Mini Shell

'''
NetNS objects
=============

A NetNS object is IPRoute-like. It runs in the main network
namespace, but also creates a proxy process running in
the required netns. All the netlink requests are done via
that proxy process.

NetNS supports standard IPRoute API, so can be used instead
of IPRoute, e.g., in IPDB::

    # start the main network settings database:
    ipdb_main = IPDB()
    # start the same for a netns:
    ipdb_test = IPDB(nl=NetNS('test'))

    # create VETH
    ipdb_main.create(ifname='v0p0', kind='veth', peer='v0p1').commit()

    # move peer VETH into the netns
    with ipdb_main.interfaces.v0p1 as veth:
        veth.net_ns_fd = 'test'

    # please keep in mind, that netns move clears all the settings
    # on a VETH interface pair, so one should run netns assignment
    # as a separate operation only

    # assign addresses
    # please notice, that `v0p1` is already in the `test` netns,
    # so should be accessed via `ipdb_test`
    with ipdb_main.interfaces.v0p0 as veth:
        veth.add_ip('172.16.200.1/24')
        veth.up()
    with ipdb_test.interfaces.v0p1 as veth:
        veth.add_ip('172.16.200.2/24')
        veth.up()

Please review also the test code, under `tests/test_netns.py` for
more examples.

By default, NetNS creates requested netns, if it doesn't exist,
or uses existing one. To control this behaviour, one can use flags
as for `open(2)` system call::

    # create a new netns or fail, if it already exists
    netns = NetNS('test', flags=os.O_CREAT | os.O_EXCL)

    # create a new netns or use existing one
    netns = NetNS('test', flags=os.O_CREAT)

    # the same as above, the default behaviour
    netns = NetNS('test')

To remove a network namespace::

    from pyroute2 import NetNS
    netns = NetNS('test')
    netns.close()
    netns.remove()

One should stop it first with `close()`, and only after that
run `remove()`.

'''

import atexit
import errno
import logging
import os
from functools import partial

from pyroute2.iproute import RTNL_API
from pyroute2.netlink.rtnl import RTMGRP_DEFAULTS
from pyroute2.netlink.rtnl.iprsocket import MarshalRtnl
from pyroute2.netns import remove, setns

from ..remote.transport import RemoteSocket, Server, Transport

log = logging.getLogger(__name__)


class FD(object):
    def __init__(self, fd):
        self.fd = fd
        for name in ('read', 'write', 'close'):
            setattr(self, name, partial(getattr(os, name), self.fd))

    def fileno(self):
        return self.fd

    def flush(self):
        return None


class NetNS(RTNL_API, RemoteSocket):
    '''
    NetNS is the IPRoute API with network namespace support.

    **Why not IPRoute?**

    The task to run netlink commands in some network namespace, being in
    another network namespace, requires the architecture, that differs
    too much from a simple Netlink socket.

    NetNS starts a proxy process in a network namespace and uses
    `multiprocessing` communication channels between the main and the proxy
    processes to route all `recv()` and `sendto()` requests/responses.

    **Any specific API calls?**

    Nope. `NetNS` supports all the same, that `IPRoute` does, in the same
    way. It provides full `socket`-compatible API and can be used in
    poll/select as well.

    The only difference is the `close()` call. In the case of `NetNS` it
    is **mandatory** to close the socket before exit.

    '''

    def __init__(
        self,
        netns,
        flags=os.O_CREAT,
        target=None,
        libc=None,
        groups=RTMGRP_DEFAULTS,
    ):
        self.netns = netns
        self.flags = flags
        target = target or netns
        trnsp_in, self.remote_trnsp_out = [Transport(FD(x)) for x in os.pipe()]
        self.remote_trnsp_in, trnsp_out = [Transport(FD(x)) for x in os.pipe()]

        self.child = os.fork()
        if self.child == 0:
            # child process
            trnsp_in.close()
            trnsp_out.close()
            trnsp_in.file_obj.close()
            trnsp_out.file_obj.close()
            try:
                setns(self.netns, self.flags, libc=libc)
            except OSError as e:
                (self.remote_trnsp_out.send({'stage': 'init', 'error': e}))
                os._exit(e.errno)
            except Exception as e:
                (
                    self.remote_trnsp_out.send(
                        {
                            'stage': 'init',
                            'error': OSError(errno.ECOMM, str(e), self.netns),
                        }
                    )
                )
                os._exit(255)

            try:
                Server(
                    self.remote_trnsp_in,
                    self.remote_trnsp_out,
                    target=target,
                    groups=groups,
                )
            finally:
                os._exit(0)

        try:
            self.remote_trnsp_in.close()
            self.remote_trnsp_out.close()
            super(NetNS, self).__init__(trnsp_in, trnsp_out, groups=groups)
            self.target = target
        except Exception:
            self.close()
            raise
        atexit.register(self.close)
        self.marshal = MarshalRtnl()

    def clone(self):
        return type(self)(self.netns, self.flags)

    def _cleanup_atexit(self):
        if hasattr(atexit, 'unregister'):
            atexit.unregister(self.close)
        else:
            try:
                atexit._exithandlers.remove((self.close, (), {}))
            except ValueError:
                pass

    def close(self, code=errno.ECONNRESET):
        self._cleanup_atexit()
        try:
            super(NetNS, self).close(code=code)
        except:
            # something went wrong, force server shutdown
            try:
                self.trnsp_out.send({'stage': 'shutdown'})
            except Exception:
                pass
            log.error('forced shutdown procedure, clean up netns manually')

    def open_file(self, path):
        '''Proxy the open_file method if we are the parent.'''
        if self.child != 0:
            return self.proxy('open_file', path)

        return super(NetNS, self).open_file(path)

    def close_file(self, fd):
        '''Proxy the close_file method if we are the parent.'''
        if self.child != 0:
            return self.proxy('close_file', fd)

        return super(NetNS, self).close_file(fd)

    def get_pid(self):
        '''Proxy the get_pid method if we are the parent.'''
        if self.child != 0:
            return self.proxy('get_pid')

        return super(NetNS, self).get_pid()

    def post_init(self):
        pass

    def remove(self):
        '''
        Try to remove this network namespace from the system.
        '''
        remove(self.netns)