+
+#[test]
+fn test_blocked_chan_preimage_release() {
+ // Test that even if a channel's `ChannelMonitorUpdate` flow is blocked waiting on an event to
+ // be handled HTLC preimage `ChannelMonitorUpdate`s will still go out.
+ let chanmon_cfgs = create_chanmon_cfgs(3);
+ let node_cfgs = create_node_cfgs(3, &chanmon_cfgs);
+ let node_chanmgrs = create_node_chanmgrs(3, &node_cfgs, &[None, None, None]);
+ let mut nodes = create_network(3, &node_cfgs, &node_chanmgrs);
+
+ create_announced_chan_between_nodes(&nodes, 0, 1).2;
+ create_announced_chan_between_nodes(&nodes, 1, 2).2;
+
+ send_payment(&nodes[0], &[&nodes[1], &nodes[2]], 5_000_000);
+
+ // Tee up two payments in opposite directions across nodes[1], one it sent to generate a
+ // PaymentSent event and one it forwards.
+ let (payment_preimage_1, payment_hash_1, _) = route_payment(&nodes[1], &[&nodes[2]], 1_000_000);
+ let (payment_preimage_2, payment_hash_2, _) = route_payment(&nodes[2], &[&nodes[1], &nodes[0]], 1_000_000);
+
+ // Claim the first payment to get a `PaymentSent` event (but don't handle it yet).
+ nodes[2].node.claim_funds(payment_preimage_1);
+ check_added_monitors(&nodes[2], 1);
+ expect_payment_claimed!(nodes[2], payment_hash_1, 1_000_000);
+
+ let cs_htlc_fulfill_updates = get_htlc_update_msgs!(nodes[2], nodes[1].node.get_our_node_id());
+ nodes[1].node.handle_update_fulfill_htlc(&nodes[2].node.get_our_node_id(), &cs_htlc_fulfill_updates.update_fulfill_htlcs[0]);
+ do_commitment_signed_dance(&nodes[1], &nodes[2], &cs_htlc_fulfill_updates.commitment_signed, false, false);
+ check_added_monitors(&nodes[1], 0);
+
+ // Now claim the second payment on nodes[0], which will ultimately result in nodes[1] trying to
+ // claim an HTLC on its channel with nodes[2], but that channel is blocked on the above
+ // `PaymentSent` event.
+ nodes[0].node.claim_funds(payment_preimage_2);
+ check_added_monitors(&nodes[0], 1);
+ expect_payment_claimed!(nodes[0], payment_hash_2, 1_000_000);
+
+ let as_htlc_fulfill_updates = get_htlc_update_msgs!(nodes[0], nodes[1].node.get_our_node_id());
+ nodes[1].node.handle_update_fulfill_htlc(&nodes[0].node.get_our_node_id(), &as_htlc_fulfill_updates.update_fulfill_htlcs[0]);
+ check_added_monitors(&nodes[1], 1); // We generate only a preimage monitor update
+ assert!(nodes[1].node.get_and_clear_pending_msg_events().is_empty());
+
+ // Finish the CS dance between nodes[0] and nodes[1].
+ do_commitment_signed_dance(&nodes[1], &nodes[0], &as_htlc_fulfill_updates.commitment_signed, false, false);
+ check_added_monitors(&nodes[1], 0);
+
+ let events = nodes[1].node.get_and_clear_pending_events();
+ assert_eq!(events.len(), 3);
+ if let Event::PaymentSent { .. } = events[0] {} else { panic!(); }
+ if let Event::PaymentPathSuccessful { .. } = events[2] {} else { panic!(); }
+ if let Event::PaymentForwarded { .. } = events[1] {} else { panic!(); }
+
+ // The event processing should release the last RAA update.
+ check_added_monitors(&nodes[1], 1);
+
+ // When we fetch the next update the message getter will generate the next update for nodes[2],
+ // generating a further monitor update.
+ let bs_htlc_fulfill_updates = get_htlc_update_msgs!(nodes[1], nodes[2].node.get_our_node_id());
+ check_added_monitors(&nodes[1], 1);
+
+ nodes[2].node.handle_update_fulfill_htlc(&nodes[1].node.get_our_node_id(), &bs_htlc_fulfill_updates.update_fulfill_htlcs[0]);
+ do_commitment_signed_dance(&nodes[2], &nodes[1], &bs_htlc_fulfill_updates.commitment_signed, false, false);
+ expect_payment_sent(&nodes[2], payment_preimage_2, None, true, true);
+}