Nginx proxy_pass如何记录response?

使用了两种方式记录response日志，但是发现两种日志的数据都是乱码，怀疑是直接记录了内存中的数据，这是什么原因呢？

第一种方式：

采用yexiaobai大神的方式，源地址如下：
http://.com/blog/yexiaobai/1190000000606867

worker_processes  1;
error_log logs/error.log;
events {
    worker_connections 1024;
}
http {
    log_format log_req_resp '$remote_addr - $remote_user [$time_local] '
        '"$request" $status $body_bytes_sent '
        '"$http_referer" "$http_user_agent" $request_time
        req_body:"$request_body" resp_body:"$resp_body"';
    server {
    listen       8088;
    server_name  localhost;
    access_log /tmp/nginx.resp.access.log log_req_resp;
    lua_need_request_body on;
    set $resp_body "";
    body_filter_by_lua '
        local resp_body = string.sub(ngx.arg[1], 1, 1000)
        ngx.ctx.buffered = (ngx.ctx.buffered or "") .. resp_body
        if ngx.arg[2] then
             ngx.var.resp_body = ngx.ctx.buffered
        end
    ';
    location / {
        proxy_pass http://173.194.14.40/;
    }
    }
}

第二种方式：

location /test {
    content_by_lua '
        -- res = ngx.location.capture("http://173.194.14.57/")
        local res = ngx.location.capture("/", { share_all_vars = true })
        file = io.open("/tmp/capture.log", "a+")
        file:write(res.body)
        file:close()
        -- ngx.var.resp_body = res.body
        ngx.print(res_s)
';

}

location / {
    proxy_pass http://173.194.14.40/;
}

---

已解决，解决方案：

error_log /tmp/nginx.resp.info.log info;

location / {
    proxy_pass http://vpsea.flvcd.com/;
    body_filter_by_lua 'ngx.log(ngx.INFO, ngx.arg[1])';
}