int PyObject_AsReadBuffer(PyObject *obj,
                          const void **buffer,
                          Py_ssize_t *buffer_len)
{
    PyBufferProcs *pb;
    Py_buffer view;

    if (obj == NULL || buffer == NULL || buffer_len == NULL) {
        null_error();
        return -1;
    }
    pb = obj->ob_type->tp_as_buffer;
    if (pb == NULL ||
        pb->bf_getbuffer == NULL) {
        PyErr_SetString(PyExc_TypeError,
                        "expected an object with a buffer interface");
        return -1;
    }

    if ((*pb->bf_getbuffer)(obj, &view, PyBUF_SIMPLE)) return -1;

    *buffer = view.buf;
    *buffer_len = view.len;
    if (pb->bf_releasebuffer != NULL)
        (*pb->bf_releasebuffer)(obj, &view);
    Py_XDECREF(view.obj);
    return 0;
}