json-rpc: Add the error onion if we stored it in the DB

If we can't decode the onion, because the onion got corrupted or we used
`sendonion` without specifying the `shared_secrets` used, the best we can do
is tell the caller instead.

lightningd/pay.c

@@ -108,6 +108,10 @@ void json_add_payment_fields(struct json_stream *response,
 		json_add_string(response, "label", t->label);
 	if (t->bolt11)
 		json_add_string(response, "bolt11", t->bolt11);
+
+	if (t->failonion)
+		json_add_hex(response, "erroronion", t->failonion,
+			     tal_count(t->failonion));
 }
 
 static struct command_result *sendpay_success(struct command *cmd,
@@ -855,6 +859,7 @@ send_payment(struct lightningd *ld,
 	payment->path_secrets = tal_steal(payment, path_secrets);
 	payment->route_nodes = tal_steal(payment, ids);
 	payment->route_channels = tal_steal(payment, channels);
+	payment->failonion = NULL;
 	if (label != NULL)
 		payment->label = tal_strdup(payment, label);
 	else
@@ -1034,6 +1039,7 @@ static struct command_result *json_sendonion(struct command *cmd,
 	payment->route_nodes = NULL;
 	payment->route_channels = NULL;
 	payment->bolt11 = NULL;
+	payment->failonion = NULL;
 	payment->path_secrets = tal_steal(payment, path_secrets);
 
 	if (label != NULL)

tests/test_pay.py

@@ -2559,5 +2559,5 @@ def test_sendonion_rpc(node_factory):
     try:
         l1.rpc.waitsendpay(payment_hash=payment_hash)
     except RpcError as e:
-        assert(e.error['code'] == 202)
-        assert(e.error['message'] == "Malformed error reply")
+        assert(e.error['code'] == 204)
+        assert(e.error['data']['raw_message'] == "400f00000000000003e80000006c")

wallet/wallet.c

@@ -2244,6 +2244,13 @@ static struct wallet_payment *wallet_stmt2payment(const tal_t *ctx,
 	else
 		payment->bolt11 = NULL;
 
+	if (!db_column_is_null(stmt, 13))
+		payment->failonion =
+		    tal_dup_arr(payment, u8, db_column_blob(stmt, 13),
+				db_column_bytes(stmt, 13), 0);
+	else
+		payment->failonion = NULL;
+
 	return payment;
 }
 
@@ -2273,6 +2280,7 @@ wallet_payment_by_hash(const tal_t *ctx, struct wallet *wallet,
 					     ", msatoshi_sent"
 					     ", description"
 					     ", bolt11"
+					     ", failonionreply"
 					     " FROM payments"
 					     " WHERE payment_hash = ?"));
 
@@ -2492,6 +2500,7 @@ wallet_payment_list(const tal_t *ctx,
 						  ", msatoshi_sent"
 						  ", description"
 						  ", bolt11"
+						  ", failonionreply"
 						  " FROM payments"
 						  " WHERE payment_hash = ?;"));
 		db_bind_sha256(stmt, 0, payment_hash);
@@ -2510,6 +2519,7 @@ wallet_payment_list(const tal_t *ctx,
 						     ", msatoshi_sent"
 						     ", description"
 						     ", bolt11"
+						     ", failonionreply"
 						     " FROM payments;"));
 	}
 	db_query_prepared(stmt);

wallet/wallet.h

@@ -267,6 +267,9 @@ struct wallet_payment {
 
 	/* The label of the payment. Must support `tal_len` */
 	const char *label;
+
+	/* If we could not decode the fail onion, just add it here. */
+	const u8 *failonion;
 };
 
 struct outpoint {