mitogen/ansible_mitogen/runner.py

# Copyright 2019, David Wilson
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# 1. Redistributions of source code must retain the above copyright notice,
# this list of conditions and the following disclaimer.
#
# 2. Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
# and/or other materials provided with the distribution.
#
# 3. Neither the name of the copyright holder nor the names of its contributors
# may be used to endorse or promote products derived from this software without
# specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, 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) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, 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.

# !mitogen: minify_safe

"""
These classes implement execution for each style of Ansible module. They are
instantiated in the target context by way of target.py::run_module().

Each class in here has a corresponding Planner class in planners.py that knows
how to build arguments for it, preseed related data, etc.
"""

import atexit
import imp
import os
import re
import shlex
import shutil
import sys
import tempfile
import traceback
import types

import mitogen.core
import ansible_mitogen.target  # TODO: circular import
from mitogen.core import b
from mitogen.core import bytes_partition
from mitogen.core import str_rpartition
from mitogen.core import to_text

try:
    import ctypes
except ImportError:
    # Python 2.4
    ctypes = None

try:
    import json
except ImportError:
    # Python 2.4
    import simplejson as json

try:
    # Cannot use cStringIO as it does not support Unicode.
    from StringIO import StringIO
except ImportError:
    from io import StringIO

try:
    from shlex import quote as shlex_quote
except ImportError:
    from pipes import quote as shlex_quote

# Absolute imports for <2.5.
logging = __import__('logging')


# Prevent accidental import of an Ansible module from hanging on stdin read.
import ansible.module_utils.basic
ansible.module_utils.basic._ANSIBLE_ARGS = '{}'

# For tasks that modify /etc/resolv.conf, non-Debian derivative glibcs cache
# resolv.conf at startup and never implicitly reload it. Cope with that via an
# explicit call to res_init() on each task invocation. BSD-alikes export it
# directly, Linux #defines it as "__res_init".
libc__res_init = None
if ctypes:
    libc = ctypes.CDLL(None)
    for symbol in 'res_init', '__res_init':
        try:
            libc__res_init = getattr(libc, symbol)
        except AttributeError:
            pass

iteritems = getattr(dict, 'iteritems', dict.items)
LOG = logging.getLogger(__name__)


def shlex_split_b(s):
    """
    Use shlex.split() to split characters in some single-byte encoding, without
    knowing what that encoding is. The input is bytes, the output is a list of
    bytes.
    """
    assert isinstance(s, mitogen.core.BytesType)
    if mitogen.core.PY3:
        return [
            t.encode('latin1')
            for t in shlex.split(s.decode('latin1'), comments=True)
        ]

    return [t for t in shlex.split(s, comments=True)]


class TempFileWatcher(object):
    """
    Since Ansible 2.7.0, lineinfile leaks file descriptors returned by
    :func:`tempfile.mkstemp` (ansible/ansible#57327). Handle this and all
    similar cases by recording descriptors produced by mkstemp during module
    execution, and cleaning up any leaked descriptors on completion.
    """
    def __init__(self):
        self._real_mkstemp = tempfile.mkstemp
        # (fd, st.st_dev, st.st_ino)
        self._fd_dev_inode = []
        tempfile.mkstemp = self._wrap_mkstemp

    def _wrap_mkstemp(self, *args, **kwargs):
        fd, path = self._real_mkstemp(*args, **kwargs)
        st = os.fstat(fd)
        self._fd_dev_inode.append((fd, st.st_dev, st.st_ino))
        return fd, path

    def revert(self):
        tempfile.mkstemp = self._real_mkstemp
        for tup in self._fd_dev_inode:
            self._revert_one(*tup)

    def _revert_one(self, fd, st_dev, st_ino):
        try:
            st = os.fstat(fd)
        except OSError:
            # FD no longer exists.
            return

        if not (st.st_dev == st_dev and st.st_ino == st_ino):
            # FD reused.
            return

        LOG.info("a tempfile.mkstemp() FD was leaked during the last task")
        os.close(fd)


class EnvironmentFileWatcher(object):
    """
    Usually Ansible edits to /etc/environment and ~/.pam_environment are
    reflected in subsequent tasks if become:true or SSH multiplexing is
    disabled, due to sudo and/or SSH reinvoking pam_env. Rather than emulate
    existing semantics, do our best to ensure edits are always reflected.

    This can't perfectly replicate the existing behaviour, but it can safely
    update and remove keys that appear to originate in `path`, and that do not
    conflict with any existing environment key inherited from elsewhere.

    A more robust future approach may simply be to arrange for the persistent
    interpreter to restart when a change is detected.
    """
    # We know nothing about the character set of /etc/environment or the
    # process environment.
    environ = getattr(os, 'environb', os.environ)

    def __init__(self, path):
        self.path = os.path.expanduser(path)
        #: Inode data at time of last check.
        self._st = self._stat()
        #: List of inherited keys appearing to originated from this file.
        self._keys = [
            key for key, value in self._load()
            if value == self.environ.get(key)
        ]
        LOG.debug('%r installed; existing keys: %r', self, self._keys)

    def __repr__(self):
        return 'EnvironmentFileWatcher(%r)' % (self.path,)

    def _stat(self):
        try:
            return os.stat(self.path)
        except OSError:
            return None

    def _load(self):
        try:
            fp = open(self.path, 'rb')
            try:
                return list(self._parse(fp))
            finally:
                fp.close()
        except IOError:
            return []

    def _parse(self, fp):
        """
        linux-pam-1.3.1/modules/pam_env/pam_env.c#L207
        """
        for line in fp:
            # '   #export foo=some var  ' -> ['#export', 'foo=some var  ']
            bits = shlex_split_b(line)
            if (not bits) or bits[0].startswith(b('#')):
                continue

            if bits[0] == b('export'):
                bits.pop(0)

            key, sep, value = bytes_partition(b(' ').join(bits), b('='))
            if key and sep:
                yield key, value

    def _on_file_changed(self):
        LOG.debug('%r: file changed, reloading', self)
        for key, value in self._load():
            if key in self.environ:
                LOG.debug('%r: existing key %r=%r exists, not setting %r',
                          self, key, self.environ[key], value)
            else:
                LOG.debug('%r: setting key %r to %r', self, key, value)
                self._keys.append(key)
                self.environ[key] = value

    def _remove_existing(self):
        """
        When a change is detected, remove keys that existed in the old file.
        """
        for key in self._keys:
            if key in self.environ:
                LOG.debug('%r: removing old key %r', self, key)
                del self.environ[key]
        self._keys = []

    def check(self):
        """
        Compare the :func:`os.stat` for the pam_env style environmnt file
        `path` with the previous result `old_st`, which may be :data:`None` if
        the previous stat attempt failed. Reload its contents if the file has
        changed or appeared since last attempt.

        :returns:
            New :func:`os.stat` result. The new call to :func:`reload_env` should
            pass it as the value of `old_st`.
        """
        st = self._stat()
        if self._st == st:
            return

        self._st = st
        self._remove_existing()

        if st is None:
            LOG.debug('%r: file has disappeared', self)
        else:
            self._on_file_changed()

_pam_env_watcher = EnvironmentFileWatcher('~/.pam_environment')
_etc_env_watcher = EnvironmentFileWatcher('/etc/environment')


def utf8(s):
    """
    Coerce an object to bytes if it is Unicode.
    """
    if isinstance(s, mitogen.core.UnicodeType):
        s = s.encode('utf-8')
    return s


def reopen_readonly(fp):
    """
    Replace the file descriptor belonging to the file object `fp` with one
    open on the same file (`fp.name`), but opened with :py:data:`os.O_RDONLY`.
    This enables temporary files to be executed on Linux, which usually throws
    ``ETXTBUSY`` if any writeable handle exists pointing to a file passed to
    `execve()`.
    """
    fd = os.open(fp.name, os.O_RDONLY)
    os.dup2(fd, fp.fileno())
    os.close(fd)


class Runner(object):
    """
    Ansible module runner. After instantiation (with kwargs supplied by the
    corresponding Planner), `.run()` is invoked, upon which `setup()`,
    `_run()`, and `revert()` are invoked, with the return value of `_run()`
    returned by `run()`.

    Subclasses may override `_run`()` and extend `setup()` and `revert()`.

    :param str module:
        Name of the module to execute, e.g. "shell"
    :param mitogen.core.Context service_context:
        Context to which we should direct FileService calls. For now, always
        the connection multiplexer process on the controller.
    :param str json_args:
        Ansible module arguments. A mixture of user and internal keys created
        by :meth:`ansible.plugins.action.ActionBase._execute_module`.

        This is passed as a string rather than a dict in order to mimic the
        implicit bytes/str conversion behaviour of a 2.x controller running
        against a 3.x target.
    :param str good_temp_dir:
        The writeable temporary directory for this user account reported by
        :func:`ansible_mitogen.target.init_child` passed via the controller.
        This is specified explicitly to remain compatible with Ansible<2.5, and
        for forked tasks where init_child never runs.
    :param dict env:
        Additional environment variables to set during the run. Keys with
        :data:`None` are unset if present.
    :param str cwd:
        If not :data:`None`, change to this directory before executing.
    :param mitogen.core.ExternalContext econtext:
        When `detach` is :data:`True`, a reference to the ExternalContext the
        runner is executing in.
    :param bool detach:
        When :data:`True`, indicate the runner should detach the context from
        its parent after setup has completed successfully.
    """
    def __init__(self, module, service_context, json_args, good_temp_dir,
                 extra_env=None, cwd=None, env=None, econtext=None,
                 detach=False):
        self.module = module
        self.service_context = service_context
        self.econtext = econtext
        self.detach = detach
        self.args = json.loads(mitogen.core.to_text(json_args))
        self.good_temp_dir = good_temp_dir
        self.extra_env = extra_env
        self.env = env
        self.cwd = cwd
        #: If not :data:`None`, :meth:`get_temp_dir` had to create a temporary
        #: directory for this run, because we're in an asynchronous task, or
        #: because the originating action did not create a directory.
        self._temp_dir = None

    def get_temp_dir(self):
        path = self.args.get('_ansible_tmpdir')
        if path is not None:
            return path

        if self._temp_dir is None:
            self._temp_dir = tempfile.mkdtemp(
                prefix='ansible_mitogen_runner_',
                dir=self.good_temp_dir,
            )

        return self._temp_dir

    def revert_temp_dir(self):
        if self._temp_dir is not None:
            ansible_mitogen.target.prune_tree(self._temp_dir)
            self._temp_dir = None

    def setup(self):
        """
        Prepare for running a module, including fetching necessary dependencies
        from the parent, as :meth:`run` may detach prior to beginning
        execution. The base implementation simply prepares the environment.
        """
        self._setup_cwd()
        self._setup_environ()

    def _setup_cwd(self):
        """
        For situations like sudo to a non-privileged account, CWD could be
        $HOME of the old account, which could have mode go=, which means it is
        impossible to restore the old directory, so don't even try.
        """
        if self.cwd:
            os.chdir(self.cwd)

    def _setup_environ(self):
        """
        Apply changes from /etc/environment files before creating a
        TemporaryEnvironment to snapshot environment state prior to module run.
        """
        _pam_env_watcher.check()
        _etc_env_watcher.check()
        env = dict(self.extra_env or {})
        if self.env:
            env.update(self.env)
        self._env = TemporaryEnvironment(env)

    def _revert_cwd(self):
        """
        #591: make a best-effort attempt to return to :attr:`good_temp_dir`.
        """
        try:
            os.chdir(self.good_temp_dir)
        except OSError:
            LOG.debug('%r: could not restore CWD to %r',
                      self, self.good_temp_dir)

    def revert(self):
        """
        Revert any changes made to the process after running a module. The base
        implementation simply restores the original environment.
        """
        self._revert_cwd()
        self._env.revert()
        self.revert_temp_dir()

    def _run(self):
        """
        The _run() method is expected to return a dictionary in the form of
        ActionBase._low_level_execute_command() output, i.e. having::

            {
                "rc": int,
                "stdout": "stdout data",
                "stderr": "stderr data"
            }
        """
        raise NotImplementedError()

    def run(self):
        """
        Set up the process environment in preparation for running an Ansible
        module. This monkey-patches the Ansible libraries in various places to
        prevent it from trying to kill the process on completion, and to
        prevent it from reading sys.stdin.

        :returns:
            Module result dictionary.
        """
        self.setup()
        if self.detach:
            self.econtext.detach()

        try:
            return self._run()
        finally:
            self.revert()


class AtExitWrapper(object):
    """
    issue #397, #454: Newer Ansibles use :func:`atexit.register` to trigger
    tmpdir cleanup when AnsibleModule.tmpdir is responsible for creating its
    own temporary directory, however with Mitogen processes are preserved
    across tasks, meaning cleanup must happen earlier.

    Patch :func:`atexit.register`, catching :func:`shutil.rmtree` calls so they
    can be executed on task completion, rather than on process shutdown.
    """
    # Wrapped in a dict to avoid instance method decoration.
    original = {
        'register': atexit.register
    }

    def __init__(self):
        assert atexit.register == self.original['register'], \
            "AtExitWrapper installed twice."
        atexit.register = self._atexit__register
        self.deferred = []

    def revert(self):
        """
        Restore the original :func:`atexit.register`.
        """
        assert atexit.register == self._atexit__register, \
            "AtExitWrapper not installed."
        atexit.register = self.original['register']

    def run_callbacks(self):
        while self.deferred:
            func, targs, kwargs = self.deferred.pop()
            try:
                func(*targs, **kwargs)
            except Exception:
                LOG.exception('While running atexit callbacks')

    def _atexit__register(self, func, *targs, **kwargs):
        """
        Intercept :func:`atexit.register` calls, diverting any to
        :func:`shutil.rmtree` into a private list.
        """
        if func == shutil.rmtree:
            self.deferred.append((func, targs, kwargs))
            return

        self.original['register'](func, *targs, **kwargs)


class ModuleUtilsImporter(object):
    """
    :param list module_utils:
        List of `(fullname, path, is_pkg)` tuples.
    """
    def __init__(self, context, module_utils):
        self._context = context
        self._by_fullname = dict(
            (fullname, (path, is_pkg))
            for fullname, path, is_pkg in module_utils
        )
        self._loaded = set()
        sys.meta_path.insert(0, self)

    def revert(self):
        sys.meta_path.remove(self)
        for fullname in self._loaded:
            sys.modules.pop(fullname, None)

    def find_module(self, fullname, path=None):
        if fullname in self._by_fullname:
            return self

    def load_module(self, fullname):
        path, is_pkg = self._by_fullname[fullname]
        source = ansible_mitogen.target.get_small_file(self._context, path)
        code = compile(source, path, 'exec', 0, 1)
        mod = sys.modules.setdefault(fullname, imp.new_module(fullname))
        mod.__file__ = "master:%s" % (path,)
        mod.__loader__ = self
        if is_pkg:
            mod.__path__ = []
            mod.__package__ = str(fullname)
        else:
            mod.__package__ = str(str_rpartition(to_text(fullname), '.')[0])
        exec(code, mod.__dict__)
        self._loaded.add(fullname)
        return mod


class TemporaryEnvironment(object):
    """
    Apply environment changes from `env` until :meth:`revert` is called. Values
    in the dict may be :data:`None` to indicate the relevant key should be
    deleted.
    """
    def __init__(self, env=None):
        self.original = dict(os.environ)
        self.env = env or {}
        for key, value in iteritems(self.env):
            key = mitogen.core.to_text(key)
            value = mitogen.core.to_text(value)
            if value is None:
                os.environ.pop(key, None)
            else:
                os.environ[key] = str(value)

    def revert(self):
        """
        Revert changes made by the module to the process environment. This must
        always run, as some modules (e.g. git.py) set variables like GIT_SSH
        that must be cleared out between runs.
        """
        os.environ.clear()
        os.environ.update(self.original)


class TemporaryArgv(object):
    def __init__(self, argv):
        self.original = sys.argv[:]
        sys.argv[:] = map(str, argv)

    def revert(self):
        sys.argv[:] = self.original


class NewStyleStdio(object):
    """
    Patch ansible.module_utils.basic argument globals.
    """
    def __init__(self, args, temp_dir):
        self.temp_dir = temp_dir
        self.original_stdout = sys.stdout
        self.original_stderr = sys.stderr
        self.original_stdin = sys.stdin
        sys.stdout = StringIO()
        sys.stderr = StringIO()
        encoded = json.dumps({'ANSIBLE_MODULE_ARGS': args})
        ansible.module_utils.basic._ANSIBLE_ARGS = utf8(encoded)
        sys.stdin = StringIO(mitogen.core.to_text(encoded))

        self.original_get_path = getattr(ansible.module_utils.basic,
                                        'get_module_path', None)
        ansible.module_utils.basic.get_module_path = self._get_path

    def _get_path(self):
        return self.temp_dir

    def revert(self):
        ansible.module_utils.basic.get_module_path = self.original_get_path
        sys.stdout = self.original_stdout
        sys.stderr = self.original_stderr
        sys.stdin = self.original_stdin
        ansible.module_utils.basic._ANSIBLE_ARGS = '{}'


class ProgramRunner(Runner):
    """
    Base class for runners that run external programs.

    :param str path:
        Absolute path to the program file on the master, as it can be retrieved
        via :class:`mitogen.service.FileService`.
    :param bool emulate_tty:
        If :data:`True`, execute the program with `stdout` and `stderr` merged
        into a single pipe, emulating Ansible behaviour when an SSH TTY is in
        use.
    """
    def __init__(self, path, emulate_tty=None, **kwargs):
        super(ProgramRunner, self).__init__(**kwargs)
        self.emulate_tty = emulate_tty
        self.path = path

    def setup(self):
        super(ProgramRunner, self).setup()
        self._setup_program()

    def _get_program_filename(self):
        """
        Return the filename used for program on disk. Ansible uses the original
        filename for non-Ansiballz runs, and "ansible_module_+filename for
        Ansiballz runs.
        """
        return os.path.basename(self.path)

    program_fp = None

    def _setup_program(self):
        """
        Create a temporary file containing the program code. The code is
        fetched via :meth:`_get_program`.
        """
        filename = self._get_program_filename()
        path = os.path.join(self.get_temp_dir(), filename)
        self.program_fp = open(path, 'wb')
        self.program_fp.write(self._get_program())
        self.program_fp.flush()
        os.chmod(self.program_fp.name, int('0700', 8))
        reopen_readonly(self.program_fp)

    def _get_program(self):
        """
        Fetch the module binary from the master if necessary.
        """
        return ansible_mitogen.target.get_small_file(
            context=self.service_context,
            path=self.path,
        )

    def _get_program_args(self):
        """
        Return any arguments to pass to the program.
        """
        return []

    def revert(self):
        """
        Delete the temporary program file.
        """
        if self.program_fp:
            self.program_fp.close()
        super(ProgramRunner, self).revert()

    def _get_argv(self):
        """
        Return the final argument vector used to execute the program.
        """
        return [
            self.args.get('_ansible_shell_executable', '/bin/sh'),
            '-c',
            self._get_shell_fragment(),
        ]

    def _get_shell_fragment(self):
        return "%s %s" % (
            shlex_quote(self.program_fp.name),
            ' '.join(map(shlex_quote, self._get_program_args())),
        )

    def _run(self):
        try:
            rc, stdout, stderr = ansible_mitogen.target.exec_args(
                args=self._get_argv(),
                emulate_tty=self.emulate_tty,
            )
        except Exception:
            LOG.exception('While running %s', self._get_argv())
            e = sys.exc_info()[1]
            return {
                u'rc': 1,
                u'stdout': u'',
                u'stderr': u'%s: %s' % (type(e), e),
            }

        return {
            u'rc': rc,
            u'stdout': mitogen.core.to_text(stdout),
            u'stderr': mitogen.core.to_text(stderr),
        }


class ArgsFileRunner(Runner):
    def setup(self):
        super(ArgsFileRunner, self).setup()
        self._setup_args()

    def _setup_args(self):
        """
        Create a temporary file containing the module's arguments. The
        arguments are formatted via :meth:`_get_args`.
        """
        self.args_fp = tempfile.NamedTemporaryFile(
            prefix='ansible_mitogen',
            suffix='-args',
            dir=self.get_temp_dir(),
        )
        self.args_fp.write(utf8(self._get_args_contents()))
        self.args_fp.flush()
        reopen_readonly(self.program_fp)

    def _get_args_contents(self):
        """
        Return the module arguments formatted as JSON.
        """
        return json.dumps(self.args)

    def _get_program_args(self):
        return [self.args_fp.name]

    def revert(self):
        """
        Delete the temporary argument file.
        """
        self.args_fp.close()
        super(ArgsFileRunner, self).revert()


class BinaryRunner(ArgsFileRunner, ProgramRunner):
    pass


class ScriptRunner(ProgramRunner):
    def __init__(self, interpreter_fragment, is_python, **kwargs):
        super(ScriptRunner, self).__init__(**kwargs)
        self.interpreter_fragment = interpreter_fragment
        self.is_python = is_python

    b_ENCODING_STRING = b('# -*- coding: utf-8 -*-')

    def _get_program(self):
        return self._rewrite_source(
            super(ScriptRunner, self)._get_program()
        )

    def _get_argv(self):
        return [
            self.args.get('_ansible_shell_executable', '/bin/sh'),
            '-c',
            self._get_shell_fragment(),
        ]

    def _get_shell_fragment(self):
        """
        Scripts are eligible for having their hashbang line rewritten, and to
        be executed via /bin/sh using the ansible_*_interpreter value used as a
        shell fragment prefixing to the invocation.
        """
        return "%s %s %s" % (
            self.interpreter_fragment,
            shlex_quote(self.program_fp.name),
            ' '.join(map(shlex_quote, self._get_program_args())),
        )

    def _rewrite_source(self, s):
        """
        Mutate the source according to the per-task parameters.
        """
        # While Ansible rewrites the #! using ansible_*_interpreter, it is
        # never actually used to execute the script, instead it is a shell
        # fragment consumed by shell/__init__.py::build_module_command().
        new = [b('#!') + utf8(self.interpreter_fragment)]
        if self.is_python:
            new.append(self.b_ENCODING_STRING)

        _, _, rest = bytes_partition(s, b('\n'))
        new.append(rest)
        return b('\n').join(new)


class NewStyleRunner(ScriptRunner):
    """
    Execute a new-style Ansible module, where Module Replacer-related tricks
    aren't required.
    """
    #: path => new-style module bytecode.
    _code_by_path = {}

    def __init__(self, module_map, **kwargs):
        super(NewStyleRunner, self).__init__(**kwargs)
        self.module_map = module_map

    def _setup_imports(self):
        """
        Ensure the local importer and PushFileService has everything for the
        Ansible module before setup() completes, but before detach() is called
        in an asynchronous task.

        The master automatically streams modules towards us concurrent to the
        runner invocation, however there is no public API to synchronize on the
        completion of those preloads. Instead simply reuse the importer's
        synchronization mechanism by importing everything the module will need
        prior to detaching.
        """
        for fullname, _, _ in self.module_map['custom']:
            mitogen.core.import_module(fullname)
        for fullname in self.module_map['builtin']:
            try:
                mitogen.core.import_module(fullname)
            except ImportError:
                # #590: Ansible 2.8 module_utils.distro is a package that
                # replaces itself in sys.modules with a non-package during
                # import. Prior to replacement, it is a real package containing
                # a '_distro' submodule which is used on 2.x. Given a 2.x
                # controller and 3.x target, the import hook never needs to run
                # again before this replacement occurs, and 'distro' is
                # replaced with a module from the stdlib. In this case as this
                # loop progresses to the next entry and attempts to preload
                # 'distro._distro', the import mechanism will fail. So here we
                # silently ignore any failure for it.
                if fullname != 'ansible.module_utils.distro._distro':
                    raise

    def _setup_excepthook(self):
        """
        Starting with Ansible 2.6, some modules (file.py) install a
        sys.excepthook and never clean it up. So we must preserve the original
        excepthook and restore it after the run completes.
        """
        self.original_excepthook = sys.excepthook

    def setup(self):
        super(NewStyleRunner, self).setup()

        self._stdio = NewStyleStdio(self.args, self.get_temp_dir())
        # It is possible that not supplying the script filename will break some
        # module, but this has never been a bug report. Instead act like an
        # interpreter that had its script piped on stdin.
        self._argv = TemporaryArgv([''])
        self._temp_watcher = TempFileWatcher()
        self._importer = ModuleUtilsImporter(
            context=self.service_context,
            module_utils=self.module_map['custom'],
        )
        self._setup_imports()
        self._setup_excepthook()
        self.atexit_wrapper = AtExitWrapper()
        if libc__res_init:
            libc__res_init()

    def _revert_excepthook(self):
        sys.excepthook = self.original_excepthook

    def revert(self):
        self.atexit_wrapper.revert()
        self._temp_watcher.revert()
        self._argv.revert()
        self._stdio.revert()
        self._revert_excepthook()
        super(NewStyleRunner, self).revert()

    def _get_program_filename(self):
        """
        See ProgramRunner._get_program_filename().
        """
        return 'ansible_module_' + os.path.basename(self.path)

    def _setup_args(self):
        pass

    # issue #555: in old times it was considered good form to reload sys and
    # change the default encoding. This hack was removed from Ansible long ago,
    # but not before permeating into many third party modules.
    PREHISTORIC_HACK_RE = re.compile(
        b(r'reload\s*\(\s*sys\s*\)\s*'
          r'sys\s*\.\s*setdefaultencoding\([^)]+\)')
    )

    def _setup_program(self):
        source = ansible_mitogen.target.get_small_file(
            context=self.service_context,
            path=self.path,
        )
        self.source = self.PREHISTORIC_HACK_RE.sub(b(''), source)

    def _get_code(self):
        try:
            return self._code_by_path[self.path]
        except KeyError:
            return self._code_by_path.setdefault(self.path, compile(
                # Py2.4 doesn't support kwargs.
                self.source,            # source
                "master:" + self.path,  # filename
                'exec',                 # mode
                0,                      # flags
                True,                   # dont_inherit
            ))

    if mitogen.core.PY3:
        main_module_name = '__main__'
    else:
        main_module_name = b('__main__')

    def _handle_magic_exception(self, mod, exc):
        """
        Beginning with Ansible >2.6, some modules (file.py) install a
        sys.excepthook which is a closure over AnsibleModule, redirecting the
        magical exception to AnsibleModule.fail_json().

        For extra special needs bonus points, the class is not defined in
        module_utils, but is defined in the module itself, meaning there is no
        type for isinstance() that outlasts the invocation.
        """
        klass = getattr(mod, 'AnsibleModuleError', None)
        if klass and isinstance(exc, klass):
            mod.module.fail_json(**exc.results)

    def _run_code(self, code, mod):
        try:
            if mitogen.core.PY3:
                exec(code, vars(mod))
            else:
                exec('exec code in vars(mod)')
        except Exception:
            self._handle_magic_exception(mod, sys.exc_info()[1])
            raise

    def _run(self):
        mod = types.ModuleType(self.main_module_name)
        mod.__package__ = None
        # Some Ansible modules use __file__ to find the Ansiballz temporary
        # directory. We must provide some temporary path in __file__, but we
        # don't want to pointlessly write the module to disk when it never
        # actually needs to exist. So just pass the filename as it would exist.
        mod.__file__ = os.path.join(
            self.get_temp_dir(),
            'ansible_module_' + os.path.basename(self.path),
        )

        code = self._get_code()
        rc = 2
        try:
            try:
                self._run_code(code, mod)
            except SystemExit:
                exc = sys.exc_info()[1]
                rc = exc.args[0]
            except Exception:
                # This writes to stderr by default.
                traceback.print_exc()
                rc = 1

        finally:
            self.atexit_wrapper.run_callbacks()

        return {
            u'rc': rc,
            u'stdout': mitogen.core.to_text(sys.stdout.getvalue()),
            u'stderr': mitogen.core.to_text(sys.stderr.getvalue()),
        }


class JsonArgsRunner(ScriptRunner):
    JSON_ARGS = b('<<INCLUDE_ANSIBLE_MODULE_JSON_ARGS>>')

    def _get_args_contents(self):
        return json.dumps(self.args).encode()

    def _rewrite_source(self, s):
        return (
            super(JsonArgsRunner, self)._rewrite_source(s)
            .replace(self.JSON_ARGS, self._get_args_contents())
        )


class WantJsonRunner(ArgsFileRunner, ScriptRunner):
    pass


class OldStyleRunner(ArgsFileRunner, ScriptRunner):
    def _get_args_contents(self):
        """
        Mimic the argument formatting behaviour of
        ActionBase._execute_module().
        """
        return ' '.join(
            '%s=%s' % (key, shlex_quote(str(self.args[key])))
            for key in self.args
        ) + ' '  # Bug-for-bug :(