mitogen/ansible_mitogen/target.py

# Copyright 2017, 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
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# POSSIBILITY OF SUCH DAMAGE.

"""
Helper functions intended to be executed on the target. These are entrypoints
for file transfer, module execution and sundry bits like changing file modes.
"""

from __future__ import absolute_import
from __future__ import unicode_literals

import errno
import functools
import grp
import json
import logging
import operator
import os
import pwd
import re
import signal
import stat
import subprocess
import sys
import tempfile
import traceback
import types

import mitogen.core
import mitogen.fork
import mitogen.parent
import mitogen.service

# Ansible since PR #41749 inserts "import __main__" into
# ansible.module_utils.basic. Mitogen's importer will refuse such an import, so
# we must setup a fake "__main__" before that module is ever imported. The
# str() is to cast Unicode to bytes on Python 2.6.
if not sys.modules.get(str('__main__')):
    sys.modules[str('__main__')] = types.ModuleType(str('__main__'))

import ansible.module_utils.json_utils
import ansible_mitogen.runner


LOG = logging.getLogger(__name__)

MAKE_TEMP_FAILED_MSG = (
    "Unable to find a useable temporary directory. This likely means no\n"
    "system-supplied TMP directory can be written to, or all directories\n"
    "were mounted on 'noexec' filesystems.\n"
    "\n"
    "The following paths were tried:\n"
    "    %(namelist)s\n"
    "\n"
    "Please check '-vvv' output for a log of individual path errors."
)


#: Initialized to an econtext.parent.Context pointing at a pristine fork of
#: the target Python interpreter before it executes any code or imports.
_fork_parent = None

#: Set by init_child() to a list of candidate $variable-expanded and
#: tilde-expanded directory paths that may be usable as a temporary directory.
_candidate_temp_dirs = None

#: Set by reset_temp_dir() to the single temporary directory that will exist
#: for the duration of the process.
temp_dir = None


def get_small_file(context, path):
    """
    Basic in-memory caching module fetcher. This generates an one roundtrip for
    every previously unseen file, so it is only a temporary solution.

    :param context:
        Context we should direct FileService requests to. For now (and probably
        forever) this is just the top-level Mitogen connection manager process.
    :param path:
        Path to fetch from FileService, must previously have been registered by
        a privileged context using the `register` command.
    :returns:
        Bytestring file data.
    """
    pool = mitogen.service.get_or_create_pool(router=context.router)
    service = pool.get_service('mitogen.service.PushFileService')
    return service.get(path)


def transfer_file(context, in_path, out_path, sync=False, set_owner=False):
    """
    Streamily download a file from the connection multiplexer process in the
    controller.

    :param mitogen.core.Context context:
        Reference to the context hosting the FileService that will be used to
        fetch the file.
    :param bytes in_path:
        FileService registered name of the input file.
    :param bytes out_path:
        Name of the output path on the local disk.
    :param bool sync:
        If :data:`True`, ensure the file content and metadat are fully on disk
        before renaming the temporary file over the existing file. This should
        ensure in the case of system crash, either the entire old or new file
        are visible post-reboot.
    :param bool set_owner:
        If :data:`True`, look up the metadata username and group on the local
        system and file the file owner using :func:`os.fchmod`.
    """
    out_path = os.path.abspath(out_path)
    fd, tmp_path = tempfile.mkstemp(suffix='.tmp',
                                    prefix='.ansible_mitogen_transfer-',
                                    dir=os.path.dirname(out_path))
    fp = os.fdopen(fd, 'wb', mitogen.core.CHUNK_SIZE)
    LOG.debug('transfer_file(%r) temporary file: %s', out_path, tmp_path)

    try:
        try:
            ok, metadata = mitogen.service.FileService.get(
                context=context,
                path=in_path,
                out_fp=fp,
            )
            if not ok:
                raise IOError('transfer of %r was interrupted.' % (in_path,))

            os.fchmod(fp.fileno(), metadata['mode'])
            if set_owner:
                set_fd_owner(fp.fileno(), metadata['owner'], metadata['group'])
        finally:
            fp.close()

        if sync:
            os.fsync(fp.fileno())
        os.rename(tmp_path, out_path)
    except BaseException:
        os.unlink(tmp_path)
        raise

    os.utime(out_path, (metadata['atime'], metadata['mtime']))


def prune_tree(path):
    """
    Like shutil.rmtree(), but log errors rather than discard them, and do not
    waste multiple os.stat() calls discovering whether the object can be
    deleted, just try deleting it instead.
    """
    try:
        os.unlink(path)
        return
    except OSError as e:
        if not (os.path.isdir(path) and
                e.args[0] in (errno.EPERM, errno.EISDIR)):
            LOG.error('prune_tree(%r): %s', path, e)
            return

    try:
        # Ensure write access for readonly directories. Ignore error in case
        # path is on a weird filesystem (e.g. vfat).
        os.chmod(path, int('0700', 8))
    except OSError as e:
        LOG.warning('prune_tree(%r): %s', path, e)

    try:
        for name in os.listdir(path):
            if name not in ('.', '..'):
                prune_tree(os.path.join(path, name))
        os.rmdir(path)
    except OSError as e:
        LOG.error('prune_tree(%r): %s', path, e)


def _on_broker_shutdown():
    """
    Respond to broker shutdown (graceful termination by parent, or loss of
    connection to parent) by deleting our sole temporary directory.
    """
    prune_tree(temp_dir)


def find_good_temp_dir():
    """
    Given a list of candidate temp directories extracted from ``ansible.cfg``
    and stored in _candidate_temp_dirs, combine it with the Python-builtin list
    of candidate directories used by :mod:`tempfile`, then iteratively try each
    in turn until one is found that is both writeable and executable.
    """
    paths = [os.path.expandvars(os.path.expanduser(p))
             for p in _candidate_temp_dirs]
    paths.extend(tempfile._candidate_tempdir_list())

    for path in paths:
        try:
            tmp = tempfile.NamedTemporaryFile(
                prefix='ansible_mitogen_find_good_temp_dir',
                dir=path,
            )
        except (OSError, IOError) as e:
            LOG.debug('temp dir %r unusable: %s', path, e)
            continue

        try:
            try:
                os.chmod(tmp.name, int('0700', 8))
            except OSError as e:
                LOG.debug('temp dir %r unusable: %s: chmod failed: %s',
                          path, e)
                continue

            try:
                # access(.., X_OK) is sufficient to detect noexec.
                if not os.access(tmp.name, os.X_OK):
                    raise OSError('filesystem appears to be mounted noexec')
            except OSError as e:
                LOG.debug('temp dir %r unusable: %s: %s', path, e)
                continue

            LOG.debug('Selected temp directory: %r (from %r)', path, paths)
            return path
        finally:
            tmp.close()

    raise IOError(MAKE_TEMP_FAILED_MSG % {
        'paths': '\n    '.join(paths),
    })


@mitogen.core.takes_econtext
def reset_temp_dir(econtext):
    """
    Create one temporary directory to be reused by all runner.py invocations
    for the lifetime of the process. The temporary directory is changed for
    each forked job, and emptied as necessary by runner.py::_cleanup_temp()
    after each module invocation.

    The result is that a context need only create and delete one directory
    during startup and shutdown, and no further filesystem writes need occur
    assuming no modules execute that create temporary files.
    """
    global temp_dir
    # https://github.com/dw/mitogen/issues/239

    basedir = find_good_temp_dir()
    temp_dir = tempfile.mkdtemp(prefix='ansible_mitogen_', dir=basedir)

    # This must be reinstalled in forked children too, since the Broker
    # instance from the parent process does not carry over to the new child.
    mitogen.core.listen(econtext.broker, 'shutdown', _on_broker_shutdown)


@mitogen.core.takes_econtext
def init_child(econtext, log_level, candidate_temp_dirs):
    """
    Called by ContextService immediately after connection; arranges for the
    (presently) spotless Python interpreter to be forked, where the newly
    forked interpreter becomes the parent of any newly forked future
    interpreters.

    This is necessary to prevent modules that are executed in-process from
    polluting the global interpreter state in a way that effects explicitly
    isolated modules.

    :param int log_level:
        Logging package level active in the master.
    :param list[str] candidate_temp_dirs:
        List of $variable-expanded and tilde-expanded directory names to add to
        candidate list of temporary directories.

    :returns:
        Dict like::

            {
                'fork_context': mitogen.core.Context.
                'home_dir': str.
            }

        Where `fork_context` refers to the newly forked 'fork parent' context
        the controller will use to start forked jobs, and `home_dir` is the
        home directory for the active user account.
    """
    global _candidate_temp_dirs
    _candidate_temp_dirs = candidate_temp_dirs

    global _fork_parent
    mitogen.parent.upgrade_router(econtext)
    _fork_parent = econtext.router.fork()
    reset_temp_dir(econtext)

    # Copying the master's log level causes log messages to be filtered before
    # they reach LogForwarder, thus reducing an influx of tiny messges waking
    # the connection multiplexer process in the master.
    LOG.setLevel(log_level)
    logging.getLogger('ansible_mitogen').setLevel(log_level)

    return {
        'fork_context': _fork_parent,
        'home_dir': mitogen.core.to_text(os.path.expanduser('~')),
        'temp_dir': temp_dir,
    }


@mitogen.core.takes_econtext
def create_fork_child(econtext):
    """
    For helper functions executed in the fork parent context, arrange for
    the context's router to be upgraded as necessary and for a new child to be
    prepared.
    """
    mitogen.parent.upgrade_router(econtext)
    context = econtext.router.fork()
    context.call(reset_temp_dir)
    LOG.debug('create_fork_child() -> %r', context)
    return context


def run_module(kwargs):
    """
    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.
    """
    runner_name = kwargs.pop('runner_name')
    klass = getattr(ansible_mitogen.runner, runner_name)
    impl = klass(**kwargs)
    return impl.run()


def _get_async_dir():
    return os.path.expanduser(
        os.environ.get('ANSIBLE_ASYNC_DIR', '~/.ansible_async')
    )


class AsyncRunner(object):
    def __init__(self, job_id, timeout_secs, econtext, kwargs):
        self.job_id = job_id
        self.timeout_secs = timeout_secs
        self.econtext = econtext
        self.kwargs = kwargs
        self._timed_out = False
        self._init_path()

    def _init_path(self):
        async_dir = _get_async_dir()
        if not os.path.exists(async_dir):
            os.makedirs(async_dir)
        self.path = os.path.join(async_dir, self.job_id)

    def _update(self, dct):
        """
        Update an async job status file.
        """
        LOG.info('%r._update(%r, %r)', self, self.job_id, dct)
        dct.setdefault('ansible_job_id', self.job_id)
        dct.setdefault('data', '')

        with open(self.path + '.tmp', 'w') as fp:
            fp.write(json.dumps(dct))
        os.rename(self.path + '.tmp', self.path)

    def _on_sigalrm(self, signum, frame):
        """
        Respond to SIGALRM (job timeout) by updating the job file and killing
        the process.
        """
        msg = "Job reached maximum time limit of %d seconds." % (
            self.timeout_secs,
        )
        self._update({
            "failed": 1,
            "finished": 1,
            "msg": msg,
        })
        self._timed_out = True
        self.econtext.broker.shutdown()

    def _install_alarm(self):
        signal.signal(signal.SIGALRM, self._on_sigalrm)
        signal.alarm(self.timeout_secs)

    def _run_module(self):
        kwargs = dict(self.kwargs, **{
            'detach': True,
            'econtext': self.econtext,
            'emulate_tty': False,
        })
        return run_module(kwargs)

    def _parse_result(self, dct):
        filtered, warnings = (
            ansible.module_utils.json_utils.
            _filter_non_json_lines(dct['stdout'])
        )
        result = json.loads(filtered)
        result.setdefault('warnings', []).extend(warnings)
        result['stderr'] = dct['stderr']
        self._update(result)

    def _run(self):
        """
        1. Immediately updates the status file to mark the job as started.
        2. Installs a timer/signal handler to implement the time limit.
        3. Runs as with run_module(), writing the result to the status file.

        :param dict kwargs:
            Runner keyword arguments.
        :param str job_id:
            String job ID.
        :param int timeout_secs:
            If >0, limit the task's maximum run time.
        """
        self._update({
            'started': 1,
            'finished': 0,
            'pid': os.getpid()
        })

        if self.timeout_secs > 0:
            self._install_alarm()

        dct = self._run_module()
        if not self._timed_out:
            # After SIGALRM fires, there is a window between broker responding
            # to shutdown() by killing the process, and work continuing on the
            # main thread. If main thread was asleep in at least
            # basic.py/select.select(), an EINTR will be raised. We want to
            # discard that exception.
            try:
                self._parse_result(dct)
            except Exception:
                self._update({
                    "failed": 1,
                    "msg": traceback.format_exc(),
                    "data": dct['stdout'],  # temporary notice only
                    "stderr": dct['stderr']
                })

    def run(self):
        try:
            try:
                self._run()
            except Exception:
                self._update({
                    "failed": 1,
                    "msg": traceback.format_exc(),
                })
        finally:
            self.econtext.broker.shutdown()


@mitogen.core.takes_econtext
def run_module_async(kwargs, job_id, timeout_secs, econtext):
    """
    Execute a module with its run status and result written to a file,
    terminating on the process on completion. This function must run in a child
    forked using :func:`create_fork_child`.
    """
    arunner = AsyncRunner(job_id, timeout_secs, econtext, kwargs)
    arunner.run()


def get_user_shell():
    """
    For commands executed directly via an SSH command-line, SSH looks up the
    user's shell via getpwuid() and only defaults to /bin/sh if that field is
    missing or empty.
    """
    try:
        pw_shell = pwd.getpwuid(os.geteuid()).pw_shell
    except KeyError:
        pw_shell = None

    return pw_shell or '/bin/sh'


def exec_args(args, in_data='', chdir=None, shell=None, emulate_tty=False):
    """
    Run a command in a subprocess, emulating the argument handling behaviour of
    SSH.

    :param list[str]:
        Argument vector.
    :param bytes in_data:
        Optional standard input for the command.
    :param bool emulate_tty:
        If :data:`True`, arrange for stdout and stderr to be merged into the
        stdout pipe and for LF to be translated into CRLF, emulating the
        behaviour of a TTY.
    :return:
        (return code, stdout bytes, stderr bytes)
    """
    LOG.debug('exec_args(%r, ..., chdir=%r)', args, chdir)
    assert isinstance(args, list)

    if emulate_tty:
        stderr = subprocess.STDOUT
    else:
        stderr = subprocess.PIPE

    proc = subprocess.Popen(
        args=args,
        stdout=subprocess.PIPE,
        stderr=stderr,
        stdin=subprocess.PIPE,
        cwd=chdir,
    )
    stdout, stderr = proc.communicate(in_data)

    if emulate_tty:
        stdout = stdout.replace(b'\n', b'\r\n')
    return proc.returncode, stdout, stderr or ''


def exec_command(cmd, in_data='', chdir=None, shell=None, emulate_tty=False):
    """
    Run a command in a subprocess, emulating the argument handling behaviour of
    SSH.

    :param bytes cmd:
        String command line, passed to user's shell.
    :param bytes in_data:
        Optional standard input for the command.
    :return:
        (return code, stdout bytes, stderr bytes)
    """
    assert isinstance(cmd, mitogen.core.UnicodeType)
    return exec_args(
        args=[get_user_shell(), '-c', cmd],
        in_data=in_data,
        chdir=chdir,
        shell=shell,
        emulate_tty=emulate_tty,
    )


def read_path(path):
    """
    Fetch the contents of a filesystem `path` as bytes.
    """
    return open(path, 'rb').read()


def set_fd_owner(fd, owner, group=None):
    if owner:
        uid = pwd.getpwnam(owner).pw_uid
    else:
        uid = os.geteuid()

    if group:
        gid = grp.getgrnam(group).gr_gid
    else:
        gid = os.getegid()

    os.fchown(fd, (uid, gid))


def write_path(path, s, owner=None, group=None, mode=None,
               utimes=None, sync=False):
    """
    Writes bytes `s` to a filesystem `path`.
    """
    path = os.path.abspath(path)
    fd, tmp_path = tempfile.mkstemp(suffix='.tmp',
                                    prefix='.ansible_mitogen_transfer-',
                                    dir=os.path.dirname(path))
    fp = os.fdopen(fd, 'wb', mitogen.core.CHUNK_SIZE)
    LOG.debug('write_path(path=%r) temporary file: %s', path, tmp_path)

    try:
        try:
            if mode:
                os.fchmod(fp.fileno(), mode)
            if owner or group:
                set_fd_owner(fp.fileno(), owner, group)
            fp.write(s)
        finally:
            fp.close()

        if sync:
            os.fsync(fp.fileno())
        os.rename(tmp_path, path)
    except BaseException:
        os.unlink(tmp_path)
        raise

    if utimes:
        os.utime(path, utimes)


CHMOD_CLAUSE_PAT = re.compile(r'([uoga]*)([+\-=])([ugo]|[rwx]*)')
CHMOD_MASKS = {
    'u': stat.S_IRWXU,
    'g': stat.S_IRWXG,
    'o': stat.S_IRWXO,
    'a': (stat.S_IRWXU | stat.S_IRWXG | stat.S_IRWXO),
}
CHMOD_BITS = {
    'u': {'r': stat.S_IRUSR, 'w': stat.S_IWUSR, 'x': stat.S_IXUSR},
    'g': {'r': stat.S_IRGRP, 'w': stat.S_IWGRP, 'x': stat.S_IXGRP},
    'o': {'r': stat.S_IROTH, 'w': stat.S_IWOTH, 'x': stat.S_IXOTH},
    'a': {
        'r': (stat.S_IRUSR | stat.S_IRGRP | stat.S_IROTH),
        'w': (stat.S_IWUSR | stat.S_IWGRP | stat.S_IWOTH),
        'x': (stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH)
    }
}


def apply_mode_spec(spec, mode):
    """
    Given a symbolic file mode change specification in the style of chmod(1)
    `spec`, apply changes in the specification to the numeric file mode `mode`.
    """
    for clause in spec.split(','):
        match = CHMOD_CLAUSE_PAT.match(clause)
        who, op, perms = match.groups()
        for ch in who or 'a':
            mask = CHMOD_MASKS[ch]
            bits = CHMOD_BITS[ch]
            cur_perm_bits = mode & mask
            new_perm_bits = functools.reduce(operator.or_, (bits[p] for p in perms), 0)
            mode &= ~mask
            if op == '=':
                mode |= new_perm_bits
            elif op == '+':
                mode |= new_perm_bits | cur_perm_bits
            else:
                mode |= cur_perm_bits & ~new_perm_bits
    return mode


def set_file_mode(path, spec):
    """
    Update the permissions of a file using the same syntax as chmod(1).
    """
    mode = os.stat(path).st_mode

    if spec.isdigit():
        new_mode = int(spec, 8)
    else:
        new_mode = apply_mode_spec(spec, mode)

    os.chmod(path, new_mode)