luaL_pushresultsize
LUALIB_API void (luaL_pushresultsize) (luaL_Buffer *B, size_t sz);
luaL_pushresultsize(&b, l);
luaL_pushresultsize(&b, l);
luaL_pushresultsize(&b, totallen);
luaL_pushresultsize(&b, n);
luaL_pushresultsize(&b, l);