chainntnfs: dispatch block notification for current tip upon registration

chainntnfs/bitcoindnotify/bitcoind.go

@@ -278,22 +278,40 @@ out:
 
 			case *blockEpochRegistration:
 				chainntnfs.Log.Infof("New block epoch subscription")
+
 				b.blockEpochClients[msg.epochID] = msg
-				if msg.bestBlock != nil {
-					missedBlocks, err :=
-						chainntnfs.GetClientMissedBlocks(
-							b.chainConn, msg.bestBlock,
-							b.bestBlock.Height, true,
-						)
-					if err != nil {
-						msg.errorChan <- err
-						continue
-					}
-					for _, block := range missedBlocks {
-						b.notifyBlockEpochClient(msg,
-							block.Height, block.Hash)
-					}
+
+				// If the client did not provide their best
+				// known block, then we'll immediately dispatch
+				// a notification for the current tip.
+				if msg.bestBlock == nil {
+					b.notifyBlockEpochClient(
+						msg, b.bestBlock.Height,
+						b.bestBlock.Hash,
+					)
+
+					msg.errorChan <- nil
+					continue
 				}
+
+				// Otherwise, we'll attempt to deliver the
+				// backlog of notifications from their best
+				// known block.
+				missedBlocks, err := chainntnfs.GetClientMissedBlocks(
+					b.chainConn, msg.bestBlock,
+					b.bestBlock.Height, true,
+				)
+				if err != nil {
+					msg.errorChan <- err
+					continue
+				}
+
+				for _, block := range missedBlocks {
+					b.notifyBlockEpochClient(
+						msg, block.Height, block.Hash,
+					)
+				}
+
 				msg.errorChan <- nil
 			}
 
@@ -951,7 +969,9 @@ type epochCancel struct {
 // RegisterBlockEpochNtfn returns a BlockEpochEvent which subscribes the
 // caller to receive notifications, of each new block connected to the main
 // chain. Clients have the option of passing in their best known block, which
-// the notifier uses to check if they are behind on blocks and catch them up.
+// the notifier uses to check if they are behind on blocks and catch them up. If
+// they do not provide one, then a notification will be dispatched immediately
+// for the current tip of the chain upon a successful registration.
 func (b *BitcoindNotifier) RegisterBlockEpochNtfn(
 	bestBlock *chainntnfs.BlockEpoch) (*chainntnfs.BlockEpochEvent, error) {
 

chainntnfs/btcdnotify/btcd.go

@@ -325,23 +325,40 @@ out:
 
 			case *blockEpochRegistration:
 				chainntnfs.Log.Infof("New block epoch subscription")
-				b.blockEpochClients[msg.epochID] = msg
-				if msg.bestBlock != nil {
-					missedBlocks, err :=
-						chainntnfs.GetClientMissedBlocks(
-							b.chainConn, msg.bestBlock,
-							b.bestBlock.Height, true,
-						)
-					if err != nil {
-						msg.errorChan <- err
-						continue
-					}
-					for _, block := range missedBlocks {
-						b.notifyBlockEpochClient(msg,
-							block.Height, block.Hash)
-					}
 
+				b.blockEpochClients[msg.epochID] = msg
+
+				// If the client did not provide their best
+				// known block, then we'll immediately dispatch
+				// a notification for the current tip.
+				if msg.bestBlock == nil {
+					b.notifyBlockEpochClient(
+						msg, b.bestBlock.Height,
+						b.bestBlock.Hash,
+					)
+
+					msg.errorChan <- nil
+					continue
 				}
+
+				// Otherwise, we'll attempt to deliver the
+				// backlog of notifications from their best
+				// known block.
+				missedBlocks, err := chainntnfs.GetClientMissedBlocks(
+					b.chainConn, msg.bestBlock,
+					b.bestBlock.Height, true,
+				)
+				if err != nil {
+					msg.errorChan <- err
+					continue
+				}
+
+				for _, block := range missedBlocks {
+					b.notifyBlockEpochClient(
+						msg, block.Height, block.Hash,
+					)
+				}
+
 				msg.errorChan <- nil
 			}
 
@@ -991,7 +1008,9 @@ type epochCancel struct {
 // RegisterBlockEpochNtfn returns a BlockEpochEvent which subscribes the
 // caller to receive notifications, of each new block connected to the main
 // chain. Clients have the option of passing in their best known block, which
-// the notifier uses to check if they are behind on blocks and catch them up.
+// the notifier uses to check if they are behind on blocks and catch them up. If
+// they do not provide one, then a notification will be dispatched immediately
+// for the current tip of the chain upon a successful registration.
 func (b *BtcdNotifier) RegisterBlockEpochNtfn(
 	bestBlock *chainntnfs.BlockEpoch) (*chainntnfs.BlockEpochEvent, error) {
 
@@ -1003,6 +1022,7 @@ func (b *BtcdNotifier) RegisterBlockEpochNtfn(
 		bestBlock:  bestBlock,
 		errorChan:  make(chan error, 1),
 	}
+
 	reg.epochQueue.Start()
 
 	// Before we send the request to the main goroutine, we'll launch a new

chainntnfs/interface.go

@@ -127,7 +127,9 @@ type ChainNotifier interface {
 	// Clients have the option of passing in their best known block.
 	// If they specify a block, the ChainNotifier checks whether the client
 	// is behind on blocks. If they are, the ChainNotifier sends a backlog
-	// of block notifications for the missed blocks.
+	// of block notifications for the missed blocks. If they do not provide
+	// one, then a notification will be dispatched immediately for the
+	// current tip of the chain upon a successful registration.
 	RegisterBlockEpochNtfn(*BlockEpoch) (*BlockEpochEvent, error)
 
 	// Start the ChainNotifier. Once started, the implementation should be

chainntnfs/interface_test.go

@@ -398,22 +398,23 @@ func testBlockEpochNotification(miner *rpctest.Harness,
 	// block epoch notifications.
 
 	const numBlocks = 10
+	const numNtfns = numBlocks + 1
 	const numClients = 5
 	var wg sync.WaitGroup
 
 	// Create numClients clients which will listen for block notifications. We
-	// expect each client to receive 10 notifications for each of the ten
-	// blocks we generate below. So we'll use a WaitGroup to synchronize the
-	// test.
+	// expect each client to receive 11 notifications, one for the current
+	// tip of the chain, and one for each of the ten blocks we generate
+	// below. So we'll use a WaitGroup to synchronize the test.
 	for i := 0; i < numClients; i++ {
 		epochClient, err := notifier.RegisterBlockEpochNtfn(nil)
 		if err != nil {
 			t.Fatalf("unable to register for epoch notification")
 		}
 
-		wg.Add(numBlocks)
+		wg.Add(numNtfns)
 		go func() {
-			for i := 0; i < numBlocks; i++ {
+			for i := 0; i < numNtfns; i++ {
 				<-epochClient.Epochs
 				wg.Done()
 			}
@@ -1494,6 +1495,16 @@ func testCatchUpOnMissedBlocks(miner *rpctest.Harness,
 		if err != nil {
 			t.Fatalf("unable to register for epoch notification: %v", err)
 		}
+
+		// Drain the notification dispatched upon registration as we're
+		// not interested in it.
+		select {
+		case <-epochClient.Epochs:
+		case <-time.After(5 * time.Second):
+			t.Fatal("expected to receive epoch for current block " +
+				"upon registration")
+		}
+
 		clients = append(clients, epochClient)
 	}
 
@@ -1669,6 +1680,16 @@ func testCatchUpOnMissedBlocksWithReorg(miner1 *rpctest.Harness,
 		if err != nil {
 			t.Fatalf("unable to register for epoch notification: %v", err)
 		}
+
+		// Drain the notification dispatched upon registration as we're
+		// not interested in it.
+		select {
+		case <-epochClient.Epochs:
+		case <-time.After(5 * time.Second):
+			t.Fatal("expected to receive epoch for current block " +
+				"upon registration")
+		}
+
 		clients = append(clients, epochClient)
 	}
 

chainntnfs/neutrinonotify/neutrino.go

@@ -334,25 +334,44 @@ out:
 
 			case *blockEpochRegistration:
 				chainntnfs.Log.Infof("New block epoch subscription")
+
 				n.blockEpochClients[msg.epochID] = msg
-				if msg.bestBlock != nil {
-					n.bestBlockMtx.Lock()
-					bestHeight := n.bestBlock.Height
-					n.bestBlockMtx.Unlock()
-					missedBlocks, err :=
-						chainntnfs.GetClientMissedBlocks(
-							n.chainConn, msg.bestBlock,
-							bestHeight, false,
-						)
-					if err != nil {
-						msg.errorChan <- err
-						continue
-					}
-					for _, block := range missedBlocks {
-						n.notifyBlockEpochClient(msg,
-							block.Height, block.Hash)
-					}
+
+				// If the client did not provide their best
+				// known block, then we'll immediately dispatch
+				// a notification for the current tip.
+				if msg.bestBlock == nil {
+					n.notifyBlockEpochClient(
+						msg, n.bestBlock.Height,
+						n.bestBlock.Hash,
+					)
+
+					msg.errorChan <- nil
+					continue
 				}
+
+				// Otherwise, we'll attempt to deliver the
+				// backlog of notifications from their best
+				// known block.
+				n.bestBlockMtx.Lock()
+				bestHeight := n.bestBlock.Height
+				n.bestBlockMtx.Unlock()
+
+				missedBlocks, err := chainntnfs.GetClientMissedBlocks(
+					n.chainConn, msg.bestBlock, bestHeight,
+					false,
+				)
+				if err != nil {
+					msg.errorChan <- err
+					continue
+				}
+
+				for _, block := range missedBlocks {
+					n.notifyBlockEpochClient(
+						msg, block.Height, block.Hash,
+					)
+				}
+
 				msg.errorChan <- nil
 
 			case *rescanFilterUpdate:
@@ -898,7 +917,9 @@ type epochCancel struct {
 // RegisterBlockEpochNtfn returns a BlockEpochEvent which subscribes the
 // caller to receive notifications, of each new block connected to the main
 // chain. Clients have the option of passing in their best known block, which
-// the notifier uses to check if they are behind on blocks and catch them up.
+// the notifier uses to check if they are behind on blocks and catch them up. If
+// they do not provide one, then a notification will be dispatched immediately
+// for the current tip of the chain upon a successful registration.
 func (n *NeutrinoNotifier) RegisterBlockEpochNtfn(
 	bestBlock *chainntnfs.BlockEpoch) (*chainntnfs.BlockEpochEvent, error) {