Support receiving multiple funding_locked messages

As a part of adding SCID aliases to channels, we now have to accept
otherwise-redundant funding_locked messages which serve only to
update the SCID alias. Previously, we'd failt he channel as such
an update used to be bogus.

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -2178,17 +2178,28 @@ impl<Signer: Sign> Channel<Signer> {
 		} else if non_shutdown_state == (ChannelState::FundingSent as u32 | ChannelState::OurFundingLocked as u32) {
 			self.channel_state = ChannelState::ChannelFunded as u32 | (self.channel_state & MULTI_STATE_FLAGS);
 			self.update_time_counter += 1;
-		} else if (self.channel_state & (ChannelState::ChannelFunded as u32) != 0 &&
-				 // Note that funding_signed/funding_created will have decremented both by 1!
-				 self.cur_holder_commitment_transaction_number == INITIAL_COMMITMENT_NUMBER - 1 &&
-				 self.cur_counterparty_commitment_transaction_number == INITIAL_COMMITMENT_NUMBER - 1) ||
-				// If we reconnected before sending our funding locked they may still resend theirs:
-				(self.channel_state & (ChannelState::FundingSent as u32 | ChannelState::TheirFundingLocked as u32) ==
-				                      (ChannelState::FundingSent as u32 | ChannelState::TheirFundingLocked as u32)) {
-			if self.counterparty_cur_commitment_point != Some(msg.next_per_commitment_point) {
+		} else if self.channel_state & (ChannelState::ChannelFunded as u32) != 0 ||
+			// If we reconnected before sending our funding locked they may still resend theirs:
+			(self.channel_state & (ChannelState::FundingSent as u32 | ChannelState::TheirFundingLocked as u32) ==
+			                      (ChannelState::FundingSent as u32 | ChannelState::TheirFundingLocked as u32))
+		{
+			// They probably disconnected/reconnected and re-sent the funding_locked, which is
+			// required, or we're getting a fresh SCID alias.
+			let expected_point =
+				if self.cur_counterparty_commitment_transaction_number == INITIAL_COMMITMENT_NUMBER - 1 {
+					// If they haven't ever sent an updated point, the point they send should match
+					// the current one.
+					self.counterparty_cur_commitment_point
+				} else {
+					// If they have sent updated points, funding_locked is always supposed to match
+					// their "first" point, which we re-derive here.
+					self.commitment_secrets.get_secret(INITIAL_COMMITMENT_NUMBER - 1)
+						.map(|secret| SecretKey::from_slice(&secret).ok()).flatten()
+						.map(|sk| PublicKey::from_secret_key(&self.secp_ctx, &sk))
+				};
+			if expected_point != Some(msg.next_per_commitment_point) {
 				return Err(ChannelError::Close("Peer sent a reconnect funding_locked with a different point".to_owned()));
 			}
-			// They probably disconnected/reconnected and re-sent the funding_locked, which is required
 			return Ok(None);
 		} else {
 			return Err(ChannelError::Close("Peer sent a funding_locked at a strange time".to_owned()));
@@ -4482,7 +4493,8 @@ impl<Signer: Sign> Channel<Signer> {
 		if need_commitment_update {
 			if self.channel_state & (ChannelState::MonitorUpdateFailed as u32) == 0 {
 				if self.channel_state & (ChannelState::PeerDisconnected as u32) == 0 {
-					let next_per_commitment_point = self.holder_signer.get_per_commitment_point(self.cur_holder_commitment_transaction_number, &self.secp_ctx);
+					let next_per_commitment_point =
+						self.holder_signer.get_per_commitment_point(INITIAL_COMMITMENT_NUMBER - 1, &self.secp_ctx);
 					return Some(msgs::FundingLocked {
 						channel_id: self.channel_id,
 						next_per_commitment_point,

lightning/src/ln/priv_short_conf_tests.rs

@@ -249,7 +249,7 @@ fn test_routed_scid_alias() {
 	let mut nodes = create_network(3, &node_cfgs, &node_chanmgrs);
 
 	create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1_000_000, 500_000_000, InitFeatures::known(), InitFeatures::known()).2;
-	create_unannounced_chan_between_nodes_with_value(&nodes, 1, 2, 1_000_000, 500_000_000, InitFeatures::known(), InitFeatures::known());
+	let mut as_funding_locked = create_unannounced_chan_between_nodes_with_value(&nodes, 1, 2, 1_000_000, 500_000_000, InitFeatures::known(), InitFeatures::known()).0;
 
 	let last_hop = nodes[2].node.list_usable_channels();
 	let hop_hints = vec![RouteHint(vec![RouteHintHop {
@@ -270,4 +270,17 @@ fn test_routed_scid_alias() {
 
 	pass_along_route(&nodes[0], &[&[&nodes[1], &nodes[2]]], 100_000, payment_hash, payment_secret);
 	claim_payment(&nodes[0], &[&nodes[1], &nodes[2]], payment_preimage);
+
+	// Now test that if a peer sends us a second funding_locked after the channel is operational we
+	// will use the new alias.
+	as_funding_locked.short_channel_id_alias = Some(0xdeadbeef);
+	nodes[2].node.handle_funding_locked(&nodes[1].node.get_our_node_id(), &as_funding_locked);
+	// Note that we always respond to a funding_locked with a channel_update. Not a lot of reason
+	// to bother updating that code, so just drop the message here.
+	get_event_msg!(nodes[2], MessageSendEvent::SendChannelUpdate, nodes[1].node.get_our_node_id());
+	let updated_channel_info = nodes[2].node.list_usable_channels();
+	assert_eq!(updated_channel_info.len(), 1);
+	assert_eq!(updated_channel_info[0].inbound_scid_alias.unwrap(), 0xdeadbeef);
+	// Note that because we never send a duplicate funding_locked we can't send a payment through
+	// the 0xdeadbeef SCID alias.
 }