tests: lnpeer: test_dont_settle_partial_mpp_trigger_with_invalid_cltv_htlc

Adds unittest to verify that lnpeer doesn't settle any htlcs of
incomplete mpp.

tests/test_lnpeer.py

@@ -1336,6 +1336,84 @@ class TestPeerDirect(TestPeer):
         with self.assertRaises(SuccessfulTest):
             await f()
 
+    async def test_dont_settle_partial_mpp_trigger_with_invalid_cltv_htlc(self):
+        """Alice gets two htlcs as part of a mpp, one has a cltv too close to expiry and will get failed.
+        Test that the other htlc won't get settled if the mpp isn't complete anymore after failing the other htlc.
+        """
+        alice_channel, bob_channel = create_test_channels()
+        p1, p2, w1, w2, _q1, _q2 = self.prepare_peers(alice_channel, bob_channel)
+        async def pay():
+            await util.wait_for2(p1.initialized, 1)
+            await util.wait_for2(p2.initialized, 1)
+            w2.features |= LnFeatures.BASIC_MPP_OPT
+            lnaddr1, _pay_req = self.prepare_invoice(w2, amount_msat=10_000, min_final_cltv_delta=144)
+            self.assertTrue(lnaddr1.get_features().supports(LnFeatures.BASIC_MPP_OPT))
+            route = (await w1.create_routes_from_invoice(amount_msat=10_000, decoded_invoice=lnaddr1))[0][0].route
+
+            # now p1 sends two htlcs, one is valid (1 msat), one is invalid (9_999 msat)
+            p1.pay(
+                route=route,
+                chan=alice_channel,
+                amount_msat=1,
+                total_msat=lnaddr1.get_amount_msat(),
+                payment_hash=lnaddr1.paymenthash,
+                # this htlc is valid and will get accepted, but it shouldn't get settled
+                min_final_cltv_delta=400,
+                payment_secret=lnaddr1.payment_secret,
+            )
+            await asyncio.sleep(0.1)
+            assert w1.get_preimage(lnaddr1.paymenthash) is None
+            p1.pay(
+                route=route,
+                chan=alice_channel,
+                amount_msat=9_999,
+                total_msat=lnaddr1.get_amount_msat(),
+                payment_hash=lnaddr1.paymenthash,
+                # this htlc will get failed directly as the cltv is too close to expiry (< 144)
+                min_final_cltv_delta=1,
+                payment_secret=lnaddr1.payment_secret,
+            )
+
+            while nhtlc_success + nhtlc_failed < 2:
+                await htlc_resolved.wait()
+            # both htlcs of the mpp set should get failed and w2 shouldn't release the preimage
+            self.assertEqual(0, nhtlc_success, f"{nhtlc_success=} | {nhtlc_failed=}")
+            self.assertEqual(2, nhtlc_failed,  f"{nhtlc_success=} | {nhtlc_failed=}")
+            assert w1.get_preimage(lnaddr1.paymenthash) is None, "w1 shouldn't get the preimage"
+            raise SuccessfulTest()
+
+        async def f():
+            async with OldTaskGroup() as group:
+                await group.spawn(p1._message_loop())
+                await group.spawn(p1.htlc_switch())
+                await group.spawn(p2._message_loop())
+                await group.spawn(p2.htlc_switch())
+                await asyncio.sleep(0.01)
+                await group.spawn(pay())
+
+        htlc_resolved = asyncio.Event()
+        nhtlc_success = 0
+        nhtlc_failed = 0
+        async def on_htlc_fulfilled(*args):
+            htlc_resolved.set()
+            htlc_resolved.clear()
+            nonlocal nhtlc_success
+            nhtlc_success += 1
+        async def on_htlc_failed(*args):
+            htlc_resolved.set()
+            htlc_resolved.clear()
+            nonlocal nhtlc_failed
+            nhtlc_failed += 1
+        util.register_callback(on_htlc_fulfilled, ["htlc_fulfilled"])
+        util.register_callback(on_htlc_failed, ["htlc_failed"])
+
+        try:
+            with self.assertRaises(SuccessfulTest):
+                await f()
+        finally:
+            util.unregister_callback(on_htlc_fulfilled)
+            util.unregister_callback(on_htlc_failed)
+
     async def test_legacy_shutdown_low(self):
         await self._test_shutdown(alice_fee=100, bob_fee=150)