_ 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 crate::blinded_path::BlindedPath;
  19 use crate::blinded_path::message::{advance_path_by_one, ForwardTlvs, ReceiveTlvs};
  20 use crate::blinded_path::utils;
  21 use crate::sign::{EntropySource, KeysManager, NodeSigner, Recipient};
  22 #[cfg(not(c_bindings))]
  23 use crate::ln::channelmanager::{SimpleArcChannelManager, SimpleRefChannelManager};
  24 use crate::ln::features::{InitFeatures, NodeFeatures};
  25 use crate::ln::msgs::{self, OnionMessage, OnionMessageHandler};
  26 use crate::ln::onion_utils;
  27 use crate::ln::peer_handler::IgnoringMessageHandler;
  28 use crate::routing::gossip::NetworkGraph;
  29 pub use super::packet::OnionMessageContents;
  30 use super::packet::ParsedOnionMessageContents;
  31 use super::offers::OffersMessageHandler;
  32 use super::packet::{BIG_PACKET_HOP_DATA_LEN, ForwardControlTlvs, Packet, Payload, ReceiveControlTlvs, SMALL_PACKET_HOP_DATA_LEN};
  33 use crate::util::logger::Logger;
  34 use crate::util::ser::Writeable;
  35
  36 use core::fmt;
  37 use core::ops::Deref;
  38 use crate::io;
  39 use crate::sync::{Arc, Mutex};
  40 use crate::prelude::*;
  41
  42 /// A sender, receiver and forwarder of [`OnionMessage`]s.
  43 ///
  44 /// # Handling Messages
  45 ///
  46 /// `OnionMessenger` implements [`OnionMessageHandler`], making it responsible for either forwarding
  47 /// messages to peers or delegating to the appropriate handler for the message type. Currently, the
  48 /// available handlers are:
  49 /// * [`OffersMessageHandler`], for responding to [`InvoiceRequest`]s and paying [`Bolt12Invoice`]s
  50 /// * [`CustomOnionMessageHandler`], for handling user-defined message types
  51 ///
  52 /// # Sending Messages
  53 ///
  54 /// [`OnionMessage`]s are sent initially using [`OnionMessenger::send_onion_message`]. When handling
  55 /// a message, the matched handler may return a response message which `OnionMessenger` will send
  56 /// on its behalf.
  57 ///
  58 /// # Example
  59 ///
  60 /// ```
  61 /// # extern crate bitcoin;
  62 /// # use bitcoin::hashes::_export::_core::time::Duration;
  63 /// # use bitcoin::hashes::hex::FromHex;
  64 /// # use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
  65 /// # use lightning::blinded_path::BlindedPath;
  66 /// # use lightning::sign::KeysManager;
  67 /// # use lightning::ln::peer_handler::IgnoringMessageHandler;
  68 /// # use lightning::onion_message::{OnionMessageContents, Destination, MessageRouter, OnionMessagePath, OnionMessenger};
  69 /// # use lightning::util::logger::{Logger, Record};
  70 /// # use lightning::util::ser::{Writeable, Writer};
  71 /// # use lightning::io;
  72 /// # use std::sync::Arc;
  73 /// # struct FakeLogger;
  74 /// # impl Logger for FakeLogger {
  75 /// #     fn log(&self, record: Record) { println!("{:?}" , record); }
  76 /// # }
  77 /// # struct FakeMessageRouter {}
  78 /// # impl MessageRouter for FakeMessageRouter {
  79 /// #     fn find_path(&self, sender: PublicKey, peers: Vec<PublicKey>, destination: Destination) -> Result<OnionMessagePath, ()> {
  80 /// #         let secp_ctx = Secp256k1::new();
  81 /// #         let node_secret = SecretKey::from_slice(&<Vec<u8>>::from_hex("0101010101010101010101010101010101010101010101010101010101010101").unwrap()[..]).unwrap();
  82 /// #         let hop_node_id1 = PublicKey::from_secret_key(&secp_ctx, &node_secret);
  83 /// #         let hop_node_id2 = hop_node_id1;
  84 /// #         Ok(OnionMessagePath {
  85 /// #             intermediate_nodes: vec![hop_node_id1, hop_node_id2],
  86 /// #             destination,
  87 /// #         })
  88 /// #     }
  89 /// # }
  90 /// # let seed = [42u8; 32];
  91 /// # let time = Duration::from_secs(123456);
  92 /// # let keys_manager = KeysManager::new(&seed, time.as_secs(), time.subsec_nanos());
  93 /// # let logger = Arc::new(FakeLogger {});
  94 /// # let node_secret = SecretKey::from_slice(&<Vec<u8>>::from_hex("0101010101010101010101010101010101010101010101010101010101010101").unwrap()[..]).unwrap();
  95 /// # let secp_ctx = Secp256k1::new();
  96 /// # let hop_node_id1 = PublicKey::from_secret_key(&secp_ctx, &node_secret);
  97 /// # let (hop_node_id3, hop_node_id4) = (hop_node_id1, hop_node_id1);
  98 /// # let destination_node_id = hop_node_id1;
  99 /// # let message_router = Arc::new(FakeMessageRouter {});
 100 /// # let custom_message_handler = IgnoringMessageHandler {};
 101 /// # let offers_message_handler = IgnoringMessageHandler {};
 102 /// // Create the onion messenger. This must use the same `keys_manager` as is passed to your
 103 /// // ChannelManager.
 104 /// let onion_messenger = OnionMessenger::new(
 105 ///     &keys_manager, &keys_manager, logger, message_router, &offers_message_handler,
 106 ///     &custom_message_handler
 107 /// );
 108
 109 /// # #[derive(Debug)]
 110 /// # struct YourCustomMessage {}
 111 /// impl Writeable for YourCustomMessage {
 112 ///     fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 113 ///             # Ok(())
 114 ///             // Write your custom onion message to `w`
 115 ///     }
 116 /// }
 117 /// impl OnionMessageContents for YourCustomMessage {
 118 ///     fn tlv_type(&self) -> u64 {
 119 ///             # let your_custom_message_type = 42;
 120 ///             your_custom_message_type
 121 ///     }
 122 /// }
 123 /// // Send a custom onion message to a node id.
 124 /// let destination = Destination::Node(destination_node_id);
 125 /// let reply_path = None;
 126 /// # let message = YourCustomMessage {};
 127 /// onion_messenger.send_onion_message(message, destination, reply_path);
 128 ///
 129 /// // Create a blinded path to yourself, for someone to send an onion message to.
 130 /// # let your_node_id = hop_node_id1;
 131 /// let hops = [hop_node_id3, hop_node_id4, your_node_id];
 132 /// let blinded_path = BlindedPath::new_for_message(&hops, &keys_manager, &secp_ctx).unwrap();
 133 ///
 134 /// // Send a custom onion message to a blinded path.
 135 /// let destination = Destination::BlindedPath(blinded_path);
 136 /// let reply_path = None;
 137 /// # let message = YourCustomMessage {};
 138 /// onion_messenger.send_onion_message(message, destination, reply_path);
 139 /// ```
 140 ///
 141 /// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
 142 /// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
 143 pub struct OnionMessenger<ES: Deref, NS: Deref, L: Deref, MR: Deref, OMH: Deref, CMH: Deref>
 144 where
 145         ES::Target: EntropySource,
 146         NS::Target: NodeSigner,
 147         L::Target: Logger,
 148         MR::Target: MessageRouter,
 149         OMH::Target: OffersMessageHandler,
 150         CMH:: Target: CustomOnionMessageHandler,
 151 {
 152         entropy_source: ES,
 153         node_signer: NS,
 154         logger: L,
 155         message_buffers: Mutex<HashMap<PublicKey, OnionMessageBuffer>>,
 156         secp_ctx: Secp256k1<secp256k1::All>,
 157         message_router: MR,
 158         offers_handler: OMH,
 159         custom_handler: CMH,
 160 }
 161
 162 /// [`OnionMessage`]s buffered to be sent.
 163 enum OnionMessageBuffer {
 164         /// Messages for a node connected as a peer.
 165         ConnectedPeer(VecDeque<OnionMessage>),
 166
 167         /// Messages for a node that is not yet connected.
 168         PendingConnection(VecDeque<OnionMessage>),
 169 }
 170
 171 impl OnionMessageBuffer {
 172         fn pending_messages(&self) -> &VecDeque<OnionMessage> {
 173                 match self {
 174                         OnionMessageBuffer::ConnectedPeer(pending_messages) => pending_messages,
 175                         OnionMessageBuffer::PendingConnection(pending_messages) => pending_messages,
 176                 }
 177         }
 178
 179         fn enqueue_message(&mut self, message: OnionMessage) {
 180                 let pending_messages = match self {
 181                         OnionMessageBuffer::ConnectedPeer(pending_messages) => pending_messages,
 182                         OnionMessageBuffer::PendingConnection(pending_messages) => pending_messages,
 183                 };
 184
 185                 pending_messages.push_back(message);
 186         }
 187
 188         fn dequeue_message(&mut self) -> Option<OnionMessage> {
 189                 let pending_messages = match self {
 190                         OnionMessageBuffer::ConnectedPeer(pending_messages) => pending_messages,
 191                         OnionMessageBuffer::PendingConnection(pending_messages) => {
 192                                 debug_assert!(false);
 193                                 pending_messages
 194                         },
 195                 };
 196
 197                 pending_messages.pop_front()
 198         }
 199
 200         #[cfg(test)]
 201         fn release_pending_messages(&mut self) -> VecDeque<OnionMessage> {
 202                 let pending_messages = match self {
 203                         OnionMessageBuffer::ConnectedPeer(pending_messages) => pending_messages,
 204                         OnionMessageBuffer::PendingConnection(pending_messages) => pending_messages,
 205                 };
 206
 207                 core::mem::take(pending_messages)
 208         }
 209
 210         fn mark_connected(&mut self) {
 211                 if let OnionMessageBuffer::PendingConnection(pending_messages) = self {
 212                         let mut new_pending_messages = VecDeque::new();
 213                         core::mem::swap(pending_messages, &mut new_pending_messages);
 214                         *self = OnionMessageBuffer::ConnectedPeer(new_pending_messages);
 215                 }
 216         }
 217 }
 218
 219 /// An [`OnionMessage`] for [`OnionMessenger`] to send.
 220 ///
 221 /// These are obtained when released from [`OnionMessenger`]'s handlers after which they are
 222 /// enqueued for sending.
 223 #[cfg(not(c_bindings))]
 224 pub struct PendingOnionMessage<T: OnionMessageContents> {
 225         /// The message contents to send in an [`OnionMessage`].
 226         pub contents: T,
 227
 228         /// The destination of the message.
 229         pub destination: Destination,
 230
 231         /// A reply path to include in the [`OnionMessage`] for a response.
 232         pub reply_path: Option<BlindedPath>,
 233 }
 234
 235 #[cfg(c_bindings)]
 236 /// An [`OnionMessage`] for [`OnionMessenger`] to send.
 237 ///
 238 /// These are obtained when released from [`OnionMessenger`]'s handlers after which they are
 239 /// enqueued for sending.
 240 pub type PendingOnionMessage<T: OnionMessageContents> = (T, Destination, Option<BlindedPath>);
 241
 242 pub(crate) fn new_pending_onion_message<T: OnionMessageContents>(
 243         contents: T, destination: Destination, reply_path: Option<BlindedPath>
 244 ) -> PendingOnionMessage<T> {
 245         #[cfg(not(c_bindings))]
 246         return PendingOnionMessage { contents, destination, reply_path };
 247         #[cfg(c_bindings)]
 248         return (contents, destination, reply_path);
 249 }
 250
 251 /// A trait defining behavior for routing an [`OnionMessage`].
 252 pub trait MessageRouter {
 253         /// Returns a route for sending an [`OnionMessage`] to the given [`Destination`].
 254         fn find_path(
 255                 &self, sender: PublicKey, peers: Vec<PublicKey>, destination: Destination
 256         ) -> Result<OnionMessagePath, ()>;
 257 }
 258
 259 /// A [`MessageRouter`] that can only route to a directly connected [`Destination`].
 260 pub struct DefaultMessageRouter<G: Deref<Target=NetworkGraph<L>>, L: Deref>
 261 where
 262         L::Target: Logger,
 263 {
 264         network_graph: G,
 265 }
 266
 267 impl<G: Deref<Target=NetworkGraph<L>>, L: Deref> DefaultMessageRouter<G, L>
 268 where
 269         L::Target: Logger,
 270 {
 271         /// Creates a [`DefaultMessageRouter`] using the given [`NetworkGraph`].
 272         pub fn new(network_graph: G) -> Self {
 273                 Self { network_graph }
 274         }
 275 }
 276
 277 impl<G: Deref<Target=NetworkGraph<L>>, L: Deref> MessageRouter for DefaultMessageRouter<G, L>
 278 where
 279         L::Target: Logger,
 280 {
 281         fn find_path(
 282                 &self, _sender: PublicKey, peers: Vec<PublicKey>, destination: Destination
 283         ) -> Result<OnionMessagePath, ()> {
 284                 if peers.contains(&destination.first_node()) {
 285                         Ok(OnionMessagePath { intermediate_nodes: vec![], destination })
 286                 } else {
 287                         Err(())
 288                 }
 289         }
 290 }
 291
 292 /// A path for sending an [`OnionMessage`].
 293 #[derive(Clone)]
 294 pub struct OnionMessagePath {
 295         /// Nodes on the path between the sender and the destination.
 296         pub intermediate_nodes: Vec<PublicKey>,
 297
 298         /// The recipient of the message.
 299         pub destination: Destination,
 300 }
 301
 302 /// The destination of an onion message.
 303 #[derive(Clone)]
 304 pub enum Destination {
 305         /// We're sending this onion message to a node.
 306         Node(PublicKey),
 307         /// We're sending this onion message to a blinded path.
 308         BlindedPath(BlindedPath),
 309 }
 310
 311 impl Destination {
 312         pub(super) fn num_hops(&self) -> usize {
 313                 match self {
 314                         Destination::Node(_) => 1,
 315                         Destination::BlindedPath(BlindedPath { blinded_hops, .. }) => blinded_hops.len(),
 316                 }
 317         }
 318
 319         fn first_node(&self) -> PublicKey {
 320                 match self {
 321                         Destination::Node(node_id) => *node_id,
 322                         Destination::BlindedPath(BlindedPath { introduction_node_id: node_id, .. }) => *node_id,
 323                 }
 324         }
 325 }
 326
 327 /// Result of successfully [sending an onion message].
 328 ///
 329 /// [sending an onion message]: OnionMessenger::send_onion_message
 330 #[derive(Debug, PartialEq, Eq)]
 331 pub enum SendSuccess {
 332         /// The message was buffered and will be sent once it is processed by
 333         /// [`OnionMessageHandler::next_onion_message_for_peer`].
 334         Buffered,
 335         /// The message was buffered and will be sent once the node is connected as a peer and it is
 336         /// processed by [`OnionMessageHandler::next_onion_message_for_peer`].
 337         BufferedAwaitingConnection(PublicKey),
 338 }
 339
 340 /// Errors that may occur when [sending an onion message].
 341 ///
 342 /// [sending an onion message]: OnionMessenger::send_onion_message
 343 #[derive(Debug, PartialEq, Eq)]
 344 pub enum SendError {
 345         /// Errored computing onion message packet keys.
 346         Secp256k1(secp256k1::Error),
 347         /// Because implementations such as Eclair will drop onion messages where the message packet
 348         /// exceeds 32834 bytes, we refuse to send messages where the packet exceeds this size.
 349         TooBigPacket,
 350         /// The provided [`Destination`] was an invalid [`BlindedPath`] due to not having any blinded
 351         /// hops.
 352         TooFewBlindedHops,
 353         /// A path from the sender to the destination could not be found by the [`MessageRouter`].
 354         PathNotFound,
 355         /// Onion message contents must have a TLV type >= 64.
 356         InvalidMessage,
 357         /// Our next-hop peer's buffer was full or our total outbound buffer was full.
 358         BufferFull,
 359         /// Failed to retrieve our node id from the provided [`NodeSigner`].
 360         ///
 361         /// [`NodeSigner`]: crate::sign::NodeSigner
 362         GetNodeIdFailed,
 363         /// We attempted to send to a blinded path where we are the introduction node, and failed to
 364         /// advance the blinded path to make the second hop the new introduction node. Either
 365         /// [`NodeSigner::ecdh`] failed, we failed to tweak the current blinding point to get the
 366         /// new blinding point, or we were attempting to send to ourselves.
 367         BlindedPathAdvanceFailed,
 368 }
 369
 370 /// Handler for custom onion messages. If you are using [`SimpleArcOnionMessenger`],
 371 /// [`SimpleRefOnionMessenger`], or prefer to ignore inbound custom onion messages,
 372 /// [`IgnoringMessageHandler`] must be provided to [`OnionMessenger::new`]. Otherwise, a custom
 373 /// implementation of this trait must be provided, with [`CustomMessage`] specifying the supported
 374 /// message types.
 375 ///
 376 /// See [`OnionMessenger`] for example usage.
 377 ///
 378 /// [`IgnoringMessageHandler`]: crate::ln::peer_handler::IgnoringMessageHandler
 379 /// [`CustomMessage`]: Self::CustomMessage
 380 pub trait CustomOnionMessageHandler {
 381         /// The message known to the handler. To support multiple message types, you may want to make this
 382         /// an enum with a variant for each supported message.
 383         type CustomMessage: OnionMessageContents;
 384
 385         /// Called with the custom message that was received, returning a response to send, if any.
 386         ///
 387         /// The returned [`Self::CustomMessage`], if any, is enqueued to be sent by [`OnionMessenger`].
 388         fn handle_custom_message(&self, msg: Self::CustomMessage) -> Option<Self::CustomMessage>;
 389
 390         /// Read a custom message of type `message_type` from `buffer`, returning `Ok(None)` if the
 391         /// message type is unknown.
 392         fn read_custom_message<R: io::Read>(&self, message_type: u64, buffer: &mut R) -> Result<Option<Self::CustomMessage>, msgs::DecodeError>;
 393
 394         /// Releases any [`Self::CustomMessage`]s that need to be sent.
 395         ///
 396         /// Typically, this is used for messages initiating a message flow rather than in response to
 397         /// another message. The latter should use the return value of [`Self::handle_custom_message`].
 398         #[cfg(not(c_bindings))]
 399         fn release_pending_custom_messages(&self) -> Vec<PendingOnionMessage<Self::CustomMessage>>;
 400
 401         /// Releases any [`Self::CustomMessage`]s that need to be sent.
 402         ///
 403         /// Typically, this is used for messages initiating a message flow rather than in response to
 404         /// another message. The latter should use the return value of [`Self::handle_custom_message`].
 405         #[cfg(c_bindings)]
 406         fn release_pending_custom_messages(&self) -> Vec<(Self::CustomMessage, Destination, Option<BlindedPath>)>;
 407 }
 408
 409 /// A processed incoming onion message, containing either a Forward (another onion message)
 410 /// or a Receive payload with decrypted contents.
 411 pub enum PeeledOnion<T: OnionMessageContents> {
 412         /// Forwarded onion, with the next node id and a new onion
 413         Forward(PublicKey, OnionMessage),
 414         /// Received onion message, with decrypted contents, path_id, and reply path
 415         Receive(ParsedOnionMessageContents<T>, Option<[u8; 32]>, Option<BlindedPath>)
 416 }
 417
 418 /// Creates an [`OnionMessage`] with the given `contents` for sending to the destination of
 419 /// `path`.
 420 ///
 421 /// Returns both the node id of the peer to send the message to and the message itself.
 422 pub fn create_onion_message<ES: Deref, NS: Deref, T: OnionMessageContents>(
 423         entropy_source: &ES, node_signer: &NS, secp_ctx: &Secp256k1<secp256k1::All>,
 424         path: OnionMessagePath, contents: T, reply_path: Option<BlindedPath>,
 425 ) -> Result<(PublicKey, OnionMessage), SendError>
 426 where
 427         ES::Target: EntropySource,
 428         NS::Target: NodeSigner,
 429 {
 430         let OnionMessagePath { intermediate_nodes, mut destination } = path;
 431         if let Destination::BlindedPath(BlindedPath { ref blinded_hops, .. }) = destination {
 432                 if blinded_hops.is_empty() {
 433                         return Err(SendError::TooFewBlindedHops);
 434                 }
 435         }
 436
 437         if contents.tlv_type() < 64 { return Err(SendError::InvalidMessage) }
 438
 439         // If we are sending straight to a blinded path and we are the introduction node, we need to
 440         // advance the blinded path by 1 hop so the second hop is the new introduction node.
 441         if intermediate_nodes.len() == 0 {
 442                 if let Destination::BlindedPath(ref mut blinded_path) = destination {
 443                         let our_node_id = node_signer.get_node_id(Recipient::Node)
 444                                 .map_err(|()| SendError::GetNodeIdFailed)?;
 445                         if blinded_path.introduction_node_id == our_node_id {
 446                                 advance_path_by_one(blinded_path, node_signer, &secp_ctx)
 447                                         .map_err(|()| SendError::BlindedPathAdvanceFailed)?;
 448                         }
 449                 }
 450         }
 451
 452         let blinding_secret_bytes = entropy_source.get_secure_random_bytes();
 453         let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
 454         let (first_node_id, blinding_point) = if let Some(first_node_id) = intermediate_nodes.first() {
 455                 (*first_node_id, PublicKey::from_secret_key(&secp_ctx, &blinding_secret))
 456         } else {
 457                 match destination {
 458                         Destination::Node(pk) => (pk, PublicKey::from_secret_key(&secp_ctx, &blinding_secret)),
 459                         Destination::BlindedPath(BlindedPath { introduction_node_id, blinding_point, .. }) =>
 460                                 (introduction_node_id, blinding_point),
 461                 }
 462         };
 463         let (packet_payloads, packet_keys) = packet_payloads_and_keys(
 464                 &secp_ctx, &intermediate_nodes, destination, contents, reply_path, &blinding_secret)
 465                 .map_err(|e| SendError::Secp256k1(e))?;
 466
 467         let prng_seed = entropy_source.get_secure_random_bytes();
 468         let onion_routing_packet = construct_onion_message_packet(
 469                 packet_payloads, packet_keys, prng_seed).map_err(|()| SendError::TooBigPacket)?;
 470
 471         Ok((first_node_id, OnionMessage {
 472                 blinding_point,
 473                 onion_routing_packet
 474         }))
 475 }
 476
 477 /// Decode one layer of an incoming [`OnionMessage`].
 478 ///
 479 /// Returns either the next layer of the onion for forwarding or the decrypted content for the
 480 /// receiver.
 481 pub fn peel_onion_message<NS: Deref, L: Deref, CMH: Deref>(
 482         msg: &OnionMessage, secp_ctx: &Secp256k1<secp256k1::All>, node_signer: NS, logger: L,
 483         custom_handler: CMH,
 484 ) -> Result<PeeledOnion<<<CMH>::Target as CustomOnionMessageHandler>::CustomMessage>, ()>
 485 where
 486         NS::Target: NodeSigner,
 487         L::Target: Logger,
 488         CMH::Target: CustomOnionMessageHandler,
 489 {
 490         let control_tlvs_ss = match node_signer.ecdh(Recipient::Node, &msg.blinding_point, None) {
 491                 Ok(ss) => ss,
 492                 Err(e) =>  {
 493                         log_error!(logger, "Failed to retrieve node secret: {:?}", e);
 494                         return Err(());
 495                 }
 496         };
 497         let onion_decode_ss = {
 498                 let blinding_factor = {
 499                         let mut hmac = HmacEngine::<Sha256>::new(b"blinded_node_id");
 500                         hmac.input(control_tlvs_ss.as_ref());
 501                         Hmac::from_engine(hmac).to_byte_array()
 502                 };
 503                 match node_signer.ecdh(Recipient::Node, &msg.onion_routing_packet.public_key,
 504                         Some(&Scalar::from_be_bytes(blinding_factor).unwrap()))
 505                 {
 506                         Ok(ss) => ss.secret_bytes(),
 507                         Err(()) => {
 508                                 log_trace!(logger, "Failed to compute onion packet shared secret");
 509                                 return Err(());
 510                         }
 511                 }
 512         };
 513         match onion_utils::decode_next_untagged_hop(
 514                 onion_decode_ss, &msg.onion_routing_packet.hop_data[..], msg.onion_routing_packet.hmac,
 515                 (control_tlvs_ss, custom_handler.deref(), logger.deref())
 516         ) {
 517                 Ok((Payload::Receive::<ParsedOnionMessageContents<<<CMH as Deref>::Target as CustomOnionMessageHandler>::CustomMessage>> {
 518                         message, control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id }), reply_path,
 519                 }, None)) => {
 520                         Ok(PeeledOnion::Receive(message, path_id, reply_path))
 521                 },
 522                 Ok((Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
 523                         next_node_id, next_blinding_override
 524                 })), Some((next_hop_hmac, new_packet_bytes)))) => {
 525                         // TODO: we need to check whether `next_node_id` is our node, in which case this is a dummy
 526                         // blinded hop and this onion message is destined for us. In this situation, we should keep
 527                         // unwrapping the onion layers to get to the final payload. Since we don't have the option
 528                         // of creating blinded paths with dummy hops currently, we should be ok to not handle this
 529                         // for now.
 530                         let new_pubkey = match onion_utils::next_hop_pubkey(&secp_ctx, msg.onion_routing_packet.public_key, &onion_decode_ss) {
 531                                 Ok(pk) => pk,
 532                                 Err(e) => {
 533                                         log_trace!(logger, "Failed to compute next hop packet pubkey: {}", e);
 534                                         return Err(())
 535                                 }
 536                         };
 537                         let outgoing_packet = Packet {
 538                                 version: 0,
 539                                 public_key: new_pubkey,
 540                                 hop_data: new_packet_bytes,
 541                                 hmac: next_hop_hmac,
 542                         };
 543                         let onion_message = OnionMessage {
 544                                 blinding_point: match next_blinding_override {
 545                                         Some(blinding_point) => blinding_point,
 546                                         None => {
 547                                                 match onion_utils::next_hop_pubkey(
 548                                                         &secp_ctx, msg.blinding_point, control_tlvs_ss.as_ref()
 549                                                 ) {
 550                                                         Ok(bp) => bp,
 551                                                         Err(e) => {
 552                                                                 log_trace!(logger, "Failed to compute next blinding point: {}", e);
 553                                                                 return Err(())
 554                                                         }
 555                                                 }
 556                                         }
 557                                 },
 558                                 onion_routing_packet: outgoing_packet,
 559                         };
 560
 561                         Ok(PeeledOnion::Forward(next_node_id, onion_message))
 562                 },
 563                 Err(e) => {
 564                         log_trace!(logger, "Errored decoding onion message packet: {:?}", e);
 565                         Err(())
 566                 },
 567                 _ => {
 568                         log_trace!(logger, "Received bogus onion message packet, either the sender encoded a final hop as a forwarding hop or vice versa");
 569                         Err(())
 570                 },
 571         }
 572 }
 573
 574 impl<ES: Deref, NS: Deref, L: Deref, MR: Deref, OMH: Deref, CMH: Deref>
 575 OnionMessenger<ES, NS, L, MR, OMH, CMH>
 576 where
 577         ES::Target: EntropySource,
 578         NS::Target: NodeSigner,
 579         L::Target: Logger,
 580         MR::Target: MessageRouter,
 581         OMH::Target: OffersMessageHandler,
 582         CMH::Target: CustomOnionMessageHandler,
 583 {
 584         /// Constructs a new `OnionMessenger` to send, forward, and delegate received onion messages to
 585         /// their respective handlers.
 586         pub fn new(
 587                 entropy_source: ES, node_signer: NS, logger: L, message_router: MR, offers_handler: OMH,
 588                 custom_handler: CMH
 589         ) -> Self {
 590                 let mut secp_ctx = Secp256k1::new();
 591                 secp_ctx.seeded_randomize(&entropy_source.get_secure_random_bytes());
 592                 OnionMessenger {
 593                         entropy_source,
 594                         node_signer,
 595                         message_buffers: Mutex::new(HashMap::new()),
 596                         secp_ctx,
 597                         logger,
 598                         message_router,
 599                         offers_handler,
 600                         custom_handler,
 601                 }
 602         }
 603
 604         /// Sends an [`OnionMessage`] with the given `contents` to `destination`.
 605         ///
 606         /// See [`OnionMessenger`] for example usage.
 607         pub fn send_onion_message<T: OnionMessageContents>(
 608                 &self, contents: T, destination: Destination, reply_path: Option<BlindedPath>
 609         ) -> Result<SendSuccess, SendError> {
 610                 self.find_path_and_enqueue_onion_message(
 611                         contents, destination, reply_path, format_args!("")
 612                 )
 613         }
 614
 615         fn find_path_and_enqueue_onion_message<T: OnionMessageContents>(
 616                 &self, contents: T, destination: Destination, reply_path: Option<BlindedPath>,
 617                 log_suffix: fmt::Arguments
 618         ) -> Result<SendSuccess, SendError> {
 619                 let result = self.find_path(destination)
 620                         .and_then(|path| self.enqueue_onion_message(path, contents, reply_path, log_suffix));
 621
 622                 match result.as_ref() {
 623                         Err(SendError::GetNodeIdFailed) => {
 624                                 log_warn!(self.logger, "Unable to retrieve node id {}", log_suffix);
 625                         },
 626                         Err(SendError::PathNotFound) => {
 627                                 log_trace!(self.logger, "Failed to find path {}", log_suffix);
 628                         },
 629                         Err(e) => {
 630                                 log_trace!(self.logger, "Failed sending onion message {}: {:?}", log_suffix, e);
 631                         },
 632                         Ok(SendSuccess::Buffered) => {
 633                                 log_trace!(self.logger, "Buffered onion message {}", log_suffix);
 634                         },
 635                         Ok(SendSuccess::BufferedAwaitingConnection(node_id)) => {
 636                                 log_trace!(
 637                                         self.logger, "Buffered onion message waiting on peer connection {}: {:?}",
 638                                         log_suffix, node_id
 639                                 );
 640                         },
 641                 }
 642
 643                 result
 644         }
 645
 646         fn find_path(&self, destination: Destination) -> Result<OnionMessagePath, SendError> {
 647                 let sender = self.node_signer
 648                         .get_node_id(Recipient::Node)
 649                         .map_err(|_| SendError::GetNodeIdFailed)?;
 650
 651                 let peers = self.message_buffers.lock().unwrap()
 652                         .iter()
 653                         .filter(|(_, buffer)| matches!(buffer, OnionMessageBuffer::ConnectedPeer(_)))
 654                         .map(|(node_id, _)| *node_id)
 655                         .collect();
 656
 657                 self.message_router
 658                         .find_path(sender, peers, destination)
 659                         .map_err(|_| SendError::PathNotFound)
 660         }
 661
 662         fn enqueue_onion_message<T: OnionMessageContents>(
 663                 &self, path: OnionMessagePath, contents: T, reply_path: Option<BlindedPath>,
 664                 log_suffix: fmt::Arguments
 665         ) -> Result<SendSuccess, SendError> {
 666                 log_trace!(self.logger, "Constructing onion message {}: {:?}", log_suffix, contents);
 667
 668                 let (first_node_id, onion_message) = create_onion_message(
 669                         &self.entropy_source, &self.node_signer, &self.secp_ctx, path, contents, reply_path
 670                 )?;
 671
 672                 let mut message_buffers = self.message_buffers.lock().unwrap();
 673                 if outbound_buffer_full(&first_node_id, &message_buffers) {
 674                         return Err(SendError::BufferFull);
 675                 }
 676
 677                 match message_buffers.entry(first_node_id) {
 678                         hash_map::Entry::Vacant(e) => {
 679                                 e.insert(OnionMessageBuffer::PendingConnection(VecDeque::new()))
 680                                         .enqueue_message(onion_message);
 681                                 Ok(SendSuccess::BufferedAwaitingConnection(first_node_id))
 682                         },
 683                         hash_map::Entry::Occupied(mut e) => {
 684                                 e.get_mut().enqueue_message(onion_message);
 685                                 Ok(SendSuccess::Buffered)
 686                         },
 687                 }
 688         }
 689
 690         #[cfg(test)]
 691         pub(super) fn send_onion_message_using_path<T: OnionMessageContents>(
 692                 &self, path: OnionMessagePath, contents: T, reply_path: Option<BlindedPath>
 693         ) -> Result<SendSuccess, SendError> {
 694                 self.enqueue_onion_message(path, contents, reply_path, format_args!(""))
 695         }
 696
 697         fn handle_onion_message_response<T: OnionMessageContents>(
 698                 &self, response: Option<T>, reply_path: Option<BlindedPath>, log_suffix: fmt::Arguments
 699         ) {
 700                 if let Some(response) = response {
 701                         match reply_path {
 702                                 Some(reply_path) => {
 703                                         let _ = self.find_path_and_enqueue_onion_message(
 704                                                 response, Destination::BlindedPath(reply_path), None, log_suffix
 705                                         );
 706                                 },
 707                                 None => {
 708                                         log_trace!(self.logger, "Missing reply path {}", log_suffix);
 709                                 },
 710                         }
 711                 }
 712         }
 713
 714         #[cfg(test)]
 715         pub(super) fn release_pending_msgs(&self) -> HashMap<PublicKey, VecDeque<OnionMessage>> {
 716                 let mut message_buffers = self.message_buffers.lock().unwrap();
 717                 let mut msgs = HashMap::new();
 718                 // We don't want to disconnect the peers by removing them entirely from the original map, so we
 719                 // release the pending message buffers individually.
 720                 for (peer_node_id, buffer) in &mut *message_buffers {
 721                         msgs.insert(*peer_node_id, buffer.release_pending_messages());
 722                 }
 723                 msgs
 724         }
 725 }
 726
 727 fn outbound_buffer_full(peer_node_id: &PublicKey, buffer: &HashMap<PublicKey, OnionMessageBuffer>) -> bool {
 728         const MAX_TOTAL_BUFFER_SIZE: usize = (1 << 20) * 128;
 729         const MAX_PER_PEER_BUFFER_SIZE: usize = (1 << 10) * 256;
 730         let mut total_buffered_bytes = 0;
 731         let mut peer_buffered_bytes = 0;
 732         for (pk, peer_buf) in buffer {
 733                 for om in peer_buf.pending_messages() {
 734                         let om_len = om.serialized_length();
 735                         if pk == peer_node_id {
 736                                 peer_buffered_bytes += om_len;
 737                         }
 738                         total_buffered_bytes += om_len;
 739
 740                         if total_buffered_bytes >= MAX_TOTAL_BUFFER_SIZE ||
 741                                 peer_buffered_bytes >= MAX_PER_PEER_BUFFER_SIZE
 742                         {
 743                                 return true
 744                         }
 745                 }
 746         }
 747         false
 748 }
 749
 750 impl<ES: Deref, NS: Deref, L: Deref, MR: Deref, OMH: Deref, CMH: Deref> OnionMessageHandler
 751 for OnionMessenger<ES, NS, L, MR, OMH, CMH>
 752 where
 753         ES::Target: EntropySource,
 754         NS::Target: NodeSigner,
 755         L::Target: Logger,
 756         MR::Target: MessageRouter,
 757         OMH::Target: OffersMessageHandler,
 758         CMH::Target: CustomOnionMessageHandler,
 759 {
 760         fn handle_onion_message(&self, _peer_node_id: &PublicKey, msg: &OnionMessage) {
 761                 match peel_onion_message(
 762                         msg, &self.secp_ctx, &*self.node_signer, &*self.logger, &*self.custom_handler
 763                 ) {
 764                         Ok(PeeledOnion::Receive(message, path_id, reply_path)) => {
 765                                 log_trace!(
 766                                         self.logger,
 767                                    "Received an onion message with path_id {:02x?} and {} reply_path: {:?}",
 768                                         path_id, if reply_path.is_some() { "a" } else { "no" }, message);
 769
 770                                 match message {
 771                                         ParsedOnionMessageContents::Offers(msg) => {
 772                                                 let response = self.offers_handler.handle_message(msg);
 773                                                 self.handle_onion_message_response(
 774                                                         response, reply_path, format_args!(
 775                                                                 "when responding to Offers onion message with path_id {:02x?}",
 776                                                                 path_id
 777                                                         )
 778                                                 );
 779                                         },
 780                                         ParsedOnionMessageContents::Custom(msg) => {
 781                                                 let response = self.custom_handler.handle_custom_message(msg);
 782                                                 self.handle_onion_message_response(
 783                                                         response, reply_path, format_args!(
 784                                                                 "when responding to Custom onion message with path_id {:02x?}",
 785                                                                 path_id
 786                                                         )
 787                                                 );
 788                                         },
 789                                 }
 790                         },
 791                         Ok(PeeledOnion::Forward(next_node_id, onion_message)) => {
 792                                 let mut message_buffers = self.message_buffers.lock().unwrap();
 793                                 if outbound_buffer_full(&next_node_id, &message_buffers) {
 794                                         log_trace!(self.logger, "Dropping forwarded onion message to peer {:?}: outbound buffer full", next_node_id);
 795                                         return
 796                                 }
 797
 798                                 #[cfg(fuzzing)]
 799                                 message_buffers
 800                                         .entry(next_node_id)
 801                                         .or_insert_with(|| OnionMessageBuffer::ConnectedPeer(VecDeque::new()));
 802
 803                                 match message_buffers.entry(next_node_id) {
 804                                         hash_map::Entry::Occupied(mut e) if matches!(
 805                                                 e.get(), OnionMessageBuffer::ConnectedPeer(..)
 806                                         ) => {
 807                                                 e.get_mut().enqueue_message(onion_message);
 808                                                 log_trace!(self.logger, "Forwarding an onion message to peer {}", next_node_id);
 809                                         },
 810                                         _ => {
 811                                                 log_trace!(self.logger, "Dropping forwarded onion message to disconnected peer {:?}", next_node_id);
 812                                                 return
 813                                         },
 814                                 }
 815                         },
 816                         Err(e) => {
 817                                 log_error!(self.logger, "Failed to process onion message {:?}", e);
 818                         }
 819                 }
 820         }
 821
 822         fn peer_connected(&self, their_node_id: &PublicKey, init: &msgs::Init, _inbound: bool) -> Result<(), ()> {
 823                 if init.features.supports_onion_messages() {
 824                         self.message_buffers.lock().unwrap()
 825                                 .entry(*their_node_id)
 826                                 .or_insert_with(|| OnionMessageBuffer::ConnectedPeer(VecDeque::new()))
 827                                 .mark_connected();
 828                 } else {
 829                         self.message_buffers.lock().unwrap().remove(their_node_id);
 830                 }
 831
 832                 Ok(())
 833         }
 834
 835         fn peer_disconnected(&self, their_node_id: &PublicKey) {
 836                 match self.message_buffers.lock().unwrap().remove(their_node_id) {
 837                         Some(OnionMessageBuffer::ConnectedPeer(..)) => {},
 838                         _ => debug_assert!(false),
 839                 }
 840         }
 841
 842         fn provided_node_features(&self) -> NodeFeatures {
 843                 let mut features = NodeFeatures::empty();
 844                 features.set_onion_messages_optional();
 845                 features
 846         }
 847
 848         fn provided_init_features(&self, _their_node_id: &PublicKey) -> InitFeatures {
 849                 let mut features = InitFeatures::empty();
 850                 features.set_onion_messages_optional();
 851                 features
 852         }
 853
 854         // Before returning any messages to send for the peer, this method will see if any messages were
 855         // enqueued in the handler by users, find a path to the corresponding blinded path's introduction
 856         // node, and then enqueue the message for sending to the first peer in the full path.
 857         fn next_onion_message_for_peer(&self, peer_node_id: PublicKey) -> Option<OnionMessage> {
 858                 // Enqueue any initiating `OffersMessage`s to send.
 859                 for message in self.offers_handler.release_pending_messages() {
 860                         #[cfg(not(c_bindings))]
 861                         let PendingOnionMessage { contents, destination, reply_path } = message;
 862                         #[cfg(c_bindings)]
 863                         let (contents, destination, reply_path) = message;
 864                         let _ = self.find_path_and_enqueue_onion_message(
 865                                 contents, destination, reply_path, format_args!("when sending OffersMessage")
 866                         );
 867                 }
 868
 869                 // Enqueue any initiating `CustomMessage`s to send.
 870                 for message in self.custom_handler.release_pending_custom_messages() {
 871                         #[cfg(not(c_bindings))]
 872                         let PendingOnionMessage { contents, destination, reply_path } = message;
 873                         #[cfg(c_bindings)]
 874                         let (contents, destination, reply_path) = message;
 875                         let _ = self.find_path_and_enqueue_onion_message(
 876                                 contents, destination, reply_path, format_args!("when sending CustomMessage")
 877                         );
 878                 }
 879
 880                 self.message_buffers.lock().unwrap()
 881                         .get_mut(&peer_node_id)
 882                         .and_then(|buffer| buffer.dequeue_message())
 883         }
 884 }
 885
 886 // TODO: parameterize the below Simple* types with OnionMessenger and handle the messages it
 887 // produces
 888 /// Useful for simplifying the parameters of [`SimpleArcChannelManager`] and
 889 /// [`SimpleArcPeerManager`]. See their docs for more details.
 890 ///
 891 /// This is not exported to bindings users as type aliases aren't supported in most languages.
 892 ///
 893 /// [`SimpleArcChannelManager`]: crate::ln::channelmanager::SimpleArcChannelManager
 894 /// [`SimpleArcPeerManager`]: crate::ln::peer_handler::SimpleArcPeerManager
 895 #[cfg(not(c_bindings))]
 896 pub type SimpleArcOnionMessenger<M, T, F, L> = OnionMessenger<
 897         Arc<KeysManager>,
 898         Arc<KeysManager>,
 899         Arc<L>,
 900         Arc<DefaultMessageRouter<Arc<NetworkGraph<Arc<L>>>, Arc<L>>>,
 901         Arc<SimpleArcChannelManager<M, T, F, L>>,
 902         IgnoringMessageHandler
 903 >;
 904
 905 /// Useful for simplifying the parameters of [`SimpleRefChannelManager`] and
 906 /// [`SimpleRefPeerManager`]. See their docs for more details.
 907 ///
 908 /// This is not exported to bindings users as type aliases aren't supported in most languages.
 909 ///
 910 /// [`SimpleRefChannelManager`]: crate::ln::channelmanager::SimpleRefChannelManager
 911 /// [`SimpleRefPeerManager`]: crate::ln::peer_handler::SimpleRefPeerManager
 912 #[cfg(not(c_bindings))]
 913 pub type SimpleRefOnionMessenger<
 914         'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, 'j, M, T, F, L
 915 > = OnionMessenger<
 916         &'a KeysManager,
 917         &'a KeysManager,
 918         &'b L,
 919         &'i DefaultMessageRouter<&'g NetworkGraph<&'b L>, &'b L>,
 920         &'j SimpleRefChannelManager<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, M, T, F, L>,
 921         IgnoringMessageHandler
 922 >;
 923
 924 /// Construct onion packet payloads and keys for sending an onion message along the given
 925 /// `unblinded_path` to the given `destination`.
 926 fn packet_payloads_and_keys<T: OnionMessageContents, S: secp256k1::Signing + secp256k1::Verification>(
 927         secp_ctx: &Secp256k1<S>, unblinded_path: &[PublicKey], destination: Destination, message: T,
 928         mut reply_path: Option<BlindedPath>, session_priv: &SecretKey
 929 ) -> Result<(Vec<(Payload<T>, [u8; 32])>, Vec<onion_utils::OnionKeys>), secp256k1::Error> {
 930         let num_hops = unblinded_path.len() + destination.num_hops();
 931         let mut payloads = Vec::with_capacity(num_hops);
 932         let mut onion_packet_keys = Vec::with_capacity(num_hops);
 933
 934         let (mut intro_node_id_blinding_pt, num_blinded_hops) = if let Destination::BlindedPath(BlindedPath {
 935                 introduction_node_id, blinding_point, blinded_hops }) = &destination {
 936                 (Some((*introduction_node_id, *blinding_point)), blinded_hops.len()) } else { (None, 0) };
 937         let num_unblinded_hops = num_hops - num_blinded_hops;
 938
 939         let mut unblinded_path_idx = 0;
 940         let mut blinded_path_idx = 0;
 941         let mut prev_control_tlvs_ss = None;
 942         let mut final_control_tlvs = None;
 943         utils::construct_keys_callback(secp_ctx, unblinded_path.iter(), Some(destination), session_priv,
 944                 |_, onion_packet_ss, ephemeral_pubkey, control_tlvs_ss, unblinded_pk_opt, enc_payload_opt| {
 945                         if num_unblinded_hops != 0 && unblinded_path_idx < num_unblinded_hops {
 946                                 if let Some(ss) = prev_control_tlvs_ss.take() {
 947                                         payloads.push((Payload::Forward(ForwardControlTlvs::Unblinded(
 948                                                 ForwardTlvs {
 949                                                         next_node_id: unblinded_pk_opt.unwrap(),
 950                                                         next_blinding_override: None,
 951                                                 }
 952                                         )), ss));
 953                                 }
 954                                 prev_control_tlvs_ss = Some(control_tlvs_ss);
 955                                 unblinded_path_idx += 1;
 956                         } else if let Some((intro_node_id, blinding_pt)) = intro_node_id_blinding_pt.take() {
 957                                 if let Some(control_tlvs_ss) = prev_control_tlvs_ss.take() {
 958                                         payloads.push((Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
 959                                                 next_node_id: intro_node_id,
 960                                                 next_blinding_override: Some(blinding_pt),
 961                                         })), control_tlvs_ss));
 962                                 }
 963                         }
 964                         if blinded_path_idx < num_blinded_hops.saturating_sub(1) && enc_payload_opt.is_some() {
 965                                 payloads.push((Payload::Forward(ForwardControlTlvs::Blinded(enc_payload_opt.unwrap())),
 966                                         control_tlvs_ss));
 967                                 blinded_path_idx += 1;
 968                         } else if let Some(encrypted_payload) = enc_payload_opt {
 969                                 final_control_tlvs = Some(ReceiveControlTlvs::Blinded(encrypted_payload));
 970                                 prev_control_tlvs_ss = Some(control_tlvs_ss);
 971                         }
 972
 973                         let (rho, mu) = onion_utils::gen_rho_mu_from_shared_secret(onion_packet_ss.as_ref());
 974                         onion_packet_keys.push(onion_utils::OnionKeys {
 975                                 #[cfg(test)]
 976                                 shared_secret: onion_packet_ss,
 977                                 #[cfg(test)]
 978                                 blinding_factor: [0; 32],
 979                                 ephemeral_pubkey,
 980                                 rho,
 981                                 mu,
 982                         });
 983                 }
 984         )?;
 985
 986         if let Some(control_tlvs) = final_control_tlvs {
 987                 payloads.push((Payload::Receive {
 988                         control_tlvs,
 989                         reply_path: reply_path.take(),
 990                         message,
 991                 }, prev_control_tlvs_ss.unwrap()));
 992         } else {
 993                 payloads.push((Payload::Receive {
 994                         control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id: None, }),
 995                         reply_path: reply_path.take(),
 996                         message,
 997                 }, prev_control_tlvs_ss.unwrap()));
 998         }
 999
1000         Ok((payloads, onion_packet_keys))
1001 }
1002
1003 /// Errors if the serialized payload size exceeds onion_message::BIG_PACKET_HOP_DATA_LEN
1004 fn construct_onion_message_packet<T: OnionMessageContents>(payloads: Vec<(Payload<T>, [u8; 32])>, onion_keys: Vec<onion_utils::OnionKeys>, prng_seed: [u8; 32]) -> Result<Packet, ()> {
1005         // Spec rationale:
1006         // "`len` allows larger messages to be sent than the standard 1300 bytes allowed for an HTLC
1007         // onion, but this should be used sparingly as it is reduces anonymity set, hence the
1008         // recommendation that it either look like an HTLC onion, or if larger, be a fixed size."
1009         let payloads_ser_len = onion_utils::payloads_serialized_length(&payloads);
1010         let hop_data_len = if payloads_ser_len <= SMALL_PACKET_HOP_DATA_LEN {
1011                 SMALL_PACKET_HOP_DATA_LEN
1012         } else if payloads_ser_len <= BIG_PACKET_HOP_DATA_LEN {
1013                 BIG_PACKET_HOP_DATA_LEN
1014         } else { return Err(()) };
1015
1016         onion_utils::construct_onion_message_packet::<_, _>(
1017                 payloads, onion_keys, prng_seed, hop_data_len)
1018 }