sambacc: make permissions module core work without xattr module

The xattr module works well if testing with the python3 packages from the
system but easily breaks when sing tox to test other python versions. This can
be resolved either by letting python compile the C code needed for xattr or by
skipping xattr support if it is not the available on our current python
version.  This patch implements the latter.


Signed-off-by: John Mulligan <[email protected]>

Author: phlogistonjohn

sambacc/_xattr.py

@@ -0,0 +1,78 @@
+#
+# sambacc: a samba container configuration tool
+# Copyright (C) 2022  John Mulligan
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>
+#
+"""xattr shim module
+
+This module exists to insulate sambacc from the platform xattr module.
+Currently it only support pyxattr. This module can be imported without
+pyxattr (xattr) present. The functions will import the required module
+and raise an ImportError if xattr is not available.
+
+This shim also provides a typed functions for xattr management. This
+could have been accomplished by writing a pyi file for xattr but since
+we need the runtime support we just add new functions.
+"""
+
+
+import pathlib
+import typing
+
+XAttrItem = typing.Union[
+    int,  # an open file descriptor, not wrapped by an object
+    pathlib.Path,  # pathlib path object
+    str,  # basic path string
+    typing.IO,  # an open file descriptor, wrapped by an object
+]
+Namespace = typing.Optional[bytes]
+
+
+def get(
+    item: XAttrItem,
+    name: str,
+    *,
+    nofollow: bool = False,
+    namespace: Namespace = None
+) -> bytes:
+    """Get an xattr from the target item and name.
+    See docs for PyXattr module for details.
+    """
+    import xattr  # type: ignore
+
+    kwargs: dict[str, typing.Any] = {"nofollow": nofollow}
+    if namespace is not None:
+        kwargs["namespace"] = namespace
+    return xattr.get(item, name, **kwargs)
+
+
+def set(
+    item: XAttrItem,
+    name: str,
+    value: str,
+    *,
+    flags: typing.Optional[int] = None,
+    nofollow: bool = False,
+    namespace: Namespace = None
+) -> None:
+    """Set an xattr. See docs for PyXattr module for details."""
+    import xattr  # type: ignore
+
+    kwargs: dict[str, typing.Any] = {"nofollow": nofollow}
+    if flags is not None:
+        kwargs["flags"] = flags
+    if namespace is not None:
+        kwargs["namespace"] = namespace
+    return xattr.set(item, name, value, **kwargs)

sambacc/permissions.py

@@ -25,7 +25,8 @@
 import os
 import typing
 
-import xattr  # type: ignore
+from sambacc import _xattr as xattr
+
 
 _logger = logging.getLogger(__name__)
 

tests/test_permissions.py

@@ -19,7 +19,7 @@
 import os
 
 import pytest
-import xattr  # type: ignore
+
 
 import sambacc.permissions
 
@@ -46,6 +46,11 @@ def test_noop_handler():
 
 @pytest.fixture(scope="function")
 def tmp_path_xattrs_ok(tmp_path_factory):
+    try:
+        import xattr  # type: ignore
+    except ImportError:
+        pytest.skip("xattr module not available")
+
     tmpp = tmp_path_factory.mktemp("needs_xattrs")
     try:
         xattr.set(str(tmpp), "user.deleteme", "1")