ncclient:NETCONF Python client

# Copyright 2009 Shikhar Bhushan

#

# Licensed under the Apache License, Version 2.0 (the "License");

# you may not use this file except in compliance with the License.

# You may obtain a copy of the License at

#

#    http://www.apache.org/licenses/LICENSE-2.0

#

# Unless required by applicable law or agreed to in writing, software

# distributed under the License is distributed on an "AS IS" BASIS,

# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

# See the License for the specific language governing permissions and

# limitations under the License.

from Queue import Queue

from threading import Thread, Lock, Event

from ncclient import xml_

from ncclient.capabilities import Capabilities

from errors import TransportError

import logging

logger = logging.getLogger('ncclient.transport.session')

class Session(Thread):

    "Base class for use by transport protocol implementations."

    def __init__(self, capabilities):

        Thread.__init__(self)

        self.setDaemon(True)

        self._listeners = set() # 3.0's weakset would be ideal

        self._lock = Lock()

        self.setName('session')

        self._q = Queue()

        self._client_capabilities = capabilities

        self._server_capabilities = None # yet

        self._id = None # session-id

        self._connected = False # to be set/cleared by subclass implementation

        logger.debug('%r created: client_capabilities=%r' %

                     (self, self._client_capabilities))

    def _dispatch_message(self, raw):

        try:

            root = xml_.parse_root(raw)

        except Exception as e:

            logger.error('error parsing dispatch message: %s' % e)

            return

        with self._lock:

            listeners = list(self._listeners)

        for l in listeners:

            logger.debug('dispatching message to %r' % l)

            l.callback(root, raw) # no try-except; fail loudly if you must!

    def _dispatch_error(self, err):

        with self._lock:

            listeners = list(self._listeners)

        for l in listeners:

            logger.debug('dispatching error to %r' % l)

            try: # here we can be more considerate with catching exceptions

                l.errback(err) 

            except Exception as e:

                logger.warning('error dispatching to %r: %r' % (l, e))

    def _post_connect(self):

        "Greeting stuff"

        init_event = Event()

        error = [None] # so that err_cb can bind error[0]. just how it is.

        # callbacks

        def ok_cb(id, capabilities):

            self._id = id

            self._server_capabilities = capabilities

            init_event.set()

        def err_cb(err):

            error[0] = err

            init_event.set()

        listener = HelloHandler(ok_cb, err_cb)

        self.add_listener(listener)

        self.send(HelloHandler.build(self._client_capabilities))

        logger.debug('starting main loop')

        self.start()

        # we expect server's hello message

        init_event.wait()

        # received hello message or an error happened

        self.remove_listener(listener)

        if error[0]:

            raise error[0]

        #if ':base:1.0' not in self.server_capabilities:

        #    raise MissingCapabilityError(':base:1.0')

        logger.info('initialized: session-id=%s | server_capabilities=%s' %

                    (self._id, self._server_capabilities))

    def add_listener(self, listener):

        """Register a listener that will be notified of incoming messages and

        errors.

        :type listener: :class:`SessionListener`

        """

        logger.debug('installing listener %r' % listener)

        if not isinstance(listener, SessionListener):

            raise SessionError("Listener must be a SessionListener type")

        with self._lock:

            self._listeners.add(listener)

    def remove_listener(self, listener):

        """Unregister some listener; ignore if the listener was never

        registered.

        :type listener: :class:`SessionListener`

        """

        logger.debug('discarding listener %r' % listener)

        with self._lock:

            self._listeners.discard(listener)

    def get_listener_instance(self, cls):

        """If a listener of the specified type is registered, returns the

        instance.

        :type cls: :class:`SessionListener`

        """

        with self._lock:

            for listener in self._listeners:

                if isinstance(listener, cls):

                    return listener

    def connect(self, *args, **kwds): # subclass implements

        raise NotImplementedError

    def run(self): # subclass implements

        raise NotImplementedError

    def send(self, message):

        """Send the supplied *message* to NETCONF server.

        :arg message: an XML document

        :type message: `string`

        """

        if not self.connected:

            raise TransportError('Not connected to NETCONF server')

        logger.debug('queueing %s' % message)

        self._q.put(message)

    ### Properties

    @property

    def connected(self):

        "Connection status of the session."

        return self._connected

    @property

    def client_capabilities(self):

        "Client's :class:`Capabilities`"

        return self._client_capabilities

    @property

    def server_capabilities(self):

        "Server's :class:`Capabilities`"

        return self._server_capabilities

    @property

    def id(self):

        """A `string` representing the `session-id`. If the session has not

        been initialized it will be :const:`None`"""

        return self._id

class SessionListener(object):

    """Base class for :class:`Session` listeners, which are notified when a new

    NETCONF message is received or an error occurs.

    .. note::

        Avoid time-intensive tasks in a callback's context.

    """

    def callback(self, root, raw):

        """Called when a new XML document is received. The `root` argument

        allows the callback to determine whether it wants to further process the

        document.

        :arg root: tuple of `(tag, attributes)` where `tag` is the qualified name of the root element and `attributes` is a dictionary of its attributes (also qualified names)

        :type root: `tuple`

        :arg raw: XML document

        :type raw: `string`

        """

        raise NotImplementedError

    def errback(self, ex):

        """Called when an error occurs.

        :type ex: :exc:`Exception`

        """

        raise NotImplementedError

class HelloHandler(SessionListener):

    def __init__(self, init_cb, error_cb):

        self._init_cb = init_cb

        self._error_cb = error_cb

    def callback(self, root, raw):

        if xml_.unqualify(root[0]) == 'hello':

            try:

                id, capabilities = HelloHandler.parse(raw)

            except Exception as e:

                self._error_cb(e)

            else:

                self._init_cb(id, capabilities)

    def errback(self, err):

        self._error_cb(err)

    @staticmethod

    def build(capabilities):

        "Given a list of capability URI's returns <hello> message XML string"

        spec = {

            'tag': 'hello',

            'attrib': {'xmlns': xml_.BASE_NS_1_0},

            'subtree': [{

                'tag': 'capabilities',

                'subtree': # this is fun :-)

                    [{'tag': 'capability', 'text': uri} for uri in capabilities]

                }]

            }

        return xml_.dtree2xml(spec)

    @staticmethod

    def parse(raw):

        "Returns tuple of (session-id (str), capabilities (Capabilities)"

        sid, capabilities = 0, []

        root = xml_.xml2ele(raw)

        for child in root.getchildren():

            tag = xml_.unqualify(child.tag)

            if tag == 'session-id':

                sid = child.text

            elif tag == 'capabilities':

                for cap in child.getchildren():

                    if xml_.unqualify(cap.tag) == 'capability':

                        capabilities.append(cap.text)

        return sid, Capabilities(capabilities)