lnd.xprv/contractcourt/chain_arbitrator.go

package contractcourt

import (
	"fmt"
	"sync"
	"sync/atomic"

	"github.com/lightningnetwork/lnd/chainntnfs"
	"github.com/lightningnetwork/lnd/channeldb"
	"github.com/lightningnetwork/lnd/lnwallet"
	"github.com/lightningnetwork/lnd/lnwire"
	"github.com/roasbeef/btcd/chaincfg/chainhash"
	"github.com/roasbeef/btcd/wire"
)

// ResolutionMsg is a message sent by resolvers to outside sub-systems once an
// outgoing contract has been fully resolved. For multi-hop contracts, if we
// resolve the outgoing contract, we'll also need to ensure that the incoming
// contract is resolved as well. We package the items required to resolve the
// incoming contracts within this message.
type ResolutionMsg struct {
	// SourceChan identifies the channel that this message is being sent
	// from. This is the channel's short channel ID.
	SourceChan lnwire.ShortChannelID

	// HtlcIndex is the index of the contract within the original
	// commitment trace.
	HtlcIndex uint64

	// Failure will be non-nil if the incoming contract should be cancelled
	// all together. This can happen if the outgoing contract was dust, if
	// if the outgoing HTLC timed out.
	Failure lnwire.FailureMessage

	// PreImage will be non-nil if the incoming contract can successfully
	// be redeemed. This can happen if we learn of the preimage from the
	// outgoing HTLC on-chain.
	PreImage *[32]byte
}

// ChainArbitratorConfig is a configuration struct that contains all the
// function closures and interface that required to arbitrate on-chain
// contracts for a particular chain.
type ChainArbitratorConfig struct {
	// ChainHash is the chain that this arbitrator is to operate within.
	ChainHash chainhash.Hash

	// BroadcastDelta is the delta that we'll use to decide when to
	// broadcast our commitment transaction.  This value should be set
	// based on our current fee estimation of the commitment transaction.
	// We use this to determine when we should broadcast instead of the
	// just the HTLC timeout, as we want to ensure that the commitment
	// transaction is already confirmed, by the time the HTLC expires.
	BroadcastDelta uint32

	// NewSweepAddr is a function that returns a new address under control
	// by the wallet. We'll use this to sweep any no-delay outputs as a
	// result of unilateral channel closes.
	//
	// NOTE: This SHOULD return a p2wkh script.
	NewSweepAddr func() ([]byte, error)

	// PublishTx reliably broadcasts a transaction to the network. Once
	// this function exits without an error, then they transaction MUST
	// continually be rebroadcast if needed.
	PublishTx func(*wire.MsgTx) error

	// DeliverResolutionMsg is a function that will append an outgoing
	// message to the "out box" for a ChannelLink. This is used to cancel
	// backwards any HTLC's that are either dust, we're timing out, or
	// settling on-chain to the incoming link.
	DeliverResolutionMsg func(...ResolutionMsg) error

	// MarkLinkInactive is a function closure that the ChainArbitrator will
	// use to mark that active HTLC's shouldn't be attempt ted to be routed
	// over a particular channel. This function will be called in that a
	// ChannelArbitrator decides that it needs to go to chain in order to
	// resolve contracts.
	//
	// TODO(Roasbeef): rename, routing based
	MarkLinkInactive func(wire.OutPoint) error

	// IncubateOutput sends either a incoming HTLC, an outgoing HTLC, or
	// both to the utxo nursery. Once this function returns, the nursery
	// should have safely persisted the outputs to disk, and should start
	// the process of incubation. This is used when a resolver wishes to
	// pass off the output to the nursery as we're inly waiting on an
	// absolute/relative item block.
	IncubateOutputs func(wire.OutPoint, *lnwallet.CommitOutputResolution,
		*lnwallet.OutgoingHtlcResolution,
		*lnwallet.IncomingHtlcResolution) error

	// PreimageDB is a global store of all known pre-images. We'll use this
	// to decide if we should broadcast a commitment transaction to claim
	// an HTLC on-chain.
	PreimageDB WitnessBeacon

	// Notifier is an instance of a chain notifier we'll use to watch for
	// certain on-chain events.
	Notifier chainntnfs.ChainNotifier

	// Signer is a signer backed by the active lnd node. This should be
	// capable of producing a signature as specified by a valid
	// SignDescriptor.
	Signer lnwallet.Signer

	// FeeEstimator will be used to return fee estimates.
	FeeEstimator lnwallet.FeeEstimator

	// ChainIO allows us to query the state of the current main chain.
	ChainIO lnwallet.BlockChainIO
}

// ChainArbitrator is a sub-system that oversees the on-chain resolution of all
// active, and channel that are in the "pending close" state. Within the
// contractcourt package, the ChainArbitrator manages a set of active
// ContractArbitrators. Each ContractArbitrators is responsible for watching
// the chain for any activity that affects the state of the channel, and also
// for monitoring each contract in order to determine if any on-chain activity is
// required. Outside sub-systems interact with the ChainArbitrator in order to
// forcibly exit a contract, update the set of live signals for each contract,
// and to receive reports on the state of contract resolution.
type ChainArbitrator struct {
	started int32
	stopped int32

	sync.Mutex

	// activeChannels is a map of all the active contracts that are still
	// open, and not fully resolved.
	activeChannels map[wire.OutPoint]*ChannelArbitrator

	// cfg is the config struct for the arbitrator that contains all
	// methods and interface it needs to operate.
	cfg ChainArbitratorConfig

	// chanSource will be used by the ChainArbitrator to fetch all the
	// active channels that it must still watch over.
	chanSource *channeldb.DB

	quit chan struct{}

	wg sync.WaitGroup
}

// NewChainArbitrator returns a new instance of the ChainArbitrator using the
// passed config struct, and backing persistent database.
func NewChainArbitrator(cfg ChainArbitratorConfig,
	db *channeldb.DB) *ChainArbitrator {

	return &ChainArbitrator{
		cfg:            cfg,
		activeChannels: make(map[wire.OutPoint]*ChannelArbitrator),
		chanSource:     db,
		quit:           make(chan struct{}),
	}
}

// newActiveChannelArbitrator creates a new instance of an active channel
// arbitrator given the state of the target channel.
func newActiveChannelArbitrator(channel *channeldb.OpenChannel,
	c *ChainArbitrator) (*ChannelArbitrator, error) {

	log.Tracef("Creating ChannelArbitrator for ChannelPoint(%v)",
		channel.FundingOutpoint)

	// We'll start by registering for a block epoch notifications so this
	// channel can keep track of the current state of the main chain.
	//
	// TODO(roasbeef): fetch best height (or pass in) so can ensure block
	// epoch delivers all the notifications to
	//
	// TODO(roasbeef): instead 1 block epoch that multi-plexes to the rest?
	//  * reduces the number of goroutines
	blockEpoch, err := c.cfg.Notifier.RegisterBlockEpochNtfn()
	if err != nil {
		return nil, err
	}

	chanPoint := channel.FundingOutpoint

	// Next we'll create the matching configuration struct that contains
	// all interfaces and methods the arbitrator needs to do its job.
	arbCfg := ChannelArbitratorConfig{
		ChanPoint:   chanPoint,
		ShortChanID: channel.ShortChanID,
		BlockEpochs: blockEpoch,
		ForceCloseChan: func() (*lnwallet.ForceCloseSummary, error) {
			// With the channels fetched, attempt to locate
			// the target channel according to its channel
			// point.
			dbChannels, err := c.chanSource.FetchAllChannels()
			if err != nil {
				return nil, err
			}
			var channel *channeldb.OpenChannel
			for _, dbChannel := range dbChannels {
				if dbChannel.FundingOutpoint == chanPoint {
					channel = dbChannel
					break
				}
			}

			// If the channel cannot be located, then we
			// exit with an error to the channel.
			if channel == nil {
				return nil, fmt.Errorf("unable to find channel")
			}

			chanMachine, err := lnwallet.NewLightningChannel(
				c.cfg.Signer, nil, c.cfg.PreimageDB, channel)
			if err != nil {
				return nil, err
			}
			chanMachine.Stop()
			chanMachine.CancelObserver()

			if err := c.cfg.MarkLinkInactive(chanPoint); err != nil {
				log.Errorf("unable to mark link inactive: %v", err)
			}

			return chanMachine.ForceClose()
		},
		CloseChannel: func(summary *channeldb.ChannelCloseSummary) error {
			log.Tracef("ChannelArbitrator(%v): closing "+
				"channel", chanPoint)

			return channel.CloseChannel(summary)
		},
		ChainArbitratorConfig: c.cfg,
	}

	// The final component needed is an arbitrator log that the arbitrator
	// will use to keep track of its internal state using a backed
	// persistent log.
	//
	// TODO(roasbeef); abstraction leak...
	//  * rework: adaptor method to set log scope w/ factory func
	chanLog, err := newBoltArbitratorLog(
		c.chanSource.DB, arbCfg, c.cfg.ChainHash, chanPoint,
	)
	if err != nil {
		blockEpoch.Cancel()
		return nil, err
	}

	arbCfg.MarkChannelResolved = func() error {
		return c.resolveContract(chanPoint, chanLog)
	}

	return NewChannelArbitrator(
		arbCfg, channel.LocalCommitment.Htlcs, chanLog,
	), nil
}

// resolveContract marks a contract as fully resolved within the database.
// This is only to be done once all contracts which were live on the channel
// before hitting the chain have been resolved.
func (c *ChainArbitrator) resolveContract(chanPoint wire.OutPoint,
	arbLog ArbitratorLog) error {

	log.Infof("Marking ChannelPoint(%v) fully resolved", chanPoint)

	// First, we'll we'll mark the channel as fully closed from the PoV of
	// the channel source.
	err := c.chanSource.MarkChanFullyClosed(&chanPoint)
	if err != nil {
		return err
	}

	// Once this has been marked as resolved, we'll wipe the log that the
	// channel arbitrator was using to store its persistent state. We do
	// this after marking the channel resolved, as otherwise, the
	// arbitrator would be re-created, and think it was starting from the
	// default state.
	if err := arbLog.WipeHistory(); err != nil {
		return err
	}

	c.Lock()
	delete(c.activeChannels, chanPoint)
	c.Unlock()

	return nil
}

// Start launches all goroutines that the ChainArbitrator needs to operate.
func (c *ChainArbitrator) Start() error {
	if !atomic.CompareAndSwapInt32(&c.started, 0, 1) {
		return nil
	}

	log.Tracef("Starting ChainArbitrator")

	// First, we'll fetch all the channels that are still open, in order to
	// collect them within our set of active contracts.
	openChannels, err := c.chanSource.FetchAllChannels()
	if err != nil {
		return err
	}

	if len(openChannels) > 0 {
		log.Infof("Creating ChannelArbitrators for %v active channels",
			len(openChannels))
	}

	// For each open channel, we'll configure then launch a corresponding
	// ChannelArbitrator.
	for _, channel := range openChannels {
		channelArb, err := newActiveChannelArbitrator(channel, c)
		if err != nil {
			return err
		}

		c.activeChannels[channel.FundingOutpoint] = channelArb
	}

	// In addition to the channels that we know to be open, we'll also
	// launch arbitrators to finishing resolving any channels that are in
	// the pending close state.
	closingChannels, err := c.chanSource.FetchClosedChannels(true)
	if err != nil {
		return err
	}

	if len(closingChannels) > 0 {
		log.Infof("Creating ChannelArbitrators for %v closing channels",
			len(closingChannels))
	}

	// Next, for each channel is the closing state, we'll launch a
	// corresponding more restricted resolver.
	for _, closeChanInfo := range closingChannels {
		blockEpoch, err := c.cfg.Notifier.RegisterBlockEpochNtfn()
		if err != nil {
			return err
		}

		// We can leave off the CloseContract and ForceCloseChan
		// methods as the channel is already closed at this point.
		chanPoint := closeChanInfo.ChanPoint
		arbCfg := ChannelArbitratorConfig{
			ChanPoint:             chanPoint,
			ShortChanID:           closeChanInfo.ShortChanID,
			BlockEpochs:           blockEpoch,
			ChainArbitratorConfig: c.cfg,
		}
		chanLog, err := newBoltArbitratorLog(
			c.chanSource.DB, arbCfg, c.cfg.ChainHash, chanPoint,
		)
		if err != nil {
			return err
		}
		arbCfg.MarkChannelResolved = func() error {
			return c.resolveContract(chanPoint, chanLog)
		}

		// We can also leave off the set of HTLC's here as since the
		// channel is already in the process of being full resolved, no
		// new HTLC's we be added.
		c.activeChannels[chanPoint] = NewChannelArbitrator(
			arbCfg, nil, chanLog,
		)
	}

	// Finally, we'll launch all the goroutines for each arbitrator so they
	// can carry out their duties.
	for _, arbitrator := range c.activeChannels {
		if err := arbitrator.Start(); err != nil {
			return err
		}
	}

	// TODO(roasbeef): eventually move all breach watching here

	return nil
}

// Stop signals the ChainArbitrator to trigger a graceful shutdown. Any active
// channel arbitrators will be signalled to exit, and this method will block
// until they've all exited.
func (c *ChainArbitrator) Stop() error {
	if !atomic.CompareAndSwapInt32(&c.stopped, 0, 1) {
		return nil
	}

	log.Infof("Stopping ChainArbitrator")

	close(c.quit)

	c.Lock()
	arbitrators := c.activeChannels
	c.Unlock()

	for chanPoint, arbitrator := range arbitrators {
		log.Tracef("Attempting to stop ChannelArbitrator(%v)",
			chanPoint)

		if err := arbitrator.Stop(); err != nil {
			log.Errorf("unable to stop arbitrator for "+
				"ChannelPoint(%v): %v", chanPoint, err)
		}
	}

	c.wg.Wait()

	return nil
}

// ContractSignals wraps the two signals that affect the state of a channel
// being watched by an arbitrator. The two signals we care about are: the
// channel has a new set of HTLC's, and the remote party has just broadcast
// their version of the commitment transaction.
type ContractSignals struct {
	// HtlcUpdates is a channel that once we new commitment updates takes
	// place, the later set of HTLC's on the commitment transaction should
	// be sent over.
	HtlcUpdates chan []channeldb.HTLC

	// UniCloseSignal is a channel that allows the ChannelArbitrator for a
	// particular channel to detect if the remote party has broadcast their
	// version of the commitment transaction.
	//
	// TODO(roasbeef): eliminate and just roll into the struct itself, all
	// watching
	UniCloseSignal chan *lnwallet.UnilateralCloseSummary

	// ShortChanID is the up to date short channel ID for a contract. This
	// can change either if when the contract was added it didn't yet have
	// a stable identifier, or in the case of a reorg.
	ShortChanID lnwire.ShortChannelID
}

// UpdateContractSignals sends a set of active, up to date contract signals to
// the ChannelArbitrator which is has been assigned to the channel infield by
// the passed channel point.
func (c *ChainArbitrator) UpdateContractSignals(chanPoint wire.OutPoint,
	signals *ContractSignals) error {

	log.Infof("Attempting to update ContractSignals for ChannelPoint(%v)",
		chanPoint)

	c.Lock()
	arbitrator, ok := c.activeChannels[chanPoint]
	c.Unlock()
	if !ok {
		return fmt.Errorf("unable to find arbitrator")
	}

	arbitrator.UpdateContractSignals(signals)

	return nil
}

// forceCloseReq is a request sent from an outsde sub-system to the arbitrator
// that watches a particular channel to broadcast the commitnet transaction,
// and enter the resolution phase of the channel.
type forceCloseReq struct {
	// errResp is a channel that will be sent upon either in the case of force
	// close success (nil error), or in the case on an erro (nil-nil error)
	//
	// NOTE; This channel MUST be buffered.
	errResp chan error

	// closeTx is a channel that carries the transaction which ultimatley
	// closed out the channel.
	closeTx chan *wire.MsgTx
}

// ForceCloseContract attempts to force close the channel infield by the passed
// channel point. A force close will immediately terminate the contract,
// causing it to enter the resolution phase. If the force close was successful,
// then the force close transaction itself will be returned.
//
// TODO(roasbeef): just return the summary itself?
func (c *ChainArbitrator) ForceCloseContract(chanPoint wire.OutPoint) (*wire.MsgTx, error) {
	c.Lock()
	arbitrator, ok := c.activeChannels[chanPoint]
	c.Unlock()
	if !ok {
		return nil, fmt.Errorf("unable to find arbitrator")
	}

	log.Infof("Attempting to force close ChannelPoint(%v)", chanPoint)

	errChan := make(chan error, 1)
	respChan := make(chan *wire.MsgTx, 1)

	// With the channel found, and the request crafted, we'll send over a
	// force close request to the arbitrator that watches this channel.
	select {
	case arbitrator.forceCloseReqs <- &forceCloseReq{
		errResp: errChan,
		closeTx: respChan,
	}:
	case <-c.quit:
		return nil, fmt.Errorf("ChainArbitrator shutting down")
	}

	// We'll await two resposnes: the error response, and the transaction
	// that closed out the channel.
	select {
	case err := <-errChan:
		if err != nil {
			return nil, err
		}
	case <-c.quit:
		return nil, fmt.Errorf("ChainArbitrator shutting down")
	}

	var closeTx *wire.MsgTx
	select {
	case closeTx = <-respChan:
	case <-c.quit:
		return nil, fmt.Errorf("ChainArbitrator shutting down")
	}

	return closeTx, nil
}

// RequestChannelArbitration sends the ChainArbitrator a message to create a
// ChannelArbitrator tasked with watching over a new channel. Once a new
// channel has finished its final funding flow, it should be registered with
// the ChainArbitrator so we can properly react to any on-chain events.
func (c *ChainArbitrator) RequestChannelArbitration(newChan *channeldb.OpenChannel) error {
	c.Lock()
	defer c.Unlock()

	log.Infof("Creating new ChannelArbitrator for ChannelPoint(%v)",
		newChan.FundingOutpoint)

	// If we're already watching this channel, then we'll ignore this
	// request.
	chanPoint := newChan.FundingOutpoint
	if _, ok := c.activeChannels[chanPoint]; ok {
		return nil
	}

	// First, we'll create a new channel arbitrator instance using this new
	// channel, and our internal state.
	channelArb, err := newActiveChannelArbitrator(newChan, c)
	if err != nil {
		return err
	}

	// With the arbitrator created, we'll add it to our set of active
	// arbitrators, then launch it.
	c.activeChannels[chanPoint] = channelArb
	return channelArb.Start()
}

// ManuallyResolveChannel is a method to be called by outside sub-systems if a
// channel becomes fully resolved, but due to manual intervention. An example
// of such a manual intervention includes a cooperative channel closuer.
//
// TODO(roasbeef): remove after arbs watch chain for all actions directly
func (c *ChainArbitrator) ManuallyResolveChannel(chanPoint wire.OutPoint) error {
	c.Lock()
	defer c.Unlock()

	log.Infof("Manually resolving ChannelArbitrator for ChannelPoint(%v)",
		chanPoint)

	channelArb, ok := c.activeChannels[chanPoint]
	if !ok {
		return fmt.Errorf("unable to find arbitrator for: %v", chanPoint)
	}

	if err := channelArb.Stop(); err != nil {
		return err
	}

	delete(c.activeChannels, chanPoint)

	return channelArb.log.WipeHistory()
}

// SubscribeChannelSignals...
func (c *ChainArbitrator) SubscribeChannelSignals() error {
	// TODO(roasbeef): gives signals of spends, breaches, etc
	//  * breach arg grabs initially
	//  * create new db method for *just* getting the outpoints for em all?

	return nil
}

// TODO(roasbeef): arbitration reports
//  * types: contested, waiting for success conf, etc