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chanbackup: add new sub-system for keeping the on disk channels.backup up to date

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In this commit, we introduce the chanbackup.SubSwapper interface. It
takes a regular Swapper implementation (defined by the
chanbackup.SubSwapper) interface along with a chanbackup.ChannelNotifier
implementation. Given these two interfaces, we're able to be notified
when a new channel is opened or closed, and then use the Swapper to
atomically replace the on-disk channel back up. As a result, a Lightning
daemon can ensure that they alwayts have a up to date channels.backup on
disk that can safely be copied away by users and be used to restore
channel funds in the event of partial/total data loss.
This commit is contained in:
Olaoluwa Osuntokun 2018-12-09 19:09:28 -08:00
parent 60999df08f
commit 3b370fa08d
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2 changed files with 481 additions and 0 deletions
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247
chanbackup/pubsub.go Normal file
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package chanbackup
import (
"bytes"
"net"
"sync"
"sync/atomic"
"github.com/btcsuite/btcd/wire"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/keychain"
)
// Swapper is an interface that allows the chanbackup.SubSwapper to update the
// main multi backup location once it learns of new channels or that prior
// channels have been closed.
type Swapper interface {
// UpdateAndSwap attempts to atomically update the main multi back up
// file location with the new fully packed multi-channel backup.
UpdateAndSwap(newBackup PackedMulti) error
}
// ChannelWithAddrs bundles an open channel along with all the addresses for
// the channel peer.
//
// TODO(roasbeef): use channel shell instead?
type ChannelWithAddrs struct {
*channeldb.OpenChannel
// Addrs is the set of addresses that we can use to reach the target
// peer.
Addrs []net.Addr
}
// ChannelEvent packages a new update of new channels since subscription, and
// channels that have been opened since prior channel event.
type ChannelEvent struct {
// ClosedChans are the set of channels that have been closed since the
// last event.
ClosedChans []wire.OutPoint
// NewChans is the set of channels that have been opened since the last
// event.
NewChans []ChannelWithAddrs
}
// ChannelSubscription represents an intent to be notified of any updates to
// the primary channel state.
type ChannelSubscription struct {
// ChanUpdates is a read-only channel that will be sent upon once the
// primary channel state is updated.
ChanUpdates <-chan ChannelEvent
// Cancel is a closure that allows the caller to cancel their
// subscription and free up any resources allocated.
Cancel func()
}
// ChannelNotifier represents a system that allows the chanbackup.SubSwapper to
// be notified of any changes to the primary channel state.
type ChannelNotifier interface {
// SubscribeChans requests a new channel subscription relative to the
// initial set of known channels. We use the knownChans as a
// synchronization point to ensure that the chanbackup.SubSwapper does
// not miss any channel open or close events in the period between when
// it's created, and when it requests the channel subscription.
SubscribeChans(map[wire.OutPoint]struct{}) (*ChannelSubscription, error)
}
// SubSwapper subscribes to new updates to the open channel state, and then
// swaps out the on-disk channel backup state in response. This sub-system
// that will ensure that the multi chan backup file on disk will always be
// updated with the latest channel back up state. We'll receive new
// opened/closed channels from the ChannelNotifier, then use the Swapper to
// update the file state on disk with the new set of open channels. This can
// be used to implement a system that always keeps the multi-chan backup file
// on disk in a consistent state for safety purposes.
//
// TODO(roasbeef): better name lol
type SubSwapper struct {
started uint32
stopped uint32
// backupState are the set of SCBs for all open channels we know of.
backupState map[wire.OutPoint]Single
// chanEvents is an active subscription to receive new channel state
// over.
chanEvents *ChannelSubscription
// keyRing is the main key ring that will allow us to pack the new
// multi backup.
keyRing keychain.KeyRing
Swapper
quit chan struct{}
wg sync.WaitGroup
}
// NewSubSwapper creates a new instance of the SubSwapper given the starting
// set of channels, and the required interfaces to be notified of new channel
// updates, pack a multi backup, and swap the current best backup from its
// storage location.
func NewSubSwapper(startingChans []Single, chanNotifier ChannelNotifier,
keyRing keychain.KeyRing, backupSwapper Swapper) (*SubSwapper, error) {
// First, we'll subscribe to the latest set of channel updates given
// the set of channels we already know of.
knownChans := make(map[wire.OutPoint]struct{})
for _, chanBackup := range startingChans {
knownChans[chanBackup.FundingOutpoint] = struct{}{}
}
chanEvents, err := chanNotifier.SubscribeChans(knownChans)
if err != nil {
return nil, err
}
// Next, we'll construct our own backup state so we can add/remove
// channels that have been opened and closed.
backupState := make(map[wire.OutPoint]Single)
for _, chanBackup := range startingChans {
backupState[chanBackup.FundingOutpoint] = chanBackup
}
return &SubSwapper{
backupState: backupState,
chanEvents: chanEvents,
keyRing: keyRing,
Swapper: backupSwapper,
quit: make(chan struct{}),
}, nil
}
// Start starts the chanbackup.SubSwapper.
func (s *SubSwapper) Start() error {
if !atomic.CompareAndSwapUint32(&s.started, 0, 1) {
return nil
}
log.Infof("Starting chanbackup.SubSwapper")
s.wg.Add(1)
go s.backupUpdater()
return nil
}
// Stop signals the SubSwapper to being a graceful shutdown.
func (s *SubSwapper) Stop() error {
if !atomic.CompareAndSwapUint32(&s.stopped, 0, 1) {
return nil
}
log.Infof("Stopping chanbackup.SubSwapper")
close(s.quit)
s.wg.Wait()
return nil
}
// backupFileUpdater is the primary goroutine of the SubSwapper which is
// responsible for listening for changes to the channel, and updating the
// persistent multi backup state with a new packed multi of the latest channel
// state.
func (s *SubSwapper) backupUpdater() {
// Ensure that once we exit, we'll cancel our active channel
// subscription.
defer s.chanEvents.Cancel()
defer s.wg.Done()
log.Debugf("SubSwapper's backupUpdater is active!")
for {
select {
// The channel state has been modified! We'll evaluate all
// changes, and swap out the old packed multi with a new one
// with the latest channel state.
case chanUpdate := <-s.chanEvents.ChanUpdates:
oldStateSize := len(s.backupState)
// For all new open channels, we'll create a new SCB
// given the required information.
for _, newChan := range chanUpdate.NewChans {
log.Debugf("Adding chanenl %v to backup state",
newChan.FundingOutpoint)
s.backupState[newChan.FundingOutpoint] = NewSingle(
newChan.OpenChannel, newChan.Addrs,
)
}
// For all closed channels, we'll remove the prior
// backup state.
for _, closedChan := range chanUpdate.ClosedChans {
log.Debugf("Removing channel %v from backup "+
"state", newLogClosure(func() string {
return closedChan.String()
}))
delete(s.backupState, closedChan)
}
newStateSize := len(s.backupState)
// With our updated channel state obtained, we'll
// create a new multi from our series of singles.
var newMulti Multi
for _, backup := range s.backupState {
newMulti.StaticBackups = append(
newMulti.StaticBackups, backup,
)
}
// Now that our multi has been assembled, we'll attempt
// to pack (encrypt+encode) the new channel state to
// our target reader.
var b bytes.Buffer
err := newMulti.PackToWriter(&b, s.keyRing)
if err != nil {
log.Errorf("unable to pack multi backup: %v",
err)
continue
}
log.Infof("Updating on-disk multi SCB backup: "+
"num_old_chans=%v, num_new_chans=%v",
oldStateSize, newStateSize)
// Finally, we'll swap out the old backup for this new
// one in a single atomic step.
err = s.Swapper.UpdateAndSwap(
PackedMulti(b.Bytes()),
)
if err != nil {
log.Errorf("unable to update multi "+
"backup: %v", err)
continue
}
// Exit at once if a quit signal is detected.
case <-s.quit:
return
}
}
}

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chanbackup/pubsub_test.go Normal file
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package chanbackup
import (
"fmt"
"reflect"
"testing"
"time"
"github.com/btcsuite/btcd/wire"
"github.com/davecgh/go-spew/spew"
"github.com/lightningnetwork/lnd/keychain"
)
type mockSwapper struct {
fail bool
swaps chan PackedMulti
}
func newMockSwapper() *mockSwapper {
return &mockSwapper{
swaps: make(chan PackedMulti),
}
}
func (m *mockSwapper) UpdateAndSwap(newBackup PackedMulti) error {
if m.fail {
return fmt.Errorf("fail")
}
m.swaps <- newBackup
return nil
}
type mockChannelNotifier struct {
fail bool
chanEvents chan ChannelEvent
}
func newMockChannelNotifier() *mockChannelNotifier {
return &mockChannelNotifier{
chanEvents: make(chan ChannelEvent),
}
}
func (m *mockChannelNotifier) SubscribeChans(chans map[wire.OutPoint]struct{}) (
*ChannelSubscription, error) {
if m.fail {
return nil, fmt.Errorf("fail")
}
return &ChannelSubscription{
ChanUpdates: m.chanEvents,
Cancel: func() {
},
}, nil
}
// TestNewSubSwapperSubscribeFail tests that if we're unable to obtain a
// channel subscription, then the entire sub-swapper will fail to start.
func TestNewSubSwapperSubscribeFail(t *testing.T) {
t.Parallel()
keyRing := &mockKeyRing{}
var swapper mockSwapper
chanNotifier := mockChannelNotifier{
fail: true,
}
_, err := NewSubSwapper(nil, &chanNotifier, keyRing, &swapper)
if err == nil {
t.Fatalf("expected fail due to lack of subscription")
}
}
func assertExpectedBackupSwap(t *testing.T, swapper *mockSwapper,
subSwapper *SubSwapper, keyRing keychain.KeyRing,
expectedChanSet map[wire.OutPoint]Single) {
t.Helper()
select {
case newPackedMulti := <-swapper.swaps:
// If we unpack the new multi, then we should find all the old
// channels, and also the new channel included and any deleted
// channel omitted..
newMulti, err := newPackedMulti.Unpack(keyRing)
if err != nil {
t.Fatalf("unable to unpack multi: %v", err)
}
// Ensure that once unpacked, the current backup has the
// expected number of Singles.
if len(newMulti.StaticBackups) != len(expectedChanSet) {
t.Fatalf("new backup wasn't included: expected %v "+
"backups have %v", len(expectedChanSet),
len(newMulti.StaticBackups))
}
// We should also find all the old and new channels in this new
// backup.
for _, backup := range newMulti.StaticBackups {
_, ok := expectedChanSet[backup.FundingOutpoint]
if !ok {
t.Fatalf("didn't find backup in original set: %v",
backup.FundingOutpoint)
}
}
// The internal state of the sub-swapper should also be one
// larger.
if !reflect.DeepEqual(expectedChanSet, subSwapper.backupState) {
t.Fatalf("backup set doesn't match: expected %v got %v",
spew.Sdump(expectedChanSet),
spew.Sdump(subSwapper.backupState))
}
case <-time.After(time.Second * 5):
t.Fatalf("update swapper didn't swap out multi")
}
}
// TestSubSwapperIdempotentStartStop tests that calling the Start/Stop methods
// multiple time is permitted.
func TestSubSwapperIdempotentStartStop(t *testing.T) {
t.Parallel()
keyRing := &mockKeyRing{}
var (
swapper mockSwapper
chanNotifier mockChannelNotifier
)
subSwapper, err := NewSubSwapper(nil, &chanNotifier, keyRing, &swapper)
if err != nil {
t.Fatalf("unable to init subSwapper: %v", err)
}
subSwapper.Start()
subSwapper.Start()
subSwapper.Stop()
subSwapper.Stop()
}
// TestSubSwapperUpdater tests that the SubSwapper will properly swap out
// new/old channels within the channel set, and notify the swapper to update
// the master multi file backup.
func TestSubSwapperUpdater(t *testing.T) {
t.Parallel()
keyRing := &mockKeyRing{}
chanNotifier := newMockChannelNotifier()
swapper := newMockSwapper()
// First, we'll start out by creating a channels set for the initial
// set of channels known to the sub-swapper.
const numStartingChans = 3
initialChanSet := make([]Single, 0, numStartingChans)
backupSet := make(map[wire.OutPoint]Single)
for i := 0; i < numStartingChans; i++ {
channel, err := genRandomOpenChannelShell()
if err != nil {
t.Fatalf("unable to make test chan: %v", err)
}
single := NewSingle(channel, nil)
backupSet[channel.FundingOutpoint] = single
initialChanSet = append(initialChanSet, single)
}
// With our channel set created, we'll make a fresh sub swapper
// instance to begin our test.
subSwapper, err := NewSubSwapper(
initialChanSet, chanNotifier, keyRing, swapper,
)
if err != nil {
t.Fatalf("unable to make swapper: %v", err)
}
if err := subSwapper.Start(); err != nil {
t.Fatalf("unable to start sub swapper: %v", err)
}
defer subSwapper.Stop()
// Now that the sub-swapper is active, we'll notify to add a brand new
// channel to the channel state.
newChannel, err := genRandomOpenChannelShell()
if err != nil {
t.Fatalf("unable to create new chan: %v", err)
}
// With the new channel created, we'll send a new update to the main
// goroutine telling it about this new channel.
select {
case chanNotifier.chanEvents <- ChannelEvent{
NewChans: []ChannelWithAddrs{
{
OpenChannel: newChannel,
},
},
}:
case <-time.After(time.Second * 5):
t.Fatalf("update swapper didn't read new channel: %v", err)
}
backupSet[newChannel.FundingOutpoint] = NewSingle(newChannel, nil)
// At this point, the sub-swapper should now have packed a new multi,
// and then sent it to the swapper so the back up can be updated.
assertExpectedBackupSwap(t, swapper, subSwapper, keyRing, backupSet)
// We'll now trigger an update to remove an existing channel.
chanToDelete := initialChanSet[0].FundingOutpoint
select {
case chanNotifier.chanEvents <- ChannelEvent{
ClosedChans: []wire.OutPoint{chanToDelete},
}:
case <-time.After(time.Second * 5):
t.Fatalf("update swapper didn't read new channel: %v", err)
}
delete(backupSet, chanToDelete)
// Verify that the new set of backups, now has one less after the
// sub-swapper switches the new set with the old.
assertExpectedBackupSwap(t, swapper, subSwapper, keyRing, backupSet)
}