Tests: tests for usage of discarded body. The client_max_body_size limit should be ignored when the request body is already discarded. In HTTP/1.x, this is done by checking the r->discard_body flag when the body is being discarded, and because r->headers_in.content_length_n is 0 when it's already discarded. This, however, does not happen with HTTP/2 and HTTP/3, and therefore "error_page 413" does not work without relaxing the limit. Further, with proxy_pass, r->headers_in.content_length_n is used to determine length of the request body, and therefore is not correct if discarding of the request body isn't yet complete. While discarding the request body, r->headers_in.content_length_n contains the rest of the body to discard (or, in case of chunked request body, the rest of the current chunk to discard). Similarly, the $content_length variable uses r->headers_in.content_length if available, and also incorrect. The $content_length variable is used when proxying with fastcgi_pass, grpc_pass, and uwsgi_pass (scgi_pass uses the value calculated based on the actual request body buffers, and therefore works correctly).