multi: let FetchLightningNode take an optional tx

In preparation for the next commit which will remove the
`*LightningNode` from the `ChannelEdgePolicy` struct,
`FetchLightningNode` is modified to take in an optional transaction so
that it can be utilised in places where a transaction exists.

channeldb/db.go

@@ -1351,7 +1351,7 @@ func (d *DB) AddrsForNode(nodePub *btcec.PublicKey) ([]net.Addr,
 	if err != nil {
 		return nil, err
 	}
-	graphNode, err := d.graph.FetchLightningNode(pubKey)
+	graphNode, err := d.graph.FetchLightningNode(nil, pubKey)
 	if err != nil && err != ErrGraphNodeNotFound {
 		return nil, err
 	} else if err == ErrGraphNodeNotFound {

channeldb/graph.go

@@ -519,7 +519,7 @@ func (c *ChannelGraph) FetchNodeFeatures(
 	}
 
 	// Fallback that uses the database.
-	targetNode, err := c.FetchLightningNode(node)
+	targetNode, err := c.FetchLightningNode(nil, node)
 	switch err {
 	// If the node exists and has features, return them directly.
 	case nil:
@@ -2779,12 +2779,13 @@ func (c *ChannelGraph) isPublic(tx kvdb.RTx, nodePub route.Vertex,
 
 // FetchLightningNode attempts to look up a target node by its identity public
 // key. If the node isn't found in the database, then ErrGraphNodeNotFound is
-// returned.
-func (c *ChannelGraph) FetchLightningNode(nodePub route.Vertex) (
+// returned. An optional transaction may be provided. If none is provided, then
+// a new one will be created.
+func (c *ChannelGraph) FetchLightningNode(tx kvdb.RTx, nodePub route.Vertex) (
 	*LightningNode, error) {
 
 	var node *LightningNode
-	err := kvdb.View(c.db, func(tx kvdb.RTx) error {
+	fetch := func(tx kvdb.RTx) error {
 		// First grab the nodes bucket which stores the mapping from
 		// pubKey to node information.
 		nodes := tx.ReadBucket(nodeBucket)
@@ -2810,9 +2811,22 @@ func (c *ChannelGraph) FetchLightningNode(nodePub route.Vertex) (
 		node = &n
 
 		return nil
-	}, func() {
-		node = nil
-	})
+	}
+
+	if tx == nil {
+		err := kvdb.View(
+			c.db, fetch, func() {
+				node = nil
+			},
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		return node, nil
+	}
+
+	err := fetch(tx)
 	if err != nil {
 		return nil, err
 	}

channeldb/graph_test.go

@@ -139,7 +139,7 @@ func TestNodeInsertionAndDeletion(t *testing.T) {
 
 	// Next, fetch the node from the database to ensure everything was
 	// serialized properly.
-	dbNode, err := graph.FetchLightningNode(testPub)
+	dbNode, err := graph.FetchLightningNode(nil, testPub)
 	require.NoError(t, err, "unable to locate node")
 
 	if _, exists, err := graph.HasLightningNode(dbNode.PubKeyBytes); err != nil {
@@ -162,7 +162,7 @@ func TestNodeInsertionAndDeletion(t *testing.T) {
 
 	// Finally, attempt to fetch the node again. This should fail as the
 	// node should have been deleted from the database.
-	_, err = graph.FetchLightningNode(testPub)
+	_, err = graph.FetchLightningNode(nil, testPub)
 	if err != ErrGraphNodeNotFound {
 		t.Fatalf("fetch after delete should fail!")
 	}
@@ -190,7 +190,7 @@ func TestPartialNode(t *testing.T) {
 
 	// Next, fetch the node from the database to ensure everything was
 	// serialized properly.
-	dbNode, err := graph.FetchLightningNode(testPub)
+	dbNode, err := graph.FetchLightningNode(nil, testPub)
 	require.NoError(t, err, "unable to locate node")
 
 	if _, exists, err := graph.HasLightningNode(dbNode.PubKeyBytes); err != nil {
@@ -220,7 +220,7 @@ func TestPartialNode(t *testing.T) {
 
 	// Finally, attempt to fetch the node again. This should fail as the
 	// node should have been deleted from the database.
-	_, err = graph.FetchLightningNode(testPub)
+	_, err = graph.FetchLightningNode(nil, testPub)
 	if err != ErrGraphNodeNotFound {
 		t.Fatalf("fetch after delete should fail!")
 	}
@@ -2560,7 +2560,7 @@ func TestPruneGraphNodes(t *testing.T) {
 
 	// Finally, we'll ensure that node3, the only fully unconnected node as
 	// properly deleted from the graph and not another node in its place.
-	_, err = graph.FetchLightningNode(node3.PubKeyBytes)
+	_, err = graph.FetchLightningNode(nil, node3.PubKeyBytes)
 	if err == nil {
 		t.Fatalf("node 3 should have been deleted!")
 	}
@@ -2594,13 +2594,13 @@ func TestAddChannelEdgeShellNodes(t *testing.T) {
 
 	// Ensure that node1 was inserted as a full node, while node2 only has
 	// a shell node present.
-	node1, err = graph.FetchLightningNode(node1.PubKeyBytes)
+	node1, err = graph.FetchLightningNode(nil, node1.PubKeyBytes)
 	require.NoError(t, err, "unable to fetch node1")
 	if !node1.HaveNodeAnnouncement {
 		t.Fatalf("have shell announcement for node1, shouldn't")
 	}
 
-	node2, err = graph.FetchLightningNode(node2.PubKeyBytes)
+	node2, err = graph.FetchLightningNode(nil, node2.PubKeyBytes)
 	require.NoError(t, err, "unable to fetch node2")
 	if node2.HaveNodeAnnouncement {
 		t.Fatalf("should have shell announcement for node2, but is full")