chanbackup/pubsub: add method ManualUpdate

This method inserts channel updates and waits for them to be processed. It will
be used to update channel.backup upon LND shutdown.

chanbackup/pubsub.go

@@ -48,6 +48,19 @@ type ChannelEvent struct {
 	NewChans []ChannelWithAddrs
 }
 
+// manualUpdate holds a group of channel state updates and an error channel
+// to send back an error happened upon update processing or file updating.
+type manualUpdate struct {
+	// singles hold channels backups. They can be either new or known
+	// channels in the Swapper.
+	singles []Single
+
+	// errChan is the channel to send an error back. If the update handling
+	// and the subsequent file updating succeeds, nil is sent.
+	// The channel must have capacity of 1 to prevent Swapper blocking.
+	errChan chan error
+}
+
 // ChannelSubscription represents an intent to be notified of any updates to
 // the primary channel state.
 type ChannelSubscription struct {
@@ -90,6 +103,8 @@ type SubSwapper struct {
 	// over.
 	chanEvents *ChannelSubscription
 
+	manualUpdates chan manualUpdate
+
 	// keyRing is the main key ring that will allow us to pack the new
 	// multi backup.
 	keyRing keychain.KeyRing
@@ -131,6 +146,7 @@ func NewSubSwapper(startingChans []Single, chanNotifier ChannelNotifier,
 		keyRing:       keyRing,
 		Swapper:       backupSwapper,
 		quit:          make(chan struct{}),
+		manualUpdates: make(chan manualUpdate),
 	}, nil
 }
 
@@ -168,6 +184,43 @@ func (s *SubSwapper) Stop() error {
 	return nil
 }
 
+// ManualUpdate inserts/updates channel states into the swapper. The updates
+// are processed in another goroutine. The method waits for the updates to be
+// fully processed and the file to be updated on-disk before returning.
+func (s *SubSwapper) ManualUpdate(singles []Single) error {
+	// Create the channel to send an error back. If the update handling
+	// and the subsequent file updating succeeds, nil is sent.
+	// The channel must have capacity of 1 to prevent Swapper blocking.
+	errChan := make(chan error, 1)
+
+	// Create the update object to insert into the processing loop.
+	update := manualUpdate{
+		singles: singles,
+		errChan: errChan,
+	}
+
+	select {
+	case s.manualUpdates <- update:
+	case <-s.quit:
+		return fmt.Errorf("swapper stopped when sending manual update")
+	}
+
+	// Wait for processing, block on errChan.
+	select {
+	case err := <-errChan:
+		if err != nil {
+			return fmt.Errorf("processing of manual update "+
+				"failed: %w", err)
+		}
+
+	case <-s.quit:
+		return fmt.Errorf("swapper stopped when waiting for outcome")
+	}
+
+	// Success.
+	return nil
+}
+
 // updateBackupFile updates the backup file in place given the current state of
 // the SubSwapper. We accept the set of channels that were closed between this
 // update and the last to make sure we leave them out of our backup set union.
@@ -301,6 +354,38 @@ func (s *SubSwapper) backupUpdater() {
 					err)
 			}
 
+		// We received a manual update. Handle it and update the file.
+		case manualUpdate := <-s.manualUpdates:
+			oldStateSize := len(s.backupState)
+
+			// For all open channels, we'll create a new SCB given
+			// the required information.
+			for _, single := range manualUpdate.singles {
+				log.Debugf("Manual update of channel %v",
+					single.FundingOutpoint)
+
+				s.backupState[single.FundingOutpoint] = single
+			}
+
+			newStateSize := len(s.backupState)
+
+			log.Infof("Updating on-disk multi SCB backup: "+
+				"num_old_chans=%v, num_new_chans=%v",
+				oldStateSize, newStateSize)
+
+			// Without new state constructed, we'll, atomically
+			// update the on-disk backup state.
+			err := s.updateBackupFile()
+			if err != nil {
+				log.Errorf("unable to update backup file: %v",
+					err)
+			}
+
+			// Send the error (or nil) to the caller of
+			// ManualUpdate. The error channel must have capacity of
+			// 1 not to block here.
+			manualUpdate.errChan <- err
+
 		// TODO(roasbeef): refresh periodically on a time basis due to
 		// possible addr changes from node
 

chanbackup/pubsub_test.go

@@ -277,4 +277,18 @@ func TestSubSwapperUpdater(t *testing.T) {
 	// Verify that the new set of backups, now has one less after the
 	// sub-swapper switches the new set with the old.
 	assertExpectedBackupSwap(t, swapper, subSwapper, keyRing, backupSet)
+
+	// Check ManualUpdate method.
+	channel, err := genRandomOpenChannelShell()
+	require.NoError(t, err)
+	single := NewSingle(channel, nil)
+	backupSet[channel.FundingOutpoint] = single
+	require.NoError(t, subSwapper.ManualUpdate([]Single{single}))
+
+	// Verify that the state of the backup is as expected.
+	assertExpectedBackupSwap(t, swapper, subSwapper, keyRing, backupSet)
+
+	// Check the case ManualUpdate returns an error.
+	swapper.fail = true
+	require.Error(t, subSwapper.ManualUpdate([]Single{single}))
 }