feat: Update ChannelConfig of open channels

In patch 2ddbee0 we mentioned that we wanted to be able to update the
`ChannelConfig` for open channels (specifically to be able to update
the routing fees charged).

coordinator/src/node.rs

@@ -106,8 +106,7 @@ impl Node {
     }
 
     pub fn update_ldk_settings(&self, ldk_config: UserConfig) {
-        tracing::info!(?ldk_config, "Updating LDK settings");
-        *self.inner.ldk_config.write() = ldk_config;
+        self.inner.update_ldk_settings(ldk_config)
     }
 
     /// Returns true or false, whether we can find an usable channel with the provided trader.

crates/ln-dlc-node/src/node/mod.rs

@@ -19,6 +19,7 @@ use crate::NetworkGraph;
 use crate::PeerManager;
 use anyhow::Context;
 use anyhow::Result;
+use bitcoin::hashes::hex::ToHex;
 use bitcoin::secp256k1::PublicKey;
 use bitcoin::Network;
 use dlc_messages::message_handler::MessageHandler as DlcMessageHandler;
@@ -770,6 +771,29 @@ where
             settings,
         })
     }
+
+    pub fn update_ldk_settings(&self, ldk_config: UserConfig) {
+        tracing::debug!("Updating LDK settings");
+        *self.ldk_config.write() = ldk_config;
+
+        tracing::info!(?ldk_config, "Updated LDK settings");
+
+        for channel in self.list_channels() {
+            let channel_id = channel.channel_id;
+            let peer_id = channel.counterparty.node_id;
+            if let Err(e) = self.channel_manager.update_channel_config(
+                &peer_id,
+                &[channel_id],
+                &ldk_config.channel_config,
+            ) {
+                tracing::error!(
+                    channel_id = %channel_id.to_hex(),
+                    %peer_id,
+                    "Failed to apply new channel configuration: {e:?}"
+                );
+            }
+        }
+    }
 }
 
 impl Display for NodeInfo {

crates/ln-dlc-node/src/tests/just_in_time_channel/payments.rs

@@ -1,4 +1,5 @@
 use crate::node::Node;
+use crate::tests::calculate_routing_fee_msat;
 use crate::tests::init_tracing;
 use crate::tests::just_in_time_channel::create::send_interceptable_payment;
 use crate::tests::setup_coordinator_payer_channel;
@@ -55,3 +56,59 @@ async fn just_in_time_channel_with_multiple_payments() {
         assert_eq!(coordinator.channel_manager.list_channels().len(), 2);
     }
 }
+
+#[tokio::test(flavor = "multi_thread")]
+#[ignore]
+async fn new_config_affects_routing_fees() {
+    init_tracing();
+
+    // Arrange
+
+    let payer = Node::start_test_app("payer").unwrap();
+    let coordinator = Node::start_test_coordinator("coordinator").unwrap();
+    let payee = Node::start_test_app("payee").unwrap();
+
+    payer.connect(coordinator.info).await.unwrap();
+    payee.connect(coordinator.info).await.unwrap();
+
+    let opening_invoice_amount = 10_000;
+    let expected_coordinator_payee_channel_value =
+        setup_coordinator_payer_channel(opening_invoice_amount, &coordinator, &payer).await;
+
+    send_interceptable_payment(
+        &payer,
+        &payee,
+        &coordinator,
+        opening_invoice_amount,
+        Some(expected_coordinator_payee_channel_value),
+    )
+    .await
+    .unwrap();
+
+    // Act
+
+    let coordinator_balance_before = coordinator.get_ldk_balance().available_msat();
+
+    let mut ldk_config_coordinator = *coordinator.ldk_config.read();
+
+    ldk_config_coordinator
+        .channel_config
+        .forwarding_fee_proportional_millionths *= 10;
+
+    coordinator.update_ldk_settings(ldk_config_coordinator);
+
+    let payment_amount_sat = 5_000;
+    send_interceptable_payment(&payer, &payee, &coordinator, payment_amount_sat, None)
+        .await
+        .unwrap();
+
+    // Assert
+
+    let coordinator_balance_after = coordinator.get_ldk_balance().available_msat();
+    let routing_fee_charged_msat = coordinator_balance_after - coordinator_balance_before;
+
+    let routing_fee_expected_msat =
+        calculate_routing_fee_msat(ldk_config_coordinator.channel_config, payment_amount_sat);
+
+    assert_eq!(routing_fee_charged_msat, routing_fee_expected_msat);
+}