Fix MIME policy failure on python version upgrade (#934)

Python 3.6 added a new `policy` attribute to `MIMEMultipart`.
MIMEMultipart may be part of the cached object pickle of a datasource.
Upgrading from an old version of python to 3.6+ will cause the
datasource to be invalid after pickle load.

This commit uses the upgrade framework to attempt to access the mime
message and fail early (thus discarding the cache) if we cannot.
Commit 78e89b03 should fix this issue more generally.

1 files changed, 30 insertions, 0 deletions

diff --git a/tests/integration_tests/modules/test_persistence.py b/tests/integration_tests/modules/test_persistence.py
new file mode 100644
index 00000000..00fdeaea
--- /dev/null
+++ b/tests/integration_tests/modules/test_persistence.py
@@ -0,0 +1,30 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+"""Test the behavior of loading/discarding pickle data"""
+from pathlib import Path
+
+import pytest
+
+from tests.integration_tests.instances import IntegrationInstance
+from tests.integration_tests.util import (
+    ASSETS_DIR,
+    verify_ordered_items_in_text,
+)
+
+
+PICKLE_PATH = Path('/var/lib/cloud/instance/obj.pkl')
+TEST_PICKLE = ASSETS_DIR / 'trusty_with_mime.pkl'
+
+
+@pytest.mark.lxd_container
+def test_log_message_on_missing_version_file(client: IntegrationInstance):
+    client.push_file(TEST_PICKLE, PICKLE_PATH)
+    client.restart()
+    assert client.execute('cloud-init status --wait').ok
+    log = client.read_from_file('/var/log/cloud-init.log')
+    verify_ordered_items_in_text([
+        "Unable to unpickle datasource: 'MIMEMultipart' object has no "
+        "attribute 'policy'. Ignoring current cache.",
+        'no cache found',
+        'Searching for local data source',
+        'SUCCESS: found local data from DataSourceNoCloud'
+    ], log)