chainntnfs/btcd: Handle block disconnects with chainUpdate.

This does not implement full handling of block disconnections, but
ensures that all chain updates are processed in order.

chainntnfs/btcdnotify/btcd.go

@@ -35,6 +35,10 @@ var (
 type chainUpdate struct {
 	blockHash   *chainhash.Hash
 	blockHeight int32
+
+	// connected is true if this update is a new block and false if it is a
+	// disconnected block.
+	connect bool
 }
 
 // txUpdate encapsulates a transaction related notification sent from btcd to
@@ -70,8 +74,6 @@ type BtcdNotifier struct {
 
 	blockEpochClients map[uint64]*blockEpochRegistration
 
-	disconnectedBlockHashes chan *blockNtfn
-
 	chainUpdates *chainntnfs.ConcurrentQueue
 	txUpdates    *chainntnfs.ConcurrentQueue
 
@@ -97,8 +99,6 @@ func New(config *rpcclient.ConnConfig) (*BtcdNotifier, error) {
 		confNotifications: make(map[chainhash.Hash][]*confirmationsNotification),
 		confHeap:          newConfirmationHeap(),
 
-		disconnectedBlockHashes: make(chan *blockNtfn, 20),
-
 		chainUpdates: chainntnfs.NewConcurrentQueue(10),
 		txUpdates:    chainntnfs.NewConcurrentQueue(10),
 
@@ -192,24 +192,28 @@ func (b *BtcdNotifier) Stop() error {
 	return nil
 }
 
-// blockNtfn packages a notification of a connected/disconnected block along
-// with its height at the time.
-type blockNtfn struct {
-	sha    *chainhash.Hash
-	height int32
-}
-
 // onBlockConnected implements on OnBlockConnected callback for rpcclient.
 // Ingesting a block updates the wallet's internal utxo state based on the
 // outputs created and destroyed within each block.
 func (b *BtcdNotifier) onBlockConnected(hash *chainhash.Hash, height int32, t time.Time) {
 	// Append this new chain update to the end of the queue of new chain
 	// updates.
-	b.chainUpdates.ChanIn() <- &chainUpdate{hash, height}
+	b.chainUpdates.ChanIn() <- &chainUpdate{
+		blockHash:   hash,
+		blockHeight: height,
+		connect:     true,
+	}
 }
 
 // onBlockDisconnected implements on OnBlockDisconnected callback for rpcclient.
 func (b *BtcdNotifier) onBlockDisconnected(hash *chainhash.Hash, height int32, t time.Time) {
+	// Append this new chain update to the end of the queue of new chain
+	// updates.
+	b.chainUpdates.ChanIn() <- &chainUpdate{
+		blockHash:   hash,
+		blockHeight: height,
+		connect:     false,
+	}
 }
 
 // onRedeemingTx implements on OnRedeemingTx callback for rpcclient.
@@ -289,16 +293,15 @@ out:
 				b.blockEpochClients[msg.epochID] = msg
 			}
 
-		case staleBlockHash := <-b.disconnectedBlockHashes:
-			// TODO(roasbeef): re-orgs
-			//  * second channel to notify of confirmation decrementing
-			//    re-org?
-			//  * notify of negative confirmations
-			chainntnfs.Log.Warnf("Block disconnected from main "+
-				"chain: %v", staleBlockHash)
-
 		case item := <-b.chainUpdates.ChanOut():
 			update := item.(*chainUpdate)
+			if update.connect {
+				if update.blockHeight != currentHeight+1 {
+					chainntnfs.Log.Warnf("Received blocks out of order: "+
+						"current height=%d, new height=%d",
+						currentHeight, update.blockHeight)
+				}
+
 				currentHeight = update.blockHeight
 
 				newBlock, err := b.chainConn.GetBlock(update.blockHash)
@@ -330,6 +333,22 @@ out:
 				// chain. Send out any N confirmation notifications
 				// which may have been triggered by this new block.
 				b.notifyConfs(newHeight)
+			} else {
+				if update.blockHeight != currentHeight {
+					chainntnfs.Log.Warnf("Received blocks out of order: "+
+						"current height=%d, disconnected height=%d",
+						currentHeight, update.blockHeight)
+				}
+
+				currentHeight = update.blockHeight - 1
+
+				// TODO(roasbeef): re-orgs
+				//  * second channel to notify of confirmation decrementing
+				//    re-org?
+				//  * notify of negative confirmations
+				chainntnfs.Log.Infof("Block disconnected from main chain: "+
+					"height=%v, sha=%v", update.blockHeight, update.blockHash)
+			}
 
 		case item := <-b.txUpdates.ChanOut():
 			newSpend := item.(*txUpdate)