Haproxy request size restriction

Is it possible to implement somehow request size restriction on haproxy side? As I understand how haproxy works it passes data from frontend socket to backend. If it works on HTTP level it might detect amount of data transferred during the session. And if this amount reach some limit, e.g. 20 MB it abororts the session. Is it possible to configure somehow such logic? Maby lua can help? But I do not want to collect all 20 MB to haproxy memory, ofcourse.