FreedomBox/plinth/action_utils.py

#
# This file is part of FreedomBox.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
"""
Python action utility functions.
"""

import logging
import os
import shutil
import subprocess
import tempfile

logger = logging.getLogger(__name__)

UWSGI_ENABLED_PATH = '/etc/uwsgi/apps-enabled/{config_name}.ini'
UWSGI_AVAILABLE_PATH = '/etc/uwsgi/apps-available/{config_name}.ini'


def is_systemd_running():
    """Return if we are running under systemd."""
    return os.path.exists('/run/systemd')


def service_is_running(servicename):
    """Return whether a service is currently running.

    Does not need to run as root.
    """
    try:
        if is_systemd_running():
            subprocess.run(['systemctl', 'status', servicename], check=True,
                           stdout=subprocess.DEVNULL)
        else:
            subprocess.run(['service', servicename, 'status'], check=True,
                           stdout=subprocess.DEVNULL)

        return True
    except subprocess.CalledProcessError:
        # If a service is not running we get a status code != 0 and
        # thus a CalledProcessError
        return False


def service_is_enabled(service_name, strict_check=False):
    """Check if service is enabled in systemd.

    In some cases, after disabling a service, systemd puts it into a state
    called 'enabled-runtime' and returns a positive response to 'is-enabled'
    query. Until we understand better, a conservative work around is to pass
    strict=True to services effected by this behavior.

    """
    try:
        process = subprocess.run(['systemctl', 'is-enabled', service_name],
                                 check=True, stdout=subprocess.PIPE,
                                 stderr=subprocess.DEVNULL)
        if not strict_check:
            return True

        return process.stdout.decode().strip() == 'enabled'
    except subprocess.CalledProcessError:
        return False


def service_enable(service_name):
    """Enable and start a service in systemd and sysvinit using update-rc.d."""
    subprocess.call(['systemctl', 'enable', service_name])
    service_start(service_name)


def service_disable(service_name):
    """Disable and stop service in systemd and sysvinit using update-rc.d."""
    try:
        service_stop(service_name)
    except subprocess.CalledProcessError:
        pass
    subprocess.call(['systemctl', 'disable', service_name])


def service_unmask(service_name):
    """Unmask a service"""
    subprocess.call(['systemctl', 'unmask', service_name])


def service_start(service_name):
    """Start a service with systemd or sysvinit."""
    service_action(service_name, 'start')


def service_stop(service_name):
    """Stop a service with systemd or sysvinit."""
    service_action(service_name, 'stop')


def service_restart(service_name):
    """Restart a service with systemd or sysvinit."""
    service_action(service_name, 'restart')


def service_try_restart(service_name):
    """Try to restart a service with systemd or sysvinit."""
    service_action(service_name, 'try-restart')


def service_reload(service_name):
    """Reload a service with systemd or sysvinit."""
    service_action(service_name, 'reload')


def service_action(service_name, action):
    """Perform the given action on the service_name."""
    if is_systemd_running():
        subprocess.run(['systemctl', action, service_name],
                       stdout=subprocess.DEVNULL)
    else:
        subprocess.run(['service', service_name, action],
                       stdout=subprocess.DEVNULL)


def webserver_is_enabled(name, kind='config'):
    """Return whether a config/module/site is enabled in Apache."""
    if not shutil.which('a2query'):
        return False

    option_map = {'config': '-c', 'site': '-s', 'module': '-m'}
    try:
        # Don't print anything on the terminal
        subprocess.check_output(['a2query', option_map[kind], name],
                                stderr=subprocess.STDOUT)
        return True
    except subprocess.CalledProcessError:
        return False


def webserver_enable(name, kind='config', apply_changes=True):
    """Enable a config/module/site in Apache.

    Restart/reload the webserver if apply_changes is True.  Return
    whether restart('restart'), reload('reload') or no action (None)
    is required.  If changes have been applied, then performed action
    is returned.
    """
    if webserver_is_enabled(name, kind) and kind == 'module':
        return

    command_map = {
        'config': 'a2enconf',
        'site': 'a2ensite',
        'module': 'a2enmod'
    }
    subprocess.check_output([command_map[kind], name])

    action_required = 'restart' if kind == 'module' else 'reload'

    if apply_changes:
        if action_required == 'restart':
            service_restart('apache2')
        else:
            service_reload('apache2')

    return action_required


def webserver_disable(name, kind='config', apply_changes=True):
    """Disable config/module/site in Apache.

    Restart/reload the webserver if apply_changes is True.  Return
    whether restart('restart'), reload('reload') or no action (None)
    is required.  If changes have been applied, then performed action
    is returned.
    """
    if not webserver_is_enabled(name, kind):
        return

    command_map = {
        'config': 'a2disconf',
        'site': 'a2dissite',
        'module': 'a2dismod'
    }
    subprocess.check_output([command_map[kind], name])

    action_required = 'restart' if kind == 'module' else 'reload'

    if apply_changes:
        if action_required == 'restart':
            service_restart('apache2')
        else:
            service_reload('apache2')

    return action_required


class WebserverChange(object):
    """Context to restart/reload Apache after configuration changes."""
    def __init__(self):
        """Initialize the context object state."""
        self.actions_required = set()

    def __enter__(self):
        """Return the context object so methods could be called on it."""
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        """Restart or reload the webserver.

        Don't suppress exceptions.  If an exception occurs
        restart/reload the webserver based on enable/disable
        operations done so far.
        """
        if 'restart' in self.actions_required:
            service_restart('apache2')
        elif 'reload' in self.actions_required:
            service_reload('apache2')

    def enable(self, name, kind='config'):
        """Enable a config/module/site in Apache.

        Don't apply the changes until the context is exited.
        """
        action_required = webserver_enable(name, kind, apply_changes=False)
        self.actions_required.add(action_required)

    def disable(self, name, kind='config'):
        """Disable a config/module/site in Apache.

        Don't apply the changes until the context is exited.
        """
        action_required = webserver_disable(name, kind, apply_changes=False)
        self.actions_required.add(action_required)


def uwsgi_is_enabled(config_name):
    """Return whether a uwsgi config is enabled."""
    enabled_path = UWSGI_ENABLED_PATH.format(config_name=config_name)
    return os.path.exists(enabled_path)


def uwsgi_enable(config_name):
    """Enable a uwsgi configuration that runs under uwsgi."""
    if uwsgi_is_enabled(config_name):
        return

    # uwsgi is started/stopped using init script. We don't know if it can
    # handle some configuration already running against newly enabled
    # configuration. So, stop first before enabling new configuration.
    service_stop('uwsgi')

    enabled_path = UWSGI_ENABLED_PATH.format(config_name=config_name)
    available_path = UWSGI_AVAILABLE_PATH.format(config_name=config_name)
    os.symlink(available_path, enabled_path)

    service_enable('uwsgi')
    service_start('uwsgi')


def uwsgi_disable(config_name):
    """Disable a uwsgi configuration that runs under uwsgi."""
    if not uwsgi_is_enabled(config_name):
        return

    # If uwsgi is restarted later, it won't stop the just disabled
    # configuration due to how init scripts are written for uwsgi.
    service_stop('uwsgi')
    enabled_path = UWSGI_ENABLED_PATH.format(config_name=config_name)
    os.unlink(enabled_path)
    service_start('uwsgi')


def get_addresses():
    """Return a list of IP addresses and hostnames."""
    addresses = get_ip_addresses()

    hostname = get_hostname()
    addresses.append({
        'kind': '4',
        'address': 'localhost',
        'numeric': False,
        'url_address': 'localhost'
    })
    addresses.append({
        'kind': '6',
        'address': 'localhost',
        'numeric': False,
        'url_address': 'localhost'
    })
    addresses.append({
        'kind': '4',
        'address': hostname,
        'numeric': False,
        'url_address': hostname
    })

    # XXX: When a hostname is resolved to IPv6 address, it may likely
    # be link-local address.  Link local IPv6 addresses are valid only
    # for a given link and need to be scoped with interface name such
    # as '%eth0' to work.  Tools such as curl don't seem to handle
    # this correctly.
    # addresses.append({'kind': '6', 'address': hostname, 'numeric': False})

    return addresses


def get_ip_addresses():
    """Return a list of IP addresses assigned to the system."""
    addresses = []

    output = subprocess.check_output(['ip', '-o', 'addr'])
    for line in output.decode().splitlines():
        parts = line.split()
        address = {
            'kind': '4' if parts[2] == 'inet' else '6',
            'address': parts[3].split('/')[0],
            'url_address': parts[3].split('/')[0],
            'numeric': True,
            'scope': parts[5],
            'interface': parts[1]
        }

        if address['kind'] == '6' and address['numeric']:
            if address['scope'] != 'link':
                address['url_address'] = '[{0}]'.format(address['address'])
            else:
                address['url_address'] = '[{0}%{1}]'.format(
                    address['url_address'], address['interface'])

        addresses.append(address)

    return addresses


def get_hostname():
    """Return the current hostname."""
    return subprocess.check_output(['hostname']).decode().strip()


def dpkg_reconfigure(package, config):
    """Reconfigure package using debconf database override."""
    override_template = '''
Name: {package}/{key}
Template: {package}/{key}
Value: {value}
Owners: {package}
'''
    override_data = ''
    for key, value in config.items():
        override_data += override_template.format(package=package, key=key,
                                                  value=value)

    with tempfile.NamedTemporaryFile(mode='w', delete=False) as override_file:
        override_file.write(override_data)

    env = os.environ.copy()
    env['DEBCONF_DB_OVERRIDE'] = 'File{' + override_file.name + \
                                 ' readonly:true}'
    env['DEBIAN_FRONTEND'] = 'noninteractive'
    subprocess.run(['dpkg-reconfigure', package], env=env)

    try:
        os.remove(override_file.name)
    except OSError:
        pass


def debconf_set_selections(presets):
    """Answer debconf questions before installing a package."""
    try:
        # Workaround Debian Bug #487300. In some situations, debconf complains
        # it can't find the question being answered even though it is supposed
        # to create a dummy question for it.
        subprocess.run(['/usr/share/debconf/fix_db.pl'], check=True)
    except (FileNotFoundError, PermissionError):
        pass

    presets = '\n'.join(presets)
    subprocess.check_output(['debconf-set-selections'], input=presets.encode())


def is_disk_image():
    """Return whether the current machine is from a disk image.

    Two primary ways to install FreedomBox are:
    - Using FreedomBox image for various hardware platforms.
    - Installing packages on a Debian machine using apt.
    """
    return os.path.exists('/var/lib/freedombox/is-freedombox-disk-image')