gossipd: provide (stripped) channel_update when resolving a channel.

I hadn't realized that lightningd asks gossipd every time we forward
a payment.  But I'm going to abuse it here to get the latest channel_update,
otherwise (as lightningd takes over error message generation) lightningd
needs to do an async request at various painful points.

So have gossipd tell us the lastest update (stripped so compatible with
the strange in-onion-error format).

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

gossipd/gossip_wire.csv

@@ -80,6 +80,8 @@ msgdata,gossip_get_channel_peer,channel_id,short_channel_id,
 
 msgtype,gossip_get_channel_peer_reply,3109
 msgdata,gossip_get_channel_peer_reply,peer_id,?node_id,
+msgdata,gossip_get_channel_peer_reply,stripped_update_len,u16,
+msgdata,gossip_get_channel_peer_reply,stripped_update,u8,stripped_update_len
 
 # gossipd->master: we're closing this channel.
 msgtype,gossip_local_channel_close,3027

gossipd/gossipd.c

@@ -1342,6 +1342,7 @@ static struct io_plan *get_channel_peer(struct io_conn *conn,
 	struct short_channel_id scid;
 	struct local_chan *local_chan;
 	const struct node_id *key;
+	const u8 *stripped_update;
 
 	if (!fromwire_gossip_get_channel_peer(msg, &scid))
 		master_badmsg(WIRE_GOSSIP_GET_CHANNEL_PEER, msg);
@@ -1351,11 +1352,28 @@ static struct io_plan *get_channel_peer(struct io_conn *conn,
 		status_debug("Failed to resolve local channel %s",
 			     type_to_string(tmpctx, struct short_channel_id, &scid));
 		key = NULL;
+		stripped_update = NULL;
 	} else {
+		const struct half_chan *hc;
+
 		key = &local_chan->chan->nodes[!local_chan->direction]->id;
+		/* Since we're going to use it, make sure it's up-to-date. */
+		refresh_local_channel(daemon, local_chan, false);
+
+		hc = &local_chan->chan->half[local_chan->direction];
+		if (is_halfchan_defined(hc)) {
+			const u8 *update;
+
+			update = gossip_store_get(tmpctx, daemon->rstate->gs,
+						  hc->bcast.index);
+			stripped_update = tal_dup_arr(tmpctx, u8, update + 2,
+						      tal_count(update) - 2, 0);
+		} else
+			stripped_update = NULL;
 	}
 	daemon_conn_send(daemon->master,
-			 take(towire_gossip_get_channel_peer_reply(NULL, key)));
+			 take(towire_gossip_get_channel_peer_reply(NULL, key,
+							   stripped_update)));
 	return daemon_conn_read_next(conn, daemon->master);
 }
 

lightningd/channel.c

@@ -265,6 +265,7 @@ struct channel *new_channel(struct peer *peer, u64 dbid,
 		= tal_steal(channel, remote_upfront_shutdown_script);
 	channel->option_static_remotekey = option_static_remotekey;
 	channel->forgets = tal_arr(channel, struct command *, 0);
+	channel->stripped_update = NULL;
 
 	list_add_tail(&peer->channels, &channel->list);
 	tal_add_destructor(channel, destroy_channel);

lightningd/channel.h

@@ -123,6 +123,9 @@ struct channel {
 
 	/* Any commands trying to forget us. */
 	struct command **forgets;
+
+	/* Lastest channel_update from gossipd, if any: type stripped! */
+	const u8 *stripped_update;
 };
 
 struct channel *new_channel(struct peer *peer, u64 dbid,

lightningd/peer_htlcs.c

@@ -510,6 +510,7 @@ static void forward_htlc(struct htlc_in *hin,
 			 struct amount_msat amt_to_forward,
 			 u32 outgoing_cltv_value,
 			 const struct node_id *next_hop,
+			 const u8 *stripped_update TAKES,
 			 const u8 next_onion[TOTAL_PACKET_SIZE])
 {
 	enum onion_type failcode;
@@ -525,9 +526,17 @@ static void forward_htlc(struct htlc_in *hin,
 					 hin, next ? next->scid : NULL, NULL,
 					 FORWARD_LOCAL_FAILED,
 					 hin->failcode);
+		if (taken(stripped_update))
+			tal_free(stripped_update);
 		return;
 	}
 
+	/* OK, apply any channel_update gossipd gave us for this channel. */
+	tal_free(next->stripped_update);
+	next->stripped_update
+			= tal_dup_arr(next, u8, stripped_update,
+				      tal_count(stripped_update), 0);
+
 	/* BOLT #7:
 	 *
 	 * The origin node:
@@ -627,8 +636,10 @@ static void channel_resolve_reply(struct subd *gossip, const u8 *msg,
 				  const int *fds UNUSED, struct gossip_resolve *gr)
 {
 	struct node_id *peer_id;
+	u8 *stripped_update;
 
-	if (!fromwire_gossip_get_channel_peer_reply(msg, msg, &peer_id)) {
+	if (!fromwire_gossip_get_channel_peer_reply(msg, msg, &peer_id,
+						    &stripped_update)) {
 		log_broken(gossip->log,
 			   "bad fromwire_gossip_get_channel_peer_reply %s",
 			   tal_hex(msg, msg));
@@ -647,6 +658,7 @@ static void channel_resolve_reply(struct subd *gossip, const u8 *msg,
 
 	forward_htlc(gr->hin, gr->hin->cltv_expiry,
 		     gr->amt_to_forward, gr->outgoing_cltv_value, peer_id,
+		     take(stripped_update),
 		     gr->next_onion);
 	tal_free(gr);
 }

wallet/test/run-wallet.c

@@ -116,7 +116,7 @@ bool fromwire_connect_peer_connected(const tal_t *ctx UNNEEDED, const void *p UN
 bool fromwire_custommsg_in(const tal_t *ctx UNNEEDED, const void *p UNNEEDED, u8 **msg UNNEEDED)
 { fprintf(stderr, "fromwire_custommsg_in called!\n"); abort(); }
 /* Generated stub for fromwire_gossip_get_channel_peer_reply */
-bool fromwire_gossip_get_channel_peer_reply(const tal_t *ctx UNNEEDED, const void *p UNNEEDED, struct node_id **peer_id UNNEEDED)
+bool fromwire_gossip_get_channel_peer_reply(const tal_t *ctx UNNEEDED, const void *p UNNEEDED, struct node_id **peer_id UNNEEDED, u8 **stripped_update UNNEEDED)
 { fprintf(stderr, "fromwire_gossip_get_channel_peer_reply called!\n"); abort(); }
 /* Generated stub for fromwire_hsm_sign_commitment_tx_reply */
 bool fromwire_hsm_sign_commitment_tx_reply(const void *p UNNEEDED, struct bitcoin_signature *sig UNNEEDED)