_ Git - rust-lightning/blob - lightning/src/onion_message/messenger.rs

   1 // This file is Copyright its original authors, visible in version control
   2 // history.
   3 //
   4 // This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
   5 // or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
   7 // You may not use this file except in accordance with one or both of these
   8 // licenses.
   9
  10 //! LDK sends, receives, and forwards onion messages via the [`OnionMessenger`]. See its docs for
  11 //! more information.
  12
  13 use bitcoin::hashes::{Hash, HashEngine};
  14 use bitcoin::hashes::hmac::{Hmac, HmacEngine};
  15 use bitcoin::hashes::sha256::Hash as Sha256;
  16 use bitcoin::secp256k1::{self, PublicKey, Scalar, Secp256k1, SecretKey};
  17
  18 use chain::keysinterface::{InMemorySigner, KeysInterface, KeysManager, Recipient, Sign};
  19 use ln::features::{InitFeatures, NodeFeatures};
  20 use ln::msgs::{self, OnionMessageHandler};
  21 use ln::onion_utils;
  22 use super::blinded_route::{BlindedRoute, ForwardTlvs, ReceiveTlvs};
  23 use super::packet::{BIG_PACKET_HOP_DATA_LEN, ForwardControlTlvs, Packet, Payload, ReceiveControlTlvs, SMALL_PACKET_HOP_DATA_LEN};
  24 use super::utils;
  25 use util::events::OnionMessageProvider;
  26 use util::logger::Logger;
  27 use util::ser::Writeable;
  28
  29 use core::ops::Deref;
  30 use sync::{Arc, Mutex};
  31 use prelude::*;
  32
  33 /// A sender, receiver and forwarder of onion messages. In upcoming releases, this object will be
  34 /// used to retrieve invoices and fulfill invoice requests from [offers]. Currently, only sending
  35 /// and receiving empty onion messages is supported.
  36 ///
  37 /// # Example
  38 ///
  39 /// ```
  40 /// # extern crate bitcoin;
  41 /// # use bitcoin::hashes::_export::_core::time::Duration;
  42 /// # use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
  43 /// # use lightning::chain::keysinterface::{InMemorySigner, KeysManager, KeysInterface};
  44 /// # use lightning::onion_message::{BlindedRoute, Destination, OnionMessenger};
  45 /// # use lightning::util::logger::{Logger, Record};
  46 /// # use std::sync::Arc;
  47 /// # struct FakeLogger {};
  48 /// # impl Logger for FakeLogger {
  49 /// #     fn log(&self, record: &Record) { unimplemented!() }
  50 /// # }
  51 /// # let seed = [42u8; 32];
  52 /// # let time = Duration::from_secs(123456);
  53 /// # let keys_manager = KeysManager::new(&seed, time.as_secs(), time.subsec_nanos());
  54 /// # let logger = Arc::new(FakeLogger {});
  55 /// # let node_secret = SecretKey::from_slice(&hex::decode("0101010101010101010101010101010101010101010101010101010101010101").unwrap()[..]).unwrap();
  56 /// # let secp_ctx = Secp256k1::new();
  57 /// # let hop_node_id1 = PublicKey::from_secret_key(&secp_ctx, &node_secret);
  58 /// # let (hop_node_id2, hop_node_id3, hop_node_id4) = (hop_node_id1, hop_node_id1,
  59 /// hop_node_id1);
  60 /// # let destination_node_id = hop_node_id1;
  61 /// #
  62 /// // Create the onion messenger. This must use the same `keys_manager` as is passed to your
  63 /// // ChannelManager.
  64 /// let onion_messenger = OnionMessenger::new(&keys_manager, logger);
  65 ///
  66 /// // Send an empty onion message to a node id.
  67 /// let intermediate_hops = [hop_node_id1, hop_node_id2];
  68 /// let reply_path = None;
  69 /// onion_messenger.send_onion_message(&intermediate_hops, Destination::Node(destination_node_id), reply_path);
  70 ///
  71 /// // Create a blinded route to yourself, for someone to send an onion message to.
  72 /// # let your_node_id = hop_node_id1;
  73 /// let hops = [hop_node_id3, hop_node_id4, your_node_id];
  74 /// let blinded_route = BlindedRoute::new::<InMemorySigner, _, _>(&hops, &keys_manager, &secp_ctx).unwrap();
  75 ///
  76 /// // Send an empty onion message to a blinded route.
  77 /// # let intermediate_hops = [hop_node_id1, hop_node_id2];
  78 /// let reply_path = None;
  79 /// onion_messenger.send_onion_message(&intermediate_hops, Destination::BlindedRoute(blinded_route), reply_path);
  80 /// ```
  81 ///
  82 /// [offers]: <https://github.com/lightning/bolts/pull/798>
  83 /// [`OnionMessenger`]: crate::onion_message::OnionMessenger
  84 pub struct OnionMessenger<Signer: Sign, K: Deref, L: Deref>
  85         where K::Target: KeysInterface<Signer = Signer>,
  86               L::Target: Logger,
  87 {
  88         keys_manager: K,
  89         logger: L,
  90         pending_messages: Mutex<HashMap<PublicKey, VecDeque<msgs::OnionMessage>>>,
  91         secp_ctx: Secp256k1<secp256k1::All>,
  92         // Coming soon:
  93         // invoice_handler: InvoiceHandler,
  94         // custom_handler: CustomHandler, // handles custom onion messages
  95 }
  96
  97 /// The destination of an onion message.
  98 pub enum Destination {
  99         /// We're sending this onion message to a node.
 100         Node(PublicKey),
 101         /// We're sending this onion message to a blinded route.
 102         BlindedRoute(BlindedRoute),
 103 }
 104
 105 impl Destination {
 106         pub(super) fn num_hops(&self) -> usize {
 107                 match self {
 108                         Destination::Node(_) => 1,
 109                         Destination::BlindedRoute(BlindedRoute { blinded_hops, .. }) => blinded_hops.len(),
 110                 }
 111         }
 112 }
 113
 114 /// Errors that may occur when [sending an onion message].
 115 ///
 116 /// [sending an onion message]: OnionMessenger::send_onion_message
 117 #[derive(Debug, PartialEq)]
 118 pub enum SendError {
 119         /// Errored computing onion message packet keys.
 120         Secp256k1(secp256k1::Error),
 121         /// Because implementations such as Eclair will drop onion messages where the message packet
 122         /// exceeds 32834 bytes, we refuse to send messages where the packet exceeds this size.
 123         TooBigPacket,
 124         /// The provided [`Destination`] was an invalid [`BlindedRoute`], due to having fewer than two
 125         /// blinded hops.
 126         TooFewBlindedHops,
 127         /// Our next-hop peer was offline or does not support onion message forwarding.
 128         InvalidFirstHop,
 129         /// Our next-hop peer's buffer was full or our total outbound buffer was full.
 130         BufferFull,
 131 }
 132
 133 impl<Signer: Sign, K: Deref, L: Deref> OnionMessenger<Signer, K, L>
 134         where K::Target: KeysInterface<Signer = Signer>,
 135               L::Target: Logger,
 136 {
 137         /// Constructs a new `OnionMessenger` to send, forward, and delegate received onion messages to
 138         /// their respective handlers.
 139         pub fn new(keys_manager: K, logger: L) -> Self {
 140                 let mut secp_ctx = Secp256k1::new();
 141                 secp_ctx.seeded_randomize(&keys_manager.get_secure_random_bytes());
 142                 OnionMessenger {
 143                         keys_manager,
 144                         pending_messages: Mutex::new(HashMap::new()),
 145                         secp_ctx,
 146                         logger,
 147                 }
 148         }
 149
 150         /// Send an empty onion message to `destination`, routing it through `intermediate_nodes`.
 151         /// See [`OnionMessenger`] for example usage.
 152         pub fn send_onion_message(&self, intermediate_nodes: &[PublicKey], destination: Destination, reply_path: Option<BlindedRoute>) -> Result<(), SendError> {
 153                 if let Destination::BlindedRoute(BlindedRoute { ref blinded_hops, .. }) = destination {
 154                         if blinded_hops.len() < 2 {
 155                                 return Err(SendError::TooFewBlindedHops);
 156                         }
 157                 }
 158                 let blinding_secret_bytes = self.keys_manager.get_secure_random_bytes();
 159                 let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
 160                 let (introduction_node_id, blinding_point) = if intermediate_nodes.len() != 0 {
 161                         (intermediate_nodes[0], PublicKey::from_secret_key(&self.secp_ctx, &blinding_secret))
 162                 } else {
 163                         match destination {
 164                                 Destination::Node(pk) => (pk, PublicKey::from_secret_key(&self.secp_ctx, &blinding_secret)),
 165                                 Destination::BlindedRoute(BlindedRoute { introduction_node_id, blinding_point, .. }) =>
 166                                         (introduction_node_id, blinding_point),
 167                         }
 168                 };
 169                 let (packet_payloads, packet_keys) = packet_payloads_and_keys(
 170                         &self.secp_ctx, intermediate_nodes, destination, reply_path, &blinding_secret)
 171                         .map_err(|e| SendError::Secp256k1(e))?;
 172
 173                 let prng_seed = self.keys_manager.get_secure_random_bytes();
 174                 let onion_routing_packet = construct_onion_message_packet(
 175                         packet_payloads, packet_keys, prng_seed).map_err(|()| SendError::TooBigPacket)?;
 176
 177                 let mut pending_per_peer_msgs = self.pending_messages.lock().unwrap();
 178                 if outbound_buffer_full(&introduction_node_id, &pending_per_peer_msgs) { return Err(SendError::BufferFull) }
 179                 match pending_per_peer_msgs.entry(introduction_node_id) {
 180                         hash_map::Entry::Vacant(_) => Err(SendError::InvalidFirstHop),
 181                         hash_map::Entry::Occupied(mut e) => {
 182                                 e.get_mut().push_back(msgs::OnionMessage { blinding_point, onion_routing_packet });
 183                                 Ok(())
 184                         }
 185                 }
 186         }
 187
 188         #[cfg(test)]
 189         pub(super) fn release_pending_msgs(&self) -> HashMap<PublicKey, VecDeque<msgs::OnionMessage>> {
 190                 let mut pending_msgs = self.pending_messages.lock().unwrap();
 191                 let mut msgs = HashMap::new();
 192                 // We don't want to disconnect the peers by removing them entirely from the original map, so we
 193                 // swap the pending message buffers individually.
 194                 for (peer_node_id, pending_messages) in &mut *pending_msgs {
 195                         msgs.insert(*peer_node_id, core::mem::take(pending_messages));
 196                 }
 197                 msgs
 198         }
 199 }
 200
 201 fn outbound_buffer_full(peer_node_id: &PublicKey, buffer: &HashMap<PublicKey, VecDeque<msgs::OnionMessage>>) -> bool {
 202         const MAX_TOTAL_BUFFER_SIZE: usize = (1 << 20) * 128;
 203         const MAX_PER_PEER_BUFFER_SIZE: usize = (1 << 10) * 256;
 204         let mut total_buffered_bytes = 0;
 205         let mut peer_buffered_bytes = 0;
 206         for (pk, peer_buf) in buffer {
 207                 for om in peer_buf {
 208                         let om_len = om.serialized_length();
 209                         if pk == peer_node_id {
 210                                 peer_buffered_bytes += om_len;
 211                         }
 212                         total_buffered_bytes += om_len;
 213
 214                         if total_buffered_bytes >= MAX_TOTAL_BUFFER_SIZE ||
 215                                 peer_buffered_bytes >= MAX_PER_PEER_BUFFER_SIZE
 216                         {
 217                                 return true
 218                         }
 219                 }
 220         }
 221         false
 222 }
 223
 224 impl<Signer: Sign, K: Deref, L: Deref> OnionMessageHandler for OnionMessenger<Signer, K, L>
 225         where K::Target: KeysInterface<Signer = Signer>,
 226               L::Target: Logger,
 227 {
 228         /// Handle an incoming onion message. Currently, if a message was destined for us we will log, but
 229         /// soon we'll delegate the onion message to a handler that can generate invoices or send
 230         /// payments.
 231         fn handle_onion_message(&self, _peer_node_id: &PublicKey, msg: &msgs::OnionMessage) {
 232                 let control_tlvs_ss = match self.keys_manager.ecdh(Recipient::Node, &msg.blinding_point, None) {
 233                         Ok(ss) => ss,
 234                         Err(e) =>  {
 235                                 log_error!(self.logger, "Failed to retrieve node secret: {:?}", e);
 236                                 return
 237                         }
 238                 };
 239                 let onion_decode_ss = {
 240                         let blinding_factor = {
 241                                 let mut hmac = HmacEngine::<Sha256>::new(b"blinded_node_id");
 242                                 hmac.input(control_tlvs_ss.as_ref());
 243                                 Hmac::from_engine(hmac).into_inner()
 244                         };
 245                         match self.keys_manager.ecdh(Recipient::Node, &msg.onion_routing_packet.public_key,
 246                                 Some(&Scalar::from_be_bytes(blinding_factor).unwrap()))
 247                         {
 248                                 Ok(ss) => ss.secret_bytes(),
 249                                 Err(()) => {
 250                                         log_trace!(self.logger, "Failed to compute onion packet shared secret");
 251                                         return
 252                                 }
 253                         }
 254                 };
 255                 match onion_utils::decode_next_hop(onion_decode_ss, &msg.onion_routing_packet.hop_data[..],
 256                         msg.onion_routing_packet.hmac, control_tlvs_ss)
 257                 {
 258                         Ok((Payload::Receive {
 259                                 control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id }), reply_path,
 260                         }, None)) => {
 261                                 log_info!(self.logger,
 262                                         "Received an onion message with path_id: {:02x?} and {}reply_path",
 263                                                 path_id, if reply_path.is_some() { "" } else { "no " });
 264                         },
 265                         Ok((Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
 266                                 next_node_id, next_blinding_override
 267                         })), Some((next_hop_hmac, new_packet_bytes)))) => {
 268                                 // TODO: we need to check whether `next_node_id` is our node, in which case this is a dummy
 269                                 // blinded hop and this onion message is destined for us. In this situation, we should keep
 270                                 // unwrapping the onion layers to get to the final payload. Since we don't have the option
 271                                 // of creating blinded routes with dummy hops currently, we should be ok to not handle this
 272                                 // for now.
 273                                 let new_pubkey = match onion_utils::next_hop_packet_pubkey(&self.secp_ctx, msg.onion_routing_packet.public_key, &onion_decode_ss) {
 274                                         Ok(pk) => pk,
 275                                         Err(e) => {
 276                                                 log_trace!(self.logger, "Failed to compute next hop packet pubkey: {}", e);
 277                                                 return
 278                                         }
 279                                 };
 280                                 let outgoing_packet = Packet {
 281                                         version: 0,
 282                                         public_key: new_pubkey,
 283                                         hop_data: new_packet_bytes,
 284                                         hmac: next_hop_hmac,
 285                                 };
 286                                 let onion_message = msgs::OnionMessage {
 287                                         blinding_point: match next_blinding_override {
 288                                                 Some(blinding_point) => blinding_point,
 289                                                 None => {
 290                                                         let blinding_factor = {
 291                                                                 let mut sha = Sha256::engine();
 292                                                                 sha.input(&msg.blinding_point.serialize()[..]);
 293                                                                 sha.input(control_tlvs_ss.as_ref());
 294                                                                 Sha256::from_engine(sha).into_inner()
 295                                                         };
 296                                                         let next_blinding_point = msg.blinding_point;
 297                                                         match next_blinding_point.mul_tweak(&self.secp_ctx, &Scalar::from_be_bytes(blinding_factor).unwrap()) {
 298                                                                 Ok(bp) => bp,
 299                                                                 Err(e) => {
 300                                                                         log_trace!(self.logger, "Failed to compute next blinding point: {}", e);
 301                                                                         return
 302                                                                 }
 303                                                         }
 304                                                 },
 305                                         },
 306                                         onion_routing_packet: outgoing_packet,
 307                                 };
 308
 309                                 let mut pending_per_peer_msgs = self.pending_messages.lock().unwrap();
 310                                 if outbound_buffer_full(&next_node_id, &pending_per_peer_msgs) {
 311                                         log_trace!(self.logger, "Dropping forwarded onion message to peer {:?}: outbound buffer full", next_node_id);
 312                                         return
 313                                 }
 314
 315                                 #[cfg(fuzzing)]
 316                                 pending_per_peer_msgs.entry(next_node_id).or_insert_with(VecDeque::new);
 317
 318                                 match pending_per_peer_msgs.entry(next_node_id) {
 319                                         hash_map::Entry::Vacant(_) => {
 320                                                 log_trace!(self.logger, "Dropping forwarded onion message to disconnected peer {:?}", next_node_id);
 321                                                 return
 322                                         },
 323                                         hash_map::Entry::Occupied(mut e) => {
 324                                                 e.get_mut().push_back(onion_message);
 325                                                 log_trace!(self.logger, "Forwarding an onion message to peer {}", next_node_id);
 326                                         }
 327                                 };
 328                         },
 329                         Err(e) => {
 330                                 log_trace!(self.logger, "Errored decoding onion message packet: {:?}", e);
 331                         },
 332                         _ => {
 333                                 log_trace!(self.logger, "Received bogus onion message packet, either the sender encoded a final hop as a forwarding hop or vice versa");
 334                         },
 335                 };
 336         }
 337
 338         fn peer_connected(&self, their_node_id: &PublicKey, init: &msgs::Init) {
 339                 if init.features.supports_onion_messages() {
 340                         let mut peers = self.pending_messages.lock().unwrap();
 341                         peers.insert(their_node_id.clone(), VecDeque::new());
 342                 }
 343         }
 344
 345         fn peer_disconnected(&self, their_node_id: &PublicKey, _no_connection_possible: bool) {
 346                 let mut pending_msgs = self.pending_messages.lock().unwrap();
 347                 pending_msgs.remove(their_node_id);
 348         }
 349
 350         fn provided_node_features(&self) -> NodeFeatures {
 351                 let mut features = NodeFeatures::empty();
 352                 features.set_onion_messages_optional();
 353                 features
 354         }
 355
 356         fn provided_init_features(&self, _their_node_id: &PublicKey) -> InitFeatures {
 357                 let mut features = InitFeatures::empty();
 358                 features.set_onion_messages_optional();
 359                 features
 360         }
 361 }
 362
 363 impl<Signer: Sign, K: Deref, L: Deref> OnionMessageProvider for OnionMessenger<Signer, K, L>
 364         where K::Target: KeysInterface<Signer = Signer>,
 365               L::Target: Logger,
 366 {
 367         fn next_onion_message_for_peer(&self, peer_node_id: PublicKey) -> Option<msgs::OnionMessage> {
 368                 let mut pending_msgs = self.pending_messages.lock().unwrap();
 369                 if let Some(msgs) = pending_msgs.get_mut(&peer_node_id) {
 370                         return msgs.pop_front()
 371                 }
 372                 None
 373         }
 374 }
 375
 376 // TODO: parameterize the below Simple* types with OnionMessenger and handle the messages it
 377 // produces
 378 /// Useful for simplifying the parameters of [`SimpleArcChannelManager`] and
 379 /// [`SimpleArcPeerManager`]. See their docs for more details.
 380 ///
 381 /// (C-not exported) as `Arc`s don't make sense in bindings.
 382 ///
 383 /// [`SimpleArcChannelManager`]: crate::ln::channelmanager::SimpleArcChannelManager
 384 /// [`SimpleArcPeerManager`]: crate::ln::peer_handler::SimpleArcPeerManager
 385 pub type SimpleArcOnionMessenger<L> = OnionMessenger<InMemorySigner, Arc<KeysManager>, Arc<L>>;
 386 /// Useful for simplifying the parameters of [`SimpleRefChannelManager`] and
 387 /// [`SimpleRefPeerManager`]. See their docs for more details.
 388 ///
 389 /// (C-not exported) as general type aliases don't make sense in bindings.
 390 ///
 391 /// [`SimpleRefChannelManager`]: crate::ln::channelmanager::SimpleRefChannelManager
 392 /// [`SimpleRefPeerManager`]: crate::ln::peer_handler::SimpleRefPeerManager
 393 pub type SimpleRefOnionMessenger<'a, 'b, L> = OnionMessenger<InMemorySigner, &'a KeysManager, &'b L>;
 394
 395 /// Construct onion packet payloads and keys for sending an onion message along the given
 396 /// `unblinded_path` to the given `destination`.
 397 fn packet_payloads_and_keys<T: secp256k1::Signing + secp256k1::Verification>(
 398         secp_ctx: &Secp256k1<T>, unblinded_path: &[PublicKey], destination: Destination, mut reply_path:
 399         Option<BlindedRoute>, session_priv: &SecretKey
 400 ) -> Result<(Vec<(Payload, [u8; 32])>, Vec<onion_utils::OnionKeys>), secp256k1::Error> {
 401         let num_hops = unblinded_path.len() + destination.num_hops();
 402         let mut payloads = Vec::with_capacity(num_hops);
 403         let mut onion_packet_keys = Vec::with_capacity(num_hops);
 404
 405         let (mut intro_node_id_blinding_pt, num_blinded_hops) = if let Destination::BlindedRoute(BlindedRoute {
 406                 introduction_node_id, blinding_point, blinded_hops }) = &destination {
 407                 (Some((*introduction_node_id, *blinding_point)), blinded_hops.len()) } else { (None, 0) };
 408         let num_unblinded_hops = num_hops - num_blinded_hops;
 409
 410         let mut unblinded_path_idx = 0;
 411         let mut blinded_path_idx = 0;
 412         let mut prev_control_tlvs_ss = None;
 413         utils::construct_keys_callback(secp_ctx, unblinded_path, Some(destination), session_priv, |_, onion_packet_ss, ephemeral_pubkey, control_tlvs_ss, unblinded_pk_opt, enc_payload_opt| {
 414                 if num_unblinded_hops != 0 && unblinded_path_idx < num_unblinded_hops {
 415                         if let Some(ss) = prev_control_tlvs_ss.take() {
 416                                 payloads.push((Payload::Forward(ForwardControlTlvs::Unblinded(
 417                                         ForwardTlvs {
 418                                                 next_node_id: unblinded_pk_opt.unwrap(),
 419                                                 next_blinding_override: None,
 420                                         }
 421                                 )), ss));
 422                         }
 423                         prev_control_tlvs_ss = Some(control_tlvs_ss);
 424                         unblinded_path_idx += 1;
 425                 } else if let Some((intro_node_id, blinding_pt)) = intro_node_id_blinding_pt.take() {
 426                         if let Some(control_tlvs_ss) = prev_control_tlvs_ss.take() {
 427                                 payloads.push((Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
 428                                         next_node_id: intro_node_id,
 429                                         next_blinding_override: Some(blinding_pt),
 430                                 })), control_tlvs_ss));
 431                         }
 432                         if let Some(encrypted_payload) = enc_payload_opt {
 433                                 payloads.push((Payload::Forward(ForwardControlTlvs::Blinded(encrypted_payload)),
 434                                         control_tlvs_ss));
 435                         } else { debug_assert!(false); }
 436                         blinded_path_idx += 1;
 437                 } else if blinded_path_idx < num_blinded_hops - 1 && enc_payload_opt.is_some() {
 438                         payloads.push((Payload::Forward(ForwardControlTlvs::Blinded(enc_payload_opt.unwrap())),
 439                                 control_tlvs_ss));
 440                         blinded_path_idx += 1;
 441                 } else if let Some(encrypted_payload) = enc_payload_opt {
 442                         payloads.push((Payload::Receive {
 443                                 control_tlvs: ReceiveControlTlvs::Blinded(encrypted_payload),
 444                                 reply_path: reply_path.take(),
 445                         }, control_tlvs_ss));
 446                 }
 447
 448                 let (rho, mu) = onion_utils::gen_rho_mu_from_shared_secret(onion_packet_ss.as_ref());
 449                 onion_packet_keys.push(onion_utils::OnionKeys {
 450                         #[cfg(test)]
 451                         shared_secret: onion_packet_ss,
 452                         #[cfg(test)]
 453                         blinding_factor: [0; 32],
 454                         ephemeral_pubkey,
 455                         rho,
 456                         mu,
 457                 });
 458         })?;
 459
 460         if let Some(control_tlvs_ss) = prev_control_tlvs_ss {
 461                 payloads.push((Payload::Receive {
 462                         control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id: None, }),
 463                         reply_path: reply_path.take(),
 464                 }, control_tlvs_ss));
 465         }
 466
 467         Ok((payloads, onion_packet_keys))
 468 }
 469
 470 /// Errors if the serialized payload size exceeds onion_message::BIG_PACKET_HOP_DATA_LEN
 471 fn construct_onion_message_packet(payloads: Vec<(Payload, [u8; 32])>, onion_keys: Vec<onion_utils::OnionKeys>, prng_seed: [u8; 32]) -> Result<Packet, ()> {
 472         // Spec rationale:
 473         // "`len` allows larger messages to be sent than the standard 1300 bytes allowed for an HTLC
 474         // onion, but this should be used sparingly as it is reduces anonymity set, hence the
 475         // recommendation that it either look like an HTLC onion, or if larger, be a fixed size."
 476         let payloads_ser_len = onion_utils::payloads_serialized_length(&payloads);
 477         let hop_data_len = if payloads_ser_len <= SMALL_PACKET_HOP_DATA_LEN {
 478                 SMALL_PACKET_HOP_DATA_LEN
 479         } else if payloads_ser_len <= BIG_PACKET_HOP_DATA_LEN {
 480                 BIG_PACKET_HOP_DATA_LEN
 481         } else { return Err(()) };
 482
 483         Ok(onion_utils::construct_onion_message_packet::<_, _>(
 484                 payloads, onion_keys, prng_seed, hop_data_len))
 485 }