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
| redis . call ( " set" , " foo" , " bar" );
return redis . call ( " get" , " foo" );
|
来自CODE的代码片
script.lua
| /* 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 ;
}
|
