Support constructing and encoding onion payloads for blinded payments

Author: valentinewallace

lightning/src/ln/msgs.rs

@@ -1419,6 +1419,7 @@ pub trait OnionMessageHandler : OnionMessageProvider {
 }
 
 mod fuzzy_internal_msgs {
+	use bitcoin::secp256k1::PublicKey;
 	use crate::prelude::*;
 	use crate::ln::{PaymentPreimage, PaymentSecret};
 
@@ -1464,6 +1465,17 @@ mod fuzzy_internal_msgs {
 			amt_msat: u64,
 			outgoing_cltv_value: u32,
 		},
+		BlindedForward {
+			encrypted_tlvs: Vec<u8>,
+			intro_node_blinding_point: Option<PublicKey>,
+		},
+		BlindedReceive {
+			amt_msat: u64,
+			total_msat: u64,
+			outgoing_cltv_value: u32,
+			encrypted_tlvs: Vec<u8>,
+			intro_node_blinding_point: Option<PublicKey>, // Set if the introduction node of the blinded path is the final node
+		}
 	}
 
 	pub struct DecodedOnionErrorPacket {
@@ -2000,6 +2012,24 @@ impl Writeable for OutboundOnionPayload {
 					(16, payment_metadata.as_ref().map(|m| WithoutLength(m)), option)
 				}, custom_tlvs.iter());
 			},
+			Self::BlindedForward { encrypted_tlvs, intro_node_blinding_point } => {
+				_encode_varint_length_prefixed_tlv!(w, {
+					(10, *encrypted_tlvs, required_vec),
+					(12, intro_node_blinding_point, option)
+				});
+			},
+			Self::BlindedReceive {
+				amt_msat, total_msat, outgoing_cltv_value, encrypted_tlvs,
+				intro_node_blinding_point,
+			} => {
+				_encode_varint_length_prefixed_tlv!(w, {
+					(2, HighZeroBytesDroppedBigSize(*amt_msat), required),
+					(4, HighZeroBytesDroppedBigSize(*outgoing_cltv_value), required),
+					(10, *encrypted_tlvs, required_vec),
+					(12, intro_node_blinding_point, option),
+					(18, HighZeroBytesDroppedBigSize(*total_msat), required)
+				});
+			},
 		}
 		Ok(())
 	}

lightning/src/ln/onion_utils.rs

@@ -12,7 +12,7 @@ use crate::ln::channelmanager::{HTLCSource, RecipientOnionFields};
 use crate::ln::msgs;
 use crate::ln::wire::Encode;
 use crate::routing::gossip::NetworkUpdate;
-use crate::routing::router::{Path, RouteHop};
+use crate::routing::router::{BlindedTail, Path, RouteHop};
 use crate::util::chacha20::{ChaCha20, ChaChaReader};
 use crate::util::errors::{self, APIError};
 use crate::util::ser::{Readable, ReadableArgs, Writeable, Writer, LengthCalculatingWriter};
@@ -177,27 +177,51 @@ pub(super) fn build_onion_payloads(path: &Path, total_msat: u64, mut recipient_o
 		// the intended recipient).
 		let value_msat = if cur_value_msat == 0 { hop.fee_msat } else { cur_value_msat };
 		let cltv = if cur_cltv == starting_htlc_offset { hop.cltv_expiry_delta + starting_htlc_offset } else { cur_cltv };
-		res.insert(0, if idx == 0 {
-			msgs::OutboundOnionPayload::Receive {
-				payment_data: if let Some(secret) = recipient_onion.payment_secret.take() {
-					Some(msgs::FinalOnionHopData {
-						payment_secret: secret,
-						total_msat,
-					})
-				} else { None },
-				payment_metadata: recipient_onion.payment_metadata.take(),
-				keysend_preimage: *keysend_preimage,
-				custom_tlvs: recipient_onion.custom_tlvs.clone(),
-				amt_msat: value_msat,
-				outgoing_cltv_value: cltv,
+		if idx == 0 {
+			if let Some(BlindedTail {
+				blinding_point, hops, final_value_msat, excess_final_cltv_expiry_delta, ..
+			}) = &path.blinded_tail {
+				let mut blinding_point = Some(*blinding_point);
+				for (i, blinded_hop) in hops.iter().enumerate() {
+					if i == hops.len() - 1 {
+						cur_value_msat += final_value_msat;
+						cur_cltv += excess_final_cltv_expiry_delta;
+						res.push(msgs::OutboundOnionPayload::BlindedReceive {
+							amt_msat: *final_value_msat,
+							total_msat,
+							outgoing_cltv_value: cltv,
+							encrypted_tlvs: blinded_hop.encrypted_payload.clone(),
+							intro_node_blinding_point: blinding_point.take(),
+						});
+					} else {
+						res.push(msgs::OutboundOnionPayload::BlindedForward {
+							encrypted_tlvs: blinded_hop.encrypted_payload.clone(),
+							intro_node_blinding_point: blinding_point.take(),
+						});
+					}
+				}
+			} else {
+				res.push(msgs::OutboundOnionPayload::Receive {
+					payment_data: if let Some(secret) = recipient_onion.payment_secret.take() {
+						Some(msgs::FinalOnionHopData {
+							payment_secret: secret,
+							total_msat,
+						})
+					} else { None },
+					payment_metadata: recipient_onion.payment_metadata.take(),
+					keysend_preimage: *keysend_preimage,
+					custom_tlvs: recipient_onion.custom_tlvs.clone(),
+					amt_msat: value_msat,
+					outgoing_cltv_value: cltv,
+				});
 			}
 		} else {
-			msgs::OutboundOnionPayload::Forward {
+			res.insert(0, msgs::OutboundOnionPayload::Forward {
 				short_channel_id: last_short_channel_id,
 				amt_to_forward: value_msat,
 				outgoing_cltv_value: cltv,
-			}
-		});
+			});
+		}
 		cur_value_msat += hop.fee_msat;
 		if cur_value_msat >= 21000000 * 100000000 * 1000 {
 			return Err(APIError::InvalidRoute{err: "Channel fees overflowed?".to_owned()});