stream settings: Fix server error on long stream description.

Add backend validations to check stream description length.

zerver/models.py

@@ -935,6 +935,7 @@ def generate_email_token_for_stream() -> str:
 
 class Stream(models.Model):
     MAX_NAME_LENGTH = 60
+    MAX_DESCRIPTION_LENGTH = 1024
     name = models.CharField(max_length=MAX_NAME_LENGTH, db_index=True)  # type: Text
     realm = models.ForeignKey(Realm, db_index=True, on_delete=CASCADE)  # type: Realm
     invite_only = models.NullBooleanField(default=False)  # type: Optional[bool]
@@ -955,7 +956,7 @@ class Stream(models.Model):
     # have plenty of room for the token.
     email_token = models.CharField(
         max_length=32, default=generate_email_token_for_stream)  # type: str
-    description = models.CharField(max_length=1024, default=u'')  # type: Text
+    description = models.CharField(max_length=MAX_DESCRIPTION_LENGTH, default=u'')  # type: Text
 
     date_created = models.DateTimeField(default=timezone_now)  # type: datetime.datetime
     deactivated = models.BooleanField(default=False)  # type: bool

zerver/tests/test_subs.py

@@ -610,12 +610,11 @@ class StreamAdminTest(ZulipTestCase):
         self.assert_json_error(result, "Invalid stream id")
 
     def test_change_stream_description(self) -> None:
-        user_profile = self.example_user('hamlet')
+        user_profile = self.example_user('iago')
         email = user_profile.email
         self.login(email)
         realm = user_profile.realm
         self.subscribe(user_profile, 'stream_name1')
-        do_change_is_admin(user_profile, True)
 
         events = []  # type: List[Mapping[str, Any]]
         with tornado_redirected_to_list(events):
@@ -644,6 +643,11 @@ class StreamAdminTest(ZulipTestCase):
 
         self.assertEqual('Test description', stream.description)
 
+        result = self.client_patch('/json/streams/%d' % (stream_id,),
+                                   {'description': ujson.dumps('a' * 1025)})
+        self.assert_json_error(result, "description is too long (limit: %s characters)."
+                               % (Stream.MAX_DESCRIPTION_LENGTH))
+
     def test_change_stream_description_requires_realm_admin(self) -> None:
         user_profile = self.example_user('hamlet')
         email = user_profile.email

zerver/views/streams.py

@@ -27,7 +27,7 @@ from zerver.lib.streams import access_stream_by_id, access_stream_by_name, \
     check_stream_name, check_stream_name_available, filter_stream_authorization, \
     list_to_streams, access_stream_for_delete_or_update, access_default_stream_group_by_id
 from zerver.lib.validator import check_string, check_int, check_list, check_dict, \
-    check_bool, check_variable_type
+    check_bool, check_variable_type, check_capped_string
 from zerver.models import UserProfile, Stream, Realm, Subscription, \
     Recipient, get_recipient, get_stream, \
     get_system_bot, get_user
@@ -144,7 +144,8 @@ def remove_default_stream(request: HttpRequest,
 def update_stream_backend(
         request: HttpRequest, user_profile: UserProfile,
         stream_id: int,
-        description: Optional[str]=REQ(validator=check_string, default=None),
+        description: Optional[str]=REQ(validator=check_capped_string(
+            Stream.MAX_DESCRIPTION_LENGTH), default=None),
         is_private: Optional[bool]=REQ(validator=check_bool, default=None),
         history_public_to_subscribers: Optional[bool]=REQ(validator=check_bool, default=None),
         new_name: Optional[str]=REQ(validator=check_string, default=None),