chainntnfs: dispatch historical block ntfns to clients

If a client passes in their best known block when registering for block notifications, check to see if it's behind our best block. If so, dispatch the missed block notifications to the client.

This is necessary because clients that persist their best known block can miss new blocks while registering for notifications.

chainntnfs/neutrinonotify/neutrino.go

@@ -370,6 +370,25 @@ func (n *NeutrinoNotifier) notificationDispatcher() {
 			case *blockEpochRegistration:
 				chainntnfs.Log.Infof("New block epoch subscription")
 				n.blockEpochClients[msg.epochID] = msg
+				if msg.bestBlock != nil {
+					n.heightMtx.Lock()
+					bestHeight := int32(n.bestHeight)
+					n.heightMtx.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 item := <-n.chainUpdates.ChanOut():
@@ -572,20 +591,25 @@ func (n *NeutrinoNotifier) handleBlockConnected(newBlock *filteredBlock) error {
 // notifyBlockEpochs notifies all registered block epoch clients of the newly
 // connected block to the main chain.
 func (n *NeutrinoNotifier) notifyBlockEpochs(newHeight int32, newSha *chainhash.Hash) {
+	for _, client := range n.blockEpochClients {
+		n.notifyBlockEpochClient(client, newHeight, newSha)
+	}
+}
+
+// notifyBlockEpochClient sends a registered block epoch client a notification
+// about a specific block.
+func (n *NeutrinoNotifier) notifyBlockEpochClient(epochClient *blockEpochRegistration,
+	height int32, sha *chainhash.Hash) {
+
 	epoch := &chainntnfs.BlockEpoch{
-		Height: newHeight,
-		Hash:   newSha,
+		Height: height,
+		Hash:   sha,
 	}
 
-	for _, epochClient := range n.blockEpochClients {
-		select {
-
-		case epochClient.epochQueue.ChanIn() <- epoch:
-
-		case <-epochClient.cancelChan:
-
-		case <-n.quit:
-		}
+	select {
+	case epochClient.epochQueue.ChanIn() <- epoch:
+	case <-epochClient.cancelChan:
+	case <-n.quit:
 	}
 }