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utxonursery.go
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1944 lines (1638 loc) · 65.7 KB
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package main
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"sync"
"sync/atomic"
"github.com/davecgh/go-spew/spew"
"github.com/lightningnetwork/lnd/chainntnfs"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/lnwallet"
"github.com/roasbeef/btcd/blockchain"
"github.com/roasbeef/btcd/txscript"
"github.com/roasbeef/btcd/wire"
"github.com/roasbeef/btcutil"
)
// SUMMARY OF OUTPUT STATES
//
// - CRIB
// - SerializedType: babyOutput
// - OriginalOutputType: HTLC
// - Awaiting: First-stage HTLC CLTV expiry
// - HeightIndexEntry: Absolute block height of CLTV expiry.
// - NextState: KNDR
// - PSCL
// - SerializedType: kidOutput
// - OriginalOutputType: Commitment
// - Awaiting: Confirmation of commitment txn
// - HeightIndexEntry: None.
// - NextState: KNDR
// - KNDR
// - SerializedType: kidOutput
// - OriginalOutputType: Commitment or HTLC
// - Awaiting: Commitment CSV expiry or second-stage HTLC CSV expiry.
// - HeightIndexEntry: Input confirmation height + relative CSV delay
// - NextState: GRAD
// - GRAD:
// - SerializedType: kidOutput
// - OriginalOutputType: Commitment or HTLC
// - Awaiting: All other outputs in channel to become GRAD.
// - NextState: Mark channel fully closed in channeldb and remove.
//
// DESCRIPTION OF OUTPUT STATES
//
// TODO(roasbeef): update comment with both new output types
//
// - CRIB (babyOutput) outputs are two-stage htlc outputs that are initially
// locked using a CLTV delay, followed by a CSV delay. The first stage of a
// crib output requires broadcasting a presigned htlc timeout txn generated
// by the wallet after an absolute expiry height. Since the timeout txns are
// predetermined, they cannot be batched after-the-fact, meaning that all
// CRIB outputs are broadcast and confirmed independently. After the first
// stage is complete, a CRIB output is moved to the KNDR state, which will
// finishing sweeping the second-layer CSV delay.
//
// - PSCL (kidOutput) outputs are commitment outputs locked under a CSV delay.
// These outputs are stored temporarily in this state until the commitment
// transaction confirms, as this solidifies an absolute height that the
// relative time lock will expire. Once this maturity height is determined,
// the PSCL output is moved into KNDR.
//
// - KNDR (kidOutput) outputs are CSV delayed outputs for which the maturity
// height has been fully determined. This results from having received
// confirmation of the UTXO we are trying to spend, contained in either the
// commitment txn or htlc timeout txn. Once the maturity height is reached,
// the utxo nursery will sweep all KNDR outputs scheduled for that height
// using a single txn.
//
// NOTE: Due to the fact that KNDR outputs can be dynamically aggregated and
// swept, we make precautions to finalize the KNDR outputs at a particular
// height on our first attempt to sweep it. Finalizing involves signing the
// sweep transaction and persisting it in the nursery store, and recording
// the last finalized height. Any attempts to replay an already finalized
// height will result in broadcasting the already finalized txn, ensuring the
// nursery does not broadcast different txids for the same batch of KNDR
// outputs. The reason txids may change is due to the probabilistic nature of
// generating the pkscript in the sweep txn's output, even if the set of
// inputs remains static across attempts.
//
// - GRAD (kidOutput) outputs are KNDR outputs that have successfully been
// swept into the user's wallet. A channel is considered mature once all of
// its outputs, including two-stage htlcs, have entered the GRAD state,
// indicating that it safe to mark the channel as fully closed.
//
//
// OUTPUT STATE TRANSITIONS IN UTXO NURSERY
//
// ┌────────────────┐ ┌──────────────┐
// │ Commit Outputs │ │ HTLC Outputs │
// └────────────────┘ └──────────────┘
// │ │
// │ │
// │ │ UTXO NURSERY
// ┌───────────┼────────────────┬───────────┼───────────────────────────────┐
// │ │ │ │
// │ │ │ │ │
// │ │ │ CLTV-Delayed │
// │ │ │ V babyOutputs │
// │ │ ┌──────┐ │
// │ │ │ │ CRIB │ │
// │ │ └──────┘ │
// │ │ │ │ │
// │ │ │ │
// │ │ │ | │
// │ │ V Wait CLTV │
// │ │ │ [ ] + │
// │ │ | Publish Txn │
// │ │ │ │ │
// │ │ │ │
// │ │ │ V ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─┐ │
// │ │ ( ) waitForTimeoutConf │
// │ │ │ | └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─┘ │
// │ │ │ │
// │ │ │ │ │
// │ │ │ │
// │ V │ │ │
// │ ┌──────┐ │ │
// │ │ PSCL │ └ ── ── ─┼ ── ── ── ── ── ── ── ─┤
// │ └──────┘ │ │
// │ │ │ │
// │ │ │ │
// │ V ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─┐ │ CSV-Delayed │
// │ ( ) waitForCommitConf │ kidOutputs │
// │ | └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─┘ │ │
// │ │ │ │
// │ │ │ │
// │ │ V │
// │ │ ┌──────┐ │
// │ └─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─▶│ KNDR │ │
// │ └──────┘ │
// │ │ │
// │ │ │
// │ | │
// │ V Wait CSV │
// │ [ ] + │
// │ | Publish Txn │
// │ │ │
// │ │ │
// │ V ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐ │
// │ ( ) waitForSweepConf │
// │ | └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘ │
// │ │ │
// │ │ │
// │ V │
// │ ┌──────┐ │
// │ │ GRAD │ │
// │ └──────┘ │
// │ │ │
// │ │ │
// │ │ │
// └────────────────────────────────────────┼───────────────────────────────┘
// │
// │
// │
// │
// V
// ┌────────────────┐
// │ Wallet Outputs │
// └────────────────┘
var byteOrder = binary.BigEndian
var (
// ErrContractNotFound is returned when the nursery is unable to
// retrieve information about a queried contract.
ErrContractNotFound = fmt.Errorf("unable to locate contract")
)
// NurseryConfig abstracts the required subsystems used by the utxo nursery. An
// instance of NurseryConfig is passed to newUtxoNursery during instantiation.
type NurseryConfig struct {
// ChainIO is used by the utxo nursery to determine the current block
// height, which drives the incubation of the nursery's outputs.
ChainIO lnwallet.BlockChainIO
// ConfDepth is the number of blocks the nursery store waits before
// determining outputs in the chain as confirmed.
ConfDepth uint32
// DB provides access to a user's channels, such that they can be marked
// fully closed after incubation has concluded.
DB *channeldb.DB
// Estimator is used when crafting sweep transactions to estimate the
// necessary fee relative to the expected size of the sweep transaction.
Estimator lnwallet.FeeEstimator
// GenSweepScript generates a P2WKH script belonging to the wallet where
// funds can be swept.
GenSweepScript func() ([]byte, error)
// Notifier provides the utxo nursery the ability to subscribe to
// transaction confirmation events, which advance outputs through their
// persistence state transitions.
Notifier chainntnfs.ChainNotifier
// PublishTransaction facilitates the process of broadcasting a signed
// transaction to the appropriate network.
PublishTransaction func(*wire.MsgTx) error
// Signer is used by the utxo nursery to generate valid witnesses at the
// time the incubated outputs need to be spent.
Signer lnwallet.Signer
// Store provides access to and modification of the persistent state
// maintained about the utxo nursery's incubating outputs.
Store NurseryStore
}
// utxoNursery is a system dedicated to incubating time-locked outputs created
// by the broadcast of a commitment transaction either by us, or the remote
// peer. The nursery accepts outputs and "incubates" them until they've reached
// maturity, then sweep the outputs into the source wallet. An output is
// considered mature after the relative time-lock within the pkScript has
// passed. As outputs reach their maturity age, they're swept in batches into
// the source wallet, returning the outputs so they can be used within future
// channels, or regular Bitcoin transactions.
type utxoNursery struct {
started uint32 // To be used atomically.
stopped uint32 // To be used atomically.
cfg *NurseryConfig
mu sync.Mutex
bestHeight uint32
quit chan struct{}
wg sync.WaitGroup
}
// newUtxoNursery creates a new instance of the utxoNursery from a
// ChainNotifier and LightningWallet instance.
func newUtxoNursery(cfg *NurseryConfig) *utxoNursery {
return &utxoNursery{
cfg: cfg,
quit: make(chan struct{}),
}
}
// Start launches all goroutines the utxoNursery needs to properly carry out
// its duties.
func (u *utxoNursery) Start() error {
if !atomic.CompareAndSwapUint32(&u.started, 0, 1) {
return nil
}
utxnLog.Tracef("Starting UTXO nursery")
// 1. Start watching for new blocks, as this will drive the nursery
// store's state machine.
// Register with the notifier to receive notifications for each newly
// connected block. We register immediately on startup to ensure that
// no blocks are missed while we are handling blocks that were missed
// during the time the UTXO nursery was unavailable.
newBlockChan, err := u.cfg.Notifier.RegisterBlockEpochNtfn()
if err != nil {
return err
}
// 2. Flush all fully-graduated channels from the pipeline.
// Load any pending close channels, which represents the super set of
// all channels that may still be incubating.
pendingCloseChans, err := u.cfg.DB.FetchClosedChannels(true)
if err != nil {
newBlockChan.Cancel()
return err
}
// Ensure that all mature channels have been marked as fully closed in
// the channeldb.
for _, pendingClose := range pendingCloseChans {
err := u.closeAndRemoveIfMature(&pendingClose.ChanPoint)
if err != nil {
newBlockChan.Cancel()
return err
}
}
// TODO(conner): check if any fully closed channels can be removed from
// utxn.
// Query the nursery store for the lowest block height we could be
// incubating, which is taken to be the last height for which the
// database was purged.
lastGraduatedHeight, err := u.cfg.Store.LastGraduatedHeight()
if err != nil {
newBlockChan.Cancel()
return err
}
// 2. Restart spend ntfns for any preschool outputs, which are waiting
// for the force closed commitment txn to confirm, or any second-layer
// HTLC success transactions.
//
// NOTE: The next two steps *may* spawn go routines, thus from this
// point forward, we must close the nursery's quit channel if we detect
// any failures during startup to ensure they terminate.
if err := u.reloadPreschool(); err != nil {
newBlockChan.Cancel()
close(u.quit)
return err
}
// 3. Replay all crib and kindergarten outputs from last pruned to
// current best height.
if err := u.reloadClasses(lastGraduatedHeight); err != nil {
newBlockChan.Cancel()
close(u.quit)
return err
}
u.wg.Add(1)
go u.incubator(newBlockChan)
return nil
}
// Stop gracefully shuts down any lingering goroutines launched during normal
// operation of the utxoNursery.
func (u *utxoNursery) Stop() error {
if !atomic.CompareAndSwapUint32(&u.stopped, 0, 1) {
return nil
}
utxnLog.Infof("UTXO nursery shutting down")
close(u.quit)
u.wg.Wait()
return nil
}
// IncubateOutputs sends a request to the utxoNursery to incubate a set of
// outputs from an existing commitment transaction. Outputs need to incubate if
// they're CLTV absolute time locked, or if they're CSV relative time locked.
// Once all outputs reach maturity, they'll be swept back into the wallet.
func (u *utxoNursery) IncubateOutputs(chanPoint wire.OutPoint,
commitResolution *lnwallet.CommitOutputResolution,
outgoingHtlcs []lnwallet.OutgoingHtlcResolution,
incomingHtlcs []lnwallet.IncomingHtlcResolution) error {
numHtlcs := len(incomingHtlcs) + len(outgoingHtlcs)
var (
hasCommit bool
// Kid outputs can be swept after an initial confirmation
// followed by a maturity period.Baby outputs are two stage and
// will need to wait for an absolute time out to reach a
// confirmation, then require a relative confirmation delay.
kidOutputs = make([]kidOutput, 0, 1+len(incomingHtlcs))
babyOutputs = make([]babyOutput, 0, len(outgoingHtlcs))
)
// 1. Build all the spendable outputs that we will try to incubate.
// It could be that our to-self output was below the dust limit. In
// that case the commit resolution would be nil and we would not have
// that output to incubate.
if commitResolution != nil {
hasCommit = true
selfOutput := makeKidOutput(
&commitResolution.SelfOutPoint,
&chanPoint,
commitResolution.MaturityDelay,
lnwallet.CommitmentTimeLock,
&commitResolution.SelfOutputSignDesc,
0,
)
// We'll skip any zero valued outputs as this indicates we
// don't have a settled balance within the commitment
// transaction.
if selfOutput.Amount() > 0 {
kidOutputs = append(kidOutputs, selfOutput)
}
}
// TODO(roasbeef): query and see if we already have, if so don't add?
// For each incoming HTLC, we'll register a kid output marked as a
// second-layer HTLC output. We effectively skip the baby stage (as the
// timelock is zero), and enter the kid stage.
for _, htlcRes := range incomingHtlcs {
htlcOutput := makeKidOutput(
&htlcRes.ClaimOutpoint, &chanPoint, htlcRes.CsvDelay,
lnwallet.HtlcAcceptedSuccessSecondLevel,
&htlcRes.SweepSignDesc, 0,
)
if htlcOutput.Amount() > 0 {
kidOutputs = append(kidOutputs, htlcOutput)
}
}
// For each outgoing HTLC, we'll create a baby output. If this is our
// commitment transaction, then we'll broadcast a second-layer
// transaction to transition to a kid output. Otherwise, we'll directly
// spend once the CLTV delay us up.
for _, htlcRes := range outgoingHtlcs {
// If this HTLC is on our commitment transaction, then it'll be
// a baby output as we need to go to the second level to sweep
// it.
if htlcRes.SignedTimeoutTx != nil {
htlcOutput := makeBabyOutput(&chanPoint, &htlcRes)
if htlcOutput.Amount() > 0 {
babyOutputs = append(babyOutputs, htlcOutput)
}
continue
}
// Otherwise, this is actually a kid output as we can sweep it
// once the commitment transaction confirms, and the absolute
// CLTV lock has expired. We set the CSV delay to zero to
// indicate this is actually a CLTV output.
htlcOutput := makeKidOutput(
&htlcRes.ClaimOutpoint, &chanPoint, 0,
lnwallet.HtlcOfferedRemoteTimeout,
&htlcRes.SweepSignDesc, htlcRes.Expiry,
)
kidOutputs = append(kidOutputs, htlcOutput)
}
// TODO(roasbeef): if want to handle outgoing on remote commit
// * need ability to cancel in the case that we learn of pre-image or
// remote party pulls
utxnLog.Infof("Incubating Channel(%s) has-commit=%v, num-htlcs=%d",
chanPoint, hasCommit, numHtlcs)
u.mu.Lock()
defer u.mu.Unlock()
// 2. Persist the outputs we intended to sweep in the nursery store
if err := u.cfg.Store.Incubate(kidOutputs, babyOutputs); err != nil {
utxnLog.Errorf("unable to begin incubation of Channel(%s): %v",
chanPoint, err)
return err
}
// As an intermediate step, we'll now check to see if any of the baby
// outputs has actually _already_ expired. This may be the case if
// blocks were mined while we processed this message.
_, bestHeight, err := u.cfg.ChainIO.GetBestBlock()
if err != nil {
return err
}
// We'll examine all the baby outputs just inserted into the database,
// if the output has already expired, then we'll *immediately* sweep
// it. This may happen if the caller raced a block to call this method.
for _, babyOutput := range babyOutputs {
if uint32(bestHeight) >= babyOutput.expiry {
err = u.sweepCribOutput(uint32(bestHeight), &babyOutput)
if err != nil {
return err
}
}
}
// 3. If we are incubating any preschool outputs, register for a
// confirmation notification that will transition it to the
// kindergarten bucket.
if len(kidOutputs) != 0 {
for _, kidOutput := range kidOutputs {
err := u.registerPreschoolConf(&kidOutput, u.bestHeight)
if err != nil {
return err
}
}
}
return nil
}
// NurseryReport attempts to return a nursery report stored for the target
// outpoint. A nursery report details the maturity/sweeping progress for a
// contract that was previously force closed. If a report entry for the target
// chanPoint is unable to be constructed, then an error will be returned.
func (u *utxoNursery) Nurse
1917
ryReport(
chanPoint *wire.OutPoint) (*contractMaturityReport, error) {
u.mu.Lock()
defer u.mu.Unlock()
utxnLog.Infof("NurseryReport: building nursery report for channel %v",
chanPoint)
report := &contractMaturityReport{
chanPoint: *chanPoint,
}
if err := u.cfg.Store.ForChanOutputs(chanPoint, func(k, v []byte) error {
switch {
case bytes.HasPrefix(k, cribPrefix):
// Cribs outputs are the only kind currently stored as
// baby outputs.
var baby babyOutput
err := baby.Decode(bytes.NewReader(v))
if err != nil {
return err
}
// Each crib output represents a stage one htlc, and
// will contribute towards the limbo balance.
report.AddLimboStage1TimeoutHtlc(&baby)
case bytes.HasPrefix(k, psclPrefix),
bytes.HasPrefix(k, kndrPrefix),
bytes.HasPrefix(k, gradPrefix):
// All others states can be deserialized as kid outputs.
var kid kidOutput
err := kid.Decode(bytes.NewReader(v))
if err != nil {
return err
}
// Now, use the state prefixes to determine how the
// this output should be represented in the nursery
// report. An output's funds are always in limbo until
// reaching the graduate state.
switch {
case bytes.HasPrefix(k, psclPrefix):
// Preschool outputs are awaiting the
// confirmation of the commitment transaction.
switch kid.WitnessType() {
case lnwallet.CommitmentTimeLock:
report.AddLimboCommitment(&kid)
// An HTLC output on our commitment transaction
// where the second-layer transaction hasn't
// yet confirmed.
case lnwallet.HtlcAcceptedSuccessSecondLevel:
report.AddLimboStage1SuccessHtlc(&kid)
}
case bytes.HasPrefix(k, kndrPrefix):
// Kindergarten outputs may originate from
// either the commitment transaction or an htlc.
// We can distinguish them via their witness
// types.
switch kid.WitnessType() {
case lnwallet.CommitmentTimeLock:
// The commitment transaction has been
// confirmed, and we are waiting the CSV
// delay to expire.
report.AddLimboCommitment(&kid)
case lnwallet.HtlcOfferedRemoteTimeout:
// This is an HTLC output on the
// commitment transaction of the remote
// party. The CLTV timelock has
// expired, and we only need to sweep
// it.
report.AddLimboDirectHtlc(&kid)
case lnwallet.HtlcAcceptedSuccessSecondLevel:
fallthrough
case lnwallet.HtlcOfferedTimeoutSecondLevel:
// The htlc timeout or success
// transaction has confirmed, and the
// CSV delay has begun ticking.
report.AddLimboStage2Htlc(&kid)
}
case bytes.HasPrefix(k, gradPrefix):
// Graduate outputs are those whose funds have
// been swept back into the wallet. Each output
// will contribute towards the recovered
// balance.
switch kid.WitnessType() {
case lnwallet.CommitmentTimeLock:
// The commitment output was
// successfully swept back into a
// regular p2wkh output.
report.AddRecoveredCommitment(&kid)
case lnwallet.HtlcAcceptedSuccessSecondLevel:
fallthrough
case lnwallet.HtlcOfferedTimeoutSecondLevel:
fallthrough
case lnwallet.HtlcOfferedRemoteTimeout:
// This htlc output successfully
// resides in a p2wkh output belonging
// to the user.
report.AddRecoveredHtlc(&kid)
}
}
default:
}
return nil
}); err != nil {
return nil, err
}
return report, nil
}
// reloadPreschool re-initializes the chain notifier with all of the outputs
// that had been saved to the "preschool" database bucket prior to shutdown.
func (u *utxoNursery) reloadPreschool() error {
psclOutputs, err := u.cfg.Store.FetchPreschools()
if err != nil {
return err
}
// For each of the preschool outputs stored in the nursery store, load
// its close summary from disk so that we can get an accurate height
// hint from which to start our range for spend notifications.
for i := range psclOutputs {
kid := &psclOutputs[i]
chanPoint := kid.OriginChanPoint()
// Load the close summary for this output's channel point.
closeSummary, err := u.cfg.DB.FetchClosedChannel(chanPoint)
if err == channeldb.ErrClosedChannelNotFound {
// This should never happen since the close summary
// should only be removed after the channel has been
// swept completely.
utxnLog.Warnf("Close summary not found for "+
"chan_point=%v, can't determine height hint"+
"to sweep commit txn", chanPoint)
continue
} else if err != nil {
return err
}
// Use the close height from the channel summary as our height
// hint to drive our spend notifications, with our confirmation
// depth as a buffer for reorgs.
heightHint := closeSummary.CloseHeight - u.cfg.ConfDepth
err = u.registerPreschoolConf(kid, heightHint)
if err != nil {
return err
}
}
return nil
}
// reloadClasses reinitializes any height-dependent state transitions for which
// the utxonursery has not received confirmation, and replays the graduation of
// all kindergarten and crib outputs for heights that have not been finalized.
// This allows the nursery to reinitialize all state to continue sweeping
// outputs, even in the event that we missed blocks while offline.
// reloadClasses is called during the startup of the UTXO Nursery.
func (u *utxoNursery) reloadClasses(lastGradHeight uint32) error {
// Begin by loading all of the still-active heights up to and including
// the last height we successfully graduated.
activeHeights, err := u.cfg.Store.HeightsBelowOrEqual(lastGradHeight)
if err != nil {
return err
}
if len(activeHeights) > 0 {
utxnLog.Infof("Re-registering confirmations for %d already "+
"graduated heights below height=%d", len(activeHeights),
lastGradHeight)
}
// Attempt to re-register notifications for any outputs still at these
// heights.
for _, classHeight := range activeHeights {
utxnLog.Debugf("Attempting to regraduate outputs at height=%v",
classHeight)
if err = u.regraduateClass(classHeight); err != nil {
utxnLog.Errorf("Failed to regraduate outputs at "+
"height=%v: %v", classHeight, err)
return err
}
}
// Get the most recently mined block.
_, bestHeight, err := u.cfg.ChainIO.GetBestBlock()
if err != nil {
return err
}
// If we haven't yet seen any registered force closes, or we're already
// caught up with the current best chain, then we can exit early.
if lastGradHeight == 0 || uint32(bestHeight) == lastGradHeight {
return nil
}
utxnLog.Infof("Processing outputs from missed blocks. Starting with "+
"blockHeight=%v, to current blockHeight=%v", lastGradHeight,
bestHeight)
// Loop through and check for graduating outputs at each of the missed
// block heights.
for curHeight := lastGradHeight + 1; curHeight <= uint32(bestHeight); curHeight++ {
utxnLog.Debugf("Attempting to graduate outputs at height=%v",
curHeight)
if err := u.graduateClass(curHeight); err != nil {
utxnLog.Errorf("Failed to graduate outputs at "+
"height=%v: %v", curHeight, err)
return err
}
}
utxnLog.Infof("UTXO Nursery is now fully synced")
return nil
}
// regraduateClass handles the steps involved in re-registering for
// confirmations for all still-active outputs at a particular height. This is
// used during restarts to ensure that any still-pending state transitions are
// properly registered, so they can be driven by the chain notifier. No
// transactions or signing are done as a result of this step.
func (u *utxoNursery) regraduateClass(classHeight uint32) error {
// Fetch all information about the crib and kindergarten outputs at
// this height. In addition to the outputs, we also retrieve the
// finalized kindergarten sweep txn, which will be nil if we have not
// attempted this height before, or if no kindergarten outputs exist at
// this height.
finalTx, kgtnOutputs, cribOutputs, err := u.cfg.Store.FetchClass(
classHeight)
if err != nil {
return err
}
if finalTx != nil {
utxnLog.Infof("Re-registering confirmation for kindergarten "+
"sweep transaction at height=%d ", classHeight)
err = u.sweepMatureOutputs(classHeight, finalTx, kgtnOutputs)
if err != nil {
utxnLog.Errorf("Failed to re-register for kindergarten "+
"sweep transaction at height=%d: %v",
classHeight, err)
return err
}
}
if len(cribOutputs) == 0 {
return nil
}
utxnLog.Infof("Re-registering confirmation for first-stage HTLC "+
"outputs at height=%d ", classHeight)
// Now, we broadcast all pre-signed htlc txns from the crib outputs at
// this height. There is no need to finalize these txns, since the txid
// is predetermined when signed in the wallet.
for i := range cribOutputs {
err := u.sweepCribOutput(classHeight, &cribOutputs[i])
if err != nil {
utxnLog.Errorf("Failed to re-register first-stage "+
"HTLC output %v", cribOutputs[i].OutPoint())
return err
}
}
return nil
}
// incubator is tasked with driving all state transitions that are dependent on
// the current height of the blockchain. As new blocks arrive, the incubator
// will attempt spend outputs at the latest height. The asynchronous
// confirmation of these spends will either 1) move a crib output into the
// kindergarten bucket or 2) move a kindergarten output into the graduated
// bucket.
func (u *utxoNursery) incubator(newBlockChan *chainntnfs.BlockEpochEvent) {
defer u.wg.Done()
defer newBlockChan.Cancel()
for {
select {
case epoch, ok := <-newBlockChan.Epochs:
// If the epoch channel has been closed, then the
// ChainNotifier is exiting which means the daemon is
// as well. Therefore, we exit early also in order to
// ensure the daemon shuts down gracefully, yet
// swiftly.
if !ok {
return
}
// TODO(roasbeef): if the BlockChainIO is rescanning
// will give stale data
// A new block has just been connected to the main
// chain, which means we might be able to graduate crib
// or kindergarten outputs at this height. This involves
// broadcasting any presigned htlc timeout txns, as well
// as signing and broadcasting a sweep txn that spends
// from all kindergarten outputs at this height.
height := uint32(epoch.Height)
if err := u.graduateClass(height); err != nil {
utxnLog.Errorf("error while graduating "+
"class at height=%d: %v", height, err)
// TODO(conner): signal fatal error to daemon
}
case <-u.quit:
return
}
}
}
// graduateClass handles the steps involved in spending outputs whose CSV or
// CLTV delay expires at the nursery's current height. This method is called
// each time a new block arrives, or during startup to catch up on heights we
// may have missed while the nursery was offline.
func (u *utxoNursery) graduateClass(classHeight uint32) error {
// Record this height as the nursery's current best height.
u.mu.Lock()
defer u.mu.Unlock()
u.bestHeight = classHeight
// Fetch all information about the crib and kindergarten outputs at
// this height. In addition to the outputs, we also retrieve the
// finalized kindergarten sweep txn, which will be nil if we have not
// attempted this height before, or if no kindergarten outputs exist at
// this height.
finalTx, kgtnOutputs, cribOutputs, err := u.cfg.Store.FetchClass(
classHeight)
if err != nil {
return err
}
utxnLog.Infof("Attempting to graduate height=%v: num_kids=%v, "+
"num_babies=%v", classHeight, len(kgtnOutputs), len(cribOutputs))
// Load the last finalized height, so we can determine if the
// kindergarten sweep txn should be crafted.
lastFinalizedHeight, err := u.cfg.Store.LastFinalizedHeight()
if err != nil {
return err
}
// If we haven't processed this height before, we finalize the
// graduating kindergarten outputs, by signing a sweep transaction that
// spends from them. This txn is persisted such that we never broadcast
// a different txn for the same height. This allows us to recover from
// failures, and watch for the correct txid.
if classHeight > lastFinalizedHeight {
// If this height has never been finalized, we have never
// generated a sweep txn for this height. Generate one if there
// are kindergarten outputs or cltv crib outputs to be spent.
if len(kgtnOutputs) > 0 {
finalTx, err = u.createSweepTx(kgtnOutputs, classHeight)
if err != nil {
utxnLog.Errorf("Failed to create sweep txn at "+
"height=%d", classHeight)
return err
}
}
// Persist the kindergarten sweep txn to the nursery store. It
// is safe to store a nil finalTx, which happens if there are
// no graduating kindergarten outputs.
err = u.cfg.Store.FinalizeKinder(classHeight, finalTx)
if err != nil {
utxnLog.Errorf("Failed to finalize kindergarten at "+
"height=%d", classHeight)
return err
}
// Log if the finalized transaction is non-trivial.
if finalTx != nil {
utxnLog.Infof("Finalized kindergarten at height=%d ",
classHeight)
}
}
// Now that the kindergarten sweep txn has either been finalized or
// restored, broadcast the txn, and set up notifications that will
// transition the swept kindergarten outputs and cltvCrib into
// graduated outputs.
if finalTx != nil {
err := u.sweepMatureOutputs(classHeight, finalTx, kgtnOutputs)
if err != nil {
utxnLog.Errorf("Failed to sweep %d kindergarten "+
"outputs at height=%d: %v",
len(kgtnOutputs), classHeight, err)
return err
}
}
// Now, we broadcast all pre-signed htlc txns from the csv crib outputs
// at this height. There is no need to finalize these txns, since the
// txid is predetermined when signed in the wallet.
for i := range cribOutputs {
err := u.sweepCribOutput(classHeight, &cribOutputs[i])
if err != nil {
utxnLog.Errorf("Failed to sweep first-stage HTLC "+
"(CLTV-delayed) output %v",
cribOutputs[i].OutPoint())
return err
}
}
return u.cfg.Store.GraduateHeight(classHeight)
}
// craftSweepTx accepts a list of kindergarten outputs, and baby
// outputs which don't require a second-layer claim, and signs and generates a
// signed txn that spends from them. This method also makes an accurate fee
// estimate before generating the required witnesses.
func (u *utxoNursery) createSweepTx(kgtnOutputs []kidOutput,
classHeight uint32) (*wire.MsgTx, error) {
// Create a transaction which sweeps all the newly mature outputs into
// an output controlled by the wallet.
// TODO(roasbeef): can be more intelligent about buffering outputs to
// be more efficient on-chain.
// Assemble the kindergarten class into a slice csv spendable outputs,
// and also a set of regular spendable outputs. The set of regular
// outputs are CLTV locked outputs that have had their timelocks
// expire.
var (
csvOutputs []CsvSpendableOutput
cltvOutputs []SpendableOutput
weightEstimate lnwallet.TxWeightEstimator
)
// Allocate enough room for both types of kindergarten outputs.
csvOutputs = make([]CsvSpendableOutput, 0, len(kgtnOutputs))
cltvOutputs = make([]SpendableOutput, 0, len(kgtnOutputs))
// Our sweep transaction will pay to a single segwit p2wkh address,
// ensure it contributes to our weight estimate.
weightEstimate.AddP2WKHOutput()
// For each kindergarten output, use its witness type to determine the
// estimate weight of its witness, and add it to the proper set of
// spendable outputs.
for i := range kgtnOutputs {
input := &kgtnOutputs[i]
switch input.WitnessType() {
// Outputs on a past commitment transaction that pay directly
// to us.
case lnwallet.CommitmentTimeLock:
weightEstimate.AddWitnessInput(
lnwallet.ToLocalTimeoutWitnessSize,
)
csvOutputs = append(csvOutputs, input)
// Outgoing second layer HTLC's that have confirmed within the
// chain, and the output they produced is now mature enough to
// sweep.
case lnwallet.HtlcOfferedTimeoutSecondLevel:
weightEstimate.AddWitnessInput(
lnwallet.SecondLevelHtlcSuccessWitnessSize,
)
csvOutputs = append(csvOutputs, input)
// Incoming second layer HTLC's that have confirmed within the
// chain, and the output they produced is now mature enough to
// sweep.
case lnwallet.HtlcAcceptedSuccessSecondLevel:
weightEstimate.AddWitnessInput(
lnwallet.SecondLevelHtlcSuccessWitnessSize,
)
csvOutputs = append(csvOutputs, input)
// An HTLC on the commitment transaction of the remote party,
// that has had its absolute timelock expire.
case lnwallet.HtlcOfferedRemoteTimeout:
weightEstimate.AddWitnessInput(
lnwallet.AcceptedHtlcTimeoutWitnessSize,
)
cltvOutputs = append(cltvOutputs, input)
default:
utxnLog.Warnf("kindergarten output in nursery store "+
"contains unexpected witness type: %v",
input.WitnessType())
continue
}
}
utxnLog.Infof("Creating sweep transaction for %v CSV inputs, %v CLTV "+
"inputs", len(csvOutputs), len(cltvOutputs))
txVSize := int64(weightEstimate.VSize())
return u.populateSweepTx(txVSize, classHeight, csvOutputs, cltvOutputs)
}