//ngx_http_write_filter_module是最后一个包体writer模块(ngx_http_top_body_filter = ngx_http_write_filter;),他是最后放包体的地方//调用ngx_http_output_filter方法即可向客户端发送HTTP响应包体,ngx_http_send_header发送响应行和响应头部ngx_http_output