package discovery import ( "errors" "sync" "time" "github.com/btcsuite/btcd/chaincfg/chainhash" "github.com/lightningnetwork/lnd/lnpeer" "github.com/lightningnetwork/lnd/lnwire" "github.com/lightningnetwork/lnd/routing" "github.com/lightningnetwork/lnd/ticker" ) const ( // DefaultSyncerRotationInterval is the default interval in which we'll // rotate a single active syncer. DefaultSyncerRotationInterval = 20 * time.Minute // DefaultHistoricalSyncInterval is the default interval in which we'll // force a historical sync to ensure we have as much of the public // network as possible. DefaultHistoricalSyncInterval = time.Hour ) var ( // ErrSyncManagerExiting is an error returned when we attempt to // start/stop a gossip syncer for a connected/disconnected peer, but the // SyncManager has already been stopped. ErrSyncManagerExiting = errors.New("sync manager exiting") ) // newSyncer in an internal message we'll use within the SyncManager to signal // that we should create a GossipSyncer for a newly connected peer. type newSyncer struct { // peer is the newly connected peer. peer lnpeer.Peer // doneChan serves as a signal to the caller that the SyncManager's // internal state correctly reflects the stale active syncer. doneChan chan struct{} } // staleSyncer is an internal message we'll use within the SyncManager to signal // that a peer has disconnected and its GossipSyncer should be removed. type staleSyncer struct { // peer is the peer that has disconnected. peer routing.Vertex // doneChan serves as a signal to the caller that the SyncManager's // internal state correctly reflects the stale active syncer. This is // needed to ensure we always create a new syncer for a flappy peer // after they disconnect if they happened to be an active syncer. doneChan chan struct{} } // SyncManagerCfg contains all of the dependencies required for the SyncManager // to carry out its duties. type SyncManagerCfg struct { // ChainHash is a hash that indicates the specific network of the active // chain. ChainHash chainhash.Hash // ChanSeries is an interface that provides access to a time series view // of the current known channel graph. Each GossipSyncer enabled peer // will utilize this in order to create and respond to channel graph // time series queries. ChanSeries ChannelGraphTimeSeries // NumActiveSyncers is the number of peers for which we should have // active syncers with. After reaching NumActiveSyncers, any future // gossip syncers will be passive. NumActiveSyncers int // RotateTicker is a ticker responsible for notifying the SyncManager // when it should rotate its active syncers. A single active syncer with // a chansSynced state will be exchanged for a passive syncer in order // to ensure we don't keep syncing with the same peers. RotateTicker ticker.Ticker // HistoricalSyncTicker is a ticker responsible for notifying the // SyncManager when it should attempt a historical sync with a gossip // sync peer. HistoricalSyncTicker ticker.Ticker } // SyncManager is a subsystem of the gossiper that manages the gossip syncers // for peers currently connected. When a new peer is connected, the manager will // create its accompanying gossip syncer and determine whether it should have an // ActiveSync or PassiveSync sync type based on how many other gossip syncers // are currently active. Any ActiveSync gossip syncers are started in a // round-robin manner to ensure we're not syncing with multiple peers at the // same time. The first GossipSyncer registered with the SyncManager will // attempt a historical sync to ensure we have as much of the public channel // graph as possible. type SyncManager struct { start sync.Once stop sync.Once cfg SyncManagerCfg // historicalSync allows us to perform an initial historical sync only // _once_ with a peer during the SyncManager's startup. historicalSync sync.Once // newSyncers is a channel we'll use to process requests to create // GossipSyncers for newly connected peers. newSyncers chan *newSyncer // staleSyncers is a channel we'll use to process requests to tear down // GossipSyncers for disconnected peers. staleSyncers chan *staleSyncer // syncersMu guards the read and write access to the activeSyncers and // inactiveSyncers maps below. syncersMu sync.Mutex // activeSyncers is the set of all syncers for which we are currently // receiving graph updates from. The number of possible active syncers // is bounded by NumActiveSyncers. activeSyncers map[routing.Vertex]*GossipSyncer // inactiveSyncers is the set of all syncers for which we are not // currently receiving new graph updates from. inactiveSyncers map[routing.Vertex]*GossipSyncer wg sync.WaitGroup quit chan struct{} } // newSyncManager constructs a new SyncManager backed by the given config. func newSyncManager(cfg *SyncManagerCfg) *SyncManager { return &SyncManager{ cfg: *cfg, newSyncers: make(chan *newSyncer), staleSyncers: make(chan *staleSyncer), activeSyncers: make( map[routing.Vertex]*GossipSyncer, cfg.NumActiveSyncers, ), inactiveSyncers: make(map[routing.Vertex]*GossipSyncer), quit: make(chan struct{}), } } // Start starts the SyncManager in order to properly carry out its duties. func (m *SyncManager) Start() { m.start.Do(func() { m.wg.Add(1) go m.syncerHandler() }) } // Stop stops the SyncManager from performing its duties. func (m *SyncManager) Stop() { m.stop.Do(func() { close(m.quit) m.wg.Wait() for _, syncer := range m.inactiveSyncers { syncer.Stop() } for _, syncer := range m.activeSyncers { syncer.Stop() } }) } // syncerHandler is the SyncManager's main event loop responsible for: // // 1. Creating and tearing down GossipSyncers for connected/disconnected peers. // 2. Finding new peers to receive graph updates from to ensure we don't only // receive them from the same set of peers. // 3. Finding new peers to force a historical sync with to ensure we have as // much of the public network as possible. // // NOTE: This must be run as a goroutine. func (m *SyncManager) syncerHandler() { defer m.wg.Done() m.cfg.RotateTicker.Resume() defer m.cfg.RotateTicker.Stop() m.cfg.HistoricalSyncTicker.Resume() defer m.cfg.HistoricalSyncTicker.Stop() var ( // attemptInitialHistoricalSync determines whether we should // attempt an initial historical sync when a new peer connects. attemptInitialHistoricalSync = true // initialHistoricalSyncCompleted serves as a barrier when // initializing new active GossipSyncers. If false, the initial // historical sync has not completed, so we'll defer // initializing any active GossipSyncers. If true, then we can // transition the GossipSyncer immediately. We set up this // barrier to ensure we have most of the graph before attempting // to accept new updates at tip. initialHistoricalSyncCompleted = false // initialHistoricalSyncer is the syncer we are currently // performing an initial historical sync with. initialHistoricalSyncer *GossipSyncer // initialHistoricalSyncSignal is a signal that will fire once // the intiial historical sync has been completed. This is // crucial to ensure that another historical sync isn't // attempted just because the initialHistoricalSyncer was // disconnected. initialHistoricalSyncSignal chan struct{} ) for { select { // A new peer has been connected, so we'll create its // accompanying GossipSyncer. case newSyncer := <-m.newSyncers: // If we already have a syncer, then we'll exit early as // we don't want to override it. if _, ok := m.GossipSyncer(newSyncer.peer.PubKey()); ok { close(newSyncer.doneChan) continue } s := m.createGossipSyncer(newSyncer.peer) m.syncersMu.Lock() switch { // If we've exceeded our total number of active syncers, // we'll initialize this GossipSyncer as passive. case len(m.activeSyncers) >= m.cfg.NumActiveSyncers: fallthrough // Otherwise, it should be initialized as active. If the // initial historical sync has yet to complete, then // we'll declare is as passive and attempt to transition // it when the initial historical sync completes. case !initialHistoricalSyncCompleted: s.setSyncType(PassiveSync) m.inactiveSyncers[s.cfg.peerPub] = s // The initial historical sync has completed, so we can // immediately start the GossipSyncer as active. default: s.setSyncType(ActiveSync) m.activeSyncers[s.cfg.peerPub] = s } m.syncersMu.Unlock() s.Start() // Once we create the GossipSyncer, we'll signal to the // caller that they can proceed since the SyncManager's // internal state has been updated. close(newSyncer.doneChan) // We'll force a historical sync with the first peer we // connect to, to ensure we get as much of the graph as // possible. if !attemptInitialHistoricalSync { continue } log.Debugf("Attempting initial historical sync with "+ "GossipSyncer(%x)", s.cfg.peerPub) if err := s.historicalSync(); err != nil { log.Errorf("Unable to attempt initial "+ "historical sync with "+ "GossipSyncer(%x): %v", s.cfg.peerPub, err) continue } // Once the historical sync has started, we'll get a // keep track of the corresponding syncer to properly // handle disconnects. We'll also use a signal to know // when the historical sync completed. attemptInitialHistoricalSync = false initialHistoricalSyncer = s initialHistoricalSyncSignal = s.ResetSyncedSignal() // An existing peer has disconnected, so we'll tear down its // corresponding GossipSyncer. case staleSyncer := <-m.staleSyncers: // Once the corresponding GossipSyncer has been stopped // and removed, we'll signal to the caller that they can // proceed since the SyncManager's internal state has // been updated. m.removeGossipSyncer(staleSyncer.peer) close(staleSyncer.doneChan) // If we don't have an initialHistoricalSyncer, or we do // but it is not the peer being disconnected, then we // have nothing left to do and can proceed. switch { case initialHistoricalSyncer == nil: fallthrough case staleSyncer.peer != initialHistoricalSyncer.cfg.peerPub: continue } // Otherwise, our initialHistoricalSyncer corresponds to // the peer being disconnected, so we'll have to find a // replacement. log.Debug("Finding replacement for intitial " + "historical sync") s := m.forceHistoricalSync() if s == nil { log.Debug("No eligible replacement found " + "for initial historical sync") attemptInitialHistoricalSync = true continue } log.Debugf("Replaced initial historical "+ "GossipSyncer(%v) with GossipSyncer(%x)", staleSyncer.peer, s.cfg.peerPub) initialHistoricalSyncer = s initialHistoricalSyncSignal = s.ResetSyncedSignal() // Our initial historical sync signal has completed, so we'll // nil all of the relevant fields as they're no longer needed. case <-initialHistoricalSyncSignal: initialHistoricalSyncer = nil initialHistoricalSyncSignal = nil initialHistoricalSyncCompleted = true log.Debug("Initial historical sync completed") // With the initial historical sync complete, we can // begin receiving new graph updates at tip. We'll // determine whether we can have any more active // GossipSyncers. If we do, we'll randomly select some // that are currently passive to transition. m.syncersMu.Lock() numActiveLeft := m.cfg.NumActiveSyncers - len(m.activeSyncers) if numActiveLeft <= 0 { m.syncersMu.Unlock() continue } log.Debugf("Attempting to transition %v passive "+ "GossipSyncers to active", numActiveLeft) for i := 0; i < numActiveLeft; i++ { chooseRandomSyncer( m.inactiveSyncers, m.transitionPassiveSyncer, ) } m.syncersMu.Unlock() // Our RotateTicker has ticked, so we'll attempt to rotate a // single active syncer with a passive one. case <-m.cfg.RotateTicker.Ticks(): m.rotateActiveSyncerCandidate() // Our HistoricalSyncTicker has ticked, so we'll randomly select // a peer and force a historical sync with them. case <-m.cfg.HistoricalSyncTicker.Ticks(): m.forceHistoricalSync() case <-m.quit: return } } } // createGossipSyncer creates the GossipSyncer for a newly connected peer. func (m *SyncManager) createGossipSyncer(peer lnpeer.Peer) *GossipSyncer { nodeID := routing.Vertex(peer.PubKey()) log.Infof("Creating new GossipSyncer for peer=%x", nodeID[:]) encoding := lnwire.EncodingSortedPlain s := newGossipSyncer(gossipSyncerCfg{ chainHash: m.cfg.ChainHash, peerPub: nodeID, channelSeries: m.cfg.ChanSeries, encodingType: encoding, chunkSize: encodingTypeToChunkSize[encoding], batchSize: requestBatchSize, sendToPeer: func(msgs ...lnwire.Message) error { return peer.SendMessageLazy(false, msgs...) }, }) // Gossip syncers are initialized by default in a PassiveSync type // and chansSynced state so that they can reply to any peer queries or // handle any sync transitions. s.setSyncState(chansSynced) s.setSyncType(PassiveSync) return s } // removeGossipSyncer removes all internal references to the disconnected peer's // GossipSyncer and stops it. In the event of an active GossipSyncer being // disconnected, a passive GossipSyncer, if any, will take its place. func (m *SyncManager) removeGossipSyncer(peer routing.Vertex) { m.syncersMu.Lock() defer m.syncersMu.Unlock() s, ok := m.gossipSyncer(peer) if !ok { return } log.Infof("Removing GossipSyncer for peer=%v", peer) // We'll stop the GossipSyncer for the disconnected peer in a goroutine // to prevent blocking the SyncManager. go s.Stop() // If it's a non-active syncer, then we can just exit now. if _, ok := m.inactiveSyncers[peer]; ok { delete(m.inactiveSyncers, peer) return } // Otherwise, we'll need find a new one to replace it, if any. delete(m.activeSyncers, peer) newActiveSyncer := chooseRandomSyncer( m.inactiveSyncers, m.transitionPassiveSyncer, ) if newActiveSyncer == nil { return } log.Debugf("Replaced active GossipSyncer(%x) with GossipSyncer(%x)", peer, newActiveSyncer.cfg.peerPub) } // rotateActiveSyncerCandidate rotates a single active syncer. In order to // achieve this, the active syncer must be in a chansSynced state in order to // process the sync transition. func (m *SyncManager) rotateActiveSyncerCandidate() { m.syncersMu.Lock() defer m.syncersMu.Unlock() // If we couldn't find an eligible active syncer to rotate, we can // return early. activeSyncer := chooseRandomSyncer(m.activeSyncers, nil) if activeSyncer == nil { log.Debug("No eligible active syncer to rotate") return } // Similarly, if we don't have a candidate to rotate with, we can return // early as well. candidate := chooseRandomSyncer(m.inactiveSyncers, nil) if candidate == nil { log.Debug("No eligible candidate to rotate active syncer") return } // Otherwise, we'll attempt to transition each syncer to their // respective new sync type. log.Debugf("Rotating active GossipSyncer(%x) with GossipSyncer(%x)", activeSyncer.cfg.peerPub, candidate.cfg.peerPub) if err := m.transitionActiveSyncer(activeSyncer); err != nil { log.Errorf("Unable to transition active GossipSyncer(%x): %v", activeSyncer.cfg.peerPub, err) return } if err := m.transitionPassiveSyncer(candidate); err != nil { log.Errorf("Unable to transition passive GossipSyncer(%x): %v", activeSyncer.cfg.peerPub, err) return } } // transitionActiveSyncer transitions an active syncer to a passive one. // // NOTE: This must be called with the syncersMu lock held. func (m *SyncManager) transitionActiveSyncer(s *GossipSyncer) error { log.Debugf("Transitioning active GossipSyncer(%x) to passive", s.cfg.peerPub) if err := s.ProcessSyncTransition(PassiveSync); err != nil { return err } delete(m.activeSyncers, s.cfg.peerPub) m.inactiveSyncers[s.cfg.peerPub] = s return nil } // transitionPassiveSyncer transitions a passive syncer to an active one. // // NOTE: This must be called with the syncersMu lock held. func (m *SyncManager) transitionPassiveSyncer(s *GossipSyncer) error { log.Debugf("Transitioning passive GossipSyncer(%x) to active", s.cfg.peerPub) if err := s.ProcessSyncTransition(ActiveSync); err != nil { return err } delete(m.inactiveSyncers, s.cfg.peerPub) m.activeSyncers[s.cfg.peerPub] = s return nil } // forceHistoricalSync chooses a syncer with a remote peer at random and forces // a historical sync with it. func (m *SyncManager) forceHistoricalSync() *GossipSyncer { m.syncersMu.Lock() defer m.syncersMu.Unlock() // We'll sample from both sets of active and inactive syncers in the // event that we don't have any inactive syncers. return chooseRandomSyncer(m.gossipSyncers(), func(s *GossipSyncer) error { return s.historicalSync() }) } // chooseRandomSyncer iterates through the set of syncers given and returns the // first one which was able to successfully perform the action enclosed in the // function closure. // // NOTE: It's possible for a nil value to be returned if there are no eligible // candidate syncers. func chooseRandomSyncer(syncers map[routing.Vertex]*GossipSyncer, action func(*GossipSyncer) error) *GossipSyncer { for _, s := range syncers { // Only syncers in a chansSynced state are viable for sync // transitions, so skip any that aren't. if s.syncState() != chansSynced { continue } if action != nil { if err := action(s); err != nil { log.Debugf("Skipping eligible candidate "+ "GossipSyncer(%x): %v", s.cfg.peerPub, err) continue } } return s } return nil } // InitSyncState is called by outside sub-systems when a connection is // established to a new peer that understands how to perform channel range // queries. We'll allocate a new GossipSyncer for it, and start any goroutines // needed to handle new queries. The first GossipSyncer registered with the // SyncManager will attempt a historical sync to ensure we have as much of the // public channel graph as possible. // // TODO(wilmer): Only mark as ActiveSync if this isn't a channel peer. func (m *SyncManager) InitSyncState(peer lnpeer.Peer) error { done := make(chan struct{}) select { case m.newSyncers <- &newSyncer{ peer: peer, doneChan: done, }: case <-m.quit: return ErrSyncManagerExiting } select { case <-done: return nil case <-m.quit: return ErrSyncManagerExiting } } // PruneSyncState is called by outside sub-systems once a peer that we were // previously connected to has been disconnected. In this case we can stop the // existing GossipSyncer assigned to the peer and free up resources. func (m *SyncManager) PruneSyncState(peer routing.Vertex) { done := make(chan struct{}) // We avoid returning an error when the SyncManager is stopped since the // GossipSyncer will be stopped then anyway. select { case m.staleSyncers <- &staleSyncer{ peer: peer, doneChan: done, }: case <-m.quit: return } select { case <-done: case <-m.quit: } } // GossipSyncer returns the associated gossip syncer of a peer. The boolean // returned signals whether there exists a gossip syncer for the peer. func (m *SyncManager) GossipSyncer(peer routing.Vertex) (*GossipSyncer, bool) { m.syncersMu.Lock() defer m.syncersMu.Unlock() return m.gossipSyncer(peer) } // gossipSyncer returns the associated gossip syncer of a peer. The boolean // returned signals whether there exists a gossip syncer for the peer. func (m *SyncManager) gossipSyncer(peer routing.Vertex) (*GossipSyncer, bool) { syncer, ok := m.inactiveSyncers[peer] if ok { return syncer, true } syncer, ok = m.activeSyncers[peer] if ok { return syncer, true } return nil, false } // GossipSyncers returns all of the currently initialized gossip syncers. func (m *SyncManager) GossipSyncers() map[routing.Vertex]*GossipSyncer { m.syncersMu.Lock() defer m.syncersMu.Unlock() return m.gossipSyncers() } // gossipSyncers returns all of the currently initialized gossip syncers. func (m *SyncManager) gossipSyncers() map[routing.Vertex]*GossipSyncer { numSyncers := len(m.inactiveSyncers) + len(m.activeSyncers) syncers := make(map[routing.Vertex]*GossipSyncer, numSyncers) for _, syncer := range m.inactiveSyncers { syncers[syncer.cfg.peerPub] = syncer } for _, syncer := range m.activeSyncers { syncers[syncer.cfg.peerPub] = syncer } return syncers }