f make sure chan updates are atomic

Author: dunxen

lightning/src/ln/channelmanager.rs

@@ -3540,6 +3540,13 @@ where
 			.ok_or_else(|| APIError::ChannelUnavailable { err: format!("Can't find a peer matching the passed counterparty node_id {}", counterparty_node_id) })?;
 		let mut peer_state_lock = peer_state_mutex.lock().unwrap();
 		let peer_state = &mut *peer_state_lock;
+		for channel_id in channel_ids {
+			if !peer_state.has_channel(channel_id) {
+				return Err(APIError::ChannelUnavailable {
+					err: format!("Channel with ID {} was not found for the passed counterparty_node_id {}", log_bytes!(*channel_id), counterparty_node_id),
+				});
+			};
+		}
 		for channel_id in channel_ids {
 			if let Some(channel) = peer_state.channel_by_id.get_mut(channel_id) {
 				let mut config = channel.context.config();
@@ -10151,6 +10158,25 @@ mod tests {
 			MessageSendEvent::BroadcastChannelUpdate { .. } => {},
 			_ => panic!("expected BroadcastChannelUpdate event"),
 		}
+
+		// If we provide a channel_id not associated with the peer, we should get an error and no updates
+		// should be applied to ensure update atomicity as specified in the API docs.
+		let bad_channel_id = [10; 32];
+		let current_fee = nodes[0].node.list_channels()[0].config.unwrap().forwarding_fee_proportional_millionths;
+		let new_fee = current_fee + 100;
+		assert!(
+			matches!(
+				nodes[0].node.update_partial_channel_config(&channel.counterparty.node_id, &[channel.channel_id, bad_channel_id], &ChannelConfigUpdate {
+					forwarding_fee_proportional_millionths: Some(new_fee),
+					..Default::default()
+				}),
+				Err(APIError::ChannelUnavailable { err: _ }),
+			)
+		);
+		// Check that the fee hasn't changed for the channel that exists.
+		assert_eq!(nodes[0].node.list_channels()[0].config.unwrap().forwarding_fee_proportional_millionths, current_fee);
+		let events = nodes[0].node.get_and_clear_pending_msg_events();
+		assert_eq!(events.len(), 0);
 	}
 }