ubus: fix legacy empty reply format

The legacy ubus protocol must not include an empty object in the result
array if the invoked ubus procedure yielded no response.

This fixes compatibility with existing legacy ubus api clients that expect
this behaviour, LuCI's fs.js in particular.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 8 insertions, 4 deletions

diff --git a/ubus.c b/ubus.c
index 39b38b2..cc7447e 100644
--- a/ubus.c
+++ b/ubus.c
@@ -465,10 +465,14 @@ uh_ubus_request_cb(struct ubus_request *req, int ret)
 		uh_ubus_init_json_rpc_response(cl, &buf);
 		r = blobmsg_open_array(&buf, "result");
 		blobmsg_add_u32(&buf, "", ret);
-		c = blobmsg_open_table(&buf, NULL);
-		blob_for_each_attr(cur, du->buf.head, rem)
-			blobmsg_add_blob(&buf, cur);
-		blobmsg_close_table(&buf, c);
+
+		if (blob_len(du->buf.head)) {
+			c = blobmsg_open_table(&buf, NULL);
+			blob_for_each_attr(cur, du->buf.head, rem)
+				blobmsg_add_blob(&buf, cur);
+			blobmsg_close_table(&buf, c);
+		}
+
 		blobmsg_close_array(&buf, r);
 		uh_ubus_send_response(cl, &buf);
 		return;