lightningd/opening: fix theoretical race.

We should start watching for the transaction before we send the
signature; we might miss it otherwise.  In practice, we only see
transactions as they enter a block, so it won't happen, but be
thorough.

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

lightningd/opening/opening.c

@@ -656,6 +656,20 @@ static u8 *recv_channel(struct state *state, const struct points *ours,
 		peer_failed(PEER_FD, &state->cs, NULL, WIRE_OPENING_BAD_PARAM,
 			      "could not create channel with given config");
 
+	/* Now, ask master to watch. */
+	status_trace("asking master to watch funding %s",
+		     type_to_string(trc, struct sha256_double, &state->funding_txid));
+	msg = towire_opening_accept_resp(state, &state->funding_txid);
+	wire_sync_write(REQ_FD, msg);
+
+	msg = wire_sync_read(state, REQ_FD);
+	if (!fromwire_opening_accept_finish(msg, NULL))
+		status_failed(WIRE_OPENING_BAD_PARAM,
+			      "Expected valid opening_accept_finish: %s",
+			      tal_hex(trc, msg));
+
+	status_trace("master said to finish");
+
 	/* BOLT #2:
 	 *
 	 * The recipient MUST fail the channel if `signature` is incorrect.
@@ -703,8 +717,7 @@ static u8 *recv_channel(struct state *state, const struct points *ours,
 		peer_failed(PEER_FD, &state->cs, NULL, WIRE_OPENING_PEER_WRITE_FAILED,
 			      "Writing funding_signed");
 
-	return towire_opening_accept_resp(state,
+	return towire_opening_accept_finish_resp(state,
-					  &state->funding_txid,
 						 state->funding_txout,
 						 state->remoteconf,
 						 &theirsig,

lightningd/opening/opening_control_wire.csv

@@ -44,18 +44,23 @@ opening_accept,4,max_feerate,4
 opening_accept,8,len,2
 opening_accept,10,msg,len,u8
 
-# This gives the txid of their funding tx: we're done.
+# This gives the txid of their funding tx to watch.
 opening_accept_resp,103
 opening_accept_resp,0,funding_txid,32,struct sha256_double
-opening_accept_resp,32,funding_txout,2,u16
+
-opening_accept_resp,33,their_config,36,struct channel_config
+# Acknowledge watch is in place, now can send sig.
-opening_accept_resp,69,first_commit_sig,64,secp256k1_ecdsa_signature
+opening_accept_finish,4
-opening_accept_resp,133,crypto_state,144,struct crypto_state
+
-opening_accept_resp,277,remote_fundingkey,33
+opening_accept_finish_resp,104
-opening_accept_resp,310,revocation_basepoint,33
+opening_accept_finish_resp,32,funding_txout,2,u16
-opening_accept_resp,343,payment_basepoint,33
+opening_accept_finish_resp,0,their_config,36,struct channel_config
-opening_accept_resp,376,delayed_payment_basepoint,33
+opening_accept_finish_resp,36,first_commit_sig,64,secp256k1_ecdsa_signature
-opening_accept_resp,409,their_per_commit_point,33
+opening_accept_finish_resp,100,crypto_state,144,struct crypto_state
+opening_accept_finish_resp,244,remote_fundingkey,33
+opening_accept_finish_resp,277,revocation_basepoint,33
+opening_accept_finish_resp,310,payment_basepoint,33
+opening_accept_finish_resp,343,delayed_payment_basepoint,33
+opening_accept_finish_resp,377,their_per_commit_point,33
 
 # You're OK to exit.
 opening_exit_req,99

lightningd/peer_control.c

@@ -531,13 +531,15 @@ static enum watch_result funding_depth_cb(struct peer *peer,
 					  const struct sha256_double *txid,
 					  void *unused)
 {
+	const char *txidstr = type_to_string(peer, struct sha256_double, txid);
+
+	log_debug(peer->log, "Funding tx %s depth %u of %u",
+		  txidstr, depth, peer->ld->dstate.config.anchor_confirms);
 	if (depth >= peer->ld->dstate.config.anchor_confirms) {
 		peer_set_condition(peer, "Funding tx reached depth %u", depth);
 		/* FIXME!  Start channel proper... */
 		return DELETE_WATCH;
 	}
-	log_debug(peer->log, "Funding tx depth %u of %u", depth,
-		  peer->ld->dstate.config.anchor_confirms);
 	return KEEP_WATCHING;
 }
 
@@ -642,10 +644,10 @@ static void opening_gen_funding(struct subdaemon *opening, const u8 *resp,
 		      opening_release_tx, fc);
 }
 
-static void opening_accept_response(struct subdaemon *opening, const u8 *resp,
+static void opening_accept_finish_response(struct subdaemon *opening,
+					   const u8 *resp,
 					   struct peer *peer)
 {
-	struct sha256_double funding_txid;
 	u16 funding_txout;
 	struct channel_config their_config;
 	secp256k1_ecdsa_signature first_commit_sig;
@@ -654,23 +656,47 @@ static void opening_accept_response(struct subdaemon *opening, const u8 *resp,
 		payment_basepoint, delayed_payment_basepoint,
 		their_per_commit_point;
 
-	log_debug(peer->log, "Got opening_accept_response");
+	log_debug(peer->log, "Got opening_accept_finish_response");
-	if (!fromwire_opening_accept_resp(resp, NULL,
+	if (!fromwire_opening_accept_finish_resp(resp, NULL,
-					  &funding_txid, &funding_txout,
+						 &funding_txout,
-					  &their_config, &first_commit_sig,
+						 &their_config,
-					  &crypto_state, &remote_fundingkey,
+						 &first_commit_sig,
+						 &crypto_state,
+						 &remote_fundingkey,
 						 &revocation_basepoint,
 						 &payment_basepoint,
 						 &delayed_payment_basepoint,
 						 &their_per_commit_point)) {
-		log_broken(peer->log, "bad OPENING_ACCEPT_RESP %s",
+		log_broken(peer->log, "bad OPENING_ACCEPT_FINISH_RESP %s",
 			   tal_hex(resp, resp));
 		tal_free(peer);
+		return;
 	}
 
 	/* FIXME: Start normal channel daemon... */
+}
+
+static void opening_accept_response(struct subdaemon *opening, const u8 *resp,
+				    struct peer *peer)
+{
+	struct sha256_double funding_txid;
+
+	if (!fromwire_opening_accept_resp(resp, NULL, &funding_txid)) {
+		log_broken(peer->log, "bad OPENING_ACCEPT_RESP %s",
+			   tal_hex(resp, resp));
+		tal_free(peer);
+		return;
+	}
+
+	log_debug(peer->log, "Watching funding tx %s",
+		     type_to_string(resp, struct sha256_double, &funding_txid));
 	watch_txid(peer, peer->ld->topology, peer, &funding_txid,
 		   funding_depth_cb, NULL);
+
+	/* Tell it we're watching. */
+	subdaemon_req(peer->owner, towire_opening_accept_finish(resp),
+		      -1, NULL,
+		      opening_accept_finish_response, peer);
 }
 
 static void channel_config(struct lightningd *ld,