From eb872b5bcdb8ba7b7f9ea4ea5c3a30e6c1330ca2 Mon Sep 17 00:00:00 2001
From: Alex Vandiver <alexmv@zulip.com>
Date: Tue, 11 Jan 2022 13:39:17 -0800
Subject: [PATCH] actions: Use check_stream_topic when editing message topics.

---
 zerver/lib/actions.py             |  6 +++---
 zerver/tests/test_message_edit.py | 16 +++++++++++++++-
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/zerver/lib/actions.py b/zerver/lib/actions.py
index ee4b639339..1e9b0198ec 100644
--- a/zerver/lib/actions.py
+++ b/zerver/lib/actions.py
@@ -155,7 +155,7 @@ from zerver.lib.streams import (
     send_stream_creation_event,
     subscribed_to_stream,
 )
-from zerver.lib.string_validation import check_stream_name
+from zerver.lib.string_validation import check_stream_name, check_stream_topic
 from zerver.lib.timestamp import datetime_to_timestamp, timestamp_to_datetime
 from zerver.lib.timezone import canonicalize_timezone
 from zerver.lib.topic import (
@@ -2975,8 +2975,8 @@ def validate_message_edit_payload(
     if propagate_mode != "change_one" and topic_name is None and stream_id is None:
         raise JsonableError(_("Invalid propagate_mode without topic edit"))
 
-    if topic_name == "":
-        raise JsonableError(_("Topic can't be empty"))
+    if topic_name is not None:
+        check_stream_topic(topic_name)
 
     if stream_id is not None and content is not None:
         raise JsonableError(_("Cannot change message content while changing stream"))
diff --git a/zerver/tests/test_message_edit.py b/zerver/tests/test_message_edit.py
index df15cd6b45..95a389df3c 100644
--- a/zerver/tests/test_message_edit.py
+++ b/zerver/tests/test_message_edit.py
@@ -192,7 +192,21 @@ class EditMessagePayloadTest(EditMessageTestCase):
                 "topic": " ",
             },
         )
-        self.assert_json_error(result, "Topic can't be empty")
+        self.assert_json_error(result, "Topic can't be empty!")
+
+    def test_edit_message_invalid_topic(self) -> None:
+        self.login("hamlet")
+        msg_id = self.send_stream_message(
+            self.example_user("hamlet"), "Denmark", topic_name="editing", content="before edit"
+        )
+        result = self.client_patch(
+            "/json/messages/" + str(msg_id),
+            {
+                "message_id": msg_id,
+                "topic": "editing\nfun",
+            },
+        )
+        self.assert_json_error(result, "Invalid characters in topic!")
 
     def test_move_message_to_stream_with_content(self) -> None:
         (user_profile, old_stream, new_stream, msg_id, msg_id_later) = self.prepare_move_topics(