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 = 30


class AlreadyMountedError(Exception):
    """Exception raised when mount point is already mounted."""


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)
    mount.add_argument('--ssh-keyfile', help='Path of private ssh key',
                       default=None, required=False)
    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 a mountpoint is mounted')
    is_mounted.add_argument('--mountpoint', help='Mountpoint to check',
                            required=True)

    subparsers.required = True
    return parser.parse_args()


def subcommand_mount(arguments):
    """Mount a remote ssh path via sshfs."""
    try:
        validate_mountpoint(arguments.mountpoint)
    except AlreadyMountedError:
        return

    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'
    ]
    if arguments.ssh_keyfile:
        cmd += ['-o', 'IdentityFile=' + arguments.ssh_keyfile]
    else:
        password = read_password()
        if not password:
            raise ValueError('mount requires either a password or ssh_keyfile')
        cmd += ['-o', 'password_stdin']
        kwargs['input'] = password.encode()

    subprocess.run(cmd, check=True, timeout=TIMEOUT, **kwargs)


def subcommand_umount(arguments):
    """Unmount a mountpoint."""
    subprocess.run(['umount', arguments.mountpoint], check=True)


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 whether a path is already mounted."""
    print(json.dumps(_is_mounted(arguments.mountpoint)))


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

    return ''.join(sys.stdin)


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()