redis执行lua lua执行redis

gqinvs

　　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

• redis能执行lua脚本
  
• 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; }