'''
Netns management overview
=========================

Pyroute2 provides basic namespaces management support.
Here's a quick overview of typical netns tasks and
related pyroute2 tools.

Move an interface to a namespace
--------------------------------

Though this task is managed not via `netns` module, it
should be mentioned here as well. To move an interface
to a netns, one should provide IFLA_NET_NS_FD nla in
a set link RTNL request. The nla is an open FD number,
that refers to already created netns. The pyroute2
library provides also a possibility to specify not a
FD number, but a netns name as a string. In that case
the library will try to lookup the corresponding netns
in the standard location.

Create veth and move the peer to a netns with IPRoute::

    from pyroute2 import IPRoute
    ipr = IPRoute()
    ipr.link('add', ifname='v0p0', kind='veth', peer='v0p1')
    idx = ipr.link_lookup(ifname='v0p1')[0]
    ipr.link('set', index=idx, net_ns_fd='netns_name')

Create veth and move the peer to a netns with IPDB::

    from pyroute2 import IPDB
    ipdb = IPDB()
    ipdb.create(ifname='v0p0', kind='veth', peer='v0p1').commit()
    with ipdb.interfaces.v0p1 as i:
        i.net_ns_fd = 'netns_name'

Manage interfaces within a netns
--------------------------------

This task can be done with `NetNS` objects. A `NetNS` object
spawns a child and runs it within a netns, providing the same
API as `IPRoute` does::

    from pyroute2 import NetNS
    ns = NetNS('netns_name')
    # do some stuff within the netns
    ns.close()

One can even start `IPDB` on the top of `NetNS`::

    from pyroute2 import NetNS
    from pyroute2 import IPDB
    ns = NetNS('netns_name')
    ipdb = IPDB(nl=ns)
    # do some stuff within the netns
    ipdb.release()
    ns.close()

Spawn a process within a netns
------------------------------

For that purpose one can use `NSPopen` API. It works just
as normal `Popen`, but starts a process within a netns.

List, set, create and remove netns
----------------------------------

These functions are described below. To use them, import
`netns` module::

    from pyroute2 import netns
    netns.listnetns()

Please be aware, that in order to run system calls the
library uses `ctypes` module. It can fail on platforms
where SELinux is enforced. If the Python interpreter,
loading this module, dumps the core, one can check the
SELinux state with `getenforce` command.

'''
import io
import os
import os.path
import errno
import ctypes
import ctypes.util
import pickle
import struct
import traceback
from pyroute2 import config
from pyroute2.common import basestring
try:
    file = file
except NameError:
    file = io.IOBase

# FIXME: arch reference
__NR = {'x86_': {'64bit': 308},
        'i386': {'32bit': 346},
        'i686': {'32bit': 346},
        'mips': {'32bit': 4344,
                 '64bit': 5303},  # FIXME: NABI32?
        'armv': {'32bit': 375},
        'aarc': {'32bit': 375,
                 '64bit': 268},  # FIXME: EABI vs. OABI?
        'ppc6': {'64bit': 350},
        's390': {'64bit': 339}}
__NR_setns = __NR.get(config.machine[:4], {}).get(config.arch, 308)

CLONE_NEWNET = 0x40000000
MNT_DETACH = 0x00000002
MS_BIND = 4096
MS_REC = 16384
MS_SHARED = 1 << 20
NETNS_RUN_DIR = '/var/run/netns'

__saved_ns = []


def _get_netnspath(name):
    netnspath = name
    dirname = os.path.dirname(name)
    if not dirname:
        netnspath = '%s/%s' % (NETNS_RUN_DIR, name)
    if hasattr(netnspath, 'encode'):
        netnspath = netnspath.encode('ascii')
    return netnspath


def listnetns(nspath=None):
    '''
    List available network namespaces.
    '''
    if nspath:
        nsdir = nspath
    else:
        nsdir = NETNS_RUN_DIR
    try:
        return os.listdir(nsdir)
    except OSError as e:
        if e.errno == errno.ENOENT:
            return []
        else:
            raise


def _get_ns_by_inode(nspath=NETNS_RUN_DIR):
    '''
    Return a dict with inode as key and
    namespace name as value
    '''
    ns_by_dev_inode = {}
    for ns_name in listnetns(nspath=nspath):
        ns_path = os.path.join(nspath, ns_name)
        st = os.stat(ns_path)
        if st.st_dev not in ns_by_dev_inode:
            ns_by_dev_inode[st.st_dev] = {}
        ns_by_dev_inode[st.st_dev][st.st_ino] = ns_name

    return ns_by_dev_inode


def ns_pids(nspath=NETNS_RUN_DIR):
    '''
    List pids in all netns

    If a pid is in a unknown netns do not return it
    '''
    result = {}
    ns_by_dev_inode = _get_ns_by_inode(nspath)

    for pid in os.listdir('/proc'):
        if not pid.isdigit():
            continue
        try:
            st = os.stat(os.path.join('/proc', pid, 'ns', 'net'))
        except OSError as e:
            if e.errno in (errno.EACCES, errno.ENOENT):
                continue
            raise
        try:
            ns_name = ns_by_dev_inode[st.st_dev][st.st_ino]
        except KeyError:
            continue
        if ns_name not in result:
            result[ns_name] = []
        result[ns_name].append(int(pid))
    return result


def pid_to_ns(pid=1, nspath=NETNS_RUN_DIR):
    '''
    Return netns name which matches the given pid,
    None otherwise
    '''
    try:
        st = os.stat(os.path.join('/proc', str(pid), 'ns', 'net'))
        ns_by_dev_inode = _get_ns_by_inode(nspath)
        return ns_by_dev_inode[st.st_dev][st.st_ino]
    except OSError as e:
        if e.errno in (errno.EACCES, errno.ENOENT):
            return None
        raise
    except KeyError:
        return None


def _create(netns, libc=None):
    libc = libc or ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True)
    netnspath = _get_netnspath(netns)
    netnsdir = os.path.dirname(netnspath)

    # init netnsdir
    try:
        os.mkdir(netnsdir)
    except OSError as e:
        if e.errno != errno.EEXIST:
            raise

    # this code is ported from iproute2
    done = False
    while libc.mount(b'', netnsdir, b'none', MS_SHARED | MS_REC, None) != 0:
        if done:
            raise OSError(ctypes.get_errno(), 'share rundir failed', netns)
        if libc.mount(netnsdir, netnsdir, b'none', MS_BIND | MS_REC,
                      None) != 0:
            raise OSError(ctypes.get_errno(), 'mount rundir failed', netns)
        done = True

    # create mountpoint
    os.close(os.open(netnspath, os.O_RDONLY | os.O_CREAT | os.O_EXCL, 0))

    # unshare
    if libc.unshare(CLONE_NEWNET) < 0:
        raise OSError(ctypes.get_errno(), 'unshare failed', netns)

    # bind the namespace
    if libc.mount(b'/proc/self/ns/net', netnspath, b'none', MS_BIND, None) < 0:
        raise OSError(ctypes.get_errno(), 'mount failed', netns)


def create(netns, libc=None):
    '''
    Create a network namespace.
    '''
    rctl, wctl = os.pipe()
    pid = os.fork()
    if pid == 0:
        # child
        error = None
        try:
            _create(netns, libc)
        except Exception as e:
            error = e
            error.tb = traceback.format_exc()
        msg = pickle.dumps(error)
        os.write(wctl, struct.pack('I', len(msg)))
        os.write(wctl, msg)
        os._exit(0)
    else:
        # parent
        msglen = struct.unpack('I', os.read(rctl, 4))[0]
        error = pickle.loads(os.read(rctl, msglen))
        os.close(rctl)
        os.close(wctl)
        os.waitpid(pid, 0)
        if error is not None:
            raise error


def remove(netns, libc=None):
    '''
    Remove a network namespace.
    '''
    libc = libc or ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True)
    netnspath = _get_netnspath(netns)
    libc.umount2(netnspath, MNT_DETACH)
    os.unlink(netnspath)


def setns(netns, flags=os.O_CREAT, libc=None):
    '''
    Set netns for the current process.

    The flags semantics is the same as for the `open(2)`
    call:

        - O_CREAT -- create netns, if doesn't exist
        - O_CREAT | O_EXCL -- create only if doesn't exist

    Note that "main" netns has no name. But you can access it with::

        setns('foo')  # move to netns foo
        setns('/proc/1/ns/net')  # go back to default netns

    See also `pushns()`/`popns()`/`dropns()`

    Changed in 0.5.1: the routine closes the ns fd if it's
    not provided via arguments.
    '''
    newfd = False
    libc = libc or ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True)
    if isinstance(netns, basestring):
        netnspath = _get_netnspath(netns)
        if os.path.basename(netns) in listnetns(os.path.dirname(netns)):
            if flags & (os.O_CREAT | os.O_EXCL) == (os.O_CREAT | os.O_EXCL):
                raise OSError(errno.EEXIST, 'netns exists', netns)
        else:
            if flags & os.O_CREAT:
                create(netns, libc=libc)
        nsfd = os.open(netnspath, os.O_RDONLY)
        newfd = True
    elif isinstance(netns, file):
        nsfd = netns.fileno()
    elif isinstance(netns, int):
        nsfd = netns
    else:
        raise RuntimeError('netns should be a string or an open fd')
    error = libc.syscall(__NR_setns, nsfd, CLONE_NEWNET)
    if newfd:
        os.close(nsfd)
    if error != 0:
        raise OSError(ctypes.get_errno(), 'failed to open netns', netns)


def pushns(newns=None, libc=None):
    '''
    Save the current netns in order to return to it later. If newns is
    specified, change to it::

        # --> the script in the "main" netns
        netns.pushns("test")
        # --> changed to "test", the "main" is saved
        netns.popns()
        # --> "test" is dropped, back to the "main"
    '''
    global __saved_ns
    __saved_ns.append(os.open('/proc/self/ns/net', os.O_RDONLY))
    if newns is not None:
        setns(newns, libc=libc)


def popns(libc=None):
    '''
    Restore the previously saved netns.
    '''
    global __saved_ns
    fd = __saved_ns.pop()
    try:
        setns(fd, libc=libc)
    except Exception:
        __saved_ns.append(fd)
        raise
    os.close(fd)


def dropns(libc=None):
    '''
    Discard the last saved with `pushns()` namespace
    '''
    global __saved_ns
    fd = __saved_ns.pop()
    try:
        os.close(fd)
    except Exception:
        pass
