xpay: add maxparts option

Changelog-Added: xpay: a command line option "maxparts" to limit the number of pending routes at any given time.

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

Author: Lagrang3

doc/schemas/xpay.json

@@ -65,6 +65,14 @@
           "A payment may be delayed for up to `maxdelay` blocks by another node; clients should be prepared for this worst case."
         ],
         "default": "2016"
+      },
+      "maxparts": {
+        "type": "u32",
+        "added": "v25.09",
+        "description": [
+          "Maximum number of pending routes at any given time."
+        ],
+        "default": "6"
       }
     }
   },

plugins/xpay/xpay.c

@@ -78,6 +78,8 @@ struct payment {
 	struct amount_msat maxfee;
 	/* Maximum delay on the route we're ok with */
 	u32 *maxdelay;
+	/* Maximum number of payment routes that can be pending. */
+	u32 *maxparts;
 	/* Do we have to do it all in a single part? */
 	bool disable_mpp;
 	/* BOLT11 payment secret (NULL for BOLT12, it uses blinded paths) */
@@ -113,6 +115,9 @@ struct payment {
 	 * call outstanding). */
 	struct amount_msat amount_being_routed;
 
+        /* Number of routes attempted and pending */
+	u32 pending_attempts;
+
 	/* Useful information from prior attempts if any. */
 	char *prior_results;
 
@@ -1281,6 +1286,9 @@ static struct command_result *getroutes_for(struct command *aux_cmd,
 	json_add_amount_msat(req->js, "maxfee_msat", maxfee);
 	json_add_u32(req->js, "final_cltv", payment->final_cltv);
 	json_add_u32(req->js, "maxdelay", *payment->maxdelay);
+        // FIXME: deduce pending_attempts: total - failed
+	json_add_u32(req->js, "maxparts",
+		     *payment->maxparts - payment->pending_attempts);
 
 	return send_payment_req(aux_cmd, payment, req);
 }
@@ -1571,6 +1579,7 @@ static struct command_result *json_xpay_core(struct command *cmd,
 			 p_opt_def("retry_for", param_number, &retryfor, 60),
 			 p_opt("partial_msat", param_msat, &partial),
 			 p_opt_def("maxdelay", param_u32, &payment->maxdelay, 2016),
+			 p_opt_def("maxparts", param_u32, &payment->maxparts, 6),
 			 NULL))
 		return command_param_failed();
 
@@ -1579,6 +1588,7 @@ static struct command_result *json_xpay_core(struct command *cmd,
 	payment->plugin = cmd->plugin;
 	payment->cmd = cmd;
 	payment->amount_being_routed = AMOUNT_MSAT(0);
+	payment->pending_attempts = 0;
 	payment->group_id = pseudorand(INT64_MAX);
 	payment->total_num_attempts = payment->num_failures = 0;
 	payment->requests = tal_arr(payment, struct out_req *, 0);