Reduce default max_channel_saturation_power_of_half to 2 (max 1/4)

Saturating a channel beyond 1/4 of its capacity seems like a more
reasonable threshold for avoiding a path than 1/2, especially given
we should still be willing to send a payment with a lower
saturation limit if it comes to that.

This requires an (obvious) change to some router tests, but also
requires a change to the `fake_network_test`, opting to simply
remove some over-limit test code there - `fake_network_test` was
our first ever functional test, and while it worked great to ensure
LDK worked at all on day one, we now have a rather large breadth
of functional tests, and a broad "does it work at all" test is no
longer all that useful.

lightning/src/ln/functional_tests.rs

@@ -1059,26 +1059,6 @@ fn fake_network_test() {
 	fail_payment(&nodes[1], &vec!(&nodes[3], &nodes[2], &nodes[1])[..], payment_hash_2);
 	claim_payment(&nodes[1], &vec!(&nodes[2], &nodes[3], &nodes[1])[..], payment_preimage_1);
 
-	// Add a duplicate new channel from 2 to 4
-	let chan_5 = create_announced_chan_between_nodes(&nodes, 1, 3, InitFeatures::known(), InitFeatures::known());
-
-	// Send some payments across both channels
-	let payment_preimage_3 = route_payment(&nodes[0], &vec!(&nodes[1], &nodes[3])[..], 3000000).0;
-	let payment_preimage_4 = route_payment(&nodes[0], &vec!(&nodes[1], &nodes[3])[..], 3000000).0;
-	let payment_preimage_5 = route_payment(&nodes[0], &vec!(&nodes[1], &nodes[3])[..], 3000000).0;
-
-
-	route_over_limit(&nodes[0], &vec!(&nodes[1], &nodes[3])[..], 3000000);
-	let events = nodes[0].node.get_and_clear_pending_msg_events();
-	assert_eq!(events.len(), 0);
-	nodes[0].logger.assert_log_regex("lightning::ln::channelmanager".to_string(), regex::Regex::new(r"Cannot send value that would put us over the max HTLC value in flight our peer will accept \(\d+\)").unwrap(), 1);
-
-	//TODO: Test that routes work again here as we've been notified that the channel is full
-
-	claim_payment(&nodes[0], &vec!(&nodes[1], &nodes[3])[..], payment_preimage_3);
-	claim_payment(&nodes[0], &vec!(&nodes[1], &nodes[3])[..], payment_preimage_4);
-	claim_payment(&nodes[0], &vec!(&nodes[1], &nodes[3])[..], payment_preimage_5);
-
 	// Close down the channels...
 	close_channel(&nodes[0], &nodes[1], &chan_1.2, chan_1.3, true);
 	check_closed_event!(nodes[0], 1, ClosureReason::CooperativeClosure);
@@ -1092,9 +1072,6 @@ fn fake_network_test() {
 	close_channel(&nodes[1], &nodes[3], &chan_4.2, chan_4.3, false);
 	check_closed_event!(nodes[1], 1, ClosureReason::CooperativeClosure);
 	check_closed_event!(nodes[3], 1, ClosureReason::CooperativeClosure);
-	close_channel(&nodes[1], &nodes[3], &chan_5.2, chan_5.3, false);
-	check_closed_event!(nodes[1], 1, ClosureReason::CooperativeClosure);
-	check_closed_event!(nodes[3], 1, ClosureReason::CooperativeClosure);
 }
 
 #[test]

lightning/src/routing/router.rs

@@ -238,7 +238,7 @@ pub struct PaymentParameters {
 	/// A value of 0 will allow payments up to and including a channel's total announced usable
 	/// capacity, a value of one will only use up to half its capacity, two 1/4, etc.
 	///
-	/// Default value: 1
+	/// Default value: 2
 	pub max_channel_saturation_power_of_half: u8,
 }
 
@@ -248,7 +248,7 @@ impl_writeable_tlv_based!(PaymentParameters, {
 	(2, features, option),
 	(3, max_path_count, (default_value, DEFAULT_MAX_PATH_COUNT)),
 	(4, route_hints, vec_type),
-	(5, max_channel_saturation_power_of_half, (default_value, 1)),
+	(5, max_channel_saturation_power_of_half, (default_value, 2)),
 	(6, expiry_time, option),
 });
 
@@ -262,7 +262,7 @@ impl PaymentParameters {
 			expiry_time: None,
 			max_total_cltv_expiry_delta: DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA,
 			max_path_count: DEFAULT_MAX_PATH_COUNT,
-			max_channel_saturation_power_of_half: 1,
+			max_channel_saturation_power_of_half: 2,
 		}
 	}
 
@@ -4745,7 +4745,7 @@ mod tests {
 				cltv_expiry_delta: 42,
 				htlc_minimum_msat: None,
 				htlc_maximum_msat: None,
-			}])]);
+			}])]).with_max_channel_saturation_power_of_half(0);
 
 		// Keep only two paths from us to nodes[2], both with a 99sat HTLC maximum, with one with
 		// no fee and one with a 1msat fee. Previously, trying to route 100 sats to nodes[2] here
@@ -5700,7 +5700,7 @@ mod tests {
 			flags: 0,
 			cltv_expiry_delta: (4 << 4) | 1,
 			htlc_minimum_msat: 0,
-			htlc_maximum_msat: OptionalField::Present(200_000_000),
+			htlc_maximum_msat: OptionalField::Present(250_000_000),
 			fee_base_msat: 0,
 			fee_proportional_millionths: 0,
 			excess_data: Vec::new()
@@ -5712,7 +5712,7 @@ mod tests {
 			flags: 0,
 			cltv_expiry_delta: (13 << 4) | 1,
 			htlc_minimum_msat: 0,
-			htlc_maximum_msat: OptionalField::Present(200_000_000),
+			htlc_maximum_msat: OptionalField::Present(250_000_000),
 			fee_base_msat: 0,
 			fee_proportional_millionths: 0,
 			excess_data: Vec::new()
@@ -5721,8 +5721,8 @@ mod tests {
 		let payment_params = PaymentParameters::from_node_id(nodes[2]).with_features(InvoiceFeatures::known());
 		let keys_manager = test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
 		let random_seed_bytes = keys_manager.get_secure_random_bytes();
-		// 150,000 sat is less than the available liquidity on each channel, set above.
-		let route = get_route(&our_id, &payment_params, &network_graph.read_only(), None, 150_000_000, 42, Arc::clone(&logger), &scorer, &random_seed_bytes).unwrap();
+		// 100,000 sat is less than the available liquidity on each channel, set above.
+		let route = get_route(&our_id, &payment_params, &network_graph.read_only(), None, 100_000_000, 42, Arc::clone(&logger), &scorer, &random_seed_bytes).unwrap();
 		assert_eq!(route.paths.len(), 2);
 		assert!((route.paths[0][1].short_channel_id == 4 && route.paths[1][1].short_channel_id == 13) ||
 			(route.paths[1][1].short_channel_id == 4 && route.paths[0][1].short_channel_id == 13));