messenger.rs

// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! LDK sends, receives, and forwards onion messages via this [`OnionMessenger`], which lives here,
//! as well as various types, traits, and utilities that it uses.

use bitcoin::hashes::hmac::{Hmac, HmacEngine};
use bitcoin::hashes::sha256::Hash as Sha256;
use bitcoin::hashes::{Hash, HashEngine};
use bitcoin::secp256k1::{self, PublicKey, Scalar, Secp256k1, SecretKey};

use super::async_payments::{AsyncPaymentsMessage, AsyncPaymentsMessageHandler};
use super::dns_resolution::{DNSResolverMessage, DNSResolverMessageHandler};
use super::offers::{OffersMessage, OffersMessageHandler};
use super::packet::OnionMessageContents;
use super::packet::ParsedOnionMessageContents;
use super::packet::{
	ForwardControlTlvs, Packet, Payload, ReceiveControlTlvs, BIG_PACKET_HOP_DATA_LEN,
	SMALL_PACKET_HOP_DATA_LEN,
};
use crate::blinded_path::message::{
	AsyncPaymentsContext, BlindedMessagePath, DNSResolverContext, ForwardTlvs, MessageContext,
	MessageForwardNode, NextMessageHop, OffersContext, ReceiveTlvs,
};
use crate::blinded_path::utils;
use crate::blinded_path::{IntroductionNode, NodeIdLookUp};
use crate::events::{Event, EventHandler, EventsProvider, ReplayEvent};
use crate::ln::msgs::{
	self, BaseMessageHandler, MessageSendEvent, OnionMessage, OnionMessageHandler, SocketAddress,
};
use crate::ln::onion_utils;
use crate::routing::gossip::{NetworkGraph, NodeId, ReadOnlyNetworkGraph};
use crate::sign::{EntropySource, NodeSigner, ReceiveAuthKey, Recipient};
use crate::types::features::{InitFeatures, NodeFeatures};
use crate::util::async_poll::{MultiResultFuturePoller, ResultFuture};
use crate::util::logger::{Logger, WithContext};
use crate::util::ser::Writeable;
use crate::util::wakers::{Future, Notifier};

use crate::io;
use crate::prelude::*;
use crate::sync::Mutex;
use core::fmt;
use core::ops::Deref;
use core::sync::atomic::{AtomicBool, Ordering};

#[cfg(not(c_bindings))]
use {
	crate::ln::channelmanager::{SimpleArcChannelManager, SimpleRefChannelManager},
	crate::ln::peer_handler::IgnoringMessageHandler,
	crate::sign::KeysManager,
	crate::sync::Arc,
};

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;
	/// A type implementing [`NodeSigner`]
	type NodeSigner: NodeSigner;
	/// A type implementing [`Logger`]
	type Logger: Logger;
	/// A type implementing [`NodeIdLookUp`]
	type NL: NodeIdLookUp;
	/// A type implementing [`MessageRouter`]
	type MessageRouter: MessageRouter;
	/// A type implementing [`OffersMessageHandler`]
	type OMH: OffersMessageHandler;
	/// A type implementing [`AsyncPaymentsMessageHandler`]
	type APH: AsyncPaymentsMessageHandler;
	/// A type implementing [`DNSResolverMessageHandler`]
	type DRH: DNSResolverMessageHandler;
	/// A type implementing [`CustomOnionMessageHandler`]
	type CMH: CustomOnionMessageHandler;
	/// Returns a reference to the actual [`OnionMessenger`] object.
	fn get_om(
		&self,
	) -> &OnionMessenger<
		Self::EntropySource,
		Self::NodeSigner,
		Self::Logger,
		Self::NL,
		Self::MessageRouter,
		Self::OMH,
		Self::APH,
		Self::DRH,
		Self::CMH,
	>;
}

impl<
		ES: EntropySource,
		NS: NodeSigner,
		L: Logger,
		NL: NodeIdLookUp,
		MR: MessageRouter,
		OMH: OffersMessageHandler,
		APH: AsyncPaymentsMessageHandler,
		DRH: DNSResolverMessageHandler,
		CMH: CustomOnionMessageHandler,
	> AOnionMessenger for OnionMessenger<ES, NS, L, NL, MR, OMH, APH, DRH, CMH>
{
	type EntropySource = ES;
	type NodeSigner = NS;
	type Logger = L;
	type NL = NL;
	type MessageRouter = MR;
	type OMH = OMH;
	type APH = APH;
	type DRH = DRH;
	type CMH = CMH;
	fn get_om(&self) -> &OnionMessenger<ES, NS, L, NL, MR, OMH, APH, DRH, CMH> {
		self
	}
}

/// A sender, receiver and forwarder of [`OnionMessage`]s.
///
/// # Handling Messages
///
/// `OnionMessenger` implements [`OnionMessageHandler`], making it responsible for either forwarding
/// messages to peers or delegating to the appropriate handler for the message type. Currently, the
/// available handlers are:
/// * [`OffersMessageHandler`], for responding to [`InvoiceRequest`]s and paying [`Bolt12Invoice`]s
/// * [`CustomOnionMessageHandler`], for handling user-defined message types
///
/// # Sending Messages
///
/// [`OnionMessage`]s are sent initially using [`OnionMessenger::send_onion_message`]. When handling
/// a message, the matched handler may return a response message which `OnionMessenger` will send
/// on its behalf.
///
/// # Example
///
/// ```
/// # extern crate bitcoin;
/// # use bitcoin::hashes::_export::_core::time::Duration;
/// # use bitcoin::hex::FromHex;
/// # use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey, self};
/// # use lightning::blinded_path::EmptyNodeIdLookUp;
/// # use lightning::blinded_path::message::{BlindedMessagePath, MessageForwardNode, MessageContext};
/// # use lightning::sign::{EntropySource, KeysManager};
/// # use lightning::ln::peer_handler::IgnoringMessageHandler;
/// # use lightning::onion_message::messenger::{Destination, MessageRouter, MessageSendInstructions, OnionMessagePath, OnionMessenger};
/// # use lightning::onion_message::packet::OnionMessageContents;
/// # use lightning::sign::{NodeSigner, ReceiveAuthKey};
/// # use lightning::util::logger::{Logger, Record};
/// # use lightning::util::ser::{Writeable, Writer};
/// # use lightning::io;
/// # use std::sync::Arc;
/// # struct FakeLogger;
/// # impl Logger for FakeLogger {
/// #     fn log(&self, record: Record) { println!("{:?}" , record); }
/// # }
/// # struct FakeMessageRouter {}
/// # impl MessageRouter for FakeMessageRouter {
/// #     fn find_path(&self, sender: PublicKey, peers: Vec<PublicKey>, destination: Destination) -> Result<OnionMessagePath, ()> {
/// #         let secp_ctx = Secp256k1::new();
/// #         let node_secret = SecretKey::from_slice(&<Vec<u8>>::from_hex("0101010101010101010101010101010101010101010101010101010101010101").unwrap()[..]).unwrap();
/// #         let hop_node_id1 = PublicKey::from_secret_key(&secp_ctx, &node_secret);
/// #         let hop_node_id2 = hop_node_id1;
/// #         Ok(OnionMessagePath {
/// #             intermediate_nodes: vec![hop_node_id1, hop_node_id2],
/// #             destination,
/// #             first_node_addresses: Vec::new(),
/// #         })
/// #     }
/// #     fn create_blinded_paths<T: secp256k1::Signing + secp256k1::Verification>(
/// #         &self, _recipient: PublicKey, _local_node_receive_key: ReceiveAuthKey,
/// #         _context: MessageContext, _peers: Vec<MessageForwardNode>, _secp_ctx: &Secp256k1<T>
/// #     ) -> Result<Vec<BlindedMessagePath>, ()> {
/// #         unreachable!()
/// #     }
/// # }
/// # let seed = [42u8; 32];
/// # let time = Duration::from_secs(123456);
/// # let keys_manager = KeysManager::new(&seed, time.as_secs(), time.subsec_nanos(), true);
/// # let logger = Arc::new(FakeLogger {});
/// # let node_secret = SecretKey::from_slice(&<Vec<u8>>::from_hex("0101010101010101010101010101010101010101010101010101010101010101").unwrap()[..]).unwrap();
/// # let secp_ctx = Secp256k1::new();
/// # let hop_node_id1 = PublicKey::from_secret_key(&secp_ctx, &node_secret);
/// # let (hop_node_id3, hop_node_id4) = (hop_node_id1, hop_node_id1);
/// # let destination_node_id = hop_node_id1;
/// # let node_id_lookup = EmptyNodeIdLookUp {};
/// # let message_router = Arc::new(FakeMessageRouter {});
/// # let custom_message_handler = IgnoringMessageHandler {};
/// # let offers_message_handler = IgnoringMessageHandler {};
/// # let async_payments_message_handler = IgnoringMessageHandler {};
/// # let dns_resolution_message_handler = IgnoringMessageHandler {};
/// // Create the onion messenger. This must use the same `keys_manager` as is passed to your
/// // ChannelManager.
/// let onion_messenger = OnionMessenger::new(
///     &keys_manager, &keys_manager, logger, &node_id_lookup, message_router,
///     &offers_message_handler, &async_payments_message_handler, &dns_resolution_message_handler,
///     &custom_message_handler,
/// );
///
/// # #[derive(Debug)]
/// # struct YourCustomMessage {}
/// impl Writeable for YourCustomMessage {
/// 	fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
/// 		# Ok(())
/// 		// Write your custom onion message to `w`
/// 	}
/// }
/// impl OnionMessageContents for YourCustomMessage {
/// 	fn tlv_type(&self) -> u64 {
/// 		# let your_custom_message_type = 42;
/// 		your_custom_message_type
/// 	}
/// 	fn msg_type(&self) -> &'static str { "YourCustomMessageType" }
/// }
/// // Send a custom onion message to a node id.
/// let destination = Destination::Node(destination_node_id);
/// let instructions = MessageSendInstructions::WithoutReplyPath { destination };
/// # let message = YourCustomMessage {};
/// onion_messenger.send_onion_message(message, instructions);
///
/// // Create a blinded path to yourself, for someone to send an onion message to.
/// # let your_node_id = hop_node_id1;
/// let hops = [
/// 	MessageForwardNode { node_id: hop_node_id3, short_channel_id: None },
/// 	MessageForwardNode { node_id: hop_node_id4, short_channel_id: None },
/// ];
/// let context = MessageContext::Custom(Vec::new());
/// let receive_key = keys_manager.get_receive_auth_key();
/// let blinded_path = BlindedMessagePath::new(&hops, your_node_id, receive_key, context, false, &keys_manager, &secp_ctx);
///
/// // Send a custom onion message to a blinded path.
/// let destination = Destination::BlindedPath(blinded_path);
/// let instructions = MessageSendInstructions::WithoutReplyPath { destination };
/// # let message = YourCustomMessage {};
/// onion_messenger.send_onion_message(message, instructions);
/// ```
///
/// [`InvoiceRequest`]: crate::offers::invoice_request::InvoiceRequest
/// [`Bolt12Invoice`]: crate::offers::invoice::Bolt12Invoice
pub struct OnionMessenger<
	ES: EntropySource,
	NS: NodeSigner,
	L: Logger,
	NL: NodeIdLookUp,
	MR: MessageRouter,
	OMH: OffersMessageHandler,
	APH: AsyncPaymentsMessageHandler,
	DRH: DNSResolverMessageHandler,
	CMH: CustomOnionMessageHandler,
> {
	entropy_source: ES,
	#[cfg(test)]
	pub(super) node_signer: NS,
	#[cfg(not(test))]
	node_signer: NS,
	logger: L,
	message_recipients: Mutex<HashMap<PublicKey, OnionMessageRecipient>>,
	secp_ctx: Secp256k1<secp256k1::All>,
	node_id_lookup: NL,
	message_router: MR,
	offers_handler: OMH,
	#[allow(unused)]
	async_payments_handler: APH,
	dns_resolver_handler: DRH,
	custom_handler: CMH,
	intercept_messages_for_offline_peers: bool,
	intercept_for_unknown_scids: bool,
	pending_intercepted_msgs_events: Mutex<Vec<Event>>,
	pending_peer_connected_events: Mutex<Vec<Event>>,
	pending_events_processor: AtomicBool,
	/// A [`Notifier`] used to wake up the background processor in case we have any [`Event`]s for
	/// it to give to users.
	event_notifier: Notifier,
}

/// [`OnionMessage`]s buffered to be sent.
enum OnionMessageRecipient {
	/// Messages for a node connected as a peer.
	ConnectedPeer(VecDeque<OnionMessage>),

	/// Messages for a node that is not yet connected, which are dropped after [`MAX_TIMER_TICKS`]
	/// and tracked here.
	PendingConnection(VecDeque<OnionMessage>, Option<Vec<SocketAddress>>, usize),
}

impl OnionMessageRecipient {
	fn pending_connection(addresses: Vec<SocketAddress>) -> Self {
		Self::PendingConnection(VecDeque::new(), Some(addresses), 0)
	}

	fn pending_messages(&self) -> &VecDeque<OnionMessage> {
		match self {
			OnionMessageRecipient::ConnectedPeer(pending_messages) => pending_messages,
			OnionMessageRecipient::PendingConnection(pending_messages, _, _) => pending_messages,
		}
	}

	fn enqueue_message(&mut self, message: OnionMessage) {
		let pending_messages = match self {
			OnionMessageRecipient::ConnectedPeer(pending_messages) => pending_messages,
			OnionMessageRecipient::PendingConnection(pending_messages, _, _) => pending_messages,
		};

		pending_messages.push_back(message);
	}

	fn dequeue_message(&mut self) -> Option<OnionMessage> {
		let pending_messages = match self {
			OnionMessageRecipient::ConnectedPeer(pending_messages) => pending_messages,
			OnionMessageRecipient::PendingConnection(pending_messages, _, _) => {
				debug_assert!(false);
				pending_messages
			},
		};

		pending_messages.pop_front()
	}

	#[cfg(test)]
	fn release_pending_messages(&mut self) -> VecDeque<OnionMessage> {
		let pending_messages = match self {
			OnionMessageRecipient::ConnectedPeer(pending_messages) => pending_messages,
			OnionMessageRecipient::PendingConnection(pending_messages, _, _) => pending_messages,
		};

		core::mem::take(pending_messages)
	}

	fn mark_connected(&mut self) {
		if let OnionMessageRecipient::PendingConnection(pending_messages, _, _) = self {
			let mut new_pending_messages = VecDeque::new();
			core::mem::swap(pending_messages, &mut new_pending_messages);
			*self = OnionMessageRecipient::ConnectedPeer(new_pending_messages);
		}
	}

	fn is_connected(&self) -> bool {
		match self {
			OnionMessageRecipient::ConnectedPeer(..) => true,
			OnionMessageRecipient::PendingConnection(..) => false,
		}
	}
}

/// The `Responder` struct creates an appropriate [`ResponseInstruction`] for responding to a
/// message.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct Responder {
	/// The path along which a response can be sent.
	reply_path: BlindedMessagePath,
}

impl_ser_tlv_based!(Responder, {
	(0, reply_path, required),
});

impl Responder {
	/// Creates a new [`Responder`] instance with the provided reply path.
	pub(super) fn new(reply_path: BlindedMessagePath) -> Self {
		Responder { reply_path }
	}

	/// Creates a [`ResponseInstruction`] for responding without including a reply path.
	///
	/// Use when the recipient doesn't need to send back a reply to us.
	pub fn respond(self) -> ResponseInstruction {
		ResponseInstruction {
			destination: Destination::BlindedPath(self.reply_path),
			context: None,
		}
	}

	/// Creates a [`ResponseInstruction`] for responding including a reply path.
	///
	/// Use when the recipient needs to send back a reply to us.
	pub fn respond_with_reply_path(self, context: MessageContext) -> ResponseInstruction {
		ResponseInstruction {
			destination: Destination::BlindedPath(self.reply_path),
			context: Some(context),
		}
	}

	/// Converts a [`Responder`] into its inner [`BlindedMessagePath`].
	pub(crate) fn into_blinded_path(self) -> BlindedMessagePath {
		self.reply_path
	}
}

/// Instructions for how and where to send the response to an onion message.
#[derive(Clone)]
pub struct ResponseInstruction {
	/// The destination in a response is always a [`Destination::BlindedPath`] but using a
	/// [`Destination`] rather than an explicit [`BlindedMessagePath`] simplifies the logic in
	/// [`OnionMessenger::send_onion_message_internal`] somewhat.
	destination: Destination,
	context: Option<MessageContext>,
}

impl ResponseInstruction {
	/// Converts this [`ResponseInstruction`] into a [`MessageSendInstructions`] so that it can be
	/// used to send the response via a normal message sending method.
	pub fn into_instructions(self) -> MessageSendInstructions {
		MessageSendInstructions::ForReply { instructions: self }
	}
}

/// Instructions for how and where to send a message.
#[derive(Clone)]
pub enum MessageSendInstructions {
	/// Indicates that a message should be sent including the provided reply path for the recipient
	/// to respond.
	WithSpecifiedReplyPath {
		/// The destination where we need to send our message.
		destination: Destination,
		/// The reply path which should be included in the message.
		reply_path: BlindedMessagePath,
	},
	/// Indicates that a message should be sent including a reply path for the recipient to
	/// respond.
	WithReplyPath {
		/// The destination where we need to send our message.
		destination: Destination,
		/// The context to include in the reply path we'll give the recipient so they can respond
		/// to us.
		context: MessageContext,
	},
	/// Indicates that a message should be sent without including a reply path, preventing the
	/// recipient from responding.
	WithoutReplyPath {
		/// The destination where we need to send our message.
		destination: Destination,
	},
	/// Indicates that a message is being sent as a reply to a received message.
	ForReply {
		/// The instructions provided by the [`Responder`].
		instructions: ResponseInstruction,
	},
	/// Indicates that this onion message did not originate from our node and is being forwarded
	/// through us from another node on the network to the destination.
	///
	/// We separate out this case because forwarded onion messages are treated differently from
	/// outbound onion messages initiated by our node. Outbounds are buffered internally, whereas, for
	/// DoS protection, forwards should never be buffered internally and instead will either be
	/// dropped or generate an [`Event::OnionMessageIntercepted`] if the next-hop node is
	/// disconnected.
	ForwardedMessage {
		/// The destination where we need to send the forwarded onion message.
		destination: Destination,
		/// The reply path which should be included in the message, that terminates at the original
		/// sender of this forwarded message.
		reply_path: Option<BlindedMessagePath>,
	},
}

/// A trait defining behavior for routing an [`OnionMessage`].
pub trait MessageRouter {
	/// Returns a route for sending an [`OnionMessage`] to the given [`Destination`].
	fn find_path(
		&self, sender: PublicKey, peers: Vec<PublicKey>, destination: Destination,
	) -> Result<OnionMessagePath, ()>;

	/// Creates [`BlindedMessagePath`]s to the `recipient` node. The nodes in `peers` are assumed to
	/// be direct peers with the `recipient`.
	///
	/// While payments will fail if most of `context` is modified, modifying
	/// [`OffersContext::InvoiceRequest::payment_metadata`] prior to blinded path construction is
	/// allowed.
	///
	fn create_blinded_paths<T: secp256k1::Signing + secp256k1::Verification>(
		&self, recipient: PublicKey, local_node_receive_key: ReceiveAuthKey,
		context: MessageContext, peers: Vec<MessageForwardNode>, secp_ctx: &Secp256k1<T>,
	) -> Result<Vec<BlindedMessagePath>, ()>;
}

impl<T: MessageRouter + ?Sized, R: Deref<Target = T>> MessageRouter for R {
	fn find_path(
		&self, sender: PublicKey, peers: Vec<PublicKey>, destination: Destination,
	) -> Result<OnionMessagePath, ()> {
		self.deref().find_path(sender, peers, destination)
	}

	fn create_blinded_paths<S: secp256k1::Signing + secp256k1::Verification>(
		&self, recipient: PublicKey, local_node_receive_key: ReceiveAuthKey,
		context: MessageContext, peers: Vec<MessageForwardNode>, secp_ctx: &Secp256k1<S>,
	) -> Result<Vec<BlindedMessagePath>, ()> {
		self.deref().create_blinded_paths(
			recipient,
			local_node_receive_key,
			context,
			peers,
			secp_ctx,
		)
	}
}

/// A [`MessageRouter`] that can only route to a directly connected [`Destination`].
///
/// [`DefaultMessageRouter`] tries to construct compact or private [`BlindedMessagePath`]s based on
/// the [`MessageContext`] given to [`MessageRouter::create_blinded_paths`]. That is, if the
/// provided context implies the path may be used in a BOLT 12 object which might appear in a QR
/// code, it reduces the amount of padding and dummy hops and prefers building compact paths when
/// short channel IDs (SCIDs) are available for intermediate peers.
///
/// # Compact Blinded Paths
///
/// Compact blinded paths use short channel IDs (SCIDs) instead of pubkeys, resulting in smaller
/// serialization. This is particularly useful when encoding data into space-constrained formats
/// such as QR codes. The SCID is communicated via a [`MessageForwardNode`], but may be `None`
/// to allow for graceful degradation.
///
/// **Note:**
/// If any SCID in the blinded path becomes invalid, the entire compact blinded path may fail to route.
/// For the immediate hop, this can happen if the corresponding channel is closed.
/// For other intermediate hops, it can happen if the channel is closed or modified (e.g., due to splicing).
///
/// # Privacy
///
/// Creating [`BlindedMessagePath`]s may affect privacy since, if a suitable path cannot be found,
/// it will create a one-hop path using the recipient as the introduction node if it is an announced
/// node. Otherwise, there is no way to find a path to the introduction node in order to send a
/// message, and thus an `Err` is returned. The impact of this may be somewhat muted when
/// additional dummy hops are added to the blinded path, but this protection is not complete.
pub struct DefaultMessageRouter<G: Deref<Target = NetworkGraph<L>>, L: Logger, ES: EntropySource> {
	network_graph: G,
	entropy_source: ES,
}

// Target total length (in hops) for blinded paths used outside of QR codes.
//
// We add dummy hops until the path reaches this length (including the recipient).
pub(crate) const DUMMY_HOPS_PATH_LENGTH: usize = 4;

// Target total length (in hops) for blinded paths included in objects which may appear in a QR
// code.
//
// We add dummy hops until the path reaches this length (including the recipient).
pub(crate) const QR_CODED_DUMMY_HOPS_PATH_LENGTH: usize = 2;

impl<G: Deref<Target = NetworkGraph<L>>, L: Logger, ES: EntropySource>
	DefaultMessageRouter<G, L, ES>
{
	/// Creates a [`DefaultMessageRouter`] using the given [`NetworkGraph`].
	pub fn new(network_graph: G, entropy_source: ES) -> Self {
		Self { network_graph, entropy_source }
	}

	pub(crate) fn create_blinded_paths_from_iter<
		I: ExactSizeIterator<Item = MessageForwardNode> + Clone,
		T: secp256k1::Signing + secp256k1::Verification,
	>(
		network_graph: &G, recipient: PublicKey, local_node_receive_key: ReceiveAuthKey,
		context: MessageContext, peers: I, entropy_source: &ES, secp_ctx: &Secp256k1<T>,
		never_compact_path: bool,
	) -> Result<Vec<BlindedMessagePath>, ()> {
		// Limit the number of blinded paths that are computed.
		const MAX_PATHS: usize = 3;

		let network_graph = network_graph.deref().read_only();
		let is_recipient_announced =
			network_graph.nodes().contains_key(&NodeId::from_pubkey(&recipient));

		let (size_constrained, path_len_incl_dummys) = match &context {
			MessageContext::Offers(OffersContext::InvoiceRequest { .. })
			| MessageContext::Offers(OffersContext::OutboundPaymentForRefund { .. }) => {
				// When including blinded paths within BOLT 12 objects that appear in QR codes, we
				// sadly need to be conservative about size, especially if the QR code ultimately
				// also includes an on-chain address.
				(true, QR_CODED_DUMMY_HOPS_PATH_LENGTH)
			},
			MessageContext::Offers(OffersContext::StaticInvoiceRequested { .. }) => {
				// Async Payments aggressively embeds the entire `InvoiceRequest` in the payment
				// onion. In a future version it should likely move to embedding only the
				// `InvoiceRequest`-specific fields instead, but until then we have to be
				// incredibly strict in the size of the blinded path we include in a static payment
				// `Offer`.
				(true, 0)
			},
			_ => {
				// If there's no need to be small, add additional dummy hops and never use
				// SCID-based next-hops as they carry additional expiry risk.
				(false, DUMMY_HOPS_PATH_LENGTH)
			},
		};

		let compact_paths = !never_compact_path && size_constrained;

		let build_path = |intermediate_hops: &[MessageForwardNode]| {
			// Calculate the dummy hops given the total hop count target (including the recipient).
			let dummy_hops_count = path_len_incl_dummys.saturating_sub(intermediate_hops.len() + 1);

			BlindedMessagePath::new_with_dummy_hops(
				intermediate_hops,
				recipient,
				dummy_hops_count,
				local_node_receive_key,
				context.clone(),
				size_constrained,
				&entropy_source,
				secp_ctx,
			)
		};

		let has_one_peer = peers.len() == 1;
		let mut paths = if !is_recipient_announced {
			let mut peer_info = peers
				.map(|peer| MessageForwardNode {
					short_channel_id: if compact_paths { peer.short_channel_id } else { None },
					..peer
				})
				.filter_map(|peer| {
					network_graph
						.node(&NodeId::from_pubkey(&peer.node_id))
						.map(|info| (peer, info.is_tor_only(), info.channels.len()))
						// Allow messages directly with the only peer
						.or_else(|| has_one_peer.then(|| (peer, false, 0)))
				})
				.collect::<Vec<_>>();

			// Prefer using non-Tor nodes with the most channels as the introduction node.
			peer_info.sort_unstable_by(
				|(_, a_tor_only, a_channels), (_, b_tor_only, b_channels)| {
					a_tor_only.cmp(b_tor_only).then(a_channels.cmp(b_channels).reverse())
				},
			);

			// Try to create paths from peer info, fall back to direct path if needed
			peer_info
				.into_iter()
				.map(|(peer, _, _)| build_path(&[peer]))
				.take(MAX_PATHS)
				.collect::<Vec<_>>()
		} else {
			vec![]
		};

		if paths.is_empty() {
			if is_recipient_announced {
				paths = vec![build_path(&[])];
			} else {
				return Err(());
			}
		}

		if compact_paths {
			for path in &mut paths {
				path.use_compact_introduction_node(&network_graph);
			}
		}

		Ok(paths)
	}

	pub(crate) fn find_path(
		network_graph: &G, sender: PublicKey, peers: Vec<PublicKey>, mut destination: Destination,
	) -> Result<OnionMessagePath, ()> {
		let network_graph = network_graph.deref().read_only();
		destination.resolve(&network_graph);

		let first_node = match destination.first_node() {
			Some(first_node) => first_node,
			None => return Err(()),
		};

		if peers.contains(&first_node) || sender == first_node {
			Ok(OnionMessagePath {
				intermediate_nodes: vec![],
				destination,
				first_node_addresses: vec![],
			})
		} else {
			let node_details = network_graph
				.node(&NodeId::from_pubkey(&first_node))
				.and_then(|node_info| node_info.announcement_info.as_ref())
				.map(|announcement_info| {
					(announcement_info.features(), announcement_info.addresses())
				});

			match node_details {
				Some((features, addresses))
					if features.supports_onion_messages() && addresses.len() > 0 =>
				{
					Ok(OnionMessagePath {
						intermediate_nodes: vec![],
						destination,
						first_node_addresses: addresses.to_vec(),
					})
				},
				None => {
					// If the destination is an unannounced node, they may be a known peer that is offline and
					// can be woken by the sender.
					Ok(OnionMessagePath {
						intermediate_nodes: vec![],
						destination,
						first_node_addresses: vec![],
					})
				},
				_ => Err(()),
			}
		}
	}
}

impl<G: Deref<Target = NetworkGraph<L>>, L: Logger, ES: EntropySource> MessageRouter
	for DefaultMessageRouter<G, L, ES>
{
	fn find_path(
		&self, sender: PublicKey, peers: Vec<PublicKey>, destination: Destination,
	) -> Result<OnionMessagePath, ()> {
		Self::find_path(&self.network_graph, sender, peers, destination)
	}

	fn create_blinded_paths<T: secp256k1::Signing + secp256k1::Verification>(
		&self, recipient: PublicKey, local_node_receive_key: ReceiveAuthKey,
		context: MessageContext, peers: Vec<MessageForwardNode>, secp_ctx: &Secp256k1<T>,
	) -> Result<Vec<BlindedMessagePath>, ()> {
		Self::create_blinded_paths_from_iter(
			&self.network_graph,
			recipient,
			local_node_receive_key,
			context,
			peers.into_iter(),
			&self.entropy_source,
			secp_ctx,
			false,
		)
	}
}

/// This message router is similar to [`DefaultMessageRouter`], but it always creates
/// non-compact blinded paths, using the peer's [`NodeId`]. It uses the same heuristics as
/// [`DefaultMessageRouter`] for deciding when to add additional dummy hops to the generated blinded
/// paths.
///
/// This may be useful in cases where you want a long-lived blinded path and anticipate channel(s)
/// may close, but connections to specific peers will remain stable.
///
/// This message router can only route to a directly connected [`Destination`].
///
/// # Privacy
///
/// Creating [`BlindedMessagePath`]s may affect privacy since, if a suitable path cannot be found,
/// it will create a one-hop path using the recipient as the introduction node if it is an announced
/// node. Otherwise, there is no way to find a path to the introduction node in order to send a
/// message, and thus an `Err` is returned. The impact of this may be somewhat muted when
/// additional dummy hops are added to the blinded path, but this protection is not complete.
pub struct NodeIdMessageRouter<G: Deref<Target = NetworkGraph<L>>, L: Logger, ES: EntropySource> {
	network_graph: G,
	entropy_source: ES,
}

impl<G: Deref<Target = NetworkGraph<L>>, L: Logger, ES: EntropySource>
	NodeIdMessageRouter<G, L, ES>
{
	/// Creates a [`NodeIdMessageRouter`] using the given [`NetworkGraph`].
	pub fn new(network_graph: G, entropy_source: ES) -> Self {
		Self { network_graph, entropy_source }
	}
}

impl<G: Deref<Target = NetworkGraph<L>>, L: Logger, ES: EntropySource> MessageRouter
	for NodeIdMessageRouter<G, L, ES>
{
	fn find_path(
		&self, sender: PublicKey, peers: Vec<PublicKey>, destination: Destination,
	) -> Result<OnionMessagePath, ()> {
		DefaultMessageRouter::<G, L, ES>::find_path(&self.network_graph, sender, peers, destination)
	}

	fn create_blinded_paths<T: secp256k1::Signing + secp256k1::Verification>(
		&self, recipient: PublicKey, local_node_receive_key: ReceiveAuthKey,
		context: MessageContext, mut peers: Vec<MessageForwardNode>, secp_ctx: &Secp256k1<T>,
	) -> Result<Vec<BlindedMessagePath>, ()> {
		for peer in peers.iter_mut() {
			peer.short_channel_id = None;
		}
		DefaultMessageRouter::create_blinded_paths_from_iter(
			&self.network_graph,
			recipient,
			local_node_receive_key,
			context,
			peers.into_iter(),
			&self.entropy_source,
			secp_ctx,
			true,
		)
	}
}

/// A special [`MessageRouter`] that performs no routing and does not create blinded paths.
/// Its purpose is to enable the creation of [`Offer`]s and [`Refund`]s without blinded paths,
/// where the user's `node_id` is used directly as the [`Destination`].
///
/// # Note
/// [`NullMessageRouter`] **must not** be used as the type parameter for [`ChannelManager`],
/// since [`ChannelManager`] requires a functioning [`MessageRouter`] to create blinded paths,
/// which are necessary for constructing reply paths in onion message communication.
/// However, [`NullMessageRouter`] *can* still be passed as an argument to [`ChannelManager`]
/// methods that accepts a [`MessageRouter`], such as [`ChannelManager::create_offer_builder_using_router`],
/// when blinded paths are not needed.
///
/// [`Offer`]: crate::offers::offer::Offer
/// [`Refund`]: crate::offers::refund::Refund
/// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
/// [`ChannelManager::create_offer_builder_using_router`]: crate::ln::channelmanager::ChannelManager::create_offer_builder_using_router
pub struct NullMessageRouter {}

impl MessageRouter for NullMessageRouter {
	fn find_path(
		&self, _sender: PublicKey, _peers: Vec<PublicKey>, _destination: Destination,
	) -> Result<OnionMessagePath, ()> {
		Err(())
	}

	fn create_blinded_paths<T: secp256k1::Signing + secp256k1::Verification>(
		&self, _recipient: PublicKey, _local_node_receive_key: ReceiveAuthKey,
		_context: MessageContext, _peers: Vec<MessageForwardNode>, _secp_ctx: &Secp256k1<T>,
	) -> Result<Vec<BlindedMessagePath>, ()> {
		Ok(vec![])
	}
}

/// A path for sending an [`OnionMessage`].
#[derive(Clone)]
pub struct OnionMessagePath {
	/// Nodes on the path between the sender and the destination.
	pub intermediate_nodes: Vec<PublicKey>,

	/// The recipient of the message.
	pub destination: Destination,

	/// Addresses that may be used to connect to [`OnionMessagePath::first_node`].
	///
	/// Only needs to be filled in if a connection to the node is required and it is not a known peer.
	/// [`OnionMessenger`] may use this to initiate such a connection.
	pub first_node_addresses: Vec<SocketAddress>,
}

impl OnionMessagePath {
	/// Returns the first node in the path.
	pub fn first_node(&self) -> Option<PublicKey> {
		self.intermediate_nodes.first().copied().or_else(|| self.destination.first_node())
	}
}

/// The destination of an onion message.
#[derive(Clone, Hash, Debug, PartialEq, Eq)]
pub enum Destination {
	/// We're sending this onion message to a node.
	Node(PublicKey),
	/// We're sending this onion message to a blinded path.
	BlindedPath(BlindedMessagePath),
}

impl Destination {
	/// Attempts to resolve the [`IntroductionNode::DirectedShortChannelId`] of a
	/// [`Destination::BlindedPath`] to a [`IntroductionNode::NodeId`], if applicable, using the
	/// provided [`ReadOnlyNetworkGraph`].
	pub fn resolve(&mut self, network_graph: &ReadOnlyNetworkGraph) {
		if let Destination::BlindedPath(path) = self {
			if let IntroductionNode::DirectedShortChannelId(..) = path.introduction_node() {
				if let Some(pubkey) = path
					.public_introduction_node_id(network_graph)
					.and_then(|node_id| node_id.as_pubkey().ok())
				{
					*path.introduction_node_mut() = IntroductionNode::NodeId(pubkey);
				}
			}
		}
	}

	pub(super) fn num_hops(&self) -> usize {
		match self {
			Destination::Node(_) => 1,
			Destination::BlindedPath(path) => path.blinded_hops().len(),
		}
	}

	fn first_node(&self) -> Option<PublicKey> {
		match self {
			Destination::Node(node_id) => Some(*node_id),
			Destination::BlindedPath(path) => match path.introduction_node() {
				IntroductionNode::NodeId(pubkey) => Some(*pubkey),
				IntroductionNode::DirectedShortChannelId(..) => None,
			},
		}
	}
}

/// Result of successfully [sending an onion message].
///
/// [sending an onion message]: OnionMessenger::send_onion_message
#[derive(Clone, Hash, Debug, PartialEq, Eq)]
pub enum SendSuccess {
	/// The message was buffered and will be sent once it is processed by
	/// [`OnionMessageHandler::next_onion_message_for_peer`].
	Buffered,
	/// The message was buffered and will be sent once the node is connected as a peer and it is
	/// processed by [`OnionMessageHandler::next_onion_message_for_peer`].
	BufferedAwaitingConnection(PublicKey),
}

/// Errors that may occur when [sending an onion message].
///
/// [sending an onion message]: OnionMessenger::send_onion_message
#[derive(Clone, Hash, Debug, PartialEq, Eq)]
pub enum SendError {
	/// Errored computing onion message packet keys.
	Secp256k1(secp256k1::Error),
	/// Because implementations such as Eclair will drop onion messages where the message packet
	/// exceeds 32834 bytes, we refuse to send messages where the packet exceeds this size.
	TooBigPacket,
	/// The provided [`Destination`] was an invalid [`BlindedMessagePath`] due to not having any
	/// blinded hops.
	TooFewBlindedHops,
	/// The first hop is not a peer and doesn't have a known [`SocketAddress`].
	InvalidFirstHop(PublicKey),
	/// Indicates that a path could not be found by the [`MessageRouter`].
	///
	/// This occurs when either:
	/// - No path from the sender to the destination was found to send the onion message
	/// - No reply path to the sender could be created when responding to an onion message
	PathNotFound,
	/// Onion message contents must have a TLV type >= 64.
	InvalidMessage,
	/// Our next-hop peer's buffer was full or our total outbound buffer was full.
	BufferFull,
	/// Failed to retrieve our node id from the provided [`NodeSigner`].
	///
	/// [`NodeSigner`]: crate::sign::NodeSigner
	GetNodeIdFailed,
	/// The provided [`Destination`] has a blinded path with an unresolved introduction node. An
	/// attempt to resolve it in the [`MessageRouter`] when finding an [`OnionMessagePath`] likely
	/// failed.
	UnresolvedIntroductionNode,
	/// We attempted to send to a blinded path where we are the introduction node, and failed to
	/// advance the blinded path to make the second hop the new introduction node. Either
	/// [`NodeSigner::ecdh`] failed, we failed to tweak the current blinding point to get the
	/// new blinding point, or we were attempting to send to ourselves.
	BlindedPathAdvanceFailed,
}

/// Handler for custom onion messages. If you are using [`SimpleArcOnionMessenger`],
/// [`SimpleRefOnionMessenger`], or prefer to ignore inbound custom onion messages,
/// [`IgnoringMessageHandler`] must be provided to [`OnionMessenger::new`]. Otherwise, a custom
/// implementation of this trait must be provided, with [`CustomMessage`] specifying the supported
/// message types.
///
/// See [`OnionMessenger`] for example usage.
///
/// [`IgnoringMessageHandler`]: crate::ln::peer_handler::IgnoringMessageHandler
/// [`CustomMessage`]: Self::CustomMessage
pub trait CustomOnionMessageHandler {
	/// The message known to the handler. To support multiple message types, you may want to make this
	/// an enum with a variant for each supported message.
	type CustomMessage: OnionMessageContents;

	/// Called with the custom message that was received, returning a response to send, if any.
	///
	/// If the provided `context` is `Some`, then the message was sent to a blinded path that we
	/// created and was authenticated as such by the [`OnionMessenger`].
	///
	/// The returned [`Self::CustomMessage`], if any, is enqueued to be sent by [`OnionMessenger`].
	fn handle_custom_message(
		&self, message: Self::CustomMessage, context: Option<Vec<u8>>, responder: Option<Responder>,
	) -> Option<(Self::CustomMessage, ResponseInstruction)>;

	/// Read a custom message of type `message_type` from `buffer`, returning `Ok(None)` if the
	/// message type is unknown.
	fn read_custom_message<R: io::Read>(
		&self, message_type: u64, buffer: &mut R,
	) -> Result<Option<Self::CustomMessage>, msgs::DecodeError>;

	/// Releases any [`Self::CustomMessage`]s that need to be sent.
	///
	/// Typically, this is used for messages initiating a message flow rather than in response to
	/// another message. The latter should use the return value of [`Self::handle_custom_message`].
	fn release_pending_custom_messages(
		&self,
	) -> Vec<(Self::CustomMessage, MessageSendInstructions)>;
}

impl<T: CustomOnionMessageHandler + ?Sized, C: Deref<Target = T>> CustomOnionMessageHandler for C {
	type CustomMessage = T::CustomMessage;
	fn handle_custom_message(
		&self, message: Self::CustomMessage, context: Option<Vec<u8>>, responder: Option<Responder>,
	) -> Option<(Self::CustomMessage, ResponseInstruction)> {
		self.deref().handle_custom_message(message, context, responder)
	}
	fn read_custom_message<R: io::Read>(
		&self, message_type: u64, buffer: &mut R,
	) -> Result<Option<Self::CustomMessage>, msgs::DecodeError> {
		self.deref().read_custom_message(message_type, buffer)
	}
	fn release_pending_custom_messages(
		&self,
	) -> Vec<(Self::CustomMessage, MessageSendInstructions)> {
		self.deref().release_pending_custom_messages()
	}
}

/// A processed incoming onion message, containing either a Forward (another onion message)
/// or a Receive payload with decrypted contents.
#[derive(Clone, Debug)]
pub enum PeeledOnion<T: OnionMessageContents> {
	/// Forwarded onion, with the next node id and a new onion
	Forward(NextMessageHop, OnionMessage),
	/// Received offers onion message, with decrypted contents, context, and reply path
	Offers(OffersMessage, Option<OffersContext>, Option<BlindedMessagePath>),
	/// Received async payments onion message, with decrypted contents, context, and reply path
	AsyncPayments(AsyncPaymentsMessage, AsyncPaymentsContext, Option<BlindedMessagePath>),
	/// Received DNS resolver onion message, with decrypted contents, context, and reply path
	DNSResolver(DNSResolverMessage, Option<DNSResolverContext>, Option<BlindedMessagePath>),
	/// Received custom onion message, with decrypted contents, context, and reply path
	Custom(T, Option<Vec<u8>>, Option<BlindedMessagePath>),
}

/// Creates an [`OnionMessage`] with the given `contents` for sending to the destination of
/// `path`, first calling [`Destination::resolve`] on `path.destination` with the given
/// [`ReadOnlyNetworkGraph`].
///
/// Returns the node id of the peer to send the message to, the message itself, and any addresses
/// needed to connect to the first node.
pub fn create_onion_message_resolving_destination<
	ES: EntropySource,
	NS: NodeSigner,
	NL: NodeIdLookUp,
	T: OnionMessageContents,
>(
	entropy_source: &ES, node_signer: &NS, node_id_lookup: &NL,
	network_graph: &ReadOnlyNetworkGraph, secp_ctx: &Secp256k1<secp256k1::All>,
	mut path: OnionMessagePath, contents: T, reply_path: Option<BlindedMessagePath>,
) -> Result<(PublicKey, OnionMessage, Vec<SocketAddress>), SendError> {
	path.destination.resolve(network_graph);
	create_onion_message(
		entropy_source,
		node_signer,
		node_id_lookup,
		secp_ctx,
		path,
		contents,
		reply_path,
	)
}

/// Creates an [`OnionMessage`] with the given `contents` for sending to the destination of
/// `path`.
///
/// Returns the node id of the peer to send the message to, the message itself, and any addresses
/// needed to connect to the first node.
///
/// Returns [`SendError::UnresolvedIntroductionNode`] if:
/// - `destination` contains a blinded path with an [`IntroductionNode::DirectedShortChannelId`],
/// - unless it can be resolved by [`NodeIdLookUp::next_node_id`].
/// Use [`create_onion_message_resolving_destination`] instead to resolve the introduction node
/// first with a [`ReadOnlyNetworkGraph`].
pub fn create_onion_message<
	ES: EntropySource,
	NS: NodeSigner,
	NL: NodeIdLookUp,
	T: OnionMessageContents,
>(
	entropy_source: &ES, node_signer: &NS, node_id_lookup: &NL,
	secp_ctx: &Secp256k1<secp256k1::All>, path: OnionMessagePath, contents: T,
	reply_path: Option<BlindedMessagePath>,
) -> Result<(PublicKey, OnionMessage, Vec<SocketAddress>), SendError> {
	let OnionMessagePath { intermediate_nodes, mut destination, first_node_addresses } = path;
	if let Destination::BlindedPath(ref path) = destination {
		if path.blinded_hops().is_empty() {
			return Err(SendError::TooFewBlindedHops);
		}
	}

	if contents.tlv_type() < 64 {
		return Err(SendError::InvalidMessage);
	}

	// If we are sending straight to a blinded path and we are the introduction node, we need to
	// advance the blinded path by 1 hop so the second hop is the new introduction node.
	if intermediate_nodes.len() == 0 {
		if let Destination::BlindedPath(ref mut blinded_path) = destination {
			let our_node_id = node_signer
				.get_node_id(Recipient::Node)
				.map_err(|()| SendError::GetNodeIdFailed)?;
			let introduction_node_id = match blinded_path.introduction_node() {
				IntroductionNode::NodeId(pubkey) => *pubkey,
				IntroductionNode::DirectedShortChannelId(direction, scid) => {
					match node_id_lookup.next_node_id(*scid) {
						Some(next_node_id) => *direction.select_pubkey(&our_node_id, &next_node_id),
						None => return Err(SendError::UnresolvedIntroductionNode),
					}
				},
			};
			if introduction_node_id == our_node_id {
				blinded_path
					.advance_path_by_one(node_signer, node_id_lookup, &secp_ctx)
					.map_err(|()| SendError::BlindedPathAdvanceFailed)?;
			}
		}
	}

	let blinding_secret_bytes = entropy_source.get_secure_random_bytes();
	let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
	let (first_node_id, blinding_point) = if let Some(first_node_id) = intermediate_nodes.first() {
		(*first_node_id, PublicKey::from_secret_key(&secp_ctx, &blinding_secret))
	} else {
		match &destination {
			Destination::Node(pk) => (*pk, PublicKey::from_secret_key(&secp_ctx, &blinding_secret)),
			Destination::BlindedPath(path) => match path.introduction_node() {
				IntroductionNode::NodeId(pubkey) => (*pubkey, path.blinding_point()),
				IntroductionNode::DirectedShortChannelId(..) => {
					return Err(SendError::UnresolvedIntroductionNode);
				},
			},
		}
	};
	let (packet_payloads, packet_keys) = packet_payloads_and_keys(
		&secp_ctx,
		intermediate_nodes,
		destination,
		contents,
		reply_path,
		&blinding_secret,
	)?;

	let prng_seed = entropy_source.get_secure_random_bytes();
	let onion_routing_packet =
		construct_onion_message_packet(packet_payloads, packet_keys, prng_seed)
			.map_err(|()| SendError::TooBigPacket)?;

	let message = OnionMessage { blinding_point, onion_routing_packet };
	Ok((first_node_id, message, first_node_addresses))
}

/// Decode one layer of an incoming [`OnionMessage`].
///
/// Returns either the next layer of the onion for forwarding or the decrypted content for the
/// receiver.
pub fn peel_onion_message<NS: NodeSigner, L: Logger, CMH: CustomOnionMessageHandler>(
	msg: &OnionMessage, secp_ctx: &Secp256k1<secp256k1::All>, node_signer: NS, logger: L,
	custom_handler: CMH,
) -> Result<PeeledOnion<CMH::CustomMessage>, ()> {
	let control_tlvs_ss = match node_signer.ecdh(Recipient::Node, &msg.blinding_point, None) {
		Ok(ss) => ss,
		Err(e) => {
			log_error!(logger, "Failed to retrieve node secret: {:?}", e);
			return Err(());
		},
	};
	let onion_decode_ss = {
		let blinding_factor = {
			let mut hmac = HmacEngine::<Sha256>::new(b"blinded_node_id");
			hmac.input(control_tlvs_ss.as_ref());
			let hmac = Hmac::from_engine(hmac).to_byte_array();
			Scalar::from_be_bytes(hmac).unwrap()
		};
		let packet_pubkey = &msg.onion_routing_packet.public_key;
		match node_signer.ecdh(Recipient::Node, packet_pubkey, Some(&blinding_factor)) {
			Ok(ss) => ss.secret_bytes(),
			Err(()) => {
				log_trace!(logger, "Failed to compute onion packet shared secret");
				return Err(());
			},
		}
	};
	let receive_auth_key = node_signer.get_receive_auth_key();
	let expanded_key = &node_signer.get_expanded_key();
	let next_hop = onion_utils::decode_next_untagged_hop(
		onion_decode_ss,
		&msg.onion_routing_packet.hop_data[..],
		msg.onion_routing_packet.hmac,
		(control_tlvs_ss, &custom_handler, receive_auth_key, expanded_key, &logger),
	);

	// Constructs the next onion message using packet data and blinding logic.
	let build_outbound_onion_message = |packet_pubkey: PublicKey,
	                                    next_hop_hmac: [u8; 32],
	                                    new_packet_bytes: Vec<u8>,
	                                    blinding_point_opt: Option<PublicKey>|
	 -> Result<OnionMessage, ()> {
		let new_pubkey =
			match onion_utils::next_hop_pubkey(&secp_ctx, packet_pubkey, &onion_decode_ss) {
				Ok(pk) => pk,
				Err(e) => {
					log_trace!(logger, "Failed to compute next hop packet pubkey: {}", e);
					return Err(());
				},
			};
		let outgoing_packet = Packet {
			version: 0,
			public_key: new_pubkey,
			hop_data: new_packet_bytes,
			hmac: next_hop_hmac,
		};
		let blinding_point = match blinding_point_opt {
			Some(bp) => bp,
			None => match onion_utils::next_hop_pubkey(
				&secp_ctx,
				msg.blinding_point,
				control_tlvs_ss.as_ref(),
			) {
				Ok(bp) => bp,
				Err(e) => {
					log_trace!(logger, "Failed to compute next blinding point: {}", e);
					return Err(());
				},
			},
		};
		Ok(OnionMessage { blinding_point, onion_routing_packet: outgoing_packet })
	};

	match next_hop {
		Ok((
			Payload::Receive {
				message,
				control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { context }),
				reply_path,
				control_tlvs_from_local_node,
				control_tlvs_from_phantom_participant: _,
			},
			None,
		)) => match (message, context) {
			(ParsedOnionMessageContents::Offers(msg), Some(MessageContext::Offers(ctx))) => {
				match ctx {
					OffersContext::InvoiceRequest { .. } => {
						// Note: We introduced the `control_tlvs_from_*` check in LDK v0.2
						// to simplify and standardize onion message authentication.
						// To continue supporting offers created before v0.2, we allow
						// unauthenticated control TLVs for these messages, as they can be
						// verified using the legacy method.
					},
					_ => {
						// In any other offers context, we only allow message authenticated as
						// coming from our local, node, not any other phantom participant.
						if !control_tlvs_from_local_node {
							log_trace!(logger, "Received an unauthenticated offers onion message");
							return Err(());
						}
					},
				}
				Ok(PeeledOnion::Offers(msg, Some(ctx), reply_path))
			},
			(ParsedOnionMessageContents::Offers(msg), None) => {
				Ok(PeeledOnion::Offers(msg, None, reply_path))
			},
			(
				ParsedOnionMessageContents::AsyncPayments(msg),
				Some(MessageContext::AsyncPayments(ctx)),
			) => {
				if !control_tlvs_from_local_node {
					log_trace!(logger, "Received an unauthenticated async payments onion message");
					return Err(());
				}
				Ok(PeeledOnion::AsyncPayments(msg, ctx, reply_path))
			},
			(ParsedOnionMessageContents::Custom(msg), Some(MessageContext::Custom(ctx))) => {
				if !control_tlvs_from_local_node {
					log_trace!(logger, "Received an unauthenticated custom onion message");
					return Err(());
				}
				Ok(PeeledOnion::Custom(msg, Some(ctx), reply_path))
			},
			(ParsedOnionMessageContents::Custom(msg), None) => {
				Ok(PeeledOnion::Custom(msg, None, reply_path))
			},
			(
				ParsedOnionMessageContents::DNSResolver(msg),
				Some(MessageContext::DNSResolver(ctx)),
			) => {
				if !control_tlvs_from_local_node {
					log_trace!(logger, "Received an unauthenticated DNS resolver onion message");
					return Err(());
				}
				Ok(PeeledOnion::DNSResolver(msg, Some(ctx), reply_path))
			},
			(ParsedOnionMessageContents::DNSResolver(msg), None) => {
				Ok(PeeledOnion::DNSResolver(msg, None, reply_path))
			},
			_ => {
				log_trace!(
					logger,
					"Received message was sent on a blinded path with wrong or missing context."
				);
				Err(())
			},
		},
		Ok((
			Payload::Dummy { control_tlvs_authenticated },
			Some((next_hop_hmac, new_packet_bytes)),
		)) => {
			if !control_tlvs_authenticated {
				log_trace!(logger, "Received an unauthenticated dummy onion message");
				return Err(());
			}

			let onion_message = build_outbound_onion_message(
				msg.onion_routing_packet.public_key,
				next_hop_hmac,
				new_packet_bytes,
				None,
			)?;
			peel_onion_message(&onion_message, secp_ctx, node_signer, logger, custom_handler)
		},
		Ok((
			Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
				next_hop,
				next_blinding_override,
			})),
			Some((next_hop_hmac, new_packet_bytes)),
		)) => {
			let onion_message = build_outbound_onion_message(
				msg.onion_routing_packet.public_key,
				next_hop_hmac,
				new_packet_bytes,
				next_blinding_override,
			)?;

			Ok(PeeledOnion::Forward(next_hop, onion_message))
		},
		Err(e) => {
			log_trace!(logger, "Errored decoding onion message packet: {:?}", e);
			Err(())
		},
		_ => {
			log_trace!(logger, "Received bogus onion message packet, either the sender encoded a final hop as a forwarding hop or vice versa");
			Err(())
		},
	}
}

macro_rules! drop_handled_events_and_abort {
	($self: expr, $res_iter: expr, $event_queue: expr) => {
		// We want to make sure to cleanly abort upon event handling failure. To this end, we drop all
		// successfully handled events from the given queue, reset the events processing flag, and
		// return, to have the events eventually replayed upon next invocation.
		{
			let mut queue_lock = $event_queue.lock().unwrap();

			// Keep all events which previously error'd *or* any that have been added since we dropped
			// the Mutex before.
			let mut any_error = false;
			queue_lock.retain(|_| {
				$res_iter.next().map_or(true, |r| {
					let is_err = r.is_err();
					any_error |= is_err;
					is_err
				})
			});

			if any_error {
				// We failed handling some events. Return to have them eventually replayed.
				$self.pending_events_processor.store(false, Ordering::Release);
				$self.event_notifier.notify();
				return;
			}
		}
	};
}

impl<
		ES: EntropySource,
		NS: NodeSigner,
		L: Logger,
		NL: NodeIdLookUp,
		MR: MessageRouter,
		OMH: OffersMessageHandler,
		APH: AsyncPaymentsMessageHandler,
		DRH: DNSResolverMessageHandler,
		CMH: CustomOnionMessageHandler,
	> OnionMessenger<ES, NS, L, NL, MR, OMH, APH, DRH, CMH>
{
	/// Constructs a new `OnionMessenger` to send, forward, and delegate received onion messages to
	/// their respective handlers.
	pub fn new(
		entropy_source: ES, node_signer: NS, logger: L, node_id_lookup: NL, message_router: MR,
		offers_handler: OMH, async_payments_handler: APH, dns_resolver: DRH, custom_handler: CMH,
	) -> Self {
		Self::new_inner(
			entropy_source,
			node_signer,
			logger,
			node_id_lookup,
			message_router,
			offers_handler,
			async_payments_handler,
			dns_resolver,
			custom_handler,
			false,
			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.
	///
	/// If `intercept_for_unknown_scids` is set, we will additionally intercept onion messages whose
	/// next hop is a [`NextMessageHop::ShortChannelId`] that cannot be resolved to a connected
	/// peer, generating an [`Event::OnionMessageIntercepted`] with a
	/// [`NextMessageHop::ShortChannelId`] next hop. This variant of the event was introduced in
	/// LDK 0.3, so users who persist [`Event::OnionMessageIntercepted`] events and may need to
	/// downgrade to LDK 0.2 must leave this disabled.
	///
	/// Interception flow:
	/// 1. If an onion message for an offline peer or (if `intercept_for_unknown_scids` is set) an
	///    unknown SCID 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, async_payments_handler: APH, dns_resolver: DRH, custom_handler: CMH,
		intercept_for_unknown_scids: bool,
	) -> Self {
		Self::new_inner(
			entropy_source,
			node_signer,
			logger,
			node_id_lookup,
			message_router,
			offers_handler,
			async_payments_handler,
			dns_resolver,
			custom_handler,
			true,
			intercept_for_unknown_scids,
		)
	}

	fn new_inner(
		entropy_source: ES, node_signer: NS, logger: L, node_id_lookup: NL, message_router: MR,
		offers_handler: OMH, async_payments_handler: APH, dns_resolver: DRH, custom_handler: CMH,
		intercept_messages_for_offline_peers: bool, intercept_for_unknown_scids: bool,
	) -> Self {
		let mut secp_ctx = Secp256k1::new();
		secp_ctx.seeded_randomize(&entropy_source.get_secure_random_bytes());
		OnionMessenger {
			entropy_source,
			node_signer,
			message_recipients: Mutex::new(new_hash_map()),
			secp_ctx,
			logger,
			node_id_lookup,
			message_router,
			offers_handler,
			async_payments_handler,
			dns_resolver_handler: dns_resolver,
			custom_handler,
			intercept_messages_for_offline_peers,
			intercept_for_unknown_scids,
			pending_intercepted_msgs_events: Mutex::new(Vec::new()),
			pending_peer_connected_events: Mutex::new(Vec::new()),
			pending_events_processor: AtomicBool::new(false),
			event_notifier: Notifier::new(),
		}
	}

	#[cfg(any(test, feature = "_test_utils"))]
	pub fn set_offers_handler(&mut self, offers_handler: OMH) {
		self.offers_handler = offers_handler;
	}

	#[cfg(any(test, feature = "_test_utils"))]
	pub fn set_async_payments_handler(&mut self, async_payments_handler: APH) {
		self.async_payments_handler = async_payments_handler;
	}

	/// Sends an [`OnionMessage`] based on its [`MessageSendInstructions`].
	pub fn send_onion_message<T: OnionMessageContents>(
		&self, contents: T, instructions: MessageSendInstructions,
	) -> Result<SendSuccess, SendError> {
		self.send_onion_message_internal(contents, instructions, format_args!(""))
	}

	fn send_onion_message_internal<T: OnionMessageContents>(
		&self, contents: T, instructions: MessageSendInstructions, log_suffix: fmt::Arguments,
	) -> Result<SendSuccess, SendError> {
		let is_forward = matches!(instructions, MessageSendInstructions::ForwardedMessage { .. });
		let (destination, reply_path) = match instructions {
			MessageSendInstructions::WithSpecifiedReplyPath { destination, reply_path } => {
				(destination, Some(reply_path))
			},
			MessageSendInstructions::WithReplyPath { destination, context }
			| MessageSendInstructions::ForReply {
				instructions: ResponseInstruction { destination, context: Some(context) },
			} => match self.create_blinded_path(context) {
				Ok(reply_path) => (destination, Some(reply_path)),
				Err(err) => {
					log_trace!(
						self.logger,
						"Failed to create reply path {}: {:?}",
						log_suffix,
						err
					);
					return Err(err);
				},
			},
			MessageSendInstructions::WithoutReplyPath { destination }
			| MessageSendInstructions::ForReply {
				instructions: ResponseInstruction { destination, context: None },
			} => (destination, None),
			MessageSendInstructions::ForwardedMessage { destination, reply_path } => {
				(destination, reply_path)
			},
		};

		let path = if is_forward {
			// If this onion message is being treated as a forward, we shouldn't pathfind to the next hop.
			OnionMessagePath {
				intermediate_nodes: Vec::new(),
				first_node_addresses: Vec::new(),
				destination,
			}
		} else {
			self.find_path(destination).map_err(|e| {
				log_trace!(self.logger, "Failed to find path {}", log_suffix);
				e
			})?
		};
		let first_hop = path.intermediate_nodes.get(0).map(|p| *p);
		let logger = WithContext::from(&self.logger, first_hop, None, None);

		log_trace!(logger, "Constructing onion message {}: {:?}", log_suffix, contents);
		let (first_node_id, onion_message, addresses) = create_onion_message(
			&self.entropy_source,
			&self.node_signer,
			&self.node_id_lookup,
			&self.secp_ctx,
			path,
			contents,
			reply_path,
		)
		.map_err(|e| {
			log_warn!(logger, "Failed to create onion message with {:?} {}", e, log_suffix);
			e
		})?;

		let result = if is_forward {
			self.enqueue_forwarded_onion_message(
				None,
				NextMessageHop::NodeId(first_node_id),
				onion_message,
				log_suffix,
			)
			.map(|()| SendSuccess::Buffered)
		} else {
			self.enqueue_outbound_onion_message(onion_message, first_node_id, addresses)
		};

		match result.as_ref() {
			Err(SendError::GetNodeIdFailed) => {
				log_warn!(logger, "Unable to retrieve node id {}", log_suffix);
			},
			Err(SendError::PathNotFound) => {
				log_trace!(logger, "Failed to find path {}", log_suffix);
			},
			Err(e) => {
				log_trace!(logger, "Failed sending onion message {}: {:?}", log_suffix, e);
			},
			Ok(SendSuccess::Buffered) => {
				log_trace!(logger, "Buffered onion message {}", log_suffix);
			},
			Ok(SendSuccess::BufferedAwaitingConnection(node_id)) => {
				log_trace!(
					logger,
					"Buffered onion message waiting on peer connection {}: {}",
					log_suffix,
					node_id
				);
			},
		}

		result
	}

	fn find_path(&self, destination: Destination) -> Result<OnionMessagePath, SendError> {
		let sender = self
			.node_signer
			.get_node_id(Recipient::Node)
			.map_err(|_| SendError::GetNodeIdFailed)?;

		let peers = self
			.message_recipients
			.lock()
			.unwrap()
			.iter()
			.filter(|(_, recipient)| matches!(recipient, OnionMessageRecipient::ConnectedPeer(_)))
			.map(|(node_id, _)| *node_id)
			.collect();

		self.message_router
			.find_path(sender, peers, destination)
			.map_err(|_| SendError::PathNotFound)
	}

	fn create_blinded_path(
		&self, context: MessageContext,
	) -> Result<BlindedMessagePath, SendError> {
		let recipient = self
			.node_signer
			.get_node_id(Recipient::Node)
			.map_err(|_| SendError::GetNodeIdFailed)?;
		let secp_ctx = &self.secp_ctx;

		let peers = {
			let message_recipients = self.message_recipients.lock().unwrap();
			message_recipients
				.iter()
				.filter(|(_, peer)| matches!(peer, OnionMessageRecipient::ConnectedPeer(_)))
				.map(|(node_id, _)| MessageForwardNode {
					node_id: *node_id,
					short_channel_id: None,
				})
				.collect::<Vec<_>>()
		};

		self.message_router
			.create_blinded_paths(
				recipient,
				self.node_signer.get_receive_auth_key(),
				context,
				peers,
				secp_ctx,
			)
			.and_then(|paths| paths.into_iter().next().ok_or(()))
			.map_err(|_| SendError::PathNotFound)
	}

	fn enqueue_outbound_onion_message(
		&self, onion_message: OnionMessage, first_node_id: PublicKey, addresses: Vec<SocketAddress>,
	) -> Result<SendSuccess, SendError> {
		let mut message_recipients = self.message_recipients.lock().unwrap();
		if outbound_buffer_full(&first_node_id, &message_recipients) {
			return Err(SendError::BufferFull);
		}

		match message_recipients.entry(first_node_id) {
			hash_map::Entry::Vacant(e) => {
				e.insert(OnionMessageRecipient::pending_connection(addresses))
					.enqueue_message(onion_message);
				self.event_notifier.notify();
				Ok(SendSuccess::BufferedAwaitingConnection(first_node_id))
			},
			hash_map::Entry::Occupied(mut e) => {
				e.get_mut().enqueue_message(onion_message);
				if e.get().is_connected() {
					Ok(SendSuccess::Buffered)
				} else {
					Ok(SendSuccess::BufferedAwaitingConnection(first_node_id))
				}
			},
		}
	}

	fn enqueue_forwarded_onion_message(
		&self, prev_hop: Option<PublicKey>, next_hop: NextMessageHop, onion_message: OnionMessage,
		log_suffix: fmt::Arguments,
	) -> Result<(), SendError> {
		let next_node_id = match next_hop {
			NextMessageHop::NodeId(pubkey) => pubkey,
			NextMessageHop::ShortChannelId(scid) => match self.node_id_lookup.next_node_id(scid) {
				Some(pubkey) => pubkey,
				None => {
					if self.intercept_for_unknown_scids {
						log_trace!(
							self.logger,
							"Generating OnionMessageIntercepted event for SCID {} {}",
							scid,
							log_suffix
						);
						self.enqueue_intercepted_event(Event::OnionMessageIntercepted {
							prev_hop,
							next_hop,
							message: onion_message,
						});
						return Ok(());
					}
					log_trace!(self.logger, "Dropping forwarded onion message: unable to resolve next hop using SCID {} {}", scid, log_suffix);
					return Err(SendError::GetNodeIdFailed);
				},
			},
		};

		let mut message_recipients = self.message_recipients.lock().unwrap();
		if outbound_buffer_full(&next_node_id, &message_recipients) {
			log_trace!(
				self.logger,
				"Dropping forwarded onion message to peer {}: outbound buffer full {}",
				next_node_id,
				log_suffix
			);
			return Err(SendError::BufferFull);
		}

		#[cfg(fuzzing)]
		message_recipients
			.entry(next_node_id)
			.or_insert_with(|| OnionMessageRecipient::ConnectedPeer(VecDeque::new()));

		match message_recipients.entry(next_node_id) {
			hash_map::Entry::Occupied(mut e)
				if matches!(e.get(), OnionMessageRecipient::ConnectedPeer(..)) =>
			{
				e.get_mut().enqueue_message(onion_message);
				log_trace!(
					self.logger,
					"Forwarding an onion message to peer {} {}",
					next_node_id,
					log_suffix
				);
				Ok(())
			},
			_ if self.intercept_messages_for_offline_peers => {
				log_trace!(
					self.logger,
					"Generating OnionMessageIntercepted event for peer {} {}",
					next_node_id,
					log_suffix
				);
				self.enqueue_intercepted_event(Event::OnionMessageIntercepted {
					prev_hop,
					// Report the resolved node id rather than `next_hop`, which may be a
					// `ShortChannelId` that we resolved to a known-but-offline peer. The
					// `ShortChannelId` variant is reserved for the unknown-SCID interception path.
					next_hop: NextMessageHop::NodeId(next_node_id),
					message: onion_message,
				});
				Ok(())
			},
			_ => {
				log_trace!(
					self.logger,
					"Dropping forwarded onion message to disconnected peer {} {}",
					next_node_id,
					log_suffix
				);
				Err(SendError::InvalidFirstHop(next_node_id))
			},
		}
	}

	/// 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<BlindedMessagePath>,
	) -> Result<SendSuccess, SendError> {
		let (first_node_id, onion_message, addresses) = create_onion_message(
			&self.entropy_source,
			&self.node_signer,
			&self.node_id_lookup,
			&self.secp_ctx,
			path,
			contents,
			reply_path,
		)?;
		self.enqueue_outbound_onion_message(onion_message, first_node_id, addresses)
	}

	pub(crate) fn peel_onion_message(
		&self, msg: &OnionMessage,
	) -> Result<PeeledOnion<CMH::CustomMessage>, ()> {
		peel_onion_message(
			msg,
			&self.secp_ctx,
			&self.node_signer,
			&self.logger,
			&self.custom_handler,
		)
	}

	/// Handles the response to an [`OnionMessage`] based on its [`ResponseInstruction`],
	/// enqueueing any response for sending.
	///
	/// This function is useful for asynchronous handling of [`OnionMessage`]s.
	/// Handlers have the option to return `None`, indicating that no immediate response should be
	/// sent. Then, they can transfer the associated [`Responder`] to another task responsible for
	/// generating the response asynchronously. Subsequently, when the response is prepared and
	/// ready for sending, that task can invoke this method to enqueue the response for delivery.
	pub fn handle_onion_message_response<T: OnionMessageContents>(
		&self, response: T, instructions: ResponseInstruction,
	) -> Result<SendSuccess, SendError> {
		let message_type = response.msg_type();
		self.send_onion_message_internal(
			response,
			instructions.into_instructions(),
			format_args!("when responding with {} to an onion message", message_type,),
		)
	}

	#[cfg(test)]
	pub(crate) fn release_pending_msgs(&self) -> HashMap<PublicKey, VecDeque<OnionMessage>> {
		self.enqueue_messages_from_handlers();

		let mut message_recipients = self.message_recipients.lock().unwrap();
		let mut msgs = new_hash_map();
		// We don't want to disconnect the peers by removing them entirely from the original map, so we
		// release the pending message buffers individually.
		for (node_id, recipient) in &mut *message_recipients {
			msgs.insert(*node_id, recipient.release_pending_messages());
		}
		msgs
	}

	// Pull pending messages from each onion message handler and enqueue them in the messenger.
	fn enqueue_messages_from_handlers(&self) {
		// Enqueue any initiating `OffersMessage`s to send.
		for (message, instructions) in self.offers_handler.release_pending_messages() {
			let _ = self.send_onion_message_internal(
				message,
				instructions,
				format_args!("when sending OffersMessage"),
			);
		}

		for (message, instructions) in self.async_payments_handler.release_pending_messages() {
			let _ = self.send_onion_message_internal(
				message,
				instructions,
				format_args!("when sending AsyncPaymentsMessage"),
			);
		}

		// Enqueue any initiating `DNSResolverMessage`s to send.
		for (message, instructions) in self.dns_resolver_handler.release_pending_messages() {
			let _ = self.send_onion_message_internal(
				message,
				instructions,
				format_args!("when sending DNSResolverMessage"),
			);
		}

		// Enqueue any initiating `CustomMessage`s to send.
		for (message, instructions) in self.custom_handler.release_pending_custom_messages() {
			let _ = self.send_onion_message_internal(
				message,
				instructions,
				format_args!("when sending CustomMessage"),
			);
		}
	}

	fn enqueue_intercepted_event(&self, event: Event) {
		const MAX_EVENTS_BUFFER_SIZE: usize = (1 << 10) * 256;
		let mut pending_intercepted_msgs_events =
			self.pending_intercepted_msgs_events.lock().unwrap();
		let total_buffered_bytes: usize =
			pending_intercepted_msgs_events.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_intercepted_msgs_events.push(event);
		self.event_notifier.notify();
	}

	/// Gets a [`Future`] that completes when an event is available via
	/// [`EventsProvider::process_pending_events`] or [`Self::process_pending_events_async`].
	///
	/// Note that callbacks registered on the [`Future`] MUST NOT call back into this
	/// [`OnionMessenger`] and should instead register actions to be taken later.
	///
	/// [`EventsProvider::process_pending_events`]: crate::events::EventsProvider::process_pending_events
	pub fn get_update_future(&self) -> Future {
		self.event_notifier.get_future()
	}

	/// 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 = Result<(), ReplayEvent>> + core::marker::Unpin,
		H: Fn(Event) -> Future,
	>(
		&self, handler: H,
	) {
		if self
			.pending_events_processor
			.compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
			.is_err()
		{
			return;
		}

		{
			let intercepted_msgs = self.pending_intercepted_msgs_events.lock().unwrap().clone();
			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() {
						let event = Event::ConnectionNeeded { node_id: *node_id, addresses };
						log_trace!(self.logger, "Handling event {:?} async...", event);
						let future = ResultFuture::Pending(handler(event));
						futures.push(future);
					}
				}
			}

			// The offset in the `futures` vec at which `intercepted_msgs` start. We don't bother
			// replaying `ConnectionNeeded` events.
			let intercepted_msgs_offset = futures.len();

			for ev in intercepted_msgs {
				if let Event::OnionMessageIntercepted { .. } = ev {
				} else {
					debug_assert!(false);
				}
				log_trace!(self.logger, "Handling event {:?} async...", ev);
				let future = ResultFuture::Pending(handler(ev));
				futures.push(future);
			}

			if !futures.is_empty() {
				// Let the `OnionMessageIntercepted` events finish before moving on to peer_connecteds
				let res = MultiResultFuturePoller::new(futures).await;
				log_trace!(self.logger, "Done handling events async, results: {:?}", res);
				let mut res_iter = res.iter().skip(intercepted_msgs_offset);
				drop_handled_events_and_abort!(
					self,
					res_iter,
					self.pending_intercepted_msgs_events
				);
			}
		}

		{
			let peer_connecteds = self.pending_peer_connected_events.lock().unwrap().clone();
			let num_peer_connecteds = peer_connecteds.len();
			if num_peer_connecteds <= 1 {
				for event in peer_connecteds {
					if handler(event).await.is_ok() {
						let mut pending_peer_connected_events =
							self.pending_peer_connected_events.lock().unwrap();
						pending_peer_connected_events.drain(..num_peer_connecteds);
					} else {
						// We failed handling the event. Return to have it eventually replayed.
						self.pending_events_processor.store(false, Ordering::Release);
						return;
					}
				}
			} else {
				let mut futures = Vec::new();
				for event in peer_connecteds {
					log_trace!(self.logger, "Handling event {:?} async...", event);
					let future = ResultFuture::Pending(handler(event));
					futures.push(future);
				}

				if !futures.is_empty() {
					let res = MultiResultFuturePoller::new(futures).await;
					log_trace!(self.logger, "Done handling events async, results: {:?}", res);
					let mut res_iter = res.iter();
					drop_handled_events_and_abort!(
						self,
						res_iter,
						self.pending_peer_connected_events
					);
				}
			}
		}
		self.pending_events_processor.store(false, Ordering::Release);
	}
}

const MAX_TOTAL_BUFFER_SIZE: usize = (1 << 20) * 128;
pub(super) const MAX_PER_PEER_BUFFER_SIZE: usize = (1 << 10) * 256;

fn outbound_buffer_full(
	peer_node_id: &PublicKey, buffer: &HashMap<PublicKey, OnionMessageRecipient>,
) -> bool {
	let mut total_buffered_bytes = 0;
	let mut peer_buffered_bytes = 0;
	for (pk, peer_buf) in buffer {
		for om in peer_buf.pending_messages() {
			let om_len = om.serialized_length();
			if pk == peer_node_id {
				peer_buffered_bytes += om_len;
			}
			total_buffered_bytes += om_len;

			if total_buffered_bytes >= MAX_TOTAL_BUFFER_SIZE
				|| peer_buffered_bytes >= MAX_PER_PEER_BUFFER_SIZE
			{
				return true;
			}
		}
	}
	false
}

impl<
		ES: EntropySource,
		NS: NodeSigner,
		L: Logger,
		NL: NodeIdLookUp,
		MR: MessageRouter,
		OMH: OffersMessageHandler,
		APH: AsyncPaymentsMessageHandler,
		DRH: DNSResolverMessageHandler,
		CMH: CustomOnionMessageHandler,
	> EventsProvider for OnionMessenger<ES, NS, L, NL, MR, OMH, APH, DRH, CMH>
{
	fn process_pending_events<H: Deref>(&self, handler: H)
	where
		H::Target: EventHandler,
	{
		if self
			.pending_events_processor
			.compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
			.is_err()
		{
			return;
		}

		for (node_id, recipient) in self.message_recipients.lock().unwrap().iter_mut() {
			if let OnionMessageRecipient::PendingConnection(_, addresses, _) = recipient {
				if let Some(addresses) = addresses.take() {
					let event = Event::ConnectionNeeded { node_id: *node_id, addresses };
					log_trace!(self.logger, "Handling event {:?}...", event);
					let res = handler.handle_event(event);
					log_trace!(self.logger, "Done handling event, ignoring result: {:?}", res);
				}
			}
		}
		let intercepted_msgs;
		let peer_connecteds;
		{
			let pending_intercepted_msgs_events =
				self.pending_intercepted_msgs_events.lock().unwrap();
			intercepted_msgs = pending_intercepted_msgs_events.clone();
			let pending_peer_connected_events = self.pending_peer_connected_events.lock().unwrap();
			peer_connecteds = pending_peer_connected_events.clone();
			#[cfg(debug_assertions)]
			{
				for ev in pending_intercepted_msgs_events.iter() {
					if let Event::OnionMessageIntercepted { .. } = ev {
					} else {
						panic!();
					}
				}
				for ev in pending_peer_connected_events.iter() {
					if let Event::OnionMessagePeerConnected { .. } = ev {
					} else {
						panic!();
					}
				}
			}
		}

		let mut handling_intercepted_msgs_failed = false;
		let mut num_handled_intercepted_events = 0;
		for ev in intercepted_msgs {
			log_trace!(self.logger, "Handling event {:?}...", ev);
			let res = handler.handle_event(ev);
			log_trace!(self.logger, "Done handling event, result: {:?}", res);
			match res {
				Ok(()) => num_handled_intercepted_events += 1,
				Err(ReplayEvent()) => {
					handling_intercepted_msgs_failed = true;
					break;
				},
			}
		}

		{
			let mut pending_intercepted_msgs_events =
				self.pending_intercepted_msgs_events.lock().unwrap();
			pending_intercepted_msgs_events.drain(..num_handled_intercepted_events);
		}

		if handling_intercepted_msgs_failed {
			self.pending_events_processor.store(false, Ordering::Release);
			self.event_notifier.notify();
			return;
		}

		let mut num_handled_peer_connecteds = 0;
		for ev in peer_connecteds {
			log_trace!(self.logger, "Handling event {:?}...", ev);
			let res = handler.handle_event(ev);
			log_trace!(self.logger, "Done handling event, result: {:?}", res);
			match res {
				Ok(()) => num_handled_peer_connecteds += 1,
				Err(ReplayEvent()) => {
					self.event_notifier.notify();
					break;
				},
			}
		}

		{
			let mut pending_peer_connected_events =
				self.pending_peer_connected_events.lock().unwrap();
			pending_peer_connected_events.drain(..num_handled_peer_connecteds);
			pending_peer_connected_events.shrink_to(10); // Limit total heap usage
		}

		self.pending_events_processor.store(false, Ordering::Release);
	}
}

impl<
		ES: EntropySource,
		NS: NodeSigner,
		L: Logger,
		NL: NodeIdLookUp,
		MR: MessageRouter,
		OMH: OffersMessageHandler,
		APH: AsyncPaymentsMessageHandler,
		DRH: DNSResolverMessageHandler,
		CMH: CustomOnionMessageHandler,
	> BaseMessageHandler for OnionMessenger<ES, NS, L, NL, MR, OMH, APH, DRH, CMH>
{
	fn provided_node_features(&self) -> NodeFeatures {
		let mut features = NodeFeatures::empty();
		features.set_onion_messages_optional();
		features | self.dns_resolver_handler.provided_node_features()
	}

	fn provided_init_features(&self, _their_node_id: PublicKey) -> InitFeatures {
		let mut features = InitFeatures::empty();
		features.set_onion_messages_optional();
		features
	}

	fn peer_connected(
		&self, their_node_id: PublicKey, init: &msgs::Init, _inbound: bool,
	) -> Result<(), ()> {
		if init.features.supports_onion_messages() {
			{
				let mut message_recipients = self.message_recipients.lock().unwrap();
				message_recipients
					.entry(their_node_id)
					.or_insert_with(|| OnionMessageRecipient::ConnectedPeer(VecDeque::new()))
					.mark_connected();
			}
			if self.intercept_messages_for_offline_peers {
				let mut pending_peer_connected_events =
					self.pending_peer_connected_events.lock().unwrap();
				pending_peer_connected_events
					.push(Event::OnionMessagePeerConnected { peer_node_id: their_node_id });
				self.event_notifier.notify();
			}
		} else {
			self.message_recipients.lock().unwrap().remove(&their_node_id);
		}

		Ok(())
	}

	fn peer_disconnected(&self, their_node_id: PublicKey) {
		match self.message_recipients.lock().unwrap().remove(&their_node_id) {
			Some(OnionMessageRecipient::ConnectedPeer(..)) => {},
			Some(_) => debug_assert!(false),
			None => {},
		}
	}

	fn get_and_clear_pending_msg_events(&self) -> Vec<MessageSendEvent> {
		Vec::new()
	}
}

impl<
		ES: EntropySource,
		NS: NodeSigner,
		L: Logger,
		NL: NodeIdLookUp,
		MR: MessageRouter,
		OMH: OffersMessageHandler,
		APH: AsyncPaymentsMessageHandler,
		DRH: DNSResolverMessageHandler,
		CMH: CustomOnionMessageHandler,
	> OnionMessageHandler for OnionMessenger<ES, NS, L, NL, MR, OMH, APH, DRH, CMH>
{
	fn handle_onion_message(&self, peer_node_id: PublicKey, msg: &OnionMessage) {
		let logger = WithContext::from(&self.logger, Some(peer_node_id), None, None);
		macro_rules! log_receive {
			($message: expr, $with_reply_path: expr) => {
				log_trace!(
					logger,
					"Received an onion message with {} reply_path: {:?}",
					if $with_reply_path { "a" } else { "no" },
					$message
				);
			};
		}

		match self.peel_onion_message(msg) {
			Ok(PeeledOnion::Offers(message, context, reply_path)) => {
				log_receive!(message, reply_path.is_some());
				let responder = reply_path.map(Responder::new);
				let response_instructions =
					self.offers_handler.handle_message(message, context, responder);
				if let Some((msg, instructions)) = response_instructions {
					let _ = self.handle_onion_message_response(msg, instructions);
				}
			},
			Ok(PeeledOnion::AsyncPayments(message, context, reply_path)) => {
				log_receive!(message, reply_path.is_some());
				let responder = reply_path.map(Responder::new);
				match message {
					AsyncPaymentsMessage::OfferPathsRequest(msg) => {
						let response_instructions = self
							.async_payments_handler
							.handle_offer_paths_request(msg, context, responder);
						if let Some((msg, instructions)) = response_instructions {
							let _ = self.handle_onion_message_response(msg, instructions);
						}
					},
					AsyncPaymentsMessage::OfferPaths(msg) => {
						let response_instructions =
							self.async_payments_handler.handle_offer_paths(msg, context, responder);
						if let Some((msg, instructions)) = response_instructions {
							let _ = self.handle_onion_message_response(msg, instructions);
						}
					},
					AsyncPaymentsMessage::ServeStaticInvoice(msg) => {
						self.async_payments_handler
							.handle_serve_static_invoice(msg, context, responder);
					},
					AsyncPaymentsMessage::StaticInvoicePersisted(msg) => {
						self.async_payments_handler.handle_static_invoice_persisted(msg, context);
					},
					AsyncPaymentsMessage::HeldHtlcAvailable(msg) => {
						let response_instructions = self
							.async_payments_handler
							.handle_held_htlc_available(msg, context, responder);
						if let Some((msg, instructions)) = response_instructions {
							let _ = self.handle_onion_message_response(msg, instructions);
						}
					},
					AsyncPaymentsMessage::ReleaseHeldHtlc(msg) => {
						self.async_payments_handler.handle_release_held_htlc(msg, context);
					},
				}
			},
			Ok(PeeledOnion::DNSResolver(message, context, reply_path)) => {
				log_receive!(message, reply_path.is_some());
				let responder = reply_path.map(Responder::new);
				match message {
					DNSResolverMessage::DNSSECQuery(msg) => {
						if context.is_some() {
							log_trace!(
								logger,
								"Ignoring DNSSECQuery onion message with unexpected context: {:?}",
								context.unwrap()
							);
							return;
						}
						let response_instructions =
							self.dns_resolver_handler.handle_dnssec_query(msg, responder);
						if let Some((msg, instructions)) = response_instructions {
							let _ = self.handle_onion_message_response(msg, instructions);
						}
					},
					DNSResolverMessage::DNSSECProof(msg) => {
						let context = match context {
							Some(ctx) => ctx,
							None => {
								log_trace!(
									logger,
									"Ignoring DNSSECProof onion message due to missing context"
								);
								return;
							},
						};
						self.dns_resolver_handler.handle_dnssec_proof(msg, context);
					},
				}
			},
			Ok(PeeledOnion::Custom(message, context, reply_path)) => {
				log_receive!(message, reply_path.is_some());
				let responder = reply_path.map(Responder::new);
				let response_instructions =
					self.custom_handler.handle_custom_message(message, context, responder);
				if let Some((msg, instructions)) = response_instructions {
					let _ = self.handle_onion_message_response(msg, instructions);
				}
			},
			Ok(PeeledOnion::Forward(next_hop, onion_message)) => {
				let _ = self.enqueue_forwarded_onion_message(
					Some(peer_node_id),
					next_hop,
					onion_message,
					format_args!("when forwarding peeled onion message from {}", peer_node_id),
				);
			},
			Err(e) => {
				log_error!(logger, "Failed to process onion message {:?}", e);
			},
		}
	}

	fn timer_tick_occurred(&self) {
		let mut message_recipients = self.message_recipients.lock().unwrap();

		// Drop any pending recipients since the last call to avoid retaining buffered messages for
		// too long.
		message_recipients.retain(|_, recipient| match recipient {
			OnionMessageRecipient::PendingConnection(_, None, ticks) => *ticks < MAX_TIMER_TICKS,
			OnionMessageRecipient::PendingConnection(_, Some(_), _) => true,
			_ => true,
		});

		// Increment a timer tick for pending recipients so that their buffered messages are dropped
		// at MAX_TIMER_TICKS.
		for recipient in message_recipients.values_mut() {
			if let OnionMessageRecipient::PendingConnection(_, None, ticks) = recipient {
				*ticks += 1;
			}
		}
	}

	// Before returning any messages to send for the peer, this method will see if any messages were
	// enqueued in the handler by users, find a path to the corresponding blinded path's introduction
	// node, and then enqueue the message for sending to the first peer in the full path.
	fn next_onion_message_for_peer(&self, peer_node_id: PublicKey) -> Option<OnionMessage> {
		self.enqueue_messages_from_handlers();

		let mut message_recipients = self.message_recipients.lock().unwrap();
		message_recipients.get_mut(&peer_node_id).and_then(|buffer| buffer.dequeue_message())
	}
}

// TODO: parameterize the below Simple* types with OnionMessenger and handle the messages it
// produces
/// Useful for simplifying the parameters of [`SimpleArcChannelManager`] and
/// [`SimpleArcPeerManager`]. See their docs for more details.
///
/// This is not exported to bindings users as type aliases aren't supported in most languages.
///
/// [`SimpleArcChannelManager`]: crate::ln::channelmanager::SimpleArcChannelManager
/// [`SimpleArcPeerManager`]: crate::ln::peer_handler::SimpleArcPeerManager
#[cfg(not(c_bindings))]
pub type SimpleArcOnionMessenger<M, T, F, L> = OnionMessenger<
	Arc<KeysManager>,
	Arc<KeysManager>,
	Arc<L>,
	Arc<SimpleArcChannelManager<M, T, F, L>>,
	Arc<DefaultMessageRouter<Arc<NetworkGraph<Arc<L>>>, Arc<L>, Arc<KeysManager>>>,
	Arc<SimpleArcChannelManager<M, T, F, L>>,
	Arc<SimpleArcChannelManager<M, T, F, L>>,
	IgnoringMessageHandler,
	IgnoringMessageHandler,
>;

/// Useful for simplifying the parameters of [`SimpleRefChannelManager`] and
/// [`SimpleRefPeerManager`]. See their docs for more details.
///
/// This is not exported to bindings users as type aliases aren't supported in most languages.
///
/// [`SimpleRefChannelManager`]: crate::ln::channelmanager::SimpleRefChannelManager
/// [`SimpleRefPeerManager`]: crate::ln::peer_handler::SimpleRefPeerManager
#[cfg(not(c_bindings))]
pub type SimpleRefOnionMessenger<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, 'j, M, T, F, L> =
	OnionMessenger<
		&'a KeysManager,
		&'a KeysManager,
		&'b L,
		&'j SimpleRefChannelManager<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, M, T, F, L>,
		&'i DefaultMessageRouter<&'g NetworkGraph<&'b L>, &'b L, &'a KeysManager>,
		&'j SimpleRefChannelManager<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, M, T, F, L>,
		&'j SimpleRefChannelManager<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h, 'i, M, T, F, L>,
		IgnoringMessageHandler,
		IgnoringMessageHandler,
	>;

/// Construct onion packet payloads and keys for sending an onion message along the given
/// `unblinded_path` to the given `destination`.
fn packet_payloads_and_keys<
	T: OnionMessageContents,
	S: secp256k1::Signing + secp256k1::Verification,
>(
	secp_ctx: &Secp256k1<S>, unblinded_path: Vec<PublicKey>, destination: Destination, message: T,
	mut reply_path: Option<BlindedMessagePath>, session_priv: &SecretKey,
) -> Result<(Vec<(Payload<T>, [u8; 32])>, Vec<onion_utils::OnionKeys>), SendError> {
	let num_hops = unblinded_path.len() + destination.num_hops();
	let mut payloads = Vec::with_capacity(num_hops);
	let mut onion_packet_keys = Vec::with_capacity(num_hops);

	let (mut intro_node_id_blinding_pt, num_blinded_hops) = match &destination {
		Destination::Node(_) => (None, 0),
		Destination::BlindedPath(path) => {
			let introduction_node_id = match path.introduction_node() {
				IntroductionNode::NodeId(pubkey) => pubkey,
				IntroductionNode::DirectedShortChannelId(..) => {
					return Err(SendError::UnresolvedIntroductionNode);
				},
			};
			(Some((*introduction_node_id, path.blinding_point())), path.blinded_hops().len())
		},
	};
	let num_unblinded_hops = num_hops - num_blinded_hops;

	let mut unblinded_path_idx = 0;
	let mut blinded_path_idx = 0;
	let mut prev_control_tlvs_ss = None;
	let mut final_control_tlvs = None;
	utils::construct_keys_for_onion_message(
		secp_ctx,
		unblinded_path.into_iter(),
		destination,
		session_priv,
		|onion_packet_ss, ephemeral_pubkey, control_tlvs_ss, unblinded_pk_opt, enc_payload_opt| {
			if num_unblinded_hops != 0 && unblinded_path_idx < num_unblinded_hops {
				if let Some(ss) = prev_control_tlvs_ss.take() {
					payloads.push((
						Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
							next_hop: NextMessageHop::NodeId(unblinded_pk_opt.unwrap()),
							next_blinding_override: None,
						})),
						ss,
					));
				}
				prev_control_tlvs_ss = Some(control_tlvs_ss);
				unblinded_path_idx += 1;
			} else if let Some((intro_node_id, blinding_pt)) = intro_node_id_blinding_pt.take() {
				if let Some(control_tlvs_ss) = prev_control_tlvs_ss.take() {
					payloads.push((
						Payload::Forward(ForwardControlTlvs::Unblinded(ForwardTlvs {
							next_hop: NextMessageHop::NodeId(intro_node_id),
							next_blinding_override: Some(blinding_pt),
						})),
						control_tlvs_ss,
					));
				}
			}
			if blinded_path_idx < num_blinded_hops.saturating_sub(1) && enc_payload_opt.is_some() {
				payloads.push((
					Payload::Forward(ForwardControlTlvs::Blinded(enc_payload_opt.unwrap())),
					control_tlvs_ss,
				));
				blinded_path_idx += 1;
			} else if let Some(encrypted_payload) = enc_payload_opt {
				final_control_tlvs = Some(ReceiveControlTlvs::Blinded(encrypted_payload));
				prev_control_tlvs_ss = Some(control_tlvs_ss);
			}

			let (rho, mu) = onion_utils::gen_rho_mu_from_shared_secret(onion_packet_ss.as_ref());
			onion_packet_keys.push(onion_utils::OnionKeys {
				#[cfg(test)]
				shared_secret: onion_packet_ss,
				#[cfg(test)]
				blinding_factor: [0; 32],
				ephemeral_pubkey,
				rho,
				mu,
			});
		},
	);

	if let Some(control_tlvs) = final_control_tlvs {
		payloads.push((
			Payload::Receive {
				control_tlvs,
				reply_path: reply_path.take(),
				message,
				control_tlvs_from_local_node: false,
				control_tlvs_from_phantom_participant: false,
			},
			prev_control_tlvs_ss.unwrap(),
		));
	} else {
		payloads.push((
			Payload::Receive {
				control_tlvs: ReceiveControlTlvs::Unblinded(ReceiveTlvs { context: None }),
				reply_path: reply_path.take(),
				message,
				control_tlvs_from_local_node: false,
				control_tlvs_from_phantom_participant: false,
			},
			prev_control_tlvs_ss.unwrap(),
		));
	}

	Ok((payloads, onion_packet_keys))
}

/// Errors if the serialized payload size exceeds onion_message::BIG_PACKET_HOP_DATA_LEN
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, ()> {
	// Spec rationale:
	// "`len` allows larger messages to be sent than the standard 1300 bytes allowed for an HTLC
	// onion, but this should be used sparingly as it is reduces anonymity set, hence the
	// recommendation that it either look like an HTLC onion, or if larger, be a fixed size."
	let payloads_ser_len = onion_utils::payloads_serialized_length(&payloads);
	let hop_data_len = if payloads_ser_len <= SMALL_PACKET_HOP_DATA_LEN {
		SMALL_PACKET_HOP_DATA_LEN
	} else if payloads_ser_len <= BIG_PACKET_HOP_DATA_LEN {
		BIG_PACKET_HOP_DATA_LEN
	} else {
		return Err(());
	};

	onion_utils::construct_onion_message_packet::<_, _>(
		payloads,
		onion_keys,
		prng_seed,
		hop_data_len,
	)
}