How does Nginx proxy_pass record response?

Question

Two methods were used to record response logs, but the data in both logs were found to be garbled. It is suspected that the data in the memory was recorded directly. What is the reason?

The first way:

Using the method of master yexiaobai, the source address is as follows:
/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/;
    }
    }
}

Second way:

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/;
}

Answer 1

Solved, solution:

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])';
}