paymod: Add a human readable failreason to payments

This makes it easier to stash a human readable failure message in an attempt.

plugins/libplugin-pay.c

@@ -22,6 +22,7 @@ struct payment *payment_new(tal_t *ctx, struct command *cmd,
 	p->why = NULL;
 	p->getroute = tal(p, struct getroute_request);
 	p->label = NULL;
+	p->failreason = NULL;
 
 	/* Copy over the relevant pieces of information. */
 	if (parent != NULL) {
@@ -75,11 +76,9 @@ static struct command_result *payment_rpc_failure(struct command *cmd,
 						  const jsmntok_t *toks,
 						  struct payment *p)
 {
-	plugin_log(p->plugin, LOG_DBG,
-		   "Failing a partial payment due to a failed RPC call: %.*s",
-		   toks->end - toks->start, buffer + toks->start);
-
-	payment_fail(p);
+	payment_fail(p,
+		     "Failing a partial payment due to a failed RPC call: %.*s",
+		     toks->end - toks->start, buffer + toks->start);
 	return command_still_pending(cmd);
 }
 
@@ -365,21 +364,19 @@ static struct command_result *payment_getroute_result(struct command *cmd,
 
 	/* Ensure that our fee and CLTV budgets are respected. */
 	if (amount_msat_greater(fee, p->constraints.fee_budget)) {
-		plugin_log(p->plugin, LOG_INFORM,
-		    "Fee exceeds our fee budget: %s > %s, discarding route",
-		    type_to_string(tmpctx, struct amount_msat, &fee),
-		    type_to_string(tmpctx, struct amount_msat, &p->constraints.fee_budget));
 		payment_exclude_most_expensive(p);
-		payment_fail(p);
+		payment_fail(
+		    p, "Fee exceeds our fee budget: %s > %s, discarding route",
+		    type_to_string(tmpctx, struct amount_msat, &fee),
+		    type_to_string(tmpctx, struct amount_msat,
+				   &p->constraints.fee_budget));
 		return command_still_pending(cmd);
 	}
 
 	if (p->route[0].delay > p->constraints.cltv_budget) {
-		plugin_log(p->plugin, LOG_INFORM,
-			   "CLTV delay exceeds our CLTV budget: %d > %d",
-			   p->route[0].delay, p->constraints.cltv_budget);
 		payment_exclude_longest_delay(p);
-		payment_fail(p);
+		payment_fail(p, "CLTV delay exceeds our CLTV budget: %d > %d",
+			     p->route[0].delay, p->constraints.cltv_budget);
 		return command_still_pending(cmd);
 	}
 
@@ -403,8 +400,16 @@ static struct command_result *payment_getroute_error(struct command *cmd,
 						     const jsmntok_t *toks,
 						     struct payment *p)
 {
+	int code;
+	const jsmntok_t *codetok = json_get_member(buffer, toks, "code"),
+			*msgtok = json_get_member(buffer, toks, "message");
+	json_to_int(buffer, codetok, &code);
 	p->route = NULL;
-	payment_fail(p);
+
+	payment_fail(
+	    p, "Error computing a route to %s: %.*s (%d)",
+	    type_to_string(tmpctx, struct node_id, p->getroute->destination),
+	    json_tok_full_len(msgtok), json_tok_full(buffer, msgtok), code);
 
 	/* Let payment_finished_ handle this, so we mark it as pending */
 	return command_still_pending(cmd);
@@ -804,7 +809,7 @@ payment_waitsendpay_finished(struct command *cmd, const char *buffer,
 		break;
 	}
 
-	payment_fail(p);
+	payment_fail(p, "%s", p->result->message);
 	return command_still_pending(cmd);
 }
 
@@ -1234,10 +1239,11 @@ void payment_continue(struct payment *p)
 	abort();
 }
 
-void payment_fail(struct payment *p)
+void payment_fail(struct payment *p, const char *fmt, ...)
 {
 	p->end_time = time_now();
 	p->step = PAYMENT_STEP_FAILED;
+	p->failreason = tal_steal(p, reason);
 	payment_continue(p);
 }
 

plugins/libplugin-pay.h

@@ -258,6 +258,9 @@ struct payment {
 	const char *why;
 
 	const char *label;
+
+	/* Human readable explanation of why this payment failed. */
+	const char *failreason;
 };
 
 struct payment_modifier {
@@ -342,7 +345,8 @@ void payment_start(struct payment *p);
 void payment_continue(struct payment *p);
 
 /* Fails a partial payment and continues with the core flow. */
-void payment_fail(struct payment *p);
+void payment_fail(struct payment *p, const char *fmt, ...) PRINTF_FMT(2,3);
+
 struct payment *payment_root(struct payment *p);
 struct payment_tree_result payment_collect_result(struct payment *p);