itest: demonstrate UpdateAddHTLC reloading bug

This commit adds a new route blinding itest that demonstrates that the
reloading and re-forwarding of an UpdateAddHTLC message on restart
currently is done incorrectly for a blinded path payment. This is due to
the fact that the blinding point member is not currently set correctly.
This is fixed in the next commit which will also change the test to
assert that the behaviour is now correct.

itest/list_on_test.go

@@ -578,6 +578,10 @@ var allTestCases = []*lntest.TestCase{
 		Name:     "update pending open channels",
 		TestFunc: testUpdateOnPendingOpenChannels,
 	},
+	{
+		Name:     "blinded payment htlc re-forward",
+		TestFunc: testBlindedPaymentHTLCReForward,
+	},
 	{
 		Name:     "query blinded route",
 		TestFunc: testQueryBlindedRoutes,

itest/lnd_route_blinding_test.go

@@ -1424,3 +1424,75 @@ func testMPPToMultipleBlindedPaths(ht *lntest.HarnessTest) {
 		ht.AssertNumWaitingClose(hn, 0)
 	}
 }
+
+// testBlindedPaymentHTLCReForward tests that an UpdateAddHTLC message is
+// correctly persisted, reloaded and resent to the next peer on restart in the
+// case where the sending peer does not get a chance to send the message before
+// restarting. This test specifically tests that this is done correctly for
+// a blinded path payment since this adds a new blinding point field to
+// UpdateAddHTLC which we need to ensure gets included in the message on
+// restart.
+//
+// NOTE: this first version of this test asserts that this fails. This is to
+// demonstrate that a bug exists in the reloading and forwarding code. This will
+// be fixed in a following commit.
+func testBlindedPaymentHTLCReForward(ht *lntest.HarnessTest) {
+	// Setup a test case.
+	ctx, testCase := newBlindedForwardTest(ht)
+	defer testCase.cleanup()
+
+	// Set up network with carol interceptor.
+	testCase.setupNetwork(ctx, true)
+
+	// Let dave create invoice.
+	blindedPaymentPath := testCase.buildBlindedPath()
+	route := testCase.createRouteToBlinded(10_000_000, blindedPaymentPath)
+
+	// Once our interceptor is set up, we can send the blinded payment.
+	hash := sha256.Sum256(testCase.preimage[:])
+	sendReq := &routerrpc.SendToRouteRequest{
+		PaymentHash: hash[:],
+		Route:       route,
+	}
+
+	// In a goroutine, we let Alice pay the invoice from dave.
+	//
+	// NOTE: for now, we assert that this attempt fails. Once the noted bug
+	// is fixed, this will be changed to a success assertion.
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+
+		htlcAttempt, err := testCase.ht.Alice.RPC.Router.SendToRouteV2(
+			ctx, sendReq,
+		)
+		require.NoError(testCase.ht, err)
+		require.Equal(
+			testCase.ht, lnrpc.HTLCAttempt_FAILED,
+			htlcAttempt.Status,
+		)
+	}()
+
+	// Wait for the HTLC to be active on Alice and Bob's channels.
+	ht.AssertOutgoingHTLCActive(ht.Alice, testCase.channels[0], hash[:])
+	ht.AssertOutgoingHTLCActive(ht.Bob, testCase.channels[1], hash[:])
+
+	// Intercept the forward on Carol's link. At this point, we know she
+	// has received the HTLC and so will persist this packet.
+	_, err := testCase.carolInterceptor.Recv()
+	require.NoError(ht, err)
+
+	// Now, restart Carol. This time, don't require an interceptor. This
+	// means that Carol should load up any previously persisted
+	// UpdateAddHTLC messages and continue the processing of them.
+	ht.RestartNodeWithExtraArgs(
+		testCase.carol, []string{"--bitcoin.timelockdelta=18"},
+	)
+
+	// Now, wait for the payment to complete.
+	select {
+	case <-done:
+	case <-time.After(defaultTimeout):
+		require.Fail(ht, "timeout waiting for sending payment")
+	}
+}