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/* SPDX-License-Identifier: MIT
*
* Copyright (C) 2017-2023 WireGuard LLC. All Rights Reserved.
*/
package tun
import (
"errors"
"fmt"
"os"
"sync"
"sync/atomic"
"time"
_ "unsafe"
"golang.org/x/sys/windows"
"golang.zx2c4.com/wintun"
)
const (
rateMeasurementGranularity = uint64((time.Second / 2) / time.Nanosecond)
spinloopRateThreshold = 800000000 / 8 // 800mbps
spinloopDuration = uint64(time.Millisecond / 80 / time.Nanosecond) // ~1gbit/s
)
type rateJuggler struct {
current atomic.Uint64
nextByteCount atomic.Uint64
nextStartTime atomic.Int64
changing atomic.Bool
}
type NativeTun struct {
wt *wintun.Adapter
name string
handle windows.Handle
rate rateJuggler
session wintun.Session
readWait windows.Handle
events chan Event
running sync.WaitGroup
closeOnce sync.Once
close atomic.Bool
forcedMTU int
}
var (
WintunTunnelType = "WireGuard"
WintunStaticRequestedGUID *windows.GUID
)
//go:linkname procyield runtime.procyield
func procyield(cycles uint32)
//go:linkname nanotime runtime.nanotime
func nanotime() int64
// CreateTUN creates a Wintun interface with the given name. Should a Wintun
// interface with the same name exist, it is reused.
func CreateTUN(ifname string, mtu int) (Device, error) {
return CreateTUNWithRequestedGUID(ifname, WintunStaticRequestedGUID, mtu)
}
// CreateTUNWithRequestedGUID creates a Wintun interface with the given name and
// a requested GUID. Should a Wintun interface with the same name exist, it is reused.
func CreateTUNWithRequestedGUID(ifname string, requestedGUID *windows.GUID, mtu int) (Device, error) {
wt, err := wintun.CreateAdapter(ifname, WintunTunnelType, requestedGUID)
if err != nil {
return nil, fmt.Errorf("Error creating interface: %w", err)
}
forcedMTU := 1420
if mtu > 0 {
forcedMTU = mtu
}
tun := &NativeTun{
wt: wt,
name: ifname,
handle: windows.InvalidHandle,
events: make(chan Event, 10),
forcedMTU: forcedMTU,
}
tun.session, err = wt.StartSession(0x800000) // Ring capacity, 8 MiB
if err != nil {
tun.wt.Close()
close(tun.events)
return nil, fmt.Errorf("Error starting session: %w", err)
}
tun.readWait = tun.session.ReadWaitEvent()
return tun, nil
}
func (tun *NativeTun) Name() (string, error) {
return tun.name, nil
}
func (tun *NativeTun) File() *os.File {
return nil
}
func (tun *NativeTun) Events() chan Event {
return tun.events
}
func (tun *NativeTun) Close() error {
var err error
tun.closeOnce.Do(func() {
tun.close.Store(true)
windows.SetEvent(tun.readWait)
tun.running.Wait()
tun.session.End()
if tun.wt != nil {
tun.wt.Close()
}
close(tun.events)
})
return err
}
func (tun *NativeTun) MTU() (int, error) {
return tun.forcedMTU, nil
}
// TODO: This is a temporary hack. We really need to be monitoring the interface in real time and adapting to MTU changes.
func (tun *NativeTun) ForceMTU(mtu int) {
update := tun.forcedMTU != mtu
tun.forcedMTU = mtu
if update {
tun.events <- EventMTUUpdate
}
}
// Note: Read() and Write() assume the caller comes only from a single thread; there's no locking.
func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
tun.running.Add(1)
defer tun.running.Done()
retry:
if tun.close.Load() {
return 0, os.ErrClosed
}
start := nanotime()
shouldSpin := tun.rate.current.Load() >= spinloopRateThreshold && uint64(start-tun.rate.nextStartTime.Load()) <= rateMeasurementGranularity*2
for {
if tun.close.Load() {
return 0, os.ErrClosed
}
packet, err := tun.session.ReceivePacket()
switch err {
case nil:
packetSize := len(packet)
copy(buff[offset:], packet)
tun.session.ReleaseReceivePacket(packet)
tun.rate.update(uint64(packetSize))
return packetSize, nil
case windows.ERROR_NO_MORE_ITEMS:
if !shouldSpin || uint64(nanotime()-start) >= spinloopDuration {
windows.WaitForSingleObject(tun.readWait, windows.INFINITE)
goto retry
}
procyield(1)
continue
case windows.ERROR_HANDLE_EOF:
return 0, os.ErrClosed
case windows.ERROR_INVALID_DATA:
return 0, errors.New("Send ring corrupt")
}
return 0, fmt.Errorf("Read failed: %w", err)
}
}
func (tun *NativeTun) Flush() error {
return nil
}
func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
tun.running.Add(1)
defer tun.running.Done()
if tun.close.Load() {
return 0, os.ErrClosed
}
packetSize := len(buff) - offset
tun.rate.update(uint64(packetSize))
packet, err := tun.session.AllocateSendPacket(packetSize)
if err == nil {
copy(packet, buff[offset:])
tun.session.SendPacket(packet)
return packetSize, nil
}
switch err {
case windows.ERROR_HANDLE_EOF:
return 0, os.ErrClosed
case windows.ERROR_BUFFER_OVERFLOW:
return 0, nil // Dropping when ring is full.
}
return 0, fmt.Errorf("Write failed: %w", err)
}
// LUID returns Windows interface instance ID.
func (tun *NativeTun) LUID() uint64 {
tun.running.Add(1)
defer tun.running.Done()
if tun.close.Load() {
return 0
}
return tun.wt.LUID()
}
// RunningVersion returns the running version of the Wintun driver.
func (tun *NativeTun) RunningVersion() (version uint32, err error) {
return wintun.RunningVersion()
}
func (rate *rateJuggler) update(packetLen uint64) {
now := nanotime()
total := rate.nextByteCount.Add(packetLen)
period := uint64(now - rate.nextStartTime.Load())
if period >= rateMeasurementGranularity {
if !rate.changing.CompareAndSwap(false, true) {
return
}
rate.nextStartTime.Store(now)
rate.current.Store(total * uint64(time.Second/time.Nanosecond) / period)
rate.nextByteCount.Store(0)
rate.changing.Store(false)
}
}
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