paymod: Add reason why a payment was attempted

This is a slight change in interface in that the string no longer spells out
that a specific node was excluded.

plugins/libplugin-pay.c

@@ -21,6 +21,7 @@ struct payment *payment_new(tal_t *ctx, struct command *cmd,
 	p->start_time = time_now();
 	p->result = NULL;
 	p->getroute_cltv = DEFAULT_FINAL_CLTV_DELTA;
+	p->why = NULL;
 
 	/* Copy over the relevant pieces of information. */
 	if (parent != NULL) {
@@ -1144,6 +1145,9 @@ static inline void retry_step_cb(struct retry_mod_data *rd,
 		subpayment = payment_new(p, NULL, p, p->modifiers);
 		payment_start(subpayment);
 		p->step = PAYMENT_STEP_RETRY;
+		subpayment->why =
+		    tal_fmt(subpayment, "Still have %d attempts left",
+			    rdata->retries - 1);
 	}
 
 	payment_continue(p);

plugins/libplugin-pay.h

@@ -228,6 +228,9 @@ struct payment {
 	/* Serialized bolt11 string, kept attachd to the root so we can filter
 	 * by the invoice. */
 	const char *bolt11;
+
+	/* Textual explanation of why this payment was attempted. */
+	const char *why;
 };
 
 struct payment_modifier {

plugins/pay.c

@@ -1497,6 +1497,8 @@ static void paystatus_add_payment(struct json_stream *s, const struct payment *p
 	utc_timestring(&p->start_time, timestr);
 
 	json_object_start(s, NULL);
+	if (p->why != NULL)
+		json_add_string(s, "strategy", p->why);
 	json_add_string(s, "start_time", timestr);
 	json_add_u64(s, "age_in_seconds",
 		     time_to_sec(time_between(time_now(), p->start_time)));
@@ -1517,6 +1519,11 @@ static void paystatus_add_payment(struct json_stream *s, const struct payment *p
 			json_object_start(s, "failure");
 		json_add_sendpay_result(s, p->result);
 		json_object_end(s);
+	} else {
+		json_object_start(s, "failure");
+		json_add_num(s, "code", PAY_ROUTE_NOT_FOUND);
+		json_add_string(s, "message", "Call to getroute: Could not find a route");
+		json_object_end(s);
 	}
 
 	json_object_end(s);
@@ -1888,6 +1895,7 @@ static struct command_result *json_paymod(struct command *cmd,
 				: NULL;
 	p->invoice = tal_steal(p, b11);
 	p->bolt11 = tal_steal(p, b11str);
+	p->why = "Initial attempt";
 	payment_start(p);
 	list_add_tail(&payments, &p->list);
 

tests/test_pay.py

@@ -156,7 +156,6 @@ def test_pay_exclude_node(node_factory, bitcoind):
     assert len(status) == 2
     assert status[0]['strategy'] == "Initial attempt"
     assert status[0]['failure']['data']['failcodename'] == 'WIRE_TEMPORARY_NODE_FAILURE'
-    assert status[1]['strategy'].startswith("Excluded node {}".format(l2.info['id']))
     assert 'failure' in status[1]
 
     # l1->l4->l5->l3 is the longer route. This makes sure this route won't be
@@ -197,7 +196,6 @@ def test_pay_exclude_node(node_factory, bitcoind):
     assert len(status) == 2
     assert status[0]['strategy'] == "Initial attempt"
     assert status[0]['failure']['data']['failcodename'] == 'WIRE_TEMPORARY_NODE_FAILURE'
-    assert status[1]['strategy'].startswith("Excluded node {}".format(l2.info['id']))
     assert 'success' in status[1]