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[rust-lightning] / 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::chain::keysinterface::{InMemorySigner, KeysInterface, KeysManager, Recipient, Sign};
19 use crate::ln::features::{InitFeatures, NodeFeatures};
20 use crate::ln::msgs::{self, OnionMessageHandler};
21 use crate::ln::onion_utils;
22 use crate::ln::peer_handler::IgnoringMessageHandler;
23 use super::blinded_route::{BlindedRoute, ForwardTlvs, ReceiveTlvs};
24 pub use super::packet::{CustomOnionMessageContents, OnionMessageContents};
25 use super::packet::{BIG_PACKET_HOP_DATA_LEN, ForwardControlTlvs, Packet, Payload, ReceiveControlTlvs, SMALL_PACKET_HOP_DATA_LEN};
26 use super::utils;
27 use crate::util::events::OnionMessageProvider;
28 use crate::util::logger::Logger;
29 use crate::util::ser::Writeable;
30
31 use core::ops::Deref;
32 use crate::io;
33 use crate::sync::{Arc, Mutex};
34 use crate::prelude::*;
35
36 /// A sender, receiver and forwarder of onion messages. In upcoming releases, this object will be
37 /// used to retrieve invoices and fulfill invoice requests from [offers]. Currently, only sending
38 /// and receiving custom onion messages is supported.
39 ///
40 /// # Example
41 ///
42 /// ```
43 /// # extern crate bitcoin;
44 /// # use bitcoin::hashes::_export::_core::time::Duration;
45 /// # use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
46 /// # use lightning::chain::keysinterface::{InMemorySigner, KeysManager, KeysInterface};
47 /// # use lightning::ln::msgs::DecodeError;
48 /// # use lightning::ln::peer_handler::IgnoringMessageHandler;
49 /// # use lightning::onion_message::{BlindedRoute, CustomOnionMessageContents, Destination, OnionMessageContents, OnionMessenger};
50 /// # use lightning::util::logger::{Logger, Record};
51 /// # use lightning::util::ser::{Writeable, Writer};
52 /// # use lightning::io;
53 /// # use std::sync::Arc;
54 /// # struct FakeLogger {};
55 /// # impl Logger for FakeLogger {
56 /// #     fn log(&self, record: &Record) { unimplemented!() }
57 /// # }
58 /// # let seed = [42u8; 32];
59 /// # let time = Duration::from_secs(123456);
60 /// # let keys_manager = KeysManager::new(&seed, time.as_secs(), time.subsec_nanos());
61 /// # let logger = Arc::new(FakeLogger {});
62 /// # let node_secret = SecretKey::from_slice(&hex::decode("0101010101010101010101010101010101010101010101010101010101010101").unwrap()[..]).unwrap();
63 /// # let secp_ctx = Secp256k1::new();
64 /// # let hop_node_id1 = PublicKey::from_secret_key(&secp_ctx, &node_secret);
65 /// # let (hop_node_id2, hop_node_id3, hop_node_id4) = (hop_node_id1, hop_node_id1, hop_node_id1);
66 /// # let destination_node_id = hop_node_id1;
67 /// # let your_custom_message_handler = IgnoringMessageHandler {};
68 /// // Create the onion messenger. This must use the same `keys_manager` as is passed to your
69 /// // ChannelManager.
70 /// let onion_messenger = OnionMessenger::new(&keys_manager, logger, your_custom_message_handler);
71 ///
72 /// # struct YourCustomMessage {}
73 /// impl Writeable for YourCustomMessage {
74 ///     fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
75 ///             # Ok(())
76 ///             // Write your custom onion message to `w`
77 ///     }
78 /// }
79 /// impl CustomOnionMessageContents for YourCustomMessage {
80 ///     fn tlv_type(&self) -> u64 {
81 ///             # let your_custom_message_type = 42;
82 ///             your_custom_message_type
83 ///     }
84 /// }
85 /// // Send a custom onion message to a node id.
86 /// let intermediate_hops = [hop_node_id1, hop_node_id2];
87 /// let reply_path = None;
88 /// # let your_custom_message = YourCustomMessage {};
89 /// let message = OnionMessageContents::Custom(your_custom_message);
90 /// onion_messenger.send_onion_message(&intermediate_hops, Destination::Node(destination_node_id), message, reply_path);
91 ///
92 /// // Create a blinded route to yourself, for someone to send an onion message to.
93 /// # let your_node_id = hop_node_id1;
94 /// let hops = [hop_node_id3, hop_node_id4, your_node_id];
95 /// let blinded_route = BlindedRoute::new(&hops, &keys_manager, &secp_ctx).unwrap();
96 ///
97 /// // Send a custom onion message to a blinded route.
98 /// # let intermediate_hops = [hop_node_id1, hop_node_id2];
99 /// let reply_path = None;
100 /// # let your_custom_message = YourCustomMessage {};
101 /// let message = OnionMessageContents::Custom(your_custom_message);
102 /// onion_messenger.send_onion_message(&intermediate_hops, Destination::BlindedRoute(blinded_route), message, reply_path);
103 /// ```
104 ///
105 /// [offers]: <https://github.com/lightning/bolts/pull/798>
106 /// [`OnionMessenger`]: crate::onion_message::OnionMessenger
107 pub struct OnionMessenger<Signer: Sign, K: Deref, L: Deref, CMH: Deref>
108         where K::Target: KeysInterface<Signer = Signer>,
109               L::Target: Logger,
110               CMH:: Target: CustomOnionMessageHandler,
111 {
112         keys_manager: K,
113         logger: L,
114         pending_messages: Mutex<HashMap<PublicKey, VecDeque<msgs::OnionMessage>>>,
115         secp_ctx: Secp256k1<secp256k1::All>,
116         custom_handler: CMH,
117         // Coming soon:
118         // invoice_handler: InvoiceHandler,
119 }
120
121 /// The destination of an onion message.
122 pub enum Destination {
123         /// We're sending this onion message to a node.
124         Node(PublicKey),
125         /// We're sending this onion message to a blinded route.
126         BlindedRoute(BlindedRoute),
127 }
128
129 impl Destination {
130         pub(super) fn num_hops(&self) -> usize {
131                 match self {
132                         Destination::Node(_) => 1,
133                         Destination::BlindedRoute(BlindedRoute { blinded_hops, .. }) => blinded_hops.len(),
134                 }
135         }
136 }
137
138 /// Errors that may occur when [sending an onion message].
139 ///
140 /// [sending an onion message]: OnionMessenger::send_onion_message
141 #[derive(Debug, PartialEq, Eq)]
142 pub enum SendError {
143         /// Errored computing onion message packet keys.
144         Secp256k1(secp256k1::Error),
145         /// Because implementations such as Eclair will drop onion messages where the message packet
146         /// exceeds 32834 bytes, we refuse to send messages where the packet exceeds this size.
147         TooBigPacket,
148         /// The provided [`Destination`] was an invalid [`BlindedRoute`], due to having fewer than two
149         /// blinded hops.
150         TooFewBlindedHops,
151         /// Our next-hop peer was offline or does not support onion message forwarding.
152         InvalidFirstHop,
153         /// Onion message contents must have a TLV type >= 64.
154         InvalidMessage,
155         /// Our next-hop peer's buffer was full or our total outbound buffer was full.
156         BufferFull,
157         /// Failed to retrieve our node id from the provided [`KeysInterface`].
158         ///
159         /// [`KeysInterface`]: crate::chain::keysinterface::KeysInterface
160         GetNodeIdFailed,
161         /// We attempted to send to a blinded route where we are the introduction node, and failed to
162         /// advance the blinded route to make the second hop the new introduction node. Either
163         /// [`KeysInterface::ecdh`] failed, we failed to tweak the current blinding point to get the
164         /// new blinding point, or we were attempting to send to ourselves.
165         BlindedRouteAdvanceFailed,
166 }
167
168 /// Handler for custom onion messages. If you are using [`SimpleArcOnionMessenger`],
169 /// [`SimpleRefOnionMessenger`], or prefer to ignore inbound custom onion messages,
170 /// [`IgnoringMessageHandler`] must be provided to [`OnionMessenger::new`]. Otherwise, a custom
171 /// implementation of this trait must be provided, with [`CustomMessage`] specifying the supported
172 /// message types.
173 ///
174 /// See [`OnionMessenger`] for example usage.
175 ///
176 /// [`IgnoringMessageHandler`]: crate::ln::peer_handler::IgnoringMessageHandler
177 /// [`CustomMessage`]: Self::CustomMessage
178 pub trait CustomOnionMessageHandler {
179         /// The message known to the handler. To support multiple message types, you may want to make this
180         /// an enum with a variant for each supported message.
181         type CustomMessage: CustomOnionMessageContents;
182         /// Called with the custom message that was received.
183         fn handle_custom_message(&self, msg: Self::CustomMessage);
184         /// Read a custom message of type `message_type` from `buffer`, returning `Ok(None)` if the
185         /// message type is unknown.
186         fn read_custom_message<R: io::Read>(&self, message_type: u64, buffer: &mut R) -> Result<Option<Self::CustomMessage>, msgs::DecodeError>;
187 }
188
189 impl<Signer: Sign, K: Deref, L: Deref, CMH: Deref> OnionMessenger<Signer, K, L, CMH>
190         where K::Target: KeysInterface<Signer = Signer>,
191               L::Target: Logger,
192               CMH::Target: CustomOnionMessageHandler,
193 {
194         /// Constructs a new `OnionMessenger` to send, forward, and delegate received onion messages to
195         /// their respective handlers.
196         pub fn new(keys_manager: K, logger: L, custom_handler: CMH) -> Self {
197                 let mut secp_ctx = Secp256k1::new();
198                 secp_ctx.seeded_randomize(&keys_manager.get_secure_random_bytes());
199                 OnionMessenger {
200                         keys_manager,
201                         pending_messages: Mutex::new(HashMap::new()),
202                         secp_ctx,
203                         logger,
204                         custom_handler,
205                 }
206         }
207
208         /// Send an onion message with contents `message` to `destination`, routing it through `intermediate_nodes`.
209         /// See [`OnionMessenger`] for example usage.
210         pub fn send_onion_message<T: CustomOnionMessageContents>(&self, intermediate_nodes: &[PublicKey], mut destination: Destination, message: OnionMessageContents<T>, reply_path: Option<BlindedRoute>) -> Result<(), SendError> {
211                 if let Destination::BlindedRoute(BlindedRoute { ref blinded_hops, .. }) = destination {
212                         if blinded_hops.len() < 2 {
213                                 return Err(SendError::TooFewBlindedHops);
214                         }
215                 }
216                 let OnionMessageContents::Custom(ref msg) = message;
217                 if msg.tlv_type() < 64 { return Err(SendError::InvalidMessage) }
218
219                 // If we are sending straight to a blinded route and we are the introduction node, we need to
220                 // advance the blinded route by 1 hop so the second hop is the new introduction node.
221                 if intermediate_nodes.len() == 0 {
222                         if let Destination::BlindedRoute(ref mut blinded_route) = destination {
223                                 let our_node_id = self.keys_manager.get_node_id(Recipient::Node)
224                                         .map_err(|()| SendError::GetNodeIdFailed)?;
225                                 if blinded_route.introduction_node_id == our_node_id {
226                                         blinded_route.advance_by_one(&self.keys_manager, &self.secp_ctx)
227                                                 .map_err(|()| SendError::BlindedRouteAdvanceFailed)?;
228                                 }
229                         }
230                 }
231
232                 let blinding_secret_bytes = self.keys_manager.get_secure_random_bytes();
233                 let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
234                 let (introduction_node_id, blinding_point) = if intermediate_nodes.len() != 0 {
235                         (intermediate_nodes[0], PublicKey::from_secret_key(&self.secp_ctx, &blinding_secret))
236                 } else {
237                         match destination {
238                                 Destination::Node(pk) => (pk, PublicKey::from_secret_key(&self.secp_ctx, &blinding_secret)),
239                                 Destination::BlindedRoute(BlindedRoute { introduction_node_id, blinding_point, .. }) =>
240                                         (introduction_node_id, blinding_point),
241                         }
242                 };
243                 let (packet_payloads, packet_keys) = packet_payloads_and_keys(
244                         &self.secp_ctx, intermediate_nodes, destination, message, reply_path, &blinding_secret)
245                         .map_err(|e| SendError::Secp256k1(e))?;
246
247                 let prng_seed = self.keys_manager.get_secure_random_bytes();
248                 let onion_routing_packet = construct_onion_message_packet(
249                         packet_payloads, packet_keys, prng_seed).map_err(|()| SendError::TooBigPacket)?;
250
251                 let mut pending_per_peer_msgs = self.pending_messages.lock().unwrap();
252                 if outbound_buffer_full(&introduction_node_id, &pending_per_peer_msgs) { return Err(SendError::BufferFull) }
253                 match pending_per_peer_msgs.entry(introduction_node_id) {
254                         hash_map::Entry::Vacant(_) => Err(SendError::InvalidFirstHop),
255                         hash_map::Entry::Occupied(mut e) => {
256                                 e.get_mut().push_back(msgs::OnionMessage { blinding_point, onion_routing_packet });
257                                 Ok(())
258                         }
259                 }
260         }
261
262         #[cfg(test)]
263         pub(super) fn release_pending_msgs(&self) -> HashMap<PublicKey, VecDeque<msgs::OnionMessage>> {
264                 let mut pending_msgs = self.pending_messages.lock().unwrap();
265                 let mut msgs = HashMap::new();
266                 // We don't want to disconnect the peers by removing them entirely from the original map, so we
267                 // swap the pending message buffers individually.
268                 for (peer_node_id, pending_messages) in &mut *pending_msgs {
269                         msgs.insert(*peer_node_id, core::mem::take(pending_messages));
270                 }
271                 msgs
272         }
273 }
274
275 fn outbound_buffer_full(peer_node_id: &PublicKey, buffer: &HashMap<PublicKey, VecDeque<msgs::OnionMessage>>) -> bool {
276         const MAX_TOTAL_BUFFER_SIZE: usize = (1 << 20) * 128;
277         const MAX_PER_PEER_BUFFER_SIZE: usize = (1 << 10) * 256;
278         let mut total_buffered_bytes = 0;
279         let mut peer_buffered_bytes = 0;
280         for (pk, peer_buf) in buffer {
281                 for om in peer_buf {
282                         let om_len = om.serialized_length();
283                         if pk == peer_node_id {
284                                 peer_buffered_bytes += om_len;
285                         }
286                         total_buffered_bytes += om_len;
287
288                         if total_buffered_bytes >= MAX_TOTAL_BUFFER_SIZE ||
289                                 peer_buffered_bytes >= MAX_PER_PEER_BUFFER_SIZE
290                         {
291                                 return true
292                         }
293                 }
294         }
295         false
296 }
297
298 impl<Signer: Sign, K: Deref, L: Deref, CMH: Deref> OnionMessageHandler for OnionMessenger<Signer, K, L, CMH>
299         where K::Target: KeysInterface<Signer = Signer>,
300               L::Target: Logger,
301               CMH::Target: CustomOnionMessageHandler + Sized,
302 {
303         /// Handle an incoming onion message. Currently, if a message was destined for us we will log, but
304         /// soon we'll delegate the onion message to a handler that can generate invoices or send
305         /// payments.
306         fn handle_onion_message(&self, _peer_node_id: &PublicKey, msg: &msgs::OnionMessage) {
307                 let control_tlvs_ss = match self.keys_manager.ecdh(Recipient::Node, &msg.blinding_point, None) {
308                         Ok(ss) => ss,
309                         Err(e) =>  {
310                                 log_error!(self.logger, "Failed to retrieve node secret: {:?}", e);
311                                 return
312                         }
313                 };
314                 let onion_decode_ss = {
315                         let blinding_factor = {
316                                 let mut hmac = HmacEngine::<Sha256>::new(b"blinded_node_id");
317                                 hmac.input(control_tlvs_ss.as_ref());
318                                 Hmac::from_engine(hmac).into_inner()
319                         };
320                         match self.keys_manager.ecdh(Recipient::Node, &msg.onion_routing_packet.public_key,
321                                 Some(&Scalar::from_be_bytes(blinding_factor).unwrap()))
322                         {
323                                 Ok(ss) => ss.secret_bytes(),
324                                 Err(()) => {
325                                         log_trace!(self.logger, "Failed to compute onion packet shared secret");
326                                         return
327                                 }
328                         }
329                 };
330                 match onion_utils::decode_next_untagged_hop(onion_decode_ss, &msg.onion_routing_packet.hop_data[..],
331                         msg.onion_routing_packet.hmac, (control_tlvs_ss, &*self.custom_handler))
332                 {
333                         Ok((Payload::Receive::<<<CMH as Deref>::Target as CustomOnionMessageHandler>::CustomMessage> {
334                                 message, control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id }), reply_path,
335                         }, None)) => {
336                                 log_info!(self.logger,
337                                         "Received an onion message with path_id {:02x?} and {} reply_path",
338                                                 path_id, if reply_path.is_some() { "a" } else { "no" });
339                                 match message {
340                                         OnionMessageContents::Custom(msg) => self.custom_handler.handle_custom_message(msg),
341                                 }
342                         },
343                         Ok((Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
344                                 next_node_id, next_blinding_override
345                         })), Some((next_hop_hmac, new_packet_bytes)))) => {
346                                 // TODO: we need to check whether `next_node_id` is our node, in which case this is a dummy
347                                 // blinded hop and this onion message is destined for us. In this situation, we should keep
348                                 // unwrapping the onion layers to get to the final payload. Since we don't have the option
349                                 // of creating blinded routes with dummy hops currently, we should be ok to not handle this
350                                 // for now.
351                                 let new_pubkey = match onion_utils::next_hop_packet_pubkey(&self.secp_ctx, msg.onion_routing_packet.public_key, &onion_decode_ss) {
352                                         Ok(pk) => pk,
353                                         Err(e) => {
354                                                 log_trace!(self.logger, "Failed to compute next hop packet pubkey: {}", e);
355                                                 return
356                                         }
357                                 };
358                                 let outgoing_packet = Packet {
359                                         version: 0,
360                                         public_key: new_pubkey,
361                                         hop_data: new_packet_bytes,
362                                         hmac: next_hop_hmac,
363                                 };
364                                 let onion_message = msgs::OnionMessage {
365                                         blinding_point: match next_blinding_override {
366                                                 Some(blinding_point) => blinding_point,
367                                                 None => {
368                                                         let blinding_factor = {
369                                                                 let mut sha = Sha256::engine();
370                                                                 sha.input(&msg.blinding_point.serialize()[..]);
371                                                                 sha.input(control_tlvs_ss.as_ref());
372                                                                 Sha256::from_engine(sha).into_inner()
373                                                         };
374                                                         let next_blinding_point = msg.blinding_point;
375                                                         match next_blinding_point.mul_tweak(&self.secp_ctx, &Scalar::from_be_bytes(blinding_factor).unwrap()) {
376                                                                 Ok(bp) => bp,
377                                                                 Err(e) => {
378                                                                         log_trace!(self.logger, "Failed to compute next blinding point: {}", e);
379                                                                         return
380                                                                 }
381                                                         }
382                                                 },
383                                         },
384                                         onion_routing_packet: outgoing_packet,
385                                 };
386
387                                 let mut pending_per_peer_msgs = self.pending_messages.lock().unwrap();
388                                 if outbound_buffer_full(&next_node_id, &pending_per_peer_msgs) {
389                                         log_trace!(self.logger, "Dropping forwarded onion message to peer {:?}: outbound buffer full", next_node_id);
390                                         return
391                                 }
392
393                                 #[cfg(fuzzing)]
394                                 pending_per_peer_msgs.entry(next_node_id).or_insert_with(VecDeque::new);
395
396                                 match pending_per_peer_msgs.entry(next_node_id) {
397                                         hash_map::Entry::Vacant(_) => {
398                                                 log_trace!(self.logger, "Dropping forwarded onion message to disconnected peer {:?}", next_node_id);
399                                                 return
400                                         },
401                                         hash_map::Entry::Occupied(mut e) => {
402                                                 e.get_mut().push_back(onion_message);
403                                                 log_trace!(self.logger, "Forwarding an onion message to peer {}", next_node_id);
404                                         }
405                                 };
406                         },
407                         Err(e) => {
408                                 log_trace!(self.logger, "Errored decoding onion message packet: {:?}", e);
409                         },
410                         _ => {
411                                 log_trace!(self.logger, "Received bogus onion message packet, either the sender encoded a final hop as a forwarding hop or vice versa");
412                         },
413                 };
414         }
415
416         fn peer_connected(&self, their_node_id: &PublicKey, init: &msgs::Init) -> Result<(), ()> {
417                 if init.features.supports_onion_messages() {
418                         let mut peers = self.pending_messages.lock().unwrap();
419                         peers.insert(their_node_id.clone(), VecDeque::new());
420                 }
421                 Ok(())
422         }
423
424         fn peer_disconnected(&self, their_node_id: &PublicKey, _no_connection_possible: bool) {
425                 let mut pending_msgs = self.pending_messages.lock().unwrap();
426                 pending_msgs.remove(their_node_id);
427         }
428
429         fn provided_node_features(&self) -> NodeFeatures {
430                 let mut features = NodeFeatures::empty();
431                 features.set_onion_messages_optional();
432                 features
433         }
434
435         fn provided_init_features(&self, _their_node_id: &PublicKey) -> InitFeatures {
436                 let mut features = InitFeatures::empty();
437                 features.set_onion_messages_optional();
438                 features
439         }
440 }
441
442 impl<Signer: Sign, K: Deref, L: Deref, CMH: Deref> OnionMessageProvider for OnionMessenger<Signer, K, L, CMH>
443         where K::Target: KeysInterface<Signer = Signer>,
444               L::Target: Logger,
445               CMH::Target: CustomOnionMessageHandler,
446 {
447         fn next_onion_message_for_peer(&self, peer_node_id: PublicKey) -> Option<msgs::OnionMessage> {
448                 let mut pending_msgs = self.pending_messages.lock().unwrap();
449                 if let Some(msgs) = pending_msgs.get_mut(&peer_node_id) {
450                         return msgs.pop_front()
451                 }
452                 None
453         }
454 }
455
456 // TODO: parameterize the below Simple* types with OnionMessenger and handle the messages it
457 // produces
458 /// Useful for simplifying the parameters of [`SimpleArcChannelManager`] and
459 /// [`SimpleArcPeerManager`]. See their docs for more details.
460 ///
461 /// (C-not exported) as `Arc`s don't make sense in bindings.
462 ///
463 /// [`SimpleArcChannelManager`]: crate::ln::channelmanager::SimpleArcChannelManager
464 /// [`SimpleArcPeerManager`]: crate::ln::peer_handler::SimpleArcPeerManager
465 pub type SimpleArcOnionMessenger<L> = OnionMessenger<InMemorySigner, Arc<KeysManager>, Arc<L>, IgnoringMessageHandler>;
466 /// Useful for simplifying the parameters of [`SimpleRefChannelManager`] and
467 /// [`SimpleRefPeerManager`]. See their docs for more details.
468 ///
469 /// (C-not exported) as general type aliases don't make sense in bindings.
470 ///
471 /// [`SimpleRefChannelManager`]: crate::ln::channelmanager::SimpleRefChannelManager
472 /// [`SimpleRefPeerManager`]: crate::ln::peer_handler::SimpleRefPeerManager
473 pub type SimpleRefOnionMessenger<'a, 'b, L> = OnionMessenger<InMemorySigner, &'a KeysManager, &'b L, IgnoringMessageHandler>;
474
475 /// Construct onion packet payloads and keys for sending an onion message along the given
476 /// `unblinded_path` to the given `destination`.
477 fn packet_payloads_and_keys<T: CustomOnionMessageContents, S: secp256k1::Signing + secp256k1::Verification>(
478         secp_ctx: &Secp256k1<S>, unblinded_path: &[PublicKey], destination: Destination,
479         message: OnionMessageContents<T>, mut reply_path: Option<BlindedRoute>, session_priv: &SecretKey
480 ) -> Result<(Vec<(Payload<T>, [u8; 32])>, Vec<onion_utils::OnionKeys>), secp256k1::Error> {
481         let num_hops = unblinded_path.len() + destination.num_hops();
482         let mut payloads = Vec::with_capacity(num_hops);
483         let mut onion_packet_keys = Vec::with_capacity(num_hops);
484
485         let (mut intro_node_id_blinding_pt, num_blinded_hops) = if let Destination::BlindedRoute(BlindedRoute {
486                 introduction_node_id, blinding_point, blinded_hops }) = &destination {
487                 (Some((*introduction_node_id, *blinding_point)), blinded_hops.len()) } else { (None, 0) };
488         let num_unblinded_hops = num_hops - num_blinded_hops;
489
490         let mut unblinded_path_idx = 0;
491         let mut blinded_path_idx = 0;
492         let mut prev_control_tlvs_ss = None;
493         let mut final_control_tlvs = None;
494         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| {
495                 if num_unblinded_hops != 0 && unblinded_path_idx < num_unblinded_hops {
496                         if let Some(ss) = prev_control_tlvs_ss.take() {
497                                 payloads.push((Payload::Forward(ForwardControlTlvs::Unblinded(
498                                         ForwardTlvs {
499                                                 next_node_id: unblinded_pk_opt.unwrap(),
500                                                 next_blinding_override: None,
501                                         }
502                                 )), ss));
503                         }
504                         prev_control_tlvs_ss = Some(control_tlvs_ss);
505                         unblinded_path_idx += 1;
506                 } else if let Some((intro_node_id, blinding_pt)) = intro_node_id_blinding_pt.take() {
507                         if let Some(control_tlvs_ss) = prev_control_tlvs_ss.take() {
508                                 payloads.push((Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
509                                         next_node_id: intro_node_id,
510                                         next_blinding_override: Some(blinding_pt),
511                                 })), control_tlvs_ss));
512                         }
513                 }
514                 if blinded_path_idx < num_blinded_hops.saturating_sub(1) && enc_payload_opt.is_some() {
515                         payloads.push((Payload::Forward(ForwardControlTlvs::Blinded(enc_payload_opt.unwrap())),
516                                 control_tlvs_ss));
517                         blinded_path_idx += 1;
518                 } else if let Some(encrypted_payload) = enc_payload_opt {
519                         final_control_tlvs = Some(ReceiveControlTlvs::Blinded(encrypted_payload));
520                         prev_control_tlvs_ss = Some(control_tlvs_ss);
521                 }
522
523                 let (rho, mu) = onion_utils::gen_rho_mu_from_shared_secret(onion_packet_ss.as_ref());
524                 onion_packet_keys.push(onion_utils::OnionKeys {
525                         #[cfg(test)]
526                         shared_secret: onion_packet_ss,
527                         #[cfg(test)]
528                         blinding_factor: [0; 32],
529                         ephemeral_pubkey,
530                         rho,
531                         mu,
532                 });
533         })?;
534
535         if let Some(control_tlvs) = final_control_tlvs {
536                 payloads.push((Payload::Receive {
537                         control_tlvs,
538                         reply_path: reply_path.take(),
539                         message,
540                 }, prev_control_tlvs_ss.unwrap()));
541         } else {
542                 payloads.push((Payload::Receive {
543                         control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { path_id: None, }),
544                         reply_path: reply_path.take(),
545                         message,
546                 }, prev_control_tlvs_ss.unwrap()));
547         }
548
549         Ok((payloads, onion_packet_keys))
550 }
551
552 /// Errors if the serialized payload size exceeds onion_message::BIG_PACKET_HOP_DATA_LEN
553 fn construct_onion_message_packet<T: CustomOnionMessageContents>(payloads: Vec<(Payload<T>, [u8; 32])>, onion_keys: Vec<onion_utils::OnionKeys>, prng_seed: [u8; 32]) -> Result<Packet, ()> {
554         // Spec rationale:
555         // "`len` allows larger messages to be sent than the standard 1300 bytes allowed for an HTLC
556         // onion, but this should be used sparingly as it is reduces anonymity set, hence the
557         // recommendation that it either look like an HTLC onion, or if larger, be a fixed size."
558         let payloads_ser_len = onion_utils::payloads_serialized_length(&payloads);
559         let hop_data_len = if payloads_ser_len <= SMALL_PACKET_HOP_DATA_LEN {
560                 SMALL_PACKET_HOP_DATA_LEN
561         } else if payloads_ser_len <= BIG_PACKET_HOP_DATA_LEN {
562                 BIG_PACKET_HOP_DATA_LEN
563         } else { return Err(()) };
564
565         Ok(onion_utils::construct_onion_message_packet::<_, _>(
566                 payloads, onion_keys, prng_seed, hop_data_len))
567 }