变量 – 脚本尝试创建全局变量

发布时间：2020-12-15 00:23:21 所属栏目：大数据来源：网络整理

导读：我想将一个脚本加载到redis中,这将导出未来脚本执行所依赖的函数,但尝试定义全局函数失败,全局变量也是如此： redis 127.0.0.1:6379 EVAL "function alex() return 3.1415 end" 0(error) ERR Error running script (call to f_f24a5a054d91ccc74c2629e113f8f

我想将一个脚本加载到redis中,这将导出未来脚本执行所依赖的函数,但尝试定义全局函数失败,全局变量也是如此：

redis 127.0.0.1:6379> EVAL "function alex() return 3.1415 end" 0
(error) ERR Error running script (call to f_f24a5a054d91ccc74c2629e113f8f639bbedbfa2): user_script:1: Script attempted to create global variable 'alex'

如何定义全局函数和变量？

解决方法

查看文件scripting.c中的源代码

/* This function installs metamethods in the global table _G that prevent
 * the creation of globals accidentally.
 *
 * It should be the last to be called in the scripting engine initialization
 * sequence,because it may interact with creation of globals. */
void scriptingEnableGlobalsProtection(lua_State *lua) {
    char *s[32];
    sds code = sdsempty();
    int j = 0;

    /* strict.lua from: http://metalua.luaforge.net/src/lib/strict.lua.html.
     * Modified to be adapted to Redis. */
    s[j++]="local mt = {}n";
    s[j++]="setmetatable(_G,mt)n";
    s[j++]="mt.__newindex = function (t,n,v)n";
    s[j++]="  if debug.getinfo(2) thenn";
    s[j++]="    local w = debug.getinfo(2,"S").whatn";
    s[j++]="    if w ~= "main" and w ~= "C" thenn";
    s[j++]="      error("Script attempted to create global variable '"..tostring(n).."'",2)n";
    s[j++]="    endn";
    s[j++]="  endn";
    s[j++]="  rawset(t,v)n";
    s[j++]="endn";
    s[j++]="mt.__index = function (t,n)n";
    s[j++]="  if debug.getinfo(2) and debug.getinfo(2,"S").what ~= "C" thenn";
    s[j++]="    error("Script attempted to access unexisting global variable '"..tostring(n).."'",2)n";
    s[j++]="  endn";
    s[j++]="  return rawget(t,n)n";
    s[j++]="endn";
    s[j++]=NULL;

    for (j = 0; s[j] != NULL; j++) code = sdscatlen(code,s[j],strlen(s[j]));
    luaL_loadbuffer(lua,code,sdslen(code),"@enable_strict_lua");
    lua_pcall(lua,0);
    sdsfree(code);
}

scriptingEnableGlobalsProtection的doc-string表明intent是通知脚本作者常见错误(不使用local).

看起来这不是安全功能,所以我们有两个解决方案：

可以删除此保护：

local mt = setmetatable(_G,nil)
-- define global functions / variables
function alex() return 3.1415 end
-- return globals protection mechanizm
setmetatable(_G,mt)

或者使用rawset：

local function alex() return 3.1415 end
rawset(_G,"alex",alex)

（编辑：李大同）

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