oci: fix handling of symlink subdirs (canonical#211)

When Rockcraft creates the tar archive from the priming area, subdirs
symlinks are skipped from archive.

Solution is to add subdirs when they are symlinks.

Fix canonical#208

---------
Co-authored-by: Tiago Nobrega <[email protected]>

rockcraft/oci.py

@@ -441,6 +441,7 @@ def _gather_layer_paths(
       A dict where the value is a path (file or dir) in ``new_layer_dir`` and the
       key is the name that this path should have in the tarball for the layer.
     """
+    # pylint: disable=too-many-locals
 
     class LayerLinker:
         """Helper to keep track of paths between the upper and lower layer."""
@@ -512,6 +513,14 @@ def get_target_path(self, path: Path) -> Path:
             archive_path = layer_linker.get_target_path(relative_path / name)
             result[f"{archive_path}"].append(upper_subpath / name)
 
+        # Add each subdir in the directory if it's a symlink, because the os.walk()
+        # call will not enter them.
+        for subdir in subdirs:
+            upper_subdir_path = upper_subpath / subdir
+            if upper_subdir_path.is_symlink():
+                archive_path = layer_linker.get_target_path(relative_path / subdir)
+                result[f"{archive_path}"].append(upper_subdir_path)
+
     return result
 
 

tests/unit/test_oci.py

@@ -283,6 +283,30 @@ def test_add_layer_directories(self, tmp_path, temp_tar_contents):
         ]
         assert temp_tar_contents == expected_tar_contents
 
+    def test_add_layer_symlinks(self, tmp_path, temp_tar_contents):
+        """
+        Test creating a new layer with symlinks (both file and dir).
+        """
+        dest_dir = tmp_path / "dest"
+        dest_dir.mkdir()
+
+        layer_dir = tmp_path / "layer_dir"
+        layer_dir.mkdir()
+
+        (layer_dir / "first_dir").mkdir()
+        (layer_dir / "first_file").touch()
+
+        (layer_dir / "second_dir").symlink_to("first_dir", target_is_directory=True)
+        (layer_dir / "second_file").symlink_to("first_file", target_is_directory=False)
+
+        image = oci.Image("a:b", dest_dir)
+
+        assert len(temp_tar_contents) == 0
+        image.add_layer("tag", layer_dir)
+
+        expected_tar_contents = ["first_dir", "first_file", "second_dir", "second_file"]
+        assert temp_tar_contents == expected_tar_contents
+
     def test_add_layer_with_base_layer_dir(self, tmp_path, temp_tar_contents):
         """Test creating a layer with a base layer dir for reference."""
         dest_dir = tmp_path / "dest"