fix(make-mime): preserve non-ASCII attachment filenames

cloudinit/cmd/devel/make_mime.py

@@ -28,7 +28,7 @@ def create_mime_message(files):
         contents = fh.read()
         sub_message = MIMEText(contents, format_type, sys.getdefaultencoding())
         sub_message.add_header(
-            "Content-Disposition", 'attachment; filename="%s"' % (filename)
+            "Content-Disposition", "attachment", filename=filename
         )
         content_type = sub_message.get_content_type().lower()
         if content_type not in get_content_types():

tests/unittests/cmd/devel/test_make_mime.py

@@ -0,0 +1,43 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+
+from email import message_from_string
+from io import StringIO
+
+import pytest
+
+from cloudinit.cmd.devel.make_mime import create_mime_message
+from cloudinit.user_data import UserDataProcessor
+
+
+@pytest.mark.parametrize(
+    "filename",
+    [
+        "config.yaml",
+        "my config.yaml",
+        'config"prod.yaml',
+        "config\\prod.yaml",
+        "café.yaml",
+        "إعداد.yaml",
+    ],
+)
+@pytest.mark.parametrize("process_user_data", [False, True])
+def test_attachment_filename_round_trip(
+    filename: str, process_user_data: bool, ud_proc: UserDataProcessor
+) -> None:
+    """Preserve attachment filenames when parsing generated MIME user-data."""
+    contents = "#cloud-config\nhostname: example\n"
+    message, errors = create_mime_message(
+        [(StringIO(contents), filename, "cloud-config")]
+    )
+    assert errors == []
+
+    serialized = message.as_string()
+    if process_user_data:
+        parsed = ud_proc.process(serialized)
+    else:
+        parsed = message_from_string(serialized)
+
+    [attachment] = parsed.get_payload()
+    assert attachment.get_filename() == filename
+    assert attachment.get_content_type() == "text/cloud-config"
+    assert attachment.get_payload(decode=True) == contents.encode("utf-8")