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

.msggen.json

@@ -781,6 +781,7 @@
         "Askrene-reservePath": {
             "AskRene-Reserve.path[].amount_msat": 3,
             "AskRene-Reserve.path[].direction": 2,
+            "AskRene-Reserve.path[].layer": 5,
             "AskRene-Reserve.path[].short_channel_id": 1,
             "AskRene-Reserve.path[].short_channel_id_dir": 4
         },
@@ -790,6 +791,7 @@
         "Askrene-unreservePath": {
             "AskRene-Unreserve.path[].amount_msat": 3,
             "AskRene-Unreserve.path[].direction": 2,
+            "AskRene-Unreserve.path[].layer": 5,
             "AskRene-Unreserve.path[].short_channel_id": 1,
             "AskRene-Unreserve.path[].short_channel_id_dir": 4
         },
@@ -4548,6 +4550,10 @@
             "added": "v24.08",
             "deprecated": null
         },
+        "AskRene-Reserve.path[].layer": {
+            "added": "v25.12",
+            "deprecated": null
+        },
         "AskRene-Reserve.path[].short_channel_id": {
             "added": "v24.08",
             "deprecated": null
@@ -4572,6 +4578,10 @@
             "added": "v24.08",
             "deprecated": null
         },
+        "AskRene-Unreserve.path[].layer": {
+            "added": "v25.12",
+            "deprecated": null
+        },
         "AskRene-Unreserve.path[].short_channel_id": {
             "added": "v24.08",
             "deprecated": null

cln-grpc/proto/node.proto

@@ -1122,7 +1122,7 @@
           "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": {
@@ -1879,6 +1879,13 @@
                   "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."
+                  ]
                 }
               }
             }
@@ -1980,6 +1987,13 @@
                   "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)."
+                  ]
                 }
               }
             }

cln-grpc/src/convert.rs

@@ -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": {

cln-rpc/src/model.rs

@@ -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."
+              ]
             }
           }
         }

contrib/msggen/msggen/schema.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)."
+              ]
             }
           }
         }

contrib/pyln-grpc-proto/pyln/grpc/node_pb2.py

@@ -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)))