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/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())
+}