gsi_util: adding file-related utilities (file_utils)

The first function is UnopenedTemporaryFile, which is similar to
tempfile.TemporaryFile, except an unopened file path is returned
instead of an opened file-like object (fd).

Bug: 70253882
Test: make gsi_util
Test: ./run_test.py
Change-Id: I11de6976a31d8612cb873212b31c3f13a79b1b3e

gsi/gsi_util/gsi_util/utils/file_utils.py

@@ -0,0 +1,44 @@
+# Copyright 2017 - The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""File-related utilities."""
+
+import contextlib
+import os
+import tempfile
+
+
+@contextlib.contextmanager
+def UnopenedTemporaryFile(**kwargs):
+  """Creates and returns a unopened temprary file path.
+
+  This function is similar to tempfile.TemporaryFile, except that an
+  unopened file path is returend instead of a file-like object.
+  The file will be deleted when the context manager is closed.
+
+  Args:
+    **kwargs: Any keyward arguments passed to tempfile.mkstemp (e.g., dir,
+      prefix and suffix).
+
+  Returns:
+    An unopened temporary file path.
+  """
+  fd, path = tempfile.mkstemp(**kwargs)
+  os.close(fd)
+
+  try:
+    yield path
+  finally:
+    if os.path.exists(path):
+      os.unlink(path)

gsi/gsi_util/gsi_util/utils/tests/file_utils_unittest.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python
+#
+# Copyright 2017 - The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unit test for gsi_util.utils.file_utils."""
+
+import os
+import tempfile
+import unittest
+
+from gsi_util.utils import file_utils
+
+
+class UnopenedTemporaryFileTest(unittest.TestCase):
+  """Unit test for UnopenedTemporaryFile."""
+
+  def test_normal(self):
+    with file_utils.UnopenedTemporaryFile(
+        prefix='prefix', suffix='suffix') as f:
+      self.assertTrue(os.path.exists(f))
+      self.assertEqual(0, os.path.getsize(f))
+      self.assertRegexpMatches(os.path.basename(f), r'prefix.+suffix')
+      self.assertEqual(tempfile.gettempdir(), os.path.dirname(f))
+    self.assertFalse(os.path.exists(f))
+
+  def test_remove_before_exit(self):
+    with file_utils.UnopenedTemporaryFile() as f:
+      self.assertTrue(os.path.exists(f))
+      os.unlink(f)
+      self.assertFalse(os.path.exists(f))
+    self.assertFalse(os.path.exists(f))
+
+  def test_rename_before_exit(self):
+    with file_utils.UnopenedTemporaryFile() as f:
+      self.assertTrue(os.path.exists(f))
+      new_name = f + '.new'
+      os.rename(f, new_name)
+      self.assertFalse(os.path.exists(f))
+    self.assertFalse(os.path.exists(f))
+    self.assertTrue(os.path.exists(new_name))
+    os.unlink(new_name)
+
+
+if __name__ == '__main__':
+  unittest.main()