1 files changed, 97 insertions, 0 deletions
diff --git a/tun/wintun/ring.go b/tun/wintun/ring.go
new file mode 100644
index 0000000..8f46bc9
--- /dev/null
+++ b/tun/wintun/ring.go
@@ -0,0 +1,97 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
+ */
+
+package wintun
+
+import (
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+const (
+	PacketAlignment    = 4        // Number of bytes packets are aligned to in rings
+	PacketSizeMax      = 0xffff   // Maximum packet size
+	PacketCapacity     = 0x800000 // Ring capacity, 8MiB
+	PacketTrailingSize = uint32(unsafe.Sizeof(PacketHeader{})) + ((PacketSizeMax + (PacketAlignment - 1)) &^ (PacketAlignment - 1)) - PacketAlignment
+	ioctlRegisterRings = (51820 << 16) | (0x970 << 2) | 0 /*METHOD_BUFFERED*/ | (0x3 /*FILE_READ_DATA | FILE_WRITE_DATA*/ << 14)
+)
+
+type PacketHeader struct {
+	Size uint32
+}
+
+type Packet struct {
+	PacketHeader
+	Data [PacketSizeMax]byte
+}
+
+type Ring struct {
+	Head      uint32
+	Tail      uint32
+	Alertable int32
+	Data      [PacketCapacity + PacketTrailingSize]byte
+}
+
+type RingDescriptor struct {
+	Send, Receive struct {
+		Size      uint32
+		Ring      *Ring
+		TailMoved windows.Handle
+	}
+}
+
+// Wrap returns value modulo ring capacity
+func (rb *Ring) Wrap(value uint32) uint32 {
+	return value & (PacketCapacity - 1)
+}
+
+// Aligns a packet size to PacketAlignment
+func PacketAlign(size uint32) uint32 {
+	return (size + (PacketAlignment - 1)) &^ (PacketAlignment - 1)
+}
+
+func (descriptor *RingDescriptor) Init() (err error) {
+	descriptor.Send.Size = uint32(unsafe.Sizeof(Ring{}))
+	descriptor.Send.Ring = &Ring{}
+	descriptor.Send.TailMoved, err = windows.CreateEvent(nil, 0, 0, nil)
+	if err != nil {
+		return
+	}
+
+	descriptor.Receive.Size = uint32(unsafe.Sizeof(Ring{}))
+	descriptor.Receive.Ring = &Ring{}
+	descriptor.Receive.TailMoved, err = windows.CreateEvent(nil, 0, 0, nil)
+	if err != nil {
+		windows.CloseHandle(descriptor.Send.TailMoved)
+		return
+	}
+
+	return
+}
+
+func (descriptor *RingDescriptor) Close() {
+	if descriptor.Send.TailMoved != 0 {
+		windows.CloseHandle(descriptor.Send.TailMoved)
+		descriptor.Send.TailMoved = 0
+	}
+	if descriptor.Send.TailMoved != 0 {
+		windows.CloseHandle(descriptor.Receive.TailMoved)
+		descriptor.Receive.TailMoved = 0
+	}
+}
+
+func (wintun *Interface) Register(descriptor *RingDescriptor) (windows.Handle, error) {
+	handle, err := wintun.handle()
+	if err != nil {
+		return 0, err
+	}
+	var bytesReturned uint32
+	err = windows.DeviceIoControl(handle, ioctlRegisterRings, (*byte)(unsafe.Pointer(descriptor)), uint32(unsafe.Sizeof(*descriptor)), nil, 0, &bytesReturned, nil)
+	if err != nil {
+		return 0, err
+	}
+	return handle, nil
+}