gossip: Consolidated direction bit computation

The direction bit was computed in several spots and was inconsistent
in some cases. Now we compute it just in routing, and once when
starting up `channeld`, this avoids recomputing it all over the place.

daemon/routing.c

@@ -258,7 +258,7 @@ struct node_connection *add_connection(struct routing_state *rstate,
 	c->active = true;
 	c->last_timestamp = 0;
 	memset(&c->short_channel_id, 0, sizeof(c->short_channel_id));
-	c->flags = pubkey_cmp(from, to) > 0;
+	c->flags = get_channel_direction(from, to);
 	return c;
 }
 
@@ -508,11 +508,11 @@ char *opt_add_route(const char *arg, struct lightningd_state *dstate)
 bool add_channel_direction(struct routing_state *rstate,
 			   const struct pubkey *from,
 			   const struct pubkey *to,
-			   const int direction,
 			   const struct short_channel_id *short_channel_id,
 			   const u8 *announcement)
 {
 	struct node_connection *c = get_connection(rstate, from, to);
+	u16 direction = get_channel_direction(from, to);
 	if (c){
 		/* Do not clobber connections added otherwise */
 		memcpy(&c->short_channel_id, short_channel_id,
@@ -677,12 +677,10 @@ void handle_channel_announcement(
 		  short_channel_id.outnum
 		);
 
-	forward |= add_channel_direction(rstate, &node_id_1,
-					 &node_id_2, 0, &short_channel_id,
-					 serialized);
-	forward |= add_channel_direction(rstate, &node_id_2,
-					 &node_id_1, 1, &short_channel_id,
-					 serialized);
+	forward |= add_channel_direction(rstate, &node_id_1, &node_id_2,
+					 &short_channel_id, serialized);
+	forward |= add_channel_direction(rstate, &node_id_2, &node_id_1,
+					 &short_channel_id, serialized);
 	if (!forward) {
 		log_debug(rstate->base_log, "Not forwarding channel_announcement");
 		tal_free(tmpctx);

daemon/routing.h

@@ -158,7 +158,6 @@ char *opt_add_route(const char *arg, struct lightningd_state *dstate);
 bool add_channel_direction(struct routing_state *rstate,
 			   const struct pubkey *from,
 			   const struct pubkey *to,
-			   const int direction,
 			   const struct short_channel_id *short_channel_id,
 			   const u8 *announcement);
 
@@ -176,4 +175,8 @@ struct route_hop *get_route(tal_t *ctx, struct routing_state *rstate,
 			    const struct pubkey *destination,
 			    const u32 msatoshi, double riskfactor);
 
+/* Utility function that, given a source and a destination, gives us
+ * the direction bit the matching channel should get */
+#define get_channel_direction(from, to) (pubkey_cmp(from, to) > 0)
+
 #endif /* LIGHTNING_DAEMON_ROUTING_H */

lightningd/channel/channel.c

@@ -8,6 +8,7 @@
 #include <ccan/structeq/structeq.h>
 #include <ccan/take/take.h>
 #include <ccan/time/time.h>
+#include <daemon/routing.h>
 #include <errno.h>
 #include <inttypes.h>
 #include <lightningd/channel.h>
@@ -66,6 +67,9 @@ struct peer {
 	struct short_channel_id short_channel_ids[NUM_SIDES];
 	secp256k1_ecdsa_signature announcement_node_sigs[NUM_SIDES];
 	secp256k1_ecdsa_signature announcement_bitcoin_sigs[NUM_SIDES];
+
+	/* Which direction of the channel do we control? */
+	u16 channel_direction;
 };
 
 static struct io_plan *gossip_client_recv(struct io_conn *conn,
@@ -97,17 +101,6 @@ static void send_announcement_signatures(struct peer *peer)
 	tal_free(tmpctx);
 }
 
-/* The direction bit is 0 if our local node-id is lexicographically
- * smaller than the remote node-id. */
-static int get_direction_bit(struct peer *peer)
-{
-	u8 local_der[33], remote_der[33];
-	/* Find out in which order we have to list the endpoints */
-	pubkey_to_der(local_der, &peer->node_ids[LOCAL]);
-	pubkey_to_der(remote_der, &peer->node_ids[REMOTE]);
-	return memcmp(local_der, remote_der, sizeof(local_der)) < 0;
-}
-
 static void send_channel_update(struct peer *peer, bool disabled)
 {
 	tal_t *tmpctx = tal_tmpctx(peer);
@@ -118,7 +111,7 @@ static void send_channel_update(struct peer *peer, bool disabled)
 	secp256k1_ecdsa_signature *sig =
 	    talz(tmpctx, secp256k1_ecdsa_signature);
 
-	flags = get_direction_bit(peer) | (disabled << 1);
+	flags = peer->channel_direction | (disabled << 1);
 	cupdate = towire_channel_update(
 	    tmpctx, sig, &peer->short_channel_ids[LOCAL], timestamp, flags, 36,
 	    1, 10, peer->channel->view[LOCAL].feerate_per_kw);
@@ -136,7 +129,7 @@ static void send_channel_announcement(struct peer *peer)
 	int first, second;
 	u8 *cannounce, *features = tal_arr(peer, u8, 0);
 
-	if (get_direction_bit(peer) == 1) {
+	if (peer->channel_direction == 0) {
 		first = LOCAL;
 		second = REMOTE;
 	} else {
@@ -271,6 +264,9 @@ static void init_channel(struct peer *peer, const u8 *msg)
 				    &points[LOCAL], &points[REMOTE],
 				    am_funder ? LOCAL : REMOTE);
 
+	peer->channel_direction = get_channel_direction(
+	    &peer->node_ids[LOCAL], &peer->node_ids[REMOTE]);
+
 	/* OK, now we can process peer messages. */
 	io_set_finish(io_new_conn(peer, PEER_FD, setup_peer_conn, peer),
 		      peer_conn_broken, peer);