routing: add methods checkTimeout and requestRoute

This commit refactors the `resumePayment` method by adding the methods
`checkTimeout` and `requestRoute` so it's easier to understand the flow
and reason about the error handling.

routing/payment_lifecycle_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/routing/route"
+	"github.com/stretchr/testify/mock"
 	"github.com/stretchr/testify/require"
 )
 
@@ -818,3 +819,296 @@ func makeAttemptInfo(total, amtForwarded int) channeldb.HTLCAttemptInfo {
 		},
 	}
 }
+
+// TestCheckTimeoutTimedOut checks that when the payment times out, it is
+// marked as failed.
+func TestCheckTimeoutTimedOut(t *testing.T) {
+	t.Parallel()
+
+	p := createTestPaymentLifecycle()
+
+	// Mock the control tower's `FailPayment` method.
+	ct := &mockControlTower{}
+	ct.On("FailPayment",
+		p.identifier, channeldb.FailureReasonTimeout).Return(nil)
+
+	// Mount the mocked control tower.
+	p.router.cfg.Control = ct
+
+	// Make the timeout happens instantly.
+	p.timeoutChan = time.After(1 * time.Nanosecond)
+
+	// Sleep one millisecond to make sure it timed out.
+	time.Sleep(1 * time.Millisecond)
+
+	// Call the function and expect no error.
+	err := p.checkTimeout()
+	require.NoError(t, err)
+
+	// Assert that `FailPayment` is called as expected.
+	ct.AssertExpectations(t)
+
+	// We now test that when `FailPayment` returns an error, it's returned
+	// by the function too.
+	//
+	// Mock `FailPayment` to return a dummy error.
+	dummyErr := errors.New("dummy")
+	ct = &mockControlTower{}
+	ct.On("FailPayment",
+		p.identifier, channeldb.FailureReasonTimeout).Return(dummyErr)
+
+	// Mount the mocked control tower.
+	p.router.cfg.Control = ct
+
+	// Make the timeout happens instantly.
+	p.timeoutChan = time.After(1 * time.Nanosecond)
+
+	// Sleep one millisecond to make sure it timed out.
+	time.Sleep(1 * time.Millisecond)
+
+	// Call the function and expect an error.
+	err = p.checkTimeout()
+	require.ErrorIs(t, err, dummyErr)
+
+	// Assert that `FailPayment` is called as expected.
+	ct.AssertExpectations(t)
+}
+
+// TestCheckTimeoutOnRouterQuit checks that when the router has quit, an error
+// is returned from checkTimeout.
+func TestCheckTimeoutOnRouterQuit(t *testing.T) {
+	t.Parallel()
+
+	p := createTestPaymentLifecycle()
+
+	close(p.router.quit)
+	err := p.checkTimeout()
+	require.ErrorIs(t, err, ErrRouterShuttingDown)
+}
+
+// createTestPaymentLifecycle creates a `paymentLifecycle` using the mocks.
+func createTestPaymentLifecycle() *paymentLifecycle {
+	paymentHash := lntypes.Hash{1, 2, 3}
+	quitChan := make(chan struct{})
+	rt := &ChannelRouter{
+		cfg:  &Config{},
+		quit: quitChan,
+	}
+
+	return &paymentLifecycle{
+		router:     rt,
+		identifier: paymentHash,
+	}
+}
+
+// TestRequestRouteSucceed checks that `requestRoute` can successfully request
+// a route.
+func TestRequestRouteSucceed(t *testing.T) {
+	t.Parallel()
+
+	p := createTestPaymentLifecycle()
+
+	// Create a mock payment session and a dummy route.
+	paySession := &mockPaymentSession{}
+	dummyRoute := &route.Route{}
+
+	// Mount the mocked payment session.
+	p.paySession = paySession
+
+	// Create a dummy payment state.
+	ps := &channeldb.MPPaymentState{
+		NumAttemptsInFlight: 1,
+		RemainingAmt:        1,
+		FeesPaid:            100,
+	}
+
+	// Mock remainingFees to be 1.
+	p.feeLimit = ps.FeesPaid + 1
+
+	// Mock the paySession's `RequestRoute` method to return no error.
+	paySession.On("RequestRoute",
+		mock.Anything, mock.Anything, mock.Anything, mock.Anything,
+	).Return(dummyRoute, nil)
+
+	result, err := p.requestRoute(ps)
+	require.NoError(t, err, "expect no error")
+	require.Equal(t, dummyRoute, result, "returned route not matched")
+
+	// Assert that `RequestRoute` is called as expected.
+	paySession.AssertExpectations(t)
+}
+
+// TestRequestRouteHandleCriticalErr checks that `requestRoute` can
+// successfully handle a critical error returned from payment session.
+func TestRequestRouteHandleCriticalErr(t *testing.T) {
+	t.Parallel()
+
+	p := createTestPaymentLifecycle()
+
+	// Create a mock payment session.
+	paySession := &mockPaymentSession{}
+
+	// Mount the mocked payment session.
+	p.paySession = paySession
+
+	// Create a dummy payment state.
+	ps := &channeldb.MPPaymentState{
+		NumAttemptsInFlight: 1,
+		RemainingAmt:        1,
+		FeesPaid:            100,
+	}
+
+	// Mock remainingFees to be 1.
+	p.feeLimit = ps.FeesPaid + 1
+
+	// Mock the paySession's `RequestRoute` method to return an error.
+	dummyErr := errors.New("dummy")
+	paySession.On("RequestRoute",
+		mock.Anything, mock.Anything, mock.Anything, mock.Anything,
+	).Return(nil, dummyErr)
+
+	result, err := p.requestRoute(ps)
+
+	// Expect an error is returned since it's critical.
+	require.ErrorIs(t, err, dummyErr, "error not matched")
+	require.Nil(t, result, "expected no route returned")
+
+	// Assert that `RequestRoute` is called as expected.
+	paySession.AssertExpectations(t)
+}
+
+// TestRequestRouteHandleNoRouteErr checks that `requestRoute` can successfully
+// handle the `noRouteError` returned from payment session.
+func TestRequestRouteHandleNoRouteErr(t *testing.T) {
+	t.Parallel()
+
+	p := createTestPaymentLifecycle()
+
+	// Create a mock payment session.
+	paySession := &mockPaymentSession{}
+
+	// Mount the mocked payment session.
+	p.paySession = paySession
+
+	// Create a dummy payment state.
+	ps := &channeldb.MPPaymentState{
+		NumAttemptsInFlight: 1,
+		RemainingAmt:        1,
+		FeesPaid:            100,
+	}
+
+	// Mock remainingFees to be 1.
+	p.feeLimit = ps.FeesPaid + 1
+
+	// Mock the paySession's `RequestRoute` method to return an error.
+	paySession.On("RequestRoute",
+		mock.Anything, mock.Anything, mock.Anything, mock.Anything,
+	).Return(nil, errNoTlvPayload)
+
+	result, err := p.requestRoute(ps)
+
+	// Expect no error is returned since it's not critical.
+	require.NoError(t, err, "expected no error")
+	require.Nil(t, result, "expected no route returned")
+
+	// Assert that `RequestRoute` is called as expected.
+	paySession.AssertExpectations(t)
+}
+
+// TestRequestRouteFailPaymentSucceed checks that `requestRoute` fails the
+// payment when received an `noRouteError` returned from payment session while
+// it has no inflight attempts.
+func TestRequestRouteFailPaymentSucceed(t *testing.T) {
+	t.Parallel()
+
+	p := createTestPaymentLifecycle()
+
+	// Create a mock payment session.
+	paySession := &mockPaymentSession{}
+
+	// Mock the control tower's `FailPayment` method.
+	ct := &mockControlTower{}
+	ct.On("FailPayment",
+		p.identifier, errNoTlvPayload.FailureReason(),
+	).Return(nil)
+
+	// Mount the mocked control tower and payment session.
+	p.router.cfg.Control = ct
+	p.paySession = paySession
+
+	// Create a dummy payment state with zero inflight attempts.
+	ps := &channeldb.MPPaymentState{
+		NumAttemptsInFlight: 0,
+		RemainingAmt:        1,
+		FeesPaid:            100,
+	}
+
+	// Mock remainingFees to be 1.
+	p.feeLimit = ps.FeesPaid + 1
+
+	// Mock the paySession's `RequestRoute` method to return an error.
+	paySession.On("RequestRoute",
+		mock.Anything, mock.Anything, mock.Anything, mock.Anything,
+	).Return(nil, errNoTlvPayload)
+
+	result, err := p.requestRoute(ps)
+
+	// Expect no error is returned since it's not critical.
+	require.NoError(t, err, "expected no error")
+	require.Nil(t, result, "expected no route returned")
+
+	// Assert that `RequestRoute` is called as expected.
+	paySession.AssertExpectations(t)
+
+	// Assert that `FailPayment` is called as expected.
+	ct.AssertExpectations(t)
+}
+
+// TestRequestRouteFailPaymentError checks that `requestRoute` returns the
+// error from calling `FailPayment`.
+func TestRequestRouteFailPaymentError(t *testing.T) {
+	t.Parallel()
+
+	p := createTestPaymentLifecycle()
+
+	// Create a mock payment session.
+	paySession := &mockPaymentSession{}
+
+	// Mock the control tower's `FailPayment` method.
+	ct := &mockControlTower{}
+	dummyErr := errors.New("dummy")
+	ct.On("FailPayment",
+		p.identifier, errNoTlvPayload.FailureReason(),
+	).Return(dummyErr)
+
+	// Mount the mocked control tower and payment session.
+	p.router.cfg.Control = ct
+	p.paySession = paySession
+
+	// Create a dummy payment state with zero inflight attempts.
+	ps := &channeldb.MPPaymentState{
+		NumAttemptsInFlight: 0,
+		RemainingAmt:        1,
+		FeesPaid:            100,
+	}
+
+	// Mock remainingFees to be 1.
+	p.feeLimit = ps.FeesPaid + 1
+
+	// Mock the paySession's `RequestRoute` method to return an error.
+	paySession.On("RequestRoute",
+		mock.Anything, mock.Anything, mock.Anything, mock.Anything,
+	).Return(nil, errNoTlvPayload)
+
+	result, err := p.requestRoute(ps)
+
+	// Expect an error is returned.
+	require.ErrorIs(t, err, dummyErr, "error not matched")
+	require.Nil(t, result, "expected no route returned")
+
+	// Assert that `RequestRoute` is called as expected.
+	paySession.AssertExpectations(t)
+
+	// Assert that `FailPayment` is called as expected.
+	ct.AssertExpectations(t)
+}