Add config knob for forwarding intercept payments

Author: valentinewallace

lightning/src/ln/channelmanager.rs

@@ -2338,7 +2338,8 @@ impl<M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelManager<M, T, K, F
 							// Note that this is likely a timing oracle for detecting whether an scid is a
 							// 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)
+							   (fake_scid::is_valid_intercept(&self.fake_scid_rand_bytes, *short_channel_id, &self.genesis_hash)
+									&& self.default_configuration.accept_intercept_htlcs)
 							{
 								None
 							} else {

lightning/src/ln/payment_tests.rs

@@ -1399,7 +1399,11 @@ fn intercepted_payment() {
 fn do_test_intercepted_payment(fail_intercept: bool) {
 	let chanmon_cfgs = create_chanmon_cfgs(3);
 	let node_cfgs = create_node_cfgs(3, &chanmon_cfgs);
-	let node_chanmgrs = create_node_chanmgrs(3, &node_cfgs, &[None, None, None]);
+
+	let mut intercept_forwards_config = test_default_channel_config();
+	intercept_forwards_config.accept_intercept_htlcs = true;
+
+	let node_chanmgrs = create_node_chanmgrs(3, &node_cfgs, &[None, Some(intercept_forwards_config), None]);
 	let nodes = create_network(3, &node_cfgs, &node_chanmgrs);
 	let scorer = test_utils::TestScorer::with_penalty(0);
 	let random_seed_bytes = chanmon_cfgs[0].keys_manager.get_secure_random_bytes();

lightning/src/util/config.rs

@@ -505,6 +505,17 @@ pub struct UserConfig {
 	/// [`msgs::OpenChannel`]: crate::ln::msgs::OpenChannel
 	/// [`msgs::AcceptChannel`]: crate::ln::msgs::AcceptChannel
 	pub manually_accept_inbound_channels: bool,
+	///  If this is set to true, LDK will intercept HTLCs that are attempting to be forwarded over
+	///  fake short channel ids generated via [`ChannelManager::get_intercept_scid`]. Upon HTLC
+	///  intercept, LDK will generate an [`Event::HTLCIntercepted`] which MUST be handled by the user.
+	///
+	///  Setting this to true may break backwards compatibility with LDK versions <= 0.0.113.
+	///
+	///  Default value: false.
+	///
+	/// [`ChannelManager::get_intercept_scid`]: crate::ln::channelmanager::ChannelManager::get_intercept_scid
+	/// [`Event::HTLCIntercepted`]: crate::util::events::Event::HTLCIntercepted
+	pub accept_intercept_htlcs: bool,
 }
 
 impl Default for UserConfig {
@@ -516,6 +527,7 @@ impl Default for UserConfig {
 			accept_forwards_to_priv_channels: false,
 			accept_inbound_channels: true,
 			manually_accept_inbound_channels: false,
+			accept_intercept_htlcs: false,
 		}
 	}
 }