renepay: add information decay linear in time

Signed-off-by: Lagrang3 <eduardo.quintana@pm.me>

plugins/renepay/flow.c

@@ -15,6 +15,9 @@
 #define SUPERVERBOSE_ENABLED 1
 #endif
 
+#define MAX(x, y) (((x) > (y)) ? (x) : (y))
+#define MIN(x, y) (((x) < (y)) ? (x) : (y))
+
 bool chan_extra_is_busy(struct chan_extra const * const ce)
 {
 	if(ce==NULL)return false;
@@ -277,7 +280,8 @@ static void chan_extra_relax_(
 	if(!amount_msat_sub(&new_a,ce->half[dir].known_min,down))
 		new_a = AMOUNT_MSAT(0);
 	if(!amount_msat_add(&new_b,ce->half[dir].known_max,up))
-		new_b = amount_msat_min(new_b,ce->capacity);
+		new_b = ce->capacity;
+	new_b = amount_msat_min(new_b,ce->capacity);
 
 	ce->half[dir].known_min = new_a;
 	ce->half[dir].known_max = new_b;
@@ -301,6 +305,23 @@ void chan_extra_relax(
 	chan_extra_relax_(ce,dir,x,y);
 }
 
+/* Forget the channel information by a fraction of the capacity. */
+void chan_extra_relax_fraction(
+		struct chan_extra* ce,
+		double fraction)
+{
+	fraction = fabs(fraction); // this number is always non-negative
+	fraction = MIN(1.0,fraction); // this number cannot be greater than 1.
+	struct amount_msat delta = amount_msat(ce->capacity.millisatoshis * fraction); /* Raw: get a fraction of the capacity */
+
+	/* The direction here is not important because the 'down' and the 'up'
+	 * limits are changed by the same amount.
+	 * Notice that if chan[0] with capacity C changes from (a,b) to (a-d,b+d)
+	 * then its counterpart chan[1] changes from (C-b,C-a) to (C-b-d,C-a+d),
+	 * hence both dirs are applied the same transformation. */
+	chan_extra_relax_(ce,/*dir=*/0,delta,delta);
+}
+
 
 /* Returns either NULL, or an entry from the hash */
 struct chan_extra_half *

plugins/renepay/flow.h

@@ -178,6 +178,11 @@ void chan_extra_relax(struct chan_extra_map *chan_extra_map,
 		      struct amount_msat down,
 		      struct amount_msat up);
 
+/* Forget the channel information by a fraction of the capacity. */
+void chan_extra_relax_fraction(
+		struct chan_extra* ce,
+		double fraction);
+
 
 /* Returns either NULL, or an entry from the hash */
 struct chan_extra_half *get_chan_extra_half_by_scid(struct chan_extra_map *chan_extra_map,

plugins/renepay/pay.c

@@ -93,6 +93,7 @@ static const char *init(struct plugin *p,
 	pay_plugin->ctx = notleak_with_children(tal(p,tal_t));
 	pay_plugin->plugin = p;
 	pay_plugin->rexmit_timer=NULL;
+	pay_plugin->last_time = 0;
 
 	rpc_scan(p, "getinfo", take(json_out_obj(NULL, NULL, NULL)),
 		 "{id:%}", JSON_SCAN(json_to_node_id, &pay_plugin->my_id));
@@ -731,6 +732,7 @@ static struct command_result *json_paystatus(struct command *cmd,
 	return command_finished(cmd, ret);
 }
 
+
 /* Taken from ./plugins/pay.c
  *
  * We are interested in any prior attempts to pay this payment_hash /
@@ -1177,10 +1179,10 @@ static struct command_result *json_pay(struct command *cmd,
 	}
 	tal_free(maxfee);
 
-	if (time_now().ts.tv_sec > invexpiry)
+	const u64 now_sec = time_now().ts.tv_sec;
+	if (now_sec > invexpiry)
 		return renepay_fail(renepay, PAY_INVOICE_EXPIRED, "Invoice expired");
 
-
 	/* To construct the uncertainty network we need to perform the following
 	 * steps:
 	 * 1. check that there is a 1-to-1 map between channels in gossmap
@@ -1199,6 +1201,16 @@ static struct command_result *json_pay(struct command *cmd,
 					   pay_plugin->chan_extra_map);
 
 
+	/* TODO(eduardo): We use a linear function to decide how to decay the
+	 * channel information. Other shapes could be used.
+	 * Also the choice of the proportional parameter TIMER_FORGET_SEC is
+	 * arbitrary.
+	 * Another idea is to measure time in blockheight. */
+	const double fraction = (now_sec - pay_plugin->last_time)*1.0/TIMER_FORGET_SEC;
+	uncertainty_network_relax_fraction(pay_plugin->chan_extra_map,
+					   fraction);
+	pay_plugin->last_time = now_sec;
+
 	// TODO(eduardo): are there route hints for B12?
 	// Add any extra hidden channel revealed by the routehints to the uncertainty network.
 	if(invstr_is_b11)
@@ -1218,12 +1230,6 @@ static struct command_result *json_pay(struct command *cmd,
 
 	json_add_sha256(req->js, "payment_hash", &p->payment_hash);
 	return send_outreq(cmd->plugin, req);
-
-	// TODO(eduardo):
-	// - get time since last payment,
-	// - forget a portion of the bounds
-	// - note that if sufficient time has passed, then we would forget
-	// everything use TIMER_FORGET_SEC.
 }
 
 static void handle_sendpay_failure_renepay(

plugins/renepay/pay.h

@@ -94,6 +94,10 @@ struct pay_plugin {
 	// sendpays.
 	/* Timers. */
 	struct plugin_timer *rexmit_timer;
+
+	/* It allows us to measure elapsed time
+	 * and forget channel information accordingly. */
+	u64 last_time;
 };
 
 /* Set in init */

plugins/renepay/uncertainty_network.c

@@ -346,3 +346,17 @@ bool uncertainty_network_update_from_listpeerchannels(
 malformed:
 	return false;
 }
+
+/* Forget ALL channels information by a fraction of the capacity. */
+void uncertainty_network_relax_fraction(
+		struct chan_extra_map* chan_extra_map,
+		double fraction)
+{
+	struct chan_extra_map_iter it;
+	for(struct chan_extra *ce=chan_extra_map_first(chan_extra_map,&it);
+	    ce;
+	    ce=chan_extra_map_next(chan_extra_map,&it))
+	{
+		chan_extra_relax_fraction(ce,fraction);
+	}
+}

plugins/renepay/uncertainty_network.h

@@ -44,4 +44,9 @@ bool uncertainty_network_update_from_listpeerchannels(
 		const char *buf,
 		const jsmntok_t *toks);
 
+/* Forget ALL channels information by a fraction of the capacity. */
+void uncertainty_network_relax_fraction(
+		struct chan_extra_map* chan_extra_map,
+		double fraction);
+
 #endif /* LIGHTNING_PLUGINS_RENEPAY_UNCERTAINTY_NETWORK_H */