package autopilot import ( "bytes" "fmt" "math/rand" "net" "sync" "time" "github.com/btcsuite/btcd/btcec" "github.com/btcsuite/btcutil" "github.com/davecgh/go-spew/spew" "github.com/lightningnetwork/lnd/lnwire" ) // Config couples all the items that an autopilot agent needs to function. // All items within the struct MUST be populated for the Agent to be able to // carry out its duties. type Config struct { // Self is the identity public key of the Lightning Network node that // is being driven by the agent. This is used to ensure that we don't // accidentally attempt to open a channel with ourselves. Self *btcec.PublicKey // Heuristic is an attachment heuristic which will govern to whom we // open channels to, and also what those channels look like in terms of // desired capacity. The Heuristic will take into account the current // state of the graph, our set of open channels, and the amount of // available funds when determining how channels are to be opened. // Additionally, a heuristic make also factor in extra-graph // information in order to make more pertinent recommendations. Heuristic AttachmentHeuristic // ChanController is an interface that is able to directly manage the // creation, closing and update of channels within the network. ChanController ChannelController // ConnectToPeer attempts to connect to the peer using one of its // advertised addresses. The boolean returned signals whether the peer // was already connected. ConnectToPeer func(*btcec.PublicKey, []net.Addr) (bool, error) // DisconnectPeer attempts to disconnect the peer with the given public // key. DisconnectPeer func(*btcec.PublicKey) error // WalletBalance is a function closure that should return the current // available balance of the backing wallet. WalletBalance func() (btcutil.Amount, error) // Graph is an abstract channel graph that the Heuristic and the Agent // will use to make decisions w.r.t channel allocation and placement // within the graph. Graph ChannelGraph // Constraints is the set of constraints the autopilot must adhere to // when opening channels. Constraints AgentConstraints // TODO(roasbeef): add additional signals from fee rates and revenue of // currently opened channels } // channelState is a type that represents the set of active channels of the // backing LN node that the Agent should be aware of. This type contains a few // helper utility methods. type channelState map[lnwire.ShortChannelID]Channel // Channels returns a slice of all the active channels. func (c channelState) Channels() []Channel { chans := make([]Channel, 0, len(c)) for _, channel := range c { chans = append(chans, channel) } return chans } // ConnectedNodes returns the set of nodes we currently have a channel with. // This information is needed as we want to avoid making repeated channels with // any node. func (c channelState) ConnectedNodes() map[NodeID]struct{} { nodes := make(map[NodeID]struct{}) for _, channels := range c { nodes[channels.Node] = struct{}{} } // TODO(roasbeef): add outgoing, nodes, allow incoming and outgoing to // per node // * only add node is chan as funding amt set return nodes } // Agent implements a closed-loop control system which seeks to autonomously // optimize the allocation of satoshis within channels throughput the network's // channel graph. An agent is configurable by swapping out different // AttachmentHeuristic strategies. The agent uses external signals such as the // wallet balance changing, or new channels being opened/closed for the local // node as an indicator to re-examine its internal state, and the amount of // available funds in order to make updated decisions w.r.t the channel graph. // The Agent will automatically open, close, and splice in/out channel as // necessary for it to step closer to its optimal state. // // TODO(roasbeef): prob re-word type Agent struct { started sync.Once stopped sync.Once // cfg houses the configuration state of the Ant. cfg Config // chanState tracks the current set of open channels. chanState channelState chanStateMtx sync.Mutex // stateUpdates is a channel that any external state updates that may // affect the heuristics of the agent will be sent over. stateUpdates chan interface{} // balanceUpdates is a channel where notifications about updates to the // wallet's balance will be sent. This channel will be buffered to // ensure we have at most one pending update of this type to handle at // a given time. balanceUpdates chan *balanceUpdate // nodeUpdates is a channel that changes to the graph node landscape // will be sent over. This channel will be buffered to ensure we have // at most one pending update of this type to handle at a given time. nodeUpdates chan *nodeUpdates // pendingOpenUpdates is a channel where updates about channel pending // opening will be sent. This channel will be buffered to ensure we // have at most one pending update of this type to handle at a given // time. pendingOpenUpdates chan *chanPendingOpenUpdate // chanOpenFailures is a channel where updates about channel open // failures will be sent. This channel will be buffered to ensure we // have at most one pending update of this type to handle at a given // time. chanOpenFailures chan *chanOpenFailureUpdate // heuristicUpdates is a channel where updates from active heurstics // will be sent. heuristicUpdates chan *heuristicUpdate // totalBalance is the total number of satoshis the backing wallet is // known to control at any given instance. This value will be updated // when the agent receives external balance update signals. totalBalance btcutil.Amount // failedNodes lists nodes that we've previously attempted to initiate // channels with, but didn't succeed. failedNodes map[NodeID]struct{} // pendingConns tracks the nodes that we are attempting to make // connections to. This prevents us from making duplicate connection // requests to the same node. pendingConns map[NodeID]struct{} // pendingOpens tracks the channels that we've requested to be // initiated, but haven't yet been confirmed as being fully opened. // This state is required as otherwise, we may go over our allotted // channel limit, or open multiple channels to the same node. pendingOpens map[NodeID]Channel pendingMtx sync.Mutex quit chan struct{} wg sync.WaitGroup } // New creates a new instance of the Agent instantiated using the passed // configuration and initial channel state. The initial channel state slice // should be populated with the set of Channels that are currently opened by // the backing Lightning Node. func New(cfg Config, initialState []Channel) (*Agent, error) { a := &Agent{ cfg: cfg, chanState: make(map[lnwire.ShortChannelID]Channel), quit: make(chan struct{}), stateUpdates: make(chan interface{}), balanceUpdates: make(chan *balanceUpdate, 1), nodeUpdates: make(chan *nodeUpdates, 1), chanOpenFailures: make(chan *chanOpenFailureUpdate, 1), heuristicUpdates: make(chan *heuristicUpdate, 1), pendingOpenUpdates: make(chan *chanPendingOpenUpdate, 1), failedNodes: make(map[NodeID]struct{}), pendingConns: make(map[NodeID]struct{}), pendingOpens: make(map[NodeID]Channel), } for _, c := range initialState { a.chanState[c.ChanID] = c } return a, nil } // Start starts the agent along with any goroutines it needs to perform its // normal duties. func (a *Agent) Start() error { var err error a.started.Do(func() { err = a.start() }) return err } func (a *Agent) start() error { rand.Seed(time.Now().Unix()) log.Infof("Autopilot Agent starting") a.wg.Add(1) go a.controller() return nil } // Stop signals the Agent to gracefully shutdown. This function will block // until all goroutines have exited. func (a *Agent) Stop() error { var err error a.stopped.Do(func() { err = a.stop() }) return err } func (a *Agent) stop() error { log.Infof("Autopilot Agent stopping") close(a.quit) a.wg.Wait() return nil } // balanceUpdate is a type of external state update that reflects an // increase/decrease in the funds currently available to the wallet. type balanceUpdate struct { } // nodeUpdates is a type of external state update that reflects an addition or // modification in channel graph node membership. type nodeUpdates struct{} // chanOpenUpdate is a type of external state update that indicates a new // channel has been opened, either by the Agent itself (within the main // controller loop), or by an external user to the system. type chanOpenUpdate struct { newChan Channel } // chanPendingOpenUpdate is a type of external state update that indicates a new // channel has been opened, either by the agent itself or an external subsystem, // but is still pending. type chanPendingOpenUpdate struct{} // chanOpenFailureUpdate is a type of external state update that indicates // a previous channel open failed, and that it might be possible to try again. type chanOpenFailureUpdate struct{} // heuristicUpdate is an update sent when one of the autopilot heuristics has // changed, and prompts the agent to make a new attempt at opening more // channels. type heuristicUpdate struct { heuristic AttachmentHeuristic } // chanCloseUpdate is a type of external state update that indicates that the // backing Lightning Node has closed a previously open channel. type chanCloseUpdate struct { closedChans []lnwire.ShortChannelID } // OnBalanceChange is a callback that should be executed each time the balance // of the backing wallet changes. func (a *Agent) OnBalanceChange() { select { case a.balanceUpdates <- &balanceUpdate{}: default: } } // OnNodeUpdates is a callback that should be executed each time our channel // graph has new nodes or their node announcements are updated. func (a *Agent) OnNodeUpdates() { select { case a.nodeUpdates <- &nodeUpdates{}: default: } } // OnChannelOpen is a callback that should be executed each time a new channel // is manually opened by the user or any system outside the autopilot agent. func (a *Agent) OnChannelOpen(c Channel) { a.wg.Add(1) go func() { defer a.wg.Done() select { case a.stateUpdates <- &chanOpenUpdate{newChan: c}: case <-a.quit: } }() } // OnChannelPendingOpen is a callback that should be executed each time a new // channel is opened, either by the agent or an external subsystems, but is // still pending. func (a *Agent) OnChannelPendingOpen() { select { case a.pendingOpenUpdates <- &chanPendingOpenUpdate{}: default: } } // OnChannelOpenFailure is a callback that should be executed when the // autopilot has attempted to open a channel, but failed. In this case we can // retry channel creation with a different node. func (a *Agent) OnChannelOpenFailure() { select { case a.chanOpenFailures <- &chanOpenFailureUpdate{}: default: } } // OnChannelClose is a callback that should be executed each time a prior // channel has been closed for any reason. This includes regular // closes, force closes, and channel breaches. func (a *Agent) OnChannelClose(closedChans ...lnwire.ShortChannelID) { a.wg.Add(1) go func() { defer a.wg.Done() select { case a.stateUpdates <- &chanCloseUpdate{closedChans: closedChans}: case <-a.quit: } }() } // OnHeuristicUpdate is a method called when a heuristic has been updated, to // trigger the agent to do a new state assessment. func (a *Agent) OnHeuristicUpdate(h AttachmentHeuristic) { select { case a.heuristicUpdates <- &heuristicUpdate{ heuristic: h, }: default: } } // mergeNodeMaps merges the Agent's set of nodes that it already has active // channels open to, with the other sets of nodes that should be removed from // consideration during heuristic selection. This ensures that the Agent doesn't // attempt to open any "duplicate" channels to the same node. func mergeNodeMaps(c map[NodeID]Channel, skips ...map[NodeID]struct{}) map[NodeID]struct{} { numNodes := len(c) for _, skip := range skips { numNodes += len(skip) } res := make(map[NodeID]struct{}, len(c)+numNodes) for nodeID := range c { res[nodeID] = struct{}{} } for _, skip := range skips { for nodeID := range skip { res[nodeID] = struct{}{} } } return res } // mergeChanState merges the Agent's set of active channels, with the set of // channels awaiting confirmation. This ensures that the agent doesn't go over // the prescribed channel limit or fund allocation limit. func mergeChanState(pendingChans map[NodeID]Channel, activeChans channelState) []Channel { numChans := len(pendingChans) + len(activeChans) totalChans := make([]Channel, 0, numChans) totalChans = append(totalChans, activeChans.Channels()...) for _, pendingChan := range pendingChans { totalChans = append(totalChans, pendingChan) } return totalChans } // controller implements the closed-loop control system of the Agent. The // controller will make a decision w.r.t channel placement within the graph // based on: its current internal state of the set of active channels open, // and external state changes as a result of decisions it makes w.r.t channel // allocation, or attributes affecting its control loop being updated by the // backing Lightning Node. func (a *Agent) controller() { defer a.wg.Done() // We'll start off by assigning our starting balance, and injecting // that amount as an initial wake up to the main controller goroutine. a.OnBalanceChange() // TODO(roasbeef): do we in fact need to maintain order? // * use sync.Cond if so updateBalance := func() { newBalance, err := a.cfg.WalletBalance() if err != nil { log.Warnf("unable to update wallet balance: %v", err) return } a.totalBalance = newBalance } // TODO(roasbeef): add 10-minute wake up timer for { select { // A new external signal has arrived. We'll use this to update // our internal state, then determine if we should trigger a // channel state modification (open/close, splice in/out). case signal := <-a.stateUpdates: log.Infof("Processing new external signal") switch update := signal.(type) { // A new channel has been opened successfully. This was // either opened by the Agent, or an external system // that is able to drive the Lightning Node. case *chanOpenUpdate: log.Debugf("New channel successfully opened, "+ "updating state with: %v", spew.Sdump(update.newChan)) newChan := update.newChan a.chanStateMtx.Lock() a.chanState[newChan.ChanID] = newChan a.chanStateMtx.Unlock() a.pendingMtx.Lock() delete(a.pendingOpens, newChan.Node) a.pendingMtx.Unlock() updateBalance() // A channel has been closed, this may free up an // available slot, triggering a new channel update. case *chanCloseUpdate: log.Debugf("Applying closed channel "+ "updates: %v", spew.Sdump(update.closedChans)) a.chanStateMtx.Lock() for _, closedChan := range update.closedChans { delete(a.chanState, closedChan) } a.chanStateMtx.Unlock() updateBalance() } // A new channel has been opened by the agent or an external // subsystem, but is still pending confirmation. case <-a.pendingOpenUpdates: updateBalance() // The balance of the backing wallet has changed, if more funds // are now available, we may attempt to open up an additional // channel, or splice in funds to an existing one. case <-a.balanceUpdates: log.Debug("Applying external balance state update") updateBalance() // The channel we tried to open previously failed for whatever // reason. case <-a.chanOpenFailures: log.Debug("Retrying after previous channel open " + "failure.") updateBalance() // New nodes have been added to the graph or their node // announcements have been updated. We will consider opening // channels to these nodes if we haven't stabilized. case <-a.nodeUpdates: log.Debugf("Node updates received, assessing " + "need for more channels") // Any of the deployed heuristics has been updated, check // whether we have new channel candidates available. case upd := <-a.heuristicUpdates: log.Debugf("Heuristic %v updated, assessing need for "+ "more channels", upd.heuristic.Name()) // The agent has been signalled to exit, so we'll bail out // immediately. case <-a.quit: return } a.pendingMtx.Lock() log.Debugf("Pending channels: %v", spew.Sdump(a.pendingOpens)) a.pendingMtx.Unlock() // With all the updates applied, we'll obtain a set of the // current active channels (confirmed channels), and also // factor in our set of unconfirmed channels. a.chanStateMtx.Lock() a.pendingMtx.Lock() totalChans := mergeChanState(a.pendingOpens, a.chanState) a.pendingMtx.Unlock() a.chanStateMtx.Unlock() // Now that we've updated our internal state, we'll consult our // channel attachment heuristic to determine if we can open // up any additional channels while staying within our // constraints. availableFunds, numChans := a.cfg.Constraints.ChannelBudget( totalChans, a.totalBalance, ) switch { case numChans == 0: continue // If the amount is too small, we don't want to attempt opening // another channel. case availableFunds == 0: continue case availableFunds < a.cfg.Constraints.MinChanSize(): continue } log.Infof("Triggering attachment directive dispatch, "+ "total_funds=%v", a.totalBalance) err := a.openChans(availableFunds, numChans, totalChans) if err != nil { log.Errorf("Unable to open channels: %v", err) } } } // openChans queries the agent's heuristic for a set of channel candidates, and // attempts to open channels to them. func (a *Agent) openChans(availableFunds btcutil.Amount, numChans uint32, totalChans []Channel) error { // As channel size we'll use the maximum channel size available. chanSize := a.cfg.Constraints.MaxChanSize() if availableFunds < chanSize { chanSize = availableFunds } if chanSize < a.cfg.Constraints.MinChanSize() { return fmt.Errorf("not enough funds available to open a " + "single channel") } // We're to attempt an attachment so we'll obtain the set of // nodes that we currently have channels with so we avoid // duplicate edges. a.chanStateMtx.Lock() connectedNodes := a.chanState.ConnectedNodes() a.chanStateMtx.Unlock() for nID := range connectedNodes { log.Tracef("Skipping node %x with open channel", nID[:]) } a.pendingMtx.Lock() for nID := range a.pendingOpens { log.Tracef("Skipping node %x with pending channel open", nID[:]) } for nID := range a.pendingConns { log.Tracef("Skipping node %x with pending connection", nID[:]) } for nID := range a.failedNodes { log.Tracef("Skipping failed node %v", nID[:]) } nodesToSkip := mergeNodeMaps(a.pendingOpens, a.pendingConns, connectedNodes, a.failedNodes, ) a.pendingMtx.Unlock() // Gather the set of all nodes in the graph, except those we // want to skip. selfPubBytes := a.cfg.Self.SerializeCompressed() nodes := make(map[NodeID]struct{}) addresses := make(map[NodeID][]net.Addr) if err := a.cfg.Graph.ForEachNode(func(node Node) error { nID := NodeID(node.PubKey()) // If we come across ourselves, them we'll continue in // order to avoid attempting to make a channel with // ourselves. if bytes.Equal(nID[:], selfPubBytes) { log.Tracef("Skipping self node %x", nID[:]) return nil } // If the node has no known addresses, we cannot connect to it, // so we'll skip it. addrs := node.Addrs() if len(addrs) == 0 { log.Tracef("Skipping node %x since no addresses known", nID[:]) return nil } addresses[nID] = addrs // Additionally, if this node is in the blacklist, then // we'll skip it. if _, ok := nodesToSkip[nID]; ok { log.Tracef("Skipping blacklisted node %x", nID[:]) return nil } nodes[nID] = struct{}{} return nil }); err != nil { return fmt.Errorf("unable to get graph nodes: %v", err) } // Use the heuristic to calculate a score for each node in the // graph. log.Debugf("Scoring %d nodes for chan_size=%v", len(nodes), chanSize) scores, err := a.cfg.Heuristic.NodeScores( a.cfg.Graph, totalChans, chanSize, nodes, ) if err != nil { return fmt.Errorf("unable to calculate node scores : %v", err) } log.Debugf("Got scores for %d nodes", len(scores)) // Now use the score to make a weighted choice which nodes to attempt // to open channels to. scores, err = chooseN(numChans, scores) if err != nil { return fmt.Errorf("unable to make weighted choice: %v", err) } chanCandidates := make(map[NodeID]*AttachmentDirective) for nID := range scores { log.Tracef("Creating attachment directive for chosen node %x", nID[:]) // Add addresses to the candidates. addrs := addresses[nID] // If the node has no known addresses, we cannot connect to it, // so we'll skip it. if len(addrs) == 0 { log.Tracef("Skipping scored node %x with no addresses", nID[:]) continue } // Track the available funds we have left. if availableFunds < chanSize { chanSize = availableFunds } availableFunds -= chanSize // If we run out of funds, we can break early. if chanSize < a.cfg.Constraints.MinChanSize() { log.Tracef("Chan size %v too small to satisfy min "+ "channel size %v, breaking", chanSize, a.cfg.Constraints.MinChanSize()) break } chanCandidates[nID] = &AttachmentDirective{ NodeID: nID, ChanAmt: chanSize, Addrs: addrs, } } if len(chanCandidates) == 0 { log.Infof("No eligible candidates to connect to") return nil } log.Infof("Attempting to execute channel attachment "+ "directives: %v", spew.Sdump(chanCandidates)) // Before proceeding, check to see if we have any slots // available to open channels. If there are any, we will attempt // to dispatch the retrieved directives since we can't be // certain which ones may actually succeed. If too many // connections succeed, we will they will be ignored and made // available to future heuristic selections. a.pendingMtx.Lock() defer a.pendingMtx.Unlock() if uint16(len(a.pendingOpens)) >= a.cfg.Constraints.MaxPendingOpens() { log.Debugf("Reached cap of %v pending "+ "channel opens, will retry "+ "after success/failure", a.cfg.Constraints.MaxPendingOpens()) return nil } // For each recommended attachment directive, we'll launch a // new goroutine to attempt to carry out the directive. If any // of these succeed, then we'll receive a new state update, // taking us back to the top of our controller loop. for _, chanCandidate := range chanCandidates { // Skip candidates which we are already trying // to establish a connection with. nodeID := chanCandidate.NodeID if _, ok := a.pendingConns[nodeID]; ok { continue } a.pendingConns[nodeID] = struct{}{} a.wg.Add(1) go a.executeDirective(*chanCandidate) } return nil } // executeDirective attempts to connect to the channel candidate specified by // the given attachment directive, and open a channel of the given size. // // NOTE: MUST be run as a goroutine. func (a *Agent) executeDirective(directive AttachmentDirective) { defer a.wg.Done() // We'll start out by attempting to connect to the peer in order to // begin the funding workflow. nodeID := directive.NodeID pub, err := btcec.ParsePubKey(nodeID[:], btcec.S256()) if err != nil { log.Errorf("Unable to parse pubkey %x: %v", nodeID, err) return } connected := make(chan bool) errChan := make(chan error) // To ensure a call to ConnectToPeer doesn't block the agent from // shutting down, we'll launch it in a non-waitgrouped goroutine, that // will signal when a result is returned. // TODO(halseth): use DialContext to cancel on transport level. go func() { alreadyConnected, err := a.cfg.ConnectToPeer( pub, directive.Addrs, ) if err != nil { select { case errChan <- err: case <-a.quit: } return } select { case connected <- alreadyConnected: case <-a.quit: return } }() var alreadyConnected bool select { case alreadyConnected = <-connected: case err = <-errChan: case <-a.quit: return } if err != nil { log.Warnf("Unable to connect to %x: %v", pub.SerializeCompressed(), err) // Since we failed to connect to them, we'll mark them as // failed so that we don't attempt to connect to them again. a.pendingMtx.Lock() delete(a.pendingConns, nodeID) a.failedNodes[nodeID] = struct{}{} a.pendingMtx.Unlock() // Finally, we'll trigger the agent to select new peers to // connect to. a.OnChannelOpenFailure() return } // The connection was successful, though before progressing we must // check that we have not already met our quota for max pending open // channels. This can happen if multiple directives were spawned but // fewer slots were available, and other successful attempts finished // first. a.pendingMtx.Lock() if uint16(len(a.pendingOpens)) >= a.cfg.Constraints.MaxPendingOpens() { // Since we've reached our max number of pending opens, we'll // disconnect this peer and exit. However, if we were // previously connected to them, then we'll make sure to // maintain the connection alive. if alreadyConnected { // Since we succeeded in connecting, we won't add this // peer to the failed nodes map, but we will remove it // from a.pendingConns so that it can be retried in the // future. delete(a.pendingConns, nodeID) a.pendingMtx.Unlock() return } err = a.cfg.DisconnectPeer(pub) if err != nil { log.Warnf("Unable to disconnect peer %x: %v", pub.SerializeCompressed(), err) } // Now that we have disconnected, we can remove this node from // our pending conns map, permitting subsequent connection // attempts. delete(a.pendingConns, nodeID) a.pendingMtx.Unlock() return } // If we were successful, we'll track this peer in our set of pending // opens. We do this here to ensure we don't stall on selecting new // peers if the connection attempt happens to take too long. delete(a.pendingConns, nodeID) a.pendingOpens[nodeID] = Channel{ Capacity: directive.ChanAmt, Node: nodeID, } a.pendingMtx.Unlock() // We can then begin the funding workflow with this peer. err = a.cfg.ChanController.OpenChannel(pub, directive.ChanAmt) if err != nil { log.Warnf("Unable to open channel to %x of %v: %v", pub.SerializeCompressed(), directive.ChanAmt, err) // As the attempt failed, we'll clear the peer from the set of // pending opens and mark them as failed so we don't attempt to // open a channel to them again. a.pendingMtx.Lock() delete(a.pendingOpens, nodeID) a.failedNodes[nodeID] = struct{}{} a.pendingMtx.Unlock() // Trigger the agent to re-evaluate everything and possibly // retry with a different node. a.OnChannelOpenFailure() // Finally, we should also disconnect the peer if we weren't // already connected to them beforehand by an external // subsystem. if alreadyConnected { return } err = a.cfg.DisconnectPeer(pub) if err != nil { log.Warnf("Unable to disconnect peer %x: %v", pub.SerializeCompressed(), err) } } // Since the channel open was successful and is currently pending, // we'll trigger the autopilot agent to query for more peers. // TODO(halseth): this triggers a new loop before all the new channels // are added to the pending channels map. Should add before executing // directive in goroutine? a.OnChannelPendingOpen() }