wintun: ring management moved to wintun.dll

Signed-off-by: Simon Rozman <simon@rozman.si>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tun/wintun/session_windows.go

@@ -0,0 +1,108 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2020 WireGuard LLC. All Rights Reserved.
+ */
+
+package wintun
+
+import (
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+type Session struct {
+	handle uintptr
+}
+
+const (
+	PacketSizeMax   = 0xffff    // Maximum packet size
+	RingCapacityMin = 0x20000   // Minimum ring capacity (128 kiB)
+	RingCapacityMax = 0x4000000 // Maximum ring capacity (64 MiB)
+)
+
+// Packet with data
+type Packet struct {
+	Next *Packet              // Pointer to next packet in queue
+	Size uint32               // Size of packet (max WINTUN_MAX_IP_PACKET_SIZE)
+	Data *[PacketSizeMax]byte // Pointer to layer 3 IPv4 or IPv6 packet
+}
+
+var (
+	procWintunAllocateSendPacket   = modwintun.NewProc("WintunAllocateSendPacket").Addr()
+	procWintunEndSession           = modwintun.NewProc("WintunEndSession")
+	procWintunGetReadWaitEvent     = modwintun.NewProc("WintunGetReadWaitEvent")
+	procWintunReceivePacket        = modwintun.NewProc("WintunReceivePacket").Addr()
+	procWintunReleaseReceivePacket = modwintun.NewProc("WintunReleaseReceivePacket").Addr()
+	procWintunSendPacket           = modwintun.NewProc("WintunSendPacket").Addr()
+	procWintunStartSession         = modwintun.NewProc("WintunStartSession")
+)
+
+func (wintun *Adapter) StartSession(capacity uint32) (session Session, err error) {
+	r0, _, e1 := syscall.Syscall(procWintunStartSession.Addr(), 2, uintptr(wintun.handle), uintptr(capacity), 0)
+	if r0 == 0 {
+		err = e1
+	} else {
+		session = Session{r0}
+	}
+	return
+}
+
+func (session Session) End() {
+	syscall.Syscall(procWintunEndSession.Addr(), 1, session.handle, 0, 0)
+	session.handle = 0
+}
+
+func (session Session) ReadWaitEvent() (handle windows.Handle) {
+	r0, _, _ := syscall.Syscall(procWintunGetReadWaitEvent.Addr(), 1, session.handle, 0, 0)
+	handle = windows.Handle(r0)
+	return
+}
+
+func (session Session) ReceivePacket() (packet []byte, err error) {
+	var packetSize uint32
+	r0, _, e1 := syscall.Syscall(procWintunReceivePacket, 2, session.handle, uintptr(unsafe.Pointer(&packetSize)), 0)
+	if r0 == 0 {
+		err = e1
+		return
+	}
+	unsafeSlice(unsafe.Pointer(&packet), unsafe.Pointer(r0), int(packetSize))
+	return
+}
+
+func (session Session) ReleaseReceivePacket(packet []byte) {
+	syscall.Syscall(procWintunReleaseReceivePacket, 2, session.handle, uintptr(unsafe.Pointer(&packet[0])), 0)
+}
+
+func (session Session) AllocateSendPacket(packetSize int) (packet []byte, err error) {
+	r0, _, e1 := syscall.Syscall(procWintunAllocateSendPacket, 2, session.handle, uintptr(packetSize), 0)
+	if r0 == 0 {
+		err = e1
+		return
+	}
+	unsafeSlice(unsafe.Pointer(&packet), unsafe.Pointer(r0), int(packetSize))
+	return
+}
+
+func (session Session) SendPacket(packet []byte) {
+	syscall.Syscall(procWintunSendPacket, 2, session.handle, uintptr(unsafe.Pointer(&packet[0])), 0)
+}
+
+// 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
+}