gossipd: tell lightningd about all our previous channel_updates at startup.

This will at least *help* the case where these were not populated, causing us
to send errors without channel_updated appended.

It's not perfect: we can still send such errors if the gossip store is
corrupted, and we still send them for private channels, but it should
help.

(The much better fix is far more invasive, so slips to next release!)

Signed-off-by: Rusty Russell <[email protected]>
Fixes: #5822

Author: rustyrussell

gossipd/gossipd.c

@@ -747,6 +747,42 @@ static void gossip_refresh_network(struct daemon *daemon)
 	route_prune(daemon->rstate);
 }
 
+static void tell_master_local_cupdates(struct daemon *daemon)
+{
+	struct chan_map_iter i;
+	struct chan *c;
+	struct node *me;
+
+	me = get_node(daemon->rstate, &daemon->id);
+	if (!me)
+		return;
+
+	for (c = first_chan(me, &i); c; c = next_chan(me, &i)) {
+		struct half_chan *hc;
+		int direction;
+		const u8 *cupdate;
+
+		/* We don't provide update_channel for unannounced channels */
+		if (!is_chan_public(c))
+			continue;
+
+		if (!local_direction(daemon->rstate, c, &direction))
+			continue;
+
+		hc = &c->half[direction];
+		if (!is_halfchan_defined(hc))
+			continue;
+
+		cupdate = gossip_store_get(tmpctx,
+					   daemon->rstate->gs,
+					   hc->bcast.index);
+		daemon_conn_send(daemon->master,
+				 take(towire_gossipd_init_cupdate(NULL,
+								  &c->scid,
+								  cupdate)));
+	}
+}
+
 /* Disables all channels connected to our node. */
 static void gossip_disable_local_channels(struct daemon *daemon)
 {
@@ -851,6 +887,10 @@ static void gossip_init(struct daemon *daemon, const u8 *msg)
 					   maybe_send_query_responses, daemon);
 	tal_add_destructor(daemon->connectd, master_or_connectd_gone);
 
+	/* Tell it about all our local (public) channel_update messages,
+	 * so it doesn't unnecessarily regenerate them. */
+	tell_master_local_cupdates(daemon);
+
 	/* OK, we are ready. */
 	daemon_conn_send(daemon->master,
 			 take(towire_gossipd_init_reply(NULL)));
@@ -1143,6 +1183,7 @@ static struct io_plan *recv_req(struct io_conn *conn,
 #endif /* !DEVELOPER */
 
 	/* We send these, we don't receive them */
+	case WIRE_GOSSIPD_INIT_CUPDATE:
 	case WIRE_GOSSIPD_INIT_REPLY:
 	case WIRE_GOSSIPD_GET_TXOUT:
 	case WIRE_GOSSIPD_DEV_MEMLEAK_REPLY:

gossipd/gossipd_wire.csv

@@ -18,6 +18,12 @@ msgdata,gossipd_init,dev_fast_gossip,bool,
 msgdata,gossipd_init,dev_fast_gossip_prune,bool,
 msgdata,gossipd_init,ip_discovery,u32,
 
+# Gossipd tells us all our public channel_udpates before init_reply.
+msgtype,gossipd_init_cupdate,3101
+msgdata,gossipd_init_cupdate,scid,short_channel_id,
+msgdata,gossipd_init_cupdate,len,u16,
+msgdata,gossipd_init_cupdate,cupdate,u8,len
+
 msgtype,gossipd_init_reply,3100
 
 # In developer mode, we can mess with time.

lightningd/gossip_control.c

@@ -109,6 +109,33 @@ static void get_txout(struct subd *gossip, const u8 *msg)
 	}
 }
 
+static void handle_init_cupdate(struct lightningd *ld, const u8 *msg)
+{
+	struct short_channel_id scid;
+	u8 *update;
+	struct channel *channel;
+
+	if (!fromwire_gossipd_init_cupdate(msg, msg, &scid, &update)) {
+		fatal("Gossip gave bad GOSSIPD_INIT_CUPDATE %s",
+		      tal_hex(msg, msg));
+	}
+
+	/* In theory this could vanish before gossipd gets around to telling
+	 * us. */
+	channel = any_channel_by_scid(ld, &scid, true);
+	if (!channel) {
+		log_unusual(ld->log, "init_cupdate for bad scid %s",
+			    type_to_string(tmpctx, struct short_channel_id,
+					   &scid));
+		return;
+	}
+
+	/* This should only happen on initialization, *but* gossipd also
+	 * disabled channels on startup, so that can set this first. */
+	if (!channel->channel_update)
+		channel->channel_update = tal_steal(channel, update);
+}
+
 static void handle_local_channel_update(struct lightningd *ld, const u8 *msg)
 {
 	struct short_channel_id scid;
@@ -177,6 +204,9 @@ static unsigned gossip_msg(struct subd *gossip, const u8 *msg, const int *fds)
 	case WIRE_GOSSIPD_DISCOVERED_IP:
 		break;
 
+	case WIRE_GOSSIPD_INIT_CUPDATE:
+		handle_init_cupdate(gossip->ld, msg);
+		break;
 	case WIRE_GOSSIPD_GET_TXOUT:
 		get_txout(gossip, msg);
 		break;