Track the sender's skimmed fee in UpdateAddHTLC

Author: valentinewallace

lightning/src/ln/channel.rs

@@ -4019,6 +4019,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 					payment_hash: htlc.payment_hash,
 					cltv_expiry: htlc.cltv_expiry,
 					onion_routing_packet: (**onion_packet).clone(),
+					skimmed_fee_msat: None,
 				});
 			}
 		}
@@ -5947,6 +5948,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 			payment_hash,
 			cltv_expiry,
 			onion_routing_packet,
+			skimmed_fee_msat: None,
 		};
 		self.next_holder_htlc_id += 1;
 

lightning/src/ln/functional_tests.rs

@@ -1387,6 +1387,7 @@ fn test_fee_spike_violation_fails_htlc() {
 		payment_hash: payment_hash,
 		cltv_expiry: htlc_cltv,
 		onion_routing_packet: onion_packet,
+		skimmed_fee_msat: None,
 	};
 
 	nodes[1].node.handle_update_add_htlc(&nodes[0].node.get_our_node_id(), &msg);
@@ -1575,6 +1576,7 @@ fn test_chan_reserve_violation_inbound_htlc_outbound_channel() {
 		payment_hash: payment_hash,
 		cltv_expiry: htlc_cltv,
 		onion_routing_packet: onion_packet,
+		skimmed_fee_msat: None,
 	};
 
 	nodes[0].node.handle_update_add_htlc(&nodes[1].node.get_our_node_id(), &msg);
@@ -1749,6 +1751,7 @@ fn test_chan_reserve_violation_inbound_htlc_inbound_chan() {
 		payment_hash: our_payment_hash_1,
 		cltv_expiry: htlc_cltv,
 		onion_routing_packet: onion_packet,
+		skimmed_fee_msat: None,
 	};
 
 	nodes[1].node.handle_update_add_htlc(&nodes[0].node.get_our_node_id(), &msg);
@@ -3402,6 +3405,7 @@ fn fail_backward_pending_htlc_upon_channel_failure() {
 			payment_hash,
 			cltv_expiry,
 			onion_routing_packet,
+			skimmed_fee_msat: None,
 		};
 		nodes[0].node.handle_update_add_htlc(&nodes[1].node.get_our_node_id(), &update_add_htlc);
 	}
@@ -6258,6 +6262,7 @@ fn test_update_add_htlc_bolt2_receiver_check_max_htlc_limit() {
 		payment_hash: our_payment_hash,
 		cltv_expiry: htlc_cltv,
 		onion_routing_packet: onion_packet.clone(),
+		skimmed_fee_msat: None,
 	};
 
 	for i in 0..50 {

lightning/src/ln/msgs.rs

@@ -605,6 +605,11 @@ pub struct UpdateAddHTLC {
 	pub payment_hash: PaymentHash,
 	/// The expiry height of the HTLC
 	pub cltv_expiry: u32,
+	/// The extra fee skimmed by the sender of this message. See
+	/// [`ChannelConfig::accept_underpaying_htlcs`].
+	///
+	/// [`ChannelConfig::accept_underpaying_htlcs`]: crate::util::config::ChannelConfig::accept_underpaying_htlcs
+	pub skimmed_fee_msat: Option<u64>,
 	pub(crate) onion_routing_packet: OnionPacket,
 }
 
@@ -1883,8 +1888,10 @@ impl_writeable_msg!(UpdateAddHTLC, {
 	amount_msat,
 	payment_hash,
 	cltv_expiry,
-	onion_routing_packet
-}, {});
+	onion_routing_packet,
+}, {
+	(65537, skimmed_fee_msat, option)
+});
 
 impl Readable for OnionMessage {
 	fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
@@ -3309,7 +3316,8 @@ mod tests {
 			amount_msat: 3608586615801332854,
 			payment_hash: PaymentHash([1; 32]),
 			cltv_expiry: 821716,
-			onion_routing_packet
+			onion_routing_packet,
+			skimmed_fee_msat: None,
 		};
 		let encoded_value = update_add_htlc.encode();
 		let target_value = hex::decode("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").unwrap();