breacharbiter: detect all spends, add terminal states

This commit modifies the breach arbiter to monitor
all breached inputs for spends and remove them from
the set of inputs to be swept if they are spent to
a terminal state. Prior, we would only watch for
spends on htlcs that may need to transition and
sweep the corresponding second-level htlc.

With these changes, we will no monitor commitment
outputs for spends, as well as spends from the
second level htlcs themselves. If either of these
is detected, we remove them from the set of inputs
to sweep via the justice transaction because there
is nothing the breach arbiter can do.

This functionality will be needed when adding
watchtower support, as the breach arbiter must
detect the case when the tower sweeps on behalf of
the user and stop pursuing the sweep itself. In
addition, this now properly handles the potential
case where somehow the remote party is able to sweep
the their commitment or second-level htlc to their
wallet, and prevent the breach arbiter from trying
to sweep the outputs as it would now.

Note that in the latter event, the internal
accounting may still be incorrect, as it is assumed
that all breached funds return to the victim.
However, these issues will deferred and fixed at a
later date, as the more crucial aspect is that the
breach arbiter doesn't blow up as a result of towers
sweeping channels.

breacharbiter.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/binary"
 	"errors"
+	"fmt"
 	"io"
 	"sync"
 	"sync/atomic"
@@ -320,6 +321,8 @@ func convertToSecondLevelRevoke(bo *breachedOutput, breachInfo *retributionInfo,
 func (b *breachArbiter) waitForSpendEvent(breachInfo *retributionInfo,
 	spendNtfns map[wire.OutPoint]*chainntnfs.SpendEvent) error {
 
+	inputs := breachInfo.breachedOutputs
+
 	// spend is used to wrap the index of the output that gets spent
 	// together with the spend details.
 	type spend struct {
@@ -330,11 +333,11 @@ func (b *breachArbiter) waitForSpendEvent(breachInfo *retributionInfo,
 	// We create a channel the first goroutine that gets a spend event can
 	// signal. We make it buffered in case multiple spend events come in at
 	// the same time.
-	anySpend := make(chan struct{}, len(breachInfo.breachedOutputs))
+	anySpend := make(chan struct{}, len(inputs))
 
 	// The allSpends channel will be used to pass spend events from all the
 	// goroutines that detects a spend before they are signalled to exit.
-	allSpends := make(chan spend, len(breachInfo.breachedOutputs))
+	allSpends := make(chan spend, len(inputs))
 
 	// exit will be used to signal the goroutines that they can exit.
 	exit := make(chan struct{})
@@ -342,17 +345,11 @@ func (b *breachArbiter) waitForSpendEvent(breachInfo *retributionInfo,
 
 	// We'll now launch a goroutine for each of the HTLC outputs, that will
 	// signal the moment they detect a spend event.
-	for i := 0; i < len(breachInfo.breachedOutputs); i++ {
-		breachedOutput := &breachInfo.breachedOutputs[i]
+	for i := range inputs {
+		breachedOutput := &inputs[i]
 
-		// If this isn't an HTLC output, then we can skip it.
-		if breachedOutput.witnessType != input.HtlcAcceptedRevoke &&
-			breachedOutput.witnessType != input.HtlcOfferedRevoke {
-			continue
-		}
-
-		brarLog.Debugf("Checking for second-level attempt on HTLC(%v) "+
-			"for ChannelPoint(%v)", breachedOutput.outpoint,
+		brarLog.Infof("Checking spend from %v(%v) for ChannelPoint(%v)",
+			breachedOutput.witnessType, breachedOutput.outpoint,
 			breachInfo.chanPoint)
 
 		// If we have already registered for a notification for this
@@ -396,9 +393,12 @@ func (b *breachArbiter) waitForSpendEvent(breachInfo *retributionInfo,
 				if !ok {
 					return
 				}
-				brarLog.Debugf("Detected spend of HTLC(%v) "+
-					"for ChannelPoint(%v)",
-					breachedOutput.outpoint,
+
+				brarLog.Infof("Detected spend on %s(%v) by "+
+					"txid(%v) for ChannelPoint(%v)",
+					inputs[index].witnessType,
+					inputs[index].outpoint,
+					sp.SpenderTxHash,
 					breachInfo.chanPoint)
 
 				// First we send the spend event on the
@@ -431,21 +431,58 @@ func (b *breachArbiter) waitForSpendEvent(breachInfo *retributionInfo,
 		// channel have exited. We can therefore safely close the
 		// channel before ranging over its content.
 		close(allSpends)
-		for s := range allSpends {
-			breachedOutput := &breachInfo.breachedOutputs[s.index]
-			brarLog.Debugf("Detected second-level spend on "+
-				"HTLC(%v) for ChannelPoint(%v)",
-				breachedOutput.outpoint, breachInfo.chanPoint)
 
+		doneOutputs := make(map[int]struct{})
+		for s := range allSpends {
+			breachedOutput := &inputs[s.index]
 			delete(spendNtfns, breachedOutput.outpoint)
 
-			// In this case we'll morph our initial revoke spend to
-			// instead point to the second level output, and update
-			// the sign descriptor in the process.
-			convertToSecondLevelRevoke(
-				breachedOutput, breachInfo, s.detail,
-			)
+			switch breachedOutput.witnessType {
+			case input.HtlcAcceptedRevoke:
+				fallthrough
+			case input.HtlcOfferedRevoke:
+				brarLog.Infof("Spend on second-level"+
+					"%s(%v) for ChannelPoint(%v) "+
+					"transitions to second-level output",
+					breachedOutput.witnessType,
+					breachedOutput.outpoint,
+					breachInfo.chanPoint)
+
+				// In this case we'll morph our initial revoke
+				// spend to instead point to the second level
+				// output, and update the sign descriptor in the
+				// process.
+				convertToSecondLevelRevoke(
+					breachedOutput, breachInfo, s.detail,
+				)
+
+				continue
+			}
+
+			brarLog.Infof("Spend on %s(%v) for ChannelPoint(%v) "+
+				"transitions output to terminal state, "+
+				"removing input from justice transaction",
+				breachedOutput.witnessType,
+				breachedOutput.outpoint, breachInfo.chanPoint)
+
+			doneOutputs[s.index] = struct{}{}
 		}
+
+		// Filter the inputs for which we can no longer proceed.
+		var nextIndex int
+		for i := range inputs {
+			if _, ok := doneOutputs[i]; ok {
+				continue
+			}
+
+			inputs[nextIndex] = inputs[i]
+			nextIndex++
+		}
+
+		// Update our remaining set of outputs before continuing with
+		// another attempt at publication.
+		breachInfo.breachedOutputs = inputs[:nextIndex]
+
 	case <-b.quit:
 		return errBrarShuttingDown
 	}
@@ -552,7 +589,24 @@ justiceTxBroadcast:
 				return
 			}
 
-			brarLog.Infof("Attempting another justice tx broadcast")
+			if len(breachInfo.breachedOutputs) == 0 {
+				brarLog.Debugf("No more outputs to sweep for "+
+					"breach, marking ChannelPoint(%v) "+
+					"fully resolved", breachInfo.chanPoint)
+
+				err = b.cleanupBreach(&breachInfo.chanPoint)
+				if err != nil {
+					brarLog.Errorf("Failed to cleanup "+
+						"breached ChannelPoint(%v): %v",
+						breachInfo.chanPoint, err)
+				}
+				return
+			}
+
+			brarLog.Infof("Attempting another justice tx "+
+				"with %d inputs",
+				len(breachInfo.breachedOutputs))
+
 			goto justiceTxBroadcast
 		}
 	}
@@ -602,19 +656,11 @@ justiceTxBroadcast:
 			"have been claimed", breachInfo.chanPoint,
 			revokedFunds, totalFunds)
 
-		// With the channel closed, mark it in the database as such.
-		err := b.cfg.DB.MarkChanFullyClosed(&breachInfo.chanPoint)
+		err = b.cleanupBreach(&breachInfo.chanPoint)
 		if err != nil {
-			brarLog.Errorf("Unable to mark chan as closed: %v", err)
-			return
-		}
-
-		// Justice has been carried out; we can safely delete the
-		// retribution info from the database.
-		err = b.cfg.Store.Remove(&breachInfo.chanPoint)
-		if err != nil {
-			brarLog.Errorf("Unable to remove retribution "+
-				"from the db: %v", err)
+			brarLog.Errorf("Failed to cleanup breached "+
+				"ChannelPoint(%v): %v", breachInfo.chanPoint,
+				err)
 		}
 
 		// TODO(roasbeef): add peer to blacklist?
@@ -628,6 +674,26 @@ justiceTxBroadcast:
 	}
 }
 
+// cleanupBreach marks the given channel point as fully resolved and removes the
+// retribution for that the channel from the retribution store.
+func (b *breachArbiter) cleanupBreach(chanPoint *wire.OutPoint) error {
+	// With the channel closed, mark it in the database as such.
+	err := b.cfg.DB.MarkChanFullyClosed(chanPoint)
+	if err != nil {
+		return fmt.Errorf("unable to mark chan as closed: %v", err)
+	}
+
+	// Justice has been carried out; we can safely delete the retribution
+	// info from the database.
+	err = b.cfg.Store.Remove(chanPoint)
+	if err != nil {
+		return fmt.Errorf("unable to remove retribution from db: %v",
+			err)
+	}
+
+	return nil
+}
+
 // handleBreachHandoff handles a new breach event, by writing it to disk, then
 // notifies the breachArbiter contract observer goroutine that a channel's
 // contract has been breached by the prior counterparty. Once notified the