Function luaL_prepbuffer 

pub fn luaL_prepbuffer(b: *mut LuaBuffer) -> *mut c_char

Returns an address to a space of size [$crate::lua::BUFFERSIZE] where you can copy a string to be added to buffer LuaBuffer b. After copying the string into this space you must call luaL_addsize with the size of the string to actually add it to the buffer.