Add a parallel async event handler to `OnionMessenger`
[rust-lightning] / lightning / src / onion_message / messenger.rs
index 2c4e86bd6a92753ca92dcae778b12c0c7f29992b..7bea65ab5af53eb3d9f7e7014454393d892dae86 100644 (file)
@@ -47,6 +47,70 @@ use {
 
 pub(super) const MAX_TIMER_TICKS: usize = 2;
 
+/// A trivial trait which describes any [`OnionMessenger`].
+///
+/// This is not exported to bindings users as general cover traits aren't useful in other
+/// languages.
+pub trait AOnionMessenger {
+       /// A type implementing [`EntropySource`]
+       type EntropySource: EntropySource + ?Sized;
+       /// A type that may be dereferenced to [`Self::EntropySource`]
+       type ES: Deref<Target = Self::EntropySource>;
+       /// A type implementing [`NodeSigner`]
+       type NodeSigner: NodeSigner + ?Sized;
+       /// A type that may be dereferenced to [`Self::NodeSigner`]
+       type NS: Deref<Target = Self::NodeSigner>;
+       /// A type implementing [`Logger`]
+       type Logger: Logger + ?Sized;
+       /// A type that may be dereferenced to [`Self::Logger`]
+       type L: Deref<Target = Self::Logger>;
+       /// A type implementing [`NodeIdLookUp`]
+       type NodeIdLookUp: NodeIdLookUp + ?Sized;
+       /// A type that may be dereferenced to [`Self::NodeIdLookUp`]
+       type NL: Deref<Target = Self::NodeIdLookUp>;
+       /// A type implementing [`MessageRouter`]
+       type MessageRouter: MessageRouter + ?Sized;
+       /// A type that may be dereferenced to [`Self::MessageRouter`]
+       type MR: Deref<Target = Self::MessageRouter>;
+       /// A type implementing [`OffersMessageHandler`]
+       type OffersMessageHandler: OffersMessageHandler + ?Sized;
+       /// A type that may be dereferenced to [`Self::OffersMessageHandler`]
+       type OMH: Deref<Target = Self::OffersMessageHandler>;
+       /// A type implementing [`CustomOnionMessageHandler`]
+       type CustomOnionMessageHandler: CustomOnionMessageHandler + ?Sized;
+       /// A type that may be dereferenced to [`Self::CustomOnionMessageHandler`]
+       type CMH: Deref<Target = Self::CustomOnionMessageHandler>;
+       /// Returns a reference to the actual [`OnionMessenger`] object.
+       fn get_om(&self) -> &OnionMessenger<Self::ES, Self::NS, Self::L, Self::NL, Self::MR, Self::OMH, Self::CMH>;
+}
+
+impl<ES: Deref, NS: Deref, L: Deref, NL: Deref, MR: Deref, OMH: Deref, CMH: Deref> AOnionMessenger
+for OnionMessenger<ES, NS, L, NL, MR, OMH, CMH> where
+       ES::Target: EntropySource,
+       NS::Target: NodeSigner,
+       L::Target: Logger,
+       NL::Target: NodeIdLookUp,
+       MR::Target: MessageRouter,
+       OMH::Target: OffersMessageHandler,
+       CMH::Target: CustomOnionMessageHandler,
+{
+       type EntropySource = ES::Target;
+       type ES = ES;
+       type NodeSigner = NS::Target;
+       type NS = NS;
+       type Logger = L::Target;
+       type L = L;
+       type NodeIdLookUp = NL::Target;
+       type NL = NL;
+       type MessageRouter = MR::Target;
+       type MR = MR;
+       type OffersMessageHandler = OMH::Target;
+       type OMH = OMH;
+       type CustomOnionMessageHandler = CMH::Target;
+       type CMH = CMH;
+       fn get_om(&self) -> &OnionMessenger<ES, NS, L, NL, MR, OMH, CMH> { self }
+}
+
 /// A sender, receiver and forwarder of [`OnionMessage`]s.
 ///
 /// # Handling Messages
@@ -176,6 +240,13 @@ where
        message_router: MR,
        offers_handler: OMH,
        custom_handler: CMH,
+       intercept_messages_for_offline_peers: bool,
+       pending_events: Mutex<PendingEvents>,
+}
+
+struct PendingEvents {
+       intercepted_msgs: Vec<Event>,
+       peer_connecteds: Vec<Event>,
 }
 
 /// [`OnionMessage`]s buffered to be sent.
@@ -841,6 +912,48 @@ where
        pub fn new(
                entropy_source: ES, node_signer: NS, logger: L, node_id_lookup: NL, message_router: MR,
                offers_handler: OMH, custom_handler: CMH
+       ) -> Self {
+               Self::new_inner(
+                       entropy_source, node_signer, logger, node_id_lookup, message_router,
+                       offers_handler, custom_handler, false
+               )
+       }
+
+       /// Similar to [`Self::new`], but rather than dropping onion messages that are
+       /// intended to be forwarded to offline peers, we will intercept them for
+       /// later forwarding.
+       ///
+       /// Interception flow:
+       /// 1. If an onion message for an offline peer is received, `OnionMessenger` will
+       ///    generate an [`Event::OnionMessageIntercepted`]. Event handlers can
+       ///    then choose to persist this onion message for later forwarding, or drop
+       ///    it.
+       /// 2. When the offline peer later comes back online, `OnionMessenger` will
+       ///    generate an [`Event::OnionMessagePeerConnected`]. Event handlers will
+       ///    then fetch all previously intercepted onion messages for this peer.
+       /// 3. Once the stored onion messages are fetched, they can finally be
+       ///    forwarded to the now-online peer via [`Self::forward_onion_message`].
+       ///
+       /// # Note
+       ///
+       /// LDK will not rate limit how many [`Event::OnionMessageIntercepted`]s
+       /// are generated, so it is the caller's responsibility to limit how many
+       /// onion messages are persisted and only persist onion messages for relevant
+       /// peers.
+       pub fn new_with_offline_peer_interception(
+               entropy_source: ES, node_signer: NS, logger: L, node_id_lookup: NL,
+               message_router: MR, offers_handler: OMH, custom_handler: CMH
+       ) -> Self {
+               Self::new_inner(
+                       entropy_source, node_signer, logger, node_id_lookup, message_router,
+                       offers_handler, custom_handler, true
+               )
+       }
+
+       fn new_inner(
+               entropy_source: ES, node_signer: NS, logger: L, node_id_lookup: NL,
+               message_router: MR, offers_handler: OMH, custom_handler: CMH,
+               intercept_messages_for_offline_peers: bool
        ) -> Self {
                let mut secp_ctx = Secp256k1::new();
                secp_ctx.seeded_randomize(&entropy_source.get_secure_random_bytes());
@@ -854,6 +967,11 @@ where
                        message_router,
                        offers_handler,
                        custom_handler,
+                       intercept_messages_for_offline_peers,
+                       pending_events: Mutex::new(PendingEvents {
+                               intercepted_msgs: Vec::new(),
+                               peer_connecteds: Vec::new(),
+                       }),
                }
        }
 
@@ -961,6 +1079,27 @@ where
                }
        }
 
+       /// Forwards an [`OnionMessage`] to `peer_node_id`. Useful if we initialized
+       /// the [`OnionMessenger`] with [`Self::new_with_offline_peer_interception`]
+       /// and want to forward a previously intercepted onion message to a peer that
+       /// has just come online.
+       pub fn forward_onion_message(
+               &self, message: OnionMessage, peer_node_id: &PublicKey
+       ) -> Result<(), SendError> {
+               let mut message_recipients = self.message_recipients.lock().unwrap();
+               if outbound_buffer_full(&peer_node_id, &message_recipients) {
+                       return Err(SendError::BufferFull);
+               }
+
+               match message_recipients.entry(*peer_node_id) {
+                       hash_map::Entry::Occupied(mut e) if e.get().is_connected() => {
+                               e.get_mut().enqueue_message(message);
+                               Ok(())
+                       },
+                       _ => Err(SendError::InvalidFirstHop(*peer_node_id))
+               }
+       }
+
        #[cfg(any(test, feature = "_test_utils"))]
        pub fn send_onion_message_using_path<T: OnionMessageContents>(
                &self, path: OnionMessagePath, contents: T, reply_path: Option<BlindedPath>
@@ -1003,6 +1142,63 @@ where
                }
                msgs
        }
+
+       fn enqueue_intercepted_event(&self, event: Event) {
+               const MAX_EVENTS_BUFFER_SIZE: usize = (1 << 10) * 256;
+               let mut pending_events = self.pending_events.lock().unwrap();
+               let total_buffered_bytes: usize =
+                       pending_events.intercepted_msgs.iter().map(|ev| ev.serialized_length()).sum();
+               if total_buffered_bytes >= MAX_EVENTS_BUFFER_SIZE {
+                       log_trace!(self.logger, "Dropping event {:?}: buffer full", event);
+                       return
+               }
+               pending_events.intercepted_msgs.push(event);
+       }
+
+       /// Processes any events asynchronously using the given handler.
+       ///
+       /// Note that the event handler is called in the order each event was generated, however
+       /// futures are polled in parallel for some events to allow for parallelism where events do not
+       /// have an ordering requirement.
+       ///
+       /// See the trait-level documentation of [`EventsProvider`] for requirements.
+       pub async fn process_pending_events_async<Future: core::future::Future<Output = ()> + core::marker::Unpin, H: Fn(Event) -> Future>(
+               &self, handler: H
+       ) {
+               let mut intercepted_msgs = Vec::new();
+               let mut peer_connecteds = Vec::new();
+               {
+                       let mut pending_events = self.pending_events.lock().unwrap();
+                       core::mem::swap(&mut pending_events.intercepted_msgs, &mut intercepted_msgs);
+                       core::mem::swap(&mut pending_events.peer_connecteds, &mut peer_connecteds);
+               }
+
+               let mut futures = Vec::with_capacity(intercepted_msgs.len());
+               for (node_id, recipient) in self.message_recipients.lock().unwrap().iter_mut() {
+                       if let OnionMessageRecipient::PendingConnection(_, addresses, _) = recipient {
+                               if let Some(addresses) = addresses.take() {
+                                       futures.push(Some(handler(Event::ConnectionNeeded { node_id: *node_id, addresses })));
+                               }
+                       }
+               }
+
+               for ev in intercepted_msgs {
+                       if let Event::OnionMessageIntercepted { .. } = ev {} else { debug_assert!(false); }
+                       futures.push(Some(handler(ev)));
+               }
+               // Let the `OnionMessageIntercepted` events finish before moving on to peer_connecteds
+               crate::util::async_poll::MultiFuturePoller(futures).await;
+
+               if peer_connecteds.len() <= 1 {
+                       for event in peer_connecteds { handler(event).await; }
+               } else {
+                       let mut futures = Vec::new();
+                       for event in peer_connecteds {
+                               futures.push(Some(handler(event)));
+                       }
+                       crate::util::async_poll::MultiFuturePoller(futures).await;
+               }
+       }
 }
 
 fn outbound_buffer_full(peer_node_id: &PublicKey, buffer: &HashMap<PublicKey, OnionMessageRecipient>) -> bool {
@@ -1047,6 +1243,24 @@ where
                                }
                        }
                }
+               let mut events = Vec::new();
+               {
+                       let mut pending_events = self.pending_events.lock().unwrap();
+                       #[cfg(debug_assertions)] {
+                               for ev in pending_events.intercepted_msgs.iter() {
+                                       if let Event::OnionMessageIntercepted { .. } = ev {} else { panic!(); }
+                               }
+                               for ev in pending_events.peer_connecteds.iter() {
+                                       if let Event::OnionMessagePeerConnected { .. } = ev {} else { panic!(); }
+                               }
+                       }
+                       core::mem::swap(&mut pending_events.intercepted_msgs, &mut events);
+                       events.append(&mut pending_events.peer_connecteds);
+                       pending_events.peer_connecteds.shrink_to(10); // Limit total heap usage
+               }
+               for ev in events {
+                       handler.handle_event(ev);
+               }
        }
 }
 
@@ -1120,6 +1334,13 @@ where
                                                e.get_mut().enqueue_message(onion_message);
                                                log_trace!(logger, "Forwarding an onion message to peer {}", next_node_id);
                                        },
+                                       _ if self.intercept_messages_for_offline_peers => {
+                                               self.enqueue_intercepted_event(
+                                                       Event::OnionMessageIntercepted {
+                                                               peer_node_id: next_node_id, message: onion_message
+                                                       }
+                                               );
+                                       },
                                        _ => {
                                                log_trace!(
                                                        logger,
@@ -1141,6 +1362,11 @@ where
                                .entry(*their_node_id)
                                .or_insert_with(|| OnionMessageRecipient::ConnectedPeer(VecDeque::new()))
                                .mark_connected();
+                       if self.intercept_messages_for_offline_peers {
+                               self.pending_events.lock().unwrap().peer_connecteds.push(
+                                       Event::OnionMessagePeerConnected { peer_node_id: *their_node_id }
+                               );
+                       }
                } else {
                        self.message_recipients.lock().unwrap().remove(their_node_id);
                }