.
+type ConnConfig struct {
+	// RxBuf is the buffer for incoming datagrams.
+	RxBuf []byte
+	// TxBuf is the buffer for outgoing datagrams.
+	TxBuf []byte
+	// RxQueueSize is the maximum number of incoming datagrams that can be queued.
+	RxQueueSize int
+	// TxQueueSize is the maximum number of outgoing datagrams that can be queued.
+	TxQueueSize int
+}
+
+// Configure initializes the connection with the given buffer and queue configuration.
+// Must be called before [Conn.Open]. Calling Configure on an active connection aborts it.
+func (conn *Conn) Configure(cfg ConnConfig) error {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	conn.abort()
+	err := conn.h.Configure(cfg)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// Abort resets the connection, discarding all buffered data and clearing deadlines.
+func (conn *Conn) Abort() {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	conn.h.Abort()
+	conn.abort()
+}
+
+func (conn *Conn) abort() {
+	conn.rdead = time.Time{}
+	conn.wdead = time.Time{}
+	conn.remoteAddr = conn.remoteAddr[:0]
+}
+
+// Open sets the local port and remote address for the connection.
+func (conn *Conn) Open(localPort, remotePort uint16, remoteAddr []byte) error {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	conn.abort()
+	err := conn.h.SetPorts(localPort, remotePort)
+	if err != nil {
+		return err
+	}
+	conn.remoteAddr = append(conn.remoteAddr[:0], remoteAddr...)
+	return nil
+}
+
+// LocalPort returns the local port set by [Conn.Open].
+func (conn *Conn) LocalPort() uint16 {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	return conn.h.lport
+}
+
+// RemotePort returns the remote port set by [Conn.Open].
+func (conn *Conn) RemotePort() uint16 { return conn.h.rport }
+
+// RemoteAddr returns the remote address set by [Conn.Open].
+func (conn *Conn) RemoteAddr() []byte {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	return conn.remoteAddr
+}
+
+// Protocol returns [lneto.IPProtoUDP].
+func (conn *Conn) Protocol() uint64 { return uint64(lneto.IPProtoUDP) }
+
+// ConnectionID returns a pointer to the connection ID. The value changes on
+// each [Conn.Configure] or [Conn.Abort] call, signaling to the stack that the
+// previous registration is no longer valid.
+func (conn *Conn) ConnectionID() *uint64 { return &conn.h.connid }
+
+// Write enqueues a single datagram to be sent. The entire payload is queued atomically.
+func (conn *Conn) Write(b []byte) (int, error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
+	backoff := internal.NewBackoff(internal.BackoffTCPConn)
+	for {
+		if conn.deadlineExceeded(&conn.wdead) {
+			return 0, os.ErrDeadlineExceeded
+		}
+		conn.mu.Lock()
+		if conn.h.closeCalled {
+			conn.mu.Unlock()
+			return 0, net.ErrClosed
+		}
+		n, err := conn.h.Write(b)
+		conn.mu.Unlock()
+		if n > 0 {
+			return n, err
+		}
+		backoff.Miss()
+	}
+}
+
+// Read dequeues a single datagram. If the buffer is smaller than the datagram,
+// the remaining bytes are discarded (SOCK_DGRAM semantics).
+func (conn *Conn) Read(b []byte) (int, error) {
+	backoff := internal.NewBackoff(internal.BackoffTCPConn)
+	for {
+		if conn.deadlineExceeded(&conn.rdead) {
+			return 0, os.ErrDeadlineExceeded
+		}
+		conn.mu.Lock()
+		if conn.h.closeCalled && conn.h.BufferedInput() == 0 {
+			conn.mu.Unlock()
+			return 0, net.ErrClosed
+		}
+		n, err := conn.h.Read(b)
+		conn.mu.Unlock()
+		if n > 0 {
+			return n, err
+		}
+		backoff.Miss()
+	}
+}
+
+// Close marks the connection as closed. Subsequent calls to [Conn.Write] and
+// [Conn.Demux] return [net.ErrClosed]. [Conn.Read] continues to return buffered
+// data until exhausted, then returns [net.ErrClosed].
+func (conn *Conn) Close() error {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	conn.h.Close()
+	return nil
+}
+
+// Demux receives an incoming UDP payload into the rx ring buffer.
+func (conn *Conn) Demux(carrierData []byte, frameOffset int) error {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	if conn.h.closeCalled {
+		return net.ErrClosed
+	}
+	return conn.h.Recv(carrierData[frameOffset:])
+}
+
+// Encapsulate writes a queued outgoing datagram into the carrier buffer.
+func (conn *Conn) Encapsulate(carrierData []byte, offsetToIP, offsetToFrame int) (int, error) {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	if conn.h.closeCalled {
+		return 0, net.ErrClosed
+	}
+	n, err := conn.h.Send(carrierData[offsetToFrame:])
+	if err != nil || n == 0 {
+		return 0, err
+	}
+	if offsetToIP >= 0 && len(conn.remoteAddr) > 0 {
+		err = internal.SetIPAddrs(carrierData[offsetToIP:], conn.ipID, nil, conn.remoteAddr)
+		if err != nil {
+			return 0, err
+		}
+		conn.ipID++
+	}
+	return n, nil
+}
+
+// SetDeadline sets both the read and write deadlines. A zero value disables the deadline.
+func (conn *Conn) SetDeadline(t time.Time) error {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	if conn.h.closeCalled {
+		return net.ErrClosed
+	}
+	conn.rdead = t
+	conn.wdead = t
+	return nil
+}
+
+// SetReadDeadline sets the read deadline. A zero value disables the deadline.
+func (conn *Conn) SetReadDeadline(t time.Time) error {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	if conn.h.closeCalled {
+		return net.ErrClosed
+	}
+	conn.rdead = t
+	return nil
+}
+
+// SetWriteDeadline sets the write deadline. A zero value disables the deadline.
+func (conn *Conn) SetWriteDeadline(t time.Time) error {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	if conn.h.closeCalled {
+		return net.ErrClosed
+	}
+	conn.wdead = t
+	return nil
+}
+
+func (conn *Conn) deadlineExceeded(deadline *time.Time) bool {
+	conn.mu.Lock()
+	defer conn.mu.Unlock()
+	return !deadline.IsZero() && time.Since(*deadline) > 0
+}
@@ -0,0 +1,240 @@
+package udp
+
+import (
+	"encoding/binary"
+	"testing"
+
+	"github.com/soypat/lneto/internal"
+)
+
+// makeUDPFrame builds a minimal UDP frame with the given ports and payload.
+func makeUDPFrame(src, dst uint16, payload []byte) []byte {
+	buf := make([]byte, 8+len(payload))
+	binary.BigEndian.PutUint16(buf[0:2], src)
+	binary.BigEndian.PutUint16(buf[2:4], dst)
+	binary.BigEndian.PutUint16(buf[4:6], uint16(8+len(payload)))
+	copy(buf[8:], payload)
+	return buf
+}
+
+func newTestConn(t *testing.T) *Conn {
+	t.Helper()
+	var conn Conn
+	err := conn.Configure(ConnConfig{
+		RxBuf:       make([]byte, 256),
+		TxBuf:       make([]byte, 256),
+		RxQueueSize: 4,
+		TxQueueSize: 4,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = conn.Open(1234, 8080, []byte{10, 0, 0, 1})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return &conn
+}
+
+func TestConn_WriteEncapsulateRoundtrip(t *testing.T) {
+	conn := newTestConn(t)
+	payload := []byte("hello udp")
+	n, err := conn.Write(payload)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != len(payload) {
+		t.Fatalf("wrote %d, want %d", n, len(payload))
+	}
+
+	var buf [128]byte
+	n, err = conn.Encapsulate(buf[:], -1, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantLen := 8 + len(payload) // UDP header + payload
+	if n != wantLen {
+		t.Fatalf("encapsulated %d, want %d", n, wantLen)
+	}
+	ufrm, err := NewFrame(buf[:n])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !internal.BytesEqual(ufrm.Payload(), payload) {
+		t.Fatalf("encapsulated payload mismatch")
+	}
+
+	// No more data pending.
+	n, err = conn.Encapsulate(buf[:], -1, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 0 {
+		t.Fatalf("expected no pending data, got %d", n)
+	}
+}
+
+func TestConn_DemuxReadRoundtrip(t *testing.T) {
+	conn := newTestConn(t)
+	payload := []byte("incoming datagram")
+	frame := makeUDPFrame(8080, 1234, payload) // remote:8080 -> local:1234
+	err := conn.Demux(frame, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var buf [64]byte
+	n, err := conn.Read(buf[:])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != len(payload) {
+		t.Fatalf("read %d, want %d", n, len(payload))
+	}
+	if !internal.BytesEqual(buf[:n], payload) {
+		t.Fatal("read data mismatch")
+	}
+}
+
+func TestConn_MultipleDatagrams(t *testing.T) {
+	conn := newTestConn(t)
+	messages := []string{"first", "second", "third"}
+	for _, msg := range messages {
+		frame := makeUDPFrame(8080, 1234, []byte(msg))
+		err := conn.Demux(frame, 0)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// Read back in order.
+	var buf [64]byte
+	for _, want := range messages {
+		n, err := conn.Read(buf[:])
+		if err != nil {
+			t.Fatal(err)
+		}
+		got := string(buf[:n])
+		if got != want {
+			t.Fatalf("got %q, want %q", got, want)
+		}
+	}
+}
+
+func TestConn_ReadTruncates(t *testing.T) {
+	conn := newTestConn(t)
+	payload := []byte("a_longer_datagram")
+	frame := makeUDPFrame(8080, 1234, payload)
+	err := conn.Demux(frame, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Read into small buffer: truncates, discards remainder.
+	var buf [4]byte
+	n, err := conn.Read(buf[:])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != len(buf) {
+		t.Fatalf("read %d, want %d", n, len(buf))
+	}
+	if !internal.BytesEqual(buf[:], payload[:4]) {
+		t.Fatal("truncated data mismatch")
+	}
+
+	// Next Demux+Read should work cleanly after truncation.
+	payload2 := []byte("ok")
+	frame2 := makeUDPFrame(8080, 1234, payload2)
+	err = conn.Demux(frame2, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var buf2 [64]byte
+	n, err = conn.Read(buf2[:])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !internal.BytesEqual(buf2[:n], payload2) {
+		t.Fatal("post-truncation read mismatch")
+	}
+}
+
+func TestConn_DemuxExhausted(t *testing.T) {
+	conn := newTestConn(t) // queue size 4
+	for i := 0; i < 4; i++ {
+		frame := makeUDPFrame(8080, 1234, []byte{byte(i)})
+		err := conn.Demux(frame, 0)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+	// 5th should fail.
+	frame := makeUDPFrame(8080, 1234, []byte{0xff})
+	err := conn.Demux(frame, 0)
+	if err == nil {
+		t.Fatal("expected error on exhausted rx queue")
+	}
+}
+
+func TestConn_ClosedBehavior(t *testing.T) {
+	conn := newTestConn(t)
+	conn.Close()
+
+	_, err := conn.Write([]byte("data"))
+	if err == nil {
+		t.Fatal("expected error writing to closed conn")
+	}
+
+	err = conn.Demux([]byte("data"), 0)
+	if err == nil {
+		t.Fatal("expected error demuxing to closed conn")
+	}
+}
+
+func TestConn_EncapsulateMultiple(t *testing.T) {
+	conn := newTestConn(t)
+	msgs := []string{"aaa", "bbb"}
+	for _, msg := range msgs {
+		_, err := conn.Write([]byte(msg))
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	var buf [128]byte
+	for _, want := range msgs {
+		n, err := conn.Encapsulate(buf[:], -1, 0)
+		if err != nil {
+			t.Fatal(err)
+		}
+		ufrm, err := NewFrame(buf[:n])
+		if err != nil {
+			t.Fatal(err)
+		}
+		got := string(ufrm.Payload())
+		if got != want {
+			t.Fatalf("got %q, want %q", got, want)
+		}
+	}
+}
+
+func TestConn_FrameOffset(t *testing.T) {
+	conn := newTestConn(t)
+	// Demux with an offset simulating IP header before the UDP frame.
+	udpFrame := makeUDPFrame(8080, 1234, []byte("hi"))
+	carrier := make([]byte, 8+len(udpFrame)) // 8 bytes of "IP header" prefix
+	copy(carrier[8:], udpFrame)
+	err := conn.Demux(carrier, 8)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var buf [8]byte
+	n, err := conn.Read(buf[:])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(buf[:n]) != "hi" {
+		t.Fatalf("got %q, want %q", string(buf[:n]), "hi")
+	}
+}
@@ -1,5 +0,0 @@
-package udp
-
-const (
-	sizeHeader = 8
-)
@@ -6,6 +6,8 @@ import (
 	"github.com/soypat/lneto"
 )

+const sizeHeader = 8
+
 // NewFrame returns a new udp.Frame with data set to buf.
 // An error is returned if the buffer size is smaller than 8.
 // Users should still call [Frame.ValidateSize] before working
@@ -0,0 +1,214 @@
+package udp
+
+import (
+	"fmt"
+	"net"
+
+	"github.com/soypat/lneto"
+	"github.com/soypat/lneto/internal"
+)
+
+// Handler implements the stateless UDP frame processing logic. It manages
+// rx/tx ring buffers and datagram queues without locking or deadlines.
+// [Conn] wraps Handler to provide a goroutine-safe socket API.
+type Handler struct {
+	connid   uint64
+	rxRing   internal.Ring
+	rxDgrams []struct {
+		length uint16
+	}
+
+	txRing   internal.Ring
+	txDgrams []struct {
+		length uint16
+	}
+	closeCalled bool
+	lport       uint16
+	rport       uint16
+}
+
+// Configure initializes the handler with the given buffer and queue configuration.
+// Increments the connection ID, invalidating any prior stack registration.
+func (h *Handler) Configure(cfg ConnConfig) error {
+	if len(cfg.RxBuf) < sizeHeader || len(cfg.TxBuf) < sizeHeader || cfg.RxQueueSize <= 0 || cfg.TxQueueSize <= 0 {
+		return lneto.ErrInvalidConfig
+	}
+	h.connid++
+	h.rxRing = internal.Ring{Buf: cfg.RxBuf}
+	h.txRing = internal.Ring{Buf: cfg.TxBuf}
+	internal.SliceReuse(&h.rxDgrams, cfg.RxQueueSize)
+	internal.SliceReuse(&h.txDgrams, cfg.TxQueueSize)
+	h.closeCalled = false
+	h.lport = 0
+	h.rport = 0
+	return nil
+}
+
+// SetPorts sets the local and remote ports for the connection.
+// Both ports must be non-zero.
+func (h *Handler) SetPorts(localPort, remotePort uint16) error {
+	if localPort == 0 {
+		return lneto.ErrZeroSource
+	} else if remotePort == 0 {
+		return lneto.ErrZeroDestination
+	}
+	h.lport = localPort
+	h.rport = remotePort
+	return nil
+}
+
+// LocalPort returns the local port set by [Handler.SetPorts].
+func (h *Handler) LocalPort() uint16 {
+	return h.lport
+}
+
+// Recv parses a UDP frame from buf, validates the ports and length fields,
+// and enqueues the payload into the rx ring buffer. Returns [lneto.ErrMismatch]
+// if source/destination ports don't match the configured ports.
+func (h *Handler) Recv(buf []byte) error {
+	if h.closeCalled {
+		return net.ErrClosed
+	}
+	ufrm, err := NewFrame(buf)
+	if err != nil {
+		return err
+	} else if ufrm.DestinationPort() != h.lport || ufrm.SourcePort() != h.rport {
+		return lneto.ErrMismatch
+	}
+	// Header size validation.
+	// No CRC validation at this level.
+	ul := ufrm.Length()
+	if ul < sizeHeader {
+		return lneto.ErrInvalidLengthField
+	} else if int(ul) > len(ufrm.RawData()) {
+		return lneto.ErrTruncatedFrame
+	}
+
+	free := cap(h.rxDgrams) - len(h.rxDgrams)
+	if free == 0 {
+		return lneto.ErrExhausted
+	}
+	payload := ufrm.Payload()
+	_, err = h.rxRing.Write(payload)
+	if err != nil {
+		return err
+	}
+	dgram := internal.SliceReclaim(&h.rxDgrams)
+	dgram.length = uint16(len(payload))
+	return nil
+}
+
+// Send dequeues the next pending datagram and writes a complete UDP frame
+// (header + payload) into buf. Returns 0, nil if no datagrams are queued.
+func (h *Handler) Send(buf []byte) (int, error) {
+	if h.closeCalled {
+		return 0, net.ErrClosed
+	} else if len(h.txDgrams) == 0 {
+		return 0, nil
+	}
+	ufrm, err := NewFrame(buf)
+	if err != nil {
+		return 0, err
+	}
+	avail := len(buf) - 8
+	if avail < int(h.txDgrams[0].length) {
+		return 0, lneto.ErrShortBuffer
+	}
+	dgram := internal.SliceDequeueFront(&h.txDgrams)
+	n, err := h.txRing.Read(buf[8 : 8+dgram.length])
+	if err != nil || n != int(dgram.length) {
+		panic(fmt.Sprintf("udp send handler failure %d %s", n, err))
+	}
+	ufrm.SetSourcePort(h.lport)
+	ufrm.SetDestinationPort(h.rport)
+	ufrm.SetLength(8 + dgram.length)
+	return int(8 + dgram.length), nil
+}
+
+// Write enqueues a datagram payload for later transmission via [Handler.Send].
+// Returns [lneto.ErrExhausted] if the tx datagram queue is full.
+func (h *Handler) Write(b []byte) (int, error) {
+	free := cap(h.txDgrams) - len(h.txDgrams)
+	if free == 0 {
+		return 0, lneto.ErrExhausted
+	}
+	_, err := h.txRing.Write(b)
+	if err != nil {
+		return 0, err
+	}
+	dgram := internal.SliceReclaim(&h.txDgrams)
+	dgram.length = uint16(len(b))
+	return len(b), nil
+}
+
+// Read dequeues the next received datagram into b. If b is smaller than the
+// datagram, the remaining bytes are discarded (SOCK_DGRAM semantics).
+// Returns 0, nil if no datagrams are available.
+func (h *Handler) Read(b []byte) (int, error) {
+	if len(h.rxDgrams) == 0 {
+		return 0, nil
+	}
+	// SOCK_DGRAM semantics. Read up to len(b) bytes and discard unread portion of datagram.
+	dgram := internal.SliceDequeueFront(&h.rxDgrams)
+	n, err := h.rxRing.Read(b[:min(len(b), int(dgram.length))])
+	if err != nil {
+		panic(fmt.Sprintf("udp read handler failure %d %s", n, err))
+	}
+	discard := int(dgram.length) - len(b)
+	if discard > 0 {
+		err = h.rxRing.ReadDiscard(discard)
+		if err != nil {
+			panic(fmt.Sprintf("udp readdiscard handler failure %d %s", n, err))
+		}
+	}
+	return n, nil
+}
+
+// Close closes the connection. Calls to [Handler.Send] and [Handler.Recv] will
+// return [net.ErrClosed] after Close is called.
+func (h *Handler) Close() {
+	h.closeCalled = true
+}
+
+// Abort resets the handler, discarding all buffered data and incrementing the
+// connection ID. Buffers are retained for reuse.
+func (h *Handler) Abort() {
+	*h = Handler{
+		connid:   h.connid + 1,
+		rxRing:   h.rxRing,
+		rxDgrams: h.rxDgrams[:0],
+		txRing:   h.txRing,
+		txDgrams: h.txDgrams[:0],
+	}
+	h.txRing.Reset()
+	h.rxRing.Reset()
+}
+
+// BufferedInputNext returns the size of the next datagram to read. A call
+// to [Handler.Read] will read up to this amount of bytes.
+func (h *Handler) BufferedInputNext() int {
+	if len(h.rxDgrams) == 0 {
+		return 0
+	}
+	return int(h.rxDgrams[0].length)
+}
+
+// BufferedInput returns the number of unread bytes in the receive buffer.
+func (h *Handler) BufferedInput() int {
+	return h.rxRing.Buffered()
+}
+
+// BufferedUnsent returns the number of written but unsent bytes in the transmit buffer.
+func (h *Handler) BufferedOutput() int {
+	return h.txRing.Buffered()
+}
+
+// SizeInput returns the total size of the receive ring buffer.
+func (h *Handler) SizeInput() int {
+	return h.rxRing.Size()
+}
+
+// SizeOutput returns the total size of the transmit ring buffer.
+func (h *Handler) SizeOutput() int {
+	return h.txRing.Size()
+}
@@ -9,11 +9,13 @@ import (

 	"github.com/soypat/lneto"
 	"github.com/soypat/lneto/tcp"
+	"github.com/soypat/lneto/udp"
 )

 // Socket types
 const (
 	sockSTREAM = 0x1
+	sockDGRAM  = 0x2
 )

 type StackGoConfig struct {
@@ -81,7 +83,37 @@ func (s StackGo) SocketNetip(ctx context.Context, network string, family, sotype
 	}
 	switch network {
 	case "udp", "udp4":
-		return nil, lneto.ErrUnsupported
+		if sotype != sockDGRAM {
+			return nil, lneto.ErrUnsupported
+		}
+		if !raddr.IsValid() || raddr.Addr() == netip.IPv4Unspecified() {
+			return nil, lneto.ErrZeroDestination
+		}
+		var conn udp.Conn
+		err = conn.Configure(udp.ConnConfig{
+			TxBuf:       make([]byte, s.plcfg.TxBufSize),
+			RxBuf:       make([]byte, s.plcfg.RxBufSize),
+			TxQueueSize: s.plcfg.QueueSize,
+			RxQueueSize: s.plcfg.QueueSize,
+		})
+		if err != nil {
+			return nil, err
+		}
+		raddr4 := raddr.Addr().As4()
+		err = conn.Open(laddr.Port(), raddr.Port(), raddr4[:])
+		if err != nil {
+			return nil, err
+		}
+		err = s.blk.async.RegisterUDP(&conn, raddr4[:], raddr.Port())
+		if err != nil {
+			return nil, err
+		}
+		uc := udpconn{
+			Conn:      &conn,
+			localAddr: net.UDPAddrFromAddrPort(laddr),
+			raddr:     net.UDPAddrFromAddrPort(raddr),
+		}
+		return uc, nil
 	case "tcp", "tcp4":
 		if sotype != sockSTREAM {
 			return nil, lneto.ErrUnsupported
@@ -206,3 +238,14 @@ func (c tcpconn) RemoteAddr() net.Addr {
 		Port: int(c.Conn.RemotePort()),
 	}
 }
+
+type udpconn struct {
+	*udp.Conn
+	localAddr net.Addr
+	raddr     net.Addr
+}
+
+var _ net.Conn = udpconn{}
+
+func (c udpconn) LocalAddr() net.Addr  { return c.localAddr }
+func (c udpconn) RemoteAddr() net.Addr { return c.raddr }