Parse the body of a http request, based on the Content-Type request
header. Currently supports the three most important content types:
application/x-www-form-urlencoded (parse_query),
multipart/form-data (parse_multipart) and
application/json (fromJSON).
parse_http(body, content_type, ...)request body of the http request
content-type http request header as specified by the client
additional arguments passed to parser function