chainntnfs/txconfnotifier: remove ntfn details, bound conf depth

Removes details field from conf notifications, in favor
of using the details on the confSet. We also bound the
requested conf depth to the reorg saftey limit, as the
behavior of state tracking within the notifier is
undefined otherwise.

chainntnfs/txconfnotifier.go

@@ -13,6 +13,10 @@ var (
 	// ErrTxConfNotifierExiting is an error returned when attempting to
 	// interact with the TxConfNotifier but it been shut down.
 	ErrTxConfNotifierExiting = errors.New("TxConfNotifier is exiting")
+
+	// ErrTxMaxConfs signals that the user requested a number of
+	// confirmations beyond the reorg safety limit.
+	ErrTxMaxConfs = errors.New("too many confirmations requested")
 )
 
 // ConfNtfn represents a notifier client's request to receive a notification
@@ -46,10 +50,6 @@ type ConfNtfn struct {
 	// this txid.
 	HeightHint uint32
 
-	// details describes the transaction's position is the blockchain. May be
-	// nil for unconfirmed transactions.
-	details *TxConfirmation
-
 	// dispatched is false if the confirmed notification has not been sent yet.
 	dispatched bool
 }
@@ -211,6 +211,12 @@ func (tcn *TxConfNotifier) Register(
 	default:
 	}
 
+	// Enforce that we will not dispatch confirmations beyond the reorg
+	// safety limit.
+	if ntfn.NumConfirmations > tcn.reorgSafetyLimit {
+		return nil, ErrTxMaxConfs
+	}
+
 	// Before proceeding to register the notification, we'll query our
 	// height hint cache to determine whether a better one exists.
 	//
@@ -259,7 +265,6 @@ func (tcn *TxConfNotifier) Register(
 	case rescanPending:
 		Log.Debugf("Waiting for pending rescan to finish before "+
 			"notifying txid=%v at tip", ntfn.TxID)
-
 		return nil, nil
 
 	// If no rescan has been dispatched, attempt to do so now.
@@ -326,6 +331,14 @@ func (tcn *TxConfNotifier) UpdateConfDetails(txid chainhash.Hash,
 		return fmt.Errorf("no notification found with TxID %v", txid)
 	}
 
+	// If the conf details were already found at tip, all existing
+	// notifications will have been dispatched or queued for dispatch. We
+	// can exit early to avoid sending too many notifications on the
+	// buffered channels.
+	if confSet.details != nil {
+		return nil
+	}
+
 	// The historical dispatch has been completed for this confSet. We'll
 	// update the rescan status and cache any details that were found. If
 	// the details are nil, that implies we did not find them and will
@@ -383,15 +396,6 @@ func (tcn *TxConfNotifier) dispatchConfDetails(
 		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
 	// notification request has reached its required number of
 	// confirmations. If it has, we'll dispatch a confirmation
@@ -512,8 +516,6 @@ func (tcn *TxConfNotifier) ConnectTip(blockHash *chainhash.Hash,
 		confSet.rescanStatus = rescanComplete
 		confSet.details = details
 		for _, ntfn := range confSet.ntfns {
-			ntfn.details = details
-
 			// In the event that this notification was aware that
 			// the transaction was reorged out of the chain, we'll
 			// consume the reorg notification if it hasn't been done
@@ -627,11 +629,13 @@ out:
 	// Then, we'll dispatch notifications for all the transactions that have
 	// become confirmed at this new block height.
 	for ntfn := range tcn.ntfnsByConfirmHeight[blockHeight] {
+		confSet := tcn.confNotifications[*ntfn.TxID]
+
 		Log.Infof("Dispatching %v conf notification for %v",
 			ntfn.NumConfirmations, ntfn.TxID)
 
 		select {
-		case ntfn.Event.Confirmed <- ntfn.details:
+		case ntfn.Event.Confirmed <- confSet.details:
 			ntfn.dispatched = true
 		case <-tcn.quit:
 			return ErrTxConfNotifierExiting