combine model serialization logic for files and directories (#257)

* combine model serialization logic for files and directories

Identical logic was being performed whether model_path pointed to a file
or a directory due to two pathlib.Path.glob behaviors:

1. The path must be a directory for the generator to yield items
2. The glob does not include the provided directory itself.

By iterating over the provided model_path first, and then continuing to
the glob, all of the serialization logic can be done in the loop. This
will help future changes which will add more serialization logic in the
form of ignore paths.

Signed-off-by: Spencer Schrock <sschrock@google.com>

* avoid using an inner function to generate the root iterator

Signed-off-by: Spencer Schrock <sschrock@google.com>

---------

Signed-off-by: Spencer Schrock <sschrock@google.com>

model_signing/serialization/serialize_by_file.py

@@ -17,6 +17,7 @@
 import abc
 import base64
 import concurrent.futures
+import itertools
 import pathlib
 from typing import Callable, Iterable, cast
 from typing_extensions import override
@@ -124,22 +125,19 @@ def serialize(self, model_path: pathlib.Path) -> manifest.Manifest:
             ValueError: The model contains a symbolic link, but the serializer
               was not initialized with `allow_symlinks=True`.
         """
-        check_file_or_directory(model_path, allow_symlinks=self._allow_symlinks)
-
         paths = []
-        if model_path.is_file():
-            paths.append(model_path)
-        else:
-            # TODO: github.com/sigstore/model-transparency/issues/200 - When
-            # Python3.12 is the minimum supported version, this can be replaced
-            # with `pathlib.Path.walk` for a clearer interface, and some speed
-            # improvement.
-            for path in model_path.glob("**/*"):
-                check_file_or_directory(
-                    path, allow_symlinks=self._allow_symlinks
-                )
-                if path.is_file():
-                    paths.append(path)
+        # TODO: github.com/sigstore/model-transparency/issues/200 - When
+        # Python3.12 is the minimum supported version, the glob can be replaced
+        # with `pathlib.Path.walk` for a clearer interface, and some speed
+        # improvement.
+        for path in itertools.chain(
+            iter([model_path]), model_path.glob("**/*")
+        ):
+            check_file_or_directory(
+                path, allow_symlinks=self._allow_symlinks
+            )
+            if path.is_file():
+                paths.append(path)
 
         manifest_items = []
         with concurrent.futures.ThreadPoolExecutor(

model_signing/serialization/serialize_by_file_shard.py

@@ -17,6 +17,7 @@
 import abc
 import base64
 import concurrent.futures
+import itertools
 import pathlib
 from typing import Callable, Iterable, cast
 from typing_extensions import override
@@ -126,24 +127,19 @@ def serialize(self, model_path: pathlib.Path) -> manifest.Manifest:
             ValueError: The model contains a symbolic link, but the serializer
               was not initialized with `allow_symlinks=True`.
         """
-        serialize_by_file.check_file_or_directory(
-            model_path, allow_symlinks=self._allow_symlinks
-        )
-
         shards = []
-        if model_path.is_file():
-            shards.extend(self._get_shards(model_path))
-        else:
-            # TODO: github.com/sigstore/model-transparency/issues/200 - When
-            # Python3.12 is the minimum supported version, this can be replaced
-            # with `pathlib.Path.walk` for a clearer interface, and some speed
-            # improvement.
-            for path in model_path.glob("**/*"):
-                serialize_by_file.check_file_or_directory(
-                    path, allow_symlinks=self._allow_symlinks
-                )
-                if path.is_file():
-                    shards.extend(self._get_shards(path))
+        # TODO: github.com/sigstore/model-transparency/issues/200 - When
+        # Python3.12 is the minimum supported version, the glob can be replaced
+        # with `pathlib.Path.walk` for a clearer interface, and some speed
+        # improvement.
+        for path in itertools.chain(
+            iter([model_path]), model_path.glob("**/*")
+        ):
+            serialize_by_file.check_file_or_directory(
+                path, allow_symlinks=self._allow_symlinks
+            )
+            if path.is_file():
+                shards.extend(self._get_shards(path))
 
         manifest_items = []
         with concurrent.futures.ThreadPoolExecutor(