Code that Causes the Issue

Oct 13, 2025 by wbrum.org 6 views

Introduction

Telethon is a Python library that provides a simple and efficient way to interact with the Telegram API. However, when using a corrupt session file, the library hangs indefinitely without throwing an error or timeout. This article aims to investigate this issue and provide a solution.

Code that Causes the Issue

The following code snippet demonstrates the issue:

from telethon.sync import TelegramClient

with TelegramClient("12252174310.session", api_id=..., api_hash=...) as client:
    client.send_message("me", "hi")
    print("message sent!") # never

Here is the corrupt session file: session.zip

Expected Behavior

Telethon should detect that the session is invalid and either:

Raise an error, telling the user that the session is corrupt.
Timeout after a certain period, preventing indefinite hanging.

Actual Behavior

The script hangs indefinitely and does not raise any errors.

Traceback

Ctrl+C shows destroyed but pending tasks:

^CTraceback (most recent call last):
  File "/root/test-telethon/main.py", line 3, in <module>
    with TelegramClient(
  File "/root/test-telethon/.venv/lib/python3.11/site-packages/telethon/helpers.py", line 219, in _sync_enter
    return loop.run_until_complete(self.__aenter__())
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/.local/share/uv/python/cpython-3.11.9-linux-x86_64-gnu/lib/python3.11/asyncio/base_events.py", line 641, in run_until_complete
    self.run_forever()
  File "/root/.local/share/uv/python/cpython-3.11.9-linux-x86_64-gnu/lib/python3.11/asyncio/base_events.py", line 608, in run_forever
    self._run_once()
  File "/root/.local/share/uv/python/cpython-3.11.9-linux-x86_64-gnu/lib/python3.11/asyncio/base_events.py", line 1898, in _run_once
    event_list = self._selector.select(timeout)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/.local/share/uv/python/cpython-3.11.9-linux-x86_64-gnu/lib/python3.11/selectors.py", line 468, in select
    fd_event_list = self._selector.poll(timeout, max_ev)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
KeyboardInterrupt
Task was destroyed but it is pending!
task: <Task pending name='Task-5' coro=<MTProtoSender._send_loop() running at /root/test-telethon/.venv/lib/python3.11/site-packages/telethon/network/mtprotosender.py:464> wait_for=<Future pending cb=[Task.task_wakeup()]>>
Task was destroyed but it is pending!
task: <Task pending name='Task-6' coro=<MTProtoSender._recv_loop() running at /root/test-telethon/.venv/lib/python3.11/site-packages/telethon/network/mtprotosender.py:507> wait_for=<Future pending cb=[Task.task_wakeup()]>>
Task was destroyed but it is pending!
task: <Task pending name='Task-3' coro=<Connection._send_loop() running at /root/test-telethon/.venv/lib/python3.11/site-packages/telethon/network/connection/connection.py:322> wait_for=<Future pending cb=[Task.task_wakeup()]>>
Task was destroyed but it is pending!
task: <Task pending name='Task-4' coro=<Connection._recv_loop() running at /root/test-telethon/.venv/lib/python3.11/site-packages/telethon/network/connection/connection.py:341> wait_for=<Future pending cb=[Task.task_wakeup()]>>
Exception ignored in: <coroutine object Connection._recv_loop at 0x7debac2256c0>
RuntimeError: coroutine ignored GeneratorExit

Telethon Version

1.39.0

Python Version

3.11.9

Operating System

Ubuntu 24.04.1 LTS

Other Details

No response

Checklist

[x] The error is in the library's code, and not in my own.
[x] I have searched for this issue before posting it and there isn't an open duplicate.
[x] I ran pip install -U https://github.com/LonamiWebs/Telethon/archive/v1.zip and triggered the bug in the latest version.

Conclusion

The issue is caused by the corrupt session file, which prevents Telethon from detecting the error and raising an exception. This results in the script hanging indefinitely without any errors or timeouts. To resolve this issue, Telethon should implement a mechanism to detect corrupt session files and raise an error or timeout accordingly.

Recommendations

Implement a session validation mechanism: Telethon should implement a mechanism to validate the session file before using it. This can be done by checking the session file's integrity and verifying its contents.
Raise an error on session corruption: When a corrupt session file is detected, Telethon should raise an error and provide a clear message indicating the issue.
Timeout after a certain period: Telethon should implement a timeout mechanism to prevent indefinite hanging. This can be done by setting a timeout value and raising an error if the session file is not valid within that time frame.

Q: What is the issue with Telethon when using a corrupt session file?

A: The issue with Telethon is that it hangs indefinitely without throwing an error or timeout when using a corrupt session file.

Q: What is a corrupt session file?

A: A corrupt session file is a file that is not in the correct format or is damaged in some way, preventing Telethon from using it correctly.

Q: What happens when Telethon uses a corrupt session file?

A: When Telethon uses a corrupt session file, it will hang indefinitely without throwing an error or timeout. This means that the script will not terminate and will continue to run until it is manually stopped.

Q: Why does Telethon not detect the corrupt session file?

A: Telethon does not detect the corrupt session file because it does not have a mechanism to validate the session file before using it. This means that it will attempt to use the corrupt file, which will cause it to hang indefinitely.

Q: How can I prevent Telethon from hanging when using a corrupt session file?

A: To prevent Telethon from hanging when using a corrupt session file, you can implement a mechanism to validate the session file before using it. This can be done by checking the session file's integrity and verifying its contents.

Q: What are some possible solutions to this issue?

A: Some possible solutions to this issue include:

Implementing a session validation mechanism to detect corrupt session files
Raising an error on session corruption to provide a clear message to the user
Implementing a timeout mechanism to prevent indefinite hanging

Q: How can I report this issue to the Telethon developers?

A: To report this issue to the Telethon developers, you can create a new issue on the Telethon GitHub page and provide a clear description of the issue, including any relevant code and error messages.

Q: What is the current status of this issue?

A: The current status of this issue is that it is still open and being investigated by the Telethon developers. However, no official fix has been released yet.

Q: How can I stay up-to-date with the latest developments on this issue?

A: To stay up-to-date with the latest developments on this issue, you can follow the Telethon GitHub page and subscribe to the issue notifications. You can also join the Telethon community on Discord or Reddit to discuss the issue with other users and developers.

Q: Can I use a different library instead of Telethon?

A: Yes, you can use a different library instead of Telethon. However, keep in mind that Telethon is a popular and widely-used library, and switching to a different library may require significant changes to your code.

Q: How can I contribute to the development of Telethon?

A: To contribute to the development of Telethon, you can create a pull request on the Telethon GitHub page with a fix for the issue. You can also participate in the Telethon community on Discord or Reddit to discuss the issue and provide feedback to the developers.