[issue43348] XMLRPC behaves strangely under pythonw, not under python

[Tim Magee]

Tim Magee  added the comment:

After a peep at the source I theorised that using logRequests=False when 
constructing the base class, SimpleXMLRPCServer. would see me right, and so it 
did.

When logRequests is True control ultimately passes to 
BaseHTTPRequestHandler.log_message which is a write to sys.stderr, meaning the 
code is unsuitable for running under pythonw.

This might be a special sort of https://bugs.python.org/issue38533 -- special 
because the code that offends pythonw is in the library.

Anyhow, now I know what the problem is I can work round it, and I'll leave it 
to you what to do with the ticket.

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[issue43348] XMLRPC behaves strangely under pythonw, not under python

[Tim Magee]

Tim Magee  added the comment:

Fragment more info.  First a typo in the description, at the end of the MTR 
"unexpected connection" should read "unexpected disconnection" of course 
(no-one expects the unexpected connection ho ho).

Looking at calls to socket functions, Procmon shows the client repeating the 
call to a server running in pythonw.exe. It seems as though the client is 
instigating the badness, but...

In a Wireshark capture each of the two sessions the client holds with that 
'bad' server is identical, and the difference between each of those and the 
'good' session (with the server in python.exe) is that the server under pythonw 
doesn't return a methodResponse packet, but instead begins tearing down the 
connection.  Which is what the exception message says, but it's still startling 
to see it actually happening.

I'll have a squint at the source.

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[issue43348] XMLRPC behaves strangely under pythonw, not under python

[Tim Magee]

New submission from Tim Magee :

Summary: I run a SimpleXMLRPCServer in pythonw. When I call an exposed function 
the call appears to be made twice and the connection ends abnormally.

This is Python 3.8.3 Windows 64-bit, with the pywin32 additions, and under 
Windows 7. Boo, hiss, I know -- I won't have access to a win10 machine for a 
week or so, but I get the impression that that won't affect this behaviour, and 
the post-3.8.3 changelog doesn't have anything that (to me) looks relevant in 
it.

I've made a small reproduction that will run on one Windows machine.
You need two small source files (see below):
  * demosrv.py - the server
  * democli.py - the client
The method, in a CMD window:
  * run: start "demosrv" python demosrv.py
[ runs in its own console window ]
  * run: python democli.py
[ one instance of notepad appears and the client exits normally ]
  * Ctrl+C in the demosrv window to stop that
  * run: pythonw demosrv.py
[ runs in background ]
  * run: python democli.py
[ TWO notepad instances pop up ]
[ the client crashes with an unexpected connection ]
I've pasted in the two files and an example session below.

This is very much cut-down from the original.  Before deciding to submit I used 
logging at the top of the exposed function, which appeared to show it being 
called twice.  Logging immediately before the call in the client showed only 
one call.

Thanks,
Tim

#--8< demosrv.py 8<--
from xmlrpc.server import SimpleXMLRPCServer
from subprocess import Popen, DEVNULL

def notepad_me():
try:
cmd = ['c:\\windows\\notepad.exe']
p = Popen(cmd, stdin=DEVNULL, stdout=DEVNULL, stderr=DEVNULL)
return True
except Exception as e:
return False

class NetServer(SimpleXMLRPCServer):
def __init__(self, address):
super(NetServer, self).__init__(address)
self.register_introspection_functions()
self.register_function(notepad_me)

with NetServer(("0.0.0.0", )) as server:
server.serve_forever()

#---8< democli.py 8<-
import sys
from xmlrpc.client import ServerProxy, Error

def go():
try:
with ServerProxy("http://localhost:/";) as proxy:
if proxy.notepad_me():
return 0
except Error as e:
pass
return 1
sys.exit(go())
#
d:\temp\demo>REM Run the server under python.exe

d:\temp\demo>start "demosrv" python demosrv.py
d:\temp\demo>python democli.py

d:\temp\demo>REM That ran up one instance of notepad
d:\temp\demo>REM Ctrl+C to break out the running demosrv.py

d:\temp\demo>pythonw demosrv.py
d:\temp\demo>REM that runs in the background

d:\temp\demo>python democli.py
Traceback (most recent call last):
  File "democli.py", line 13, in 
sys.exit(go())
  File "democli.py", line 7, in go
if proxy.notepad_me():
  File "C:\Python\lib\xmlrpc\client.py", line 1109, in __call__
return self.__send(self.__name, args)
  File "C:\Python\lib\xmlrpc\client.py", line 1450, in __request
response = self.__transport.request(
  File "C:\Python\lib\xmlrpc\client.py", line 1153, in request
return self.single_request(host, handler, request_body, verbose)
  File "C:\Python\lib\xmlrpc\client.py", line 1166, in single_request
resp = http_conn.getresponse()
  File "C:\Python\lib\http\client.py", line 1332, in getresponse
response.begin()
  File "C:\Python\lib\http\client.py", line 303, in begin
version, status, reason = self._read_status()
  File "C:\Python\lib\http\client.py", line 272, in _read_status
raise RemoteDisconnected("Remote end closed connection without"
http.client.RemoteDisconnected: Remote end closed connection without response

d:\temp\demo>REM as you see that ran amok
d:\temp\demo>REM and it created two instances of notepad

--
components: Windows
messages: 387837
nosy: paul.moore, steve.dower, tim.golden, tim_magee, zach.ware
priority: normal
severity: normal
status: open
title: XMLRPC behaves strangely under pythonw, not under python
type: behavior
versions: Python 3.8

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