Redis Lua区分空数组和对象 [英] Redis Lua Differetiating empty array and object

问题描述

当我在Redis 3.2中使用脚本在json对象中设置特定值时，我在cjson lua中遇到了该错误.

I encountered this bug in cjson lua when I was using a script in redis 3.2 to set a particular value in a json object.

当前，redis中的lua不能区分空的json数组或空的json对象.序列化其中包含数组的json对象时，这会导致严重的问题.

Currently, the lua in redis does not differentiate between an empty json array or an empty json object. Which causes serious problems when serialising json objects that have arrays within them.

eval "local json_str = '{\"items\":[],\"properties\":{}}' return cjson.encode(cjson.decode(json_str))" 0

结果:

"{\"items\":{},\"properties\":{}}"

我找到了此解决方案 https://github.com/mpx/lua-cjson/issues/11 ，但是我无法在redis脚本中实现.

I found this solution https://github.com/mpx/lua-cjson/issues/11 but I wasn't able to implement in a redis script.

这是失败的尝试:

eval 

"function cjson.mark_as_array(t) 
local mt = getmetatable(t) or {} 
mt.__is_cjson_array = true 
return setmetatable(t, mt) 
end 
function cjson.is_marked_as_array(t) 
local mt = getmetatable(t) 
return mt and mt.__is_cjson_array end 
local json_str = '{\"items\":[],\"properties\":{}}' 
return cjson.encode(cjson.decode(json_str))" 

0

感谢任何帮助或指针.

推荐答案

有两个计划.

1. 修改lua-cjson源代码并编译redis，单击通过代码固定:

   local now = redis.call("time")
   -- local timestamp = tonumber(now[1]) * 1000 + math.floor(now[2]/1000)
   math.randomseed(now[2])
   local emptyFlag = "empty_" .. now[1] .. "_" .. now[2] .. "_" .. math.random(10000)
   local emptyArrays = {}
   local function emptyArray()
       if cjson.as_array then
           -- cjson fixed:  https://github.com/xiyuan-fengyu/redis-lua-cjson-empty-table-fix
           local arr = {}
           setmetatable(arr, cjson.as_array)
           return arr
       else
           -- plan 2
           local arr = {}
           table.insert(emptyArrays, arr)
           return arr
       end
   end
   
   local function toJsonStr(obj)
       if #emptyArrays > 0 then
           -- plan 2
           for i, item in ipairs(emptyArrays) do
               if #item == 0 then
                   -- empty array, insert a special mark
                   table.insert(item, 1, emptyFlag)
               end
           end
   
           local jsonStr = cjson.encode(obj)
           -- replace empty array
           jsonStr = (string.gsub(jsonStr, '%["' .. emptyFlag ..  '"]', "[]"))
   
           for i, item in ipairs(emptyArrays) do
               if item[1] == emptyFlag then
                   table.remove(item, 1)
               end
           end
           return jsonStr
       else
           return cjson.encode(obj)
       end
   end
   
   
   -- example
   local arr = emptyArray()
   local str = toJsonStr(arr)
   print(str) -- "[]"
   

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