Fix bug where we encode flags field into all updates on htlc fail

Failing an HTLC with onion error channel_disabled requires encoding a 'flags' field into the failure
packet. However, we were encoding this 'flags' field for all failures packets that were failing on
update_add_htlc with an update (error 0x1000 UPDATE).

Discovered in the course of adding phantom payment failure tests, which also added testing for this bug

diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index e8aee263ae606be9af8ac6e06ab8f5ec13dddcca..47d6e1423bd8aa47d425364e0054ad97b34cb100 100644 (file)
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -4511,7 +4511,9 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
                                                                        onion_utils::build_first_hop_failure_packet(incoming_shared_secret, error_code, &{
                                                                                let mut res = Vec::with_capacity(8 + 128);
                                                                                // TODO: underspecified, follow https://github.com/lightningnetwork/lightning-rfc/issues/791
-                                                                               res.extend_from_slice(&byte_utils::be16_to_array(0));
+                                                                               if error_code == 0x1000 | 20 {
+                                                                                       res.extend_from_slice(&byte_utils::be16_to_array(0));
+                                                                               }
                                                                                res.extend_from_slice(&upd.encode_with_len()[..]);
                                                                                res
                                                                        }[..])

diff --git a/lightning/src/ln/onion_route_tests.rs b/lightning/src/ln/onion_route_tests.rs
index d2844c6ebcb886f56a4542c58915f58fd0ea2564..2aeecd108bccbab70abd81d972a5a7aef2fc00d1 100644 (file)
--- a/lightning/src/ln/onion_route_tests.rs
+++ b/lightning/src/ln/onion_route_tests.rs
@@ -898,3 +898,46 @@ fn test_phantom_failure_too_low_recv_amt() {
                .expected_htlc_error_data(0x4000 | 15, &error_data);
        expect_payment_failed_conditions!(nodes[0], payment_hash, true, fail_conditions);
 }
+
+#[test]
+fn test_phantom_dust_exposure_failure() {
+       // Set the max dust exposure to the dust limit.
+       let max_dust_exposure = 546;
+       let mut receiver_config = UserConfig::default();
+       receiver_config.channel_options.max_dust_htlc_exposure_msat = max_dust_exposure;
+       receiver_config.channel_options.announced_channel = true;
+
+       let chanmon_cfgs = create_chanmon_cfgs(2);
+       let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+       let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, Some(receiver_config)]);
+       let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+       let channel = create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known());
+
+       // Get the route with an amount exceeding the dust exposure threshold of nodes[1].
+       let (_, payment_hash, payment_secret) = get_payment_preimage_hash!(nodes[1], Some(max_dust_exposure + 1));
+       let (mut route, _) = get_phantom_route!(nodes, max_dust_exposure + 1, channel);
+
+       // Route the HTLC through to the destination.
+       nodes[0].node.send_payment(&route, payment_hash.clone(), &Some(payment_secret)).unwrap();
+       check_added_monitors!(nodes[0], 1);
+       let update_0 = get_htlc_update_msgs!(nodes[0], nodes[1].node.get_our_node_id());
+       let mut update_add = update_0.update_add_htlcs[0].clone();
+
+       nodes[1].node.handle_update_add_htlc(&nodes[0].node.get_our_node_id(), &update_add);
+       commitment_signed_dance!(nodes[1], nodes[0], &update_0.commitment_signed, false, true);
+
+       let update_1 = get_htlc_update_msgs!(nodes[1], nodes[0].node.get_our_node_id());
+       assert!(update_1.update_fail_htlcs.len() == 1);
+       let fail_msg = update_1.update_fail_htlcs[0].clone();
+       nodes[0].node.handle_update_fail_htlc(&nodes[1].node.get_our_node_id(), &fail_msg);
+       commitment_signed_dance!(nodes[0], nodes[1], update_1.commitment_signed, false);
+
+       // Ensure the payment fails with the expected error.
+       let mut error_data = channel.1.encode_with_len();
+       let mut fail_conditions = PaymentFailedConditions::new()
+               .blamed_scid(channel.0.contents.short_channel_id)
+               .blamed_chan_closed(false)
+               .expected_htlc_error_data(0x1000 | 7, &error_data);
+       expect_payment_failed_conditions!(nodes[0], payment_hash, false, fail_conditions);
+}