[wip] Xpay limit path length

.msggen.json

@@ -2249,6 +2249,7 @@
             "GetRoutes.layers[]": 4,
             "GetRoutes.maxdelay": 8,
             "GetRoutes.maxfee_msat": 5,
+            "GetRoutes.maxhops": 10,
             "GetRoutes.maxparts": 9,
             "GetRoutes.source": 1
         },
@@ -8816,6 +8817,10 @@
             "added": "v24.08",
             "deprecated": null
         },
+        "GetRoutes.maxhops": {
+            "added": "v26.12",
+            "deprecated": null
+        },
         "GetRoutes.maxparts": {
             "added": "v25.09",
             "deprecated": null

contrib/msggen/msggen/schema.json

@@ -17329,6 +17329,14 @@
               "Maximum number of routes in the solution."
             ],
             "default": "100"
+          },
+          "maxhops": {
+            "type": "u32",
+            "added": "v26.12",
+            "description": [
+              "Maximum number of hops for every path."
+            ],
+            "default": "100"
           }
         }
       },

doc/schemas/getroutes.json

@@ -81,6 +81,14 @@
           "Maximum number of routes in the solution."
         ],
         "default": "100"
+      },
+      "maxhops": {
+        "type": "u32",
+        "added": "v26.12",
+        "description": [
+          "Maximum number of hops for every path."
+        ],
+        "default": "100"
       }
     }
   },

plugins/askrene/askrene.c

@@ -359,6 +359,7 @@ struct getroutes_info {
 	/* Non-NULL if we are told to use "auto.localchans" */
 	struct layer *local_layer;
 	u32 maxparts;
+	u32 maxhops;
 };
 
 static void add_layer(const struct layer ***layers,
@@ -716,7 +717,11 @@ static struct command_result *do_getroutes(struct command *cmd,
 			  take(capacities),
 			  info->dev_algo == ALGO_SINGLE_PATH,
 			  deadline, srcnode, dstnode, info->amount,
-			  info->maxfee, info->finalcltv, info->maxdelay, info->maxparts,
+			  info->maxfee,
+			  info->finalcltv,
+			  info->maxdelay,
+			  info->maxparts,
+			  info->maxhops,
 			  include_fees,
 			  cmd->idstr, cmd->filter,
 			  include_next_node_id,
@@ -900,14 +905,14 @@ static struct command_result *json_getroutes(struct command *cmd,
 	/* FIXME: Typo in spec for CLTV in descripton! But it breaks our spelling check, so we omit it above */
 	const u32 maxdelay_allowed = 2016;
 	struct askrene *askrene = get_askrene(cmd->plugin);
-	const u32 default_maxparts = 100;
+	const u32 default_maxparts = 100, default_maxhops = 100;
 	struct getroutes_info *info = tal(cmd, struct getroutes_info);
 	/* param functions require pointers */
 	struct node_id *source, *dest;
 	struct amount_msat *amount, *maxfee;
 	u32 *finalcltv, *maxdelay;
 	enum algorithm *dev_algo;
-	u32 *maxparts;
+	u32 *maxparts, *maxhops;
 
 	if (!param_check(cmd, buffer, params,
 			 p_req("source", param_node_id, &source),
@@ -920,6 +925,8 @@ static struct command_result *json_getroutes(struct command *cmd,
 				   maxdelay_allowed),
 			 p_opt_def("maxparts", param_u32, &maxparts,
 				   default_maxparts),
+			 p_opt_def("maxhops", param_u32, &maxhops,
+				   default_maxhops),
 			 p_opt_dev("dev_algorithm", param_algorithm,
 				   &dev_algo, ALGO_DEFAULT),
 			 NULL))
@@ -961,6 +968,7 @@ static struct command_result *json_getroutes(struct command *cmd,
 	info->dev_algo = *dev_algo;
 	info->additional_costs = new_htable(info, additional_cost_htable);
 	info->maxparts = *maxparts;
+	info->maxhops = *maxhops;
 
 	if (askrene->num_live_requests >= askrene->max_children) {
 		cmd_log(tmpctx, cmd, LOG_INFORM,

plugins/askrene/child/child.c

@@ -219,8 +219,11 @@ void run_child(const struct gossmap *gossmap,
 	       const struct gossmap_node *srcnode,
 	       const struct gossmap_node *dstnode,
 	       struct amount_msat amount, struct amount_msat maxfee,
-	       u32 finalcltv, u32 maxdelay, size_t maxparts,
-              bool include_fees,
+	       u32 finalcltv,
+	       u32 maxdelay,
+	       size_t maxparts,
+	       u32 maxhops,
+	       bool include_fees,
 	       const char *cmd_id,
 	       struct json_filter *cmd_filter,
 	       bool include_next_node_id,
@@ -243,11 +246,11 @@ void run_child(const struct gossmap *gossmap,
 	if (single_path) {
 		err = single_path_routes(rq, rq, deadline, srcnode, dstnode,
 					 amount, maxfee, finalcltv,
-					 maxdelay, &flows, &probability, &ecode);
+					 maxdelay, maxhops, &flows, &probability, &ecode);
 	} else {
 		err = default_routes(rq, rq, deadline, srcnode, dstnode,
 				     amount, maxfee, finalcltv, maxdelay,
-				     maxparts, &flows, &probability, &ecode);
+				     maxparts, maxhops, &flows, &probability, &ecode);
 	}
 	if (err) {
 		write_all(replyfd, &ecode, sizeof(ecode));

plugins/askrene/child/child.h

@@ -27,7 +27,10 @@ void run_child(const struct gossmap *gossmap,
 	       const struct gossmap_node *srcnode,
 	       const struct gossmap_node *dstnode,
 	       struct amount_msat amount, struct amount_msat maxfee,
-	       u32 finalcltv, u32 maxdelay, size_t maxparts,
+	       u32 finalcltv,
+	       u32 maxdelay,
+	       size_t maxparts,
+	       u32 maxhops,
 	       bool include_fees,
 	       const char *cmd_id,
 	       struct json_filter *cmd_filter,

plugins/askrene/child/flow.c

@@ -173,6 +173,17 @@ u64 flows_worst_delay(struct flow **flows)
 	return maxdelay;
 }
 
+u32 flows_worst_length(struct flow **flows)
+{
+	u32 maxlen = 0;
+	for (size_t i = 0; i < tal_count(flows); i++) {
+		u32 len = tal_count(flows[i]->path);
+		if (len > maxlen)
+			maxlen = len;
+	}
+	return maxlen;
+}
+
 const char *fmt_flows_step_scid(const tal_t *ctx,
 				const struct route_query *rq,
 				const struct flow *flow, size_t i)

plugins/askrene/child/flow.h

@@ -57,6 +57,9 @@ u64 flow_delay(const struct flow *flow);
 /* Max CLTV any of these flows requires */
 u64 flows_worst_delay(struct flow **flows);
 
+/* Max number of hops any of these flows requires */
+u32 flows_worst_length(struct flow **flows);
+
 const char *fmt_flows_step_scid(const tal_t *ctx,
 				const struct route_query *rq,
 				const struct flow *flow, size_t i);