wrap some json fields for influxdb api response by nginx_lua

ngx_lua_restructure_influxdb_response.conf

    upstream influxdb{
        server 127.0.0.1:8086;
    }

    server {
        listen 18086;
        proxy_pass_request_headers off;  # handle gziped capture <https://github.com/openresty/lua-nginx-module/issues/12>

        location / {
            proxy_pass http://influxdb/query;
        }


        location /query {
            add_header Content-Type 'application/json; charset=utf-8';  # make sure content-type is json
            content_by_lua_block {
                local method_map = {
                    GET = ngx.HTTP_GET,
                    POST = ngx.HTTP_POST,
                }
                ngx.req.read_body()
                local method = method_map[ngx.req.get_method()]
                local data = ngx.req.get_body_data()
                local args = ngx.req.get_uri_args()
                local res = ngx.location.capture("/", {method=method, data=data, args=args})
                local cjson = require "cjson"
                local new_body = {}
                if res.status ~= ngx.HTTP_OK then
                    new_body["code"] = res.status
                else
                    new_body["code"] = 0
                end
                new_body["msg"] = ''
                new_body["data"] = cjson.decode(res.body)
                ngx.say(cjson.encode(new_body))

            }
        }

    }