nginx+lua+memcached，报错：curl: (52) Empty ?报错

server {
  listen 80;
  server_name localhost;
  index index.html index.htm index.jsp;
  root /www;
  
  autoindex on;
  autoindex_exact_size on;
  autoindex_localtime on;

  location / {
    default_type text/html;

    access_by_lua '
      clinetIP = ngx.req.get_headers()["X-Real-IP"]
      if clinetIP == nil then
        clientIP = ngx.req.get_headers()["x_forwarded_for"]
      end
      if clinetIP == nil then
        clinetIP = ngx.var.remote_addr
      end
      ngx.say(clientIP)
      
      local memcached = require "resty.memcached"
      local memc, err = memcached:new()
      if not memc then
        ngx.say("failed to instantiate memc: ", err)
        return
      end
      local ok, err = memc:connect("127.0.0.1", 11211)
      if not ok then
        ngx.say("failed to connect: ", err)
        return
      end
      
      local res, flags, err = memc:get("id")
      ngx.say(res)
    
      if err then
        ngx.say("failed to get clientIP ", err)
        return
      end

      if res == "1" then
        ngx.exec("@client_test")
        return
      end

      ngx.exec("@client")
    ';
  }

  location @client{
    echo "client";
  }

  location @client_test{
    echo "client_test";
  }
}

但是执行curl http://localhost/，报错：

curl: (52) Empty reply from server

这是什么意思？