routing: Skip channels that don't have sufficient capacity

We know the total channel capacity after checking for its existence on-chain, so
we can actually make use of that information to discard channels that don't have
a sufficient capacity anyway, reducing the number of failed attempts.

gossipd/routing.c

@@ -389,15 +389,21 @@ static void bfg_one_edge(struct node *node,
 		/* FIXME: Bias against smaller channels. */
 		u64 fee;
 		u64 risk;
+		u64 requiredcap;
 
 		if (node->bfg[h].total == INFINITE)
 			continue;
 
 		fee = connection_fee(c, node->bfg[h].total) * fee_scale;
-		risk = node->bfg[h].risk + risk_fee(node->bfg[h].total + fee,
-						    c->delay, riskfactor);
+		requiredcap = node->bfg[h].total + fee;
+		risk = node->bfg[h].risk +
+		       risk_fee(requiredcap, c->delay, riskfactor);
 
-		if (node->bfg[h].total + fee + risk >= MAX_MSATOSHI) {
+		if (requiredcap > chan->satoshis * 1000) {
+			/* Skip this edge if the channel has insufficient
+			 * capacity to route the required amount */
+			continue;
+		} else if (requiredcap + risk >= MAX_MSATOSHI) {
 			SUPERVERBOSE("...extreme %"PRIu64
 				     " + fee %"PRIu64
 				     " + risk %"PRIu64" ignored",
@@ -407,13 +413,13 @@ static void bfg_one_edge(struct node *node,
 
 		/* nodes[0] is src for connections[0] */
 		src = chan->nodes[idx];
-		if (node->bfg[h].total + fee + risk
-		    < src->bfg[h+1].total + src->bfg[h+1].risk) {
+		if (requiredcap + risk <
+		    src->bfg[h + 1].total + src->bfg[h + 1].risk) {
 			SUPERVERBOSE("...%s can reach here in hoplen %zu total %"PRIu64,
 				     type_to_string(trc, struct pubkey,
 						    &src->id),
 				     h, node->bfg[h].total + fee);
-			src->bfg[h+1].total = node->bfg[h].total + fee;
+			src->bfg[h+1].total = requiredcap;
 			src->bfg[h+1].risk = risk;
 			src->bfg[h+1].prev = chan;
 		}

gossipd/test/run-find_route-specific.c

@@ -110,7 +110,8 @@ static struct half_chan *
 get_or_make_connection(struct routing_state *rstate,
 		       const struct pubkey *from_id,
 		       const struct pubkey *to_id,
-		       const char *shortid)
+		       const char *shortid,
+		       const u64 satoshis)
 {
 	struct short_channel_id scid;
 	struct chan *chan;
@@ -123,6 +124,7 @@ get_or_make_connection(struct routing_state *rstate,
 
 	/* Make sure it's seen as initialized (update non-NULL). */
 	chan->half[pubkey_idx(from_id, to_id)].channel_update = (void *)chan;
+	chan->satoshis = satoshis;
 	return &chan->half[pubkey_idx(from_id, to_id)];
 }
 
@@ -169,7 +171,8 @@ int main(void)
 	rstate = new_routing_state(tmpctx, &zerohash, &a, 0);
 
 	/* [{'active': True, 'short_id': '6990:2:1/1', 'fee_per_kw': 10, 'delay': 5, 'flags': 1, 'destination': '0230ad0e74ea03976b28fda587bb75bdd357a1938af4424156a18265167f5e40ae', 'source': '02ea622d5c8d6143f15ed3ce1d501dd0d3d09d3b1c83a44d0034949f8a9ab60f06', 'last_update': 1504064344}, */
-	nc = get_or_make_connection(rstate, &c, &b, "6990:2:1");
+
+	nc = get_or_make_connection(rstate, &c, &b, "6990:2:1", 1000);
 	nc->base_fee = 0;
 	nc->proportional_fee = 10;
 	nc->delay = 5;
@@ -177,7 +180,7 @@ int main(void)
 	nc->last_timestamp = 1504064344;
 
 	/* {'active': True, 'short_id': '6989:2:1/0', 'fee_per_kw': 10, 'delay': 5, 'flags': 0, 'destination': '03c173897878996287a8100469f954dd820fcd8941daed91c327f168f3329be0bf', 'source': '0230ad0e74ea03976b28fda587bb75bdd357a1938af4424156a18265167f5e40ae', 'last_update': 1504064344}, */
-	nc = get_or_make_connection(rstate, &b, &a, "6989:2:1");
+	nc = get_or_make_connection(rstate, &b, &a, "6989:2:1", 1000);
 	nc->base_fee = 0;
 	nc->proportional_fee = 10;
 	nc->delay = 5;
@@ -185,7 +188,7 @@ int main(void)
 	nc->last_timestamp = 1504064344;
 
 	/* {'active': True, 'short_id': '6990:2:1/0', 'fee_per_kw': 10, 'delay': 5, 'flags': 0, 'destination': '02ea622d5c8d6143f15ed3ce1d501dd0d3d09d3b1c83a44d0034949f8a9ab60f06', 'source': '0230ad0e74ea03976b28fda587bb75bdd357a1938af4424156a18265167f5e40ae', 'last_update': 1504064344}, */
-	nc = get_or_make_connection(rstate, &b, &c, "6990:2:1");
+	nc = get_or_make_connection(rstate, &b, &c, "6990:2:1", 1000);
 	nc->base_fee = 0;
 	nc->proportional_fee = 10;
 	nc->delay = 5;
@@ -193,7 +196,7 @@ int main(void)
 	nc->last_timestamp = 1504064344;
 
 	/* {'active': True, 'short_id': '6989:2:1/1', 'fee_per_kw': 10, 'delay': 5, 'flags': 1, 'destination': '0230ad0e74ea03976b28fda587bb75bdd357a1938af4424156a18265167f5e40ae', 'source': '03c173897878996287a8100469f954dd820fcd8941daed91c327f168f3329be0bf', 'last_update': 1504064344}]} */
-	nc = get_or_make_connection(rstate, &a, &b, "6989:2:1");
+	nc = get_or_make_connection(rstate, &a, &b, "6989:2:1", 1000);
 	nc->base_fee = 0;
 	nc->proportional_fee = 10;
 	nc->delay = 5;
@@ -206,6 +209,16 @@ int main(void)
 	assert(channel_is_between(route[0], &a, &b));
 	assert(channel_is_between(route[1], &b, &c));
 
+
+	/* We should not be able to find a route that exceeds our own capacity */
+	route = find_route(tmpctx, rstate, &a, &c, 1000001, riskfactor, 0.0, NULL, &fee);
+	assert(!route);
+
+	/* Now test with a query that exceeds the channel capacity after adding
+	 * some fees */
+	route = find_route(tmpctx, rstate, &a, &c, 999999, riskfactor, 0.0, NULL, &fee);
+	assert(!route);
+
 	tal_free(tmpctx);
 	secp256k1_context_destroy(secp256k1_ctx);
 	return 0;

gossipd/test/run-find_route.c

@@ -121,6 +121,8 @@ static void add_connection(struct routing_state *rstate,
 	if (!chan)
 		chan = new_chan(rstate, &scid, from, to);
 
+	chan->satoshis = 100000;
+
 	c = &chan->half[pubkey_idx(from, to)];
 	/* Make sure it's seen as initialized (update non-NULL). */
 	c->channel_update = (void *)c;