renepay: refactor and bugfixes

We remove the auxiliary RPC renesenday (only used internally) in favor
of a function that builds the onion, stores the shared secrets
needed to recover the onion reply, and calls sendonion/injectpaymentonion.

This solves a concurrency race
```
**BROKEN** plugin-cln-renepay: Unable to parse sendpay_failure
```
in which we are waiting for renesenday to return in order to record the shared
secrets but we get the a sendpay_failure notification with an onionreply
before we have secrets to decode it.

It also solves a missing JSON id seen in the logs
```
DEBUG   plugin-cln-renepay: JSON reply with unknown id
```
because renesendpay was using his command variable to issue an RPC
to sendonion/injecpaymentonion and would fail or succeed the command
before those RPCs were done. This also meant that the callback
functions were silently being ignored.

Signed-off-by: Lagrang3 <lagrang3@protonmail.com>

Author: Lagrang3

plugins/renepay/Makefile

@@ -10,7 +10,6 @@ PLUGIN_RENEPAY_SRC :=				\
 	plugins/renepay/routebuilder.c		\
 	plugins/renepay/routetracker.c		\
 	plugins/renepay/routefail.c		\
-	plugins/renepay/sendpay.c		\
 	plugins/renepay/uncertainty.c		\
 	plugins/renepay/mods.c			\
 	plugins/renepay/errorcodes.c		\
@@ -30,7 +29,6 @@ PLUGIN_RENEPAY_HDRS :=				\
 	plugins/renepay/routebuilder.h		\
 	plugins/renepay/routetracker.h		\
 	plugins/renepay/routefail.h		\
-	plugins/renepay/sendpay.h		\
 	plugins/renepay/uncertainty.h		\
 	plugins/renepay/mods.h			\
 	plugins/renepay/errorcodes.h		\

plugins/renepay/main.c

@@ -19,7 +19,6 @@
 #include <plugins/renepay/mods.h>
 #include <plugins/renepay/payplugin.h>
 #include <plugins/renepay/routetracker.h>
-#include <plugins/renepay/sendpay.h>
 #include <stdio.h>
 
 // TODO(eduardo): notice that pending attempts performed with another
@@ -460,10 +459,6 @@ static const struct plugin_command commands[] = {
 		"renepay",
 		json_renepay
 	},
-	{
-		"renesendpay",
-		json_renesendpay
-	},
 };
 
 static const struct plugin_notification notifications[] = {

plugins/renepay/mods.c

@@ -753,10 +753,30 @@ REGISTER_PAYMENT_MODIFIER(compute_routes, compute_routes_cb);
  * request calling sendpay.
  */
 
-static struct command_result *send_routes_cb(struct payment *payment)
+static struct command_result *waitblockheight_done(struct command *cmd,
+						   const char *method UNUSED,
+						   const char *buf,
+						   const jsmntok_t *result,
+						   struct payment *payment)
 {
-	assert(payment);
-	struct routetracker *routetracker = payment->routetracker;
+	const char *err;
+	struct command *aux_cmd;
+	struct route *route;
+	struct routetracker *routetracker;
+
+	err = json_scan(tmpctx, buf, result, "{blockheight:%}",
+			JSON_SCAN(json_to_u32, &payment->blockheight));
+	payment->blockheight += 1;
+
+	if (err) {
+		plugin_err(pay_plugin->plugin,
+			   "Failed to read blockheight from waitblockheight "
+			   "response: %s",
+			   err);
+		return payment_continue(payment);
+	}
+
+	routetracker = payment->routetracker;
 	assert(routetracker);
 	if (!routetracker->computed_routes ||
 	    tal_count(routetracker->computed_routes) == 0) {
@@ -765,12 +785,11 @@ static struct command_result *send_routes_cb(struct payment *payment)
 			   __func__);
 		return payment_continue(payment);
 	}
-	struct command *cmd = payment_command(payment);
-	assert(cmd);
 	for (size_t i = 0; i < tal_count(routetracker->computed_routes); i++) {
-		struct route *route = routetracker->computed_routes[i];
+		aux_cmd = aux_command(cmd);
+		route = routetracker->computed_routes[i];
 
-		route_sendpay_request(cmd, take(route), payment);
+		route_sendpay_request(aux_cmd, take(route), payment);
 
 		payment_note(payment, LOG_INFORM,
 			     "Sent route request: partid=%" PRIu64
@@ -785,6 +804,22 @@ static struct command_result *send_routes_cb(struct payment *payment)
 	return payment_continue(payment);
 }
 
+static struct command_result *send_routes_cb(struct payment *payment)
+{
+	struct command *cmd;
+	struct out_req *req;
+	assert(payment);
+	cmd = payment_command(payment);
+	if (!cmd)
+		plugin_err(pay_plugin->plugin,
+			   "send_routes_pay_mod: cannot get a valid cmd.");
+	req =
+	    jsonrpc_request_start(cmd, "waitblockheight", waitblockheight_done,
+				  payment_rpc_failure, payment);
+	json_add_num(req->js, "blockheight", 0);
+	return send_outreq(req);
+}
+
 REGISTER_PAYMENT_MODIFIER(send_routes, send_routes_cb);
 
 /*****************************************************************************

plugins/renepay/payment.h

@@ -73,6 +73,9 @@ struct payment {
 	struct plugin_timer *waitresult_timer;
 
 	struct routetracker *routetracker;
+
+	/* use this to build the onions */
+	u32 blockheight;
 };
 
 static inline const struct sha256 payment_hash(const struct payment *p)