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