cros_utils/no_pseudo_terminal_test.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
#
# Copyright 2019 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Test to ensure we're not touching /dev/ptmx when running commands."""

from __future__ import print_function

import os
import subprocess
import tempfile
import time
import unittest
from cros_utils import command_executer


class NoPsuedoTerminalTest(unittest.TestCase):
  """Test to ensure we're not touching /dev/ptmx when running commands."""

  _strace_process = None
  STRACE_TIMEOUT = 10

  def _AttachStraceToSelf(self, output_file):
    """Attaches strace to the current process."""
    args = ['sudo', 'strace', '-o', output_file, '-p', str(os.getpid())]
    print(args)
    # pylint: disable=bad-option-value, subprocess-popen-preexec-fn
    self._strace_process = subprocess.Popen(args, preexec_fn=os.setpgrp)
    # Wait until we see some activity.
    start_time = time.time()
    while time.time() - start_time < self.STRACE_TIMEOUT:
      if os.path.isfile(output_file) and open(output_file).read(1):
        return True
      time.sleep(1)
    return False

  def _KillStraceProcess(self):
    """Kills strace that was started by _AttachStraceToSelf()."""
    pgid = os.getpgid(self._strace_process.pid)
    args = ['sudo', 'kill', str(pgid)]
    if subprocess.call(args) == 0:
      os.waitpid(pgid, 0)
      return True
    return False

  def testNoPseudoTerminalWhenRunningCommand(self):
    """Test to make sure we're not touching /dev/ptmx when running commands."""
    temp_file = tempfile.mktemp()
    self.assertTrue(self._AttachStraceToSelf(temp_file))

    ce = command_executer.GetCommandExecuter()
    ce.RunCommand('echo')

    self.assertTrue(self._KillStraceProcess())

    strace_contents = open(temp_file).read()
    self.assertFalse('/dev/ptmx' in strace_contents)


if __name__ == '__main__':
  unittest.main()