channeld: send option_data_loss_protect fields.

We ignore incoming for now, but this means we advertize the option and
we send the required fields.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

CHANGELOG.md

@@ -20,6 +20,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - JSON API: Added description to invoices and payments (#1740).
 - pylightning: RpcError now has `method` and `payload` fields.
 - Sending lightningd a SIGHUP will make it reopen its `log-file`, if any.
+- Protocol: `option_data_loss_protect` now supported to protect peers
+  against being out-of-date.
 
 ### Changed
 

channeld/channel.c

@@ -1830,7 +1830,8 @@ static void resend_commitment(struct peer *peer, const struct changed_htlc *last
 			       peer->revocations_received);
 }
 
-static void peer_reconnect(struct peer *peer)
+static void peer_reconnect(struct peer *peer,
+			   const struct secret *last_remote_per_commit_secret)
 {
 	struct channel_id channel_id;
 	/* Note: BOLT #2 uses these names, which are sender-relative! */
@@ -1839,6 +1840,10 @@ static void peer_reconnect(struct peer *peer)
 	struct htlc_map_iter it;
 	const struct htlc *htlc;
 	u8 *msg;
+	struct pubkey my_current_per_commitment_point;
+
+	get_per_commitment_point(peer->next_index[LOCAL]-1,
+				 &my_current_per_commitment_point, NULL);
 
 	/* BOLT #2:
 	 *
@@ -1856,10 +1861,19 @@ static void peer_reconnect(struct peer *peer)
 	 *     of the next `commitment_signed` it expects to receive.
 	 *   - MUST set `next_remote_revocation_number` to the commitment number
 	 *     of the next `revoke_and_ack` message it expects to receive.
+	 *   - if it supports `option_data_loss_protect`:
+	 *     - if `next_remote_revocation_number` equals 0:
+	 *       - MUST set `your_last_per_commitment_secret` to all zeroes
+	 *     - otherwise:
+	 *       - MUST set `your_last_per_commitment_secret` to the last
+	 *         `per_commitment_secret` it received
 	 */
-	msg = towire_channel_reestablish(NULL, &peer->channel_id,
+	msg = towire_channel_reestablish_option_data_loss_protect
+		(NULL, &peer->channel_id,
 		 peer->next_index[LOCAL],
-					 peer->revocations_received);
+		 peer->revocations_received,
+		 last_remote_per_commit_secret,
+		 &my_current_per_commitment_point);
 	sync_crypto_write(&peer->cs, PEER_FD, take(msg));
 
 	peer_billboard(false, "Sent reestablish, waiting for theirs");
@@ -2337,6 +2351,7 @@ static void init_channel(struct peer *peer)
 	u8 *funding_signed;
 	const u8 *msg;
 	u32 feerate_per_kw[NUM_SIDES];
+	struct secret last_remote_per_commit_secret;
 
 	assert(!(fcntl(MASTER_FD, F_GETFL) & O_NONBLOCK));
 
@@ -2387,7 +2402,8 @@ static void init_channel(struct peer *peer)
 				   &peer->final_scriptpubkey,
 				   &peer->channel_flags,
 				   &funding_signed,
-				   &peer->announce_depth_reached))
+				   &peer->announce_depth_reached,
+				   &last_remote_per_commit_secret))
 		master_badmsg(WIRE_CHANNEL_INIT, msg);
 
 	status_trace("init %s: remote_per_commit = %s, old_remote_per_commit = %s"
@@ -2447,7 +2463,7 @@ static void init_channel(struct peer *peer)
 
 	/* OK, now we can process peer messages. */
 	if (reconnected)
-		peer_reconnect(peer);
+		peer_reconnect(peer, &last_remote_per_commit_secret);
 
 	/* If we have a funding_signed message, send that immediately */
 	if (funding_signed)

channeld/channel_wire.csv

@@ -58,6 +58,7 @@ channel_init,,flags,u8
 channel_init,,init_peer_pkt_len,u16
 channel_init,,init_peer_pkt,init_peer_pkt_len*u8
 channel_init,,reached_announce_depth,bool
+channel_init,,last_remote_secret,struct secret
 
 # master->channeld funding hit new depth >= lock depth
 channel_funding_locked,1002

common/features.c

@@ -4,6 +4,7 @@
 #include <wire/peer_wire.h>
 
 static const u32 local_features[] = {
+	LOCAL_DATA_LOSS_PROTECT,
 	LOCAL_INITIAL_ROUTING_SYNC,
 	LOCAL_GOSSIP_QUERIES
 };

lightningd/channel_control.c

@@ -188,6 +188,7 @@ void peer_start_channeld(struct channel *channel,
 	struct lightningd *ld = channel->peer->ld;
 	const struct config *cfg = &ld->config;
 	bool reached_announce_depth;
+	struct secret last_remote_per_commit_secret;
 
 	hsmfd = hsm_get_client_fd(ld, &channel->peer->id,
 				  channel->dbid,
@@ -235,6 +236,27 @@ void peer_start_channeld(struct channel *channel,
 
 	num_revocations = revocations_received(&channel->their_shachain.chain);
 
+	/* BOLT #2:
+	 *
+ 	 *   - if it supports `option_data_loss_protect`:
+	 *     - if `next_remote_revocation_number` equals 0:
+	 *       - MUST set `your_last_per_commitment_secret` to all zeroes
+	 *     - otherwise:
+	 *       - MUST set `your_last_per_commitment_secret` to the last
+	 *         `per_commitment_secret` it received
+	 */
+	if (num_revocations == 0)
+		memset(&last_remote_per_commit_secret, 0,
+		       sizeof(last_remote_per_commit_secret));
+	else if (!shachain_get_secret(&channel->their_shachain.chain,
+				      num_revocations-1,
+				      &last_remote_per_commit_secret)) {
+		channel_fail_permanent(channel,
+				       "Could not get revocation secret %"PRIu64,
+				       num_revocations-1);
+		return;
+	}
+
 	/* Warn once. */
 	if (ld->config.ignore_fee_limits)
 		log_debug(channel->log, "Ignoring fee limits!");
@@ -284,7 +306,8 @@ void peer_start_channeld(struct channel *channel,
 							channel->final_key_idx),
 				      channel->channel_flags,
 				      funding_signed,
-				      reached_announce_depth);
+				      reached_announce_depth,
+				      &last_remote_per_commit_secret);
 
 	/* We don't expect a response: we are triggered by funding_depth_cb. */
 	subd_send_msg(channel->owner, take(initmsg));

tests/test_connection.py

@@ -1006,7 +1006,7 @@ def test_peerinfo(node_factory, bitcoind):
     # Gossiping but no node announcement yet
     assert l1.rpc.getpeer(l2.info['id'])['connected']
     assert len(l1.rpc.getpeer(l2.info['id'])['channels']) == 0
-    assert l1.rpc.getpeer(l2.info['id'])['local_features'] == '88'
+    assert l1.rpc.getpeer(l2.info['id'])['local_features'] == '8a'
     assert l1.rpc.getpeer(l2.info['id'])['global_features'] == ''
 
     # Fund a channel to force a node announcement