Merge pull request #4592 from joostjager/sweep-deadline

cnct+sweep: cpfp-aware anchor sweeping

breacharbiter.go

@@ -914,6 +914,11 @@ func (bo *breachedOutput) HeightHint() uint32 {
 	return bo.confHeight
 }
 
+// UnconfParent returns information about a possibly unconfirmed parent tx.
+func (bo *breachedOutput) UnconfParent() *input.TxInfo {
+	return nil
+}
+
 // Add compile-time constraint ensuring breachedOutput implements the Input
 // interface.
 var _ input.Input = (*breachedOutput)(nil)

contractcourt/anchor_resolver.go

@@ -89,6 +89,9 @@ func (c *anchorResolver) Resolve() (ContractResolver, error) {
 	// An exclusive group is not necessary anymore, because we know that
 	// this is the only anchor that can be swept.
 	//
+	// We also clear the parent tx information for cpfp, because the
+	// commitment tx is confirmed.
+	//
 	// After a restart or when the remote force closes, the sweeper is not
 	// yet aware of the anchor. In that case, it will be added as new input
 	// to the sweeper.
@@ -99,6 +102,7 @@ func (c *anchorResolver) Resolve() (ContractResolver, error) {
 		input.CommitmentAnchor,
 		&c.anchorSignDescriptor,
 		c.broadcastHeight,
+		nil,
 	)
 
 	resultChan, err := c.Sweeper.SweepInput(

contractcourt/channel_arbitrator.go

@@ -30,6 +30,12 @@ var (
 		"process of being force closed")
 )
 
+const (
+	// anchorSweepConfTarget is the conf target used when sweeping
+	// commitment anchors.
+	anchorSweepConfTarget = 6
+)
+
 // WitnessSubscription represents an intent to be notified once new witnesses
 // are discovered by various active contract resolvers. A contract resolver may
 // use this to be notified of when it can satisfy an incoming contract after we
@@ -1060,9 +1066,6 @@ func (c *ChannelArbitrator) sweepAnchors(anchors []*lnwallet.AnchorResolution,
 	// anchors from being batched together.
 	exclusiveGroup := c.cfg.ShortChanID.ToUint64()
 
-	// Retrieve the current minimum fee rate from the sweeper.
-	minFeeRate := c.cfg.Sweeper.RelayFeePerKW()
-
 	for _, anchor := range anchors {
 		log.Debugf("ChannelArbitrator(%v): pre-confirmation sweep of "+
 			"anchor of tx %v", c.cfg.ChanPoint, anchor.CommitAnchor)
@@ -1073,18 +1076,25 @@ func (c *ChannelArbitrator) sweepAnchors(anchors []*lnwallet.AnchorResolution,
 			input.CommitmentAnchor,
 			&anchor.AnchorSignDescriptor,
 			heightHint,
+			&input.TxInfo{
+				Fee:    anchor.CommitFee,
+				Weight: anchor.CommitWeight,
+			},
 		)
 
-		// Sweep anchor output with the minimum fee rate. This usually
-		// (up to a min relay fee of 3 sat/b) means that the anchor
-		// sweep will be economical. Also signal that this is a force
-		// sweep. If the user decides to bump the fee on the anchor
-		// sweep, it will be swept even if it isn't economical.
+		// Sweep anchor output with a confirmation target fee
+		// preference. Because this is a cpfp-operation, the anchor will
+		// only be attempted to sweep when the current fee estimate for
+		// the confirmation target exceeds the commit fee rate.
+		//
+		// Also signal that this is a force sweep, so that the anchor
+		// will be swept even if it isn't economical purely based on the
+		// anchor value.
 		_, err := c.cfg.Sweeper.SweepInput(
 			&anchorInput,
 			sweep.Params{
 				Fee: sweep.FeePreference{
-					FeeRate: minFeeRate,
+					ConfTarget: anchorSweepConfTarget,
 				},
 				Force:          true,
 				ExclusiveGroup: &exclusiveGroup,

input/input.go

@@ -3,6 +3,7 @@ package input
 import (
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
+	"github.com/btcsuite/btcutil"
 )
 
 // Input represents an abstract UTXO which is to be spent using a sweeping
@@ -41,6 +42,19 @@ type Input interface {
 	// HeightHint returns the minimum height at which a confirmed spending
 	// tx can occur.
 	HeightHint() uint32
+
+	// UnconfParent returns information about a possibly unconfirmed parent
+	// tx.
+	UnconfParent() *TxInfo
+}
+
+// TxInfo describes properties of a parent tx that are relevant for CPFP.
+type TxInfo struct {
+	// Fee is the fee of the tx.
+	Fee btcutil.Amount
+
+	// Weight is the weight of the tx.
+	Weight int64
 }
 
 type inputKit struct {
@@ -49,6 +63,10 @@ type inputKit struct {
 	signDesc        SignDescriptor
 	heightHint      uint32
 	blockToMaturity uint32
+
+	// unconfParent contains information about a potential unconfirmed
+	// parent transaction.
+	unconfParent *TxInfo
 }
 
 // OutPoint returns the breached output's identifier that is to be included as
@@ -82,6 +100,11 @@ func (i *inputKit) BlocksToMaturity() uint32 {
 	return i.blockToMaturity
 }
 
+// Cpfp returns information about a possibly unconfirmed parent tx.
+func (i *inputKit) UnconfParent() *TxInfo {
+	return i.unconfParent
+}
+
 // BaseInput contains all the information needed to sweep a basic output
 // (CSV/CLTV/no time lock)
 type BaseInput struct {
@@ -91,14 +114,16 @@ type BaseInput struct {
 // MakeBaseInput assembles a new BaseInput that can be used to construct a
 // sweep transaction.
 func MakeBaseInput(outpoint *wire.OutPoint, witnessType WitnessType,
-	signDescriptor *SignDescriptor, heightHint uint32) BaseInput {
+	signDescriptor *SignDescriptor, heightHint uint32,
+	unconfParent *TxInfo) BaseInput {
 
 	return BaseInput{
 		inputKit{
-			outpoint:    *outpoint,
-			witnessType: witnessType,
-			signDesc:    *signDescriptor,
-			heightHint:  heightHint,
+			outpoint:     *outpoint,
+			witnessType:  witnessType,
+			signDesc:     *signDescriptor,
+			heightHint:   heightHint,
+			unconfParent: unconfParent,
 		},
 	}
 }
@@ -109,7 +134,7 @@ func NewBaseInput(outpoint *wire.OutPoint, witnessType WitnessType,
 	signDescriptor *SignDescriptor, heightHint uint32) *BaseInput {
 
 	input := MakeBaseInput(
-		outpoint, witnessType, signDescriptor, heightHint,
+		outpoint, witnessType, signDescriptor, heightHint, nil,
 	)
 
 	return &input

lntest/itest/lnd_channel_backup_test.go

@@ -368,6 +368,10 @@ func testChannelBackupRestore(net *lntest.NetworkHarness, t *harnessTest) {
 	for _, testCase := range testCases {
 		success := t.t.Run(testCase.name, func(t *testing.T) {
 			h := newHarnessTest(t, net)
+
+			// Start each test with the default static fee estimate.
+			net.SetFeeEstimate(12500)
+
 			testChanRestoreScenario(h, net, &testCase, password)
 		})
 		if !success {

lntest/itest/lnd_multi-hop_htlc_local_chain_claim_test.go

@@ -96,6 +96,10 @@ func testMultiHopHtlcLocalChainClaim(net *lntest.NetworkHarness, t *harnessTest,
 	// hop logic.
 	waitForInvoiceAccepted(t, carol, payHash)
 
+	// Increase the fee estimate so that the following force close tx will
+	// be cpfp'ed.
+	net.SetFeeEstimate(30000)
+
 	// At this point, Bob decides that he wants to exit the channel
 	// immediately, so he force closes his commitment transaction.
 	ctxt, _ = context.WithTimeout(ctxb, channelCloseTimeout)

lntest/itest/lnd_multi-hop_htlc_local_timeout_test.go

@@ -105,6 +105,10 @@ func testMultiHopHtlcLocalTimeout(net *lntest.NetworkHarness, t *harnessTest,
 		t.Fatalf("htlc mismatch: %v", predErr)
 	}
 
+	// Increase the fee estimate so that the following force close tx will
+	// be cpfp'ed.
+	net.SetFeeEstimate(30000)
+
 	// We'll now mine enough blocks to trigger Bob's broadcast of his
 	// commitment transaction due to the fact that the HTLC is about to
 	// timeout. With the default outgoing broadcast delta of zero, this will

lntest/itest/lnd_multi-hop_htlc_receiver_chain_claim_test.go

@@ -117,6 +117,10 @@ func testMultiHopReceiverChainClaim(net *lntest.NetworkHarness, t *harnessTest,
 		t.Fatalf("settle invoice: %v", err)
 	}
 
+	// Increase the fee estimate so that the following force close tx will
+	// be cpfp'ed.
+	net.SetFeeEstimate(30000)
+
 	// Now we'll mine enough blocks to prompt carol to actually go to the
 	// chain in order to sweep her HTLC since the value is high enough.
 	// TODO(roasbeef): modify once go to chain policy changes

lntest/itest/lnd_multi-hop_htlc_remote_chain_claim_test.go

@@ -96,6 +96,10 @@ func testMultiHopHtlcRemoteChainClaim(net *lntest.NetworkHarness, t *harnessTest
 	// hop logic.
 	waitForInvoiceAccepted(t, carol, payHash)
 
+	// Increase the fee estimate so that the following force close tx will
+	// be cpfp'ed.
+	net.SetFeeEstimate(30000)
+
 	// Next, Alice decides that she wants to exit the channel, so she'll
 	// immediately force close the channel by broadcast her commitment
 	// transaction.

lntest/itest/lnd_multi-hop_local_force_close_on_chain_htlc_timeout_test.go

@@ -79,6 +79,10 @@ func testMultiHopLocalForceCloseOnChainHtlcTimeout(net *lntest.NetworkHarness,
 		t.Fatalf("htlc mismatch: %v", err)
 	}
 
+	// Increase the fee estimate so that the following force close tx will
+	// be cpfp'ed.
+	net.SetFeeEstimate(30000)
+
 	// Now that all parties have the HTLC locked in, we'll immediately
 	// force close the Bob -> Carol channel. This should trigger contract
 	// resolution mode for both of them.

lntest/itest/lnd_multi-hop_remote_force_close_on_chain_htlc_timeout_test.go

@@ -80,6 +80,10 @@ func testMultiHopRemoteForceCloseOnChainHtlcTimeout(net *lntest.NetworkHarness,
 		t.Fatalf("htlc mismatch: %v", predErr)
 	}
 
+	// Increase the fee estimate so that the following force close tx will
+	// be cpfp'ed.
+	net.SetFeeEstimate(30000)
+
 	// At this point, we'll now instruct Carol to force close the
 	// transaction. This will let us exercise that Bob is able to sweep the
 	// expired HTLC on Carol's version of the commitment transaction. If

lntest/itest/lnd_multi-hop_test.go

@@ -101,6 +101,10 @@ func testMultiHopHtlcClaims(net *lntest.NetworkHarness, t *harnessTest) {
 				success := ht.t.Run(subTest.name, func(t *testing.T) {
 					ht := newHarnessTest(t, net)
 
+					// Start each test with the default
+					// static fee estimate.
+					net.SetFeeEstimate(12500)
+
 					subTest.test(net, ht, alice, bob, commitType)
 				})
 				if !success {

lntest/itest/lnd_test.go

@@ -22,6 +22,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/btcsuite/btcd/blockchain"
 	"github.com/btcsuite/btcd/btcjson"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -3460,6 +3461,9 @@ func channelForceClosureTest(net *lntest.NetworkHarness, t *harnessTest,
 		numInvoices = 6
 	)
 
+	const commitFeeRate = 20000
+	net.SetFeeEstimate(commitFeeRate)
+
 	// TODO(roasbeef): should check default value in config here
 	// instead, or make delay a param
 	defaultCLTV := uint32(lnd.DefaultBitcoinTimeLockDelta)
@@ -3574,6 +3578,9 @@ func channelForceClosureTest(net *lntest.NetworkHarness, t *harnessTest,
 	// 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.
+	const actualFeeRate = 30000
+	net.SetFeeEstimate(actualFeeRate)
+
 	ctxt, _ = context.WithTimeout(ctxb, channelCloseTimeout)
 	_, closingTxID, err := net.CloseChannel(ctxt, alice, chanPoint, true)
 	if err != nil {
@@ -3635,17 +3642,35 @@ func channelForceClosureTest(net *lntest.NetworkHarness, t *harnessTest,
 	// broadcast as a result of the force closure. If there are anchors, we
 	// also expect the anchor sweep tx to be in the mempool.
 	expectedTxes := 1
+	expectedFeeRate := commitFeeRate
 	if channelType == commitTypeAnchors {
 		expectedTxes = 2
+		expectedFeeRate = actualFeeRate
 	}
 
-	sweepTxns, err := waitForNTxsInMempool(
+	sweepTxns, err := getNTxsFromMempool(
 		net.Miner.Node, expectedTxes, minerMempoolTimeout,
 	)
 	if err != nil {
 		t.Fatalf("failed to find commitment in miner mempool: %v", err)
 	}
 
+	// Verify fee rate of the commitment tx plus anchor if present.
+	var totalWeight, totalFee int64
+	for _, tx := range sweepTxns {
+		utx := btcutil.NewTx(tx)
+		totalWeight += blockchain.GetTransactionWeight(utx)
+
+		fee, err := getTxFee(net.Miner.Node, tx)
+		require.NoError(t.t, err)
+		totalFee += int64(fee)
+	}
+	feeRate := totalFee * 1000 / totalWeight
+
+	// Allow some deviation because weight estimates during tx generation
+	// are estimates.
+	require.InEpsilon(t.t, expectedFeeRate, feeRate, 0.005)
+
 	// Find alice's commit sweep and anchor sweep (if present) in the
 	// mempool.
 	aliceCloseTx := waitingClose.Commitments.LocalTxid
@@ -3737,7 +3762,7 @@ func channelForceClosureTest(net *lntest.NetworkHarness, t *harnessTest,
 	// Carol's sweep tx should be in the mempool already, as her output is
 	// not timelocked. If there are anchors, we also expect Carol's anchor
 	// sweep now.
-	sweepTxns, err = waitForNTxsInMempool(
+	sweepTxns, err = getNTxsFromMempool(
 		net.Miner.Node, expectedTxes, minerMempoolTimeout,
 	)
 	if err != nil {
@@ -4416,12 +4441,13 @@ type sweptOutput struct {
 // we have to bring another input to add fees to the anchor. Note that the
 // anchor swept output may be nil if the channel did not have anchors.
 func findCommitAndAnchor(t *harnessTest, net *lntest.NetworkHarness,
-	sweepTxns []*chainhash.Hash, closeTx string) (*sweptOutput, *sweptOutput) {
+	sweepTxns []*wire.MsgTx, closeTx string) (*sweptOutput, *sweptOutput) {
 
 	var commitSweep, anchorSweep *sweptOutput
 
 	for _, tx := range sweepTxns {
-		sweepTx, err := net.Miner.Node.GetRawTransaction(tx)
+		txHash := tx.TxHash()
+		sweepTx, err := net.Miner.Node.GetRawTransaction(&txHash)
 		require.NoError(t.t, err)
 
 		// We expect our commitment sweep to have a single input, and,
@@ -4434,7 +4460,7 @@ func findCommitAndAnchor(t *harnessTest, net *lntest.NetworkHarness,
 		if len(inputs) == 1 {
 			commitSweep = &sweptOutput{
 				OutPoint: inputs[0].PreviousOutPoint,
-				SweepTx:  tx.String(),
+				SweepTx:  txHash.String(),
 			}
 		} else {
 			// Since we have more than one input, we run through
@@ -4445,7 +4471,7 @@ func findCommitAndAnchor(t *harnessTest, net *lntest.NetworkHarness,
 				if outpointStr == closeTx {
 					anchorSweep = &sweptOutput{
 						OutPoint: txin.PreviousOutPoint,
-						SweepTx:  tx.String(),
+						SweepTx:  txHash.String(),
 					}
 				}
 			}
@@ -7574,6 +7600,28 @@ func getNTxsFromMempool(miner *rpcclient.Client, n int,
 	return txes, nil
 }
 
+// getTxFee retrieves parent transactions and reconstructs the fee paid.
+func getTxFee(miner *rpcclient.Client, tx *wire.MsgTx) (btcutil.Amount, error) {
+	var balance btcutil.Amount
+	for _, in := range tx.TxIn {
+		parentHash := in.PreviousOutPoint.Hash
+		rawTx, err := miner.GetRawTransaction(&parentHash)
+		if err != nil {
+			return 0, err
+		}
+		parent := rawTx.MsgTx()
+		balance += btcutil.Amount(
+			parent.TxOut[in.PreviousOutPoint.Index].Value,
+		)
+	}
+
+	for _, out := range tx.TxOut {
+		balance -= btcutil.Amount(out.Value)
+	}
+
+	return balance, nil
+}
+
 // testFailingChannel tests that we will fail the channel by force closing ii
 // in the case where a counterparty tries to settle an HTLC with the wrong
 // preimage.
@@ -9423,6 +9471,10 @@ func assertDLPExecuted(net *lntest.NetworkHarness, t *harnessTest,
 	dave *lntest.HarnessNode, daveStartingBalance int64,
 	anchors bool) {
 
+	// Increase the fee estimate so that the following force close tx will
+	// be cpfp'ed.
+	net.SetFeeEstimate(30000)
+
 	// We disabled auto-reconnect for some tests to avoid timing issues.
 	// To make sure the nodes are initiating DLP now, we have to manually
 	// re-connect them.
@@ -14535,6 +14587,9 @@ func TestLightningNetworkDaemon(t *testing.T) {
 			t.Fatalf("unable to add to log: %v", err)
 		}
 
+		// Start every test with the default static fee estimate.
+		lndHarness.SetFeeEstimate(12500)
+
 		success := t.Run(testCase.name, func(t1 *testing.T) {
 			ht := newHarnessTest(t1, lndHarness)
 			ht.RunTestCase(testCase)

lnwallet/channel.go

@@ -5961,6 +5961,12 @@ type AnchorResolution struct {
 
 	// CommitAnchor is the anchor outpoint on the commit tx.
 	CommitAnchor wire.OutPoint
+
+	// CommitFee is the fee of the commit tx.
+	CommitFee btcutil.Amount
+
+	// CommitWeight is the weight of the commit tx.
+	CommitWeight int64
 }
 
 // LocalForceCloseSummary describes the final commitment state before the
@@ -6399,9 +6405,24 @@ func NewAnchorResolution(chanState *channeldb.OpenChannel,
 		HashType: txscript.SigHashAll,
 	}
 
+	// Calculate commit tx weight. This commit tx doesn't yet include the
+	// witness spending the funding output, so we add the (worst case)
+	// weight for that too.
+	utx := btcutil.NewTx(commitTx)
+	weight := blockchain.GetTransactionWeight(utx) +
+		input.WitnessCommitmentTxWeight
+
+	// Calculate commit tx fee.
+	fee := chanState.Capacity
+	for _, out := range commitTx.TxOut {
+		fee -= btcutil.Amount(out.Value)
+	}
+
 	return &AnchorResolution{
 		CommitAnchor:         *outPoint,
 		AnchorSignDescriptor: *signDesc,
+		CommitWeight:         weight,
+		CommitFee:            fee,
 	}, nil
 }
 

sweep/sweeper.go

@@ -505,8 +505,11 @@ func (s *UtxoSweeper) collector(blockEpochs <-chan *chainntnfs.BlockEpoch) {
 				log.Debugf("Already pending input %v received",
 					outpoint)
 
-				// Update sweep parameters.
+				// Update input details and sweep parameters.
+				// The re-offered input details may contain a
+				// change to the unconfirmed parent tx info.
 				pendInput.params = input.params
+				pendInput.Input = input.input
 
 				// Add additional result channel to signal
 				// spend of this input.
@@ -763,6 +766,26 @@ func (s *UtxoSweeper) clusterBySweepFeeRate() []inputCluster {
 			log.Warnf("Skipping input %v: %v", op, err)
 			continue
 		}
+
+		// Only try to sweep inputs with an unconfirmed parent if the
+		// current sweep fee rate exceeds the parent tx fee rate. This
+		// assumes that such inputs are offered to the sweeper solely
+		// for the purpose of anchoring down the parent tx using cpfp.
+		parentTx := input.UnconfParent()
+		if parentTx != nil {
+			parentFeeRate :=
+				chainfee.SatPerKWeight(parentTx.Fee*1000) /
+					chainfee.SatPerKWeight(parentTx.Weight)
+
+			if parentFeeRate >= feeRate {
+				log.Debugf("Skipping cpfp input %v: fee_rate=%v, "+
+					"parent_fee_rate=%v", op, feeRate,
+					parentFeeRate)
+
+				continue
+			}
+		}
+
 		feeGroup := s.bucketForFeeRate(feeRate)
 
 		// Create a bucket list for this fee rate if there isn't one

sweep/sweeper_test.go

@@ -17,6 +17,7 @@ import (
 	"github.com/lightningnetwork/lnd/lntest/mock"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
+	"github.com/stretchr/testify/require"
 )
 
 var (
@@ -77,6 +78,7 @@ func createTestInput(value int64, witnessType input.WitnessType) input.BaseInput
 			},
 		},
 		0,
+		nil,
 	)
 
 	testInputCount++
@@ -176,6 +178,18 @@ func (ctx *sweeperTestContext) tick() {
 	}
 }
 
+// assertNoTick asserts that the sweeper does not wait for a tick.
+func (ctx *sweeperTestContext) assertNoTick() {
+	ctx.t.Helper()
+
+	select {
+	case <-ctx.timeoutChan:
+		ctx.t.Fatal("unexpected tick")
+
+	case <-time.After(processingDelay):
+	}
+}
+
 func (ctx *sweeperTestContext) assertNoNewTimer() {
 	select {
 	case <-ctx.timeoutChan:
@@ -337,9 +351,10 @@ func assertTxFeeRate(t *testing.T, tx *wire.MsgTx,
 	outputAmt := tx.TxOut[0].Value
 
 	fee := btcutil.Amount(inputAmt - outputAmt)
-	_, txWeight := getWeightEstimate(inputs)
+	_, estimator := getWeightEstimate(inputs, 0)
+	txWeight := estimator.weight()
 
-	expectedFee := expectedFeeRate.FeeForWeight(txWeight)
+	expectedFee := expectedFeeRate.FeeForWeight(int64(txWeight))
 	if fee != expectedFee {
 		t.Fatalf("expected fee rate %v results in %v fee, got %v fee",
 			expectedFeeRate, expectedFee, fee)
@@ -1293,3 +1308,71 @@ func TestExclusiveGroup(t *testing.T) {
 		t.Fatal("expected third input to be canceled")
 	}
 }
+
+// TestCpfp tests that the sweeper spends cpfp inputs at a fee rate that exceeds
+// the parent tx fee rate.
+func TestCpfp(t *testing.T) {
+	ctx := createSweeperTestContext(t)
+
+	ctx.estimator.updateFees(1000, chainfee.FeePerKwFloor)
+
+	// Offer an input with an unconfirmed parent tx to the sweeper. The
+	// parent tx pays 3000 sat/kw.
+	hash := chainhash.Hash{1}
+	input := input.MakeBaseInput(
+		&wire.OutPoint{Hash: hash},
+		input.CommitmentTimeLock,
+		&input.SignDescriptor{
+			Output: &wire.TxOut{
+				Value: 330,
+			},
+			KeyDesc: keychain.KeyDescriptor{
+				PubKey: testPubKey,
+			},
+		},
+		0,
+		&input.TxInfo{
+			Weight: 300,
+			Fee:    900,
+		},
+	)
+
+	feePref := FeePreference{ConfTarget: 6}
+	result, err := ctx.sweeper.SweepInput(
+		&input, Params{Fee: feePref, Force: true},
+	)
+	require.NoError(t, err)
+
+	// Because we sweep at 1000 sat/kw, the parent cannot be paid for. We
+	// expect the sweeper to remain idle.
+	ctx.assertNoTick()
+
+	// Increase the fee estimate to above the parent tx fee rate.
+	ctx.estimator.updateFees(5000, chainfee.FeePerKwFloor)
+
+	// Signal a new block. This is a trigger for the sweeper to refresh fee
+	// estimates.
+	ctx.notifier.NotifyEpoch(1000)
+
+	// Now we do expect a sweep transaction to be published with our input
+	// and an attached wallet utxo.
+	ctx.tick()
+	tx := ctx.receiveTx()
+	require.Len(t, tx.TxIn, 2)
+	require.Len(t, tx.TxOut, 1)
+
+	// As inputs we have 10000 sats from the wallet and 330 sats from the
+	// cpfp input. The sweep tx is weight expected to be 759 units. There is
+	// an additional 300 weight units from the parent to include in the
+	// package, making a total of 1059. At 5000 sat/kw, the required fee for
+	// the package is 5295 sats. The parent already paid 900 sats, so there
+	// is 4395 sat remaining to be paid. The expected output value is
+	// therefore: 10000 + 330 - 4395 = 5935.
+	require.Equal(t, int64(5935), tx.TxOut[0].Value)
+
+	// Mine the tx and assert that the result is passed back.
+	ctx.backend.mine()
+	ctx.expectResult(result, nil)
+
+	ctx.finish(1)
+}

sweep/test_utils.go

@@ -13,6 +13,7 @@ import (
 
 var (
 	defaultTestTimeout = 5 * time.Second
+	processingDelay    = 1 * time.Second
 	mockChainHash, _   = chainhash.NewHashFromStr("00aabbccddeeff")
 	mockChainHeight    = int32(100)
 )

sweep/tx_input_set.go

@@ -33,7 +33,7 @@ const (
 type txInputSetState struct {
 	// weightEstimate is the (worst case) tx weight with the current set of
 	// inputs.
-	weightEstimate input.TxWeightEstimator
+	weightEstimate *weightEstimator
 
 	// inputTotal is the total value of all inputs.
 	inputTotal btcutil.Amount
@@ -54,7 +54,7 @@ type txInputSetState struct {
 
 func (t *txInputSetState) clone() txInputSetState {
 	s := txInputSetState{
-		weightEstimate:   t.weightEstimate,
+		weightEstimate:   t.weightEstimate.clone(),
 		inputTotal:       t.inputTotal,
 		outputValue:      t.outputValue,
 		walletInputTotal: t.walletInputTotal,
@@ -71,9 +71,6 @@ func (t *txInputSetState) clone() txInputSetState {
 type txInputSet struct {
 	txInputSetState
 
-	// feePerKW is the fee rate used to calculate the tx fee.
-	feePerKW chainfee.SatPerKWeight
-
 	// dustLimit is the minimum output value of the tx.
 	dustLimit btcutil.Amount
 
@@ -95,15 +92,19 @@ func newTxInputSet(wallet Wallet, feePerKW,
 		btcutil.Amount(relayFee.FeePerKVByte()),
 	)
 
+	state := txInputSetState{
+		weightEstimate: newWeightEstimator(feePerKW),
+	}
+
 	b := txInputSet{
-		feePerKW:  feePerKW,
-		dustLimit: dustLimit,
-		maxInputs: maxInputs,
-		wallet:    wallet,
+		dustLimit:       dustLimit,
+		maxInputs:       maxInputs,
+		wallet:          wallet,
+		txInputSetState: state,
 	}
 
 	// Add the sweep tx output to the weight estimate.
-	b.weightEstimate.AddP2WKHOutput()
+	b.weightEstimate.addP2WKHOutput()
 
 	return &b
 }
@@ -126,30 +127,22 @@ func (t *txInputSet) addToState(inp input.Input, constraints addConstraints) *tx
 		return nil
 	}
 
-	// Can ignore error, because it has already been checked when
-	// calculating the yields.
-	size, isNestedP2SH, _ := inp.WitnessType().SizeUpperBound()
-
 	// Clone the current set state.
 	s := t.clone()
 
 	// Add the new input.
 	s.inputs = append(s.inputs, inp)
 
-	// Add weight of the new input.
-	if isNestedP2SH {
-		s.weightEstimate.AddNestedP2WSHInput(size)
-	} else {
-		s.weightEstimate.AddWitnessInput(size)
-	}
+	// Can ignore error, because it has already been checked when
+	// calculating the yields.
+	_ = s.weightEstimate.add(inp)
 
 	// Add the value of the new input.
 	value := btcutil.Amount(inp.SignDesc().Output.Value)
 	s.inputTotal += value
 
 	// Recalculate the tx fee.
-	weight := s.weightEstimate.Weight()
-	fee := t.feePerKW.FeeForWeight(int64(weight))
+	fee := s.weightEstimate.fee()
 
 	// Calculate the new output value.
 	s.outputValue = s.inputTotal - fee

sweep/txgenerator.go

@@ -120,7 +120,7 @@ func generateInputPartitionings(sweepableInputs []txInput,
 			"has yield=%v, weight=%v",
 			inputCount, len(txInputs.inputs)-inputCount,
 			txInputs.outputValue-txInputs.walletInputTotal,
-			txInputs.weightEstimate.Weight())
+			txInputs.weightEstimate.weight())
 
 		sets = append(sets, txInputs.inputs)
 		sweepableInputs = sweepableInputs[inputCount:]
@@ -134,9 +134,9 @@ func createSweepTx(inputs []input.Input, outputPkScript []byte,
 	currentBlockHeight uint32, feePerKw chainfee.SatPerKWeight,
 	signer input.Signer) (*wire.MsgTx, error) {
 
-	inputs, txWeight := getWeightEstimate(inputs)
+	inputs, estimator := getWeightEstimate(inputs, feePerKw)
 
-	txFee := feePerKw.FeeForWeight(txWeight)
+	txFee := estimator.fee()
 
 	// Sum up the total value contained in the inputs.
 	var totalSum btcutil.Amount
@@ -208,25 +208,33 @@ func createSweepTx(inputs []input.Input, outputPkScript []byte,
 	}
 
 	log.Infof("Creating sweep transaction %v for %v inputs (%s) "+
-		"using %v sat/kw, tx_fee=%v", sweepTx.TxHash(), len(inputs),
-		inputTypeSummary(inputs), int64(feePerKw), txFee)
+		"using %v sat/kw, tx_weight=%v, tx_fee=%v, parents_count=%v, "+
+		"parents_fee=%v, parents_weight=%v",
+		sweepTx.TxHash(), len(inputs),
+		inputTypeSummary(inputs), int64(feePerKw),
+		estimator.weight(), txFee,
+		len(estimator.parents), estimator.parentsFee,
+		estimator.parentsWeight,
+	)
 
 	return sweepTx, nil
 }
 
 // getWeightEstimate returns a weight estimate for the given inputs.
 // Additionally, it returns counts for the number of csv and cltv inputs.
-func getWeightEstimate(inputs []input.Input) ([]input.Input, int64) {
+func getWeightEstimate(inputs []input.Input, feeRate chainfee.SatPerKWeight) (
+	[]input.Input, *weightEstimator) {
+
 	// We initialize a weight estimator so we can accurately asses the
 	// amount of fees we need to pay for this sweep transaction.
 	//
 	// TODO(roasbeef): can be more intelligent about buffering outputs to
 	// be more efficient on-chain.
-	var weightEstimate input.TxWeightEstimator
+	weightEstimate := newWeightEstimator(feeRate)
 
 	// Our sweep transaction will pay to a single segwit p2wkh address,
 	// ensure it contributes to our weight estimate.
-	weightEstimate.AddP2WKHOutput()
+	weightEstimate.addP2WKHOutput()
 
 	// For each output, use its witness type to determine the estimate
 	// weight of its witness, and add it to the proper set of spendable
@@ -235,8 +243,7 @@ func getWeightEstimate(inputs []input.Input) ([]input.Input, int64) {
 	for i := range inputs {
 		inp := inputs[i]
 
-		wt := inp.WitnessType()
-		err := wt.AddWeightEstimation(&weightEstimate)
+		err := weightEstimate.add(inp)
 		if err != nil {
 			log.Warn(err)
 
@@ -248,7 +255,7 @@ func getWeightEstimate(inputs []input.Input) ([]input.Input, int64) {
 		sweepInputs = append(sweepInputs, inp)
 	}
 
-	return sweepInputs, int64(weightEstimate.Weight())
+	return sweepInputs, weightEstimate
 }
 
 // inputSummary returns a string containing a human readable summary about the

sweep/txgenerator_test.go

@@ -39,7 +39,8 @@ func TestWeightEstimate(t *testing.T) {
 		))
 	}
 
-	_, weight := getWeightEstimate(inputs)
+	_, estimator := getWeightEstimate(inputs, 0)
+	weight := int64(estimator.weight())
 	if weight != expectedWeight {
 		t.Fatalf("unexpected weight. expected %d but got %d.",
 			expectedWeight, weight)

sweep/walletsweep.go

@@ -255,7 +255,9 @@ func CraftSweepAllTx(feeRate chainfee.SatPerKWeight, blockHeight uint32,
 		// Now that we've constructed the items required, we'll make an
 		// input which can be passed to the sweeper for ultimate
 		// sweeping.
-		input := input.MakeBaseInput(&output.OutPoint, witnessType, signDesc, 0)
+		input := input.MakeBaseInput(
+			&output.OutPoint, witnessType, signDesc, 0, nil,
+		)
 		inputsToSweep = append(inputsToSweep, &input)
 	}
 

sweep/weight_estimator.go

@@ -0,0 +1,120 @@
+package sweep
+
+import (
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcutil"
+	"github.com/lightningnetwork/lnd/input"
+	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
+)
+
+// weightEstimator wraps a standard weight estimator instance and adds to that
+// support for child-pays-for-parent.
+type weightEstimator struct {
+	estimator     input.TxWeightEstimator
+	feeRate       chainfee.SatPerKWeight
+	parents       map[chainhash.Hash]struct{}
+	parentsFee    btcutil.Amount
+	parentsWeight int64
+}
+
+// newWeightEstimator instantiates a new sweeper weight estimator.
+func newWeightEstimator(feeRate chainfee.SatPerKWeight) *weightEstimator {
+	return &weightEstimator{
+		feeRate: feeRate,
+		parents: make(map[chainhash.Hash]struct{}),
+	}
+}
+
+// clone returns a copy of this weight estimator.
+func (w *weightEstimator) clone() *weightEstimator {
+	parents := make(map[chainhash.Hash]struct{}, len(w.parents))
+	for hash := range w.parents {
+		parents[hash] = struct{}{}
+	}
+
+	return &weightEstimator{
+		estimator:     w.estimator,
+		feeRate:       w.feeRate,
+		parents:       parents,
+		parentsFee:    w.parentsFee,
+		parentsWeight: w.parentsWeight,
+	}
+}
+
+// add adds the weight of the given input to the weight estimate.
+func (w *weightEstimator) add(inp input.Input) error {
+	// If there is a parent tx, add the parent's fee and weight.
+	w.tryAddParent(inp)
+
+	wt := inp.WitnessType()
+
+	return wt.AddWeightEstimation(&w.estimator)
+}
+
+// tryAddParent examines the input and updates parent tx totals if required for
+// cpfp.
+func (w *weightEstimator) tryAddParent(inp input.Input) {
+	// Get unconfirmed parent info from the input.
+	unconfParent := inp.UnconfParent()
+
+	// If there is no parent, there is nothing to add.
+	if unconfParent == nil {
+		return
+	}
+
+	// If we've already accounted for the parent tx, don't do it
+	// again. This can happens when two outputs of the parent tx are
+	// included in the same sweep tx.
+	parentHash := inp.OutPoint().Hash
+	if _, ok := w.parents[parentHash]; ok {
+		return
+	}
+
+	// Calculate parent fee rate.
+	parentFeeRate := chainfee.SatPerKWeight(unconfParent.Fee) * 1000 /
+		chainfee.SatPerKWeight(unconfParent.Weight)
+
+	// Ignore parents that pay at least the fee rate of this transaction.
+	// Parent pays for child is not happening.
+	if parentFeeRate >= w.feeRate {
+		return
+	}
+
+	// Include parent.
+	w.parents[parentHash] = struct{}{}
+	w.parentsFee += unconfParent.Fee
+	w.parentsWeight += unconfParent.Weight
+}
+
+// addP2WKHOutput updates the weight estimate to account for an additional
+// native P2WKH output.
+func (w *weightEstimator) addP2WKHOutput() {
+	w.estimator.AddP2WKHOutput()
+}
+
+// weight gets the estimated weight of the transaction.
+func (w *weightEstimator) weight() int {
+	return w.estimator.Weight()
+}
+
+// fee returns the tx fee to use for the aggregated inputs and outputs, taking
+// into account unconfirmed parent transactions (cpfp).
+func (w *weightEstimator) fee() btcutil.Amount {
+	// Calculate fee and weight for just this tx.
+	childWeight := int64(w.estimator.Weight())
+
+	// Add combined weight of unconfirmed parent txes.
+	totalWeight := childWeight + w.parentsWeight
+
+	// Subtract fee already paid by parents.
+	fee := w.feeRate.FeeForWeight(totalWeight) - w.parentsFee
+
+	// Clamp the fee to what would be required if no parent txes were paid
+	// for. This is to make sure no rounding errors can get us into trouble.
+	childFee := w.feeRate.FeeForWeight(childWeight)
+	if childFee > fee {
+		fee = childFee
+	}
+
+	return fee
+}

sweep/weight_estimator_test.go

@@ -0,0 +1,79 @@
+package sweep
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/input"
+	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
+	"github.com/stretchr/testify/require"
+)
+
+// TestWeightEstimator tests weight estimation for inputs with and without
+// unconfirmed parents.
+func TestWeightEstimator(t *testing.T) {
+	testFeeRate := chainfee.SatPerKWeight(20000)
+
+	w := newWeightEstimator(testFeeRate)
+
+	// Add an input without unconfirmed parent tx.
+	input1 := input.MakeBaseInput(
+		&wire.OutPoint{}, input.CommitmentAnchor,
+		&input.SignDescriptor{}, 0, nil,
+	)
+
+	require.NoError(t, w.add(&input1))
+
+	// The expectations is that this input is added.
+	const expectedWeight1 = 322
+	require.Equal(t, expectedWeight1, w.weight())
+	require.Equal(t, testFeeRate.FeeForWeight(expectedWeight1), w.fee())
+
+	// Define a parent transaction that pays a fee of 30000 sat/kw.
+	parentTxHighFee := &input.TxInfo{
+		Weight: 100,
+		Fee:    3000,
+	}
+
+	// Add an output of the parent tx above.
+	input2 := input.MakeBaseInput(
+		&wire.OutPoint{}, input.CommitmentAnchor,
+		&input.SignDescriptor{}, 0,
+		parentTxHighFee,
+	)
+
+	require.NoError(t, w.add(&input2))
+
+	// Pay for parent isn't possible because the parent pays a higher fee
+	// rate than the child. We expect no additional fee on the child.
+	const expectedWeight2 = expectedWeight1 + 280
+	require.Equal(t, expectedWeight2, w.weight())
+	require.Equal(t, testFeeRate.FeeForWeight(expectedWeight2), w.fee())
+
+	// Define a parent transaction that pays a fee of 10000 sat/kw.
+	parentTxLowFee := &input.TxInfo{
+		Weight: 100,
+		Fee:    1000,
+	}
+
+	// Add an output of the low-fee parent tx above.
+	input3 := input.MakeBaseInput(
+		&wire.OutPoint{}, input.CommitmentAnchor,
+		&input.SignDescriptor{}, 0,
+		parentTxLowFee,
+	)
+	require.NoError(t, w.add(&input3))
+
+	// Expect the weight to increase because of the third input.
+	const expectedWeight3 = expectedWeight2 + 280
+	require.Equal(t, expectedWeight3, w.weight())
+
+	// Expect the fee to cover the child and the parent transaction at 20
+	// sat/kw after subtraction of the fee that was already paid by the
+	// parent.
+	expectedFee := testFeeRate.FeeForWeight(
+		expectedWeight3+parentTxLowFee.Weight,
+	) - parentTxLowFee.Fee
+
+	require.Equal(t, expectedFee, w.fee())
+}