settings: Make `MAX_MESSAGE_LENGTH` a server-level setting.

This will offer users who are self-hosting to adjust
this value. Moreover, this will help to reduce the
overall time taken to test `test_markdown.py` (since
this can be now overridden with `override_settings`
Django decorator).

This is done as a prep commit for #18641.

zerver/lib/actions.py

@@ -187,7 +187,6 @@ from zerver.lib.utils import generate_api_key, log_statsd_event
 from zerver.lib.validator import check_widget_content
 from zerver.lib.widget import do_widget_post_save_actions, is_widget_message
 from zerver.models import (
-    MAX_MESSAGE_LENGTH,
     Attachment,
     Client,
     CustomProfileField,
@@ -3197,7 +3196,7 @@ def _internal_prep_message(
     Call do_send_messages with a list of the return values of this method.
     """
     # Remove any null bytes from the content
-    if len(content) > MAX_MESSAGE_LENGTH:
+    if len(content) > settings.MAX_MESSAGE_LENGTH:
         content = content[0:3900] + "\n\n[message was too long and has been truncated]"
 
     # If we have a stream name, and the stream doesn't exist, we

zerver/lib/events.py

@@ -50,7 +50,6 @@ from zerver.lib.user_mutes import get_user_mutes
 from zerver.lib.user_status import get_user_info_dict
 from zerver.lib.users import get_cross_realm_dicts, get_raw_user_data, is_administrator_role
 from zerver.models import (
-    MAX_MESSAGE_LENGTH,
     MAX_TOPIC_NAME_LENGTH,
     Client,
     CustomProfileField,
@@ -300,7 +299,7 @@ def fetch_initial_state_data(
         state["max_stream_name_length"] = Stream.MAX_NAME_LENGTH
         state["max_stream_description_length"] = Stream.MAX_DESCRIPTION_LENGTH
         state["max_topic_length"] = MAX_TOPIC_NAME_LENGTH
-        state["max_message_length"] = MAX_MESSAGE_LENGTH
+        state["max_message_length"] = settings.MAX_MESSAGE_LENGTH
 
     if want("realm_domains"):
         state["realm_domains"] = get_realm_domains(realm)

zerver/lib/markdown/__init__.py

@@ -62,7 +62,6 @@ from zerver.lib.types import LinkifierDict
 from zerver.lib.url_encoding import encode_stream, hash_util_encode
 from zerver.lib.url_preview import preview as link_preview
 from zerver.models import (
-    MAX_MESSAGE_LENGTH,
     Message,
     Realm,
     UserGroup,
@@ -2612,6 +2611,7 @@ def do_convert(
         # Throw an exception if the content is huge; this protects the
         # rest of the codebase from any bugs where we end up rendering
         # something huge.
+        MAX_MESSAGE_LENGTH = settings.MAX_MESSAGE_LENGTH
         if len(rendered_content) > MAX_MESSAGE_LENGTH * 10:
             raise MarkdownRenderingException(
                 f"Rendered content exceeds {MAX_MESSAGE_LENGTH * 10} characters (message {logging_message_id})"

zerver/lib/message.py

@@ -6,6 +6,7 @@ from typing import Any, Dict, List, Optional, Sequence, Set, Tuple
 
 import ahocorasick
 import orjson
+from django.conf import settings
 from django.db import connection
 from django.db.models import Max, Sum
 from django.utils.timezone import now as timezone_now
@@ -38,7 +39,6 @@ from zerver.lib.timestamp import datetime_to_timestamp
 from zerver.lib.topic import DB_TOPIC_NAME, MESSAGE__TOPIC, TOPIC_LINKS, TOPIC_NAME
 from zerver.lib.topic_mutes import build_topic_mute_checker, topic_is_muted
 from zerver.models import (
-    MAX_MESSAGE_LENGTH,
     MAX_TOPIC_NAME_LENGTH,
     Message,
     Reaction,
@@ -129,7 +129,7 @@ def normalize_body(body: str) -> str:
         raise JsonableError(_("Message must not be empty"))
     if "\x00" in body:
         raise JsonableError(_("Message must not contain null bytes"))
-    return truncate_content(body, MAX_MESSAGE_LENGTH, "\n[message truncated]")
+    return truncate_content(body, settings.MAX_MESSAGE_LENGTH, "\n[message truncated]")
 
 
 def truncate_topic(topic: str) -> str:

zerver/models.py

@@ -90,7 +90,6 @@ from zerver.lib.validator import (
 )
 
 MAX_TOPIC_NAME_LENGTH = 60
-MAX_MESSAGE_LENGTH = 10000
 MAX_LANGUAGE_ID_LENGTH: int = 50
 
 STREAM_NAMES = TypeVar("STREAM_NAMES", Sequence[str], AbstractSet[str])

zerver/tests/test_markdown.py

@@ -48,7 +48,6 @@ from zerver.lib.test_classes import ZulipTestCase
 from zerver.lib.tex import render_tex
 from zerver.lib.user_groups import create_user_group
 from zerver.models import (
-    MAX_MESSAGE_LENGTH,
     Message,
     RealmEmoji,
     RealmFilter,
@@ -2748,10 +2747,11 @@ class MarkdownErrorTests(ZulipTestCase):
             with self.assertRaises(JsonableError):
                 self.send_stream_message(self.example_user("othello"), "Denmark", message)
 
+    @override_settings(MAX_MESSAGE_LENGTH=10)
     def test_ultra_long_rendering(self) -> None:
         """A rendered message with an ultra-long length (> 10 * MAX_MESSAGE_LENGTH)
         throws an exception"""
-        msg = "mock rendered message\n" * MAX_MESSAGE_LENGTH
+        msg = "mock rendered message\n" * settings.MAX_MESSAGE_LENGTH
 
         with mock.patch("zerver.lib.markdown.timeout", return_value=msg), mock.patch(
             "zerver.lib.markdown.markdown_logger"

zerver/tests/test_message_send.py

@@ -48,7 +48,6 @@ from zerver.lib.test_helpers import (
 )
 from zerver.lib.timestamp import convert_to_UTC, datetime_to_timestamp
 from zerver.models import (
-    MAX_MESSAGE_LENGTH,
     MAX_TOPIC_NAME_LENGTH,
     Message,
     Realm,
@@ -900,12 +899,14 @@ class MessagePOSTTest(ZulipTestCase):
         sent_message = self.get_last_message()
         self.assertEqual(sent_message.content, "  I like whitespace at the end!")
 
+    @override_settings(MAX_MESSAGE_LENGTH=25)
     def test_long_message(self) -> None:
         """
         Sending a message longer than the maximum message length succeeds but is
         truncated.
         """
         self.login("hamlet")
+        MAX_MESSAGE_LENGTH = settings.MAX_MESSAGE_LENGTH
         long_message = "A" * (MAX_MESSAGE_LENGTH + 1)
         post_data = {
             "type": "stream",

zproject/default_settings.py

@@ -452,3 +452,8 @@ SERVER_UPGRADE_NAG_DEADLINE_DAYS = 30 * 18
 
 # How long servers have to respond to outgoing webhook requests
 OUTGOING_WEBHOOK_TIMEOUT_SECONDS = 10
+
+# Maximum length of message content allowed.
+# Any message content exceeding this limit will be truncated.
+# See: `_internal_prep_message` function in zerver/lib/actions.py.
+MAX_MESSAGE_LENGTH = 10000