fix(storage): remove partial file on any download_to_filename error

packages/google-cloud-storage/google/cloud/storage/blob.py

@@ -1271,18 +1271,23 @@ def _handle_filename_and_download(self, filename, *args, **kwargs):
         For *args and **kwargs, refer to the documentation for download_to_filename() for more information.
         """
 
-        try:
-            with open(filename, "wb") as file_obj:
+        with open(filename, "wb") as file_obj:
+            try:
                 self._prep_and_do_download(
                     file_obj,
                     *args,
                     **kwargs,
                 )
-
-        except (DataCorruption, NotFound):
-            # Delete the corrupt or empty downloaded file.
-            os.remove(filename)
-            raise
+            except Exception:
+                # Remove the (empty or partial) file before re-raising so
+                # callers never see a corrupt destination file.  This extends
+                # the existing DataCorruption/NotFound cleanup to cover network
+                # errors, timeouts, and any other unexpected failures.
+                try:
+                    os.remove(filename)
+                except OSError:
+                    pass  # file may not exist if open() itself failed
+                raise
 
         updated = self.updated
         if updated is not None:
@@ -1312,6 +1317,13 @@ def download_to_filename(
         If :attr:`user_project` is set on the bucket, bills the API request
         to that project.
 
+        .. note::
+            If the download fails for any reason (network error, timeout,
+            :exc:`~google.cloud.exceptions.NotFound`, etc.), any partially
+            written destination file is removed before re-raising the
+            exception, so the filesystem is never left with an empty or
+            incomplete file.
+
         See a [code sample](https://cloud.google.com/storage/docs/samples/storage-download-encrypted-file#storage_download_encrypted_file-python)
         to download a file with a [`customer-supplied encryption key`](https://cloud.google.com/storage/docs/encryption#customer-supplied).
 

packages/google-cloud-storage/tests/unit/test_blob.py

@@ -1962,6 +1962,91 @@ def test_download_to_filename_notfound(self):
             stream = blob._prep_and_do_download.mock_calls[0].args[0]
             self.assertEqual(stream.name, filename)
 
+    def test_download_to_filename_cleans_up_on_connection_error(self):
+        import requests.exceptions
+
+        blob_name = "blob-name"
+        client = self._make_client()
+        bucket = _Bucket(client)
+        blob = self._make_one(blob_name, bucket=bucket)
+
+        with mock.patch.object(blob, "_prep_and_do_download"):
+            blob._prep_and_do_download.side_effect = requests.exceptions.ConnectionError(
+                "Network is unreachable"
+            )
+
+            filehandle, filename = tempfile.mkstemp()
+            os.close(filehandle)
+            self.assertTrue(os.path.exists(filename))
+
+            with self.assertRaises(requests.exceptions.ConnectionError):
+                blob.download_to_filename(filename)
+
+            self.assertFalse(os.path.exists(filename))
+
+    def test_download_to_filename_cleans_up_on_timeout(self):
+        import requests.exceptions
+
+        blob_name = "blob-name"
+        client = self._make_client()
+        bucket = _Bucket(client)
+        blob = self._make_one(blob_name, bucket=bucket)
+
+        with mock.patch.object(blob, "_prep_and_do_download"):
+            blob._prep_and_do_download.side_effect = requests.exceptions.Timeout(
+                "Timeout of 120.0s exceeded"
+            )
+
+            filehandle, filename = tempfile.mkstemp()
+            os.close(filehandle)
+            self.assertTrue(os.path.exists(filename))
+
+            with self.assertRaises(requests.exceptions.Timeout):
+                blob.download_to_filename(filename)
+
+            self.assertFalse(os.path.exists(filename))
+
+    def test_download_to_filename_cleans_up_on_generic_exception(self):
+        blob_name = "blob-name"
+        client = self._make_client()
+        bucket = _Bucket(client)
+        blob = self._make_one(blob_name, bucket=bucket)
+
+        with mock.patch.object(blob, "_prep_and_do_download"):
+            blob._prep_and_do_download.side_effect = RuntimeError("unexpected failure")
+
+            filehandle, filename = tempfile.mkstemp()
+            os.close(filehandle)
+            self.assertTrue(os.path.exists(filename))
+
+            with self.assertRaises(RuntimeError):
+                blob.download_to_filename(filename)
+
+            self.assertFalse(os.path.exists(filename))
+
+    def test_download_to_filename_keeps_file_on_success(self):
+        blob_name = "blob-name"
+        client = self._make_client()
+        bucket = _Bucket(client)
+        blob = self._make_one(blob_name, bucket=bucket)
+
+        def _write_data(file_obj, **kwargs):
+            file_obj.write(b"hello world")
+
+        with mock.patch.object(
+            blob, "_prep_and_do_download", side_effect=_write_data
+        ):
+            filehandle, filename = tempfile.mkstemp()
+            os.close(filehandle)
+            try:
+                blob.download_to_filename(filename)
+                self.assertTrue(os.path.exists(filename))
+                with open(filename, "rb") as f:
+                    self.assertEqual(f.read(), b"hello world")
+            finally:
+                if os.path.exists(filename):
+                    os.remove(filename)
+
     def _download_as_bytes_helper(
         self, raw_download, timeout=None, single_shot_download=False, **extra_kwargs
     ):