Clean up existing and add range-based closing_signed negotiation

This adds the new range-based closing_signed negotiation specified
in lightning/bolts#847 as
well as cleans up the existing closing_signed negotiation to unify
the new codepaths and the old ones.

Note that because the new range-based closing_signed negotiation
allows the channel fundee to ultimately select the fee out of a
range specified by the funder, which we, of course, always select
the highest allowed amount from. Thus, we've added an extra round
of closing_signed in the common case as we will not simply accept
the first fee we see, always preferring to make the funder pay as
much as they're willing to.

Author: TheBlueMatt

fuzz/src/full_stack.rs

@@ -476,7 +476,7 @@ pub fn do_test(data: &[u8], logger: &Arc<dyn Logger>) {
 				let channel_id = get_slice!(1)[0] as usize;
 				if channel_id >= channels.len() { return; }
 				channels.sort_by(|a, b| { a.channel_id.cmp(&b.channel_id) });
-				if channelmanager.close_channel(&channels[channel_id].channel_id).is_err() { return; }
+				if channelmanager.close_channel(&channels[channel_id].channel_id, None).is_err() { return; }
 			},
 			7 => {
 				if should_forward {

lightning/src/ln/chanmon_update_fail_tests.rs

@@ -2576,7 +2576,7 @@ fn test_temporary_error_during_shutdown() {
 	*nodes[0].chain_monitor.update_ret.lock().unwrap() = Some(Err(ChannelMonitorUpdateErr::TemporaryFailure));
 	*nodes[1].chain_monitor.update_ret.lock().unwrap() = Some(Err(ChannelMonitorUpdateErr::TemporaryFailure));
 
-	nodes[0].node.close_channel(&channel_id).unwrap();
+	nodes[0].node.close_channel(&channel_id, None).unwrap();
 	nodes[1].node.handle_shutdown(&nodes[0].node.get_our_node_id(), &InitFeatures::known(), &get_event_msg!(nodes[0], MessageSendEvent::SendShutdown, nodes[1].node.get_our_node_id()));
 	check_added_monitors!(nodes[1], 1);
 
@@ -2597,14 +2597,16 @@ fn test_temporary_error_during_shutdown() {
 	*nodes[1].chain_monitor.update_ret.lock().unwrap() = None;
 	let (outpoint, latest_update) = nodes[1].chain_monitor.latest_monitor_update_id.lock().unwrap().get(&channel_id).unwrap().clone();
 	nodes[1].node.channel_monitor_updated(&outpoint, latest_update);
-	let (_, closing_signed_b) = get_closing_signed_broadcast!(nodes[1].node, nodes[0].node.get_our_node_id());
-	nodes[0].node.handle_closing_signed(&nodes[1].node.get_our_node_id(), &closing_signed_b.unwrap());
-	let txn_b = nodes[1].tx_broadcaster.txn_broadcasted.lock().unwrap().split_off(0);
 
-	let (_, none_a) = get_closing_signed_broadcast!(nodes[0].node, nodes[1].node.get_our_node_id());
-	assert!(none_a.is_none());
+	nodes[0].node.handle_closing_signed(&nodes[1].node.get_our_node_id(), &get_event_msg!(nodes[1], MessageSendEvent::SendClosingSigned, nodes[0].node.get_our_node_id()));
+	let (_, closing_signed_a) = get_closing_signed_broadcast!(nodes[0].node, nodes[1].node.get_our_node_id());
 	let txn_a = nodes[0].tx_broadcaster.txn_broadcasted.lock().unwrap().split_off(0);
 
+	nodes[1].node.handle_closing_signed(&nodes[0].node.get_our_node_id(), &closing_signed_a.unwrap());
+	let (_, none_b) = get_closing_signed_broadcast!(nodes[1].node, nodes[0].node.get_our_node_id());
+	assert!(none_b.is_none());
+	let txn_b = nodes[1].tx_broadcaster.txn_broadcasted.lock().unwrap().split_off(0);
+
 	assert_eq!(txn_a, txn_b);
 	assert_eq!(txn_a.len(), 1);
 	check_spends!(txn_a[0], funding_tx);
@@ -2625,7 +2627,7 @@ fn test_permanent_error_during_sending_shutdown() {
 	let channel_id = create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known()).2;
 	*nodes[0].chain_monitor.update_ret.lock().unwrap() = Some(Err(ChannelMonitorUpdateErr::PermanentFailure));
 
-	assert!(nodes[0].node.close_channel(&channel_id).is_ok());
+	assert!(nodes[0].node.close_channel(&channel_id, None).is_ok());
 	check_closed_broadcast!(nodes[0], true);
 	check_added_monitors!(nodes[0], 2);
 }
@@ -2645,7 +2647,7 @@ fn test_permanent_error_during_handling_shutdown() {
 	let channel_id = create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known()).2;
 	*nodes[1].chain_monitor.update_ret.lock().unwrap() = Some(Err(ChannelMonitorUpdateErr::PermanentFailure));
 
-	assert!(nodes[0].node.close_channel(&channel_id).is_ok());
+	assert!(nodes[0].node.close_channel(&channel_id, None).is_ok());
 	let shutdown = get_event_msg!(nodes[0], MessageSendEvent::SendShutdown, nodes[1].node.get_our_node_id());
 	nodes[1].node.handle_shutdown(&nodes[0].node.get_our_node_id(), &InitFeatures::known(), &shutdown);
 	check_closed_broadcast!(nodes[1], true);