lnwallet/channel: make ErrCommitSyncLocalDataLoss type

This commit converts the ErrCommitSyncLocalDataLoss error into a struct,
that also holds the received last unrevoked commit point from the remote
party.

htlcswitch/link.go

@@ -895,6 +895,11 @@ func (l *channelLink) htlcManager() {
 	if l.cfg.SyncStates {
 		err := l.syncChanStates()
 		if err != nil {
+			log.Warnf("Error when syncing channel states: %v", err)
+
+			_, localDataLoss :=
+				err.(*lnwallet.ErrCommitSyncLocalDataLoss)
+
 			switch {
 			case err == ErrLinkShuttingDown:
 				log.Debugf("unable to sync channel states, " +
@@ -936,7 +941,7 @@ func (l *channelLink) htlcManager() {
 			// TODO(halseth): mark this, such that we prevent
 			// channel from being force closed by the user or
 			// contractcourt etc.
-			case err == lnwallet.ErrCommitSyncLocalDataLoss:
+			case localDataLoss:
 
 			// We determined the commit chains were not possible to
 			// sync. We cautiously fail the channel, but don't

lnwallet/channel.go

@@ -81,16 +81,6 @@ var (
 	ErrInvalidLocalUnrevokedCommitPoint = fmt.Errorf("unrevoked commit " +
 		"point is invalid")
 
-	// ErrCommitSyncLocalDataLoss is returned in the case that we receive a
-	// valid commit secret within the ChannelReestablish message from the
-	// remote node AND they advertise a RemoteCommitTailHeight higher than
-	// our current known height. This means we have lost some critical
-	// data, and must fail the channel and MUST NOT force close it. Instead
-	// we should wait for the remote to force close it, such that we can
-	// attempt to sweep our funds.
-	ErrCommitSyncLocalDataLoss = fmt.Errorf("possible local commitment " +
-		"state data loss")
-
 	// ErrCommitSyncRemoteDataLoss is returned in the case that we receive
 	// a ChannelReestablish message from the remote that advertises a
 	// NextLocalCommitHeight that is lower than what they have already
@@ -101,6 +91,30 @@ var (
 		"state data loss")
 )
 
+// ErrCommitSyncLocalDataLoss is returned in the case that we receive a valid
+// commit secret within the ChannelReestablish message from the remote node AND
+// they advertise a RemoteCommitTailHeight higher than our current known
+// height. This means we have lost some critical data, and must fail the
+// channel and MUST NOT force close it. Instead we should wait for the remote
+// to force close it, such that we can attempt to sweep our funds. The
+// commitment point needed to sweep the remote's force close is encapsuled.
+type ErrCommitSyncLocalDataLoss struct {
+	// ChannelPoint is the identifier for the channel that experienced data
+	// loss.
+	ChannelPoint wire.OutPoint
+
+	// CommitPoint is the last unrevoked commit point, sent to us by the
+	// remote when we determined we had lost state.
+	CommitPoint *btcec.PublicKey
+}
+
+// Error returns a string representation of the local data loss error.
+func (e *ErrCommitSyncLocalDataLoss) Error() string {
+	return fmt.Sprintf("ChannelPoint(%v) with CommitPoint(%x) had "+
+		"possible local commitment state data loss", e.ChannelPoint,
+		e.CommitPoint.SerializeCompressed())
+}
+
 // channelState is an enum like type which represents the current state of a
 // particular channel.
 // TODO(roasbeef): actually update state
@@ -3313,7 +3327,11 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 		if err != nil {
 			return nil, nil, nil, err
 		}
-		return nil, nil, nil, ErrCommitSyncLocalDataLoss
+
+		return nil, nil, nil, &ErrCommitSyncLocalDataLoss{
+			ChannelPoint: lc.channelState.FundingOutpoint,
+			CommitPoint:  msg.LocalUnrevokedCommitPoint,
+		}
 
 	// If the height of our commitment chain reported by the remote party
 	// is behind our view of the chain, then they probably lost some state,

lnwallet/channel_test.go

@@ -3688,7 +3688,7 @@ func TestChanSyncFailure(t *testing.T) {
 
 		// Alice should detect from Bob's message that she lost state.
 		_, _, _, err = aliceOld.ProcessChanSyncMsg(bobSyncMsg)
-		if err != ErrCommitSyncLocalDataLoss {
+		if _, ok := err.(*ErrCommitSyncLocalDataLoss); !ok {
 			t.Fatalf("wrong error, expected "+
 				"ErrCommitSyncLocalDataLoss instead got: %v",
 				err)
@@ -4377,7 +4377,7 @@ func TestChanSyncInvalidLastSecret(t *testing.T) {
 	// Alice's former self should conclude that she possibly lost data as
 	// Bob is sending a valid commit secret for the latest state.
 	_, _, _, err = aliceOld.ProcessChanSyncMsg(bobChanSync)
-	if err != ErrCommitSyncLocalDataLoss {
+	if _, ok := err.(*ErrCommitSyncLocalDataLoss); !ok {
 		t.Fatalf("wrong error, expected ErrCommitSyncLocalDataLoss "+
 			"instead got: %v", err)
 	}