如何在NGINX + Lua中仅读取文本POST参数并丢弃文件上传？

我有一个小的 ngx_lua 脚本，它通过 post_action 将一些使用统计数据收集到 Redis（lua-resty-redis），我想只收集文本参数并丢弃文件上传。

我的配置：

worker_processes  1;
error_log logs/error.log;
daemon  off;

events {
  worker_connections  1024;
}

http {
  server {
    listen 8080;

    location / {
      proxy_read_timeout  30s;
      proxy_pass  http://localhost:8081;
      proxy_set_header  Host  $http_host;
      proxy_http_version  1.1;
      proxy_set_header  Upgrade $http_upgrade;
      proxy_set_header  Connection  "upgrade";
      proxy_set_header  X-Forwaded-For $proxy_add_x_forwarded_for;
      proxy_set_header  X-Real-IP $remote_addr;

      post_action @post_action;
    }

    location /test {
      content_by_lua_file capture.lua;
    }

    location @post_action {
      internal;
      content_by_lua_file capture.lua;
    }
  }
}

Lua 脚本（简化）：

local json = require "cjson"
local redis = require "resty.redis"
local red = redis:new()

red:set_timeout(1000)

local ok, err = red:connect("127.0.0.1", 6379)

if not ok then
    ngx.say("failed to connect: ", err)
    return
end

local data = {}

ngx.req.read_body()

local data = json.encode(ngx.req.get_post_args())

local ok, err = red:rpush("post_data", data)

if not ok then
    ngx.say("failed to push request data: ", err)
    return
end

当我收到同时包含文件和文本的请求时，脚本会崩溃并显示此错误：

request body in temp file not supported