How to allocate into a vector<char> in libuv?

gistfile1.cpp

uv_buf_t alloc_buffer(uv_handle_t * handle, size_t suggested_size) {
  vector<char> * data = new vector<char>(suggested_size);
  return uv_buf_init(data->data(), suggested_size);
}

void on_read(uv_stream_t* stream, ssize_t nread, uv_buf_t buf) {
  vector<char> * data = reinterpret_cast<vector<char> * >(buf.__data);
  // do something else
  delete data;
}

The handle is the same across calls to on_read though right? so there's be no way to know which on_read applied to which on_alloc