redis 脚本尝试创建全局变量

jdgnovmf  于 2023-10-15  发布在  Redis
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我想加载一个脚本到redis,将导出函数,未来执行的脚本将依赖于,但试图定义全局函数失败,同样适用于全局变量:

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?

zte4gxcn

zte4gxcn1#

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) then\n";
    s[j++]="    local w = debug.getinfo(2, \"S\").what\n";
    s[j++]="    if w ~= \"main\" and w ~= \"C\" then\n";
    s[j++]="      error(\"Script attempted to create global variable '\"..tostring(n)..\"'\", 2)\n";
    s[j++]="    end\n";
    s[j++]="  end\n";
    s[j++]="  rawset(t, n, v)\n";
    s[j++]="end\n";
    s[j++]="mt.__index = function (t, n)\n";
    s[j++]="  if debug.getinfo(2) and debug.getinfo(2, \"S\").what ~= \"C\" then\n";
    s[j++]="    error(\"Script attempted to access unexisting global variable '\"..tostring(n)..\"'\", 2)\n";
    s[j++]="  end\n";
    s[j++]="  return rawget(t, n)\n";
    s[j++]="end\n";
    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,0,0,0);
    sdsfree(code);
}

scriptingEnableGlobalsProtection的文档字符串表明其意图是通知脚本作者常见的错误(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:
可以解除这种保护:

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)
yqkkidmi

yqkkidmi2#

你可以将你定义的函数赋给一个var,并通过var名称调用,例如:

local add = function(a, b)
  return a + b
end

local sum = add(1, 3)

这种方式对我来说很好,即使是在3.x版本的redis上。

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