_ 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 ln::peer_handler::IgnoringMessageHandler;
  23 use super::blinded_route::{BlindedRoute, ForwardTlvs, ReceiveTlvs};
  24 pub use super::packet::CustomOnionMessageContents;
  25 use super::packet::{BIG_PACKET_HOP_DATA_LEN, ForwardControlTlvs, Packet, Payload, ReceiveControlTlvs, SMALL_PACKET_HOP_DATA_LEN};
  26 use super::utils;
  27 use util::events::OnionMessageProvider;
  28 use util::logger::Logger;
  29 use util::ser::Writeable;
  30
  31 use core::ops::Deref;
  32 use sync::{Arc, Mutex};
  33 use prelude::*;
  34
  35 /// A sender, receiver and forwarder of onion messages. In upcoming releases, this object will be
  36 /// used to retrieve invoices and fulfill invoice requests from [offers]. Currently, only sending
  37 /// and receiving empty onion messages is supported.
  38 ///
  39 /// # Example
  40 ///
  41 /// ```
  42 /// # extern crate bitcoin;
  43 /// # use bitcoin::hashes::_export::_core::time::Duration;
  44 /// # use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
  45 /// # use lightning::chain::keysinterface::{InMemorySigner, KeysManager, KeysInterface};
  46 /// # use lightning::ln::msgs::DecodeError;
  47 /// # use lightning::ln::peer_handler::IgnoringMessageHandler;
  48 /// # use lightning::onion_message::{BlindedRoute, CustomOnionMessageContents, Destination, OnionMessenger};
  49 /// # use lightning::util::logger::{Logger, Record};
  50 /// # use lightning::util::ser::{MaybeReadableArgs, Writeable, Writer};
  51 /// # use lightning::io;
  52 /// # use std::sync::Arc;
  53 /// # struct FakeLogger {};
  54 /// # impl Logger for FakeLogger {
  55 /// #     fn log(&self, record: &Record) { unimplemented!() }
  56 /// # }
  57 /// # let seed = [42u8; 32];
  58 /// # let time = Duration::from_secs(123456);
  59 /// # let keys_manager = KeysManager::new(&seed, time.as_secs(), time.subsec_nanos());
  60 /// # let logger = Arc::new(FakeLogger {});
  61 /// # let node_secret = SecretKey::from_slice(&hex::decode("0101010101010101010101010101010101010101010101010101010101010101").unwrap()[..]).unwrap();
  62 /// # let secp_ctx = Secp256k1::new();
  63 /// # let hop_node_id1 = PublicKey::from_secret_key(&secp_ctx, &node_secret);
  64 /// # let (hop_node_id2, hop_node_id3, hop_node_id4) = (hop_node_id1, hop_node_id1, hop_node_id1);
  65 /// # let destination_node_id = hop_node_id1;
  66 /// # let your_custom_message_handler = IgnoringMessageHandler {};
  67 /// // Create the onion messenger. This must use the same `keys_manager` as is passed to your
  68 /// // ChannelManager.
  69 /// let onion_messenger = OnionMessenger::new(&keys_manager, logger, your_custom_message_handler);
  70 ///
  71 /// # struct YourCustomMessage {}
  72 /// impl Writeable for YourCustomMessage {
  73 ///     fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
  74 ///             # Ok(())
  75 ///             // Write your custom onion message to `w`
  76 ///     }
  77 /// }
  78 /// impl CustomOnionMessageContents for YourCustomMessage {
  79 ///     fn tlv_type(&self) -> u64 {
  80 ///             # let your_custom_message_type = 42;
  81 ///             your_custom_message_type
  82 ///     }
  83 /// }
  84 /// impl MaybeReadableArgs<u64> for YourCustomMessage {
  85 ///     fn read<R: io::Read>(r: &mut R, message_type: u64) -> Result<Option<Self>, DecodeError> {
  86 ///             # unreachable!()
  87 ///             // Read your custom onion message of type `message_type` from `r`, or return `None`
  88 ///             // if the message type is unknown
  89 ///     }
  90 /// }
  91 /// let intermediate_hops = [hop_node_id1, hop_node_id2];
  92 /// let reply_path = None;
  93 /// onion_messenger.send_onion_message(&intermediate_hops, Destination::Node(destination_node_id), reply_path);
  94 ///
  95 /// // Create a blinded route to yourself, for someone to send an onion message to.
  96 /// # let your_node_id = hop_node_id1;
  97 /// let hops = [hop_node_id3, hop_node_id4, your_node_id];
  98 /// let blinded_route = BlindedRoute::new(&hops, &keys_manager, &secp_ctx).unwrap();
  99 ///
 100 /// // Send an empty onion message to a blinded route.
 101 /// # let intermediate_hops = [hop_node_id1, hop_node_id2];
 102 /// let reply_path = None;
 103 /// onion_messenger.send_onion_message(&intermediate_hops, Destination::BlindedRoute(blinded_route), reply_path);
 104 /// ```
 105 ///
 106 /// [offers]: <https://github.com/lightning/bolts/pull/798>
 107 /// [`OnionMessenger`]: crate::onion_message::OnionMessenger
 108 pub struct OnionMessenger<Signer: Sign, K: Deref, L: Deref, CMH: Deref>
 109         where K::Target: KeysInterface<Signer = Signer>,
 110               L::Target: Logger,
 111               CMH:: Target: CustomOnionMessageHandler,
 112 {
 113         keys_manager: K,
 114         logger: L,
 115         pending_messages: Mutex<HashMap<PublicKey, VecDeque<msgs::OnionMessage>>>,
 116         secp_ctx: Secp256k1<secp256k1::All>,
 117         custom_handler: CMH,
 118         // Coming soon:
 119         // invoice_handler: InvoiceHandler,
 120 }
 121
 122 /// The destination of an onion message.
 123 pub enum Destination {
 124         /// We're sending this onion message to a node.
 125         Node(PublicKey),
 126         /// We're sending this onion message to a blinded route.
 127         BlindedRoute(BlindedRoute),
 128 }
 129
 130 impl Destination {
 131         pub(super) fn num_hops(&self) -> usize {
 132                 match self {
 133                         Destination::Node(_) => 1,
 134                         Destination::BlindedRoute(BlindedRoute { blinded_hops, .. }) => blinded_hops.len(),
 135                 }
 136         }
 137 }
 138
 139 /// Errors that may occur when [sending an onion message].
 140 ///
 141 /// [sending an onion message]: OnionMessenger::send_onion_message
 142 #[derive(Debug, PartialEq)]
 143 pub enum SendError {
 144         /// Errored computing onion message packet keys.
 145         Secp256k1(secp256k1::Error),
 146         /// Because implementations such as Eclair will drop onion messages where the message packet
 147         /// exceeds 32834 bytes, we refuse to send messages where the packet exceeds this size.
 148         TooBigPacket,
 149         /// The provided [`Destination`] was an invalid [`BlindedRoute`], due to having fewer than two
 150         /// blinded hops.
 151         TooFewBlindedHops,
 152         /// Our next-hop peer was offline or does not support onion message forwarding.
 153         InvalidFirstHop,
 154         /// Our next-hop peer's buffer was full or our total outbound buffer was full.
 155         BufferFull,
 156 }
 157
 158 /// Handler for custom onion messages. If you are using [`SimpleArcOnionMessenger`],
 159 /// [`SimpleRefOnionMessenger`], or prefer to ignore inbound custom onion messages,
 160 /// [`IgnoringMessageHandler`] must be provided to [`OnionMessenger::new`]. Otherwise, a custom
 161 /// implementation of this trait must be provided, with [`CustomMessage`] specifying the supported
 162 /// message types.
 163 ///
 164 /// See [`OnionMessenger`] for example usage.
 165 ///
 166 /// [`IgnoringMessageHandler`]: crate::ln::peer_handler::IgnoringMessageHandler
 167 /// [`CustomMessage`]: Self::CustomMessage
 168 pub trait CustomOnionMessageHandler {
 169         /// The message known to the handler. To support multiple message types, you may want to make this
 170         /// an enum with a variant for each supported message.
 171         type CustomMessage: CustomOnionMessageContents;
 172         /// Called with the custom message that was received.
 173         fn handle_custom_message(&self, msg: Self::CustomMessage);
 174 }
 175
 176 impl<Signer: Sign, K: Deref, L: Deref, CMH: Deref> OnionMessenger<Signer, K, L, CMH>
 177         where K::Target: KeysInterface<Signer = Signer>,
 178               L::Target: Logger,
 179               CMH::Target: CustomOnionMessageHandler,
 180 {
 181         /// Constructs a new `OnionMessenger` to send, forward, and delegate received onion messages to
 182         /// their respective handlers.
 183         pub fn new(keys_manager: K, logger: L, custom_handler: CMH) -> Self {
 184                 let mut secp_ctx = Secp256k1::new();
 185                 secp_ctx.seeded_randomize(&keys_manager.get_secure_random_bytes());
 186                 OnionMessenger {
 187                         keys_manager,
 188                         pending_messages: Mutex::new(HashMap::new()),
 189                         secp_ctx,
 190                         logger,
 191                         custom_handler,
 192                 }
 193         }
 194
 195         /// Send an empty onion message to `destination`, routing it through `intermediate_nodes`.
 196         /// See [`OnionMessenger`] for example usage.
 197         pub fn send_onion_message(&self, intermediate_nodes: &[PublicKey], destination: Destination, reply_path: Option<BlindedRoute>) -> Result<(), SendError> {
 198                 if let Destination::BlindedRoute(BlindedRoute { ref blinded_hops, .. }) = destination {
 199                         if blinded_hops.len() < 2 {
 200                                 return Err(SendError::TooFewBlindedHops);
 201                         }
 202                 }
 203                 let blinding_secret_bytes = self.keys_manager.get_secure_random_bytes();
 204                 let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
 205                 let (introduction_node_id, blinding_point) = if intermediate_nodes.len() != 0 {
 206                         (intermediate_nodes[0], PublicKey::from_secret_key(&self.secp_ctx, &blinding_secret))
 207                 } else {
 208                         match destination {
 209                                 Destination::Node(pk) => (pk, PublicKey::from_secret_key(&self.secp_ctx, &blinding_secret)),
 210                                 Destination::BlindedRoute(BlindedRoute { introduction_node_id, blinding_point, .. }) =>
 211                                         (introduction_node_id, blinding_point),
 212                         }
 213                 };
 214                 let (packet_payloads, packet_keys) = packet_payloads_and_keys(
 215                         &self.secp_ctx, intermediate_nodes, destination, reply_path, &blinding_secret)
 216                         .map_err(|e| SendError::Secp256k1(e))?;
 217
 218                 let prng_seed = self.keys_manager.get_secure_random_bytes();
 219                 let onion_routing_packet = construct_onion_message_packet(
 220                         packet_payloads, packet_keys, prng_seed).map_err(|()| SendError::TooBigPacket)?;
 221
 222                 let mut pending_per_peer_msgs = self.pending_messages.lock().unwrap();
 223                 if outbound_buffer_full(&introduction_node_id, &pending_per_peer_msgs) { return Err(SendError::BufferFull) }
 224                 match pending_per_peer_msgs.entry(introduction_node_id) {
 225                         hash_map::Entry::Vacant(_) => Err(SendError::InvalidFirstHop),
 226                         hash_map::Entry::Occupied(mut e) => {
 227                                 e.get_mut().push_back(msgs::OnionMessage { blinding_point, onion_routing_packet });
 228                                 Ok(())
 229                         }
 230                 }
 231         }
 232
 233         #[cfg(test)]
 234         pub(super) fn release_pending_msgs(&self) -> HashMap<PublicKey, VecDeque<msgs::OnionMessage>> {
 235                 let mut pending_msgs = self.pending_messages.lock().unwrap();
 236                 let mut msgs = HashMap::new();
 237                 // We don't want to disconnect the peers by removing them entirely from the original map, so we
 238                 // swap the pending message buffers individually.
 239                 for (peer_node_id, pending_messages) in &mut *pending_msgs {
 240                         msgs.insert(*peer_node_id, core::mem::take(pending_messages));
 241                 }
 242                 msgs
 243         }
 244 }
 245
 246 fn outbound_buffer_full(peer_node_id: &PublicKey, buffer: &HashMap<PublicKey, VecDeque<msgs::OnionMessage>>) -> bool {
 247         const MAX_TOTAL_BUFFER_SIZE: usize = (1 << 20) * 128;
 248         const MAX_PER_PEER_BUFFER_SIZE: usize = (1 << 10) * 256;
 249         let mut total_buffered_bytes = 0;
 250         let mut peer_buffered_bytes = 0;
 251         for (pk, peer_buf) in buffer {
 252                 for om in peer_buf {
 253                         let om_len = om.serialized_length();
 254                         if pk == peer_node_id {
 255                                 peer_buffered_bytes += om_len;
 256                         }
 257                         total_buffered_bytes += om_len;
 258
 259                         if total_buffered_bytes >= MAX_TOTAL_BUFFER_SIZE ||
 260                                 peer_buffered_bytes >= MAX_PER_PEER_BUFFER_SIZE
 261                         {
 262                                 return true
 263                         }
 264                 }
 265         }
 266         false
 267 }
 268
 269 impl<Signer: Sign, K: Deref, L: Deref, CMH: Deref> OnionMessageHandler for OnionMessenger<Signer, K, L, CMH>
 270         where K::Target: KeysInterface<Signer = Signer>,
 271               L::Target: Logger,
 272               CMH::Target: CustomOnionMessageHandler,
 273 {
 274         /// Handle an incoming onion message. Currently, if a message was destined for us we will log, but
 275         /// soon we'll delegate the onion message to a handler that can generate invoices or send
 276         /// payments.
 277         fn handle_onion_message(&self, _peer_node_id: &PublicKey, msg: &msgs::OnionMessage) {
 278                 let control_tlvs_ss = match self.keys_manager.ecdh(Recipient::Node, &msg.blinding_point, None) {
 279                         Ok(ss) => ss,
 280                         Err(e) =>  {
 281                                 log_error!(self.logger, "Failed to retrieve node secret: {:?}", e);
 282                                 return
 283                         }
 284                 };
 285                 let onion_decode_ss = {
 286                         let blinding_factor = {
 287                                 let mut hmac = HmacEngine::<Sha256>::new(b"blinded_node_id");
 288                                 hmac.input(control_tlvs_ss.as_ref());
 289                                 Hmac::from_engine(hmac).into_inner()
 290                         };
 291                         match self.keys_manager.ecdh(Recipient::Node, &msg.onion_routing_packet.public_key,
 292                                 Some(&Scalar::from_be_bytes(blinding_factor).unwrap()))
 293                         {
 294                                 Ok(ss) => ss.secret_bytes(),
 295                                 Err(()) => {
 296                                         log_trace!(self.logger, "Failed to compute onion packet shared secret");
 297                                         return
 298                                 }
 299                         }
 300                 };
 301                 match onion_utils::decode_next_hop(onion_decode_ss, &msg.onion_routing_packet.hop_data[..],
 302                         msg.onion_routing_packet.hmac, control_tlvs_ss)
 303                 {
 304                         Ok((Payload::Receive {
 305                                 control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id }), reply_path,
 306                         }, None)) => {
 307                                 log_info!(self.logger,
 308                                         "Received an onion message with path_id {:02x?} and {} reply_path",
 309                                                 path_id, if reply_path.is_some() { "a" } else { "no" });
 310                         },
 311                         Ok((Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
 312                                 next_node_id, next_blinding_override
 313                         })), Some((next_hop_hmac, new_packet_bytes)))) => {
 314                                 // TODO: we need to check whether `next_node_id` is our node, in which case this is a dummy
 315                                 // blinded hop and this onion message is destined for us. In this situation, we should keep
 316                                 // unwrapping the onion layers to get to the final payload. Since we don't have the option
 317                                 // of creating blinded routes with dummy hops currently, we should be ok to not handle this
 318                                 // for now.
 319                                 let new_pubkey = match onion_utils::next_hop_packet_pubkey(&self.secp_ctx, msg.onion_routing_packet.public_key, &onion_decode_ss) {
 320                                         Ok(pk) => pk,
 321                                         Err(e) => {
 322                                                 log_trace!(self.logger, "Failed to compute next hop packet pubkey: {}", e);
 323                                                 return
 324                                         }
 325                                 };
 326                                 let outgoing_packet = Packet {
 327                                         version: 0,
 328                                         public_key: new_pubkey,
 329                                         hop_data: new_packet_bytes,
 330                                         hmac: next_hop_hmac,
 331                                 };
 332                                 let onion_message = msgs::OnionMessage {
 333                                         blinding_point: match next_blinding_override {
 334                                                 Some(blinding_point) => blinding_point,
 335                                                 None => {
 336                                                         let blinding_factor = {
 337                                                                 let mut sha = Sha256::engine();
 338                                                                 sha.input(&msg.blinding_point.serialize()[..]);
 339                                                                 sha.input(control_tlvs_ss.as_ref());
 340                                                                 Sha256::from_engine(sha).into_inner()
 341                                                         };
 342                                                         let next_blinding_point = msg.blinding_point;
 343                                                         match next_blinding_point.mul_tweak(&self.secp_ctx, &Scalar::from_be_bytes(blinding_factor).unwrap()) {
 344                                                                 Ok(bp) => bp,
 345                                                                 Err(e) => {
 346                                                                         log_trace!(self.logger, "Failed to compute next blinding point: {}", e);
 347                                                                         return
 348                                                                 }
 349                                                         }
 350                                                 },
 351                                         },
 352                                         onion_routing_packet: outgoing_packet,
 353                                 };
 354
 355                                 let mut pending_per_peer_msgs = self.pending_messages.lock().unwrap();
 356                                 if outbound_buffer_full(&next_node_id, &pending_per_peer_msgs) {
 357                                         log_trace!(self.logger, "Dropping forwarded onion message to peer {:?}: outbound buffer full", next_node_id);
 358                                         return
 359                                 }
 360
 361                                 #[cfg(fuzzing)]
 362                                 pending_per_peer_msgs.entry(next_node_id).or_insert_with(VecDeque::new);
 363
 364                                 match pending_per_peer_msgs.entry(next_node_id) {
 365                                         hash_map::Entry::Vacant(_) => {
 366                                                 log_trace!(self.logger, "Dropping forwarded onion message to disconnected peer {:?}", next_node_id);
 367                                                 return
 368                                         },
 369                                         hash_map::Entry::Occupied(mut e) => {
 370                                                 e.get_mut().push_back(onion_message);
 371                                                 log_trace!(self.logger, "Forwarding an onion message to peer {}", next_node_id);
 372                                         }
 373                                 };
 374                         },
 375                         Err(e) => {
 376                                 log_trace!(self.logger, "Errored decoding onion message packet: {:?}", e);
 377                         },
 378                         _ => {
 379                                 log_trace!(self.logger, "Received bogus onion message packet, either the sender encoded a final hop as a forwarding hop or vice versa");
 380                         },
 381                 };
 382         }
 383
 384         fn peer_connected(&self, their_node_id: &PublicKey, init: &msgs::Init) -> Result<(), ()> {
 385                 if init.features.supports_onion_messages() {
 386                         let mut peers = self.pending_messages.lock().unwrap();
 387                         peers.insert(their_node_id.clone(), VecDeque::new());
 388                 }
 389                 Ok(())
 390         }
 391
 392         fn peer_disconnected(&self, their_node_id: &PublicKey, _no_connection_possible: bool) {
 393                 let mut pending_msgs = self.pending_messages.lock().unwrap();
 394                 pending_msgs.remove(their_node_id);
 395         }
 396
 397         fn provided_node_features(&self) -> NodeFeatures {
 398                 let mut features = NodeFeatures::empty();
 399                 features.set_onion_messages_optional();
 400                 features
 401         }
 402
 403         fn provided_init_features(&self, _their_node_id: &PublicKey) -> InitFeatures {
 404                 let mut features = InitFeatures::empty();
 405                 features.set_onion_messages_optional();
 406                 features
 407         }
 408 }
 409
 410 impl<Signer: Sign, K: Deref, L: Deref, CMH: Deref> OnionMessageProvider for OnionMessenger<Signer, K, L, CMH>
 411         where K::Target: KeysInterface<Signer = Signer>,
 412               L::Target: Logger,
 413               CMH::Target: CustomOnionMessageHandler,
 414 {
 415         fn next_onion_message_for_peer(&self, peer_node_id: PublicKey) -> Option<msgs::OnionMessage> {
 416                 let mut pending_msgs = self.pending_messages.lock().unwrap();
 417                 if let Some(msgs) = pending_msgs.get_mut(&peer_node_id) {
 418                         return msgs.pop_front()
 419                 }
 420                 None
 421         }
 422 }
 423
 424 // TODO: parameterize the below Simple* types with OnionMessenger and handle the messages it
 425 // produces
 426 /// Useful for simplifying the parameters of [`SimpleArcChannelManager`] and
 427 /// [`SimpleArcPeerManager`]. See their docs for more details.
 428 ///
 429 /// (C-not exported) as `Arc`s don't make sense in bindings.
 430 ///
 431 /// [`SimpleArcChannelManager`]: crate::ln::channelmanager::SimpleArcChannelManager
 432 /// [`SimpleArcPeerManager`]: crate::ln::peer_handler::SimpleArcPeerManager
 433 pub type SimpleArcOnionMessenger<L> = OnionMessenger<InMemorySigner, Arc<KeysManager>, Arc<L>, IgnoringMessageHandler>;
 434 /// Useful for simplifying the parameters of [`SimpleRefChannelManager`] and
 435 /// [`SimpleRefPeerManager`]. See their docs for more details.
 436 ///
 437 /// (C-not exported) as general type aliases don't make sense in bindings.
 438 ///
 439 /// [`SimpleRefChannelManager`]: crate::ln::channelmanager::SimpleRefChannelManager
 440 /// [`SimpleRefPeerManager`]: crate::ln::peer_handler::SimpleRefPeerManager
 441 pub type SimpleRefOnionMessenger<'a, 'b, L> = OnionMessenger<InMemorySigner, &'a KeysManager, &'b L, IgnoringMessageHandler>;
 442
 443 /// Construct onion packet payloads and keys for sending an onion message along the given
 444 /// `unblinded_path` to the given `destination`.
 445 fn packet_payloads_and_keys<T: secp256k1::Signing + secp256k1::Verification>(
 446         secp_ctx: &Secp256k1<T>, unblinded_path: &[PublicKey], destination: Destination, mut reply_path:
 447         Option<BlindedRoute>, session_priv: &SecretKey
 448 ) -> Result<(Vec<(Payload, [u8; 32])>, Vec<onion_utils::OnionKeys>), secp256k1::Error> {
 449         let num_hops = unblinded_path.len() + destination.num_hops();
 450         let mut payloads = Vec::with_capacity(num_hops);
 451         let mut onion_packet_keys = Vec::with_capacity(num_hops);
 452
 453         let (mut intro_node_id_blinding_pt, num_blinded_hops) = if let Destination::BlindedRoute(BlindedRoute {
 454                 introduction_node_id, blinding_point, blinded_hops }) = &destination {
 455                 (Some((*introduction_node_id, *blinding_point)), blinded_hops.len()) } else { (None, 0) };
 456         let num_unblinded_hops = num_hops - num_blinded_hops;
 457
 458         let mut unblinded_path_idx = 0;
 459         let mut blinded_path_idx = 0;
 460         let mut prev_control_tlvs_ss = None;
 461         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| {
 462                 if num_unblinded_hops != 0 && unblinded_path_idx < num_unblinded_hops {
 463                         if let Some(ss) = prev_control_tlvs_ss.take() {
 464                                 payloads.push((Payload::Forward(ForwardControlTlvs::Unblinded(
 465                                         ForwardTlvs {
 466                                                 next_node_id: unblinded_pk_opt.unwrap(),
 467                                                 next_blinding_override: None,
 468                                         }
 469                                 )), ss));
 470                         }
 471                         prev_control_tlvs_ss = Some(control_tlvs_ss);
 472                         unblinded_path_idx += 1;
 473                 } else if let Some((intro_node_id, blinding_pt)) = intro_node_id_blinding_pt.take() {
 474                         if let Some(control_tlvs_ss) = prev_control_tlvs_ss.take() {
 475                                 payloads.push((Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
 476                                         next_node_id: intro_node_id,
 477                                         next_blinding_override: Some(blinding_pt),
 478                                 })), control_tlvs_ss));
 479                         }
 480                         if let Some(encrypted_payload) = enc_payload_opt {
 481                                 payloads.push((Payload::Forward(ForwardControlTlvs::Blinded(encrypted_payload)),
 482                                         control_tlvs_ss));
 483                         } else { debug_assert!(false); }
 484                         blinded_path_idx += 1;
 485                 } else if blinded_path_idx < num_blinded_hops - 1 && enc_payload_opt.is_some() {
 486                         payloads.push((Payload::Forward(ForwardControlTlvs::Blinded(enc_payload_opt.unwrap())),
 487                                 control_tlvs_ss));
 488                         blinded_path_idx += 1;
 489                 } else if let Some(encrypted_payload) = enc_payload_opt {
 490                         payloads.push((Payload::Receive {
 491                                 control_tlvs: ReceiveControlTlvs::Blinded(encrypted_payload),
 492                                 reply_path: reply_path.take(),
 493                         }, control_tlvs_ss));
 494                 }
 495
 496                 let (rho, mu) = onion_utils::gen_rho_mu_from_shared_secret(onion_packet_ss.as_ref());
 497                 onion_packet_keys.push(onion_utils::OnionKeys {
 498                         #[cfg(test)]
 499                         shared_secret: onion_packet_ss,
 500                         #[cfg(test)]
 501                         blinding_factor: [0; 32],
 502                         ephemeral_pubkey,
 503                         rho,
 504                         mu,
 505                 });
 506         })?;
 507
 508         if let Some(control_tlvs_ss) = prev_control_tlvs_ss {
 509                 payloads.push((Payload::Receive {
 510                         control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id: None, }),
 511                         reply_path: reply_path.take(),
 512                 }, control_tlvs_ss));
 513         }
 514
 515         Ok((payloads, onion_packet_keys))
 516 }
 517
 518 /// Errors if the serialized payload size exceeds onion_message::BIG_PACKET_HOP_DATA_LEN
 519 fn construct_onion_message_packet(payloads: Vec<(Payload, [u8; 32])>, onion_keys: Vec<onion_utils::OnionKeys>, prng_seed: [u8; 32]) -> Result<Packet, ()> {
 520         // Spec rationale:
 521         // "`len` allows larger messages to be sent than the standard 1300 bytes allowed for an HTLC
 522         // onion, but this should be used sparingly as it is reduces anonymity set, hence the
 523         // recommendation that it either look like an HTLC onion, or if larger, be a fixed size."
 524         let payloads_ser_len = onion_utils::payloads_serialized_length(&payloads);
 525         let hop_data_len = if payloads_ser_len <= SMALL_PACKET_HOP_DATA_LEN {
 526                 SMALL_PACKET_HOP_DATA_LEN
 527         } else if payloads_ser_len <= BIG_PACKET_HOP_DATA_LEN {
 528                 BIG_PACKET_HOP_DATA_LEN
 529         } else { return Err(()) };
 530
 531         Ok(onion_utils::construct_onion_message_packet::<_, _>(
 532                 payloads, onion_keys, prng_seed, hop_data_len))
 533 }