itest: add peer bootstrapping itest

Test the automatic peer bootstrapping logic via an itest.

itest/list_on_test.go

@@ -707,6 +707,10 @@ var allTestCases = []*lntest.TestCase{
 		Name:     "partially specified route blinded invoice",
 		TestFunc: testPartiallySpecifiedBlindedPath,
 	},
+	{
+		Name:     "peer bootstrapping",
+		TestFunc: testPeerBootstrapping,
+	},
 }
 
 // appendPrefixed is used to add a prefix to each test name in the subtests

itest/lnd_graph.go

@@ -0,0 +1,77 @@
+package itest
+
+import (
+	"time"
+
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/lightningnetwork/lnd/lntest"
+	"github.com/lightningnetwork/lnd/lntest/wait"
+	"github.com/stretchr/testify/require"
+)
+
+// testPeerBootstrapping tests that a node is able to use persisted node
+// announcements to bootstrap its peer connections. This is done by
+// connecting a node to a channel network so that it syncs the necessary gossip
+// and then:
+//  1. Asserting that on a restart where bootstrapping is _disabled_, the node
+//     does not connect to any peers.
+//  2. Asserting that on a restart where bootstrapping is _enabled_, the node
+//     does connect to peers.
+func testPeerBootstrapping(ht *lntest.HarnessTest) {
+	// 1) Set up the following node/channel network.
+	// 	Alice <- Bob <- Charlie
+	_, nodes := ht.CreateSimpleNetwork(
+		[][]string{nil, nil, nil}, lntest.OpenChannelParams{
+			Amt: btcutil.Amount(100000),
+		},
+	)
+	carol, bob, alice := nodes[0], nodes[1], nodes[2]
+
+	// Assert that they all know about each other and the channels.
+	ht.AssertNumEdges(alice, 2, false)
+	ht.AssertNumEdges(bob, 2, false)
+	ht.AssertNumEdges(carol, 2, false)
+
+	// Spin up a new node, Dave.
+	dave := ht.NewNode("Dave", nil)
+
+	// Explicitly assert that Dave was started with bootstrapping disabled.
+	require.False(ht, dave.Cfg.WithPeerBootstrap)
+
+	// Assert that Dave's current view of the graph is empty.
+	ht.AssertNumEdges(dave, 0, false)
+
+	// Now, connect Dave to Alice and wait for gossip sync to complete.
+	ht.EnsureConnected(dave, alice)
+	ht.AssertNumEdges(dave, 2, false)
+
+	// Disconnect Dave from Alice and restart Dave. Since Alice and Dave
+	// did not have channels between them, the nodes should not reconnect
+	// to each other.
+	ht.DisconnectNodes(dave, alice)
+	ht.RestartNode(dave)
+
+	// Dave still has bootstrapping disabled and so it should not connect
+	// to any peers.
+	err := wait.Invariant(func() bool {
+		peerResp := dave.RPC.ListPeers()
+
+		return len(peerResp.Peers) == 0
+	}, time.Second*5)
+	require.NoError(ht, err)
+
+	// Dave should still know about the full graph though since it was
+	// synced previously from Alice.
+	ht.AssertNumEdges(dave, 2, false)
+
+	// Restart Dave again but this time with bootstrapping enabled.
+	dave.Cfg.WithPeerBootstrap = true
+	ht.RestartNode(dave)
+
+	// Show that Dave now does connect to some peers. The default minimum
+	// number of peers that will be connected to is 3, so we
+	// expect Dave to connect to all three nodes in the network.
+	ht.AssertConnected(dave, alice)
+	ht.AssertConnected(dave, bob)
+	ht.AssertConnected(dave, carol)
+}