chainntfns/btcdnotify: add support for multi-dispatch spend notifications

This commit adds support for dispatching the same spend notification to
multiple clients. This is now required by the ChainNotiifer interface
documentation and will be needed within the daemon in order to support
some upcoming refactors.

chainntnfs/btcdnotify/btcd.go

@@ -47,9 +47,7 @@ type BtcdNotifier struct {
 
 	notificationRegistry chan interface{}
 
-	// TODO(roasbeef): make map point to slices? Would allow for multiple
+	spendNotifications map[wire.OutPoint][]*spendNotification
-	// clients to listen for same spend. Would we ever need this?
-	spendNotifications map[wire.OutPoint]*spendNotification
 
 	confNotifications map[wire.ShaHash][]*confirmationsNotification
 	confHeap          *confirmationHeap
@@ -74,13 +72,13 @@ type BtcdNotifier struct {
 var _ chainntnfs.ChainNotifier = (*BtcdNotifier)(nil)
 
 // New returns a new BtcdNotifier instance. This function assumes the btcd node
-// detailed in the passed configuration is already running, and
+// detailed in the passed configuration is already running, and willing to
-// willing to accept new websockets clients.
+// accept new websockets clients.
 func New(config *btcrpcclient.ConnConfig) (*BtcdNotifier, error) {
 	notifier := &BtcdNotifier{
 		notificationRegistry: make(chan interface{}),
 
-		spendNotifications: make(map[wire.OutPoint]*spendNotification),
+		spendNotifications: make(map[wire.OutPoint][]*spendNotification),
 		confNotifications:  make(map[wire.ShaHash][]*confirmationsNotification),
 		confHeap:           newConfirmationHeap(),
 
@@ -150,8 +148,10 @@ func (b *BtcdNotifier) Stop() error {
 
 	// Notify all pending clients of our shutdown by closing the related
 	// notification channels.
-	for _, spendClient := range b.spendNotifications {
+	for _, spendClients := range b.spendNotifications {
-		close(spendClient.spendChan)
+		for _, spendClient := range spendClients {
+			close(spendClient.spendChan)
+		}
 	}
 	for _, confClients := range b.confNotifications {
 		for _, confClient := range confClients {
@@ -194,8 +194,8 @@ func (b *BtcdNotifier) onBlockDisconnected(hash *wire.ShaHash, height int32, t t
 
 // onRedeemingTx implements on OnRedeemingTx callback for btcrpcclient.
 func (b *BtcdNotifier) onRedeemingTx(tx *btcutil.Tx, details *btcjson.BlockDetails) {
-	// Append this new transaction update to the end of the queue of new chain
+	// Append this new transaction update to the end of the queue of new
-	// updates.
+	// chain updates.
 	b.txUpdateMtx.Lock()
 	b.txUpdates = append(b.txUpdates, &txUpdate{tx, details})
 	b.txUpdateMtx.Unlock()
@@ -219,11 +219,15 @@ out:
 			case *spendNotification:
 				chainntnfs.Log.Infof("New spend subscription: "+
 					"utxo=%v", msg.targetOutpoint)
-				b.spendNotifications[*msg.targetOutpoint] = msg
+				op := *msg.targetOutpoint
+				b.spendNotifications[op] = append(b.spendNotifications[op], msg)
 			case *confirmationsNotification:
 				chainntnfs.Log.Infof("New confirmations "+
 					"subscription: txid=%v, numconfs=%v",
 					*msg.txid, msg.numConfirmations)
+				// TODO(roasbeef): perform a N-block look
+				// behind to catch race-condition due to faster
+				// inter-block time?
 				txid := *msg.txid
 				b.confNotifications[txid] = append(b.confNotifications[txid], msg)
 			case *blockEpochRegistration:
@@ -264,9 +268,10 @@ out:
 				// Check if the inclusion of this transaction
 				// within a block by itself triggers a block
 				// confirmation threshold, if so send a
-				// notification. Otherwise, place the notification
+				// notification. Otherwise, place the
-				// on a heap to be triggered in the future once
+				// notification on a heap to be triggered in
-				// additional confirmations are attained.
+				// the future once additional confirmations are
+				// attained.
 				txSha := tx.Sha()
 				b.checkConfirmationTrigger(txSha, newHeight)
 			}
@@ -292,24 +297,27 @@ out:
 				prevOut := txIn.PreviousOutPoint
 
 				// If this transaction indeed does spend an
-				// output which we have a registered notification
+				// output which we have a registered
-				// for, then create a spend summary, finally
+				// notification for, then create a spend
-				// sending off the details to the notification
+				// summary, finally sending off the details to
-				// subscriber.
+				// the notification subscriber.
-				if ntfn, ok := b.spendNotifications[prevOut]; ok {
+				if clients, ok := b.spendNotifications[prevOut]; ok {
 					spenderSha := newSpend.tx.Sha()
-					spendDetails := &chainntnfs.SpendDetail{
+					for _, ntfn := range clients {
-						SpentOutPoint: ntfn.targetOutpoint,
+						spendDetails := &chainntnfs.SpendDetail{
-						SpenderTxHash: spenderSha,
+							SpentOutPoint: ntfn.targetOutpoint,
-						// TODO(roasbeef): copy tx?
+							SpenderTxHash: spenderSha,
-						SpendingTx:        spendingTx.MsgTx(),
+							// TODO(roasbeef): copy tx?
-						SpenderInputIndex: uint32(i),
+							SpendingTx:        spendingTx.MsgTx(),
+							SpenderInputIndex: uint32(i),
+						}
+
+						chainntnfs.Log.Infof("Dispatching "+
+							"spend notification for "+
+							"outpoint=%v", ntfn.targetOutpoint)
+						ntfn.spendChan <- spendDetails
 					}
 
-					chainntnfs.Log.Infof("Dispatching "+
-						"spend notification for "+
-						"outpoint=%v", ntfn.targetOutpoint)
-					ntfn.spendChan <- spendDetails
 					delete(b.spendNotifications, prevOut)
 				}
 			}