package autopilot import ( "sync" "sync/atomic" "github.com/davecgh/go-spew/spew" "github.com/lightningnetwork/lnd/lnwire" "github.com/roasbeef/btcd/btcec" "github.com/roasbeef/btcutil" ) // 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 // WalletBalance is a function closure that should return the current // available balance o 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 // MaxPendingOpens is the maximum number of pending channel // establishment goroutines that can be lingering. We cap this value in // order to control the level of parallelism caused by the autopiloit // agent. MaxPendingOpens uint16 // 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 ware 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 { // Only to be used atomically. started uint32 stopped uint32 // cfg houses the configuration state of the Ant. cfg Config // chanState tracks the current set of open channels. chanState channelState // stateUpdates is a channel that any external state updates that may // affect the heuristics of the agent will be sent over. stateUpdates chan interface{} // 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 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{}), } 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 { if !atomic.CompareAndSwapUint32(&a.started, 0, 1) { return nil } log.Infof("Autopilot Agent starting") startingBalance, err := a.cfg.WalletBalance() if err != nil { return err } a.wg.Add(1) go a.controller(startingBalance) return nil } // Stop signals the Agent to gracefully shutdown. This function will block // until all goroutines have exited. func (a *Agent) Stop() error { if !atomic.CompareAndSwapUint32(&a.stopped, 0, 1) { return nil } 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 { balanceDelta btcutil.Amount } // chanOpenUpdate is a type of external state update the 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 } // 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{} // 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(delta btcutil.Amount) { go func() { a.stateUpdates <- &balanceUpdate{ balanceDelta: delta, } }() } // 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) { go func() { a.stateUpdates <- &chanOpenUpdate{ newChan: c, } }() } // 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() { go func() { a.stateUpdates <- &chanOpenFailureUpdate{} }() } // 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) { go func() { a.stateUpdates <- &chanCloseUpdate{ closedChans: closedChans, } }() } // mergeNodeMaps merges the Agent's set of nodes that it already has active // channels open to, with the set of nodes that are pending new channels. This // ensures that the Agent doesn't attempt to open any "duplicate" channels to // the same node. func mergeNodeMaps(a map[NodeID]struct{}, b map[NodeID]struct{}, c map[NodeID]Channel) map[NodeID]struct{} { res := make(map[NodeID]struct{}, len(a)+len(b)+len(c)) for nodeID := range a { res[nodeID] = struct{}{} } for nodeID := range b { res[nodeID] = struct{}{} } for nodeID := range c { 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) for _, activeChan := range activeChans.Channels() { totalChans = append(totalChans, activeChan) } 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(startingBalance btcutil.Amount) { 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(startingBalance) // TODO(roasbeef): do we in fact need to maintain order? // * use sync.Cond if so // failedNodes lists nodes that we've previously attempted to initiate // channels with, but didn't succeed. failedNodes := make(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 := make(map[NodeID]Channel) var pendingMtx sync.Mutex 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) { // 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 *balanceUpdate: log.Debugf("Applying external balance state "+ "update of: %v", update.balanceDelta) a.totalBalance += update.balanceDelta // The channel we tried to open previously failed for // whatever reason. case *chanOpenFailureUpdate: log.Debug("Retrying after previous channel open failure.") updateBalance() // 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.chanState[newChan.ChanID] = newChan pendingMtx.Lock() delete(pendingOpens, newChan.Node) 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)) for _, closedChan := range update.closedChans { delete(a.chanState, closedChan) } updateBalance() } pendingMtx.Lock() log.Debugf("Pending channels: %v", spew.Sdump(pendingOpens)) 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. confirmedChans := a.chanState pendingMtx.Lock() totalChans := mergeChanState(pendingOpens, confirmedChans) pendingMtx.Unlock() // Now that we've updated our internal state, we'll // consult our channel attachment heuristic to // determine if we should open up any additional // channels or modify existing channels. availableFunds, numChans, needMore := a.cfg.Heuristic.NeedMoreChans( totalChans, a.totalBalance, ) if !needMore { continue } log.Infof("Triggering attachment directive dispatch, "+ "total_funds=%v", a.totalBalance) // We're to attempt an attachment so we'll o obtain the // set of nodes that we currently have channels with so // we avoid duplicate edges. connectedNodes := a.chanState.ConnectedNodes() pendingMtx.Lock() nodesToSkip := mergeNodeMaps(connectedNodes, failedNodes, pendingOpens) pendingMtx.Unlock() // If we reach this point, then according to our // heuristic we should modify our channel state to tend // towards what it determines to the optimal state. So // we'll call Select to get a fresh batch of attachment // directives, passing in the amount of funds available // for us to use. chanCandidates, err := a.cfg.Heuristic.Select( a.cfg.Self, a.cfg.Graph, availableFunds, numChans, nodesToSkip, ) if err != nil { log.Errorf("Unable to select candidates for "+ "attachment: %v", err) continue } if len(chanCandidates) == 0 { log.Infof("No eligible candidates to connect to") continue } log.Infof("Attempting to execute channel attachment "+ "directives: %v", spew.Sdump(chanCandidates)) // 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. pendingMtx.Lock() for _, chanCandidate := range chanCandidates { // Before we proceed, we'll check to see if // this attempt would take us past the total // number of allowed pending opens. If so, then // we'll skip this round and wait for an // attempt to either fail or succeed. if uint16(len(pendingOpens))+1 > a.cfg.MaxPendingOpens { log.Debugf("Reached cap of %v pending "+ "channel opens, will retry "+ "after success/failure", a.cfg.MaxPendingOpens) continue } nID := NewNodeID(chanCandidate.PeerKey) pendingOpens[nID] = Channel{ Capacity: chanCandidate.ChanAmt, Node: nID, } go func(directive AttachmentDirective) { pub := directive.PeerKey err := a.cfg.ChanController.OpenChannel( directive.PeerKey, directive.ChanAmt, directive.Addrs, ) 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 it from the set of // pending channels. pendingMtx.Lock() nID := NewNodeID(directive.PeerKey) delete(pendingOpens, nID) // Mark this node as failed so we don't // attempt it again. failedNodes[nID] = struct{}{} pendingMtx.Unlock() // Trigger the autopilot controller to // re-evaluate everything and possibly // retry with a different node. a.OnChannelOpenFailure() } }(chanCandidate) } pendingMtx.Unlock() // The agent has been signalled to exit, so we'll bail out // immediately. case <-a.quit: return } } }