text: # Copyright (c) 2012 The Chromium Authors. All rights reserved.
  # Use of this source code is governed by a BSD-style license that can be
  # found in the LICENSE file.
  
  import android_commands
  import constants
  import logging
  import os
  import subprocess
  import time
  
  
  class FakeDns(object):
    """Wrapper class for the fake_dns tool."""
    _FAKE_DNS_PATH = '/data/local/tmp/fake_dns'
  
    def __init__(self, adb):
      """
        Args:
          adb: the AndroidCommands to use.
      """
      self._adb = adb
      self._fake_dns = None
      self._original_dns = None
  
    def _PushAndStartFakeDns(self):
      """Starts the fake_dns server that replies all name queries 127.0.0.1.
  
      Returns:
        subprocess instance connected to the fake_dns process on the device.
      """
      self._adb.PushIfNeeded(
          os.path.join(constants.CHROME_DIR, 'out', 'Release', 'fake_dns'),
          FakeDns._FAKE_DNS_PATH)
      return subprocess.Popen(
          ['adb', '-s', self._adb._adb.GetSerialNumber(),
           'shell', '%s -D' % FakeDns._FAKE_DNS_PATH])
  
    def SetUp(self):
      """Configures the system to point to a DNS server that replies 127.0.0.1.
  
      This can be used in combination with the forwarder to forward all web
      traffic to a replay server.
  
      The TearDown() method will perform all cleanup.
      """
      self._adb.RunShellCommand('ip route add 8.8.8.0/24 via 127.0.0.1 dev lo')
      self._fake_dns = self._PushAndStartFakeDns()
      self._original_dns = self._adb.RunShellCommand('getprop net.dns1')[0]
      self._adb.RunShellCommand('setprop net.dns1 127.0.0.1')
      time.sleep(2)  # Time for server to start and the setprop to take effect.
  
    def TearDown(self):
      """Shuts down the fake_dns."""
      if self._fake_dns:
        if not self._original_dns or self._original_dns == '127.0.0.1':
          logging.warning('Bad original DNS, falling back to Google DNS.')
          self._original_dns = '8.8.8.8'
        self._adb.RunShellCommand('setprop net.dns1 %s' % self._original_dns)
        self._fake_dns.kill()
        self._adb.RunShellCommand('ip route del 8.8.8.0/24 via 127.0.0.1 dev lo')
  