lnd.xprv/contractcourt/channel_arbitrator.go

1556 lines
50 KiB
Go

package contractcourt
import (
"fmt"
"sync"
"sync/atomic"
"github.com/btcsuite/btcd/wire"
"github.com/davecgh/go-spew/spew"
"github.com/lightningnetwork/lnd/chainntnfs"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/lnwallet"
"github.com/lightningnetwork/lnd/lnwire"
)
const (
// broadcastRedeemMultiplier is the additional factor that we'll scale
// the normal broadcastDelta by when deciding whether or not to
// broadcast a commitment to claim an HTLC on-chain. We use a scaled
// value, as when redeeming we want to ensure that we have enough time
// to redeem the HTLC, well before it times out.
broadcastRedeemMultiplier = 2
)
// WitnessSubscription represents an intent to be notified once new witnesses
// are discovered by various active contract resolvers. A contract resolver may
// use this to be notified of when it can satisfy an incoming contract after we
// discover the witness for an outgoing contract.
type WitnessSubscription struct {
// WitnessUpdates is a channel that newly discovered witnesses will be
// sent over.
//
// TODO(roasbeef): couple with WitnessType?
WitnessUpdates <-chan []byte
// CancelSubscription is a function closure that should be used by a
// client to cancel the subscription once they are no longer interested
// in receiving new updates.
CancelSubscription func()
}
// WitnessBeacon is a global beacon of witnesses. Contract resolvers will use
// this interface to lookup witnesses (preimages typically) of contracts
// they're trying to resolve, add new preimages they resolve, and finally
// receive new updates each new time a preimage is discovered.
//
// TODO(roasbeef): need to delete the pre-images once we've used them
// and have been sufficiently confirmed?
type WitnessBeacon interface {
// SubscribeUpdates returns a channel that will be sent upon *each* time
// a new preimage is discovered.
SubscribeUpdates() *WitnessSubscription
// LookupPreImage attempts to lookup a preimage in the global cache.
// True is returned for the second argument if the preimage is found.
LookupPreimage(payhash []byte) ([]byte, bool)
// AddPreImage adds a newly discovered preimage to the global cache.
AddPreimage(pre []byte) error
}
// ChannelArbitratorConfig contains all the functionality that the
// ChannelArbitrator needs in order to properly arbitrate any contract dispute
// on chain.
type ChannelArbitratorConfig struct {
// ChanPoint is the channel point that uniquely identifies this
// channel.
ChanPoint wire.OutPoint
// ShortChanID describes the exact location of the channel within the
// chain. We'll use this to address any messages that we need to send
// to the switch during contract resolution.
ShortChanID lnwire.ShortChannelID
// BlockEpochs is an active block epoch event stream backed by an
// active ChainNotifier instance. We will use new block notifications
// sent over this channel to decide when we should go on chain to
// reclaim/redeem the funds in an HTLC sent to/from us.
BlockEpochs *chainntnfs.BlockEpochEvent
// ChainEvents is an active subscription to the chain watcher for this
// channel to be notified of any on-chain activity related to this
// channel.
ChainEvents *ChainEventSubscription
// ForceCloseChan should force close the contract that this attendant
// is watching over. We'll use this when we decide that we need to go
// to chain. It should in addition tell the switch to remove the
// corresponding link, such that we won't accept any new updates. The
// returned summary contains all items needed to eventually resolve all
// outputs on chain.
ForceCloseChan func() (*lnwallet.LocalForceCloseSummary, error)
// MarkCommitmentBroadcasted should mark the channel as the commitment
// being broadcast, and we are waiting for the commitment to confirm.
MarkCommitmentBroadcasted func() error
// MarkChannelResolved is a function closure that serves to mark a
// channel as "fully resolved". A channel itself can be considered
// fully resolved once all active contracts have individually been
// fully resolved.
//
// TODO(roasbeef): need RPC's to combine for pendingchannels RPC
MarkChannelResolved func() error
ChainArbitratorConfig
}
// htlcSet represents the set of active HTLCs on a given commitment
// transaction.
type htlcSet struct {
// incomingHTLCs is a map of all incoming HTLCs on our commitment
// transaction. We may potentially go onchain to claim the funds sent
// to us within this set.
incomingHTLCs map[uint64]channeldb.HTLC
// outgoingHTLCs is a map of all outgoing HTLCs on our commitment
// transaction. We may potentially go onchain to reclaim the funds that
// are currently in limbo.
outgoingHTLCs map[uint64]channeldb.HTLC
}
// newHtlcSet constructs a new HTLC set from a slice of HTLC's.
func newHtlcSet(htlcs []channeldb.HTLC) htlcSet {
outHTLCs := make(map[uint64]channeldb.HTLC)
inHTLCs := make(map[uint64]channeldb.HTLC)
for _, htlc := range htlcs {
if htlc.Incoming {
inHTLCs[htlc.HtlcIndex] = htlc
continue
}
outHTLCs[htlc.HtlcIndex] = htlc
}
return htlcSet{
incomingHTLCs: inHTLCs,
outgoingHTLCs: outHTLCs,
}
}
// ChannelArbitrator is the on-chain arbitrator for a particular channel. The
// struct will keep in sync with the current set of HTLCs on the commitment
// transaction. The job of the attendant is to go on-chain to either settle or
// cancel an HTLC as necessary iff: an HTLC times out, or we known the
// pre-image to an HTLC, but it wasn't settled by the link off-chain. The
// ChannelArbitrator will factor in an expected confirmation delta when
// broadcasting to ensure that we avoid any possibility of race conditions, and
// sweep the output(s) without contest.
type ChannelArbitrator struct {
started int32 // To be used atomically.
stopped int32 // To be used atomically.
// log is a persistent log that the attendant will use to checkpoint
// its next action, and the state of any unresolved contracts.
log ArbitratorLog
// activeHTLCs is the set of active incoming/outgoing HTLC's on the
// commitment transaction.
activeHTLCs htlcSet
// cfg contains all the functionality that the ChannelArbitrator requires
// to do its duty.
cfg ChannelArbitratorConfig
// signalUpdates is a channel that any new live signals for the channel
// we're watching over will be sent.
signalUpdates chan *signalUpdateMsg
// htlcUpdates is a channel that is sent upon with new updates from the
// active channel. Each time a new commitment state is accepted, the
// set of HTLC's on the new state should be sent across this channel.
htlcUpdates <-chan []channeldb.HTLC
// activeResolvers is a slice of any active resolvers. This is used to
// be able to signal them for shutdown in the case that we shutdown.
activeResolvers []ContractResolver
// resolutionSignal is a channel that will be sent upon by contract
// resolvers once their contract has been fully resolved. With each
// send, we'll check to see if the contract is fully resolved.
resolutionSignal chan struct{}
// forceCloseReqs is a channel that requests to forcibly close the
// contract will be sent over.
forceCloseReqs chan *forceCloseReq
// state is the current state of the arbitrator. This state is examined
// upon start up to decide which actions to take.
state ArbitratorState
wg sync.WaitGroup
quit chan struct{}
}
// NewChannelArbitrator returns a new instance of a ChannelArbitrator backed by
// the passed config struct.
func NewChannelArbitrator(cfg ChannelArbitratorConfig,
startingHTLCs []channeldb.HTLC, log ArbitratorLog) *ChannelArbitrator {
return &ChannelArbitrator{
log: log,
signalUpdates: make(chan *signalUpdateMsg),
htlcUpdates: make(<-chan []channeldb.HTLC),
resolutionSignal: make(chan struct{}),
forceCloseReqs: make(chan *forceCloseReq),
activeHTLCs: newHtlcSet(startingHTLCs),
cfg: cfg,
quit: make(chan struct{}),
}
}
// Start starts all the goroutines that the ChannelArbitrator needs to operate.
func (c *ChannelArbitrator) Start() error {
if !atomic.CompareAndSwapInt32(&c.started, 0, 1) {
return nil
}
var (
err error
unresolvedContracts []ContractResolver
)
log.Debugf("Starting ChannelArbitrator(%v), htlc_set=%v",
c.cfg.ChanPoint, newLogClosure(func() string {
return spew.Sdump(c.activeHTLCs)
}),
)
// First, we'll read our last state from disk, so our internal state
// machine can act accordingly.
c.state, err = c.log.CurrentState()
if err != nil {
c.cfg.BlockEpochs.Cancel()
return err
}
log.Infof("ChannelArbitrator(%v): starting state=%v", c.cfg.ChanPoint,
c.state)
_, bestHeight, err := c.cfg.ChainIO.GetBestBlock()
if err != nil {
c.cfg.BlockEpochs.Cancel()
return err
}
// We'll now attempt to advance our state forward based on the current
// on-chain state, and our set of active contracts.
startingState := c.state
nextState, _, err := c.advanceState(
uint32(bestHeight), chainTrigger, nil,
)
if err != nil {
c.cfg.BlockEpochs.Cancel()
return err
}
// If we start and ended at the awaiting full resolution state, then
// we'll relaunch our set of unresolved contracts.
if startingState == StateWaitingFullResolution &&
nextState == StateWaitingFullResolution {
// We'll now query our log to see if there are any active
// unresolved contracts. If this is the case, then we'll
// relaunch all contract resolvers.
unresolvedContracts, err = c.log.FetchUnresolvedContracts()
if err != nil {
c.cfg.BlockEpochs.Cancel()
return err
}
log.Infof("ChannelArbitrator(%v): relaunching %v contract "+
"resolvers", c.cfg.ChanPoint, len(unresolvedContracts))
c.activeResolvers = unresolvedContracts
for _, contract := range unresolvedContracts {
c.wg.Add(1)
go c.resolveContract(contract)
}
}
// TODO(roasbeef): cancel if breached
c.wg.Add(1)
go c.channelAttendant(bestHeight)
return nil
}
// Stop signals the ChannelArbitrator for a graceful shutdown.
func (c *ChannelArbitrator) Stop() error {
if !atomic.CompareAndSwapInt32(&c.stopped, 0, 1) {
return nil
}
log.Debugf("Stopping ChannelArbitrator(%v)", c.cfg.ChanPoint)
if c.cfg.ChainEvents.Cancel != nil {
go c.cfg.ChainEvents.Cancel()
}
for _, activeResolver := range c.activeResolvers {
activeResolver.Stop()
}
close(c.quit)
c.wg.Wait()
return nil
}
// transitionTrigger is an enum that denotes exactly *why* a state transition
// was initiated. This is useful as depending on the initial trigger, we may
// skip certain states as those actions are expected to have already taken
// place as a result of the external trigger.
type transitionTrigger uint8
const (
// chainTrigger is a transition trigger that has been attempted due to
// changing on-chain conditions such as a block which times out HTLC's
// being attached.
chainTrigger transitionTrigger = iota
// userTrigger is a transition trigger driven by user action. Examples
// of such a trigger include a user requesting a force closure of the
// channel.
userTrigger
// remoteCloseTrigger is a transition trigger driven by the remote
// peer's commitment being confirmed.
remoteCloseTrigger
// localCloseTrigger is a transition trigger driven by our commitment
// being confirmed.
localCloseTrigger
)
// String returns a human readable string describing the passed
// transitionTrigger.
func (t transitionTrigger) String() string {
switch t {
case chainTrigger:
return "chainTrigger"
case remoteCloseTrigger:
return "remoteCloseTrigger"
case userTrigger:
return "userTrigger"
case localCloseTrigger:
return "localCloseTrigger"
default:
return "unknown trigger"
}
}
// stateStep is a help method that examines our internal state, and attempts
// the appropriate state transition if necessary. The next state we transition
// to is returned, Additionally, if the next transition results in a commitment
// broadcast, the commitment transaction itself is returned.
func (c *ChannelArbitrator) stateStep(triggerHeight uint32,
trigger transitionTrigger) (ArbitratorState, *wire.MsgTx, error) {
var (
nextState ArbitratorState
closeTx *wire.MsgTx
)
switch c.state {
// If we're in the default state, then we'll check our set of actions
// to see if while we were down, conditions have changed.
case StateDefault:
log.Debugf("ChannelArbitrator(%v): new block (height=%v) "+
"examining active HTLC's", c.cfg.ChanPoint,
triggerHeight)
// As a new block has been connected to the end of the main
// chain, we'll check to see if we need to make any on-chain
// claims on behalf of the channel contract that we're
// arbitrating for.
chainActions := c.checkChainActions(triggerHeight, trigger)
// If there are no actions to be made, then we'll remain in the
// default state. If this isn't a self initiated event (we're
// checking due to a chain update), then we'll exit now.
if len(chainActions) == 0 && trigger == chainTrigger {
log.Tracef("ChannelArbitrator(%v): no actions for "+
"chain trigger, terminating", c.cfg.ChanPoint)
return StateDefault, closeTx, nil
}
// Otherwise, we'll log that we checked the HTLC actions as the
// commitment transaction has already been broadcast.
log.Tracef("ChannelArbitrator(%v): logging chain_actions=%v",
c.cfg.ChanPoint,
newLogClosure(func() string {
return spew.Sdump(chainActions)
}))
if err := c.log.LogChainActions(chainActions); err != nil {
return StateError, closeTx, err
}
// Depending on the type of trigger, we'll either "tunnel"
// through to a farther state, or just proceed linearly to the
// next state.
switch trigger {
// If this is a chain trigger, then we'll go straight to the
// next state, as we still need to broadcast the commitment
// transaction.
case chainTrigger:
fallthrough
case userTrigger:
nextState = StateBroadcastCommit
// Otherwise, if this state advance was triggered by a
// commitment being confirmed on chain, then we'll jump
// straight to the state where the contract has already been
// closed.
case localCloseTrigger:
log.Errorf("ChannelArbitrator(%v): unexpected local "+
"commitment confirmed while in StateDefault",
c.cfg.ChanPoint)
fallthrough
case remoteCloseTrigger:
nextState = StateContractClosed
}
// If we're in this state, then we've decided to broadcast the
// commitment transaction. We enter this state either due to an outside
// sub-system, or because an on-chain action has been triggered.
case StateBroadcastCommit:
log.Infof("ChannelArbitrator(%v): force closing "+
"chan", c.cfg.ChanPoint)
// Now that we have all the actions decided for the set of
// HTLC's, we'll broadcast the commitment transaction, and
// signal the link to exit.
// We'll tell the switch that it should remove the link for
// this channel, in addition to fetching the force close
// summary needed to close this channel on chain.
closeSummary, err := c.cfg.ForceCloseChan()
if err != nil {
log.Errorf("ChannelArbitrator(%v): unable to "+
"force close: %v", c.cfg.ChanPoint, err)
return StateError, closeTx, err
}
closeTx = closeSummary.CloseTx
// With the close transaction in hand, broadcast the
// transaction to the network, thereby entering the post
// channel resolution state.
log.Infof("Broadcasting force close transaction, "+
"ChannelPoint(%v): %v", c.cfg.ChanPoint,
newLogClosure(func() string {
return spew.Sdump(closeTx)
}))
// At this point, we'll now broadcast the commitment
// transaction itself.
if err := c.cfg.PublishTx(closeTx); err != nil {
log.Errorf("ChannelArbitrator(%v): unable to broadcast "+
"close tx: %v", c.cfg.ChanPoint, err)
if err != lnwallet.ErrDoubleSpend {
return StateError, closeTx, err
}
}
if err := c.cfg.MarkCommitmentBroadcasted(); err != nil {
log.Errorf("ChannelArbitrator(%v): unable to "+
"mark commitment broadcasted: %v",
c.cfg.ChanPoint, err)
}
// We go to the StateCommitmentBroadcasted state, where we'll
// be waiting for the commitment to be confirmed.
nextState = StateCommitmentBroadcasted
// In this state we have broadcasted our own commitment, and will need
// to wait for a commitment (not necessarily the one we broadcasted!)
// to be confirmed.
case StateCommitmentBroadcasted:
switch trigger {
// We are waiting for a commitment to be confirmed, so any
// other trigger will be ignored.
case chainTrigger, userTrigger:
log.Infof("ChannelArbitrator(%v): noop state %v",
c.cfg.ChanPoint, trigger)
nextState = StateCommitmentBroadcasted
// If this state advance was triggered by any of the
// commitments being confirmed, then we'll jump to the state
// where the contract has been closed.
case localCloseTrigger, remoteCloseTrigger:
log.Infof("ChannelArbitrator(%v): state %v, "+
" going to StateContractClosed",
c.cfg.ChanPoint, trigger)
nextState = StateContractClosed
}
// If we're in this state, then the contract has been fully closed to
// outside sub-systems, so we'll process the prior set of on-chain
// contract actions and launch a set of resolvers.
case StateContractClosed:
// First, we'll fetch our chain actions, and both sets of
// resolutions so we can process them.
chainActions, err := c.log.FetchChainActions()
if err != nil {
log.Errorf("unable to fetch chain actions: %v", err)
return StateError, closeTx, err
}
contractResolutions, err := c.log.FetchContractResolutions()
if err != nil {
log.Errorf("unable to fetch contract resolutions: %v",
err)
return StateError, closeTx, err
}
// If the resolution is empty, then we're done here. We don't
// need to launch any resolvers, and can go straight to our
// final state.
if contractResolutions.IsEmpty() {
log.Infof("ChannelArbitrator(%v): contract "+
"resolutions empty, marking channel as fully resolved!",
c.cfg.ChanPoint)
nextState = StateFullyResolved
break
}
// If we've have broadcast the commitment transaction, we send
// our commitment output for incubation, but only if it wasn't
// trimmed. We'll need to wait for a CSV timeout before we can
// reclaim the funds.
commitRes := contractResolutions.CommitResolution
if commitRes != nil && commitRes.MaturityDelay > 0 {
log.Infof("ChannelArbitrator(%v): sending commit "+
"output for incubation", c.cfg.ChanPoint)
err = c.cfg.IncubateOutputs(
c.cfg.ChanPoint, commitRes,
nil, nil,
)
if err != nil {
// TODO(roasbeef): check for AlreadyExists errors
log.Errorf("unable to incubate commitment "+
"output: %v", err)
return StateError, closeTx, err
}
}
// Now that we know we'll need to act, we'll process the htlc
// actions, wen create the structures we need to resolve all
// outstanding contracts.
htlcResolvers, pktsToSend, err := c.prepContractResolutions(
chainActions, contractResolutions, triggerHeight,
)
if err != nil {
log.Errorf("ChannelArbitrator(%v): unable to "+
"resolve contracts: %v", c.cfg.ChanPoint, err)
return StateError, closeTx, err
}
log.Debugf("ChannelArbitrator(%v): sending resolution message=%v",
c.cfg.ChanPoint,
newLogClosure(func() string {
return spew.Sdump(pktsToSend)
}))
// With the commitment broadcast, we'll then send over all
// messages we can send immediately.
err = c.cfg.DeliverResolutionMsg(pktsToSend...)
if err != nil {
// TODO(roasbeef): make sure packet sends are idempotent
log.Errorf("unable to send pkts: %v", err)
return StateError, closeTx, err
}
log.Debugf("ChannelArbitrator(%v): inserting %v contract "+
"resolvers", c.cfg.ChanPoint, len(htlcResolvers))
err = c.log.InsertUnresolvedContracts(htlcResolvers...)
if err != nil {
return StateError, closeTx, err
}
// Finally, we'll launch all the required contract resolvers.
// Once they're all resolved, we're no longer needed.
c.activeResolvers = htlcResolvers
for _, contract := range htlcResolvers {
c.wg.Add(1)
go c.resolveContract(contract)
}
nextState = StateWaitingFullResolution
// This is our terminal state. We'll keep returning this state until
// all contracts are fully resolved.
case StateWaitingFullResolution:
log.Infof("ChannelArbitrator(%v): still awaiting contract "+
"resolution", c.cfg.ChanPoint)
nextState = StateWaitingFullResolution
// If we start as fully resolved, then we'll end as fully resolved.
case StateFullyResolved:
// To ensure that the state of the contract in persistent
// storage is properly reflected, we'll mark the contract as
// fully resolved now.
nextState = StateFullyResolved
log.Infof("ChannelPoint(%v) has been fully resolved "+
"on-chain at height=%v", c.cfg.ChanPoint, triggerHeight)
return nextState, closeTx, c.cfg.MarkChannelResolved()
}
if err := c.log.CommitState(nextState); err != nil {
return StateError, nil, err
}
log.Tracef("ChannelArbitrator(%v): next_state=%v", c.cfg.ChanPoint,
nextState)
c.state = nextState
return nextState, closeTx, nil
}
// advanceState is the main driver of our state machine. This method is an
// iterative function which repeatedly attempts to advance the internal state
// of the channel arbitrator. The state will be advanced until we reach a
// redundant transition, meaning that the state transition is a noop. The final
// param is a callback that allows the caller to execute an arbitrary action
// after each state transition.
func (c *ChannelArbitrator) advanceState(triggerHeight uint32,
trigger transitionTrigger, stateCallback func(ArbitratorState) error) (
ArbitratorState, *wire.MsgTx, error) {
var (
priorState ArbitratorState
forceCloseTx *wire.MsgTx
)
// We'll continue to advance our state forward until the state we
// transition to is that same state that we started at.
for {
priorState = c.state
log.Tracef("ChannelArbitrator(%v): attempting state step with "+
"trigger=%v from state=%v", c.cfg.ChanPoint, trigger,
priorState)
nextState, closeTx, err := c.stateStep(
triggerHeight, trigger,
)
if err != nil {
log.Errorf("unable to advance state: %v", err)
return priorState, nil, err
}
if forceCloseTx == nil && closeTx != nil {
forceCloseTx = closeTx
}
// If we have a state callback, then we'll attempt to execute
// it. If the callback doesn't execute successfully, then we'll
// exit early.
if stateCallback != nil {
if err := stateCallback(nextState); err != nil {
return nextState, closeTx, err
}
}
// Our termination transition is a noop transition. If we get
// our prior state back as the next state, then we'll
// terminate.
if nextState == priorState {
log.Tracef("ChannelArbitrator(%v): terminating at state=%v",
c.cfg.ChanPoint, nextState)
return nextState, forceCloseTx, nil
}
}
}
// ChainAction is an enum that encompasses all possible on-chain actions
// we'll take for a set of HTLC's.
type ChainAction uint8
const (
// NoAction is the min chainAction type, indicating that no action
// needs to be taken for a given HTLC.
NoAction ChainAction = 0
// HtlcTimeoutAction indicates that the HTLC will timeout soon. As a
// result, we should get ready to sweep it on chain after the timeout.
HtlcTimeoutAction = 1
// HtlcClaimAction indicates that we should claim the HTLC on chain
// before its timeout period.
HtlcClaimAction = 2
// HtlcFailNowAction indicates that we should fail an outgoing HTLC
// immediately by cancelling it backwards as it has no corresponding
// output in our commitment transaction.
HtlcFailNowAction = 3
// HtlcOutgoingWatchAction indicates that we can't yet timeout this
// HTLC, but we had to go to chain on order to resolve an existing
// HTLC. In this case, we'll either: time it out once it expires, or
// will learn the pre-image if the remote party claims the output. In
// this case, well add the pre-image to our global store.
HtlcOutgoingWatchAction = 4
// HtlcIncomingWatchAction indicates that we don't yet have the
// pre-image to claim incoming HTLC, but we had to go to chain in order
// to resolve and existing HTLC. In this case, we'll either: let the
// other party time it out, or eventually learn of the pre-image, in
// which case we'll claim on chain.
HtlcIncomingWatchAction = 5
)
// String returns a human readable string describing a chain action.
func (c ChainAction) String() string {
switch c {
case NoAction:
return "NoAction"
case HtlcTimeoutAction:
return "HtlcTimeoutAction"
case HtlcClaimAction:
return "HtlcClaimAction"
case HtlcFailNowAction:
return "HtlcFailNowAction"
case HtlcOutgoingWatchAction:
return "HtlcOutgoingWatchAction"
case HtlcIncomingWatchAction:
return "HtlcIncomingWatchAction"
default:
return "<unknown action>"
}
}
// ChainActionMap is a map of a chain action, to the set of HTLC's that need to
// be acted upon for a given action type. The channel
type ChainActionMap map[ChainAction][]channeldb.HTLC
// shouldGoOnChain takes into account the absolute timeout of the HTLC, if the
// confirmation delta that we need is close, and returns a bool indicating if
// we should go on chain to claim. We do this rather than waiting up until the
// last minute as we want to ensure that when we *need* (HTLC is timed out) to
// sweep, the commitment is already confirmed.
func (c *ChannelArbitrator) shouldGoOnChain(htlcExpiry, broadcastDelta,
currentHeight uint32) bool {
// We'll calculate the broadcast cut off for this HTLC. This is the
// height that (based on our current fee estimation) we should
// broadcast in order to ensure the commitment transaction is confirmed
// before the HTLC fully expires.
broadcastCutOff := htlcExpiry - broadcastDelta
log.Tracef("ChannelArbitrator(%v): examining outgoing contract: "+
"expiry=%v, cutoff=%v, height=%v", c.cfg.ChanPoint, htlcExpiry,
broadcastCutOff, currentHeight)
// TODO(roasbeef): take into account default HTLC delta, don't need to
// broadcast immediately
// * can then batch with SINGLE | ANYONECANPAY
// We should on-chain for this HTLC, iff we're within out broadcast
// cutoff window.
return currentHeight >= broadcastCutOff
}
// checkChainActions is called for each new block connected to the end of the
// main chain. Given the new block height, this new method will examine all
// active HTLC's, and determine if we need to go on-chain to claim any of them.
// A map of action -> []htlc is returned, detailing what action (if any) should
// be performed for each HTLC. For timed out HTLC's, once the commitment has
// been sufficiently confirmed, the HTLC's should be canceled backwards. For
// redeemed HTLC's, we should send the pre-image back to the incoming link.
func (c *ChannelArbitrator) checkChainActions(height uint32,
trigger transitionTrigger) ChainActionMap {
// TODO(roasbeef): would need to lock channel? channel totem?
// * race condition if adding and we broadcast, etc
// * or would make each instance sync?
log.Debugf("ChannelArbitrator(%v): checking chain actions at "+
"height=%v", c.cfg.ChanPoint, height)
actionMap := make(ChainActionMap)
redeemCutoff := c.cfg.BroadcastDelta * broadcastRedeemMultiplier
// First, we'll make an initial pass over the set of incoming and
// outgoing HTLC's to decide if we need to go on chain at all.
haveChainActions := false
for _, htlc := range c.activeHTLCs.outgoingHTLCs {
// If any of our HTLC's triggered an on-chain action, then we
// can break early.
if haveChainActions {
break
}
// We'll need to go on-chain for an outgoing HTLC if it was
// never resolved downstream, and it's "close" to timing out.
haveChainActions = haveChainActions || c.shouldGoOnChain(
htlc.RefundTimeout, c.cfg.BroadcastDelta, height,
)
}
for _, htlc := range c.activeHTLCs.incomingHTLCs {
// If any of our HTLC's triggered an on-chain action, then we
// can break early.
if haveChainActions {
break
}
// We'll need to go on-chain to pull an incoming HTLC iff we
// know the pre-image and it's close to timing out. We need to
// ensure that we claim the funds that our rightfully ours
// on-chain.
if _, ok := c.cfg.PreimageDB.LookupPreimage(htlc.RHash[:]); !ok {
continue
}
haveChainActions = haveChainActions || c.shouldGoOnChain(
htlc.RefundTimeout, redeemCutoff, height,
)
}
// If we don't have any actions to make, then we'll return an empty
// action map. We only do this if this was a chain trigger though, as
// if we're going to broadcast the commitment (or the remote party) did
// we're *forced* to act on each HTLC.
if !haveChainActions && trigger == chainTrigger {
log.Tracef("ChannelArbitrator(%v): no actions to take at "+
"height=%v", c.cfg.ChanPoint, height)
return actionMap
}
// Now that we know we'll need to go on-chain, we'll examine all of our
// active outgoing HTLC's to see if we either need to: sweep them after
// a timeout (then cancel backwards), cancel them backwards
// immediately, or watch them as they're still active contracts.
for _, htlc := range c.activeHTLCs.outgoingHTLCs {
switch {
// If the HTLC is dust, then we can cancel it backwards
// immediately as there's no matching contract to arbitrate
// on-chain. We know the HTLC is dust, if the OutputIndex
// negative.
case htlc.OutputIndex < 0:
log.Tracef("ChannelArbitrator(%v): immediately "+
"failing dust htlc=%x", c.cfg.ChanPoint,
htlc.RHash[:])
actionMap[HtlcFailNowAction] = append(
actionMap[HtlcFailNowAction], htlc,
)
// If we don't need to immediately act on this HTLC, then we'll
// mark it still "live". After we broadcast, we'll monitor it
// until the HTLC times out to see if we can also redeem it
// on-chain.
case !c.shouldGoOnChain(
htlc.RefundTimeout, c.cfg.BroadcastDelta, height,
):
// TODO(roasbeef): also need to be able to query
// circuit map to see if HTLC hasn't been fully
// resolved
//
// * can't fail incoming until if outgoing not yet
// failed
log.Tracef("ChannelArbitrator(%v): watching chain to "+
"decide action for outgoing htlc=%x",
c.cfg.ChanPoint, htlc.RHash[:])
actionMap[HtlcOutgoingWatchAction] = append(
actionMap[HtlcOutgoingWatchAction], htlc,
)
// Otherwise, we'll update our actionMap to mark that we need
// to sweep this HTLC on-chain
default:
log.Tracef("ChannelArbitrator(%v): going on-chain to "+
"timeout htlc=%x", c.cfg.ChanPoint, htlc.RHash[:])
actionMap[HtlcTimeoutAction] = append(
actionMap[HtlcTimeoutAction], htlc,
)
}
}
// Similarly, for each incoming HTLC, now that we need to go on-chain,
// we'll either: sweep it immediately if we know the pre-image, or
// observe the output on-chain if we don't In this last, case we'll
// either learn of it eventually from the outgoing HTLC, or the sender
// will timeout the HTLC.
for _, htlc := range c.activeHTLCs.incomingHTLCs {
payHash := htlc.RHash
// If we have the pre-image, then we should go on-chain to
// redeem the HTLC immediately.
if _, ok := c.cfg.PreimageDB.LookupPreimage(payHash[:]); ok {
log.Tracef("ChannelArbitrator(%v): preimage for "+
"htlc=%x is known!", c.cfg.ChanPoint, payHash[:])
actionMap[HtlcClaimAction] = append(
actionMap[HtlcClaimAction], htlc,
)
continue
}
log.Tracef("ChannelArbitrator(%v): watching chain to decide "+
"action for incoming htlc=%x", c.cfg.ChanPoint,
payHash[:])
// Otherwise, we don't yet have the pre-image, but should watch
// on-chain to see if either: the remote party times out the
// HTLC, or we learn of the pre-image.
actionMap[HtlcIncomingWatchAction] = append(
actionMap[HtlcIncomingWatchAction], htlc,
)
}
return actionMap
}
// prepContractResolutions is called either int he case that we decide we need
// to go to chain, or the remote party goes to chain. Given a set of actions we
// need to take for each HTLC, this method will return a set of contract
// resolvers that will resolve the contracts on-chain if needed, and also a set
// of packets to send to the htlcswitch in order to ensure all incoming HTLC's
// are properly resolved.
func (c *ChannelArbitrator) prepContractResolutions(htlcActions ChainActionMap,
contractResolutions *ContractResolutions, height uint32,
) ([]ContractResolver, []ResolutionMsg, error) {
// There may be a class of HTLC's which we can fail back immediately,
// for those we'll prepare a slice of packets to add to our outbox. Any
// packets we need to send, will be cancels.
var (
msgsToSend []ResolutionMsg
)
incomingResolutions := contractResolutions.HtlcResolutions.IncomingHTLCs
outgoingResolutions := contractResolutions.HtlcResolutions.OutgoingHTLCs
// We'll use these two maps to quickly look up an active HTLC with its
// matching HTLC resolution.
outResolutionMap := make(map[wire.OutPoint]lnwallet.OutgoingHtlcResolution)
inResolutionMap := make(map[wire.OutPoint]lnwallet.IncomingHtlcResolution)
for i := 0; i < len(incomingResolutions); i++ {
inRes := incomingResolutions[i]
// If we have a success transaction, then the htlc's outpoint
// is the transaction's only input. Otherwise, it's the claim
// point.
var htlcPoint wire.OutPoint
if inRes.SignedSuccessTx != nil {
htlcPoint = inRes.SignedSuccessTx.TxIn[0].PreviousOutPoint
} else {
htlcPoint = inRes.ClaimOutpoint
}
inResolutionMap[htlcPoint] = inRes
}
for i := 0; i < len(outgoingResolutions); i++ {
outRes := outgoingResolutions[i]
// If we have a timeout transaction, then the htlc's outpoint
// is the transaction's only input. Otherwise, it's the claim
// point.
var htlcPoint wire.OutPoint
if outRes.SignedTimeoutTx != nil {
htlcPoint = outRes.SignedTimeoutTx.TxIn[0].PreviousOutPoint
} else {
htlcPoint = outRes.ClaimOutpoint
}
outResolutionMap[htlcPoint] = outRes
}
// We'll create the resolver kit that we'll be cloning for each
// resolver so they each can do their duty.
resKit := ResolverKit{
ChannelArbitratorConfig: c.cfg,
Checkpoint: func(res ContractResolver) error {
return c.log.InsertUnresolvedContracts(res)
},
}
commitHash := contractResolutions.CommitHash
failureMsg := &lnwire.FailPermanentChannelFailure{}
// For each HTLC, we'll either act immediately, meaning we'll instantly
// fail the HTLC, or we'll act only once the transaction has been
// confirmed, in which case we'll need an HTLC resolver.
var htlcResolvers []ContractResolver
for htlcAction, htlcs := range htlcActions {
switch htlcAction {
// If we can fail an HTLC immediately (an outgoing HTLC with no
// contract), then we'll assemble an HTLC fail packet to send.
case HtlcFailNowAction:
for _, htlc := range htlcs {
failMsg := ResolutionMsg{
SourceChan: c.cfg.ShortChanID,
HtlcIndex: htlc.HtlcIndex,
Failure: failureMsg,
}
msgsToSend = append(msgsToSend, failMsg)
}
// If we can claim this HTLC, we'll create an HTLC resolver to
// claim the HTLC (second-level or directly), then add the pre
case HtlcClaimAction:
for _, htlc := range htlcs {
htlcOp := wire.OutPoint{
Hash: commitHash,
Index: uint32(htlc.OutputIndex),
}
resolution, ok := inResolutionMap[htlcOp]
if !ok {
// TODO(roasbeef): panic?
log.Errorf("ChannelArbitrator(%v) unable to find "+
"incoming resolution: %v",
c.cfg.ChanPoint, htlcOp)
continue
}
resKit.Quit = make(chan struct{})
resolver := &htlcSuccessResolver{
htlcResolution: resolution,
broadcastHeight: height,
payHash: htlc.RHash,
ResolverKit: resKit,
}
htlcResolvers = append(htlcResolvers, resolver)
}
// If we can timeout the HTLC directly, then we'll create the
// proper resolver to do so, who will then cancel the packet
// backwards.
case HtlcTimeoutAction:
for _, htlc := range htlcs {
htlcOp := wire.OutPoint{
Hash: commitHash,
Index: uint32(htlc.OutputIndex),
}
resolution, ok := outResolutionMap[htlcOp]
if !ok {
log.Errorf("ChannelArbitrator(%v) unable to find "+
"outgoing resolution: %v", c.cfg.ChanPoint, htlcOp)
continue
}
resKit.Quit = make(chan struct{})
resolver := &htlcTimeoutResolver{
htlcResolution: resolution,
broadcastHeight: height,
htlcIndex: htlc.HtlcIndex,
ResolverKit: resKit,
}
htlcResolvers = append(htlcResolvers, resolver)
}
// If this is an incoming HTLC, but we can't act yet, then
// we'll create an incoming resolver to redeem the HTLC if we
// learn of the pre-image, or let the remote party time out.
case HtlcIncomingWatchAction:
for _, htlc := range htlcs {
htlcOp := wire.OutPoint{
Hash: commitHash,
Index: uint32(htlc.OutputIndex),
}
// TODO(roasbeef): need to handle incoming dust...
// TODO(roasbeef): can't be negative!!!
resolution, ok := inResolutionMap[htlcOp]
if !ok {
log.Errorf("ChannelArbitrator(%v) unable to find "+
"incoming resolution: %v",
c.cfg.ChanPoint, htlcOp)
continue
}
resKit.Quit = make(chan struct{})
resolver := &htlcIncomingContestResolver{
htlcExpiry: htlc.RefundTimeout,
htlcSuccessResolver: htlcSuccessResolver{
htlcResolution: resolution,
broadcastHeight: height,
payHash: htlc.RHash,
ResolverKit: resKit,
},
}
htlcResolvers = append(htlcResolvers, resolver)
}
// Finally, if this is an outgoing HTLC we've sent, then we'll
// launch a resolver to watch for the pre-image (and settle
// backwards), or just timeout.
case HtlcOutgoingWatchAction:
for _, htlc := range htlcs {
htlcOp := wire.OutPoint{
Hash: commitHash,
Index: uint32(htlc.OutputIndex),
}
resolution, ok := outResolutionMap[htlcOp]
if !ok {
log.Errorf("ChannelArbitrator(%v) unable to find "+
"outgoing resolution: %v",
c.cfg.ChanPoint, htlcOp)
continue
}
resKit.Quit = make(chan struct{})
resolver := &htlcOutgoingContestResolver{
htlcTimeoutResolver{
htlcResolution: resolution,
broadcastHeight: height,
htlcIndex: htlc.HtlcIndex,
ResolverKit: resKit,
},
}
htlcResolvers = append(htlcResolvers, resolver)
}
}
}
// Finally, if this is was a unilateral closure, then we'll also create
// a resolver to sweep our commitment output (but only if it wasn't
// trimmed).
if contractResolutions.CommitResolution != nil {
resKit.Quit = make(chan struct{})
resolver := &commitSweepResolver{
commitResolution: *contractResolutions.CommitResolution,
broadcastHeight: height,
chanPoint: c.cfg.ChanPoint,
ResolverKit: resKit,
}
htlcResolvers = append(htlcResolvers, resolver)
}
return htlcResolvers, msgsToSend, nil
}
// resolveContract is a goroutine tasked with fully resolving an unresolved
// contract. Either the initial contract will be resolved after a single step,
// or the contract will itself create another contract to be resolved. In
// either case, one the contract has been fully resolved, we'll signal back to
// the main goroutine so it can properly keep track of the set of unresolved
// contracts.
//
// NOTE: This MUST be run as a goroutine.
func (c *ChannelArbitrator) resolveContract(currentContract ContractResolver) {
defer c.wg.Done()
log.Debugf("ChannelArbitrator(%v): attempting to resolve %T",
c.cfg.ChanPoint, currentContract)
// Until the contract is fully resolved, we'll continue to iteratively
// resolve the contract one step at a time.
for !currentContract.IsResolved() {
log.Debugf("ChannelArbitrator(%v): contract %T not yet resolved",
c.cfg.ChanPoint, currentContract)
select {
// If we've been signalled to quit, then we'll exit early.
case <-c.quit:
return
default:
// Otherwise, we'll attempt to resolve the current
// contract.
nextContract, err := currentContract.Resolve()
if err != nil {
log.Errorf("ChannelArbitrator(%v): unable to "+
"progress resolver: %v",
c.cfg.ChanPoint, err)
return
}
switch {
// If this contract produced another, then this means
// the current contract was only able to be partially
// resolved in this step. So we'll not a contract swap
// within our logs: the new contract will take the
// place of the old one.
case nextContract != nil:
log.Debugf("ChannelArbitrator(%v): swapping "+
"out contract %T for %T ",
c.cfg.ChanPoint, currentContract,
nextContract)
err := c.log.SwapContract(
currentContract, nextContract,
)
if err != nil {
log.Errorf("unable to add recurse "+
"contract: %v", err)
}
// As this contract produced another, we'll
// re-assign, so we can continue our resolution
// loop.
currentContract = nextContract
// If this contract is actually fully resolved, then
// we'll mark it as such within the database.
case currentContract.IsResolved():
log.Debugf("ChannelArbitrator(%v): marking "+
"contract %T fully resolved",
c.cfg.ChanPoint, currentContract)
err := c.log.ResolveContract(currentContract)
if err != nil {
log.Errorf("unable to resolve contract: %v",
err)
}
// Now that the contract has been resolved,
// well signal to the main goroutine.
select {
case c.resolutionSignal <- struct{}{}:
case <-c.quit:
return
}
}
}
}
}
// signalUpdateMsg is a struct that carries fresh signals to the
// ChannelArbitrator. We need to receive a message like this each time the
// channel becomes active, as it's internal state may change.
type signalUpdateMsg struct {
// newSignals is the set of new active signals to be sent to the
// arbitrator.
newSignals *ContractSignals
// doneChan is a channel that will be closed on the arbitrator has
// attached the new signals.
doneChan chan struct{}
}
// UpdateContractSignals updates the set of signals the ChannelArbitrator needs
// to receive from a channel in real-time in order to keep in sync with the
// latest state of the contract.
func (c *ChannelArbitrator) UpdateContractSignals(newSignals *ContractSignals) {
done := make(chan struct{})
select {
case c.signalUpdates <- &signalUpdateMsg{
newSignals: newSignals,
doneChan: done,
}:
case <-c.quit:
}
select {
case <-done:
case <-c.quit:
}
}
// channelAttendant is the primary goroutine that acts at the judicial
// arbitrator between our channel state, the remote channel peer, and the
// blockchain Our judge). This goroutine will ensure that we faithfully execute
// all clauses of our contract in the case that we need to go on-chain for a
// dispute. Currently, two such conditions warrant our intervention: when an
// outgoing HTLC is about to timeout, and when we know the pre-image for an
// incoming HTLC, but it hasn't yet been settled off-chain. In these cases,
// we'll: broadcast our commitment, cancel/settle any HTLC's backwards after
// sufficient confirmation, and finally send our set of outputs to the UTXO
// Nursery for incubation, and ultimate sweeping.
//
// NOTE: This MUST be run as a goroutine.
func (c *ChannelArbitrator) channelAttendant(bestHeight int32) {
// TODO(roasbeef): tell top chain arb we're done
defer func() {
c.cfg.BlockEpochs.Cancel()
c.wg.Done()
}()
for {
select {
// A new block has arrived, we'll examine all the active HTLC's
// to see if any of them have expired, and also update our
// track of the best current height.
case blockEpoch, ok := <-c.cfg.BlockEpochs.Epochs:
if !ok {
return
}
bestHeight = blockEpoch.Height
// If we're not in the default state, then we can
// ignore this signal as we're waiting for contract
// resolution.
if c.state != StateDefault {
continue
}
// Now that a new block has arrived, we'll attempt to
// advance our state forward.
nextState, _, err := c.advanceState(
uint32(bestHeight), chainTrigger, nil,
)
if err != nil {
log.Errorf("unable to advance state: %v", err)
}
// If as a result of this trigger, the contract is
// fully resolved, then well exit.
if nextState == StateFullyResolved {
return
}
// A new signal update was just sent. This indicates that the
// channel under watch is now live, and may modify its internal
// state, so we'll get the most up to date signals to we can
// properly do our job.
case signalUpdate := <-c.signalUpdates:
log.Tracef("ChannelArbitrator(%v) got new signal "+
"update!", c.cfg.ChanPoint)
// First, we'll update our set of signals.
c.htlcUpdates = signalUpdate.newSignals.HtlcUpdates
c.cfg.ShortChanID = signalUpdate.newSignals.ShortChanID
// Now that the signals have been updated, we'll now
// close the done channel to signal to the caller we've
// registered the new contracts.
close(signalUpdate.doneChan)
// A new set of HTLC's has been added or removed from the
// commitment transaction. So we'll update our activeHTLCs map
// accordingly.
case newStateHTLCs := <-c.htlcUpdates:
// We'll wipe out our old set of HTLC's and instead
// monitor only the HTLC's that are still active on the
// current commitment state.
c.activeHTLCs = newHtlcSet(newStateHTLCs)
log.Tracef("ChannelArbitrator(%v): fresh set of "+
"htlcs=%v", c.cfg.ChanPoint,
newLogClosure(func() string {
return spew.Sdump(c.activeHTLCs)
}),
)
// We've cooperatively closed the channel, so we're no longer
// needed. We'll mark the channel as resolved and exit.
case <-c.cfg.ChainEvents.CooperativeClosure:
log.Infof("ChannelArbitrator(%v) closing due to co-op "+
"closure", c.cfg.ChanPoint)
if err := c.cfg.MarkChannelResolved(); err != nil {
log.Errorf("Unable to mark contract "+
"resolved: %v", err)
}
return
// We have broadcasted our commitment, and it is now confirmed
// on-chain.
case closeInfo := <-c.cfg.ChainEvents.LocalUnilateralClosure:
log.Infof("ChannelArbitrator(%v): local on-chain "+
"channel close", c.cfg.ChanPoint)
if c.state != StateCommitmentBroadcasted {
log.Errorf("ChannelArbitrator(%v): unexpected "+
"local on-chain channel close",
c.cfg.ChanPoint)
}
closeTx := closeInfo.CloseTx
contractRes := &ContractResolutions{
CommitHash: closeTx.TxHash(),
CommitResolution: closeInfo.CommitResolution,
HtlcResolutions: *closeInfo.HtlcResolutions,
}
// When processing a unilateral close event, we'll
// transition directly to the ContractClosed state.
// When the state machine reaches that state, we'll log
// out the set of resolutions.
stateCb := func(nextState ArbitratorState) error {
if nextState != StateContractClosed {
return nil
}
err := c.log.LogContractResolutions(
contractRes,
)
if err != nil {
return fmt.Errorf("unable to "+
"write resolutions: %v",
err)
}
return nil
}
// We'll now advance our state machine until it reaches
// a terminal state.
_, _, err := c.advanceState(
uint32(closeInfo.SpendingHeight),
localCloseTrigger, stateCb,
)
if err != nil {
log.Errorf("unable to advance state: %v", err)
}
// The remote party has broadcast the commitment on-chain.
// We'll examine our state to determine if we need to act at
// all.
case uniClosure := <-c.cfg.ChainEvents.RemoteUnilateralClosure:
log.Infof("ChannelArbitrator(%v): remote party has "+
"closed channel out on-chain", c.cfg.ChanPoint)
// If we don't have a self output, and there are no
// active HTLC's, then we can immediately mark the
// contract as fully resolved and exit.
contractRes := &ContractResolutions{
CommitHash: *uniClosure.SpenderTxHash,
CommitResolution: uniClosure.CommitResolution,
HtlcResolutions: *uniClosure.HtlcResolutions,
}
// TODO(roasbeef): modify signal to also detect
// cooperative closures?
// As we're now acting upon an event triggered by the
// broadcast of the remote commitment transaction,
// we'll swap out our active HTLC set with the set
// present on their commitment.
c.activeHTLCs = newHtlcSet(uniClosure.RemoteCommit.Htlcs)
// When processing a unilateral close event, we'll
// transition directly to the ContractClosed state.
// When the state machine reaches that state, we'll log
// out the set of resolutions.
stateCb := func(nextState ArbitratorState) error {
if nextState != StateContractClosed {
return nil
}
err := c.log.LogContractResolutions(
contractRes,
)
if err != nil {
return fmt.Errorf("unable to write "+
"resolutions: %v", err)
}
return nil
}
// We'll now advance our state machine until it reaches
// a terminal state.
_, _, err := c.advanceState(
uint32(uniClosure.SpendingHeight),
remoteCloseTrigger, stateCb,
)
if err != nil {
log.Errorf("unable to advance state: %v", err)
}
// A new contract has just been resolved, we'll now check our
// log to see if all contracts have been resolved. If so, then
// we can exit as the contract is fully resolved.
case <-c.resolutionSignal:
log.Infof("ChannelArbitrator(%v): a contract has been "+
"fully resolved!", c.cfg.ChanPoint)
numUnresolved, err := c.log.FetchUnresolvedContracts()
if err != nil {
log.Errorf("unable to query resolved "+
"contracts: %v", err)
}
// If we still have unresolved contracts, then we'll
// stay alive to oversee their resolution.
if len(numUnresolved) != 0 {
continue
}
log.Infof("ChannelArbitrator(%v): all contracts fully "+
"resolved, exiting", c.cfg.ChanPoint)
// Otherwise, our job is finished here, the contract is
// now fully resolved! We'll mark it as such, then exit
// ourselves.
if err := c.cfg.MarkChannelResolved(); err != nil {
log.Errorf("unable to mark contract "+
"resolved: %v", err)
}
return
// We've just received a request to forcibly close out the
// channel. We'll
case closeReq := <-c.forceCloseReqs:
if c.state != StateDefault {
continue
}
nextState, closeTx, err := c.advanceState(
uint32(bestHeight), userTrigger, nil,
)
if err != nil {
log.Errorf("unable to advance state: %v", err)
}
select {
case closeReq.closeTx <- closeTx:
case <-c.quit:
return
}
select {
case closeReq.errResp <- err:
case <-c.quit:
return
}
// If we don't have anything further to do after
// advancing our state, then we'll exit.
if nextState == StateFullyResolved {
log.Infof("ChannelArbitrator(%v): all "+
"contracts resolved, exiting",
c.cfg.ChanPoint)
return
}
case <-c.quit:
return
}
}
}