FreedomBox/actions/sshfs

#!/usr/bin/python3
# -*- mode: python -*-
#
# 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/>.
#
"""
Actions for sshfs.
"""

import argparse
import json
import os
import subprocess
import sys

TIMEOUT = 5


class AlreadyMountedError(Exception):
    pass


def parse_arguments():
    """Return parsed command line arguments as dictionary."""
    parser = argparse.ArgumentParser()
    subparsers = parser.add_subparsers(dest='subcommand', help='Sub command')

    mount = subparsers.add_parser('mount', help='mount an ssh filesystem')
    mount.add_argument('--mountpoint', help='Local mountpoint', required=True)
    mount.add_argument('--path', help='Remote ssh path to mount',
                       required=True)
    umount = subparsers.add_parser('umount',
                                   help='unmount an ssh filesystem')
    umount.add_argument('--mountpoint', help='Mountpoint to unmount',
                        required=True)
    is_mounted = subparsers.add_parser('is-mounted',
                                       help='Check whether an sshfs is mouned')
    is_mounted.add_argument('--mountpoint', help='Mountpoint to check',
                            required=True)

    subparsers.required = True
    return parser.parse_args()


def get_env(arguments, read_input=True):
    """Create encryption and ssh kwargs out of given arguments"""
    env = dict(os.environ)
    password = read_password() if read_input else None
    if password:
        env['SSHPASS'] = password
        env['BORG_RSH'] = 'sshpass -e ssh -o StrictHostKeyChecking=no'
    return env


def subcommand_mount(arguments):
    """Show repository information."""
    try:
        validate_mountpoint(arguments.mountpoint)
    except AlreadyMountedError:
        return

    env = get_env(arguments)
    remote_path = arguments.path
    kwargs = {}
    # the shell would expand ~/ to the local home directory
    remote_path = remote_path.replace('~/', '').replace('~', '')
    cmd = ['sshfs', remote_path, arguments.mountpoint, '-o',
           'UserKnownHostsFile=/dev/null', '-o',
           'StrictHostKeyChecking=no']
    timeout = None
    if 'SSHPASS' in env:
        cmd += ['-o', 'password_stdin']
        kwargs['input'] = env['SSHPASS'].encode()
    elif 'SSHKEY' in env:
        cmd += ['-o', 'IdentityFile=$SSHKEY']
        timeout = TIMEOUT
    else:
        raise ValueError('mount requires either SSHPASS or SSHKEY in env')
    subprocess.run(cmd, check=True, env=env, timeout=timeout, **kwargs)


def subcommand_umount(arguments):
    """Show repository information."""
    run(['umount', arguments.mountpoint])


def validate_mountpoint(mountpoint):
    """Check that the folder is empty, and create it if it doesn't exist"""
    if os.path.exists(mountpoint):
        if _is_mounted(mountpoint):
            raise AlreadyMountedError('Mountpoint %s already mounted' %
                                      mountpoint)
        if os.listdir(mountpoint) or not os.path.isdir(mountpoint):
            raise ValueError('Mountpoint %s is not an empty directory' %
                             mountpoint)
    else:
        os.makedirs(mountpoint)


def _is_mounted(mountpoint):
    """Return boolean whether a local directory is a mountpoint."""
    cmd = ['mountpoint', '-q', mountpoint]
    # mountpoint exits with status non-zero if it didn't find a mountpoint
    try:
        subprocess.run(cmd, check=True)
        return True
    except subprocess.CalledProcessError:
        return False


def subcommand_is_mounted(arguments):
    print(json.dumps(_is_mounted(arguments.mountpoint)))


def read_password():
    """Read the password from stdin."""
    if sys.stdin.isatty():
        return ''
    else:
        return ''.join(sys.stdin)


def run(cmd, env=None, check=True):
    """Wrap the command with ssh password or keyfile authentication"""
    # Set a timeout to not get stuck if the remote server asks for a password.
    subprocess.run(cmd, check=check, env=env, timeout=TIMEOUT)


def main():
    """Parse arguments and perform all duties."""
    arguments = parse_arguments()

    subcommand = arguments.subcommand.replace('-', '_')
    subcommand_method = globals()['subcommand_' + subcommand]
    subcommand_method(arguments)


if __name__ == '__main__':
    main()