13725358077

Committed 07 Mar 2025 04:51PM UTC coverage: 58.224% (-10.4%) from 68.615%

Build # 13725358077

Build Type

Pull #9458

github

Committed by

web-flow

Commit Message

Merge bf4c6625f into ab2dc09eb

Pull Request Pull Request #9458: multi+server.go: add initial permissions for some peers

Run Details

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0.0

/autopilot/agent.go

package autopilot

import (
        "bytes"
        "fmt"
        "math/rand"
        "net"
        "sync"
        "time"

        "github.com/btcsuite/btcd/btcec/v2"
        "github.com/btcsuite/btcd/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]LocalChannel

// Channels returns a slice of all the active channels.
func (c channelState) Channels() []LocalChannel {
        chans := make([]LocalChannel, 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 heuristics
        // 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]LocalChannel
        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 []LocalChannel) (*Agent, error) {
        a := &Agent{
                cfg:                cfg,
                chanState:          make(map[lnwire.ShortChannelID]LocalChannel),
                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]LocalChannel),
        }

        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 LocalChannel
}

// 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 LocalChannel) {
        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]LocalChannel,
        skips ...map[NodeID]struct{}) map[NodeID]struct{} {

        numNodes := len(c)
        for _, skip := range skips {
                numNodes += len(skip)
        }

        res := make(map[NodeID]struct{}, 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]LocalChannel,
        activeChans channelState) []LocalChannel {

        numChans := len(pendingChans) + len(activeChans)
        totalChans := make([]LocalChannel, 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 []LocalChannel) 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: %w", 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 : %w", 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: %w",
                        err)
        }

        chanCandidates := make(map[NodeID]*AttachmentDirective)
        for nID := range scores {
                log.Tracef("Creating attachment directive for chosen node %x",
                        nID[:])

                // 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:   addresses[nID],
                }
        }

        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, 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[:])
        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] = LocalChannel{
                Balance: 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()
}

lightningnetwork / lnd / 13725358077

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