lnwallet: update channel close to use fee estimation interface

This commit switches the channel close workflow to use the lnwallet fee
estimation interface rather than the hardcoded proposedFee.

lnwallet/channel.go

@@ -2532,39 +2532,42 @@ func (lc *LightningChannel) ForceClose() (*ForceCloseSummary, error) {
 //
 // TODO(roasbeef): caller should initiate signal to reject all incoming HTLCs,
 // settle any inflight.
-func (lc *LightningChannel) CreateCloseProposal(feeRate uint64) ([]byte, error) {
+func (lc *LightningChannel) CreateCloseProposal(feeRate uint64) ([]byte, uint64,
+	error) {
+
 	lc.Lock()
 	defer lc.Unlock()
 
 	// If we're already closing the channel, then ignore this request.
 	if lc.status == channelClosing || lc.status == channelClosed {
 		// TODO(roasbeef): check to ensure no pending payments
-		return nil, ErrChanClosing
+		return nil, 0, ErrChanClosing
 	}
 
-	// Calculate the fee for the commitment transaction based on its size.
-	// For a cooperative close, there should be no HTLCs.
-	commitFee := (lc.channelState.FeePerKw * commitWeight) / 1000
+	// Subtract the proposed fee from the appropriate balance, taking care
+	// not to persist the adjusted balance, as the feeRate may change
+	// during the channel closing process.
+	proposedFee := uint64(btcutil.Amount(feeRate) * commitWeight / 1000)
+	ourBalance := lc.channelState.OurBalance
+	theirBalance := lc.channelState.TheirBalance
 
 	if lc.channelState.IsInitiator {
-		lc.channelState.OurBalance = lc.channelState.OurBalance - commitFee
+		ourBalance = ourBalance - btcutil.Amount(proposedFee)
 	} else {
-		lc.channelState.TheirBalance = lc.channelState.TheirBalance - commitFee
+		theirBalance = theirBalance - btcutil.Amount(proposedFee)
 	}
 
 	closeTx := CreateCooperativeCloseTx(lc.fundingTxIn,
 		lc.channelState.OurDustLimit, lc.channelState.TheirDustLimit,
-		lc.channelState.OurBalance, lc.channelState.TheirBalance,
-		lc.channelState.OurDeliveryScript,
-		lc.channelState.TheirDeliveryScript,
-		lc.channelState.IsInitiator)
+		ourBalance, theirBalance, lc.channelState.OurDeliveryScript,
+		lc.channelState.TheirDeliveryScript, lc.channelState.IsInitiator)
 
 	// Ensure that the transaction doesn't explicitly violate any
 	// consensus rules such as being too big, or having any value with a
 	// negative output.
 	tx := btcutil.NewTx(closeTx)
 	if err := blockchain.CheckTransactionSanity(tx); err != nil {
-		return nil, err
+		return nil, 0, err
 	}
 
 	// Finally, sign the completed cooperative closure transaction. As the
@@ -2574,14 +2577,14 @@ func (lc *LightningChannel) CreateCloseProposal(feeRate uint64) ([]byte, error)
 	lc.signDesc.SigHashes = txscript.NewTxSigHashes(closeTx)
 	sig, err := lc.signer.SignOutputRaw(closeTx, lc.signDesc)
 	if err != nil {
-		return nil, err
+		return nil, 0, err
 	}
 
 	// As everything checks out, indicate in the channel status that a
 	// channel closure has been initiated.
 	lc.status = channelClosing
 
-	return sig, nil
+	return sig, proposedFee, nil
 }
 
 // CompleteCooperativeClose completes the cooperative closure of the target
@@ -2590,8 +2593,8 @@ func (lc *LightningChannel) CreateCloseProposal(feeRate uint64) ([]byte, error)
 //
 // NOTE: The passed local and remote sigs are expected to be fully complete
 // signatures including the proper sighash byte.
-func (lc *LightningChannel) CompleteCooperativeClose(localSig,
-	remoteSig []byte, proposedFee uint64) (*wire.MsgTx, error) {
+func (lc *LightningChannel) CompleteCooperativeClose(localSig, remoteSig []byte,
+	feeRate uint64) (*wire.MsgTx, error) {
 	lc.Lock()
 	defer lc.Unlock()
 
@@ -2601,15 +2604,26 @@ func (lc *LightningChannel) CompleteCooperativeClose(localSig,
 		return nil, ErrChanClosing
 	}
 
+	// Subtract the proposed fee from the appropriate balance, taking care
+	// not to persist the adjusted balance, as the feeRate may change
+	// during the channel closing process.
+	proposedFee := uint64(btcutil.Amount(feeRate) * commitWeight / 1000)
+	ourBalance := lc.channelState.OurBalance
+	theirBalance := lc.channelState.TheirBalance
+
+	if lc.channelState.IsInitiator {
+		ourBalance = ourBalance - btcutil.Amount(proposedFee)
+	} else {
+		theirBalance = theirBalance - btcutil.Amount(proposedFee)
+	}
+
 	// Create the transaction used to return the current settled balance
 	// on this active channel back to both parties. In this current model,
 	// the initiator pays full fees for the cooperative close transaction.
 	closeTx := CreateCooperativeCloseTx(lc.fundingTxIn,
 		lc.channelState.OurDustLimit, lc.channelState.TheirDustLimit,
-		lc.channelState.OurBalance, lc.channelState.TheirBalance,
-		lc.channelState.OurDeliveryScript,
-		lc.channelState.TheirDeliveryScript,
-		lc.channelState.IsInitiator)
+		ourBalance, theirBalance, lc.channelState.OurDeliveryScript,
+		lc.channelState.TheirDeliveryScript, lc.channelState.IsInitiator)
 
 	// Ensure that the transaction doesn't explicitly validate any
 	// consensus rules such as being too big, or having any value with a

lnwallet/channel_test.go

@@ -53,12 +53,6 @@ var (
 	numReqConfs = uint16(1)
 )
 
-const (
-	// proposedFee is a hard-coded fee value, intended to be replaced by a
-	// more robust fee estimation implemention.
-	proposedFee = 5000
-)
-
 type mockSigner struct {
 	key *btcec.PrivateKey
 }
@@ -250,7 +244,8 @@ func createTestChannels(revocationWindow int) (*LightningChannel, *LightningChan
 	var obsfucator [StateHintSize]byte
 	copy(obsfucator[:], aliceFirstRevoke[:])
 
-	feePerKw := btcutil.Amount(6000)
+	estimator := &StaticFeeEstimator{24, 6}
+	feePerKw := btcutil.Amount(estimator.EstimateFeePerWeight(1) * 1000)
 	aliceChannelState := &channeldb.OpenChannel{
 		IdentityPub:            aliceKeyPub,
 		ChanID:                 prevOut,
@@ -315,7 +310,6 @@ func createTestChannels(revocationWindow int) (*LightningChannel, *LightningChan
 	bobSigner := &mockSigner{bobKeyPriv}
 
 	notifier := &mockNotfier{}
-	estimator := &StaticFeeEstimator{24, 6}
 
 	channelAlice, err := NewLightningChannel(aliceSigner, notifier,
 		estimator, aliceChannelState)
@@ -711,28 +705,32 @@ func TestCooperativeChannelClosure(t *testing.T) {
 	}
 	defer cleanUp()
 
+	aliceFeeRate := uint64(aliceChannel.channelState.FeePerKw)
+	bobFeeRate := uint64(bobChannel.channelState.FeePerKw)
+
 	// First we test creating of cooperative close proposals.
-	aliceSig, err := aliceChannel.CreateCloseProposal(proposedFee)
+	aliceSig, _, err := aliceChannel.CreateCloseProposal(
+		aliceFeeRate)
 	if err != nil {
 		t.Fatalf("unable to create alice coop close proposal: %v", err)
 	}
 	aliceCloseSig := append(aliceSig, byte(txscript.SigHashAll))
 
-	bobSig, err := bobChannel.CreateCloseProposal(proposedFee)
+	bobSig, _, err := bobChannel.CreateCloseProposal(bobFeeRate)
 	if err != nil {
 		t.Fatalf("unable to create bob coop close proposal: %v", err)
 	}
 	bobCloseSig := append(bobSig, byte(txscript.SigHashAll))
 
 	aliceCloseTx, err := bobChannel.CompleteCooperativeClose(bobCloseSig,
-		aliceCloseSig, proposedFee)
+		aliceCloseSig, bobFeeRate)
 	if err != nil {
 		t.Fatalf("unable to complete alice cooperative close: %v", err)
 	}
 	bobCloseSha := aliceCloseTx.TxHash()
 
 	bobCloseTx, err := aliceChannel.CompleteCooperativeClose(aliceCloseSig,
-		bobCloseSig, proposedFee)
+		bobCloseSig, aliceFeeRate)
 	if err != nil {
 		t.Fatalf("unable to complete bob cooperative close: %v", err)
 	}
@@ -1555,6 +1553,9 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 	}
 	defer cleanUp()
 
+	aliceFeeRate := uint64(aliceChannel.channelState.FeePerKw)
+	bobFeeRate := uint64(bobChannel.channelState.FeePerKw)
+
 	setDustLimit := func(dustVal btcutil.Amount) {
 		aliceChannel.channelState.OurDustLimit = dustVal
 		aliceChannel.channelState.TheirDustLimit = dustVal
@@ -1582,20 +1583,20 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 	// Both sides currently have over 1 BTC settled as part of their
 	// balances. As a result, performing a cooperative closure now result
 	// in both sides having an output within the closure transaction.
-	aliceSig, err := aliceChannel.CreateCloseProposal(proposedFee)
+	aliceSig, _, err := aliceChannel.CreateCloseProposal(aliceFeeRate)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
 	aliceCloseSig := append(aliceSig, byte(txscript.SigHashAll))
 
-	bobSig, err := bobChannel.CreateCloseProposal(proposedFee)
+	bobSig, _, err := bobChannel.CreateCloseProposal(bobFeeRate)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
 	bobCloseSig := append(bobSig, byte(txscript.SigHashAll))
 
 	closeTx, err := bobChannel.CompleteCooperativeClose(bobCloseSig,
-		aliceCloseSig, proposedFee)
+		aliceCloseSig, bobFeeRate)
 	if err != nil {
 		t.Fatalf("unable to accept channel close: %v", err)
 	}
@@ -1617,20 +1618,20 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 
 	// Attempt another cooperative channel closure. It should succeed
 	// without any issues.
-	aliceSig, err = aliceChannel.CreateCloseProposal(proposedFee)
+	aliceSig, _, err = aliceChannel.CreateCloseProposal(aliceFeeRate)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
 	aliceCloseSig = append(aliceSig, byte(txscript.SigHashAll))
 
-	bobSig, err = bobChannel.CreateCloseProposal(proposedFee)
+	bobSig, _, err = bobChannel.CreateCloseProposal(bobFeeRate)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
 	bobCloseSig = append(bobSig, byte(txscript.SigHashAll))
 
 	closeTx, err = bobChannel.CompleteCooperativeClose(bobCloseSig,
-		aliceCloseSig, proposedFee)
+		aliceCloseSig, bobFeeRate)
 	if err != nil {
 		t.Fatalf("unable to accept channel close: %v", err)
 	}
@@ -1653,20 +1654,20 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 
 	// Our final attempt at another cooperative channel closure. It should
 	// succeed without any issues.
-	aliceSig, err = aliceChannel.CreateCloseProposal(proposedFee)
+	aliceSig, _, err = aliceChannel.CreateCloseProposal(aliceFeeRate)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
 	aliceCloseSig = append(aliceSig, byte(txscript.SigHashAll))
 
-	bobSig, err = bobChannel.CreateCloseProposal(proposedFee)
+	bobSig, _, err = bobChannel.CreateCloseProposal(bobFeeRate)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
 	bobCloseSig = append(bobSig, byte(txscript.SigHashAll))
 
 	closeTx, err = bobChannel.CompleteCooperativeClose(bobCloseSig,
-		aliceCloseSig, proposedFee)
+		aliceCloseSig, bobFeeRate)
 	if err != nil {
 		t.Fatalf("unable to accept channel close: %v", err)
 	}

peer.go

@@ -39,10 +39,6 @@ const (
 	// messages to be sent across the wire, requested by objects outside
 	// this struct.
 	outgoingQueueLen = 50
-
-	// proposedFee is a hard-coded fee value, intended to be replaced by a
-	// more robust fee estimation implemention.
-	proposedFee = 5000
 )
 
 // outgoinMsg packages an lnwire.Message to be sent out on the wire, along with
@@ -938,18 +934,26 @@ func (p *peer) handleInitClosingSigned(req *closeLinkReq, msg *lnwire.ClosingSig
 	channel := p.activeChannels[chanID]
 	p.activeChanMtx.RUnlock()
 
-	initiatorSig, err := channel.CreateCloseProposal(proposedFee)
+	// Calculate a fee rate that we believe to be fair.
+	// TODO(bvu): with a dynamic fee implementation, we will compare this to
+	// the fee proposed by the responder in their ClosingSigned message.
+	feeRate := p.server.feeEstimator.EstimateFeePerWeight(1) * 1000
+
+	// We agree with the proposed channel close transaction and fee rate,
+	// so generate our signature.
+	initiatorSig, proposedFee, err := channel.CreateCloseProposal(feeRate)
 	if err != nil {
 		req.err <- err
 		return
 	}
 	initSig := append(initiatorSig, byte(txscript.SigHashAll))
 
-	// Complete coop close transaction.
+	// Complete coop close transaction with the signatures of the close
+	// initiator and responder.
 	responderSig := msg.Signature
 	respSig := append(responderSig.Serialize(), byte(txscript.SigHashAll))
 	closeTx, err := channel.CompleteCooperativeClose(initSig, respSig,
-		proposedFee)
+		feeRate)
 	if err != nil {
 		req.err <- err
 		// TODO(roasbeef): send ErrorGeneric to other side
@@ -1063,8 +1067,10 @@ func (p *peer) handleResponseClosingSigned(msg *lnwire.ClosingSigned,
 	initSig := append(initiatorSig.Serialize(), byte(txscript.SigHashAll))
 	chanPoint := channel.ChannelPoint()
 
+	// Calculate our expected fee rate.
+	feeRate := p.server.feeEstimator.EstimateFeePerWeight(1) * 1000
 	closeTx, err := channel.CompleteCooperativeClose(respSig, initSig,
-		proposedFee)
+		feeRate)
 	if err != nil {
 		peerLog.Errorf("unable to complete cooperative "+
 			"close for ChannelPoint(%v): %v",
@@ -1195,9 +1201,12 @@ func (p *peer) sendShutdown(channel *lnwallet.LightningChannel) error {
 // sendClosingSigned handles the creation and sending of  proposed channel
 // close transactions.
 func (p *peer) sendClosingSigned(channel *lnwallet.LightningChannel) ([]byte, error) {
-	// We agree with the proposed fee, so we send back our signature
-	// for the proposed transaction.
-	closeSig, err := channel.CreateCloseProposal(proposedFee)
+
+	// Calculate an initial proposed fee rate for the close transaction.
+	feeRate := p.server.feeEstimator.EstimateFeePerWeight(1) * 1000
+
+	// Create a proposed channel close transaction with our fee proposal.
+	closeSig, proposedFee, err := channel.CreateCloseProposal(feeRate)
 	if err != nil {
 		return nil, err
 	}