package chanbackup import ( "bytes" "fmt" "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 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 } // updateBackupFile updates the backup file in place given the current state of // the SubSwapper. func (s *SubSwapper) updateBackupFile() error { // 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 { return fmt.Errorf("unable to pack multi backup: %v", err) } // 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 { return fmt.Errorf("unable to update multi backup: %v", err) } 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!") // Before we enter our main loop, we'll update the on-disk state with // the latest Single state, as nodes may have new advertised addresses. if err := s.updateBackupFile(); err != nil { log.Errorf("Unable to refresh backup file: %v", err) } 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 channel %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) log.Infof("Updating on-disk multi SCB backup: "+ "num_old_chans=%v, num_new_chans=%v", oldStateSize, newStateSize) // With out new state constructed, we'll, atomically // update the on-disk backup state. if err := s.updateBackupFile(); err != nil { log.Errorf("unable to update backup file: %v", err) } // TODO(roasbeef): refresh periodically on a time basis due to // possible addr changes from node // Exit at once if a quit signal is detected. case <-s.quit: return } } }