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

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116

/* 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 ; }