graph/db: introduce ForEachSourceNodeChannel

In preparation for creating a clean interface for the graph store, we
want to hide anything that is DB specific from the exposed methods on
the interface. Currently the `ForEachNodeChannel` and the
`FetchOtherNode` methods of the `KVStore` expose a `kvdb.RTx` parameter
which is bbolt specific. There is only one call-site of
`ForEachNodeChannel` actually makes use of the passed `kvdb.RTx`
parameter, and that is in the `establishPersistentConnections` method of
the `server` which then passes the tx parameter to `FetchOtherNode`.

So to clean-up the interface such that the `kvdb.RTx` is no longer
exposed: we instead create one new method called
`ForEachSourceNodeChannel` which can be used to replace the above
mentioned call-site. So as of this commit, all the remaining call-site
of `ForEachNodeChannel` pass in a nil param for `kvdb.RTx` - meaning we
can remove the parameter in a future commit.

graph/db/graph_test.go

@@ -618,7 +618,7 @@ func createChannelEdge(node1, node2 *models.LightningNode) (
 	chanID := uint64(prand.Int63())
 	outpoint := wire.OutPoint{
 		Hash:  rev,
-		Index: 9,
+		Index: prand.Uint32(),
 	}
 
 	// Add the new edge to the database, this should proceed without any
@@ -991,6 +991,97 @@ func newEdgePolicy(chanID uint64, updateTime int64) *models.ChannelEdgePolicy {
 	}
 }
 
+// TestForEachSourceNodeChannel tests that the ForEachSourceNodeChannel
+// correctly iterates through the channels of the set source node.
+func TestForEachSourceNodeChannel(t *testing.T) {
+	t.Parallel()
+
+	graph, err := MakeTestGraph(t)
+	require.NoError(t, err, "unable to make test database")
+
+	// Create a source node (A) and set it as such in the DB.
+	nodeA := createTestVertex(t)
+	require.NoError(t, graph.SetSourceNode(nodeA))
+
+	// Now, create a few more nodes (B, C, D) along with some channels
+	// between them. We'll create the following graph:
+	//
+	// 	A -- B -- D
+	//  	|
+	// 	C
+	//
+	// The graph includes a channel (B-D) that does not belong to the source
+	// node along with 2 channels (A-B and A-C) that do belong to the source
+	// node. For the A-B channel, we will let the source node set an
+	// outgoing policy but for the A-C channel, we will set only an incoming
+	// policy.
+
+	nodeB := createTestVertex(t)
+	nodeC := createTestVertex(t)
+	nodeD := createTestVertex(t)
+
+	abEdge, abPolicy1, abPolicy2 := createChannelEdge(nodeA, nodeB)
+	require.NoError(t, graph.AddChannelEdge(abEdge))
+	acEdge, acPolicy1, acPolicy2 := createChannelEdge(nodeA, nodeC)
+	require.NoError(t, graph.AddChannelEdge(acEdge))
+	bdEdge, _, _ := createChannelEdge(nodeB, nodeD)
+	require.NoError(t, graph.AddChannelEdge(bdEdge))
+
+	// Figure out which of the policies returned above are node A's so that
+	// we know which to persist.
+	//
+	// First, set the outgoing policy for the A-B channel.
+	abPolicyAOutgoing := abPolicy1
+	if !bytes.Equal(abPolicy1.ToNode[:], nodeB.PubKeyBytes[:]) {
+		abPolicyAOutgoing = abPolicy2
+	}
+	require.NoError(t, graph.UpdateEdgePolicy(abPolicyAOutgoing))
+
+	// Now, set the incoming policy for the A-C channel.
+	acPolicyAIncoming := acPolicy1
+	if !bytes.Equal(acPolicy1.ToNode[:], nodeA.PubKeyBytes[:]) {
+		acPolicyAIncoming = acPolicy2
+	}
+	require.NoError(t, graph.UpdateEdgePolicy(acPolicyAIncoming))
+
+	type sourceNodeChan struct {
+		otherNode  route.Vertex
+		havePolicy bool
+	}
+
+	// Put together our expected source node channels.
+	expectedSrcChans := map[wire.OutPoint]*sourceNodeChan{
+		abEdge.ChannelPoint: {
+			otherNode:  nodeB.PubKeyBytes,
+			havePolicy: true,
+		},
+		acEdge.ChannelPoint: {
+			otherNode:  nodeC.PubKeyBytes,
+			havePolicy: false,
+		},
+	}
+
+	// Now, we'll use the ForEachSourceNodeChannel and assert that it
+	// returns the expected data in the call-back.
+	err = graph.ForEachSourceNodeChannel(func(chanPoint wire.OutPoint,
+		havePolicy bool, otherNode *models.LightningNode) error {
+
+		require.Contains(t, expectedSrcChans, chanPoint)
+		expected := expectedSrcChans[chanPoint]
+
+		require.Equal(
+			t, expected.otherNode[:], otherNode.PubKeyBytes[:],
+		)
+		require.Equal(t, expected.havePolicy, havePolicy)
+
+		delete(expectedSrcChans, chanPoint)
+
+		return nil
+	})
+	require.NoError(t, err)
+	require.Empty(t, expectedSrcChans)
+}
+
 func TestGraphTraversal(t *testing.T) {
 	t.Parallel()
 

graph/db/kv_store.go

@@ -3109,6 +3109,44 @@ func (c *KVStore) ForEachNodeChannel(nodePub route.Vertex,
 	return nodeTraversal(nil, nodePub[:], c.db, cb)
 }
 
+// ForEachSourceNodeChannel iterates through all channels of the source node,
+// executing the passed callback on each. The callback is provided with the
+// channel's outpoint, whether we have a policy for the channel and the channel
+// peer's node information.
+func (c *KVStore) ForEachSourceNodeChannel(cb func(chanPoint wire.OutPoint,
+	havePolicy bool, otherNode *models.LightningNode) error) error {
+
+	return kvdb.View(c.db, func(tx kvdb.RTx) error {
+		nodes := tx.ReadBucket(nodeBucket)
+		if nodes == nil {
+			return ErrGraphNotFound
+		}
+
+		node, err := c.sourceNode(nodes)
+		if err != nil {
+			return err
+		}
+
+		return nodeTraversal(
+			tx, node.PubKeyBytes[:], c.db, func(tx kvdb.RTx,
+				info *models.ChannelEdgeInfo,
+				policy, _ *models.ChannelEdgePolicy) error {
+
+				peer, err := c.FetchOtherNode(
+					tx, info, node.PubKeyBytes[:],
+				)
+				if err != nil {
+					return err
+				}
+
+				return cb(
+					info.ChannelPoint, policy != nil, peer,
+				)
+			},
+		)
+	}, func() {})
+}
+
 // ForEachNodeChannelTx iterates through all channels of the given node,
 // executing the passed callback with an edge info structure and the policies
 // of each end of the channel. The first edge policy is the outgoing edge *to*