Using wp_handle_upload in the XML-RPC

[markoheijnen]

At this moment there isn't a check for file size when uploading an image through the XML-RPC. The reason is that the method wp_upload_bits is used. This only checks it does is if the file size is to big for a network installation.

The function check_upload_size() is something what you want except that it will use wp_die() if there is an error like this. The function is used as a filter: wp_handle_upload_prefilter. Which only get applied in the function wp_handle_upload.

We should change some of the functions to allow to return an error instead of using wp_die(). When you look into check_upload_size() this should get a second parameter instead of checking if there is a $_POST variable set.

related: #6559 and #21085