terminal: wait for lnd to be synced

Now that we can use lndclient's new "block until chain synced" feature,
we use that instead of polling until the chain notifier is ready. This
should work properly even for slower/more elaborate chain backends like
Neutrino.

Author: guggero

terminal.go

@@ -257,7 +257,10 @@ func (g *LightningTerminal) startSubservers(network string) error {
 	var basicClient lnrpc.LightningClient
 
 	// The main RPC listener of lnd might need some time to start, it could
-	// be that we run into a connection refused a few times.
+	// be that we run into a connection refused a few times. We use the
+	// basic client connection to find out if the RPC server is started yet
+	// because that doesn't do anything else than just connect. We'll check
+	// if lnd is also ready to be used in the next step.
 	err := wait.NoError(func() error {
 		// Create an lnd client now that we have the full configuration.
 		// We'll need a basic client and a full client because not all
@@ -270,61 +273,52 @@ func (g *LightningTerminal) startSubservers(network string) error {
 				g.cfg.Lnd.AdminMacPath,
 			)),
 		)
-		if err != nil {
-			return err
-		}
-		g.lndClient, err = lndclient.NewLndServices(
-			&lndclient.LndServicesConfig{
-				LndAddress:  g.lndAddr,
-				Network:     lndclient.Network(network),
-				MacaroonDir: filepath.Dir(g.cfg.Lnd.AdminMacPath),
-				TLSPath:     g.cfg.Lnd.TLSCertPath,
-			},
-		)
 		return err
-
 	}, defaultStartupTimeout)
 	if err != nil {
 		return err
 	}
 
-	// The chain notifier also needs some time to start. Loop will subscribe
-	// to the notifier and crash if it isn't ready yet, so we need to wait
-	// here as a workaround.
-	//
-	// TODO(guggero): Remove once loop can retry itself.
-	err = wait.NoError(func() error {
-		ctxt, cancel := context.WithTimeout(
-			context.Background(), defaultStartupTimeout,
-		)
-		defer cancel()
+	// Now we know that the connection itself is ready. But we also need to
+	// wait for two things: The chain notifier to be ready and the lnd
+	// wallet being fully synced to its chain backend. The chain notifier
+	// will always be ready first so if we instruct the lndclient to wait
+	// for the wallet sync, we should be fully ready to start all our
+	// subservers. This will just block until lnd signals readiness. But we
+	// still want to react to shutdown requests, so we need to listen for
+	// those.
+	ctxc, cancel := context.WithCancel(context.Background())
+	defer cancel()
 
-		notifier := g.lndClient.ChainNotifier
-		resChan, errChan, err := notifier.RegisterBlockEpochNtfn(
-			ctxt,
-		)
-		if err != nil {
-			return err
-		}
-
-		// Block until we get a positive/negative answer or the timeout
-		// is reached.
+	// Make sure the context is canceled if the user requests shutdown.
+	go func() {
 		select {
-		case <-resChan:
-			return nil
+		// Client requests shutdown, cancel the wait.
+		case <-signal.ShutdownChannel():
+			cancel()
 
-		case err := <-errChan:
-			return err
-
-		case <-ctxt.Done():
-			return fmt.Errorf("wait for chain notifier to be " +
-				"ready timed out")
+		// The check was completed and the above defer canceled the
+		// context. We can just exit the goroutine, nothing more to do.
+		case <-ctxc.Done():
 		}
-	}, defaultStartupTimeout)
+	}()
+	g.lndClient, err = lndclient.NewLndServices(
+		&lndclient.LndServicesConfig{
+			LndAddress: g.lndAddr,
+			Network:    lndclient.Network(network),
+			MacaroonDir: filepath.Dir(
+				g.cfg.Lnd.AdminMacPath,
+			),
+			TLSPath:               g.cfg.Lnd.TLSCertPath,
+			BlockUntilChainSynced: true,
+			ChainSyncCtx:          ctxc,
+		},
+	)
 	if err != nil {
 		return err
 	}
 
+	// Both connection types are ready now, let's start our subservers.
 	err = g.faradayServer.StartAsSubserver(g.lndClient.LndServices)
 	if err != nil {
 		return err