Mini Shell

"""Windows-specific implementation of process utilities.

This file is only meant to be imported by process.py, not by end-users.
"""

#-----------------------------------------------------------------------------
#  Copyright (C) 2010-2011  The IPython Development Team
#
#  Distributed under the terms of the BSD License.  The full license is in
#  the file COPYING, distributed as part of this software.
#-----------------------------------------------------------------------------

#-----------------------------------------------------------------------------
# Imports
#-----------------------------------------------------------------------------

# stdlib
import os
import sys
import ctypes
import time

from ctypes import c_int, POINTER
from ctypes.wintypes import LPCWSTR, HLOCAL
from subprocess import STDOUT, TimeoutExpired
from threading import Thread

# our own imports
from ._process_common import read_no_interrupt, process_handler, arg_split as py_arg_split
from . import py3compat
from .encoding import DEFAULT_ENCODING

#-----------------------------------------------------------------------------
# Function definitions
#-----------------------------------------------------------------------------

class AvoidUNCPath(object):
    """A context manager to protect command execution from UNC paths.

    In the Win32 API, commands can't be invoked with the cwd being a UNC path.
    This context manager temporarily changes directory to the 'C:' drive on
    entering, and restores the original working directory on exit.

    The context manager returns the starting working directory *if* it made a
    change and None otherwise, so that users can apply the necessary adjustment
    to their system calls in the event of a change.

    Examples
    --------
    ::
        cmd = 'dir'
        with AvoidUNCPath() as path:
            if path is not None:
                cmd = '"pushd %s &&"%s' % (path, cmd)
            os.system(cmd)
    """
    def __enter__(self):
        self.path = os.getcwd()
        self.is_unc_path = self.path.startswith(r"\\")
        if self.is_unc_path:
            # change to c drive (as cmd.exe cannot handle UNC addresses)
            os.chdir("C:")
            return self.path
        else:
            # We return None to signal that there was no change in the working
            # directory
            return None

    def __exit__(self, exc_type, exc_value, traceback):
        if self.is_unc_path:
            os.chdir(self.path)


def _system_body(p):
    """Callback for _system."""
    enc = DEFAULT_ENCODING

    def stdout_read():
        for line in read_no_interrupt(p.stdout).splitlines():
            line = line.decode(enc, 'replace')
            print(line, file=sys.stdout)

    def stderr_read():
        for line in read_no_interrupt(p.stderr).splitlines():
            line = line.decode(enc, 'replace')
            print(line, file=sys.stderr)

    Thread(target=stdout_read).start()
    Thread(target=stderr_read).start()

    # Wait to finish for returncode. Unfortunately, Python has a bug where
    # wait() isn't interruptible (https://bugs.python.org/issue28168) so poll in
    # a loop instead of just doing `return p.wait()`.
    while True:
        result = p.poll()
        if result is None:
            time.sleep(0.01)
        else:
            return result


def system(cmd):
    """Win32 version of os.system() that works with network shares.

    Note that this implementation returns None, as meant for use in IPython.

    Parameters
    ----------
    cmd : str or list
        A command to be executed in the system shell.

    Returns
    -------
    int : child process' exit code.
    """
    # The controller provides interactivity with both
    # stdin and stdout
    #import _process_win32_controller
    #_process_win32_controller.system(cmd)

    with AvoidUNCPath() as path:
        if path is not None:
            cmd = '"pushd %s &&"%s' % (path, cmd)
        return process_handler(cmd, _system_body)

def getoutput(cmd):
    """Return standard output of executing cmd in a shell.

    Accepts the same arguments as os.system().

    Parameters
    ----------
    cmd : str or list
        A command to be executed in the system shell.

    Returns
    -------
    stdout : str
    """

    with AvoidUNCPath() as path:
        if path is not None:
            cmd = '"pushd %s &&"%s' % (path, cmd)
        out = process_handler(cmd, lambda p: p.communicate()[0], STDOUT)

    if out is None:
        out = b''
    return py3compat.decode(out)

try:
    CommandLineToArgvW = ctypes.windll.shell32.CommandLineToArgvW
    CommandLineToArgvW.arg_types = [LPCWSTR, POINTER(c_int)]
    CommandLineToArgvW.restype = POINTER(LPCWSTR)
    LocalFree = ctypes.windll.kernel32.LocalFree
    LocalFree.res_type = HLOCAL
    LocalFree.arg_types = [HLOCAL]
    
    def arg_split(commandline, posix=False, strict=True):
        """Split a command line's arguments in a shell-like manner.

        This is a special version for windows that use a ctypes call to CommandLineToArgvW
        to do the argv splitting. The posix parameter is ignored.

        If strict=False, process_common.arg_split(...strict=False) is used instead.
        """
        #CommandLineToArgvW returns path to executable if called with empty string.
        if commandline.strip() == "":
            return []
        if not strict:
            # not really a cl-arg, fallback on _process_common
            return py_arg_split(commandline, posix=posix, strict=strict)
        argvn = c_int()
        result_pointer = CommandLineToArgvW(py3compat.cast_unicode(commandline.lstrip()), ctypes.byref(argvn))
        result_array_type = LPCWSTR * argvn.value
        result = [arg for arg in result_array_type.from_address(ctypes.addressof(result_pointer.contents))]
        retval = LocalFree(result_pointer)
        return result
except AttributeError:
    arg_split = py_arg_split

def check_pid(pid):
    # OpenProcess returns 0 if no such process (of ours) exists
    # positive int otherwise
    return bool(ctypes.windll.kernel32.OpenProcess(1,0,pid))