WIP: Multi-hop blinded paths

Author: jkczyz

lightning/src/ln/channelmanager.rs

@@ -65,7 +65,7 @@ use crate::offers::merkle::SignError;
 use crate::offers::offer::{DerivedMetadata, Offer, OfferBuilder};
 use crate::offers::parse::Bolt12SemanticError;
 use crate::offers::refund::{Refund, RefundBuilder};
-use crate::onion_message::{Destination, OffersMessage, OffersMessageHandler, PendingOnionMessage, new_pending_onion_message};
+use crate::onion_message::{Destination, MessageRouter, OffersMessage, OffersMessageHandler, PendingOnionMessage, new_pending_onion_message};
 use crate::sign::{EntropySource, KeysManager, NodeSigner, Recipient, SignerProvider};
 use crate::sign::ecdsa::WriteableEcdsaChannelSigner;
 use crate::util::config::{UserConfig, ChannelConfig, ChannelConfigUpdate};
@@ -7416,10 +7416,13 @@ where
 	///
 	/// # Privacy
 	///
-	/// Uses a one-hop [`BlindedPath`] for the offer with [`ChannelManager::get_our_node_id`] as the
-	/// introduction node and a derived signing pubkey for recipient privacy. As such, currently,
-	/// the node must be announced. Otherwise, there is no way to find a path to the introduction
-	/// node in order to send the [`InvoiceRequest`].
+	/// Uses [`MessageRouter::create_blinded_paths`] to construct a [`BlindedPath`] for the offer.
+	/// However, if one is not found, uses a one-hop [`BlindedPath`] with
+	/// [`ChannelManager::get_our_node_id`] as the introduction node instead. In the latter case,
+	/// the node must be announced, otherwise, there is no way to find a path to the introduction in
+	/// order to send the [`InvoiceRequest`].
+	///
+	/// Also, uses a derived signing pubkey in the offer for recipient privacy.
 	///
 	/// # Limitations
 	///
@@ -7437,11 +7440,10 @@ where
 		let expanded_key = &self.inbound_payment_key;
 		let entropy = &*self.entropy_source;
 		let secp_ctx = &self.secp_ctx;
-		let path = self.create_one_hop_blinded_path();
 
 		OfferBuilder::deriving_signing_pubkey(description, node_id, expanded_key, entropy, secp_ctx)
 			.chain_hash(self.chain_hash)
-			.path(path)
+			.path(self.create_blinded_path())
 	}
 
 	/// Creates a [`RefundBuilder`] such that the [`Refund`] it builds is recognized by the
@@ -7466,10 +7468,13 @@ where
 	///
 	/// # Privacy
 	///
-	/// Uses a one-hop [`BlindedPath`] for the refund with [`ChannelManager::get_our_node_id`] as
-	/// the introduction node and a derived payer id for payer privacy. As such, currently, the
-	/// node must be announced. Otherwise, there is no way to find a path to the introduction node
-	/// in order to send the [`Bolt12Invoice`].
+	/// Uses [`MessageRouter::create_blinded_paths`] to construct a [`BlindedPath`] for the refund.
+	/// However, if one is not found, uses a one-hop [`BlindedPath`] with
+	/// [`ChannelManager::get_our_node_id`] as the introduction node instead. In the latter case,
+	/// the node must be announced, otherwise, there is no way to find a path to the introduction in
+	/// order to send the [`Bolt12Invoice`].
+	///
+	/// Also, uses a derived payer id in the refund for payer privacy.
 	///
 	/// # Limitations
 	///
@@ -7494,14 +7499,13 @@ where
 		let expanded_key = &self.inbound_payment_key;
 		let entropy = &*self.entropy_source;
 		let secp_ctx = &self.secp_ctx;
-		let path = self.create_one_hop_blinded_path();
 
 		let builder = RefundBuilder::deriving_payer_id(
 			description, node_id, expanded_key, entropy, secp_ctx, amount_msats, payment_id
 		)?
 			.chain_hash(self.chain_hash)
 			.absolute_expiry(absolute_expiry)
-			.path(path);
+			.path(self.create_blinded_path());
 
 		let expiration = StaleExpiration::AbsoluteTimeout(absolute_expiry);
 		self.pending_outbound_payments
@@ -7587,9 +7591,8 @@ where
 			None => builder,
 			Some(payer_note) => builder.payer_note(payer_note),
 		};
-
 		let invoice_request = builder.build_and_sign()?;
-		let reply_path = self.create_one_hop_blinded_path();
+		let reply_path = self.create_blinded_path();
 
 		let expiration = StaleExpiration::TimerTicks(1);
 		self.pending_outbound_payments
@@ -7665,7 +7668,7 @@ where
 					payment_paths, payment_hash, created_at, expanded_key, entropy
 				)?;
 				let invoice = builder.allow_mpp().build_and_sign(secp_ctx)?;
-				let reply_path = self.create_one_hop_blinded_path();
+				let reply_path = self.create_blinded_path();
 
 				let mut pending_offers_messages = self.pending_offers_messages.lock().unwrap();
 				if refund.paths().is_empty() {
@@ -7792,6 +7795,15 @@ where
 		inbound_payment::get_payment_preimage(payment_hash, payment_secret, &self.inbound_payment_key)
 	}
 
+	/// Creates a multi-hop blinded path by delegating to [`MessageRouter::create_blinded_paths`].
+	/// If the router returns an error or no paths, creates a one-hop blinded path instead.
+	fn create_blinded_path(&self) -> BlindedPath {
+		self.create_multi_hop_blinded_paths(1)
+			.ok()
+			.and_then(|paths| paths.into_iter().next())
+			.unwrap_or_else(|| self.create_one_hop_blinded_path())
+	}
+
 	/// Creates a one-hop blinded path with [`ChannelManager::get_our_node_id`] as the introduction
 	/// node.
 	fn create_one_hop_blinded_path(&self) -> BlindedPath {
@@ -7800,6 +7812,25 @@ where
 		BlindedPath::one_hop_for_message(self.get_our_node_id(), entropy_source, secp_ctx).unwrap()
 	}
 
+	/// Creates `count` blinded paths by delegating to [`MessageRouter::create_blinded_paths`].
+	///
+	/// May return fewer paths if there are fewer than `count` peers that [support onion messages].
+	///
+	/// [support onion messages]: crate::ln::features::InitFeatures::supports_onion_messages
+	fn create_multi_hop_blinded_paths(&self, count: usize) -> Result<Vec<BlindedPath>, ()> {
+		let recipient = self.get_our_node_id();
+		let entropy_source = self.entropy_source.deref();
+		let secp_ctx = &self.secp_ctx;
+
+		let peers = self.per_peer_state.read().unwrap()
+			.iter()
+			.filter(|(_, peer)| peer.lock().unwrap().latest_features.supports_onion_messages())
+			.map(|(node_id, _)| *node_id)
+			.collect::<Vec<_>>();
+
+		self.router.create_blinded_paths(recipient, peers, count, entropy_source, secp_ctx)
+	}
+
 	/// Creates a one-hop blinded payment path with [`ChannelManager::get_our_node_id`] as the
 	/// introduction node.
 	fn create_one_hop_blinded_payment_path(