X-Git-Url: http://git.bitcoin.ninja/index.cgi?a=blobdiff_plain;f=lightning%2Fsrc%2Fln%2Fchannelmanager.rs;h=de86a8e703c44ce59cfb8b5664412755f8d7d2f3;hb=c1f1b78ea6fcfb72686fd4be34ddb09931b706af;hp=58db00e14070d6c6dbf8ff48d5d2b8c4b750f9e1;hpb=129e1f6be24485497990ad8c119f2b20f22861e8;p=rust-lightning

diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index 58db00e1..de86a8e7 100644
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -92,8 +92,8 @@ use core::ops::Deref;
 pub(super) enum PendingHTLCRouting {
 	Forward {
 		onion_packet: msgs::OnionPacket,
-		/// The SCID from the onion that we should forward to. This could be a "real" SCID, an
-		/// outbound SCID alias, or a phantom node SCID.
+		/// The SCID from the onion that we should forward to. This could be a real SCID or a fake one
+		/// generated using `get_fake_scid` from the scid_utils::fake_scid module.
 		short_channel_id: u64, // This should be NonZero<u64> eventually when we bump MSRV
 	},
 	Receive {
@@ -684,6 +684,8 @@ pub type SimpleRefChannelManager<'a, 'b, 'c, 'd, 'e, M, T, F, L> = ChannelManage
 // `total_consistency_lock`
 //  |
 //  |__`forward_htlcs`
+//  |   |
+//  |   |__`pending_intercepted_htlcs`
 //  |
 //  |__`pending_inbound_payments`
 //  |   |
@@ -2230,8 +2232,10 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
 					let forwarding_id_opt = match id_option {
 						None => { // unknown_next_peer
 							// Note that this is likely a timing oracle for detecting whether an scid is a
-							// phantom.
-							if fake_scid::is_valid_phantom(&self.fake_scid_rand_bytes, *short_channel_id, &self.genesis_hash) {
+							// phantom or an intercept.
+							if fake_scid::is_valid_phantom(&self.fake_scid_rand_bytes, *short_channel_id, &self.genesis_hash) ||
+							   fake_scid::is_valid_intercept(&self.fake_scid_rand_bytes, *short_channel_id, &self.genesis_hash)
+							{
 								None
 							} else {
 								break Some(("Don't have available channel for forwarding as requested.", 0x4000 | 10, None));
@@ -3047,6 +3051,57 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
 		Ok(())
 	}
 
+	/// Attempts to forward an intercepted HTLC over the provided channel id and with the provided
+	/// amount to forward. Should only be called in response to an [`HTLCIntercepted`] event.
+	///
+	/// Intercepted HTLCs can be useful for Lightning Service Providers (LSPs) to open a just-in-time
+	/// channel to a receiving node if the node lacks sufficient inbound liquidity.
+	///
+	/// To make use of intercepted HTLCs, use [`ChannelManager::get_intercept_scid`] to generate short
+	/// channel id(s) to put in the receiver's invoice route hints. These route hints will signal to
+	/// LDK to generate an [`HTLCIntercepted`] event when it receives the forwarded HTLC.
+	///
+	/// Note that LDK does not enforce fee requirements in `amt_to_forward_msat`, and will not stop
+	/// you from forwarding more than you received.
+	///
+	/// [`HTLCIntercepted`]: events::Event::HTLCIntercepted
+	// TODO: when we move to deciding the best outbound channel at forward time, only take
+	// `next_node_id` and not `next_hop_channel_id`
+	pub fn forward_intercepted_htlc(&self, intercept_id: InterceptId, next_hop_channel_id: &[u8; 32], _next_node_id: PublicKey, amt_to_forward_msat: u64) -> Result<(), APIError> {
+		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(&self.total_consistency_lock, &self.persistence_notifier);
+
+		let next_hop_scid = match self.channel_state.lock().unwrap().by_id.get(next_hop_channel_id) {
+			Some(chan) => chan.get_short_channel_id().unwrap_or(chan.outbound_scid_alias()),
+			None => return Err(APIError::APIMisuseError {
+				err: format!("Channel with id {:?} not found", next_hop_channel_id)
+			})
+		};
+
+		let payment = self.pending_intercepted_htlcs.lock().unwrap().remove(&intercept_id)
+			.ok_or_else(|| APIError::APIMisuseError {
+				err: format!("Payment with intercept id {:?} not found", intercept_id.0)
+			})?;
+
+		let routing = match payment.forward_info.routing {
+			PendingHTLCRouting::Forward { onion_packet, .. } => {
+				PendingHTLCRouting::Forward { onion_packet, short_channel_id: next_hop_scid }
+			},
+			_ => unreachable!() // Only `PendingHTLCRouting::Forward`s are intercepted
+		};
+		let pending_htlc_info = PendingHTLCInfo {
+			outgoing_amt_msat: amt_to_forward_msat, routing, ..payment.forward_info
+		};
+
+		let mut per_source_pending_forward = [(
+			payment.prev_short_channel_id,
+			payment.prev_funding_outpoint,
+			payment.prev_user_channel_id,
+			vec![(pending_htlc_info, payment.prev_htlc_id)]
+		)];
+		self.forward_htlcs(&mut per_source_pending_forward);
+		Ok(())
+	}
+
 	/// Processes HTLCs which are pending waiting on random forward delay.
 	///
 	/// Should only really ever be called in response to a PendingHTLCsForwardable event.
@@ -5091,28 +5146,82 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
 	fn forward_htlcs(&self, per_source_pending_forwards: &mut [(u64, OutPoint, u128, Vec<(PendingHTLCInfo, u64)>)]) {
 		for &mut (prev_short_channel_id, prev_funding_outpoint, prev_user_channel_id, ref mut pending_forwards) in per_source_pending_forwards {
 			let mut forward_event = None;
+			let mut new_intercept_events = Vec::new();
+			let mut failed_intercept_forwards = Vec::new();
 			if !pending_forwards.is_empty() {
-				let mut forward_htlcs = self.forward_htlcs.lock().unwrap();
-				if forward_htlcs.is_empty() {
-					forward_event = Some(Duration::from_millis(MIN_HTLC_RELAY_HOLDING_CELL_MILLIS))
-				}
 				for (forward_info, prev_htlc_id) in pending_forwards.drain(..) {
-					match forward_htlcs.entry(match forward_info.routing {
-							PendingHTLCRouting::Forward { short_channel_id, .. } => short_channel_id,
-							PendingHTLCRouting::Receive { .. } => 0,
-							PendingHTLCRouting::ReceiveKeysend { .. } => 0,
-					}) {
+					let scid = match forward_info.routing {
+						PendingHTLCRouting::Forward { short_channel_id, .. } => short_channel_id,
+						PendingHTLCRouting::Receive { .. } => 0,
+						PendingHTLCRouting::ReceiveKeysend { .. } => 0,
+					};
+					// Pull this now to avoid introducing a lock order with `forward_htlcs`.
+					let is_our_scid = self.short_to_chan_info.read().unwrap().contains_key(&scid);
+
+					let mut forward_htlcs = self.forward_htlcs.lock().unwrap();
+					let forward_htlcs_empty = forward_htlcs.is_empty();
+					match forward_htlcs.entry(scid) {
 						hash_map::Entry::Occupied(mut entry) => {
 							entry.get_mut().push(HTLCForwardInfo::AddHTLC(PendingAddHTLCInfo {
 								prev_short_channel_id, prev_funding_outpoint, prev_htlc_id, prev_user_channel_id, forward_info }));
 						},
 						hash_map::Entry::Vacant(entry) => {
-							entry.insert(vec!(HTLCForwardInfo::AddHTLC(PendingAddHTLCInfo {
-								prev_short_channel_id, prev_funding_outpoint, prev_htlc_id, prev_user_channel_id, forward_info })));
+							if !is_our_scid && forward_info.incoming_amt_msat.is_some() &&
+							   fake_scid::is_valid_intercept(&self.fake_scid_rand_bytes, scid, &self.genesis_hash)
+							{
+								let intercept_id = InterceptId(Sha256::hash(&forward_info.incoming_shared_secret).into_inner());
+								let mut pending_intercepts = self.pending_intercepted_htlcs.lock().unwrap();
+								match pending_intercepts.entry(intercept_id) {
+									hash_map::Entry::Vacant(entry) => {
+										new_intercept_events.push(events::Event::HTLCIntercepted {
+											requested_next_hop_scid: scid,
+											payment_hash: forward_info.payment_hash,
+											inbound_amount_msat: forward_info.incoming_amt_msat.unwrap(),
+											expected_outbound_amount_msat: forward_info.outgoing_amt_msat,
+											intercept_id
+										});
+										entry.insert(PendingAddHTLCInfo {
+											prev_short_channel_id, prev_funding_outpoint, prev_htlc_id, prev_user_channel_id, forward_info });
+									},
+									hash_map::Entry::Occupied(_) => {
+										log_info!(self.logger, "Failed to forward incoming HTLC: detected duplicate intercepted payment over short channel id {}", scid);
+										let htlc_source = HTLCSource::PreviousHopData(HTLCPreviousHopData {
+											short_channel_id: prev_short_channel_id,
+											outpoint: prev_funding_outpoint,
+											htlc_id: prev_htlc_id,
+											incoming_packet_shared_secret: forward_info.incoming_shared_secret,
+											phantom_shared_secret: None,
+										});
+
+										failed_intercept_forwards.push((htlc_source, forward_info.payment_hash,
+												HTLCFailReason::Reason { failure_code: 0x4000 | 10, data: Vec::new() },
+												HTLCDestination::InvalidForward { requested_forward_scid: scid },
+										));
+									}
+								}
+							} else {
+								// We don't want to generate a PendingHTLCsForwardable event if only intercepted
+								// payments are being processed.
+								if forward_htlcs_empty {
+									forward_event = Some(Duration::from_millis(MIN_HTLC_RELAY_HOLDING_CELL_MILLIS));
+								}
+								entry.insert(vec!(HTLCForwardInfo::AddHTLC(PendingAddHTLCInfo {
+									prev_short_channel_id, prev_funding_outpoint, prev_htlc_id, prev_user_channel_id, forward_info })));
+							}
 						}
 					}
 				}
 			}
+
+			for (htlc_source, payment_hash, failure_reason, destination) in failed_intercept_forwards.drain(..) {
+				self.fail_htlc_backwards_internal(htlc_source, &payment_hash, failure_reason, destination);
+			}
+
+			if !new_intercept_events.is_empty() {
+				let mut events = self.pending_events.lock().unwrap();
+				events.append(&mut new_intercept_events);
+			}
+
 			match forward_event {
 				Some(time) => {
 					let mut pending_events = self.pending_events.lock().unwrap();
@@ -5714,6 +5823,23 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
 		}
 	}
 
+	/// Gets a fake short channel id for use in receiving intercepted payments. These fake scids are
+	/// used when constructing the route hints for HTLCs intended to be intercepted. See
+	/// [`ChannelManager::forward_intercepted_htlc`].
+	///
+	/// Note that this method is not guaranteed to return unique values, you may need to call it a few
+	/// times to get a unique scid.
+	pub fn get_intercept_scid(&self) -> u64 {
+		let best_block_height = self.best_block.read().unwrap().height();
+		let short_to_chan_info = self.short_to_chan_info.read().unwrap();
+		loop {
+			let scid_candidate = fake_scid::Namespace::Intercept.get_fake_scid(best_block_height, &self.genesis_hash, &self.fake_scid_rand_bytes, &self.keys_manager);
+			// Ensure the generated scid doesn't conflict with a real channel.
+			if short_to_chan_info.contains_key(&scid_candidate) { continue }
+			return scid_candidate
+		}
+	}
+
 	/// Gets inflight HTLC information by processing pending outbound payments that are in
 	/// our channels. May be used during pathfinding to account for in-use channel liquidity.
 	pub fn compute_inflight_htlcs(&self) -> InFlightHtlcs {