Add route exclusion payment modifier and pay rpc exclude arg

Changelog-Added: Add `exclude` option for `pay` command to manually exclude channels or nodes when finding a route.

plugins/libplugin-pay.c

@@ -3885,3 +3885,45 @@ static void payee_incoming_limit_step_cb(void *d UNUSED, struct payment *p)
 
 REGISTER_PAYMENT_MODIFIER(payee_incoming_limit, void *, NULL,
 			  payee_incoming_limit_step_cb);
+
+static struct route_exclusions_data *
+route_exclusions_data_init(struct payment *p)
+{
+	struct route_exclusions_data *d;
+	if (p->parent != NULL) {
+		return payment_mod_route_exclusions_get_data(p->parent);
+	} else {
+		d = tal(p, struct route_exclusions_data);
+		d->exclusions = NULL;
+	}
+	return d;
+}
+
+static void route_exclusions_step_cb(struct route_exclusions_data *d,
+		struct payment *p)
+{
+	if (p->parent)
+		return payment_continue(p);
+	struct route_exclusion **exclusions = d->exclusions;
+	for (size_t i = 0; i < tal_count(exclusions); i++) {
+		struct route_exclusion *e = exclusions[i];
+		if (e->type == EXCLUDE_CHANNEL) {
+			channel_hints_update(p, e->u.chan_id.scid, e->u.chan_id.dir,
+				false, false, NULL, NULL);
+		} else {
+			if (node_id_eq(&e->u.node_id, p->destination)) {
+				payment_abort(p, "Payee is manually excluded");
+				return;
+			} else if (node_id_eq(&e->u.node_id, p->local_id)) {
+				payment_abort(p, "Payer is manually excluded");
+				return;
+			}
+
+			tal_arr_expand(&p->excluded_nodes, e->u.node_id);
+		}
+	}
+	payment_continue(p);
+}
+
+REGISTER_PAYMENT_MODIFIER(route_exclusions, struct route_exclusions_data *,
+	route_exclusions_data_init, route_exclusions_step_cb);

plugins/libplugin-pay.h

@@ -406,6 +406,10 @@ struct adaptive_split_mod_data {
 	u32 htlc_budget;
 };
 
+struct route_exclusions_data {
+	struct route_exclusion **exclusions;
+};
+
 /* List of globally available payment modifiers. */
 REGISTER_PAYMENT_MODIFIER_HEADER(retry, struct retry_mod_data);
 REGISTER_PAYMENT_MODIFIER_HEADER(routehints, struct routehints_data);
@@ -426,6 +430,8 @@ REGISTER_PAYMENT_MODIFIER_HEADER(local_channel_hints, void);
  * we detect the payee to have, in order to not exhaust the number of HTLCs
  * each of those channels can bear.  */
 REGISTER_PAYMENT_MODIFIER_HEADER(payee_incoming_limit, void);
+REGISTER_PAYMENT_MODIFIER_HEADER(route_exclusions, struct route_exclusions_data);
+
 
 struct payment *payment_new(tal_t *ctx, struct command *cmd,
 			    struct payment *parent,

plugins/pay.c

@@ -2255,7 +2255,14 @@ payment_listsendpays_previous(struct command *cmd, const char *buf,
 }
 
 struct payment_modifier *paymod_mods[] = {
+	/* NOTE: The order in which these four paymods are executed is
+	 * significant!
+	 * local_channel_hints *must* execute first before route_exclusions
+	 * which *must* execute before directpay.
+	 * exemptfee *must* also execute before directpay.
+	 */
 	&local_channel_hints_pay_mod,
+	&route_exclusions_pay_mod,
 	&exemptfee_pay_mod,
 	&directpay_pay_mod,
 	&shadowroute_pay_mod,
@@ -2305,6 +2312,7 @@ static struct command_result *json_paymod(struct command *cmd,
 	struct sha256 *local_offer_id;
 	const struct tlv_invoice *b12;
 	struct out_req *req;
+	struct route_exclusion **exclusions;
 #if DEVELOPER
 	bool *use_shadow;
 #endif
@@ -2326,6 +2334,7 @@ static struct command_result *json_paymod(struct command *cmd,
 			     maxdelay_default),
 		   p_opt_def("exemptfee", param_msat, &exemptfee, AMOUNT_MSAT(5000)),
 		   p_opt("localofferid", param_sha256, &local_offer_id),
+		   p_opt("exclude", param_route_exclusion_array, &exclusions),
 #if DEVELOPER
 		   p_opt_def("use_shadow", param_bool, &use_shadow, true),
 #endif
@@ -2479,6 +2488,7 @@ static struct command_result *json_paymod(struct command *cmd,
 	shadow_route = payment_mod_shadowroute_get_data(p);
 	payment_mod_presplit_get_data(p)->disable = disablempp;
 	payment_mod_adaptive_splitter_get_data(p)->disable = disablempp;
+	payment_mod_route_exclusions_get_data(p)->exclusions = exclusions;
 
 	/* This is an MPP enabled pay command, disable amount fuzzing. */
 	shadow_route->fuzz_amount = false;