From 6815a1d9a285e7f6299dec6b7bb07af5396703ff Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Wed, 26 Aug 2020 10:10:48 +0930
Subject: [PATCH] common/route: routing helpers built on gossmap and dijksra.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 common/Makefile |   1 +
 common/route.c  | 102 ++++++++++++++++++++++++++++++++++++++++++++++++
 common/route.h  |  49 +++++++++++++++++++++++
 3 files changed, 152 insertions(+)
 create mode 100644 common/route.c
 create mode 100644 common/route.h

diff --git a/common/Makefile b/common/Makefile
index 6096266cb..b75e89a75 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -61,6 +61,7 @@ COMMON_SRC_NOGEN :=				\
 	common/pseudorand.c			\
 	common/random_select.c			\
 	common/read_peer_msg.c			\
+	common/route.c				\
 	common/setup.c				\
 	common/socket_close.c			\
 	common/sphinx.c				\
diff --git a/common/route.c b/common/route.c
new file mode 100644
index 000000000..a3ae3ac01
--- /dev/null
+++ b/common/route.c
@@ -0,0 +1,102 @@
+#include <assert.h>
+#include <ccan/err/err.h>
+#include <ccan/tal/str/str.h>
+#include <ccan/time/time.h>
+#include <common/dijkstra.h>
+#include <common/gossmap.h>
+#include <common/node_id.h>
+#include <common/pseudorand.h>
+#include <common/random_select.h>
+#include <common/route.h>
+#include <common/type_to_string.h>
+#include <inttypes.h>
+#include <stdio.h>
+
+bool route_can_carry_even_disabled(const struct gossmap *map,
+				   const struct gossmap_chan *c,
+				   int dir,
+				   struct amount_msat amount,
+				   void *unused)
+{
+	if (!gossmap_chan_set(c, dir))
+		return false;
+	if (!gossmap_chan_capacity(c, dir, amount))
+		return false;
+	return true;
+}
+
+/* Generally only one side gets marked disabled, but it's disabled. */
+bool route_can_carry(const struct gossmap *map,
+		       const struct gossmap_chan *c,
+		       int dir,
+		       struct amount_msat amount,
+		       void *arg)
+{
+	if (!c->half[dir].enabled || !c->half[!dir].enabled)
+		return false;
+	return route_can_carry_even_disabled(map, c, dir, amount, arg);
+}
+
+bool route_path_shorter(u32 old_distance, u32 new_distance,
+			struct amount_msat old_cost,
+			struct amount_msat new_cost,
+			struct amount_msat old_risk,
+			struct amount_msat new_risk,
+			void *unused)
+{
+	if (new_distance > old_distance)
+		return false;
+	if (new_distance < old_distance)
+		return true;
+
+	/* Tiebreak by cost */
+	if (!amount_msat_add(&old_cost, old_cost, old_risk)
+	    || !amount_msat_add(&new_cost, new_cost, new_risk))
+		return false;
+	return amount_msat_less(new_cost, old_cost);
+}
+
+bool route_path_cheaper(u32 old_distance, u32 new_distance,
+			struct amount_msat old_cost,
+			struct amount_msat new_cost,
+			struct amount_msat old_risk,
+			struct amount_msat new_risk,
+			void *unused)
+{
+	if (!amount_msat_add(&old_cost, old_cost, old_risk)
+	    || !amount_msat_add(&new_cost, new_cost, new_risk))
+		return false;
+
+	if (amount_msat_greater(new_cost, old_cost))
+		return false;
+	if (amount_msat_less(new_cost, old_cost))
+		return true;
+
+	/* Tiebreak by distance */
+	return new_distance < old_distance;
+}
+
+struct route **route_from_dijkstra(const struct gossmap *map,
+				   const struct dijkstra *dij,
+				   const struct gossmap_node *cur)
+{
+	struct route **path = tal_arr(map, struct route *, 0);
+	u32 curidx = gossmap_node_idx(map, cur);
+
+	while (dijkstra_distance(dij, curidx) != 0) {
+		struct route *r;
+
+		r = tal(path, struct route);
+		r->c = dijkstra_best_chan(dij, curidx);
+		if (r->c->half[0].nodeidx == curidx) {
+			r->dir = 0;
+		} else {
+			assert(r->c->half[1].nodeidx == curidx);
+			r->dir = 1;
+		}
+		tal_arr_expand(&path, r);
+		cur = gossmap_nth_node(map, r->c, !r->dir);
+		curidx = gossmap_node_idx(map, cur);
+	}
+	return path;
+}
diff --git a/common/route.h b/common/route.h
new file mode 100644
index 000000000..fdb7c02d1
--- /dev/null
+++ b/common/route.h
@@ -0,0 +1,49 @@
+/* Routing helpers for use with dijkstra */
+#ifndef LIGHTNING_COMMON_ROUTE_H
+#define LIGHTNING_COMMON_ROUTE_H
+#include "config.h"
+#include <common/amount.h>
+
+struct dijkstra;
+struct gossmap;
+
+struct route {
+	int dir;
+	struct gossmap_chan *c;
+};
+
+/* Can c carrt amount in dir? */
+bool route_can_carry(const struct gossmap *map,
+		     const struct gossmap_chan *c,
+		     int dir,
+		     struct amount_msat amount,
+		     void *arg);
+
+/* Same, but ignore disabled flags on channel */
+bool route_can_carry_even_disabled(const struct gossmap *map,
+				   const struct gossmap_chan *c,
+				   int dir,
+				   struct amount_msat amount,
+				   void *unused);
+
+/* Shortest path, with lower amount tiebreak */
+bool route_path_shorter(u32 old_distance, u32 new_distance,
+			struct amount_msat old_cost,
+			struct amount_msat new_cost,
+			struct amount_msat old_risk,
+			struct amount_msat new_risk,
+			void *unused);
+
+/* Cheapest path, with shorter path tiebreak */
+bool route_path_cheaper(u32 old_distance, u32 new_distance,
+			struct amount_msat old_cost,
+			struct amount_msat new_cost,
+			struct amount_msat old_risk,
+			struct amount_msat new_risk,
+			void *unused);
+
+/* Extract route tal_arr from completed dijkstra */
+struct route **route_from_dijkstra(const struct gossmap *map,
+				   const struct dijkstra *dij,
+				   const struct gossmap_node *cur);
+#endif /* LIGHTNING_COMMON_ROUTE_H */