[New-bugs-announce] [issue29054] pty.py: pty.spawn hangs after client disconnect over nc (netcat)

[Cornelius Diekmann]

New submission from Cornelius Diekmann:

My OS: Debian GNU/Linux 8.6 (jessie)
Python 3.4.2
pty.py from Python-3.5.2/Lib (pty.py is just a tiny, portable python file which did not see many changes)


Bug Report

Steps to Reproduce:

I wrote a very simple python remote shell:

#!/usr/bin/env python3
import pty
pty.spawn('/bin/sh')


It can be run in a terminal (call it TermA) with `nc -e ./myfancypythonremoteshell.py -l -p 6699`
In a different terminal (call it TermB), I connect to my fancy remote shell with `nc 127.0.0.1 6699`.
The shell works fine. In TermB, I quit by pressing ctrl+c.

Observed Behavior: In TermA, the nc process, the python process, and the spawned /bin/sh still exist. They still occupy TermA.

Expected Behavior: The client in TermB has disconnected, /bin/sh in TermA can no longer read anything from stdin and it should close down. Ultimately, in TermA, nc should have exited successfully.

Fix: End the _copy loop in pty.py once EOF in STDIN is reached. Everything shuts itself down automatically. I included a small patch to demonstrate this behavior.

This patch is not meant to go straight into production. I have not verified if this behavior somehow breaks other use cases. This bug report is meant to document exactly one specific use case and supply exactly one line of code change for it.

This issue is related to issue26228. Actually, it is complementary. issue26228 wants to return if master_fd is EOF, this issue wants to return if stdin is EOF. Both behaviors together looks good to me. By the way, I hacked a hacky `assert False` into my patch as a placeholder for issue26228's proper handling of exec failures at that part of the code.

I suggest to combine the patches of this issue and issue26228.

----------
components: Library (Lib)
files: pty.patch
keywords: patch
messages: 283880
nosy: Cornelius Diekmann, martin.panter
priority: normal
severity: normal
status: open
title: pty.py: pty.spawn hangs after client disconnect over nc (netcat)
type: enhancement
versions: Python 3.4, Python 3.5
Added file: http://bugs.python.org/file46006/pty.patch

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29054>
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