Fixing python 2.7 windows unicode issue with ``subprocess.Popen``.

win_subprocess.py

# -*- coding: utf-8 -*-

## Copyright (C) 2021 Valentin Lab
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## modification, are permitted provided that the following conditions
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## 1. Redistributions of source code must retain the above copyright
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## copyright notice, this list of conditions and the following
## disclaimer in the documentation and/or other materials provided
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## LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
## FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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## INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
## (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
## SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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## STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
## ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
## OF THE POSSIBILITY OF SUCH DAMAGE.
##

## issue: https://bugs.python.org/issue19264

import ctypes
import subprocess
import _subprocess
from ctypes import byref, windll, c_char_p, c_wchar_p, c_void_p, \
     Structure, sizeof, c_wchar, WinError
from ctypes.wintypes import BYTE, WORD, LPWSTR, BOOL, DWORD, LPVOID, \
     HANDLE


##
## Types
##

CREATE_UNICODE_ENVIRONMENT = 0x00000400
LPCTSTR = c_char_p
LPTSTR = c_wchar_p
LPSECURITY_ATTRIBUTES = c_void_p
LPBYTE  = ctypes.POINTER(BYTE)

class STARTUPINFOW(Structure):
    _fields_ = [
        ("cb",              DWORD),  ("lpReserved",    LPWSTR),
        ("lpDesktop",       LPWSTR), ("lpTitle",       LPWSTR),
        ("dwX",             DWORD),  ("dwY",           DWORD),
        ("dwXSize",         DWORD),  ("dwYSize",       DWORD),
        ("dwXCountChars",   DWORD),  ("dwYCountChars", DWORD),
        ("dwFillAtrribute", DWORD),  ("dwFlags",       DWORD),
        ("wShowWindow",     WORD),   ("cbReserved2",   WORD),
        ("lpReserved2",     LPBYTE), ("hStdInput",     HANDLE),
        ("hStdOutput",      HANDLE), ("hStdError",     HANDLE),
    ]

LPSTARTUPINFOW = ctypes.POINTER(STARTUPINFOW)


class PROCESS_INFORMATION(Structure):
    _fields_ = [
        ("hProcess",         HANDLE), ("hThread",          HANDLE),
        ("dwProcessId",      DWORD),  ("dwThreadId",       DWORD),
    ]

LPPROCESS_INFORMATION = ctypes.POINTER(PROCESS_INFORMATION)


class DUMMY_HANDLE(ctypes.c_void_p):

    def __init__(self, *a, **kw):
        super(DUMMY_HANDLE, self).__init__(*a, **kw)
        self.closed = False

    def Close(self):
        if not self.closed:
            windll.kernel32.CloseHandle(self)
            self.closed = True

    def __int__(self):
        return self.value


CreateProcessW = windll.kernel32.CreateProcessW
CreateProcessW.argtypes = [
    LPCTSTR, LPTSTR, LPSECURITY_ATTRIBUTES,
    LPSECURITY_ATTRIBUTES, BOOL, DWORD, LPVOID, LPCTSTR,
    LPSTARTUPINFOW, LPPROCESS_INFORMATION,
]
CreateProcessW.restype = BOOL


##
## Patched functions/classes
##

def CreateProcess(executable, args, _p_attr, _t_attr,
                  inherit_handles, creation_flags, env, cwd,
                  startup_info):
    """Create a process supporting unicode executable and args for win32

    Python implementation of CreateProcess using CreateProcessW for Win32

    """

    si = STARTUPINFOW(
        dwFlags=startup_info.dwFlags,
        wShowWindow=startup_info.wShowWindow,
        cb=sizeof(STARTUPINFOW),
        ## XXXvlab: not sure of the casting here to ints.
        hStdInput=int(startup_info.hStdInput),
        hStdOutput=int(startup_info.hStdOutput),
        hStdError=int(startup_info.hStdError),
    )

    wenv = None
    if env is not None:
        ## LPCWSTR seems to be c_wchar_p, so let's say CWSTR is c_wchar
        env = (unicode("").join([
            unicode("%s=%s\0") % (k, v)
            for k, v in env.items()])) + unicode("\0")
        wenv = (c_wchar * len(env))()
        wenv.value = env

    pi = PROCESS_INFORMATION()
    creation_flags |= CREATE_UNICODE_ENVIRONMENT

    if CreateProcessW(executable, args, None, None,
                      inherit_handles, creation_flags,
                      wenv, cwd, byref(si), byref(pi)):
        return (DUMMY_HANDLE(pi.hProcess), DUMMY_HANDLE(pi.hThread),
                pi.dwProcessId, pi.dwThreadId)
    raise WinError()


class Popen(subprocess.Popen):
    """This superseeds Popen and corrects a bug in cPython 2.7 implem"""

    def _execute_child(self, args, executable, preexec_fn, close_fds,
                       cwd, env, universal_newlines,
                       startupinfo, creationflags, shell, to_close,
                       p2cread, p2cwrite,
                       c2pread, c2pwrite,
                       errread, errwrite):
        """Code from part of _execute_child from Python 2.7 (9fbb65e)

        There are only 2 little changes concerning the construction of
        the the final string in shell mode: we preempt the creation of
        the command string when shell is True, because original function
        will try to encode unicode args which we want to avoid to be able to
        sending it as-is to ``CreateProcess``.

        """
        if not isinstance(args, subprocess.types.StringTypes):
            args = subprocess.list2cmdline(args)

        if startupinfo is None:
            startupinfo = subprocess.STARTUPINFO()
        if shell:
            startupinfo.dwFlags |= _subprocess.STARTF_USESHOWWINDOW
            startupinfo.wShowWindow = _subprocess.SW_HIDE
            comspec = os.environ.get("COMSPEC", unicode("cmd.exe"))
            args = unicode('{} /c "{}"').format(comspec, args)
            if (_subprocess.GetVersion() >= 0x80000000 or
                    os.path.basename(comspec).lower() == "command.com"):
                w9xpopen = self._find_w9xpopen()
                args = unicode('"%s" %s') % (w9xpopen, args)
                creationflags |= _subprocess.CREATE_NEW_CONSOLE

        super(Popen, self)._execute_child(args, executable,
            preexec_fn, close_fds, cwd, env, universal_newlines,
            startupinfo, creationflags, False, to_close, p2cread,
            p2cwrite, c2pread, c2pwrite, errread, errwrite)

_subprocess.CreateProcess = CreateProcess

@JokerQyou sorry for the late answer. Can you make a little test script to illustrate the problem, that would help tremendously for thinking about a fix. As of now, I have no idea of the context and why startup_info can be None. I'm sure this will make more sense with your example. Thanks for you report !

Very useful, thanks a lot!

I couldn't find a licence for your code on the page, did you have one in mind?

I'm not sure of the usage of this. I tried the following: 1) create file called win_subprocess.py 3) copy the contents above into it 3) included standard python header with utf-8 usage. 4) Use an if statement to include this file ONLY on Windows (below). 5) Include standard subprocess for any other platform 6) I also moved my library calls over to Popen. 7) make no other changes to my code?

I haven't had to do this type of modification in Python before. This type of thing is almost normal with #defines in C or C++. Can somebody confirm my steps? I'll try what I said below but thought this a good comment for others that follow.

For step 4 I do this:

sysPlat = sys.platform'
    if ( sysPlat == 'win32' or sysPlat == 'win64' ):
        import win_subprocess'
        from win_subprocess import CalledProcessError
    else:
        import subprocess
        from subprocess import CalledProcessError 

I'm about to move over to the Windows side and see if it works. :)

Could not get the patch to work. I guess my steps where not enough.

@KeithProctor, you just need to import win_subprocess at the start of your code for Windows platforms, after that use subprocess as normal. Something like this, based on what I think the above aims to do:

if sys.platform == 'win32':
    import win_subprocess
import subprocess
from subprocess import CalledProcessError 

Note that there is no 'win64' platform string - 32-bit and 64-bit Windows are both 'win32'. There's also something weird going on with quotes and leading whitespace in your code that would make it break.

Very cool - fixes the issue with minimal effort. Thanks a lot!

Upps, a little too ecstatic... Now subprocess.call() uses the new function as well, but it breaks because all stdin, stdout, stderr are None. It dies in line 91, trying to convert None to an int(). If I just do call(['ls', '-l']), all three streams are None, and deliberately stay None (line 816, in _get_handles()). Is call() now unusable in general?

@vaab I wonder if you'd mind sticking a GPL-compatible license on this so I can use it in tahoe-lafs/tahoe-lafs to replace some gross unicode hacks?

@exarkun Here you are. Is that good for you ?

@vaab That is perfect. Thank you kindly.

Some argument types are not correct, causing errors in some situations. It should be (https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-createprocessw):

CreateProcessW.argtypes = [
    LPCWSTR, LPWSTR, LPSECURITY_ATTRIBUTES,
    LPSECURITY_ATTRIBUTES, BOOL, DWORD, LPVOID, LPCWSTR,
    LPSTARTUPINFOW, LPPROCESS_INFORMATION,
]

Thank you for this. I still run a few programs I wrote in python2 (I really should rewrite them) and this issue has been a pain for years. At one point I was even using windows shortnames to get around the issue (does not always work). with this, now it just works.