Pushing C pointer to stack, getting table - c

Question

I have two functions defined in C code:
static int luaMp4_load(lua_State *L){
LPP_Mp4 *ret = LPP_Mp4Load(luaL_checkstring(L, 1));
*pushMp4(L) = ret;
return(1);
}
static int luaMp4_play(lua_State *L){
LPP_Mp4Play(*toMp4(L, 1), luaL_checknumber(L, 2));
return 0;
}
which are called one by one in Lua:
Mp4.load(movie)
Mp4:play(60)
Functions pushMp4 and toMp4 are
LPP_Mp4** toMp4 (lua_State *L, int index){
LPP_Mp4** handle = (LPP_Mp4**)lua_touserdata(L, index);
if (handle == NULL) luaL_typerror(L, index, "Mp4");
return handle;
}
LPP_Mp4** pushMp4(lua_State *L) {
LPP_Mp4** newvalue = (LPP_Mp4**)lua_newuserdata(L, sizeof(LPP_Mp4*));
lua_getfield(L, LUA_REGISTRYINDEX, "Mp4");
lua_setmetatable(L, -2);
return newvalue;
}
The problem is, I'm getting a NULL handle in luaMp4_play, and it says that object in the first index of stack is table (while Mp4 expected) - inside of luaL_typerror(lua_State *L, int narg, const char *tname):
const char *msg = lua_pushfstring(L, "%s expected, got %s",
tname, lua_typename(L, lua_type(L,(narg))));
How can I get rid of it?
Edit:
LPP_Mp4 struct:
typedef struct {
struct mp4_read_struct reader;
Mp4AvcNalStruct nal;
struct mp4_video_read_output_struct v_packet;
Mp4AvcDecoderStruct *avc;
Mp4AvcCscStruct *csc;
} LPP_Mp4;
lua_touserdata is a Lua API library function:
LUA_API void *lua_touserdata (lua_State *L, int idx) {
StkId o = index2adr(L, idx);
switch (ttype(o)) {
case LUA_TUSERDATA: return (rawuvalue(o) + 1);
case LUA_TLIGHTUSERDATA: return pvalue(o);
default: return NULL;
}
}
https://github.com/lua/lua/blob/master/src/lapi.c - line 413

Answer 1

I was confused with return(1); in C code and had no doubt that Mp4:load() returns any value
Thanks to Etan Reisner for pointing to it, worked with:
mv = Mp4.load(movie)
mv:play(60)