zulip/zerver/lib/export.py

import datetime
from boto.s3.connection import S3Connection
from boto.s3.key import Key  # for mypy
from django.apps import apps
from django.conf import settings
from django.forms.models import model_to_dict
from django.utils.timezone import make_aware as timezone_make_aware
from django.utils.timezone import is_naive as timezone_is_naive
import glob
import logging
import os
import ujson
import subprocess
import tempfile
import shutil
from scripts.lib.zulip_tools import overwrite_symlink
from zerver.lib.avatar_hash import user_avatar_path_from_ids
from analytics.models import RealmCount, UserCount, StreamCount
from zerver.models import UserProfile, Realm, Client, Huddle, Stream, \
    UserMessage, Subscription, Message, RealmEmoji, RealmFilter, Reaction, \
    RealmDomain, Recipient, DefaultStream, get_user_profile_by_id, \
    UserPresence, UserActivity, UserActivityInterval, CustomProfileField, \
    CustomProfileFieldValue, get_display_recipient, Attachment, get_system_bot, \
    RealmAuditLog, UserHotspot, MutedTopic, Service, UserGroup, \
    UserGroupMembership, BotStorageData, BotConfigData
from zerver.lib.parallel import run_parallel
from typing import Any, Callable, Dict, List, Optional, Set, Tuple, \
    Union

# Custom mypy types follow:
Record = Dict[str, Any]
TableName = str
TableData = Dict[TableName, List[Record]]
Field = str
Path = str
Context = Dict[str, Any]
FilterArgs = Dict[str, Any]
IdSource = Tuple[TableName, Field]
SourceFilter = Callable[[Record], bool]

# These next two types are callbacks, which mypy does not
# support well, because PEP 484 says "using callbacks
# with keyword arguments is not perceived as a common use case."
# CustomFetch = Callable[[TableData, Config, Context], None]
# PostProcessData = Callable[[TableData, Config, Context], None]
CustomFetch = Any  # TODO: make more specific, see above
PostProcessData = Any  # TODO: make more specific

# The keys of our MessageOutput variables are normally
# List[Record], but when we write partials, we can get
# lists of integers or a single integer.
# TODO: This could maybe be improved using TypedDict?
MessageOutput = Dict[str, Union[List[Record], List[int], int]]

MESSAGE_BATCH_CHUNK_SIZE = 1000

ALL_ZULIP_TABLES = {
    'analytics_fillstate',
    'analytics_installationcount',
    'analytics_realmcount',
    'analytics_streamcount',
    'analytics_usercount',
    'otp_static_staticdevice',
    'otp_static_statictoken',
    'otp_totp_totpdevice',
    'social_auth_association',
    'social_auth_code',
    'social_auth_nonce',
    'social_auth_partial',
    'social_auth_usersocialauth',
    'two_factor_phonedevice',
    'zerver_archivedattachment',
    'zerver_archivedattachment_messages',
    'zerver_archivedmessage',
    'zerver_archivedusermessage',
    'zerver_attachment',
    'zerver_attachment_messages',
    'zerver_botconfigdata',
    'zerver_botstoragedata',
    'zerver_client',
    'zerver_customprofilefield',
    'zerver_customprofilefieldvalue',
    'zerver_defaultstream',
    'zerver_defaultstreamgroup',
    'zerver_defaultstreamgroup_streams',
    'zerver_emailchangestatus',
    'zerver_huddle',
    'zerver_message',
    'zerver_multiuseinvite',
    'zerver_multiuseinvite_streams',
    'zerver_preregistrationuser',
    'zerver_preregistrationuser_streams',
    'zerver_pushdevicetoken',
    'zerver_reaction',
    'zerver_realm',
    'zerver_realmauditlog',
    'zerver_realmdomain',
    'zerver_realmemoji',
    'zerver_realmfilter',
    'zerver_recipient',
    'zerver_scheduledemail',
    'zerver_scheduledmessage',
    'zerver_service',
    'zerver_stream',
    'zerver_submessage',
    'zerver_subscription',
    'zerver_useractivity',
    'zerver_useractivityinterval',
    'zerver_usergroup',
    'zerver_usergroupmembership',
    'zerver_userhotspot',
    'zerver_usermessage',
    'zerver_userpresence',
    'zerver_userprofile',
    'zerver_userprofile_groups',
    'zerver_userprofile_user_permissions',
    'zerver_userstatus',
    'zerver_mutedtopic',
}

NON_EXPORTED_TABLES = {
    # These invitation/confirmation flow tables don't make sense to
    # export, since invitations links will be broken by the server URL
    # change anyway:
    'zerver_emailchangestatus',
    'zerver_multiuseinvite',
    'zerver_multiuseinvite_streams',
    'zerver_preregistrationuser',
    'zerver_preregistrationuser_streams',

    # When switching servers, clients will need to re-login and
    # reregister for push notifications anyway.
    'zerver_pushdevicetoken',

    # We don't use these generated Django tables
    'zerver_userprofile_groups',
    'zerver_userprofile_user_permissions',

    # These is used for scheduling future activity; it could make
    # sense to export, but is relatively low value.
    'zerver_scheduledemail',
    'zerver_scheduledmessage',

    # These tables are related to a user's 2FA authentication
    # configuration, which will need to be re-setup on the new server.
    'two_factor_phonedevice',
    'otp_static_staticdevice',
    'otp_static_statictoken',
    'otp_totp_totpdevice',

    # These archive tables should not be exported (they are to support
    # restoring content accidentally deleted due to software bugs in
    # the retention policy feature)
    'zerver_archivedmessage',
    'zerver_archivedusermessage',
    'zerver_archivedattachment',
    'zerver_archivedattachment_messages',

    # Social auth tables are not needed post-export, since we don't
    # use any of this state outside of a direct authentication flow.
    'social_auth_association',
    'social_auth_code',
    'social_auth_nonce',
    'social_auth_partial',
    'social_auth_usersocialauth',

    # We will likely never want to migrate this table, since it's a
    # total of all the realmcount values on the server.  Might need to
    # recompute it after a fillstate import.
    'analytics_installationcount',

    # Fillstate will require some cleverness to do the right partial export.
    'analytics_fillstate',

    # These are for unfinished features; we'll want to add them ot the
    # export before they reach full production status.
    'zerver_defaultstreamgroup',
    'zerver_defaultstreamgroup_streams',
    'zerver_submessage',

    # This is low priority, since users can easily just reset themselves to away.
    'zerver_userstatus',

    # For any tables listed below here, it's a bug that they are not present in the export.
}

IMPLICIT_TABLES = {
    # ManyToMany relationships are exported implicitly.
    'zerver_attachment_messages',
}

ATTACHMENT_TABLES = {
    'zerver_attachment',
}

MESSAGE_TABLES = {
    # message tables get special treatment, because they're so big
    'zerver_message',
    'zerver_usermessage',
    # zerver_reaction belongs here, since it's added late
    'zerver_reaction',
}

DATE_FIELDS = {
    'zerver_attachment': ['create_time'],
    'zerver_message': ['last_edit_time', 'pub_date'],
    'zerver_realm': ['date_created'],
    'zerver_stream': ['date_created'],
    'zerver_useractivity': ['last_visit'],
    'zerver_useractivityinterval': ['start', 'end'],
    'zerver_userpresence': ['timestamp'],
    'zerver_userprofile': ['date_joined', 'last_login', 'last_reminder'],
    'zerver_realmauditlog': ['event_time'],
    'zerver_userhotspot': ['timestamp'],
    'analytics_installationcount': ['end_time'],
    'analytics_realmcount': ['end_time'],
    'analytics_usercount': ['end_time'],
    'analytics_streamcount': ['end_time'],
}  # type: Dict[TableName, List[Field]]

def sanity_check_output(data: TableData) -> None:
    # First, we verify that the export tool has a declared
    # configuration for every table.
    target_models = (
        list(apps.get_app_config('analytics').get_models(include_auto_created=True)) +
        list(apps.get_app_config('django_otp').get_models(include_auto_created=True)) +
        list(apps.get_app_config('otp_static').get_models(include_auto_created=True)) +
        list(apps.get_app_config('otp_totp').get_models(include_auto_created=True)) +
        list(apps.get_app_config('social_django').get_models(include_auto_created=True)) +
        list(apps.get_app_config('two_factor').get_models(include_auto_created=True)) +
        list(apps.get_app_config('zerver').get_models(include_auto_created=True))
    )
    all_tables_db = set(model._meta.db_table for model in target_models)

    # These assertion statements will fire when we add a new database
    # table that is not included in Zulip's data exports.  Generally,
    # you can add your new table to `ALL_ZULIP_TABLES` and
    # `NON_EXPORTED_TABLES` during early work on a new feature so that
    # CI passes.
    #
    # We'll want to make sure we handle it for exports before
    # releasing the new feature, but doing so correctly requires some
    # expertise on this export system.
    assert ALL_ZULIP_TABLES == all_tables_db
    assert NON_EXPORTED_TABLES.issubset(ALL_ZULIP_TABLES)
    assert IMPLICIT_TABLES.issubset(ALL_ZULIP_TABLES)
    assert ATTACHMENT_TABLES.issubset(ALL_ZULIP_TABLES)

    tables = set(ALL_ZULIP_TABLES)
    tables -= NON_EXPORTED_TABLES
    tables -= IMPLICIT_TABLES
    tables -= MESSAGE_TABLES
    tables -= ATTACHMENT_TABLES

    for table in tables:
        if table not in data:
            logging.warning('??? NO DATA EXPORTED FOR TABLE %s!!!' % (table,))

def write_data_to_file(output_file: Path, data: Any) -> None:
    with open(output_file, "w") as f:
        f.write(ujson.dumps(data, indent=4))

def make_raw(query: Any, exclude: Optional[List[Field]]=None) -> List[Record]:
    '''
    Takes a Django query and returns a JSONable list
    of dictionaries corresponding to the database rows.
    '''
    rows = []
    for instance in query:
        data = model_to_dict(instance, exclude=exclude)
        """
        In Django 1.11.5, model_to_dict evaluates the QuerySet of
        many-to-many field to give us a list of instances. We require
        a list of primary keys, so we get the primary keys from the
        instances below.
        """
        for field in instance._meta.many_to_many:
            value = data[field.name]
            data[field.name] = [row.id for row in value]

        rows.append(data)

    return rows

def floatify_datetime_fields(data: TableData, table: TableName) -> None:
    for item in data[table]:
        for field in DATE_FIELDS[table]:
            orig_dt = item[field]
            if orig_dt is None:
                continue
            if timezone_is_naive(orig_dt):
                logging.warning("Naive datetime:", item)
                dt = timezone_make_aware(orig_dt)
            else:
                dt = orig_dt
            utc_naive  = dt.replace(tzinfo=None) - dt.utcoffset()
            item[field] = (utc_naive - datetime.datetime(1970, 1, 1)).total_seconds()

class Config:
    '''
    A Config object configures a single table for exporting (and,
    maybe some day importing as well.

    You should never mutate Config objects as part of the export;
    instead use the data to determine how you populate other
    data structures.

    There are parent/children relationships between Config objects.
    The parent should be instantiated first.  The child will
    append itself to the parent's list of children.

    '''

    def __init__(self, table: Optional[str]=None,
                 model: Optional[Any]=None,
                 normal_parent: Optional['Config']=None,
                 virtual_parent: Optional['Config']=None,
                 filter_args: Optional[FilterArgs]=None,
                 custom_fetch: Optional[CustomFetch]=None,
                 custom_tables: Optional[List[TableName]]=None,
                 post_process_data: Optional[PostProcessData]=None,
                 concat_and_destroy: Optional[List[TableName]]=None,
                 id_source: Optional[IdSource]=None,
                 source_filter: Optional[SourceFilter]=None,
                 parent_key: Optional[Field]=None,
                 use_all: bool=False,
                 is_seeded: bool=False,
                 exclude: Optional[List[Field]]=None) -> None:
        assert table or custom_tables
        self.table = table
        self.model = model
        self.normal_parent = normal_parent
        self.virtual_parent = virtual_parent
        self.filter_args = filter_args
        self.parent_key = parent_key
        self.use_all = use_all
        self.is_seeded = is_seeded
        self.exclude = exclude
        self.custom_fetch = custom_fetch
        self.custom_tables = custom_tables
        self.post_process_data = post_process_data
        self.concat_and_destroy = concat_and_destroy
        self.id_source = id_source
        self.source_filter = source_filter
        self.children = []  # type: List[Config]

        if normal_parent is not None:
            self.parent = normal_parent  # type: Optional[Config]
        else:
            self.parent = None

        if virtual_parent is not None and normal_parent is not None:
            raise AssertionError('''
                If you specify a normal_parent, please
                do not create a virtual_parent.
                ''')

        if normal_parent is not None:
            normal_parent.children.append(self)
        elif virtual_parent is not None:
            virtual_parent.children.append(self)
        elif is_seeded is None:
            raise AssertionError('''
                You must specify a parent if you are
                not using is_seeded.
                ''')

        if self.id_source is not None:
            if self.virtual_parent is None:
                raise AssertionError('''
                    You must specify a virtual_parent if you are
                    using id_source.''')
            if self.id_source[0] != self.virtual_parent.table:
                raise AssertionError('''
                    Configuration error.  To populate %s, you
                    want data from %s, but that differs from
                    the table name of your virtual parent (%s),
                    which suggests you many not have set up
                    the ordering correctly.  You may simply
                    need to assign a virtual_parent, or there
                    may be deeper issues going on.''' % (
                    self.table,
                    self.id_source[0],
                    self.virtual_parent.table))


def export_from_config(response: TableData, config: Config, seed_object: Optional[Any]=None,
                       context: Optional[Context]=None) -> None:
    table = config.table
    parent = config.parent
    model = config.model

    if context is None:
        context = {}

    if table:
        exported_tables = [table]
    else:
        if config.custom_tables is None:
            raise AssertionError('''
                You must specify config.custom_tables if you
                are not specifying config.table''')
        exported_tables = config.custom_tables

    for t in exported_tables:
        logging.info('Exporting via export_from_config:  %s' % (t,))

    rows = None
    if config.is_seeded:
        rows = [seed_object]

    elif config.custom_fetch:
        config.custom_fetch(
            response=response,
            config=config,
            context=context
        )
        if config.custom_tables:
            for t in config.custom_tables:
                if t not in response:
                    raise AssertionError('Custom fetch failed to populate %s' % (t,))

    elif config.concat_and_destroy:
        # When we concat_and_destroy, we are working with
        # temporary "tables" that are lists of records that
        # should already be ready to export.
        data = []  # type: List[Record]
        for t in config.concat_and_destroy:
            data += response[t]
            del response[t]
            logging.info('Deleted temporary %s' % (t,))
        assert table is not None
        response[table] = data

    elif config.use_all:
        assert model is not None
        query = model.objects.all()
        rows = list(query)

    elif config.normal_parent:
        # In this mode, our current model is figuratively Article,
        # and normal_parent is figuratively Blog, and
        # now we just need to get all the articles
        # contained by the blogs.
        model = config.model
        assert parent is not None
        assert parent.table is not None
        assert config.parent_key is not None
        parent_ids = [r['id'] for r in response[parent.table]]
        filter_parms = {config.parent_key: parent_ids}  # type: Dict[str, Any]
        if config.filter_args is not None:
            filter_parms.update(config.filter_args)
        assert model is not None
        query = model.objects.filter(**filter_parms)
        rows = list(query)

    elif config.id_source:
        # In this mode, we are the figurative Blog, and we now
        # need to look at the current response to get all the
        # blog ids from the Article rows we fetched previously.
        model = config.model
        assert model is not None
        # This will be a tuple of the form ('zerver_article', 'blog').
        (child_table, field) = config.id_source
        child_rows = response[child_table]
        if config.source_filter:
            child_rows = [r for r in child_rows if config.source_filter(r)]
        lookup_ids = [r[field] for r in child_rows]
        filter_parms = dict(id__in=lookup_ids)
        if config.filter_args:
            filter_parms.update(config.filter_args)
        query = model.objects.filter(**filter_parms)
        rows = list(query)

    # Post-process rows (which won't apply to custom fetches/concats)
    if rows is not None:
        assert table is not None  # Hint for mypy
        response[table] = make_raw(rows, exclude=config.exclude)
        if table in DATE_FIELDS:
            floatify_datetime_fields(response, table)

    if config.post_process_data:
        config.post_process_data(
            response=response,
            config=config,
            context=context
        )

    # Now walk our children.  It's extremely important to respect
    # the order of children here.
    for child_config in config.children:
        export_from_config(
            response=response,
            config=child_config,
            context=context,
        )

def get_realm_config() -> Config:
    # This is common, public information about the realm that we can share
    # with all realm users.

    realm_config = Config(
        table='zerver_realm',
        is_seeded=True
    )

    Config(
        table='zerver_defaultstream',
        model=DefaultStream,
        normal_parent=realm_config,
        parent_key='realm_id__in',
    )

    Config(
        table='zerver_customprofilefield',
        model=CustomProfileField,
        normal_parent=realm_config,
        parent_key='realm_id__in',
    )

    Config(
        table='zerver_realmemoji',
        model=RealmEmoji,
        normal_parent=realm_config,
        parent_key='realm_id__in',
    )

    Config(
        table='zerver_realmdomain',
        model=RealmDomain,
        normal_parent=realm_config,
        parent_key='realm_id__in',
    )

    Config(
        table='zerver_realmfilter',
        model=RealmFilter,
        normal_parent=realm_config,
        parent_key='realm_id__in',
    )

    Config(
        table='zerver_client',
        model=Client,
        virtual_parent=realm_config,
        use_all=True
    )

    user_profile_config = Config(
        custom_tables=[
            'zerver_userprofile',
            'zerver_userprofile_mirrordummy',
        ],
        # set table for children who treat us as normal parent
        table='zerver_userprofile',
        virtual_parent=realm_config,
        custom_fetch=fetch_user_profile,
    )

    user_groups_config = Config(
        table='zerver_usergroup',
        model=UserGroup,
        normal_parent=realm_config,
        parent_key='realm__in',
    )

    Config(
        table='zerver_usergroupmembership',
        model=UserGroupMembership,
        normal_parent=user_groups_config,
        parent_key='user_group__in',
    )

    Config(
        custom_tables=[
            'zerver_userprofile_crossrealm',
        ],
        virtual_parent=user_profile_config,
        custom_fetch=fetch_user_profile_cross_realm,
    )

    Config(
        table='zerver_userpresence',
        model=UserPresence,
        normal_parent=user_profile_config,
        parent_key='user_profile__in',
    )

    Config(
        table='zerver_customprofilefieldvalue',
        model=CustomProfileFieldValue,
        normal_parent=user_profile_config,
        parent_key='user_profile__in',
    )

    Config(
        table='zerver_useractivity',
        model=UserActivity,
        normal_parent=user_profile_config,
        parent_key='user_profile__in',
    )

    Config(
        table='zerver_useractivityinterval',
        model=UserActivityInterval,
        normal_parent=user_profile_config,
        parent_key='user_profile__in',
    )

    Config(
        table='zerver_realmauditlog',
        model=RealmAuditLog,
        normal_parent=user_profile_config,
        parent_key='modified_user__in',
    )

    Config(
        table='zerver_userhotspot',
        model=UserHotspot,
        normal_parent=user_profile_config,
        parent_key='user__in',
    )

    Config(
        table='zerver_mutedtopic',
        model=MutedTopic,
        normal_parent=user_profile_config,
        parent_key='user_profile__in',
    )

    Config(
        table='zerver_service',
        model=Service,
        normal_parent=user_profile_config,
        parent_key='user_profile__in',
    )

    Config(
        table='zerver_botstoragedata',
        model=BotStorageData,
        normal_parent=user_profile_config,
        parent_key='bot_profile__in',
    )

    Config(
        table='zerver_botconfigdata',
        model=BotConfigData,
        normal_parent=user_profile_config,
        parent_key='bot_profile__in',
    )

    # Some of these tables are intermediate "tables" that we
    # create only for the export.  Think of them as similar to views.

    user_subscription_config = Config(
        table='_user_subscription',
        model=Subscription,
        normal_parent=user_profile_config,
        filter_args={'recipient__type': Recipient.PERSONAL},
        parent_key='user_profile__in',
    )

    Config(
        table='_user_recipient',
        model=Recipient,
        virtual_parent=user_subscription_config,
        id_source=('_user_subscription', 'recipient'),
    )

    #
    stream_subscription_config = Config(
        table='_stream_subscription',
        model=Subscription,
        normal_parent=user_profile_config,
        filter_args={'recipient__type': Recipient.STREAM},
        parent_key='user_profile__in',
    )

    stream_recipient_config = Config(
        table='_stream_recipient',
        model=Recipient,
        virtual_parent=stream_subscription_config,
        id_source=('_stream_subscription', 'recipient'),
    )

    Config(
        table='zerver_stream',
        model=Stream,
        virtual_parent=stream_recipient_config,
        id_source=('_stream_recipient', 'type_id'),
        source_filter=lambda r: r['type'] == Recipient.STREAM,
        exclude=['email_token'],
        post_process_data=sanity_check_stream_data
    )

    #

    Config(
        custom_tables=[
            '_huddle_recipient',
            '_huddle_subscription',
            'zerver_huddle',
        ],
        normal_parent=user_profile_config,
        custom_fetch=fetch_huddle_objects,
    )

    # Now build permanent tables from our temp tables.
    Config(
        table='zerver_recipient',
        virtual_parent=user_profile_config,
        concat_and_destroy=[
            '_user_recipient',
            '_stream_recipient',
            '_huddle_recipient',
        ],
    )

    Config(
        table='zerver_subscription',
        virtual_parent=user_profile_config,
        concat_and_destroy=[
            '_user_subscription',
            '_stream_subscription',
            '_huddle_subscription',
        ]
    )

    # Analytics tables
    Config(
        table='analytics_realmcount',
        model=RealmCount,
        normal_parent=realm_config,
        parent_key='realm_id__in',
    )

    Config(
        table='analytics_usercount',
        model=UserCount,
        normal_parent=realm_config,
        parent_key='realm_id__in',
    )

    Config(
        table='analytics_streamcount',
        model=StreamCount,
        normal_parent=realm_config,
        parent_key='realm_id__in',
    )

    return realm_config

def sanity_check_stream_data(response: TableData, config: Config, context: Context) -> None:

    if context['exportable_user_ids'] is not None:
        # If we restrict which user ids are exportable,
        # the way that we find # streams is a little too
        # complex to have a sanity check.
        return

    actual_streams = set([stream.name for stream in Stream.objects.filter(
        realm=response["zerver_realm"][0]['id'])])
    streams_in_response = set([stream['name'] for stream in response['zerver_stream']])

    if len(streams_in_response - actual_streams) > 0:
        print("Error: Streams not present in the realm were exported:")
        print("   ", streams_in_response - actual_streams)
        print("This is likely due to a bug in the export tool.")
        raise AssertionError("Aborting!  Please investigate.")
    if len(actual_streams - streams_in_response) > 0:
        print("Error: Some streams present in the realm were not exported:")
        print("    ", actual_streams - streams_in_response)
        print("Usually, this is caused by a stream having been created that never had subscribers.")
        print("(Due to a bug elsewhere in Zulip, not in the export tool)")
        raise AssertionError("Aborting!  Please investigate.")

def fetch_user_profile(response: TableData, config: Config, context: Context) -> None:
    realm = context['realm']
    exportable_user_ids = context['exportable_user_ids']

    query = UserProfile.objects.filter(realm_id=realm.id)
    exclude = ['password', 'api_key']
    rows = make_raw(list(query), exclude=exclude)

    normal_rows = []  # type: List[Record]
    dummy_rows = []  # type: List[Record]

    for row in rows:
        if exportable_user_ids is not None:
            if row['id'] in exportable_user_ids:
                assert not row['is_mirror_dummy']
            else:
                # Convert non-exportable users to
                # inactive is_mirror_dummy users.
                row['is_mirror_dummy'] = True
                row['is_active'] = False

        if row['is_mirror_dummy']:
            dummy_rows.append(row)
        else:
            normal_rows.append(row)

    response['zerver_userprofile'] = normal_rows
    response['zerver_userprofile_mirrordummy'] = dummy_rows

def fetch_user_profile_cross_realm(response: TableData, config: Config, context: Context) -> None:
    realm = context['realm']
    response['zerver_userprofile_crossrealm'] = []

    if realm.string_id == settings.SYSTEM_BOT_REALM:
        return

    for bot_user in [
            get_system_bot(settings.NOTIFICATION_BOT),
            get_system_bot(settings.EMAIL_GATEWAY_BOT),
            get_system_bot(settings.WELCOME_BOT),
    ]:
        recipient_id = Recipient.objects.get(type_id=bot_user.id, type=Recipient.PERSONAL).id
        response['zerver_userprofile_crossrealm'].append(dict(
            email=bot_user.email,
            id=bot_user.id,
            recipient_id=recipient_id,
        ))

def fetch_attachment_data(response: TableData, realm_id: int, message_ids: Set[int]) -> None:
    filter_args = {'realm_id': realm_id}
    query = Attachment.objects.filter(**filter_args)
    response['zerver_attachment'] = make_raw(list(query))
    floatify_datetime_fields(response, 'zerver_attachment')

    '''
    We usually export most messages for the realm, but not
    quite ALL messages for the realm.  So, we need to
    clean up our attachment data to have correct
    values for response['zerver_attachment'][<n>]['messages'].
    '''
    for row in response['zerver_attachment']:
        filterer_message_ids = set(row['messages']).intersection(message_ids)
        row['messages'] = sorted(list(filterer_message_ids))

    '''
    Attachments can be connected to multiple messages, although
    it's most common to have just one message. Regardless,
    if none of those message(s) survived the filtering above
    for a particular attachment, then we won't export the
    attachment row.
    '''
    response['zerver_attachment'] = [
        row for row in response['zerver_attachment']
        if row['messages']]

def fetch_reaction_data(response: TableData, message_ids: Set[int]) -> None:
    query = Reaction.objects.filter(message_id__in=list(message_ids))
    response['zerver_reaction'] = make_raw(list(query))

def fetch_huddle_objects(response: TableData, config: Config, context: Context) -> None:

    realm = context['realm']
    assert config.parent is not None
    assert config.parent.table is not None
    user_profile_ids = set(r['id'] for r in response[config.parent.table])

    # First we get all huddles involving someone in the realm.
    realm_huddle_subs = Subscription.objects.select_related("recipient").filter(
        recipient__type=Recipient.HUDDLE, user_profile__in=user_profile_ids)
    realm_huddle_recipient_ids = set(sub.recipient_id for sub in realm_huddle_subs)

    # Mark all Huddles whose recipient ID contains a cross-realm user.
    unsafe_huddle_recipient_ids = set()
    for sub in Subscription.objects.select_related().filter(recipient__in=realm_huddle_recipient_ids):
        if sub.user_profile.realm != realm:
            # In almost every case the other realm will be zulip.com
            unsafe_huddle_recipient_ids.add(sub.recipient_id)

    # Now filter down to just those huddles that are entirely within the realm.
    #
    # This is important for ensuring that the User objects needed
    # to import it on the other end exist (since we're only
    # exporting the users from this realm), at the cost of losing
    # some of these cross-realm messages.
    huddle_subs = [sub for sub in realm_huddle_subs if sub.recipient_id not in unsafe_huddle_recipient_ids]
    huddle_recipient_ids = set(sub.recipient_id for sub in huddle_subs)
    huddle_ids = set(sub.recipient.type_id for sub in huddle_subs)

    huddle_subscription_dicts = make_raw(huddle_subs)
    huddle_recipients = make_raw(Recipient.objects.filter(id__in=huddle_recipient_ids))

    response['_huddle_recipient'] = huddle_recipients
    response['_huddle_subscription'] = huddle_subscription_dicts
    response['zerver_huddle'] = make_raw(Huddle.objects.filter(id__in=huddle_ids))

def fetch_usermessages(realm: Realm,
                       message_ids: Set[int],
                       user_profile_ids: Set[int],
                       message_filename: Path) -> List[Record]:
    # UserMessage export security rule: You can export UserMessages
    # for the messages you exported for the users in your realm.
    user_message_query = UserMessage.objects.filter(user_profile__realm=realm,
                                                    message_id__in=message_ids)
    user_message_chunk = []
    for user_message in user_message_query:
        if user_message.user_profile_id not in user_profile_ids:
            continue
        user_message_obj = model_to_dict(user_message)
        user_message_obj['flags_mask'] = user_message.flags.mask
        del user_message_obj['flags']
        user_message_chunk.append(user_message_obj)
    logging.info("Fetched UserMessages for %s" % (message_filename,))
    return user_message_chunk

def export_usermessages_batch(input_path: Path, output_path: Path) -> None:
    """As part of the system for doing parallel exports, this runs on one
    batch of Message objects and adds the corresponding UserMessage
    objects. (This is called by the export_usermessage_batch
    management command)."""
    with open(input_path, "r") as input_file:
        output = ujson.loads(input_file.read())
    message_ids = [item['id'] for item in output['zerver_message']]
    user_profile_ids = set(output['zerver_userprofile_ids'])
    del output['zerver_userprofile_ids']
    realm = Realm.objects.get(id=output['realm_id'])
    del output['realm_id']
    output['zerver_usermessage'] = fetch_usermessages(realm, set(message_ids), user_profile_ids, output_path)
    write_message_export(output_path, output)
    os.unlink(input_path)

def write_message_export(message_filename: Path, output: MessageOutput) -> None:
    write_data_to_file(output_file=message_filename, data=output)
    logging.info("Dumped to %s" % (message_filename,))

def export_partial_message_files(realm: Realm,
                                 response: TableData,
                                 chunk_size: int=MESSAGE_BATCH_CHUNK_SIZE,
                                 output_dir: Optional[Path]=None,
                                 public_only: bool=False) -> Set[int]:
    if output_dir is None:
        output_dir = tempfile.mkdtemp(prefix="zulip-export")

    def get_ids(records: List[Record]) -> Set[int]:
        return set(x['id'] for x in records)

    # Basic security rule: You can export everything either...
    #   - sent by someone in your exportable_user_ids
    #        OR
    #   - received by someone in your exportable_user_ids (which
    #     equates to a recipient object we are exporting)
    #
    # TODO: In theory, you should be able to export messages in
    # cross-realm PM threads; currently, this only exports cross-realm
    # messages received by your realm that were sent by Zulip system
    # bots (e.g. emailgateway, notification-bot).

    # Here, "we" and "us" refers to the inner circle of users who
    # were specified as being allowed to be exported.  "Them"
    # refers to other users.
    user_ids_for_us = get_ids(
        response['zerver_userprofile']
    )
    ids_of_our_possible_senders = get_ids(
        response['zerver_userprofile'] +
        response['zerver_userprofile_mirrordummy'] +
        response['zerver_userprofile_crossrealm'])

    if public_only:
        recipient_streams = Stream.objects.filter(realm=realm, invite_only=False)
        recipient_ids = Recipient.objects.filter(
            type=Recipient.STREAM, type_id__in=recipient_streams).values_list("id", flat=True)
        recipient_ids_for_us = get_ids(response['zerver_recipient']) & set(recipient_ids)
    else:
        recipient_ids_for_us = get_ids(response['zerver_recipient'])

    # We capture most messages here, since the
    # recipients we subscribe to are also the
    # recipients of most messages we send.
    messages_we_received = Message.objects.filter(
        sender__in=ids_of_our_possible_senders,
        recipient__in=recipient_ids_for_us,
    ).order_by('id')

    if public_only:
        # For the public stream export, we only need the messages those streams received.
        message_queries = [
            messages_we_received,
        ]
    else:
        # This should pick up stragglers; messages we sent
        # where we the recipient wasn't subscribed to by any of
        # us (such as PMs to "them").
        ids_of_non_exported_possible_recipients = ids_of_our_possible_senders - user_ids_for_us

        recipients_for_them = Recipient.objects.filter(
            type=Recipient.PERSONAL,
            type_id__in=ids_of_non_exported_possible_recipients).values("id")
        recipient_ids_for_them = get_ids(recipients_for_them)

        messages_we_sent_to_them = Message.objects.filter(
            sender__in=user_ids_for_us,
            recipient__in=recipient_ids_for_them,
        ).order_by('id')

        message_queries = [
            messages_we_received,
            messages_we_sent_to_them,
        ]

    all_message_ids = set()  # type: Set[int]
    dump_file_id = 1

    for message_query in message_queries:
        dump_file_id = write_message_partial_for_query(
            realm=realm,
            message_query=message_query,
            dump_file_id=dump_file_id,
            all_message_ids=all_message_ids,
            output_dir=output_dir,
            user_profile_ids=user_ids_for_us,
            chunk_size=chunk_size,
        )

    return all_message_ids

def write_message_partial_for_query(realm: Realm, message_query: Any, dump_file_id: int,
                                    all_message_ids: Set[int], output_dir: Path,
                                    user_profile_ids: Set[int],
                                    chunk_size: int=MESSAGE_BATCH_CHUNK_SIZE) -> int:
    min_id = -1

    while True:
        actual_query = message_query.filter(id__gt=min_id)[0:chunk_size]
        message_chunk = make_raw(actual_query)
        message_ids = set(m['id'] for m in message_chunk)
        assert len(message_ids.intersection(all_message_ids)) == 0

        all_message_ids.update(message_ids)

        if len(message_chunk) == 0:
            break

        # Figure out the name of our shard file.
        message_filename = os.path.join(output_dir, "messages-%06d.json" % (dump_file_id,))
        message_filename += '.partial'
        logging.info("Fetched Messages for %s" % (message_filename,))

        # Clean up our messages.
        table_data = {}  # type: TableData
        table_data['zerver_message'] = message_chunk
        floatify_datetime_fields(table_data, 'zerver_message')

        # Build up our output for the .partial file, which needs
        # a list of user_profile_ids to search for (as well as
        # the realm id).
        output = {}  # type: MessageOutput
        output['zerver_message'] = table_data['zerver_message']
        output['zerver_userprofile_ids'] = list(user_profile_ids)
        output['realm_id'] = realm.id

        # And write the data.
        write_message_export(message_filename, output)
        min_id = max(message_ids)
        dump_file_id += 1

    return dump_file_id

def export_uploads_and_avatars(realm: Realm, output_dir: Path) -> None:
    uploads_output_dir = os.path.join(output_dir, 'uploads')
    avatars_output_dir = os.path.join(output_dir, 'avatars')
    emoji_output_dir = os.path.join(output_dir, 'emoji')

    for output_dir in (uploads_output_dir, avatars_output_dir, emoji_output_dir):
        if not os.path.exists(output_dir):
            os.makedirs(output_dir)

    if settings.LOCAL_UPLOADS_DIR:
        # Small installations and developers will usually just store files locally.
        export_uploads_from_local(realm,
                                  local_dir=os.path.join(settings.LOCAL_UPLOADS_DIR, "files"),
                                  output_dir=uploads_output_dir)
        export_avatars_from_local(realm,
                                  local_dir=os.path.join(settings.LOCAL_UPLOADS_DIR, "avatars"),
                                  output_dir=avatars_output_dir)
        export_emoji_from_local(realm,
                                local_dir=os.path.join(settings.LOCAL_UPLOADS_DIR, "avatars"),
                                output_dir=emoji_output_dir)
    else:
        # Some bigger installations will have their data stored on S3.
        export_files_from_s3(realm,
                             settings.S3_AVATAR_BUCKET,
                             output_dir=avatars_output_dir,
                             processing_avatars=True)
        export_files_from_s3(realm,
                             settings.S3_AUTH_UPLOADS_BUCKET,
                             output_dir=uploads_output_dir)
        export_files_from_s3(realm,
                             settings.S3_AVATAR_BUCKET,
                             output_dir=emoji_output_dir,
                             processing_emoji=True)

def _check_key_metadata(email_gateway_bot: Optional[UserProfile],
                        key: Key, processing_avatars: bool,
                        realm: Realm, user_ids: Set[int]) -> None:
    # Helper function for export_files_from_s3
    if 'realm_id' in key.metadata and key.metadata['realm_id'] != str(realm.id):
        if email_gateway_bot is None or key.metadata['user_profile_id'] != str(email_gateway_bot.id):
            raise AssertionError("Key metadata problem: %s %s / %s" % (key.name, key.metadata, realm.id))
        # Email gateway bot sends messages, potentially including attachments, cross-realm.
        print("File uploaded by email gateway bot: %s / %s" % (key.name, key.metadata))
    elif processing_avatars:
        if 'user_profile_id' not in key.metadata:
            raise AssertionError("Missing user_profile_id in key metadata: %s" % (key.metadata,))
        if int(key.metadata['user_profile_id']) not in user_ids:
            raise AssertionError("Wrong user_profile_id in key metadata: %s" % (key.metadata,))
    elif 'realm_id' not in key.metadata:
        raise AssertionError("Missing realm_id in key metadata: %s" % (key.metadata,))

def _get_exported_s3_record(
        bucket_name: str,
        key: Key,
        processing_avatars: bool,
        processing_emoji: bool) -> Dict[str, Union[str, int]]:
    # Helper function for export_files_from_s3
    record = dict(s3_path=key.name, bucket=bucket_name,
                  size=key.size, last_modified=key.last_modified,
                  content_type=key.content_type, md5=key.md5)
    record.update(key.metadata)

    if processing_emoji:
        record['file_name'] = os.path.basename(key.name)

    # A few early avatars don't have 'realm_id' on the object; fix their metadata
    user_profile = get_user_profile_by_id(record['user_profile_id'])
    if 'realm_id' not in record:
        record['realm_id'] = user_profile.realm_id
    record['user_profile_email'] = user_profile.email

    # Fix the record ids
    record['user_profile_id'] = int(record['user_profile_id'])
    record['realm_id'] = int(record['realm_id'])

    return record

def _save_s3_object_to_file(
        key: Key,
        output_dir: str,
        processing_avatars: bool,
        processing_emoji: bool) -> None:

    # Helper function for export_files_from_s3
    if processing_avatars or processing_emoji:
        filename = os.path.join(output_dir, key.name)
    else:
        fields = key.name.split('/')
        if len(fields) != 3:
            raise AssertionError("Suspicious key with invalid format %s" % (key.name))
        filename = os.path.join(output_dir, key.name)

    dirname = os.path.dirname(filename)
    if not os.path.exists(dirname):
        os.makedirs(dirname)
    key.get_contents_to_filename(filename)

def export_files_from_s3(realm: Realm, bucket_name: str, output_dir: Path,
                         processing_avatars: bool=False,
                         processing_emoji: bool=False) -> None:
    conn = S3Connection(settings.S3_KEY, settings.S3_SECRET_KEY)
    bucket = conn.get_bucket(bucket_name, validate=True)
    records = []

    logging.info("Downloading uploaded files from %s" % (bucket_name))

    avatar_hash_values = set()
    user_ids = set()
    if processing_avatars:
        bucket_list = bucket.list()
        for user_profile in UserProfile.objects.filter(realm=realm):
            avatar_path = user_avatar_path_from_ids(user_profile.id, realm.id)
            avatar_hash_values.add(avatar_path)
            avatar_hash_values.add(avatar_path + ".original")
            user_ids.add(user_profile.id)
    if processing_emoji:
        bucket_list = bucket.list(prefix="%s/emoji/images/" % (realm.id,))
    else:
        bucket_list = bucket.list(prefix="%s/" % (realm.id,))

    if settings.EMAIL_GATEWAY_BOT is not None:
        email_gateway_bot = get_system_bot(settings.EMAIL_GATEWAY_BOT)  # type: Optional[UserProfile]
    else:
        email_gateway_bot = None

    count = 0
    for bkey in bucket_list:
        if processing_avatars and bkey.name not in avatar_hash_values:
            continue
        key = bucket.get_key(bkey.name)

        # This can happen if an email address has moved realms
        _check_key_metadata(email_gateway_bot, key, processing_avatars, realm, user_ids)
        record = _get_exported_s3_record(bucket_name, key, processing_avatars, processing_emoji)

        record['path'] = key.name
        _save_s3_object_to_file(key, output_dir, processing_avatars, processing_emoji)

        records.append(record)
        count += 1

        if (count % 100 == 0):
            logging.info("Finished %s" % (count,))

    with open(os.path.join(output_dir, "records.json"), "w") as records_file:
        ujson.dump(records, records_file, indent=4)

def export_uploads_from_local(realm: Realm, local_dir: Path, output_dir: Path) -> None:

    count = 0
    records = []
    for attachment in Attachment.objects.filter(realm_id=realm.id):
        local_path = os.path.join(local_dir, attachment.path_id)
        output_path = os.path.join(output_dir, attachment.path_id)
        os.makedirs(os.path.dirname(output_path), exist_ok=True)
        shutil.copy2(local_path, output_path)
        stat = os.stat(local_path)
        record = dict(realm_id=attachment.realm_id,
                      user_profile_id=attachment.owner.id,
                      user_profile_email=attachment.owner.email,
                      s3_path=attachment.path_id,
                      path=attachment.path_id,
                      size=stat.st_size,
                      last_modified=stat.st_mtime,
                      content_type=None)
        records.append(record)

        count += 1

        if (count % 100 == 0):
            logging.info("Finished %s" % (count,))
    with open(os.path.join(output_dir, "records.json"), "w") as records_file:
        ujson.dump(records, records_file, indent=4)

def export_avatars_from_local(realm: Realm, local_dir: Path, output_dir: Path) -> None:

    count = 0
    records = []

    users = list(UserProfile.objects.filter(realm=realm))
    users += [
        get_system_bot(settings.NOTIFICATION_BOT),
        get_system_bot(settings.EMAIL_GATEWAY_BOT),
        get_system_bot(settings.WELCOME_BOT),
    ]
    for user in users:
        if user.avatar_source == UserProfile.AVATAR_FROM_GRAVATAR:
            continue

        avatar_path = user_avatar_path_from_ids(user.id, realm.id)
        wildcard = os.path.join(local_dir, avatar_path + '.*')

        for local_path in glob.glob(wildcard):
            logging.info('Copying avatar file for user %s from %s' % (
                user.email, local_path))
            fn = os.path.relpath(local_path, local_dir)
            output_path = os.path.join(output_dir, fn)
            os.makedirs(str(os.path.dirname(output_path)), exist_ok=True)
            shutil.copy2(str(local_path), str(output_path))
            stat = os.stat(local_path)
            record = dict(realm_id=realm.id,
                          user_profile_id=user.id,
                          user_profile_email=user.email,
                          s3_path=fn,
                          path=fn,
                          size=stat.st_size,
                          last_modified=stat.st_mtime,
                          content_type=None)
            records.append(record)

            count += 1

            if (count % 100 == 0):
                logging.info("Finished %s" % (count,))

    with open(os.path.join(output_dir, "records.json"), "w") as records_file:
        ujson.dump(records, records_file, indent=4)

def export_emoji_from_local(realm: Realm, local_dir: Path, output_dir: Path) -> None:

    count = 0
    records = []
    for realm_emoji in RealmEmoji.objects.filter(realm_id=realm.id):
        emoji_path = RealmEmoji.PATH_ID_TEMPLATE.format(
            realm_id=realm.id,
            emoji_file_name=realm_emoji.file_name
        )
        local_path = os.path.join(local_dir, emoji_path)
        output_path = os.path.join(output_dir, emoji_path)
        os.makedirs(os.path.dirname(output_path), exist_ok=True)
        shutil.copy2(local_path, output_path)
        record = dict(realm_id=realm.id,
                      author=realm_emoji.author.id,
                      path=emoji_path,
                      s3_path=emoji_path,
                      file_name=realm_emoji.file_name,
                      name=realm_emoji.name,
                      deactivated=realm_emoji.deactivated)
        records.append(record)

        count += 1
        if (count % 100 == 0):
            logging.info("Finished %s" % (count,))
    with open(os.path.join(output_dir, "records.json"), "w") as records_file:
        ujson.dump(records, records_file, indent=4)

def do_write_stats_file_for_realm_export(output_dir: Path) -> None:
    stats_file = os.path.join(output_dir, 'stats.txt')
    realm_file = os.path.join(output_dir, 'realm.json')
    attachment_file = os.path.join(output_dir, 'attachment.json')
    message_files = glob.glob(os.path.join(output_dir, 'messages-*.json'))
    fns = sorted([attachment_file] + message_files + [realm_file])

    logging.info('Writing stats file: %s\n' % (stats_file,))
    with open(stats_file, 'w') as f:
        for fn in fns:
            f.write(os.path.basename(fn) + '\n')
            payload = open(fn).read()
            data = ujson.loads(payload)
            for k in sorted(data):
                f.write('%5d %s\n' % (len(data[k]), k))
            f.write('\n')

        avatar_file = os.path.join(output_dir, 'avatars/records.json')
        uploads_file = os.path.join(output_dir, 'uploads/records.json')

        for fn in [avatar_file, uploads_file]:
            f.write(fn+'\n')
            payload = open(fn).read()
            data = ujson.loads(payload)
            f.write('%5d records\n' % len(data))
            f.write('\n')

def do_export_realm(realm: Realm, output_dir: Path, threads: int,
                    exportable_user_ids: Optional[Set[int]]=None,
                    public_only: bool=False) -> None:
    response = {}  # type: TableData

    # We need at least one thread running to export
    # UserMessage rows.  The management command should
    # enforce this for us.
    if not settings.TEST_SUITE:
        assert threads >= 1

    realm_config = get_realm_config()

    create_soft_link(source=output_dir, in_progress=True)

    logging.info("Exporting data from get_realm_config()...")
    export_from_config(
        response=response,
        config=realm_config,
        seed_object=realm,
        context=dict(realm=realm, exportable_user_ids=exportable_user_ids)
    )
    logging.info('...DONE with get_realm_config() data')

    sanity_check_output(response)

    logging.info("Exporting uploaded files and avatars")
    export_uploads_and_avatars(realm, output_dir)

    # We (sort of) export zerver_message rows here.  We write
    # them to .partial files that are subsequently fleshed out
    # by parallel processes to add in zerver_usermessage data.
    # This is for performance reasons, of course.  Some installations
    # have millions of messages.
    logging.info("Exporting .partial files messages")
    message_ids = export_partial_message_files(realm, response, output_dir=output_dir,
                                               public_only=public_only)
    logging.info('%d messages were exported' % (len(message_ids)))

    # zerver_reaction
    zerver_reaction = {}  # type: TableData
    fetch_reaction_data(response=zerver_reaction, message_ids=message_ids)
    response.update(zerver_reaction)

    # Write realm data
    export_file = os.path.join(output_dir, "realm.json")
    write_data_to_file(output_file=export_file, data=response)
    logging.info('Writing realm data to %s' % (export_file,))

    # zerver_attachment
    export_attachment_table(realm=realm, output_dir=output_dir, message_ids=message_ids)

    # Start parallel jobs to export the UserMessage objects.
    launch_user_message_subprocesses(threads=threads, output_dir=output_dir)

    logging.info("Finished exporting %s" % (realm.string_id))
    create_soft_link(source=output_dir, in_progress=False)

def export_attachment_table(realm: Realm, output_dir: Path, message_ids: Set[int]) -> None:
    response = {}  # type: TableData
    fetch_attachment_data(response=response, realm_id=realm.id, message_ids=message_ids)
    output_file = os.path.join(output_dir, "attachment.json")
    logging.info('Writing attachment table data to %s' % (output_file,))
    write_data_to_file(output_file=output_file, data=response)

def create_soft_link(source: Path, in_progress: bool=True) -> None:
    is_done = not in_progress
    if settings.DEVELOPMENT:
        in_progress_link = os.path.join(settings.DEPLOY_ROOT, 'var', 'export-in-progress')
        done_link = os.path.join(settings.DEPLOY_ROOT, 'var', 'export-most-recent')
    else:
        in_progress_link = '/home/zulip/export-in-progress'
        done_link = '/home/zulip/export-most-recent'

    if in_progress:
        new_target = in_progress_link
    else:
        try:
            os.remove(in_progress_link)
        except FileNotFoundError:
            pass
        new_target = done_link

    overwrite_symlink(source, new_target)
    if is_done:
        logging.info('See %s for output files' % (new_target,))


def launch_user_message_subprocesses(threads: int, output_dir: Path) -> None:
    logging.info('Launching %d PARALLEL subprocesses to export UserMessage rows' % (threads,))

    def run_job(shard: str) -> int:
        subprocess.call(["./manage.py", 'export_usermessage_batch', '--path',
                         str(output_dir), '--thread', shard])
        return 0

    for (status, job) in run_parallel(run_job,
                                      [str(x) for x in range(0, threads)],
                                      threads=threads):
        print("Shard %s finished, status %s" % (job, status))

def do_export_user(user_profile: UserProfile, output_dir: Path) -> None:
    response = {}  # type: TableData

    export_single_user(user_profile, response)
    export_file = os.path.join(output_dir, "user.json")
    write_data_to_file(output_file=export_file, data=response)
    logging.info("Exporting messages")
    export_messages_single_user(user_profile, output_dir)

def export_single_user(user_profile: UserProfile, response: TableData) -> None:

    config = get_single_user_config()
    export_from_config(
        response=response,
        config=config,
        seed_object=user_profile,
    )

def get_single_user_config() -> Config:

    # zerver_userprofile
    user_profile_config = Config(
        table='zerver_userprofile',
        is_seeded=True,
        exclude=['password', 'api_key'],
    )

    # zerver_subscription
    subscription_config = Config(
        table='zerver_subscription',
        model=Subscription,
        normal_parent=user_profile_config,
        parent_key='user_profile__in',
    )

    # zerver_recipient
    recipient_config = Config(
        table='zerver_recipient',
        model=Recipient,
        virtual_parent=subscription_config,
        id_source=('zerver_subscription', 'recipient'),
    )

    # zerver_stream
    Config(
        table='zerver_stream',
        model=Stream,
        virtual_parent=recipient_config,
        id_source=('zerver_recipient', 'type_id'),
        source_filter=lambda r: r['type'] == Recipient.STREAM,
        exclude=['email_token'],
    )

    return user_profile_config

def export_messages_single_user(user_profile: UserProfile, output_dir: Path,
                                chunk_size: int=MESSAGE_BATCH_CHUNK_SIZE) -> None:
    user_message_query = UserMessage.objects.filter(user_profile=user_profile).order_by("id")
    min_id = -1
    dump_file_id = 1
    while True:
        actual_query = user_message_query.select_related(
            "message", "message__sending_client").filter(id__gt=min_id)[0:chunk_size]
        user_message_chunk = [um for um in actual_query]
        user_message_ids = set(um.id for um in user_message_chunk)

        if len(user_message_chunk) == 0:
            break

        message_chunk = []
        for user_message in user_message_chunk:
            item = model_to_dict(user_message.message)
            item['flags'] = user_message.flags_list()
            item['flags_mask'] = user_message.flags.mask
            # Add a few nice, human-readable details
            item['sending_client_name'] = user_message.message.sending_client.name
            item['display_recipient'] = get_display_recipient(user_message.message.recipient)
            message_chunk.append(item)

        message_filename = os.path.join(output_dir, "messages-%06d.json" % (dump_file_id,))
        logging.info("Fetched Messages for %s" % (message_filename,))

        output = {'zerver_message': message_chunk}
        floatify_datetime_fields(output, 'zerver_message')
        message_output = dict(output)  # type: MessageOutput

        write_message_export(message_filename, message_output)
        min_id = max(user_message_ids)
        dump_file_id += 1