CBson

static VALUE method_deserialize(VALUE self, VALUE bson) {
    const char* buffer = RSTRING_PTR(bson);
    int remaining = RSTRING_LENINT(bson);

    // NOTE we just swallow the size and end byte here
    buffer += 4;
    remaining -= 5;

    return elements_to_hash(buffer, remaining);
}

static VALUE method_max_bson_size(VALUE self) {
    return INT2FIX(max_bson_size);
}

static VALUE method_serialize(VALUE self, VALUE doc, VALUE check_keys,
    VALUE move_id, VALUE max_size) {

    VALUE result;
    bson_buffer_t buffer = bson_buffer_new();
    bson_buffer_set_max_size(buffer, FIX2INT(max_size));
    if (buffer == NULL) {
        rb_raise(rb_eNoMemError, "failed to allocate memory in buffer.c");
    }

    write_doc(buffer, doc, check_keys, move_id);

    result = rb_str_new(bson_buffer_get_buffer(buffer), bson_buffer_get_position(buffer));
    if (bson_buffer_free(buffer) != 0) {
        rb_raise(rb_eRuntimeError, "failed to free buffer");
    }
    return result;
}

static VALUE method_update_max_bson_size(VALUE self, VALUE connection) {
    max_bson_size = FIX2INT(rb_funcall(connection, rb_intern("max_bson_size"), 0));
    return INT2FIX(max_bson_size);
}