build/android/pylib/flag_changer.py

   1 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 # Use of this source code is governed by a BSD-style license that can be
   3 # found in the LICENSE file.
   4
   5 import logging
   6
   7 import pylib.android_commands
   8 import pylib.device.device_utils
   9
  10 from pylib.device import device_errors
  11
  12
  13 class FlagChanger(object):
  14   """Changes the flags Chrome runs with.
  15
  16   There are two different use cases for this file:
  17   * Flags are permanently set by calling Set().
  18   * Flags can be temporarily set for a particular set of unit tests.  These
  19     tests should call Restore() to revert the flags to their original state
  20     once the tests have completed.
  21   """
  22
  23   def __init__(self, device, cmdline_file):
  24     """Initializes the FlagChanger and records the original arguments.
  25
  26     Args:
  27       device: A DeviceUtils instance.
  28       cmdline_file: Path to the command line file on the device.
  29     """
  30     # TODO(jbudorick) Remove once telemetry switches over.
  31     assert not isinstance(device, pylib.android_commands.AndroidCommands)
  32     self._device = device
  33     self._cmdline_file = cmdline_file
  34
  35     # Save the original flags.
  36     try:
  37       self._orig_line = self._device.ReadFile(self._cmdline_file).strip()
  38     except device_errors.CommandFailedError:
  39       self._orig_line = ''
  40
  41     # Parse out the flags into a list to facilitate adding and removing flags.
  42     self._current_flags = self._TokenizeFlags(self._orig_line)
  43
  44   def Get(self):
  45     """Returns list of current flags."""
  46     return self._current_flags
  47
  48   def Set(self, flags):
  49     """Replaces all flags on the current command line with the flags given.
  50
  51     Args:
  52       flags: A list of flags to set, eg. ['--single-process'].
  53     """
  54     if flags:
  55       assert flags[0] != 'chrome'
  56
  57     self._current_flags = flags
  58     self._UpdateCommandLineFile()
  59
  60   def AddFlags(self, flags):
  61     """Appends flags to the command line if they aren't already there.
  62
  63     Args:
  64       flags: A list of flags to add on, eg. ['--single-process'].
  65     """
  66     if flags:
  67       assert flags[0] != 'chrome'
  68
  69     # Avoid appending flags that are already present.
  70     for flag in flags:
  71       if flag not in self._current_flags:
  72         self._current_flags.append(flag)
  73     self._UpdateCommandLineFile()
  74
  75   def RemoveFlags(self, flags):
  76     """Removes flags from the command line, if they exist.
  77
  78     Args:
  79       flags: A list of flags to remove, eg. ['--single-process'].  Note that we
  80              expect a complete match when removing flags; if you want to remove
  81              a switch with a value, you must use the exact string used to add
  82              it in the first place.
  83     """
  84     if flags:
  85       assert flags[0] != 'chrome'
  86
  87     for flag in flags:
  88       if flag in self._current_flags:
  89         self._current_flags.remove(flag)
  90     self._UpdateCommandLineFile()
  91
  92   def Restore(self):
  93     """Restores the flags to their original state."""
  94     self._current_flags = self._TokenizeFlags(self._orig_line)
  95     self._UpdateCommandLineFile()
  96
  97   def _UpdateCommandLineFile(self):
  98     """Writes out the command line to the file, or removes it if empty."""
  99     logging.info('Current flags: %s', self._current_flags)
 100     # Root is not required to write to /data/local/tmp/.
 101     use_root = '/data/local/tmp/' not in self._cmdline_file
 102     if self._current_flags:
 103       # The first command line argument doesn't matter as we are not actually
 104       # launching the chrome executable using this command line.
 105       cmd_line = ' '.join(['_'] + self._current_flags)
 106       self._device.WriteFile(
 107           self._cmdline_file, cmd_line, as_root=use_root)
 108       file_contents = self._device.ReadFile(
 109           self._cmdline_file, as_root=use_root).rstrip()
 110       assert file_contents == cmd_line, (
 111           'Failed to set the command line file at %s' % self._cmdline_file)
 112     else:
 113       self._device.RunShellCommand('rm ' + self._cmdline_file,
 114                                    as_root=use_root)
 115       assert not self._device.FileExists(self._cmdline_file), (
 116           'Failed to remove the command line file at %s' % self._cmdline_file)
 117
 118   @staticmethod
 119   def _TokenizeFlags(line):
 120     """Changes the string containing the command line into a list of flags.
 121
 122     Follows similar logic to CommandLine.java::tokenizeQuotedArguments:
 123     * Flags are split using whitespace, unless the whitespace is within a
 124       pair of quotation marks.
 125     * Unlike the Java version, we keep the quotation marks around switch
 126       values since we need them to re-create the file when new flags are
 127       appended.
 128
 129     Args:
 130       line: A string containing the entire command line.  The first token is
 131             assumed to be the program name.
 132     """
 133     if not line:
 134       return []
 135
 136     tokenized_flags = []
 137     current_flag = ""
 138     within_quotations = False
 139
 140     # Move through the string character by character and build up each flag
 141     # along the way.
 142     for c in line.strip():
 143       if c is '"':
 144         if len(current_flag) > 0 and current_flag[-1] == '\\':
 145           # Last char was a backslash; pop it, and treat this " as a literal.
 146           current_flag = current_flag[0:-1] + '"'
 147         else:
 148           within_quotations = not within_quotations
 149           current_flag += c
 150       elif not within_quotations and (c is ' ' or c is '\t'):
 151         if current_flag is not "":
 152           tokenized_flags.append(current_flag)
 153           current_flag = ""
 154       else:
 155         current_flag += c
 156
 157     # Tack on the last flag.
 158     if not current_flag:
 159       if within_quotations:
 160         logging.warn('Unterminated quoted argument: ' + line)
 161     else:
 162       tokenized_flags.append(current_flag)
 163
 164     # Return everything but the program name.
 165     return tokenized_flags[1:]