From 82a24d6b531519bcd212fb547b8dbe7fbed31797 Mon Sep 17 00:00:00 2001
From: marfer <amarfey@gmail.com>
Date: Sun, 21 Sep 2025 17:43:34 +0200
Subject: [PATCH] Correct handling of trailing zeros in _rle_encode (#4702)

---
 telethon/utils.py            | 2 ++
 tests/telethon/test_utils.py | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/telethon/utils.py b/telethon/utils.py
index d570f8cb..9e71ef7d 100644
--- a/telethon/utils.py
+++ b/telethon/utils.py
@@ -1095,6 +1095,8 @@ def _rle_encode(string):
                 count = 0
 
             new += bytes([cur])
+    if count != 0:
+        new += b'\0' + bytes([count])
     return new
 
 
diff --git a/tests/telethon/test_utils.py b/tests/telethon/test_utils.py
index 99a46efb..f1ab33e9 100644
--- a/tests/telethon/test_utils.py
+++ b/tests/telethon/test_utils.py
@@ -52,3 +52,7 @@ def test_private_get_extension():
     assert utils._get_extension(empty_buffer) == ''
     assert utils._get_extension(empty_buffer) == ''  # make sure it did seek back
     assert utils._get_extension(CustomFd('foo')) == ''
+
+
+def test_rle_encode_trailing_zeros():
+    assert utils._rle_encode(b'\x12\x00\x00\x00\x00') == b'\x12\x00\x04'