askrene: add expiration parameter to create-layer

This could be useful if we want to create one-time use layers
on the flight and not worry about memory leaks (one time used
layers that are not removed constitute a memory leak in a sense).

Changelog-Added: askrene: add an optional self-destruction timer (expiration parameter) to new layers.

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

Author: Lagrang3

doc/schemas/lightning-askrene-create-layer.json

@@ -25,6 +25,13 @@
         "description": [
           "True if askrene should save and restore this layer.  As a side-effect, create-layer also succeeds if the layer already exists and persistent is true."
         ]
+      },
+      "expiration": {
+        "type": "u64",
+        "description": [
+          "Sets the number of seconds until this layer expires.  If this number is specified the layer will be automatically deleted at expiration.  A layer cannot be persistent and have an expiration time."
+        ],
+        "added": "v25.02"
       }
     }
   },

plugins/askrene/askrene.c

@@ -14,6 +14,7 @@
 #include <common/gossmods_listpeerchannels.h>
 #include <common/json_param.h>
 #include <common/json_stream.h>
+#include <common/memleak.h>
 #include <common/route.h>
 #include <errno.h>
 #include <math.h>
@@ -623,6 +624,7 @@ static struct command_result *do_getroutes(struct command *cmd,
 			 *info->amount, *info->maxfee, *info->finalcltv,
 			 info->layers, localmods, info->local_layer,
 			 &routes, &amounts, info->additional_costs, &probability);
+
 	if (err)
 		return command_fail(cmd, PAY_ROUTE_NOT_FOUND, "%s", err);
 
@@ -1060,6 +1062,27 @@ static struct command_result *json_askrene_disable_node(struct command *cmd,
 	return command_finished(cmd, response);
 }
 
+static struct command_result *expire_layer_done(struct command *timer_cmd,
+						const char *method,
+						const char *buf,
+						const jsmntok_t *result,
+						void *unused)
+{
+	return timer_complete(timer_cmd);
+}
+
+static struct command_result *expire_layer(struct command *timer_cmd,
+					   struct layer *l)
+{
+	struct out_req *req;
+	req = jsonrpc_request_start(timer_cmd, "askrene-remove-layer",
+				    expire_layer_done, plugin_broken_cb, NULL);
+	json_add_string(req->js, "layer", layer_name(l));
+	plugin_log(timer_cmd->plugin, LOG_DBG, "removing expired layer '%s'",
+		   layer_name(l));
+	return send_outreq(req);
+}
+
 static struct command_result *json_askrene_create_layer(struct command *cmd,
 							const char *buffer,
 							const jsmntok_t *params)
@@ -1069,10 +1092,12 @@ static struct command_result *json_askrene_create_layer(struct command *cmd,
 	const char *layername;
 	struct json_stream *response;
 	bool *persistent;
+	u64 *expire_seconds;
 
 	if (!param_check(cmd, buffer, params,
 			 p_req("layer", param_string, &layername),
 			 p_opt_def("persistent", param_bool, &persistent, false),
+			 p_opt("expiration", param_u64, &expire_seconds),
 			 NULL))
 		return command_param_failed();
 
@@ -1086,13 +1111,23 @@ static struct command_result *json_askrene_create_layer(struct command *cmd,
 		return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 				    "Layer already exists");
 	}
+	if (persistent && expire_seconds && *persistent == true) {
+		return command_fail(
+		    cmd, JSONRPC2_INVALID_PARAMS,
+		    "A persistent layer cannot have an expiration time.");
+	}
 
 	if (command_check_only(cmd))
 		return command_check_done(cmd);
 
 	if (!layer)
 		layer = new_layer(askrene, layername, *persistent);
 
+	if (expire_seconds)
+		notleak(global_timer(cmd->plugin,
+				     time_from_sec(*expire_seconds),
+				     expire_layer, layer));
+
 	response = jsonrpc_stream_success(cmd);
 	json_add_layers(response, askrene, "layers", layer);
 	return command_finished(cmd, response);

tests/test_askrene.py

@@ -367,6 +367,31 @@ def test_layer_persistence(node_factory):
     assert l1.rpc.askrene_listlayers() == {'layers': []}
 
 
+def test_layer_expiration(node_factory):
+    l1 = node_factory.get_nodes(1, opts={"disable-plugin": "cln-xpay"})[0]
+    expect = {
+        "layer": "tmp_layer",
+        "persistent": False,
+        "disabled_nodes": [],
+        "created_channels": [],
+        "channel_updates": [],
+        "constraints": [],
+        "biases": [],
+    }
+
+    assert l1.rpc.askrene_listlayers() == {"layers": []}
+    # Add a self-destructing layer
+    l1.rpc.askrene_create_layer(layer="tmp_layer", expiration=5)
+    assert l1.rpc.askrene_listlayers() == {"layers": [expect]}
+    time.sleep(6)
+    assert l1.rpc.askrene_listlayers() == {"layers": []}
+
+    with pytest.raises(
+        RpcError, match="A persistent layer cannot have an expiration time."
+    ):
+        l1.rpc.askrene_create_layer(layer="pers_layer", persistent=True, expiration=5)
+
+
 def check_route_as_expected(routes, paths):
     """Make sure all fields in paths are match those in routes"""
     def dict_subset_eq(a, b):