sweep: make sweeper aware of unconfirmed parent transactions.

Extend the fee estimator to take into account parent transactions with
their weights and fees.

Do not try to cpfp parent transactions that have a higher fee rate than
the sweep tx fee rate.

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)
+}