gossipd: don't include private announcements into broadcast map.

Basically, if we don't have an announcement for the channel, stash it,
and once we get an announcement, replay if necessary.

Fixes: #1485
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

gossipd/gossip.c

@@ -902,7 +902,7 @@ static void handle_get_update(struct peer *peer, const u8 *msg)
 					      &scid));
 		update = NULL;
 	} else {
-		/* We want update that comes from our end. */
+		/* We want (public) update that comes from our end. */
 		if (pubkey_eq(&chan->nodes[0]->id, &peer->daemon->id))
 			update = get_broadcast(rstate->broadcasts,
 					       chan->half[0]

gossipd/routing.c

@@ -194,6 +194,7 @@ static void init_half_chan(struct routing_state *rstate,
 	struct half_chan *c = &chan->half[idx];
 
 	c->channel_update_msgidx = 0;
+	c->private_update = NULL;
 	c->unroutable_until = 0;
 	c->active = false;
 	c->flags = idx;
@@ -641,6 +642,17 @@ bool routing_add_channel_announcement(struct routing_state *rstate,
 			      old_msgidx, chan->channel_announce_msgidx);
 		return false;
 	}
+
+	/* If we have previously private updates for channels, process now */
+	for (size_t i = 0; i < ARRAY_SIZE(chan->half); i++) {
+		const u8 *update = chan->half[i].private_update;
+
+		if (update) {
+			chan->half[i].private_update = NULL;
+			routing_add_channel_update(rstate, take(update));
+		}
+	}
+
 	return true;
 }
 
@@ -948,6 +960,15 @@ bool routing_add_channel_update(struct routing_state *rstate,
 			      (flags & ROUTING_FLAGS_DISABLED) == 0, timestamp,
 			      htlc_minimum_msat);
 
+	/* For private channels, we get updates without an announce: don't
+	 * broadcast them! */
+	if (chan->channel_announce_msgidx == 0) {
+		tal_free(chan->half[direction].private_update);
+		chan->half[direction].private_update
+			= tal_dup_arr(chan, u8, update, tal_len(update), 0);
+		return true;
+	}
+
 	replace_broadcast(chan, rstate->broadcasts,
 			  &chan->half[direction].channel_update_msgidx,
 			  update);

gossipd/routing.h

@@ -37,6 +37,9 @@ struct half_chan {
 	/* Cached `channel_update` we might forward to new peers (or 0) */
 	u64 channel_update_msgidx;
 
+	/* If it's a private update, it's not in the broadcast map. */
+	const u8 *private_update;
+
 	/* If greater than current time, this connection should not
 	 * be used for routing. */
 	time_t unroutable_until;