redis执行lua lua执行redis

redis-2.6支持通过EVAL命令来执行lua脚本，对lua脚本的支持扩展了redis的应用场景，redis支持路脚本需要做2件事

1. redis能执行lua脚本
2. 在lua脚本里能执行redis的命令

接下来，我将通过一个简单的实例来解析redis如何完成上述两个工作的。

 

构建一个简单的redis

#define DICT_SIZE 100
struct redisDict {
  char* key[DICT_SIZE];
  char* value[DICT_SIZE];
  int  idx;
};

static void setCommand(const char *key, const char *value)
{
    /* ignore memory issue for simple */
    if (dict.idx + 1 <= DICT_SIZE) {
    dict.key[dict.idx] = (char *)malloc(strlen(key) + 1);
    strcpy(dict.key[dict.idx], key);

    dict.value[dict.idx] = (char *)malloc(strlen(value) + 1);
    strcpy(dict.value[dict.idx], value);

    dict.idx += 1;
  }
}

static const char *getCommand(const char *key)
{
  int j;
  for (j = 0; j <= dict.idx; j++) {
    if (strcmp(dict.key[j], key) == 0) {
      return dict.value[j];
    }
  }
  return "KeyNotFound";
}

上述代码实现了一个伪redis，支持setCommand、getCommand。

C调用lua脚本

具体例子参考http://lua-users.org/wiki/SimpleLuaApiExample

/*
 * All Lua contexts are held in this structure. We work with it almost
 * all the time.
 */
lua_State *L = luaL_newstate();

luaL_openlibs(L); /* Load Lua libraries */

/* Load the file containing the script we are going to run */
status = luaL_loadfile(L, "script.lua");

/* Ask Lua to run our little script */
result = lua_pcall(L, 0, LUA_MULTRET, 0);

上述代码片段中，其中script.lua是一个lua脚本。redis里稍有不同，redis里的脚本是通过EVAL命令传递到服务器端，redis将脚本拼成一个lua函数，然后调用loadbuffer，而这里从文件执行脚本调用的loadfile。

lua调用C函数

下面的lua代码里，调用的是redis的setCommand和getCommand。

redis.call("set", "foo", "bar");

return redis.call("get", "foo");

要想lua脚本能调用C代码，需要现在lua环境注册对应的C函数，参考redis的scriptingInit函数。

static int call(lua_State *L)
{
  int argc = lua_gettop(L);
  const char *cmd = lua_tostring(L, 1);
  const char *key = lua_tostring(L, 2);
  if (strcmp(cmd, "set") == 0) {
    assert(argc == 3);
    const char *value = lua_tostring(L, 3);
    setCommand(key, value);
   return 0;
  } else if (strcmp(cmd, "get") == 0) {
    assert(argc == 2);
    lua_pushstring(L, getCommand(key));
    return 1;
  }

  lua_pushstring(L, "Invalid Command");
  return 1;
}

static void scriptingInit()
{

  L = luaL_newstate();

  luaL_openlibs(L);

  /* Register the redis commands table and fields */
  lua_newtable(L);

  /* redis.call */
  lua_pushstring(L, "call");
  lua_pushcfunction(L, call);
  lua_settable(L, -3);

  /* Finally set the table as 'redis' global var. */
  lua_setglobal(L, "redis");
}

完整示例代码

1 2	redis.call("set", "foo", "bar"); return redis.call("get", "foo");

来自CODE的代码片

script.lua

 

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/* gcc -o test_lua lua.c -llua -lm -ldl */ #include <lua.h> #include <lauxlib.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <assert.h>   #define DICT_SIZE 100 struct redisDict { char* key[DICT_SIZE]; char* value[DICT_SIZE]; int idx; };   struct redisDict dict; lua_State *L;   static void setCommand(const char *key, const char *value) { /* ignore memory issue for simple */ if (dict.idx + 1 <= DICT_SIZE) { dict.key[dict.idx] = (char *)malloc(strlen(key) + 1); strcpy(dict.key[dict.idx], key);   dict.value[dict.idx] = (char *)malloc(strlen(value) + 1); strcpy(dict.value[dict.idx], value);   dict.idx += 1; } }   static const char *getCommand(const char *key) { int j; for (j = 0; j <= dict.idx; j++) { if (strcmp(dict.key[j], key) == 0) { return dict.value[j]; } } return "KeyNotFound"; }   static int call(lua_State *L) { int argc = lua_gettop(L); const char *cmd = lua_tostring(L, 1); const char *key = lua_tostring(L, 2); if (strcmp(cmd, "set") == 0) { assert(argc == 3); const char *value = lua_tostring(L, 3); setCommand(key, value); return 0; } else if (strcmp(cmd, "get") == 0) { assert(argc == 2); lua_pushstring(L, getCommand(key)); return 1; }   lua_pushstring(L, "Invalid Command"); return 1; }   static void scriptingRun(const char* filename) { int status = luaL_loadfile(L, filename); if (status) { fprintf(stderr, "Couldn't load file: %s\n", lua_tostring(L, -1)); exit(1); }   /* Ask Lua to run our little script */ int result = lua_pcall(L, 0, LUA_MULTRET, 0); if (result) { fprintf(stderr, "Failed to run script: %s\n", lua_tostring(L, -1)); exit(1); }   /* Get the returned value at the top of the stack (index -1) */ const char *value = lua_tostring(L, -1);   printf("%s\n", value);   lua_pop(L, 1); /* Take the returned value out of the stack */ lua_close(L); /* Cya, Lua */ }   static void scriptingInit() { /* * All Lua contexts are held in this structure. We work with it almost * all the time. */ L = luaL_newstate();   /* Load Lua libraries */ luaL_openlibs(L);   /* Register the redis commands table and fields */ lua_newtable(L);   /* redis.call */ lua_pushstring(L, "call"); lua_pushcfunction(L, call); lua_settable(L, -3);   /* Finally set the table as 'redis' global var. */ lua_setglobal(L, "redis"); }   int main(void) { scriptingInit(); scriptingRun("script.lua"); return 0; }