zulip/zerver/decorator.py

import base64
import datetime
import logging
import urllib
from functools import wraps
from io import BytesIO
from typing import Callable, Dict, Optional, Tuple, TypeVar, Union, cast

import django_otp
from django.conf import settings
from django.contrib.auth import REDIRECT_FIELD_NAME
from django.contrib.auth import login as django_login
from django.contrib.auth.decorators import user_passes_test as django_user_passes_test
from django.contrib.auth.models import AnonymousUser
from django.http import HttpRequest, HttpResponse, HttpResponseRedirect, QueryDict
from django.http.multipartparser import MultiPartParser
from django.shortcuts import resolve_url
from django.template.response import SimpleTemplateResponse, TemplateResponse
from django.utils.timezone import now as timezone_now
from django.utils.translation import ugettext as _
from django.views.decorators.csrf import csrf_exempt
from django_otp import user_has_device
from two_factor.utils import default_device

from zerver.lib.exceptions import (
    ErrorCode,
    InvalidAPIKeyError,
    InvalidAPIKeyFormatError,
    InvalidJSONError,
    JsonableError,
    OrganizationAdministratorRequired,
    OrganizationMemberRequired,
    OrganizationOwnerRequired,
    UnsupportedWebhookEventType,
)
from zerver.lib.queue import queue_json_publish
from zerver.lib.rate_limiter import RateLimitedUser
from zerver.lib.request import REQ, has_request_variables
from zerver.lib.response import json_error, json_method_not_allowed, json_success, json_unauthorized
from zerver.lib.subdomains import get_subdomain, user_matches_subdomain
from zerver.lib.timestamp import datetime_to_timestamp, timestamp_to_datetime
from zerver.lib.types import ViewFuncT
from zerver.lib.user_agent import parse_user_agent
from zerver.lib.utils import has_api_key_format, statsd
from zerver.models import Realm, UserProfile, get_client, get_user_profile_by_api_key

if settings.ZILENCER_ENABLED:
    from zilencer.models import RemoteZulipServer, get_remote_server_by_uuid

webhook_logger = logging.getLogger("zulip.zerver.webhooks")
webhook_unsupported_events_logger = logging.getLogger("zulip.zerver.webhooks.unsupported")

FuncT = TypeVar('FuncT', bound=Callable[..., object])

def cachify(method: FuncT) -> FuncT:
    dct: Dict[Tuple[object, ...], object] = {}

    def cache_wrapper(*args: object) -> object:
        tup = tuple(args)
        if tup in dct:
            return dct[tup]
        result = method(*args)
        dct[tup] = result
        return result
    return cast(FuncT, cache_wrapper)  # https://github.com/python/mypy/issues/1927

def update_user_activity(request: HttpRequest, user_profile: UserProfile,
                         query: Optional[str]) -> None:
    # update_active_status also pushes to RabbitMQ, and it seems
    # redundant to log that here as well.
    if request.META["PATH_INFO"] == '/json/users/me/presence':
        return

    if query is not None:
        pass
    elif hasattr(request, '_query'):
        query = request._query
    else:
        query = request.META['PATH_INFO']

    event = {'query': query,
             'user_profile_id': user_profile.id,
             'time': datetime_to_timestamp(timezone_now()),
             'client_id': request.client.id}
    queue_json_publish("user_activity", event, lambda event: None)

# Based on django.views.decorators.http.require_http_methods
def require_post(func: ViewFuncT) -> ViewFuncT:
    @wraps(func)
    def wrapper(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
        if request.method != "POST":
            err_method = request.method
            logging.warning('Method Not Allowed (%s): %s', err_method, request.path,
                            extra={'status_code': 405, 'request': request})
            if request.error_format == 'JSON':
                return json_method_not_allowed(["POST"])
            else:
                return TemplateResponse(request, "404.html", context={'status_code': 405}, status=405)
        return func(request, *args, **kwargs)
    return cast(ViewFuncT, wrapper)  # https://github.com/python/mypy/issues/1927

def require_realm_owner(func: ViewFuncT) -> ViewFuncT:
    @wraps(func)
    def wrapper(request: HttpRequest, user_profile: UserProfile, *args: object, **kwargs: object) -> HttpResponse:
        if not user_profile.is_realm_owner:
            raise OrganizationOwnerRequired()
        return func(request, user_profile, *args, **kwargs)
    return cast(ViewFuncT, wrapper)  # https://github.com/python/mypy/issues/1927

def require_realm_admin(func: ViewFuncT) -> ViewFuncT:
    @wraps(func)
    def wrapper(request: HttpRequest, user_profile: UserProfile, *args: object, **kwargs: object) -> HttpResponse:
        if not user_profile.is_realm_admin:
            raise OrganizationAdministratorRequired()
        return func(request, user_profile, *args, **kwargs)
    return cast(ViewFuncT, wrapper)  # https://github.com/python/mypy/issues/1927

def require_organization_member(func: ViewFuncT) -> ViewFuncT:
    @wraps(func)
    def wrapper(request: HttpRequest, user_profile: UserProfile, *args: object, **kwargs: object) -> HttpResponse:
        if user_profile.role > UserProfile.ROLE_MEMBER:
            raise OrganizationMemberRequired()
        return func(request, user_profile, *args, **kwargs)
    return cast(ViewFuncT, wrapper)  # https://github.com/python/mypy/issues/1927

def require_billing_access(func: ViewFuncT) -> ViewFuncT:
    @wraps(func)
    def wrapper(request: HttpRequest, user_profile: UserProfile, *args: object, **kwargs: object) -> HttpResponse:
        if not user_profile.has_billing_access:
            raise JsonableError(_("Must be a billing administrator or an organization owner"))
        return func(request, user_profile, *args, **kwargs)
    return cast(ViewFuncT, wrapper)  # https://github.com/python/mypy/issues/1927

def get_client_name(request: HttpRequest) -> str:
    # If the API request specified a client in the request content,
    # that has priority.  Otherwise, extract the client from the
    # User-Agent.
    if 'client' in request.GET:  # nocoverage
        return request.GET['client']
    if 'client' in request.POST:
        return request.POST['client']
    if "HTTP_USER_AGENT" in request.META:
        user_agent: Optional[Dict[str, str]] = parse_user_agent(request.META["HTTP_USER_AGENT"])
    else:
        user_agent = None
    if user_agent is not None:
        return user_agent["name"]

    # In the future, we will require setting USER_AGENT, but for
    # now we just want to tag these requests so we can review them
    # in logs and figure out the extent of the problem
    return "Unspecified"

def process_client(request: HttpRequest, user_profile: UserProfile,
                   *, is_browser_view: bool=False,
                   client_name: Optional[str]=None,
                   skip_update_user_activity: bool=False,
                   query: Optional[str]=None) -> None:
    if client_name is None:
        client_name = get_client_name(request)

    # We could check for a browser's name being "Mozilla", but
    # e.g. Opera and MobileSafari don't set that, and it seems
    # more robust to just key off whether it was a browser view
    if is_browser_view and not client_name.startswith("Zulip"):
        # Avoid changing the client string for browsers, but let
        # the Zulip desktop apps be themselves.
        client_name = "website"

    request.client = get_client(client_name)
    if not skip_update_user_activity and user_profile.is_authenticated:
        update_user_activity(request, user_profile, query)

class InvalidZulipServerError(JsonableError):
    code = ErrorCode.INVALID_ZULIP_SERVER
    data_fields = ['role']

    def __init__(self, role: str) -> None:
        self.role: str = role

    @staticmethod
    def msg_format() -> str:
        return "Zulip server auth failure: {role} is not registered"

class InvalidZulipServerKeyError(InvalidZulipServerError):
    @staticmethod
    def msg_format() -> str:
        return "Zulip server auth failure: key does not match role {role}"

def validate_api_key(request: HttpRequest, role: Optional[str],
                     api_key: str, allow_webhook_access: bool=False,
                     client_name: Optional[str]=None) -> Union[UserProfile, "RemoteZulipServer"]:
    # Remove whitespace to protect users from trivial errors.
    api_key = api_key.strip()
    if role is not None:
        role = role.strip()

    # If `role` doesn't look like an email, it might be a uuid.
    if settings.ZILENCER_ENABLED and role is not None and '@' not in role:
        try:
            remote_server = get_remote_server_by_uuid(role)
        except RemoteZulipServer.DoesNotExist:
            raise InvalidZulipServerError(role)
        if api_key != remote_server.api_key:
            raise InvalidZulipServerKeyError(role)

        if get_subdomain(request) != Realm.SUBDOMAIN_FOR_ROOT_DOMAIN:
            raise JsonableError(_("Invalid subdomain for push notifications bouncer"))
        request.user = remote_server
        remote_server.rate_limits = ""
        # Skip updating UserActivity, since remote_server isn't actually a UserProfile object.
        process_client(request, remote_server, skip_update_user_activity=True)
        return remote_server

    user_profile = access_user_by_api_key(request, api_key, email=role)
    if user_profile.is_incoming_webhook and not allow_webhook_access:
        raise JsonableError(_("This API is not available to incoming webhook bots."))

    request.user = user_profile
    process_client(request, user_profile, client_name=client_name)

    return user_profile

def validate_account_and_subdomain(request: HttpRequest, user_profile: UserProfile) -> None:
    if user_profile.realm.deactivated:
        raise JsonableError(_("This organization has been deactivated"))
    if not user_profile.is_active:
        raise JsonableError(_("Account is deactivated"))

    # Either the subdomain matches, or we're accessing Tornado from
    # and to localhost (aka spoofing a request as the user).
    if (not user_matches_subdomain(get_subdomain(request), user_profile) and
        not (settings.RUNNING_INSIDE_TORNADO and
             request.META["SERVER_NAME"] == "127.0.0.1" and
             request.META["REMOTE_ADDR"] == "127.0.0.1")):
        logging.warning(
            "User %s (%s) attempted to access API on wrong subdomain (%s)",
            user_profile.delivery_email, user_profile.realm.subdomain, get_subdomain(request),
        )
        raise JsonableError(_("Account is not associated with this subdomain"))

def access_user_by_api_key(request: HttpRequest, api_key: str, email: Optional[str]=None) -> UserProfile:
    if not has_api_key_format(api_key):
        raise InvalidAPIKeyFormatError()

    try:
        user_profile = get_user_profile_by_api_key(api_key)
    except UserProfile.DoesNotExist:
        raise InvalidAPIKeyError()
    if email is not None and email.lower() != user_profile.delivery_email.lower():
        # This covers the case that the API key is correct, but for a
        # different user.  We may end up wanting to relaxing this
        # constraint or give a different error message in the future.
        raise InvalidAPIKeyError()

    validate_account_and_subdomain(request, user_profile)

    return user_profile

def log_exception_to_webhook_logger(
    summary: str,
    unsupported_event: bool,
) -> None:
    if unsupported_event:
        webhook_unsupported_events_logger.exception(summary, stack_info=True)
    else:
        webhook_logger.exception(summary, stack_info=True)

def full_webhook_client_name(raw_client_name: Optional[str]=None) -> Optional[str]:
    if raw_client_name is None:
        return None
    return f"Zulip{raw_client_name}Webhook"

# Use this for webhook views that don't get an email passed in.
def webhook_view(
        webhook_client_name: str,
        notify_bot_owner_on_invalid_json: bool=True,
) -> Callable[[Callable[..., HttpResponse]], Callable[..., HttpResponse]]:
    # Unfortunately, callback protocols are insufficient for this:
    # https://mypy.readthedocs.io/en/stable/protocols.html#callback-protocols
    # Variadic generics are necessary: https://github.com/python/typing/issues/193
    def _wrapped_view_func(view_func: Callable[..., HttpResponse]) -> Callable[..., HttpResponse]:
        @csrf_exempt
        @has_request_variables
        @wraps(view_func)
        def _wrapped_func_arguments(request: HttpRequest, api_key: str=REQ(),
                                    *args: object, **kwargs: object) -> HttpResponse:
            user_profile = validate_api_key(request, None, api_key, allow_webhook_access=True,
                                            client_name=full_webhook_client_name(webhook_client_name))

            if settings.RATE_LIMITING:
                rate_limit_user(request, user_profile, domain='api_by_user')
            try:
                return view_func(request, user_profile, *args, **kwargs)
            except Exception as err:
                if isinstance(err, InvalidJSONError) and notify_bot_owner_on_invalid_json:
                    # NOTE: importing this at the top of file leads to a
                    # cyclic import; correct fix is probably to move
                    # notify_bot_owner_about_invalid_json to a smaller file.
                    from zerver.lib.webhooks.common import notify_bot_owner_about_invalid_json
                    notify_bot_owner_about_invalid_json(user_profile, webhook_client_name)
                elif isinstance(err, JsonableError) and not isinstance(err, UnsupportedWebhookEventType):
                    pass
                else:
                    if isinstance(err, UnsupportedWebhookEventType):
                        err.webhook_name = webhook_client_name
                    log_exception_to_webhook_logger(
                        summary=str(err),
                        unsupported_event=isinstance(err, UnsupportedWebhookEventType),
                    )
                raise err

        return _wrapped_func_arguments
    return _wrapped_view_func

# From Django 1.8, modified to leave off ?next=/
def redirect_to_login(next: str, login_url: Optional[str]=None,
                      redirect_field_name: str=REDIRECT_FIELD_NAME) -> HttpResponseRedirect:
    """
    Redirects the user to the login page, passing the given 'next' page
    """
    resolved_url = resolve_url(login_url or settings.LOGIN_URL)

    login_url_parts = list(urllib.parse.urlparse(resolved_url))
    if redirect_field_name:
        querystring = QueryDict(login_url_parts[4], mutable=True)
        querystring[redirect_field_name] = next
        # Don't add ?next=/, to keep our URLs clean
        if next != '/':
            login_url_parts[4] = querystring.urlencode(safe='/')

    return HttpResponseRedirect(urllib.parse.urlunparse(login_url_parts))

# From Django 2.2, modified to pass the request rather than just the
# user into test_func; this is useful so that we can revalidate the
# subdomain matches the user's realm.  It is likely that we could make
# the subdomain validation happen elsewhere and switch to using the
# stock Django version.
def user_passes_test(test_func: Callable[[HttpResponse], bool], login_url: Optional[str]=None,
                     redirect_field_name: str=REDIRECT_FIELD_NAME) -> Callable[[ViewFuncT], ViewFuncT]:
    """
    Decorator for views that checks that the user passes the given test,
    redirecting to the log-in page if necessary. The test should be a callable
    that takes the user object and returns True if the user passes.
    """
    def decorator(view_func: ViewFuncT) -> ViewFuncT:
        @wraps(view_func)
        def _wrapped_view(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
            if test_func(request):
                return view_func(request, *args, **kwargs)
            path = request.build_absolute_uri()
            resolved_login_url = resolve_url(login_url or settings.LOGIN_URL)
            # If the login URL is the same scheme and net location then just
            # use the path as the "next" url.
            login_scheme, login_netloc = urllib.parse.urlparse(resolved_login_url)[:2]
            current_scheme, current_netloc = urllib.parse.urlparse(path)[:2]
            if ((not login_scheme or login_scheme == current_scheme) and
                    (not login_netloc or login_netloc == current_netloc)):
                path = request.get_full_path()
            return redirect_to_login(
                path, resolved_login_url, redirect_field_name)
        return cast(ViewFuncT, _wrapped_view)  # https://github.com/python/mypy/issues/1927
    return decorator

def logged_in_and_active(request: HttpRequest) -> bool:
    if not request.user.is_authenticated:
        return False
    if not request.user.is_active:
        return False
    if request.user.realm.deactivated:
        return False
    return user_matches_subdomain(get_subdomain(request), request.user)

def do_two_factor_login(request: HttpRequest, user_profile: UserProfile) -> None:
    device = default_device(user_profile)
    if device:
        django_otp.login(request, device)

def do_login(request: HttpRequest, user_profile: UserProfile) -> None:
    """Creates a session, logging in the user, using the Django method,
    and also adds helpful data needed by our server logs.
    """
    django_login(request, user_profile)
    request._requestor_for_logs = user_profile.format_requestor_for_logs()
    process_client(request, user_profile, is_browser_view=True)
    if settings.TWO_FACTOR_AUTHENTICATION_ENABLED:
        # Login with two factor authentication as well.
        do_two_factor_login(request, user_profile)

def log_view_func(view_func: ViewFuncT) -> ViewFuncT:
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
        request._query = view_func.__name__
        return view_func(request, *args, **kwargs)
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

def add_logging_data(view_func: ViewFuncT) -> ViewFuncT:
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
        process_client(request, request.user, is_browser_view=True,
                       query=view_func.__name__)
        return rate_limit()(view_func)(request, *args, **kwargs)
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

def human_users_only(view_func: ViewFuncT) -> ViewFuncT:
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
        if request.user.is_bot:
            return json_error(_("This endpoint does not accept bot requests."))
        return view_func(request, *args, **kwargs)
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

# Based on Django 1.8's @login_required
def zulip_login_required(
        function: Optional[ViewFuncT]=None,
        redirect_field_name: str=REDIRECT_FIELD_NAME,
        login_url: str=settings.HOME_NOT_LOGGED_IN,
) -> Union[Callable[[ViewFuncT], ViewFuncT], ViewFuncT]:
    actual_decorator = lambda function: user_passes_test(
        logged_in_and_active,
        login_url=login_url,
        redirect_field_name=redirect_field_name,
    )(
        zulip_otp_required(
            redirect_field_name=redirect_field_name, login_url=login_url,
        )(add_logging_data(function))
    )

    if function:
        return actual_decorator(function)
    return actual_decorator  # nocoverage # We don't use this without a function

def require_server_admin(view_func: ViewFuncT) -> ViewFuncT:
    @zulip_login_required
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
        if not request.user.is_staff:
            return HttpResponseRedirect(settings.HOME_NOT_LOGGED_IN)

        return add_logging_data(view_func)(request, *args, **kwargs)
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

def require_server_admin_api(view_func: ViewFuncT) -> ViewFuncT:
    @zulip_login_required
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, user_profile: UserProfile, *args: object,
                           **kwargs: object) -> HttpResponse:
        if not user_profile.is_staff:
            raise JsonableError(_("Must be an server administrator"))
        return view_func(request, user_profile, *args, **kwargs)
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

def require_non_guest_user(view_func: ViewFuncT) -> ViewFuncT:
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, user_profile: UserProfile, *args: object,
                           **kwargs: object) -> HttpResponse:
        if user_profile.is_guest:
            raise JsonableError(_("Not allowed for guest users"))
        return view_func(request, user_profile, *args, **kwargs)
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

def require_member_or_admin(view_func: ViewFuncT) -> ViewFuncT:
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, user_profile: UserProfile, *args: object,
                           **kwargs: object) -> HttpResponse:
        if user_profile.is_guest:
            raise JsonableError(_("Not allowed for guest users"))
        if user_profile.is_bot:
            return json_error(_("This endpoint does not accept bot requests."))
        return view_func(request, user_profile, *args, **kwargs)
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

def require_user_group_edit_permission(view_func: ViewFuncT) -> ViewFuncT:
    @require_member_or_admin
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, user_profile: UserProfile,
                           *args: object, **kwargs: object) -> HttpResponse:
        realm = user_profile.realm
        if realm.user_group_edit_policy != Realm.USER_GROUP_EDIT_POLICY_MEMBERS and \
                not user_profile.is_realm_admin:
            raise OrganizationAdministratorRequired()
        return view_func(request, user_profile, *args, **kwargs)
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

# This API endpoint is used only for the mobile apps.  It is part of a
# workaround for the fact that React Native doesn't support setting
# HTTP basic authentication headers.
def authenticated_uploads_api_view(
    skip_rate_limiting: bool = False,
) -> Callable[[Callable[..., HttpResponse]], Callable[..., HttpResponse]]:
    def _wrapped_view_func(view_func: Callable[..., HttpResponse]) -> Callable[..., HttpResponse]:
        @csrf_exempt
        @has_request_variables
        @wraps(view_func)
        def _wrapped_func_arguments(request: HttpRequest,
                                    api_key: str=REQ(),
                                    *args: object, **kwargs: object) -> HttpResponse:
            user_profile = validate_api_key(request, None, api_key, False)
            if not skip_rate_limiting:
                limited_func = rate_limit()(view_func)
            else:
                limited_func = view_func
            return limited_func(request, user_profile, *args, **kwargs)
        return _wrapped_func_arguments
    return _wrapped_view_func

# A more REST-y authentication decorator, using, in particular, HTTP basic
# authentication.
#
# If webhook_client_name is specific, the request is a webhook view
# with that string as the basis for the client string.
def authenticated_rest_api_view(
    *,
    webhook_client_name: Optional[str] = None,
    allow_webhook_access: bool = False,
    skip_rate_limiting: bool = False,
) -> Callable[[Callable[..., HttpResponse]], Callable[..., HttpResponse]]:
    if webhook_client_name is not None:
        allow_webhook_access = True

    def _wrapped_view_func(view_func: Callable[..., HttpResponse]) -> Callable[..., HttpResponse]:
        @csrf_exempt
        @wraps(view_func)
        def _wrapped_func_arguments(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
            # First try block attempts to get the credentials we need to do authentication
            try:
                # Grab the base64-encoded authentication string, decode it, and split it into
                # the email and API key
                auth_type, credentials = request.META['HTTP_AUTHORIZATION'].split()
                # case insensitive per RFC 1945
                if auth_type.lower() != "basic":
                    return json_error(_("This endpoint requires HTTP basic authentication."))
                role, api_key = base64.b64decode(credentials).decode('utf-8').split(":")
            except ValueError:
                return json_unauthorized(_("Invalid authorization header for basic auth"))
            except KeyError:
                return json_unauthorized(_("Missing authorization header for basic auth"))

            # Now we try to do authentication or die
            try:
                # profile is a Union[UserProfile, RemoteZulipServer]
                profile = validate_api_key(request, role, api_key,
                                           allow_webhook_access=allow_webhook_access,
                                           client_name=full_webhook_client_name(webhook_client_name))
            except JsonableError as e:
                return json_unauthorized(e.msg)
            try:
                if not skip_rate_limiting:
                    # Apply rate limiting
                    target_view_func = rate_limit()(view_func)
                else:
                    target_view_func = view_func
                return target_view_func(request, profile, *args, **kwargs)
            except Exception as err:
                if not webhook_client_name:
                    raise err
                if isinstance(err, JsonableError) and not isinstance(err, UnsupportedWebhookEventType):  # nocoverage
                    raise err

                if isinstance(err, UnsupportedWebhookEventType):
                    err.webhook_name = webhook_client_name
                log_exception_to_webhook_logger(
                    summary=str(err),
                    unsupported_event=isinstance(err, UnsupportedWebhookEventType),
                )
                raise err
        return _wrapped_func_arguments
    return _wrapped_view_func

def process_as_post(view_func: ViewFuncT) -> ViewFuncT:
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
        # Adapted from django/http/__init__.py.
        # So by default Django doesn't populate request.POST for anything besides
        # POST requests. We want this dict populated for PATCH/PUT, so we have to
        # do it ourselves.
        #
        # This will not be required in the future, a bug will be filed against
        # Django upstream.

        if not request.POST:
            # Only take action if POST is empty.
            if request.META.get('CONTENT_TYPE', '').startswith('multipart'):
                # Note that request._files is just the private attribute that backs the
                # FILES property, so we are essentially setting request.FILES here.  (In
                # Django 1.5 FILES was still a read-only property.)
                request.POST, request._files = MultiPartParser(
                    request.META,
                    BytesIO(request.body),
                    request.upload_handlers,
                    request.encoding,
                ).parse()
            else:
                request.POST = QueryDict(request.body, encoding=request.encoding)

        return view_func(request, *args, **kwargs)

    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

def authenticate_log_and_execute_json(
    request: HttpRequest,
    view_func: ViewFuncT,
    *args: object,
    skip_rate_limiting: bool = False,
    allow_unauthenticated: bool = False,
    **kwargs: object,
) -> HttpResponse:
    if not skip_rate_limiting:
        limited_view_func = rate_limit()(view_func)
    else:
        limited_view_func = view_func

    if not request.user.is_authenticated:
        if not allow_unauthenticated:
            return json_unauthorized()

        process_client(request, request.user, is_browser_view=True,
                       skip_update_user_activity=True,
                       query=view_func.__name__)
        return limited_view_func(request, request.user, *args, **kwargs)

    user_profile = request.user
    validate_account_and_subdomain(request, user_profile)

    if user_profile.is_incoming_webhook:
        raise JsonableError(_("Webhook bots can only access webhooks"))

    process_client(request, user_profile, is_browser_view=True,
                   query=view_func.__name__)
    return limited_view_func(request, user_profile, *args, **kwargs)

# Checks if the user is logged in.  If not, return an error (the
# @login_required behavior of redirecting to a login page doesn't make
# sense for json views)
def authenticated_json_view(
    view_func: Callable[..., HttpResponse],
    skip_rate_limiting: bool = False,
    allow_unauthenticated: bool = False,
) -> Callable[..., HttpResponse]:
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest,
                           *args: object, **kwargs: object) -> HttpResponse:
        return authenticate_log_and_execute_json(
            request,
            view_func,
            *args,
            skip_rate_limiting=skip_rate_limiting,
            allow_unauthenticated=allow_unauthenticated,
            **kwargs,
        )
    return _wrapped_view_func

def is_local_addr(addr: str) -> bool:
    return addr in ('127.0.0.1', '::1')

# These views are used by the main Django server to notify the Tornado server
# of events.  We protect them from the outside world by checking a shared
# secret, and also the originating IP (for now).
def authenticate_notify(request: HttpRequest) -> bool:
    return (is_local_addr(request.META['REMOTE_ADDR']) and
            request.POST.get('secret') == settings.SHARED_SECRET)

def client_is_exempt_from_rate_limiting(request: HttpRequest) -> bool:

    # Don't rate limit requests from Django that come from our own servers,
    # and don't rate-limit dev instances
    return ((request.client and request.client.name.lower() == 'internal') and
            (is_local_addr(request.META['REMOTE_ADDR']) or
             settings.DEBUG_RATE_LIMITING))

def internal_notify_view(is_tornado_view: bool) -> Callable[[ViewFuncT], ViewFuncT]:
    # The typing here could be improved by using the Extended Callable types:
    # https://mypy.readthedocs.io/en/latest/kinds_of_types.html#extended-callable-types
    """Used for situations where something running on the Zulip server
    needs to make a request to the (other) Django/Tornado processes running on
    the server."""
    def _wrapped_view_func(view_func: ViewFuncT) -> ViewFuncT:
        @csrf_exempt
        @require_post
        @wraps(view_func)
        def _wrapped_func_arguments(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
            if not authenticate_notify(request):
                return json_error(_('Access denied'), status=403)
            is_tornado_request = hasattr(request, '_tornado_handler')
            # These next 2 are not security checks; they are internal
            # assertions to help us find bugs.
            if is_tornado_view and not is_tornado_request:
                raise RuntimeError('Tornado notify view called with no Tornado handler')
            if not is_tornado_view and is_tornado_request:
                raise RuntimeError('Django notify view called with Tornado handler')
            request._requestor_for_logs = "internal"
            return view_func(request, *args, **kwargs)
        return _wrapped_func_arguments
    return _wrapped_view_func

def to_utc_datetime(timestamp: str) -> datetime.datetime:
    return timestamp_to_datetime(float(timestamp))

def statsd_increment(counter: str, val: int=1) -> Callable[[FuncT], FuncT]:
    """Increments a statsd counter on completion of the
    decorated function.

    Pass the name of the counter to this decorator-returning function."""
    def wrapper(func: FuncT) -> FuncT:
        @wraps(func)
        def wrapped_func(*args: object, **kwargs: object) -> object:
            ret = func(*args, **kwargs)
            statsd.incr(counter, val)
            return ret
        return cast(FuncT, wrapped_func)  # https://github.com/python/mypy/issues/1927
    return wrapper

def rate_limit_user(request: HttpRequest, user: UserProfile, domain: str) -> None:
    """Returns whether or not a user was rate limited. Will raise a RateLimited exception
    if the user has been rate limited, otherwise returns and modifies request to contain
    the rate limit information"""

    RateLimitedUser(user, domain=domain).rate_limit_request(request)

def rate_limit(domain: str='api_by_user') -> Callable[[ViewFuncT], ViewFuncT]:
    """Rate-limits a view. Takes an optional 'domain' param if you wish to
    rate limit different types of API calls independently.

    Returns a decorator"""
    def wrapper(func: ViewFuncT) -> ViewFuncT:
        @wraps(func)
        def wrapped_func(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:

            # It is really tempting to not even wrap our original function
            # when settings.RATE_LIMITING is False, but it would make
            # for awkward unit testing in some situations.
            if not settings.RATE_LIMITING:
                return func(request, *args, **kwargs)

            if client_is_exempt_from_rate_limiting(request):
                return func(request, *args, **kwargs)

            user = request.user

            if isinstance(user, AnonymousUser) or (settings.ZILENCER_ENABLED and
                                                   isinstance(user, RemoteZulipServer)):
                # We can only rate-limit logged-in users for now.
                # We also only support rate-limiting authenticated
                # views right now.
                # TODO: implement per-IP non-authed rate limiting
                return func(request, *args, **kwargs)

            assert isinstance(user, UserProfile)
            rate_limit_user(request, user, domain)

            return func(request, *args, **kwargs)
        return cast(ViewFuncT, wrapped_func)  # https://github.com/python/mypy/issues/1927
    return wrapper

def return_success_on_head_request(view_func: ViewFuncT) -> ViewFuncT:
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
        if request.method == 'HEAD':
            return json_success()
        return view_func(request, *args, **kwargs)
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927

def zulip_otp_required(
    redirect_field_name: str='next',
    login_url: str=settings.HOME_NOT_LOGGED_IN,
) -> Callable[[ViewFuncT], ViewFuncT]:
    """
    The reason we need to create this function is that the stock
    otp_required decorator doesn't play well with tests. We cannot
    enable/disable if_configured parameter during tests since the decorator
    retains its value due to closure.

    Similar to :func:`~django.contrib.auth.decorators.login_required`, but
    requires the user to be :term:`verified`. By default, this redirects users
    to :setting:`OTP_LOGIN_URL`.
    """

    def test(user: UserProfile) -> bool:
        """
        :if_configured: If ``True``, an authenticated user with no confirmed
        OTP devices will be allowed. Also, non-authenticated users will be
        allowed as web_public_visitor users. Default is ``False``. If ``False``,
        2FA will not do any authentication.
        """
        if_configured = settings.TWO_FACTOR_AUTHENTICATION_ENABLED
        if not if_configured:
            return True

        # User has completed 2FA verification
        if user.is_verified():
            return True

        # This request is unauthenticated (logged-out) access; 2FA is
        # not required or possible.
        if not user.is_authenticated:  # nocoverage
            return True

        # If the user doesn't have 2FA set up, we can't enforce 2FA.
        if not user_has_device(user):
            return True

        # User has configured 2FA and is not verified, so the user
        # fails the test (and we should redirect to the 2FA view).
        return False

    decorator = django_user_passes_test(test,
                                        login_url=login_url,
                                        redirect_field_name=redirect_field_name)

    return decorator

def add_google_analytics_context(context: Dict[str, object]) -> None:
    if settings.GOOGLE_ANALYTICS_ID is not None:  # nocoverage
        page_params = context.setdefault("page_params", {})
        assert isinstance(page_params, dict)
        page_params["google_analytics_id"] = settings.GOOGLE_ANALYTICS_ID

def add_google_analytics(view_func: ViewFuncT) -> ViewFuncT:
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, *args: object, **kwargs: object) -> HttpResponse:
        response = view_func(request, *args, **kwargs)
        if isinstance(response, SimpleTemplateResponse):
            if response.context_data is None:
                response.context_data = {}
            add_google_analytics_context(response.context_data)
        elif response.status_code == 200:  # nocoverage
            raise TypeError("add_google_analytics requires a TemplateResponse")
        return response
    return cast(ViewFuncT, _wrapped_view_func)  # https://github.com/python/mypy/issues/1927