From 4f2da1cc1d24cbc47025cc8613c0d3ec287a20f9 Mon Sep 17 00:00:00 2001 From: Daniel Watkins Date: Tue, 17 Nov 2020 16:37:29 -0500 Subject: introduce an upgrade framework and related testing (#659) This commit does the following: * introduces the `cloudinit.persistence` module, containing `CloudInitPickleMixin` which provides lightweight versioning of objects' pickled representations (and associated testing) * introduces a basic upgrade testing framework (in `cloudinit.tests.test_upgrade`) which unpickles pickles from previous versions of cloud-init (stored in `tests/data/old_pickles`) and tests invariants that the current cloud-init codebase expects * uses the versioning framework to address an upgrade issue where `Distro.networking` could get into an unexpected state, and uses the upgrade testing framework to confirm that the issue is addressed --- cloudinit/persistence.py | 67 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 cloudinit/persistence.py (limited to 'cloudinit/persistence.py') diff --git a/cloudinit/persistence.py b/cloudinit/persistence.py new file mode 100644 index 00000000..85aa79df --- /dev/null +++ b/cloudinit/persistence.py @@ -0,0 +1,67 @@ +# Copyright (C) 2020 Canonical Ltd. +# +# Author: Daniel Watkins +# +# This file is part of cloud-init. See LICENSE file for license information. + + +class CloudInitPickleMixin: + """Scaffolding for versioning of pickles. + + This class implements ``__getstate__`` and ``__setstate__`` to provide + lightweight versioning of the pickles that are generated for classes which + use it. Versioning is done at the class level. + + The current version of a class's pickle should be set in the class variable + ``_ci_pkl_version``, as an int. If not overriden, it will default to 0. + + On unpickle, the object's state will be restored and then + ``self._unpickle`` is called with the version of the stored pickle as the + only argument: this is where classes should implement any deserialization + fixes they require. (If the stored pickle has no version, 0 is passed.) + """ + + _ci_pkl_version = 0 + + def __getstate__(self): + """Persist instance state, adding a pickle version attribute. + + This adds a ``_ci_pkl_version`` attribute to ``self.__dict__`` and + returns that for serialisation. The attribute is stripped out in + ``__setstate__`` on unpickle. + + The value of ``_ci_pkl_version`` is ``type(self)._ci_pkl_version``. + """ + state = self.__dict__.copy() + state["_ci_pkl_version"] = type(self)._ci_pkl_version + return state + + def __setstate__(self, state: dict) -> None: + """Restore instance state and handle missing attributes on upgrade. + + This will be called when an instance of this class is unpickled; the + previous instance's ``__dict__`` is passed as ``state``. This method + removes the pickle version from the stored state, restores the + remaining state into the current instance, and then calls + ``self._unpickle`` with the version (or 0, if no version is found in + the stored state). + + See https://docs.python.org/3/library/pickle.html#object.__setstate__ + for further background. + """ + version = state.pop("_ci_pkl_version", 0) + self.__dict__.update(state) + self._unpickle(version) + + def _unpickle(self, ci_pkl_version: int) -> None: + """Perform any deserialization fixes required. + + By default, this does nothing. Classes using this mixin should + override this method if they have fixes they need to apply. + + ``ci_pkl_version`` will be the version stored in the pickle for this + object, or 0 if no version is present. + """ + + +# vi: ts=4 expandtab -- cgit v1.2.3