New submission from San <[email protected]>:
I was trying to wrap an old game server executable with a built-in console
using Popen.
class ServerWrapper(Thread):
def __init__(self, pathToExecutable: str, statusMonitor: Popen = None,
active: bool = False):
super().__init__()
self.pathToExecutable = pathToExecutable
self.statusMonitor = statusMonitor
self.active = active
def run(self):
self.statusMonitor = Popen(['./bf1942_lnxded', "+statusMonitor", '1'],
encoding='latin_1', stdout=PIPE,
stdin=PIPE, cwd=self.pathToExecutable)
while self.active:
currentLine = self.statusMonitor.stdout.readline()
if currentLine:
print(currentLine)
input('')
def start(self):
self.active = True
super().start()
def stop(self):
self.active = False
I expected to be able to read the output line-by-line using enter, in a 'normal
fashion'.
After importing this from a terminal and setting it up somewhat like so:
wrapper = ServerWrapper('bf1942')
wrapper.start()
However, once the server process started and thereby started writing to stdout,
weird stuff started to happen to my shell with the python interpreter.
Apparently, there are control characters and ansi-escape codes sent from the
process, that somehow manage to manipulate my shell if I specify an encoding.
Consequentially the lines output with 'print(currentLine)' are reduced by these
chars.
Is this the desired behaviour of the decoder? If so then I think this should
potentially be further clarified in the documentation of Popen. I would have
expected the chars to be escaped because the worst thing is, this happens even
if you don't actually read from stdout at all. Seemingly the decoder executes
incoming control sequences immediately (probably for the buffer?), regardless
of if you actually bother to read the stdout or not.
The paragraph in
https://docs.python.org/3.7/library/subprocess.html#security-considerations
sounds like this shouldn't be happening if 'shell' is not set to 'True' at
least.
----------
files: shell.png
messages: 397986
nosy: San
priority: normal
severity: normal
status: open
title: [3.7] Popen Control Characters in stdout affect shell session
versions: Python 3.7
Added file: https://bugs.python.org/file50170/shell.png
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Python tracker <[email protected]>
<https://bugs.python.org/issue44709>
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