BOLT2: Check we don't send and accept 0-msat HTLC

lightning/src/ln/channel.rs

@@ -433,10 +433,6 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 		cmp::max(at_open_background_feerate * B_OUTPUT_PLUS_SPENDING_INPUT_WEIGHT / 1000, 546) //TODO
 	}
 
-	fn derive_our_htlc_minimum_msat(_at_open_channel_feerate_per_kw: u64) -> u64 {
-		1000 // TODO
-	}
-
 	// Constructors:
 	pub fn new_outbound<K: Deref, F: Deref>(fee_estimator: &F, keys_provider: &K, their_node_id: PublicKey, channel_value_satoshis: u64, push_msat: u64, user_id: u64, logger: Arc<Logger>, config: &UserConfig) -> Result<Channel<ChanSigner>, APIError>
 	where K::Target: KeysInterface<ChanKeySigner = ChanSigner>,
@@ -519,7 +515,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 			their_max_htlc_value_in_flight_msat: 0,
 			their_channel_reserve_satoshis: 0,
 			their_htlc_minimum_msat: 0,
-			our_htlc_minimum_msat: Channel::<ChanSigner>::derive_our_htlc_minimum_msat(feerate),
+			our_htlc_minimum_msat: if config.own_channel_config.our_htlc_minimum_msat == 0 { 1 } else { config.own_channel_config.our_htlc_minimum_msat },
 			their_to_self_delay: 0,
 			our_to_self_delay: config.own_channel_config.our_to_self_delay,
 			their_max_accepted_htlcs: 0,
@@ -744,7 +740,7 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 			their_max_htlc_value_in_flight_msat: cmp::min(msg.max_htlc_value_in_flight_msat, msg.funding_satoshis * 1000),
 			their_channel_reserve_satoshis: msg.channel_reserve_satoshis,
 			their_htlc_minimum_msat: msg.htlc_minimum_msat,
-			our_htlc_minimum_msat: Channel::<ChanSigner>::derive_our_htlc_minimum_msat(msg.feerate_per_kw as u64),
+			our_htlc_minimum_msat: if config.own_channel_config.our_htlc_minimum_msat == 0 { 1 } else { config.own_channel_config.our_htlc_minimum_msat },
 			their_to_self_delay: msg.to_self_delay,
 			our_to_self_delay: config.own_channel_config.our_to_self_delay,
 			their_max_accepted_htlcs: msg.max_accepted_htlcs,
@@ -1656,6 +1652,9 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 		if msg.amount_msat > self.channel_value_satoshis * 1000 {
 			return Err(ChannelError::Close("Remote side tried to send more than the total value of the channel"));
 		}
+		if msg.amount_msat == 0 {
+			return Err(ChannelError::Close("Remote side tried to send a 0-msat HTLC"));
+		}
 		if msg.amount_msat < self.our_htlc_minimum_msat {
 			return Err(ChannelError::Close("Remote side tried to send less than our minimum HTLC value"));
 		}
@@ -3493,6 +3492,11 @@ impl<ChanSigner: ChannelKeys> Channel<ChanSigner> {
 		if amount_msat > self.channel_value_satoshis * 1000 {
 			return Err(ChannelError::Ignore("Cannot send more than the total value of the channel"));
 		}
+
+		if amount_msat == 0 {
+			return Err(ChannelError::Ignore("Cannot send 0-msat HTLC"));
+		}
+
 		if amount_msat < self.their_htlc_minimum_msat {
 			return Err(ChannelError::Ignore("Cannot send less than their minimum HTLC value"));
 		}

lightning/src/ln/functional_test_utils.rs

@@ -1005,6 +1005,7 @@ pub fn create_node_chanmgrs<'a, 'b>(node_count: usize, cfgs: &'a Vec<NodeCfg<'b>
 		let mut default_config = UserConfig::default();
 		default_config.channel_options.announced_channel = true;
 		default_config.peer_channel_config_limits.force_announced_channel_preference = false;
+		default_config.own_channel_config.our_htlc_minimum_msat = 1000; // sanitization being done by the sender, to exerce receiver logic we need to lift of limit
 		let node = ChannelManager::new(Network::Testnet, cfgs[i].fee_estimator, &cfgs[i].chan_monitor, cfgs[i].tx_broadcaster, cfgs[i].logger.clone(), &cfgs[i].keys_manager, if node_config[i].is_some() { node_config[i].clone().unwrap() } else { default_config }, 0).unwrap();
 		chanmgrs.push(node);
 	}

lightning/src/ln/functional_tests.rs

@@ -5486,7 +5486,6 @@ fn bolt2_open_channel_sending_node_checks_part2() {
 
 #[test]
 fn test_update_add_htlc_bolt2_sender_value_below_minimum_msat() {
-	//BOLT2 Requirement: MUST offer amount_msat greater than 0.
 	//BOLT2 Requirement: MUST NOT offer amount_msat below the receiving node's htlc_minimum_msat (same validation check catches both of these)
 	let chanmon_cfgs = create_chanmon_cfgs(2);
 	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
@@ -5496,7 +5495,7 @@ fn test_update_add_htlc_bolt2_sender_value_below_minimum_msat() {
 	let mut route = nodes[0].router.get_route(&nodes[1].node.get_our_node_id(), None, &[], 100000, TEST_FINAL_CLTV).unwrap();
 	let (_, our_payment_hash) = get_payment_preimage_hash!(nodes[0]);
 
-	route.hops[0].fee_msat = 0;
+	route.hops[0].fee_msat = 100;
 
 	let err = nodes[0].node.send_payment(route, our_payment_hash);
 
@@ -5509,6 +5508,51 @@ fn test_update_add_htlc_bolt2_sender_value_below_minimum_msat() {
 	nodes[0].logger.assert_log("lightning::ln::channelmanager".to_string(), "Cannot send less than their minimum HTLC value".to_string(), 1);
 }
 
+#[test]
+fn test_update_add_htlc_bolt2_sender_zero_value_msat() {
+	//BOLT2 Requirement: MUST offer amount_msat greater than 0.
+	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, None]);
+	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+	let _chan = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100000, 95000000, InitFeatures::supported(), InitFeatures::supported());
+	let mut route = nodes[0].router.get_route(&nodes[1].node.get_our_node_id(), None, &[], 100000, TEST_FINAL_CLTV).unwrap();
+	let (_, our_payment_hash) = get_payment_preimage_hash!(nodes[0]);
+
+	route.hops[0].fee_msat = 0;
+
+	let err = nodes[0].node.send_payment(route, our_payment_hash);
+
+	if let Err(APIError::ChannelUnavailable{err}) = err {
+		assert_eq!(err, "Cannot send 0-msat HTLC");
+	} else {
+		assert!(false);
+	}
+	assert!(nodes[0].node.get_and_clear_pending_msg_events().is_empty());
+	nodes[0].logger.assert_log("lightning::ln::channelmanager".to_string(), "Cannot send 0-msat HTLC".to_string(), 1);
+}
+
+#[test]
+fn test_update_add_htlc_bolt2_receiver_zero_value_msat() {
+	//BOLT2 Requirement: MUST offer amount_msat greater than 0.
+	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, None]);
+	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+	let _chan = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 100000, 95000000, InitFeatures::supported(), InitFeatures::supported());
+	let route = nodes[0].router.get_route(&nodes[1].node.get_our_node_id(), None, &[], 100000, TEST_FINAL_CLTV).unwrap();
+	let (_, our_payment_hash) = get_payment_preimage_hash!(nodes[0]);
+
+	nodes[0].node.send_payment(route, our_payment_hash);
+	check_added_monitors!(nodes[0], 1);
+	let mut updates = get_htlc_update_msgs!(nodes[0], nodes[1].node.get_our_node_id());
+	updates.update_add_htlcs[0].amount_msat = 0;
+
+	nodes[1].node.handle_update_add_htlc(&nodes[0].node.get_our_node_id(), &updates.update_add_htlcs[0]);
+	nodes[1].logger.assert_log("lightning::ln::channelmanager".to_string(), "Remote side tried to send a 0-msat HTLC".to_string(), 1);
+	check_closed_broadcast!(nodes[1], true).unwrap();
+}
+
 #[test]
 fn test_update_add_htlc_bolt2_sender_cltv_expiry_too_high() {
 	//BOLT 2 Requirement: MUST set cltv_expiry less than 500000000.
@@ -7271,3 +7315,21 @@ fn test_override_channel_config() {
 	assert_eq!(res.channel_flags, 0);
 	assert_eq!(res.to_self_delay, 200);
 }
+
+#[test]
+fn test_override_0msat_htlc_minimum() {
+	let mut zero_config = UserConfig::default();
+	zero_config.own_channel_config.our_htlc_minimum_msat = 0;
+	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(zero_config.clone())]);
+	let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	nodes[0].node.create_channel(nodes[1].node.get_our_node_id(), 16_000_000, 12_000_000, 42, Some(zero_config)).unwrap();
+	let res = get_event_msg!(nodes[0], MessageSendEvent::SendOpenChannel, nodes[1].node.get_our_node_id());
+	assert_eq!(res.htlc_minimum_msat, 1);
+
+	nodes[1].node.handle_open_channel(&nodes[0].node.get_our_node_id(), InitFeatures::supported(), &res);
+	let res = get_event_msg!(nodes[1], MessageSendEvent::SendAcceptChannel, nodes[0].node.get_our_node_id());
+	assert_eq!(res.htlc_minimum_msat, 1);
+}

lightning/src/util/config.rs

@@ -51,13 +51,22 @@ pub struct ChannelHandshakeConfig {
 	/// Default value: BREAKDOWN_TIMEOUT (currently 144), we enforce it as a minimum at channel
 	/// opening so you can tweak config to ask for more security, not less.
 	pub our_to_self_delay: u16,
+	/// Set to the smallest value HTLC we will accept to process.
+	///
+	/// This value is sent to our counterparty on channel-open and we close the channel any time
+	/// our counterparty misbehaves by sending us an HTLC with a value smaller than this.
+	///
+	/// Default value: 1. If the value is less than 1, it is ignored and set to 1, as is required
+	/// by the protocol.
+	pub our_htlc_minimum_msat: u64,
 }
 
 impl Default for ChannelHandshakeConfig {
 	fn default() -> ChannelHandshakeConfig {
 		ChannelHandshakeConfig {
 			minimum_depth: 6,
 			our_to_self_delay: BREAKDOWN_TIMEOUT,
+			our_htlc_minimum_msat: 1,
 		}
 	}
 }