askrene: add test for reservation leaks

Changelog-None.

Signed-off-by: Lagrang3 <lagrang3@protonmail.com>

Author: Lagrang3

tests/test_askrene.py

@@ -1473,3 +1473,58 @@ def test_simple_dummy_channel(node_factory):
         final_cltv=5,
         layers=["mylayer"],
     )
+
+
+def test_reservations_leak(node_factory, executor):
+    l1, l2, l3, l4, l5 = node_factory.get_nodes(
+        5,
+        opts=[
+            {},
+            {},
+            {"plugin": os.path.join(os.getcwd(), "tests/plugins/hold_htlcs.py")},
+            {},
+            {},
+        ],
+    )
+
+    # There must be a common non-local channel in both payment paths.
+    # With a local channel we cannot trigger the reservation leak because we
+    # reserve slightly different amounts locally due to HTLC onchain costs.
+    node_factory.join_nodes([l1, l2, l4, l3], wait_for_announce=True)
+    node_factory.join_nodes([l1, l2, l4, l5], wait_for_announce=True)
+
+    # Use offers instead of bolt11 because we are going to pay through a blinded
+    # path and trigger a fake channel collision between both payments.
+    offer1 = l3.rpc.offer("any")["bolt12"]
+    offer2 = l5.rpc.offer("any")["bolt12"]
+
+    inv1 = l1.rpc.fetchinvoice(offer1, "100sat")["invoice"]
+    inv2 = l1.rpc.fetchinvoice(offer2, "100sat")["invoice"]
+
+    # Initiate the first payment that has a delay.
+    fut = executor.submit(l1.rpc.xpay, (inv1))
+
+    # Wait for the first payment to reserve the path.
+    l1.daemon.wait_for_log(r"json_askrene_reserve called")
+
+    # A second payment starts.
+    l1.rpc.xpay(inv2)
+    l1.daemon.wait_for_log(r"json_askrene_unreserve called")
+
+    l3.daemon.wait_for_log(r"Holding onto an incoming htlc for 10 seconds")
+
+    # There is a payment pending therefore we expect reservations.
+    reservations = l1.rpc.askrene_listreservations()
+    assert reservations != {"reservations": []}
+
+    l3.daemon.wait_for_log(r"htlc_accepted hook called")
+    fut.result()
+    l1.daemon.wait_for_log(r"json_askrene_unreserve called")
+
+    # The first payment has finished we expect no reservations.
+    reservations = l1.rpc.askrene_listreservations()
+    assert reservations == {"reservations": []}
+
+    # We shouldn't fail askrene-unreserve. If it does it means something went
+    # wrong.
+    assert l1.daemon.is_in_log("askrene-unreserve failed") is None