lnd.xprv/contractcourt/htlc_incoming_contest_resolver.go

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package contractcourt
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"io"
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"github.com/btcsuite/btcutil"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/htlcswitch/hop"
"github.com/lightningnetwork/lnd/invoices"
"github.com/lightningnetwork/lnd/lntypes"
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"github.com/lightningnetwork/lnd/lnwallet"
)
// htlcIncomingContestResolver is a ContractResolver that's able to resolve an
// incoming HTLC that is still contested. An HTLC is still contested, if at the
// time of commitment broadcast, we don't know of the preimage for it yet, and
// it hasn't expired. In this case, we can resolve the HTLC if we learn of the
// preimage, otherwise the remote party will sweep it after it expires.
//
// TODO(roasbeef): just embed the other resolver?
type htlcIncomingContestResolver struct {
// htlcExpiry is the absolute expiry of this incoming HTLC. We use this
// value to determine if we can exit early as if the HTLC times out,
// before we learn of the preimage then we can't claim it on chain
// successfully.
htlcExpiry uint32
// htlcSuccessResolver is the inner resolver that may be utilized if we
// learn of the preimage.
*htlcSuccessResolver
}
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// newIncomingContestResolver instantiates a new incoming htlc contest resolver.
func newIncomingContestResolver(
res lnwallet.IncomingHtlcResolution, broadcastHeight uint32,
htlc channeldb.HTLC, resCfg ResolverConfig) *htlcIncomingContestResolver {
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success := newSuccessResolver(
res, broadcastHeight, htlc, resCfg,
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)
return &htlcIncomingContestResolver{
htlcExpiry: htlc.RefundTimeout,
htlcSuccessResolver: success,
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}
}
// Resolve attempts to resolve this contract. As we don't yet know of the
// preimage for the contract, we'll wait for one of two things to happen:
//
// 1. We learn of the preimage! In this case, we can sweep the HTLC incoming
// and ensure that if this was a multi-hop HTLC we are made whole. In this
// case, an additional ContractResolver will be returned to finish the
// job.
//
// 2. The HTLC expires. If this happens, then the contract is fully resolved
// as we have no remaining actions left at our disposal.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) Resolve() (ContractResolver, error) {
// If we're already full resolved, then we don't have anything further
// to do.
if h.resolved {
return nil, nil
}
// First try to parse the payload. If that fails, we can stop resolution
// now.
payload, err := h.decodePayload()
if err != nil {
log.Debugf("ChannelArbitrator(%v): cannot decode payload of "+
"htlc %v", h.ChanPoint, h.HtlcPoint())
// If we've locked in an htlc with an invalid payload on our
// commitment tx, we don't need to resolve it. The other party
// will time it out and get their funds back. This situation can
// present itself when we crash before processRemoteAdds in the
// link has ran.
h.resolved = true
// We write a report to disk that indicates we could not decode
// the htlc.
resReport := h.report().resolverReport(
nil, channeldb.ResolverTypeIncomingHtlc,
channeldb.ResolverOutcomeAbandoned,
)
return nil, h.PutResolverReport(nil, resReport)
}
// Register for block epochs. After registration, the current height
// will be sent on the channel immediately.
blockEpochs, err := h.Notifier.RegisterBlockEpochNtfn(nil)
if err != nil {
return nil, err
}
defer blockEpochs.Cancel()
var currentHeight int32
select {
case newBlock, ok := <-blockEpochs.Epochs:
if !ok {
return nil, errResolverShuttingDown
}
currentHeight = newBlock.Height
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case <-h.quit:
return nil, errResolverShuttingDown
}
// We'll first check if this HTLC has been timed out, if so, we can
// return now and mark ourselves as resolved. If we're past the point of
// expiry of the HTLC, then at this point the sender can sweep it, so
// we'll end our lifetime. Here we deliberately forego the chance that
// the sender doesn't sweep and we already have or will learn the
// preimage. Otherwise the resolver could potentially stay active
// indefinitely and the channel will never close properly.
if uint32(currentHeight) >= h.htlcExpiry {
// TODO(roasbeef): should also somehow check if outgoing is
// resolved or not
// * may need to hook into the circuit map
// * can't timeout before the outgoing has been
log.Infof("%T(%v): HTLC has timed out (expiry=%v, height=%v), "+
"abandoning", h, h.htlcResolution.ClaimOutpoint,
h.htlcExpiry, currentHeight)
h.resolved = true
// Finally, get our report and checkpoint our resolver with a
// timeout outcome report.
report := h.report().resolverReport(
nil, channeldb.ResolverTypeIncomingHtlc,
channeldb.ResolverOutcomeTimeout,
)
return nil, h.Checkpoint(h, report)
}
// applyPreimage is a helper function that will populate our internal
// resolver with the preimage we learn of. This should be called once
// the preimage is revealed so the inner resolver can properly complete
// its duties. The error return value indicates whether the preimage
// was properly applied.
applyPreimage := func(preimage lntypes.Preimage) error {
// Sanity check to see if this preimage matches our htlc. At
// this point it should never happen that it does not match.
if !preimage.Matches(h.htlc.RHash) {
return errors.New("preimage does not match hash")
}
// Update htlcResolution with the matching preimage.
h.htlcResolution.Preimage = preimage
log.Infof("%T(%v): extracted preimage=%v from beacon!", h,
h.htlcResolution.ClaimOutpoint, preimage)
// If this is our commitment transaction, then we'll need to
// populate the witness for the second-level HTLC transaction.
if h.htlcResolution.SignedSuccessTx != nil {
// Within the witness for the success transaction, the
// preimage is the 4th element as it looks like:
//
// * <sender sig> <recvr sig> <preimage> <witness script>
//
// We'll populate it within the witness, as since this
// was a "contest" resolver, we didn't yet know of the
// preimage.
h.htlcResolution.SignedSuccessTx.TxIn[0].Witness[3] = preimage[:]
}
return nil
}
// Define a closure to process htlc resolutions either directly or
// triggered by future notifications.
processHtlcResolution := func(e invoices.HtlcResolution) (
ContractResolver, error) {
// Take action based on the type of resolution we have
// received.
switch resolution := e.(type) {
// If the htlc resolution was a settle, apply the
// preimage and return a success resolver.
case *invoices.HtlcSettleResolution:
err := applyPreimage(resolution.Preimage)
if err != nil {
return nil, err
}
return h.htlcSuccessResolver, nil
// If the htlc was failed, mark the htlc as
// resolved.
case *invoices.HtlcFailResolution:
log.Infof("%T(%v): Exit hop HTLC canceled "+
"(expiry=%v, height=%v), abandoning", h,
h.htlcResolution.ClaimOutpoint,
h.htlcExpiry, currentHeight)
h.resolved = true
// Checkpoint our resolver with an abandoned outcome
// because we take no further action on this htlc.
report := h.report().resolverReport(
nil, channeldb.ResolverTypeIncomingHtlc,
channeldb.ResolverOutcomeAbandoned,
)
return nil, h.Checkpoint(h, report)
// Error if the resolution type is unknown, we are only
// expecting settles and fails.
default:
return nil, fmt.Errorf("unknown resolution"+
" type: %v", e)
}
}
var (
hodlChan chan interface{}
witnessUpdates <-chan lntypes.Preimage
)
if payload.FwdInfo.NextHop == hop.Exit {
// Create a buffered hodl chan to prevent deadlock.
hodlChan = make(chan interface{}, 1)
// Notify registry that we are potentially resolving as an exit
// hop on-chain. If this HTLC indeed pays to an existing
// invoice, the invoice registry will tell us what to do with
// the HTLC. This is identical to HTLC resolution in the link.
circuitKey := channeldb.CircuitKey{
ChanID: h.ShortChanID,
HtlcID: h.htlc.HtlcIndex,
}
resolution, err := h.Registry.NotifyExitHopHtlc(
h.htlc.RHash, h.htlc.Amt, h.htlcExpiry, currentHeight,
circuitKey, hodlChan, payload,
)
if err != nil {
return nil, err
}
defer h.Registry.HodlUnsubscribeAll(hodlChan)
// Take action based on the resolution we received. If the htlc
// was settled, or a htlc for a known invoice failed we can
// resolve it directly. If the resolution is nil, the htlc was
// neither accepted nor failed, so we cannot take action yet.
switch res := resolution.(type) {
case *invoices.HtlcFailResolution:
// In the case where the htlc failed, but the invoice
// was known to the registry, we can directly resolve
// the htlc.
if res.Outcome != invoices.ResultInvoiceNotFound {
return processHtlcResolution(resolution)
}
// If we settled the htlc, we can resolve it.
case *invoices.HtlcSettleResolution:
return processHtlcResolution(resolution)
// If the resolution is nil, the htlc was neither settled nor
// failed so we cannot take action at present.
case nil:
default:
return nil, fmt.Errorf("unknown htlc resolution type: %T",
resolution)
}
} else {
// If the HTLC hasn't expired yet, then we may still be able to
// claim it if we learn of the pre-image, so we'll subscribe to
// the preimage database to see if it turns up, or the HTLC
// times out.
//
// NOTE: This is done BEFORE opportunistically querying the db,
// to ensure the preimage can't be delivered between querying
// and registering for the preimage subscription.
preimageSubscription := h.PreimageDB.SubscribeUpdates()
defer preimageSubscription.CancelSubscription()
// With the epochs and preimage subscriptions initialized, we'll
// query to see if we already know the preimage.
preimage, ok := h.PreimageDB.LookupPreimage(h.htlc.RHash)
if ok {
// If we do, then this means we can claim the HTLC!
// However, we don't know how to ourselves, so we'll
// return our inner resolver which has the knowledge to
// do so.
if err := applyPreimage(preimage); err != nil {
return nil, err
}
return h.htlcSuccessResolver, nil
}
witnessUpdates = preimageSubscription.WitnessUpdates
}
for {
select {
case preimage := <-witnessUpdates:
// We received a new preimage, but we need to ignore
// all except the preimage we are waiting for.
if !preimage.Matches(h.htlc.RHash) {
continue
}
if err := applyPreimage(preimage); err != nil {
return nil, err
}
// We've learned of the preimage and this information
// has been added to our inner resolver. We return it so
// it can continue contract resolution.
return h.htlcSuccessResolver, nil
case hodlItem := <-hodlChan:
htlcResolution := hodlItem.(invoices.HtlcResolution)
return processHtlcResolution(htlcResolution)
case newBlock, ok := <-blockEpochs.Epochs:
if !ok {
return nil, errResolverShuttingDown
}
// If this new height expires the HTLC, then this means
// we never found out the preimage, so we can mark
// resolved and exit.
newHeight := uint32(newBlock.Height)
if newHeight >= h.htlcExpiry {
log.Infof("%T(%v): HTLC has timed out "+
"(expiry=%v, height=%v), abandoning", h,
h.htlcResolution.ClaimOutpoint,
h.htlcExpiry, currentHeight)
h.resolved = true
report := h.report().resolverReport(
nil,
channeldb.ResolverTypeIncomingHtlc,
channeldb.ResolverOutcomeTimeout,
)
return nil, h.Checkpoint(h, report)
}
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case <-h.quit:
return nil, errResolverShuttingDown
}
}
}
// report returns a report on the resolution state of the contract.
func (h *htlcIncomingContestResolver) report() *ContractReport {
// No locking needed as these values are read-only.
finalAmt := h.htlc.Amt.ToSatoshis()
if h.htlcResolution.SignedSuccessTx != nil {
finalAmt = btcutil.Amount(
h.htlcResolution.SignedSuccessTx.TxOut[0].Value,
)
}
return &ContractReport{
Outpoint: h.htlcResolution.ClaimOutpoint,
Type: ReportOutputIncomingHtlc,
Amount: finalAmt,
MaturityHeight: h.htlcExpiry,
LimboBalance: finalAmt,
Stage: 1,
}
}
// Stop signals the resolver to cancel any current resolution processes, and
// suspend.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) Stop() {
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close(h.quit)
}
// IsResolved returns true if the stored state in the resolve is fully
// resolved. In this case the target output can be forgotten.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) IsResolved() bool {
return h.resolved
}
// Encode writes an encoded version of the ContractResolver into the passed
// Writer.
//
// NOTE: Part of the ContractResolver interface.
func (h *htlcIncomingContestResolver) Encode(w io.Writer) error {
// We'll first write out the one field unique to this resolver.
if err := binary.Write(w, endian, h.htlcExpiry); err != nil {
return err
}
// Then we'll write out our internal resolver.
return h.htlcSuccessResolver.Encode(w)
}
// newIncomingContestResolverFromReader attempts to decode an encoded ContractResolver
// from the passed Reader instance, returning an active ContractResolver
// instance.
func newIncomingContestResolverFromReader(r io.Reader, resCfg ResolverConfig) (
*htlcIncomingContestResolver, error) {
h := &htlcIncomingContestResolver{}
// We'll first read the one field unique to this resolver.
if err := binary.Read(r, endian, &h.htlcExpiry); err != nil {
return nil, err
}
// Then we'll decode our internal resolver.
successResolver, err := newSuccessResolverFromReader(r, resCfg)
if err != nil {
return nil, err
}
h.htlcSuccessResolver = successResolver
return h, nil
}
// Supplement adds additional information to the resolver that is required
// before Resolve() is called.
//
// NOTE: Part of the htlcContractResolver interface.
func (h *htlcIncomingContestResolver) Supplement(htlc channeldb.HTLC) {
h.htlc = htlc
}
// decodePayload (re)decodes the hop payload of a received htlc.
func (h *htlcIncomingContestResolver) decodePayload() (*hop.Payload, error) {
onionReader := bytes.NewReader(h.htlc.OnionBlob)
iterator, err := h.OnionProcessor.ReconstructHopIterator(
onionReader, h.htlc.RHash[:],
)
if err != nil {
return nil, err
}
return iterator.HopPayload()
}
// A compile time assertion to ensure htlcIncomingContestResolver meets the
// ContractResolver interface.
var _ htlcContractResolver = (*htlcIncomingContestResolver)(nil)