chainntnfs/txconfnotifier: split out ntfn dispatch into helper

chainntnfs/txconfnotifier.go

@@ -222,9 +222,6 @@ func (tcn *TxConfNotifier) Register(
 	tcn.Lock()
 	defer tcn.Unlock()
 
-	// TODO(conner): promote immediately to confNotifications if a
-	// historical dispatch has already completed.
-
 	confSet, ok := tcn.confNotifications[*ntfn.TxID]
 	if !ok {
 		confSet = newConfNtfnSet()
@@ -238,6 +235,10 @@ func (tcn *TxConfNotifier) Register(
 	// A prior rescan has already completed and we are actively watching at
 	// tip for this txid.
 	case rescanComplete:
+		// If conf details for this set of notifications has already
+		// been found, we'll attempt to deliver them immediately to this
+		// client.
+		tcn.dispatchConfDetails(ntfn, confSet.details)
 		return nil, nil
 
 	// A rescan is already in progress, return here to prevent dispatching
@@ -327,12 +328,37 @@ func (tcn *TxConfNotifier) UpdateConfDetails(txid chainhash.Hash,
 			details.BlockHeight, txid, err)
 	}
 
-	// Update the conf details of all ntfns that don't yet have them.
+	// Cache the details found in the rescan and attempt to dispatch any
+	// notifications that have not yet been delivered.
+	confSet.details = details
 	for _, ntfn := range confSet.ntfns {
-		if ntfn.details != nil {
+		err = tcn.dispatchConfDetails(ntfn, details)
-			continue
+		if err != nil {
+			return err
+		}
 	}
 
+	return nil
+}
+
+// dispatchConfDetails attempts to cache and dispatch details to a particular
+// client if the transaction has sufficiently confirmed. If the provided details
+// are nil, this method will be a no-op.
+func (tcn *TxConfNotifier) dispatchConfDetails(
+	ntfn *ConfNtfn, details *TxConfirmation) error {
+
+	// If no details are provided, return early as we can't dispatch.
+	if details == nil {
+		return nil
+	}
+
+	// Set the confirmation details for this notification, only if the
+	// notification doesn't already have details. This ensure we only fall
+	// through the following logic at most once, which could cause the
+	// buffered channels to block when exceeding their allocated capacity.
+	if ntfn.details != nil {
+		return nil
+	}
 	ntfn.details = details
 
 	// Now, we'll examine whether the transaction of this
@@ -391,8 +417,7 @@ func (tcn *TxConfNotifier) UpdateConfDetails(txid chainhash.Hash,
 			txSet = make(map[chainhash.Hash]struct{})
 			tcn.txsByInitialHeight[blockHeight] = txSet
 		}
-			txSet[txid] = struct{}{}
+		txSet[*ntfn.TxID] = struct{}{}
-		}
 	}
 
 	return nil