cnct: cpfp-sweep anchors

For unconfirmed commit tx anchors, supply the sweeper with cpfp info and
a confirmation target fee estimate.

The sweeper will try to pay for the parent commit tx as long as the
current fee estimate exceeds the pre-signed commit tx fee rate.

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.

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)
@@ -1073,19 +1076,25 @@ func (c *ChannelArbitrator) sweepAnchors(anchors []*lnwallet.AnchorResolution,
 			input.CommitmentAnchor,
 			&anchor.AnchorSignDescriptor,
 			heightHint,
-			nil,
+			&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,

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.
@@ -14527,6 +14579,9 @@ 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
 }