zulip/zerver/lib/rest.py

from functools import wraps
from typing import Any, Callable, Dict

from django.utils.module_loading import import_string
from django.utils.cache import add_never_cache_headers
from django.views.decorators.csrf import csrf_exempt, csrf_protect

from zerver.decorator import authenticated_json_view, authenticated_rest_api_view, \
    process_as_post, authenticated_uploads_api_view, RespondAsynchronously, \
    ReturnT
from zerver.lib.response import json_method_not_allowed, json_unauthorized
from django.http import HttpRequest, HttpResponse, HttpResponseRedirect
from django.conf import settings

METHODS = ('GET', 'HEAD', 'POST', 'PUT', 'DELETE', 'PATCH')
FLAGS = ('override_api_url_scheme')

def default_never_cache_responses(
        view_func: Callable[..., HttpResponse]) -> Callable[..., HttpResponse]:
    """Patched version of the standard Django never_cache_responses
    decorator that adds headers to a response so that it will never be
    cached, unless the view code has already set a Cache-Control
    header.

    We also need to patch this because our Django+Tornado
    RespondAsynchronously hack involves returning a value that isn't a
    Django response object, on which add_never_cache_headers would
    crash.  This only occurs in a case where client-side caching
    wouldn't be possible anyway (we aren't returning a response to the
    client yet -- it's for longpolling).
    """
    @wraps(view_func)
    def _wrapped_view_func(request: HttpRequest, *args: Any, **kwargs: Any) -> ReturnT:
        response = view_func(request, *args, **kwargs)
        if response is RespondAsynchronously or response.has_header("Cache-Control"):
            return response

        add_never_cache_headers(response)
        return response
    return _wrapped_view_func

@default_never_cache_responses
@csrf_exempt
def rest_dispatch(request: HttpRequest, **kwargs: Any) -> HttpResponse:
    """Dispatch to a REST API endpoint.

    Unauthenticated endpoints should not use this, as authentication is verified
    in the following ways:
        * for paths beginning with /api, HTTP Basic auth
        * for paths beginning with /json (used by the web client), the session token

    This calls the function named in kwargs[request.method], if that request
    method is supported, and after wrapping that function to:

        * protect against CSRF (if the user is already authenticated through
          a Django session)
        * authenticate via an API key (otherwise)
        * coerce PUT/PATCH/DELETE into having POST-like semantics for
          retrieving variables

    Any keyword args that are *not* HTTP methods are passed through to the
    target function.

    Never make a urls.py pattern put user input into a variable called GET, POST,
    etc, as that is where we route HTTP verbs to target functions.
    """
    supported_methods = {}  # type: Dict[str, Any]

    # duplicate kwargs so we can mutate the original as we go
    for arg in list(kwargs):
        if arg in METHODS:
            supported_methods[arg] = kwargs[arg]
            del kwargs[arg]

    if 'GET' in supported_methods:
        supported_methods.setdefault('HEAD', supported_methods['GET'])

    if request.method == 'OPTIONS':
        response = HttpResponse(status=204)  # No content
        response['Allow'] = ', '.join(sorted(supported_methods.keys()))
        return response

    # Override requested method if magic method=??? parameter exists
    method_to_use = request.method
    if request.POST and 'method' in request.POST:
        method_to_use = request.POST['method']

    if method_to_use in supported_methods:
        entry = supported_methods[method_to_use]
        if isinstance(entry, tuple):
            target_function, view_flags = entry
            target_function = import_string(target_function)
        else:
            target_function = import_string(supported_methods[method_to_use])
            view_flags = set()

        # Set request._query for update_activity_user(), which is called
        # by some of the later wrappers.
        request._query = target_function.__name__

        # We want to support authentication by both cookies (web client)
        # and API keys (API clients). In the former case, we want to
        # do a check to ensure that CSRF etc is honored, but in the latter
        # we can skip all of that.
        #
        # Security implications of this portion of the code are minimal,
        # as we should worst-case fail closed if we miscategorise a request.

        # for some special views (e.g. serving a file that has been
        # uploaded), we support using the same url for web and API clients.
        if ('override_api_url_scheme' in view_flags and
                request.META.get('HTTP_AUTHORIZATION', None) is not None):
            # This request uses standard API based authentication.
            # For override_api_url_scheme views, we skip our normal
            # rate limiting, because there are good reasons clients
            # might need to (e.g.) request a large number of uploaded
            # files or avatars in quick succession.
            target_function = authenticated_rest_api_view(skip_rate_limiting=True)(target_function)
        elif ('override_api_url_scheme' in view_flags and
              request.GET.get('api_key') is not None):
            # This request uses legacy API authentication.  We
            # unfortunately need that in the React Native mobile apps,
            # because there's no way to set HTTP_AUTHORIZATION in
            # React Native.  See last block for rate limiting notes.
            target_function = authenticated_uploads_api_view(skip_rate_limiting=True)(target_function)
        # /json views (web client) validate with a session token (cookie)
        elif not request.path.startswith("/api") and request.user.is_authenticated:
            # Authenticated via sessions framework, only CSRF check needed
            auth_kwargs = {}
            if 'override_api_url_scheme' in view_flags:
                auth_kwargs["skip_rate_limiting"] = True
            target_function = csrf_protect(authenticated_json_view(target_function, **auth_kwargs))

        # most clients (mobile, bots, etc) use HTTP Basic Auth and REST calls, where instead of
        # username:password, we use email:apiKey
        elif request.META.get('HTTP_AUTHORIZATION', None):
            # Wrap function with decorator to authenticate the user before
            # proceeding
            view_kwargs = {}
            if 'allow_incoming_webhooks' in view_flags:
                view_kwargs['is_webhook'] = True
            target_function = authenticated_rest_api_view(**view_kwargs)(target_function)  # type: ignore # likely mypy bug
        # Pick a way to tell user they're not authed based on how the request was made
        else:
            # If this looks like a request from a top-level page in a
            # browser, send the user to the login page
            if 'text/html' in request.META.get('HTTP_ACCEPT', ''):
                # TODO: It seems like the `?next=` part is unlikely to be helpful
                return HttpResponseRedirect('%s?next=%s' % (settings.HOME_NOT_LOGGED_IN, request.path))
            # Ask for basic auth (email:apiKey)
            elif request.path.startswith("/api"):
                return json_unauthorized()
            # Logged out user accessing an endpoint with anonymous user access on JSON; proceed.
            elif request.path.startswith("/json") and 'allow_anonymous_user_web' in view_flags:
                auth_kwargs = dict(allow_unauthenticated=True)
                target_function = csrf_protect(authenticated_json_view(
                    target_function, **auth_kwargs))
            # Session cookie expired, notify the client
            else:
                return json_unauthorized(www_authenticate='session')

        if request.method not in ["GET", "POST"]:
            # process_as_post needs to be the outer decorator, because
            # otherwise we might access and thus cache a value for
            # request.REQUEST.
            target_function = process_as_post(target_function)

        return target_function(request, **kwargs)

    return json_method_not_allowed(list(supported_methods.keys()))