reestablish: Send announcement sigs when asked

A new TLV in `channel_reestablish` lets our peer request announcement signatures. This updates CLN to (re)send them when requested.

As per splice spec PR https://github.com/lightning/bolts/pull/1160/changes#diff-ed04ca2c673fd6aabde69389511fa9ee60cb44d6b2ef6c88b549ffaa753d6afeR3303-R3308

Changelog-None

Author: ddustin

channeld/channeld.c

@@ -5526,6 +5526,7 @@ static void peer_reconnect(struct peer *peer,
 			   const struct secret *last_remote_per_commit_secret)
 {
 	struct channel_id channel_id;
+	bool announcement_sigs_requested;
 	/* Note: BOLT #2 uses these names! */
 	u64 next_commitment_number, next_revocation_number;
 	bool retransmit_revoke_and_ack, retransmit_commitment_signed;
@@ -6020,6 +6021,24 @@ static void peer_reconnect(struct peer *peer,
 	if (retransmit_revoke_and_ack && peer->last_was_revoke)
 		resend_revoke(peer);
 
+	/* BOLT-??? #2
+	 *     1. type: 5 (`my_current_funding_locked`)
+	 *     2. data:
+	 *         * [`sha256`:`my_current_funding_locked_txid`]
+	 *         * [`byte`:`retransmit_flags`]
+	 *
+	 * The `retransmit_flags` bitfield is used to let our peer know which messages
+	 * we expect them to retransmit after the reconnection:
+	 *
+	 * | Bit Position  | Name                      |
+	 * | ------------- | --------------------------|
+	 * | 0             | `announcement_signatures` |
+	 */
+	announcement_sigs_requested = false;
+	if (recv_tlvs && recv_tlvs->my_current_funding_locked
+	    && recv_tlvs->my_current_funding_locked->retransmit_flags & 1)
+		announcement_sigs_requested = true;
+
 	/* BOLT #2:
 	 *
 	 *   - upon reconnection:
@@ -6032,7 +6051,7 @@ static void peer_reconnect(struct peer *peer,
 	tal_free(send_tlvs);
 
 	/* We've reestablished! */
-	wire_sync_write(MASTER_FD, take(towire_channeld_reestablished(NULL)));
+	wire_sync_write(MASTER_FD, take(towire_channeld_reestablished(NULL, announcement_sigs_requested)));
 
 	/* Corner case: we didn't send shutdown before because update_add_htlc
 	 * pending, but now they're cleared by restart, and we're actually

channeld/channeld_wire.csv

@@ -78,6 +78,7 @@ msgdata,channeld_init,scid_alias,short_channel_id,
 
 # channeld->lightningd: successfully negotated reestablishment.
 msgtype,channeld_reestablished,1101
+msgdata,channeld_reestablished,announcement_sigs_requested,bool,
 
 # master->channeld funding hit new depth(funding locked if >= lock depth)
 # short_channel_id != NULL once we have 3+ confirmations

lightningd/channel_control.c

@@ -1311,6 +1311,17 @@ static void peer_got_shutdown(struct channel *channel, const u8 *msg)
 	wallet_channel_save(ld->wallet, channel);
 }
 
+static void peer_channeld_reestablished(struct channel *channel, const u8* msg)
+{
+	bool announcement_sigs_requested;
+	if (!fromwire_channeld_reestablished(msg, &announcement_sigs_requested))
+		channel_internal_error(channel,
+				       "bad channeld_reestablished %s",
+				       tal_hex(channel, msg));
+
+	channel_gossip_channel_reestablished(channel, announcement_sigs_requested);
+}
+
 void channel_fallen_behind(struct channel *channel)
 {
 	channel->has_future_per_commitment_point = true;
@@ -1565,7 +1576,7 @@ static unsigned channel_msg(struct subd *sd, const u8 *msg, const int *fds)
 		peer_got_shutdown(sd->channel, msg);
 		break;
 	case WIRE_CHANNELD_REESTABLISHED:
-		channel_gossip_channel_reestablished(sd->channel);
+		peer_channeld_reestablished(sd->channel, msg);
 		break;
 	case WIRE_CHANNELD_SHUTDOWN_COMPLETE:
 		/* We expect 1 fd. */
@@ -1923,7 +1934,7 @@ bool peer_start_channeld(struct channel *channel,
 
 	/* "Reestablished" if we've just opened. */
 	if (!reconnected)
-		channel_gossip_channel_reestablished(channel);
+		channel_gossip_channel_reestablished(channel, false);
 
 	/* FIXME: DTODO: Use a pointer to a txid instead of zero'ing one out. */
 	memset(&txid, 0, sizeof(txid));

lightningd/channel_gossip.c

@@ -687,25 +687,22 @@ static void stash_remote_announce_sigs(struct channel *channel,
  *   - MUST NOT send the `announcement_signatures` message.
  */
 
-static void send_channel_announce_sigs(struct channel *channel)
+static bool send_channel_announce_sigs(struct channel *channel)
 {
 	/* First 2 + 256 byte are the signatures and msg type, skip them */
 	const size_t offset = 258;
 	struct lightningd *ld = channel->peer->ld;
 	struct sha256_double hash;
-	secp256k1_ecdsa_signature local_node_sig, local_bitcoin_sig;
 	struct channel_gossip *cg = channel->channel_gossip;
+	secp256k1_ecdsa_signature local_node_sig, local_bitcoin_sig;
 	const u8 *ca, *msg;
 
 	/* Wait until we've exchanged reestablish messages */
 	if (!channel->reestablished) {
 		log_debug(channel->log, "channel_gossip: not sending channel_announcement_sigs until reestablished");
-		return;
+		return false;
 	}
 
-	if (cg->sent_sigs)
-		return;
-
 	ca = create_channel_announcement(tmpctx, channel, *channel->scid,
 					 NULL, NULL, NULL, NULL);
 
@@ -722,20 +719,30 @@ static void send_channel_announce_sigs(struct channel *channel)
 	if (!check_signed_hash(&hash, &local_node_sig, &ld->our_pubkey)) {
 		channel_internal_error(channel,
 				       "HSM returned an invalid node signature");
-		return;
+		return false;
 	}
 
 	if (!check_signed_hash(&hash, &local_bitcoin_sig, &channel->local_funding_pubkey)) {
 		channel_internal_error(channel,
 				       "HSM returned an invalid bitcoin signature");
-		return;
+		return false;
 	}
 
 	msg = towire_announcement_signatures(NULL,
 					     &channel->cid, *channel->scid,
 					     &local_node_sig, &local_bitcoin_sig);
 	msg_to_peer(channel->peer, take(msg));
-	cg->sent_sigs = true;
+	return cg->sent_sigs = true;
+}
+
+static bool send_channel_announce_sigs_once(struct channel *channel)
+{
+	struct channel_gossip *cg = channel->channel_gossip;
+
+	if (cg->sent_sigs)
+		return false;
+
+	return send_channel_announce_sigs(channel);
 }
 
 /* Sends channel_announcement */
@@ -829,7 +836,7 @@ static void set_gossip_state(struct channel *channel,
 	case CGOSSIP_ANNOUNCED:
 		/* In case this snuck up on us (fast confirmations),
 		 * make sure we sent sigs */
-		send_channel_announce_sigs(channel);
+		send_channel_announce_sigs_once(channel);
 
 		/* BOLT #7:
 		 * A recipient node:
@@ -897,7 +904,7 @@ static void update_gossip_state(struct channel *channel)
 		return;
 	case CGOSSIP_WAITING_FOR_MATCHING_PEER_SIGS:
 	case CGOSSIP_WAITING_FOR_ANNOUNCE_DEPTH:
-		send_channel_announce_sigs(channel);
+		send_channel_announce_sigs_once(channel);
 		/* fall thru */
 	case CGOSSIP_WAITING_FOR_SCID:
 	case CGOSSIP_PRIVATE:
@@ -1005,7 +1012,7 @@ void channel_gossip_got_announcement_sigs(struct channel *channel,
 
 send_our_sigs:
 	/* This only works once, so we won't spam them. */
-	send_channel_announce_sigs(channel);
+	send_channel_announce_sigs_once(channel);
 }
 
 /* Short channel id changed (splice, or reorg). */
@@ -1198,7 +1205,8 @@ static void channel_reestablished_stable(struct channel *channel)
 }
 
 /* Peer has connected and successfully reestablished channel. */
-void channel_gossip_channel_reestablished(struct channel *channel)
+void channel_gossip_channel_reestablished(struct channel *channel,
+					  bool announcement_sigs_requested)
 {
 	channel->reestablished = true;
 	tal_free(channel->stable_conn_timer);
@@ -1216,6 +1224,9 @@ void channel_gossip_channel_reestablished(struct channel *channel)
 	/* We can re-xmit sigs once per reconnect */
 	channel->channel_gossip->sent_sigs = false;
 
+	if (announcement_sigs_requested)
+		send_channel_announce_sigs(channel);
+
 	/* BOLT #7:
 	 * - Upon reconnection (once the above timing requirements have
 	 *   been met):
@@ -1236,7 +1247,7 @@ void channel_gossip_channel_reestablished(struct channel *channel)
 		check_channel_gossip(channel);
 		return;
 	case CGOSSIP_WAITING_FOR_MATCHING_PEER_SIGS:
-		send_channel_announce_sigs(channel);
+		send_channel_announce_sigs_once(channel);
 		/* fall thru */
 	case CGOSSIP_PRIVATE:
 	case CGOSSIP_WAITING_FOR_ANNOUNCE_DEPTH:

lightningd/channel_gossip.h

@@ -43,7 +43,8 @@ void channel_gossip_update_from_gossipd(struct channel *channel,
 void channel_gossip_init_done(struct lightningd *ld);
 
 /* Peer has connected and successfully reestablished channel. */
-void channel_gossip_channel_reestablished(struct channel *channel);
+void channel_gossip_channel_reestablished(struct channel *channel,
+					  bool announcement_sigs_requested);
 
 /* Peer has disconnected */
 void channel_gossip_channel_disconnect(struct channel *channel);

tests/plugins/channeld_fakenet.c

@@ -1167,7 +1167,7 @@ static struct channel *handle_init(struct info *info, const u8 *init_msg)
 	channel->htlcs = htlc_map;
 
 	status_debug("Created channel");
-	daemon_conn_send(info->dc, take(towire_channeld_reestablished(NULL)));
+	daemon_conn_send(info->dc, take(towire_channeld_reestablished(NULL, false)));
 
 	return channel;
 }

wallet/test/run-wallet.c

@@ -380,6 +380,9 @@ bool fromwire_onchaind_dev_memleak_reply(const void *p UNNEEDED, bool *leak UNNE
 bool fromwire_openingd_dev_memleak_reply(const void *p UNNEEDED, bool *leak UNNEEDED)
 { fprintf(stderr, "fromwire_openingd_dev_memleak_reply called!\n"); abort(); }
 /* Generated stub for get_network_blockheight */
+bool fromwire_channeld_reestablished(const void *p UNNEEDED, bool *leak UNNEEDED)
+{ fprintf(stderr, "fromwire_channeld_reestablished called!\n"); abort(); }
+/* Generated stub for get_network_blockheight */
 u32 get_network_blockheight(const struct chain_topology *topo UNNEEDED)
 { fprintf(stderr, "get_network_blockheight called!\n"); abort(); }
 /* Generated stub for hash_cid */