sweepbatcher: notify caller about confirmations

Add fields ConfChan and ConfErrChan to SpendNotifier type which is a part of
SweepRequest passed to AddSweep method.

This is needed to reuse confirmation notifications on the calling side the same
way it is done for spending notifications.

Author: starius

sweepbatcher/sweep_batch.go

@@ -1882,6 +1882,8 @@ func (b *batch) monitorConfirmations(ctx context.Context) error {
 			}
 
 		case err := <-errChan:
+			b.writeToConfErrChan(ctx, err)
+
 			b.writeToErrChan(fmt.Errorf("confirmations "+
 				"monitoring error: %w", err))
 
@@ -2158,7 +2160,55 @@ func (b *batch) handleConf(ctx context.Context,
 	b.Infof("confirmed in txid %s", b.batchTxid)
 	b.state = Confirmed
 
-	return b.store.ConfirmBatch(ctx, b.id)
+	if err := b.store.ConfirmBatch(ctx, b.id); err != nil {
+		return fmt.Errorf("failed to store confirmed state: %w", err)
+	}
+
+	// Calculate the fee portion that each sweep should pay for the batch.
+	// TODO: make sure spendTx matches b.sweeps.
+	var totalSweptAmt btcutil.Amount
+	for _, s := range b.sweeps {
+		totalSweptAmt += s.value
+	}
+	feePortionPaidPerSweep, roundingDifference := getFeePortionForSweep(
+		spendTx, len(b.sweeps), totalSweptAmt,
+	)
+
+	// Send the confirmation to all the notifiers.
+	for _, s := range b.sweeps {
+		// If the sweep's notifier is empty then this means that
+		// a swap is not waiting to read an update from it, so
+		// we can skip the notification part.
+		if s.notifier == nil || s.notifier.ConfChan == nil {
+			continue
+		}
+
+		confDetail := &ConfDetail{
+			TxConfirmation: conf,
+			OnChainFeePortion: getFeePortionPaidBySweep(
+				spendTx, feePortionPaidPerSweep,
+				roundingDifference, &s,
+			),
+		}
+
+		// Notify the caller in a goroutine to avoid possible dead-lock.
+		go func(notifier *SpendNotifier) {
+			// Note that we don't unblock on ctx, because it will
+			// expire soon, when batch.Run completes. The caller is
+			// responsible to consume ConfChan or close QuitChan.
+			select {
+			// Try to write the confirmation to the notification
+			// channel.
+			case notifier.ConfChan <- confDetail:
+
+			// If a quit signal was provided by the swap,
+			// continue.
+			case <-notifier.QuitChan:
+			}
+		}(s.notifier)
+	}
+
+	return nil
 }
 
 // isComplete returns true if the batch is completed. This method is used by the
@@ -2314,6 +2364,44 @@ func (b *batch) writeToSpendErrChan(ctx context.Context, spendErr error) {
 	}
 }
 
+// writeToConfErrChan sends an error to confirmation error channels of all the
+// sweeps.
+func (b *batch) writeToConfErrChan(ctx context.Context, confErr error) {
+	done, err := b.scheduleNextCall()
+	if err != nil {
+		done()
+
+		return
+	}
+	notifiers := make([]*SpendNotifier, 0, len(b.sweeps))
+	for _, s := range b.sweeps {
+		// If the sweep's notifier is empty then this means that a swap
+		// is not waiting to read an update from it, so we can skip
+		// the notification part.
+		if s.notifier == nil || s.notifier.ConfErrChan == nil {
+			continue
+		}
+
+		notifiers = append(notifiers, s.notifier)
+	}
+	done()
+
+	for _, notifier := range notifiers {
+		select {
+		// Try to write the error to the notification
+		// channel.
+		case notifier.ConfErrChan <- confErr:
+
+		// If a quit signal was provided by the swap,
+		// continue.
+		case <-notifier.QuitChan:
+
+		// If the context was canceled, stop.
+		case <-ctx.Done():
+		}
+	}
+}
+
 func (b *batch) persistSweep(ctx context.Context, sweep sweep,
 	completed bool) error {
 

sweepbatcher/sweep_batcher.go

@@ -20,6 +20,7 @@ import (
 	"github.com/lightninglabs/loop/loopdb"
 	"github.com/lightninglabs/loop/swap"
 	"github.com/lightninglabs/loop/utils"
+	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/clock"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -280,6 +281,8 @@ type addSweepsRequest struct {
 	parentBatch *dbBatch
 }
 
+// SpendDetail is a notification that is send to the user of sweepbatcher when
+// a batch gets the first confirmation.
 type SpendDetail struct {
 	// Tx is the transaction that spent the outpoint.
 	Tx *wire.MsgTx
@@ -291,6 +294,19 @@ type SpendDetail struct {
 	OnChainFeePortion btcutil.Amount
 }
 
+// ConfDetail is a notification that is send to the user of sweepbatcher when
+// a batch is fully confirmed, i.e. gets batchConfHeight confirmations.
+type ConfDetail struct {
+	// TxConfirmation has data about the confirmation of the transaction.
+	*chainntnfs.TxConfirmation
+
+	// OnChainFeePortion is the fee portion that was paid to get this sweep
+	// confirmed on chain. This is the difference between the value of the
+	// outpoint and the value of all sweeps that were included in the batch
+	// divided by the number of sweeps.
+	OnChainFeePortion btcutil.Amount
+}
+
 // SpendNotifier is a notifier that is used to notify the requester of a sweep
 // that the sweep was successful.
 type SpendNotifier struct {
@@ -300,6 +316,14 @@ type SpendNotifier struct {
 	// SpendErrChan is a channel where spend errors are received.
 	SpendErrChan chan<- error
 
+	// ConfChan is a channel where the confirmation details are received.
+	// This channel is optional.
+	ConfChan chan<- *ConfDetail
+
+	// ConfErrChan is a channel where confirmation errors are received.
+	// This channel is optional.
+	ConfErrChan chan<- error
+
 	// QuitChan is a channel that can be closed to stop the notifier.
 	QuitChan <-chan bool
 }
@@ -1114,7 +1138,9 @@ func (b *Batcher) FetchUnconfirmedBatches(ctx context.Context) ([]*batch,
 }
 
 // monitorSpendAndNotify monitors the spend of a specific outpoint and writes
-// the response back to the response channel.
+// the response back to the response channel. It is called if the batch is fully
+// confirmed and we just need to deliver the data back to the caller though
+// SpendNotifier.
 func (b *Batcher) monitorSpendAndNotify(ctx context.Context, sweep *sweep,
 	parentBatchID int32, notifier *SpendNotifier) error {
 
@@ -1172,6 +1198,16 @@ func (b *Batcher) monitorSpendAndNotify(ctx context.Context, sweep *sweep,
 			select {
 			// Try to write the update to the notification channel.
 			case notifier.SpendChan <- spendDetail:
+				err := b.monitorConfAndNotify(
+					ctx, sweep, notifier, spendTx,
+					onChainFeePortion,
+				)
+				if err != nil {
+					b.writeToErrChan(
+						ctx, fmt.Errorf("monitor conf "+
+							"failed: %w", err),
+					)
+				}
 
 			// If a quit signal was provided by the swap, continue.
 			case <-notifier.QuitChan:
@@ -1215,6 +1251,84 @@ func (b *Batcher) monitorSpendAndNotify(ctx context.Context, sweep *sweep,
 	return nil
 }
 
+// monitorConfAndNotify monitors the confirmation of a specific transaction and
+// writes the response back to the response channel. It is called if the batch
+// is fully confirmed and we just need to deliver the data back to the caller
+// though SpendNotifier.
+func (b *Batcher) monitorConfAndNotify(ctx context.Context, sweep *sweep,
+	notifier *SpendNotifier, spendTx *wire.MsgTx,
+	onChainFeePortion btcutil.Amount) error {
+
+	// If confirmation notifications were not requested, stop.
+	if notifier.ConfChan == nil && notifier.ConfErrChan == nil {
+		return nil
+	}
+
+	batchTxid := spendTx.TxHash()
+
+	if len(spendTx.TxOut) != 1 {
+		return fmt.Errorf("unexpected number of outputs in batch: %d, "+
+			"want %d", len(spendTx.TxOut), 1)
+	}
+	batchPkScript := spendTx.TxOut[0].PkScript
+
+	reorgChan := make(chan struct{})
+
+	confCtx, cancel := context.WithCancel(ctx)
+
+	confChan, errChan, err := b.chainNotifier.RegisterConfirmationsNtfn(
+		confCtx, &batchTxid, batchPkScript, batchConfHeight,
+		sweep.initiationHeight, lndclient.WithReOrgChan(reorgChan),
+	)
+	if err != nil {
+		cancel()
+		return err
+	}
+
+	b.wg.Add(1)
+	go func() {
+		defer cancel()
+		defer b.wg.Done()
+
+		select {
+		case conf := <-confChan:
+			if notifier.ConfChan != nil {
+				confDetail := &ConfDetail{
+					TxConfirmation:    conf,
+					OnChainFeePortion: onChainFeePortion,
+				}
+
+				select {
+				case notifier.ConfChan <- confDetail:
+				case <-notifier.QuitChan:
+				case <-ctx.Done():
+				}
+			}
+
+		case err := <-errChan:
+			if notifier.ConfErrChan != nil {
+				select {
+				case notifier.ConfErrChan <- err:
+				case <-notifier.QuitChan:
+				case <-ctx.Done():
+				}
+			}
+
+			b.writeToErrChan(ctx, fmt.Errorf("confirmations "+
+				"monitoring error: %w", err))
+
+		case <-reorgChan:
+			// A re-org has been detected, but the batch is fully
+			// confirmed and this is unexpected. Crash the batcher.
+			b.writeToErrChan(ctx, fmt.Errorf("unexpected reorg"))
+
+		case <-ctx.Done():
+		}
+	}()
+
+	return nil
+}
+
 func (b *Batcher) writeToErrChan(ctx context.Context, err error) {
 	select {
 	case b.errChan <- err: