lnd/itest/lnd_channel_force_close_test.go

package itest

import (
	"bytes"
	"fmt"

	"github.com/btcsuite/btcd/btcutil"
	"github.com/btcsuite/btcd/chaincfg/chainhash"
	"github.com/btcsuite/btcd/wire"
	"github.com/go-errors/errors"
	"github.com/lightningnetwork/lnd"
	"github.com/lightningnetwork/lnd/lnrpc"
	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
	"github.com/lightningnetwork/lnd/lntest"
	"github.com/lightningnetwork/lnd/lntest/node"
	"github.com/lightningnetwork/lnd/lntest/wait"
	"github.com/lightningnetwork/lnd/routing"
	"github.com/stretchr/testify/require"
)

const pushAmt = btcutil.Amount(5e5)

// testChannelForceClosureAnchor runs `runChannelForceClosureTest` with anchor
// channels.
func testChannelForceClosureAnchor(ht *lntest.HarnessTest) {
	// Create a simple network: Alice -> Carol, using anchor channels.
	//
	// Prepare params.
	openChannelParams := lntest.OpenChannelParams{
		Amt:            chanAmt,
		PushAmt:        pushAmt,
		CommitmentType: lnrpc.CommitmentType_ANCHORS,
	}

	cfg := node.CfgAnchor
	cfgCarol := append([]string{"--hodl.exit-settle"}, cfg...)
	cfgs := [][]string{cfg, cfgCarol}

	runChannelForceClosureTest(ht, cfgs, openChannelParams)
}

// testChannelForceClosureSimpleTaproot runs `runChannelForceClosureTest` with
// simple taproot channels.
func testChannelForceClosureSimpleTaproot(ht *lntest.HarnessTest) {
	// Create a simple network: Alice -> Carol, using simple taproot
	// channels.
	//
	// Prepare params.
	openChannelParams := lntest.OpenChannelParams{
		Amt:     chanAmt,
		PushAmt: pushAmt,
		// If the channel is a taproot channel, then we'll need to
		// create a private channel.
		//
		// TODO(roasbeef): lift after G175
		CommitmentType: lnrpc.CommitmentType_SIMPLE_TAPROOT,
		Private:        true,
	}

	cfg := node.CfgSimpleTaproot
	cfgCarol := append([]string{"--hodl.exit-settle"}, cfg...)
	cfgs := [][]string{cfg, cfgCarol}

	runChannelForceClosureTest(ht, cfgs, openChannelParams)
}

// runChannelForceClosureTest performs a test to exercise the behavior of
// "force" closing a channel or unilaterally broadcasting the latest local
// commitment state on-chain. The test creates a new channel between Alice and
// Carol, then force closes the channel after some cursory assertions. Within
// the test, a total of 3 + n transactions will be broadcast, representing the
// commitment transaction, a transaction sweeping the local CSV delayed output,
// a transaction sweeping the CSV delayed 2nd-layer htlcs outputs, and n htlc
// timeout transactions, where n is the number of payments Alice attempted
// to send to Carol.  This test includes several restarts to ensure that the
// transaction output states are persisted throughout the forced closure
// process.
func runChannelForceClosureTest(ht *lntest.HarnessTest,
	cfgs [][]string, params lntest.OpenChannelParams) {

	const (
		numInvoices   = 6
		commitFeeRate = 20000
	)

	ht.SetFeeEstimate(commitFeeRate)

	// Create a three hop network: Alice -> Carol.
	chanPoints, nodes := ht.CreateSimpleNetwork(cfgs, params)
	alice, carol := nodes[0], nodes[1]
	chanPoint := chanPoints[0]

	// We need one additional UTXO for sweeping the remote anchor.
	if ht.IsNeutrinoBackend() {
		ht.FundCoins(btcutil.SatoshiPerBitcoin, alice)
	}

	// Before we start, obtain Carol's current wallet balance, we'll check
	// to ensure that at the end of the force closure by Alice, Carol
	// recognizes his new on-chain output.
	carolBalResp := carol.RPC.WalletBalance()
	carolStartingBalance := carolBalResp.ConfirmedBalance

	// Send payments from Alice to Carol, since Carol is htlchodl mode, the
	// htlc outputs should be left unsettled, and should be swept by the
	// utxo nursery.
	carolPubKey := carol.PubKey[:]
	for i := 0; i < numInvoices; i++ {
		req := &routerrpc.SendPaymentRequest{
			Dest:           carolPubKey,
			Amt:            int64(paymentAmt),
			PaymentHash:    ht.Random32Bytes(),
			FinalCltvDelta: finalCltvDelta,
			TimeoutSeconds: 60,
			FeeLimitMsat:   noFeeLimitMsat,
		}
		ht.SendPaymentAssertInflight(alice, req)
	}

	// Once the HTLC has cleared, all the nodes n our mini network should
	// show that the HTLC has been locked in.
	ht.AssertNumActiveHtlcs(alice, numInvoices)
	ht.AssertNumActiveHtlcs(carol, numInvoices)

	// Fetch starting height of this test so we can compute the block
	// heights we expect certain events to take place.
	curHeight := int32(ht.CurrentHeight())

	// Using the current height of the chain, derive the relevant heights
	// for sweeping two-stage htlcs.
	var (
		startHeight           = uint32(curHeight)
		commCsvMaturityHeight = startHeight + 1 + defaultCSV
		htlcExpiryHeight      = padCLTV(startHeight + finalCltvDelta)
		htlcCsvMaturityHeight = padCLTV(
			startHeight + finalCltvDelta + 1 + defaultCSV,
		)
	)

	aliceChan := ht.QueryChannelByChanPoint(alice, chanPoint)
	require.NotZero(ht, aliceChan.NumUpdates,
		"alice should see at least one update to her channel")

	// Now that the channel is open and we have unsettled htlcs,
	// immediately execute a force closure of the channel. This will also
	// assert that the commitment transaction was immediately broadcast in
	// order to fulfill the force closure request.
	ht.CloseChannelAssertPending(alice, chanPoint, true)

	// Now that the channel has been force closed, it should show up in the
	// PendingChannels RPC under the waiting close section.
	waitingClose := ht.AssertChannelWaitingClose(alice, chanPoint)

	// Immediately after force closing, all of the funds should be in
	// limbo.
	require.NotZero(ht, waitingClose.LimboBalance,
		"all funds should still be in limbo")

	// Create a map of outpoints to expected resolutions for alice and
	// carol which we will add reports to as we sweep outputs.
	var (
		aliceReports = make(map[string]*lnrpc.Resolution)
		carolReports = make(map[string]*lnrpc.Resolution)
	)

	// The several restarts in this test are intended to ensure that when a
	// channel is force-closed, the contract court has persisted the state
	// of the channel in the closure process and will recover the correct
	// state when the system comes back on line. This restart tests state
	// persistence at the beginning of the process, when the commitment
	// transaction has been broadcast but not yet confirmed in a block.
	ht.RestartNode(alice)

	// We expect to see Alice's force close tx in the mempool.
	ht.AssertNumTxsInMempool(1)

	// Mine a block which should confirm the commitment transaction
	// broadcast as a result of the force closure. Once mined, we also
	// expect Alice's anchor sweeping tx being published.
	ht.MineBlocksAndAssertNumTxes(1, 1)

	// Assert Alice's has one pending anchor output - because she doesn't
	// have incoming HTLCs, her outgoing HTLC won't have a deadline, thus
	// she won't use the anchor to perform CPFP.
	aliceAnchor := ht.AssertNumPendingSweeps(alice, 1)[0]
	require.Equal(ht, aliceAnchor.Outpoint.TxidStr,
		waitingClose.Commitments.LocalTxid)

	// Now that the commitment has been confirmed, the channel should be
	// marked as force closed.
	err := wait.NoError(func() error {
		forceClose := ht.AssertChannelPendingForceClose(
			alice, chanPoint,
		)

		// Now that the channel has been force closed, it should now
		// have the height and number of blocks to confirm populated.
		err := checkCommitmentMaturity(
			forceClose, commCsvMaturityHeight, int32(defaultCSV),
		)
		if err != nil {
			return err
		}

		// None of our outputs have been swept, so they should all be
		// in limbo.
		if forceClose.LimboBalance == 0 {
			return errors.New("all funds should still be in limbo")
		}
		if forceClose.RecoveredBalance != 0 {
			return errors.New("no funds should be recovered")
		}

		return nil
	}, defaultTimeout)
	require.NoError(ht, err, "timeout while checking force closed channel")

	// The following restart is intended to ensure that outputs from the
	// force close commitment transaction have been persisted once the
	// transaction has been confirmed, but before the outputs are
	// spendable.
	ht.RestartNode(alice)

	// Carol should offer her commit and anchor outputs to the sweeper.
	sweepTxns := ht.AssertNumPendingSweeps(carol, 2)

	// Identify Carol's pending sweeps.
	var carolAnchor, carolCommit = sweepTxns[0], sweepTxns[1]
	if carolAnchor.AmountSat != uint32(anchorSize) {
		carolAnchor, carolCommit = carolCommit, carolAnchor
	}

	// Carol's sweep tx should be in the mempool already, as her output is
	// not timelocked. This sweep tx should spend her to_local output as
	// the anchor output is not economical to spend.
	carolTx := ht.GetNumTxsFromMempool(1)[0]

	// Carol's sweeping tx should have 1-input-1-output shape.
	require.Len(ht, carolTx.TxIn, 1)
	require.Len(ht, carolTx.TxOut, 1)

	// Calculate the total fee Carol paid.
	totalFeeCarol := ht.CalculateTxFee(carolTx)

	// Carol's anchor report won't be created since it's uneconomical to
	// sweep. So we expect to see only the commit sweep report.
	op := fmt.Sprintf("%v:%v", carolCommit.Outpoint.TxidStr,
		carolCommit.Outpoint.OutputIndex)
	carolReports[op] = &lnrpc.Resolution{
		ResolutionType: lnrpc.ResolutionType_COMMIT,
		Outcome:        lnrpc.ResolutionOutcome_CLAIMED,
		Outpoint:       carolCommit.Outpoint,
		AmountSat:      uint64(pushAmt),
		SweepTxid:      carolTx.TxHash().String(),
	}

	// Currently within the codebase, the default CSV is 4 relative blocks.
	// For the persistence test, we generate two blocks, then trigger a
	// restart and then generate the final block that should trigger the
	// creation of the sweep transaction.
	//
	// We also expect Carol to broadcast her sweeping tx which spends her
	// commit and anchor outputs.
	ht.MineBlocksAndAssertNumTxes(1, 1)

	// Alice should still have the anchor sweeping request.
	ht.AssertNumPendingSweeps(alice, 1)

	// The following restart checks to ensure that outputs in the contract
	// court are persisted while waiting for the required number of
	// confirmations to be reported.
	ht.RestartNode(alice)

	// Alice should see the channel in her set of pending force closed
	// channels with her funds still in limbo.
	var aliceBalance int64
	var closingTxID *chainhash.Hash
	err = wait.NoError(func() error {
		forceClose := ht.AssertChannelPendingForceClose(
			alice, chanPoint,
		)

		// Get the closing txid.
		txid, err := chainhash.NewHashFromStr(forceClose.ClosingTxid)
		if err != nil {
			return err
		}
		closingTxID = txid

		// Make a record of the balances we expect for alice and carol.
		aliceBalance = forceClose.Channel.LocalBalance

		// At this point, the nursery should show that the commitment
		// output has 3 block left before its CSV delay expires. In
		// total, we have mined exactly defaultCSV blocks, so the htlc
		// outputs should also reflect that this many blocks have
		// passed.
		err = checkCommitmentMaturity(
			forceClose, commCsvMaturityHeight, 3,
		)
		if err != nil {
			return err
		}

		// All funds should still be shown in limbo.
		if forceClose.LimboBalance == 0 {
			return errors.New("all funds should still be in " +
				"limbo")
		}
		if forceClose.RecoveredBalance != 0 {
			return errors.New("no funds should be recovered")
		}

		return nil
	}, defaultTimeout)
	require.NoError(ht, err, "timeout while checking force closed channel")

	// Generate two blocks, which should cause the CSV delayed output from
	// the commitment txn to expire.
	ht.MineBlocks(2)

	// At this point, the CSV will expire in the next block, meaning that
	// the output should be offered to the sweeper.
	sweeps := ht.AssertNumPendingSweeps(alice, 2)
	commitSweep, anchorSweep := sweeps[0], sweeps[1]
	if commitSweep.AmountSat < anchorSweep.AmountSat {
		commitSweep, anchorSweep = anchorSweep, commitSweep
	}

	// Mine one block and the sweeping transaction should now be broadcast.
	// So we fetch the node's mempool to ensure it has been properly
	// broadcast.
	sweepingTXID := ht.AssertNumTxsInMempool(1)[0]

	// Fetch the sweep transaction, all input it's spending should be from
	// the commitment transaction which was broadcast on-chain.
	sweepTx := ht.GetRawTransaction(sweepingTXID)
	for _, txIn := range sweepTx.MsgTx().TxIn {
		require.Equal(ht, &txIn.PreviousOutPoint.Hash, closingTxID,
			"sweep transaction not spending from commit")
	}

	// For neutrino backend, due to it has no mempool, we need to check the
	// sweep tx has already been saved to db before restarting. This is due
	// to the possible race,
	// - the fee bumper returns a TxPublished event, which is received by
	//   the sweeper and the sweep tx is saved to db.
	// - the sweeper receives a shutdown signal before it receives the
	//   above event.
	//
	// TODO(yy): fix the above race.
	if ht.IsNeutrinoBackend() {
		// Check that we can find the commitment sweep in our set of
		// known sweeps, using the simple transaction id ListSweeps
		// output.
		ht.AssertSweepFound(alice, sweepingTXID.String(), false, 0)
	}

	// Restart Alice to ensure that she resumes watching the finalized
	// commitment sweep txid.
	ht.RestartNode(alice)

	// Alice's anchor report won't be created since it's uneconomical to
	// sweep. We expect a resolution which spends our commit output.
	op = fmt.Sprintf("%v:%v", commitSweep.Outpoint.TxidStr,
		commitSweep.Outpoint.OutputIndex)
	aliceReports[op] = &lnrpc.Resolution{
		ResolutionType: lnrpc.ResolutionType_COMMIT,
		Outcome:        lnrpc.ResolutionOutcome_CLAIMED,
		SweepTxid:      sweepingTXID.String(),
		Outpoint:       commitSweep.Outpoint,
		AmountSat:      uint64(aliceBalance),
	}

	// Check that we can find the commitment sweep in our set of known
	// sweeps, using the simple transaction id ListSweeps output.
	ht.AssertSweepFound(alice, sweepingTXID.String(), false, 0)

	// Next, we mine an additional block which should include the sweep
	// transaction as the input scripts and the sequence locks on the
	// inputs should be properly met.
	ht.MineBlocksAndAssertNumTxes(1, 1)

	// Update current height
	curHeight = int32(ht.CurrentHeight())

	// checkForceClosedChannelNumHtlcs verifies that a force closed channel
	// has the proper number of htlcs.
	checkPendingChannelNumHtlcs := func(
		forceClose lntest.PendingForceClose) error {

		if len(forceClose.PendingHtlcs) != numInvoices {
			return fmt.Errorf("expected force closed channel to "+
				"have %d pending htlcs, found %d instead",
				numInvoices, len(forceClose.PendingHtlcs))
		}

		return nil
	}

	err = wait.NoError(func() error {
		// Now that the commit output has been fully swept, check to
		// see that the channel remains open for the pending htlc
		// outputs.
		forceClose := ht.AssertChannelPendingForceClose(
			alice, chanPoint,
		)

		// The commitment funds will have been recovered after the
		// commit txn was included in the last block. The htlc funds
		// will be shown in limbo.
		err := checkPendingChannelNumHtlcs(forceClose)
		if err != nil {
			return err
		}

		err = checkPendingHtlcStageAndMaturity(
			forceClose, 1, htlcExpiryHeight,
			int32(htlcExpiryHeight)-curHeight,
		)
		if err != nil {
			return err
		}

		if forceClose.LimboBalance == 0 {
			return fmt.Errorf("expected funds in limbo, found 0")
		}

		return nil
	}, defaultTimeout)
	require.NoError(ht, err, "timeout checking pending force close channel")

	// Compute the height preceding that which will cause the htlc CLTV
	// timeouts will expire. The outputs entered at the same height as the
	// output spending from the commitment txn, so we must deduct the
	// number of blocks we have generated since adding it to the nursery,
	// and take an additional block off so that we end up one block shy of
	// the expiry height, and add the block padding.
	currentHeight := int32(ht.CurrentHeight())
	cltvHeightDelta := int(htlcExpiryHeight - uint32(currentHeight) - 1)

	// Advance the blockchain until just before the CLTV expires, nothing
	// exciting should have happened during this time.
	ht.MineBlocks(cltvHeightDelta)

	// We now restart Alice, to ensure that she will broadcast the
	// presigned htlc timeout txns after the delay expires after
	// experiencing a while waiting for the htlc outputs to incubate.
	ht.RestartNode(alice)

	// Alice should now see the channel in her set of pending force closed
	// channels with one pending HTLC.
	err = wait.NoError(func() error {
		forceClose := ht.AssertChannelPendingForceClose(
			alice, chanPoint,
		)

		// We should now be at the block just before the utxo nursery
		// will attempt to broadcast the htlc timeout transactions.
		err = checkPendingChannelNumHtlcs(forceClose)
		if err != nil {
			return err
		}
		err = checkPendingHtlcStageAndMaturity(
			forceClose, 1, htlcExpiryHeight, 1,
		)
		if err != nil {
			return err
		}

		// Now that our commitment confirmation depth has been
		// surpassed, we should now see a non-zero recovered balance.
		// All htlc outputs are still left in limbo, so it should be
		// non-zero as well.
		if forceClose.LimboBalance == 0 {
			return errors.New("htlc funds should still be in limbo")
		}

		return nil
	}, defaultTimeout)
	require.NoError(ht, err, "timeout while checking force closed channel")

	// Now, generate the block which will cause Alice to offer the
	// presigned htlc timeout txns to the sweeper.
	ht.MineBlocks(1)

	// Since Alice had numInvoices (6) htlcs extended to Carol before force
	// closing, we expect Alice to broadcast an htlc timeout txn for each
	// one. We also expect Alice to still have her anchor since it's not
	// swept.
	ht.AssertNumPendingSweeps(alice, numInvoices+1)

	// Wait for them all to show up in the mempool
	htlcTxIDs := ht.AssertNumTxsInMempool(1)

	// Retrieve each htlc timeout txn from the mempool, and ensure it is
	// well-formed. The sweeping tx should spend all the htlc outputs.
	//
	// NOTE: We also add 1 output as the outgoing HTLC is swept using twice
	// its value as its budget, so a wallet utxo is used.
	numInputs := 6 + 1

	// Construct a map of the already confirmed htlc timeout outpoints,
	// that will count the number of times each is spent by the sweep txn.
	// We prepopulate it in this way so that we can later detect if we are
	// spending from an output that was not a confirmed htlc timeout txn.
	var htlcTxOutpointSet = make(map[wire.OutPoint]int)

	var htlcLessFees uint64

	//nolint:ll
	for _, htlcTxID := range htlcTxIDs {
		// Fetch the sweep transaction, all input it's spending should
		// be from the commitment transaction which was broadcast
		// on-chain. In case of an anchor type channel, we expect one
		// extra input that is not spending from the commitment, that
		// is added for fees.
		htlcTx := ht.GetRawTransaction(htlcTxID)

		// Ensure the htlc transaction has the expected number of
		// inputs.
		inputs := htlcTx.MsgTx().TxIn
		require.Len(ht, inputs, numInputs, "num inputs mismatch")

		// The number of outputs should be the same.
		outputs := htlcTx.MsgTx().TxOut
		require.Len(ht, outputs, numInputs, "num outputs mismatch")

		// Ensure all the htlc transaction inputs are spending from the
		// commitment transaction, except if this is an extra input
		// added to pay for fees for anchor channels.
		nonCommitmentInputs := 0
		for i, txIn := range inputs {
			if !closingTxID.IsEqual(&txIn.PreviousOutPoint.Hash) {
				nonCommitmentInputs++

				require.Lessf(ht, nonCommitmentInputs, 2,
					"htlc transaction not "+
						"spending from commit "+
						"tx %v, instead spending %v",
					closingTxID, txIn.PreviousOutPoint)

				// This was an extra input added to pay fees,
				// continue to the next one.
				continue
			}

			// For each htlc timeout transaction, we expect a
			// resolver report recording this on chain resolution
			// for both alice and carol.
			outpoint := txIn.PreviousOutPoint
			resolutionOutpoint := &lnrpc.OutPoint{
				TxidBytes:   outpoint.Hash[:],
				TxidStr:     outpoint.Hash.String(),
				OutputIndex: outpoint.Index,
			}

			// We expect alice to have a timeout tx resolution with
			// an amount equal to the payment amount.
			//nolint:ll
			aliceReports[outpoint.String()] = &lnrpc.Resolution{
				ResolutionType: lnrpc.ResolutionType_OUTGOING_HTLC,
				Outcome:        lnrpc.ResolutionOutcome_FIRST_STAGE,
				SweepTxid:      htlcTx.Hash().String(),
				Outpoint:       resolutionOutpoint,
				AmountSat:      uint64(paymentAmt),
			}

			// We expect carol to have a resolution with an
			// incoming htlc timeout which reflects the full amount
			// of the htlc. It has no spend tx, because carol stops
			// monitoring the htlc once it has timed out.
			//nolint:ll
			carolReports[outpoint.String()] = &lnrpc.Resolution{
				ResolutionType: lnrpc.ResolutionType_INCOMING_HTLC,
				Outcome:        lnrpc.ResolutionOutcome_TIMEOUT,
				SweepTxid:      "",
				Outpoint:       resolutionOutpoint,
				AmountSat:      uint64(paymentAmt),
			}

			// Recorf the HTLC outpoint, such that we can later
			// check whether it gets swept
			op := wire.OutPoint{
				Hash:  htlcTxID,
				Index: uint32(i),
			}
			htlcTxOutpointSet[op] = 0
		}

		// We record the htlc amount less fees here, so that we know
		// what value to expect for the second stage of our htlc
		// resolution.
		htlcLessFees = uint64(outputs[0].Value)
	}

	// With the htlc timeout txns still in the mempool, we restart Alice to
	// verify that she can resume watching the htlc txns she broadcasted
	// before crashing.
	ht.RestartNode(alice)

	// Generate a block that mines the htlc timeout txns. Doing so now
	// activates the 2nd-stage CSV delayed outputs.
	ht.MineBlocksAndAssertNumTxes(1, 1)

	// Alice is restarted here to ensure that her contract court properly
	// handles the 2nd-stage sweeps after the htlc timeout txns were
	// confirmed.
	ht.RestartNode(alice)

	// Advance the chain until just before the 2nd-layer CSV delays expire.
	// For anchor channels this is one block earlier.
	currentHeight = int32(ht.CurrentHeight())
	ht.Logf("current height: %v, htlcCsvMaturityHeight=%v", currentHeight,
		htlcCsvMaturityHeight)
	numBlocks := int(htlcCsvMaturityHeight - uint32(currentHeight) - 1)
	ht.MineBlocks(numBlocks)

	ht.AssertNumPendingSweeps(alice, numInvoices+1)

	// Restart Alice to ensure that she can recover from a failure.
	//
	// TODO(yy): Skip this step for neutrino as it cannot recover the
	// sweeping txns from the mempool. We need to also store the txns in
	// the sweeper store to make it work for the neutrino case.
	if !ht.IsNeutrinoBackend() {
		ht.RestartNode(alice)
	}

	// Now that the channel has been fully swept, it should no longer show
	// incubated, check to see that Alice's node still reports the channel
	// as pending force closed.
	err = wait.NoError(func() error {
		forceClose := ht.AssertChannelPendingForceClose(
			alice, chanPoint,
		)

		if forceClose.LimboBalance == 0 {
			return fmt.Errorf("htlc funds should still be in limbo")
		}

		return checkPendingChannelNumHtlcs(forceClose)
	}, defaultTimeout)
	require.NoError(ht, err, "timeout while checking force closed channel")

	ht.AssertNumPendingSweeps(alice, numInvoices+1)

	// Wait for the single sweep txn to appear in the mempool.
	htlcSweepTxid := ht.AssertNumTxsInMempool(1)[0]

	// Fetch the htlc sweep transaction from the mempool.
	htlcSweepTx := ht.GetRawTransaction(htlcSweepTxid)

	// Ensure the htlc sweep transaction only has one input for each htlc
	// Alice extended before force closing.
	require.Len(ht, htlcSweepTx.MsgTx().TxIn, numInvoices,
		"htlc transaction has wrong num of inputs")
	require.Len(ht, htlcSweepTx.MsgTx().TxOut, 1,
		"htlc sweep transaction should have one output")

	// Ensure that each output spends from exactly one htlc timeout output.
	for _, txIn := range htlcSweepTx.MsgTx().TxIn {
		outpoint := txIn.PreviousOutPoint

		// Check that the input is a confirmed htlc timeout txn.
		_, ok := htlcTxOutpointSet[outpoint]
		require.Truef(ht, ok, "htlc sweep output not spending from "+
			"htlc tx, instead spending output %v", outpoint)

		// Increment our count for how many times this output was spent.
		htlcTxOutpointSet[outpoint]++

		// Check that each is only spent once.
		require.Lessf(ht, htlcTxOutpointSet[outpoint], 2,
			"htlc sweep tx has multiple spends from "+
				"outpoint %v", outpoint)

		// Since we have now swept our htlc timeout tx, we expect to
		// have timeout resolutions for each of our htlcs.
		output := txIn.PreviousOutPoint
		aliceReports[output.String()] = &lnrpc.Resolution{
			ResolutionType: lnrpc.ResolutionType_OUTGOING_HTLC,
			Outcome:        lnrpc.ResolutionOutcome_TIMEOUT,
			SweepTxid:      htlcSweepTx.Hash().String(),
			Outpoint: &lnrpc.OutPoint{
				TxidBytes:   output.Hash[:],
				TxidStr:     output.Hash.String(),
				OutputIndex: output.Index,
			},
			AmountSat: htlcLessFees,
		}
	}

	// Check that each HTLC output was spent exactly once.
	for op, num := range htlcTxOutpointSet {
		require.Equalf(ht, 1, num,
			"HTLC outpoint:%s was spent times", op)
	}

	// Check that we can find the htlc sweep in our set of sweeps using
	// the verbose output of the listsweeps output.
	ht.AssertSweepFound(alice, htlcSweepTxid.String(), true, 0)

	// The following restart checks to ensure that the sweeper is storing
	// the txid of the previously broadcast htlc sweep txn, and that it
	// begins watching that txid after restarting.
	ht.RestartNode(alice)

	// Now that the channel has been fully swept, it should no longer show
	// incubated, check to see that Alice's node still reports the channel
	// as pending force closed.
	err = wait.NoError(func() error {
		forceClose := ht.AssertChannelPendingForceClose(
			alice, chanPoint,
		)
		err := checkPendingChannelNumHtlcs(forceClose)
		if err != nil {
			return err
		}

		err = checkPendingHtlcStageAndMaturity(
			forceClose, 2, htlcCsvMaturityHeight-1, 0,
		)
		if err != nil {
			return err
		}

		return nil
	}, defaultTimeout)
	require.NoError(ht, err, "timeout while checking force closed channel")

	// Generate the final block that sweeps all htlc funds into the user's
	// wallet, and make sure the sweep is in this block.
	block := ht.MineBlocksAndAssertNumTxes(1, 1)[0]
	ht.AssertTxInBlock(block, htlcSweepTxid)

	// Now that the channel has been fully swept, it should no longer show
	// up within the pending channels RPC.
	err = wait.NoError(func() error {
		ht.AssertNumPendingForceClose(alice, 0)
		// In addition to there being no pending channels, we verify
		// that pending channels does not report any money still in
		// limbo.
		pendingChanResp := alice.RPC.PendingChannels()
		if pendingChanResp.TotalLimboBalance != 0 {
			return errors.New("no user funds should be left " +
				"in limbo after incubation")
		}

		return nil
	}, defaultTimeout)
	require.NoError(ht, err, "timeout checking limbo balance")

	// At this point, Carol should now be aware of her new immediately
	// spendable on-chain balance, as it was Alice who broadcast the
	// commitment transaction.
	carolBalResp = carol.RPC.WalletBalance()

	// Carol's expected balance should be its starting balance plus the
	// push amount sent by Alice and minus the miner fee paid.
	carolExpectedBalance := btcutil.Amount(carolStartingBalance) +
		pushAmt - totalFeeCarol

	require.Equal(ht, carolExpectedBalance,
		btcutil.Amount(carolBalResp.ConfirmedBalance),
		"carol's balance is incorrect")

	// Finally, we check that alice and carol have the set of resolutions
	// we expect.
	assertReports(ht, alice, chanPoint, aliceReports)
	assertReports(ht, carol, chanPoint, carolReports)
}

// padCLTV is a small helper function that pads a cltv value with a block
// padding.
func padCLTV(cltv uint32) uint32 {
	return cltv + uint32(routing.BlockPadding)
}

// testFailingChannel tests that we will fail the channel by force closing it
// in the case where a counterparty tries to settle an HTLC with the wrong
// preimage.
func testFailingChannel(ht *lntest.HarnessTest) {
	chanAmt := lnd.MaxFundingAmount

	// We'll introduce Carol, which will settle any incoming invoice with a
	// totally unrelated preimage.
	carol := ht.NewNode("Carol", []string{"--hodl.bogus-settle"})

	alice := ht.NewNodeWithCoins("Alice", nil)
	ht.ConnectNodes(alice, carol)

	// Let Alice connect and open a channel to Carol,
	ht.OpenChannel(alice, carol, lntest.OpenChannelParams{Amt: chanAmt})

	// With the channel open, we'll create a invoice for Carol that Alice
	// will attempt to pay.
	preimage := bytes.Repeat([]byte{byte(192)}, 32)
	invoice := &lnrpc.Invoice{
		Memo:      "testing",
		RPreimage: preimage,
		Value:     invoiceAmt,
	}
	resp := carol.RPC.AddInvoice(invoice)

	// Send the payment from Alice to Carol. We expect Carol to attempt to
	// settle this payment with the wrong preimage.
	//
	// NOTE: cannot use `CompletePaymentRequestsNoWait` here as the channel
	// will be force closed, so the num of updates check in that function
	// won't work as the channel cannot be found.
	req := &routerrpc.SendPaymentRequest{
		PaymentRequest: resp.PaymentRequest,
		TimeoutSeconds: 60,
		FeeLimitMsat:   noFeeLimitMsat,
	}
	ht.SendPaymentAndAssertStatus(alice, req, lnrpc.Payment_IN_FLIGHT)

	// Since Alice detects that Carol is trying to trick her by providing a
	// fake preimage, she should fail and force close the channel.
	ht.AssertNumWaitingClose(alice, 1)

	// Mine a block to confirm the broadcasted commitment.
	block := ht.MineBlocksAndAssertNumTxes(1, 1)[0]
	require.Len(ht, block.Transactions, 2, "transaction wasn't mined")

	// The channel should now show up as force closed both for Alice and
	// Carol.
	ht.AssertNumPendingForceClose(alice, 1)
	ht.AssertNumPendingForceClose(carol, 1)

	// Carol will use the correct preimage to resolve the HTLC on-chain.
	ht.AssertNumPendingSweeps(carol, 1)

	// Mine a block to trigger the sweep. This is needed because the
	// preimage extraction logic from the link is not managed by the
	// blockbeat, which means the preimage may be sent to the contest
	// resolver after it's launched.
	//
	// TODO(yy): Expose blockbeat to the link layer.
	ht.MineEmptyBlocks(1)

	// Carol should have broadcast her sweeping tx.
	ht.AssertNumTxsInMempool(1)

	// Mine two blocks to confirm Carol's sweeping tx, which will by now
	// Alice's commit output should be offered to her sweeper.
	ht.MineBlocksAndAssertNumTxes(2, 1)

	// Alice's should have one pending sweep request for her commit output.
	ht.AssertNumPendingSweeps(alice, 1)

	// Mine Alice's sweeping tx.
	ht.MineBlocksAndAssertNumTxes(1, 1)

	// No pending channels should be left.
	ht.AssertNumPendingForceClose(alice, 0)
}

// assertReports checks that the count of resolutions we have present per
// type matches a set of expected resolutions.
//
// NOTE: only used in current test file.
func assertReports(ht *lntest.HarnessTest, hn *node.HarnessNode,
	chanPoint *lnrpc.ChannelPoint, expected map[string]*lnrpc.Resolution) {

	op := ht.OutPointFromChannelPoint(chanPoint)

	// Get our node's closed channels.
	req := &lnrpc.ClosedChannelsRequest{Abandoned: false}
	closed := hn.RPC.ClosedChannels(req)

	var resolutions []*lnrpc.Resolution
	for _, close := range closed.Channels {
		if close.ChannelPoint == op.String() {
			resolutions = close.Resolutions
			break
		}
	}
	require.NotNil(ht, resolutions)

	// Copy the expected resolutions so we can remove them as we find them.
	notFound := make(map[string]*lnrpc.Resolution)
	for k, v := range expected {
		notFound[k] = v
	}

	for _, res := range resolutions {
		outPointStr := fmt.Sprintf("%v:%v", res.Outpoint.TxidStr,
			res.Outpoint.OutputIndex)

		require.Contains(ht, expected, outPointStr)
		require.Equal(ht, expected[outPointStr], res)

		delete(notFound, outPointStr)
	}

	// We should have found all the resolutions.
	require.Empty(ht, notFound)
}

// checkCommitmentMaturity checks that both the maturity height and blocks
// maturity height are as expected.
//
// NOTE: only used in current test file.
func checkCommitmentMaturity(forceClose lntest.PendingForceClose,
	maturityHeight uint32, blocksTilMaturity int32) error {

	if forceClose.MaturityHeight != maturityHeight {
		return fmt.Errorf("expected commitment maturity height to be "+
			"%d, found %d instead", maturityHeight,
			forceClose.MaturityHeight)
	}
	if forceClose.BlocksTilMaturity != blocksTilMaturity {
		return fmt.Errorf("expected commitment blocks til maturity to "+
			"be %d, found %d instead", blocksTilMaturity,
			forceClose.BlocksTilMaturity)
	}

	return nil
}

// checkPendingHtlcStageAndMaturity uniformly tests all pending htlc's belonging
// to a force closed channel, testing for the expected stage number, blocks till
// maturity, and the maturity height.
//
// NOTE: only used in current test file.
func checkPendingHtlcStageAndMaturity(
	forceClose *lnrpc.PendingChannelsResponse_ForceClosedChannel,
	stage, maturityHeight uint32, blocksTillMaturity int32) error {

	for _, pendingHtlc := range forceClose.PendingHtlcs {
		if pendingHtlc.Stage != stage {
			return fmt.Errorf("expected pending htlc to be stage "+
				"%d, found %d", stage, pendingHtlc.Stage)
		}
		if pendingHtlc.MaturityHeight != maturityHeight {
			return fmt.Errorf("expected pending htlc maturity "+
				"height to be %d, instead has %d",
				maturityHeight, pendingHtlc.MaturityHeight)
		}
		if pendingHtlc.BlocksTilMaturity != blocksTillMaturity {
			return fmt.Errorf("expected pending htlc blocks til "+
				"maturity to be %d, instead has %d",
				blocksTillMaturity,
				pendingHtlc.BlocksTilMaturity)
		}
	}

	return nil
}