renepay: bugfix reading pending sendpays

When renepay starts, one of the first operations it does is to check for
pending sendpays for the same invoice. Those are added up to an internal
database to keep track of. Also the amount they deliver to the
destination is computed so that the current payment rpc call would try
to complete the payment for whatever amount remains to pay.
For an incomplete payment after calling the RPC renepay I found this in
the logs:

2024-05-22T19:44:19.853Z DEBUG   plugin-cln-renepay: There are pending sendpays to this invoice. groupid = 6 delivering = 0msat, last_partid = 10

Where delivering should be the sum of the amounts delivered by pending routes.

Author: Lagrang3

plugins/renepay/mods.c

@@ -253,6 +253,18 @@ static struct command_result *previous_sendpays_done(struct command *cmd,
 		// max_partid for the pending_group_id
 		payment->next_partid = max_pending_partid + 1;
 
+		for (size_t j = 0; j < tal_count(pending_routes); j++) {
+			route_pending_register(payment->routetracker,
+					       pending_routes[j]);
+		}
+		if (!routetracker_get_amount(payment->routetracker,
+					     &payment->total_delivering,
+					     &payment->total_sent))
+			plugin_err(pay_plugin->plugin,
+				   "(%s:%d) routetracker_get_amount failed "
+				   "probably due to an amount_msat overflow.",
+				   __PRETTY_FUNCTION__, __LINE__);
+
 		plugin_log(pay_plugin->plugin, LOG_DBG,
 			   "There are pending sendpays to this invoice. "
 			   "groupid = %" PRIu32 " "
@@ -271,12 +283,6 @@ static struct command_result *previous_sendpays_done(struct command *cmd,
 			    "Payment is pending with full amount "
 			    "already commited");
 		}
-
-		for (size_t j = 0; j < tal_count(pending_routes); j++) {
-			route_pending_register(payment->routetracker,
-					       pending_routes[j]);
-		}
-
 	} else {
 		/* There are no pending nor completed sendpays, get me the last
 		 * sendpay group. */

plugins/renepay/routetracker.c

@@ -134,6 +134,28 @@ void route_pending_register(struct routetracker *routetracker,
 	}
 }
 
+bool routetracker_get_amount(struct routetracker *routetracker,
+			     struct amount_msat *amount,
+			     struct amount_msat *amount_sent)
+{
+	assert(routetracker);
+	assert(amount);
+	assert(amount_sent);
+
+	*amount = AMOUNT_MSAT(0);
+	*amount_sent = AMOUNT_MSAT(0);
+
+	struct route_map *rmap = routetracker->pending_routes;
+	struct route_map_iter it;
+	for (struct route *r = route_map_first(rmap, &it); r;
+	     r = route_map_next(rmap, &it)) {
+		if (!amount_msat_add(amount, *amount, route_delivers(r)) ||
+		    !amount_msat_add(amount_sent, *amount_sent, route_sends(r)))
+			return false;
+	}
+	return true;
+}
+
 static void route_result_collected(struct routetracker *routetracker,
 				   struct route *route TAKES)
 {

plugins/renepay/routetracker.h

@@ -50,6 +50,11 @@ struct command_result *notification_sendpay_success(struct command *cmd,
 void route_failure_register(struct routetracker *routetracker,
 			    struct route *route);
 
+/* How much is the amount being tracked. */
+bool routetracker_get_amount(struct routetracker *routetracker,
+			     struct amount_msat *amount,
+			     struct amount_msat *amount_sent);
+
 // FIXME: double-check that we actually get one notification for each sendpay,
 // ie. that after some time we don't have yet pending sendpays for old failed or
 // successful payments that we havent processed because we haven't received the