chainntnfs: notify BlockHeight in Updates event

diff --git a/chainntnfs/interface.go b/chainntnfs/interface.go
index 798a2f4..342d268 100644
--- a/chainntnfs/interface.go
+++ b/chainntnfs/interface.go
@@ -203,6 +203,20 @@ type TxConfirmation struct {
 	Block *wire.MsgBlock
 }
 
+// TxUpdateInfo contains information about a transaction before it has reached
+// its required number of confirmations. Transactions are registered for
+// notification for a specific number of "required" confirmations, this struct
+// will update the caller incrementally after each new block is found as long as
+// the transaction is not yet fully regarded as confirmed.
+type TxUpdateInfo struct {
+	// BlockHeight is the height of the block that contains the transaction.
+	BlockHeight uint32
+
+	// NumConfsLeft is the number of confirmations left for the transaction
+	// to be regarded as fully confirmed.
+	NumConfsLeft uint32
+}
+
 // ConfirmationEvent encapsulates a confirmation notification. With this struct,
 // callers can be notified of: the instance the target txid reaches the targeted
 // number of confirmations, how many confirmations are left for the target txid
@@ -229,11 +243,12 @@ type ConfirmationEvent struct {
 
 	// Updates is a channel that will sent upon, at every incremental
 	// confirmation, how many confirmations are left to declare the
-	// transaction as fully confirmed.
+	// transaction as fully confirmed, along with the height of the block
+	// that contains the transaction.
 	//
 	// NOTE: This channel must be buffered with the number of required
 	// confirmations.
-	Updates chan uint32
+	Updates chan TxUpdateInfo
 
 	// NegativeConf is a channel that will be sent upon if the transaction
 	// confirms, but is later reorged out of the chain. The integer sent
@@ -262,7 +277,7 @@ func NewConfirmationEvent(numConfs uint32, cancel func()) *ConfirmationEvent {
 		// the channel so we need to create a larger buffer to avoid
 		// blocking the notifier.
 		Confirmed:    make(chan *TxConfirmation, 1),
-		Updates:      make(chan uint32, numConfs),
+		Updates:      make(chan TxUpdateInfo, numConfs),
 		NegativeConf: make(chan int32, 1),
 		Done:         make(chan struct{}, 1),
 		Cancel:       cancel,
diff --git a/chainntnfs/txnotifier.go b/chainntnfs/txnotifier.go
index 9055d85..57eee84 100644
--- a/chainntnfs/txnotifier.go
+++ b/chainntnfs/txnotifier.go
@@ -947,8 +947,12 @@ func (n *TxNotifier) dispatchConfDetails(
 
 		// We'll send a 0 value to the Updates channel,
 		// indicating that the transaction/output script has already
-		// been confirmed.
-		err := n.notifyNumConfsLeft(ntfn, 0)
+		// been confirmed, and include the block height at which the
+		// transaction was included.
+		err := n.notifyNumConfsLeft(ntfn, TxUpdateInfo{
+			NumConfsLeft: 0,
+			BlockHeight:  details.BlockHeight,
+		})
 		if err != nil {
 			return err
 		}
@@ -977,7 +981,10 @@ func (n *TxNotifier) dispatchConfDetails(
 		// confirmations are left for the transaction/output script to
 		// be confirmed.
 		numConfsLeft := confHeight - n.currentHeight
-		err := n.notifyNumConfsLeft(ntfn, numConfsLeft)
+		err := n.notifyNumConfsLeft(ntfn, TxUpdateInfo{
+			NumConfsLeft: numConfsLeft,
+			BlockHeight:  details.BlockHeight,
+		})
 		if err != nil {
 			return err
 		}
@@ -1731,7 +1738,10 @@ func (n *TxNotifier) NotifyHeight(height uint32) error {
 		for confRequest := range confRequests {
 			confSet := n.confNotifications[confRequest]
 			for _, ntfn := range confSet.ntfns {
-				txConfHeight := confSet.details.BlockHeight +
+				// blockHeight is the height of the block which
+				// contains the transaction.
+				blockHeight := confSet.details.BlockHeight
+				txConfHeight := blockHeight +
 					ntfn.NumConfirmations - 1
 				numConfsLeft := txConfHeight - height
 
@@ -1744,7 +1754,10 @@ func (n *TxNotifier) NotifyHeight(height uint32) error {
 					continue
 				}
 
-				err := n.notifyNumConfsLeft(ntfn, numConfsLeft)
+				err := n.notifyNumConfsLeft(ntfn, TxUpdateInfo{
+					NumConfsLeft: numConfsLeft,
+					BlockHeight:  blockHeight,
+				})
 				if err != nil {
 					return err
 				}
@@ -2113,25 +2126,28 @@ func (n *TxNotifier) TearDown() {
 }
 
 // notifyNumConfsLeft sends the number of confirmations left to the
-// notification subscriber through the Event.Updates channel.
+// notification subscriber through the Event.Updates channel, along with the
+// block height in which the transaction was included.
 //
 // NOTE: must be used with the TxNotifier's lock held.
-func (n *TxNotifier) notifyNumConfsLeft(ntfn *ConfNtfn, num uint32) error {
+func (n *TxNotifier) notifyNumConfsLeft(ntfn *ConfNtfn,
+	info TxUpdateInfo) error {
+
 	// If the number left is no less than the recorded value, we can skip
 	// sending it as it means this same value has already been sent before.
-	if num >= ntfn.numConfsLeft {
+	if info.NumConfsLeft >= ntfn.numConfsLeft {
 		Log.Debugf("Skipped dispatched update (numConfsLeft=%v) for "+
-			"request %v conf_id=%v", num, ntfn.ConfRequest,
-			ntfn.ConfID)
+			"request %v conf_id=%v", info.NumConfsLeft,
+			ntfn.ConfRequest, ntfn.ConfID)
 
 		return nil
 	}
 
 	// Update the number of confirmations left to the notification.
-	ntfn.numConfsLeft = num
+	ntfn.numConfsLeft = info.NumConfsLeft
 
 	select {
-	case ntfn.Event.Updates <- num:
+	case ntfn.Event.Updates <- info:
 	case <-n.quit:
 		return ErrTxNotifierExiting
 	}
diff --git a/chainntnfs/txnotifier_test.go b/chainntnfs/txnotifier_test.go
index 1279330..1bd9f4f 100644
--- a/chainntnfs/txnotifier_test.go
+++ b/chainntnfs/txnotifier_test.go
@@ -271,13 +271,12 @@ func TestTxNotifierFutureConfDispatch(t *testing.T) {
 	// We should only receive one update for tx1 since it only requires
 	// one confirmation and it already met it.
 	select {
-	case numConfsLeft := <-ntfn1.Event.Updates:
-		const expected = 0
-		if numConfsLeft != expected {
-			t.Fatalf("Received incorrect confirmation update: tx1 "+
-				"expected %d confirmations left, got %d",
-				expected, numConfsLeft)
+	case updDetails := <-ntfn1.Event.Updates:
+		expected := chainntnfs.TxUpdateInfo{
+			NumConfsLeft: 0,
+			BlockHeight:  11,
 		}
+		require.Equal(t, expected, updDetails)
 	default:
 		t.Fatal("Expected confirmation update for tx1")
 	}
@@ -300,13 +299,12 @@ func TestTxNotifierFutureConfDispatch(t *testing.T) {
 	// We should only receive one update for tx2 since it only has one
 	// confirmation so far and it requires two.
 	select {
-	case numConfsLeft := <-ntfn2.Event.Updates:
-		const expected = 1
-		if numConfsLeft != expected {
-			t.Fatalf("Received incorrect confirmation update: tx2 "+
-				"expected %d confirmations left, got %d",
-				expected, numConfsLeft)
+	case updDetails := <-ntfn2.Event.Updates:
+		expected := chainntnfs.TxUpdateInfo{
+			NumConfsLeft: 1,
+			BlockHeight:  11,
 		}
+		require.Equal(t, expected, updDetails)
 	default:
 		t.Fatal("Expected confirmation update for tx2")
 	}
@@ -341,13 +339,12 @@ func TestTxNotifierFutureConfDispatch(t *testing.T) {
 	// We should only receive one update since the last at the new height,
 	// indicating how many confirmations are still left.
 	select {
-	case numConfsLeft := <-ntfn2.Event.Updates:
-		const expected = 0
-		if numConfsLeft != expected {
-			t.Fatalf("Received incorrect confirmation update: tx2 "+
-				"expected %d confirmations left, got %d",
-				expected, numConfsLeft)
+	case updDetails := <-ntfn2.Event.Updates:
+		expected := chainntnfs.TxUpdateInfo{
+			NumConfsLeft: 0,
+			BlockHeight:  11,
 		}
+		require.Equal(t, expected, updDetails)
 	default:
 		t.Fatal("Expected confirmation update for tx2")
 	}
@@ -411,13 +408,12 @@ func TestTxNotifierHistoricalConfDispatch(t *testing.T) {
 	err = n.UpdateConfDetails(ntfn1.HistoricalDispatch.ConfRequest, &txConf1)
 	require.NoError(t, err, "unable to update conf details")
 	select {
-	case numConfsLeft := <-ntfn1.Event.Updates:
-		const expected = 0
-		if numConfsLeft != expected {
-			t.Fatalf("Received incorrect confirmation update: tx1 "+
-				"expected %d confirmations left, got %d",
-				expected, numConfsLeft)
+	case updDetails := <-ntfn1.Event.Updates:
+		expected := chainntnfs.TxUpdateInfo{
+			NumConfsLeft: 0,
+			BlockHeight:  9,
 		}
+		require.Equal(t, expected, updDetails)
 	default:
 		t.Fatal("Expected confirmation update for tx1")
 	}
@@ -443,13 +439,12 @@ func TestTxNotifierHistoricalConfDispatch(t *testing.T) {
 	err = n.UpdateConfDetails(ntfn2.HistoricalDispatch.ConfRequest, &txConf2)
 	require.NoError(t, err, "unable to update conf details")
 	select {
-	case numConfsLeft := <-ntfn2.Event.Updates:
-		const expected = 1
-		if numConfsLeft != expected {
-			t.Fatalf("Received incorrect confirmation update: tx2 "+
-				"expected %d confirmations left, got %d",
-				expected, numConfsLeft)
+	case updDetails := <-ntfn2.Event.Updates:
+		expected := chainntnfs.TxUpdateInfo{
+			NumConfsLeft: 1,
+			BlockHeight:  9,
 		}
+		require.Equal(t, expected, updDetails)
 	default:
 		t.Fatal("Expected confirmation update for tx2")
 	}
@@ -485,13 +480,12 @@ func TestTxNotifierHistoricalConfDispatch(t *testing.T) {
 	// We should only receive one update for tx2 since the last one,
 	// indicating how many confirmations are still left.
 	select {
-	case numConfsLeft := <-ntfn2.Event.Updates:
-		const expected = 0
-		if numConfsLeft != expected {
-			t.Fatalf("Received incorrect confirmation update: tx2 "+
-				"expected %d confirmations left, got %d",
-				expected, numConfsLeft)
+	case updDetails := <-ntfn2.Event.Updates:
+		expected := chainntnfs.TxUpdateInfo{
+			NumConfsLeft: 0,
+			BlockHeight:  9,
 		}
+		require.Equal(t, expected, updDetails)
 	default:
 		t.Fatal("Expected confirmation update for tx2")
 	}
@@ -1490,13 +1484,12 @@ func TestTxNotifierConfReorg(t *testing.T) {
 	// We should only receive one update for tx2 since it only requires
 	// one confirmation and it already met it.
 	select {
-	case numConfsLeft := <-ntfn2.Event.Updates:
-		const expected = 0
-		if numConfsLeft != expected {
-			t.Fatalf("Received incorrect confirmation update: tx2 "+
-				"expected %d confirmations left, got %d",
-				expected, numConfsLeft)
+	case updDetails := <-ntfn2.Event.Updates:
+		expected := chainntnfs.TxUpdateInfo{
+			NumConfsLeft: 0,
+			BlockHeight:  12,
 		}
+		require.Equal(t, expected, updDetails)
 	default:
 		t.Fatal("Expected confirmation update for tx2")
 	}
@@ -1520,15 +1513,14 @@ func TestTxNotifierConfReorg(t *testing.T) {
 	// confirmations and it has already met them.
 	for i := uint32(1); i <= 2; i++ {
 		select {
-		case numConfsLeft := <-ntfn3.Event.Updates:
-			expected := tx3NumConfs - i
-			if numConfsLeft != expected {
-				t.Fatalf("Received incorrect confirmation update: tx3 "+
-					"expected %d confirmations left, got %d",
-					expected, numConfsLeft)
+		case updDetails := <-ntfn3.Event.Updates:
+			expected := chainntnfs.TxUpdateInfo{
+				NumConfsLeft: tx3NumConfs - i,
+				BlockHeight:  12,
 			}
+			require.Equal(t, expected, updDetails)
 		default:
-			t.Fatal("Expected confirmation update for tx2")
+			t.Fatal("Expected confirmation update for tx3")
 		}
 	}