gossipd: only broadcast channel_announcement once we have a channel_update.

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

gossipd/routing.c

@@ -635,10 +635,8 @@ bool routing_add_channel_announcement(struct routing_state *rstate,
 	/* Channel is now public. */
 	chan->channel_announce = tal_dup_arr(chan, u8, msg, tal_len(msg), 0);
 
-	/* Now we can broadcast channel announce */
-	insert_broadcast(rstate->broadcasts, chan->channel_announce);
-
-	/* Clear any private updates. */
+	/* Clear any private updates: new updates will trigger broadcast of
+	 * this channel_announce. */
 	for (size_t i = 0; i < ARRAY_SIZE(chan->half); i++)
 		chan->half[i].channel_update
 			= tal_free(chan->half[i].channel_update);
@@ -934,6 +932,7 @@ bool routing_add_channel_update(struct routing_state *rstate,
 	struct bitcoin_blkid chain_hash;
 	struct chan *chan;
 	u8 direction;
+	bool have_broadcast_announce;
 
 	if (!fromwire_channel_update(update, &signature, &chain_hash,
 				     &short_channel_id, &timestamp, &flags,
@@ -944,6 +943,10 @@ bool routing_add_channel_update(struct routing_state *rstate,
 	if (!chan)
 		return false;
 
+	/* We broadcast announce once we have one update */
+	have_broadcast_announce = is_halfchan_defined(&chan->half[0])
+		|| is_halfchan_defined(&chan->half[1]);
+
 	direction = flags & 0x1;
 	set_connection_values(chan, direction, fee_base_msat,
 			      fee_proportional_millionths, expiry,
@@ -959,6 +962,13 @@ bool routing_add_channel_update(struct routing_state *rstate,
 	if (!chan->channel_announce)
 		return true;
 
+	/* BOLT #7:
+	 *   - MUST consider whether to send the `channel_announcement` after
+	 *     receiving the first corresponding `channel_update`.
+	 */
+	if (!have_broadcast_announce)
+		insert_broadcast(rstate->broadcasts, chan->channel_announce);
+
 	insert_broadcast(rstate->broadcasts,
 			 chan->half[direction].channel_update);
 	return true;

tests/test_lightningd.py

@@ -2642,7 +2642,6 @@ class LightningDTests(BaseLightningDTests):
         for n in [l1, l2, l3]:
             wait_for(lambda: len(n.rpc.listchannels()['channels']) == 4)
 
-    @unittest.expectedFailure
     @unittest.skipIf(not DEVELOPER, "needs DEVELOPER=1")
     def test_gossip_no_empty_announcements(self):
         # Need full IO logging so we can see gossip