Update from https://crrev.com/328418

build/android/pylib/device/shared_prefs.py

Index: build/android/pylib/device/shared_prefs.py
diff --git a/build/android/pylib/device/shared_prefs.py b/build/android/pylib/device/shared_prefs.py
new file mode 100644
index 0000000000000000000000000000000000000000..32cef4b535b87ce87171323fe70793ac2bf23ab6
--- /dev/null
+++ b/build/android/pylib/device/shared_prefs.py
@@ -0,0 +1,391 @@
+# Copyright 2015 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.
+
+"""Helper object to read and modify Shared Preferences from Android apps.
+
+See e.g.:
+  http://developer.android.com/reference/android/content/SharedPreferences.html
+"""
+
+import collections
+import logging
+import posixpath
+
+from xml.etree import ElementTree
+
+
+_XML_DECLARATION = "<?xml version='1.0' encoding='utf-8' standalone='yes' ?>\n"
+
+
+class BasePref(object):
+  """Base class for getting/setting the value of a specific preference type.
+
+  Should not be instantiated directly. The SharedPrefs collection will
+  instantiate the appropriate subclasses, which directly manipulate the
+  underlying xml document, to parse and serialize values according to their
+  type.
+
+  Args:
+    elem: An xml ElementTree object holding the preference data.
+
+  Properties:
+    tag_name: A string with the tag that must be used for this preference type.
+  """
+  tag_name = None
+
+  def __init__(self, elem):
+    if elem.tag != type(self).tag_name:
+      raise TypeError('Property %r has type %r, but trying to access as %r' %
+                      (elem.get('name'), elem.tag, type(self).tag_name))
+    self._elem = elem
+
+  def __str__(self):
+    """Get the underlying xml element as a string."""
+    return ElementTree.tostring(self._elem)
+
+  def get(self):
+    """Get the value of this preference."""
+    return self._elem.get('value')
+
+  def set(self, value):
+    """Set from a value casted as a string."""
+    self._elem.set('value', str(value))
+
+  @property
+  def has_value(self):
+    """Check whether the element has a value."""
+    return self._elem.get('value') is not None
+
+
+class BooleanPref(BasePref):
+  """Class for getting/setting a preference with a boolean value.
+
+  The underlying xml element has the form, e.g.:
+      <boolean name="featureEnabled" value="false" />
+  """
+  tag_name = 'boolean'
+  VALUES = {'true': True, 'false': False}
+
+  def get(self):
+    """Get the value as a Python bool."""
+    return type(self).VALUES[super(BooleanPref, self).get()]
+
+  def set(self, value):
+    """Set from a value casted as a bool."""
+    super(BooleanPref, self).set('true' if value else 'false')
+
+
+class FloatPref(BasePref):
+  """Class for getting/setting a preference with a float value.
+
+  The underlying xml element has the form, e.g.:
+      <float name="someMetric" value="4.7" />
+  """
+  tag_name = 'float'
+
+  def get(self):
+    """Get the value as a Python float."""
+    return float(super(FloatPref, self).get())
+
+
+class IntPref(BasePref):
+  """Class for getting/setting a preference with an int value.
+
+  The underlying xml element has the form, e.g.:
+      <int name="aCounter" value="1234" />
+  """
+  tag_name = 'int'
+
+  def get(self):
+    """Get the value as a Python int."""
+    return int(super(IntPref, self).get())
+
+
+class LongPref(IntPref):
+  """Class for getting/setting a preference with a long value.
+
+  The underlying xml element has the form, e.g.:
+      <long name="aLongCounter" value="1234" />
+
+  We use the same implementation from IntPref.
+  """
+  tag_name = 'long'
+
+
+class StringPref(BasePref):
+  """Class for getting/setting a preference with a string value.
+
+  The underlying xml element has the form, e.g.:
+      <string name="someHashValue">249b3e5af13d4db2</string>
+  """
+  tag_name = 'string'
+
+  def get(self):
+    """Get the value as a Python string."""
+    return self._elem.text
+
+  def set(self, value):
+    """Set from a value casted as a string."""
+    self._elem.text = str(value)
+
+
+class StringSetPref(StringPref):
+  """Class for getting/setting a preference with a set of string values.
+
+  The underlying xml element has the form, e.g.:
+      <set name="managed_apps">
+          <string>com.mine.app1</string>
+          <string>com.mine.app2</string>
+          <string>com.mine.app3</string>
+      </set>
+  """
+  tag_name = 'set'
+
+  def get(self):
+    """Get a list with the string values contained."""
+    value = []
+    for child in self._elem:
+      assert child.tag == 'string'
+      value.append(child.text)
+    return value
+
+  def set(self, value):
+    """Set from a sequence of values, each casted as a string."""
+    for child in list(self._elem):
+      self._elem.remove(child)
+    for item in value:
+      ElementTree.SubElement(self._elem, 'string').text = str(item)
+
+
+_PREF_TYPES = {c.tag_name: c for c in [BooleanPref, FloatPref, IntPref,
+                                       LongPref, StringPref, StringSetPref]}
+
+
+class SharedPrefs(object):
+  def __init__(self, device, package, filename):
+    """Helper object to read and update "Shared Prefs" of Android apps.
+
+    Such files typically look like, e.g.:
+
+        <?xml version='1.0' encoding='utf-8' standalone='yes' ?>
+        <map>
+          <int name="databaseVersion" value="107" />
+          <boolean name="featureEnabled" value="false" />
+          <string name="someHashValue">249b3e5af13d4db2</string>
+        </map>
+
+    Example usage:
+
+        prefs = shared_prefs.SharedPrefs(device, 'com.my.app', 'my_prefs.xml')
+        prefs.Load()
+        prefs.GetString('someHashValue') # => '249b3e5af13d4db2'
+        prefs.SetInt('databaseVersion', 42)
+        prefs.Remove('featureEnabled')
+        prefs.Commit()
+
+    The object may also be used as a context manager to automatically load and
+    commit, respectively, upon entering and leaving the context.
+
+    Args:
+      device: A DeviceUtils object.
+      package: A string with the package name of the app that owns the shared
+        preferences file.
+      filename: A string with the name of the preferences file to read/write.
+    """
+    self._device = device
+    self._xml = None
+    self._package = package
+    self._filename = filename
+    self._path = '/data/data/%s/shared_prefs/%s' % (package, filename)
+    self._changed = False
+
+  def __repr__(self):
+    """Get a useful printable representation of the object."""
+    return '<{cls} file {filename} for {package} on {device}>'.format(
+      cls=type(self).__name__, filename=self.filename, package=self.package,
+      device=str(self._device))
+
+  def __str__(self):
+    """Get the underlying xml document as a string."""
+    return _XML_DECLARATION + ElementTree.tostring(self.xml)
+
+  @property
+  def package(self):
+    """Get the package name of the app that owns the shared preferences."""
+    return self._package
+
+  @property
+  def filename(self):
+    """Get the filename of the shared preferences file."""
+    return self._filename
+
+  @property
+  def path(self):
+    """Get the full path to the shared preferences file on the device."""
+    return self._path
+
+  @property
+  def changed(self):
+    """True if properties have changed and a commit would be needed."""
+    return self._changed
+
+  @property
+  def xml(self):
+    """Get the underlying xml document as an ElementTree object."""
+    if self._xml is None:
+      self._xml = ElementTree.Element('map')
+    return self._xml
+
+  def Load(self):
+    """Load the shared preferences file from the device.
+
+    A empty xml document, which may be modified and saved on |commit|, is
+    created if the file does not already exist.
+    """
+    if self._device.FileExists(self.path):
+      self._xml = ElementTree.fromstring(
+          self._device.ReadFile(self.path, as_root=True))
+      assert self._xml.tag == 'map'
+    else:
+      self._xml = None
+    self._changed = False
+
+  def Clear(self):
+    """Clear all of the preferences contained in this object."""
+    if self._xml is not None and len(self): # only clear if not already empty
+      self._xml = None
+      self._changed = True
+
+  def Commit(self):
+    """Save the current set of preferences to the device.
+
+    Only actually saves if some preferences have been modified.
+    """
+    if not self.changed:
+      return
+    self._device.RunShellCommand(
+        ['mkdir', '-p', posixpath.dirname(self.path)],
+        as_root=True, check_return=True)
+    self._device.WriteFile(self.path, str(self), as_root=True)
+    self._device.KillAll(self.package, as_root=True, quiet=True)
+    self._changed = False
+
+  def __len__(self):
+    """Get the number of preferences in this collection."""
+    return len(self.xml)
+
+  def PropertyType(self, key):
+    """Get the type (i.e. tag name) of a property in the collection."""
+    return self._GetChild(key).tag
+
+  def HasProperty(self, key):
+    try:
+      self._GetChild(key)
+      return True
+    except KeyError:
+      return False
+
+  def GetBoolean(self, key):
+    """Get a boolean property."""
+    return BooleanPref(self._GetChild(key)).get()
+
+  def SetBoolean(self, key, value):
+    """Set a boolean property."""
+    self._SetPrefValue(key, value, BooleanPref)
+
+  def GetFloat(self, key):
+    """Get a float property."""
+    return FloatPref(self._GetChild(key)).get()
+
+  def SetFloat(self, key, value):
+    """Set a float property."""
+    self._SetPrefValue(key, value, FloatPref)
+
+  def GetInt(self, key):
+    """Get an int property."""
+    return IntPref(self._GetChild(key)).get()
+
+  def SetInt(self, key, value):
+    """Set an int property."""
+    self._SetPrefValue(key, value, IntPref)
+
+  def GetLong(self, key):
+    """Get a long property."""
+    return LongPref(self._GetChild(key)).get()
+
+  def SetLong(self, key, value):
+    """Set a long property."""
+    self._SetPrefValue(key, value, LongPref)
+
+  def GetString(self, key):
+    """Get a string property."""
+    return StringPref(self._GetChild(key)).get()
+
+  def SetString(self, key, value):
+    """Set a string property."""
+    self._SetPrefValue(key, value, StringPref)
+
+  def GetStringSet(self, key):
+    """Get a string set property."""
+    return StringSetPref(self._GetChild(key)).get()
+
+  def SetStringSet(self, key, value):
+    """Set a string set property."""
+    self._SetPrefValue(key, value, StringSetPref)
+
+  def Remove(self, key):
+    """Remove a preference from the collection."""
+    self.xml.remove(self._GetChild(key))
+
+  def AsDict(self):
+    """Return the properties and their values as a dictionary."""
+    d = {}
+    for child in self.xml:
+      pref = _PREF_TYPES[child.tag](child)
+      d[child.get('name')] = pref.get()
+    return d
+
+  def __enter__(self):
+    """Load preferences file from the device when entering a context."""
+    self.Load()
+    return self
+
+  def __exit__(self, exc_type, _exc_value, _traceback):
+    """Save preferences file to the device when leaving a context."""
+    if not exc_type:
+      self.Commit()
+
+  def _GetChild(self, key):
+    """Get the underlying xml node that holds the property of a given key.
+
+    Raises:
+      KeyError when the key is not found in the collection.
+    """
+    for child in self.xml:
+      if child.get('name') == key:
+        return child
+    raise KeyError(key)
+
+  def _SetPrefValue(self, key, value, pref_cls):
+    """Set the value of a property.
+
+    Args:
+      key: The key of the property to set.
+      value: The new value of the property.
+      pref_cls: A subclass of BasePref used to access the property.
+
+    Raises:
+      TypeError when the key already exists but with a different type.
+    """
+    try:
+      pref = pref_cls(self._GetChild(key))
+      old_value = pref.get()
+    except KeyError:
+      pref = pref_cls(ElementTree.SubElement(
+          self.xml, pref_cls.tag_name, {'name': key}))
+      old_value = None
+    if old_value != value:
+      pref.set(value)
+      self._changed = True
+      logging.info('Setting property: %s', pref)