syncthing/lib/stun/stun.go

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// Copyright (C) 2019 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
package stun
import (
"net"
"sync/atomic"
"time"
"github.com/AudriusButkevicius/pfilter"
"github.com/ccding/go-stun/stun"
"github.com/thejerf/suture"
"github.com/syncthing/syncthing/lib/config"
"github.com/syncthing/syncthing/lib/util"
)
const stunRetryInterval = 5 * time.Minute
type Host = stun.Host
type NATType = stun.NATType
// NAT types.
const (
NATError = stun.NATError
NATUnknown = stun.NATUnknown
NATNone = stun.NATNone
NATBlocked = stun.NATBlocked
NATFull = stun.NATFull
NATSymmetric = stun.NATSymmetric
NATRestricted = stun.NATRestricted
NATPortRestricted = stun.NATPortRestricted
NATSymmetricUDPFirewall = stun.NATSymmetricUDPFirewall
)
type writeTrackingPacketConn struct {
lastWrite int64 // atomic, must remain 64-bit aligned
net.PacketConn
}
func (c *writeTrackingPacketConn) WriteTo(p []byte, addr net.Addr) (n int, err error) {
atomic.StoreInt64(&c.lastWrite, time.Now().Unix())
return c.PacketConn.WriteTo(p, addr)
}
func (c *writeTrackingPacketConn) getLastWrite() time.Time {
unix := atomic.LoadInt64(&c.lastWrite)
return time.Unix(unix, 0)
}
type Subscriber interface {
OnNATTypeChanged(natType NATType)
OnExternalAddressChanged(address *Host, via string)
}
type Service struct {
suture.Service
name string
cfg config.Wrapper
subscriber Subscriber
stunConn net.PacketConn
client *stun.Client
writeTrackingPacketConn *writeTrackingPacketConn
natType NATType
addr *Host
}
func New(cfg config.Wrapper, subscriber Subscriber, conn net.PacketConn) (*Service, net.PacketConn) {
// Wrap the original connection to track writes on it
writeTrackingPacketConn := &writeTrackingPacketConn{lastWrite: 0, PacketConn: conn}
// Wrap it in a filter and split it up, so that stun packets arrive on stun conn, others arrive on the data conn
filterConn := pfilter.NewPacketFilter(writeTrackingPacketConn)
otherDataConn := filterConn.NewConn(otherDataPriority, nil)
stunConn := filterConn.NewConn(stunFilterPriority, &stunFilter{
ids: make(map[string]time.Time),
})
filterConn.Start()
// Construct the client to use the stun conn
client := stun.NewClientWithConnection(stunConn)
client.SetSoftwareName("") // Explicitly unset this, seems to freak some servers out.
// Return the service and the other conn to the client
s := &Service{
name: "Stun@" + conn.LocalAddr().Network() + "://" + conn.LocalAddr().String(),
cfg: cfg,
subscriber: subscriber,
stunConn: stunConn,
client: client,
writeTrackingPacketConn: writeTrackingPacketConn,
natType: NATUnknown,
addr: nil,
}
s.Service = util.AsService(s.serve)
return s, otherDataConn
}
func (s *Service) Stop() {
_ = s.stunConn.Close()
s.Service.Stop()
}
func (s *Service) serve(stop chan struct{}) {
for {
disabled:
s.setNATType(NATUnknown)
s.setExternalAddress(nil, "")
if s.cfg.Options().IsStunDisabled() {
select {
case <-stop:
return
case <-time.After(time.Second):
continue
}
}
l.Debugf("Starting stun for %s", s)
for _, addr := range s.cfg.StunServers() {
// This blocks until we hit an exit condition or there are issues with the STUN server.
// This returns a boolean signifying if a different STUN server should be tried (oppose to the whole thing
// shutting down and this winding itself down.
if !s.runStunForServer(addr, stop) {
// Check exit conditions.
// Have we been asked to stop?
select {
case <-stop:
return
default:
}
// Are we disabled?
if s.cfg.Options().IsStunDisabled() {
l.Infoln("STUN disabled")
goto disabled
}
// Unpunchable NAT? Chillout for some time.
if !s.isCurrentNATTypePunchable() {
break
}
}
}
// Failed all servers, sad.
s.setNATType(NATUnknown)
s.setExternalAddress(nil, "")
// We failed to contact all provided stun servers or the nat is not punchable.
// Chillout for a while.
select {
case <-time.After(stunRetryInterval):
case <-stop:
return
}
}
}
func (s *Service) runStunForServer(addr string, stop chan struct{}) (tryNext bool) {
l.Debugf("Running stun for %s via %s", s, addr)
// Resolve the address, so that in case the server advertises two
// IPs, we always hit the same one, as otherwise, the mapping might
// expire as we hit the other address, and cause us to flip flop
// between servers/external addresses, as a result flooding discovery
// servers.
udpAddr, err := net.ResolveUDPAddr("udp", addr)
if err != nil {
l.Debugf("%s stun addr resolution on %s: %s", s, addr, err)
return true
}
s.client.SetServerAddr(udpAddr.String())
natType, extAddr, err := s.client.Discover()
if err != nil || extAddr == nil {
l.Debugf("%s stun discovery on %s: %s", s, addr, err)
return true
}
// The stun server is most likely borked, try another one.
if natType == NATError || natType == NATUnknown || natType == NATBlocked {
l.Debugf("%s stun discovery on %s resolved to %s", s, addr, natType)
return true
}
s.setNATType(natType)
s.setExternalAddress(extAddr, addr)
l.Debugf("%s detected NAT type: %s via %s", s, natType, addr)
// We can't punch through this one, so no point doing keepalives
// and such, just let the caller check the nat type and work it out themselves.
if !s.isCurrentNATTypePunchable() {
l.Debugf("%s cannot punch %s, skipping", s, natType)
return false
}
return s.stunKeepAlive(addr, extAddr, stop)
}
func (s *Service) stunKeepAlive(addr string, extAddr *Host, stop chan struct{}) (tryNext bool) {
var err error
nextSleep := time.Duration(s.cfg.Options().StunKeepaliveStartS) * time.Second
l.Debugf("%s starting stun keepalive via %s, next sleep %s", s, addr, nextSleep)
for {
if areDifferent(s.addr, extAddr) {
// If the port has changed (addresses are not equal but the hosts are equal),
// we're probably spending too much time between keepalives, reduce the sleep.
if s.addr != nil && extAddr != nil && s.addr.IP() == extAddr.IP() {
nextSleep /= 2
l.Debugf("%s stun port change (%s to %s), next sleep %s", s, s.addr.TransportAddr(), extAddr.TransportAddr(), nextSleep)
}
s.setExternalAddress(extAddr, addr)
// The stun server is probably stuffed, we've gone beyond min timeout, yet the address keeps changing.
minSleep := time.Duration(s.cfg.Options().StunKeepaliveMinS) * time.Second
if nextSleep < minSleep {
l.Debugf("%s keepalive aborting, sleep below min: %s < %s", s, nextSleep, minSleep)
return true
}
}
// Adjust the keepalives to fire only nextSleep after last write.
lastWrite := s.writeTrackingPacketConn.getLastWrite()
minSleep := time.Duration(s.cfg.Options().StunKeepaliveMinS) * time.Second
if nextSleep < minSleep {
nextSleep = minSleep
}
tryLater:
sleepFor := nextSleep
timeUntilNextKeepalive := time.Until(lastWrite.Add(sleepFor))
if timeUntilNextKeepalive > 0 {
sleepFor = timeUntilNextKeepalive
}
l.Debugf("%s stun sleeping for %s", s, sleepFor)
select {
case <-time.After(sleepFor):
case <-stop:
l.Debugf("%s stopping, aborting stun", s)
return false
}
if s.cfg.Options().IsStunDisabled() {
// Disabled, give up
l.Debugf("%s disabled, aborting stun ", s)
return false
}
// Check if any writes happened while we were sleeping, if they did, sleep again
lastWrite = s.writeTrackingPacketConn.getLastWrite()
if gap := time.Since(lastWrite); gap < nextSleep {
l.Debugf("%s stun last write gap less than next sleep: %s < %s. Will try later", s, gap, nextSleep)
goto tryLater
}
l.Debugf("%s stun keepalive", s)
extAddr, err = s.client.Keepalive()
if err != nil {
l.Debugf("%s stun keepalive on %s: %s (%v)", s, addr, err, extAddr)
return true
}
}
}
func (s *Service) setNATType(natType NATType) {
if natType != s.natType {
l.Debugf("Notifying %s of NAT type change: %s", s.subscriber, natType)
s.subscriber.OnNATTypeChanged(natType)
}
s.natType = natType
}
func (s *Service) setExternalAddress(addr *Host, via string) {
if areDifferent(s.addr, addr) {
l.Debugf("Notifying %s of address change: %s via %s", s.subscriber, addr, via)
s.subscriber.OnExternalAddressChanged(addr, via)
}
s.addr = addr
}
func (s *Service) String() string {
return s.name
}
func (s *Service) isCurrentNATTypePunchable() bool {
return s.natType == NATNone || s.natType == NATPortRestricted || s.natType == NATRestricted || s.natType == NATFull || s.natType == NATSymmetricUDPFirewall
}
func areDifferent(first, second *Host) bool {
if (first == nil) != (second == nil) {
return true
}
if first != nil {
return first.TransportAddr() != second.TransportAddr()
}
return false
}