Support sending custom TLVs to blinded recipients.

Author: valentinewallace

lightning/src/ln/msgs.rs

@@ -1737,6 +1737,7 @@ mod fuzzy_internal_msgs {
 			encrypted_tlvs: Vec<u8>,
 			intro_node_blinding_point: Option<PublicKey>, // Set if the introduction node of the blinded path is the final node
 			keysend_preimage: Option<PaymentPreimage>,
+			custom_tlvs: Vec<(u64, Vec<u8>)>,
 		}
 	}
 
@@ -2581,16 +2582,21 @@ impl Writeable for OutboundOnionPayload {
 			},
 			Self::BlindedReceive {
 				sender_intended_htlc_amt_msat, total_msat, cltv_expiry_height, encrypted_tlvs,
-				intro_node_blinding_point, keysend_preimage,
+				intro_node_blinding_point, keysend_preimage, ref custom_tlvs,
 			} => {
+				// We need to update [`ln::outbound_payment::RecipientOnionFields::with_custom_tlvs`]
+				// to reject any reserved types in the experimental range if new ones are ever
+				// standardized.
+				let keysend_tlv = keysend_preimage.map(|preimage| (5482373484, preimage.encode()));
+				let mut custom_tlvs: Vec<&(u64, Vec<u8>)> = custom_tlvs.iter().chain(keysend_tlv.iter()).collect();
+				custom_tlvs.sort_unstable_by_key(|(typ, _)| *typ);
 				_encode_varint_length_prefixed_tlv!(w, {
 					(2, HighZeroBytesDroppedBigSize(*sender_intended_htlc_amt_msat), required),
 					(4, HighZeroBytesDroppedBigSize(*cltv_expiry_height), required),
 					(10, *encrypted_tlvs, required_vec),
 					(12, intro_node_blinding_point, option),
-					(18, HighZeroBytesDroppedBigSize(*total_msat), required),
-					(5482373484, keysend_preimage, option)
-				});
+					(18, HighZeroBytesDroppedBigSize(*total_msat), required)
+				}, custom_tlvs.iter());
 			},
 		}
 		Ok(())

lightning/src/ln/onion_utils.rs

@@ -214,6 +214,7 @@ pub(super) fn build_onion_payloads(
 							encrypted_tlvs: blinded_hop.encrypted_payload.clone(),
 							intro_node_blinding_point: blinding_point.take(),
 							keysend_preimage: *keysend_preimage,
+							custom_tlvs: recipient_onion.custom_tlvs.clone(),
 						});
 					} else {
 						res.push(msgs::OutboundOnionPayload::BlindedForward {