askrene: add optional layers to reservations.

We have the issue of aliases: xpay uses scids like 0x0x0 for
routehints and blinded paths, and then can apply reservations to them.  But
generally, reservations are *global*, so we need to differentiate.

Changelog-Added: Plugins: `askrene-reserve` and `askrene-unreserve` can take an optional `layer` inside `path` elements.
Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

doc/schemas/askrene-inform-channel.json

@@ -19,7 +19,7 @@
       "layer": {
         "type": "string",
         "description": [
-          "The name of the layer to apply this change to."
+          "The name of the layer to apply this change to.  Also causes us to consider any reservations which are local to that layer (which is useful for fake channels where `layer` is set in an `askrene-reserve` `path` object)."
         ]
       },
       "short_channel_id_dir": {

doc/schemas/askrene-reserve.json

@@ -36,6 +36,13 @@
               "description": [
                 "The amount to send into this hop."
               ]
+            },
+            "layer": {
+              "added": "v25.12",
+              "type": "string",
+              "description": [
+                "The layer to restrict this reservation to.  This is only useful for fake channels which are not uniquely identified by `short_channel_id_dir`, which would otherwise confuse multiple unrelated callers."
+              ]
             }
           }
         }

doc/schemas/askrene-unreserve.json

@@ -36,6 +36,13 @@
               "description": [
                 "The amount to send into this hop."
               ]
+            },
+            "layer": {
+              "added": "v25.12",
+              "type": "string",
+              "description": [
+                "The layer to restrict this reservation to (useful for fake channels)."
+              ]
             }
           }
         }

plugins/askrene/askrene.c

@@ -147,12 +147,21 @@ static struct command_result *parse_reserve_hop(struct command *cmd,
 						struct reserve_hop *rhop)
 {
 	const char *err;
+	const char *layername = NULL;
 
-	err = json_scan(tmpctx, buffer, tok, "{short_channel_id_dir:%,amount_msat:%}",
+	err = json_scan(tmpctx, buffer, tok, "{short_channel_id_dir:%,amount_msat:%,layer?:%}",
 			JSON_SCAN(json_to_short_channel_id_dir, &rhop->scidd),
-			JSON_SCAN(json_to_msat, &rhop->amount));
+			JSON_SCAN(json_to_msat, &rhop->amount),
+			JSON_SCAN_TAL(tmpctx, json_strdup, &layername));
 	if (err)
 		return command_fail_badparam(cmd, name, buffer, tok, err);
+	if (layername) {
+		rhop->layer = find_layer(get_askrene(cmd->plugin), layername);
+		if (!rhop->layer)
+			return command_fail_badparam(cmd, name, buffer, tok, "Unknown layer");
+	} else
+		rhop->layer = NULL;
+
 	return NULL;
 }
 
@@ -548,8 +557,8 @@ void get_constraints(const struct route_query *rq,
 		*max = gossmap_chan_get_capacity(rq->gossmap, chan);
 
 	/* Finally, if any is in use, subtract that! */
-	reserve_sub(rq->reserved, &scidd, min);
-	reserve_sub(rq->reserved, &scidd, max);
+	reserve_sub(rq->reserved, &scidd, rq->layers, min);
+	reserve_sub(rq->reserved, &scidd, rq->layers, max);
 }
 
 static struct command_result *do_getroutes(struct command *cmd,
@@ -916,9 +925,11 @@ static struct command_result *json_askrene_unreserve(struct command *cmd,
 	for (size_t i = 0; i < tal_count(path); i++) {
 		if (!reserve_remove(askrene->reserved, &path[i])) {
 			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
-					    "Unknown reservation for %s",
+					    "Unknown reservation for %s%s%s",
 					    fmt_short_channel_id_dir(tmpctx,
-								     &path[i].scidd));
+								     &path[i].scidd),
+					    path[i].layer ? " on layer " : "",
+					    path[i].layer ? layer_name(path[i].layer) : "");
 		}
  	}
 
@@ -933,14 +944,15 @@ static struct command_result *json_askrene_listreservations(struct command *cmd,
 	struct askrene *askrene = get_askrene(cmd->plugin);
 	struct json_stream *response;
 
+	/* FIXME: We could allow layer names here? */
 	if (!param(cmd, buffer, params,
 		   NULL))
 		return command_param_failed();
 	plugin_log(cmd->plugin, LOG_TRACE, "%s called: %.*s", __func__,
 		   json_tok_full_len(params), json_tok_full(buffer, params));
 
 	response = jsonrpc_stream_success(cmd);
-	json_add_reservations(response, askrene->reserved, "reservations");
+	json_add_reservations(response, askrene->reserved, "reservations", NULL);
 	return command_finished(cmd, response);
 }
 
@@ -1065,7 +1077,7 @@ static struct command_result *json_askrene_inform_channel(struct command *cmd,
 	case INFORM_CONSTRAINED:
 		/* It didn't pass, so minimal assumption is that reserve was all used
 		 * then there we were one msat short. */
-		if (!reserve_accumulate(askrene->reserved, scidd, amount))
+		if (!reserve_accumulate(askrene->reserved, scidd, layer, amount))
 			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
 					    "Amount overflow with reserves");
 		if (!amount_msat_deduct(amount, AMOUNT_MSAT(1)))

plugins/askrene/explain_failure.c

@@ -60,7 +60,7 @@ static const char *why_max_constrained(const tal_t *ctx,
 			       fmt_amount_msat(tmpctx, max));
 	}
 
-	reservations = fmt_reservations(tmpctx, rq->reserved, scidd);
+	reservations = fmt_reservations(tmpctx, rq->reserved, scidd, rq->layers);
 	if (reservations) {
 		if (!ret)
 			ret = tal_strdup(ctx, "");

plugins/askrene/refine.c

@@ -72,6 +72,9 @@ static void add_reservation(struct reserve_hop **reservations,
 	}
 	rhop.scidd = *scidd;
 	rhop.amount = amt;
+	/* We don't have to restrict it to a layer, since it's transitory:
+	 * nobody else will see this. */
+	rhop.layer = NULL;
 	reserve_add(askrene->reserved, &rhop, rq->cmd->id);
 
 	/* Set capacities entry to 0 so it get_constraints() looks in reserve. */

plugins/askrene/reserve.c

@@ -40,6 +40,12 @@ struct reserve_htable *new_reserve_htable(const tal_t *ctx)
 	return new_htable(ctx, reserve_htable);
 }
 
+static void destroy_reserve(struct reserve *r, struct reserve_htable *reserved)
+{
+	if (!reserve_htable_del(reserved, r))
+		abort();
+}
+
 void reserve_add(struct reserve_htable *reserved,
 		 const struct reserve_hop *rhop,
 		 const char *cmd_id TAKES)
@@ -49,6 +55,11 @@ void reserve_add(struct reserve_htable *reserved,
 	r->timestamp = time_mono();
 	r->cmd_id = tal_strdup(r, cmd_id);
 
+	/* If owned by a layer, clean up when layer destroyed */
+	if (rhop->layer) {
+		tal_steal(rhop->layer, r);
+		tal_add_destructor2(r, destroy_reserve, reserved);
+	}
 	reserve_htable_add(reserved, r);
 }
 
@@ -65,8 +76,12 @@ bool reserve_remove(struct reserve_htable *reserved,
 	     r = reserve_htable_getnext(reserved, &rhop->scidd, &rit)) {
 		if (!amount_msat_eq(r->rhop.amount, rhop->amount))
 			continue;
+		if (r->rhop.layer != rhop->layer)
+			continue;
 
-		reserve_htable_del(reserved, r);
+		/* hops on layers have a destructor which does this. */
+		if (r->rhop.layer == NULL)
+			reserve_htable_del(reserved, r);
 		tal_free(r);
 		return true;
 	}
@@ -93,8 +108,18 @@ void reserves_clear_capacities(struct reserve_htable *reserved,
 	}
 }
 
+static bool layer_in(const struct layer *layer,
+		     const struct layer **layers)
+{
+	for (size_t i = 0; i < tal_count(layers); i++)
+		if (layer == layers[i])
+			return true;
+	return false;
+}
+
 void reserve_sub(const struct reserve_htable *reserved,
 		 const struct short_channel_id_dir *scidd,
+		 const struct layer **layers,
 		 struct amount_msat *amount)
 {
 	struct reserve *r;
@@ -103,13 +128,16 @@ void reserve_sub(const struct reserve_htable *reserved,
 	for (r = reserve_htable_getfirst(reserved, scidd, &rit);
 	     r;
 	     r = reserve_htable_getnext(reserved, scidd, &rit)) {
+		if (r->rhop.layer && !layer_in(r->rhop.layer, layers))
+			continue;
 		if (!amount_msat_deduct(amount, r->rhop.amount))
 			*amount = AMOUNT_MSAT(0);
 	}
 }
 
 bool reserve_accumulate(const struct reserve_htable *reserved,
 			const struct short_channel_id_dir *scidd,
+			const struct layer *layer,
 			struct amount_msat *amount)
 {
 	struct reserve *r;
@@ -118,6 +146,10 @@ bool reserve_accumulate(const struct reserve_htable *reserved,
 	for (r = reserve_htable_getfirst(reserved, scidd, &rit);
 	     r;
 	     r = reserve_htable_getnext(reserved, scidd, &rit)) {
+		/* Non-layer ones always get counted.  Layered ones have
+		 * to match this layer. */
+		if (r->rhop.layer && r->rhop.layer != layer)
+			continue;
 		if (!amount_msat_add(amount, *amount, r->rhop.amount))
 			return false;
 	}
@@ -126,7 +158,8 @@ bool reserve_accumulate(const struct reserve_htable *reserved,
 
 void json_add_reservations(struct json_stream *js,
 			   const struct reserve_htable *reserved,
-			   const char *fieldname)
+			   const char *fieldname,
+			   const struct layer **layers)
 {
 	struct reserve *r;
 	struct reserve_htable_iter rit;
@@ -135,6 +168,8 @@ void json_add_reservations(struct json_stream *js,
 	for (r = reserve_htable_first(reserved, &rit);
 	     r;
 	     r = reserve_htable_next(reserved, &rit)) {
+		if (r->rhop.layer && !layer_in(r->rhop.layer, layers))
+			continue;
 		json_object_start(js, NULL);
 		json_add_short_channel_id_dir(js,
 					      "short_channel_id_dir",
@@ -152,7 +187,8 @@ void json_add_reservations(struct json_stream *js,
 
 const char *fmt_reservations(const tal_t *ctx,
 			     const struct reserve_htable *reserved,
-			     const struct short_channel_id_dir *scidd)
+			     const struct short_channel_id_dir *scidd,
+			     const struct layer **layers)
 {
 	struct reserve *r;
 	struct reserve_htable_iter rit;
@@ -162,6 +198,8 @@ const char *fmt_reservations(const tal_t *ctx,
 	     r;
 	     r = reserve_htable_getnext(reserved, scidd, &rit)) {
 		u64 seconds;
+		if (r->rhop.layer && !layer_in(r->rhop.layer, layers))
+			continue;
 		if (!ret)
 			ret = tal_strdup(ctx, "");
 		else

plugins/askrene/reserve.h

@@ -14,9 +14,11 @@ struct reserve_htable *new_reserve_htable(const tal_t *ctx);
 struct reserve_hop {
 	struct short_channel_id_dir scidd;
 	struct amount_msat amount;
+	/* If non-NULL, only applies to this layer */
+	const struct layer *layer;
 };
 
-/* Add a reservation */
+/* Add a reservation. */
 void reserve_add(struct reserve_htable *reserved,
 		 const struct reserve_hop *rhop,
 		 const char *cmd_id TAKES);
@@ -33,21 +35,25 @@ void reserves_clear_capacities(struct reserve_htable *reserved,
 /* Subtract any reserves for scidd from this amount */
 void reserve_sub(const struct reserve_htable *reserved,
 		 const struct short_channel_id_dir *scidd,
+		 const struct layer **layers,
 		 struct amount_msat *amount);
 
 /* Add any reserves for scidd to this amount */
 bool reserve_accumulate(const struct reserve_htable *reserved,
 			const struct short_channel_id_dir *scidd,
+			const struct layer *layer,
 			struct amount_msat *amount);
 
 /* To explain why we couldn't route */
 const char *fmt_reservations(const tal_t *ctx,
 			     const struct reserve_htable *reserved,
-			     const struct short_channel_id_dir *scidd);
+			     const struct short_channel_id_dir *scidd,
+			     const struct layer **layers);
 
 /* Print out a json object for all reservations */
 void json_add_reservations(struct json_stream *js,
 			   const struct reserve_htable *reserved,
-			   const char *fieldname);
+			   const char *fieldname,
+			   const struct layer **layers);
 
 #endif /* LIGHTNING_PLUGINS_ASKRENE_RESERVE_H */

tests/test_askrene.py

@@ -1847,7 +1847,6 @@ def test_askrene_timeout(node_factory, bitcoind):
                      final_cltv=5)
 
 
-@pytest.mark.xfail(strict=True)
 def test_askrene_reserve_clash(node_factory, bitcoind):
     """Reserves get (erroneously) counted globally by scid, even for fake scids."""
     l1 = node_factory.get_node()
@@ -1897,7 +1896,7 @@ def test_askrene_reserve_clash(node_factory, bitcoind):
 
     l1.rpc.askrene_reserve(path=[{'short_channel_id_dir': '0x0x0/1',
                                   'amount_msat': 950000,
-#                                  'layer': 'layer1'
+                                  'layer': 'layer1'
                                   }])
 
     # We can't use this on layer 1 anymore, only 50000 msat left.