renepay: resolve self payments with fake node

Always use a fake destination node, the self-payments are no longer a
corner case for the routing problem in this way. Also it is ok for
get_routes to return routes with zero length.

Changelog-None.

Signed-off-by: Lagrang3 <[email protected]>

Author: Lagrang3

plugins/renepay/json.c

@@ -76,6 +76,8 @@ struct payment_result *tal_sendpay_result_from_json(const tal_t *ctx,
 						    const char *buffer,
 						    const jsmntok_t *toks)
 {
+	// FIXME: we will be getting onionreply try to decode these with
+	// shared_secrets
 	const jsmntok_t *idtok = json_get_member(buffer, toks, "created_index");
 	const jsmntok_t *hashtok =
 	    json_get_member(buffer, toks, "payment_hash");

plugins/renepay/main.c

@@ -344,7 +344,6 @@ static struct command_result *json_pay(struct command *cmd, const char *buf,
 
 			pinfo->blinded_paths = NULL;
 			pinfo->blinded_payinfos = NULL;
-			payment->routing_destination = &pinfo->destination;
 		} else {
 			pinfo->payment_secret = NULL;
 			pinfo->routehints = NULL;
@@ -370,19 +369,18 @@ static struct command_result *json_pay(struct command *cmd, const char *buf,
 					max_final_cltv = final_cltv;
 			}
 			pinfo->final_cltv = max_final_cltv;
-
-			/* When dealing with BOLT12 blinded paths we compute the
-			 * routing targeting a fake node to enable
-			 * multi-destination minimum-cost-flow. Every blinded
-			 * path entry node will be linked to this fake node
-			 * using fake channels as well. */
-			payment->routing_destination =
-			    tal(payment, struct node_id);
-			if (!node_id_from_hexstr(
-				"02""0000000000000000000000000000000000000000000000000000000000000001",
-				66, payment->routing_destination))
-				abort();
 		}
+		/* When dealing with BOLT12 blinded paths we compute the
+		 * routing targeting a fake node to enable
+		 * multi-destination minimum-cost-flow. Every blinded
+		 * path entry node will be linked to this fake node
+		 * using fake channels as well. This is also useful for
+		 * solving self-payments. */
+		payment->routing_destination = tal(payment, struct node_id);
+		if (!node_id_from_hexstr("0200000000000000000000000000000000000"
+					 "00000000000000000000000000001",
+					 66, payment->routing_destination))
+			abort();
 
 		if (!payment_set_constraints(
 			payment, *msat, *maxfee, *maxdelay, *retryfor,

plugins/renepay/mods.c

@@ -92,6 +92,13 @@ static struct command_result *payment_rpc_failure(struct command *cmd,
 	    json_tok_full_len(toks), json_tok_full(buffer, toks));
 }
 
+static void add_hintchan(struct payment *payment, const struct node_id *src,
+			 const struct node_id *dst, u16 cltv_expiry_delta,
+			 const struct short_channel_id scid, u32 fee_base_msat,
+			 u32 fee_proportional_millionths,
+			 const struct amount_msat *chan_htlc_min,
+			 const struct amount_msat *chan_htlc_max);
+
 /*****************************************************************************
  * previoussuccess
  *
@@ -249,88 +256,23 @@ REGISTER_PAYMENT_MODIFIER(initial_sanity_checks, initial_sanity_checks_cb);
 
 /*****************************************************************************
  * selfpay
- *
- * Checks if the payment destination is the sender's node and perform a self
- * payment.
  */
 
-static struct command_result *selfpay_success(struct command *cmd,
-					      const char *method UNUSED,
-					      const char *buf,
-					      const jsmntok_t *tok,
-					      struct payment *payment)
-{
-	struct preimage preimage;
-	const char *err;
-	err = json_scan(tmpctx, buf, tok, "{payment_preimage:%}",
-			JSON_SCAN(json_to_preimage, &preimage));
-	if (err)
-		plugin_err(
-		    cmd->plugin, "selfpay didn't have payment_preimage: %.*s",
-		    json_tok_full_len(tok), json_tok_full(buf, tok));
-
-
-	payment_note(payment, LOG_DBG, "Paid with self-pay.");
-	return payment_success(payment, &preimage);
-}
-static struct command_result *selfpay_failure(struct command *cmd,
-					      const char *method UNUSED,
-					      const char *buf,
-					      const jsmntok_t *tok,
-					      struct payment *payment)
-{
-	struct payment_result *result =
-	    tal_sendpay_result_from_json(tmpctx, buf, tok);
-	if (result == NULL) {
-		plugin_log(pay_plugin->plugin, LOG_UNUSUAL,
-			   "Unable to parse sendpay failure: %.*s",
-			   json_tok_full_len(tok), json_tok_full(buf, tok));
-		return payment_fail(payment, LIGHTNINGD,
-				    "Self pay failed for unknown reason");
-	}
-	return payment_fail(payment, result->code, "%s", result->message);
-}
-
 static struct command_result *selfpay_cb(struct payment *payment)
 {
-	if (!node_id_eq(&pay_plugin->my_id,
-			&payment->payment_info.destination)) {
-		return payment_continue(payment);
-	}
-
-	struct command *cmd = payment_command(payment);
-	if (!cmd)
-		plugin_err(pay_plugin->plugin,
-			   "Selfpay: cannot get a valid cmd.");
-
-	struct payment_info *pinfo = &payment->payment_info;
-	struct out_req *req;
-	req = jsonrpc_request_start(cmd, "renesendpay", selfpay_success,
-				    selfpay_failure, payment);
-	json_add_sha256(req->js, "payment_hash", &pinfo->payment_hash);
-	json_add_u64(req->js, "partid", 0);
-	json_add_u64(req->js, "groupid", payment->groupid);
-	json_add_string(req->js, "invoice", pinfo->invstr);
-	json_add_node_id(req->js, "destination", &pinfo->destination);
-	json_add_amount_msat(req->js, "amount_msat", pinfo->amount);
-	json_add_amount_msat(req->js, "total_amount_msat", pinfo->amount);
-	json_add_u32(req->js, "final_cltv", pinfo->final_cltv);
-	if (pinfo->label)
-		json_add_string(req->js, "label", pinfo->label);
-	if (pinfo->description)
-		json_add_string(req->js, "description", pinfo->description);
-	/* An empty route means a payment to oneself, pathlen=0 */
-	json_array_start(req->js, "route");
-	json_array_end(req->js);
-	if (pinfo->payment_secret)
-		json_add_secret(req->js, "payment_secret",
-				pinfo->payment_secret);
-	else {
-		assert(pinfo->blinded_paths);
-		const struct blinded_path *bpath = pinfo->blinded_paths[0];
-		json_myadd_blinded_path(req->js, "blinded_path", bpath);
+	/* A different approach to self-pay: create a fake channel from the
+	 * bolt11 destination to the routing_destination (a fake node_id). */
+	if (!payment->payment_info.blinded_paths) {
+		struct amount_msat htlc_min = AMOUNT_MSAT(0);
+		struct amount_msat htlc_max = AMOUNT_MSAT((u64)1000*100000000);
+		struct short_channel_id scid = {.u64 = 0};
+		add_hintchan(payment, &payment->payment_info.destination,
+			     payment->routing_destination,
+			     /* cltv delta = */ 0, scid,
+			     /* base fee = */ 0,
+			     /* ppm = */ 0, &htlc_min, &htlc_max);
 	}
-	return send_outreq(req);
+	return payment_continue(payment);
 }
 
 REGISTER_PAYMENT_MODIFIER(selfpay, selfpay_cb);
@@ -755,8 +697,7 @@ static struct command_result *compute_routes_cb(struct payment *payment)
 
 	/* Send get_routes a note that it should discard the last hop because we
 	 * are actually solving a multiple destinations problem. */
-	bool blinded_destination =
-	    payment->payment_info.blinded_paths != NULL;
+	bool blinded_destination = true;
 
 	// TODO: add an algorithm selector here
 	/* We let this return an unlikely path, as it's better to try  once than
@@ -1291,9 +1232,9 @@ REGISTER_PAYMENT_CONDITION(retry, retry_cb);
 // add check pre-approved invoice
 void *payment_virtual_program[] = {
     /*0*/ OP_CALL, &previoussuccess_pay_mod,
-    /*2*/ OP_CALL, &selfpay_pay_mod,
-    /*4*/ OP_CALL, &knowledgerelax_pay_mod,
-    /*6*/ OP_CALL, &getmychannels_pay_mod,
+    /*2*/ OP_CALL, &knowledgerelax_pay_mod,
+    /*4*/ OP_CALL, &getmychannels_pay_mod,
+    /*6*/ OP_CALL, &selfpay_pay_mod,
     /*8*/ OP_CALL, &refreshgossmap_pay_mod,
     /*10*/ OP_CALL, &routehints_pay_mod,
     /*12*/ OP_CALL, &blindedhints_pay_mod,

plugins/renepay/route.h

@@ -170,7 +170,8 @@ static inline u32 route_delay(const struct route *route)
 {
 	assert(route);
 	assert(route->hops);
-	assert(tal_count(route->hops) > 0);
+	if (tal_count(route->hops) == 0)
+		return 0;
 	const size_t pathlen = tal_count(route->hops);
 	assert(route->hops[0].delay >= route->hops[pathlen - 1].delay);
 	return route->hops[0].delay - route->hops[pathlen - 1].delay;

plugins/renepay/routebuilder.c

@@ -65,6 +65,8 @@ route_check_constraints(struct route *route, struct gossmap *gossmap,
 	assert(route);
 	assert(route->hops);
 	const size_t pathlen = tal_count(route->hops);
+	if (pathlen == 0)
+		return RENEPAY_NOERROR;
 	if (!amount_msat_eq(route->amount_deliver,
 			    route->hops[pathlen - 1].amount))
 		return RENEPAY_PRECONDITION_ERROR;

plugins/renepay/sendpay.c

@@ -435,8 +435,6 @@ static struct command_result *waitblockheight_done(struct command *cmd,
 				     renesendpay->sent_amount);
 		json_add_amount_msat(req->js, "destination_msat",
 				     renesendpay->deliver_amount);
-		json_add_amount_msat(req->js, "destination_msat",
-				     renesendpay->deliver_amount);
 		json_add_u32(req->js, "cltv_expiry",
 			     initial_cltv_delta(renesendpay) +
 				 renesendpay->blockheight);

tests/test_renepay.py

@@ -848,3 +848,11 @@ def test_offers(node_factory):
     invoice = l1.rpc.fetchinvoice(offer)['invoice']
     response = l1.rpc.call("renepay", {"invstring": invoice})
     assert response["status"] == "complete"
+
+
+def test_offer_selfpay(node_factory):
+    """We can fetch an pay our own offer"""
+    l1 = node_factory.get_node()
+    offer = l1.rpc.offer(amount="2msat", description="test_offer_path_self")["bolt12"]
+    inv = l1.rpc.fetchinvoice(offer)["invoice"]
+    l1.rpc.call("renepay", {"invstring": inv})