From 30bf6706b7738779f5dd920a8c22a6d340854792 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Tue, 20 Oct 2020 14:28:06 +1030
Subject: [PATCH] route: return NULL if destination is unreachable.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 common/route.c      | 8 ++++++--
 common/route.h      | 5 +++--
 devtools/route.c    | 2 +-
 devtools/topology.c | 2 +-
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/common/route.c b/common/route.c
index e734a3cbe..e07737138 100644
--- a/common/route.c
+++ b/common/route.c
@@ -61,16 +61,20 @@ u64 route_score_cheaper(u32 distance,
 	return (costs << 32) + distance;
 }
 
-struct route **route_from_dijkstra(const struct gossmap *map,
+struct route **route_from_dijkstra(const tal_t *ctx,
+				   const struct gossmap *map,
 				   const struct dijkstra *dij,
 				   const struct gossmap_node *cur)
 {
-	struct route **path = tal_arr(map, struct route *, 0);
+	struct route **path = tal_arr(ctx, struct route *, 0);
 	u32 curidx = gossmap_node_idx(map, cur);
 
 	while (dijkstra_distance(dij, curidx) != 0) {
 		struct route *r;
 
+		if (dijkstra_distance(dij, curidx) == UINT_MAX)
+			return tal_free(path);
+
 		r = tal(path, struct route);
 		r->c = dijkstra_best_chan(dij, curidx);
 		if (r->c->half[0].nodeidx == curidx) {
diff --git a/common/route.h b/common/route.h
index b864c23d1..78631670a 100644
--- a/common/route.h
+++ b/common/route.h
@@ -36,8 +36,9 @@ u64 route_score_cheaper(u32 distance,
 			struct amount_msat cost,
 			struct amount_msat risk);
 
-/* Extract route tal_arr from completed dijkstra */
-struct route **route_from_dijkstra(const struct gossmap *map,
+/* Extract route tal_arr from completed dijkstra: NULL if none. */
+struct route **route_from_dijkstra(const tal_t *ctx,
+				   const struct gossmap *map,
 				   const struct dijkstra *dij,
 				   const struct gossmap_node *cur);
 #endif /* LIGHTNING_COMMON_ROUTE_H */
diff --git a/devtools/route.c b/devtools/route.c
index 91d54f6af..ffca5d458 100644
--- a/devtools/route.c
+++ b/devtools/route.c
@@ -69,7 +69,7 @@ static struct route **least_cost(struct gossmap *map,
 		return NULL;
 	}
 
-	path = route_from_dijkstra(map, dij, src);
+	path = route_from_dijkstra(map, map, dij, src);
 	printf("# path length %zu\n", tal_count(path));
 	/* We don't pay fee on first hop! */
 	if (!amount_msat_sub(&fee,
diff --git a/devtools/topology.c b/devtools/topology.c
index e2eb2d9ff..2965fb73e 100644
--- a/devtools/topology.c
+++ b/devtools/topology.c
@@ -209,7 +209,7 @@ static bool measure_least_cost(struct gossmap *map,
 		return false;
 	}
 
-	path = route_from_dijkstra(map, dij, src);
+	path = route_from_dijkstra(map, map, dij, src);
 	printf("# path length %zu\n", tal_count(path));
 	if (!amount_msat_sub(&fee, dijkstra_amount(dij, srcidx), sent))
 		abort();