vt.py

"""
    :codeauthor: Pedro Algarvio (pedro@algarvio.me)


    salt.utils.vt
    ~~~~~~~~~~~~~

    Virtual Terminal

    This code has been heavily inspired by Python's subprocess code, the `non
    blocking version of it`__, some minor online snippets about TTY handling
    with python including `Python's own ``pty`` source code`__ and `Pexpect`__
    which has already surpassed some of the pitfalls that some systems would
    get us into.

    .. __: http://code.activestate.com/recipes/440554/
    .. __: https://github.com/python/cpython/blob/3.3/Lib/pty.py
    .. __: https://github.com/pexpect/pexpect

"""

import errno
import functools
import logging
import os
import select
import signal
import subprocess
import sys
import time

import salt.utils.crypt
import salt.utils.data
import salt.utils.stringutils
from salt._logging import LOG_LEVELS

mswindows = sys.platform == "win32"

try:
    # pylint: disable=F0401,W0611
    import msvcrt

    import win32api
    import win32con
    import win32process
    from win32file import ReadFile, WriteFile
    from win32pipe import PeekNamedPipe

    # pylint: enable=F0401,W0611
except ImportError:
    import fcntl
    import pty
    import struct
    import termios


log = logging.getLogger(__name__)


class TerminalException(Exception):
    """
    Terminal specific exception
    """


def setwinsize(child, rows=80, cols=80):
    """
    This sets the terminal window size of the child tty. This will
    cause a SIGWINCH signal to be sent to the child. This does not
    change the physical window size. It changes the size reported to
    TTY-aware applications like vi or curses -- applications that
    respond to the SIGWINCH signal.

    Thank you for the shortcut PEXPECT
    """
    TIOCSWINSZ = getattr(termios, "TIOCSWINSZ", -2146929561)
    if TIOCSWINSZ == 2148037735:
        # Same bits, but with sign.
        TIOCSWINSZ = -2146929561
    # Note, assume ws_xpixel and ws_ypixel are zero.
    packed = struct.pack(b"HHHH", rows, cols, 0, 0)
    fcntl.ioctl(child, TIOCSWINSZ, packed)


def getwinsize(child):
    """
    This returns the terminal window size of the child tty. The return
    value is a tuple of (rows, cols).

    Thank you for the shortcut PEXPECT
    """
    TIOCGWINSZ = getattr(termios, "TIOCGWINSZ", 1074295912)
    packed = struct.pack(b"HHHH", 0, 0, 0, 0)
    ioctl = fcntl.ioctl(child, TIOCGWINSZ, packed)
    return struct.unpack(b"HHHH", ioctl)[0:2]


class Terminal:
    """
    I'm a virtual terminal
    """

    def __init__(
        self,
        args=None,
        executable=None,
        shell=False,
        cwd=None,
        env=None,
        preexec_fn=None,
        # Terminal Size
        rows=None,
        cols=None,
        # Logging options
        log_stdin=None,
        log_stdin_level="debug",
        log_stdout=None,
        log_stdout_level="debug",
        log_stderr=None,
        log_stderr_level="debug",
        log_sanitize=None,
        # sys.stdXYZ streaming options
        stream_stdout=None,
        stream_stderr=None,
        # Used for tests
        force_receive_encoding=__salt_system_encoding__,
    ):
        if not args and not executable:
            raise TerminalException(
                'You need to pass at least one of "args", "executable" '
            )
        self.args = args
        self.executable = executable
        self.shell = shell
        self.cwd = cwd
        self.env = env
        self.preexec_fn = preexec_fn
        self.receive_encoding = force_receive_encoding

        if rows is None and cols is None:
            rows, cols = self.__detect_parent_terminal_size()
        elif rows is not None and cols is None:
            _, cols = self.__detect_parent_terminal_size()
        elif rows is None and cols is not None:
            rows, _ = self.__detect_parent_terminal_size()
        self.rows = rows
        self.cols = cols
        self.pid = None
        self.stdin = None
        self.stdout = None
        self.stderr = None

        self.child_fd = None
        self.child_fde = None

        self.partial_data_stdout = b""
        self.partial_data_stderr = b""

        self.closed = True
        self.flag_eof_stdout = False
        self.flag_eof_stderr = False
        self.terminated = True
        self.exitstatus = None
        self.signalstatus = None
        # status returned by os.waitpid
        self.status = None

        if stream_stdout is True:
            self.stream_stdout = sys.stdout
        elif stream_stdout is False:
            self.stream_stdout = None
        elif stream_stdout is not None:
            if (
                not hasattr(stream_stdout, "write")
                or not hasattr(stream_stdout, "flush")
                or not hasattr(stream_stdout, "close")
            ):
                raise TerminalException(
                    "'stream_stdout' needs to have at least 3 methods, "
                    "'write()', 'flush()' and 'close()'."
                )
            self.stream_stdout = stream_stdout
        else:
            raise TerminalException(
                "Don't know how to handle '{}' as the VT's "
                "'stream_stdout' parameter.".format(stream_stdout)
            )

        if stream_stderr is True:
            self.stream_stderr = sys.stderr
        elif stream_stderr is False:
            self.stream_stderr = None
        elif stream_stderr is not None:
            if (
                not hasattr(stream_stderr, "write")
                or not hasattr(stream_stderr, "flush")
                or not hasattr(stream_stderr, "close")
            ):
                raise TerminalException(
                    "'stream_stderr' needs to have at least 3 methods, "
                    "'write()', 'flush()' and 'close()'."
                )
            self.stream_stderr = stream_stderr
        else:
            raise TerminalException(
                "Don't know how to handle '{}' as the VT's "
                "'stream_stderr' parameter.".format(stream_stderr)
            )

        try:
            self._spawn()
        except Exception as err:  # pylint: disable=W0703
            # A lot can go wrong, so that's why we're catching the most general
            # exception type
            log.warning(
                "Failed to spawn the VT: %s", err, exc_info_on_loglevel=logging.DEBUG
            )
            raise TerminalException("Failed to spawn the VT. Error: {}".format(err))

        log.debug(
            "Child Forked! PID: %s  STDOUT_FD: %s  STDERR_FD: %s",
            self.pid,
            self.child_fd,
            self.child_fde,
        )
        if log_sanitize:
            if not isinstance(log_sanitize, str):
                raise RuntimeError("'log_sanitize' needs to be a str type")
            self.log_sanitize = log_sanitize
        else:
            self.log_sanitize = None

        terminal_command = " ".join(self.args)
        if self.log_sanitize:
            terminal_command = terminal_command.replace(self.log_sanitize, ("*" * 6))
        if (
            'decode("base64")' in terminal_command
            or "base64.b64decode(" in terminal_command
        ):
            log.debug("VT: Salt-SSH SHIM Terminal Command executed. Logged to TRACE")
            log.trace("Terminal Command: %s", terminal_command)
        else:
            log.debug("Terminal Command: %s", terminal_command)

        # Setup logging after spawned in order to have a pid value
        self.stdin_logger_level = LOG_LEVELS.get(log_stdin_level, log_stdin_level)
        if log_stdin is True:
            self.stdin_logger = logging.getLogger(
                "{}.{}.PID-{}.STDIN".format(__name__, self.__class__.__name__, self.pid)
            )
        elif log_stdin is not None:
            if not isinstance(log_stdin, logging.Logger):
                raise RuntimeError("'log_stdin' needs to subclass `logging.Logger`")
            self.stdin_logger = log_stdin
        else:
            self.stdin_logger = None

        self.stdout_logger_level = LOG_LEVELS.get(log_stdout_level, log_stdout_level)
        if log_stdout is True:
            self.stdout_logger = logging.getLogger(
                "{}.{}.PID-{}.STDOUT".format(
                    __name__, self.__class__.__name__, self.pid
                )
            )
        elif log_stdout is not None:
            if not isinstance(log_stdout, logging.Logger):
                raise RuntimeError("'log_stdout' needs to subclass `logging.Logger`")
            self.stdout_logger = log_stdout
        else:
            self.stdout_logger = None

        self.stderr_logger_level = LOG_LEVELS.get(log_stderr_level, log_stderr_level)
        if log_stderr is True:
            self.stderr_logger = logging.getLogger(
                "{}.{}.PID-{}.STDERR".format(
                    __name__, self.__class__.__name__, self.pid
                )
            )
        elif log_stderr is not None:
            if not isinstance(log_stderr, logging.Logger):
                raise RuntimeError("'log_stderr' needs to subclass `logging.Logger`")
            self.stderr_logger = log_stderr
        else:
            self.stderr_logger = None

    def send(self, data):
        """
        Send data to the terminal. You are responsible to send any required
        line feeds.
        """
        return self._send(data)

    def sendline(self, data, linesep=os.linesep):
        """
        Send the provided data to the terminal appending a line feed.
        """
        return self.send("{}{}".format(data, linesep))

    def recv(self, maxsize=None):
        """
        Receive data from the terminal as a (``stdout``, ``stderr``) tuple. If
        any of those is ``None`` we can no longer communicate with the
        terminal's child process.
        """
        if maxsize is None:
            maxsize = 1024
        elif maxsize < 1:
            maxsize = 1
        return self._recv(maxsize)

    def close(self, terminate=True, kill=False):
        """
        Close the communication with the terminal's child.
        If ``terminate`` is ``True`` then additionally try to terminate the
        terminal, and if ``kill`` is also ``True``, kill the terminal if
        terminating it was not enough.
        """
        if not self.closed:
            if self.child_fd is not None:
                os.close(self.child_fd)
                self.child_fd = None
            if self.child_fde is not None:
                os.close(self.child_fde)
                self.child_fde = None
            time.sleep(0.1)
            if terminate:
                if not self.terminate(kill):
                    raise TerminalException("Failed to terminate child process.")
            self.closed = True

    @property
    def has_unread_data(self):
        return self.flag_eof_stderr is False or self.flag_eof_stdout is False

    def _translate_newlines(self, data):
        if data is None or not data:
            return
        # PTY's always return \r\n as the line feeds
        return data.replace("\r\n", os.linesep)

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        self.close(terminate=True, kill=True)
        # Wait for the process to terminate, to avoid zombies.
        if self.isalive():
            self.wait()

    if mswindows:

        def _execute(self):
            raise NotImplementedError

        def _spawn(self):
            raise NotImplementedError

        def _recv(self, maxsize):
            raise NotImplementedError

        def _send(self, data):
            raise NotImplementedError

        def send_signal(self, sig):
            """
            Send a signal to the process
            """
            # pylint: disable=E1101
            if sig == signal.SIGTERM:
                self.terminate()
            elif sig == signal.CTRL_C_EVENT:
                os.kill(self.pid, signal.CTRL_C_EVENT)
            elif sig == signal.CTRL_BREAK_EVENT:
                os.kill(self.pid, signal.CTRL_BREAK_EVENT)
            else:
                raise ValueError("Unsupported signal: {}".format(sig))
            # pylint: enable=E1101

        def terminate(self, force=False):
            """
            Terminates the process
            """
            try:
                win32api.TerminateProcess(self._handle, 1)
            except OSError:
                # ERROR_ACCESS_DENIED (winerror 5) is received when the
                # process already died.
                ecode = win32process.GetExitCodeProcess(self._handle)
                if ecode == win32con.STILL_ACTIVE:
                    raise
                self.exitstatus = ecode

        kill = terminate
    else:

        def _spawn(self):
            if not isinstance(self.args, str) and self.shell is True:
                self.args = " ".join(self.args)
            parent, child = pty.openpty()
            err_parent, err_child = os.pipe()
            child_name = os.ttyname(child)
            proc = subprocess.Popen(  # pylint: disable=subprocess-popen-preexec-fn
                self.args,
                preexec_fn=functools.partial(
                    self._preexec, child_name, self.rows, self.cols, self.preexec_fn
                ),
                shell=self.shell,  # nosec
                executable=self.executable,
                cwd=self.cwd,
                stdin=child,
                stdout=child,
                stderr=err_child,
                env=self.env,
                close_fds=True,
            )
            os.close(child)
            os.close(err_child)
            self.child_fd = parent
            self.child_fde = err_parent
            self.pid = proc.pid
            self.proc = proc
            self.closed = False
            self.terminated = False

        @staticmethod
        def _preexec(child_name, rows=80, cols=80, preexec_fn=None):
            # Disconnect from controlling tty. Harmless if not already
            # connected
            try:
                tty_fd = os.open("/dev/tty", os.O_RDWR | os.O_NOCTTY)
                if tty_fd >= 0:
                    os.close(tty_fd)
            # which exception, shouldn't we catch explicitly .. ?
            except Exception:  # pylint: disable=broad-except
                # Already disconnected. This happens if running inside cron
                pass
            try:
                os.setsid()
            except OSError:
                pass
            try:
                tty_fd = os.open("/dev/tty", os.O_RDWR | os.O_NOCTTY)
                if tty_fd >= 0:
                    os.close(tty_fd)
                    raise TerminalException(
                        "Could not open child pty, {}".format(child_name)
                    )
            # which exception, shouldn't we catch explicitly .. ?
            except Exception:  # pylint: disable=broad-except
                # Good! We are disconnected from a controlling tty.
                pass
            tty_fd = os.open(child_name, os.O_RDWR)
            setwinsize(tty_fd, rows, cols)
            if tty_fd < 0:
                raise TerminalException(
                    "Could not open child pty, {}".format(child_name)
                )
            else:
                os.close(tty_fd)
            if os.name != "posix":
                tty_fd = os.open("/dev/tty", os.O_WRONLY)
                if tty_fd < 0:
                    raise TerminalException("Could not open controlling tty, /dev/tty")
                else:
                    os.close(tty_fd)

            salt.utils.crypt.reinit_crypto()

            if preexec_fn is not None:
                preexec_fn()

        def _send(self, data):
            if self.child_fd is None:
                return None

            if not select.select([], [self.child_fd], [], 0)[1]:
                return 0

            try:
                if self.stdin_logger:
                    self.stdin_logger.log(self.stdin_logger_level, data)
                written = os.write(self.child_fd, data.encode(__salt_system_encoding__))
            except OSError as why:
                if why.errno == errno.EPIPE:  # broken pipe
                    os.close(self.child_fd)
                    self.child_fd = None
                    return
                raise
            return written

        def _recv(self, maxsize):
            rfds = []
            if self.child_fd:
                rfds.append(self.child_fd)
            if self.child_fde:
                rfds.append(self.child_fde)

            if not self.isalive():
                if not rfds:
                    self.close()
                    return None, None
                rlist, _, _ = select.select(rfds, [], [], 0)
                if not rlist:
                    self.flag_eof_stdout = self.flag_eof_stderr = True
                    log.debug("End of file(EOL). Brain-dead platform.")
                    if self.partial_data_stdout or self.partial_data_stderr:
                        # There is data that was received but for which
                        # decoding failed, attempt decoding again to generate
                        # relevant exception
                        self.close()
                        return (
                            salt.utils.stringutils.to_unicode(self.partial_data_stdout),
                            salt.utils.stringutils.to_unicode(self.partial_data_stderr),
                        )
                    self.close()
                    return None, None

            stderr = ""
            stdout = ""

            if self.child_fd:
                fd_flags = fcntl.fcntl(self.child_fd, fcntl.F_GETFL)
            if self.child_fde:
                fde_flags = fcntl.fcntl(self.child_fde, fcntl.F_GETFL)
            if self.child_fd:
                fcntl.fcntl(self.child_fd, fcntl.F_SETFL, fd_flags | os.O_NONBLOCK)
            if self.child_fde:
                fcntl.fcntl(self.child_fde, fcntl.F_SETFL, fde_flags | os.O_NONBLOCK)

            rlist, _, _ = select.select(rfds, [], [], 0)

            if not rlist:
                if not self.isalive():
                    self.flag_eof_stdout = self.flag_eof_stderr = True
                    log.debug("End of file(EOL). Very slow platform.")
                    return None, None

            def read_and_decode_fd(fd, maxsize, partial_data_attr=None):
                bytes_read = getattr(self, partial_data_attr, b"")
                # Only read one byte if we already have some existing data
                # to try and complete a split multibyte character
                bytes_read += os.read(fd, maxsize if not bytes_read else 1)
                try:
                    decoded_data = self._translate_newlines(
                        salt.utils.stringutils.to_unicode(
                            bytes_read, self.receive_encoding
                        )
                    )
                    if partial_data_attr is not None:
                        setattr(self, partial_data_attr, b"")
                    return decoded_data, False
                except UnicodeDecodeError as ex:
                    max_multibyte_character_length = 4
                    if ex.start > (
                        len(bytes_read) - max_multibyte_character_length
                    ) and ex.end == len(bytes_read):
                        # We weren't able to decode the received data possibly
                        # because it is a multibyte character split across
                        # blocks. Save what data we have to try and decode
                        # later. If the error wasn't caused by a multibyte
                        # character being split then the error start position
                        # should remain the same each time we get here but the
                        # length of the bytes_read will increase so we will
                        # give up and raise an exception instead.
                        if partial_data_attr is not None:
                            setattr(self, partial_data_attr, bytes_read)
                        else:
                            # We haven't been given anywhere to store partial
                            # data so raise the exception instead
                            raise
                        # No decoded data to return, but indicate that there
                        # is buffered data
                        return "", True
                    else:
                        raise

            if self.child_fde in rlist and not self.flag_eof_stderr:
                try:
                    stderr, partial_data = read_and_decode_fd(
                        self.child_fde, maxsize, "partial_data_stderr"
                    )

                    if not stderr and not partial_data:
                        self.flag_eof_stderr = True
                        stderr = None
                    else:
                        if self.stream_stderr:
                            self.stream_stderr.write(stderr)
                            self.stream_stderr.flush()

                        if self.stderr_logger:
                            stripped = stderr.rstrip()
                            if self.log_sanitize:
                                stripped = stripped.replace(
                                    self.log_sanitize, ("*" * 6)
                                )
                            if stripped.startswith(os.linesep):
                                stripped = stripped[len(os.linesep) :]
                            if stripped:
                                self.stderr_logger.log(
                                    self.stderr_logger_level, stripped
                                )
                except OSError:
                    os.close(self.child_fde)
                    self.child_fde = None
                    self.flag_eof_stderr = True
                    stderr = None
                finally:
                    if self.child_fde is not None:
                        fcntl.fcntl(self.child_fde, fcntl.F_SETFL, fde_flags)

            if self.child_fd in rlist and not self.flag_eof_stdout:
                try:
                    stdout, partial_data = read_and_decode_fd(
                        self.child_fd, maxsize, "partial_data_stdout"
                    )

                    if not stdout and not partial_data:
                        self.flag_eof_stdout = True
                        stdout = None
                    else:
                        if self.stream_stdout:
                            self.stream_stdout.write(
                                salt.utils.stringutils.to_str(stdout)
                            )
                            self.stream_stdout.flush()

                        if self.stdout_logger:
                            stripped = stdout.rstrip()
                            if self.log_sanitize:
                                stripped = stripped.replace(
                                    self.log_sanitize, ("*" * 6)
                                )
                            if stripped.startswith(os.linesep):
                                stripped = stripped[len(os.linesep) :]
                            if stripped:
                                self.stdout_logger.log(
                                    self.stdout_logger_level, stripped
                                )
                except OSError:
                    os.close(self.child_fd)
                    self.child_fd = None
                    self.flag_eof_stdout = True
                    stdout = None
                finally:
                    if self.child_fd is not None:
                        fcntl.fcntl(self.child_fd, fcntl.F_SETFL, fd_flags)
            # <---- Process STDOUT -------------------------------------------
            return stdout, stderr

        def __detect_parent_terminal_size(self):
            try:
                TIOCGWINSZ = getattr(termios, "TIOCGWINSZ", 1074295912)
                packed = struct.pack(b"HHHH", 0, 0, 0, 0)
                ioctl = fcntl.ioctl(sys.stdin.fileno(), TIOCGWINSZ, packed)
                return struct.unpack(b"HHHH", ioctl)[0:2]
            except OSError:
                # Return a default value of 24x80
                return 24, 80

        # <---- Internal API -------------------------------------------------

        # ----- Public API -------------------------------------------------->
        def getwinsize(self):
            """
            This returns the terminal window size of the child tty. The return
            value is a tuple of (rows, cols).

            Thank you for the shortcut PEXPECT
            """
            if self.child_fd is None:
                raise TerminalException(
                    "Can't check the size of the terminal since we're not "
                    "connected to the child process."
                )
            return getwinsize(self.child_fd)

        def setwinsize(self, child, rows=80, cols=80):
            setwinsize(self.child_fd, rows, cols)

        def isalive(
            self,
            _waitpid=os.waitpid,
            _wnohang=os.WNOHANG,
            _wifexited=os.WIFEXITED,
            _wexitstatus=os.WEXITSTATUS,
            _wifsignaled=os.WIFSIGNALED,
            _wifstopped=os.WIFSTOPPED,
            _wtermsig=os.WTERMSIG,
            _os_error=os.error,
            _errno_echild=errno.ECHILD,
            _terminal_exception=TerminalException,
        ):
            """
            This tests if the child process is running or not. This is
            non-blocking. If the child was terminated then this will read the
            exitstatus or signalstatus of the child. This returns True if the
            child process appears to be running or False if not. It can take
            literally SECONDS for Solaris to return the right status.
            """
            if self.terminated:
                return False

            if self.has_unread_data is False:
                # This is for Linux, which requires the blocking form
                # of waitpid to get status of a defunct process.
                # This is super-lame. The flag_eof_* would have been set
                # in recv(), so this should be safe.
                waitpid_options = 0
            else:
                waitpid_options = _wnohang

            try:
                pid, status = _waitpid(self.pid, waitpid_options)
            except ChildProcessError:
                # check if process is really dead or if it is just pretending and we should exit normally through the gift center
                polled = self.proc.poll()
                if polled is None:
                    return True
                # process must have returned on it's own process the return code
                pid = self.pid
                status = polled
            except _os_error:
                err = sys.exc_info()[1]
                # No child processes
                if err.errno == _errno_echild:
                    raise _terminal_exception(
                        'isalive() encountered condition where "terminated" '
                        "is 0, but there was no child process. Did someone "
                        "else call waitpid() on our process?"
                    )
                else:
                    raise

            # I have to do this twice for Solaris.
            # I can't even believe that I figured this out...
            # If waitpid() returns 0 it means that no child process
            # wishes to report, and the value of status is undefined.
            if pid == 0:
                try:
                    ### os.WNOHANG # Solaris!
                    pid, status = _waitpid(self.pid, waitpid_options)
                except _os_error as exc:
                    # This should never happen...
                    if exc.errno == _errno_echild:
                        raise _terminal_exception(
                            "isalive() encountered condition that should "
                            "never happen. There was no child process. Did "
                            "someone else call waitpid() on our process?"
                        )
                    else:
                        raise

                # If pid is still 0 after two calls to waitpid() then the
                # process really is alive. This seems to work on all platforms,
                # except for Irix which seems to require a blocking call on
                # waitpid or select, so I let recv take care of this situation
                # (unfortunately, this requires waiting through the timeout).
                if pid == 0:
                    return True

            if pid == 0:
                return True

            if _wifexited(status):
                self.status = status
                self.exitstatus = _wexitstatus(status)
                self.signalstatus = None
                self.terminated = True
            elif _wifsignaled(status):
                self.status = status
                self.exitstatus = None
                self.signalstatus = _wtermsig(status)
                self.terminated = True
            elif _wifstopped(status):
                raise _terminal_exception(
                    "isalive() encountered condition where child process is "
                    "stopped. This is not supported. Is some other process "
                    "attempting job control with our child pid?"
                )
            return False

        def terminate(self, force=False):
            """
            This forces a child process to terminate. It starts nicely with
            SIGHUP and SIGINT. If "force" is True then moves onto SIGKILL. This
            returns True if the child was terminated. This returns False if the
            child could not be terminated.
            """
            if not self.closed:
                self.close(terminate=False)

            if not self.isalive():
                return True
            try:
                self.send_signal(signal.SIGHUP)
                time.sleep(0.1)
                if not self.isalive():
                    return True
                self.send_signal(signal.SIGCONT)
                time.sleep(0.1)
                if not self.isalive():
                    return True
                self.send_signal(signal.SIGINT)
                time.sleep(0.1)
                if not self.isalive():
                    return True
                if force:
                    self.send_signal(signal.SIGKILL)
                    time.sleep(0.1)
                    if not self.isalive():
                        return True
                    else:
                        return False
                return False
            except OSError:
                # I think there are kernel timing issues that sometimes cause
                # this to happen. I think isalive() reports True, but the
                # process is dead to the kernel.
                # Make one last attempt to see if the kernel is up to date.
                time.sleep(0.1)
                if not self.isalive():
                    return True
                else:
                    return False

        def wait(self):
            """
            This waits until the child exits internally consuming any remaining
            output from the child, thus, no blocking forever because the child
            has unread data.
            """
            if self.isalive():
                while self.isalive():
                    stdout, stderr = self.recv()
                    if stdout is None:
                        break
                    if stderr is None:
                        break
            else:
                raise TerminalException("Cannot wait for dead child process.")
            return self.exitstatus

        def send_signal(self, sig):
            """
            Send a signal to the process
            """
            os.kill(self.pid, sig)

        def kill(self):
            """
            Kill the process with SIGKILL
            """
            self.send_signal(signal.SIGKILL)