13558005087

Committed 27 Feb 2025 03:04AM UTC coverage: 58.834% (-0.001%) from 58.835%

Build # 13558005087

Build Type

Pull #8453

github

Committed by

Roasbeef

Commit Message

lnwallet/chancloser: increase test coverage of state machine

Pull Request Pull Request #8453: [4/4] - multi: integrate new rbf coop close FSM into the existing peer flow

Run Details

1079 of 1370 new or added lines in 23 files covered. (78.76%)

578 existing lines in 40 files now uncovered.

137063 of 232965 relevant lines covered (58.83%)

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Source File
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91.65

/lnwallet/chancloser/rbf_coop_transitions.go

package chancloser

import (
        "bytes"
        "fmt"

        "github.com/btcsuite/btcd/btcec/v2"
        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/chaincfg"
        "github.com/btcsuite/btcd/mempool"
        "github.com/btcsuite/btcd/wire"
        "github.com/davecgh/go-spew/spew"
        "github.com/lightningnetwork/lnd/fn/v2"
        "github.com/lightningnetwork/lnd/input"
        "github.com/lightningnetwork/lnd/labels"
        "github.com/lightningnetwork/lnd/lntypes"
        "github.com/lightningnetwork/lnd/lnutils"
        "github.com/lightningnetwork/lnd/lnwallet"
        "github.com/lightningnetwork/lnd/lnwallet/chainfee"
        "github.com/lightningnetwork/lnd/lnwire"
        "github.com/lightningnetwork/lnd/protofsm"
        "github.com/lightningnetwork/lnd/tlv"
)

var (
        // ErrInvalidStateTransition is returned if the remote party tries to
        // close, but the thaw height hasn't been matched yet.
        ErrThawHeightNotReached = fmt.Errorf("thaw height not reached")
)

// sendShutdownEvents is a helper function that returns a set of daemon events
// we need to emit when we decide that we should send a shutdown message. We'll
// also mark the channel as borked as well, as at this point, we no longer want
// to continue with normal operation.
func sendShutdownEvents(chanID lnwire.ChannelID, chanPoint wire.OutPoint,
        deliveryAddr lnwire.DeliveryAddress, peerPub btcec.PublicKey,
        postSendEvent fn.Option[ProtocolEvent],
        chanState ChanStateObserver) (protofsm.DaemonEventSet, error) {

        // We'll emit a daemon event that instructs the daemon to send out a
        // new shutdown message to the remote peer.
        msgsToSend := &protofsm.SendMsgEvent[ProtocolEvent]{
                TargetPeer: peerPub,
                Msgs: []lnwire.Message{&lnwire.Shutdown{
                        ChannelID: chanID,
                        Address:   deliveryAddr,
                }},
                SendWhen: fn.Some(func() bool {
                        ok := chanState.NoDanglingUpdates()
                        if ok {
                                chancloserLog.Infof("ChannelPoint(%v): no "+
                                        "dangling updates sending shutdown "+
                                        "message", chanPoint)
                        }

                        return ok
                }),
                PostSendEvent: postSendEvent,
        }

        // If a close is already in process (we're in the RBF loop), then we
        // can skip everything below, and just send out the shutdown message.
        if chanState.FinalBalances().IsSome() {
                return protofsm.DaemonEventSet{msgsToSend}, nil
        }

        // Before closing, we'll attempt to send a disable update for the
        // channel.  We do so before closing the channel as otherwise the
        // current edge policy won't be retrievable from the graph.
        if err := chanState.DisableChannel(); err != nil {
                return nil, fmt.Errorf("unable to disable channel: %w", err)
        }

        // If we have a post-send event, then this means that we're the
        // responder. We'll use this fact below to update state in the DB.
        isInitiator := postSendEvent.IsNone()

        chancloserLog.Infof("ChannelPoint(%v): disabling outgoing adds",
                chanPoint)

        // As we're about to send a shutdown, we'll disable adds in the
        // outgoing direction.
        if err := chanState.DisableOutgoingAdds(); err != nil {
                return nil, fmt.Errorf("unable to disable outgoing "+
                        "adds: %w", err)
        }

        // To be able to survive a restart, we'll also write to disk
        // information about the shutdown we're about to send out.
        err := chanState.MarkShutdownSent(deliveryAddr, isInitiator)
        if err != nil {
                return nil, fmt.Errorf("unable to mark shutdown sent: %w", err)
        }

        chancloserLog.Debugf("ChannelPoint(%v): marking channel as borked",
                chanPoint)

        return protofsm.DaemonEventSet{msgsToSend}, nil
}

// validateShutdown is a helper function that validates that the shutdown has a
// proper delivery script, and can be sent based on the current thaw height of
// the channel.
func validateShutdown(chanThawHeight fn.Option[uint32],
        upfrontAddr fn.Option[lnwire.DeliveryAddress],
        msg *ShutdownReceived, chanPoint wire.OutPoint,
        chainParams chaincfg.Params) error {

        // If we've received a shutdown message, and we have a thaw height,
        // then we need to make sure that the channel can now be co-op closed.
        err := fn.MapOptionZ(chanThawHeight, func(thawHeight uint32) error {
                // If the current height is below the thaw height, then we'll
                // reject the shutdown message as we can't yet co-op close the
                // channel.
                if msg.BlockHeight < thawHeight {
                        return fmt.Errorf("%w: initiator attempting to "+
                                "co-op close frozen ChannelPoint(%v) "+
                                "(current_height=%v, thaw_height=%v)",
                                ErrThawHeightNotReached, chanPoint,
                                msg.BlockHeight, thawHeight)
                }

                return nil
        })
        if err != nil {
                return err
        }

        // Next, we'll verify that the remote party is sending the expected
        // shutdown script.
        return fn.MapOption(func(addr lnwire.DeliveryAddress) error {
                return validateShutdownScript(
                        addr, msg.ShutdownScript, &chainParams,
                )
        })(upfrontAddr).UnwrapOr(nil)
}

// ProcessEvent takes a protocol event, and implements a state transition for
// the state. From this state, we can receive two possible incoming events:
// SendShutdown and ShutdownReceived. Both of these will transition us to the
// ChannelFlushing state.
func (c *ChannelActive) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        switch msg := event.(type) {
        // If we get a confirmation, then a prior transaction we broadcasted
        // has confirmed, so we can move to our terminal state early.
        case *SpendEvent:
                return &CloseStateTransition{
                        NextState: &CloseFin{
                                ConfirmedTx: msg.Tx,
                        },
                }, nil

        // If we receive the SendShutdown event, then we'll send our shutdown
        // with a special SendPredicate, then go to the ShutdownPending where
        // we'll wait for the remote to send their shutdown.
        case *SendShutdown:
                // If we have an upfront shutdown addr or a delivery addr then
                // we'll use that. Otherwise, we'll generate a new delivery
                // addr.
                shutdownScript, err := env.LocalUpfrontShutdown.Alt(
                        msg.DeliveryAddr,
                ).UnwrapOrFuncErr(env.NewDeliveryScript)
                if err != nil {
                        return nil, err
                }

                // We'll emit some daemon events to send the shutdown message
                // and disable the channel on the network level. In this case,
                // we don't need a post send event as receive their shutdown is
                // what'll move us beyond the ShutdownPending state.
                daemonEvents, err := sendShutdownEvents(
                        env.ChanID, env.ChanPoint, shutdownScript,
                        env.ChanPeer, fn.None[ProtocolEvent](),
                        env.ChanObserver,
                )
                if err != nil {
                        return nil, err
                }

                chancloserLog.Infof("ChannelPoint(%v): sending shutdown msg, "+
                        "delivery_script=%x", env.ChanPoint, shutdownScript)

                // From here, we'll transition to the shutdown pending state. In
                // this state we await their shutdown message (self loop), then
                // also the flushing event.
                return &CloseStateTransition{
                        NextState: &ShutdownPending{
                                IdealFeeRate: fn.Some(msg.IdealFeeRate),
                                ShutdownScripts: ShutdownScripts{
                                        LocalDeliveryScript: shutdownScript,
                                },
                        },
                        NewEvents: fn.Some(RbfEvent{
                                ExternalEvents: daemonEvents,
                        }),
                }, nil

        // When we receive a shutdown from the remote party, we'll validate the
        // shutdown message, then transition to the ShutdownPending state. We'll
        // also emit similar events like the above to send out shutdown, and
        // also disable the channel.
        case *ShutdownReceived:
                chancloserLog.Infof("ChannelPoint(%v): received shutdown msg")

                // Validate that they can send the message now, and also that
                // they haven't violated their commitment to a prior upfront
                // shutdown addr.
                err := validateShutdown(
                        env.ThawHeight, env.RemoteUpfrontShutdown, msg,
                        env.ChanPoint, env.ChainParams,
                )
                if err != nil {
                        chancloserLog.Errorf("ChannelPoint(%v): rejecting "+
                                "shutdown attempt: %v", err)

                        return nil, err
                }

                // If we have an upfront shutdown addr we'll use that,
                // otherwise, we'll generate a new delivery script.
                shutdownAddr, err := env.LocalUpfrontShutdown.UnwrapOrFuncErr(
                        env.NewDeliveryScript,
                )
                if err != nil {
                        return nil, err
                }

                chancloserLog.Infof("ChannelPoint(%v): sending shutdown msg "+
                        "at next clean commit state", env.ChanPoint)

                // Now that we know the shutdown message is valid, we'll obtain
                // the set of daemon events we need to emit. We'll also specify
                // that once the message has actually been sent, that we
                // generate receive an input event of a ShutdownComplete.
                daemonEvents, err := sendShutdownEvents(
                        env.ChanID, env.ChanPoint, shutdownAddr,
                        env.ChanPeer,
                        fn.Some[ProtocolEvent](&ShutdownComplete{}),
                        env.ChanObserver,
                )
                if err != nil {
                        return nil, err
                }

                chancloserLog.Infof("ChannelPoint(%v): disabling incoming adds",
                        env.ChanPoint)

                // We just received a shutdown, so we'll disable the adds in
                // the outgoing direction.
                if err := env.ChanObserver.DisableIncomingAdds(); err != nil {
                        return nil, fmt.Errorf("unable to disable incoming "+
                                "adds: %w", err)
                }

                remoteAddr := msg.ShutdownScript

                return &CloseStateTransition{
                        NextState: &ShutdownPending{
                                ShutdownScripts: ShutdownScripts{
                                        LocalDeliveryScript:  shutdownAddr,
                                        RemoteDeliveryScript: remoteAddr,
                                },
                        },
                        NewEvents: fn.Some(protofsm.EmittedEvent[ProtocolEvent]{
                                ExternalEvents: daemonEvents,
                        }),
                }, nil

        // Any other messages in this state will result in an error, as this is
        // an undefined state transition.
        default:
                return nil, fmt.Errorf("%w: received %T while in ChannelActive",
                        ErrInvalidStateTransition, msg)
        }
}

// ProcessEvent takes a protocol event, and implements a state transition for
// the state. Our path to this state will determine the set of valid events. If
// we were the one that sent the shutdown, then we'll just wait on the
// ShutdownReceived event. Otherwise, we received the shutdown, and can move
// forward once we receive the ShutdownComplete event. Receiving
// ShutdownComplete means that we've sent our shutdown, as this was specified
// as a post send event.
func (s *ShutdownPending) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        switch msg := event.(type) {
        // If we get a confirmation, then a prior transaction we broadcasted
        // has confirmed, so we can move to our terminal state early.
        case *SpendEvent:
                return &CloseStateTransition{
                        NextState: &CloseFin{
                                ConfirmedTx: msg.Tx,
                        },
                }, nil

        // The remote party sent an offer early. We'll go to the ChannelFlushing
        // case, and then emit the offer as a internal event, which'll be
        // handled as an early offer.
        case *OfferReceivedEvent:
                chancloserLog.Infof("ChannelPoint(%v): got an early offer "+
                        "in ShutdownPending, emitting as external event",
                        env.ChanPoint)

                s.EarlyRemoteOffer = fn.Some(*msg)

                // We'll perform a noop update so we can wait for the actual
                // channel flushed event.
                return &CloseStateTransition{
                        NextState: s,
                }, nil

        // When we receive a shutdown from the remote party, we'll validate the
        // shutdown message, then transition to the ChannelFlushing state.
        case *ShutdownReceived:
                chancloserLog.Infof("ChannelPoint(%v): received shutdown msg",
                        env.ChanPoint)

                // Validate that they can send the message now, and also that
                // they haven't violated their commitment to a prior upfront
                // shutdown addr.
                err := validateShutdown(
                        env.ThawHeight, env.RemoteUpfrontShutdown, msg,
                        env.ChanPoint, env.ChainParams,
                )
                if err != nil {
                        chancloserLog.Errorf("ChannelPoint(%v): rejecting "+
                                "shutdown attempt: %v", err)

                        return nil, err
                }

                // If the channel is *already* flushed, and the close is
                // go straight into negotiation, as this is the RBF loop.
                // already in progress, then we can skip the flushing state and
                var eventsToEmit []ProtocolEvent
                finalBalances := env.ChanObserver.FinalBalances().UnwrapOr(
                        unknownBalance,
                )
                if finalBalances != unknownBalance {
                        channelFlushed := ProtocolEvent(&ChannelFlushed{
                                ShutdownBalances: finalBalances,
                        })
                        eventsToEmit = append(eventsToEmit, channelFlushed)
                }

                chancloserLog.Infof("ChannelPoint(%v): disabling incoming adds",
                        env.ChanPoint)

                // We just received a shutdown, so we'll disable the adds in
                // the outgoing direction.
                if err := env.ChanObserver.DisableIncomingAdds(); err != nil {
                        return nil, fmt.Errorf("unable to disable incoming "+
                                "adds: %w", err)
                }

                chancloserLog.Infof("ChannelPoint(%v): waiting for channel to "+
                        "be flushed...", env.ChanPoint)

                // If we received a remote offer early from the remote party,
                // then we'll add that to the set of internal events to emit.
                s.EarlyRemoteOffer.WhenSome(func(offer OfferReceivedEvent) {
                        eventsToEmit = append(eventsToEmit, &offer)
                })

                var newEvents fn.Option[RbfEvent]
                if len(eventsToEmit) > 0 {
                        newEvents = fn.Some(RbfEvent{
                                InternalEvent: eventsToEmit,
                        })
                }

                // We transition to the ChannelFlushing state, where we await
                // the ChannelFlushed event.
                return &CloseStateTransition{
                        NextState: &ChannelFlushing{
                                IdealFeeRate: s.IdealFeeRate,
                                ShutdownScripts: ShutdownScripts{
                                        LocalDeliveryScript:  s.LocalDeliveryScript, //nolint:ll
                                        RemoteDeliveryScript: msg.ShutdownScript,    //nolint:ll
                                },
                        },
                        NewEvents: newEvents,
                }, nil

        // If we get this message, then this means that we were finally able to
        // send out shutdown after receiving it from the remote party. We'll
        // now transition directly to the ChannelFlushing state.
        case *ShutdownComplete:
                chancloserLog.Infof("ChannelPoint(%v): waiting for channel to "+
                        "be flushed...", env.ChanPoint)

                // If the channel is *already* flushed, and the close is
                // already in progress, then we can skip the flushing state and
                // go straight into negotiation, as this is the RBF loop.
                var eventsToEmit []ProtocolEvent
                finalBalances := env.ChanObserver.FinalBalances().UnwrapOr(
                        unknownBalance,
                )
                if finalBalances != unknownBalance {
                        channelFlushed := ProtocolEvent(&ChannelFlushed{
                                ShutdownBalances: finalBalances,
                        })
                        eventsToEmit = append(eventsToEmit, channelFlushed)
                }

                // If we received a remote offer early from the remote party,
                // then we'll add that to the set of internal events to emit.
                s.EarlyRemoteOffer.WhenSome(func(offer OfferReceivedEvent) {
                        eventsToEmit = append(eventsToEmit, &offer)
                })

                var newEvents fn.Option[RbfEvent]
                if len(eventsToEmit) > 0 {
                        newEvents = fn.Some(RbfEvent{
                                InternalEvent: eventsToEmit,
                        })
                }

                // From here, we'll transition to the channel flushing state.
                // We'll stay here until we receive the ChannelFlushed event.
                return &CloseStateTransition{
                        NextState: &ChannelFlushing{
                                IdealFeeRate:    s.IdealFeeRate,
                                ShutdownScripts: s.ShutdownScripts,
                        },
                        NewEvents: newEvents,
                }, nil

        // Any other messages in this state will result in an error, as this is
        // an undefined state transition.
        default:
                return nil, fmt.Errorf("%w: received %T while in "+
                        "ShutdownPending", ErrInvalidStateTransition, msg)
        }
}

// ProcessEvent takes a new protocol event, and figures out if we can
// transition to the next state, or just loop back upon ourself. If we receive
// a ShutdownReceived event, then we'll stay in the ChannelFlushing state, as
// we haven't yet fully cleared the channel. Otherwise, we can move to the
// CloseReady state which'll being the channel closing process.
func (c *ChannelFlushing) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        switch msg := event.(type) {
        // If we get a confirmation, then a prior transaction we broadcasted
        // has confirmed, so we can move to our terminal state early.
        case *SpendEvent:
                return &CloseStateTransition{
                        NextState: &CloseFin{
                                ConfirmedTx: msg.Tx,
                        },
                }, nil

        // If we get an OfferReceived event, then the channel is flushed from
        // the PoV of the remote party. However, due to propagation delay or
        // concurrency, we may not have received the ChannelFlushed event yet.
        // In this case, we'll stash the event and wait for the ChannelFlushed
        // event.
        case *OfferReceivedEvent:
                chancloserLog.Infof("ChannelPoint(%v): received remote offer "+
                        "early, stashing...", env.ChanPoint)

                c.EarlyRemoteOffer = fn.Some(*msg)

                // We'll perform a noop update so we can wait for the actual
                // channel flushed event.
                return &CloseStateTransition{
                        NextState: c,
                }, nil

        // If we receive the ChannelFlushed event, then the coast is clear so
        // we'll now morph into the dual peer state so we can handle any
        // messages needed to drive forward the close process.
        case *ChannelFlushed:
                // Both the local and remote losing negotiation needs the terms
                // we'll be using to close the channel, so we'll create them
                // here.
                closeTerms := CloseChannelTerms{
                        ShutdownScripts:  c.ShutdownScripts,
                        ShutdownBalances: msg.ShutdownBalances,
                }

                chancloserLog.Infof("ChannelPoint(%v): channel flushed! "+
                        "proceeding with co-op close", env.ChanPoint)

                // Now that the channel has been flushed, we'll mark on disk
                // that we're approaching the point of no return where we'll
                // send a new signature to the remote party.
                //
                // TODO(roasbeef): doesn't actually matter if initiator here?
                if msg.FreshFlush {
                        err := env.ChanObserver.MarkCoopBroadcasted(nil, true)
                        if err != nil {
                                return nil, err
                        }
                }

                // If an ideal fee rate was specified, then we'll use that,
                // otherwise we'll fall back to the default value given in the
                // env.
                idealFeeRate := c.IdealFeeRate.UnwrapOr(env.DefaultFeeRate)

                // We'll then use that fee rate to determine the absolute fee
                // we'd propose.
                localTxOut, remoteTxOut := closeTerms.DeriveCloseTxOuts()
                absoluteFee := env.FeeEstimator.EstimateFee(
                        env.ChanType, localTxOut, remoteTxOut,
                        idealFeeRate.FeePerKWeight(),
                )

                chancloserLog.Infof("ChannelPoint(%v): using ideal_fee=%v, "+
                        "absolute_fee=%v", env.ChanPoint, idealFeeRate,
                        absoluteFee)

                var (
                        internalEvents []ProtocolEvent
                        newEvents      fn.Option[RbfEvent]
                )

                // If we received a remote offer early from the remote party,
                // then we'll add that to the set of internal events to emit.
                c.EarlyRemoteOffer.WhenSome(func(offer OfferReceivedEvent) {
                        internalEvents = append(internalEvents, &offer)
                })

                // Only if we have enough funds to pay for the fees do we need
                // to emit a localOfferSign event.
                //
                // TODO(roasbeef): also only proceed if was higher than fee in
                // last round?
                if closeTerms.LocalCanPayFees(absoluteFee) {
                        // Each time we go into this negotiation flow, we'll
                        // kick off our local state with a new close attempt.
                        // So we'll emit a internal event to drive forward that
                        // part of the state.
                        localOfferSign := ProtocolEvent(&SendOfferEvent{
                                TargetFeeRate: idealFeeRate,
                        })
                        internalEvents = append(internalEvents, localOfferSign)
                } else {
                        chancloserLog.Infof("ChannelPoint(%v): unable to pay "+
                                "fees with local balance, skipping "+
                                "closing_complete", env.ChanPoint)
                }

                if len(internalEvents) > 0 {
                        newEvents = fn.Some(RbfEvent{
                                InternalEvent: internalEvents,
                        })
                }

                return &CloseStateTransition{
                        NextState: &ClosingNegotiation{
                                PeerState: lntypes.Dual[AsymmetricPeerState]{
                                        Local: &LocalCloseStart{
                                                CloseChannelTerms: &closeTerms,
                                        },
                                        Remote: &RemoteCloseStart{
                                                CloseChannelTerms: &closeTerms,
                                        },
                                },
                                CloseChannelTerms: &closeTerms,
                        },
                        NewEvents: newEvents,
                }, nil

        default:
                return nil, fmt.Errorf("%w: received %T while in "+
                        "ChannelFlushing", ErrInvalidStateTransition, msg)
        }
}

// processNegotiateEvent is a helper function that processes a new event to
// local channel state once we're in the ClosingNegotiation state.
func processNegotiateEvent(c *ClosingNegotiation, event ProtocolEvent,
        env *Environment, chanPeer lntypes.ChannelParty,
) (*CloseStateTransition, error) {

        targetPeerState := c.PeerState.GetForParty(chanPeer)

        // Drive forward the remote state based on the next event.
        transition, err := targetPeerState.ProcessEvent(
                event, env,
        )
        if err != nil {
                return nil, err
        }

        nextPeerState, ok := transition.NextState.(AsymmetricPeerState) //nolint:ll
        if !ok {
                return nil, fmt.Errorf("expected %T to be "+
                        "AsymmetricPeerState", transition.NextState)
        }

        // Make a copy of the input state, then update the peer state of the
        // proper party.
        newPeerState := *c
        newPeerState.PeerState.SetForParty(chanPeer, nextPeerState)

        return &CloseStateTransition{
                NextState: &newPeerState,
                NewEvents: transition.NewEvents,
        }, nil
}

// updateAndValidateCloseTerms is a helper function that validates examines the
// incoming event, and decide if we need to update the remote party's address,
// or reject it if it doesn't include our latest address.
func (c *ClosingNegotiation) updateAndValidateCloseTerms(event ProtocolEvent,
) error {

        assertLocalScriptMatches := func(localScriptInMsg []byte) error {
                if !bytes.Equal(
                        c.LocalDeliveryScript, localScriptInMsg,
                ) {

                        return fmt.Errorf("%w: remote party sent wrong "+
                                "script, expected %x, got %x",
                                ErrWrongLocalScript, c.LocalDeliveryScript,
                                localScriptInMsg,
                        )
                }

                return nil
        }

        switch msg := event.(type) {
        // The remote party is sending us a new request to counter sign their
        // version of the commitment transaction.
        case *OfferReceivedEvent:
                // Make sure that they're sending our local script, and not
                // something else.
                err := assertLocalScriptMatches(msg.SigMsg.CloseeScript)
                if err != nil {
                        return err
                }

                oldRemoteAddr := c.RemoteDeliveryScript
                newRemoteAddr := msg.SigMsg.CloserScript

                // If they're sending a new script, then we'll update to the new
                // one.
                if !bytes.Equal(oldRemoteAddr, newRemoteAddr) {
                        c.RemoteDeliveryScript = newRemoteAddr
                }

        // The remote party responded to our sig request with a signature for
        // our version of the commitment transaction.
        case *LocalSigReceived:
                // Make sure that they're sending our local script, and not
                // something else.
                err := assertLocalScriptMatches(msg.SigMsg.CloserScript)
                if err != nil {
                        return err
                }

                return nil
        }

        return nil
}

// ProcessEvent drives forward the composite states for the local and remote
// party in response to new events. From this state, we'll continue to drive
// forward the local and remote states until we arrive at the StateFin stage,
// or we loop back up to the ShutdownPending state.
func (c *ClosingNegotiation) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        // There're two classes of events that can break us out of this state:
        // we receive a confirmation event, or we receive a signal to restart
        // the co-op close process.
        switch msg := event.(type) {
        // Ignore any potential duplicate channel flushed events.
        case *ChannelFlushed:
                return &CloseStateTransition{
                        NextState: c,
                }, nil

        // If we get a confirmation, then the spend request we issued when we
        // were leaving the ChannelFlushing state has been confirmed.  We'll
        // now transition to the StateFin state.
        case *SpendEvent:
                return &CloseStateTransition{
                        NextState: &CloseFin{
                                ConfirmedTx: msg.Tx,
                        },
                }, nil
        }

        // At this point, we know its a new signature message. We'll validate,
        // and maybe update the set of close terms based on what we receive. We
        // might update the remote party's address for example.
        if err := c.updateAndValidateCloseTerms(event); err != nil {
                return nil, fmt.Errorf("event violates close terms: %w", err)
        }

        shouldRouteTo := func(party lntypes.ChannelParty) bool {
                state := c.PeerState.GetForParty(party)
                if state == nil {
                        return false
                }

                return state.ShouldRouteTo(event)
        }

        // If we get to this point, then we have an event that'll drive forward
        // the negotiation process.  Based on the event, we'll figure out which
        // state we'll be modifying.
        switch {
        case shouldRouteTo(lntypes.Local):
                chancloserLog.Infof("ChannelPoint(%v): routing %T to local "+
                        "chan state", env.ChanPoint, event)

                // Drive forward the local state based on the next event.
                return processNegotiateEvent(c, event, env, lntypes.Local)

        case shouldRouteTo(lntypes.Remote):
                chancloserLog.Infof("ChannelPoint(%v): routing %T to remote "+

                        "chan state", env.ChanPoint, event)
                // Drive forward the remote state based on the next event.
                return processNegotiateEvent(c, event, env, lntypes.Remote)
        }

        return nil, fmt.Errorf("%w: received %T while in %v",
                ErrInvalidStateTransition, event, c)
}

// newSigTlv is a helper function that returns a new optional TLV sig field for
// the parametrized tlv.TlvType value.
func newSigTlv[T tlv.TlvType](s lnwire.Sig) tlv.OptionalRecordT[T, lnwire.Sig] {
        return tlv.SomeRecordT(tlv.NewRecordT[T](s))
}

// ProcessEvent implements the event processing to kick off the process of
// obtaining a new (possibly RBF'd) signature for our commitment transaction.
func (l *LocalCloseStart) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        switch msg := event.(type) { //nolint:gocritic
        // If we receive a SendOfferEvent, then we'll use the specified fee
        // rate to generate for the closing transaction with our ideal fee
        // rate.
        case *SendOfferEvent:
                // given the state of the local/remote outputs.
                // First, we'll figure out the absolute fee rate we should pay
                localTxOut, remoteTxOut := l.DeriveCloseTxOuts()
                absoluteFee := env.FeeEstimator.EstimateFee(
                        env.ChanType, localTxOut, remoteTxOut,
                        msg.TargetFeeRate.FeePerKWeight(),
                )

                // If we can't actually pay for fees here, then we'll just do a
                // noop back to the same state to await a new fee rate.
                if !l.LocalCanPayFees(absoluteFee) {
                        chancloserLog.Infof("ChannelPoint(%v): unable to pay "+
                                "fee=%v with local balance %v, skipping "+
                                "closing_complete", env.ChanPoint, absoluteFee,
                                l.LocalBalance)

                        return &CloseStateTransition{
                                NextState: &CloseErr{
                                        CloseChannelTerms: l.CloseChannelTerms,
                                        Party:             lntypes.Local,
                                        ErrState: NewErrStateCantPayForFee(
                                                l.LocalBalance.ToSatoshis(),
                                                absoluteFee,
                                        ),
                                },
                        }, nil
                }

                // Now that we know what fee we want to pay, we'll create a new
                // signature over our co-op close transaction. For our
                // proposals, we'll just always use the known RBF sequence
                // value.
                localScript := l.LocalDeliveryScript
                rawSig, closeTx, closeBalance, err := env.CloseSigner.CreateCloseProposal( //nolint:ll
                        absoluteFee, localScript, l.RemoteDeliveryScript,
                        lnwallet.WithCustomSequence(mempool.MaxRBFSequence),
                        lnwallet.WithCustomPayer(lntypes.Local),
                )
                if err != nil {
                        return nil, err
                }
                wireSig, err := lnwire.NewSigFromSignature(rawSig)
                if err != nil {
                        return nil, err
                }

                chancloserLog.Infof("closing w/ local_addr=%x, "+
                        "remote_addr=%x, fee=%v", localScript[:],
                        l.RemoteDeliveryScript[:], absoluteFee)

                chancloserLog.Infof("proposing closing_tx=%v",
                        spew.Sdump(closeTx))

                // Now that we have our signature, we'll set the proper
                // closingSigs field based on if the remote party's output is
                // dust or not.
                var closingSigs lnwire.ClosingSigs
                switch {
                // If the remote party's output is dust, then we'll set the
                // CloserNoClosee field.
                case remoteTxOut == nil:
                        closingSigs.CloserNoClosee = newSigTlv[tlv.TlvType1](
                                wireSig,
                        )

                // If after paying for fees, our balance is below dust, then
                // we'll set the NoCloserClosee field.
                case closeBalance < lnwallet.DustLimitForSize(len(localScript)):
                        closingSigs.NoCloserClosee = newSigTlv[tlv.TlvType2](
                                wireSig,
                        )

                // Otherwise, we'll set the CloserAndClosee field.
                //
                // TODO(roasbeef): should actually set both??
                default:
                        closingSigs.CloserAndClosee = newSigTlv[tlv.TlvType3](
                                wireSig,
                        )
                }

                // Now that we have our sig, we'll emit a daemon event to send
                // it to the remote party, then transition to the
                // LocalOfferSent state.
                //
                // TODO(roasbeef): type alias for protocol event
                sendEvent := protofsm.DaemonEventSet{&protofsm.SendMsgEvent[ProtocolEvent]{ //nolint:ll
                        TargetPeer: env.ChanPeer,
                        Msgs: []lnwire.Message{&lnwire.ClosingComplete{
                                ChannelID:    env.ChanID,
                                CloserScript: l.LocalDeliveryScript,
                                CloseeScript: l.RemoteDeliveryScript,
                                FeeSatoshis:  absoluteFee,
                                LockTime:     env.BlockHeight,
                                ClosingSigs:  closingSigs,
                        }},
                }}

                chancloserLog.Infof("ChannelPoint(%v): sending closing sig "+
                        "to remote party, fee_sats=%v", env.ChanPoint,
                        absoluteFee)

                return &CloseStateTransition{
                        NextState: &LocalOfferSent{
                                ProposedFee:       absoluteFee,
                                ProposedFeeRate:   msg.TargetFeeRate,
                                LocalSig:          wireSig,
                                CloseChannelTerms: l.CloseChannelTerms,
                        },
                        NewEvents: fn.Some(RbfEvent{
                                ExternalEvents: sendEvent,
                        }),
                }, nil
        }

        return nil, fmt.Errorf("%w: received %T while in LocalCloseStart",
                ErrInvalidStateTransition, event)
}

// extractSig extracts the expected signature from the closing sig message.
// Only one of them should actually be populated as the closing sig message is
// sent in response to a ClosingComplete message, it should only sign the same
// version of the co-op close tx as the sender did.
func extractSig(msg lnwire.ClosingSig) fn.Result[lnwire.Sig] {
        // First, we'll validate that only one signature is included in their
        // response to our initial offer. If not, then we'll exit here, and
        // trigger a recycle of the connection.
        sigInts := []bool{
                msg.CloserNoClosee.IsSome(), msg.NoCloserClosee.IsSome(),
                msg.CloserAndClosee.IsSome(),
        }
        numSigs := fn.Foldl(0, sigInts, func(acc int, sigInt bool) int {
                if sigInt {
                        return acc + 1
                }

                return acc
        })
        if numSigs != 1 {
                return fn.Errf[lnwire.Sig]("%w: only one sig should be set, "+
                        "got %v", ErrTooManySigs, numSigs)
        }

        // The final sig is the one that's actually set.
        sig := msg.CloserAndClosee.ValOpt().Alt(
                msg.NoCloserClosee.ValOpt(),
        ).Alt(
                msg.CloserNoClosee.ValOpt(),
        )

        return fn.NewResult(sig.UnwrapOrErr(ErrNoSig))
}

// ProcessEvent implements the state transition function for the
// LocalOfferSent state. In this state, we'll wait for the remote party to
// send a close_signed message which gives us the ability to broadcast a new
// co-op close transaction.
func (l *LocalOfferSent) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        switch msg := event.(type) { //nolint:gocritic
        // If we receive a LocalSigReceived event, then we'll attempt to
        // validate the signature from the remote party. If valid, then we can
        // broadcast the transaction, and transition to the ClosePending state.
        case *LocalSigReceived:
                // Extract and validate that only one sig field is set.
                sig, err := extractSig(msg.SigMsg).Unpack()
                if err != nil {
                        return nil, err
                }

                remoteSig, err := sig.ToSignature()
                if err != nil {
                        return nil, err
                }
                localSig, err := l.LocalSig.ToSignature()
                if err != nil {
                        return nil, err
                }

                // Now that we have their signature, we'll attempt to validate
                // it, then extract a valid closing signature from it.
                closeTx, _, err := env.CloseSigner.CompleteCooperativeClose(
                        localSig, remoteSig, l.LocalDeliveryScript,
                        l.RemoteDeliveryScript, l.ProposedFee,
                        lnwallet.WithCustomSequence(mempool.MaxRBFSequence),
                        lnwallet.WithCustomPayer(lntypes.Local),
                )
                if err != nil {
                        return nil, err
                }

                // As we're about to broadcast a new version of the co-op close
                // transaction, we'll mark again as broadcast, but with this
                // variant of the co-op close tx.
                err = env.ChanObserver.MarkCoopBroadcasted(closeTx, true)
                if err != nil {
                        return nil, err
                }

                broadcastEvent := protofsm.DaemonEventSet{&protofsm.BroadcastTxn{ //nolint:ll
                        Tx: closeTx,
                        Label: labels.MakeLabel(
                                labels.LabelTypeChannelClose, &env.Scid,
                        ),
                }}

                chancloserLog.Infof("ChannelPoint(%v): received sig from "+
                        "remote party, broadcasting: tx=%v", env.ChanPoint,
                        lnutils.SpewLogClosure(closeTx),
                )

                return &CloseStateTransition{
                        NextState: &ClosePending{
                                CloseTx:           closeTx,
                                FeeRate:           l.ProposedFeeRate,
                                CloseChannelTerms: l.CloseChannelTerms,
                                Party:             lntypes.Local,
                        },
                        NewEvents: fn.Some(protofsm.EmittedEvent[ProtocolEvent]{
                                ExternalEvents: broadcastEvent,
                        }),
                }, nil
        }

        return nil, fmt.Errorf("%w: received %T while in LocalOfferSent",
                ErrInvalidStateTransition, event)
}

// ProcessEvent implements the state transition function for the
// RemoteCloseStart. In this state, we'll wait for the remote party to send a
// closing_complete message. Assuming they can pay for the fees, we'll sign it
// ourselves, then transition to the next state of ClosePending.
func (l *RemoteCloseStart) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        switch msg := event.(type) { //nolint:gocritic
        // If we receive a OfferReceived event, we'll make sure they can
        // actually pay for the fee. If so, then we'll counter sign and
        // transition to a terminal state.
        case *OfferReceivedEvent:
                // To start, we'll perform some basic validation of the sig
                // message they've sent. We'll validate that the remote party
                // actually has enough fees to pay the closing fees.
                if !l.RemoteCanPayFees(msg.SigMsg.FeeSatoshis) {
                        return nil, fmt.Errorf("%w: %v vs %v",
                                ErrRemoteCannotPay,
                                msg.SigMsg.FeeSatoshis,
                                l.RemoteBalance.ToSatoshis())
                }

                // With the basic sanity checks out of the way, we'll now
                // figure out which signature that we'll attempt to sign
                // against.
                var (
                        remoteSig input.Signature
                        noClosee  bool
                )
                switch {
                // If our balance is dust, then we expect the CloserNoClosee
                // sig to be set.
                case l.LocalAmtIsDust():
                        if msg.SigMsg.CloserNoClosee.IsNone() {
                                return nil, ErrCloserNoClosee
                        }
                        msg.SigMsg.CloserNoClosee.WhenSomeV(func(s lnwire.Sig) {
                                remoteSig, _ = s.ToSignature()
                                noClosee = true
                        })

                // Otherwise, we'll assume that CloseAndClosee is set.
                //
                // TODO(roasbeef): NoCloserClosee, but makes no sense?
                default:
                        if msg.SigMsg.CloserAndClosee.IsNone() {
                                return nil, ErrCloserAndClosee
                        }
                        msg.SigMsg.CloserAndClosee.WhenSomeV(func(s lnwire.Sig) { //nolint:ll
                                remoteSig, _ = s.ToSignature()
                        })
                }

                chanOpts := []lnwallet.ChanCloseOpt{
                        lnwallet.WithCustomSequence(mempool.MaxRBFSequence),
                        lnwallet.WithCustomLockTime(msg.SigMsg.LockTime),
                        lnwallet.WithCustomPayer(lntypes.Remote),
                }

                chancloserLog.Infof("responding to close w/ local_addr=%x, "+
                        "remote_addr=%x, fee=%v",
                        l.LocalDeliveryScript[:], l.RemoteDeliveryScript[:],
                        msg.SigMsg.FeeSatoshis)

                // Now that we have the remote sig, we'll sign the version they
                // signed, then attempt to complete the cooperative close
                // process.
                //
                // TODO(roasbeef): need to be able to omit an output when
                // signing based on the above, as closing opt
                rawSig, _, _, err := env.CloseSigner.CreateCloseProposal(
                        msg.SigMsg.FeeSatoshis, l.LocalDeliveryScript,
                        l.RemoteDeliveryScript, chanOpts...,
                )
                if err != nil {
                        return nil, err
                }
                wireSig, err := lnwire.NewSigFromSignature(rawSig)
                if err != nil {
                        return nil, err
                }

                localSig, err := wireSig.ToSignature()
                if err != nil {
                        return nil, err
                }

                // With our signature created, we'll now attempt to finalize the
                // close process.
                closeTx, _, err := env.CloseSigner.CompleteCooperativeClose(
                        localSig, remoteSig, l.LocalDeliveryScript,
                        l.RemoteDeliveryScript, msg.SigMsg.FeeSatoshis,
                        chanOpts...,
                )
                if err != nil {
                        return nil, err
                }

                chancloserLog.Infof("ChannelPoint(%v): received sig (fee=%v "+
                        "sats) from remote party, signing new tx=%v",
                        env.ChanPoint, msg.SigMsg.FeeSatoshis,
                        lnutils.SpewLogClosure(closeTx),
                )

                var closingSigs lnwire.ClosingSigs
                if noClosee {
                        closingSigs.CloserNoClosee = newSigTlv[tlv.TlvType1](
                                wireSig,
                        )
                } else {
                        closingSigs.CloserAndClosee = newSigTlv[tlv.TlvType3](
                                wireSig,
                        )
                }

                // As we're about to broadcast a new version of the co-op close
                // transaction, we'll mark again as broadcast, but with this
                // variant of the co-op close tx.
                //
                // TODO(roasbeef): db will only store one instance, store both?
                err = env.ChanObserver.MarkCoopBroadcasted(closeTx, false)
                if err != nil {
                        return nil, err
                }

                // As we transition, we'll omit two events: one to broadcast
                // the transaction, and the other to send our ClosingSig
                // message to the remote party.
                sendEvent := &protofsm.SendMsgEvent[ProtocolEvent]{
                        TargetPeer: env.ChanPeer,
                        Msgs: []lnwire.Message{&lnwire.ClosingSig{
                                ChannelID:    env.ChanID,
                                CloserScript: l.RemoteDeliveryScript,
                                CloseeScript: l.LocalDeliveryScript,
                                FeeSatoshis:  msg.SigMsg.FeeSatoshis,
                                LockTime:     msg.SigMsg.LockTime,
                                ClosingSigs:  closingSigs,
                        }},
                }
                broadcastEvent := &protofsm.BroadcastTxn{
                        Tx: closeTx,
                        Label: labels.MakeLabel(
                                labels.LabelTypeChannelClose, &env.Scid,
                        ),
                }
                daemonEvents := protofsm.DaemonEventSet{
                        sendEvent, broadcastEvent,
                }

                // We'll also compute the final fee rate that the remote party
                // paid based off the absolute fee and the size of the closing
                // transaction.
                vSize := mempool.GetTxVirtualSize(btcutil.NewTx(closeTx))
                feeRate := chainfee.SatPerVByte(
                        int64(msg.SigMsg.FeeSatoshis) / vSize,
                )

                // Now that we've extracted the signature, we'll transition to
                // the next state where we'll sign+broadcast the sig.
                return &CloseStateTransition{
                        NextState: &ClosePending{
                                CloseTx:           closeTx,
                                FeeRate:           feeRate,
                                CloseChannelTerms: l.CloseChannelTerms,
                                Party:             lntypes.Remote,
                        },
                        NewEvents: fn.Some(protofsm.EmittedEvent[ProtocolEvent]{
                                ExternalEvents: daemonEvents,
                        }),
                }, nil
        }

        return nil, fmt.Errorf("%w: received %T while in RemoteCloseStart",
                ErrInvalidStateTransition, event)
}

// ProcessEvent is a semi-terminal state in the rbf-coop close state machine.
// In this state, we're waiting for either a confirmation, or for either side
// to attempt to create a new RBF'd co-op close transaction.
func (c *ClosePending) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        switch msg := event.(type) {
        // If we can a spend while waiting for the close, then we'll go to our
        // terminal state.
        case *SpendEvent:
                return &CloseStateTransition{
                        NextState: &CloseFin{
                                ConfirmedTx: msg.Tx,
                        },
                }, nil

        // If we get a send offer event in this state, then we're doing a state
        // transition to the LocalCloseStart state, so we can sign a new closing
        // tx.
        case *SendOfferEvent:
                return &CloseStateTransition{
                        NextState: &LocalCloseStart{
                                CloseChannelTerms: c.CloseChannelTerms,
                        },
                        NewEvents: fn.Some(protofsm.EmittedEvent[ProtocolEvent]{
                                InternalEvent: []ProtocolEvent{msg},
                        }),
                }, nil

        // If we get an offer received event, then we're doing a state
        // transition to the RemoteCloseStart, as the remote peer wants to sign
        // a new closing tx.
        case *OfferReceivedEvent:
                return &CloseStateTransition{
                        NextState: &RemoteCloseStart{
                                CloseChannelTerms: c.CloseChannelTerms,
                        },
                        NewEvents: fn.Some(protofsm.EmittedEvent[ProtocolEvent]{
                                InternalEvent: []ProtocolEvent{msg},
                        }),
                }, nil

        default:

                return &CloseStateTransition{
                        NextState: c,
                }, nil
        }
}

// ProcessEvent is the event processing for out terminal state. In this state,
// we just keep looping back on ourselves.
func (c *CloseFin) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        return &CloseStateTransition{
                NextState: c,
        }, nil
}

// ProcessEvent is a semi-terminal state in the rbf-coop close state machine.
// In this state, we hit a validation error in an earlier state, so we'll remain
// in this state for the user to examine. We may also process new requests to
// continue the state machine.
func (c *CloseErr) ProcessEvent(event ProtocolEvent, env *Environment,
) (*CloseStateTransition, error) {

        switch msg := event.(type) {

        // If we get a send offer event in this state, then we're doing a state
        // transition to the LocalCloseStart state, so we can sign a new closing
        // tx.
        case *SendOfferEvent:
                return &CloseStateTransition{
                        NextState: &LocalCloseStart{
                                CloseChannelTerms: c.CloseChannelTerms,
                        },
                        NewEvents: fn.Some(protofsm.EmittedEvent[ProtocolEvent]{
                                InternalEvent: []ProtocolEvent{msg},
                        }),
                }, nil

        // If we get an offer received event, then we're doing a state
        // transition to the RemoteCloseStart, as the remote peer wants to sign
        // a new closing tx.
        case *OfferReceivedEvent:
                return &CloseStateTransition{
                        NextState: &RemoteCloseStart{
                                CloseChannelTerms: c.CloseChannelTerms,
                        },
                        NewEvents: fn.Some(protofsm.EmittedEvent[ProtocolEvent]{
                                InternalEvent: []ProtocolEvent{msg},
                        }),
                }, nil

        default:
                return &CloseStateTransition{
                        NextState: c,
                }, nil
        }
}

lightningnetwork / lnd / 13558005087

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