chanbackup: add new sub-system for keeping the on disk channels.backup up to date
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
parent
60999df08f
commit
3b370fa08d
247
chanbackup/pubsub.go
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247
chanbackup/pubsub.go
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package chanbackup
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import (
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"bytes"
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"net"
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"sync"
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"sync/atomic"
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"github.com/btcsuite/btcd/wire"
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"github.com/lightningnetwork/lnd/channeldb"
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"github.com/lightningnetwork/lnd/keychain"
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)
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// Swapper is an interface that allows the chanbackup.SubSwapper to update the
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// main multi backup location once it learns of new channels or that prior
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// channels have been closed.
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type Swapper interface {
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// UpdateAndSwap attempts to atomically update the main multi back up
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// file location with the new fully packed multi-channel backup.
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UpdateAndSwap(newBackup PackedMulti) error
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}
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// ChannelWithAddrs bundles an open channel along with all the addresses for
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// the channel peer.
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//
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// TODO(roasbeef): use channel shell instead?
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type ChannelWithAddrs struct {
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*channeldb.OpenChannel
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// Addrs is the set of addresses that we can use to reach the target
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// peer.
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Addrs []net.Addr
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}
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// ChannelEvent packages a new update of new channels since subscription, and
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// channels that have been opened since prior channel event.
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type ChannelEvent struct {
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// ClosedChans are the set of channels that have been closed since the
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// last event.
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ClosedChans []wire.OutPoint
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// NewChans is the set of channels that have been opened since the last
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// event.
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NewChans []ChannelWithAddrs
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}
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// ChannelSubscription represents an intent to be notified of any updates to
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// the primary channel state.
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type ChannelSubscription struct {
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// ChanUpdates is a read-only channel that will be sent upon once the
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// primary channel state is updated.
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ChanUpdates <-chan ChannelEvent
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// Cancel is a closure that allows the caller to cancel their
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// subscription and free up any resources allocated.
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Cancel func()
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}
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// ChannelNotifier represents a system that allows the chanbackup.SubSwapper to
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// be notified of any changes to the primary channel state.
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type ChannelNotifier interface {
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// SubscribeChans requests a new channel subscription relative to the
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// initial set of known channels. We use the knownChans as a
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// synchronization point to ensure that the chanbackup.SubSwapper does
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// not miss any channel open or close events in the period between when
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// it's created, and when it requests the channel subscription.
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SubscribeChans(map[wire.OutPoint]struct{}) (*ChannelSubscription, error)
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}
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// SubSwapper subscribes to new updates to the open channel state, and then
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// swaps out the on-disk channel backup state in response. This sub-system
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// that will ensure that the multi chan backup file on disk will always be
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// updated with the latest channel back up state. We'll receive new
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// opened/closed channels from the ChannelNotifier, then use the Swapper to
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// update the file state on disk with the new set of open channels. This can
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// be used to implement a system that always keeps the multi-chan backup file
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// on disk in a consistent state for safety purposes.
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//
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// TODO(roasbeef): better name lol
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type SubSwapper struct {
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started uint32
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stopped uint32
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// backupState are the set of SCBs for all open channels we know of.
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backupState map[wire.OutPoint]Single
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// chanEvents is an active subscription to receive new channel state
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// over.
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chanEvents *ChannelSubscription
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// keyRing is the main key ring that will allow us to pack the new
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// multi backup.
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keyRing keychain.KeyRing
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Swapper
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quit chan struct{}
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wg sync.WaitGroup
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}
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// NewSubSwapper creates a new instance of the SubSwapper given the starting
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// set of channels, and the required interfaces to be notified of new channel
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// updates, pack a multi backup, and swap the current best backup from its
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// storage location.
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func NewSubSwapper(startingChans []Single, chanNotifier ChannelNotifier,
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keyRing keychain.KeyRing, backupSwapper Swapper) (*SubSwapper, error) {
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// First, we'll subscribe to the latest set of channel updates given
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// the set of channels we already know of.
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knownChans := make(map[wire.OutPoint]struct{})
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for _, chanBackup := range startingChans {
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knownChans[chanBackup.FundingOutpoint] = struct{}{}
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}
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chanEvents, err := chanNotifier.SubscribeChans(knownChans)
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if err != nil {
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return nil, err
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}
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// Next, we'll construct our own backup state so we can add/remove
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// channels that have been opened and closed.
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backupState := make(map[wire.OutPoint]Single)
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for _, chanBackup := range startingChans {
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backupState[chanBackup.FundingOutpoint] = chanBackup
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}
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return &SubSwapper{
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backupState: backupState,
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chanEvents: chanEvents,
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keyRing: keyRing,
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Swapper: backupSwapper,
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quit: make(chan struct{}),
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}, nil
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}
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// Start starts the chanbackup.SubSwapper.
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func (s *SubSwapper) Start() error {
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if !atomic.CompareAndSwapUint32(&s.started, 0, 1) {
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return nil
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}
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log.Infof("Starting chanbackup.SubSwapper")
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s.wg.Add(1)
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go s.backupUpdater()
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return nil
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}
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// Stop signals the SubSwapper to being a graceful shutdown.
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func (s *SubSwapper) Stop() error {
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if !atomic.CompareAndSwapUint32(&s.stopped, 0, 1) {
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return nil
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}
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log.Infof("Stopping chanbackup.SubSwapper")
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close(s.quit)
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s.wg.Wait()
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return nil
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}
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// backupFileUpdater is the primary goroutine of the SubSwapper which is
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// responsible for listening for changes to the channel, and updating the
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// persistent multi backup state with a new packed multi of the latest channel
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// state.
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func (s *SubSwapper) backupUpdater() {
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// Ensure that once we exit, we'll cancel our active channel
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// subscription.
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defer s.chanEvents.Cancel()
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defer s.wg.Done()
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log.Debugf("SubSwapper's backupUpdater is active!")
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for {
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select {
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// The channel state has been modified! We'll evaluate all
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// changes, and swap out the old packed multi with a new one
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// with the latest channel state.
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case chanUpdate := <-s.chanEvents.ChanUpdates:
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oldStateSize := len(s.backupState)
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// For all new open channels, we'll create a new SCB
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// given the required information.
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for _, newChan := range chanUpdate.NewChans {
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log.Debugf("Adding chanenl %v to backup state",
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newChan.FundingOutpoint)
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s.backupState[newChan.FundingOutpoint] = NewSingle(
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newChan.OpenChannel, newChan.Addrs,
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)
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}
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// For all closed channels, we'll remove the prior
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// backup state.
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for _, closedChan := range chanUpdate.ClosedChans {
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log.Debugf("Removing channel %v from backup "+
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"state", newLogClosure(func() string {
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return closedChan.String()
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}))
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delete(s.backupState, closedChan)
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}
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newStateSize := len(s.backupState)
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// With our updated channel state obtained, we'll
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// create a new multi from our series of singles.
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var newMulti Multi
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for _, backup := range s.backupState {
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newMulti.StaticBackups = append(
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newMulti.StaticBackups, backup,
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)
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}
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// Now that our multi has been assembled, we'll attempt
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// to pack (encrypt+encode) the new channel state to
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// our target reader.
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var b bytes.Buffer
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err := newMulti.PackToWriter(&b, s.keyRing)
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if err != nil {
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log.Errorf("unable to pack multi backup: %v",
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err)
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continue
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}
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log.Infof("Updating on-disk multi SCB backup: "+
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"num_old_chans=%v, num_new_chans=%v",
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oldStateSize, newStateSize)
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// Finally, we'll swap out the old backup for this new
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// one in a single atomic step.
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err = s.Swapper.UpdateAndSwap(
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PackedMulti(b.Bytes()),
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)
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if err != nil {
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log.Errorf("unable to update multi "+
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"backup: %v", err)
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continue
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}
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// Exit at once if a quit signal is detected.
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case <-s.quit:
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return
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}
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}
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}
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234
chanbackup/pubsub_test.go
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234
chanbackup/pubsub_test.go
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package chanbackup
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import (
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"fmt"
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"reflect"
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"testing"
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"time"
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"github.com/btcsuite/btcd/wire"
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"github.com/davecgh/go-spew/spew"
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"github.com/lightningnetwork/lnd/keychain"
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)
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type mockSwapper struct {
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fail bool
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swaps chan PackedMulti
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}
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func newMockSwapper() *mockSwapper {
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return &mockSwapper{
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swaps: make(chan PackedMulti),
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}
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}
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func (m *mockSwapper) UpdateAndSwap(newBackup PackedMulti) error {
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if m.fail {
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return fmt.Errorf("fail")
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}
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m.swaps <- newBackup
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return nil
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}
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type mockChannelNotifier struct {
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fail bool
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chanEvents chan ChannelEvent
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}
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func newMockChannelNotifier() *mockChannelNotifier {
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return &mockChannelNotifier{
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chanEvents: make(chan ChannelEvent),
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}
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}
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func (m *mockChannelNotifier) SubscribeChans(chans map[wire.OutPoint]struct{}) (
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*ChannelSubscription, error) {
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if m.fail {
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return nil, fmt.Errorf("fail")
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}
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return &ChannelSubscription{
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ChanUpdates: m.chanEvents,
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Cancel: func() {
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},
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}, nil
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}
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// TestNewSubSwapperSubscribeFail tests that if we're unable to obtain a
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// channel subscription, then the entire sub-swapper will fail to start.
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func TestNewSubSwapperSubscribeFail(t *testing.T) {
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t.Parallel()
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keyRing := &mockKeyRing{}
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var swapper mockSwapper
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chanNotifier := mockChannelNotifier{
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fail: true,
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}
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_, err := NewSubSwapper(nil, &chanNotifier, keyRing, &swapper)
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if err == nil {
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t.Fatalf("expected fail due to lack of subscription")
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}
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}
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func assertExpectedBackupSwap(t *testing.T, swapper *mockSwapper,
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subSwapper *SubSwapper, keyRing keychain.KeyRing,
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expectedChanSet map[wire.OutPoint]Single) {
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t.Helper()
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select {
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case newPackedMulti := <-swapper.swaps:
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// If we unpack the new multi, then we should find all the old
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// channels, and also the new channel included and any deleted
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// channel omitted..
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newMulti, err := newPackedMulti.Unpack(keyRing)
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if err != nil {
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t.Fatalf("unable to unpack multi: %v", err)
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}
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// Ensure that once unpacked, the current backup has the
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// expected number of Singles.
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if len(newMulti.StaticBackups) != len(expectedChanSet) {
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t.Fatalf("new backup wasn't included: expected %v "+
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"backups have %v", len(expectedChanSet),
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len(newMulti.StaticBackups))
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}
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// We should also find all the old and new channels in this new
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// backup.
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for _, backup := range newMulti.StaticBackups {
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_, ok := expectedChanSet[backup.FundingOutpoint]
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if !ok {
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t.Fatalf("didn't find backup in original set: %v",
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backup.FundingOutpoint)
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}
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}
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// The internal state of the sub-swapper should also be one
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// larger.
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if !reflect.DeepEqual(expectedChanSet, subSwapper.backupState) {
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t.Fatalf("backup set doesn't match: expected %v got %v",
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spew.Sdump(expectedChanSet),
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spew.Sdump(subSwapper.backupState))
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}
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case <-time.After(time.Second * 5):
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t.Fatalf("update swapper didn't swap out multi")
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}
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}
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// TestSubSwapperIdempotentStartStop tests that calling the Start/Stop methods
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// multiple time is permitted.
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func TestSubSwapperIdempotentStartStop(t *testing.T) {
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t.Parallel()
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keyRing := &mockKeyRing{}
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var (
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swapper mockSwapper
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chanNotifier mockChannelNotifier
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)
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subSwapper, err := NewSubSwapper(nil, &chanNotifier, keyRing, &swapper)
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if err != nil {
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t.Fatalf("unable to init subSwapper: %v", err)
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}
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subSwapper.Start()
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subSwapper.Start()
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subSwapper.Stop()
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subSwapper.Stop()
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}
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// TestSubSwapperUpdater tests that the SubSwapper will properly swap out
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// new/old channels within the channel set, and notify the swapper to update
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// the master multi file backup.
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func TestSubSwapperUpdater(t *testing.T) {
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t.Parallel()
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keyRing := &mockKeyRing{}
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chanNotifier := newMockChannelNotifier()
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swapper := newMockSwapper()
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// First, we'll start out by creating a channels set for the initial
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// set of channels known to the sub-swapper.
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const numStartingChans = 3
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initialChanSet := make([]Single, 0, numStartingChans)
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backupSet := make(map[wire.OutPoint]Single)
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for i := 0; i < numStartingChans; i++ {
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channel, err := genRandomOpenChannelShell()
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if err != nil {
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t.Fatalf("unable to make test chan: %v", err)
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}
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single := NewSingle(channel, nil)
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backupSet[channel.FundingOutpoint] = single
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initialChanSet = append(initialChanSet, single)
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}
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// With our channel set created, we'll make a fresh sub swapper
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// instance to begin our test.
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subSwapper, err := NewSubSwapper(
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initialChanSet, chanNotifier, keyRing, swapper,
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)
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if err != nil {
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t.Fatalf("unable to make swapper: %v", err)
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}
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if err := subSwapper.Start(); err != nil {
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t.Fatalf("unable to start sub swapper: %v", err)
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}
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defer subSwapper.Stop()
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// Now that the sub-swapper is active, we'll notify to add a brand new
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// channel to the channel state.
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newChannel, err := genRandomOpenChannelShell()
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if err != nil {
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t.Fatalf("unable to create new chan: %v", err)
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}
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// With the new channel created, we'll send a new update to the main
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// goroutine telling it about this new channel.
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select {
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case chanNotifier.chanEvents <- ChannelEvent{
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NewChans: []ChannelWithAddrs{
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{
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OpenChannel: newChannel,
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},
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},
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}:
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case <-time.After(time.Second * 5):
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t.Fatalf("update swapper didn't read new channel: %v", err)
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}
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backupSet[newChannel.FundingOutpoint] = NewSingle(newChannel, nil)
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// At this point, the sub-swapper should now have packed a new multi,
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// and then sent it to the swapper so the back up can be updated.
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assertExpectedBackupSwap(t, swapper, subSwapper, keyRing, backupSet)
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// We'll now trigger an update to remove an existing channel.
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chanToDelete := initialChanSet[0].FundingOutpoint
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select {
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case chanNotifier.chanEvents <- ChannelEvent{
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ClosedChans: []wire.OutPoint{chanToDelete},
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}:
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case <-time.After(time.Second * 5):
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t.Fatalf("update swapper didn't read new channel: %v", err)
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}
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delete(backupSet, chanToDelete)
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// Verify that the new set of backups, now has one less after the
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// sub-swapper switches the new set with the old.
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assertExpectedBackupSwap(t, swapper, subSwapper, keyRing, backupSet)
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}
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