zulip/zerver/views/messages.py

from __future__ import absolute_import

from django.utils.translation import ugettext as _
from django.utils.timezone import now as timezone_now
from django.conf import settings
from django.core import validators
from django.core.exceptions import ValidationError
from django.db import connection
from django.db.models import Q
from django.http import HttpRequest, HttpResponse
from typing import Dict, List, Set, Text
from typing import Any, AnyStr, Callable, Iterable, Optional, Tuple, Union
from zerver.lib.str_utils import force_bytes, force_text
from zerver.lib.html_diff import highlight_html_differences

from zerver.decorator import authenticated_api_view, authenticated_json_post_view, \
    has_request_variables, REQ, JsonableError, \
    to_non_negative_int
from django.utils.html import escape as escape_html
from zerver.lib import bugdown
from zerver.lib.actions import recipient_for_emails, do_update_message_flags, \
    compute_mit_user_fullname, compute_irc_user_fullname, compute_jabber_user_fullname, \
    create_mirror_user_if_needed, check_send_message, do_update_message, \
    extract_recipients, truncate_body, render_incoming_message
from zerver.lib.queue import queue_json_publish
from zerver.lib.cache import (
    generic_bulk_cached_fetch,
    to_dict_cache_key_id,
)
from zerver.lib.message import (
    access_message,
    MessageDict,
    extract_message_dict,
    render_markdown,
    stringify_message_dict,
)
from zerver.lib.response import json_success, json_error
from zerver.lib.sqlalchemy_utils import get_sqlalchemy_connection
from zerver.lib.timestamp import datetime_to_timestamp
from zerver.lib.utils import statsd
from zerver.lib.validator import \
    check_list, check_int, check_dict, check_string, check_bool
from zerver.models import Message, UserProfile, Stream, Subscription, \
    Realm, RealmDomain, Recipient, UserMessage, bulk_get_recipients, get_recipient, \
    get_user_profile_by_email, get_stream, \
    parse_usermessage_flags, \
    email_to_domain, get_realm, get_active_streams, \
    bulk_get_streams, get_user_profile_by_id

from sqlalchemy import func
from sqlalchemy.sql import select, join, column, literal_column, literal, and_, \
    or_, not_, union_all, alias, Selectable, Select, ColumnElement, table

import re
import ujson
import datetime

from six.moves import map
import six

LARGER_THAN_MAX_MESSAGE_ID = 10000000000000000

class BadNarrowOperator(JsonableError):
    def __init__(self, desc, status_code=400):
        # type: (str, int) -> None
        self.desc = desc
        self.status_code = status_code

    def to_json_error_msg(self):
        # type: () -> str
        return _('Invalid narrow operator: {}').format(self.desc)

Query = Any # TODO: Should be Select, but sqlalchemy stubs are busted
ConditionTransform = Any # TODO: should be Callable[[ColumnElement], ColumnElement], but sqlalchemy stubs are busted

# When you add a new operator to this, also update zerver/lib/narrow.py
class NarrowBuilder(object):
    def __init__(self, user_profile, msg_id_column):
        # type: (UserProfile, str) -> None
        self.user_profile = user_profile
        self.msg_id_column = msg_id_column

    def add_term(self, query, term):
        # type: (Query, Dict[str, Any]) -> Query

        # We have to be careful here because we're letting users call a method
        # by name! The prefix 'by_' prevents it from colliding with builtin
        # Python __magic__ stuff.
        operator = term['operator']
        operand = term['operand']

        negated = term.get('negated', False)

        method_name = 'by_' + operator.replace('-', '_')
        method = getattr(self, method_name, None)
        if method is None:
            raise BadNarrowOperator('unknown operator ' + operator)

        if negated:
            maybe_negate = not_
        else:
            maybe_negate = lambda cond: cond

        return method(query, operand, maybe_negate)

    def by_has(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        if operand not in ['attachment', 'image', 'link']:
            raise BadNarrowOperator("unknown 'has' operand " + operand)
        col_name = 'has_' + operand
        cond = column(col_name)
        return query.where(maybe_negate(cond))

    def by_in(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        if operand == 'home':
            conditions = exclude_muting_conditions(self.user_profile, [])
            return query.where(and_(*conditions))
        elif operand == 'all':
            return query

        raise BadNarrowOperator("unknown 'in' operand " + operand)

    def by_is(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        if operand == 'private':
            query = query.select_from(join(query.froms[0], table("zerver_recipient"),
                                           column("recipient_id") ==
                                           literal_column("zerver_recipient.id")))
            cond = or_(column("type") == Recipient.PERSONAL,
                       column("type") == Recipient.HUDDLE)
            return query.where(maybe_negate(cond))
        elif operand == 'starred':
            cond = column("flags").op("&")(UserMessage.flags.starred.mask) != 0
            return query.where(maybe_negate(cond))
        elif operand == 'mentioned' or operand == 'alerted':
            cond = column("flags").op("&")(UserMessage.flags.mentioned.mask) != 0
            return query.where(maybe_negate(cond))
        raise BadNarrowOperator("unknown 'is' operand " + operand)

    _alphanum = frozenset(
        'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789')

    def _pg_re_escape(self, pattern):
        # type: (Text) -> Text
        """
        Escape user input to place in a regex

        Python's re.escape escapes unicode characters in a way which postgres
        fails on, u'\u03bb' to u'\\\u03bb'. This function will correctly escape
        them for postgres, u'\u03bb' to u'\\u03bb'.
        """
        s = list(pattern)
        for i, c in enumerate(s):
            if c not in self._alphanum:
                if ord(c) >= 128:
                    # convert the character to hex postgres regex will take
                    # \uXXXX
                    s[i] = '\\u{:0>4x}'.format(ord(c))
                else:
                    s[i] = '\\' + c
        return ''.join(s)

    def by_stream(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        try:
            stream = get_stream(operand, self.user_profile.realm)
        except Stream.DoesNotExist:
            raise BadNarrowOperator('unknown stream ' + operand)

        if self.user_profile.realm.is_zephyr_mirror_realm:
            # MIT users expect narrowing to "social" to also show messages to /^(un)*social(.d)*$/
            # (unsocial, ununsocial, social.d, etc)
            m = re.search(r'^(?:un)*(.+?)(?:\.d)*$', stream.name, re.IGNORECASE)
            # Since the regex has a `.+` in it and "" is invalid as a
            # stream name, this will always match
            assert(m is not None)
            base_stream_name = m.group(1)

            matching_streams = get_active_streams(self.user_profile.realm).filter(
                name__iregex=r'^(un)*%s(\.d)*$' % (self._pg_re_escape(base_stream_name),))
            matching_stream_ids = [matching_stream.id for matching_stream in matching_streams]
            recipients_map = bulk_get_recipients(Recipient.STREAM, matching_stream_ids)
            cond = column("recipient_id").in_([recipient.id for recipient in recipients_map.values()])
            return query.where(maybe_negate(cond))

        recipient = get_recipient(Recipient.STREAM, type_id=stream.id)
        cond = column("recipient_id") == recipient.id
        return query.where(maybe_negate(cond))

    def by_topic(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        if self.user_profile.realm.is_zephyr_mirror_realm:
            # MIT users expect narrowing to topic "foo" to also show messages to /^foo(.d)*$/
            # (foo, foo.d, foo.d.d, etc)
            m = re.search(r'^(.*?)(?:\.d)*$', operand, re.IGNORECASE)
            # Since the regex has a `.*` in it, this will always match
            assert(m is not None)
            base_topic = m.group(1)

            # Additionally, MIT users expect the empty instance and
            # instance "personal" to be the same.
            if base_topic in ('', 'personal', '(instance "")'):
                cond = or_(
                    func.upper(column("subject")) == func.upper(literal("")),
                    func.upper(column("subject")) == func.upper(literal(".d")),
                    func.upper(column("subject")) == func.upper(literal(".d.d")),
                    func.upper(column("subject")) == func.upper(literal(".d.d.d")),
                    func.upper(column("subject")) == func.upper(literal(".d.d.d.d")),
                    func.upper(column("subject")) == func.upper(literal("personal")),
                    func.upper(column("subject")) == func.upper(literal("personal.d")),
                    func.upper(column("subject")) == func.upper(literal("personal.d.d")),
                    func.upper(column("subject")) == func.upper(literal("personal.d.d.d")),
                    func.upper(column("subject")) == func.upper(literal("personal.d.d.d.d")),
                    func.upper(column("subject")) == func.upper(literal('(instance "")')),
                    func.upper(column("subject")) == func.upper(literal('(instance "").d')),
                    func.upper(column("subject")) == func.upper(literal('(instance "").d.d')),
                    func.upper(column("subject")) == func.upper(literal('(instance "").d.d.d')),
                    func.upper(column("subject")) == func.upper(literal('(instance "").d.d.d.d')),
                )
            else:
                # We limit `.d` counts, since postgres has much better
                # query planning for this than they do for a regular
                # expression (which would sometimes table scan).
                cond = or_(
                    func.upper(column("subject")) == func.upper(literal(base_topic)),
                    func.upper(column("subject")) == func.upper(literal(base_topic + ".d")),
                    func.upper(column("subject")) == func.upper(literal(base_topic + ".d.d")),
                    func.upper(column("subject")) == func.upper(literal(base_topic + ".d.d.d")),
                    func.upper(column("subject")) == func.upper(literal(base_topic + ".d.d.d.d")),
                )
            return query.where(maybe_negate(cond))

        cond = func.upper(column("subject")) == func.upper(literal(operand))
        return query.where(maybe_negate(cond))

    def by_sender(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        try:
            sender = get_user_profile_by_email(operand)
        except UserProfile.DoesNotExist:
            raise BadNarrowOperator('unknown user ' + operand)

        cond = column("sender_id") == literal(sender.id)
        return query.where(maybe_negate(cond))

    def by_near(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        return query

    def by_id(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        cond = self.msg_id_column == literal(operand)
        return query.where(maybe_negate(cond))

    def by_pm_with(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        if ',' in operand:
            # Huddle
            try:
                emails = [e.strip() for e in operand.split(',')]
                recipient = recipient_for_emails(emails, False,
                                                 self.user_profile, self.user_profile)
            except ValidationError:
                raise BadNarrowOperator('unknown recipient ' + operand)
            cond = column("recipient_id") == recipient.id
            return query.where(maybe_negate(cond))
        else:
            # Personal message
            self_recipient = get_recipient(Recipient.PERSONAL, type_id=self.user_profile.id)
            if operand == self.user_profile.email:
                # Personals with self
                cond = and_(column("sender_id") == self.user_profile.id,
                            column("recipient_id") == self_recipient.id)
                return query.where(maybe_negate(cond))

            # Personals with other user; include both directions.
            try:
                narrow_profile = get_user_profile_by_email(operand)
            except UserProfile.DoesNotExist:
                raise BadNarrowOperator('unknown user ' + operand)

            narrow_recipient = get_recipient(Recipient.PERSONAL, narrow_profile.id)
            cond = or_(and_(column("sender_id") == narrow_profile.id,
                            column("recipient_id") == self_recipient.id),
                       and_(column("sender_id") == self.user_profile.id,
                            column("recipient_id") == narrow_recipient.id))
            return query.where(maybe_negate(cond))

    def by_group_pm_with(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        try:
            narrow_profile = get_user_profile_by_email(operand)
        except UserProfile.DoesNotExist:
            raise BadNarrowOperator('unknown user ' + operand)

        self_recipient_ids = [
            recipient_tuple['recipient_id'] for recipient_tuple
            in Subscription.objects.filter(
                user_profile=self.user_profile,
                recipient__type=Recipient.HUDDLE
            ).values("recipient_id")]
        narrow_recipient_ids = [
            recipient_tuple['recipient_id'] for recipient_tuple
            in Subscription.objects.filter(
                user_profile=narrow_profile,
                recipient__type=Recipient.HUDDLE
            ).values("recipient_id")]

        recipient_ids = set(self_recipient_ids) & set(narrow_recipient_ids)
        cond = column("recipient_id").in_(recipient_ids)
        return query.where(maybe_negate(cond))

    def by_search(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        if settings.USING_PGROONGA:
            return self._by_search_pgroonga(query, operand, maybe_negate)
        else:
            return self._by_search_tsearch(query, operand, maybe_negate)

    def _by_search_pgroonga(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        match_positions_character = func.pgroonga.match_positions_character
        query_extract_keywords = func.pgroonga.query_extract_keywords
        keywords = query_extract_keywords(operand)
        query = query.column(match_positions_character(column("rendered_content"),
                                                       keywords).label("content_matches"))
        query = query.column(match_positions_character(column("subject"),
                                                       keywords).label("subject_matches"))
        condition = column("search_pgroonga").op("@@")(operand)
        return query.where(maybe_negate(condition))

    def _by_search_tsearch(self, query, operand, maybe_negate):
        # type: (Query, str, ConditionTransform) -> Query
        tsquery = func.plainto_tsquery(literal("zulip.english_us_search"), literal(operand))
        ts_locs_array = func.ts_match_locs_array
        query = query.column(ts_locs_array(literal("zulip.english_us_search"),
                                           column("rendered_content"),
                                           tsquery).label("content_matches"))
        # We HTML-escape the subject in Postgres to avoid doing a server round-trip
        query = query.column(ts_locs_array(literal("zulip.english_us_search"),
                                           func.escape_html(column("subject")),
                                           tsquery).label("subject_matches"))

        # Do quoted string matching.  We really want phrase
        # search here so we can ignore punctuation and do
        # stemming, but there isn't a standard phrase search
        # mechanism in Postgres
        for term in re.findall('"[^"]+"|\S+', operand):
            if term[0] == '"' and term[-1] == '"':
                term = term[1:-1]
                term = '%' + connection.ops.prep_for_like_query(term) + '%'
                cond = or_(column("content").ilike(term),
                           column("subject").ilike(term))
                query = query.where(maybe_negate(cond))

        cond = column("search_tsvector").op("@@")(tsquery)
        return query.where(maybe_negate(cond))

# Apparently, the offsets we get from tsearch_extras are counted in
# unicode characters, not in bytes, so we do our processing with text,
# not bytes.
def highlight_string(text, locs):
    # type: (AnyStr, Iterable[Tuple[int, int]]) -> Text
    string = force_text(text)
    highlight_start = u'<span class="highlight">'
    highlight_stop = u'</span>'
    pos = 0
    result = u''
    in_tag = False
    for loc in locs:
        (offset, length) = loc
        for character in string[pos:offset + length]:
            if character == u'<':
                in_tag = True
            elif character == u'>':
                in_tag = False
        if in_tag:
            result += string[pos:offset + length]
        else:
            result += string[pos:offset]
            result += highlight_start
            result += string[offset:offset + length]
            result += highlight_stop
        pos = offset + length
    result += string[pos:]
    return result

def get_search_fields(rendered_content, subject, content_matches, subject_matches):
    # type: (Text, Text, Iterable[Tuple[int, int]], Iterable[Tuple[int, int]]) -> Dict[str, Text]
    return dict(match_content=highlight_string(rendered_content, content_matches),
                match_subject=highlight_string(escape_html(subject), subject_matches))

def narrow_parameter(json):
    # type: (str) -> Optional[List[Dict[str, Any]]]

    data = ujson.loads(json)
    if not isinstance(data, list):
        raise ValueError("argument is not a list")
    if len(data) == 0:
        # The "empty narrow" should be None, and not []
        return None

    def convert_term(elem):
        # type: (Union[Dict, List]) -> Dict[str, Any]

        # We have to support a legacy tuple format.
        if isinstance(elem, list):
            if (len(elem) != 2 or
                any(not isinstance(x, str) and not isinstance(x, Text)
                    for x in elem)):
                raise ValueError("element is not a string pair")
            return dict(operator=elem[0], operand=elem[1])

        if isinstance(elem, dict):
            validator = check_dict([
                ('operator', check_string),
                ('operand', check_string),
            ])

            error = validator('elem', elem)
            if error:
                raise JsonableError(error)

            # whitelist the fields we care about for now
            return dict(
                operator=elem['operator'],
                operand=elem['operand'],
                negated=elem.get('negated', False),
            )

        raise ValueError("element is not a dictionary")

    return list(map(convert_term, data))

def is_public_stream(stream_name, realm):
    # type: (Text, Realm) -> bool
    """
    Determine whether a stream is public, so that
    our caller can decide whether we can get
    historical messages for a narrowing search.

    Because of the way our search is currently structured,
    we may be passed an invalid stream here.  We return
    False in that situation, and subsequent code will do
    validation and raise the appropriate JsonableError.
    """
    try:
        stream = get_stream(stream_name, realm)
    except Stream.DoesNotExist:
        return False
    return stream.is_public()


def ok_to_include_history(narrow, realm):
    # type: (Optional[Iterable[Dict[str, Any]]], Realm) -> bool

    # There are occasions where we need to find Message rows that
    # have no corresponding UserMessage row, because the user is
    # reading a public stream that might include messages that
    # were sent while the user was not subscribed, but which they are
    # allowed to see.  We have to be very careful about constructing
    # queries in those situations, so this function should return True
    # only if we are 100% sure that we're gonna add a clause to the
    # query that narrows to a particular public stream on the user's realm.
    # If we screw this up, then we can get into a nasty situation of
    # polluting our narrow results with messages from other realms.
    include_history = False
    if narrow is not None:
        for term in narrow:
            if term['operator'] == "stream" and not term.get('negated', False):
                if is_public_stream(term['operand'], realm):
                    include_history = True
        # Disable historical messages if the user is narrowing on anything
        # that's a property on the UserMessage table.  There cannot be
        # historical messages in these cases anyway.
        for term in narrow:
            if term['operator'] == "is":
                include_history = False

    return include_history

def get_stream_name_from_narrow(narrow):
    # type: (Optional[Iterable[Dict[str, Any]]]) -> Optional[Text]
    if narrow is not None:
        for term in narrow:
            if term['operator'] == 'stream':
                return term['operand'].lower()
    return None

def exclude_muting_conditions(user_profile, narrow):
    # type: (UserProfile, Optional[Iterable[Dict[str, Any]]]) -> List[Selectable]
    conditions = []
    stream_name = get_stream_name_from_narrow(narrow)

    if stream_name is None:
        rows = Subscription.objects.filter(
            user_profile=user_profile,
            active=True,
            in_home_view=False,
            recipient__type=Recipient.STREAM
        ).values('recipient_id')
        muted_recipient_ids = [row['recipient_id'] for row in rows]
        if len(muted_recipient_ids) > 0:
            # Only add the condition if we have muted streams to simplify/avoid warnings.
            condition = not_(column("recipient_id").in_(muted_recipient_ids))
            conditions.append(condition)

    muted_topics = ujson.loads(user_profile.muted_topics)
    if muted_topics:
        if stream_name is not None:
            muted_topics = [m for m in muted_topics if m[0].lower() == stream_name]
            if not muted_topics:
                return conditions

        muted_streams = bulk_get_streams(user_profile.realm,
                                         [muted[0] for muted in muted_topics])
        muted_recipients = bulk_get_recipients(Recipient.STREAM,
                                               [stream.id for stream in six.itervalues(muted_streams)])
        recipient_map = dict((s.name.lower(), muted_recipients[s.id].id)
                             for s in six.itervalues(muted_streams))

        muted_topics = [m for m in muted_topics if m[0].lower() in recipient_map]

        if muted_topics:
            def mute_cond(muted):
                # type: (Tuple[str, str]) -> Selectable
                stream_cond = column("recipient_id") == recipient_map[muted[0].lower()]
                topic_cond = func.upper(column("subject")) == func.upper(muted[1])
                return and_(stream_cond, topic_cond)

            condition = not_(or_(*list(map(mute_cond, muted_topics))))
            return conditions + [condition]

    return conditions

@has_request_variables
def get_messages_backend(request, user_profile,
                         anchor = REQ(converter=int),
                         num_before = REQ(converter=to_non_negative_int),
                         num_after = REQ(converter=to_non_negative_int),
                         narrow = REQ('narrow', converter=narrow_parameter, default=None),
                         use_first_unread_anchor = REQ(default=False, converter=ujson.loads),
                         apply_markdown=REQ(default=True,
                                            converter=ujson.loads)):
    # type: (HttpRequest, UserProfile, int, int, int, Optional[List[Dict[str, Any]]], bool, bool) -> HttpResponse
    include_history = ok_to_include_history(narrow, user_profile.realm)

    if include_history and not use_first_unread_anchor:
        query = select([column("id").label("message_id")], None, table("zerver_message"))
        inner_msg_id_col = literal_column("zerver_message.id")
    elif narrow is None and not use_first_unread_anchor:
        query = select([column("message_id"), column("flags")],
                       column("user_profile_id") == literal(user_profile.id),
                       table("zerver_usermessage"))
        inner_msg_id_col = column("message_id")
    else:
        # TODO: Don't do this join if we're not doing a search
        query = select([column("message_id"), column("flags")],
                       column("user_profile_id") == literal(user_profile.id),
                       join(table("zerver_usermessage"), table("zerver_message"),
                            literal_column("zerver_usermessage.message_id") ==
                            literal_column("zerver_message.id")))
        inner_msg_id_col = column("message_id")

    num_extra_messages = 1
    is_search = False

    if narrow is not None:
        # Add some metadata to our logging data for narrows
        verbose_operators = []
        for term in narrow:
            if term['operator'] == "is":
                verbose_operators.append("is:" + term['operand'])
            else:
                verbose_operators.append(term['operator'])
        request._log_data['extra'] = "[%s]" % (",".join(verbose_operators),)

        # Build the query for the narrow
        num_extra_messages = 0
        builder = NarrowBuilder(user_profile, inner_msg_id_col)
        search_term = None # type: Optional[Dict[str, Any]]
        for term in narrow:
            if term['operator'] == 'search':
                if not is_search:
                    search_term = term
                    query = query.column(column("subject")).column(column("rendered_content"))
                    is_search = True
                else:
                    # Join the search operators if there are multiple of them
                    search_term['operand'] += ' ' + term['operand']
            else:
                query = builder.add_term(query, term)
        if is_search:
            query = builder.add_term(query, search_term)

    # We add 1 to the number of messages requested if no narrow was
    # specified to ensure that the resulting list always contains the
    # anchor message.  If a narrow was specified, the anchor message
    # might not match the narrow anyway.
    if num_after != 0:
        num_after += num_extra_messages
    else:
        num_before += num_extra_messages

    sa_conn = get_sqlalchemy_connection()
    if use_first_unread_anchor:
        condition = column("flags").op("&")(UserMessage.flags.read.mask) == 0

        # We exclude messages on muted topics when finding the first unread
        # message in this narrow
        muting_conditions = exclude_muting_conditions(user_profile, narrow)
        if muting_conditions:
            condition = and_(condition, *muting_conditions)

        # The mobile app uses narrow=[] and use_first_unread_anchor=True to
        # determine what messages to show when you first load the app.
        # Unfortunately, this means that if you have a years-old unread
        # message, the mobile app could get stuck in the past.
        #
        # To fix this, we enforce that the "first unread anchor" must be on or
        # after the user's current pointer location. Since the pointer
        # location refers to the latest the user has read in the home view,
        # we'll only apply this logic in the home view (ie, when narrow is
        # empty).
        if not narrow:
            pointer_condition = inner_msg_id_col >= user_profile.pointer
            condition = and_(condition, pointer_condition)

        first_unread_query = query.where(condition)
        first_unread_query = first_unread_query.order_by(inner_msg_id_col.asc()).limit(1)
        first_unread_result = list(sa_conn.execute(first_unread_query).fetchall())
        if len(first_unread_result) > 0:
            anchor = first_unread_result[0][0]
        else:
            anchor = LARGER_THAN_MAX_MESSAGE_ID

    before_query = None
    after_query = None
    if num_before != 0:
        before_anchor = anchor
        if num_after != 0:
            # Don't include the anchor in both the before query and the after query
            before_anchor = anchor - 1
        before_query = query.where(inner_msg_id_col <= before_anchor) \
                            .order_by(inner_msg_id_col.desc()).limit(num_before)
    if num_after != 0:
        after_query = query.where(inner_msg_id_col >= anchor) \
                           .order_by(inner_msg_id_col.asc()).limit(num_after)

    if anchor == LARGER_THAN_MAX_MESSAGE_ID:
        # There's no need for an after_query if we're targeting just the target message.
        after_query = None

    if before_query is not None:
        if after_query is not None:
            query = union_all(before_query.self_group(), after_query.self_group())
        else:
            query = before_query
    elif after_query is not None:
        query = after_query
    else:
        # This can happen when a narrow is specified.
        query = query.where(inner_msg_id_col == anchor)

    main_query = alias(query)
    query = select(main_query.c, None, main_query).order_by(column("message_id").asc())
    # This is a hack to tag the query we use for testing
    query = query.prefix_with("/* get_messages */")
    query_result = list(sa_conn.execute(query).fetchall())

    # The following is a little messy, but ensures that the code paths
    # are similar regardless of the value of include_history.  The
    # 'user_messages' dictionary maps each message to the user's
    # UserMessage object for that message, which we will attach to the
    # rendered message dict before returning it.  We attempt to
    # bulk-fetch rendered message dicts from remote cache using the
    # 'messages' list.
    search_fields = dict() # type: Dict[int, Dict[str, Text]]
    message_ids = [] # type: List[int]
    user_message_flags = {} # type: Dict[int, List[str]]
    if include_history:
        message_ids = [row[0] for row in query_result]

        # TODO: This could be done with an outer join instead of two queries
        user_message_flags = dict((user_message.message_id, user_message.flags_list()) for user_message in
                                  UserMessage.objects.filter(user_profile=user_profile,
                                                             message__id__in=message_ids))
        for row in query_result:
            message_id = row[0]
            if user_message_flags.get(message_id) is None:
                user_message_flags[message_id] = ["read", "historical"]
            if is_search:
                (_, subject, rendered_content, content_matches, subject_matches) = row
                search_fields[message_id] = get_search_fields(rendered_content, subject,
                                                              content_matches, subject_matches)
    else:
        for row in query_result:
            message_id = row[0]
            flags = row[1]
            user_message_flags[message_id] = parse_usermessage_flags(flags)

            message_ids.append(message_id)

            if is_search:
                (_, _, subject, rendered_content, content_matches, subject_matches) = row
                search_fields[message_id] = get_search_fields(rendered_content, subject,
                                                              content_matches, subject_matches)

    cache_transformer = lambda row: MessageDict.build_dict_from_raw_db_row(row, apply_markdown)
    id_fetcher = lambda row: row['id']

    message_dicts = generic_bulk_cached_fetch(lambda message_id: to_dict_cache_key_id(message_id, apply_markdown),
                                              Message.get_raw_db_rows,
                                              message_ids,
                                              id_fetcher=id_fetcher,
                                              cache_transformer=cache_transformer,
                                              extractor=extract_message_dict,
                                              setter=stringify_message_dict)

    message_list = []
    for message_id in message_ids:
        msg_dict = message_dicts[message_id]
        msg_dict.update({"flags": user_message_flags[message_id]})
        msg_dict.update(search_fields.get(message_id, {}))
        message_list.append(msg_dict)

    statsd.incr('loaded_old_messages', len(message_list))
    ret = {'messages': message_list,
           "result": "success",
           "msg": ""}
    return json_success(ret)

@has_request_variables
def update_message_flags(request, user_profile,
                         messages=REQ(validator=check_list(check_int)),
                         operation=REQ('op'), flag=REQ(),
                         all=REQ(validator=check_bool, default=False),
                         stream_name=REQ(default=None),
                         topic_name=REQ(default=None)):
    # type: (HttpRequest, UserProfile, List[int], Text, Text, bool, Optional[Text], Optional[Text]) -> HttpResponse
    if all:
        target_count_str = "all"
    else:
        target_count_str = str(len(messages))
    log_data_str = "[%s %s/%s]" % (operation, flag, target_count_str)
    request._log_data["extra"] = log_data_str
    stream = None
    if stream_name is not None:
        try:
            stream = get_stream(stream_name, user_profile.realm)
        except Stream.DoesNotExist:
            raise JsonableError(_('No such stream \'%s\'') % (stream_name,))
        if topic_name:
            topic_exists = UserMessage.objects.filter(user_profile=user_profile,
                                                      message__recipient__type_id=stream.id,
                                                      message__recipient__type=Recipient.STREAM,
                                                      message__subject__iexact=topic_name).exists()
            if not topic_exists:
                raise JsonableError(_('No such topic \'%s\'') % (topic_name,))
    count = do_update_message_flags(user_profile, operation, flag, messages,
                                    all, stream, topic_name)

    # If we succeed, update log data str with the actual count for how
    # many messages were updated.
    if count != len(messages):
        log_data_str = "[%s %s/%s] actually %s" % (operation, flag, target_count_str, count)
    request._log_data["extra"] = log_data_str

    return json_success({'result': 'success',
                         'messages': messages,
                         'msg': ''})

def create_mirrored_message_users(request, user_profile, recipients):
    # type: (HttpResponse, UserProfile, Iterable[Text]) -> Tuple[bool, Optional[UserProfile]]
    if "sender" not in request.POST:
        return (False, None)

    sender_email = request.POST["sender"].strip().lower()
    referenced_users = set([sender_email])
    if request.POST['type'] == 'private':
        for email in recipients:
            referenced_users.add(email.lower())

    if request.client.name == "zephyr_mirror":
        user_check = same_realm_zephyr_user
        fullname_function = compute_mit_user_fullname
    elif request.client.name == "irc_mirror":
        user_check = same_realm_irc_user
        fullname_function = compute_irc_user_fullname
    elif request.client.name in ("jabber_mirror", "JabberMirror"):
        user_check = same_realm_jabber_user
        fullname_function = compute_jabber_user_fullname
    else:
        # Unrecognized mirroring client
        return (False, None)

    for email in referenced_users:
        # Check that all referenced users are in our realm:
        if not user_check(user_profile, email):
            return (False, None)

    # Create users for the referenced users, if needed.
    for email in referenced_users:
        create_mirror_user_if_needed(user_profile.realm, email, fullname_function)

    sender = get_user_profile_by_email(sender_email)
    return (True, sender)

def same_realm_zephyr_user(user_profile, email):
    # type: (UserProfile, Text) -> bool
    #
    # Are the sender and recipient both addresses in the same Zephyr
    # mirroring realm?  We have to handle this specially, inferring
    # the domain from the e-mail address, because the recipient may
    # not existing in Zulip and we may need to make a stub Zephyr
    # mirroring user on the fly.
    try:
        validators.validate_email(email)
    except ValidationError:
        return False

    domain = email_to_domain(email)

    # Assumes allow_subdomains=False for all RealmDomain's corresponding to
    # these realms.
    return user_profile.realm.is_zephyr_mirror_realm and \
        RealmDomain.objects.filter(realm=user_profile.realm, domain=domain).exists()

def same_realm_irc_user(user_profile, email):
    # type: (UserProfile, Text) -> bool
    # Check whether the target email address is an IRC user in the
    # same realm as user_profile, i.e. if the domain were example.com,
    # the IRC user would need to be username@irc.example.com
    try:
        validators.validate_email(email)
    except ValidationError:
        return False

    domain = email_to_domain(email).replace("irc.", "")

    # Assumes allow_subdomains=False for all RealmDomain's corresponding to
    # these realms.
    return RealmDomain.objects.filter(realm=user_profile.realm, domain=domain).exists()

def same_realm_jabber_user(user_profile, email):
    # type: (UserProfile, Text) -> bool
    try:
        validators.validate_email(email)
    except ValidationError:
        return False

    # If your Jabber users have a different email domain than the
    # Zulip users, this is where you would do any translation.
    domain = email_to_domain(email)

    # Assumes allow_subdomains=False for all RealmDomain's corresponding to
    # these realms.
    return RealmDomain.objects.filter(realm=user_profile.realm, domain=domain).exists()

# We do not @require_login for send_message_backend, since it is used
# both from the API and the web service.  Code calling
# send_message_backend should either check the API key or check that
# the user is logged in.
@has_request_variables
def send_message_backend(request, user_profile,
                         message_type_name = REQ('type'),
                         message_to = REQ('to', converter=extract_recipients, default=[]),
                         forged = REQ(default=False),
                         subject_name = REQ('subject', lambda x: x.strip(), None),
                         message_content = REQ('content'),
                         realm_str = REQ('realm_str', default=None),
                         local_id = REQ(default=None),
                         queue_id = REQ(default=None)):
    # type: (HttpRequest, UserProfile, Text, List[Text], bool, Optional[Text], Text, Optional[Text], Optional[Text], Optional[Text]) -> HttpResponse
    client = request.client
    is_super_user = request.user.is_api_super_user
    if forged and not is_super_user:
        return json_error(_("User not authorized for this query"))

    realm = None
    if realm_str and realm_str != user_profile.realm.string_id:
        if not is_super_user:
            # The email gateway bot needs to be able to send messages in
            # any realm.
            return json_error(_("User not authorized for this query"))
        realm = get_realm(realm_str)
        if not realm:
            return json_error(_("Unknown realm %s") % (realm_str,))

    if client.name in ["zephyr_mirror", "irc_mirror", "jabber_mirror", "JabberMirror"]:
        # Here's how security works for mirroring:
        #
        # For private messages, the message must be (1) both sent and
        # received exclusively by users in your realm, and (2)
        # received by the forwarding user.
        #
        # For stream messages, the message must be (1) being forwarded
        # by an API superuser for your realm and (2) being sent to a
        # mirrored stream (any stream for the Zephyr and Jabber
        # mirrors, but only streams with names starting with a "#" for
        # IRC mirrors)
        #
        # The security checks are split between the below code
        # (especially create_mirrored_message_users which checks the
        # same-realm constraint) and recipient_for_emails (which
        # checks that PMs are received by the forwarding user)
        if "sender" not in request.POST:
            return json_error(_("Missing sender"))
        if message_type_name != "private" and not is_super_user:
            return json_error(_("User not authorized for this query"))
        (valid_input, mirror_sender) = \
            create_mirrored_message_users(request, user_profile, message_to)
        if not valid_input:
            return json_error(_("Invalid mirrored message"))
        if client.name == "zephyr_mirror" and not user_profile.realm.is_zephyr_mirror_realm:
            return json_error(_("Invalid mirrored realm"))
        if (client.name == "irc_mirror" and message_type_name != "private" and
                not message_to[0].startswith("#")):
            return json_error(_("IRC stream names must start with #"))
        sender = mirror_sender
    else:
        sender = user_profile

    ret = check_send_message(sender, client, message_type_name, message_to,
                             subject_name, message_content, forged=forged,
                             forged_timestamp = request.POST.get('time'),
                             forwarder_user_profile=user_profile, realm=realm,
                             local_id=local_id, sender_queue_id=queue_id)
    return json_success({"id": ret})

def fill_edit_history_entries(message_history, message):
    # type: (List[Dict[str, Any]], Message) -> None
    """This fills out the message edit history entries from the database,
    which are designed to have the minimum data possible, to instead
    have the current topic + content as of that time, plus data on
    whatever changed.  This makes it much simpler to do future
    processing.

    Note that this mutates what is passed to it, which is sorta a bad pattern.
    """
    prev_content = message.content
    prev_rendered_content = message.rendered_content
    prev_topic = message.subject
    assert(datetime_to_timestamp(message.last_edit_time) == message_history[0]['timestamp'])

    for entry in message_history:
        entry['topic'] = prev_topic
        if 'prev_subject' in entry:
            # We replace use of 'subject' with 'topic' for downstream simplicity
            prev_topic = entry['prev_subject']
            entry['prev_topic'] = prev_topic
            del entry['prev_subject']

        entry['content'] = prev_content
        entry['rendered_content'] = prev_rendered_content
        if 'prev_content' in entry:
            del entry['prev_rendered_content_version']
            prev_content = entry['prev_content']
            prev_rendered_content = entry['prev_rendered_content']
            entry['content_html_diff'] = highlight_html_differences(
                prev_rendered_content,
                entry['rendered_content'])

    message_history.append(dict(
        topic = prev_topic,
        content = prev_content,
        rendered_content = prev_rendered_content,
        timestamp = datetime_to_timestamp(message.pub_date),
        user_id = message.sender_id,
    ))

@has_request_variables
def get_message_edit_history(request, user_profile,
                             message_id=REQ(converter=to_non_negative_int)):
    # type: (HttpRequest, UserProfile, int) -> HttpResponse
    message, ignored_user_message = access_message(user_profile, message_id)

    # Extract the message edit history from the message
    message_edit_history = ujson.loads(message.edit_history)

    # Fill in all the extra data that will make it usable
    fill_edit_history_entries(message_edit_history, message)
    return json_success({"message_history": reversed(message_edit_history)})

@has_request_variables
def update_message_backend(request, user_profile,
                           message_id=REQ(converter=to_non_negative_int),
                           subject=REQ(default=None),
                           propagate_mode=REQ(default="change_one"),
                           content=REQ(default=None)):
    # type: (HttpRequest, UserProfile, int, Optional[Text], Optional[str], Optional[Text]) -> HttpResponse
    if not user_profile.realm.allow_message_editing:
        return json_error(_("Your organization has turned off message editing."))

    message, ignored_user_message = access_message(user_profile, message_id)

    # You only have permission to edit a message if:
    # you change this value also change those two parameters in message_edit.js.
    # 1. You sent it, OR:
    # 2. This is a topic-only edit for a (no topic) message, OR:
    # 3. This is a topic-only edit and you are an admin.
    if message.sender == user_profile:
        pass
    elif (content is None) and ((message.topic_name() == "(no topic)") or
                                user_profile.is_realm_admin):
        pass
    else:
        raise JsonableError(_("You don't have permission to edit this message"))

    # If there is a change to the content, check that it hasn't been too long
    # Allow an extra 20 seconds since we potentially allow editing 15 seconds
    # past the limit, and in case there are network issues, etc. The 15 comes
    # from (min_seconds_to_edit + seconds_left_buffer) in message_edit.js; if
    # you change this value also change those two parameters in message_edit.js.
    edit_limit_buffer = 20
    if content is not None and user_profile.realm.message_content_edit_limit_seconds > 0:
        deadline_seconds = user_profile.realm.message_content_edit_limit_seconds + edit_limit_buffer
        if (timezone_now() - message.pub_date) > datetime.timedelta(seconds=deadline_seconds):
            raise JsonableError(_("The time limit for editing this message has past"))

    if subject is None and content is None:
        return json_error(_("Nothing to change"))
    if subject is not None:
        subject = subject.strip()
        if subject == "":
            raise JsonableError(_("Topic can't be empty"))
    rendered_content = None
    links_for_embed = set()  # type: Set[Text]
    if content is not None:
        content = content.strip()
        if content == "":
            content = "(deleted)"
        content = truncate_body(content)

        # We exclude UserMessage.flags.historical rows since those
        # users did not receive the message originally, and thus
        # probably are not relevant for reprocessed alert_words,
        # mentions and similar rendering features.  This may be a
        # decision we change in the future.
        ums = UserMessage.objects.filter(
            message=message.id,
            flags=~UserMessage.flags.historical)

        message_users = UserProfile.objects.select_related().filter(
            id__in={um.user_profile_id for um in ums})

        # We render the message using the current user's realm; since
        # the cross-realm bots never edit messages, this should be
        # always correct.
        # Note: If rendering fails, the called code will raise a JsonableError.
        rendered_content = render_incoming_message(message,
                                                   content,
                                                   message_users,
                                                   user_profile.realm)
        links_for_embed |= message.links_for_preview

    number_changed = do_update_message(user_profile, message, subject,
                                       propagate_mode, content, rendered_content)
    # Include the number of messages changed in the logs
    request._log_data['extra'] = "[%s]" % (number_changed,)
    if links_for_embed and bugdown.url_embed_preview_enabled_for_realm(message):
        event_data = {
            'message_id': message.id,
            'message_content': message.content,
            # The choice of `user_profile.realm_id` rather than
            # `sender.realm_id` must match the decision made in the
            # `render_incoming_message` call earlier in this function.
            'message_realm_id': user_profile.realm_id,
            'urls': links_for_embed}
        queue_json_publish('embed_links', event_data, lambda x: None)
    return json_success()

@has_request_variables
def json_fetch_raw_message(request, user_profile,
                           message_id=REQ(converter=to_non_negative_int)):
    # type: (HttpRequest, UserProfile, int) -> HttpResponse
    (message, user_message) = access_message(user_profile, message_id)
    return json_success({"raw_content": message.content})

@has_request_variables
def render_message_backend(request, user_profile, content=REQ()):
    # type: (HttpRequest, UserProfile, Text) -> HttpResponse
    message = Message()
    message.sender = user_profile
    message.content = content
    message.sending_client = request.client

    rendered_content = render_markdown(message, content, realm=user_profile.realm)
    return json_success({"rendered": rendered_content})

@authenticated_json_post_view
def json_messages_in_narrow(request, user_profile):
    # type: (HttpRequest, UserProfile) -> HttpResponse
    return messages_in_narrow_backend(request, user_profile)

@has_request_variables
def messages_in_narrow_backend(request, user_profile,
                               msg_ids = REQ(validator=check_list(check_int)),
                               narrow = REQ(converter=narrow_parameter)):
    # type: (HttpRequest, UserProfile, List[int], Optional[List[Dict[str, Any]]]) -> HttpResponse

    # Note that this function will only work on messages the user
    # actually received

    # TODO: We assume that the narrow is a search.  For now this works because
    # the browser only ever calls this function for searches, since it can't
    # apply that narrow operator itself.

    query = select([column("message_id"), column("subject"), column("rendered_content")],
                   and_(column("user_profile_id") == literal(user_profile.id),
                        column("message_id").in_(msg_ids)),
                   join(table("zerver_usermessage"), table("zerver_message"),
                        literal_column("zerver_usermessage.message_id") ==
                        literal_column("zerver_message.id")))

    builder = NarrowBuilder(user_profile, column("message_id"))
    if narrow is not None:
        for term in narrow:
            query = builder.add_term(query, term)

    sa_conn = get_sqlalchemy_connection()
    query_result = list(sa_conn.execute(query).fetchall())

    search_fields = dict()
    for row in query_result:
        (message_id, subject, rendered_content, content_matches, subject_matches) = row
        search_fields[message_id] = get_search_fields(rendered_content, subject,
                                                      content_matches, subject_matches)

    return json_success({"messages": search_fields})