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; } |
来自CODE的代码片
lua.c