rem: snprintf(buf, sizeof(buf), "%lu", upload->chunk->stop - upload->chunk->start); tcp_writestr(upload->con, buf);
add: tcp_writestr(upload->con, stringf("%lu", upload->chunk->stop - upload->chunk->start));
context: static void on_upload_send_filesize(int fd, input_id input,                                    void *udata){	OpnUpload *upload = (OpnUpload *) udata;	char buf[16];	input_remove(input);	snprintf(buf, sizeof(buf), "%lu",	         upload->chunk->stop - upload->chunk->start);	tcp_writestr(upload->con, buf);		input_add(upload->con->fd, upload, INPUT_WRITE,	          on_upload_write, TIMEOUT_DEF);}