tornado: Use a machine-readable error code when an event queue is gone.

This fixes the original issue that #5598 was the root cause of; when
the user returns to a Zulip browser tab after they've been idle past
the timeout (10 min, per IDLE_EVENT_QUEUE_TIMEOUT_SECS), we now
correctly reload the page even if they're using Zulip in German or
another non-English language where we have a translation for the
relevant error message.

static/js/server_events.js

@@ -188,7 +188,7 @@ function get_events(options) {
                 // If we're old enough that our message queue has been
                 // garbage collected, immediately reload.
                 if ((xhr.status === 400) &&
-                    (JSON.parse(xhr.responseText).msg.indexOf("Bad event queue id") !== -1)) {
+                    (JSON.parse(xhr.responseText).code === 'BAD_EVENT_QUEUE_ID')) {
                     page_params.event_queue_expired = true;
                     reload.initiate({immediate: true,
                                      save_pointer: false,

zerver/lib/exceptions.py

@@ -35,6 +35,7 @@ class ErrorCode(AbstractEnum):
     QUOTA_EXCEEDED = ()
     BAD_NARROW = ()
     UNAUTHORIZED_PRINCIPAL = ()
+    BAD_EVENT_QUEUE_ID = ()
 
 class JsonableError(Exception):
     '''A standardized error format we can turn into a nice JSON HTTP response.

zerver/tornado/event_queue.py

@@ -33,6 +33,7 @@ from zerver.lib.queue import queue_json_publish
 from zerver.lib.request import JsonableError
 from zerver.lib.timestamp import timestamp_to_datetime
 from zerver.tornado.descriptors import clear_descriptor_by_handler_id, set_descriptor_by_handler_id
+from zerver.tornado.exceptions import BadEventQueueIdError
 import copy
 import six
 
@@ -513,7 +514,7 @@ def fetch_events(query):
                 raise JsonableError(_("Missing 'last_event_id' argument"))
             client = get_client_descriptor(queue_id)
             if client is None:
-                raise JsonableError(_("Bad event queue id: %s") % (queue_id,))
+                raise BadEventQueueIdError(queue_id)
             if user_profile_id != client.user_profile_id:
                 raise JsonableError(_("You are not authorized to get events from this queue"))
             client.event_queue.prune(last_event_id)

zerver/tornado/exceptions.py

@@ -0,0 +1,19 @@
+from __future__ import absolute_import
+from typing import Text
+
+from django.utils.translation import ugettext as _
+
+from zerver.lib.exceptions import JsonableError, ErrorCode
+
+class BadEventQueueIdError(JsonableError):
+    code = ErrorCode.BAD_EVENT_QUEUE_ID
+    data_fields = ['queue_id']
+
+    def __init__(self, queue_id):
+        # type: (Text) -> None
+        self.queue_id = queue_id  # type: Text
+
+    @staticmethod
+    def msg_format():
+        # type: () -> Text
+        return _("Bad event queue id: {queue_id}")

zerver/tornado/socket.py

@@ -31,6 +31,7 @@ from zerver.middleware import record_request_start_data, record_request_stop_dat
 from zerver.lib.redis_utils import get_redis_client
 from zerver.lib.sessions import get_session_user
 from zerver.tornado.event_queue import get_client_descriptor
+from zerver.tornado.exceptions import BadEventQueueIdError
 
 logger = logging.getLogger('zulip.socket')
 
@@ -137,7 +138,7 @@ class SocketConnection(sockjs.tornado.SockJSConnection):
         queue_id = msg['request']['queue_id']
         client = get_client_descriptor(queue_id)
         if client is None:
-            raise JsonableError(_('Bad event queue id: %s') % (queue_id,))
+            raise BadEventQueueIdError(queue_id)
 
         if user_profile.id != client.user_profile_id:
             raise JsonableError(_("You are not the owner of the queue with id '%s'") % (queue_id,))

zerver/tornado/views.py

@@ -13,6 +13,7 @@ from zerver.lib.response import json_success, json_error, json_response_from_err
 from zerver.lib.validator import check_bool, check_list, check_string
 from zerver.tornado.event_queue import get_client_descriptor, \
     process_notification, fetch_events
+from zerver.tornado.exceptions import BadEventQueueIdError
 from django.core.handlers.base import BaseHandler
 
 from typing import Union, Optional, Iterable, Sequence, List, Text
@@ -30,7 +31,7 @@ def cleanup_event_queue(request, user_profile, queue_id=REQ()):
     # type: (HttpRequest, UserProfile, Text) -> HttpResponse
     client = get_client_descriptor(str(queue_id))
     if client is None:
-        return json_error(_("Bad event queue id: %s") % (queue_id,))
+        return json_response_from_error(BadEventQueueIdError(queue_id))
     if user_profile.id != client.user_profile_id:
         return json_error(_("You are not authorized to access this queue"))
     request._log_data['extra'] = "[%s]" % (queue_id,)