conn: implement RIO for fast Windows UDP sockets

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

5 files changed, 827 insertions, 60 deletions

diff --git a/conn/bind_std.go b/conn/bind_std.go
index 193c4fe..28d1464 100644
--- a/conn/bind_std.go
+++ b/conn/bind_std.go
@@ -128,6 +128,8 @@ func (bind *StdNetBind) Close() error {
 		err2 = bind.ipv6.Close()
 		bind.ipv6 = nil
 	}
+	bind.blackhole4 = false
+	bind.blackhole6 = false
 	if err1 != nil {
 		return err1
 	}
diff --git a/conn/bind_windows.go b/conn/bind_windows.go
new file mode 100644
index 0000000..1e2712e
--- /dev/null
+++ b/conn/bind_windows.go
@@ -0,0 +1,581 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package conn
+
+import (
+	"encoding/binary"
+	"io"
+	"net"
+	"strconv"
+	"sync"
+	"sync/atomic"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+
+	"golang.zx2c4.com/wireguard/conn/winrio"
+)
+
+const (
+	packetsPerRing = 1024
+	bytesPerPacket = 2048 - 32
+	receiveSpins   = 15
+)
+
+type ringPacket struct {
+	addr WinRingEndpoint
+	data [bytesPerPacket]byte
+}
+
+type ringBuffer struct {
+	packets    uintptr
+	head, tail uint32
+	id         winrio.BufferId
+	iocp       windows.Handle
+	isFull     bool
+	cq         winrio.Cq
+	mu         sync.Mutex
+	overlapped windows.Overlapped
+}
+
+func (rb *ringBuffer) Push() *ringPacket {
+	for rb.isFull {
+		panic("ring is full")
+	}
+	ret := (*ringPacket)(unsafe.Pointer(rb.packets + (uintptr(rb.tail%packetsPerRing) * unsafe.Sizeof(ringPacket{}))))
+	rb.tail += 1
+	if rb.tail == rb.head {
+		rb.isFull = true
+	}
+	return ret
+}
+
+func (rb *ringBuffer) Return(count uint32) {
+	if rb.head%packetsPerRing == rb.tail%packetsPerRing && !rb.isFull {
+		return
+	}
+	rb.head += count
+	rb.isFull = false
+}
+
+type afWinRingBind struct {
+	sock      windows.Handle
+	rx, tx    ringBuffer
+	rq        winrio.Rq
+	mu        sync.Mutex
+	blackhole bool
+}
+
+// WinRingBind uses Windows registered I/O for fast ring buffered networking.
+type WinRingBind struct {
+	v4, v6 afWinRingBind
+	mu     sync.RWMutex
+	isOpen uint32
+}
+
+func NewDefaultBind() Bind { return NewWinRingBind() }
+
+func NewWinRingBind() Bind {
+	if !winrio.Initialize() {
+		return NewStdNetBind()
+	}
+	return new(WinRingBind)
+}
+
+type WinRingEndpoint struct {
+	family uint16
+	data   [30]byte
+}
+
+var _ Bind = (*WinRingBind)(nil)
+var _ Endpoint = (*WinRingEndpoint)(nil)
+
+func (*WinRingBind) ParseEndpoint(s string) (Endpoint, error) {
+	host, port, err := net.SplitHostPort(s)
+	if err != nil {
+		return nil, err
+	}
+	host16, err := windows.UTF16PtrFromString(host)
+	if err != nil {
+		return nil, err
+	}
+	port16, err := windows.UTF16PtrFromString(port)
+	if err != nil {
+		return nil, err
+	}
+	hints := windows.AddrinfoW{
+		Flags:    windows.AI_NUMERICHOST,
+		Family:   windows.AF_UNSPEC,
+		Socktype: windows.SOCK_DGRAM,
+		Protocol: windows.IPPROTO_UDP,
+	}
+	var addrinfo *windows.AddrinfoW
+	err = windows.GetAddrInfoW(host16, port16, &hints, &addrinfo)
+	if err != nil {
+		return nil, err
+	}
+	defer windows.FreeAddrInfoW(addrinfo)
+	if (addrinfo.Family != windows.AF_INET && addrinfo.Family != windows.AF_INET6) || addrinfo.Addrlen > unsafe.Sizeof(WinRingEndpoint{}) {
+		return nil, windows.ERROR_INVALID_ADDRESS
+	}
+	var src []byte
+	var dst [unsafe.Sizeof(WinRingEndpoint{})]byte
+	unsafeSlice(unsafe.Pointer(&src), unsafe.Pointer(addrinfo.Addr), int(addrinfo.Addrlen))
+	copy(dst[:], src)
+	return (*WinRingEndpoint)(unsafe.Pointer(&dst[0])), nil
+}
+
+func (*WinRingEndpoint) ClearSrc() {}
+
+func (e *WinRingEndpoint) DstIP() net.IP {
+	switch e.family {
+	case windows.AF_INET:
+		return append([]byte{}, e.data[2:6]...)
+	case windows.AF_INET6:
+		return append([]byte{}, e.data[6:22]...)
+	}
+	return nil
+}
+
+func (e *WinRingEndpoint) SrcIP() net.IP {
+	return nil // not supported
+}
+
+func (e *WinRingEndpoint) DstToBytes() []byte {
+	switch e.family {
+	case windows.AF_INET:
+		b := make([]byte, 0, 6)
+		b = append(b, e.data[2:6]...)
+		b = append(b, e.data[1], e.data[0])
+		return b
+	case windows.AF_INET6:
+		b := make([]byte, 0, 18)
+		b = append(b, e.data[6:22]...)
+		b = append(b, e.data[1], e.data[0])
+		return b
+	}
+	return nil
+}
+
+func (e *WinRingEndpoint) DstToString() string {
+	switch e.family {
+	case windows.AF_INET:
+		addr := net.UDPAddr{IP: e.data[2:6], Port: int(binary.BigEndian.Uint16(e.data[0:2]))}
+		return addr.String()
+	case windows.AF_INET6:
+		var zone string
+		if scope := *(*uint32)(unsafe.Pointer(&e.data[22])); scope > 0 {
+			zone = strconv.FormatUint(uint64(scope), 10)
+		}
+		addr := net.UDPAddr{IP: e.data[6:22], Zone: zone, Port: int(binary.BigEndian.Uint16(e.data[0:2]))}
+		return addr.String()
+	}
+	return ""
+}
+
+func (e *WinRingEndpoint) SrcToString() string {
+	return ""
+}
+
+func (ring *ringBuffer) CloseAndZero() {
+	if ring.cq != 0 {
+		winrio.CloseCompletionQueue(ring.cq)
+		ring.cq = 0
+	}
+	if ring.iocp != 0 {
+		windows.CloseHandle(ring.iocp)
+		ring.iocp = 0
+	}
+	if ring.id != 0 {
+		winrio.DeregisterBuffer(ring.id)
+		ring.id = 0
+	}
+	if ring.packets != 0 {
+		windows.VirtualFree(ring.packets, 0, windows.MEM_RELEASE)
+		ring.packets = 0
+	}
+}
+
+func (bind *afWinRingBind) CloseAndZero() {
+	bind.rx.CloseAndZero()
+	bind.tx.CloseAndZero()
+	if bind.sock != 0 {
+		windows.CloseHandle(bind.sock)
+		bind.sock = 0
+	}
+	bind.blackhole = false
+}
+
+func (bind *WinRingBind) closeAndZero() {
+	atomic.StoreUint32(&bind.isOpen, 0)
+	bind.v4.CloseAndZero()
+	bind.v6.CloseAndZero()
+}
+
+func (ring *ringBuffer) Open() error {
+	var err error
+	packetsLen := unsafe.Sizeof(ringPacket{}) * packetsPerRing
+	ring.packets, err = windows.VirtualAlloc(0, packetsLen, windows.MEM_COMMIT|windows.MEM_RESERVE, windows.PAGE_READWRITE)
+	if err != nil {
+		return err
+	}
+	ring.id, err = winrio.RegisterPointer(unsafe.Pointer(ring.packets), uint32(packetsLen))
+	if err != nil {
+		return err
+	}
+	ring.iocp, err = windows.CreateIoCompletionPort(windows.InvalidHandle, 0, 0, 0)
+	if err != nil {
+		return err
+	}
+	ring.cq, err = winrio.CreateIOCPCompletionQueue(packetsPerRing, ring.iocp, 0, &ring.overlapped)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func (bind *afWinRingBind) Open(family int32, sa windows.Sockaddr) (windows.Sockaddr, error) {
+	var err error
+	bind.sock, err = winrio.Socket(family, windows.SOCK_DGRAM, windows.IPPROTO_UDP)
+	if err != nil {
+		return nil, err
+	}
+	err = bind.rx.Open()
+	if err != nil {
+		return nil, err
+	}
+	err = bind.tx.Open()
+	if err != nil {
+		return nil, err
+	}
+	bind.rq, err = winrio.CreateRequestQueue(bind.sock, packetsPerRing, 1, packetsPerRing, 1, bind.rx.cq, bind.tx.cq, 0)
+	if err != nil {
+		return nil, err
+	}
+	err = windows.Bind(bind.sock, sa)
+	if err != nil {
+		return nil, err
+	}
+	sa, err = windows.Getsockname(bind.sock)
+	if err != nil {
+		return nil, err
+	}
+	return sa, nil
+}
+
+func (bind *WinRingBind) Open(port uint16) (selectedPort uint16, err error) {
+	bind.mu.Lock()
+	defer bind.mu.Unlock()
+	defer func() {
+		if err != nil {
+			bind.closeAndZero()
+		}
+	}()
+	if atomic.LoadUint32(&bind.isOpen) != 0 {
+		return 0, ErrBindAlreadyOpen
+	}
+	var sa windows.Sockaddr
+	sa, err = bind.v4.Open(windows.AF_INET, &windows.SockaddrInet4{Port: int(port)})
+	if err != nil {
+		return 0, err
+	}
+	sa, err = bind.v6.Open(windows.AF_INET6, &windows.SockaddrInet6{Port: sa.(*windows.SockaddrInet4).Port})
+	if err != nil {
+		return 0, err
+	}
+	selectedPort = uint16(sa.(*windows.SockaddrInet6).Port)
+	for i := 0; i < packetsPerRing; i++ {
+		err = bind.v4.InsertReceiveRequest()
+		if err != nil {
+			return 0, err
+		}
+		err = bind.v6.InsertReceiveRequest()
+		if err != nil {
+			return 0, err
+		}
+	}
+	atomic.StoreUint32(&bind.isOpen, 1)
+	return
+}
+
+func (bind *WinRingBind) Close() error {
+	bind.mu.RLock()
+	if atomic.LoadUint32(&bind.isOpen) != 1 {
+		bind.mu.RUnlock()
+		return nil
+	}
+	atomic.StoreUint32(&bind.isOpen, 2)
+	windows.PostQueuedCompletionStatus(bind.v4.rx.iocp, 0, 0, nil)
+	windows.PostQueuedCompletionStatus(bind.v4.tx.iocp, 0, 0, nil)
+	windows.PostQueuedCompletionStatus(bind.v6.rx.iocp, 0, 0, nil)
+	windows.PostQueuedCompletionStatus(bind.v6.tx.iocp, 0, 0, nil)
+	bind.mu.RUnlock()
+	bind.mu.Lock()
+	defer bind.mu.Unlock()
+	bind.closeAndZero()
+	return nil
+}
+
+func (bind *WinRingBind) SetMark(mark uint32) error {
+	return nil
+}
+
+func (bind *afWinRingBind) InsertReceiveRequest() error {
+	packet := bind.rx.Push()
+	dataBuffer := &winrio.Buffer{
+		Id:     bind.rx.id,
+		Offset: uint32(uintptr(unsafe.Pointer(&packet.data[0])) - bind.rx.packets),
+		Length: uint32(len(packet.data)),
+	}
+	addressBuffer := &winrio.Buffer{
+		Id:     bind.rx.id,
+		Offset: uint32(uintptr(unsafe.Pointer(&packet.addr)) - bind.rx.packets),
+		Length: uint32(unsafe.Sizeof(packet.addr)),
+	}
+	bind.mu.Lock()
+	defer bind.mu.Unlock()
+	return winrio.ReceiveEx(bind.rq, dataBuffer, 1, nil, addressBuffer, nil, nil, 0, uintptr(unsafe.Pointer(packet)))
+}
+
+//go:linkname procyield runtime.procyield
+func procyield(cycles uint32)
+
+func (bind *afWinRingBind) Receive(buf []byte, isOpen *uint32) (int, Endpoint, error) {
+	if atomic.LoadUint32(isOpen) != 1 {
+		return 0, nil, net.ErrClosed
+	}
+	bind.rx.mu.Lock()
+	defer bind.rx.mu.Unlock()
+	var count uint32
+	var results [1]winrio.Result
+	for tries := 0; count == 0 && tries < receiveSpins; tries++ {
+		if tries > 0 {
+			if atomic.LoadUint32(isOpen) != 1 {
+				return 0, nil, net.ErrClosed
+			}
+			procyield(1)
+		}
+		count = winrio.DequeueCompletion(bind.rx.cq, results[:])
+	}
+	if count == 0 {
+		err := winrio.Notify(bind.rx.cq)
+		if err != nil {
+			return 0, nil, err
+		}
+		var bytes uint32
+		var key uintptr
+		var overlapped *windows.Overlapped
+		err = windows.GetQueuedCompletionStatus(bind.rx.iocp, &bytes, &key, &overlapped, windows.INFINITE)
+		if err != nil {
+			return 0, nil, err
+		}
+		if atomic.LoadUint32(isOpen) != 1 {
+			return 0, nil, net.ErrClosed
+		}
+		count = winrio.DequeueCompletion(bind.rx.cq, results[:])
+		if count == 0 {
+			return 0, nil, io.ErrNoProgress
+
+		}
+	}
+	bind.rx.Return(1)
+	err := bind.InsertReceiveRequest()
+	if err != nil {
+		return 0, nil, err
+	}
+	if results[0].Status != 0 {
+		return 0, nil, windows.Errno(results[0].Status)
+	}
+	packet := (*ringPacket)(unsafe.Pointer(uintptr(results[0].RequestContext)))
+	ep := packet.addr
+	n := copy(buf, packet.data[:results[0].BytesTransferred])
+	return n, &ep, nil
+}
+
+func (bind *WinRingBind) ReceiveIPv4(buf []byte) (int, Endpoint, error) {
+	bind.mu.RLock()
+	defer bind.mu.RUnlock()
+	return bind.v4.Receive(buf, &bind.isOpen)
+}
+
+func (bind *WinRingBind) ReceiveIPv6(buf []byte) (int, Endpoint, error) {
+	bind.mu.RLock()
+	defer bind.mu.RUnlock()
+	return bind.v6.Receive(buf, &bind.isOpen)
+}
+
+func (bind *afWinRingBind) Send(buf []byte, nend *WinRingEndpoint, isOpen *uint32) error {
+	if atomic.LoadUint32(isOpen) != 1 {
+		return net.ErrClosed
+	}
+	if len(buf) > bytesPerPacket {
+		return io.ErrShortBuffer
+	}
+	bind.tx.mu.Lock()
+	defer bind.tx.mu.Unlock()
+	var results [packetsPerRing]winrio.Result
+	count := winrio.DequeueCompletion(bind.tx.cq, results[:])
+	if count == 0 && bind.tx.isFull {
+		err := winrio.Notify(bind.tx.cq)
+		if err != nil {
+			return err
+		}
+		var bytes uint32
+		var key uintptr
+		var overlapped *windows.Overlapped
+		err = windows.GetQueuedCompletionStatus(bind.tx.iocp, &bytes, &key, &overlapped, windows.INFINITE)
+		if err != nil {
+			return err
+		}
+		if atomic.LoadUint32(isOpen) != 1 {
+			return net.ErrClosed
+		}
+		count = winrio.DequeueCompletion(bind.tx.cq, results[:])
+		if count == 0 {
+			return io.ErrNoProgress
+		}
+	}
+	if count > 0 {
+		bind.tx.Return(count)
+	}
+	packet := bind.tx.Push()
+	packet.addr = *nend
+	copy(packet.data[:], buf)
+	dataBuffer := &winrio.Buffer{
+		Id:     bind.tx.id,
+		Offset: uint32(uintptr(unsafe.Pointer(&packet.data[0])) - bind.tx.packets),
+		Length: uint32(len(buf)),
+	}
+	addressBuffer := &winrio.Buffer{
+		Id:     bind.tx.id,
+		Offset: uint32(uintptr(unsafe.Pointer(&packet.addr)) - bind.tx.packets),
+		Length: uint32(unsafe.Sizeof(packet.addr)),
+	}
+	bind.mu.Lock()
+	defer bind.mu.Unlock()
+	return winrio.SendEx(bind.rq, dataBuffer, 1, nil, addressBuffer, nil, nil, 0, 0)
+}
+
+func (bind *WinRingBind) Send(buf []byte, endpoint Endpoint) error {
+	nend, ok := endpoint.(*WinRingEndpoint)
+	if !ok {
+		return ErrWrongEndpointType
+	}
+	bind.mu.RLock()
+	defer bind.mu.RUnlock()
+	switch nend.family {
+	case windows.AF_INET:
+		if bind.v4.blackhole {
+			return nil
+		}
+		return bind.v4.Send(buf, nend, &bind.isOpen)
+	case windows.AF_INET6:
+		if bind.v6.blackhole {
+			return nil
+		}
+		return bind.v6.Send(buf, nend, &bind.isOpen)
+	}
+	return nil
+}
+
+func (bind *StdNetBind) BindSocketToInterface4(interfaceIndex uint32, blackhole bool) error {
+	sysconn, err := bind.ipv4.SyscallConn()
+	if err != nil {
+		return err
+	}
+	err2 := sysconn.Control(func(fd uintptr) {
+		err = bindSocketToInterface4(windows.Handle(fd), interfaceIndex)
+	})
+	if err2 != nil {
+		return err2
+	}
+	if err != nil {
+		return err
+	}
+	bind.blackhole4 = blackhole
+	return nil
+}
+
+func (bind *StdNetBind) BindSocketToInterface6(interfaceIndex uint32, blackhole bool) error {
+	sysconn, err := bind.ipv6.SyscallConn()
+	if err != nil {
+		return err
+	}
+	err2 := sysconn.Control(func(fd uintptr) {
+		err = bindSocketToInterface6(windows.Handle(fd), interfaceIndex)
+	})
+	if err2 != nil {
+		return err2
+	}
+	if err != nil {
+		return err
+	}
+	bind.blackhole6 = blackhole
+	return nil
+}
+func (bind *WinRingBind) BindSocketToInterface4(interfaceIndex uint32, blackhole bool) error {
+	bind.mu.RLock()
+	defer bind.mu.RUnlock()
+	if atomic.LoadUint32(&bind.isOpen) != 1 {
+		return net.ErrClosed
+	}
+	err := bindSocketToInterface4(bind.v4.sock, interfaceIndex)
+	if err != nil {
+		return err
+	}
+	bind.v4.blackhole = blackhole
+	return nil
+}
+
+func (bind *WinRingBind) BindSocketToInterface6(interfaceIndex uint32, blackhole bool) error {
+	bind.mu.RLock()
+	defer bind.mu.RUnlock()
+	if atomic.LoadUint32(&bind.isOpen) != 1 {
+		return net.ErrClosed
+	}
+	err := bindSocketToInterface6(bind.v6.sock, interfaceIndex)
+	if err != nil {
+		return err
+	}
+	bind.v6.blackhole = blackhole
+	return nil
+}
+
+func bindSocketToInterface4(handle windows.Handle, interfaceIndex uint32) error {
+	const IP_UNICAST_IF = 31
+	/* MSDN says for IPv4 this needs to be in net byte order, so that it's like an IP address with leading zeros. */
+	var bytes [4]byte
+	binary.BigEndian.PutUint32(bytes[:], interfaceIndex)
+	interfaceIndex = *(*uint32)(unsafe.Pointer(&bytes[0]))
+	err := windows.SetsockoptInt(handle, windows.IPPROTO_IP, IP_UNICAST_IF, int(interfaceIndex))
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func bindSocketToInterface6(handle windows.Handle, interfaceIndex uint32) error {
+	const IPV6_UNICAST_IF = 31
+	return windows.SetsockoptInt(handle, windows.IPPROTO_IPV6, IPV6_UNICAST_IF, int(interfaceIndex))
+}
+
+// unsafeSlice updates the slice slicePtr to be a slice
+// referencing the provided data with its length & capacity set to
+// lenCap.
+//
+// TODO: when Go 1.16 or Go 1.17 is the minimum supported version,
+// update callers to use unsafe.Slice instead of this.
+func unsafeSlice(slicePtr, data unsafe.Pointer, lenCap int) {
+	type sliceHeader struct {
+		Data unsafe.Pointer
+		Len  int
+		Cap  int
+	}
+	h := (*sliceHeader)(slicePtr)
+	h.Data = data
+	h.Len = lenCap
+	h.Cap = lenCap
+}
diff --git a/conn/boundif_windows.go b/conn/boundif_windows.go
deleted file mode 100644
index 6f6fdd8..0000000
--- a/conn/boundif_windows.go
+++ /dev/null
@@ -1,59 +0,0 @@
-/* SPDX-License-Identifier: MIT
- *
- * Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
- */
-
-package conn
-
-import (
-	"encoding/binary"
-	"unsafe"
-
-	"golang.org/x/sys/windows"
-)
-
-const (
-	sockoptIP_UNICAST_IF   = 31
-	sockoptIPV6_UNICAST_IF = 31
-)
-
-func (bind *StdNetBind) BindSocketToInterface4(interfaceIndex uint32, blackhole bool) error {
-	/* MSDN says for IPv4 this needs to be in net byte order, so that it's like an IP address with leading zeros. */
-	bytes := make([]byte, 4)
-	binary.BigEndian.PutUint32(bytes, interfaceIndex)
-	interfaceIndex = *(*uint32)(unsafe.Pointer(&bytes[0]))
-
-	sysconn, err := bind.ipv4.SyscallConn()
-	if err != nil {
-		return err
-	}
-	err2 := sysconn.Control(func(fd uintptr) {
-		err = windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IP, sockoptIP_UNICAST_IF, int(interfaceIndex))
-	})
-	if err2 != nil {
-		return err2
-	}
-	if err != nil {
-		return err
-	}
-	bind.blackhole4 = blackhole
-	return nil
-}
-
-func (bind *StdNetBind) BindSocketToInterface6(interfaceIndex uint32, blackhole bool) error {
-	sysconn, err := bind.ipv6.SyscallConn()
-	if err != nil {
-		return err
-	}
-	err2 := sysconn.Control(func(fd uintptr) {
-		err = windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IPV6, sockoptIPV6_UNICAST_IF, int(interfaceIndex))
-	})
-	if err2 != nil {
-		return err2
-	}
-	if err != nil {
-		return err
-	}
-	bind.blackhole6 = blackhole
-	return nil
-}
diff --git a/conn/default.go b/conn/default.go
index cd9bfb0..161454a 100644
--- a/conn/default.go
+++ b/conn/default.go
@@ -1,4 +1,4 @@
-// +build !linux
+// +build !linux,!windows
 
 /* SPDX-License-Identifier: MIT
  *
diff --git a/conn/winrio/rio_windows.go b/conn/winrio/rio_windows.go
new file mode 100644
index 0000000..1785a02
--- /dev/null
+++ b/conn/winrio/rio_windows.go
@@ -0,0 +1,243 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package winrio
+
+import (
+	"log"
+	"sync"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+const (
+	MsgDontNotify = 1
+	MsgDefer      = 2
+	MsgWaitAll    = 4
+	MsgCommitOnly = 8
+
+	MaxCqSize = 0x8000000
+
+	invalidBufferId = 0xFFFFFFFF
+	invalidCq       = 0
+	invalidRq       = 0
+	corruptCq       = 0xFFFFFFFF
+)
+
+var extensionFunctionTable struct {
+	cbSize                   uint32
+	rioReceive               uintptr
+	rioReceiveEx             uintptr
+	rioSend                  uintptr
+	rioSendEx                uintptr
+	rioCloseCompletionQueue  uintptr
+	rioCreateCompletionQueue uintptr
+	rioCreateRequestQueue    uintptr
+	rioDequeueCompletion     uintptr
+	rioDeregisterBuffer      uintptr
+	rioNotify                uintptr
+	rioRegisterBuffer        uintptr
+	rioResizeCompletionQueue uintptr
+	rioResizeRequestQueue    uintptr
+}
+
+type Cq uintptr
+
+type Rq uintptr
+
+type BufferId uintptr
+
+type Buffer struct {
+	Id     BufferId
+	Offset uint32
+	Length uint32
+}
+
+type Result struct {
+	Status           int32
+	BytesTransferred uint32
+	SocketContext    uint64
+	RequestContext   uint64
+}
+
+type notificationCompletionType uint32
+
+const (
+	eventCompletion notificationCompletionType = 1
+	iocpCompletion  notificationCompletionType = 2
+)
+
+type eventNotificationCompletion struct {
+	completionType notificationCompletionType
+	event          windows.Handle
+	notifyReset    uint32
+}
+
+type iocpNotificationCompletion struct {
+	completionType notificationCompletionType
+	iocp           windows.Handle
+	key            uintptr
+	overlapped     *windows.Overlapped
+}
+
+var initialized sync.Once
+var available bool
+
+func Initialize() bool {
+	initialized.Do(func() {
+		var (
+			err    error
+			socket windows.Handle
+			cq     Cq
+		)
+		defer func() {
+			if err == nil {
+				return
+			}
+			if maj, _, _ := windows.RtlGetNtVersionNumbers(); maj <= 7 {
+				return
+			}
+			log.Printf("Registered I/O is unavailable: %v", err)
+		}()
+		socket, err = Socket(windows.AF_INET, windows.SOCK_DGRAM, windows.IPPROTO_UDP)
+		if err != nil {
+			return
+		}
+		defer windows.CloseHandle(socket)
+		var WSAID_MULTIPLE_RIO = &windows.GUID{0x8509e081, 0x96dd, 0x4005, [8]byte{0xb1, 0x65, 0x9e, 0x2e, 0xe8, 0xc7, 0x9e, 0x3f}}
+		const SIO_GET_MULTIPLE_EXTENSION_FUNCTION_POINTER = 0xc8000024
+		ob := uint32(0)
+		err = windows.WSAIoctl(socket, SIO_GET_MULTIPLE_EXTENSION_FUNCTION_POINTER,
+			(*byte)(unsafe.Pointer(WSAID_MULTIPLE_RIO)), uint32(unsafe.Sizeof(*WSAID_MULTIPLE_RIO)),
+			(*byte)(unsafe.Pointer(&extensionFunctionTable)), uint32(unsafe.Sizeof(extensionFunctionTable)),
+			&ob, nil, 0)
+		if err != nil {
+			return
+		}
+		// While we should be able to stop here, after getting the function pointers, some anti-virus actually causes
+		// failures in RIOCreateRequestQueue, so keep going to be certain this is supported.
+		cq, err = CreatePolledCompletionQueue(2)
+		if err != nil {
+			return
+		}
+		defer CloseCompletionQueue(cq)
+		_, err = CreateRequestQueue(socket, 1, 1, 1, 1, cq, cq, 0)
+		if err != nil {
+			return
+		}
+		available = true
+	})
+	return available
+}
+
+func Socket(af, typ, proto int32) (windows.Handle, error) {
+	return windows.WSASocket(af, typ, proto, nil, 0, windows.WSA_FLAG_REGISTERED_IO)
+}
+
+func CloseCompletionQueue(cq Cq) {
+	_, _, _ = syscall.Syscall(extensionFunctionTable.rioCloseCompletionQueue, 1, uintptr(cq), 0, 0)
+}
+
+func CreateEventCompletionQueue(queueSize uint32, event windows.Handle, notifyReset bool) (Cq, error) {
+	notificationCompletion := &eventNotificationCompletion{
+		completionType: eventCompletion,
+		event:          event,
+	}
+	if notifyReset {
+		notificationCompletion.notifyReset = 1
+	}
+	ret, _, err := syscall.Syscall(extensionFunctionTable.rioCreateCompletionQueue, 2, uintptr(queueSize), uintptr(unsafe.Pointer(notificationCompletion)), 0)
+	if ret == invalidCq {
+		return 0, err
+	}
+	return Cq(ret), nil
+}
+
+func CreateIOCPCompletionQueue(queueSize uint32, iocp windows.Handle, key uintptr, overlapped *windows.Overlapped) (Cq, error) {
+	notificationCompletion := &iocpNotificationCompletion{
+		completionType: iocpCompletion,
+		iocp:           iocp,
+		overlapped:     overlapped,
+	}
+	ret, _, err := syscall.Syscall(extensionFunctionTable.rioCreateCompletionQueue, 2, uintptr(queueSize), uintptr(unsafe.Pointer(notificationCompletion)), 0)
+	if ret == invalidCq {
+		return 0, err
+	}
+	return Cq(ret), nil
+}
+
+func CreatePolledCompletionQueue(queueSize uint32) (Cq, error) {
+	ret, _, err := syscall.Syscall(extensionFunctionTable.rioCreateCompletionQueue, 2, uintptr(queueSize), 0, 0)
+	if ret == invalidCq {
+		return 0, err
+	}
+	return Cq(ret), nil
+}
+
+func CreateRequestQueue(socket windows.Handle, maxOutstandingReceive, maxReceiveDataBuffers, maxOutstandingSend, maxSendDataBuffers uint32, receiveCq, sendCq Cq, socketContext uintptr) (Rq, error) {
+	ret, _, err := syscall.Syscall9(extensionFunctionTable.rioCreateRequestQueue, 8, uintptr(socket), uintptr(maxOutstandingReceive), uintptr(maxReceiveDataBuffers), uintptr(maxOutstandingSend), uintptr(maxSendDataBuffers), uintptr(receiveCq), uintptr(sendCq), socketContext, 0)
+	if ret == invalidRq {
+		return 0, err
+	}
+	return Rq(ret), nil
+}
+
+func DequeueCompletion(cq Cq, results []Result) uint32 {
+	var array uintptr
+	if len(results) > 0 {
+		array = uintptr(unsafe.Pointer(&results[0]))
+	}
+	ret, _, _ := syscall.Syscall(extensionFunctionTable.rioDequeueCompletion, 3, uintptr(cq), array, uintptr(len(results)))
+	if ret == corruptCq {
+		panic("cq is corrupt")
+	}
+	return uint32(ret)
+}
+
+func DeregisterBuffer(id BufferId) {
+	_, _, _ = syscall.Syscall(extensionFunctionTable.rioDeregisterBuffer, 1, uintptr(id), 0, 0)
+}
+
+func RegisterBuffer(buffer []byte) (BufferId, error) {
+	var buf unsafe.Pointer
+	if len(buffer) > 0 {
+		buf = unsafe.Pointer(&buffer[0])
+	}
+	return RegisterPointer(buf, uint32(len(buffer)))
+}
+
+func RegisterPointer(ptr unsafe.Pointer, size uint32) (BufferId, error) {
+	ret, _, err := syscall.Syscall(extensionFunctionTable.rioRegisterBuffer, 2, uintptr(ptr), uintptr(size), 0)
+	if ret == invalidBufferId {
+		return 0, err
+	}
+	return BufferId(ret), nil
+}
+
+func SendEx(rq Rq, buf *Buffer, dataBufferCount uint32, localAddress, remoteAddress, controlContext, flags *Buffer, sflags uint32, requestContext uintptr) error {
+	ret, _, err := syscall.Syscall9(extensionFunctionTable.rioSendEx, 9, uintptr(rq), uintptr(unsafe.Pointer(buf)), uintptr(dataBufferCount), uintptr(unsafe.Pointer(localAddress)), uintptr(unsafe.Pointer(remoteAddress)), uintptr(unsafe.Pointer(controlContext)), uintptr(unsafe.Pointer(flags)), uintptr(sflags), requestContext)
+	if ret == 0 {
+		return err
+	}
+	return nil
+}
+
+func ReceiveEx(rq Rq, buf *Buffer, dataBufferCount uint32, localAddress, remoteAddress, controlContext, flags *Buffer, sflags uint32, requestContext uintptr) error {
+	ret, _, err := syscall.Syscall9(extensionFunctionTable.rioReceiveEx, 9, uintptr(rq), uintptr(unsafe.Pointer(buf)), uintptr(dataBufferCount), uintptr(unsafe.Pointer(localAddress)), uintptr(unsafe.Pointer(remoteAddress)), uintptr(unsafe.Pointer(controlContext)), uintptr(unsafe.Pointer(flags)), uintptr(sflags), requestContext)
+	if ret == 0 {
+		return err
+	}
+	return nil
+}
+
+func Notify(cq Cq) error {
+	ret, _, _ := syscall.Syscall(extensionFunctionTable.rioNotify, 1, uintptr(cq), 0, 0)
+	if ret != 0 {
+		return windows.Errno(ret)
+	}
+	return nil
+}