path: root/sync/tools/testserver/chromiumsync.py

# Copyright 2013 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.

"""An implementation of the server side of the Chromium sync protocol.

The details of the protocol are described mostly by comments in the protocol
buffer definition at chrome/browser/sync/protocol/sync.proto.
"""

import base64
import cgi
import copy
import google.protobuf.text_format
import hashlib
import operator
import pickle
import random
import string
import sys
import threading
import time
import urlparse
import uuid

import app_list_specifics_pb2
import app_notification_specifics_pb2
import app_setting_specifics_pb2
import app_specifics_pb2
import article_specifics_pb2
import autofill_specifics_pb2
import bookmark_specifics_pb2
import client_commands_pb2
import dictionary_specifics_pb2
import get_updates_caller_info_pb2
import extension_setting_specifics_pb2
import extension_specifics_pb2
import favicon_image_specifics_pb2
import favicon_tracking_specifics_pb2
import history_delete_directive_specifics_pb2
import managed_user_setting_specifics_pb2
import managed_user_specifics_pb2
import managed_user_shared_setting_specifics_pb2
import managed_user_whitelist_specifics_pb2
import nigori_specifics_pb2
import password_specifics_pb2
import preference_specifics_pb2
import priority_preference_specifics_pb2
import search_engine_specifics_pb2
import session_specifics_pb2
import sync_pb2
import sync_enums_pb2
import synced_notification_app_info_specifics_pb2
import synced_notification_specifics_pb2
import theme_specifics_pb2
import typed_url_specifics_pb2
import wifi_credential_specifics_pb2

# An enumeration of the various kinds of data that can be synced.
# Over the wire, this enumeration is not used: a sync object's type is
# inferred by which EntitySpecifics field it has.  But in the context
# of a program, it is useful to have an enumeration.
ALL_TYPES = (
    TOP_LEVEL,  # The type of the 'Google Chrome' folder.
    APPS,
    APP_LIST,
    APP_NOTIFICATION,
    APP_SETTINGS,
    ARTICLE,
    AUTOFILL,
    AUTOFILL_PROFILE,
    BOOKMARK,
    DEVICE_INFO,
    DICTIONARY,
    EXPERIMENTS,
    EXTENSIONS,
    HISTORY_DELETE_DIRECTIVE,
    MANAGED_USER_SETTING,
    MANAGED_USER_SHARED_SETTING,
    MANAGED_USER_WHITELIST,
    MANAGED_USER,
    NIGORI,
    PASSWORD,
    PREFERENCE,
    PRIORITY_PREFERENCE,
    SEARCH_ENGINE,
    SESSION,
    SYNCED_NOTIFICATION,
    SYNCED_NOTIFICATION_APP_INFO,
    THEME,
    TYPED_URL,
    EXTENSION_SETTINGS,
    FAVICON_IMAGES,
    FAVICON_TRACKING,
    WIFI_CREDENTIAL) = range(32)

# An enumeration on the frequency at which the server should send errors
# to the client. This would be specified by the url that triggers the error.
# Note: This enum should be kept in the same order as the enum in sync_test.h.
SYNC_ERROR_FREQUENCY = (
    ERROR_FREQUENCY_NONE,
    ERROR_FREQUENCY_ALWAYS,
    ERROR_FREQUENCY_TWO_THIRDS) = range(3)

# Well-known server tag of the top level 'Google Chrome' folder.
TOP_LEVEL_FOLDER_TAG = 'google_chrome'

# Given a sync type from ALL_TYPES, find the FieldDescriptor corresponding
# to that datatype.  Note that TOP_LEVEL has no such token.
SYNC_TYPE_FIELDS = sync_pb2.EntitySpecifics.DESCRIPTOR.fields_by_name
SYNC_TYPE_TO_DESCRIPTOR = {
    APP_LIST: SYNC_TYPE_FIELDS['app_list'],
    APP_NOTIFICATION: SYNC_TYPE_FIELDS['app_notification'],
    APP_SETTINGS: SYNC_TYPE_FIELDS['app_setting'],
    APPS: SYNC_TYPE_FIELDS['app'],
    ARTICLE: SYNC_TYPE_FIELDS['article'],
    AUTOFILL: SYNC_TYPE_FIELDS['autofill'],
    AUTOFILL_PROFILE: SYNC_TYPE_FIELDS['autofill_profile'],
    BOOKMARK: SYNC_TYPE_FIELDS['bookmark'],
    DEVICE_INFO: SYNC_TYPE_FIELDS['device_info'],
    DICTIONARY: SYNC_TYPE_FIELDS['dictionary'],
    EXPERIMENTS: SYNC_TYPE_FIELDS['experiments'],
    EXTENSION_SETTINGS: SYNC_TYPE_FIELDS['extension_setting'],
    EXTENSIONS: SYNC_TYPE_FIELDS['extension'],
    FAVICON_IMAGES: SYNC_TYPE_FIELDS['favicon_image'],
    FAVICON_TRACKING: SYNC_TYPE_FIELDS['favicon_tracking'],
    HISTORY_DELETE_DIRECTIVE: SYNC_TYPE_FIELDS['history_delete_directive'],
    MANAGED_USER_SHARED_SETTING:
        SYNC_TYPE_FIELDS['managed_user_shared_setting'],
    MANAGED_USER_SETTING: SYNC_TYPE_FIELDS['managed_user_setting'],
    MANAGED_USER_WHITELIST: SYNC_TYPE_FIELDS['managed_user_whitelist'],
    MANAGED_USER: SYNC_TYPE_FIELDS['managed_user'],
    NIGORI: SYNC_TYPE_FIELDS['nigori'],
    PASSWORD: SYNC_TYPE_FIELDS['password'],
    PREFERENCE: SYNC_TYPE_FIELDS['preference'],
    PRIORITY_PREFERENCE: SYNC_TYPE_FIELDS['priority_preference'],
    SEARCH_ENGINE: SYNC_TYPE_FIELDS['search_engine'],
    SESSION: SYNC_TYPE_FIELDS['session'],
    SYNCED_NOTIFICATION: SYNC_TYPE_FIELDS["synced_notification"],
    SYNCED_NOTIFICATION_APP_INFO:
        SYNC_TYPE_FIELDS["synced_notification_app_info"],
    THEME: SYNC_TYPE_FIELDS['theme'],
    TYPED_URL: SYNC_TYPE_FIELDS['typed_url'],
    WIFI_CREDENTIAL: SYNC_TYPE_FIELDS["wifi_credential"],
    }

# The parent ID used to indicate a top-level node.
ROOT_ID = '0'

# Unix time epoch +1 day in struct_time format. The tuple corresponds to
# UTC Thursday Jan 2 1970, 00:00:00, non-dst.
# We have to add one day after start of epoch, since in timezones with positive
# UTC offset time.mktime throws an OverflowError,
# rather then returning negative number.
FIRST_DAY_UNIX_TIME_EPOCH = (1970, 1, 2, 0, 0, 0, 4, 2, 0)
ONE_DAY_SECONDS = 60 * 60 * 24

# The number of characters in the server-generated encryption key.
KEYSTORE_KEY_LENGTH = 16

# The hashed client tags for some experiment nodes.
KEYSTORE_ENCRYPTION_EXPERIMENT_TAG = "pis8ZRzh98/MKLtVEio2mr42LQA="
PRE_COMMIT_GU_AVOIDANCE_EXPERIMENT_TAG = "Z1xgeh3QUBa50vdEPd8C/4c7jfE="

class Error(Exception):
  """Error class for this module."""


class ProtobufDataTypeFieldNotUnique(Error):
  """An entry should not have more than one data type present."""


class DataTypeIdNotRecognized(Error):
  """The requested data type is not recognized."""


class MigrationDoneError(Error):
  """A server-side migration occurred; clients must re-sync some datatypes.

  Attributes:
    datatypes: a list of the datatypes (python enum) needing migration.
  """

  def __init__(self, datatypes):
    self.datatypes = datatypes


class StoreBirthdayError(Error):
  """The client sent a birthday that doesn't correspond to this server."""


class TransientError(Error):
  """The client would be sent a transient error."""


class SyncInducedError(Error):
  """The client would be sent an error."""


class InducedErrorFrequencyNotDefined(Error):
  """The error frequency defined is not handled."""


class ClientNotConnectedError(Error):
  """The client is not connected to the server."""


def GetEntryType(entry):
  """Extract the sync type from a SyncEntry.

  Args:
    entry: A SyncEntity protobuf object whose type to determine.
  Returns:
    An enum value from ALL_TYPES if the entry's type can be determined, or None
    if the type cannot be determined.
  Raises:
    ProtobufDataTypeFieldNotUnique: More than one type was indicated by
    the entry.
  """
  if entry.server_defined_unique_tag == TOP_LEVEL_FOLDER_TAG:
    return TOP_LEVEL
  entry_types = GetEntryTypesFromSpecifics(entry.specifics)
  if not entry_types:
    return None

  # If there is more than one, either there's a bug, or else the caller
  # should use GetEntryTypes.
  if len(entry_types) > 1:
    raise ProtobufDataTypeFieldNotUnique
  return entry_types[0]


def GetEntryTypesFromSpecifics(specifics):
  """Determine the sync types indicated by an EntitySpecifics's field(s).

  If the specifics have more than one recognized data type field (as commonly
  happens with the requested_types field of GetUpdatesMessage), all types
  will be returned.  Callers must handle the possibility of the returned
  value having more than one item.

  Args:
    specifics: A EntitySpecifics protobuf message whose extensions to
      enumerate.
  Returns:
    A list of the sync types (values from ALL_TYPES) associated with each
    recognized extension of the specifics message.
  """
  return [data_type for data_type, field_descriptor
          in SYNC_TYPE_TO_DESCRIPTOR.iteritems()
          if specifics.HasField(field_descriptor.name)]


def SyncTypeToProtocolDataTypeId(data_type):
  """Convert from a sync type (python enum) to the protocol's data type id."""
  return SYNC_TYPE_TO_DESCRIPTOR[data_type].number


def ProtocolDataTypeIdToSyncType(protocol_data_type_id):
  """Convert from the protocol's data type id to a sync type (python enum)."""
  for data_type, field_descriptor in SYNC_TYPE_TO_DESCRIPTOR.iteritems():
    if field_descriptor.number == protocol_data_type_id:
      return data_type
  raise DataTypeIdNotRecognized


def DataTypeStringToSyncTypeLoose(data_type_string):
  """Converts a human-readable string to a sync type (python enum).

  Capitalization and pluralization don't matter; this function is appropriate
  for values that might have been typed by a human being; e.g., command-line
  flags or query parameters.
  """
  if data_type_string.isdigit():
    return ProtocolDataTypeIdToSyncType(int(data_type_string))
  name = data_type_string.lower().rstrip('s')
  for data_type, field_descriptor in SYNC_TYPE_TO_DESCRIPTOR.iteritems():
    if field_descriptor.name.lower().rstrip('s') == name:
      return data_type
  raise DataTypeIdNotRecognized


def MakeNewKeystoreKey():
  """Returns a new random keystore key."""
  return ''.join(random.choice(string.ascii_uppercase + string.digits)
        for x in xrange(KEYSTORE_KEY_LENGTH))


def SyncTypeToString(data_type):
  """Formats a sync type enum (from ALL_TYPES) to a human-readable string."""
  return SYNC_TYPE_TO_DESCRIPTOR[data_type].name


def CallerInfoToString(caller_info_source):
  """Formats a GetUpdatesSource enum value to a readable string."""
  return get_updates_caller_info_pb2.GetUpdatesCallerInfo \
      .DESCRIPTOR.enum_types_by_name['GetUpdatesSource'] \
      .values_by_number[caller_info_source].name


def ShortDatatypeListSummary(data_types):
  """Formats compactly a list of sync types (python enums) for human eyes.

  This function is intended for use by logging.  If the list of datatypes
  contains almost all of the values, the return value will be expressed
  in terms of the datatypes that aren't set.
  """
  included = set(data_types) - set([TOP_LEVEL])
  if not included:
    return 'nothing'
  excluded = set(ALL_TYPES) - included - set([TOP_LEVEL])
  if not excluded:
    return 'everything'
  simple_text = '+'.join(sorted([SyncTypeToString(x) for x in included]))
  all_but_text = 'all except %s' % (
      '+'.join(sorted([SyncTypeToString(x) for x in excluded])))
  if len(included) < len(excluded) or len(simple_text) <= len(all_but_text):
    return simple_text
  else:
    return all_but_text


def GetDefaultEntitySpecifics(data_type):
  """Get an EntitySpecifics having a sync type's default field value."""
  specifics = sync_pb2.EntitySpecifics()
  if data_type in SYNC_TYPE_TO_DESCRIPTOR:
    descriptor = SYNC_TYPE_TO_DESCRIPTOR[data_type]
    getattr(specifics, descriptor.name).SetInParent()
  return specifics


class PermanentItem(object):
  """A specification of one server-created permanent item.

  Attributes:
    tag: A known-to-the-client value that uniquely identifies a server-created
      permanent item.
    name: The human-readable display name for this item.
    parent_tag: The tag of the permanent item's parent.  If ROOT_ID, indicates
      a top-level item.  Otherwise, this must be the tag value of some other
      server-created permanent item.
    sync_type: A value from ALL_TYPES, giving the datatype of this permanent
      item.  This controls which types of client GetUpdates requests will
      cause the permanent item to be created and returned.
    create_by_default: Whether the permanent item is created at startup or not.
      This value is set to True in the default case. Non-default permanent items
      are those that are created only when a client explicitly tells the server
      to do so.
  """

  def __init__(self, tag, name, parent_tag, sync_type, create_by_default=True):
    self.tag = tag
    self.name = name
    self.parent_tag = parent_tag
    self.sync_type = sync_type
    self.create_by_default = create_by_default


class MigrationHistory(object):
  """A record of the migration events associated with an account.

  Each migration event invalidates one or more datatypes on all clients
  that had synced the datatype before the event.  Such clients will continue
  to receive MigrationDone errors until they throw away their progress and
  re-sync that datatype from the beginning.
  """
  def __init__(self):
    self._migrations = {}
    for datatype in ALL_TYPES:
      self._migrations[datatype] = [1]
    self._next_migration_version = 2

  def GetLatestVersion(self, datatype):
    return self._migrations[datatype][-1]

  def CheckAllCurrent(self, versions_map):
    """Raises an error if any the provided versions are out of date.

    This function intentionally returns migrations in the order that they were
    triggered.  Doing it this way allows the client to queue up two migrations
    in a row, so the second one is received while responding to the first.

    Arguments:
      version_map: a map whose keys are datatypes and whose values are versions.

    Raises:
      MigrationDoneError: if a mismatch is found.
    """
    problems = {}
    for datatype, client_migration in versions_map.iteritems():
      for server_migration in self._migrations[datatype]:
        if client_migration < server_migration:
          problems.setdefault(server_migration, []).append(datatype)
    if problems:
      raise MigrationDoneError(problems[min(problems.keys())])

  def Bump(self, datatypes):
    """Add a record of a migration, to cause errors on future requests."""
    for idx, datatype in enumerate(datatypes):
      self._migrations[datatype].append(self._next_migration_version)
    self._next_migration_version += 1


class UpdateSieve(object):
  """A filter to remove items the client has already seen."""
  def __init__(self, request, migration_history=None):
    self._original_request = request
    self._state = {}
    self._migration_history = migration_history or MigrationHistory()
    self._migration_versions_to_check = {}
    if request.from_progress_marker:
      for marker in request.from_progress_marker:
        data_type = ProtocolDataTypeIdToSyncType(marker.data_type_id)
        if marker.HasField('timestamp_token_for_migration'):
          timestamp = marker.timestamp_token_for_migration
          if timestamp:
            self._migration_versions_to_check[data_type] = 1
        elif marker.token:
          (timestamp, version) = pickle.loads(marker.token)
          self._migration_versions_to_check[data_type] = version
        elif marker.HasField('token'):
          timestamp = 0
        else:
          raise ValueError('No timestamp information in progress marker.')
        data_type = ProtocolDataTypeIdToSyncType(marker.data_type_id)
        self._state[data_type] = timestamp
    elif request.HasField('from_timestamp'):
      for data_type in GetEntryTypesFromSpecifics(request.requested_types):
        self._state[data_type] = request.from_timestamp
        self._migration_versions_to_check[data_type] = 1
    if self._state:
      self._state[TOP_LEVEL] = min(self._state.itervalues())

  def SummarizeRequest(self):
    timestamps = {}
    for data_type, timestamp in self._state.iteritems():
      if data_type == TOP_LEVEL:
        continue
      timestamps.setdefault(timestamp, []).append(data_type)
    return ', '.join('<%s>@%d' % (ShortDatatypeListSummary(types), stamp)
                     for stamp, types in sorted(timestamps.iteritems()))

  def CheckMigrationState(self):
    self._migration_history.CheckAllCurrent(self._migration_versions_to_check)

  def ClientWantsItem(self, item):
    """Return true if the client hasn't already seen an item."""
    return self._state.get(GetEntryType(item), sys.maxint) < item.version

  def HasAnyTimestamp(self):
    """Return true if at least one datatype was requested."""
    return bool(self._state)

  def GetMinTimestamp(self):
    """Return true the smallest timestamp requested across all datatypes."""
    return min(self._state.itervalues())

  def GetFirstTimeTypes(self):
    """Return a list of datatypes requesting updates from timestamp zero."""
    return [datatype for datatype, timestamp in self._state.iteritems()
            if timestamp == 0]

  def GetCreateMobileBookmarks(self):
    """Return true if the client has requested to create the 'Mobile Bookmarks'
       folder.
    """
    return (self._original_request.HasField('create_mobile_bookmarks_folder')
            and self._original_request.create_mobile_bookmarks_folder)

  def SaveProgress(self, new_timestamp, get_updates_response):
    """Write the new_timestamp or new_progress_marker fields to a response."""
    if self._original_request.from_progress_marker:
      for data_type, old_timestamp in self._state.iteritems():
        if data_type == TOP_LEVEL:
          continue
        new_marker = sync_pb2.DataTypeProgressMarker()
        new_marker.data_type_id = SyncTypeToProtocolDataTypeId(data_type)
        final_stamp = max(old_timestamp, new_timestamp)
        final_migration = self._migration_history.GetLatestVersion(data_type)
        new_marker.token = pickle.dumps((final_stamp, final_migration))
        get_updates_response.new_progress_marker.add().MergeFrom(new_marker)
    elif self._original_request.HasField('from_timestamp'):
      if self._original_request.from_timestamp < new_timestamp:
        get_updates_response.new_timestamp = new_timestamp


class SyncDataModel(object):
  """Models the account state of one sync user."""
  _BATCH_SIZE = 100

  # Specify all the permanent items that a model might need.
  _PERMANENT_ITEM_SPECS = [
      PermanentItem('google_chrome_apps', name='Apps',
                    parent_tag=ROOT_ID, sync_type=APPS),
      PermanentItem('google_chrome_app_list', name='App List',
                    parent_tag=ROOT_ID, sync_type=APP_LIST),
      PermanentItem('google_chrome_app_notifications', name='App Notifications',
                    parent_tag=ROOT_ID, sync_type=APP_NOTIFICATION),
      PermanentItem('google_chrome_app_settings',
                    name='App Settings',
                    parent_tag=ROOT_ID, sync_type=APP_SETTINGS),
      PermanentItem('google_chrome_bookmarks', name='Bookmarks',
                    parent_tag=ROOT_ID, sync_type=BOOKMARK),
      PermanentItem('bookmark_bar', name='Bookmark Bar',
                    parent_tag='google_chrome_bookmarks', sync_type=BOOKMARK),
      PermanentItem('other_bookmarks', name='Other Bookmarks',
                    parent_tag='google_chrome_bookmarks', sync_type=BOOKMARK),
      PermanentItem('synced_bookmarks', name='Synced Bookmarks',
                    parent_tag='google_chrome_bookmarks', sync_type=BOOKMARK,
                    create_by_default=False),
      PermanentItem('google_chrome_autofill', name='Autofill',
                    parent_tag=ROOT_ID, sync_type=AUTOFILL),
      PermanentItem('google_chrome_autofill_profiles', name='Autofill Profiles',
                    parent_tag=ROOT_ID, sync_type=AUTOFILL_PROFILE),
      PermanentItem('google_chrome_device_info', name='Device Info',
                    parent_tag=ROOT_ID, sync_type=DEVICE_INFO),
      PermanentItem('google_chrome_experiments', name='Experiments',
                    parent_tag=ROOT_ID, sync_type=EXPERIMENTS),
      PermanentItem('google_chrome_extension_settings',
                    name='Extension Settings',
                    parent_tag=ROOT_ID, sync_type=EXTENSION_SETTINGS),
      PermanentItem('google_chrome_extensions', name='Extensions',
                    parent_tag=ROOT_ID, sync_type=EXTENSIONS),
      PermanentItem('google_chrome_history_delete_directives',
                    name='History Delete Directives',
                    parent_tag=ROOT_ID,
                    sync_type=HISTORY_DELETE_DIRECTIVE),
      PermanentItem('google_chrome_favicon_images',
                    name='Favicon Images',
                    parent_tag=ROOT_ID,
                    sync_type=FAVICON_IMAGES),
      PermanentItem('google_chrome_favicon_tracking',
                    name='Favicon Tracking',
                    parent_tag=ROOT_ID,
                    sync_type=FAVICON_TRACKING),
      PermanentItem('google_chrome_managed_user_settings',
                    name='Managed User Settings',
                    parent_tag=ROOT_ID, sync_type=MANAGED_USER_SETTING),
      PermanentItem('google_chrome_managed_users',
                    name='Managed Users',
                    parent_tag=ROOT_ID, sync_type=MANAGED_USER),
      PermanentItem('google_chrome_managed_user_shared_settings',
                    name='Managed User Shared Settings',
                    parent_tag=ROOT_ID, sync_type=MANAGED_USER_SHARED_SETTING),
      PermanentItem('google_chrome_managed_user_whitelists',
                    name='Managed User Whitelists', parent_tag=ROOT_ID,
                    sync_type=MANAGED_USER_WHITELIST),
      PermanentItem('google_chrome_nigori', name='Nigori',
                    parent_tag=ROOT_ID, sync_type=NIGORI),
      PermanentItem('google_chrome_passwords', name='Passwords',
                    parent_tag=ROOT_ID, sync_type=PASSWORD),
      PermanentItem('google_chrome_preferences', name='Preferences',
                    parent_tag=ROOT_ID, sync_type=PREFERENCE),
      PermanentItem('google_chrome_priority_preferences',
                    name='Priority Preferences',
                    parent_tag=ROOT_ID, sync_type=PRIORITY_PREFERENCE),
      PermanentItem('google_chrome_synced_notifications',
                    name='Synced Notifications',
                    parent_tag=ROOT_ID, sync_type=SYNCED_NOTIFICATION),
      PermanentItem('google_chrome_synced_notification_app_info',
                    name='Synced Notification App Info',
                    parent_tag=ROOT_ID, sync_type=SYNCED_NOTIFICATION_APP_INFO),
      PermanentItem('google_chrome_search_engines', name='Search Engines',
                    parent_tag=ROOT_ID, sync_type=SEARCH_ENGINE),
      PermanentItem('google_chrome_sessions', name='Sessions',
                    parent_tag=ROOT_ID, sync_type=SESSION),
      PermanentItem('google_chrome_themes', name='Themes',
                    parent_tag=ROOT_ID, sync_type=THEME),
      PermanentItem('google_chrome_typed_urls', name='Typed URLs',
                    parent_tag=ROOT_ID, sync_type=TYPED_URL),
      PermanentItem('google_chrome_wifi_credentials', name='WiFi Credentials',
                    parent_tag=ROOT_ID, sync_type=WIFI_CREDENTIAL),
      PermanentItem('google_chrome_dictionary', name='Dictionary',
                    parent_tag=ROOT_ID, sync_type=DICTIONARY),
      PermanentItem('google_chrome_articles', name='Articles',
                    parent_tag=ROOT_ID, sync_type=ARTICLE),
      ]

  def __init__(self):
    # Monotonically increasing version number.  The next object change will
    # take on this value + 1.
    self._version = 0

    # The definitive copy of this client's items: a map from ID string to a
    # SyncEntity protocol buffer.
    self._entries = {}

    self.ResetStoreBirthday()
    self.migration_history = MigrationHistory()
    self.induced_error = sync_pb2.ClientToServerResponse.Error()
    self.induced_error_frequency = 0
    self.sync_count_before_errors = 0
    self.acknowledge_managed_users = False
    self._keys = [MakeNewKeystoreKey()]

  def _SaveEntry(self, entry):
    """Insert or update an entry in the change log, and give it a new version.

    The ID fields of this entry are assumed to be valid server IDs.  This
    entry will be updated with a new version number and sync_timestamp.

    Args:
      entry: The entry to be added or updated.
    """
    self._version += 1
    # Maintain a global (rather than per-item) sequence number and use it
    # both as the per-entry version as well as the update-progress timestamp.
    # This simulates the behavior of the original server implementation.
    entry.version = self._version
    entry.sync_timestamp = self._version

    # Preserve the originator info, which the client is not required to send
    # when updating.
    base_entry = self._entries.get(entry.id_string)
    if base_entry:
      entry.originator_cache_guid = base_entry.originator_cache_guid
      entry.originator_client_item_id = base_entry.originator_client_item_id

    self._entries[entry.id_string] = copy.deepcopy(entry)

  def _ServerTagToId(self, tag):
    """Determine the server ID from a server-unique tag.

    The resulting value is guaranteed not to collide with the other ID
    generation methods.

    Args:
      tag: The unique, known-to-the-client tag of a server-generated item.
    Returns:
      The string value of the computed server ID.
    """
    if not tag or tag == ROOT_ID:
      return tag
    spec = [x for x in self._PERMANENT_ITEM_SPECS if x.tag == tag][0]
    return self._MakeCurrentId(spec.sync_type, '<server tag>%s' % tag)

  def _TypeToTypeRootId(self, model_type):
    """Returns the server ID for the type root node of the given type."""
    tag = [x.tag for x in self._PERMANENT_ITEM_SPECS
           if x.sync_type == model_type][0]
    return self._ServerTagToId(tag)

  def _ClientTagToId(self, datatype, tag):
    """Determine the server ID from a client-unique tag.

    The resulting value is guaranteed not to collide with the other ID
    generation methods.

    Args:
      datatype: The sync type (python enum) of the identified object.
      tag: The unique, opaque-to-the-server tag of a client-tagged item.
    Returns:
      The string value of the computed server ID.
    """
    return self._MakeCurrentId(datatype, '<client tag>%s' % tag)

  def _ClientIdToId(self, datatype, client_guid, client_item_id):
    """Compute a unique server ID from a client-local ID tag.

    The resulting value is guaranteed not to collide with the other ID
    generation methods.

    Args:
      datatype: The sync type (python enum) of the identified object.
      client_guid: A globally unique ID that identifies the client which
        created this item.
      client_item_id: An ID that uniquely identifies this item on the client
        which created it.
    Returns:
      The string value of the computed server ID.
    """
    # Using the client ID info is not required here (we could instead generate
    # a random ID), but it's useful for debugging.
    return self._MakeCurrentId(datatype,
        '<server ID originally>%s/%s' % (client_guid, client_item_id))

  def _MakeCurrentId(self, datatype, inner_id):
    return '%d^%d^%s' % (datatype,
                         self.migration_history.GetLatestVersion(datatype),
                         inner_id)

  def _ExtractIdInfo(self, id_string):
    if not id_string or id_string == ROOT_ID:
      return None
    datatype_string, separator, remainder = id_string.partition('^')
    migration_version_string, separator, inner_id = remainder.partition('^')
    return (int(datatype_string), int(migration_version_string), inner_id)

  def _WritePosition(self, entry, parent_id):
    """Ensure the entry has an absolute, numeric position and parent_id.

    Historically, clients would specify positions using the predecessor-based
    references in the insert_after_item_id field; starting July 2011, this
    was changed and Chrome now sends up the absolute position.  The server
    must store a position_in_parent value and must not maintain
    insert_after_item_id.
    Starting in Jan 2013, the client will also send up a unique_position field
    which should be saved and returned on subsequent GetUpdates.

    Args:
      entry: The entry for which to write a position.  Its ID field are
        assumed to be server IDs.  This entry will have its parent_id_string,
        position_in_parent and unique_position fields updated; its
        insert_after_item_id field will be cleared.
      parent_id: The ID of the entry intended as the new parent.
    """

    entry.parent_id_string = parent_id
    if not entry.HasField('position_in_parent'):
      entry.position_in_parent = 1337  # A debuggable, distinctive default.
    entry.ClearField('insert_after_item_id')

  def _ItemExists(self, id_string):
    """Determine whether an item exists in the changelog."""
    return id_string in self._entries

  def _CreatePermanentItem(self, spec):
    """Create one permanent item from its spec, if it doesn't exist.

    The resulting item is added to the changelog.

    Args:
      spec: A PermanentItem object holding the properties of the item to create.
    """
    id_string = self._ServerTagToId(spec.tag)
    if self._ItemExists(id_string):
      return
    print 'Creating permanent item: %s' % spec.name
    entry = sync_pb2.SyncEntity()
    entry.id_string = id_string
    entry.non_unique_name = spec.name
    entry.name = spec.name
    entry.server_defined_unique_tag = spec.tag
    entry.folder = True
    entry.deleted = False
    entry.specifics.CopyFrom(GetDefaultEntitySpecifics(spec.sync_type))
    self._WritePosition(entry, self._ServerTagToId(spec.parent_tag))
    self._SaveEntry(entry)

  def _CreateDefaultPermanentItems(self, requested_types):
    """Ensure creation of all default permanent items for a given set of types.

    Args:
      requested_types: A list of sync data types from ALL_TYPES.
        All default permanent items of only these types will be created.
    """
    for spec in self._PERMANENT_ITEM_SPECS:
      if spec.sync_type in requested_types and spec.create_by_default:
        self._CreatePermanentItem(spec)

  def ResetStoreBirthday(self):
    """Resets the store birthday to a random value."""
    # TODO(nick): uuid.uuid1() is better, but python 2.5 only.
    self.store_birthday = '%0.30f' % random.random()

  def StoreBirthday(self):
    """Gets the store birthday."""
    return self.store_birthday

  def GetChanges(self, sieve):
    """Get entries which have changed, oldest first.

    The returned entries are limited to being _BATCH_SIZE many.  The entries
    are returned in strict version order.

    Args:
      sieve: An update sieve to use to filter out updates the client
        has already seen.
    Returns:
      A tuple of (version, entries, changes_remaining).  Version is a new
      timestamp value, which should be used as the starting point for the
      next query.  Entries is the batch of entries meeting the current
      timestamp query.  Changes_remaining indicates the number of changes
      left on the server after this batch.
    """
    if not sieve.HasAnyTimestamp():
      return (0, [], 0)
    min_timestamp = sieve.GetMinTimestamp()
    first_time_types = sieve.GetFirstTimeTypes()
    self._CreateDefaultPermanentItems(first_time_types)
    # Mobile bookmark folder is not created by default, create it only when
    # client requested it.
    if (sieve.GetCreateMobileBookmarks() and
        first_time_types.count(BOOKMARK) > 0):
      self.TriggerCreateSyncedBookmarks()

    self.TriggerAcknowledgeManagedUsers()

    change_log = sorted(self._entries.values(),
                        key=operator.attrgetter('version'))
    new_changes = [x for x in change_log if x.version > min_timestamp]
    # Pick batch_size new changes, and then filter them.  This matches
    # the RPC behavior of the production sync server.
    batch = new_changes[:self._BATCH_SIZE]
    if not batch:
      # Client is up to date.
      return (min_timestamp, [], 0)

    # Restrict batch to requested types.  Tombstones are untyped
    # and will always get included.
    filtered = [copy.deepcopy(item) for item in batch
                if item.deleted or sieve.ClientWantsItem(item)]

    # The new client timestamp is the timestamp of the last item in the
    # batch, even if that item was filtered out.
    return (batch[-1].version, filtered, len(new_changes) - len(batch))

  def GetKeystoreKeys(self):
    """Returns the encryption keys for this account."""
    print "Returning encryption keys: %s" % self._keys
    return self._keys

  def _CopyOverImmutableFields(self, entry):
    """Preserve immutable fields by copying pre-commit state.

    Args:
      entry: A sync entity from the client.
    """
    if entry.id_string in self._entries:
      if self._entries[entry.id_string].HasField(
          'server_defined_unique_tag'):
        entry.server_defined_unique_tag = (
            self._entries[entry.id_string].server_defined_unique_tag)

  def _CheckVersionForCommit(self, entry):
    """Perform an optimistic concurrency check on the version number.

    Clients are only allowed to commit if they report having seen the most
    recent version of an object.

    Args:
      entry: A sync entity from the client.  It is assumed that ID fields
        have been converted to server IDs.
    Returns:
      A boolean value indicating whether the client's version matches the
      newest server version for the given entry.
    """
    if entry.id_string in self._entries:
      # Allow edits/deletes if the version matches, and any undeletion.
      return (self._entries[entry.id_string].version == entry.version or
              self._entries[entry.id_string].deleted)
    else:
      # Allow unknown ID only if the client thinks it's new too.
      return entry.version == 0

  def _CheckParentIdForCommit(self, entry):
    """Check that the parent ID referenced in a SyncEntity actually exists.

    Args:
      entry: A sync entity from the client.  It is assumed that ID fields
        have been converted to server IDs.
    Returns:
      A boolean value indicating whether the entity's parent ID is an object
      that actually exists (and is not deleted) in the current account state.
    """
    if entry.parent_id_string == ROOT_ID:
      # This is generally allowed.
      return True
    if (not entry.HasField('parent_id_string') and
        entry.HasField('client_defined_unique_tag')):
      return True  # Unique client tag items do not need to specify a parent.
    if entry.parent_id_string not in self._entries:
      print 'Warning: Client sent unknown ID.  Should never happen.'
      return False
    if entry.parent_id_string == entry.id_string:
      print 'Warning: Client sent circular reference.  Should never happen.'
      return False
    if self._entries[entry.parent_id_string].deleted:
      # This can happen in a race condition between two clients.
      return False
    if not self._entries[entry.parent_id_string].folder:
      print 'Warning: Client sent non-folder parent.  Should never happen.'
      return False
    return True

  def _RewriteIdsAsServerIds(self, entry, cache_guid, commit_session):
    """Convert ID fields in a client sync entry to server IDs.

    A commit batch sent by a client may contain new items for which the
    server has not generated IDs yet.  And within a commit batch, later
    items are allowed to refer to earlier items.  This method will
    generate server IDs for new items, as well as rewrite references
    to items whose server IDs were generated earlier in the batch.

    Args:
      entry: The client sync entry to modify.
      cache_guid: The globally unique ID of the client that sent this
        commit request.
      commit_session: A dictionary mapping the original IDs to the new server
        IDs, for any items committed earlier in the batch.
    """
    if entry.version == 0:
      data_type = GetEntryType(entry)
      if entry.HasField('client_defined_unique_tag'):
        # When present, this should determine the item's ID.
        new_id = self._ClientTagToId(data_type, entry.client_defined_unique_tag)
      else:
        new_id = self._ClientIdToId(data_type, cache_guid, entry.id_string)
        entry.originator_cache_guid = cache_guid
        entry.originator_client_item_id = entry.id_string
      commit_session[entry.id_string] = new_id  # Remember the remapping.
      entry.id_string = new_id
    if entry.parent_id_string in commit_session:
      entry.parent_id_string = commit_session[entry.parent_id_string]
    if entry.insert_after_item_id in commit_session:
      entry.insert_after_item_id = commit_session[entry.insert_after_item_id]

  def ValidateCommitEntries(self, entries):
    """Raise an exception if a commit batch contains any global errors.

    Arguments:
      entries: an iterable containing commit-form SyncEntity protocol buffers.

    Raises:
      MigrationDoneError: if any of the entries reference a recently-migrated
        datatype.
    """
    server_ids_in_commit = set()
    local_ids_in_commit = set()
    for entry in entries:
      if entry.version:
        server_ids_in_commit.add(entry.id_string)
      else:
        local_ids_in_commit.add(entry.id_string)
      if entry.HasField('parent_id_string'):
        if entry.parent_id_string not in local_ids_in_commit:
          server_ids_in_commit.add(entry.parent_id_string)

    versions_present = {}
    for server_id in server_ids_in_commit:
      parsed = self._ExtractIdInfo(server_id)
      if parsed:
        datatype, version, _ = parsed
        versions_present.setdefault(datatype, []).append(version)

    self.migration_history.CheckAllCurrent(
         dict((k, min(v)) for k, v in versions_present.iteritems()))

  def CommitEntry(self, entry, cache_guid, commit_session):
    """Attempt to commit one entry to the user's account.

    Args:
      entry: A SyncEntity protobuf representing desired object changes.
      cache_guid: A string value uniquely identifying the client; this
        is used for ID generation and will determine the originator_cache_guid
        if the entry is new.
      commit_session: A dictionary mapping client IDs to server IDs for any
        objects committed earlier this session.  If the entry gets a new ID
        during commit, the change will be recorded here.
    Returns:
      A SyncEntity reflecting the post-commit value of the entry, or None
      if the entry was not committed due to an error.
    """
    entry = copy.deepcopy(entry)

    # Generate server IDs for this entry, and write generated server IDs
    # from earlier entries into the message's fields, as appropriate.  The
    # ID generation state is stored in 'commit_session'.
    self._RewriteIdsAsServerIds(entry, cache_guid, commit_session)

    # Sets the parent ID field for a client-tagged item.  The client is allowed
    # to not specify parents for these types of items.  The server can figure
    # out on its own what the parent ID for this entry should be.
    self._RewriteParentIdForUniqueClientEntry(entry)

    # Perform the optimistic concurrency check on the entry's version number.
    # Clients are not allowed to commit unless they indicate that they've seen
    # the most recent version of an object.
    if not self._CheckVersionForCommit(entry):
      return None

    # Check the validity of the parent ID; it must exist at this point.
    # TODO(nick): Implement cycle detection and resolution.
    if not self._CheckParentIdForCommit(entry):
      return None

    self._CopyOverImmutableFields(entry);

    # At this point, the commit is definitely going to happen.

    # Deletion works by storing a limited record for an entry, called a
    # tombstone.  A sync server must track deleted IDs forever, since it does
    # not keep track of client knowledge (there's no deletion ACK event).
    if entry.deleted:
      def MakeTombstone(id_string, datatype):
        """Make a tombstone entry that will replace the entry being deleted.

        Args:
          id_string: Index of the SyncEntity to be deleted.
        Returns:
          A new SyncEntity reflecting the fact that the entry is deleted.
        """
        # Only the ID, version and deletion state are preserved on a tombstone.
        tombstone = sync_pb2.SyncEntity()
        tombstone.id_string = id_string
        tombstone.deleted = True
        tombstone.name = ''
        tombstone.specifics.CopyFrom(GetDefaultEntitySpecifics(datatype))
        return tombstone

      def IsChild(child_id):
        """Check if a SyncEntity is a child of entry, or any of its children.

        Args:
          child_id: Index of the SyncEntity that is a possible child of entry.
        Returns:
          True if it is a child; false otherwise.
        """
        if child_id not in self._entries:
          return False
        if self._entries[child_id].parent_id_string == entry.id_string:
          return True
        return IsChild(self._entries[child_id].parent_id_string)

      # Identify any children entry might have.
      child_ids = [child.id_string for child in self._entries.itervalues()
                   if IsChild(child.id_string)]

      # Mark all children that were identified as deleted.
      for child_id in child_ids:
        datatype = GetEntryType(self._entries[child_id])
        self._SaveEntry(MakeTombstone(child_id, datatype))

      # Delete entry itself.
      datatype = GetEntryType(self._entries[entry.id_string])
      entry = MakeTombstone(entry.id_string, datatype)
    else:
      # Comments in sync.proto detail how the representation of positional
      # ordering works.
      #
      # We've almost fully deprecated the 'insert_after_item_id' field.
      # The 'position_in_parent' field is also deprecated, but as of Jan 2013
      # is still in common use.  The 'unique_position' field is the latest
      # and greatest in positioning technology.
      #
      # This server supports 'position_in_parent' and 'unique_position'.
      self._WritePosition(entry, entry.parent_id_string)

    # Preserve the originator info, which the client is not required to send
    # when updating.
    base_entry = self._entries.get(entry.id_string)
    if base_entry and not entry.HasField('originator_cache_guid'):
      entry.originator_cache_guid = base_entry.originator_cache_guid
      entry.originator_client_item_id = base_entry.originator_client_item_id

    # Store the current time since the Unix epoch in milliseconds.
    entry.mtime = (int((time.mktime(time.gmtime()) -
        (time.mktime(FIRST_DAY_UNIX_TIME_EPOCH) - ONE_DAY_SECONDS))*1000))

    # Commit the change.  This also updates the version number.
    self._SaveEntry(entry)
    return entry

  def _RewriteVersionInId(self, id_string):
    """Rewrites an ID so that its migration version becomes current."""
    parsed_id = self._ExtractIdInfo(id_string)
    if not parsed_id:
      return id_string
    datatype, old_migration_version, inner_id = parsed_id
    return self._MakeCurrentId(datatype, inner_id)

  def _RewriteParentIdForUniqueClientEntry(self, entry):
    """Sets the entry's parent ID field to the appropriate value.

    The client must always set enough of the specifics of the entries it sends
    up such that the server can identify its type.  (See crbug.com/373859)

    The client is under no obligation to set the parent ID field.  The server
    can always infer what the appropriate parent for this model type should be.
    Having the client not send the parent ID is a step towards the removal of
    type root nodes.  (See crbug.com/373869)

    This server implements these features by "faking" the existing of a parent
    ID early on in the commit processing.

    This function has no effect on non-client-tagged items.
    """
    if not entry.HasField('client_defined_unique_tag'):
      return  # Skip this processing for non-client-tagged types.
    data_type = GetEntryType(entry)
    entry.parent_id_string = self._TypeToTypeRootId(data_type)

  def TriggerMigration(self, datatypes):
    """Cause a migration to occur for a set of datatypes on this account.

    Clients will see the MIGRATION_DONE error for these datatypes until they
    resync them.
    """
    versions_to_remap = self.migration_history.Bump(datatypes)
    all_entries = self._entries.values()
    self._entries.clear()
    for entry in all_entries:
      new_id = self._RewriteVersionInId(entry.id_string)
      entry.id_string = new_id
      if entry.HasField('parent_id_string'):
        entry.parent_id_string = self._RewriteVersionInId(
            entry.parent_id_string)
      self._entries[entry.id_string] = entry

  def TriggerSyncTabFavicons(self):
    """Set the 'sync_tab_favicons' field to this account's nigori node.

    If the field is not currently set, will write a new nigori node entry
    with the field set. Else does nothing.
    """

    nigori_tag = "google_chrome_nigori"
    nigori_original = self._entries.get(self._ServerTagToId(nigori_tag))
    if (nigori_original.specifics.nigori.sync_tab_favicons):
      return
    nigori_new = copy.deepcopy(nigori_original)
    nigori_new.specifics.nigori.sync_tabs = True
    self._SaveEntry(nigori_new)

  def TriggerCreateSyncedBookmarks(self):
    """Create the Synced Bookmarks folder under the Bookmarks permanent item.

    Clients will then receive the Synced Bookmarks folder on future
    GetUpdates, and new bookmarks can be added within the Synced Bookmarks
    folder.
    """

    synced_bookmarks_spec, = [spec for spec in self._PERMANENT_ITEM_SPECS
                              if spec.name == "Synced Bookmarks"]
    self._CreatePermanentItem(synced_bookmarks_spec)

  def TriggerEnableKeystoreEncryption(self):
    """Create the keystore_encryption experiment entity and enable it.

    A new entity within the EXPERIMENTS datatype is created with the unique
    client tag "keystore_encryption" if it doesn't already exist. The
    keystore_encryption message is then filled with |enabled| set to true.
    """

    experiment_id = self._ServerTagToId("google_chrome_experiments")
    keystore_encryption_id = self._ClientTagToId(
        EXPERIMENTS,
        KEYSTORE_ENCRYPTION_EXPERIMENT_TAG)
    keystore_entry = self._entries.get(keystore_encryption_id)
    if keystore_entry is None:
      keystore_entry = sync_pb2.SyncEntity()
      keystore_entry.id_string = keystore_encryption_id
      keystore_entry.name = "Keystore Encryption"
      keystore_entry.client_defined_unique_tag = (
          KEYSTORE_ENCRYPTION_EXPERIMENT_TAG)
      keystore_entry.folder = False
      keystore_entry.deleted = False
      keystore_entry.specifics.CopyFrom(GetDefaultEntitySpecifics(EXPERIMENTS))
      self._WritePosition(keystore_entry, experiment_id)

    keystore_entry.specifics.experiments.keystore_encryption.enabled = True

    self._SaveEntry(keystore_entry)

  def TriggerRotateKeystoreKeys(self):
    """Rotate the current set of keystore encryption keys.

    |self._keys| will have a new random encryption key appended to it. We touch
    the nigori node so that each client will receive the new encryption keys
    only once.
    """

    # Add a new encryption key.
    self._keys += [MakeNewKeystoreKey(), ]

    # Increment the nigori node's timestamp, so clients will get the new keys
    # on their next GetUpdates (any time the nigori node is sent back, we also
    # send back the keystore keys).
    nigori_tag = "google_chrome_nigori"
    self._SaveEntry(self._entries.get(self._ServerTagToId(nigori_tag)))

  def TriggerAcknowledgeManagedUsers(self):
    """Set the "acknowledged" flag for any managed user entities that don't have
       it set already.
    """

    if not self.acknowledge_managed_users:
      return

    managed_users = [copy.deepcopy(entry) for entry in self._entries.values()
                     if entry.specifics.HasField('managed_user')
                     and not entry.specifics.managed_user.acknowledged]
    for user in managed_users:
      user.specifics.managed_user.acknowledged = True
      self._SaveEntry(user)

  def TriggerEnablePreCommitGetUpdateAvoidance(self):
    """Sets the experiment to enable pre-commit GetUpdate avoidance."""
    experiment_id = self._ServerTagToId("google_chrome_experiments")
    pre_commit_gu_avoidance_id = self._ClientTagToId(
        EXPERIMENTS,
        PRE_COMMIT_GU_AVOIDANCE_EXPERIMENT_TAG)
    entry = self._entries.get(pre_commit_gu_avoidance_id)
    if entry is None:
      entry = sync_pb2.SyncEntity()
      entry.id_string = pre_commit_gu_avoidance_id
      entry.name = "Pre-commit GU avoidance"
      entry.client_defined_unique_tag = PRE_COMMIT_GU_AVOIDANCE_EXPERIMENT_TAG
      entry.folder = False
      entry.deleted = False
      entry.specifics.CopyFrom(GetDefaultEntitySpecifics(EXPERIMENTS))
      self._WritePosition(entry, experiment_id)
    entry.specifics.experiments.pre_commit_update_avoidance.enabled = True
    self._SaveEntry(entry)

  def SetInducedError(self, error, error_frequency,
                      sync_count_before_errors):
    self.induced_error = error
    self.induced_error_frequency = error_frequency
    self.sync_count_before_errors = sync_count_before_errors

  def GetInducedError(self):
    return self.induced_error

  def _GetNextVersionNumber(self):
    """Set the version to one more than the greatest version number seen."""
    entries = sorted(self._entries.values(), key=operator.attrgetter('version'))
    if len(entries) < 1:
      raise ClientNotConnectedError
    return entries[-1].version + 1


class TestServer(object):
  """An object to handle requests for one (and only one) Chrome Sync account.

  TestServer consumes the sync command messages that are the outermost
  layers of the protocol, performs the corresponding actions on its
  SyncDataModel, and constructs an appropriate response message.
  """

  def __init__(self):
    # The implementation supports exactly one account; its state is here.
    self.account = SyncDataModel()
    self.account_lock = threading.Lock()
    # Clients that have talked to us: a map from the full client ID
    # to its nickname.
    self.clients = {}
    self.client_name_generator = ('+' * times + chr(c)
        for times in xrange(0, sys.maxint) for c in xrange(ord('A'), ord('Z')))
    self.transient_error = False
    self.sync_count = 0
    # Gaia OAuth2 Token fields and their default values.
    self.response_code = 200
    self.request_token = 'rt1'
    self.access_token = 'at1'
    self.expires_in = 3600
    self.token_type = 'Bearer'
    # The ClientCommand to send back on each ServerToClientResponse. If set to
    # None, no ClientCommand should be sent.
    self._client_command = None


  def GetShortClientName(self, query):
    parsed = cgi.parse_qs(query[query.find('?')+1:])
    client_id = parsed.get('client_id')
    if not client_id:
      return '?'
    client_id = client_id[0]
    if client_id not in self.clients:
      self.clients[client_id] = self.client_name_generator.next()
    return self.clients[client_id]

  def CheckStoreBirthday(self, request):
    """Raises StoreBirthdayError if the request's birthday is a mismatch."""
    if not request.HasField('store_birthday'):
      return
    if self.account.StoreBirthday() != request.store_birthday:
      raise StoreBirthdayError

  def CheckTransientError(self):
    """Raises TransientError if transient_error variable is set."""
    if self.transient_error:
      raise TransientError

  def CheckSendError(self):
     """Raises SyncInducedError if needed."""
     if (self.account.induced_error.error_type !=
         sync_enums_pb2.SyncEnums.UNKNOWN):
       # Always means return the given error for all requests.
       if self.account.induced_error_frequency == ERROR_FREQUENCY_ALWAYS:
         raise SyncInducedError
       # This means the FIRST 2 requests of every 3 requests
       # return an error. Don't switch the order of failures. There are
       # test cases that rely on the first 2 being the failure rather than
       # the last 2.
       elif (self.account.induced_error_frequency ==
             ERROR_FREQUENCY_TWO_THIRDS):
         if (((self.sync_count -
               self.account.sync_count_before_errors) % 3) != 0):
           raise SyncInducedError
       else:
         raise InducedErrorFrequencyNotDefined

  def HandleMigrate(self, path):
    query = urlparse.urlparse(path)[4]
    code = 200
    self.account_lock.acquire()
    try:
      datatypes = [DataTypeStringToSyncTypeLoose(x)
                   for x in urlparse.parse_qs(query).get('type',[])]
      if datatypes:
        self.account.TriggerMigration(datatypes)
        response = 'Migrated datatypes %s' % (
            ' and '.join(SyncTypeToString(x).upper() for x in datatypes))
      else:
        response = 'Please specify one or more <i>type=name</i> parameters'
        code = 400
    except DataTypeIdNotRecognized, error:
      response = 'Could not interpret datatype name'
      code = 400
    finally:
      self.account_lock.release()
    return (code, '<html><title>Migration: %d</title><H1>%d %s</H1></html>' %
                (code, code, response))

  def HandleSetInducedError(self, path):
     query = urlparse.urlparse(path)[4]
     self.account_lock.acquire()
     code = 200
     response = 'Success'
     error = sync_pb2.ClientToServerResponse.Error()
     try:
       error_type = urlparse.parse_qs(query)['error']
       action = urlparse.parse_qs(query)['action']
       error.error_type = int(error_type[0])
       error.action = int(action[0])
       try:
         error.url = (urlparse.parse_qs(query)['url'])[0]
       except KeyError:
         error.url = ''
       try:
         error.error_description =(
         (urlparse.parse_qs(query)['error_description'])[0])
       except KeyError:
         error.error_description = ''
       try:
         error_frequency = int((urlparse.parse_qs(query)['frequency'])[0])
       except KeyError:
         error_frequency = ERROR_FREQUENCY_ALWAYS
       self.account.SetInducedError(error, error_frequency, self.sync_count)
       response = ('Error = %d, action = %d, url = %s, description = %s' %
                   (error.error_type, error.action,
                    error.url,
                    error.error_description))
     except error:
       response = 'Could not parse url'
       code = 400
     finally:
       self.account_lock.release()
     return (code, '<html><title>SetError: %d</title><H1>%d %s</H1></html>' %
                (code, code, response))

  def HandleCreateBirthdayError(self):
    self.account.ResetStoreBirthday()
    return (
        200,
        '<html><title>Birthday error</title><H1>Birthday error</H1></html>')

  def HandleSetTransientError(self):
    self.transient_error = True
    return (
        200,
        '<html><title>Transient error</title><H1>Transient error</H1></html>')

  def HandleSetSyncTabFavicons(self):
    """Set 'sync_tab_favicons' field of the nigori node for this account."""
    self.account.TriggerSyncTabFavicons()
    return (
        200,
        '<html><title>Tab Favicons</title><H1>Tab Favicons</H1></html>')

  def HandleCreateSyncedBookmarks(self):
    """Create the Synced Bookmarks folder under Bookmarks."""
    self.account.TriggerCreateSyncedBookmarks()
    return (
        200,
        '<html><title>Synced Bookmarks</title><H1>Synced Bookmarks</H1></html>')

  def HandleEnableKeystoreEncryption(self):
    """Enables the keystore encryption experiment."""
    self.account.TriggerEnableKeystoreEncryption()
    return (
        200,
        '<html><title>Enable Keystore Encryption</title>'
            '<H1>Enable Keystore Encryption</H1></html>')

  def HandleRotateKeystoreKeys(self):
    """Rotate the keystore encryption keys."""
    self.account.TriggerRotateKeystoreKeys()
    return (
        200,
        '<html><title>Rotate Keystore Keys</title>'
            '<H1>Rotate Keystore Keys</H1></html>')

  def HandleEnableManagedUserAcknowledgement(self):
    """Enable acknowledging newly created managed users."""
    self.account.acknowledge_managed_users = True
    return (
        200,
        '<html><title>Enable Managed User Acknowledgement</title>'
            '<h1>Enable Managed User Acknowledgement</h1></html>')

  def HandleEnablePreCommitGetUpdateAvoidance(self):
    """Enables the pre-commit GU avoidance experiment."""
    self.account.TriggerEnablePreCommitGetUpdateAvoidance()
    return (
        200,
        '<html><title>Enable pre-commit GU avoidance</title>'
            '<H1>Enable pre-commit GU avoidance</H1></html>')

  def HandleCommand(self, query, raw_request):
    """Decode and handle a sync command from a raw input of bytes.

    This is the main entry point for this class.  It is safe to call this
    method from multiple threads.

    Args:
      raw_request: An iterable byte sequence to be interpreted as a sync
        protocol command.
    Returns:
      A tuple (response_code, raw_response); the first value is an HTTP
      result code, while the second value is a string of bytes which is the
      serialized reply to the command.
    """
    self.account_lock.acquire()
    self.sync_count += 1
    def print_context(direction):
      print '[Client %s %s %s.py]' % (self.GetShortClientName(query), direction,
                                      __name__),

    try:
      request = sync_pb2.ClientToServerMessage()
      request.MergeFromString(raw_request)
      contents = request.message_contents

      response = sync_pb2.ClientToServerResponse()
      response.error_code = sync_enums_pb2.SyncEnums.SUCCESS

      if self._client_command:
        response.client_command.CopyFrom(self._client_command)

      self.CheckStoreBirthday(request)
      response.store_birthday = self.account.store_birthday
      self.CheckTransientError()
      self.CheckSendError()

      print_context('->')

      if contents == sync_pb2.ClientToServerMessage.AUTHENTICATE:
        print 'Authenticate'
        # We accept any authentication token, and support only one account.
        # TODO(nick): Mock out the GAIA authentication as well; hook up here.
        response.authenticate.user.email = 'syncjuser@chromium'
        response.authenticate.user.display_name = 'Sync J User'
      elif contents == sync_pb2.ClientToServerMessage.COMMIT:
        print 'Commit %d item(s)' % len(request.commit.entries)
        self.HandleCommit(request.commit, response.commit)
      elif contents == sync_pb2.ClientToServerMessage.GET_UPDATES:
        print 'GetUpdates',
        self.HandleGetUpdates(request.get_updates, response.get_updates)
        print_context('<-')
        print '%d update(s)' % len(response.get_updates.entries)
      else:
        print 'Unrecognizable sync request!'
        return (400, None)  # Bad request.
      return (200, response.SerializeToString())
    except MigrationDoneError, error:
      print_context('<-')
      print 'MIGRATION_DONE: <%s>' % (ShortDatatypeListSummary(error.datatypes))
      response = sync_pb2.ClientToServerResponse()
      response.store_birthday = self.account.store_birthday
      response.error_code = sync_enums_pb2.SyncEnums.MIGRATION_DONE
      response.migrated_data_type_id[:] = [
          SyncTypeToProtocolDataTypeId(x) for x in error.datatypes]
      return (200, response.SerializeToString())
    except StoreBirthdayError, error:
      print_context('<-')
      print 'NOT_MY_BIRTHDAY'
      response = sync_pb2.ClientToServerResponse()
      response.store_birthday = self.account.store_birthday
      response.error_code = sync_enums_pb2.SyncEnums.NOT_MY_BIRTHDAY
      return (200, response.SerializeToString())
    except TransientError, error:
      ### This is deprecated now. Would be removed once test cases are removed.
      print_context('<-')
      print 'TRANSIENT_ERROR'
      response.store_birthday = self.account.store_birthday
      response.error_code = sync_enums_pb2.SyncEnums.TRANSIENT_ERROR
      return (200, response.SerializeToString())
    except SyncInducedError, error:
      print_context('<-')
      print 'INDUCED_ERROR'
      response.store_birthday = self.account.store_birthday
      error = self.account.GetInducedError()
      response.error.error_type = error.error_type
      response.error.url = error.url
      response.error.error_description = error.error_description
      response.error.action = error.action
      return (200, response.SerializeToString())
    finally:
      self.account_lock.release()

  def HandleCommit(self, commit_message, commit_response):
    """Respond to a Commit request by updating the user's account state.

    Commit attempts stop after the first error, returning a CONFLICT result
    for any unattempted entries.

    Args:
      commit_message: A sync_pb.CommitMessage protobuf holding the content
        of the client's request.
      commit_response: A sync_pb.CommitResponse protobuf into which a reply
        to the client request will be written.
    """
    commit_response.SetInParent()
    batch_failure = False
    session = {}  # Tracks ID renaming during the commit operation.
    guid = commit_message.cache_guid

    self.account.ValidateCommitEntries(commit_message.entries)

    for entry in commit_message.entries:
      server_entry = None
      if not batch_failure:
        # Try to commit the change to the account.
        server_entry = self.account.CommitEntry(entry, guid, session)

      # An entryresponse is returned in both success and failure cases.
      reply = commit_response.entryresponse.add()
      if not server_entry:
        reply.response_type = sync_pb2.CommitResponse.CONFLICT
        reply.error_message = 'Conflict.'
        batch_failure = True  # One failure halts the batch.
      else:
        reply.response_type = sync_pb2.CommitResponse.SUCCESS
        # These are the properties that the server is allowed to override
        # during commit; the client wants to know their values at the end
        # of the operation.
        reply.id_string = server_entry.id_string
        if not server_entry.deleted:
          # Note: the production server doesn't actually send the
          # parent_id_string on commit responses, so we don't either.
          reply.position_in_parent = server_entry.position_in_parent
          reply.version = server_entry.version
          reply.name = server_entry.name
          reply.non_unique_name = server_entry.non_unique_name
        else:
          reply.version = entry.version + 1

  def HandleGetUpdates(self, update_request, update_response):
    """Respond to a GetUpdates request by querying the user's account.

    Args:
      update_request: A sync_pb.GetUpdatesMessage protobuf holding the content
        of the client's request.
      update_response: A sync_pb.GetUpdatesResponse protobuf into which a reply
        to the client request will be written.
    """
    update_response.SetInParent()
    update_sieve = UpdateSieve(update_request, self.account.migration_history)

    print CallerInfoToString(update_request.caller_info.source),
    print update_sieve.SummarizeRequest()

    update_sieve.CheckMigrationState()

    new_timestamp, entries, remaining = self.account.GetChanges(update_sieve)

    update_response.changes_remaining = remaining
    sending_nigori_node = False
    for entry in entries:
      if entry.name == 'Nigori':
        sending_nigori_node = True
      reply = update_response.entries.add()
      reply.CopyFrom(entry)
    update_sieve.SaveProgress(new_timestamp, update_response)

    if update_request.need_encryption_key or sending_nigori_node:
      update_response.encryption_keys.extend(self.account.GetKeystoreKeys())

  def HandleGetOauth2Token(self):
    return (int(self.response_code),
            '{\n'
            '  \"refresh_token\": \"' + self.request_token + '\",\n'
            '  \"access_token\": \"' + self.access_token + '\",\n'
            '  \"expires_in\": ' + str(self.expires_in) + ',\n'
            '  \"token_type\": \"' + self.token_type +'\"\n'
            '}')

  def HandleSetOauth2Token(self, response_code, request_token, access_token,
                           expires_in, token_type):
    if response_code != 0:
      self.response_code = response_code
    if request_token != '':
      self.request_token = request_token
    if access_token != '':
      self.access_token = access_token
    if expires_in != 0:
      self.expires_in = expires_in
    if token_type != '':
      self.token_type = token_type

    return (200,
            '<html><title>Set OAuth2 Token</title>'
            '<H1>This server will now return the OAuth2 Token:</H1>'
            '<p>response_code: ' + str(self.response_code) + '</p>'
            '<p>request_token: ' + self.request_token + '</p>'
            '<p>access_token: ' + self.access_token + '</p>'
            '<p>expires_in: ' + str(self.expires_in) + '</p>'
            '<p>token_type: ' + self.token_type + '</p>'
            '</html>')

  def CustomizeClientCommand(self, sessions_commit_delay_seconds):
    """Customizes the value of the ClientCommand of ServerToClientResponse.

    Currently, this only allows for changing the sessions_commit_delay_seconds
    field.

    Args:
      sessions_commit_delay_seconds: The desired sync delay time for sessions.
    """
    if not self._client_command:
      self._client_command = client_commands_pb2.ClientCommand()

    self._client_command.sessions_commit_delay_seconds = \
        sessions_commit_delay_seconds
    return self._client_command