Hetzner: support reading user-data that is base64 encoded. (#448)

Hetzner cloud only supports user-data as a string (presumably utf-8).

In order to allow users on Hetzner to provide binary data to cloud-init,
we will attempt to base64decode the userdata.

The change here adds a 'maybe_b64decode' function that will decode data
if and only if is base64 encoded.

The reason for not using util.b64d is that we do not want the return value
decoded to a string, and util.b64d will do that if it can.  Additionally
we call decode with validate=True which oddly is not the default.

LP: #1884071

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/unittests/test_datasource/test_hetzner.py b/tests/unittests/test_datasource/test_hetzner.py
index a9c12597..d0879545 100644
--- a/tests/unittests/test_datasource/test_hetzner.py
+++ b/tests/unittests/test_datasource/test_hetzner.py
@@ -5,10 +5,14 @@
 # This file is part of cloud-init. See LICENSE file for license information.
 
 from cloudinit.sources import DataSourceHetzner
+import cloudinit.sources.helpers.hetzner as hc_helper
 from cloudinit import util, settings, helpers
 
 from cloudinit.tests.helpers import mock, CiTestCase
 
+import base64
+import pytest
+
 METADATA = util.load_yaml("""
 hostname: cloudinit-test
 instance-id: 123456
@@ -115,3 +119,22 @@ class TestDataSourceHetzner(CiTestCase):
         # These are a white box attempt to ensure it did not search.
         m_find_fallback.assert_not_called()
         m_read_md.assert_not_called()
+
+
+class TestMaybeB64Decode:
+    """Test the maybe_b64decode helper function."""
+
+    @pytest.mark.parametrize("invalid_input", (str("not bytes"), int(4)))
+    def test_raises_error_on_non_bytes(self, invalid_input):
+        """maybe_b64decode should raise error if data is not bytes."""
+        with pytest.raises(TypeError):
+            hc_helper.maybe_b64decode(invalid_input)
+
+    @pytest.mark.parametrize("in_data,expected", [
+        # If data is not b64 encoded, then return value should be the same.
+        (b"this is my data", b"this is my data"),
+        # If data is b64 encoded, then return value should be decoded.
+        (base64.b64encode(b"data"), b"data"),
+    ])
+    def test_happy_path(self, in_data, expected):
+        assert expected == hc_helper.maybe_b64decode(in_data)