Pathfinding: ignore blinded route hints where we are the intro node

See tests, but the fuzzer found several panics from not fully ignoring these
hints.

We should support these route hints eventually, but it will involve some
reworking of the Path/BlindedTail structs.

lightning/src/routing/router.rs

@@ -2042,7 +2042,7 @@ where L::Target: Logger {
 				// in the regular network graph.
 				first_hop_targets.get(&intro_node_id).is_some() ||
 				network_nodes.get(&intro_node_id).is_some();
-			if !have_intro_node_in_graph { continue }
+			if !have_intro_node_in_graph || our_node_id == intro_node_id { continue }
 			let candidate = if hint.1.blinded_hops.len() == 1 {
 				CandidateRouteHop::OneHopBlinded { hint, hint_idx }
 			} else { CandidateRouteHop::Blinded { hint, hint_idx } };
@@ -7075,6 +7075,116 @@ mod tests {
 		assert_eq!(route.get_total_fees(), blinded_payinfo.fee_base_msat as u64);
 		assert_eq!(route.get_total_amount(), amt_msat);
 	}
+
+	#[test]
+	fn we_are_intro_node_candidate_hops() {
+		// This previously led to a panic in the router because we'd generate a Path with only a
+		// BlindedTail and 0 unblinded hops, due to the only candidate hops being blinded route hints
+		// where the origin node is the intro node. We now fully disallow considering candidate hops
+		// where the origin node is the intro node.
+		let (secp_ctx, network_graph, _, _, logger) = build_graph();
+		let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+		let scorer = ln_test_utils::TestScorer::new();
+		let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+		let random_seed_bytes = keys_manager.get_secure_random_bytes();
+		let config = UserConfig::default();
+
+		// Values are taken from the fuzz input that uncovered this panic.
+		let amt_msat = 21_7020_5185_1423_0019;
+
+		let blinded_path = BlindedPath {
+			introduction_node_id: our_id,
+			blinding_point: ln_test_utils::pubkey(42),
+			blinded_hops: vec![
+				BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+				BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+			],
+		};
+		let blinded_payinfo = BlindedPayInfo {
+			fee_base_msat: 5052_9027,
+			fee_proportional_millionths: 5052_9027,
+			htlc_minimum_msat: 21_7020_5185_1423_0019,
+			htlc_maximum_msat: 1844_6744_0737_0955_1615,
+			cltv_expiry_delta: 0,
+			features: BlindedHopFeatures::empty(),
+		};
+		let mut blinded_hints = vec![
+			(blinded_payinfo.clone(), blinded_path.clone()),
+			(blinded_payinfo.clone(), blinded_path.clone()),
+		];
+		blinded_hints[1].1.introduction_node_id = nodes[6];
+
+		let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+		let payment_params = PaymentParameters::blinded(blinded_hints.clone())
+			.with_bolt12_features(bolt12_features.clone()).unwrap();
+
+		let netgraph = network_graph.read_only();
+		let route_params = RouteParameters::from_payment_params_and_value(
+			payment_params, amt_msat);
+		if let Err(LightningError { err, .. }) = get_route(
+			&our_id, &route_params, &netgraph, None, Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+		) {
+			assert_eq!(err, "Failed to find a path to the given destination");
+		} else { panic!() }
+	}
+
+	#[test]
+	fn we_are_intro_node_bp_in_final_path_fee_calc() {
+		// This previously led to a debug panic in the router because we'd find an invalid Path with
+		// 0 unblinded hops and a blinded tail, leading to the generation of a final
+		// PaymentPathHop::fee_msat that included both the blinded path fees and the final value of
+		// the payment, when it was intended to only include the final value of the payment.
+		let (secp_ctx, network_graph, _, _, logger) = build_graph();
+		let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+		let scorer = ln_test_utils::TestScorer::new();
+		let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+		let random_seed_bytes = keys_manager.get_secure_random_bytes();
+		let config = UserConfig::default();
+
+		// Values are taken from the fuzz input that uncovered this panic.
+		let amt_msat = 21_7020_5185_1423_0019;
+
+		let blinded_path = BlindedPath {
+			introduction_node_id: our_id,
+			blinding_point: ln_test_utils::pubkey(42),
+			blinded_hops: vec![
+				BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+				BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+			],
+		};
+		let blinded_payinfo = BlindedPayInfo {
+			fee_base_msat: 10_4425_1395,
+			fee_proportional_millionths: 1_6973_9011,
+			htlc_minimum_msat: 21_7301_9934_9094_0931,
+			htlc_maximum_msat: 1844_6744_0737_0955_1615,
+			cltv_expiry_delta: 0,
+			features: BlindedHopFeatures::empty(),
+		};
+		let mut blinded_hints = vec![
+			(blinded_payinfo.clone(), blinded_path.clone()),
+			(blinded_payinfo.clone(), blinded_path.clone()),
+			(blinded_payinfo.clone(), blinded_path.clone()),
+		];
+		blinded_hints[1].0.fee_base_msat = 5052_9027;
+		blinded_hints[1].0.fee_proportional_millionths = 5052_9027;
+		blinded_hints[1].0.htlc_minimum_msat = 21_7020_5185_1423_0019;
+		blinded_hints[1].0.htlc_maximum_msat = 1844_6744_0737_0955_1615;
+
+		blinded_hints[2].1.introduction_node_id = nodes[6];
+
+		let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+		let payment_params = PaymentParameters::blinded(blinded_hints.clone())
+			.with_bolt12_features(bolt12_features.clone()).unwrap();
+
+		let netgraph = network_graph.read_only();
+		let route_params = RouteParameters::from_payment_params_and_value(
+			payment_params, amt_msat);
+		if let Err(LightningError { err, .. }) = get_route(
+			&our_id, &route_params, &netgraph, None, Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+		) {
+			assert_eq!(err, "Failed to find a path to the given destination");
+		} else { panic!() }
+	}
 }
 
 #[cfg(all(any(test, ldk_bench), not(feature = "no-std")))]