'Preserve the cached image id, version for consumption by the
process_response method of this middleware'

@staticmethod
def _fetch_request_info(request):

    try:
        image_id = request.environ['api.cache.image_id']
        method = request.environ['api.cache.method']
        version = request.environ['api.cache.version']
    except KeyError:
        return None
    else:
        return (image_id, method, version)
