From 1eb878be825d9397ce2d45983f30ad5f2eeb4060 Mon Sep 17 00:00:00 2001
From: Christian Decker <decker.christian@gmail.com>
Date: Thu, 25 Jul 2024 17:38:57 +0200
Subject: [PATCH] route: Add the total capacity to route_hops

We need to know the overall channel capacity, i.e., the amount_msat
that the channel was funded with, in order to relax the channel_hint
to refill over time.
---
 common/route.c          |  6 ++++++
 common/route.h          |  2 ++
 plugins/libplugin-pay.c | 12 +++++++++++-
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/common/route.c b/common/route.c
index 19ee2215c..06bf205a2 100644
--- a/common/route.c
+++ b/common/route.c
@@ -81,6 +81,7 @@ static bool dijkstra_to_hops(struct route_hop **hops,
 	const struct gossmap_node *next;
 	size_t num_hops = tal_count(*hops);
 	const struct half_chan *h;
+	struct amount_sat total;
 
 	if (dist == 0)
 		return true;
@@ -92,6 +93,11 @@ static bool dijkstra_to_hops(struct route_hop **hops,
 
 	/* OK, populate other fields. */
 	c = dijkstra_best_chan(dij, curidx);
+
+	gossmap_chan_get_capacity(gossmap, c, &total);
+	if (!amount_sat_to_msat(&(*hops)[num_hops].total_amount, total))
+		abort();
+
 	if (c->half[0].nodeidx == curidx) {
 		(*hops)[num_hops].direction = 0;
 	} else {
diff --git a/common/route.h b/common/route.h
index d6ea2b066..6d8936220 100644
--- a/common/route.h
+++ b/common/route.h
@@ -18,6 +18,7 @@ struct gossmap_node;
  * @direction: 0 (dest node_id < src node_id), 1 (dest node_id > src).
  * @node_id: the node_id of the destination of this hop.
  * @amount: amount to send through this hop.
+ * @total_amount: The amount the channel was funded with.
  * @delay: total cltv delay at this hop.
  */
 struct route_hop {
@@ -25,6 +26,7 @@ struct route_hop {
 	int direction;
 	struct node_id node_id;
 	struct amount_msat amount;
+	struct amount_msat total_amount;
 	u32 delay;
 };
 
diff --git a/plugins/libplugin-pay.c b/plugins/libplugin-pay.c
index 4fdad99c3..c166111fa 100644
--- a/plugins/libplugin-pay.c
+++ b/plugins/libplugin-pay.c
@@ -3215,7 +3215,15 @@ static void routehint_step_cb(struct routehints_data *d, struct payment *p)
 		routehint_pre_getroute(d, p);
 	} else if (p->step == PAYMENT_STEP_GOT_ROUTE && d->current_routehint != NULL) {
 		/* Now it's time to stitch the two partial routes together. */
-		struct amount_msat dest_amount;
+		struct amount_msat dest_amount, estimate;
+		/* We do not have the exact final amount, however we
+		 * know that we should be able to use the channel in
+		 * the routehint, so let's fake it as being 2x the
+		 * amount we want to route. */
+
+		if(!amount_msat_mul(&estimate, p->final_amount, 2))
+			abort();
+
 		struct route_info *routehint = d->current_routehint;
 		struct route_hop *prev_hop;
 		for (ssize_t i = 0; i < tal_count(routehint); i++) {
@@ -3233,6 +3241,7 @@ static void routehint_step_cb(struct routehints_data *d, struct payment *p)
 			hop.amount = dest_amount;
 			hop.delay = route_cltv(d->final_cltv, routehint + i + 1,
 					       tal_count(routehint) - i - 1);
+			hop.total_amount = estimate;
 
 			/* Should we get a failure inside the routehint we'll
 			 * need the direction so we can exclude it. Luckily
@@ -3601,6 +3610,7 @@ static void direct_pay_override(struct payment *p) {
 		p->route[0].scid = hint->scid.scid;
 		p->route[0].direction = hint->scid.dir;
 		p->route[0].node_id = *p->route_destination;
+		p->route[0].total_amount = hint->overall_capacity;
 		paymod_log(p, LOG_DBG,
 			   "Found a direct channel (%s) with sufficient "
 			   "capacity, skipping route computation.",